Direct Cupric Chloride Leaching of Gold from Refractory Sulfide Ore

Funding Information: The authors would like to thank the Emil Aaltonen Foundation for financially supporting the “Sustainable gold” project. The study was also supported by GoldTail (Grant No. 319691), funded by the Academy of Finland, and the Finnish Foundation for Technology Promotion. This work was also supported by “RawMatTERS Finland Infrastructure” (RAMI) by the Academy of Finland. Publisher Copyright: © 2021 The Author(s). Published with license by Taylor & Francis Group, LLC. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.A simulation-based life cycle assessment was conducted to compare the impacts of different cyanide-free chloride processing routes for refractory ores to determine whether one-stage leaching of gold from the ores could be advantageous over chloride leaching after conventional pressure oxidation from an environmental perspective. It was shown that both leaching conditions and the refractoriness of the ore strongly affect the environmental impacts of the process. The global warming potential in the direct leaching route was determined to vary between 7.7–17.0 t CO2-eq for 1 kg gold/Au. Prerequisites for the sustainable application of the direct leaching process are suggested.Peer reviewe

Effect of process variables on oxidative pressurized acid leaching of copper electrorefining anode slimes

Extraction of Cu, Ni, As and Te from copper electrorefining anode slimes was studied. Such parameters as sulfuric acid concentration, temperature and oxygen partial pressure had a positive effect on the oxidative pressurized acid leaching in the decreasing order in contrast to the solids concentration. For nickel extraction, temperature, sulfuric acid concentration, combined effect of temperature and sulfuric acid concentration as well as solids concentration and sulfuric acid concentration had a positive effect, in a decreasing order. In the case of arsenic extraction, combined effect of temperature and sulfuric acid concentration, temperature as well as sulfuric acid concentration had positive in the decreasing order. During tellurium extraction, none of the parameters investigated gave the statistically valid response. Basing on the regression analysis, appropriate models for the dissolution of copper and arsenic could be build.Peer reviewe

Effect of process variables on oxidative pressurized acid leaching of copper electrorefining anode slimes

Extraction of Cu, Ni, As and Te from copper electrorefining anode slimes was studied. Such parameters as sulfuric acid concentration, temperature and oxygen partial pressure had a positive effect on the oxidative pressurized acid leaching in the decreasing order in contrast to the solids concentration. For nickel extraction, temperature, sulfuric acid concentration, combined effect of temperature and sulfuric acid concentration as well as solids concentration and sulfuric acid concentration had a positive effect, in a decreasing order. In the case of arsenic extraction, combined effect of temperature and sulfuric acid concentration, temperature as well as sulfuric acid concentration had positive in the decreasing order. During tellurium extraction, none of the parameters investigated gave the statistically valid response. Basing on the regression analysis, appropriate models for the dissolution of copper and arsenic could be build

Models for viscosity and density of copper electrorefining electrolytes

Viscosity and density of copper electrorefining electrolytes affect energy consumption and purity of cathode copper. Decreasing the viscosity and density increases the rate of falling of the anode slimes to the bottom of an electrorefining cell and increases the diffusivity and mobility of ions. Increasing the falling rate of the anode slimes decreases a risk of anode slime impurities ending up on the cathode and being entrapped into the copper deposit. This work introduces two new models for both viscosity and density of copper electrorefining electrolytes with high accuracy and one reconstructed improved model for some electrorefining data of viscosity published previously. The experimental work to build up these new models was carried out as a function of temperature (50, 60, 70 °C), copper (40, 50, 60 g/dm3), nickel (0, 10, 20 g/dm3) and sulfuric acid (130, 145, 160 g/dm3) concentrations for all models, and additionally arsenic concentration (0, 15, 30, 32, 64 g/dm3) was included in the viscosity models. Increasing concentrations of Cu, Ni, As and H2SO4 were found to increase the viscosity and density, whereas increasing temperature decreased both viscosity and density. The viscosity models were validated with industrial electrolyte samples from the Boliden Harjavalta Pori tankhouse. The experimental and modeling work carried out in this study resulted in improved viscosity models, having the strongest agreement with the industrial electrorefining electrolytes.Peer reviewe

Comparison of Different Leaching Media and Their Effect on REEs Recovery from Spent Nd-Fe-B Magnets

Recycling rare-earth elements (REEs) from Nd-Fe-B magnet waste is an important step towards building a sustainable REE supply chain. In this study, two different processes were systematically investigated and compared. In the leaching stage, the effect of increasing H2SO4 or HCl concentrations were studied and it was determined that, although both can successfully promote REEs, B, Fe and Co leaching, HCl solutions extracted a wider range of metals. After leaching, the oxalate and double-sulfate precipitation methods were utilized to separate REEs from either HCl or H2SO4 leachates. Results suggest that, although > 99% REEs precipitation rates could be achieved with oxalate, the purity of REE-containing products is significantly affected by impurities like Fe and Co. In contrast, REE double-sulfate precipitation resulted in a product purity of > 99%; however, high levels of Na2SO4 (8 times the stoichiometric amount) were needed to achieve > 98% of REE precipitation.Peer reviewe

Behavior of gallium and germanium associated with zinc sulfide concentrate in oxygen pressure leaching

The Fankou zinc concentrate (Guangdong province, China) was mineralogically characterized and results showed that the main germanium-bearing minerals in the sample comprised of zinc sulfide and galena, whereas gallium-bearing minerals were pyrite, sphalerite and silicate. Oxygen pressure leaching of zinc sulfide concentrate was carried out in order to investigate the effect of pressure, leaching time, sulfuric acid and copper concentrations on the leaching behavior of gallium and germanium. Under optimum conditions, leaching of Zn, Fe, Ge and Ga reached 98.21, 90.45, 97.45 and 96.65%, respectively. In the leach residues, it was determined that some new precipitates, such as PbSO4, CaSO4 and SiO2, were formed, which co-precipitated a certain amount of Ga and Ge from the leach solution. The results clearly indicated that Ga and Ge were much more difficult to leach than Zn, and provided answers to why the leaching efficiency of Ga is 10% lower when compared to Ge.Peer reviewe

Effect of process variables on oxidative pressurized acid leaching of copper electrorefining anode slimes

Extraction of Cu, Ni, As and Te from copper electrorefining anode slimes was studied. Such parameters as sulfuric acid concentration, temperature and oxygen partial pressure had a positive effect on the oxidative pressurized acid leaching in the decreasing order in contrast to the solids concentration. For nickel extraction, temperature, sulfuric acid concentration, combined effect of temperature and sulfuric acid concentration as well as solids concentration and sulfuric acid concentration had a positive effect, in a decreasing order. In the case of arsenic extraction, combined effect of temperature and sulfuric acid concentration, temperature as well as sulfuric acid concentration had positive in the decreasing order. During tellurium extraction, none of the parameters investigated gave the statistically valid response. Basing on the regression analysis, appropriate models for the dissolution of copper and arsenic could be build

Thiosulfate-copper-ammonia leaching of pure gold and pressure oxidized concentrate

In this research cyanide-free leaching of pure gold and pressure oxidized refractory gold concentrate by thiosulfate-copper-ammonia solutions were examined. A quartz crystal microbalance (QCM) was used to study gold leaching as a factorial series where the best gold leaching rate (2.987 mg/(cm2·h)) was achieved with a solution consisting of 0.2 M (NH4)2S2O3, 1.2 M NH3, 0.01 M CuSO4 and 0.4 M Na2SO4. Temperature had the greatest effect on the gold leaching rate. An increase in thiosulfate concentration (0.1-0.2 M) increased gold dissolution. The combined effect of temperature and ammonia concentration had a statistically significant effect on the gold leaching rate at 0.1 M M2S2O3. Combination of applied potential and NH3:S2O3 ratio had a statistically significant effect on the gold leaching rate at 0.2 M M2S2O3. An increase in applied potential decreased the gold dissolution rate at low ammonia concentrations but increased it at high concentrations. A pressure oxidized gold concentrate was leached for 6 hoursin the batch reactor leaching experiments. The effect of rotative velocity (1.26-1.56 m/s) and slurry density (10-30 wt%) was investigated at the following leaching parameters: 0.2 M Na2S2O3, 0.6 M NH3, 0.01 M CuSO4, 0.4 M Na2SO4. Lower slurry density (10 wt%) resulted in a higher Au leaching efficiency. An increase in the rotation rate did not have an effect on the final Au leaching recovery. The best Au leaching efficiency (89%) was achieved with 590 rpm mixing, 1.56 m/s rotative velocity and 10 wt% slurry density.Peer reviewe

Physicochemical Problems of Mineral Processing Thiosulfate-copper-ammonia leaching of pure gold and pressure oxidized concentrate

Abstract: In this research cyanide-free leaching of pure gold and pressure oxidized refractory gold concentrate by thiosulfate-copper-ammonia solutions were examined. A quartz crystal microbalance (QCM) was used to study gold leaching as a factorial series where the best gold leaching rate (2.987 mg/(cm 2 •h)) was achieved with a solution consisting of 0.2 M (NH 4 ) 2 S 2 O 3 , 1.2 M NH 3 , 0.01 M CuSO 4 and 0.4 M Na 2 SO 4 . Temperature had the greatest effect on the gold leaching rate. An increase in thiosulfate concentration (0.1-0.2 M) increased gold dissolution. The combined effect of temperature and ammonia concentration had a statistically significant effect on the gold leaching rate at 0.1 M M 2 S 2 O 3 . Combination of applied potential and NH 3 :S 2 O 3 ratio had a statistically significant effect on the gold leaching rate at 0.2 M M 2 S 2 O 3 . An increase in applied potential decreased the gold dissolution rate at low ammonia concentrations but increased it at high concentrations. A pressure oxidized gold concentrate was leached for 6 hours in the batch reactor leaching experiments. The effect of rotative velocity (1.26-1.56 m/s) and slurry density (10-30 wt%) was investigated at the following leaching parameters: 0.2 M Na 2 S 2 O 3 , 0.6 M NH 3 , 0.01 M CuSO 4 , 0.4 M Na 2 SO 4 . Lower slurry density (10 wt%) resulted in a higher Au leaching efficiency. An increase in the rotation rate did not have an effect on the final Au leaching recovery. The best Au leaching efficiency (89%) was achieved with 590 rpm mixing, 1.56 m/s rotative velocity and 10 wt% slurry density