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Article

Precision Remediation of Mining Soils through On-Site Investigation and Large-Scale Synthesized Ferrosilicate

by
Han Xu
1,†,
Jie Liu
2,†,
Na Huang
1,
Anqing Yu
2,
Jingyuan Li
2,
Qiao Li
2,
Qiunan Yang
3 and
Lulu Long
1,*
1
College of Environment Sciences, Sichuan Agricultural University, Chengdu 611130, China
2
Power China of Chengdu Engnieering Corporation Limited, Chengdu 611130, China
3
Nanchong Institute for Food and Drug Control, Nanchong 637000, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Sustainability 2024, 16(17), 7426; https://doi.org/10.3390/su16177426
Submission received: 8 July 2024 / Revised: 8 August 2024 / Accepted: 10 August 2024 / Published: 28 August 2024
(This article belongs to the Special Issue Toxic Metal Remediation: Recent Advances in the Development of a Green and Sustainable Environment)
Browse Figures
Versions Notes

Abstract

:
To seek a restoration plan for the safe use of agricultural land around mining areas, this study focuses on the regions around a mining plant in Huidong County, western Sichuan Province, affected by lead–zinc mining, and the precise remediation of heavy metal pollution through large-scale synthesis of iron silicate. In this study, we investigated heavy metal pollution in the vicinity of the mining area and proposed a treatment strategy using large-scale synthesis of iron silicate to mitigate this pollution. According to field investigation and sampling analysis, the collected soil samples contained excessive Cd, Pb, and Zn. Cd is a heavy metal related to lead–zinc mining. The planting of crops such as loquats and garlic with a high accumulation coefficient for Cd was found inappropriate for the research area. Instead, it was recommended to plant economically important crops like mangoes and peaches which had lower heavy metal accumulation. On the basis of field investigation, the study area was seriously polluted by heavy metals, among which Cd was 4.0 times higher than the standard of agricultural land. In order to accurately passivate excessive Cd, Zn, and Pb, iron silicate material was put into mass production. In situ passivation experiments showed that when the soil water content was between 25% and 20%, adding 4% silicate material could rapidly reduce the content of effective heavy metals in the soil and the heavy metal content of garlic and other cash crops in the research area by about 8%. After conducting a field investigation, it has been determined that the large-scale preparation of iron silicate can accurately repair soil contaminated by heavy metals in the vicinity of mining areas. In conclusion, iron silicate is capable of effectively reducing the pollution of heavy metals on agricultural land and facilitating the safe utilization of such land.

1. Introduction

Nowadays, lead and zinc are common mineral resources that are widely applied in such industries as electrical and electronics, manufacturing, and machinery [1]. However, China, as the world’s largest producer of lead and zinc, has drawn much attention to the energy consumption and environmental impact in the process of lead–zinc mining [2]. Southwest China, in particular, is abundant in mineral resources, with its metal mineral reserves ranking among the largest in the world. Local mining has led to acid mine drainage and generation of washing wastewater, posing a significant threat to the soil environment due to the high concentrations of heavy metals such as lead (Pb), zinc (Zn), and cadmium (Cd). This has caused serious safety hazards and exacerbated the potential risks to the soil in the research area [3,4]. The excessive accumulation of heavy metals is a serious threat to the soil–plant system, impairing the sustainable development of agriculture. The heavy metals enter organisms through the food chain and thus affect people’s life and health [5]. To address this issue, it is crucial to conduct field investigations on cultivated land and products, analyze the levels of heavy metals, and gain insights into local heavy metal contamination.
Most of the recent articles about mining contamination investigations mainly focus on ecological risk assessments. Huang et al. [6] investigated topsoil contamination near a small abandoned polymetallic mining area, finding that the local farmland soil was moderately or severely contaminated with a high potential ecological risk of heavy metal contamination [4]. Researchers investigated the concentrations of eight heavy metals, including As and Cd, in the tailings of lead–zinc mines in China [4], and conducted pollution assessments, geographic distribution analysis, and health risk assessments. The results showed that the average concentration exceeded the corresponding background value. Mining produces a large amount of mine waste, which is considered a major source of heavy metals [7]. In China, mining has contaminated over 1.5 million hectares of land, with the contamination area increasing by 46,700 hectares every year [7]. Recently, researchers have conducted a new quantitative mineralogical assessment to evaluate the geochemical behavior of toxic elements in the soil from lead–zinc mining areas [8]. Cd, Pb, and Zn were among the most toxic heavy metals found in the soil, accumulating in the environment and posing serious health risks to people, animals, and plants. Cadmium, known for its carcinogenic properties, can damage kidneys, liver, and bone. Lead functions as a neurotoxin, causing developmental delays in children and neurological issues in adults. Zinc is essential in small amounts, but excessive zinc is harmful and can lead to gastrointestinal issues and destroy the balance of other essential nutrients [9].
In response to the severity and wide spreading of heavy-metal-contaminated sites, a variety of remediation technologies have been developed, including soil thermal desorption, soil washing, phytoremediation, etc. [10]. In particular, in situ passivation has become one of the mainstream soil heavy metal remediation technologies due to its cost-effectiveness and operability [11]. However, conventional alkaline passivators such as quicklime [12], hydroxyapatite [13], and biochar [14] are unsuitable for alkaline-contaminated soil in the specific target areas, for their use can exacerbate soil salinization and hinder crop growth. To address the above issues, researchers have spared no effort to develop relevant materials and work out effective solutions. It has been frequently reported that silica, a naturally occurring soil component, does not significantly alter the physical and chemical properties of the soil [15,16]. Additionally, relevant studies have shown that the thiol groups grafted onto the silica surface can effectively remediate soil heavy metal contamination in situ [17,18]. The addition of exogenous silicon can reduce cadmium translocation to the aboveground parts [19]. Despite this, the synthesis process of thiol nano-silica is complex and costly, posing a challenge to its practical application in site remediation of heavy-metal-contaminated soil [20]. Therefore, the adoption of remediation measures that are tailored to the specific characteristics of environmental pollution in the research area is considered to be an inevitable trend in sustainable agricultural development [21]. Many studies have not taken into account the specific attributes of the local research area, such as the climate and the nature of heavy-metal-contaminated soil.
In this study, we investigated the heavy metals in the soil of a moderately alkaline mining area. Based on the study field investigations, we selected in situ remediation technology and passivation materials for the lead–zinc mining area. The contents of heavy metals in farmland soil and products were initially investigated and detected. Subsequently, the geoaccumulation index and bioconcentration factor assessment methods were used to evaluate the heavy metal contamination in the local soil and its accumulation in agricultural products. Considering the hot weather and moderately alkaline soil in the research area, large-scale synthesized iron silicate (FeSi) was selected as a passivation material for in situ remediation of the soil. This study examines the effects of different dosages, passivation time, water holding capacity, and desorption on the redistribution of heavy metal components in the soil. The findings will help enhance the understanding of the contamination level in the research area, provide valuable insights for a strategy to rehabilitate soils in the research area, and promote agricultural development in the research area.

2. Experimental Section

2.1. Materials and Reagents

Sodium silicate (Na2SiO3), ferric nitrate (Fe(NO)3), glacial acetic acid, hydroxylamine hydrochloride, ammonium acetate, hydrogen peroxide, nitric acid, hydrofluoric acid, perchloric acid, ammonium dihydrogen phosphate, and other reagents were purchased from China Chengdu Kelong Chemical Reagent Co., Ltd. Deionized water was used for all experiments, and the pH of the solution was adjusted using NaOH and HNO3 during the experiment.

2.2. Field Investigation and Sample Collection

The survey area, which is located in and around the mining plant in Huidong County, western Sichuan Province, China, is affected by lead and zinc mining (Figure S1). The survey focuses on mature cash crops and the intercropping of fruits (such as Eriobotrya japonica and Mangifera indica L.) and vegetables (such as Brassica oleracea var. capitata and Ipomoea batatas) in the agricultural region. In the survey area, fruit orchards are typically integrated with vegetable crops by using a conventional farming system. Fertilization primarily relies on farmyard manure and chemical fertilizers. Irrigation water for farmland is sourced from the surface water of the Jinsha River Dayan Irrigation Canal. The soil contamination in the area is mainly caused by lead and zinc mining and improper discharge of washing wastewater. Field investigations were conducted to gain insights into the Zn and Pb ore pollution in the study area, laying the groundwork for subsequent development of remediation strategies. Currently, soil remediation projects are already in place, focusing on stripping the contaminated surface soil and applying uncontaminated soil as a cover to restore the soil quality.
Field investigation and sample collection were conducted in April 2021. The local production status was investigated, and the local soil and agricultural products were preliminarily analyzed by using X-ray fluorescence (XRF) and pH rapid measurements on site. Following the five-point sampling method, surface soil samples (with a depth of 20 cm) and corresponding crop samples were collected. The collected samples were air-dried and sieved (20 mesh) for further use. The speciation of heavy metals in the experimental soil was determined by applied the modified four-step Sequential Extraction Procedure (SEP) established by the BCR to evaluate the changes in the types of heavy metals in the soil before and after passivation [22,23]. The specific findings and data are detailed in Table S1.

2.3. Evaluation of Heavy Metals

Soil evaluation usually involves comparing soil risk screening values and control values for agricultural land. Screening values indicate the potential risk of soil contaminants, helping identify the areas that may require further investigation or remediation [24]. Control values are used to evaluate whether the concentrations of soil contaminants are within acceptable limits for agricultural use. The contents of heavy metals in the soil at these points were determined through HNO3+HF+HClO4 (4:1:1) digestion and analyzed by using ICP-MS [25]. After comparing these results with the soil background values of Sichuan Province and the risk screening values and control values specified in Soil Environmental Quality--Risk Control Standard for Soil Contamination of Agricultural Land (GB15618-2018) concentrations with these values, we can determine the extent of contamination and the potential risks of the soil, carry out appropriate management, and take corresponding remediation actions.
The bioconcentration factor (BCF) is used to evaluate the level of heavy metal enrichment in the plants and the enrichment capability of plants. The BCF is calculated through the following formula:
B C F = C p C s
where Cp is the content of heavy metals in the plants (mg kg−1) and Cs is the content of heavy metals in the soil at this point (mg kg−1) [26].
A Bureau Communautaire de Référence method is employed to extract various forms of heavy metals from soil, assessing their bioavailability and potential for bioaccumulation in the environment. This method entails multiple steps and chemical extractants to differentiate heavy metals in soil into soluble, exchangeable, and organic-bound.

2.4. Characteristics of Research Area

The lead-zinc mining area in regions around the mining plant in Huidong County, western Sichuan Province, China is characterized by hot weather and severe contamination of Cd, Pb, and Zn nearby farmlands, with Cd contamination being prominent. The soil in the research area is moderately alkaline. Furthermore, it is inhabited as a residential area and enjoys a favorable climate, with fruit cultivation serving as a major source of income for local residents. To cope with the local heavy metal contamination in the soil without hindering local farming activities, insitu passivation remediation technology emerges as one of the most feasible solutions. Given the specific characteristics of the research area, it is a pressing concern to select a passivation material with mild acidity, high remediation efficiency at low water content, and economic feasibility. Among the available materials, FeSi features rapid adsorption, large volume, and simple synthesis, making it one of the most suitable materials for remediating heavy metal contamination in the research area.

2.5. Preparation of Large-Sized Materials

FeSi was prepared at room temperature via a straightforward co-precipitation method. The experiments were conducted in an 80 L glass reactor. The precondition solution contained Fe (NO3)3, into which Na2SiO3 solution was slowly added through mechanical stirring (Fe/Si molar ratio: 0.67). The mixture was then aged at 60 °C for 24 h. After that, the aged catalyst solid was repeatedly washed with ethanol and ultrapure water to remove salts and impurities, and then it was dried. The dried solid materials were stored and sealed in a sample vial.

2.6. Basic Physical and Chemical Properties of Soil

The soil pH value was determined following the national standard potentiometric method [26]. Soil organic matter was determined according to the national standard method [27]. The cation exchange capacity of the soil was determined using the ammonium salt replacement method, measuring the amount of exchanged ammonium ions in the soil [28]. Soil samples were reacted with a sodium hydroxide solution to determine the content of alkali-hydrolyzed nitrogen in the soil using the colorimetric method [29]. The content of phosphorus absorbed by plants in the soil was determined using the chemical extraction method [30]. The content of available potassium in the soil was determined using flame spectrophotometry [31].

2.7. Passivation Experiment

The experimental soil for passivation was sourced from local project spoil and prepared through natural air-drying and sieving to ensure its suitability for subsequent experiments. In this experiment, we adopted a single-factor experimental method to establish different addition levels: CK (control group without addition), F-1% (1% addition), F-2% (2% addition), F-4% (4% addition), and F-6% (6% addition) (F represents FeSi). In addition, we varied the field water holding capacity across three gradients: CK (control group with 15–20% water holding capacity), 35–40%, and 65–70%. The dosage of the passivating agent was set at 4%. In each treatment group, 100 g of the contaminated soil was weighed, and the corresponding amount of passivating agent was added. Then, soil and passivating agent were thoroughly mixed to ensure uniform distribution. Subsequently, a proper amount of water was added, and then the mixture was sealed with plastic wrap to prevent rapid water loss. The entire passivation experiment was conducted under outdoor natural conditions, with each treatment group replicated three times for parallel comparisons. At the same time, soil samples were collected at 7d, 14d, 28d, and 35d through destructive sampling, and the forms of heavy metals in the soil were determined after freeze-drying [32]. It was observed whether it can reduce the effective content of heavy metals in soil.
Acid desorption and salt desorption were conducted on the passivated soil by using acids with various pH values and salts with different concentrations. To process a specific quantity of passivated soil, we adopted the following steps: the soil sample was treated with a desorption solution and shaken at 250 rpm for 12 h. Then, centrifugation was performed to separate the solution from the soil particles. The resulting solution was filtered through a 0.45 µm membrane to remove any remaining solid particles. Finally, the filtrate was collected to determine the heavy metal content by using inductively coupled plasma mass spectrometry (ICP-MS: PerkinElmer NexION 300×). Standard samples were inserted every 10 test samples to ensure the accuracy and quality of the test samples.

2.8. Data Analysis

The experimental data were analyzed and processed by Excel 2016 and SPSS Statistics 27.0 software, while the graphs were generated by OriginPro 2022b software. Each sample was assayed in triplicate, and the data are presented as mean ± standard deviation (n = 3) to account for variability and measure precision.

3. Results and Discussion

3.1. Analysis of Soil Samples

Soil samples were collected around the soil remediation project, with eight sampling points selected at specific distances from the project site. The results are given in Table S2. After comparing these results with the soil background values of Sichuan Province and the risk screening values and control values specified in Soil Environmental Quality--Risk Control Standard for Soil Contamination of Agricultural Land (GB15618-2018) (Table 1), it was found that the levels of Cd, Pb, and Zn at seven sampling points exceeded the risk screening values when the pH was greater than 7.5 [33]. In contrast, the levels of Cu, Cr, and Ni were below the risk screening values. At sampling point 3, the total amount of lead in the soil exceeded the control value, and the total amount of Cd exceeded the control value at each sampling point. These findings indicate the need for significant attention and appropriate measures to manage the elevated concentrations of lead and cadmium in the soil [34].
The heatmap of the Pearson correlation coefficient was also used to analyze the soil at each site, revealing the internal relationship between the total amounts of heavy metals in Figure 1. A significant correlation between Pb and Zn was observed, which might be likely due to the simultaneous mining of lead and zinc in the lead-zinc mining area. The correlation coefficients among Cd, Pb, and Zn were significantly correlated, suggesting that Cd, Pb, and Zn shared similar sources and migration routes [35]. This might be related to the fact that Cd, a highly toxic element, is associated with lead-zinc mining areas, and its spatial dispersion is primarily influenced by surface runoff and atmospheric deposition [2]. The contents of Cu, Ni, and Cr were found to be lower than the risk value of heavy metal contamination in the farmland, indicating that their presence was likely attributed to the local soil geological background.

3.2. Plant Sample Analysis

The bioconcentration factor (BCF) is used to indicate a plant’s capacity to absorb heavy metals from soil into its roots [36]. The greater the enrichment capability of plants for heavy metals, the higher the enrichment coefficient [37]. We evaluated the heavy metal contents in the edible parts of crops from seven different points within the research area and calculated the BCF of these edible parts. The results are shown in Figure 2. Notably, garlic at point 1 displayed elevated enrichment coefficients for several metals. Mangoes, grown extensively across points 1, 2, 4, 5, 6, and 7, exhibited lower enrichment coefficients for Cd, Pb, and Zn when compared to other crops in Table S6. Peaches at points 2 and 5 showed relatively low enrichment coefficients for Cd, Pb, and Zn. In contrast, loquats at points 1, 4, 5, and 7 displayed the enrichment coefficients 0.2052, 0.2450, 0.4139, and 0.2982 for Cd, respectively. Significantly, garlic at point 1 revealed a Cd enrichment index of 0.7072, indicating significant soil Cd contamination in the research area and an elevated risk associated with garlic cultivation. Garlic, known for its resilience to both biotic and abiotic stressors, exhibited strong resistance to Cd stress, which might contribute to its Cd accumulation [38]. The variations in BCF values for the same crops at different points may be due to the differences in the soil metal forms and intercropping practices [39]. Therefore, in the lead–zinc mining area, it is essential to take stringent control measures for Pb and Zn and closely monitor Cd content, migration, and transformation routes [2]. Overall, the local soil environment may not be suitable for growing such agricultural products as loquats and garlic but may be suited for cultivating economically valuable fruits like mangoes and peaches.

3.3. Physical and Chemical Properties of Soil

The effect of in situ passivation and restoration on soil physical and chemical properties is one of the important indexes to evaluate the properties of passivating agents. In this way, the soil physical and chemical properties of each treatment group after in situ passivation restoration were measured, and the results are shown in Figure 3. From Figure 3a. It can be seen that the pH of the tested soil is 7.72, which is medium alkaline. The pH of the soil repaired by FeSi was low. However, due to the small error between experimental parallelism, the results of significance analysis show differences.

3.4. Passivation Experiment

In this study, we investigated the potential environmental risks of the elevated levels of Cd, Pb, and Zn in the soil of mineral-rich regions of southwest China. Then, we succeeded in synthesizing a significant amount of iron silicate (FeSi) with excellent cadmium, lead, and zinc immobilization properties through a room-temperature synthesis approach. Fe(NO₃)₃ and Na₂SiO₃ served as precursors that reacted in the simulated aqueous solution. SEM analysis explained the microstructure of iron silicate, highlighting that its morphology is favorable for heavy metal adsorption. The experimental flow is shown in Figure 4. Adsorption experiments demonstrated the remarkable efficiency of iron silicate in adsorbing Cd, Pb, and Zn. Passivation materials at room temperature offer a promising strategy to cope with heavy metal contamination in the mineral-rich regions of southwest China.
Table 2 lists the contents of conventional heavy metals in engineering spoil samples collected from the research area. The soil pH was measured in 0.01 mol/L CaCl2 solution at 1:2.5 (w/w) using a pH meter, indicating that the soil was moderately alkaline. Although the heavy metal content in the engineering spoil still exceeded the standard, it was significantly lower than that of the surface soil at the above seven points. This suggests that the background values of Cd, Pb, and Zn in the research area were high. Combining the soil risk control index value of agricultural land with the soil background value of Sichuan Province, the results indicated relatively severe heavy metal contamination in the research area, with the Cd level exceeding the standard by 17 times. Many studies have shown that the toxicity of heavy metals in the soil was closely correlated with their morphology in the soil [16,22]. As only Cd, Pb, and Zn exceeded the standards in the original soil, subsequent studies mainly focused on these three metals. The results of the morphological classification of soil heavy metals using the BCR method are shown in Figure 5. The forms of heavy metals in the soil are categorized into the acid-extractable fraction (S1), reducible fraction (S2), oxidizable fraction (S3), and residual fraction (S4). In the soil, Cd exists in four forms, accounting for 61%, 32%, 7%, and 0%, respectively. Pb exists in four forms, accounting for 2%, 54%, 18%, and 26%, respectively. Zn also exists in four forms, accounting for 33%, 36%, 8%, and 24%, respectively. The acid-extractable fraction (S1) and reducible fraction (S2) are highly bioavailable and easily absorbed by plant roots [40]. The relatively high percentages of S1 and S2 for Cd, Pb, and Zn in the soil suggest that the soil in the research area has significant potential ecological risks and safety hazards.
According to the previous investigations, despite the severe heavy metal contamination, the local residents were still engaged in agricultural activities. In this study, we employed in situ passivation technology to remediate the local highly contaminated soil, aiming to reduce the activity of heavy metals in the soil without affecting the crop planting conditions. As shown in Figure 5 and Figure 6, heavy metals in the soil are categorized into the acid-extractable fraction (S1), the reducible fraction (S2), the oxidizable fraction (S3), and the residual fraction (S4). Among these fractions, a decrease in the S1 content indicates a reduction in soil toxicity [41]. Figure 6 provides the concentrations of Cd, Pb, and Zn in the soil before passivation, while Figure 7 demonstrate a decrease in the S1 content and suggest that iron silicate acts as a passivating agent to effectively mitigate the toxicity of heavy metals.
Various experiments were conducted to evaluate the effect of FeSi on soil heavy metal species under different conditions including dosage, time, and moisture content. The effect of passivator quality on the distribution of heavy metal species (Cd, Pb, and Zn) is depicted in Figure 7. The results revealed that with the increase in passivation materials, the acid-extractable state trend of Cd was opposite to that of reduction and oxidation states. When the dosage of FeSi was 4%, the percentage of S1 decreased from 62.26% to 56.74%, an 8.87% reduction in the content of the acid-extractable fraction. In addition, the content of the acid-extractable state of Pb was low, showing an unobvious change. The percentage of the highly active reduced state (S2) decreased. The S4 fraction of Pb increased by 11.67%, which indicated that the addition of FeSi could increase the content of the stable fraction and reduce its migration capability [16]. The morphological trend of Zn in the soil was similar to that of Cd. Consequently, the decreased bioavailability of Cd, Pb, and Zn could be attributed to FeSi [42]. However, excessive addition of FeSi might increase the iron content in the soil and affect crop growth. Therefore, a dosage of 4% is recommended in the practical application of FeSi for soil remediation in the research area.
The variations in field capacity might affect the passivation efficiency of FeSi for heavy metals. We set three gradients of field capacity: 15–20%, 35–40%, and 65–70%, with the results displayed in Figure 6. The field capacity of 15–20% had the best passivation efficiency. Compared to the 35–40% field capacity group, the S1 Cd content decreased to 52%, and the S2-Cd content of the 15–20% group decreased to 31%. Notably, the S4-Cd content increased from 0 to 11%, which significantly reduced the activity of Cd in the soil and its ecological risk. The possible reason for this is that the soil microorganisms in the research area were well-adapted to arid conditions [43]. Additionally, excessive moisture might lead to the hydrolysis of R-SH on the surface of the passivator, making water molecules occupy the active sites and obstruct the binding of heavy metal ions. Therefore, FeSi could be effectively used to remediate heavy metal contamination in the soils of regions with a warm climate.
The effect of passivation time on the distribution of heavy metal species (Cd, Pb, and Zn) is described in Figure 6. The results demonstrated that the percentages of Cd and Zn in the acid-extractable fraction (S1) reached the maximum value within the first 14 days of passivation, and then witnessed a slight increase. The Pb content in the acid-extractable fraction was relatively low and did not have any significant changes. However, the percentages of heavy metals in the residue fraction and oxidizable fraction increased significantly after 28 days, indicating a decrease in the bioavailability and activity of Pb in the soil. In conclusion, FeSi was proved to be an effective passivator for remediating the heavy metal contamination in the soil.

3.5. Desorption Experiment

From the results of acid desorption in Table S4 and salt desorption in Table S5, it is clear that the desorption amounts of Cd, Pb, and Zn in the soil were minimal after passivation. In the buffer solution (pH = 5) [44,45], the desorption amounts of Cd, Pb, and Zn were 0.0717 ± 0.0014 mg kg−1, 0.1418 ± 0.0006 mg kg−1, and 1.7956 ± 0.2250 mg kg−1, respectively. When the salt concentration was 1.5 mol L−1, the desorption amounts of Cd, Pb, and Zn were 0.0170 ± 0.0004 mg kg−1, 0.0949 ± 0.0337 mg kg−1, and 0.8705 ± 0.2002 mg kg−1, respectively. These findings indicate that the FeSi passivator is adaptable to the changes in the soil environment and has satisfactory stability.

4. Conclusions

This study, through field investigations, sampling, testing, and analysis, has shown that the soil in the research area was severely contaminated with heavy metals such as Cd, Pb, and Zn with concentrations significantly exceeding agricultural surface soil standards. Based on this, large-scale synthesis of ferric silicate was carried out to mitigate heavy metal contamination in the study area. Additionally, some local crops such as loquats (with a high concentration of Cd) showed relatively high heavy metal accumulation, while mangoes, peaches, and green dates exhibited relatively low heavy metal accumulation. In addition, there are a large number of treatment methods for the hazards of heavy metals in moderately alkaline soils. In this study, the research area is suitable for cultivating crops such as mangoes, peaches, and green dates that have low heavy metal accumulation and the purpose of soil safety management is achieved. Moreover, the application of iron silicate (FeSi) has been proven to be effective in reducing the toxicity of heavy metals in the soil, making it a viable option for passivation remediation in the local soil environment. This study introduces an environmentally friendly functional material that adapts to the local climate and soil conditions, providing valuable insights for developing strategies to remediate the local heavy metal contamination.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su16177426/s1, Figure S1: The scene map of the research area; Table S1: Soil pollution risk screening values for agricultural land (Basic items); Table S2: Speciation classification of heavy metals by BCR method; Table S3: The total amount of heavy metals in soil at sampling points within the study area (mg kg−1); Table S4: The total amount of heavy metals in the soil of the study area (mg kg−1); Table S5: Acid desorption and passivation experiment of soil heavy metals at different pH (mg kg−1); Table S6: Desorption and passivation experiments of salts with different concentrations of heavy metals in soil (mg kg−1); Table S7: Fruit heavy metal content (mg/kg); Table S8: Basic physical and chemical properties of soil.

Author Contributions

Conceptualization, H.X. and N.H.; methodology, N.H.; software, A.Y.; validation, H.X., N.H. and A.Y.; formal analysis, J.L. (Jingyuan Li); investigation, Q.L. and Q.Y.; resources, J.L. (Jingyuan Li); data curation, H.X. writing—original draft preparation, H.X.; writing—review and editing, H.X.; visualization N.H.; supervision, N.H. and J.L. (Jie Liu); project administration, L.L.; funding acquisition, L.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work is supported by the Power Construction of China (P42819, DJ-ZDXM-2019-42) and Bureau of Science and Technology Nanchong City (21YFZJ0003).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Conflicts of Interest

Authors J.L. (Jie Liu), J.L. (Jingyuan Li), A.Y. and Q.L. were employed by the company Power China of Chengdu Engnieering Corporation Limited, The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Correlation analysis between heavy metals and soil properties (heatmap of Pearson correlation coefficient: * represents p < 0.05; ** represents p < 0.01; ***. represents p < 0.001).
Figure 1. Correlation analysis between heavy metals and soil properties (heatmap of Pearson correlation coefficient: * represents p < 0.05; ** represents p < 0.01; ***. represents p < 0.001).
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Figure 2. Bioconcentration factors of heavy metals in the edible parts of plants in the research area. Error bars represent the standard deviations of three replicates.The bioconcentration factor (BCF) values of crops at sampling sites 1–7 (a–g).
Figure 2. Bioconcentration factors of heavy metals in the edible parts of plants in the research area. Error bars represent the standard deviations of three replicates.The bioconcentration factor (BCF) values of crops at sampling sites 1–7 (a–g).
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Figure 3. Changes in soil physicochemical properties: (a) pH. (b) Organic matter. (c) CEC. (d) Hydrolyzed N. (e) Available P. (f) Quick available K. The letters on the error bars in the figure indicate a significant difference in the results.
Figure 3. Changes in soil physicochemical properties: (a) pH. (b) Organic matter. (c) CEC. (d) Hydrolyzed N. (e) Available P. (f) Quick available K. The letters on the error bars in the figure indicate a significant difference in the results.
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Figure 4. Iron silicate was synthesized at room temperature and characterized through SEM and XRD analysis, revealing an advantageous adsorptive morphology and a structural phase, indicating a distinctive capacity to adsorb heavy metals such as Cd, Pb, Zn, Cr, Ni, and Cu.
Figure 4. Iron silicate was synthesized at room temperature and characterized through SEM and XRD analysis, revealing an advantageous adsorptive morphology and a structural phase, indicating a distinctive capacity to adsorb heavy metals such as Cd, Pb, Zn, Cr, Ni, and Cu.
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Figure 5. The proportion of heavy metal forms in the test soil. S1, S2, S3, and S4 represent acid-exchangeable, reducible, oxidizable, and residual heavy metal forms, respectively.
Figure 5. The proportion of heavy metal forms in the test soil. S1, S2, S3, and S4 represent acid-exchangeable, reducible, oxidizable, and residual heavy metal forms, respectively.
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Figure 6. Effects of iron silicate dosage (a–c) and soil moisture content (d–f) on the forms of Cd, Pb, and Zn.
Figure 6. Effects of iron silicate dosage (a–c) and soil moisture content (d–f) on the forms of Cd, Pb, and Zn.
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Figure 7. The effect of passivation time of iron silicate on the forms of Cd, Pb, and Zn (a–c).
Figure 7. The effect of passivation time of iron silicate on the forms of Cd, Pb, and Zn (a–c).
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Table 1. Soil background values in Sichuan Province and Soil Environmental Quality--Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018).
Table 1. Soil background values in Sichuan Province and Soil Environmental Quality--Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018).
TypesCdPbZnCuCrNi
Soil background value in Sichuan Province0.0830.986.531.179.032.6
Risk screening value (pH > 7.5)0.6170300200250190
Risk control value (pH > 7.5)4.01000//1300/
Table 2. The total amounts of heavy metals in the soil of the research area (mg kg−1).
Table 2. The total amounts of heavy metals in the soil of the research area (mg kg−1).
TypesCdPbZnCuCrNi
Content (mg Kg−1)10.2192.4782.588.0176.082.4
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Xu, H.; Liu, J.; Huang, N.; Yu, A.; Li, J.; Li, Q.; Yang, Q.; Long, L. Precision Remediation of Mining Soils through On-Site Investigation and Large-Scale Synthesized Ferrosilicate. Sustainability 2024, 16, 7426. https://doi.org/10.3390/su16177426

AMA Style

Xu H, Liu J, Huang N, Yu A, Li J, Li Q, Yang Q, Long L. Precision Remediation of Mining Soils through On-Site Investigation and Large-Scale Synthesized Ferrosilicate. Sustainability. 2024; 16(17):7426. https://doi.org/10.3390/su16177426

Chicago/Turabian Style

Xu, Han, Jie Liu, Na Huang, Anqing Yu, Jingyuan Li, Qiao Li, Qiunan Yang, and Lulu Long. 2024. "Precision Remediation of Mining Soils through On-Site Investigation and Large-Scale Synthesized Ferrosilicate" Sustainability 16, no. 17: 7426. https://doi.org/10.3390/su16177426

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