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Recovery of Gallium and Aluminum from Electrofilter Dust of Alumina Calcination Plant in Bayer Process
Separation Science and Technology
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.
... The most significant environmental concern, apart from the massive amounts of red mud produced, is alkalinity. According to data reported in the literature, the main constituents are 70% red mud and 30% NaOH bauxite residue (pH = [11][12][13] [5]. ...
... Rare earth elements (REE) (scandium, yttrium, cerium, thulium, lanthanum, praseodymium, lutetium, dysprosium, etc.) have a wide range of applications and are used in new electronic devices, such as mobile phones, displays, high-capacity batteries, permanent magnets for wind energy, ceramics, etc. Scandium is used in the production of lenses and prisms used for movie or photographic equipment. In addition, scandium is also used in the field of astronomy [5,[10][11][12]. ...
Industry represents a fundamental component of modern society, with the generation of massive amounts of industrial waste being the inevitable result of development activities in recent years. Red mud is an industrial waste generated during alumina production using the Bayer process of refining bauxite ore. It is a highly alkaline waste due to the incomplete removal of NaOH. There are several opinions in both the literature and legislation on the hazards of red mud. According to European and national legislation, this mud is not on the list of hazardous wastes; however, if the list of criteria are taken into account, it can be considered as hazardous. The complex processing of red mud is cost-effective because it contains elements such as iron, manganese, sodium, calcium, magnesium, zinc, strontium, lead, copper, cadmium, bismuth, barium and rare earths, especially scandium. Therefore, the selection of an extraction method depends on the form in which the element is present in solution. Extraction is one of the prospective separation and concentration methods. In this study, we evaluated the kinetic modelling of the solid–liquid acid extraction process of predominantly scandium as well as other elements present in red mud. Therefore, three acids (HCl, HNO3 and H2SO4) at different concentrations (10, 20 and 30%) were targeted for the extraction of Sc(III) from solid red mud. Specific parameters of the kinetics of the extraction process were studied, namely the solid:liquid ratio, initial acid concentration, contact time and temperature. The extraction kinetics of Sc(III) with acids was evaluated using first- and second-order kinetic models, involving kinetic parameters, rate constants, saturation concentration and activation energy. The second-order kinetic model was able to describe the mechanism of Sc(III) extraction from red mud. In addition, this study provides an overview on the mechanism of mass transfer involved in the acid extraction process of Sc(III), thereby enabling the design, optimization and control of large-scale processes for red mud recovery.
... The majority of gallium coexists with various minerals, the most important of which are bauxite, zinc ore and coal. Because it is uneconomical to extract gallium minerals alone, gallium is currently recovered primarily from secondary resources, such as solid or liquid waste from the Bayer process [6][7][8][9], coal fly ash [10,11], phosphorus dust [12], E-waste [13][14][15] and various tailings [16][17][18]. With the growth in global industries such as power electronics [19][20][21], semiconductors [22][23][24], medicine [25][26][27], aerospace [28,29], and so on, the use of gallium is becoming more and more widespread, and thus the market demand for gallium is expanding. ...
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 × (CNaOH)2.12 (L/S)0.43exp[−42835/(RT)] t.
... However, Ga has little tendency to concentrate naturally, and high-Ga minerals are exceedingly scarce, with a crustal abundance of only 15-19 ppm, which results in very limited Ga production in mining (Gray, Kramer, and Bliss 2005;Nguyen and Lee 2019). Due to the small content of Ga in the host mineral, it is always recovered as a by-product of other mineral processing, among which Ga recovered from bauxite accounts for 90% of the total output (Okudan et al. 2015). ...
Rare metal gallium is classified as a strategic material because of continued high demand, uncertain supply, and low reserves. Corundum flue dust (CFD) is generated during bauxite smelting to produce brown corundum. Gallium (Ga), Zinc (Zn), and potassium in the bauxite could be enriched with CFD through this process, so CFD is regarded as one of the potential sources of Ga and Zn. A novel that utilizes ultrasound to enhance the H 2 SO 4 leaching efficiency of Ga and Zn from CFD was developed from CFD. The effects of ultrasound power, leaching time, sulfuric acid concentration, and leaching temperature on the leaching behavior of Ga and Zn were studied, and the corresponding kinetics model was established. It was found that the maximum Ga and Zn leaching efficiencies of 81.22% and 96.72% were obtained at optimum leaching conditions: the leaching temperature of 90°C, the leaching time of 60 min, 3 M H 2 SO 4 , the solid-to-liquid ratio of 1:5 (g/mL), and the ultrasound power of 750 W. In all cases, the leaching effect of Zn is not significantly improved by ultrasonic treatment, but the leaching efficiency of Ga has a positive effect (more than an 18% increase). Kinetic analysis shows that the leaching process of Ga and Zn were controlled by chemical reaction and diffusion, respectively. The apparent activation energy values are 20.39 kJ/mol for Ga and 13.44 kJ/mol for Zn. The characterization of the leaching residues reveals that the ultrasound effected to enable the whole block to be fractured or dispersed into fragments, accelerating the penetration of H 2 SO 4 into the pores and cracks at the solid, which further prompts the dissolution of the encapsulated gallium and achieves the conspicuous improvement to Ga leaching efficiency.
... 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) . ...
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. ...
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]. ...
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). ...
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). ...
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.
Compared with conventional high-temperature methods based on electricity and fossil fuels, concentrated solar energy route offers distinct advantages in terms of mitigating emissions of contaminants and shortening processing times. Nevertheless, solar-based route also encounters challenges in producing significant quantities of materials, although the deployment of this technology is still conditioned by the limited investigation in the field. This study presents a novel high-temperature process based on solar energy to produce MgAl2O4 spinel, which employs as source of Al2O3 a waste from the aluminum industry: waste alumina fines from the Bayer process. First, mixtures were prepared by mechanical mixing in a molar ratio 1:1 in agreement with the MgO–Al2O3 binary phase diagram. Then, synthesis of the MgAl2O4 spinel was conducted by static experiments (5 min) with direct application of concentrated solar energy (1150 W/cm2) at temperatures greatly exceeding 1800 °C as reported by ANSYS software. Wastes from three Bayer process factories were studied, which exhibited after the synthesis process a good crystallinity. The carbon dioxide emissions avoidance would range from the 200 to 500 tons of CO2/year in the case of a small plant producing 1000 tons/year to 5000 to 12,000 tons of CO2/year in the case of a commercial plant producing 25,000 tons/year, thus contributing to mitigate climate change. The proposed process might lead to smaller volume of wastes in the aluminum industry, while the MgAl2O4 may be used as raw material in the numerous fields based on the chemical, thermal, dielectric, mechanical and optical properties.
Gallium is widely used in electronic devices. The development of Ga recovery technology is an important issue. In this study, D2EHPA‐modified resin (DMR) is prepared by solvent‐nonsolvent modification method. This method can improve the distribution and amount of immobilized D2EHPA in DMR. The amount of modified D2EHPA is 2.68 mmol g–1 of resins. The adsorption isotherm can be described with the Langmuir isotherm model with the Ga(III) adsorption capacity of 28.13 mg g–1 of DMR at 25 °C. The Ga(III) adsorption kinetics follows the pseudo‐second‐order model. The DMR has good stability and reusability for Ga(III) recovery. The results for the treatment of practical Ga(III)‐contained leaching solution from GaN/Al2O3 wafer further demonstrate that DMR can be used effectively.
Electrofilter powder (EP) is a residue generated in large amounts during the calcination of aluminium hydroxide in the Bayer process. The production of high temperature structural insulator (HTSI) using EP is proposed. Different tests were made using different proportions of the starting materials, although the optimal mixture contained (in wt%) 52% EP, 14.7% silica fume (or quartz), 12% refractory aluminous cement and 21.3% water. Besides, 900 cm³ of polystyrene flakes were added to the mixture to promote a fine structure of pores. The brick was formed using manual mixing and vibration compacting in silicone molds. Then, it was dried at 100°C for 24 h, and after that, subjected to pre-sintering by heating up to 1050°C, and finally it was sintered at 1400° or 1450°C for 2 h. At the end of the process, the brick comprised 63% mullite, 24% anorthite and 13% corundum, with the following properties: density values within 0.75 and 0.80 g.cm⁻³, thermal conductivity values within 0.25 and 0.29 W.m⁻¹.K⁻¹, compressive strength values higher than 3.5 MPa, total porosity in the range 75–79% and overheat stability at 1400°C for 24 h with no appreciable dimensional changes.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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Recoverable resources of by-products in the Bayer process: Seydisehir Aluminum Plant (Turkey)
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Recovery of gallium from industrial products of chemical and metallurgical industries
- Z S Abisheva
- A N Zagorodnyaya
- Y G Bochevskaya
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