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Abstract

In this study, the recovery of gallium (Ga) and aluminum (Al) from the by-product of Bayer process, the electrofilter dust of a calcination plant, was studied. Factorial leaching tests were also designed based on the results of the preliminary tests. Effects of factors and their interactions on the extraction of Ga and Al were demonstrated using Analysis of Variance of the findings. In the factorial design, nitric acid (HNO3) leaching tests up to 43.4% Ga and 35.2% Al were leached from the electrofilter dust. The addition of oxalic acid (H2C2O4) significantly enhanced the sulphuric acid (H2SO4) leaching of the dust with up to 48.3% Ga and 39.6% Al extractions.

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... However, gallium rarely forms a significant concentration (ore deposit), which makes it a typical scattered metal further leading to very limited gallium production from mining (Gray et al., 2005). Gallium is usually associated with the crystal lattice of the host mineral in the form of isomorphism, so the amount of gallium in the host mineral is very small, which results in gallium always being obtained as a by-product from processing of ores for other metals and power generation in power plants (Okudan et al., 2015). In recent years, research into the recovery of gallium from various sources has been carried out, including Bayer liquor (Zhao et al., 2012), bauxite residue (Lu et al., 2018), coal fly ash (Zhao et al., 2020), spent copper indium gallium selenide (Hu et al., 2022), phosphorus flue dust (Ji et al., 2022), and corundum flue dust (CFD) . ...
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In this study, the effect and mechanism of ultrasound on gallium and zinc leaching from corundum flue dust (CFD) were investigated systematically. The conditions for the leaching of valuable metals were optimized while varying the parameters such as leaching time, sulfuric acid concentration and leaching temperature. It was found that under the conditions of a sulfuric acid concentration of 25 wt%, 90 °C leaching temperature and 50 min leaching duration, the leaching efficiencies of gallium and zinc can be increased from 62.78% to 82.56% and 94.43% to 99.57% as ultrasound was implemented, respectively. The kinetics analysis indicated that the leaching process of gallium from CFD is controlled by mixed of diffusion and chemical reactions, while the leaching process of zinc is controlled by diffusion. The enhancement of ultrasound on the leaching rate and leaching efficiency was mainly ascribed to that the ultrasound effect causes the agglomerates of particles to break into small pieces or generate cracks, which would augment the diffusion of sulfuric acid and the product layer on the particle surface. On the other hand, the reaction of sulfuric acid with amorphous silicate (or aluminosilicate) is accelerated, so that the gallium in the form of encapsulated can be dissolved.
... In order to investigate the effect of temperature on the fraction of ore reacted, the extraction kinetics experiments were carried out in the temperature range of 25-75°C by 2.0 mol/L phosphoric acid solution at a moderate stirring rate. From Figure 5, it is observed thatdissolution rate is highly sensitive to reaction temperature [27]. With increasing reaction temperature from 25 to 75°C, the extent of the ore dissolution reached 87.0% within 120 min at optimized conditions. ...
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Increasing demands for aluminium and aluminium oxide with diverse industrial applications have prompted the development of a low-cost and eco-friendly technique as a substitute for conventional ore treatments by reduction-roasting route, requiring high energy consumption. For example, the demand for high-grade industrial alumina (Al 2 O 3 ) as valuable materials in refractories, pigments, adsorbents, catalysis, water purification, aluminium production and metallurgical applications cannot be over emphasized. Thus, the upgrading of a Nigerian biotite-rich kaolinite ore containing admixture of kaolinite (Al 2.00 Si 2.00 O 9.00 : 96-900-9231), biotite (Mg 6.55 Fe 3.46 Al 5.29 Ti 1.34 Si 11.36 K 4.00 O 48.00 : 96-900-0844) and quartz (Si 3.00 O 6.00 : 96-900-9667) impurities by hydrometallurgical route was investigated in phosphoric acid media. During leaching, parameters such as leachant concentration, particle size and reaction temperature on the extent of ore dissolution were accordingly examined. At optimal leaching conditions (2.0 mol/L H 3 PO 4 , 75 °C), 87.0% of the initial 10 g/L ore reacted within 120 min. The activation energy of 16.6 kJ/mol supported the diffusion control reaction mechanism. The unreacted product (∼13.0%) analyzed by XRD was found to contain siliceous impurities including iron silicate and manganese silicate which could serve as valuable by-products for some defined industries. The leach liquor at optimal leaching conditions was accordingly treated to obtain pure aluminium solution which was further beneficiated to obtain high-grade alumina (α-Al 2 O 3 ) of industrial value with 96.3% purity.
... After washing, the residues were leached with 2.4 mol/L hydrochloric acid solution (200 mL) at 313 K for 0.5 h. The alkali leaching temperature was within a range of 393 K-513 K, which is the suitable temperature range for aluminum production by the Bayer process [17][18][19][20]. ...
Article
Sericite is a typical silicate impurity in microcrystalline graphite ores, and its removal is important in the preparation of high-purity graphite preparations. Alkali-acid leaching is an effective method used to purify graphite and remove silicate minerals. In this study, the dissolution behavior and mechanism of sericite in alkali-acid leaching were investigated. The dissolution of sericite was mainly affected by alkali leaching temperature, sodium hydroxide concentration, and alkali leaching time. According to the XRD, FTIR, and SEM-EDS analyses, the dissolution mechanism of sericite is a three-stage process: (1) sericite is dissolved in the form of soluble silicate and aluminate; (2) the dissolved silicate and aluminate then react with each other to form aluminosilicate; and (3) finally the aluminosilicate mainly composed of hydroxycancrinite and sodalite is almost completely dissolved in the hydrochloric acid solution.
... Thulium is used to make high power magnets for laptops, lasers, while samarium is utilized for making high-temperature magnets. Lutetium finds its application in X-ray phosphor, dysprosium in high- power magnets, lasers and terbium in phosphors for light and displays ( Abhilash et al., 2015;Gladyshev et al., 2013Gladyshev et al., , 2015Massari and Marcello, 2013;Okudan et al., 2015a,b). ...
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The paper provides an overview of the methods used for processing of red mud to extract rare earth elements (REEs). Red mud is a toxic and highly alkaline waste. Several methods have been adopted and being practiced all over the world for the processing of red mud. Complex processing of red mud is cost-effective since red mud contains iron, aluminum, titanium, calcium, rare earth metals etc. It has been observed that the acid leaching of red mud can almost completely recover the rare earth elements in the solution with various individual techniques and also a combination of them. Therefore, the choice of extraction method depends on the form in which the element occurs in the solution. However, relatively low concentrations of rare earth in the solution and significant amount of impurities increase the cost of getting the final commercial products. To ensure the cost-effectiveness of the process involving rare earth’s extraction from red mud, it is necessary to increase their content by several times. This article presents the various studies that have been carried out in these aspects and the possibility of making this resource a sustainable one for REE extraction with a special focus on scandium replenishment.
... After washing, residue was leached by 2.4 mol/L hydrochloric acid solution (200 mL) at temperature of 313 K for 0.5 h. The alkali-leaching temperature was within 363-513 K, which was also the common temperature range for aluminum production by Bayer process (Gladyshev et al., 2015;Hairi et al., 2015;Liu et al., 2015;Okudan et al., 2015). ...
Article
Kaolinite is a typical silicate impurity in microcrystalline graphite ore. Removal of kaolinite from graphite ores is important to achieve high purity graphite product. Alkali-acid leaching is effective to remove silicate impurity in microcrystalline graphite. For in-depth understanding of phase transformation of kaolinite in microcrystalline graphite purification process, dissolution behavior and mechanism in alkali-acid leaching process were studied in this paper. As shown in alkali-acid leaching tests and analyses (FTIR, XRD, and SEM-EDS), silicon extraction of kaolinite was mainly affected by sodium hydroxide concentration, alkali-leaching temperature, and alkali-leaching time. The dissolution mechanism of kaolinite was regarded as a three-stage process: kaolinite firstly dissolved in alkaline solution in form of soluble silicate and aluminate. Dissolved silicate and aluminate in alkaline solution then reacted with each other and aluminosilicate transient phase with Si/Al ≈ 1 precipitated when silicon ion concentration exceeded its equilibrium concentration. Finally, the aluminosilicate precipitate composed of nepheline and sodalite dissolved in hydrochloric acid solution. As a consequence, kaolinite dissolved completely in alkali-acid leaching process.
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In this study, scandium and lithium extractions were investigated using the atmospheric pressure agitation leaching method at acidic medium. The leaching tests were carried out at two stages. To remove the ionic impurities such as Na and Al first stage leaching was performed at relatively higher pH. Following solid-liquid separation of leach cake of the first stage leaching, it was subjected to the second stage leaching. The second stage leaching resulted in 95.1% Sc and 94.7% Li extractions. The overall Sc and Li recoveries were determined as 82.4% and 86.5%, respectively. Regarding the kinetic studies, it was understood that scandium and lithium leaching processes were controlled by a combination of chemical reaction and ash diffusion models. In this case, the activation energies were determined as 29.52 and 30.22 kJmol-1, respectively for scandium and lithium. As a result, while direct H2SO4 leaching of red mud is a challenge due to physical and chemical problems, an alternative solution was suggested using H2SO4
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IBC Advanced Technologies' Molecular Recognition Technology (MRT) SuperLig(r) products selectively and rapidly bind with target species enabling their selective removal from solutions. The MRT process can produce a high purity separation product of maximum added value at a competitive cost. SuperLig(r) products have high selectivity for many target species which can include metal ions, anions, and neutral molecules. In operation, the SuperLig(r) product is first placed in a packed column. A solution containing a mixture of the target species and other chemical species is then passed through the column. The target species is removed selectively by the SuperLig(r) product, the column is washed to remove residual feed solution, and the target species is recovered by a minimal quantity of eluent. The result is a pure and concentrated species that can be kept for its value or disposed of safely. The process is environmentally and ecologically friendly with no organic solvents being used. This paper provides a review of some examples of applications of MRT to separations of interest to the Chinese metallurgical industry. Included are several applications of MRT, including Pd separations from Pt metal refinery streams and low-grade spent catalyst wastes, Rh recovery from spent auto catalyst and other feeds, Re removal from selected impurity ions, Cd removal from Co electrolyte, Bi removal from Cu electrolyte, In and Ge separations from difficult matrices, and removal of bivalent first transition series and other metal ions from acid mine drainage (Berkeley Pit, Montana). Finally, the potential application of MRT to separations involving the recovery of rare earth metals and Li from low-level waste solutions and end-of-life products is discussed.
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Gallium is a silvery blue and soft metallic element that enjoys vast application in optoelectronics (e.g., LED’s), telecommunication, aerospace, and many commercial and household items such as alloys, computers and DVD’s. Albeit that gallium represents a small annual tonnage of material, its important impact as the backbone of the worldwide electronics sector goes unnoticed by the popularity of key base metals such as Cu/Ni/Co and attraction of the platinum group metals. Although gallite is a host mineral, gallium occurrence is associated with aluminosilicates such as bauxite and clays, plus zinc-bearing ores (e.g., sphalerite). Gallium is extracted primarily from the residue obtained during the processing of aluminum and secondly via electrolytic zinc. Other sources include fly ash collected from burning coal. Whilst countries such as Australia, China, Germany, Kazakhstan, Japan and Russia are the main suppliers of primary (i.e., virgin) gallium, France is the largest single source of refined gallium in the world. GEO Chemicals in France accounted for the lion’s share of the world’s annual production of refined gallium in recent years. At present, 60 companies located in 18 countries are actively engaged in the supply of gallium products. The majority of gallium is employed to produce gallium arsenide (GaAS) wafers for the electronics industry. The supply and demand of gallium-bearing products has gradually declined during the past decade. This was mainly attributed to bursting of the technology bubble worldwide while also being subject to swings in market price in relation to purity. The mandate of the paper was to simply pinpoint the salient facts regarding gallium globally and identify applicable sources of information thereby creating an ideal reference document.
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Sulphuric acid leaching of electrofilter fines Bayer Plant was investigated at different temperatures, using various particle size fractions and acid concentrations. Results showed that extraction was affected by acid concentration, initial particle size fraction and temperature of leaching. Aluminium dissolution in sulphuric acid increases as temperature does. At 90 °C, the increase in both acid concentration and reaction time has a positive effect on the extraction rate, which is also favoured by the decrease in particle size and solid:liquid ratio.The results of a leaching kinetic study are presented. Heterogeneity of the residue implies the existence of two different kinetics, the first one fundamentally due to the dissolution of the hydrate and the second one, being the case in study, due to the dissolution of transition alumina. The data obtained for the leaching kinetics in this second case, indicated that the dissolution of aluminium is a diffusion controlled reaction.
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The extraction of Ga(III) from HCl, HNO3 and H2SO4 media using 0.50 mol/L Cyanex 923 in toluene is investigated. Ga(III) is quantitatively extracted over a wide range of HCl at high concentration while the extraction is poor over the entire concentration range of HNO3 and H2SO4. The extracted Ga(III) is recovered by stripping with 0.10 mol/L HCl. The extracted species is identified as GaCl3.3Cyanex 923. The extraction behaviour of some commonly associated metal ions is also investigated. Based on the partition data, conditions have been identified for attaining some binary and ternary separations involving Ga(III) and V(IV), Al(III), Fe(III), In(III), Ti(IV), Ni(II), Mn(II), Cu(II), Zn(II), and Hg(II). The conditions are extended for the recovery of pure gallium from light emitting diode (LED) waste and bottom ash. The extractant is stable towards prolonged acid contact and there is a negligible loss in its extraction efficiency even after recycling ten times.
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A procedure is proposed to recover gallium from flue dust aluminum residues produced in plants by using solid-phase extraction with a commercial polyether-type polyurethane foam (PUF). Gallium can be separated from high concentrations of aluminum, iron, nickel, titanium, vanadium, copper, zinc, sulfate, fluoride, and chloride by extraction with PUF from 3 M sulfuric acid and 3 M sodium chloride concentration medium with at least a 92% efficiency. Gallium backextraction was fast and quantitative with ethanol solution. In all recovery steps commercial-grade reagents could be used, including tap water. The recovered gallium was precipitated with sodium hydroxide solution, purified by dissolution and precipitation, calcinated, and the final oxide was 98.6% pure.
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Concentrations of trace metals in hydrothermal solutions from the southern Juan de Fuca Ridge (SJFR) and the TAG Hydrothermal Field on the Mid-Atlantic Ridge are influenced by the combined effects of source rock composition, brine–seawater mixing and complex interplay among various metals and minerals deposited and remineralized in vent mounds and chimneys. Copper, Mo, and Co show predicted, sharp decreases in concentration for vent fluids as temperatures decrease below 350°C; however, concentrations of Cu in 363°C fluids at the TAG site are well above values determined from seawater/basalt interactions due to subseafloor-refining processes and remineralization of chalcopyrite. Concentrations of Zn, Cd, Pb, As, and Ga do not show any temperature dependence between 214 to 363°C. However, Zn values do correlate well with Cl on an area-by-area basis due to subseafloor mixing of brine with altered seawater. Zinc levels also correlate well with concentrations of Cd, Pb, and As for all vent fluid samples, as well as with basalt and Zn-rich sulfides, implying some continuity in behavior from source rock to vent fluid to sulfide minerals. Gallium values correlate with Zn and Cl levels for the SJFR, but are high relative to Zn at the TAG site due to subseafloor refining processes. Concentrations of Tl follow Cl, K, and Rb, consistent with the behavior predicted for Tl+. Overall, the Cl- and Zn-rich fluids from the SJFR are characteristic of a brine-dominated system formed during recent volcanism. In contrast, high-temperature fluids from the TAG area are representative of a system that has evolved over the past 100,000 yr with high concentrations of Cu, Co, and Ga that result from higher temperatures and complex refining processes within a large vent mound.
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Gallium has become increasingly popular as a substrate material for electronic devices. Aside from ore, gallium can be obtained from such industrial sources as the Bayer process caustic liquor that is a byproduct of bauxite processing, flue dust removed from the fume-collection system in plants that produce aluminum by the electrolytic process, zinc refinery residues, gallium scrap materials, and coal fly ash. The purification process for gallium can start with solvent-extraction processes where the concentrations of impurities, especially metals, are reduced to the ppm range. This article describes how ultra-purification techniques can be employed to reduce the undesirable impurities to the low ppb range. The various procedures described give an idea as to the extent of work needed to obtain and prepare high-purity gallium for electronic application.
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This paper is an overview of the application of hydrometallurgy in the processing of minerals in Kazakhstan. Hydrometallurgical processes are generally used for the recovery of rare metals.
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Electrofilter powders, a by-product of the Bayer process for the production of alumina from bauxite, were leached with sulphuric acid to dissolve gibbsite and transition aluminas, thus obtaining a commercial aluminium sulphate solution and a solid residue. This residue is treated again under more drastic conditions with sulphuric acidic in a furnace at a higher temperature, is then leached with water and filtered, a small amount of solid remaining (alpha-alumina). The liquid is a highly acidic aluminium sulphate solution which does not fulfil commercial grade specifications; the liquor is accordingly treated with potassium hydroxide or ammonium hydroxide to obtain potassium or ammonium alum. Experimental tests were conducted to investigate the synthesis of alum by crystallization. The effects on alum formation of various operating conditions, including the amount of potassium or ammonium hydroxide, temperature and seed alum dosage, were examined. The crystallization process was found to be quite effective in obtaining alum.
Article
The Puertollano Integrated Coal Gasification Combined Cycle (IGCC) Power Plant (Spain) fly ash is characterized by a relatively high content of Ga and V, which occurs mainly as Ga2O3 and as Ga3+ and V3+ substituting for Al3+ in the Al-Si fly ash glass matrix. Investigations focused on evaluating the potential recovery of Ga and V from these fly ashes. Several NaOH based extraction tests were performed on the IGCC fly ash, at different temperatures, NaOH/fly ash (NaOH/FA) ratios, NaOH concentrations and extraction times. The optimal Ga extraction conditions was determined as 25 degrees C, NaOH 0.7-1 M, NaOH/FA ratio of 5 L/kg and 6 h, attaining Ga extraction yields of 60-86%, equivalent to 197-275 mg of Ga/kg of fly ash. Re-circulation of leachates increased initial Ga concentrations (25-38 mg/L) to 188-215 mg/L, while reducing both content of impurities and NaOH consumption. Carbonation of concentrated Ga leachate demonstrated that 99% of the bulk Ga content in the leachate precipitates at pH 7.4. At pH 10.5 significant proportions of impurities, mainly Al (91%), co-precipitate while >98% of the bulk Ga remains in solution. A second carbonation of the remaining solution (at pH 7.5) recovers the 98.8% of the bulk Ga. Re-dissolution (at pH 0) of the precipitate increases Ga purity from 7 to 30%, this being a suitable Ga end product for further purification by electrolysis. This method produces higher recovery efficiency than currently applied for Ga on an industrial scale. In contrast, low V extraction yields (<64%) were obtained even when using extreme alkaline extraction conditions, which given the current marked price of this element, limits considerably the feasibility of V recovery from IGCC fly ash.
Article
Supercritical carbon dioxide extraction, which is a feasible "green" alternative, was applied in this study as a sample pretreatment step for the removal of gallium (III) ions from acidic aqueous solution. The effect of various process parameters, including various chelating agents, extraction pressure and temperature, dimensionless CO(2) volume, the concentration of the chelating agent, and the pH of the solution, governing the efficiency and throughput of the procedure were systematically investigated. The performance of the various chelating agents from different studies indicated that the extraction efficiency of supercritical CO(2) was in the order: thiopyridine (PySH)>thenoyltrifluoroacetone (TTAH)>acetylacetone (AcAcH). The optimal extraction pressure and temperature for the supercritical CO(2) extraction of gallium (III) with chelating agent PySH were found to be 70 degrees C and 3000psi, respectively. The optimum concentration of the chelating agent was found to be 50ppm. A value of 7.5 was selected as the optimum dimensionless CO(2) volume. The optimum pH of the solution for supercritical CO(2) extraction should fall in the range of 2.0-3.0.
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