Search Results (22)

High-alumina fly ash may potentially be a valuable source of Ga with a concentration of Ga at 80 mg/kg. Direct adsorption and enrichment of Ga from sulfuric acid leach liquor of high-alumina fly ash is developed in this study. The H-type chelating resin with two carboxy groups exhibited the best adsorption capacity for Ga. The maximum adsorption capacity for Ga was 55 mg/g resin with an adsorption time of 24 h, an initial Ga concentration of 500 mg/L, an adsorption temperature of 55 °C, and an initial acid concentration of 0.1 mol/L. The adsorption process of Ga was in good fit with the Langmuir isotherm and pseudo-second-order reaction kinetics model. The chemical adsorption rate was controlled by an internal diffusion mechanism. The resin had a high selectivity for Ga³⁺ with a K_d over 3600 compared with Fe²⁺, Al³⁺, K⁺, Ca²⁺, and Mg²⁺. The adsorption mechanism was found to be the ion exchange reaction between Ga and H of carboxy and hydroxyl groups. The concentration of Ga in sulfuric acid leach liquor from high-alumina fly ash achieved enrichment from 200 mg/L to 2 g/L. It is an attractive medium for large-scale Ga extraction from high-alumina fly ash. Full article

Xinjiang is one of China’s most significant energy bases, and the generated fly ash (FA) contains a high concentration of metallic elements that can be used as a valuable resource. In this study, we looked into a roasting-acid leaching process technique for efficiently extracting gallium metal (Ga) from FA, employing sodium fluoride (NaF) as the roasting auxiliary and citric acid inzter (C₆H₈O₇) acid leaching. After high-temperature activation by NaF, the glassy phase of FA was converted into silica aluminate with excellent acid solubility, and Ga was extracted from FA via acid leaching. The effects of optimal roasting and acid leaching process conditions on the Ga leaching rate were investigated. The results showed that it exhibited 83.71% Ga extraction under the conditions of a roasting temperature of 850 °C, FA-NaF coordination ratio of 1:0.5, roasting time of 10 min, C₆H₈O₇ solution concentration of 1.75 mol/L, ratio (S/L) of 1:15, acid leaching temperature of 100 °C, and acid leaching time of 1 h. The results also indicated that it was possible to obtain a higher extraction efficiency for the Ga extracts under the conditions of roasting temperature of 850 °C and FA-NaF coordination ratio of 1:0.5. Full article

Investigation of the critical metal elements in coal and coal-bearing strata has become one of the hottest research topics in coal geology and coal industry. Coal-hosted Ga-Al-Li-REE deposits have been discovered in the Jungar and Daqingshan Coalfields of Inner Mongolia, China. Gallium, Al, and Li in the Jungar coals have been successfully extracted and utilized. This paper reviews the discovery history of coal-hosted Ga-Al-Li-REE deposits, including contents, modes of occurrence, and enrichment origin of critical metals in each coal mine, including Heidaigou, Harewusu, and Guanbanwusu Mines in the Jungar Coalfield and the Adaohai Coal Mine in the Daqingshan Coalfield, as well as the recently reported Lao Sangou Mine. Gallium and Al in the coals investigated mainly occur in kaolinite, boehmite, diaspore, and gorceixite; REEs are mainly hosted by gorceixite and kaolinite; and Li is mainly hosted by cholorite. Gallium, Al, and REEs are mainly derived from the sediment-source region, i.e., weathered bauxite in the Benxi Formation. In addition, REE enrichment is also attributed to the intra-seam parting leaching by groundwater. Lithium enrichment in the coals is of hydrothermal fluid input. The content of Al₂O₃ and Ga in coal combustions (e.g., fly ash) is higher than 50% and ~100 µg/g, respectively; concentrations of Li in these coals also reach the cut-off grade for industrial recovery (for example, Li concentration in the Haerwusu coals is ~116 µg/g). Investigations of the content, distribution, and mineralization of critical elements in coal not only provide important references for the potential discovery of similar deposits but also offer significant coal geochemical and coal mineralogical evidence for revealing the geological genesis of coal seams, coal seam correlation, the formation and post-depositional modification of coal basins, regional geological evolution, and geological events. Meanwhile, such investigation also has an important practical significance for the economic circular development of the coal industry, environmental protection during coal utilization, and the security of critical metal resources. Full article

Gallium, a critical and strategic material for advanced technologies, is anomalously enriched in certain coal deposits and coal by-products. Recovering gallium from solid residues generated during coal production and utilization can yield economic benefits and positive environmental gains through more efficient waste processing. This systematic literature review focuses on gallium concentrations in coal and its combustion or gasification by-products, modes of occurrence, gallium-hosting phases, and hydrometallurgical recovery methods, including pretreatment procedures that facilitate metal release from inert aluminosilicate minerals. Coal gangue, and especially fly ashes from coal combustion and gasification, are particularly promising due to their higher gallium content and recovery rates, which can exceed 90% under optimal conditions. However, the low concentrations of gallium and the high levels of impurities in the leachates require innovative and selective separation techniques, primarily involving ion exchange and adsorption. The scientific literature review revealed that coal, bottom ash, and coarse slag have not yet been evaluated for gallium recovery, even though the wastes can contain higher gallium levels than the original material. Full article

Being not as popular as other elements, such as cobalt, lithium, and rare earth elements, both gallium and germanium have wide use in target developments/industries, thus making them valuable and strategically critical metals. The principal sources for the recovery of both metals are secondary wastes of the bauxite (gallium) or zinc (germanium) industries; also, their recycling from waste materials is necessary. The characteristics of these materials make hydrometallurgical operations widely useful in recovering both gallium and germanium from the various sources containing them. The present work reviews the most recent applications (in 2024) of the various operations applied to the recovery of gallium or germanium from various resources. Full article

This study presents an innovative approach to utilize coal gasification coarse slag (CGCS) for efficient and low-cost gallium extraction. Using a one-step acid leaching process, mesoporous silica with a surface area of 258 m²/g and a pore volume of 0.15 cm³/g was synthesized. The properties of CGCS before and after acid leaching were characterized through SEM, FTIR, XRD, and BET analyses, with optimal conditions identified for maximizing specific surface area and generating saturated silanol groups. The prepared mesoporous silica demonstrated a 99% Ga(III) adsorption efficiency. Adsorption conditions were optimized, and adsorption kinetics, isotherms, and competitive adsorption behaviors were evaluated. Competitive adsorption with vanadium suggests potential application in Ga(III) extraction from vanadium-rich waste solutions. Furthermore, the recyclability of both the acid and adsorbent was explored, with the adsorbent maintaining over 85% adsorption efficiency after five cycles. The adsorption mechanism was further elucidated through SEM-EDS, XPS, and FTIR analyses. This work not only advances resource recovery from industrial waste but also offers a sustainable method for gallium extraction with industrial applications. Full article

This article presents the results of studies on the distribution of rare metals among the products of the alkali sulfate processing of nepheline syenites. In response to the limited reserves of Bayer bauxite in the alumina industrial production region of Kazakhstan, the feasibility of using alternative alumina-containing nonbauxite raw materials was investigated. The most promising nonbauxite raw materials in Kazakhstan are nepheline and kaolinite clays. At present, there is no effective technology for processing nepheline ores. This article describes a proposed complex technology involving nepheline processing with the associated extraction of gallium and vanadium. The technology includes the activation of raw materials, followed by two-stage leaching, where potassium is extracted in the first stage. The sludge and solution obtained from the second stage of the leaching process are utilized for calcium silicate production and two-stage carbonization, respectively. In the first stage, aluminum hydroxide is extracted, and, in the second stage, a concentration of rare metals, such as gallium and vanadium, is obtained. Vanadium is extracted from the solution via crystallization, and gallium is extracted via electrodeposition. Overall, 38.48% of the Ga₂O₃ and 56.12% of the V₂O₅ are recovered from raw nepheline syenite. A technological scheme of the developed technology is presented in this article. Full article

Gallium (Ga), indium (In), and germanium (Ge) play an important role in the modern high-tech material field. Due to their low content and scattered distribution in the crust, and the increasing demand for these metals in recent years, their supply risks have sharply increased. Therefore, the recycling of these metals is of great significance. In this work, a systematic review was performed using the Web of Science, Scopus, MDPI, Elsevier, and Springer Link databases. The combined terms used for the search were Ga/In/Ge, extraction, separation, and recycling. After a careful evaluation of the titles, abstracts, and full texts, a total of 106 articles were included. This paper briefly describes the resource features of Ga, In, and Ge. After that, the chemical principles, technical parameters, and metal recovery in various extraction and separation methods from monometallic and polymetallic resources are systematically reviewed. Leaching followed by solvent extraction or ion exchange is the main process for Ga, In, and Ge recovery. Although many attempts have been made to separate multiple metals from leaching solutions, highly selective solvents and resins are still the research priority. This review can provide theoretical and technical guidance for the separation of Ga, In, and Ge from various resources. Full article

Gallium and indium are crucial metals in various industries, such as the medical and telecommunication industries. They can find applications as pure metals, alloys and alloy admixtures, oxides, organometallic compounds, and compounds with elements such as nitrogen or arsenic. Recovery of these two metals from waste is an important issue for two main reasons. First, gallium and indium are scattered in the Earth’s crust and their minerals are too rare to serve as a primary source. Second, e-waste contributes to the rapidly growing problem of Earth littering, as its amount increased significantly in recent years. Therefore, it is essential to develop and implement procedures that will enable the recovery of valuable elements from waste and limit the emission of harmful substances into the environment. This paper discusses technological operations and methods that are currently used or may be used to produce pure gallium and indium or their oxides from waste. The first step was described—waste pretreatment, including disassembly and sorting in several stages. Then, mechanical treatment as well as physical, chemical, and physicochemical separations were discussed. The greatest emphasis was placed on the hydrometallurgical methods of gallium and indium recovery, to be more precise on the extraction and various sorption methods following the leaching stage. Methods of obtaining pure metals or metal oxides and their refining processes were also mentioned. Full article

The production of photovoltaic modules is increasing to reduce greenhouse gas emissions. However, this results in a significant amount of waste at the end of their lifespan. Therefore, recycling these solar panels is important for environmental and economic reasons. However, collecting and separating crystalline silicon, cadmium telluride, and copper–indium–gallium–selenide panels can be challenging, especially in underdeveloped countries. The innovation in this work is the development of a process to recycle all solar panel waste. The dissolution of all metals through the leaching process is studied as the main step of the flowchart. In the first step of leaching, 98% of silver can be recovered by 0.5 M nitric acid. Then, the second and third step involves the use of glycine for base metal dissolution, followed by the leaching of valuable metals with hydrochloric acid. The effect of parameters such as the initial pH, acid concentration, solid/liquid ratio, and hydrogen peroxide concentration is studied. The results show that up to 100% of Cu, Pb, Sn, Zn, Cd, In, Ga, and Se can be recovered under optimal conditions. The optimal conditions for the dissolution of Cu, Zn, and Cd were a glycine concentration of 0.5 M, a temperature of 25 °C, a solid/liquid ratio of 10 gr/L, and 1% of hydrogen peroxide. The optimized glycine concentration for the leaching of lead and tin was 1.5 M. Indium and gallium were recovered at 100% by the use of 5 M hydrochloric acid, S/L ratio = 10 gr/L, and T = 45 °C. Separation of selenium and tellurium occurred using 0.5 M HCl at a temperature of 60 °C. Additionally, for the first time, a general outlook for the recycling of various end-of-life solar panels is suggested. Full article

Brown corundum dust, which is created during the manufacturing of brown corundum using bauxite as the raw material, is a vital carrier of gallium. To ascertain the presence of the contained gallium, the brown corundum dust was measured and characterized (XRF, XRD, ICP-OES, EPMA, SEM-EDS, etc.). Gallium was extracted from the brown corundum dust using a one-step alkali leaching process, and thermodynamic calculations were utilized to assess the viability of the leaching reactions. The effects of leaching parameters (NaOH solution concentration, leaching time, leaching temperature, solid–liquid ratio and stirring speed) on the recovery of gallium during the leaching process were investigated. A gallium recovery of 96.83% was discovered to be possible with the following parameters: 200 g/L of NaOH, 363 K for the leaching temperature, 60 min for the leaching time, 1:10 g/mL for the solid–liquid ratio, and 850 rpm for the stirring rate. Gallium extraction was negatively impacted by raising the leaching temperature above 363 K and the concentration of NaOH solution above 200 g/L due to the accelerated side reactions between Na⁺, K⁺, SiO₄⁴⁻ and AlO₂⁻, which led to the precipitation of aluminosilicates that absorbed gallium from the solution. The influences of leaching parameters such as the temperature, NaOH solution concentration, and solid–liquid ratio on the leaching kinetics were examined. It was demonstrated that the leaching process followed the unreacted shrinking core model, that the interfacial diffusion associated with the contacting surface area served as the controlling step, and that the apparent activation energy was 42.83 kJ/mol. It turned out that the final kinetic equation was 1/(1 − α)^1/3 − 1 = 4.34 × 10⁴ × (C_NaOH)^2.12 (L/S)^0.43exp[−42835/(RT)] t. Full article

Brown corundum dust is a solid waste produced during the preparation of brown corundum with bauxite as the raw material. The dust has a relatively high gallium content; therefore, it is of great value to recover the gallium from this kind of dust. In this paper, a range of analysis and characterization methods, including XRD, XRF, SEM-EDS, and EPMA, were used to determine the occurrence of gallium. It was found that gallium was mainly present in the potassium-rich phase, wrapped by amorphous silicate and the corundum phase. Roasting activation followed by an acid leaching process was proposed to extract gallium from brown corundum dust. An investigation was carried out on the effects of roasting temperature, roasting time, and additive dosage on the recovery of gallium and the evolution of the phase composition of the dust. The results show that the roasting activation of sodium carbonate was better than that of calcium oxide. After roasting at 1073 K for 40 min with a sodium carbonate dosage of 0.5 (mass ratio of sodium carbonate to dust), the phase composition changed completely to mainly consist of sodium silicate, sodium aluminosilicate, and potassium aluminosilicate. In that case, around 93% of Ga could be recovered from the roasted dust through H₂SO₄ (4.6 mol/L) leaching for 90 min. The leaching process was described well by the kinetic equation of k₃t = 1/(1 − α)^1/3 − 1, with an apparent activation energy of 16.81 kJ/mol, suggesting that the leaching rate was limited by the transfer of leaching agent across the contacting interface of the dust particles. Full article

This study presents experimental results for the development of a process for the recovery of indium and gallium from EoL CIGS (CuGa_1−xIn_xSe₂) panels. The process consists of a thermal treatment of the panels, followed by a hydrometallurgical treatment, where quantitative leaching of In, Ga, Mo, Cu and Zn is achieved. The elements are subsequently separated and recovered from the leachate by solvent extraction. For the development of the process, samples of EoL CIGS PV panels were used, which contained a thin film of Mo (metal base electrode), sputtered on the supporting soda-lime glass and covered by the thin film containing In, Ga, Cu and Se (1 μm). These films were detected by SEM-EDS in polished sections. The thermal treatment at 550 °C for 15 min, in excess of air, led to the successful disintegration of ethyl vinyl acetate (EVA) and delamination of the thin film-coated glass from the front protective glass. The glass fragments coated by the thin film contained the following: Se: 0.03–0.05%; In: 0.02%; Cu: 0.05%; Ga: 0.004–0.006%; and Mo: 0.04%. Following thermal treatment, thin film-coated glass fragments of about 1.5 cm × 1.5 cm were used in acid leaching experiments using HNO₃, HCl and H₂SO₄. Quantitative leaching of Cu, Ga, In, Mo, Zn and Cu was achieved by HNO₃ at ambient temperature. The effects of pulp density and acid concentration on the efficiency of metal leaching were investigated. Part of Se volatilized during the thermal treatment, whereas the rest was insoluble and separated from the solution by filtration. Finally, the separation of the elements was achieved via solvent extraction by D2EHPA. Full article

Unit operations (UO) are mostly used in non-ferrous extractive metallurgy (NFEM) and usually separated into three categories: (1) hydrometallurgy (leaching under atmospheric and high pressure conditions, mixing of solution with gas and mechanical parts, neutralization of solution, precipitation and cementation of metals from solution aiming purification, and compound productions during crystallization), (2) pyrometallurgy (roasting, smelting, refining), and (3) electrometallurgy (aqueous electrolysis and molten salt electrolysis). The high demand for critical metals, such as rare earth elements (REE), indium, scandium, and gallium raises the need for an advance in understanding of the UO in NFEM. The aimed metal is first transferred from ores and concentrates to a solution using a selective dissolution (leaching or dry digestion) under an atmospheric pressure below 1 bar at 100 °C in an agitating glass reactor and under a high pressure (40–50 bar) at high temperatures (below 270 °C) in an autoclave and tubular reactor. The purification of the obtained solution was performed using neutralization agents such as sodium hydroxide and calcium carbonate or more selective precipitation agents such as sodium carbonate and oxalic acid. The separation of metals is possible using liquid (water solution)/liquid (organic phase) extraction (solvent extraction (SX) in mixer-settler) and solid-liquid filtration in chamber filter-press under pressure until 5 bar. Crystallization is the process by which a metallic compound is converted from a liquid into a crystalline state via a supersaturated solution. The final step is metal production using different methods (aqueous electrolysis for basic metals such as copper, zinc, silver, and molten salt electrolysis for REE and aluminum). Advanced processes, such as ultrasonic spray pyrolysis, microwave assisted leaching, and can be combined with reduction processes in order to produce metallic powders. Some preparation for the leaching process is performed via a roasting process in a rotary furnace, where the sulfidic ore was first oxidized in an oxidic form which is a suitable for the metal transfer to water solution. UO in extractive metallurgy of REE can be successfully used not only for the metal wining from primary materials, but also for its recovery from secondary materials. Full article

This study identifies unstable and soluble layers in commercial photovoltaic modules during 1.5 year long-term leaching. Our experiments cover modules from all major photovoltaic technologies containing solar cells from crystalline silicon (c-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). These technologies cover more than 99.9% of the world market. We cut out module pieces of 5 × 5 cm${}^2$ in size from these modules and leached them in water-based solutions with pH 4, pH 7, and pH 11, in order to simulate different environmental conditions. Unstable layers open penetration paths for water-based solutions; finally, the leaching results in delamination. In CdTe containing module pieces, the CdTe itself and the back contact are unstable and highly soluble. In CIGS containing module pieces, all of the module layers are more or less soluble. In the case of c-Si module pieces, the cells’ aluminum back contact is unstable. Module pieces from a-Si technology also show a soluble back contact. Long-term leaching leads to delamination in all kinds of module pieces; delamination depends strongly on the pH value of the solutions. For low pH-values, the time dependent leaching is well described by an exponential saturation behavior and a leaching time constant. The time constant depends on the pH, as well as on accelerating conditions such as increased temperature and/or agitation. Our long-term experiments clearly demonstrate that it is possible to leach out all, or at least a large amount, of the (toxic) elements from the photovoltaic modules. It is therefore not sufficient to carry out experiments just over 24 h and to conclude on the stability and environmental impact of photovoltaic modules. Full article