Selective separation of copper and nickel by solvent extraction using LIX 984N

Selective separation of copper and nickel from ammoniacal/ammonium carbonate medium was carried out by using LIX 984N diluted with deodourised kerosene. The study of the influence of equilibration time, equilibrium pH, extractant concentration and selective stripping of copper and nickel has been optimized. It was found that both the metal extractions were unaffected by the changes in pH. Nickel extraction equilibrium was reached at a longer contact time than that for copper and nickel extraction depends greatly on the extractant concentration in the organic phase. Co-extraction, ammonia scrubbing and selective stripping of copper and nickel were performed for a solution containing 3 g dm^− 3 each of copper and nickel and 60 g dm^− 3 ammonium carbonate. The extraction and the percentage of stripping for nickel and copper were almost quantitative.     

Properties of electrolyte solutions relevant to high concentration chloride leaching. III. Solubility of pertinent solids and iron(III)/iron(II) redox potential measured in concentrated magnesium chloride solutions

Results of solubility measurements of nickel chloride, manganese chloride, iron(II) chloride, hematite and akaganeite in aqueous solutions of MgCl₂ (0.5–3.5 mol L^− 1) at temperatures of 60 and 90 °C are reported. Solubilities of metal(II) chlorides decrease almost linearly with MgCl₂ concentration due to the common ion effect. Nickel chloride and iron(II) chloride solubilities are very similar, while manganese chloride is about 30% more soluble.Hematite is more stable (i.e. less soluble) than akaganeite under all conditions investigated in this study, while ferrihydrite is considerably less stable. In other words, there is no change in the relative stabilities of these phases effected by the presence of high magnesium chloride concentrations. The solubility of all of these phases decreases with temperature and, for each temperature, the solubility constants increase linearly with the MgCl₂ concentration. The present results allow the prediction of the iron concentration as a function of the H⁺ and MgCl₂ molality at equilibrium with hematite or akaganeite.The Fe(III)/Fe(II) redox behaviour has been characterized in concentrated aqueous solutions of MgCl₂ (1.5–3.5 mol L^− 1) at a temperature of 25 °C. Standard redox potentials are ca. 100 mV lower than at infinite dilution and change linearly by only 13 mV in the range 2–4 mol L^− 1 MgCl₂.     

Adsorption behavior of Cd(II) from aqueous solutions onto gel-type weak acid resin

The adsorption and desorption behaviors of Cd(II) on gel-type weak acid resin (GTWAR) have been investigated. The influence of operational conditions such as contact time, initial concentration of Cd(II), initial pH of solution and temperature on the adsorption of Cd(II) has also been examined. The results show that the optimal adsorption condition of GTWAR for Cd(II) is achieved at pH = 5.95 in HAc–NaAc medium. The maximum uptake capacity of Cd(II) is 282 mg/g GTWAR at 298 K. The adsorption of Cd(II) follows the Langmuir isotherm and Freundlich isotherm, and the correlation coefficients have been evaluated. Even kinetics on the adsorption of Cd(II) has been studied. The apparent activation energy E_a and adsorption rate constant k₂₉₈ values are 2.95 kJ/mol and 3.02 × 10^− 5 s^− 1, respectively. The calculation data of thermodynamic parameters which ΔS value of 110 J/(mol K) and ΔH value of 13.1 kJ/mol indicate the endothermic nature of the adsorption process. Whilst, a decrease of Gibb's free energy (ΔG) with increasing temperature indicates the spontaneous nature of the adsorption process. Finally, Cd(II) can be eluted by using 0.5 mol/L HCl solution and the gel-type weak acid resin can be regenerated and reused. The sample was described by IR spectroscopy and scanning electron micrographs (SEM).     

Adsorption of rhenium(VII) on 4-amino-1,2,4-triazole resin

The adsorption properties of 4-amino-1,2,4-triazole resin (4-ATR) for Re(VII) were investigated by static and dynamic adsorption–desorption measurements with ultraviolet–visible spectroscopy. The influence of conditions such as temperature, initial solution pH and contact time on the adsorption curve was studied. It was found that the 4-amino-1,2,4-triazole resin was suitable for adsorption of Re(VII). The saturated adsorption capacity was 354 mg·g^− 1resin at pH 2.6 in HAc–NaAc medium at 298 K. The adsorption rate constant was k₂₉₈ = 8.2 × 10^− 5 s^− 1. The adsorption behavior of 4-ATR for Re(VII) obeyed the Freundlich empirical equation; whilst changes in adsorption with temperature gave an enthalpy change ΔH  = − 11.8 kJ·mol^− 1. The molar ratio of the functional group of 4-ATR to Re(VII) was about 2:1. Re(VII) adsorbed on 4-ATR was eluted by 1.0 ~ 5.0 mol·L^− 1 HCl with 100% quantitative elution in 4.0 mol·L^− 1 HCl solution. The resin can be regenerated and reused without apparent decrease in adsorption capacity.     

Properties of electrolyte solutions relevant to high concentration chloride leaching. II. Density, viscosity and heat capacity of mixed aqueous solutions of magnesium chloride and nickel chloride measured to 90 °C

Results of density and viscosity measurements for aqueous solutions of MgCl₂ (0.5–3.5 mol L^− 1) and MgCl₂ + 10% NiCl₂ (0.5–3.5 mol L^− 1) at temperatures of 25, 60 and 90 °C show an almost linear increase in density with total concentration, while low nickel contents and temperature have comparatively small effects. Viscosities of MgCl₂ solutions rise sharply at 25 °C but are significantly lower at 90 °C. The viscosity of 3–4 mol kg^− 1 MgCl₂ at 90 °C is similar to water at 25 °C. Nickel has no significant effect on the viscosity of these solutions.Results of heat capacity measurements for aqueous solutions of MgCl₂ (0.5–3.5 mol L^− 1) and MgCl₂ + 10% NiCl₂ (0.5–3.5 mol L^− 1) at temperatures of 60 and 90 °C show that the heat capacities of these solution decrease significantly with total concentration, while the effects of low nickel contents and temperature are again comparatively small.     

Extraction of Fe(III) from hydrochloric acid solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921)

Ferric ions were efficiently removed from HCl solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921). Iron was removed under the form HFeCl₄ through direct binding on the resin or by extraction with Cyanex 921 involving a solvation mechanism. High concentrations of HCl and intermediary extractant loadings were required for maximum sorption efficiency and rationale use of the extractant. At intermediary extractant loading (in the range 300–450 mg Cyanex 921 g^− 1) the maximum sorption capacity increased with extractant loading. Maximum sorption capacity slightly increased with temperature, the reaction is endothermic and the enthalpy change was found close to − 30.8 kJ mol^− 1. Sorption isotherms were fitted with the Langmuir equation and maximum sorption capacity reached values as high as 20–22 mg Fe g^− 1 in 3 M HCl solutions. Despite the good fit of experimental data with the pseudo second-order rate equation, sorption kinetics was controlled by the resistance to intraparticle diffusion. The intraparticle diffusion coefficient (D_e) varying in the range 1.2 × 10^− 11–4.7 × 10^− 10 m² min^− 1 was found to increase with metal concentration and with temperature, while varying the extractant loading it reached a maximum at a loading close to 453 mg Cyanex 921 g^− 1. The desorption of Fe(III) can be achieved using 0.1 M solutions of nitric acid, sulfuric acid, sodium sulfate and even water, maintaining high efficiencies for sorption and desorption for at least 5 cycles.     

Stability of 3CaO · Al2O3 · 6H2O in KOH + K2CO3 + H2O system for chromate production

In the novel clean chromate production process, the alkali liquor recycled to decompose the chromite ore mainly consists of KOH and K₂CO₃ which accumulates aluminium impurity and affects the quality of the product greatly. Aluminium impurity can be removed by adding CaO to precipitate as 3CaO · Al₂O₃ · 6H₂O (C₃AH₆). A study of the effects of various parameters, such as KOH concentration, K₂CO₃ concentration and temperature on the behaviour of C₃AH₆ show that C₃AH₆ is decomposed to 3CaO · Al₂O₃ · CaCO₃ · 11H₂O and CaCO₃ below 150 g L^− 1 KOH, and decomposed to Ca(OH)₂ above 150 g L^− 1 KOH. With K₂CO₃ concentration increasing, C₃AH₆ decomposes significantly, which results in more CaCO₃ or 3CaO · Al₂O₃ · CaCO₃ · 11H₂O produced. Temperature has a large positive effect on the decomposition of C₃AH₆ at 45 g L^− 1 KOH but has no significant effect at 150 g L^− 1 KOH. The optimal condition for removing aluminium impurity in the KOH + K₂CO₃ + H₂O system is 150 g L^− 1 KOH, 50 g L^− 1 K₂CO₃ and 80 °C.     

Arsenic removal from copper ores and concentrates through alkaline leaching in NaHS media

Removal of arsenic impurity in ores and concentrates containing copper (Cu) through alkaline leaching in NaHS media was investigated in this work. Samples containing Cu from 10 to 40 wt.% and arsenic from 0.8 to 14 wt.% with enargite (Cu₃AsS₄) as main arsenic bearing mineral were used as starting materials and all leaching tests were conducted at 80 °C under normal atmospheric pressure. Solution and/or slurry potential and pH were maintained consistently below − 500 mV (SHE) and above 12.5 respectively with the addition of NaHS and NaOH, creating a reducing environment for arsenic dissolution and conversion of Cu₃AsS₄ to Cu₂S. Pulp density ranged from 100 to 1000 g/L, NaHS and NaOH reagents were added at 50–200 g/L each and leaching time varied from 10 min to 10 h.Characterization of solid samples (original and leach residue) by XRD and XRF analyses and chemical analysis of both solid and solution samples by ICP analysis showed that Cu₃AsS₄ in the starting material was completely decomposed or transformed to Cu₂S and arsenic released into solution as As (III)/As³⁺ ions (Na₃AsS₃). Over 90% of arsenic in the starting materials was removed within 1–3 h for materials with arsenic content from 1 to 4 wt.% and within 3–6 h for materials with arsenic content over 4–10 wt.%. Dissolution and analysis of leach residues obtained after leaching by ICP indicated that arsenic in the starting materials has been reduced in all cases to below 0.5 wt.%. In all test conditions dissolution of Cu and Fe into solution was not detected, indicating selective leaching of arsenic. NaHS application for removal of arsenic in Cu-ores and/or concentrates was demonstrated in this work and further research is in progress to develop a process to include treatment of arsenic leached into solution.     

Comparative leaching of a sulfidic gold ore in ionic liquid and aqueous acid with thiourea and halides using Fe(III) or HSO5 oxidant

The leaching of gold, silver and base metals from a sulfidic gold ore in the presence of an oxidant (peroxomonosulfate (HSO₅⁻) or iron(III)) and leaching agent (thiourea, chloride, bromide or iodide) is compared in 1-butyl-3-methylimidazolium hydrogen sulfate (bmimHSO₄) and chloride (bmimCl) ionic liquids, as well as in aqueous saturated K₂SO₄ as the solvent medium. Over 85% of gold and silver was recovered in the presence of HSO₅⁻/ thiourea at 25–50 °C in both bmimHSO₄ and bmimCl, with silver recovery significantly enhanced compared with that from aqueous sulfate medium. The leaching efficiency with HSO₅⁻ was similar to that with Fe(III) as oxidant in bmimHSO₄ and was far superior in bmimCl. With HSO₅⁻ /halide ion (Cl⁻, Br⁻, I⁻) as leaching agent, gold and silver recovery in bmimHSO₄, bmimCl or saturated aqueous K₂SO₄ improved from Cl⁻ to Br⁻ to I⁻, but only I⁻ gave a high recovery in the bmimCl ionic liquid due to the particular stability of the iodo complex anion in this medium. However, recovery was significantly higher than in an aqueous medium. Negligible recovery of base metals occurred in the ionic liquid medium, making it highly selective for Au and Ag. Concentration dependence studies with respect to halide and oxidant have defined optimum conditions for gold and silver recovery.     

Influence of malonic acid and triethyl-benzylammonium chloride on Zn electrowinning in zinc electrolyte

The influence of malonic acid and other additives has been investigated during the electrowinning of zinc from acid sulphate solutions containing manganese ions. It was found that adding malonic acid “MA” increased the current efficiency and decreased the anodic and cathodic potentials and the cell voltage in the standard electrolyte. Adding malonic acid to the industrial electrolyte containing antimony impurity also led to an increase in the current efficiency. Triethyl-benzylammonium chloride “TEBACl” was the best additive to improve current efficiency with the presence of 5 mg/L Ni²⁺ impurity and it also counteracted the deleterious effect of Sb³⁺ better than the other additives such as polyethylene glycol, sodium lauryl sulphate, perfluoro-heptanoic acid and malonic acid—these were not as good as glue and chloride ion together. Adding 2 mg/L of “TEBACl” to sulphuric acid solution with the presence of nickel ions increased the cathodic potential of hydrogen evolution on the zinc deposit, much more than that of 100 mg/L “MA”.     

A novel recovery process of metal values from the cathode active materials of the lithium-ion secondary batteries

A novel process was conducted with experiments which separated and recovered metal values such as Co, Mn, Ni and Li from the cathode active materials of the lithium-ion secondary batteries. A leaching efficiency of more than 99% of Co, Mn, Ni and Li could be achieved with a 4 M hydrochloric acid solution, 80 °C leaching temperature, 1 hour leaching time and 0.02 gml^− 1 solid-to-liquid ratio. For the recovery process of the mixture, firstly the Mn in the leaching liquor was selectively reacted and nearly completed with a KMnO₄ reagent, the Mn was recovered as MnO₂ and manganese hydroxide. Secondly, the Ni in the leaching liquor was selectively extracted and nearly completed with dimethylglyoxime. Thirdly, the aqueous solution in addition to the 1 M sodium hydroxide solution to reach pH = 11 allowed the selective precipitation of the cobalt hydroxide. The remaining Li in the aqueous solution was readily recovered as Li₂CO₃ precipitated by the addition of a saturated Na₂CO₃ solution. The purity of the recovery powder of lithium, manganese, cobalt and nickel was 96.97, 98.23, 96.94 and 97.43 wt.%, respectively.     

Properties of electrolyte solutions relevant to high concentration chloride leaching I. Mixed aqueous solutions of hydrochloric acid and magnesium chloride

A computer code based on a Pitzer model has been developed for the comprehensive prediction of the thermodynamic properties of MgCl₂–HCl aqueous solutions over a wide range of conditions from 25 to 120 °C and from 0–350 g L^− 1 chloride. This code was applied to the calculation of (i) water activities and mean ionic activity coefficients for mixed aqueous solutions of hydrochloric acid and magnesium chloride over a wide range of concentrations and to 100 °C, (ii) solubilities of MgCl₂·6H₂O in MgCl₂–HCl solutions to 80 °C, (iii) partial pressures of HCl(g) and H₂O(g) over MgCl₂–HCl aqueous solutions at various temperatures and (iv) partial pressures of HCl(g) at the normal boiling point of these mixed electrolyte solutions. The model predictions are in excellent agreement with available experimental data and confirm evidence from the literature that MgCl₂(aq) and HCl(aq) mix almost ideally at constant water activity.     

Manganese metallurgy review. Part III: Manganese control in zinc and copper electrolytes

Manganese is often associated with zinc and copper minerals, and can build up in the processing circuits. Part III of the review outlines the current practice and new developments to get a better understanding of manganese behaviour and control in electrowinning of zinc and copper, and identifies suitable methods and processes to control manganese.In zinc electrowinning, the presence of small amounts of manganese (1–5 g/L) can minimise the corrosion rate of the anodes and reduce the contamination of the cathodic zinc with lead, but excess manganese results in significant decreases in the current efficiency. The neutralized zinc feed solution that contains little acid is considered to be the best place to implement manganese control. Various methods and processes for manganese control in zinc electrowinning have been developed. Oxidative precipitation and solvent extraction are the most important methods. For the neutralized zinc solution at pH 5, oxidative precipitation using a strong oxidant such as Caro's acid and SO₂/O₂ can selectively precipitate manganese as insoluble MnO₂ or Mn(OOH), leaving other impurities, e.g., Mg, Cl⁻, F⁻, etc. in the circuit. Solvent extraction of zinc using D2EHPA (di-2-ethylhexyl phosphoric acid) can selectively recover zinc from the solution and leave other impurities including manganese in the raffinate.In copper solvent and electrowinning circuits, the problem of manganese is mainly associated with the decrease in the current efficiency and degradation of the solvent caused by the higher valent manganese species generated on the anode. The prevention or minimisation of Mn(II) oxidation during the electrowinning is critical. This can be achieved by adding ferrous ions or sulfur dioxide to control the cell potential.     

Comparative study of dewatering characteristics of metal precipitates generated during treatment synthetic polymetallic and AMD solutions

The sludge dewatering characteristics expressed in terms of settling, filtration and centrifugation of metal precipitates generated during treatment of polymetallic solutions and synthetic acid mine drainage have been evaluated in this research. Results show that dewatering properties of metallic sludge vary depending on the type of matrix (Cl⁻; SO₄²⁻), precipitating agent, and metals present in effluent. Metal hydroxides (at pH 10.0) and metal phosphates precipitates (at pH 7.0) are amorphous in nature, thus difficult to dewater. In these treatment methods, the substitution of chloride matrix by sulphate one improves considerably dewatering properties (specific resistance to filtration = 6.60 × 10¹³ and 2.35 × 10¹³ m/kg for the chloride and sulphate matrix, respectively). In the case of sulphide and carbonate treatments (pH 8.0), precipitates obtained are semi crystalline, and crystalline form, respectively, and no influence of the matrix was detected on dewatering characteristics.     

Palladium(II) complexes adsorption from the chloride solutions with macrocomponent addition using strongly basic anion exchange resins, type 1

The use of the strongly basic anion exchange resins, type 1 such as Lewatit MP-500 and Lewatit MP-500A for palladium(II) complexes adsorption has been investigated. The adsorption process was carried out from the chloride solutions with macrocomponent (sodium chloride) addition (x M HCl–1.0 M NaCl; x M HCl–2.0 M NaCl) where the concentration of hydrochloric acid was constant and equal to x = 0; 0.1; 0.5; 1.0; and 2.0 M, respectively. The breakthrough curves of Pd(II) were determined and the sorption parameters (weight and bed distribution coefficients, working anion exchange capacity) were calculated. The pseudo-second kinetic order was applied in kinetic studies as well as to calculate the kinetic parameters. The values of the working anion exchange capacities (0.029 g/cm³; 0.028 g/cm³) for Lewatit MP-500 and Lewatit MP-500A (0.028 g/cm³; 0.027 g/cm³) in the 1.0 M NaCl and 0.1 M HCl–1.0 M NaCl solutions, respectively are really close and in other solutions under discussion Lewatit MP-500 possess slightly higher values of capacities, and therefore is insignificantly more efficient in the adsorption process of palladium(II) ions than Lewatit MP-500A. The equilibrium adsorption capacities changed in the range 8.84–9.99 and 8.40–9.38 mg/g for Lewatit MP-500 as well as 8.12–9.57 and 7.26–8.85 mg/g for Lewatit MP-500A in the chloride x M HCl-1.0 M NaCl and x M HCl-2.0 M NaCl solutions, respectively. The adsorption process proceeds according to the pseudo-second kinetic order.     

Measurement of pH in the vicinity of a cathode during the chloride electrowinning of nickel

An antimony microelectrode was prepared by quenching a molten Sb-Sb₂O₃ mixture (2 pct Sb₂O₃). The local pH in the vicinity of a nickel-plated copper cathode was directly measured using the microelectrode during the chloride electrowinning of nickel for a MCLE (matte chlorine leach electrowinning) process, where nickel metal is electrodeposited with a high current efficiency, 94 to 97 pct, from low-pH baths. The local pH at 328 K was increased by proton consumption during the electrolysis of aqueous electrolytes containing NiCl₂ (1.20 mol dm⁻³) and NaCl (0.43 mol dm⁻³) with the same concentrations as employed for the MCLE process. The difference in pH between the cathode surface and bulk solution increased with increasing cathodic current density. Nickel deposits with a metallic luster were obtained when the difference was not more than 1.2 pH units. The current efficiency was a maximum for electrolysis with a current density of 265 A m⁻² and bulk pH of 1.0 to 1.5; these optimal conditions coincided with those reported for the MCLE process: temperature 328 to 333 K, bulk pH 1.1 to 1.5, and current density 230 to 260 A m⁻². Electrolytes with lower NiCl₂ and NaCl concentrations resulted in a drop in current efficiency.     

Kinetics of reductive leaching of manganese oxide ore with molasses in nitric acid solution

The kinetics of reductive leaching of manganese from a low grade manganese ore in dilute nitric acid in the presence of molasses is examined. The rate is controlled by diffusion through the “product” layer composed of the associated minerals. The leaching process follows the kinetic model 1 − 2/3X − (1 − X)^2/3 = kt with an apparent activation energy of 25.7 kJ/mole. It is concluded that the concentration of HNO₃ and molasses as well as temperature are the main factors influencing the leaching rate. The results indicate a reaction order of 1.2 for HNO₃ concentration and 1.9 for molasses concentration.     

Electrochemical Behavior of Dissolved Fe2O3 in Molten CaCl2-KF

The electrochemical behavior of dissolved Fe2O2 in 82.5CaCl2-17.5KF （mole percent, %） was studied using cy clic voltammetry, chronoamperometry, and galvanostatic electrolysis at 827 ℃, and the deposits were characterized by XRD and SEM. Pure iron was deposited on a rotating cylinder （210 r/min） with a cell voltage less than -- 1.0 V. Deposition rate was controlled by diffusion on a molybdenum electrode. The diffusion coefficient of iron species Fe（ Ⅲ ） in the melt at 827 ℃ was found to be 9.7×10^-5 cm^2/s.     

Heavy metals in the environment. Part VI: Recovery of cobalt values from spent cobalt/manganese bromide oxidation catalysts

Cobalt is recovered from a series of spent cobalt/ manganese bromide oxidation catalysts containing 27–31% Co, 25–33% Mn, 0–14% Fe together with Cr, Cu and Ni. While ammoniacal leaching in the presence of reducing agents can be used to extract cobalt, the process has to be separately optimized for each sample. Leaching with 4 M HCl at 80°C for 4 hours, however, proved successful for all the catalysts. A method of successive neutralization is used for the separation of cobalt from the acid solutions. Addition of solid NaOH to pH 2 removes Fe and Cr as hydroxide, while addition of ammonia to pH 10 precipitates manganese oxide from an aerated solution leaving Co as a Co^III hexammine complex. Cobalt can be recovered from this solution by chemical or electrochemical processes. After crystallization the complex is converted to anhydrous cobalt chloride by heating it to 320°r to Co₂O₃ by roasting it in air at 500°C. Either of these materials may be readily converted into other cobalt chemicals. Alternatively, fluidized bed cell electrolysis of the Co^III. complex solution yields cobalt with purity > 99.5%.     

Desilication of sodium aluminate solution by Friedel's salt (FS: 3CaO·A12O3·CaCl2·10H2O)

Controlling silica level in Bayer liquor is critical in order to prevent scaling or alumina quality issues. The conventional method of removing silicates from aluminate solutions requires the introduction of calcium oxide or calcium hydroxide. In this work, Friedel's salt (FS: 3CaO·A1₂O₃·CaCl₂·10H₂O) is proved for the first time to remove up to 95% silica from sodium aluminate solution. FS is a mineral anion exchanger belonging to the layered double hydroxides (LDHs) which was prepared by adding calcium chloride to sodium aluminate over the temperature range of 50–90 °C. It was characterized by XRD, SEM, Particle Size Analyzer and TG-DSC. FS prepared at 50 °C has a relatively high desilication capacity, better than calcium oxide.Experimental parameters affecting the desilication process, such as temperature, sodium aluminate liquor composition, initial silica concentration (4–10 g/L) and FS dosage were investigated in detail and a comparison of desilication between FS and CaO was carried out. The desilication products (DSP) were mainly calcium aluminium silicates, identified by XRD to be Chabazite and Wadalite and the final chloride concentration in the sodium aluminate solution after anion exchange with FS was  0.015 g/L. The rate of desilication by FS was first order with a rate constant 2.582 × 10⁶ min^− 1. The apparent activation energy was estimated to be 57.7 kJ mol^− 1 over the temperature range of 80–110 °C.