Recovery of scandium from bauxite residue——red mud:a review

Red mud is a slimy caustic residue generated from alumina production. Taking into account the relatively considerable content and availability of scandium, red mud can be viewed as an important and promising scandium resource rather than a solid waste. This paper is primarily to review the investigations of scandium recovery from red mud based on the most widely used hydrometallurgical processes including acid leaching, solvent extraction and ion exchange adsorption. It is thought that recovery of scandium from red mud should be considered as a direct objective rather than a by-product in the development of overall flowsheet. In order to achieve environmentally-friendly processes with high scandium recovery and low cost, more attention is required to be paid to optimizing the selective leaching of scandium to decrease mineral acid consumption and alleviate pollution, and developing new solvent extraction systems and novel ion exchange adsorption materials with high selectivity and recognition for scandium.     

Scandium Recovery from Uranium Solutions

The commercial recovery of scandium as a by-product of uranium extraction is described. A flouride strip system was developed to recover scandium from the solvent in concentrated form, and high purity scandium oxide was prepared in multi-pound lots by chemical separation techniques.     

Solvent extraction and stripping of lithium ion from aqueous solution and its application to seawater

For the development of lithium ion recovery process from seawater, a series of experimental researches were performed. Solvent extraction of lithium ion from aqueous solution using kerosene as solvent was proposed.Lithium ion is effectively extracted by thenoyltrifluoroacetone–trioctylphosphine oxide(TTA–TOPO) in kerosene within 80 min. Extraction efficiency is severely influenced by stoichiometric parameters. Among the stoichiometric parameters, volume ratio of aqueous(A) to extraction(E) solution is the most influential parameter. After extraction, lithium ion could be easily stripped from the extraction solution by acidic solutions. Stripping efficiency decreases with p H of acidic solutions, and the kind of acid does not affect the stripping efficiency. Extraction efficiency maintains at more than 93 % even when the extraction solution is recycled three times. 65 % of lithium ion can be extracted from seawater by this solvent extraction process when magnesium ion is precipitated by NH4 OH prior to solvent extraction process. Other metallic ions in seawater decrease the extraction efficiency of lithium ion.     

Enhancing recovery of uranium column bioleaching by process optimization and kinetic modeling

This research aimed to enhance the column bioleaching recovery of uranium ore by Acidithiobacillus ferrooxidans. Seven factors were examined for their significance on bioleaching using a Plackett–Burman factorial design. Four significant variables ([Fe²⁺]_initial, pH, aeration rate and inoculation percent) were selected for the optimization studies. The effect of these variables on uranium bioleaching was studied using a central composite design (CCD). The optimal values of the variables for the maximum uranium bioleaching recovery (90.27±0.98)% were as follows: [Fe²⁺]_initial=2.89 g/L, aeration rate 420 mL/min, pH 1.45 and inoculation 6% (v/v). [Fe²⁺]_initial was found to be the most effective parameter. The maximum uranium recovery from the predicted models was 92.01%. This value was in agreement with the actual experimental value. The analysis of bioleaching residue of uranium ore under optimum conditions confirmed the formation of K-jarosite on the surface of minerals. By using optimal conditions, uranium bioleaching recovery is increased at column and jarosite precipitation is minimized. The kinetic model showed that uranium recovery has a direct relation with ferric ion concentration.     

Treatment of arsenic ions from produced water through hollow fiber supported liquid membrane

Treatment of arsenic ions from produced water coming along with a gas separation plant in the Gulf of Thailand by hollow fiber supported liquid membrane (HFSLM) was studied. Cyanex^® 923 (a mixture of phosphine oxide), tri-n-butylphosphate (TBP), bis(2, 4, 4-trimethylpentyl) dithiophosphinic acid (Cyanex^® 301), tri-n-octylamine (TOA) and methyltrioctylammonium chloride (Aliquat 336) were used as the extractants. The stripping solution was sodium hydroxide. The concentration of the extractant in liquid membrane and concentration of sodium hydroxide were examined. In addition, the influence of various numbers of runs of the stripping solution through the HFSLM on the concentration of arsenic ions in the outlet stripping solution was observed. Of all the extractants used, 35% (v/v) Aliquat 336 attained high percentages of extraction and recovery of arsenic ions because it reacted with both undissociated arsenic (H₃AsO₃) and dissociated arsenics (H₂AsO₄⁻ and HAsO₄²⁻). Cyanex^® 923, TBP and TOA had low extractability since Cyanex^® 923 and TBP reacted only with undissociated forms while TOA reacted only with dissociated forms. In case of Cyanex^® 301, although it offered a relatively high percentage of extraction but very poor recovery due to this extractant formed very strong complex species with arsenic ions, which slowed down and made the stripping difficult. It was found that the percentage of arsenic recovery increased with the concentration of sodium hydroxide and was almost constant after 0.5 M due to the limitation of mass transfer area of the hollow fibers. After 3-cycle separation, the extraction and recovery of arsenic ions from produced water were 91% and 72%, respectively. Accordingly, the concentration of arsenic ions of 0.1201 ppm in produced water was observed, which was in accordance with the legislation discharge of industrial effluent in Thailand. More arsenic ions were recovered by increasing the numbers of runs of the recycling stripping solution through the HFSLM.     

高位阻β-二酮从氨性蚀刻废液中萃取铜

采用高位阻β-二酮（1-（4’十二烷基）苯基-3-叔丁基-1,3-丙二酮）作为萃取剂从模拟印刷电路板（PCBs）蚀刻废液中萃取铜。利用离子强度与萃取反应平衡常数的关系校正模拟的萃取等温线,该模拟萃取等温线与实验测得萃取等温线基本相符。通过实验确定萃取剂浓度、相比、萃取级数和反萃级数等萃取工艺参数。结果表明,在室温下对于铜离子浓度为112g/L、总氨浓度为7mol/L的模拟氨性蚀刻废液的最佳萃取条件为：萃取剂浓度为40%,相比为5：4,萃取时间为5min。在此条件下,经过一级萃取,蚀刻废液中铜离子浓度可降低至63.24g/L,能返回到电路板的生产中循环使用。用含铜30g/L,硫酸浓度180g/L的模拟废电解液对负载有机相进行反萃,相比（O/A）为1：2,经一级反萃,铜的反萃率可达98.27%。     

A novel approach to synthesis of scandia-doped tungsten nano-particles for high-current-density cathode applications

A novel synthesis approach for scandia-doped tungsten nano-powder using a sol–gel method is developed. It involves dissolving tungsten oxide at 300 °C in the presence of a mixture of nitric acid, citric acid and ammonia. The dissolved tungsten oxide reacts with an aqueous solution of scandium nitrate in the liquid–liquid phase, which results in the homogeneous mixing of tungsten and scandium particles. A spherical shape particle was obtained due to the dissolving of tungsten oxide in the solution. Citric acid enhances the mixing of ions at the atomic scale, which affects the hydrolysis reactions and leads to the formation of the phase pure nano-particle. The synthesized nano-powder was characterized by SEM (Scanning Electron Microscopy), EDS (Energy-dispersive X-ray spectroscopy), TEM (Transmission Electron Microscopy), and XRD (X-ray Diffraction) analyses. The spherical morphology was observed via a SEM analysis and a narrow particle size distribution was noted by means of a TEM analysis. The XRD analysis of the powder showed the complete formation of the phase pure nano-particle with an average diameter of 50 nm without any contamination by other materials.     

Molybdenum recovery from oxygen pressure water leaching residue of Ni–Mo ore

This article investigated molybdenum recovery from oxygen pressure water leaching residue of Ni–Mo ore using alkaline leaching, followed by chemical treatment of leach liquor. Parameters affecting Mo leaching rate, such as sodium hydroxide concentration, reaction time, a liquid-to-solid ratio, and temperature for the preliminary alkaline leaching were experimentally determined. The results showed that more than 88 % of molybdenum was leached under the optimum conditions (2.5 ml·g^?1 NaOH, 80 °C, a liquid to solid ratio 3 ml·g^?1, and reaction time 3 h). After the purification of leach liquor, a CaMoO₄ product of 99.2 % purity could be obtained by CaCl₂ precipitation method. The whole Mo recovery reached about 82.7 %.     

Ida~（2-）-H_2O体系浸出低品位氧化锌矿

采用Ida2--H2O体系（亚氨二乙酸盐水溶液）处理高碱性脉石型低品位氧化锌矿,考察浸出时间、液固比、配体总浓度、温度及pH值对矿物中主金属Zn及杂质元素Ca、Mg、Cu、Ni、Fe、Pb、Cd的溶出影响。结果表明：在弱碱性Ida2--H2O体系中,Ca、Mg、Fe不会被大量溶出,有价金属Cu、Ni、Pb、Cd可部分随主金属Zn溶出而进入浸出液;在浸出时间4h、液固比5：1、配体总浓度0.9mol/L、温度70℃、pH8的优化条件下,锌浸出率为76.6%。     

Copper and elemental sulphur from chalcopyrite by pressure leaching

Processes employing direct oxidation under an over-pressure of air or oxygen in an aqueous sulphuric acid medium have been developed in the Sherritt Gordon Laboratories for iron, nickel, cobalt, zinc and lead sulphide concentrates. This study has recently also been extended to chalcocite, Cu₂S, concentrates. The rising interest in processes employing direct aqueous oxidation is stimulated by the fact that elemental sulphur can be produced as a by-product rather than sulphur dioxide or sulphuric acid.The present paper outlines a process which features the direct pressure oxidation of the most abundant copper sulphide mineral, chalcopyrite, CuFeS₂. The optimum conditions for a practical pressure leaching step have now been developed in the laboratory which results in the production of copper sulphate solution suitable for copper winninq by electrolysis, hydrogen reduction, solvent extraction combined with electrolysis, or other means. The leach residue yields pure elemental sulphur by-product. Copper and elemental sulphur recoveries of 98 and 85% respectively have been recorded. The fastest oxidation rate, corresponding to a leach retention time of 2.5 hr, was obtained when the copper concentrate was ground to 99.5% — 325 mesh, when a 50% stoichiometric excess of concentrate over the amount of available sulphuric acid for copper was used and when the oxygen partial pressure and temperature were maintained at 500 psi and 240°F, respectively. In an idealized form, the pressure leaching reaction can be expressed as follows:—CuFeS₂ + H₂SO₄ + 1 1/40₂ + 1/2H₂O → CuSO₄ + Fe(OH)₃ + 2S°After separation of the copper sulphate solution by filtration, elemental sulphur and excess concentrate ore recovered from the iron oxide tailing by flotation. The tailing, containing iron oxide and insolubles, is rejected. The elemental sulphur is separated from the concentrate by hot filtration, solvent extraction, distillation, or other means, and the unleached chalcopyrite is recycled to the leaching step.     

Copper hydrometallurgy-current status,preliminary economics,future direction and positioning versus smelting

The heap leaching of oxide copper ores with copper cathode recovery by solvent extraction and electrowinning is now well established as a low-cost method of copper recovery. This technology has recently been applied successfully to mixed oxide and chalcocite ores, notably in Chile at Cerro Colorado, Quebrada Blanca and Zaldivar.Currently, there are significant development efforts underway to try to extend heap leaching to chalcopyrite ores.The success of heap leaching/SX/EW has also led to a revival in the development of hydrometallurgical processes to recover copper from chalcopyrite and other copper concentrates. The current status of copper hydrometallurgy is reviewed and the most commercially attractive potential applications are explored. The advantages and disadvantages of the hydrometallurgical treatment of chalcopyrite concentrates and its preliminary economics are compared with those for the current best practices in copper smelting and refining.     

A photo-electron and secondary ion mass spectrometric study of the chemical composition of thermal oxide layers on technically pure aluminium

The thickness and chemical composition of oxide films on aluminium of technical purity (Al 99.2–99.5) has been studied by photo-electron spectroscopy and secondary ion mass-spectrometry for differently prepared surfaces. Special emphasis has been placed in understanding quantitatively the oxidative surface enrichment processes of alkali and alkaline earth elements that take place during annealing at higher temperatures (250–340°C). The concentration of these elements (particularly those of lithium and magnesium) in the oxide layers of annealed foil samples is higher by a factor of 10³ to 10⁴ compared to the bulk metal contents. How these surface enrichment processes modify the chemical properties of the oxide film is discussed. An enhanced susceptibility of the surface to corrosion in the presence of humidity is found which can cause interfacial reactions and delamination problems in the case of lacquered foil.     

Selective recovery of cobalt,nickel and lithium from sulfate leachate of cathode scrap of Li-ion batteries using liquid-liquid extraction

This paper focuses on the extractive separation and selective recovery of cobalt, nickel and lithium from the sulfate leachate of cathode scrap generated during manufacture of lithium ion batteries (LIBs). The conditions for extraction, scrubbing and stripping of cobalt from nickel and lithium are optimized with an aqueous feed containing 25.1 g·dm^?3 cobalt, 2.54 g·dm^?3 nickel and 6.2 g·dm^?3 lithium using Na-PC-88A. 99.8% Co is extracted with 60% Na-0.56 mol·dm^?3 PC-88A in two counter-current stages at an O/A phase ratio of 3/1 and an equilibrium pH of 4.5. The “crowding effect” shown for the first time provides effective scrubbing of impurities (Ni and Li) with 2.0 g·dm^?3 CoSO₄ solution. The McCabe-Thiele diagram predicts the scrubbing of 99.9% Ni and 99.9% Li at an equilibrium pH of 4.75 and O/A of 2/1 in two stages. High purity (99.9%) cobalt sulfate along with Ni and Li from the leach liquor of cathode scrap is recovered by solvent extraction. The proposed process ensures complete recycling of the waste of the manufacturing process of LIBs.     

Recovering in,Ge and Ga from zinc residues

A novel solvent extraction process has been developed to selectively recover indium, germanium and gallium from the cement residue sulfuric acid leach solutions in a hydrometallurgical zinc plant. The key work was to determine a special organic molecule for gallium and germanium extraction. Continuous countercurrent tests on the mini-pilot plant level were performed successfully with 90.7%, 94.2% and 92.9% yield from cement residue to metals, for indium, gallium and germanium, respectively.     

Copper hydrometallurgy——current status, preliminary economics, future direction and positioning versus smelting

The heap leaching of oxide copper ores with copper cathode recovery by solvent extraction and electro-winning is now well established as a low-cost method of copper recovery. This technology has recently been applied successfully to mixed oxide and chalcocite ores, notably in Chile at Cerro Colorado, Quebrada Blanca and Zaldivar.Currently, there are significant development efforts underway to try to extend heap leaching to chalcopyrite ores.The success of heap leaching/SX/EW has also led to a revival in the development of hydrometallurgical processes to recover copper from chalcopyrite and other copper concentrates. The current status of copper hydrometallurgy is re-viewed and the most commercially attractive potential applications are explored. The advantages and disadvantages of the hydrometallurgical treatment of chalcopyrite concentrates and its preliminary economics are compared with those for the current best practices in copper smelting and refining.     

Effect of Scandium Additions on the Tensile Properties of Cast Al-6Mg alloys

Effect of aging on the mechanical properties of Al-6Mg alloy doped with varying concentration of scandium ranging from 0.2 to 0.6 wt.% is analyzed. As-cast samples were aged isochronally for 60 min at different temperatures ranging from 100 to 500 °C. Evaluation of mechanical properties of the aged Al-6Mg (Sc) alloys was done by employing an Instron testing machine. Various strain rate of testing were used to find out the values of strain-rate sensitivity of the experimental alloys. The influence of scandium is much pronounced on yield strength than on the tensile strength. Alloys with higher scandium content have shown higher yield strength and the values of strain-rate sensitivity ‘m’ at peak-aged condition have been found to be comparatively high at higher scandium concentration. The fracture of the experimental alloys occurs through microvoid coalescence.     

A new model for prediction of dispersoid precipitation in aluminium alloys containing zirconium and scandium

A model has been developed to predict precipitation of ternary Al₃(Sc, Zr) dispersoids in aluminium alloys containing zirconium and scandium. The model is based on the classical numerical method of Kampmann and Wagner, extended to predict precipitation of a ternary phase. The model has been applied to the precipitation of dispersoids in scandium containing AA7050. The dispersoid precipitation kinetics and number density are predicted to be sensitive to the scandium concentration, whilst the dispersoid radius is not. The dispersoids are predicted to enrich in zirconium during precipitation. Coarsening has been investigated in detail and it has been predicted that a steady-state size distribution is only reached once coarsening is well advanced. The addition of scandium is predicted to eliminate the dispersoid free zones observed in scandium free 7050, greatly increasing recrystallization resistance.     

Improving mechanical properties of 2219 aluminium alloy GTA welds by scandium addition

Abstract

The effect of scandium additions to 2219 aluminium alloy weld metal has been investigated. At low levels (0·16%) of scandium, in spite of grain refinement in the weld metal, improvement in the mechanical properties has been nominal. At higher levels of scandium (0·37%), a substantial improvement in the tensile properties has been obtained. Further improvement in mechanical properties has been achieved by adding small amounts of magnesium. Transmission electron microscopy revealed the presence of fine precipitate particles in the scandium containing weld metals. Electron probe microanalysis (EPMA) and SEM–EDX revealed extensive copper segregation to grain and subgrain boundaries. The presence of scandium reduces the severity of segregation by producing fine equiaxed grains in the weld metals and also by refining the grain substructure. The morphology and size of the high copper eutectic phase at grain boundaries and sub-boundaries have been found to be finer and well distributed in the case of scandium containing weld metals. EPMA linescans and quantitative analyses proved that the depletion of copper in the matrix is minimised as a result of the fine grained structure.     

Migration and distribution of saline ions in bauxite residue during water leaching

Bauxite residue, a highly saline solid waste produced from digestion of bauxite for alumina production, is hazardous to the environment and restricts vegetation establishment in bauxite residue disposal areas. A novel water leaching process proposed here was used to investigate the dynamic migration and vertical distribution of saline ions in bauxite residue. The results show that water leaching significantly reduced the salinity of bauxite residue, leaching both saline cations Na⁺, K⁺, Ca²⁺ and anions CO^2?₃, SO^2?₄, HCO^?₃. Na⁺ and K⁺ migrated from 40–50 to 20–30 cm of the column, presenting a high migration capacity. The migration capacity of Ca²⁺ was lower and accumulated at 30–40 cm of the column. CO^2?₃ initially distributed at 20–30 cm of the column, subsequently transported to 30–40 cm of the column, and finally returned to 20–30 cm of the column along with evaporation. SO^2?₄ was originally distributed at 40–50 cm, but finally migrated to 20–30 cm of the column. Nevertheless, HCO^?₃ remained at the bottom of the column, and its migratory was less affected by evaporation.     

Material performance in a solvent extraction Liquefaction plant in Japan

Corrosion behaviour of various steels and alloys in the solvent extraction coal liquefaction process in Japan has been studied by the inplant testing in a 1 ton/ day plant and by the laboratory tests related to it. The severest corrosion was observed in the high pressure separator, corrosion thickness loss and pitting depth being the greatest and stress corrosion cracking being observed for 18–8 series austenitic stainless steels. The cause may be the occurrence of water condensate containing high Cl^? and H₂S. Otherwise corrosion was relatively mild. No obvious symptom of notorious organic-chloride corrosion reported in the U.S. has been observed.