Leaching Duration Research Articles

Vanadium extraction from vanadinite and high carbon v-bearing stone coal by coupling reduction smelting and oxalic acid hydrothermal leaching

Vanadinite and high-carbon vanadium-bearing (V-bearing) stone coals are important vanadium sources widely used in vanadium extraction. The traditional sulfuric acid leaching method for extracting vanadium consumes a large amount of acid, wastes significant amounts of lead and carbon, and causes serious environmental pollution. This study discusses the integration of reduction smelting and oxalic acid hydrothermal leaching for processing vanadinite and high-carbon V-bearing stone coals. Specifically, high-carbon V-bearing stone coal is selectively added to vanadinite to produce coarse lead blocks and V-bearing slag during reduction smelting. Then, the oxalic acid hydrothermal leaching process is employed to extract vanadium from the V-bearing slag. This approach reduces the waste of lead and carbon resources and achieves co-extraction of vanadium from both V-bearing minerals. The results show that when the mass ratio of high-carbon V-bearing stone coal to vanadinite is 25%, and smelting is conducted at 1150°C for 15 min under argon protection, a separation efficiency of 90.67% for metallic lead and V-bearing slag is achieved, the grade of V2O5 in vanadium slag is 12.37%, and the recovery rate is 95.64% by ICP-OES analysis. Furthermore, the leaching rate of vanadium in the V-bearing slag can reach 85.34% via oxalic acid hydrothermal leaching under conditions of a leaching temperature of 100°C, a leaching duration of 30 min, an oxalic acid concentration of 25 wt%, a liquid-to-solid ratio of 10:1 mL/g, and a stirring speed of 500 rpm. The integration of reduction smelting and oxalic acid hydrothermal leaching offers benefits such as improved resource utilization, waste reduction, cost savings, and environmental enhancements. Thus, the findings of this research can serve as references for the vanadium extraction processes of related vanadium-containing minerals.

Environmentally sound geotechnologies for leaching metals from polymetallic ore processing wastes and wastewater

Global challenges (increased consumption of georesources, climatic changes, limited reserves) increase the relevance of the problems of growing waste accumulation and environmentally-sound modernization of mineral extraction. In this regard, the existing approaches to the design of geotechnologies for metal mining need to be improved based on a concept of so-called circulation waste management and ecologization of technological processes. The paper is devoted to the issue of formation of conceptual bases and directions of ecologization of geotechnologies at leaching metals from polymetallic ore processing wastes and wastewater. The study presents recommendations for improving in-situ leaching of ores in blocks, allowing to determine the optimal conditions for increasing the completeness of subsoil use and reducing environmental damage. It was revealed that at metal extraction with solution circulation through brine chambers the content of Na, Cl, SO4 and Ca ions in dialysate was low, while without circulation through brine, it significantly exceeded corresponding MPCs. This proves the fundamental feasibility of controlling natural leaching processes by enhancing the oxidizing potential of natural solvents through the addition of industrial oxidizing agents. It was found that increasing the duration of agitation leaching (both with and without mechanoactivation) leads to a uniform expansion of the local maximums of Pb yield from the pulp when the minimum NaCl concentration decreases from 11–12 to 7% at H2SO4 concentration of 0.6%. One of key results of the study is justifying the expansion of the use of disintegrators to realize targeted activation of tailings. The practical significance of the obtained results lies in the proved feasibility of optimizing the flow sheet of electrochemical extraction of metals from wastewater on the basis of the obtained regularities of the use of brine circulation through brine chambers. In addition, the totality of the obtained results of using a disintegrator for reextraction of lead from geomaterials will allow developing a methodology for calculating the parameters of mechanoactivation action to increase the degree of metal recovery from the tailings of North Ossetia-Alania’s (Zgidskoe, Sadonskoe, Arkhonskoe deposits) polymetallic ores beneficiation. The most promising way for further research is to substantiate methods of using underground space for complete removal of wastes (wastewater and tailings) after their multistage treatment.

An optimisation study for leaching synthetic scheelite in H2SO4 and H2O2 solution

ABSTRACT Tungsten production primarily relies on scheelite, a secondary resource due to its complex ore composition and lower grade compared to high-grade wolframite. Synthetic scheelite gains significance for its low impurity content and accessibility in ongoing laboratory-based investigations. Recent advancements offer a feasible environment-friendly leaching method using a mixed solution of H2SO4 and H2O2 under normal pressure and moderate temperatures. However, comprehensive research on this novel method is lacking, emphasising the need for collaborative exploration and operational optimisation. The present work is to provide insights and improvements in reagent usage to promote economic and environmental sustainability. A detailed investigation into the thermal decomposition process was also conducted without compromising leaching efficiency. The findings suggest the potential for eco-friendly lixivium recycling with reduced levels of chemicals, decreasing operational costs. Notably, optimising the thermal decomposition duration to 6 hours at an L/S (mL/g) ratio of 10 enhances H2WO4 crystallization. Furthermore, experiments without H2SO4 supplementation highlight the system's optimisation potential. Finally, the leaching process was optimised by decreasing H2SO4 concentration to 1 mol/L from 3 mol/L, increasing the temperature to 60°C, and extending the leaching duration to 120 minutes. This leads to a cost-effective synthetic scheelite leaching process with environmental benefits.

Enhanced heavy metal leaching from volcanic muds: Synergistic effects of citric acid and EDTA composite system

The soil leaching technology is a well-established technique commonly employed for the remediation of soils contaminated with heavy metals. Volcanic muds share similar properties to those of soil. This study utilizes soil leaching technology to tackle the presence of heavy metals in volcanic muds. It examines the leaching removal effect of the synergistic system of organic acid citric acid (CA) and chelating agent EDTA on heavy metals Pb, Cd, Cr, and Ni in volcanic muds. The leaching conditions were initially selected and subsequently optimized through the application of response surface methodology (RSM). The priority of leaching conditions can be ranked as follows: leaching duration is found to be more crucial than leaching agent concentration, which is noted to be more pivotal than the solid-liquid ratio. Following an in-depth evaluation of model predictions and experimental validation, it has been established that the optimal leaching concentration of EDTA is 0.15 mol·L−1, the optimal leaching duration is 9 h, and the optimal solid-liquid ratio is 1:10. For the compound CA, the most effective leaching concentration is 0.3 mol·L−1, the optimal leaching duration is 8 h, and the optimal ratio of solid to liquid is 1:10. The significance of the leaching conditions was further explored in conjunction with RSM. Furthermore, the integration of both leaching methods, namely combined leaching and stepwise leaching, has been demonstrated to amplify the removal efficiency of heavy metals, with stepwise leaching showing the highest removal rate. The experimental findings suggest that the leaching technique involving CA and EDTA composite system is an effective approach for the remediation of heavy metals such as Pb, Cd, Cr, and Ni in volcanic muds. This study provides theoretical rationale for the adoption of soil leaching technology in the remediation of heavy metals in volcanic muds. Additionally, the heavy metal content of the remediated volcanic muds substantially meets with the standards for cosmetic raw materials.

Optimization of a Rare Earth and Aluminum Leaching Process from Weathered Crust Elution-Deposited Rare Earth Ore with Surfactant CTAB

Ammonium sulfate is typically employed as a leaching agent in the in situ leaching of weathered crust elution-deposited rare earth ore. However, it is associated with challenges such as low efficiency in mass transfer for rare earth (RE) leaching, high usage of the leaching agent, and prolonged leaching duration. To address the issues mentioned above, the surfactant cetyltrimethyl ammonium bromide (CTAB) was compounded with 2% ammonium sulfate to form a leaching agent in this paper. The effects of CTAB concentration, temperature, pH, and leaching agent flow rate on the rare earth (RE) and aluminum (Al) leaching mass transfer process from RE ore were investigated using chromatographic plate theory. The results revealed that CTAB addition improved the RE mass transfer process while moderately inhibiting the Al mass transfer efficiency. Increasing the temperature and pH of the leaching solution led to higher theoretical plate numbers for RE and Al leaching, lowered theoretical plate height (HETP), and enhanced leaching mass transfer efficiency. However, under high temperature and alkaline conditions, the mass transfer efficiency begins to decrease, indicating that high temperature and alkaline conditions are not conducive to the synergistic enhancement of RE and Al leaching by CTAB. Considering that clay minerals have good pH buffering properties, adjusting the pH of the leaching solution during rare earth ore leaching operations was deemed unnecessary. The optimal mass transfer conditions for leaching RE and Al were identified as 2% ammonium sulfate concentration, 0.00103 mol/L CTAB concentration, pH range of 5.2–5.5 for the leaching solution, 0.6 mL/min leaching solution flow rate, and room temperature. The rare earth leaching mass transfer effect could be enhanced during summer operations.

Selective leaching of indium from spent LCD screens by siderophore desferrioxamine E

Given the criticality of indium (In) in high-tech applications, spent LCD screens can represent a viable secondary In resource. In this work, an innovative and alternative technology to selectively leach In from spent LCD screens using a microbial chelating agent, desferrioxamine E (DFOE), was developed. Indium was concentrated from spent LCD screens by implementing an adapted pre-treatment procedure, allowing the isolation of an indium-rich glassy fraction. During leaching, the competition between aluminum (Al) and In for complexation with DFOE leads to the precipitation of In(OH)3 at low DFOE concentrations (12–240 µM). After adjusting the optimal conditions (fraction size: 0–36 μM, pH: 5.5, S/L ratio: 1 g/L, 25 °C), the In leaching yield reached 32%, ten times higher than Al over 90 days with 5 mM DFOE. Thus, achieving high In recovery is possible through i) prolonging leaching durations, ii) selective leaching, and iii) minimizing Al interference. This is the first attempt to selectively leach In using a selected siderophore from end-of-life products with high concentrations of non-targeted elements (i.e. Al, Si, and Ca). This study demonstrates the potential of generating indium-rich leachates, which can be subsequently processed through the GaLIophore technology for In refining.

Zinc removal from metallurgical dusts with iron- and sulfur-oxidizing bacteria

The generation of currently partially recyclable metallurgical dusts during the steel production represents a challenge for the realization of a circular economy in this industrial sector. Due to a high iron concentration, the reutilization of blast furnace and cast house dusts in internal crude steel processes, is state of the art. However, heavy metal impurities such as zinc, act as an interference due to diverse negative effects. The aim of this study is to utilize Acidithiobacillus ferrooxidans, an iron- and sulfur-oxidizing bacteria, to solubilize zinc whilst retaining iron in the dust residue intended for reuse. To achieve this, the biooxidation of elemental sulfur is of crucial relevance. Two different strains of A. ferrooxidans (DSM 583 and CCM 4253) were cultivated and their leaching performances were compared to each other using a stirred tank reactor operated in a fed batch set-up, with a working volume of 3 L, at an operation temperature of 30 °C. The dust concentration was gradually increased until a maximum of 125 g/L, after which the reactors were left to run for three additional cycles to ensure replicability of results. For both strains, at a cast house dust concentration of 125 g/L paired with a leaching duration of two weeks, an average zinc removal of 56 % was achieved whereas solely an average of 4 % of iron was leached.

Weakening of mechanical parameters of ion-absorbed rare-earth ores subjected to leaching

Ion-adsorbed rare-earth ores are mined using in-situ leaching, and their mechanical properties significantly affect the efficient and safe recovery of rare earth elements. However, the mechanism of the change in the mechanical properties of the ore body due to the physicochemical processes caused by leaching remains unclear. To explore the strength evolution characteristics of the ore body during the leaching process, unconsolidated undrained triaxial tests were conducted to confirm how the stress–strain curve and shear strength of rare-earth samples change during leaching. Magnetic resonance imaging and T2 spectral characterizations were obtained by using nuclear magnetic resonance technology to measure the interior pore structure of samples during leaching. A scanning electron microscope equipped with an energy dispersive spectrometer was used to investigate the morphology evolution and the composition changes of the internal micro-area of the samples, to demonstrate the correlation between the microstructural change and the macroscopic mechanical properties. The results show that when a 2% ammonium sulfate solution is employed for mineral leaching, the effective leaching duration is 0–3 h. During this time, ion exchange occurs along the direction of solution seepage, resulting in the dispersion and migration of fine particles from the top to the bottom of the sample, which further triggers a change in the sample's pore structure and pore size. In addition, the local loss of fine particles resulted in a reduced bond strength between minerals, forming an unstable soil structure with a loose upper part and a dense lower part, which is macroscopically expressed as a declining shear strength parameter of the rare-earth sample.Graphical abstract

Calcium Leaching of 3D-Printed Cement Paste Exposed to Ammonium Chloride Solutions

Understanding the degradation of 3D-printed cement paste (3DPC) is essential to evaluate changes in the long-term durability of concrete structures subjected to aggressive water. However, the degradation mechanism of 3DPC has yet to be reported, as the microstructure and pore characteristics of 3DPC are very different from those of its cast counterparts. This work studies the performance anisotropy of 3DPC due to calcium leaching to investigate the degradation mechanism. Samples with aggregate micro fines (AMF) and fly ash (FA) were prepared. A 6 mol/L NH4Cl solution was used in the accelerated experiment. At specific leaching durations, performances were tested on the samples in different leaching directions. The performance anisotropy of 3DPC exposed to aggressive water was investigated by comparing the changes in bulk density, water absorption, leaching depths, and compressive strength in different leaching directions. X-ray diffraction (XRD), differential thermal gravity-thermogravimetric (DTG−TG), and mercury intrusion porosimetry (MIP) were used to characterize the changes in hydration products and pore structure in different leaching directions. The results show that the performances of 3DPC in aggressive water have a significant anisotropic behavior. The evolution of pore defects and hydration products mainly governs the performance anisotropy of degraded 3DPC. The remaining hydration products of the surface of 3DPC leached in the Z direction are fewer than the other two directions because calcium ions leached in the Z direction are difficult to compensate through weak interfaces between layers. The test results clearly show that the calcium leaching mechanism of 3DPC in aggressive water is directly influenced by the hydration products, such as portlandite (CH) and C-S-H, and the pores. The current study may help us understand the degradation mechanism of 3DPC to assess its durability performance anisotropy.

Underground Development of Mineral Subsoil Using Microorganisms: A Mini-Review

This mini-review is devoted to the analysis of the current state of the relatively rarely used underground bio-mining of natural minerals. On the basis of this analysis, it is substantiated that bacterial leaching technology has no alternative for environmentally safe and economically break-even mining of ore-bearing rocks and off -balance metal-bearing formations that are difficult to access, or unprofitable for traditional methods. It is emphasized that the efficiency of biotechnology depends on the accuracy of modeling and operational control of the working parameters of the process of biological extraction of metals, for which it is necessary to develop a new combined hydro-technical system with the possibility of the reverse technological influence on the regimes of leaching. Such controlled modes of the process are the intensity of forced aeration, pH level of the bacterial solution, amount of nutrient medium, and duration of leaching. To improve the accuracy of prediction and control of underground microbiological development, the use of a control method based on an adaptive-network-based fuzzy inference system (ANFIS) is recommended.

Synthesis of Cu and CuO nanoparticles from e-waste and evaluation of their antibacterial and photocatalytic properties

Waste printed circuit boards (WPCBs) contain a plethora of valuable metals, considered an attractive secondary resource. In the current research, a hydrometallurgical process combined ammonia/ammonium chloride leaching and reduction (using L-ascorbic acid) to recover copper and its oxide (CuO) as nanosized particles from WPCBs was investigated. The results of leaching indicated that 96.7% of copper could be recovered at a temperature of 35 °C for a leaching duration of 2 h with ammonium chloride and ammonia concentration of 2 mol/L at a solid:liquid ratio of 1:10 g/cm3. The synthesized particles exhibit spherical and distorted sphere morphology with average particle size of 460 nm and 50 nm for Cu and CuO NPs, respectively. The antibacterial activity of Cu, CuO, and a (1:1) blend of both (Cu/CuO) has been examined against five different bacterial and fungal strains. The highest zone of inhibition was measured as 21.2 mm for Cu NPs toward Escherichia coli and 16.7 mm for Cu/CuO blend toward Bacillus cereus bacteria. The highest zone of inhibition was measured as 13 mm and 13.8 mm for Cu/CuO blend toward Fusarium proliferatum and Penicillium verrucosum fungi. Cu/CuO blend showed notable photocatalytic activity towards Rhodamine B dye under visible light irradiation with 96% degradation rate within 120 min. Using the process developed in this study, copper and its oxide as nanoparticles can be produced from WPCBs and used for multifunctional applications.Graphical abstract

Improving the quality of metallurgical-grade silicon by acid leaching

This work deals with the problem of hydrometallurgical refining of metallurgical-grade silicon. Samples of metallurgical-grade silicon after oxidative refining from JSC Silicon, RUSAL (Shelekhov, Irkutsk Oblast, Russia) were subjected to X-ray fluorescence and electron microprobe analysis. The conducted elemental analysis determined their following composition, wt%: Al – 0.53, Fe – 0.6094, Ti – 0.0491, Ca – 0.0628, V – 0.0066, Cr – 0.002, Mn – 0.014, Cu – 0.003, P – 0.010, Ba – 0.007, Ni – 0.007, and Zn – 0.002. The examined samples were found to comprise the following intermetallic compounds: AlFeSi2 (with an admixture of Ca), FeSi2 (with an admixture of Al), and FeSi2Ti (with an admixture of Zr). In order to purify silicon from impurities, 10% H2SO2, HCl, HNO3, as well as 4% HF in different ratios were used as solvents. The feasibility of interactions between the intermetallic compounds and the selected solvents was assessed by calculating changes in the Gibbs energy, which had negative values. Experiments on impurity leaching were carried out using silicon samples with a particle size of –200 µm under constant stirring with a magnetic stirrer under the temperature of 600С, the liquid-to-solid ratio of 5:1, and the leaching duration of 60 min. The highest degree of silicon purification (86.85%) was achieved under leaching with a mixture of sulfuric and hydrofluoric acids in a ratio of 1:1. The use of a mixture of sulfuric and hydrochloric acids at a ratio of 1:3 resulted in the silicon purification of 41.48%. Thus, optimal solvents allowing the maximum purification of silicon from impurities were determined.

Increasing the Duration of Dump Leaching of Copper Under Winter Conditions

Increasing the Duration of Dump Leaching of Copper Under Winter Conditions

Bioleaching of valuable metals from spent LIBs followed by selective recovery of manganese using the precipitation method: Metabolite maximization and process optimization

Despite the increased demand for resource recovery from spent lithium-ion batteries (LIBs), low Mn leaching efficiencies have hindered the development of this technology. A novel process was devised to enhance the dissolution of metals by producing citric acid using a molasses medium by Penicillium citrinum. This investigation used response surface methodology to investigate the influence of molasses concentration and media components on citric acid production, which demonstrated that molasses (18.5% w/w), KH2PO4 (3.8 g/L), MgSO4.7H2O (0.11 g/L), and methanol (1.2% (v/v)) were the optimum values leading to the production of 31.50 g/L citric acid. Afterward, optimum inhibitor concentrations (iodoacetic acid: 0.05 mM) were added to accumulate citric acid, resulting in maximum bio-production (40.12 g/L) of citric acid. The pulp density and leaching time effect on metals dissolution was investigated in enriched-citric acid spent medium. The suitable conditions were a pulp density of 70 g/L and a leaching duration of 6 days, which led to the highest dissolution of Mn (79%) and Li (90%). Based on the results of the TCLP tests, the bioleaching residue is non-hazardous, suitable for safe disposal, and does not pose an environmental threat. Moreover, nearly 98% of Mn was extracted from the bioleaching solution with oxalic acid at 1.2 M. XRD, and FE-SEM analyses were utilized for further bioleaching and precipitation mechanism analysis.

Combined hydrometallurgical route for recovery of metals from spent LIB using hydrochloric acid and phosphonium ionic liquid

ABSTRACT This research explored the significance of Cyphos IL 101 in recovering metal values from waste LiMn2O4 batteries. Several leaching parameters were investigated to recover metals from the leach liquor of the battery material. The maximum leaching efficiency of Li (100%) and Mn (99.6%) was attained with 3.0 mol/L hydrochloric acid, 30°C, S/L ratio of 10 g/L, and 60 min leaching duration. The leaching process was diffusion-controlled. At pH 5.5, the separation of manganese and lithium exhibited excellent selectivity towards manganese over lithium using 0.1 mol/L Cyphos IL 101. 99.6% manganese extraction and negligible lithium extraction were obtained with two stages of counter-current extraction at A/O 1:1 predicted by the McCabe-Thiele plot. Using 0.1 mol/L hydrochloric acid, a stripping efficiency of 99.4% was attained for manganese.

Extraction of scandium from bauxite residue by high-pressure leaching in sulfuric acid solution

Rare earth elements, such as yttrium, scandium, neodymium, and praseodymium, have been reported to be associated with minerals in bauxite and transferred to the refining residue when bauxite is refined to alumina (Al2O3) by Bayer Process. In terms of price, scandium is the most valuable rare-earth element in bauxite residue. This research discusses the effectiveness of scandium extraction from the bauxite residue through pressure leaching in sulfuric acid solution. The method was selected to obtain high scandium recovery and leaching selectivity to iron and aluminium. Series of leaching experiments were conducted under variations of H2SO4 concentration (0.5–1.5 M), leaching duration (1–4 h), leaching temperature (200–240 °C), and slurry density (10–30% (w/w)). Taguchi method with L9:34 orthogonal array was adopted to design the experiments. Analysis of Variance (ANOVA) was performed to determine the most influential variables of the extracted scandium. The experimental result and statistical analysis revealed that the optimum condition for scandium extraction was at 1.5 M H2SO4, a leaching duration of 1 h, a temperature of 200 °C, and a slurry density of 30% (w/w). The leaching experiment carried out at this optimum condition resulted in scandium extraction of 90.97% and co-extracted iron and aluminium of 32.44% and 75.23%, respectively. Analysis of Variance showed that solid/liquid ratio was the most influential variable with a contribution of 62%, followed by acid concentration (21.2%), temperature (16.4%), and leaching duration (0.3%).

The Leaching Kinetics of Iron from Titanium Gypsum in a Citric Acid Medium and Obtain Materials by Leaching Liquid.

In this study, the effect of citric acid on iron leaching from titanium gypsum (TiG) was systematically investigated. The conditions for the leaching of valuable metals were optimized while varying such parameters as the leaching time, citric acid mass fraction, leaching temperature, and the liquid-solid ratio. It was found that under the conditions of a citric acid mass fraction of 10%, at a 80 °C leaching temperature, a leaching duration of 80-90 min and a liquid-solid ratio of 8, the whiteness of titanium gypsum (TiG) increased from 8.1 to 36.5, and the leaching efficiencies of iron reached 84.37%. The kinetic analysis indicated that the leaching process of iron from TiG was controlled by the reaction product layer from 0-20 min, while the leaching process of iron from TiG was controlled by internal diffusion from 20-90 min. The apparent activation energy of the leaching reactions was 33.91 kJ/mol and 16.59 kJ/mol, respectively. High-value-added calcium oxalate and ferrous oxalate were prepared from the calcium and iron in the filtrate of the oxalic acid extraction. The leaching liquid could be recycled, which will provide a new way to utilize titanium gypsum.

Pore solution alkalinity of cement paste as determined by Cold Water Extraction

Cold Water Extraction (CWE) is a technique used to extract the pore solution of cementitious materials and to study its alkalinity. CWE can be used on paste, mortar or concrete, and requires only standard laboratory equipment. The method is not yet standardised, so several parameters must be arbitrarily selected when conducting the test.This work investigated the influence of four parameters on the calculated alkali metal concentrations in the pore solution: the method for determining the amount of pore solution (oven-drying at 40 and 105 °C, desiccator with silica gel and solvent exchange), the size fraction of the powdered material, the leaching duration and the liquid-to-solid ratio. A comparison with values obtained by Pore Water Extraction (PWE) on two cement types emphasises and quantifies the crucial impact of the amount of pore solution on CWE results. The results suggest that some bound alkali metals may be released during CWE. A mechanism is proposed, and recommendations are made to limit any effect of this on CWE results.

Effective leaching of spent lithium-ion batteries using DL-lactic acid as lixiviant and selective separation of metals through precipitation and solvent extraction.

Recycling cathodic materials from spent lithium-ion batteries (LIBs) is crucial not just for the environmental aspects but also for the supply of precious raw materials such as cobalt and lithium. As a result, developing a leaching process with low acid consumption, cost-effectiveness, low environmental impact, and high metal recovery is essential. In this article, the sustainable hydrometallurgical route for recovery of Li and Co from spent LIBs using DL-lactic acid as lixiviant is proposed. The different leaching parameters were studied to optimize the leaching conditions. With increasing lactic acid concentration from 0.1mol/L to 1.0mol/L, the leaching efficiency of Li and Co increased from 23% to 41% and 2% to 14%, respectively. The reductant H2O2 has a major role which reduced Co3+ to Co2+ and increasing the leaching efficiency of Co from 15.2% (1% H2O2) to 73.4% (6% H2O2). The maximum leaching efficiency of Li (99.8%) and Co (99%) was attained with 1.0mol/L lactic acid, 6% H2O2, 60°C, S/L ratio of 10g/L, and 60min leaching duration. The R2 values for the surface chemical reaction model were greater than 0.98, indicating that the lactic acid leaching process was controlled by the surface chemical reaction model. With 1.0mol/L 70% saponified Cyanex 272, a solvent extraction study showed a higher separation factor (βCo/Li) of 35.7 compared to other saponified and nonsaponified organophosphorus extractants. Using the precipitation method, 99.9% of Co and 99% of Li were precipitated as [Formula: see text] and [Formula: see text] with a purity of 99.4% and 98.3%, respectively.

Extraction of Al and rare earth elements via high-pressure leaching of boehmite-kaolinite bauxite using NH4HSO4 and H2SO4

High-silica bauxite is not used to obtain sandy-grade alumina owing to its low alumina/silica ratio (μSi < 3). Acidic methods, such as the use of HCl and NH4HSO4, show promise for treating this raw material. The leaching of boehmite-kaolinite bauxite from the Severoonezhsk deposit mine (Arkhangelsk region, Russia) using a mixture of NH4HSO4 and H2SO4 was investigated for the first time. The bisulfate method, which combines the advantages of the acidic and alkaline methods, involves bauxite leaching, precipitation of ammonium alum, recrystallization for gibbsite precipitation, and calcination for alumina production. The effects of temperature (130–200 °C), liquid-to-solid ratio (8–12), and duration of leaching (5–90 min) on the degrees of extraction of Al, and rare earth elements (REEs) were evaluated. The extractions of Al, Fe, and Ga were found to be >90%, with most of the silica and titania remaining in the residue; moreover, a REEs extraction of 70%–80% was achieved. Residues obtained after leaching were studied by laser diffraction, XRD, XRF, and SEM to elucidate the leaching mechanism and the solubility of Al-containing minerals, such as boehmite (AlOOH), kaolinite (Al4[Si4O10](OH)8), and muscovite (KAl2[AlSi3O10](OH)2). The acquired data can be used to facilitate the development of an effective technology for the treatment of high-silica bauxite in Russia.