Search Results (289)

In Chile, Eucalyptus globulus stands out as a significant forest species, yielding around 2 million tonnes of bark; this by-product is a valuable source of phenolic compounds. This research evaluated the valorization of E. globulus bark using alkali-assisted extraction (AAE) and obtained extracts intended to protect the wood against fungal degradation and ultraviolet (UV) radiation. The chemical and thermal properties of the extracts were characterized using total phenolic content (TPC), antioxidant capacity, FTIR spectroscopy, LC-LTQ-Orbitrap-MS, and thermal analyses (TGA and DSC). Pine wood samples were impregnated using the Bethel process, and their absorption, retention, leaching, UV resistance, gloss, and antifungal efficacy were evaluated. The AAE showed an extraction yield of 8.79%, almost double that of aqueous extraction, with a phenolic content of 970 mg GAE/100 g dry bark and good antioxidant capacity. The MS/MS analysis tentatively identified low-molecular-weight organic acids, phenolic acids, a hydrolyzable tannin derivative, ellagic acid, methylated flavonol glycosides, and an iridoid non-phenolic metabolite. Thermal analysis indicated greater stability of the alkaline extracts, with a mass loss of less than 10% up to 200 °C, and significant degradation between 220 and 300 °C. Leaching tests showed a lower release of polyphenols from alkali-treated wood, indicating reduced mobility and/or greater retention of the extractives within the wood structure. Biological assays demonstrated effective inhibition of stain fungi and strong resistance to brown rot. Furthermore, UV aging tests showed less color change (Delta E*) and greater resistance to surface degradation. These results demonstrate the potential of alkaline extracts from E. globulus bark as sustainable additives for wood protection. Full article

The increasing accumulation of mine waste and the associated release of toxic elements represent a major environmental challenge, particularly in regions impacted by Pb–Zn mining activities. In this context, this study aims to investigate the valorization of mine waste from Lakhouat, an abandoned Pb–Zn site in Northern Tunisia, as a sustainable additive in metakaolin-based geopolymers. This approach contributes to circular economy strategies by transforming hazardous waste into value-added materials for environmental and construction applications. Geopolymer formulations were synthesized by incorporating mine waste at different proportions (0, 5, 10, 20, and 30 wt.%) with metakaolin, while maintaining constant SiO₂/Al₂O₃ and Na₂O/Al₂O₃ molar ratios. The materials were prepared through alkali activation using sodium silicate and sodium hydroxide, followed by curing. Comprehensive characterization was carried out using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). In addition, adsorption experiments using methylene blue (MB) were conducted to evaluate the environmental performance of the synthesized geopolymers. The results revealed that the mine waste contains high concentrations of potentially toxic elements (up to 2.23 wt.% Pb and 8.2 wt.% Zn), highlighting the need for effective stabilization. Microstructural analysis confirmed the formation of predominantly amorphous geopolymer matrices with varying degrees of reaction depending on MW content. The highest compressive strengths (25–30 MPa) were achieved for formulations containing 5–10 wt.% MW after 28 days of curing. Furthermore, the geopolymers demonstrated efficient methylene blue removal, following pseudo-second-order kinetics and fitting the Langmuir isotherm model, with enhanced adsorption performance observed at higher MW contents. These findings indicate that MW-based geopolymers are promising materials for mine waste valorization and methylene blue removal. However, standardized leaching tests are required to confirm the long-term immobilization of Pb, Zn, Cd, As, and other potentially toxic elements within the geopolymer matrix. The study highlights their potential as sustainable, low-impact materials, supporting waste valorization and contributing to the development of environmentally resilient systems within a circular economy framework. Full article

This study aims to explore the preparation process and properties of unburned lightweight aggregate using red mud synergistically with fly ash, granulated blast-furnace slag, and other multi-source solid wastes. Curing regimes and alkali-activated systems were controlled. Their effects on physical properties and environmental safety of lightweight aggregate were systematically evaluated. Results show that curing temperature and alkali activator exert significant synergistic effects on physical properties of lightweight aggregates. Steam curing performs better than standard curing. Performance improves with increasing steam temperature. Sodium silicate solution with a modulus of 1.0 is determined as the optimal activator. Under 90 °C steam curing, Sample D2 achieves the best overall performance. Its cylinder compressive strength reaches 6.92 MPa. 1 h water absorption is 14.8%. Softening coefficient is 0.93. Porosity is as low as 31.07%. Microscopic analysis reveals that higher curing temperature significantly accelerates the hydration reaction of the RMLWA system. It promotes the formation of abundant cementitious products such as C-S-H gel. These products fully fill internal pores and microcracks of the aggregate. A dense three-dimensional network skeleton structure is finally formed. For environmental safety, heavy metal leaching concentrations of steam-cured samples are generally lower than those of standard-cured samples. This study realizes high-value resource utilization of industrial solid wastes. It also provides a new technical route for the development of green building lightweight aggregate. Full article

Vanadium extraction tailings, as a highly alkaline and hazardous solid waste, pose not only serious environmental risks but also severely hinder the large-scale recycling of secondary iron resources. This study proposes an innovative process of “mild alkali leaching for vanadium extraction coupled with deep calcification and dealkali removal”. The vanadium extraction slag from a steel plant in China was used as a raw material to carry out the experimental and pilot study of alkali leaching of vanadium and calcification dealkalization. Experimental results show that under the conditions of 120 °C, 1% NaOH solution, liquid-solid ratio of 4:1 to 6:1, and reaction time of 1 h, vanadium leaching rate can reach 50%, which can be effectively used as a high-value-added economic hedge. Subsequently, under the conditions of 200 °C, calcium oxide concentration of 19.29%, stirring speed of 800 rpm, liquid-solid ratio of 4:1, and reaction time of 1 h, the Na₂O content in the tailings was successfully reduced to below 1%. A large number of tailings can be converted into high-quality secondary iron ore resources, which are suitable for subsequent iron-bearing briquette preparation and blast furnace ironmaking. Furthermore, pilot-scale testing in a 200 L reactor verified the engineering scalability of this combined process, maintaining a vanadium extraction rate of over 50% and an alkali removal rate of over 80%. This study provides a robust, scalable, and highly profitable pathway for the comprehensive utilization of high-alkali metallurgical solid waste. Full article

As lithium demand surges and primary resources face depletion, lithium-bearing wastewater from urban mines has become a crucial secondary resource. For highly alkaline (pH 9–12), low-lithium (Li⁺ 0.5–5 g/L), high-sodium (Na/Li mass ratio > 30) wastewater generated from the alkaline leaching-washing of spent lithium-ion batteries in urban mining, a single-component, synergist-free extraction process employing HBL121 in sulfonated kerosene was developed, and its extraction stoichiometry, reaction mechanism, and industrial feasibility were elucidated. Saponification significantly enhanced extraction under moderate alkalinity: the saponified system achieved over 99% extraction efficiency at pH 11.0, whereas the non-saponified system required pH > 13.5 for comparable performance, thereby lowering alkali consumption by 81%. Under optimal conditions (saponification degree 40%, 30% (v/v) HBL121 and 70% (v/v) sulfonated kerosene, organic-to-aqueous phase ratio O/A = 1:1, extraction time 5 min), single-stage extraction efficiency exceeded 99%. A McCabe-Thiele diagram was used to determine the theoretical stage number for lithium stripping, showing that essentially all lithium ions can be stripped via a three-stage countercurrent process. Using 3.0 mol/L H₂SO₄ at an aqueous-to-organic phase ratio of 1:4, the stripping efficiency exceeded 99% from the loaded organic. Slope analysis, FT-IR, and ESI-MS confirmed a coordination mechanism between HBL121 and metal ions, forming a stable anionic bisphosphonate complex [LiNa₂(C₂₈H₄₄O₇P₂)]⁻, whose neutral parent form is HLiNa₂(C₂₈H₄₄O₇P₂). Full article

Saline water irrigation has emerged as a promising approach to mitigate agricultural water shortages; however, its improper use may induce secondary soil salinization. In this study, saline-alkali soil collected from Hami, Xinjiang, was used to conduct a series of indoor one-dimensional vertical soil column experiments. The aim was to systematically investigate the effects of sodium humate and desulfurization gypsum on soil infiltration behavior and the distribution patterns of key cations and anions under different levels of irrigation water salinity. The results showed that sodium humate application markedly improved soil infiltration capacity, while the duration of infiltration decreased with increasing salinity. Under salinity levels of 12 and 16 g/L, the 4 g/kg sodium humate treatment exhibited the most rapid advancement of the wetting front. In contrast, desulfurization gypsum reduced infiltration rates, with the lowest infiltration observed under the 12.5 g/kg treatment at 16 g/L salinity. Under different treatments, the adjusted coefficients of determination (adjusted R²) for the Philip, Kostiakov, and Horton models ranged from 0.8450 to 0.9841, 0.9901 to 0.9989, and 0.9748 to 0.9942, respectively, while the global performance indicator (GPI) ranged from 1.619 × 10⁻³ to 5.103 × 10⁻¹, 4.998 × 10⁻⁹ to 2.166 × 10⁻⁵, and 1.505 × 10⁻⁶ to 2.438 × 10⁻⁴, respectively. These results indicate that the Kostiakov model outperformed the other models in terms of fitting accuracy and overall performance for describing the soil infiltration process. In addition, sodium humate generally increased the sorptivity parameter S in the Philip model and the empirical coefficient K in the Kostiakov model, whereas desulfurization gypsum showed the opposite trend. In terms of salt regulation, sodium humate demonstrated optimal desalination performance at application rates of 6–8 g/kg under low salinity and 4–6 g/kg under high salinity conditions. Conversely, excessive gypsum application tended to exacerbate salt accumulation, although a moderate dosage (5 g/kg) effectively limited the downward migration and accumulation of Na⁺ and Cl⁻. These two ions were identified as the dominant contributors to soil salinization, showing strong positive correlations with soil salt content (SSC), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP). In contrast, Ca²⁺, Mg²⁺, and HCO₃⁻ played beneficial roles in alleviating sodicity through ion exchange and buffering mechanisms. Overall, sodium humate enhanced infiltration and facilitated salt leaching in the upper soil layers under saline irrigation conditions. Although desulfurization gypsum reduced infiltration and increased overall salt content, it contributed to mitigating Na⁺ accumulation in deeper soil profiles. These findings highlight the critical importance of selecting appropriate soil amendments and optimizing their application rates to improve saline water use efficiency and promote sustainable management of saline-alkali soils. Full article

Soil salinization is one of the most severe forms of land degradation in arid and semi-arid regions, posing substantial threats to agroecosystem stability and food security. In this study, saline–alkali soil collected from the Wuding River Basin in Yulin, Shaanxi Province was used to construct a three-factor amendment system comprising superabsorbent polymers (SAP), biochar, and humic acid. A systematic assessment was conducted to elucidate their combined effects on soil water–salt transport and crop growth. Results from one-dimensional constant-head infiltration experiments using indoor soil columns demonstrated that the application of amendments significantly increased cumulative infiltration and improved the uniformity of wetting-front advancement. Specifically, the treatments regulated the redistribution of salts within the soil profile; while surface salinity reduction varied, the leaching efficiency was significantly enhanced in the A2B2C2 treatment. Soil bulk density (BD) showed dynamic fluctuations during the growth cycle, peaking at 1.628 cm⁻³ during the branching stage, while high-rate biochar (A3) reduced BD by up to 13.64% compared to the control by the initial flowering stage. Fitting results based on the Philip and Kostiakov models further indicated that the combined amendment strategy—particularly the A2B2C2 treatment (30 kg/ha SAP, 15,000 kg/ha biochar, and 600 kg/ha humic acid)—markedly enhanced both the initial infiltration rate and the steady infiltration capacity. Field experiments corroborated the indoor findings: plant height and dry biomass of Melilotus officinalis (L.)Lam. were significantly higher under amendment treatments than in the control, driven by improved water availability, mitigated salt stress, and enhanced soil structure. Single-factor and multi-factor interaction analyses revealed that SAP exerted pronounced effects during early growth stages, whereas biochar and humic acid contributed more substantially during the middle to late stages through sustained regulatory functions. Collectively, the results demonstrate that the combined application of SAP, biochar, and humic acid improves the water–salt regime of saline–alkali soils through a coupled “water–salt–structure–plant” mechanism, ultimately enhancing crop productivity. This study provides both theoretical insights and practical guidance for the amelioration of saline–alkali soils. Full article

In order to evaluate the utilization potential and environmental risk of iron tailings in ameliorating soda saline–alkali soil, a leaching experiment of iron tailings was carried out by simulating the soil acid–base environment and the saline–alkali stress environment of soda saline–alkali, and the basic physicochemical properties and the content and leaching characteristics of metal elements of iron tailings were analyzed to evaluate the environmental risk. The results showed that the iron tailings sand had a large specific surface area (0.66~0.91 m²·g⁻¹) and a rich pore structure (pore diameter 9.07~11.48 nm), which was conducive to the adsorption of salt-alkali by iron tailings sand. The main chemical composition of iron tailings is SiO₂ (33.39%~57.32%) and Fe₂O₃ (8.47%~14.94%), the content of plant nutrient elements in iron tailings is abundant, and the content of risk elements is far below the national standard limit. The leaching experiment results indicated that under acid or alkali conditions, the leaching amounts of various metal elements from the iron tailings met the national water quality standards for farmland irrigation, with Cd, Hg, Mn, Al, Ca, and others being more readily leached under acidic conditions. Under the same pH conditions, Cd, Hg, As, Al, and others were more readily leached under the soda saline–alkali environment. Unlike in the soil acid–base environment, the correlations between the leaching amounts of different metals were weaker under the combined soda saline–alkali stress, with only As and Al showing a positive correlation with the pH of the leachate, though the correlation was not significant. This study confirms that the environmental risk of using iron tailings for the improvement of soda saline–alkali soil is relatively low, and long-term changes in the contents of heavy metals such as As and Al in the soil should be given focused attention in future work. Full article

Silicomanganese slag (SiMnS), a Mn-bearing by-product from silicomanganese alloy production, is often stockpiled in large quantities and may pose environmental concerns due to potential metal leaching. This study develops an OPC-rich hybrid SiMnS–steel slag–fly ash–OPC-activated composite binder, referred to as SMSAB, in which OPC accounts for 55% of the solid precursor mass. Different alkali contents and sodium silicate moduli were investigated, and the optimised paste was characterised in terms of mechanical strength, reaction products, pore structure, carbon-footprint and heavy-metal leaching. The best performance was obtained at an alkali content of 4% and a sodium silicate modulus of 1.0, giving 28-day compressive and flexural strengths of 65.13 MPa and 3.37 MPa, respectively. XRD, SEM-EDS, FTIR and MIP results showed that the main reaction products were C-(A)-S-H, N-A-S-H and C-N-A-S-H gels, which refined the pore structure and produced a dense matrix. The reduction in Mn leaching may be associated with physical encapsulation, possible charge-balancing interactions within gel structures, changes in Mn-related bonding environments and the presence of Mn-bearing phases. Leaching concentrations of Zn, Mn, Cr, Cu and Ni satisfied the Grade III groundwater limits used in China. The calculated carbon intensity of SMSAB was 3.97 kg·(m³·MPa)⁻¹, indicating a favourable strength-to-emission balance compared with the reference systems considered. It should be noted that the present work examines paste specimens only; aggregate skeleton, traffic loading, freeze–thaw cycling and wet–dry/moisture cycling were not included. Therefore, the results demonstrate binder-level potential rather than direct qualification of SMSAB as a pavement base or subbase material. Full article

The construction sector consumes significant amounts of natural resources and contributes substantially to global CO₂ emissions, making it necessary to develop materials with a reduced environmental impact. In this context, the valorization of reusable industrial waste as secondary raw materials represents a strategic direction for applying circular economy principles and for decarbonizing the construction materials industry. The scientific problem addressed in this review is the urgent need to develop construction materials with a reduced environmental footprint, given that the construction sector is a major consumer of natural resources and a significant contributor to global CO₂ emissions. This challenge requires the identification and critical evaluation of sustainable solutions that support decarbonization and the transition toward a circular economy. The main findings indicate that the valorization of industrial waste offers high decarbonization potential: supplementary cementitious materials (SCMs), such as ground granulated blast furnace slag and fly ash, can reduce CO₂ emissions by approximately 20–50%, while alkali-activated binders and geopolymers achieve reductions of 40–80% compared to Portland cement. These materials also enhance durability, extending service life by 10–20% in aggressive environments, although early-age strength may decrease by 10–30%; recycled aggregates derived from construction and demolition waste (CDW) can substitute up to 100% of natural aggregates, while rubber fibers can increase impact resistance by 30–50% and reduce density by 10–20%. However, key limitations relate to waste variability, heavy metal leaching risks (requiring immobilization efficiencies > 90%), and the relatively low technological maturity of many solutions (TRL < 7), leading to the TRL–CO₂ paradox and highlighting the need for standardization and performance-based regulatory frameworks. The synthesized results indicate that the appropriate integration of industrial waste enables a significant reduction in clinker content, lowers associated CO₂ emissions, and decreases primary energy consumption while maintaining physical–mechanical properties and durability characteristics comparable to or in some cases superior to those of traditional materials, if mix design is based on clear performance criteria, stratified according to the type of waste, dosage used, curing regime, binder chemistry, and the target application. Full article

The global construction industry urgently requires sustainable alternatives to ordinary Portland cement (OPC) to mitigate its immense carbon footprint. Red mud (RM), a highly alkaline bauxite residue, presents tremendous but challenging potential as a supplementary cementitious material. This review systematically bridges the gap between atomic-level interfacial bonding mechanisms and macroscopic engineering performance, highlighting how these properties are significantly dictated by specific RM sources (e.g., Bayer vs. Sintering processes). We first elucidate advanced pretreatment strategies, notably CO₂ mineralization, which synergistically mitigates extreme alkalinity and sequesters carbon. Crucially, the fundamental bonding mechanisms are decoded: beyond physical filling, RM integration induces significant micro-morphological densification via intense aluminosilicate depolymerization—evidenced by the Al[VI] to Al[IV] coordination shift—and the quantitative integration of approximately 40% reactive iron phases into stable Fe-S-H networks. By clearly distinguishing between traditional hydration and clinker-free alkali-activation pathways, we evaluate holistic structural parameters beyond mere 28-day compressive strength (40–67 MPa), explicitly addressing flexural capacity, modulus of elasticity, and volume stability. Environmental assessments confirm exceptional heavy metal immobilization (>95% efficiency, leaching < 0.010 mg/L) and a substantial 50–80% reduction in Global Warming Potential (GWP), provided the environmental burden of alkaline activators is rigorously accounted for. Furthermore, the long-term risk of Alkali–Silica Reaction (ASR) is evaluated as a primary durability concern. Finally, to overcome persistent rheological bottlenecks, this paper highlights transformative future trajectories, particularly data-driven Machine Learning (ML) for complex mix optimization and 3D concrete printing for advanced infrastructure. Ultimately, this review provides a robust theoretical foundation and a pragmatic roadmap for upcycling RM into safe, high-performance, and ultra-low-carbon building materials. Full article

Calcium–silicate–hydrate (C-S-H), the primary binding phase governing cement paste cohesion, undergoes progressive physicochemical transformation upon carbonation—a process that critically dictates concrete durability in atmospheric environments. When CO₂ penetrates the porous cement matrix, it triggers a cascade of degradation mechanisms: calcium leaching decalcifies the C-S-H structure, inducing polymerization of silicate chains from dimeric to longer-chain configurations, while concurrent precipitation of calcium carbonate and amorphous silica gel fundamentally reconstitutes the nanoscale architecture. These nanoscale alterations propagate to macroscopic property evolution, manifesting as initial strength and stiffness gains due to pore-filling carbonation products followed by eventual deterioration as the cohesive binding network deteriorates. This review synthesizes current understanding of carbonation-induced structural evolution, examining the coupled influences of environmental parameters—CO₂ concentration, relative humidity, and temperature—alongside C-S-H intrinsic chemistry (Ca/Si ratio, aluminum substitution, and alkali content) on reaction kinetics and material performance. However, significant knowledge gaps persist: predictive models for in-service carbonation rates remain elusive due to the disconnect between idealized laboratory conditions and the heterogeneous, cracked reality of field concrete; the causal linkage between nanoscale C-S-H alteration and macroscale cracking patterns along with physical performance is poorly resolved, and most mechanistic studies rely on synthetic C-S-H, neglecting the compositional complexity of real Portland cement systems. We further propose emerging protection strategies, including surface barrier coatings and low-carbon alternative binders (geopolymers, calcium sulfoaluminate cements, carbon-negative materials such as recycled cement), which demonstrate enhanced carbonation resistance. Future research priorities include developing effective coating barriers for carbonation protection, developing operando characterization techniques for real-time reaction monitoring, deploying machine learning algorithms to bridge atomistic simulations with structural-scale predictions, and establishing long-term field performance databases to validate laboratory-derived degradation models. Full article

To address the limited simultaneous optimization of mechanical performance and heavy-metal stabilization in waste-based alkali-activated systems, this study investigates the development and characterization of a novel composite cementitious material for potential construction applications, utilizing lead and zinc smelting slag (LZSS) and electroplating sludge (ES) as precursors. The novelty of this study lies in the co-modification of an LZSS-based alkali-activated matrix with PVA and KH792 to improve both compressive behavior and heavy-metal stabilization in ES-containing specimens. Based on single-factor optimization, the optimal matrix was obtained at 3.5% alkali content, a water-glass modulus of 1.4, and a liquid-to-solid ratio of 0.22, followed by 28 days of curing before testing. On this basis, ES and PVA-KH792 were introduced to investigate their effects on mechanical behavior, heavy-metal leaching, and immobilization mechanisms. The results showed that adding ES reduced the compressive strength of the alkali-activated matrix, whereas PVA-KH792 modification partially restored matrix integrity and improved performance. At 5% ES content, the compressive strength of the modified specimen increased by 7.66% compared with that of the unmodified ES-containing sample. More importantly, under the sulfuric acid–nitric acid leaching method, the Cr leaching concentration decreased from 20.1 mg/L to 13.7 mg/L, meeting the relevant regulatory limit (GB5085.3-2007 and EPA limit). Microstructural and spectroscopic analyses indicated that the beneficial effect of PVA-KH792 was associated with matrix densification and enhanced heavy-metal immobilization. The immobilization mechanisms were mainly attributed to Cr(VI) reduction by Fe(II), complexation/coordination with functional groups introduced by PVA-KH792, and physical encapsulation within the alkali-activated matrix. The findings provide a promising approach to waste valorization and the development of sustainable building materials, contributing to resource efficiency and reducing the environmental impact of the construction sector. Full article

This research explores the use of industrial waste as an alternative to natural raw materials, promoting a circular economy in the construction sector. It specifically investigates the manufacturing of paving blocks using blast furnace slag and recycled aggregates. Paving blocks were produced without altering typical industry conditions, entirely replacing cement with alkaline-activated blast furnace slag. The study replaced natural aggregate in three proportions (20%, 50%, and 100%) with three types of recycled aggregates: concrete recycled aggregate (CA), masonry recycled aggregate (MA), and recycled mixed aggregate (RMA), in both coarse and fine fractions. The experimental procedure analysed the impact of recycled aggregates in an alkaline-activated slag matrix through three phases: characterising physical properties (mechanical properties, water absorption, density, abrasion resistance, and slip resistance), evaluating leaching behaviour, and conducting a life cycle analysis. The results of physical characterisation were statistically analysed using principal component analysis (PCA). The results obtained show the feasibility of manufacturing paving blocks with blast furnace slag by completely replacing the natural aggregate with the coarse fraction of the three recycled aggregates used and replacing up to 20% in the case of using the fine fraction. The properties of the paving blocks manufactured with slag depend mainly on the degree of substitution of natural aggregate with the recycled aggregate. All paving blocks can be considered environmentally safe from leaching according to the Dutch Soil Quality Decree. Paving blocks made from alkali-activated ground granulated blast furnace slag and recycled aggregates generate a lower carbon footprint compared to concrete paving blocks. Full article

This study investigated the extraction of aluminum from aluminum silicate-rich coal ash from the ash-slag waste of the Almaty CHP-2 power station using microwave-assisted alkaline leaching. The high chemical stability of the quartz and mullite phases in the ash leads to high energy consumption during conventional acid–base treatment. To improve the kinetic parameters of the leaching process, amorphous graphite was therefore used as an active additive, which effectively absorbs microwave energy. The experiments were conducted in the temperature range of 50–200 °C, in 1–6 M NaOH solution, and over a period of 5–30 min. The amount of amorphous graphite varied between 5 and 20 wt%. The proportion of amorphous graphite varied between 5 and 20 wt%. Upon microwave irradiation, the graphite-free ash reached a temperature of 200 °C within approximately 12 min, whereas this temperature was reached in the system with 15% amorphous graphite after only 8–9 min. At low alkali concentrations (1–2 M NaOH), the aluminum transfer into solution in the graphite-free system was approximately 18%–35%. With increasing NaOH concentrations to 3–4 M, the aluminum removal efficiency increased to 38%–58%. Under the same temperature conditions, the leaching process was significantly accelerated by the addition of amorphous graphite; thus, at temperatures near 200 °C and in a 5–6 M NaOH solution, 70%–72% of aluminum was removed. The leaching kinetics were analyzed using the shrinking core model. The results showed that the apparent activation energy of the reaction decreased from 54 kJ/mol to 32 kJ/mol in the presence of graphite. These results suggest that microwave-assisted alkaline leaching in the presence of amorphous graphite is an energy-efficient and promising method for aluminum recovery from coal ash. Full article