Leaching Mechanism Research Articles

Effect of Si/Al molar ratio and curing temperatures on the immobilization of radioactive borate waste in metakaolin-based geopolymer waste form

Immobilization of radioactive borate waste (RBW) using a geopolymer with a high Si/Al ratio has been challenging because boron-silicon networks lower the compressive strength and delay the setting time. In this study, metakaolin-based geopolymer waste form to immobilize simulant RBW was fabricated using different Si/Al ratios (1.0–1.4) and curing temperatures (26 and 60 ℃). The 7-day compressive strength results revealed that a certain amount of silicon and an elevated curing temperature are required to achieve high compressive strength and waste loading. Following waste acceptance criteria tests, all geopolymers exhibited compressive strengths higher than 3.445 MPa. The leachability index of boron was higher than 6.0, and the leaching mechanism was identified as diffusion. No significant structural changes in the geopolymer were observed after thermal cycling and gamma irradiation tests. The physically bound or unincorporated RBW was leached out of the geopolymer during water immersion and leaching tests; however, boron, which was chemically connected with silicon, was present as an inert phase together with a geopolymer binder. Consequently, immobilizing RBW using a geopolymer with a low Si/Al ratio (1.4) is beneficial in terms of RBW loading and structural durability.

Evaluation of the function of polymeric bentonite adsorbent to retain strontium and cobalt radionuclides in OPC matrices

The effect of polyacrylamide-bentonite (PAAmB) as an adsorbent/cement-enhancement material was examined for the retention of strontium (Sr2+) and cobalt (Co2+) ions from aqueous system. PAAmB composite was synthesized and analyzed by diverse characterization techniques. The acquired experimental data revealed that the addition of bentonite to polyacrylamide polymer (PAAmP) enhanced the adsorption of strontium and cobalt ions capacities. To examine the adsorption mechanism onto PAAmB, the experimental data were fitted using hyperbolic and Langmuir equations at different temperatures. It was found that the adsorption nature was chemisorption and the adsorbed amount of the studied ions increased with increasing the temperature. Immobilization of spent polyacrylamide-bentonite composite loaded with 85Sr and 60Co radionuclides in different extents with Ordinary Portland Cement (OPC) was investigated. The results showed that the optimal compressive strength was attained at OPC blended with 5% PAAmB composite. The leaching patterns of the studied radionuclides from the immobilized waste form were compared with the standard static long-term leaching approach of International Atomic Energy Agency (IAEA). The cumulative leaching fraction (CLF) of the studied radionuclides from PAAmB-OPC was found to be < 5% in all scrutinized conditions, which suggests the applicability of the IAEA-recommended approach for assessing the diffusion coefficient. The acquired leaching data were nonlinearly regressed with numerous mathematical kinetic models to determine the leaching parameters and to evaluate the prevailing leaching mechanism. The results from the regression scrutiny showed that 85Sr and 60Co leaching resulted from three succeeding leaching mechanisms that were the first-order reaction exchange among the waste matrix surface and the leaching solution, diffusion and dissolution. Compliant with IAEA, the calculated leachability indices values implied that the studied matrices performance was within a suitable range and the immobilized spent PAAmB matrices had an adequate mechanical efficacy.

Leaching of rare earth elements from coal ash using low molecular weight organocarboxylic acids: Complexation overview and kinetic evaluation

AbstractThe study of thermodynamics and kinetics of leaching rare earth elements (REEs) is a fundamental aspect in understanding the mechanism behind the leaching process. Leaching of REEs from coal ash with aqueous solution of organocarboxylic acid is a heterogeneous fluid‐particle system. In the present study, the leaching mechanisms of these three potential organocarboxylic acids, tartaric acid, lactic acid, and citric acid were examined over a range of temperature (30–90°C) at various leaching durations. The kinetic data thus obtained were found to follow deviation from the conventional shrinking core model (SCM). A mixed mechanism model was deduced to be the optimum fit to the data with high precision (R2 &gt; 0.95) and desired graphical linearity with closer interception to the origin. Aluminosilicate matrix remained unaltered after acid treatment which is the unchanged core concluded as from the kinetic mechanism. Morphological analysis using Scanning Electron Microscope (SEM) and particle size determinations were suggestive of significant reduction in grain size post leaching with organocarboxylic acids, tartaric acid being the most effective of all.

Phosphorus recovery from municipal sludge-derived hydrochar: Insights into leaching mechanisms and hydroxyapatite synthesis

Hydrothermal liquefaction has the potential to exploit resources from municipal sewage sludge. It converts most organics into a liquid biofuel (biocrude), concentrates P in the solid residue (hydrochar), and consequently enables its efficient recovery. This study thoroughly evaluated the effects of extraction conditions on P and metal release from hydrochar by nitric acid. Among assessed factors, acid normality (0.02–1 N), liquid-to-solid ratio (5–100 mL/g), and contact time (0–24 h) had positive effects while decreasing eluate pH (0.5–4) improved leaching efficiencies of P and metals. Notably, eluate pH played a dominant role in P leaching and pH < 1.5 was crucial for complete extraction. P and metal leaching from hydrochar have strong interactions and their leaching mechanism was identified as product layer diffusion using the shrinking core model. This suggests that the leaching efficiency is susceptible to agitation and particle size but not temperature. Using 10 mL/g of 0.6 N HNO3 for 2 h was considered the best extraction condition for efficient P leaching (nearly 100%) and minimization of cost and contaminants (heavy metals). Following extraction, adding Ca(OH)2 at a Ca:P molar ratio of 1.7–2 precipitated most P (99–100%) at pH 5–6, while a higher pH (13) synthesized hydroxyapatite. The recovered precipitates had high plant availability (61–100%) of P and satisfactory concentrations of heavy metals as fertilizers in Canada and the US. Overall, this study established reproducible procedures for P recovery from hydrochar and advanced one step closer to wastewater biorefinery.

Leaching Efficiency and Kinetics of Platinum from Spent Proton Exchange Membrane Fuel Cells by H2O2/HCl

The increasing carbon emissions from various fossil fuels have led to the search for efficient and clean energy sources to replace them. Proton exchange membrane fuel cells (PEMFCs) are a promising alternative, but the use of platinum as a catalyst material poses challenges due to its limited resources and low abundance. This study proposes an efficient method for platinum recovery while retaining spent membranes. The membrane and catalyst were separated using isopropanol, and the spent membrane was dissolved in a 50% ethanol solution to prepare the precursor for subsequent membrane regeneration. Hydrochloric acid (HCl) was used as the leaching agent, and the experimental parameters such as HCl concentration, H2O2 concentration, contact time, and operating temperature were optimized to achieve the highest platinum leaching rate. Finally, through isothermal leaching experiments, the leaching mechanism was investigated using the shrinking core model, indicating the involvement of both surface chemical and inner diffusion mechanisms in the platinum leaching process, primarily controlled by the inner diffusion mechanism. Under optimal conditions, the platinum leaching rate was about 90%, and the activation energy of the reaction was calculated to be 6.89 kJ/mol using the Arrhenius equation.

Highly selective separation of palladium from spent catalysts by ozonation with ultrasonic enhancement in a low-acid medium

It is of great significance to consider the recovery of palladium from spent catalyst in terms of resource reserve and environmental protection. However, the leaching percentage of palladium is limited by high oxidation potential and cladding layer. In order to solve this process problem, externalfield enhancementmethod with ultrasonic-assisted ozone is proposed for the recycling of palladium in this study. Mechanical and cavitation effects of ultrasonic can destroy cladding layer and promote solid–liquid interface reaction. The highly oxidizing free radicals generated by ultrasonic excitation of ozone can improve the oxidation of the reaction system and accelerate the oxidation rate of palladium. The leaching percentage of palladium is 93.7% under ultrasonic/ozone condition, which is 23.7% higher than that under conventional conditions. The leaching reaction kinetics shows that the reaction barrier is reduced and the apparent activation energy is reduced by 35.25 kJ/mol after introducing ultrasound and ozone. Additionally, mineralogical analysis is carried out to analyze the enhanced leaching mechanism of palladium. This work demonstrates the value of advanced oxidation process with ultrasonic-assisted ozone in efficient and green recovery of precious metals from secondary resources.

A Detailed Kinetic Analysis of the Environmentally Friendly Leaching of Spent Lithium-Ion Batteries Using Monocarboxylic Acid

It is essential to develop a leaching procedure that uses minimal acid consumption, is economical, recovers large amounts of metal, and has a minimal negative impact on the environment. In this paper, a viable hydrometallurgical method using acetic acid as a leachant is suggested for recovering critical metals from waste LCO-type batteries. Several leaching parameters were examined in order to optimize the leaching conditions. With 1.2 mol/L acetic acid, 7% H2O2, 90 °C, an S/L ratio of 10 g/L, and a 60 min leaching period, the maximum leaching efficiencies of Li (99.6%) and Co (95.6%) were attained. By investigating the different kinetic models, it was feasible to figure out the reaction’s pace, as well as the mechanism involved in the leaching process. It was found, through the comprehensive kinetic studies of the leaching process, that the surface chemical reaction controls the leaching mechanism for waste LCO-type batteries. The economic viability of the current leaching procedure in comparison to those of earlier approaches is also discussed.

Promotion Mechanism of Atrazine Removal from Soil Microbial Fuel Cells by Semiconductor Minerals

In recent years, soil microbial fuel cells (Soil-MFCs) have attracted attention due to their simultaneous electricity production and contaminant removal functions, but soil electron transfer resistance limits their contaminant removal effectiveness. To overcome the above-mentioned drawbacks, in this study, a dual-chamber Soil-MFC was constructed using atrazine (ATR) as the target contaminant, and the electrochemical performance of Soil-MFC and ATR removal were enhanced by semiconductor mineral addition. Analysis of atrazine was performed in soil using HPLC and GC-MS, and analysis of metallic minerals using XPS. Anodic microorganisms were determined using high-throughput sequencing technology. The results showed that the addition of Fe3O4 increased the maximum output voltage of the device by 2.56 times, and the degradation efficiency of atrazine in the soil to 63.35%, while the addition of MnO2 increased the internal resistance of the device and affected the current output, and these changes were closely related to the ion dissolution rate of the semiconductor minerals. In addition, the addition of both minerals significantly increased the relative abundance of both Proteobacteria and Bacteroidota, and Fe3O4 simultaneously promoted the significant enrichment of Firmicutes, indicating that the semiconductor minerals significantly enhanced the enrichment of electroactive microorganisms near the anode. The structural equation modeling indicated that the semiconductor minerals achieved efficient degradation of ATR in the soil through a synergistic mechanism of metal ion leaching and microbial community structure changes. The detection of ATR and its degradation products in soil revealed that the degradation of ATR mainly included: (1) hydrolysis of atrazine by microorganisms to generate dehydroxylated atrazine (HYA); (2) reduced to diethyl atrazine (DEA) and diisopropyl atrazine (DIA) by extracellular electron reduction and re-dechlorination and hydrolysis to HYA. Semiconductor minerals make an important contribution to promoting microbial activity and extracellular electron reduction processes. The results of this study strengthen the power production and ATR removal efficiency of the Soil-MFC system and provide important theoretical support for the on-site removal of organic pollutants and the sustainable application of converting biomass energy into electricity.

Kinetics and mechanism of manganese reductive leaching from electrolytic manganese anode slag with elemental sulfur in sulfuric acid solution

Recycling EMAS in an eco-friendly manner is crucial to alleviate the demand for manganese resource and reduce environmental pollution. Hydrometallurgical reductive leaching of EMAS with elemental sulfur is proposed, but sulfur is chemically inert. To improve the rate and degree of reductive dissolution of EMAS using elemental sulfur. Reductive leaching kinetics of EMAS by elemental sulfur with the aid of H2SO4 at atmospheric pressure have been conducted. A shrinking core model was used to explain the leaching data obtained, and the apparent activation energy was determined to be 63.8 kJ mol−1, indicating the leaching was controlled by chemical reation. The reaction order with respect to sulfuric acid concentration and mass ratio of sulfur to EMAS were 2.6 and 0.9, respectively. The leaching rate equation was established based on the shrinking core model, and good agreement between experimental data and predicted rate curves was obtained. Mechanism of reductive leaching was reasonably speculated with the assistance of X-ray diffraction and scanning electron microscope, revealing that the manganese reduction and sulfur oxidation progressed step by step, following the order Mn4+→Mn3+→Mn2+ and S0→S1+→S2+→ S4+→S6+. The ring opening reaction of [S8]•+ was identified as the rate-determining step. The results of this research provide a theoretical guidance for improving the speed and degree of manganese reduction leaching.

Selective leaching process for efficient and rapid recycling of spent lithium iron phosphate batteries.

With the continuous development of new energy vehicles, the number of decommissioned lithium iron phosphate (LiFePO4) batteries has been constantly increasing. Therefore, it is necessary to recover metal from spent LiFePO4 batteries due to the high potential for environmental protection and high resource value. In this study, sodium persulfate (Na2S2O8) was selected as the oxidant to regulate and control the oxidation state and proton activity of the leaching solution through its high oxidizing ability. Selective recovery of lithium from LiFePO4 batteries was achieved by oxidizing LiFePO4 to iron phosphate (FePO4) during the leaching process. This paper reports an extensive investigation of the effects of various factors, including the acid concentration, initial volume fraction of the oxidant, reaction temperature, solid-liquid ratio, and reaction time, on lithium leaching. Li+ reached a high leaching rate of 93.3% within 5 minutes even at a low concentration of sulphuric acid (H2SO4), and high-purity lithium carbonate (Li2CO3) was obtained through impurity removal and precipitation reactions. In addition, the leaching mechanism was analysed by both X-ray diffraction and X-ray photoelectron spectroscopy characterization. The results show that the obtained high lithium-ion (Li+) leaching efficiency and fast Li+ leaching time can be ascribed to the superior oxidizing properties of Na2S2O8 and the stability of the crystal structure of LiFePO4 during the oxidative leaching process. The adopted method has significant advantages in terms of safety, efficiency and environmental protection, which are conducive to the sustainable development of lithium batteries.

Mechanistic Study of Lithium-Ion Battery Cathode Recycling Using Deep Eutectic Solvents

The colossal increase in the use of Lithium-ion batteries (LiBs) necessitates their efficient recycling to ensure a steady supply of essential cathode materials, e.g., Li, Co, and Ni, as well as to tackle huge bulks of battery waste. Deep Eutectic Solvents (DESs) are green solvents with immense potential in the hydrometallurgical recycling of LiB cathodes, although their leaching mechanism has not been explored. We investigate the leaching mechanism of the different transition metals (TM), e.g., Co, Ni, and Li, from the most abundantly used LiB cathode materials NMC and NCA in an ethylene glycol (EG):choline chloride(ChCl) based DES. Leaching experiments performed by altering different parameters and density functional theory (DFT) calculations imply that EG participates in H-bonding and weakens the metal–oxygen bond of the TMs, whereas Cl– attacks the metal center to form chlorometalate complexes. Li on the other hand is surrounded by Cl– ions and leached in the solution. The increased concentration of ChCl in DES ensures the facile formation of these complexes and enhances leaching.

Review of rare earth element (REE) adsorption on and desorption from clay minerals: Application to formation and mining of ion-adsorption REE deposits

Ion-adsorption rare earth elements (iREE) deposits are the globally predominant source of heavy rare earth elements (HREE), which are mainly discovered and mined in southern China. This paper reviews the genesis and mining mechanisms of iREE deposits. These deposits are mainly formed in the weathering crust of rare earth elements (REE)-rich granites, volcanic rocks and metamorphic rocks. During the weathering and eluviation, REE are released by the dissolution of REE-bearing minerals, depending on the weathering resistance of such minerals. Then, aqueous REE cations migrate downwards and are adsorbed by clay minerals. The adsorption and fractionation of REE are affected by variations in oxygen, pH and ionic species and strength. REE are mainly adsorbed on clay minerals through ion exchange and surface complexation. The former reaction cannot cause evident REE fractionation, whereas the latter induces an enrichment of HREE over LREE. The enrichment and fractionation characteristics of REE are also constrained by their occurrence states. REE with different occurrence states can be distinguished via sequential extraction, and the micro-occurrence states of REE can be probed using high-sensitivity, high-resolution characterisation. Furthermore, the leaching mechanism of iREE deposits is summarized, where REE are exchanged by foreign cations. Ammonium sulphate is the main leaching agent, but its excessive use can cause serious environmental pollution. Thus, leaching agents with little or no ammonium, such as MgSO4 and CaCl2, have been recommended. The controlling factors of REE leaching are the concentration of leaching agents, pH, temperature and solid/liquid ratio. The above summary deepens the understanding of the formation mechanism of iREE deposits and provides beneficial information for the efficient but green mining of iREE deposits.

Basic performance, heavy metal leaching mechanism and risk assessment analysis of waste concrete

Basic performance, heavy metal leaching mechanism and risk assessment analysis of waste concrete

Production and mechanism analysis of clean coal from low-rank coal

ABSTRACT There are abundant low-rank coal resources in China. However, its higher AAEMs (alkali and alkaline earth metals) content and the release of AAEMs during combustion cause serious fouling and slagging problems. In this paper, a method of removing AAEMs and ash from low-rank coal to produce clean coal by organic acid leaching was proposed. The leaching effects of four organic acids were compared, the leaching mechanism of citric acid was analyzed, and the removal behavior of AAEMs and ash was investigated. The results show the effect of citric acid is better than others. During the leaching process, the citric acid ionizes H+, which reacts with inorganic minerals of AAEMs, completes ion exchange with AAEMs Organics. Under the relative optimized experimental conditions, the content of Na2O in coal ash is 0.9%, which is in line with the standard of power coal in China. The removal efficiency of alkaline earth metals Ca and Mg are significantly lower than those of alkali metals Na and K. The trend in the removal efficiency of Ca and ash are consistent. Citric acid leaching is an effective and promising method to produce clean coal from low-rank coal.

Study on the mechanism and thermodynamics of potassium leaching from phosphorus-potassium associated ore

This paper has mainly focused on the technology of transforming potassium minerals from phosphate-potassium associated minerals into soluble potassium by acid hydrolysis, and discussed the leaching mechanism of potassium in the process of leaching. As it is shown from the research, in the acid leaching system, [H+] = 8.71 mol L–1, mNH4F:mphosphorushboxpotassiumassociatedore = 0.25, the leaching rate of potassium reaches 74% at 413 K for 2 h. And the release of potassium ion is the result of the interaction of “oxidation” and “ion exchange”. It was found from the Eh-pH diagram of K-(Si)-(P)-(F)-H2O system that, when P-F or Si-F appeared in K-H2O system, the K+ stable region became narrow, and the excess fluorine was not conducive to the stability of K+ in aqueous solution.

Universal and efficient extraction of lithium for lithium-ion battery recycling using mechanochemistry

The increasing lithium-ion battery production calls for profitable and ecologically benign technologies for their recycling. Unfortunately, all used recycling technologies are always associated with large energy consumption and utilization of corrosive reagents, which creates a risk to the environment. Herein we report a highly efficient mechanochemically induced acid-free process for recycling Li from cathode materials of different chemistries such as LiCoO2, LiMn2O4, Li(CoNiMn)O2, and LiFePO4. The introduced technology uses Al as a reducing agent in the mechanochemical reaction. Two different processes have been developed to regenerate lithium and transform it into pure Li2CO3. The mechanisms of mechanochemical transformation, aqueous leaching, and lithium purification were investigated. The presented technology achieves a recovery rate for Li of up to 70% without applying any corrosive leachates or utilizing high temperatures. The key innovation is that the regeneration of lithium was successfully performed for all relevant cathode chemistries, including their mixture.

Microorganisms used for bioleaching of metals from typical solid wastes and their leaching mechanism: a review

Typical solid wastes contain many metal resources, which are worthy of recycling. The bioleaching of typical solid waste is affected by multiple factors. Green and efficient recovery of metals based on the characterization of leaching microorganisms and the elucidation of leaching mechanisms may contribute to the implementation of China's "dual carbon" strategic goals. This paper reviews various types of microorganisms used for leaching metals from typical solid wastes, analyzes the action mechanism of metallurgical microorganisms, and prospects the application of metallurgical microorganisms to facilitate the application of metallurgical microorganisms in typical solid wastes.

A green process for selective REEs recovery from Rare earth waste through mechanochemical activation

Rare earth elements (REEs) are vital to industry development, it is important to recycle REEs from RE-contained waste; however, it still faces challenges of high acid consumption and heavy pollution. In this work, the effect of phase evolution on the leaching behavior of REEs in roasted NdFeB waste was studied and found that the insoluble phase of NdFeO3 significantly inhibited the leaching efficiency of REEs. The formation of the NdFeO3 phase reduced the leaching efficiency of REEs to about 40%, which will increase the acid consumption in the subsequent leaching process. Density functional theory calculation was used to clarify the leaching mechanism of the insoluble phase by comparing the structural stability differences between Nd2O3 and NdFeO3. Mechanical activation was an effective method to destroy the structure of the insoluble NdFeO3 phase. After mechanical activation for 4 hours, the content of the NdFeO3 phase decreased from 21.0 wt% to 3.50 wt%, and the leaching efficiency of REEs increased about twice. The present work would provide a green strategy and corresponding theoretical basis for efficiently recovering REEs from NdFeB waste.

Vanadium Extraction from the Flotation Concentrate of Vanadium-Bearing Shale by Process of Non-Roasting Enhanced Acid Leaching and Thermodynamics

The purpose of this work is to significantly improve the vanadium grade of vanadium-bearing shale after flotation preconcentration, which is conducive to reducing the acid consumption and industrial costs in the subsequently enhanced acid leaching of vanadium. Vanadium concentrate from vanadium-bearing shale enriched by flotation is used for acid-leaching feed. The leaching effects of two kinds of acid-leaching systems were compared, and the mechanism of acid leaching on the mineral structure was also described. The difficulty of spontaneous reactions of vanadium-bearing minerals such as garnet in an acid-leaching system was studied through thermodynamics. Additionally, several characterization methods were used to evaluate the improvement of leaching performance. The addition of oxidants and fluorinating aids strengthens the acid-leaching process, which greatly destroys the structure of a garnet, which is conducive to the extraction of vanadium in a flotation concentrate. The leaching efficiency can reach 94.86%, and the acid consumption is also reduced. Through the mechanism study of the leaching system, it is expected that when the enhanced acid-leaching process is put into industrial production, the effective leaching of vanadium can be accurately controlled, and the difficulty of subsequent vanadium enrichment and purification can be reduced.

Study on properties of sewage sludge cemented paste backfill and leaching mechanism of heavy metals.

In order to achieve sustainable development and control environmental pollution, this paper proposes sewage sludge (SS) as an auxiliary cementitious material, which is mixed with ordinary Portland cement (OPC), fly ash (FA), and gangue to produce sewage sludge cemented paste backfill (SS-CPB) material. The fluidity and mechanical properties of backfill materials with different SS contents and the heavy metal leaching mechanism of SS-CPB are investigated. The results reveal that (1) with the increase of SS content from 10 to 30%, the slump of fresh SS-CPB mortar decreased from 21.7 to 18.2cm, the initial setting time decreased from 2.83 to 0.58h, and the final setting time decreased from 4.92 to 0.83h. (2) Compared with the control group, the 3-day unconfined compressive strength (UCS) of the SS-CPB mixed with 10% SS increased by 49.5%, and the UCS decreased slightly in the later stage, but it also met the actual needs of coal mines. (3) Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy were used to study the SS-CPB samples. It was found that the free Al3+ in SS promoted the formation of ettringite (AFt), provided part of the early UCS, and accelerated the setting time. (4) The leaching rule of heavy metal ions was analyzed in combination with leaching kinetics, and the change of heavy metal ion mass concentration in the rising stage was in line with the contraction core model controlled by diffusion.