Microbial Fuel Cells for Power Generation by Treating Mine Tailings: Recent Advances and Emerging Trends

Abstract

Microbial fuel cells (MFCs) have gained considerable attention in recent years due to their dual potential in waste treatment and clean energy production. In the field of mine tailings treatment, MFCs exhibit a unique advantage by integrating pollutant degradation with electricity generation, gradually emerging as a significant research focus. Based on 1321 relevant publications retrieved from the Web of Science Core Collection (WoSCC) from 2004 to 2024, this study employs bibliometric analysis to systematically explore the research status and future trends of MFCs in mine tailings treatment and power generation. The main research themes include (1) distinctive publication characteristics of MFC studies in the context of mine tailings treatment; (2) key information on leading countries, institutions, journals, and disciplines contributing to this field; and (3) a comprehensive summary of technological breakthroughs, emerging research hotspots, and future development directions of MFCs in mine tailings management. By thoroughly evaluating the existing body of research, this study provides valuable guidance for scholars new to the fields of MFCs and mine tailings treatment while offering insights into the technological advancements shaping the future of this domain.

1. Introduction

In today’s world, the global issues of energy shortages and environmental pollution are becoming increasingly severe, making the development of clean and sustainable new energy technologies a pressing global need. The long-term reliance on fossil fuels not only exacerbates geopolitical tensions related to energy supply but also has profound impacts on the global environment, such as air pollution and climate change [1]. Simultaneously, mine tailings, as a byproduct of mineral resource extraction, have drawn widespread attention due to the potential hazards they pose to the ecological environment. The main components of mine tailings vary significantly depending on the type of mineral, primarily including silicon, iron, aluminum, heavy metals, and some radioactive elements [2]. These components, when exposed to water and air, are prone to leaching heavy metals and generating acid mine drainage, which subsequently contaminates soil and water bodies, thereby destabilizing ecosystems and reducing biodiversity [3]. For instance, heavy metals such as lead, cadmium, and mercury can infiltrate water sources and enter the food chain, posing significant threats to human health. Additionally, the accumulation of mine tailings occupies substantial land resources, potentially leading to land degradation and decreased agricultural productivity. Traditional tailings treatment methods, such as tailings pond storage, dumping, and chemical processing, can mitigate pollution to some extent but are subject to significant limitations. Tailings pond storage requires extensive land use and may trigger landslides or dam failures during extreme weather events, exacerbating environmental risks. Dumping methods risk introducing heavy metal pollutants into soils and water bodies, thereby threatening ecosystems and the health of nearby residents. While chemical treatment can achieve short-term pollutant removal, it often necessitates the use of large quantities of chemical reagents, increasing treatment costs and resulting in secondary pollution. Therefore, exploring green treatment and resource utilization of mine tailings—particularly through innovative technologies that transform hazardous substances into valuable resources—has become a critical research focus in the fields of mining and environmental protection.

In comparison, microbial fuel cells (MFCs), as an innovative clean energy technology, demonstrate significant potential in the treatment of mine tailings and power generation. First, MFCs utilize microbial catalysis to oxidize organic compounds in mine tailings, achieving green treatment without the involvement of chemical reagents and fundamentally avoiding the secondary pollution associated with traditional chemical methods [4,5]. Second, MFCs can directly convert chemical energy into electricity, effectively removing tailings pollutants while simultaneously recovering energy, thereby offering low operational costs and energy self-sufficiency [6]. Additionally, MFC technology facilitates the fixation of heavy metals through adsorption and precipitation processes, transforming them into recyclable resources and significantly enhancing the resource utilization efficiency of mine tailings [7,8]. More importantly, MFC systems exhibit flexibility in the selection of anode materials [9], microbial communities [10], and reactor designs [11], allowing the adjustment of treatment strategies to accommodate different types of tailings. This adaptability ensures higher applicability and sustainability in practical applications. Despite significant progress, MFCs still face challenges in practical applications, including insufficient energy output, low operational stability, and scalability issues [12].

Bibliometric analysis serves as a powerful tool to display research dynamics and development trends within specific fields, through systematic analysis of academic literature, revealing research hotspots, collaboration networks, and trajectories of technological advancement [13]. In the fields of environmental engineering and energy technology, this method has been widely adopted. For instance, Castañeda et al. (2022) utilized bibliometric analysis on 1703 journal articles published from January 2015 to September 2021, unveiling the knowledge structure and major trends in highway planning such as life cycle analysis, smart cities, sustainability issues, and multi-objective optimization, thus providing guidance for future research directions [14]. Similarly, Xuan et al. (2024) analyzed the literature from 2008 to 2024 on emerging pollutants in wastewater treatment, highlighting the significant impact of pharmaceuticals and personal care products on aquatic environments and emphasizing the urgent need for the development of low-energy, high-efficiency treatment technologies and enhancing the accuracy and speed of monitoring emerging pollutants [15]. CiteSpace, introduced by Chen et al. (2009) as a Java-based text mining and scientific visualization tool, vividly depicts research themes, focuses, and trends through co-occurrence and co-citation analysis tools [16]. Wang et al. (2024) conducted a CiteSpace visual analysis of 815 articles related to the intensity of coal mining, revealing not only the current research status and network relationships in this field but also pointing out that future research should focus on high-intensity mining, mining disturbance, and influential factors [17]. Moreover, HistCite software (version 2.1) developed by Eugene Garfield has been used to analyze core literature datasets (CLDs), evaluating various aspects such as the h-index, total local citation score (TLCS), average TLCS (ATLCS), total global citation score (TGCS), and average TGCS (ATGCS), providing insights into journal impact [18].

Although research on the use of MFCs for power generation in the treatment of mine tailings has accumulated to some extent, systematic bibliometric analyses in this field remain scarce. To address this knowledge gap, this study conducts a comprehensive analysis of relevant literature from the past two decades based on the Web of Science database, employing CiteSpace (version 6.2.R7) and HistCite as analytical tools. The bibliometric analysis is carried out from multiple perspectives, including publication trends, disciplinary distribution, collaboration networks of countries and institutions, keyword clustering, and the evolution of research hotspots. The findings aim to provide a comprehensive overview of the research focus and future directions in this field. This study not only offers valuable insights into the current applications of microbial fuel cells in mine tailings treatment and energy recovery but also provides data-driven support and theoretical guidance for subsequent research in related domains.

2. Materials and Methods

2.1. Data Collection

This study utilized the WOSCC database, developed by the Institute for Scientific Information (ISI), as the primary data source. Renowned for its extensive coverage and robust functionality, WOSCC supports a variety of bibliometric analysis methods and includes comprehensive academic resources spanning disciplines such as natural sciences, biomedicine, and engineering technology. This makes it a reliable source of high-quality data for research purposes. The following search strategy was employed for data retrieval: TS = (“microbial fuel cell” OR “MFC” OR “bioelectrochemical system” OR “biocatalysis”) AND TS = (“power generation” OR “electricity production” OR “energy recovery” OR “bioenergy”) AND TS = (“mine tailings” OR “mining waste” OR “metal-contaminated waste” OR “heavy metal waste” OR “industrial waste” OR “environmental remediation” OR “wastewater treatment” OR “polluted soils”). The search period was set from 2004 to 2024, with the final retrieval conducted on 14 November 2024. This timeframe was chosen because bibliometric analysis indicated that publications prior to 2004 were limited in number and less representative of the research domain. To ensure the comprehensiveness and scientific rigor of the study, the timeframe was extended to include the most recent research findings. A total of 1321 records were retrieved based on this search strategy.

2.2. Analytical Methods

CiteSpace and HistCite were selected as the primary bibliometric analysis tools for this study due to their significant advantages in literature visualization, core literature identification, and large-scale data processing (Figure 1). CiteSpace offers robust visualization capabilities, enabling the intuitive representation of research topics, hotspots, and development trends through co-occurrence and co-citation analyses. This makes it particularly suitable for elucidating the knowledge structure and technological evolution within the field of MFCs. Additionally, CiteSpace supports various analytical modes, such as timeline views and collaboration network analyses, which comprehensively address multiple dimensions, including publication volume and disciplinary distribution. Conversely, HistCite excels in identifying and evaluating core literature, with the ability to calculate metrics such as the h-index and TLCS. This facilitates the quantification of research impact and efficient processing of extensive literature datasets, making it ideal for systematic analyses of publications over the past two decades. In constructing the knowledge map, the network structure is composed of nodes and links. Each node represents a specific element, such as cited literature, research institutions, or countries, while the links reflect collaborative relationships, co-occurrence, or co-citation. The thickness or intensity of the links indicates the strength of these relationships, and their colors correspond to different time periods, visually illustrating the dynamic changes within the research domain. Notably, in CiteSpace network analysis, nodes with high betweenness centrality (BC) often play critical roles within the network [19]. Such nodes can indicate significant research breakthroughs or interdisciplinary connections. The BC value is calculated using Equation (1). This metric allows the study to more accurately identify the core nodes within the network, thereby uncovering the primary research directions and knowledge dissemination pathways in the field.

$$B{C}_i={\sum }_{i\ne j\ne k}{\displaystyle \frac{n_{st}^i}{g_{st}}}$$

(1)

In the equation, $g_{st}$ represents the total number of shortest paths connecting nodes s and t, while $n_{st}^i$ denotes the number of such paths that pass through node i. The BC index serves as a metric to evaluate the importance of an individual node within the overall network structure. A higher BC value indicates a more significant mediating role of the node in the network, highlighting its influence on information flow and structural connectivity. When the BC value exceeds 0.1, CiteSpace marks the node with a purple ring, typically identifying it as a pivotal research turning point or an event of notable significance within a specific domain [20].

Figure 1. Framework of the study design.

Figure 1. Framework of the study design.

In CiteSpace research, a burst typically refers to a phenomenon where a node’s metric value experiences a significant increase over a short period, often reflecting dynamic changes within its research domain. For instance, when a particular paper is heavily cited within a brief timeframe, it generates a citation burst. If multiple nodes within a cluster exhibit notable citation bursts, it suggests that the field may be forming new research hotspots or trend directions. Accordingly, this study employs cluster analysis and burst detection to identify significant changes and emerging research patterns in the field of microbial fuel cells for electricity generation from mine tailings [21]. To evaluate the effectiveness of clustering, two key metrics are utilized: Modularity Q and the Mean Silhouette. Modularity Q measures the overall effectiveness of the clustering. When the Q-value exceeds 0.3, the clustering structure is considered robust. The Mean Silhouette coefficient assesses the homogeneity within clusters; higher values indicate greater similarity among elements within a cluster. Typically, a Mean Silhouette coefficient above 0.7 indicates high reliability of the clustering results [22]. In the keyword clustering map, each module corresponds to a cluster, and modules containing a larger number of keywords are generally represented as larger clusters. CiteSpace employs the Log-Likelihood Ratio (LLR) algorithm to label keyword clusters, with cluster names automatically formatted as “# + number + label”. In the timeline visualization, the diameter of a node is proportional to the co-citation frequency of the corresponding paper, while the color represents the distribution across different years. The timeline on the left indicates the years, and clusters are arranged sequentially from left to right, illustrating their evolution over time. The color of cluster labels reflects the average publication year of the cluster: warm colors (e.g., red, orange, yellow) denote newer research clusters, whereas cool colors (e.g., cyan, blue, green) signify earlier research clusters.

In the field of academic evaluation, the Impact Factor (IF) is widely utilized as a key indicator for assessing the academic quality and ranking of journals. This metric, derived from citation index data [23], is typically sourced from the Journal Citation Reports (JCR) by ISI. In this study, IF values of relevant journals were integrated with key parameters from Histcite software (version 2.1), such as TLCS and TGCS, to efficiently identify influential journals and assess their impact in the field. In Histcite, TGCS represents the total number of citations a paper has received within the WOSCC, reflecting its global academic influence. Conversely, TLCS indicates the number of times a paper has been cited within a specific dataset, namely the collection of papers filtered through keyword searches. Compared to TGCS, TLCS is better suited for assessing the centrality of a paper within a specific research domain. Papers with high TLCS values are often considered key contributions with significant influence in their respective fields [24]. Furthermore, by analyzing the frequency of node occurrences across different categories, it is possible to preliminarily evaluate the productivity of literature within each category. Nodes with high frequency and significant centrality typically correspond to key research areas or trending topics within the domain. By combining Impact Factors with citation metrics, this study systematically evaluated academic resources in the field of microbial fuel cells for electricity generation from mine tailings from multiple dimensions, providing a comprehensive reference for future research.

A paper indexed in the Web of Science (WOS) is typically assigned to one or more subject categories. Analyzing the co-occurrence relationships among these categories can reveal the key disciplines driving scientific progress and the interdisciplinary characteristics of a specific knowledge domain. CiteSpace’s burst detection analysis not only reflects the dynamic changes in publication intensity but also uncovers trends in the expansion of subject categories. Rapid growth in a particular subject category often signals a shift in research hotspots or a transformation in research directions. Thus, analyzing the burst patterns of subject categories is instrumental in identifying the most vibrant research areas. In this study, CiteSpace’s co-occurrence analysis and burst detection functionalities were utilized to conduct an in-depth exploration of subject categories within the field of microbial fuel cells for electricity generation from mine tailings. By analyzing relevant subject categories and their burst patterns, this study illuminates the core disciplines underpinning research in this domain and explores their interconnections. Furthermore, it highlights the active research topics in microbial fuel cell technology as applied to mine tailings treatment and electricity generation, uncovering the interdisciplinary nature of this field and potential future development directions.

3. Results

3.1. Characteristics of Publication Output

Between 2004 and 2024, a total of 1321 publications related to microbial fuel cell treatment of mine tailings for power generation were recorded. These publications were classified into nine different types, including journal articles, proceedings papers, reviews, and others. Among them, journal articles accounted for the largest proportion at 76%, followed by review papers at 17.8%, and proceedings papers at 4.4%. Early access papers comprised 1.4% of the total publications. The remaining types of literature, such as book chapters and meeting abstracts, collectively accounted for only about 0.4%. As shown in Figure 2, the field has made significant progress in research output, with annual publication volumes showing an increasing trend from 2004 to 2024. As of 14 November 2024, a total of 138 related papers have been published this year. Overall, the annual number of publications increased from 1 in 2004 to 138 in 2024. Before 2014, the average annual output in this field was relatively low (fewer than 70 publications per year). However, since 2014, the annual output has been steadily increasing, reaching over 73 publications per year. This growth is primarily driven by technological advancements, policy support, and increasing environmental demands. Breakthroughs in the energy conversion efficiency and system stability of MFC technology, along with the impetus provided by environmental policies such as the Paris Agreement, have significantly fueled research in this field. Additionally, the ecological challenges posed by mine tailings have underscored the potential of MFCs in pollution mitigation and energy recovery, further advancing the development of this domain. In 2022, the number of publications reached its peak, with a total of 167 papers, indicating an average publication frequency of nearly one paper every two days. From 2020 to 14 November 2024, approximately 51.93% of the related papers were published, reflecting the sustained and efficient growth in research activity in this field. The overall trend indicates that academic interest in this area has increased significantly over the past two decades, particularly in recent years.

To analyze this publication trend, the fitted curve model shown in Equation (2) was employed. Based on this model, the variation in publication frequency related to microbial fuel cell treatment of mine tailings for power generation was described using the equation (see Figure 3):

$$y=8.08x-\mathrm{16,216.49}$$

(2)

In this equation, y represents the cumulative number of publications, and x denotes the year. The goodness of fit R² reaches 0.92, indicating a high degree of fitting accuracy. Based on this equation, it can be projected that research activity in the field of microbial fuel cell treatment of mine tailings for power generation will continue to grow rapidly in the future.

3.2. Journal Performance

According to HistCite analysis, the top 20 most productive journals contributed over 44.6% of the total publications (see

Table 1. Top 20 journals ranked by the number of publications on the topic of microbial fuel cells for power.

Ranking	Journal Title	Category	IF	Country	H-Index	Records	% of 1321	TLCS	TGCS	ATLCS	ATGCS
1	BIORESOURCE TECHNOLOGY	BIOTECHNOLOGY & APPLIED MICROBIOLOGY	9.7	NETHERLANDS	49	96	7.3	1343	7703	13.99	80.24
2	CHEMICAL ENGINEERING JOURNAL	ENGINEERING, CHEMICAL	13.4	SWITZERLAND	25	47	3.6	383	3049	8.15	64.87
3	INTERNATIONAL JOURNAL OF HYDROGEN ENERGY	ELECTROCHEMISTRY	8.1	ENGLAND	27	43	3.3	315	1713	7.33	39.84
4	SCIENCE OF THE TOTAL ENVIRONMENT	ENVIRONMENTAL SCIENCES	8.2	NETHERLANDS	22	41	3.1	42	1509	1.02	36.80
5	CHEMOSPHERE	ENVIRONMENTAL SCIENCES	8.1	ENGLAND	24	33	2.5	49	1389	1.48	42.09
6	ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH	ENVIRONMENTAL SCIENCES	1.0	GERMANY	12	32	2.4	75	459	2.34	14.34
7	JOURNAL OF CLEANER PRODUCTION	ENVIRONMENTAL SCIENCES	9.8	USA	18	27	2.0	196	1943	7.26	71.96
8	WATER SCIENCE AND TECHNOLOGY	ENVIRONMENTAL SCIENCES	2.5	ENGLAND	17	27	2.0	213	986	7.89	36.52
9	WATER RESEARCH	ENVIRONMENTAL SCIENCES	11.5	ENGLAND	22	26	2.0	588	2964	22.62	114.00
10	JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING	ENGINEERING, CHEMICAL	7.4	ENGLAND	12	26	2.0	36	480	1.38	18.46
11	JOURNAL OF POWER SOURCES	ELECTROCHEMISTRY	8.1	NETHERLANDS	17	25	1.9	155	1190	6.20	47.60
12	JOURNAL OF WATER PROCESS ENGINEERING	ENGINEERING, CHEMICAL	6.3	NETHERLANDS	10	25	1.9	6	302	0.24	12.08
13	JOURNAL OF ENVIRONMENTAL MANAGEMENT	ENVIRONMENTAL SCIENCES	8.0	ENGLAND	13	22	1.7	76	644	3.45	29.27
14	JOURNAL OF CHEMICAL TECHNOLOGY AND BIOTECHNOLOGY	ENGINEERING, CHEMICAL	2.8	ENGLAND	14	20	1.5	131	678	6.55	33.90
15	ENERGIES	ENERGY & FUELS	3.0	SWITZERLAND	9	19	1.4	3	215	0.16	11.32
16	RENEWABLE & SUSTAINABLE ENERGY REVIEWS	ENERGY & FUELS	16.3	USA	17	17	1.3	245	1719	14.41	101.12
17	ENVIRONMENTAL TECHNOLOGY	ENVIRONMENTAL SCIENCES	2.2	ENGLAND	8	16	1.2	49	248	3.06	15.50
18	RSC ADVANCES	CHEMISTRY, MULTIDISCIPLINARY	3.9	ENGLAND	11	16	1.2	67	509	4.19	31.81
19	SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS	ENERGY & FUELS	7.1	USA	9	16	1.2	0	330	0.00	20.63
20	DESALINATION AND WATER TREATMENT	ENGINEERING, CHEMICAL	1.0	ITALY	5	15	1.1	15	114	1.00	7.60

). Most of the literature on microbial fuel cells for power generation by treating mine tailings has been published in journals such as BIORESOURCE TECHNOLOGY, CHEMICAL ENGINEERING JOURNAL, and INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, accounting for 9.7%, 13.4%, and 8.1%, respectively. These research outputs are widely distributed among leading journals in the fields of biotechnology and applied microbiology, chemical engineering, and electrochemistry. To comprehensively evaluate journal performance, impact factors and H-index values were considered. In 2024, the journals with the highest impact factors were RENEWABLE & SUSTAINABLE ENERGY REVIEWS (16.3), CHEMICAL ENGINEERING JOURNAL (13.4), and WATER RESEARCH (11.5). In terms of the H-index, the top three journals were BIORESOURCE TECHNOLOGY (49), INTERNATIONAL JOURNAL OF HYDROGEN ENERGY (27), and CHEMICAL ENGINEERING JOURNAL (25). Additionally, the average citation per journal was calculated by dividing the total number of citations of articles related to microbial fuel cell treatment of mine tailings by the number of articles in each journal. The results indicated that WATER RESEARCH, RENEWABLE & SUSTAINABLE ENERGY REVIEWS, and BIORESOURCE TECHNOLOGY were the three most important journals in this field, exhibiting the highest ATLCS or ATGCS values.

3.3. National Collaboration

The analysis of publication volumes from various countries provides an assessment of their research activity in the field of MFCs for the treatment of mine tailings and power generation. Between 2004 and 2024, researchers from 72 countries or regions contributed articles to this field. To further explore the roles of different countries in MFC technology, an international collaboration network was constructed using CiteSpace (version 6.2.R7) based on co-authorship relationships. The colors of nodes and links in the network graph represent temporal changes from 2004 to 2024. Colors transitioning from purple to blue indicate the period from 2004 to 2009, cyan to green represent 2010 to 2016, yellow to orange correspond to 2017 to 2020, and red represents 2021 to 2024 (as illustrated in the legend on the left side of Figure 4). The color meanings of nodes and links are consistent across Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9. In the collaboration network, the size of a node is proportional to the number of publications from the respective country. Nodes highlighted with purple circles indicate countries with high betweenness centrality, signifying their pivotal roles within the network. The thickness of the links between nodes represents the frequency and intensity of collaboration between countries.

Figure 4 illustrates that China, India, the United States, Malaysia, and South Korea are the primary contributors to research on MFCs for treating mine tailings and generating electricity. These countries occupy prominent nodes in the international collaboration network and maintain close cooperative relationships. As early as 2011, Chinese researchers presented experimental studies at the ISEST conference on the application of MFCs for sludge treatment and power generation. The results demonstrated that MFCs effectively reduce sludge volume while generating electricity [25]. Meanwhile, U.S. researchers investigated the performance of different MFC configurations in wastewater treatment and power generation. Their findings indicated that air-cathode MFCs outperform liquid-cathode MFCs in electricity generation. However, the chemical oxygen demand (COD) of the effluent still failed to meet discharge standards, requiring further treatment [26]. Early research on MFCs for mine tailings treatment was primarily conducted in the United States, England, China, and Belgium. These countries are represented with purple circles in the international collaboration network (Figure 4), highlighting their pivotal roles. According to the data presented in

Table 2. Top 10 countries/regions in the cooperation network (ranked by count or centrality).

Ranking	Countries	Count	Centrality	Ranking	Countries	Count	Centrality
1	PEOPLES R CHINA	447	0.05	1	TURKEY	18	0.9
2	INDIA	316	0	2	ENGLAND	42	0.62
3	USA	161	0.21	3	FRANCE	11	0.57
4	MALAYSIA	86	0	4	SOUTH KOREA	79	0.51
5	SOUTH KOREA	79	0.51	5	SCOTLAND	6	0.43
6	SPAIN	66	0.22	6	FINLAND	4	0.39
7	IRAN	62	0.05	7	GERMANY	17	0.38
8	ENGLAND	42	0.62	8	CZECH REPUBLIC	9	0.37
9	PAKISTAN	36	0.05	9	SINGAPORE	11	0.35
10	ITALY	33	0.05	10	ESTONIA	3	0.34

and Figure 5, the 10 most influential countries in the international collaboration network from 2004 to 2024 were ranked based on publication volume and centrality. Among them, England and South Korea not only contributed a significant number of publications but also maintained close collaborations with multiple countries. For instance, researchers from South Korea and India systematically reviewed the latest advancements in algae-based microbial fuel cells (A-MFCs) for power generation and wastewater treatment. They analyzed key parameters influencing A-MFC performance, as well as developments in electrode materials, providing new insights and directions for commercialization [27]. Additionally, researchers from England and the United States were the first to reveal the interaction dynamics between the anode and cathode in MFCs. They found that reducing voltage losses at one electrode increases losses at the other, leading to the development of corresponding models that offer new theoretical support for improving MFC performance in wastewater treatment and energy production [28]. Although Scotland, Finland, and Estonia have made relatively smaller contributions to research on large-scale MFC applications, they remain integral parts of the international collaboration network and have significantly contributed to the practical application of this technology.

Figure 4. Collaboration network of manufacturing nations/regions from 2004 to 2024.

Figure 4. Collaboration network of manufacturing nations/regions from 2004 to 2024.

Figure 5. Leading countries in publication outputs and network centrality (2004–2024).

Figure 5. Leading countries in publication outputs and network centrality (2004–2024).

3.4. Institutional Collaboration

Based on the institutional affiliations of the authors, a total of 862 organizations have made significant contributions to the research field of MFCs for treating mine tailings and generating electricity. A visual representation of the distribution of research institutions in this field is provided by Figure 6, generated using CiteSpace software (version 6.2.R7). In this figure, each node represents a research institution, and the size of the node reflects the number of research papers published by that institution.

Table 3. Leading 10 institutions in the collaboration network (ranked by publication count or centrality).

Ranking	Institutions	Count	Centrality	Ranking	Institutions	Count	Centrality
1	Indian Institute of Technology System (IIT System)	447	0.05	1	Chinese Academy of Sciences	18	0.9
2	Indian Institute of Technology (IIT)—Kharagpur	316	0	2	Harbin Institute of Technology	42	0.62
3	Council of Scientific & Industrial Research (CSIR)—India	161	0.21	3	Council of Scientific & Industrial Research (CSIR)—India	11	0.57
4	Chinese Academy of Sciences	86	0	4	Universiti Kebangsaan Malaysia	79	0.51
5	Harbin Institute of Technology	79	0.51	5	Indian Institute of Technology System (IIT System)	6	0.43
6	National Institute of Technology (NIT System)	66	0.22	6	Tsinghua University	4	0.39
7	Virginia Polytechnic Institute & State University	62	0.05	7	Egyptian Knowledge Bank (EKB)	17	0.38
8	CSIR—Indian Institute of Chemical Technology (IICT)	42	0.62	8	VITO	9	0.37
9	Tsinghua University	36	0.05	9	Gwangju Institute of Science & Technology (GIST)	11	0.35
10	Egyptian Knowledge Bank (EKB)	33	0.05	10	Centre National de la Recherche Scientifique (CNRS)	3	0.34

and Figure 7 present the top 10 institutions with the highest number of publications or centrality scores in this field from 2004 to 2024. Most of these leading institutions are based in Asia, particularly in China and India, while others are located in Malaysia, Egypt, South Korea, Belgium, and France. For example, a study conducted by the Indian Institute of Technology System (IIT System) in 2021 demonstrated that combining bismuth (Bi) with ruthenium (Ru) as a photocathode catalyst (Bi-Ru) in MFCs significantly improved performance. The coulombic efficiency and power density reached 26.7% and 10.0 W/m³, respectively, which represented increases of 12.5% and 22% compared to conventional platinum (Pt) catalysts. Additionally, Bi-Ru achieved higher COD removal rates and energy recovery efficiencies, indicating its potential as a viable alternative to Pt for large-scale MFC applications [29]. The Chinese Academy of Sciences explored the effects of static magnetic fields (MFs) on the bioelectrochemical activities of anodic microorganisms in MFCs. Under a 100 mT magnetic field, reactor startup was accelerated, electricity output was enhanced, and activation losses were reduced. The study attributed these effects primarily to oxidative stress and magnetohydrodynamic effects, rather than increased secretion of redox mediators. This finding suggests that weak magnetic fields could serve as a simple and effective method to enhance microbial activity for bioelectrochemical energy production and pollutant removal [30]. The Harbin Institute of Technology investigated an application-oriented stackable horizontal microbial fuel cell (SHMFC) designed for wastewater treatment and energy recovery. The system consisted of multiple 250 L modules, making it the largest single MFC module to date. During stable operation, each module produced a maximum current of 0.435 A under an external resistance of 1 Ω and achieved a power density of 116 mW. Additionally, the system achieved 79% COD removal and 71% TN removal. The study also revealed that as the scale of MFCs increases, internal resistance distribution changes, and contact resistance becomes a significant or even limiting factor [31].

From 2004 to 2024, the Indian Institute of Technology System (IIT System), Indian Institute of Technology (IIT)—Kharagpur, and the Council of Scientific and Industrial Research (CSIR) collectively published 118, 62, and 56 research papers, respectively, on the application of MFCs for treating mine tailings and energy generation. These figures not only highlight India’s leading position in this research field but also reflect the global academic community’s significant attention to this sustainable development technology. In terms of international collaboration, the Chinese Academy of Sciences occupies a central role in the institutional collaboration network, maintaining close partnerships with Tsinghua University and Babol Noshirvani University of Technology. Similarly, the Harbin Institute of Technology, the Council of Scientific and Industrial Research (CSIR), and Universiti Kebangsaan Malaysia have established extensive collaborative networks with various institutions, with centrality scores of 0.14, 0.13, and 0.12, respectively. Such robust international cooperation not only advances research progress in the use of MFC technology for mine tailings treatment and clean energy development but also strengthens global research synergies, contributing to a more collaborative and interdisciplinary approach in this critical area.

Figure 6. Collaboration network of leading institutions (2004–2024).

Figure 6. Collaboration network of leading institutions (2004–2024).

Figure 7. Leading institutions in publication outputs and network centrality (2004–2024).

Figure 7. Leading institutions in publication outputs and network centrality (2004–2024).

3.5. Co-Occurrence Analysis of Subject Categories

Through the path network scaling simplification method, a co-occurrence network of subject categories covering the period from 2004 to 2024 was constructed (as shown in Figure 8). From 1321 search results, 54 distinct subject categories were identified. The research field of MFCs for treating mine tailings and generating electricity demonstrates a remarkable interdisciplinary nature, encompassing various research directions, including “Environmental Sciences”, “Energy & Fuels”, “Chemical Engineering”, “Biotechnology; Applied Microbiology”, “Electrochemistry”, “Water Resources”, “Green & Sustainable Science & Technology”, “Physical Chemistry”, “Agricultural Engineering”, “Materials Science (Multidisciplinary)”, “Thermodynamics”, and “Nanoscience & Nanotechnology”. The results of the co-occurrence analysis indicate that high-frequency nodes such as “Environmental Sciences”, “Energy & Fuels”, and “Chemical Engineering” are particularly prominent in the research network, representing the core focus of this field. Further analysis reveals that the color-coded circles highlight the evolution of research hotspots: early studies were primarily concentrated in fields such as “Environmental Sciences”, “Environmental Engineering”, “Biotechnology; Applied Microbiology”, and “Water Resources”. These nodes, often marked with purple inner circles, reflect their critical role as the foundation of early research. In recent years, however, emerging research topics have gradually appeared, such as “Biomedical Engineering”, “Materials Science (Coatings & Films)”, “Plant Sciences”, “Agronomy”, and “Computer Science (Artificial Intelligence)”. These topics are distinguished by circles of different colors, indicating their increasing integration into the research framework for microbial fuel cells. Additionally, subject categories such as “Materials Science (Multidisciplinary)”, “Water Resources”, “Green & Sustainable Science & Technology”, and “Mechanics” are surrounded by dense purple circles, highlighting their bridging roles in the co-occurrence network. These nodes play a crucial role in connecting different academic disciplines, and their absence could result in a more fragmented network structure, increasing the number of isolated nodes and weakening interdisciplinary synergies.

Figure 8. A co-occurrence network of subject categories spanning 2004 to 2024.

Figure 8. A co-occurrence network of subject categories spanning 2004 to 2024.

Table 4. Top 10 subject categories in the network of co-occurrence (left: ranked by frequency, right: ranked by centrality).

Ranking	Subject Categories	Count	Centrality	Ranking	Subject Ranked by Frequency or Centrality Categories	Centrality	Count
1	ENVIRONMENTAL SCIENCES	447	0.05	1	MATERIALS SCIENCE, MULTIDISCIPLINARY	0.9	18
2	ENERGY & FUELS	316	0	2	WATER RESOURCES	0.62	42
3	ENGINEERING, CHEMICAL	161	0.21	3	GREEN; SUSTAINABLE SCIENCE; TECHNOLOGY	0.57	11
4	ENGINEERING, ENVIRONMENTAL	86	0	4	MECHANICS	0.51	79
5	BIOTECHNOLOGY; APPLIED MICROBIOLOGY	79	0.51	5	THERMODYNAMICS	0.43	6
6	ELECTROCHEMISTRY	66	0.22	6	ENGINEERING, CHEMICAL	0.39	4
7	WATER RESOURCES	62	0.05	7	ENERGY & FUELS	0.38	17
8	GREEN; SUSTAINABLE SCIENCE; TECHNOLOGY	42	0.62	8	ELECTROCHEMISTRY	0.37	9
9	CHEMISTRY, PHYSICAL	36	0.05	9	ENVIRONMENTAL SCIENCES	0.35	11
10	AGRICULTURAL ENGINEERING	33	0.05	10	NANOSCIENCE & NANOTECHNOLOGY	0.34	3

presents the top 10 subject categories identified through co-occurrence analysis, ranked by frequency and centrality. Key research areas related to the application of MFC technology for treating mine tailings and generating electricity include foundational fields such as “Environmental Sciences”, “Energy & Fuels”, and “Chemical Engineering”. Additionally, interdisciplinary topics such as “Materials Science (Multidisciplinary)”, “Water Resources”, and “Green & Sustainable Science & Technology” are also of significant research value. In the field of Environmental Sciences, Park et al. (2009) demonstrated that MFCs exhibit outstanding performance in efficiently treating coal tar wastewater, achieving a COD removal rate of 87.9% and generating a maximum power density of 4.54 mW/m². These findings highlight the cost-effectiveness and application potential of MFCs in wastewater treatment [32]. In the domain of Energy & Fuels, Kusmayadi et al. (2020) provided a comprehensive summary of the fundamental principles and practical applications of MFCs and microalgae-microbial fuel cells (mMFCs). They emphasized that mMFCs integrate multiple functions, including power generation, wastewater treatment, CO₂ sequestration, and biomass production, showcasing their tremendous potential in green energy development and environmental management. The study also explored performance optimization parameters, advantages, and challenges associated with mMFCs [33]. In the field of Materials Science (Multidisciplinary), Zou et al. (2022) developed a photocatalytic microbial fuel cell (photo-MFC) using an Ag₃PO₄ photocatalyst. Through the synergistic effects of photodegradation and biodegradation, the photo-MFC achieved 95.8% methylene blue (MB) decolorization, 83.21% COD removal, and a maximum power density of 2.90 W/m². This research demonstrates the significant advantages of photo-MFCs in wastewater treatment and energy recovery, offering new directions and technical support for advancing the practical applications of MFC technology [34].

Furthermore, the results indicate that all 54 identified subject categories exhibit citation burst phenomena.

Table 5. Detailed information of the top 30 subject categories with the strongest citation bursts in the co-occurrence network.

Subject Categories	Strength	Duration	Begin	End	2004–2024	Count	Centrality
BIOTECHNOLOGY; APPLIED MICROBIOLOGY	17.41	10	2005	2014		262	0.13
AGRICULTURAL ENGINEERING	7.40	7	2010	2016		100	0
ENGINEERING, CHEMICAL	4.21	2	2023	2024		317	0.39
PUBLIC, ENVIRONMENTAL; OCCUPATIONAL HEALTH	4.19	3	2022	2024		20	0
NANOSCIENCE & NANOTECHNOLOGY	3.47	5	2011	2015		28	0.3
ENGINEERING, ELECTRICAL & ELECTRONIC	3.44	4	2013	2016		11	0.15
CHEMISTRY, ANALYTICAL	2.42	2	2018	2019		30	0
PHYSICS, APPLIED	2.34	4	2014	2017		17	0.27
ENGINEERING, ENVIRONMENTAL	2.29	4	2004	2007		300	0.2
ELECTROCHEMISTRY	2.25	2	2009	2010		136	0.38
CHEMISTRY, MULTIDISCIPLINARY	1.89	1	2012	2012		82	0.02
MICROBIOLOGY	1.74	3	2022	2024		15	0
BIOPHYSICS	1.47	1	2019	2019		22	0.19
FOOD SCIENCE & TECHNOLOGY	1.42	2	2023	2024		15	0
ENGINEERING, AEROSPACE	1.28	2	2010	2011		2	0
NUCLEAR SCIENCE & TECHNOLOGY	1.25	1	2022	2022		13	0
WATER RESOURCES	1.22	1	2015	2015		131	0.47
THERMODYNAMICS	1.10	2	2016	2017		19	0.45
ENGINEERING, CIVIL	1.08	2	2023	2024		11	0.13
ENVIRONMENTAL SCIENCES	1.07	2	2004	2005		405	0.31
ENGINEERING, MANUFACTURING	1.05	4	2012	2015		2	0.2
POLYMER SCIENCE	1.03	2	2023	2024		13	0
MATERIALS SCIENCE, COATINGS & FILMS	0.95	2	2021	2022		2	0
PHYSICS, CONDENSED MATTER	0.94	1	2018	2018		7	0.07
GREEN; SUSTAINABLE SCIENCE; TECHNOLOGY	0.87	2	2023	2024		105	0.47
TOXICOLOGY	0.82	2	2023	2024		3	0.07
MULTIDISCIPLINARY SCIENCES	0.81	2	2018	2019		27	0
ECOLOGY	0.80	1	2015	2015		9	0.19
BIOCHEMISTRY; MOLECULAR BIOLOGY	0.79	1	2020	2020		39	0.13
ENGINEERING, BIOMEDICAL	0.77	4	2021	2024		2	0

lists the top 30 subject categories with the strongest citation bursts. Based on the burst detection tool in CiteSpace (version 6.2.R7), the top five categories in terms of citation burst intensity are “Biotechnology; Applied Microbiology” (17.41), “Agricultural Engineering” (7.4), “Chemical Engineering” (4.21), “Public, Environmental; Occupational Health” (4.19), and “Nanoscience & Nanotechnology” (3.47). These categories received significant attention during specific time periods, highlighting their critical role in the corresponding research fields. The colored bars in Table 5 clearly indicate the time intervals of the citation bursts for each category, with red segments representing the onset and duration of the burst periods. For example, the category “Biotechnology; Applied Microbiology” exhibited a citation burst intensity of 17.41 between 2005 and 2014, indicating a substantial increase in research output in this area during that time. This underscores its key role in the study of MFC technology for treating mine tailings. Notably, “Biotechnology; Applied Microbiology” has the longest burst period, lasting 10 years, further reflecting its central importance in interdisciplinary applications. In the early stages of research, the application of MFC technology was primarily focused on fields such as “Environmental Engineering”, “Environmental Sciences”, “Biotechnology; Applied Microbiology”, “Electrochemistry”, “Agricultural Engineering”, and “Engineering, Aerospace”. This multidisciplinary perspective reflects the complexity of mine tailings treatment, encompassing knowledge and methods related to environmental remediation technologies, microbial metabolic mechanisms, electrochemical reaction dynamics, engineering structural design, and resource recycling. In the past two years, significant advancements have been observed in fields such as “Biomedical Engineering”, “Civil Engineering”, “Materials Science (Coatings & Films)”, and “Nuclear Science & Technology”, which have become critical areas in the application of MFC technology for treating mine tailings. This shift from a single disciplinary to a multidisciplinary perspective demonstrates that researchers increasingly recognize the importance of MFC technology not only for its efficiency in pollutant removal, electricity generation, and wastewater resource recovery but also for its potential in enhancing energy conversion efficiency, optimizing microbe–electrode interactions, and developing novel multifunctional materials. With continuous technological advancements, an increasing number of disciplines are expected to provide new perspectives and innovative approaches for the broader application of MFC technology, thereby driving sustained progress in this field, addressing emerging challenges, and seizing new opportunities.

3.6. Keyword Cluster Analysis

Keywords provide concise summaries and descriptions of research themes. Keyword cluster analysis is a valuable bibliometric technique for effectively presenting significant research findings. Table 6 and Figure 9 visually display 16 keyword clusters and their associated attributes, with all key terms arranged according to cluster size. The most prominent cluster is labeled as “#0”. The clustering quality metrics, Q-value and S-value, for this study are 0.7549 and 0.9033, respectively, indicating high reliability of the research outcomes. Clusters #0, #1, #3, #4, #5, #7, #9, and #14 focus primarily on the core applications of MFCs in power generation and energy recovery from mine tailings, encompassing themes such as electricity production, proton exchange membrane optimization, redox reactions, reactor design, and system scalability. Relevant keywords include “electricity production”, “energy recovery”, “power density”, “proton exchange membrane”, and “upscaling”. These clusters highlight research advancements and critical technologies aimed at optimizing MFC systems to enhance the efficiency of energy recovery from mine tailings. Clusters #2, #6, #8, #11, and #15 emphasize the significant applications of MFCs in mine tailings wastewater treatment and pollutant removal, particularly in nitrogen and phosphorus pollution control, constructed wetland development, and innovative ecological technologies. Keywords such as “wastewater treatment”, “nitrogen removal”, “constructed wetland”, “eco-innovative technologies”, and “COD removal” showcase the tremendous potential of MFCs in purifying tailings wastewater and promoting resource recovery. Additionally, clusters #10, #12, and #13 focus on structural optimization of MFC systems and emerging technological applications in comprehensive tailings resource utilization. Key research themes include “forward osmosis”, “microbial community”, and “bioelectrochemical systems”. The top three extensive clusters are “electricity production”, “energy recovery”, and “wastewater treatment”. In contrast, “COD removal” and “microbial fuel cell” are among the earliest identified clusters, while “wastewater treatment”, “oxygen reduction reaction”, “bioelectrochemical systems”, and “forward osmosis” represent the most recent research trends.

The largest cluster (#0) centers on “electricity production”, encompassing 41 keywords such as “microbial fuel cell”, “wastewater treatment”, “microbial electrolysis cell”, “acetogenic wastewater”, “microbial electrochemical technologies”, “electricity production”, and “polymer inclusion membrane”. Studies have demonstrated that optimizing anode and cathode materials in MFCs can significantly enhance power output and pollutant removal efficiency. For instance, Liu et al. (2017) highlighted that integrating anaerobic acidification and forward osmosis (FO) membrane into air-cathode microbial fuel cells (AAFO-MFCs) substantially improved wastewater treatment and energy recovery, achieving a maximum power density of 4.38 W/m³ and removal rates of over 97% for organics and total phosphorus [35]. Similarly, the research by Wlodarczyk et al. (2019) demonstrated the application potential of microbial fuel cells (MFCs) with Cu-B alloy as the cathode catalyst for wastewater treatment and electricity production. The study achieved a current density of 0.21–0.35 mA/cm² and a nitrate (NO3⁻) removal efficiency of 90%, underscoring the feasibility of employing Cu-B alloy in MFCs for sustainable wastewater treatment and energy generation [36].

The second-largest cluster (#1) revolves around “energy recovery”, encompassing 40 keywords such as “microbial fuel cell”, “anaerobic sludge”, “microbial electrocatalysis system”, “microbial electrolytic cell”, “hydrogen production”, “wastewater treatment”, “acetogenic wastewater”, “microbial electrochemical technologies”, and “green synthesis”. This cluster highlights the significant role of MFC technology in energy and resource conversion. By converting the chemical energy in organic waste into electricity, MFC technology not only enables energy recovery but also offers a green and sustainable approach to waste management. Within this cluster, research primarily focuses on optimizing reactor design, enhancing power output efficiency, and achieving large-scale application. These studies provide theoretical support for improving the practicality of MFCs and further promote their broad adoption in the renewable energy sector. Studies have demonstrated that optimizing MFC design and integration can significantly enhance energy recovery efficiency. For example, Li et al. (2014) evaluated the performance of normalized energy recovery (NER) in MFCs, focusing on the effects of reactor size and anode substrate. Their findings revealed that while larger MFCs exhibited lower maximum power density, their NER could be comparable to that of smaller MFCs at the same anode liquid flow rate. This indicates that MFCs can be scaled up under specific conditions without compromising energy recovery. Moreover, low-intensity substrates were found to be more suitable for improving energy recovery and organic removal in wastewater treatment. However, a trade-off exists between energy recovery and pollutant removal efficiency in MFCs, requiring prioritization based on the primary objective [37]. In addition, Su et al. (2013) proposed an innovative system combining sludge microbial fuel cells (S-MFCs) and membrane bioreactors (MBRs) for wastewater treatment, sludge reduction, energy recovery, and membrane fouling mitigation. The study demonstrated that a single S-MFC could convert 75 mg/L of COD into electricity, achieving an average voltage of 430 mV and a maximum power density of 51 mW/m². The combined system not only showed significant energy recovery but also effectively mitigated membrane fouling through sludge modification, highlighting its potential for integrated wastewater treatment and resource recovery [38].

The third major cluster (#2) focuses on “wastewater treatment” and involves 39 keywords, including “microbial fuel cells”, “carbon nanofibers”, “extracellular electron transfer”, “iron-based materials”, “spinel oxide catalysis”, and “bioenergy production”. Research within this cluster primarily focuses on enhancing the capacity of MFCs to treat complex wastewater, including the development of novel high-performance electrode materials, improvement of microbial activity, and optimization of reactor design. Mine tailings wastewater often contains significant amounts of heavy metal ions and organic pollutants, providing abundant electron donors for MFCs. By utilizing iron-based or carbon-based electrode materials with high catalytic activity and excellent conductivity, MFCs can simultaneously treat tailings wastewater and recover electricity [39]. Specifically, iron-based materials and spinel oxide catalysts play a critical role in enhancing the catalytic activity of MFC anodes and improving energy conversion efficiency [40]. Moreover, emerging materials such as carbon nanofibers significantly enhance the conductivity of anodes and improve extracellular electron transfer efficiency, thereby optimizing wastewater treatment capacity and power generation performance [41]. These studies indicate that MFC technology holds significant potential for applications in wastewater treatment plants and the management of mine tailings wastewater, demonstrating its critical role in environmental protection and resource recovery.

The fourth major cluster (#3) focuses on “power density”, encompassing 36 key topics, including “microbial fuel cells”, “anaerobic sludge”, “electricity generation”, “terephthalic acid”, “biochemical oxygen demand”, and “coulombic efficiency”. Power density serves as a critical metric for evaluating the energy recovery efficiency of MFCs, and its optimization directly influences the effectiveness of electricity generation during the treatment of tailings wastewater. Anaerobic sludge, as a key source of electron donors in MFC systems, generates electrons through metabolic activities, which are subsequently transferred to the anode and then to the external circuit to form electric currents. The abundance of organic matter and complex compounds in tailings wastewater provides essential nutrients for anaerobic sludge, and the activity and efficiency of the sludge are crucial for enhancing power density [42]. Moreover, complex organic compounds such as terephthalic acid, commonly found in industrial and tailings wastewater, play a significant role in reducing the system’s biochemical oxygen demand (BOD) and improving coulombic efficiency. The reduction in BOD reflects the degree of biodegradable organic matter removal from the wastewater, while coulombic efficiency measures the proportion of electrons transferred to the anode relative to the total theoretical electrons available [43].

Cluster #4 centers on the theme of “reactor”, encompassing key topics such as “microbial fuel cells”, “wastewater treatment”, “chemical production”, “microbial electrolysis cells”, “green synthesis”, “aerated filters”, “proton exchange membranes”, “carbon fiber electrodes”, and “landfill leachate composition”. The removal of heavy metals and organic pollutants from tailings wastewater often requires efficient reactor designs. Materials such as proton exchange membranes and carbon fiber electrodes play a pivotal role in optimizing electron transfer processes within tailings wastewater treatment systems [44,45]. Additionally, advancements in aerated filters within the reactor can enhance oxygen utilization efficiency at the cathode, thereby improving power generation performance [46].

Cluster #5 focuses on “proton exchange membranes”, encompassing key topics such as “microbial fuel cells”, “proton exchange membranes”, “green energy”, “material costs”, “electron transfer mechanisms”, “wastewater treatment”, “membrane toxicity assessment”, and “wetland-microbial fuel cells”. Proton exchange membranes (PEMs) are one of the core components of MFC systems, with their performance directly influencing electron transfer efficiency and energy recovery outcomes. Optimizing PEM materials not only significantly reduces manufacturing costs but also enhances the stability and durability of MFCs in treating domestic and industrial wastewater [44]. Additionally, wetland-microbial fuel cells, as an emerging wastewater treatment technology, integrate PEMs with wetland systems, effectively improving both wastewater purification efficiency and electricity generation capacity [47].

Cluster #6 focuses on “nitrogen removal”, encompassing key topics such as “microbial fuel cells”, “renewable energy”, “power density”, “heavy metals”, “agro-industrial wastewater”, “microbial community”, “triple-chamber microbial fuel cells”, and “electrode potential”. In MFC systems, nitrogen removal is primarily achieved through biochemical processes such as nitrification, denitrification, and anaerobic ammonium oxidation (ANAMMOX). During nitrification, ammonium (NH₄⁺) is oxidized to nitrate (NO₃⁻) in the anode chamber, while denitrification reduces nitrate to nitrogen gas (N₂) in the cathode chamber. These processes are facilitated by nitrifying and denitrifying bacteria and are accompanied by electron generation and transfer [48,49]. Additionally, under anaerobic conditions, the ANAMMOX process directly converts NH₄⁺ and nitrite (NO₂⁻) into N₂, significantly enhancing nitrogen removal efficiency while reducing electron donor consumption, thereby improving energy recovery efficiency. The relationship between nitrogen removal and energy recovery lies in the utilization of electron donors. Although a portion of organic substrates is consumed during nitrogen removal, optimizing the anode substrate concentration and flow rate can achieve a synergistic effect between the two processes. Furthermore, the introduction of three-chamber MFCs, which spatially separate the anode, cathode, and middle chambers, provides independent environments for nitrification and denitrification, substantially improving nitrogen removal efficiency [50]. Advances in electrode materials, such as the application of doped nanomaterials, and optimization of electrode potentials further enhance the activity of denitrifying bacteria, thereby improving nitrogen removal performance and significantly increasing power density, supporting the effective treatment of complex wastewater and resource recovery.

Cluster #7 focuses on “oxygen reduction reaction (ORR)” and includes key topics such as “microbial fuel cells”, “wastewater treatment”, “Bi-TiO₂ cathode catalyst”, “photocatalyst”, “electrochemical properties”, “oxygen reduction reaction”, “graphene oxide”, “cuprous oxide nanoparticles”, “livestock wastewater”, and “pollution control”. The ORR is a critical process in the cathode of MFCs, primarily responsible for combining electrons with oxygen to produce water or hydrogen peroxide, thereby completing electron transfer and maintaining circuit closure [51]. To enhance the efficiency of ORR, researchers have extensively focused on developing high-performance catalysts. Catalysts such as Bi-TiO₂, graphene oxide, and cuprous oxide nanoparticles have demonstrated significant improvements in cathodic catalytic activity and electron transfer efficiency [52].

Cluster #8 focuses on “bioelectrochemical systems” and includes key topics such as “microbial fuel cells”, “bio-electrochemical treatment”, “bioelectrochemical systems”, “anaerobic mixed consortia”, “nutrient recovery”, “wastewater treatment”, “contaminant removal”, “metalloids recovery”, “biofuel recovery”, and “nutrient recovery”. Bioelectrochemical systems (BESs) represent an advanced technology that combines biological and electrochemical processes. These systems leverage microbial communities, typically in anaerobic environments, to facilitate electron transfer, drive pollutant removal, and simultaneously recover valuable resources such as nutrients, biofuels, and metalloid compounds [53,54]. Moreover, the integration of BES with MFCs demonstrates significant potential. In this hybrid system, MFCs convert electrons generated by microbial metabolism into electrical energy via electrodes, while BES, through its unique electrochemical mechanisms, achieves precise degradation of complex pollutants and efficient resource recovery [55].

Cluster #9 focuses on “upscaling”, encompassing key topics such as “microbial fuel cells”, “urban wastewater treatment”, “electrochemical snorkel”, “active biofilms”, “closed circuit”, “wastewater treatment”, “bioelectrochemical systems”, “titanium oxide”, “carbon nanotubes”, and “membrane microbial fuel cells”. The upscaling of MFCs is a critical pathway for transitioning this technology from laboratory research to practical engineering applications. During the upscaling process, MFCs face several key challenges, including increased system complexity, optimization of electrode materials, maintenance of electron transfer efficiency, and stability in wastewater treatment performance. Among these, novel materials such as titanium oxide and carbon nanotubes have demonstrated exceptional potential in enhancing electrode performance by significantly improving conductivity and catalytic activity while also strengthening the stability of biofilms and electron transfer capabilities [56]. Additionally, the optimization of active biofilms contributes to more efficient electron capture and transfer, thereby enhancing the overall energy recovery efficiency of the system [57].

Cluster #10 focuses on “forward osmosis”, encompassing key topics such as “microbial fuel cells”, “artificial intelligence”, “parameter estimation”, “bioresource recovery”, “carbon sequestration”, “wastewater treatment”, “carbon nanofibers”, “membrane fouling”, “silver nanoparticles”, and “osmotic microbial fuel cells”. Forward osmosis is a membrane technology that achieves high-efficiency water separation with low energy consumption. When integrated with MFCs, it forms the osmotic microbial fuel cell (OMFC) system, which exhibits significant potential in the fields of wastewater treatment and resource recovery. FO not only enhances the wastewater treatment performance of MFCs but also effectively reduces energy consumption, thereby improving the overall efficiency of the system [58]. Furthermore, advanced materials such as carbon nanofibers and silver nanoparticles have been utilized to enhance membrane performance, significantly mitigating membrane fouling and extending membrane lifespan, which further improves the stability and economic feasibility of the system [41].

Cluster #11 focuses on “constructed wetlands”, encompassing key topics such as “microbial fuel cells”, “hexavalent chromium”, “hydrodynamic effects”, “organic frameworks”, “resource recovery”, “wastewater treatment”, “electricity generation”, “liquid velocity”, “parallel modes”, and “electroactive wetlands”. The integration of constructed wetland systems with MFCs enables simultaneous pollutant removal and electricity recovery. The fundamental mechanism relies on the synergistic effects of wetland plants and microorganisms to promote the degradation, transformation, and valorization of pollutants [59]. Additionally, electroactive wetland systems enhance the efficiency of electron transfer pathways by optimizing hydrodynamic effects, such as controlling liquid velocity, thereby improving electricity recovery capabilities [60]. For the treatment of hexavalent chromium, electroactive materials within the system (e.g., organic framework materials) facilitate redox reactions that convert hexavalent chromium into the less toxic trivalent chromium, significantly reducing wastewater toxicity [61]. Furthermore, by employing parallel modes, the system can achieve large-scale tailings wastewater treatment capacity, meeting the high-flow demands of practical applications in the mining sector [62].

Cluster #12 focuses on “eco-innovative technologies”, encompassing key topics such as “microbial fuel cells”, “roughened surface graphite”, “salt removal”, “energy production”, “microbial desalination cells”, “wastewater treatment”, “bioelectrochemical systems”, “eco-innovative technologies”, “electro-active bacteria”, and “dairy industry wastewater”. Eco-innovative technologies aim to optimize resource utilization and pollution control through environmentally friendly methods. As a representative eco-innovative technology, microbial desalination cells (MDCs) integrate the electron transfer mechanism of MFCs with membrane separation technology, enabling multifunctional applications, including wastewater treatment, salt removal, and energy production [63]. This technology demonstrates significant advantages in treating high-salinity wastewater (e.g., dairy industry wastewater) and highly mineralized polluted water. The introduction of advanced electrode materials such as roughened surface graphite substantially enhances the conductivity of the system and promotes microbial attachment, thereby improving electron transfer efficiency and power generation capacity [64]. Additionally, electro-active bacteria, through their synergistic interaction with the electrodes, facilitate pollutant degradation and resource recovery, ensuring the stable operation of the system even in complex water environments [65].

Cluster #13 focuses on “microbial community”, encompassing key topics such as “microbial community”, “bioelectricity production”, “wetland-microbial fuel cell (Wetland-MFC)”, “NB wastewater”, “radial oxygen loss”, “microbial fuel cell”, “renewable energy”, “power density”, “ryegrass litter”, and “Alicyclobacillus hesperidum”. Microbial communities play a crucial role in MFCs, particularly in wetland-MFC systems, where they participate in organic matter degradation and electron transfer, driving the bioelectricity generation process. Ryegrass litter serves as a potential electrode material that enhances the structural stability and electrical conductivity of the system [66]. Furthermore, the introduction of electroactive bacteria such as Alicyclobacillus hesperidum significantly improves the electron transfer capabilities of the electrodes. In addition, the impact of microbial communities on oxygen loss is a critical area of research. By optimizing the interactions between electrode surfaces and microbial communities, radial oxygen loss can be effectively mitigated, thereby improving the power density and stability of the MFC system [67].

Cluster #14 focuses on “microbial fuel cells”, encompassing key topics such as “microbial fuel cells”, “microfiltration membranes”, “performance improvement”, “multiple sludge systems”, “wastewater treatment”, “electricity production”, “electrochemical analysis”, and “fish market wastewater”. As an innovative technology that integrates wastewater treatment with electricity generation, MFCs utilize microbial metabolic activities to degrade organic matter and convert it into electrical energy. The key to this technology lies in optimizing the synergy between electrode materials, membrane components, and microbial communities to enhance system performance and stability. The introduction of microfiltration membranes provides critical support for improving MFC performance, effectively separating sludge and pollutants and increasing wastewater treatment efficiency [68]. Furthermore, the application of multiple sludge systems enables more efficient degradation of complex organic matter, such as that found in fish market wastewater, thereby enhancing electricity recovery. Electrochemical analysis serves as a precise tool to evaluate electron transfer and electrode reactions within the MFC system, offering guidance for further performance optimization [69,70].

Cluster #15 focuses on “chemical oxygen demand (COD) removal”, encompassing key topics such as “microbial fuel cells”, “wastewater treatment”, “environmental sustainability”, “electrode fabrication”, “electron transfer mechanisms”, “continuous flow”, “manganese dioxide”, “octahedral molecular sieves”, and “operational condition effects”. COD, a critical indicator of organic matter concentration in wastewater, is one of the primary targets for efficient removal in wastewater treatment. In MFC systems, COD removal is achieved through microbial communities metabolizing organic matter and releasing electrons. These electrons are transferred to the external circuit via the electrodes, where they are converted into electrical energy. Electrode fabrication and electron transfer mechanisms are pivotal factors influencing both COD removal efficiency and energy recovery performance [71,72]. The introduction of novel electrode materials, such as manganese dioxide and octahedral molecular sieves, significantly enhances the conductivity and catalytic properties of the electrodes, enabling more efficient electron capture and transfer to the external circuit [73]. Additionally, the implementation of continuous flow operation optimizes wastewater flow paths and retention times, thereby improving system stability and wastewater treatment performance [74].

The clusters highlight the technological innovations of microbial fuel cells in mine tailings treatment and power generation, covering areas such as performance optimization, material development, pollutant removal, and resource recovery, showcasing their potential applications in environmental remediation and energy recovery.

Figure 9. A cluster analysis of research keywords on microbial fuel cell applications for mine tailings treatment and power generation (2004–2024).

Figure 9. A cluster analysis of research keywords on microbial fuel cell applications for mine tailings treatment and power generation (2004–2024).

Table 6. Analysis of keyword clusters and associated features.

Cluster ID	Cluster Name	Size	Silhouette	Mean (Year)	Main Keywords
0	electricity production	41	0.879	2009	microbial fuel cell; wastewater treatment; microbial electrolysis cell; acetogenic wastewater; microbial electrochemical technologies | microbial fuel cells; electricity generation; electricity production; water depuration; polymer inclusion membrane
1	energy recovery	40	0.894	2010	microbial fuel cell; anaerobic sludge; microbial electrocatalysis system; microbial electrolytic cell; hydrogen production | wastewater treatment; microbial electrolysis cell; acetogenic wastewater; microbial electrochemical technologies; green syntheses
2	wastewater treatment	39	0.840	2011	wastewater treatment; microbial fuel cell; carbon nanofibers; extracellular electron; fe-based material | microbial fuel cells; power performance; spinel oxides; catalytic activity; bioenergy production
3	power density	36	0.852	2010	microbial fuel cell; anaerobic sludge; electricity generation; terephthalic acid; biological oxygen demand | power density; coulombic efficiency; current density; industrial wastewater; organic load
4	reactor	34	0.879	2009	microbial fuel cell; wastewater treatment; chemical production; microbial electrolysis cells; green syntheses | microbial fuel cells; biological aerated filters; proton exchange membranes; carbon veil electrodes; landfill leachate composition
5	proton exchange membrane	33	0.876	2010	microbial fuel cell; proton exchange membrane; green energy; materials cost; electron transfer mechanism | wastewater treatment; membrane microbial fuel cell; domestic wastewater; toxicity assessment; wetland-microbial fuel cell
6	nitrogen removal	32	0.975	2010	microbial fuel cell; renewable energy; power density; heavy metals; agro-industrial wastewater | nitrogen removal; microbial community; triple-chamber microbial fuel cell; heavy metals; electrode potential
7	oxygen reduction reaction	32	0.864	2011	microbial fuel cell; wastewater treatment; bi-tio2 cathode catalyst; photo catalyst; electro-chemical properties | oxygen reduction reaction; graphene oxide; cuprous oxide nanoparticles; cattle wastewater; pollution control
8	bioelectrochemical systems	30	0.945	2011	microbial fuel cell; bio-electrochemical treatment; bio-electrochemical system; anaerobic mixed consortia; nutrient recovery | wastewater treatment; contaminant removal; metalloids recovery; biofuel recovery; nutrients recovery
9	upscaling	28	0.920	2009	microbial fuel cell; urban wastewater treatment; electrochemical snorkel; active biofilms; closed circuit | wastewater treatment; bioelectrochemical system; titanium oxide; carbon nanotube; membrane microbial fuel cell
10	forward osmosis	28	0.955	2011	microbial fuel cell; artificial intelligence; parameter estimation; bioresource recovery; carbon sequestration | wastewater treatment; carbon nanofibers; membrane fouling; silver nanoparticle; osmotic microbial fuel cell
11	constructed wetland	23	0.916	2009	microbial fuel cell; hexavalent chromium; hydrodynamics effects; organic framework; resources recovery | wastewater treatment; electricity generation; liquid velocity; parallel modes; electroactive wetlands
12	eco-innovative technologies	19	0.881	2010	microbial fuel cell; roughened surface graphite; salt removal; energy production; microbial desalination cell | wastewater treatment; bioelectrochemical systems; eco-innovative technologies; electro-active bacteria; dairy industry wastewater
13	microbial community	19	0.947	2010	microbial community; bioelectricity generation; wetland-microbial fuel cell; nb wastewater; radial oxygen loss | microbial fuel cell; renewable energy; power density; ryegrass litter; alicyclobacillus hesperidum
14	microbial fuel cell	17	0.969	2008	microbial fuel cell; microfiltration membrane; performance improvement; multiple sludge; performance | wastewater treatment; microbial fuel cells; electricity production; electrochemical analysis; fish market wastewater
15	cod removal	14	1	2007	microbial fuel cell; wastewater treatment; environmental sustainability; electrode fabrication; electron transfer mechanism | microbial fuel cells; continuous flow; manganese dioxides; octahedral molecular sieves; operation condition effect

Table 6. Analysis of keyword clusters and associated features.

Cluster ID	Cluster Name	Size	Silhouette	Mean (Year)	Main Keywords
0	electricity production	41	0.879	2009	microbial fuel cell; wastewater treatment; microbial electrolysis cell; acetogenic wastewater; microbial electrochemical technologies | microbial fuel cells; electricity generation; electricity production; water depuration; polymer inclusion membrane
1	energy recovery	40	0.894	2010	microbial fuel cell; anaerobic sludge; microbial electrocatalysis system; microbial electrolytic cell; hydrogen production | wastewater treatment; microbial electrolysis cell; acetogenic wastewater; microbial electrochemical technologies; green syntheses
2	wastewater treatment	39	0.840	2011	wastewater treatment; microbial fuel cell; carbon nanofibers; extracellular electron; fe-based material | microbial fuel cells; power performance; spinel oxides; catalytic activity; bioenergy production
3	power density	36	0.852	2010	microbial fuel cell; anaerobic sludge; electricity generation; terephthalic acid; biological oxygen demand | power density; coulombic efficiency; current density; industrial wastewater; organic load
4	reactor	34	0.879	2009	microbial fuel cell; wastewater treatment; chemical production; microbial electrolysis cells; green syntheses | microbial fuel cells; biological aerated filters; proton exchange membranes; carbon veil electrodes; landfill leachate composition
5	proton exchange membrane	33	0.876	2010	microbial fuel cell; proton exchange membrane; green energy; materials cost; electron transfer mechanism | wastewater treatment; membrane microbial fuel cell; domestic wastewater; toxicity assessment; wetland-microbial fuel cell
6	nitrogen removal	32	0.975	2010	microbial fuel cell; renewable energy; power density; heavy metals; agro-industrial wastewater | nitrogen removal; microbial community; triple-chamber microbial fuel cell; heavy metals; electrode potential
7	oxygen reduction reaction	32	0.864	2011	microbial fuel cell; wastewater treatment; bi-tio2 cathode catalyst; photo catalyst; electro-chemical properties | oxygen reduction reaction; graphene oxide; cuprous oxide nanoparticles; cattle wastewater; pollution control
8	bioelectrochemical systems	30	0.945	2011	microbial fuel cell; bio-electrochemical treatment; bio-electrochemical system; anaerobic mixed consortia; nutrient recovery | wastewater treatment; contaminant removal; metalloids recovery; biofuel recovery; nutrients recovery
9	upscaling	28	0.920	2009	microbial fuel cell; urban wastewater treatment; electrochemical snorkel; active biofilms; closed circuit | wastewater treatment; bioelectrochemical system; titanium oxide; carbon nanotube; membrane microbial fuel cell
10	forward osmosis	28	0.955	2011	microbial fuel cell; artificial intelligence; parameter estimation; bioresource recovery; carbon sequestration | wastewater treatment; carbon nanofibers; membrane fouling; silver nanoparticle; osmotic microbial fuel cell
11	constructed wetland	23	0.916	2009	microbial fuel cell; hexavalent chromium; hydrodynamics effects; organic framework; resources recovery | wastewater treatment; electricity generation; liquid velocity; parallel modes; electroactive wetlands
12	eco-innovative technologies	19	0.881	2010	microbial fuel cell; roughened surface graphite; salt removal; energy production; microbial desalination cell | wastewater treatment; bioelectrochemical systems; eco-innovative technologies; electro-active bacteria; dairy industry wastewater
13	microbial community	19	0.947	2010	microbial community; bioelectricity generation; wetland-microbial fuel cell; nb wastewater; radial oxygen loss | microbial fuel cell; renewable energy; power density; ryegrass litter; alicyclobacillus hesperidum
14	microbial fuel cell	17	0.969	2008	microbial fuel cell; microfiltration membrane; performance improvement; multiple sludge; performance | wastewater treatment; microbial fuel cells; electricity production; electrochemical analysis; fish market wastewater
15	cod removal	14	1	2007	microbial fuel cell; wastewater treatment; environmental sustainability; electrode fabrication; electron transfer mechanism | microbial fuel cells; continuous flow; manganese dioxides; octahedral molecular sieves; operation condition effect

3.7. Co-Citation Clustering Analysis of References

Previous studies have laid a solid foundation for scientific exploration. In simple terms, subsequent research typically cites prior publications within the same field or on closely related topics. When two articles are simultaneously cited in the same reference list, a co-citation relationship is formed [75]. Co-citation analysis reveals the interconnections and structure within academic topics, as co-cited publications often share potential relevance. By employing clustering tools in co-citation networks, references can be categorized into different clusters based on the strength of their associations. References within the same cluster exhibit strong connections, whereas those in different clusters are relatively loosely connected. In this study, the constructed reference co-citation network was divided into 15 clusters. Figure 8 illustrates the clustering results, with an average Q-value of 0.7541 and an average S-value of 0.905, indicating high accuracy of the analysis. Detailed information about these clusters is presented in Table 7. From Figure 10 and Table 7, significant differences in cluster sizes can be observed: the largest cluster (#0) consists of 153 nodes, accounting for 16.9% of the total network nodes, while the smallest cluster (#15) represents only 0.7% of the network. The following discussion focuses on analyzing the 16 clusters (including Cluster #0) related to the application of microbial fuel cells in treating mine tailings for electricity generation: Cluster #0 is titled “cathode catalyst”, Cluster #1 “internal resistance”, Cluster #2 “bioelectricity generation”, Cluster #3 “mixed consortia”, Cluster #4 “membrane bioreactor”, Cluster #5 “electricity”, Cluster #6 “scaling-up”, Cluster #7 “chlorella vulgaris”, Cluster #8 “constructed wetland”, Cluster #9 “eco-innovative technologies”, Cluster #10 “photosynthetic microbial fuel cell”, Cluster #11 “electrode materials”, Cluster #12 “fuel cells”, Cluster #13 “bio-electrochemical system”, Cluster #14 “energy saving”, and Cluster #15 “source inoculum”. Among these, Cluster #0 and Cluster #10 represent recent research hotspots, while Cluster #3 and Cluster #5 are associated with earlier developments in the field.

Clusters #0, #4, and #5 emphasize the complex research on materials and electrochemical performance in MFCs. Cluster #0, termed “cathode catalyst”, primarily focuses on optimizing cathode catalysts to enhance electron transfer efficiency and power density in MFCs. The study by Bhowmick et al. (2021) developed a Bi-Ru catalyst for MFCs, significantly improving power density, coulombic efficiency, and energy recovery compared to platinum-based catalysts, demonstrating its potential as a viable alternative to platinum in MFC applications [29]. Cluster #4, “membrane bioreactor”, explores the application of membrane technology in MFCs to optimize ion exchange processes and reduce internal resistance. Wang et al. (2012) proposed an integrated system combining MFCs and a membrane bioreactor (MBR), achieving simultaneous optimization of wastewater treatment and energy recovery. The system demonstrated promising electricity generation and effluent quality, highlighting its potential for practical applications [76]. Cluster #5, “electricity”, focuses on the electrochemical characteristics of MFCs in generating power during the treatment of mine tailings. Mahto et al. (2024) reviewed the role of electroactive bacterial communities in MFCs for wastewater treatment and bioelectricity generation, with a particular emphasis on the composition, structure, and function of electroactive biofilms, as well as electron transfer mechanisms. The study also summarized strategies for optimizing process parameters and genetic engineering to enhance MFC performance, while highlighting applications of MFCs in wastewater treatment, bioelectricity generation, and biosensor development [77].

Clusters #1, #2, and #3 focus on the environmental applications of MFCs. Cluster #1, “internal resistance”, investigates strategies for reducing internal resistance, a key factor limiting MFC performance. Enhancing electrode structures and optimizing separator materials have been shown to significantly lower internal resistance and improve overall efficiency [78]. Cluster #2, “bioelectricity generation”, emphasizes the practical application of bioelectricity generation in MFCs during the treatment of mine tailings. Thulasinathan et al. (2022) explored the advancements in utilizing industrial wastewater rich in organic matter as substrates for bioelectricity generation in MFCs. The study analyzed the impact of substrate selection on green energy recovery and highlighted technological improvements and future challenges [79]. Cluster #3, “mixed consortia”, examines approaches to enhancing power generation by employing mixed microbial communities. Leveraging microbial diversity optimizes degradation pathways and increases current density, providing an effective strategy to improve MFC performance [80].

Clusters #6 and #7 highlight the innovative role of MFCs in sustainable development. Cluster #6, “scaling-up”, discusses the challenges and strategies involved in expanding MFC systems from laboratory-scale to pilot or industrial-scale applications. Liang et al. (2018) constructed a 1000 L modularized MFC system for practical municipal wastewater treatment, demonstrating its stable performance under varying initial COD concentrations and showcasing the potential of MFC technology for large-scale applications [81]. Cluster #7, “chlorella vulgaris”, introduces the integration of algae with MFCs. The study by Reddy et al. (2019) explored the feasibility of using chlorella vulgaris as a bio-cathode, leveraging photosynthesis to enhance electron transfer while simultaneously achieving carbon sequestration [82].

Clusters #10, #13, and #15 reveal emerging research directions in MFC technology. Cluster #10, “photosynthetic microbial fuel cell”, investigates systems combining photosynthetic microorganisms with electroactive microbes to achieve higher energy output, affording potential advantages in the treatment of mine tailings containing residual organic carbon [83]. Cluster #13, “bio-electrochemical system”, emphasizes the integration of MFCs with other bio-electrochemical processes to enhance waste valorization capabilities [84]. Cluster #15, “source inoculum”, explores the impact of inoculum sources on MFC performance, particularly how the selection of inoculum from different environments affects electrochemical properties and biofilm formation [85].

In summary, the co-citation analysis of research on MFCs for power generation during mine tailings treatment has revealed several key directions, including material optimization, environmental sustainability, challenges in scaling-up applications, and system innovation and integration. MFC technology demonstrates potential not only in addressing complex environmental issues but also in enabling the production of renewable energy. These findings reflect the dynamic evolution of MFC technology, providing interdisciplinary and innovative solutions for the sustainable management and resource utilization of mine tailings.

Figure 10. A co-citation cluster analysis of literature on microbial fuel cells for mine tailings power generation (2004–2024).

Figure 10. A co-citation cluster analysis of literature on microbial fuel cells for mine tailings power generation (2004–2024).

Table 7. Analysis of document co-citation clusters and their features.

Cluster ID	Cluster Name	Size	Silhouette	Mean (Year)	Top Three Most Cited Publications
0	cathode catalyst	153	0.942	2019	Santoro, C. (2017); Palanisamy, G. (2019); Slate, A.J. (2019)
1	internal resistance	102	0.802	2009	Pant, D. (2010); Logan, B. (2007); Zhou, M.H. (2011)
2	bioelectricity generation	98	0.893	2019	Gupta, S. (2021); Srivastava, P. (2020); Xu, F. (2018)
3	mixed consortia	88	0.878	2006	Rabaey, K. (2005); Moon, H. (2006); Lu, N. (2009)
4	membrane bioreactor	83	0.837	2012	Li, W.W. (2014); Logan, B.E. (2012); Zhang, F. (2013)
5	electricity	83	0.967	2003	Logan, B.E. (2006); Liu, H. (2004); Liu, H. (2005)
6	scaling-up	70	0.904	2017	Liang, P. (2018); Logan, B.E. (2015); Dong, Y. (2015)
7	chlorella vulgaris	51	0.913	2012	Pandey, P. (2016); Rahimnejad, M. (2015); Mohan, S.V. (2014)
8	constructed wetland	38	0.948	2014	Liu, S.T. (2014); Doherty, L. (2015); Doherty, L. (2015)
9	eco-innovative technologies	38	0.968	2015	Gude, V.G. (2016); Kim, K.Y. (2016); Kim, K.Y. (2015)
10	photosynthetic microbial fuel cell	28	0.929	2019	Mohamed, S.N. (2020); Yang, Z.G. (2018); Reddy, C.N. (2019)
11	electrode materials	27	0.952	2012	Hernández-Fernández, F.J. (2015); Leong, J.X. (2013); Xiao, L. (2012)
12	fuel cells	23	0.955	2009	Cao, X.X. (2009); Freguia, S. (2008); Kim, J.R. (2007)
13	bio-electrochemical system	10	0.928	2013	Wang, H.M. (2013); Cusick, R.D. (2012); Wang, H.M. (2014)
14	energy saving	7	0.991	2011	Kiely, P.D. (2011); Chae, K.J. (2009); Yu, C.P. (2011)
15	source inoculum	6	0.991	2009	de Schamphelaire, L. (2008); Osman, M.H. (2010); Wagner, R.C. (2009)

Table 7. Analysis of document co-citation clusters and their features.

Cluster ID	Cluster Name	Size	Silhouette	Mean (Year)	Top Three Most Cited Publications
0	cathode catalyst	153	0.942	2019	Santoro, C. (2017); Palanisamy, G. (2019); Slate, A.J. (2019)
1	internal resistance	102	0.802	2009	Pant, D. (2010); Logan, B. (2007); Zhou, M.H. (2011)
2	bioelectricity generation	98	0.893	2019	Gupta, S. (2021); Srivastava, P. (2020); Xu, F. (2018)
3	mixed consortia	88	0.878	2006	Rabaey, K. (2005); Moon, H. (2006); Lu, N. (2009)
4	membrane bioreactor	83	0.837	2012	Li, W.W. (2014); Logan, B.E. (2012); Zhang, F. (2013)
5	electricity	83	0.967	2003	Logan, B.E. (2006); Liu, H. (2004); Liu, H. (2005)
6	scaling-up	70	0.904	2017	Liang, P. (2018); Logan, B.E. (2015); Dong, Y. (2015)
7	chlorella vulgaris	51	0.913	2012	Pandey, P. (2016); Rahimnejad, M. (2015); Mohan, S.V. (2014)
8	constructed wetland	38	0.948	2014	Liu, S.T. (2014); Doherty, L. (2015); Doherty, L. (2015)
9	eco-innovative technologies	38	0.968	2015	Gude, V.G. (2016); Kim, K.Y. (2016); Kim, K.Y. (2015)
10	photosynthetic microbial fuel cell	28	0.929	2019	Mohamed, S.N. (2020); Yang, Z.G. (2018); Reddy, C.N. (2019)
11	electrode materials	27	0.952	2012	Hernández-Fernández, F.J. (2015); Leong, J.X. (2013); Xiao, L. (2012)
12	fuel cells	23	0.955	2009	Cao, X.X. (2009); Freguia, S. (2008); Kim, J.R. (2007)
13	bio-electrochemical system	10	0.928	2013	Wang, H.M. (2013); Cusick, R.D. (2012); Wang, H.M. (2014)
14	energy saving	7	0.991	2011	Kiely, P.D. (2011); Chae, K.J. (2009); Yu, C.P. (2011)
15	source inoculum	6	0.991	2009	de Schamphelaire, L. (2008); Osman, M.H. (2010); Wagner, R.C. (2009)

In the field of MFC research, nodes marked with a purple outer ring represent publications that exhibit co-citation links with multiple other works. These nodes serve as hubs during specific periods, reflecting the focus and direction of research. In contrast, nodes with a red outer ring indicate highly cited publications that constitute the foundational knowledge in the study of MFC-based power generation for mine tailings treatment. These publications hold critical importance and are likely to attract significant attention from researchers. The timeline view (Figure 11) provides researchers with a concise overview of research trends and guidance in this field. For instance, when searching for “cathode catalyst”, the seminal study by Huggins et al. (2015) demonstrates a representative example. This study utilized high-temperature pyrolysis and alkaline post-treatment to prepare lignocellulosic-derived graphitized biochar (BCw), which was then employed as a support material for manganese oxide electrocatalysts (MnO/BCw) in MFC air cathodes. The research successfully anchored nanostructured MnO₂ crystals onto the surface of the graphitized biochar and characterized its properties using physical, chemical, and electrochemical techniques. Results showed that MnO/BCw exhibited excellent electrocatalytic activity and oxygen reduction reaction performance, achieving high power density in MFC applications. This material represents a cost-effective and scalable cathode material suitable for energy recovery in the context of tailings treatment [86]. In comparison to earlier studies, recent key literature has focused on the extensive applications of MFCs in mine tailings treatment and the resource utilization of other industrial waste. These studies emphasize the optimization of MFC system structures, the development of novel catalysts and electrode materials, and the interactions between microbial communities and complex substrates. Specifically, these studies summarize the potential of MFCs in treating heavy metal-contaminated tailings wastewater, recovering valuable metallic elements, generating green electricity, and achieving carbon sequestration. They also highlight the challenges faced by this technology in industrial applications and propose directions for future development [87]. Within this research trajectory, 2019 emerged as a significant milestone for MFC applications in mine tailings treatment. MFC technology, leveraging the bioelectrochemical activity of electroactive microorganisms, not only facilitates processes such as COD removal, nitrification, denitrification, and sulfate reduction in tailings wastewater but also enables the effective removal and recovery of heavy metal ions [88]. For example, integrating MFCs with traditional wastewater treatment technologies can create hybrid systems that achieve energy neutrality and resource recovery simultaneously. As a multifunctional technology, MFCs demonstrate unique advantages in addressing critical challenges in tailings wastewater treatment and energy recovery. Moreover, they show significant potential for large-scale applications, providing essential support for the sustainable development of the mining industry.

3.8. Latest Advances and Emerging Trends in MFCs for Mine Tailings Treatment and Power Generation

Through an in-depth analysis of key literature and main themes in this field, the research focus and development trends of MFCs in mine tailings treatment and power generation over the past 21 years have been comprehensively reviewed.

3.8.1. Application of MFCs in Tailings Treatment

Microbial fuel cells are bioelectrochemical systems that utilize electroactive microorganisms to directly convert chemical energy into electrical energy under specific environmental conditions. Due to its unique advantages in wastewater treatment, pollutant degradation, and electricity generation, MFC technology has gradually gained widespread attention in the field of mine tailings treatment. Mine tailings typically contain high concentrations of toxic pollutants, particularly heavy metals and organic compounds, which pose significant threats to the environment and ecosystems. MFCs not only effectively treat these pollutants but also generate electrical energy, providing a green energy solution for the disposal of mine tailings. To provide a more intuitive understanding of the specific performance of different types of MFCs in tailings treatment, this paper has compiled relevant research performance indicators, as shown in

Table 8. Performance of different types of MFCs in tailings treatment.

MFC Type	Tailings Characteristics	Operating Conditions	Design Features	Performance and Innovations
Single-Chamber MFC	High iron content (Fe2+ concentration: several hundred mg/L), initial pH 4–5	Temperature controlled at 20–30 °C, pH maintained at 4–5 using buffers, influent flow rate ~1 L/d	Utilizes activated carbon or carbon fiber as anode material, simple single-chamber structure	Achieves high organic degradation (≈80–90%), partial iron recovery, optimizes economic aspects of tailings treatment
Dual-Chamber MFC	Sulfur-containing tailings (sulfide concentration: several hundred mg/L), initial pH 5–7	Temperature maintained at 25–35 °C, pH regulated automatically, reaction time ~24–72 h	Dual-chamber design with proton exchange membrane, cathode may use platinum catalysts or other catalytic materials	Effective sulfide removal (≈85-95%), enhances sulfide oxidation efficiency, reduces environmental pollution risks, and optimizes energy output
Multi-Stage MFC System	High moisture content (≥70%), high heavy metal concentration	Temperature set at 30–40 °C, pH automatically adjusted through multi-stage cycling system	Multi-stage series reactor design, each stage equipped with different functional electrode materials	Significantly improves heavy metal removal efficiency (≈90–98%), further degrades organic matter, optimizes energy recovery efficiency, enhances overall system performance through multi-stage processing
Fixed-Membrane MFC	Arsenic-containing tailings (arsenic concentration: tens of mg/L), initial pH 5–6	Temperature controlled at 25–30 °C, pH maintained at 5–6, utilizes fixed membrane structure	Fixed membrane design enhances microbial attachment, anode typically made of carbon fiber fixed membrane	High arsenic removal rate (≈85–95%), significant organic degradation, fixed membrane design improves microbial stability and attachment, enhances treatment efficiency
Nanomaterial-Modified MFC	High copper content (Cu2+ concentration: hundreds of mg/L), initial pH 6–8	Temperature set at 30–35 °C, pH stabilized using buffering system, electrodes modified with nanomaterials	Electrode materials use nanostructured silver, carbon, or other nanocomposites, enhancing conductivity and catalytic activity	Significantly improves copper removal rate (≈90–99%), enhances organic degradation efficiency, increases energy output, nanomaterial modification significantly enhances electrode performance and overall system efficiency

.

• Pollutant Degradation and Resource Recovery: In the treatment of mine tailings, microbial fuel cells primarily function by reducing heavy metals and degrading organic pollutants, thereby removing pollutants and recovering valuable resources. Electroactive microorganisms play a key role in MFCs, as these microorganisms are capable of oxidizing organic matter in the tailings wastewater through their metabolic activities, releasing electrons in the process [89]. These electrons flow through an external circuit to the cathode, establishing an electrochemical gradient between the anode and cathode, which drives the generation of electrical energy. At the cathode, electrochemical reduction reactions enable heavy metal ions, such as copper, nickel, and lead, to be reduced to metallic forms or converted into less toxic species [90]. This process not only facilitates the removal of heavy metals, reducing their environmental toxicity, but also enables the recovery of metals. For example, in copper-containing mine tailings, copper ions can be electrochemically reduced to metallic copper within the MFC system, providing raw materials for subsequent metal extraction processes. Additionally, electrochemical reduction reactions in MFCs offer an effective method for removing other harmful substances in the tailings, such as cyanides and arsenic.
• Simultaneous Power Generation Function: In the operation of microbial fuel cells, electroactive microorganisms not only perform the task of pollutant degradation but also generate an electric current between the anode and cathode through their metabolic activities. This concurrent power generation capability is especially crucial in mining areas or environments located in remote regions where traditional power infrastructure is lacking. Specifically, MFCs can provide stable electrical output while processing mine tailings, wastewater, and other harmful substances, sufficient to power on-site monitoring equipment, sensor systems, data acquisition devices, and low-power electronic devices. In many remote mining areas, power supply often relies on diesel generators or other non-renewable energy sources, which result in high operational costs and increased environmental burdens. MFCs, with their independent power generation function, offer a green and sustainable energy solution for these regions. For instance, at mining sites, MFCs can supply electricity to water quality monitoring devices or real-time data collection systems, ensuring the continuous monitoring and feedback of pollutant concentrations, thereby enhancing the efficiency and accuracy of tailings treatment [91]. Moreover, the concurrent power generation characteristic of MFCs provides a unique competitive advantage in resource-limited environments.
• Environmentally Friendly Technology: Microbial fuel cells exhibit significant advantages in terms of mild operational conditions and environmental sustainability. Compared to traditional chemical or physical treatment methods, MFC systems operate without the need for additional chemical reagents or catalysts, nor do they require high-temperature or high-pressure conditions. This results in a mild operating environment, low energy consumption, and a reduced dependency on external energy sources. Compared to conventional fuel cells, MFCs offer significant advantages in operating conditions and environmental impact.

  Table 9. Comparison of microbial fuel cells and conventional fuel cells.

  Characteristic	Microbial Fuel Cells	Conventional Fuel Cells
  Energy Source	Organic wastewater, mine tailings wastewater, etc.	Hydrogen, methanol, etc.
  Operating Principle	Electrons generated through microbial metabolic activity, transferred via electrodes to produce electricity	Chemical reactions (e.g., hydrogen or methanol oxidation) generate electricity
  Operating Conditions	Ambient temperature and pressure, mild operating conditions	High temperature and pressure, often requiring catalysts
  Environmental Impact	Simultaneously treats pollutants and generates clean energy, environmentally friendly	May rely on non-renewable fuels or precious metal catalysts
  Applications	Suitable for wastewater treatment, mine tailings management, and energy supply in remote areas	Primarily used for clean energy supply (e.g., vehicles, power stations)
  Technical Challenges	Low power density; optimizing and maintaining microbial communities is critical	Dependence on high-purity fuels and high-cost catalysts

  summarizes the differences between the two in terms of operating principles, energy efficiency, and environmental impact, providing a clearer view of their technical features and applications. As the operation of MFCs does not rely on chemical additives or physical interventions, the quantity of by-products generated is minimal, typically consisting of small amounts of water, carbon dioxide, and low-toxicity metal products [92]. This significantly reduces the risk of waste emissions, in contrast to traditional chemical treatment methods, which often involve the use of large quantities of chemicals such as oxidizing agents or reducing agents. Such chemicals not only increase operational costs but may also lead to secondary pollution. In MFCs, the microorganisms themselves can complete the transformation and removal of pollutants through bioelectrochemical processes, effectively avoiding the negative environmental impacts associated with chemical reagents. Additionally, MFCs present clear advantages over traditional physical treatment methods, such as membrane filtration, adsorption, or flotation. These conventional physical methods often require substantial energy input, particularly in the treatment of high-concentration pollutants, resulting in significant energy consumption. In contrast, MFCs generate electricity based on biological metabolic activity, using biodegradation pathways to remove pollutants, which leads to relatively low energy consumption. Furthermore, MFCs can simultaneously generate electrical power, further reducing the overall energy consumption and operational costs of the system.

3.8.2. Recent Research Advances in MFCs for Tailings Treatment

In recent years, with the continuous development of MFC technology, significant progress has been made in its application to mine tailings treatment. These studies have not only led to breakthroughs in improving the treatment efficiency and electrical power output of MFCs, but have also provided more efficient and sustainable technological solutions for the removal of pollutants and resource recovery in tailings treatment. Pollutant Degradation and Resource Recovery:

• Development of High-Efficiency Electrode Materials: Anodes and cathodes are critical components in MFCs, and their performance directly influences both the electrical power output and pollutant degradation efficiency. In recent years, significant progress has been made in the selection and optimization of electrode materials, particularly in the development of anode and cathode materials, which have driven substantial improvements in MFC performance. In the case of anodes, traditional carbon-based electrodes, while exhibiting good electrical conductivity, often face limitations in microbial attachment and electron transfer efficiency. To address this issue, researchers have developed modified carbon fibers with higher biocompatibility, electrochemically activated graphite electrodes, and composite electrodes incorporating nanomaterials. These novel anode materials provide a larger surface area for electroactive microorganisms to adhere to, promoting microbial growth and proliferation, which enhances their ability to degrade pollutants. Additionally, these materials improve electron transfer efficiency, enabling MFCs to generate electricity more efficiently during the treatment of mine tailings. In addition, metal-organic framework (MOF) materials have demonstrated significant potential in the study of MFC anodes due to their highly tunable porous structures and large specific surface areas. The synergistic interaction between the metal ion nodes and organic linkers in MOFs provides abundant attachment sites for electroactive microorganisms, while simultaneously facilitating electron and ion transfer. For instance, certain copper- or zinc-based MOF materials have been shown to enhance the electrochemical activity of anodes while maintaining high electrical conductivity [93]. By integrating MOFs with carbon nanomaterials to form composite electrodes, researchers have achieved improved structural stability of the anodes, along with enhanced corrosion resistance under complex environmental conditions [94]. To further enhance the performance of MFCs, researchers have also explored the modification of electrodes by introducing nanomaterials, such as incorporating metal nanoparticles, conductive polymers, and carbon nanotubes. These nanomaterials possess high surface areas, high electrical conductivity, and excellent electron transfer properties, which significantly enhance the overall performance of the electrodes. In particular, the combination of nano-carbon materials and conductive polymers can further increase the electrochemical activity and corrosion resistance of the electrodes, maintaining long-term stability even in harsh tailings environments. In the case of cathodes, to improve the efficiency of the oxygen reduction reaction, researchers have gradually shifted away from using precious metal catalysts and explored the application of non-precious metal catalysts. Novel catalysts, such as metal-doped carbon materials, metal oxides, and conductive polymers, not only exhibit high catalytic activity but also significantly reduce the cost of catalysis. For example, manganese- or iron-doped carbon-based materials have been shown to possess excellent catalytic performance in oxygen reduction reactions, and, compared to precious metal catalysts, are lower in cost and more abundant in resources [95]. The use of metal oxides and conductive polymers further enhances the rate of oxygen reduction reactions, effectively improving the energy recovery efficiency of MFCs in mine tailings treatment. Moreover, catalysts based on phosphides and sulfides have been widely employed in MFC cathode research due to their excellent electron transfer capabilities and low fabrication costs. These materials can enhance the kinetics of the oxygen reduction reaction (ORR) through unique electronic structure modulation, thereby further improving the energy recovery efficiency of MFCs. For example, composite catalysts doped with nickel phosphide (NiP) or molybdenum disulfide (MoS₂) have been successfully applied in the treatment of mine tailings, demonstrating excellent corrosion resistance and long-term stability under harsh conditions [96,97]. To clarify the types and characteristics of MFC catalysts,

  Table 10. Types, advantages, limitations, and applications of MFC catalysts.

  Catalyst Type	Advantages	Limitations	Typical Applications
  Noble metal catalysts (e.g., Pt)	High catalytic activity, strong stability	High cost, limited resource availability	Traditional MFC cathode catalysts for oxygen reduction
  Non-noble metal catalysts (e.g., Fe, Mn)	Low cost, abundant resources	Fewer active sites, requires further optimization	Substitutes for noble metal catalysts, used for mine wastewater treatment
  Phosphide/sulfide catalysts (e.g., NiP, MoS2)	Excellent electron transfer ability, low cost	Insufficient durability, possible performance degradation under extreme conditions	Oxygen reduction reactions in tailings treatment, improving energy recovery efficiency
  Composite material catalysts (e.g., CNTs + metal oxides)	Abundant active sites, excellent overall performance	Complex manufacturing process, cost still needs control	High-performance cathode catalysts, suitable for treating pollutants in complex environments

  lists common catalysts with their advantages, disadvantages, and application examples.

• Reactor Design and System Optimization: To enhance the efficiency of electrical power generation and pollutant degradation, researchers have made numerous innovations in reactor design, developing various high-efficiency reactors and exploring the integration of MFCs with other treatment units. These innovations not only improve the mass transfer efficiency and electron transfer processes of MFCs, but also significantly enhance the overall performance of mine tailings wastewater treatment. Firstly, in the area of reactor design, researchers have proposed several novel structures to enhance the reaction efficiency of microbial fuel cells. For example, air-cathode MFCs, which utilize air as the cathode reaction medium, avoid the use of expensive precious metal catalysts while improving the efficiency of the oxygen reduction reaction. This design not only reduces system costs but also enhances oxygen transfer efficiency, thereby boosting the overall power output of the MFC [98]. In addition, stacked MFCs have emerged as an important direction for optimizing MFC system design. By vertically stacking multiple MFC units, the stacked design can significantly increase the power density of the cell. This structure makes more efficient use of space, and by optimizing electrode spacing and current transfer pathways, it reduces the resistance of the system, further enhancing the performance of the cell. Stacked MFCs are particularly suitable for large-scale tailings treatment and energy recovery applications, demonstrating good stability and efficiency when handling high-concentration pollutants. Furthermore, flow-through MFCs have been developed, incorporating wastewater flow designs that allow the tailings water to come into full contact with the electrode surface within the reactor, optimizing the mass transfer process. The flow-through design effectively increases the mass transfer area in the reaction zone, improving the contact efficiency between microorganisms and pollutants, which in turn enhances the degradation of pollutants. This reactor is particularly effective for treating complex mine tailings wastewater, especially those containing large amounts of suspended solids or high-viscosity liquids. To further improve the comprehensive performance of MFCs, researchers have integrated MFCs with other treatment units to form hybrid treatment systems. For example, coupling MFCs with membrane bioreactors (MBRs) allows for the removal of suspended solids and fine particles from the tailings wastewater through membrane filtration, while MFCs handle the dissolved pollutants and organic matter. In this way, MFCs not only facilitate effective energy recovery but also work synergistically with membrane technology to enhance overall water treatment efficiency. Similarly, MFC-integrated biofilters degrade and remove organic pollutants, while the MFC provides necessary power output and further processes dissolved pollutants in the wastewater, forming a complementary treatment system. The design of such hybrid systems significantly improves the ability of MFCs to treat complex mine tailings wastewater, especially when dealing with multiple coexisting pollutants, demonstrating strong adaptability and efficiency [99].
• Optimization of Microbial Communities: In the research and application of MFCs, the selection and optimization of electroactive microorganisms are critical factors in improving system performance and pollutant treatment efficiency. To enhance the performance of MFCs in mine tailings wastewater treatment, researchers have focused on screening and acclimating electroactive microorganisms, particularly those with high electron transfer capabilities and excellent pollutant degradation properties, thus improving the overall treatment capacity and electrical power output of MFCs. Moreover, the application of genetic engineering techniques has provided new pathways to further enhance the performance of microorganisms, becoming an important tool for optimizing microbial communities. First, many studies have concentrated on the screening and enrichment of electroactive microorganisms to select strains capable of efficiently transferring electrons. To systematically summarize the role of typical electroactive bacteria in MFCs,

  Table 11. Typical electroactive bacteria and their advantages and limitations.

  Bacterial Genus	Advantages	Limitations
  Geobacter	High electron transfer efficiency, adapts to low-oxygen environments, capable of degrading various organic compounds	Requires specific environmental conditions (e.g., low oxygen), struggles to survive in high-temperature or strongly oxidative conditions
  Shewanella	Capable of degrading organic compounds and metal ions, exhibits strong adaptability across diverse environmental conditions	Lower electron transfer efficiency compared to Geobacter, may require additional optimization to improve degradation efficiency
  Pseudomonas	Excellent pollutant degradation capabilities, particularly effective in treating complex organic compounds	Relatively low electrochemical activity, typically requires co-cultivation with other bacteria to enhance electron transfer efficiency
  Clostridium	Efficiently decomposes complex organic compounds under anaerobic conditions, provides electrons for the anode region	Difficult to directly interact with electrode surfaces, often requires assistance from other bacteria for electron transfer

  lists common bacteria along with their performance, adaptability, and limitations. For example, Geobacter and Shewanella are two widely studied genera of electroactive bacteria that can exchange electrons with the electrode surface through conductive proteins on their cell membranes. These bacteria degrade pollutants and convert energy into electrical current. Geobacter species are widely used in MFCs due to their high electron transfer efficiency and excellent electrochemical activity in low-oxygen environments [100]. Shewanella species, on the other hand, have unique advantages in the degradation of organic compounds and the reduction or transformation of metal ions, particularly in mitigating heavy metal pollution in mine tailings. By using acclimation techniques, researchers can further optimize the performance of these microorganisms, making them more stable and adaptable to specific mine tailings wastewater environments. During the acclimation process, microbial communities gradually adapt to the specific conditions of the tailings wastewater, enhancing their pollutant degradation capabilities and improving their activity in electrochemical reactions. For example, by adjusting the nutrient composition, pH, temperature, and oxygen concentration in the culture medium, microorganisms can gradually optimize their metabolic pathways, ultimately improving their electron transfer efficiency and pollutant removal capabilities [101]. Additionally, genetic engineering techniques offer more precise means for further optimizing microbial communities. Through genetic editing, such as CRISPR-Cas9, researchers can directly modify the genomes of microorganisms to enhance their ability to degrade specific pollutants [102]. For example, the metabolic pathways of Geobacter or Shewanella can be engineered to more efficiently degrade specific organic pollutants or heavy metal ions. Some studies have also explored the use of genetic engineering to improve the electron transfer efficiency of these microorganisms, such as increasing or optimizing the expression of conductive proteins on the cell membrane, or introducing exogenous electron transfer chains, which significantly enhances the electrical power output of MFCs.
• Synergistic Treatment of Multiple Pollutants: With the co-existence of multiple pollutants in mine tailings wastewater, the treatment of single pollutants often fails to meet practical needs. Therefore, efficiently and simultaneously removing heavy metal ions and organic pollutants from tailings wastewater has become a key research focus for MFCs in tailings treatment. In recent years, researchers have introduced various technological approaches into MFCs to achieve the synergistic removal of multiple pollutants, significantly improving the efficiency of tailings wastewater treatment and the overall performance of the system. First, the simultaneous removal of heavy metal ions and organic pollutants is a major advantage of MFCs for multi-pollutant treatment. Traditional methods for heavy metal removal often rely on chemical precipitation, adsorption, or electrochemical reduction, all of which are costly, inefficient, and prone to secondary pollution. In contrast, MFCs utilize the metabolic activity of electroactive microorganisms to simultaneously degrade organic substances in tailings wastewater while reducing heavy metal ions into less toxic or elemental forms, thus achieving the simultaneous removal of pollutants. Microorganisms oxidize organic pollutants to generate electrons and protons. The electrons are transferred to the cathode through the external circuit, while the protons pass through the proton exchange membrane to the cathode region, where they react with reducing agents on the cathode surface, reducing heavy metal ions to their metallic form or low-toxicity compounds. This process not only effectively removes organic pollutants but also reduces the toxicity of heavy metals in the wastewater, facilitating resource recovery. Furthermore, to further enhance the efficiency of tailings wastewater treatment, researchers have introduced sulfate-reducing bacteria (SRB) to promote the biological reduction of sulfate. SRBs are capable of reducing sulfate to hydrogen sulfide (H₂S), a process that not only helps lower the acidity of wastewater and improves water quality but also reacts with heavy metal ions to form insoluble metal sulfide precipitates, further removing heavy metals from the wastewater. The formation of sulfides not only reduces the solubility and toxicity of heavy metals but also provides another effective pathway for wastewater purification. Another advantage of introducing SRBs into MFCs is the improvement of wastewater pH. Mine tailings wastewater typically exhibits high acidity, which increases the solubility of metal ions, exacerbating pollution. Through the biological reduction of sulfate by SRBs, sulfate in the wastewater is converted into hydrogen sulfide, and with the consumption of hydrogen ions, the acidity of the wastewater is effectively neutralized. This improvement in pH not only enhances the growth environment for microorganisms but also promotes the degradation activities of electroactive microorganisms, thereby boosting the electrical power output of the MFC [103,104,105].

3.8.3. Challenges and Future Prospects of MFCs in Tailings Treatment

Despite significant progress in the application of MFCs for mine tailings wastewater treatment, several challenges remain for their practical implementation. In order to successfully transition this technology from the laboratory to large-scale industrial applications, further research and technological breakthroughs are needed in several key areas. The following outlines the main challenges and future development directions for MFCs in tailings treatment:

• Enhancement of Power Density and Efficiency: Currently, the power output of MFCs is generally low, which limits their widespread application in industrial environments. Although MFCs can generate some electricity during the treatment of tailings wastewater, their power density falls short of meeting the demands of large-scale applications. Increasing the power density of MFCs is an important direction for future research. To achieve this, researchers are exploring the development of novel, high-efficiency electrode materials, particularly those with high conductivity and good biocompatibility. For example, the use of nanomaterials, composite materials, and electrochemically activated carbon-based materials can significantly enhance the electron transfer efficiency and stability of electrodes. Additionally, optimizing the composition of microbial communities, and screening and acclimating more efficient electroactive bacteria, is an effective way to improve MFC performance. By regulating the metabolic pathways of microorganisms, enhancing electron transfer capacity, and developing more adaptable microbial populations, the current output and energy conversion efficiency of MFCs can be significantly increased. Furthermore, improving reactor design, especially the layout and structural design of the anode and cathode, can contribute to enhancing the mass transfer efficiency and overall treatment performance of MFCs. Feasibility of Scaling Up for Industrial Application: When laboratory-scale results are expanded to industrial scales, challenges such as mass transfer limitations, anode passivation, and microbial community imbalance may arise. To address these issues, pilot-scale studies are necessary to accumulate data and experience during the scaling-up process, and to develop modular, scalable MFC systems.
• Feasibility of Large-Scale Application: Despite preliminary success at the laboratory scale, the large-scale application of MFCs still faces several challenges. When transitioning MFC technology from small-scale laboratory setups to industrial-scale applications, issues such as mass transfer limitations, anode passivation, and microbial community imbalance may arise. Mass transfer limitations are particularly evident when treating high-concentration wastewater, where the contact efficiency between microorganisms and pollutants is low, significantly affecting the pollutant removal efficiency and electricity output of the MFC. Anode passivation is another challenge; over time, the anode surface may become covered with microbial metabolites or chemicals from the wastewater, leading to a decrease in electron transfer efficiency, thereby impacting the long-term operation of the system. Furthermore, at large scale, an imbalance in the microbial community may cause fluctuations or failure in system performance. To address these challenges, future research should focus on accumulating experience through pilot-scale experiments and exploring effective solutions, for example, by optimizing reactor design to enhance pollutant mass transfer efficiency, utilizing anti-fouling materials or regularly cleaning anode surfaces to prevent passivation, and maintaining microbial community stability through co-culturing systems and dynamic regulation methods. Additionally, developing modular and scalable MFC systems is essential for achieving industrial applications, as this will enable flexible deployment and stable operation across various scales and types of mine tailings treatment.
• Economic Cost and Sustainability: Although MFC technology holds great potential for tailings treatment, its economic feasibility remains a key issue. Currently, the high costs of the high-performance electrode materials, reactor equipment, and other critical components needed for MFC systems result in poor overall economic viability. In order to enhance the market competitiveness of MFC technology, it is necessary to reduce costs and improve resource utilization efficiency. To achieve this, researchers are seeking low-cost, renewable materials as alternatives for electrodes and other components, such as utilizing waste resources or biomass materials to fabricate electrodes and developing biodegradable membrane materials. Simultaneously, optimizing process flows, improving energy conversion efficiency, and reducing energy consumption are key strategies for lowering the overall operating costs of MFC systems. Additionally, the cost of system operation and maintenance is another factor influencing the widespread application of MFCs. Future research should focus on developing low-maintenance, user-friendly systems to further improve economic benefits and sustainability.
• Long-Term Stability and Durability: The long-term stability and durability of MFCs are critical factors determining whether they can operate effectively in real-world applications over extended periods. While MFCs demonstrate excellent performance in the short term, various factors, including biological contamination, material aging, and performance degradation, may affect their operation during long-term use. Biological contamination, particularly the proliferation of harmful microorganisms under anaerobic conditions, can interfere with the growth and metabolism of electroactive microorganisms, leading to a decline in system performance. The aging of electrode materials and the accumulation of surface deposits may also reduce electron transfer efficiency, impacting the long-term stable operation of MFCs. Therefore, researchers need to develop contamination-resistant electrode materials, design more durable reactor structures, and formulate effective maintenance and regeneration strategies to ensure the stability and durability of MFCs during extended operation. This not only enhances the system’s lifespan but also ensures its economic viability in industrial applications.
• Policy Support and Social Acceptance: Despite the significant potential of MFC technology in tailings treatment and other environmental remediation fields, its promotion and application are still constrained by the lack of clear industry standards and policy support. In many countries and regions, the policies supporting emerging environmental technologies are not well-developed, resulting in a slow market adoption process. Therefore, governments and industry associations should strengthen collaboration to develop relevant standards and regulations for MFC technology, promoting its standardization and large-scale application. Additionally, increasing public awareness and understanding of MFC technology is crucial for fostering support and driving its application. Through policy guidance, financial support, and public education, a favorable environment for the widespread adoption of MFC technology can be created, contributing to the sustainable development of this green technology.
• Integration of MFCs with Other Renewable Energy Technologies for Sustaina-bility: To enhance the sustainability of MFCs, future research could explore their integration with other renewable energy technologies to achieve synergistic effects and efficient resource utilization. For instance, solar energy could provide power support to MFCs or enhance pollutant degradation efficiency; wind energy could drive air supply systems to improve the oxygen reduction reaction rate at the cathode; and geothermal energy could offer stable operating temperatures, optimizing microbial activity and improving system stability. Additionally, the development of modular, multifunctional systems that integrate MFCs with multiple energy technologies could further enhance their efficiency and cost-effectiveness, supporting the industrial application of MFCs in mine tailings wastewater treatment and resource recovery.

4. Conclusions

This study utilized CiteSpace (version 6.2.R7) and Histcite (version 2.1) to conduct an in-depth analysis of 1321 publications indexed in the WOSCC from 2004 to 2024 concerning the application of MFCs in mine tailings treatment and power generation. The analysis revealed publication characteristics, journal performance, collaboration among countries and institutions, co-occurrence of subject categories, keyword clustering, and reference co-citation in this field. These findings provide important references for a comprehensive understanding of the development status of MFCs in mine tailings treatment. The main conclusions are as follows:

First, the results indicate that since 2004, the annual number of publications on MFCs in the field of mine tailings treatment and power generation has shown a continuous upward trend, especially since 2014, with a significant increase in annual publications. As of 14 November 2024, the annual number of publications has reached 138 articles, suggesting that future research activities in this field will continue to maintain rapid growth. This trend reflects the global academic community’s strong interest in and emphasis on MFC technology in mine tailings treatment.

Second, journal analysis shows that high-impact journals such as Bioresource Technology, Chemical Engineering Journal, International Journal of Hydrogen Energy, Renewable & Sustainable Energy Reviews, and Water Research have played a key role in disseminating important research findings in this field. These journals have not only published a large number of relevant papers but have also demonstrated outstanding performance in terms of impact factors and H-indices, reflecting their leading position in MFC research.

Third, analysis of national and institutional collaborations reveals that countries such as China, India, the United States, Malaysia, and South Korea, along with research institutions like the Indian Institutes of Technology system, the Chinese Academy of Sciences, and Harbin Institute of Technology, have made significant contributions and exerted considerable influence in the research on using MFCs for mine tailings treatment and power generation. Their close cooperation has promoted research progress and technological innovation in this field.

Furthermore, co-occurrence analysis of subject categories indicates that research on MFCs in mine tailings treatment and power generation exhibits notable multidisciplinary characteristics, involving fields such as environmental science, energy and fuels, chemical engineering, biotechnology, and applied microbiology. This interdisciplinary research approach provides new ideas and methods for solving complex problems associated with mine tailings treatment.

Keyword clustering and reference co-citation analyses further reveal the research hotspots and development trends in this area. The research focus is mainly concentrated on enhancing the power density of MFCs, developing efficient electrode materials, optimizing microbial communities, improving reactor design, and achieving synergistic treatment of multiple pollutants. These research directions offer important support for improving the application efficiency of MFCs in mine tailings treatment.

Despite significant research progress, MFCs still face challenges in practical applications, such as low power output, feasibility issues for large-scale deployment, high economic costs, stability in long-term operation, and lack of policy support. Therefore, future research should focus on the development of novel high-efficiency electrode materials, further optimization of microbial communities, improvements in reactor design, and the development of modular and scalable MFC systems. Additionally, strengthening cooperation with government departments and industry associations, formulating relevant standards and regulations, enhancing public awareness, and promoting policy support are crucial for advancing the practical application of MFC technology.