Metal recovery from anode slime leach solutions and its applications

In this study, the usage of imidazolium-based ionic liquids and deep eutectic solvents with superior chemical and physical properties compared to conventional leaching agents were investigated for precious metal leaching from copper anode slime, which is classified as a valuable industrial waste with economic value due to its precious metals (Au, Ag, and Cu) amount. The physical, chemical, and mineralogical characterization of copper anode slime was determined with various methods and compared with previous studies. In the leaching processes, 1-butyl-3-methyl imidazolium tetrafluoroborate (BmimBF4), 1-butyl-3-methyl imidazolium chloride (BmimCl) ionic liquids, and deep eutectic solvents (DES) prepared in different compositions were used as leaching reagents. The optimum leaching conditions for the investigated leaching reagents were determined by the Taguchi method. In addition, copper recovery from leach solution was studied with the cementation method after leaching processes. According to the chemical analysis, it was determined that the copper anode slime was mainly composed of Cu, Sn, and Pb elements and contained a significant amount of gold and silver metals. As a result of mineralogical characterization of copper anode slime, it was detected that Cu2O, SnO2, and PbSO4 were the main phases. Optimum leaching conditions for copper after DES leaching were determined as DES compositions: ChCl-urea, leaching temperature: 95 oC, leaching time: 4 hours, and solid/liquid ratio: 1/25 g/mL and 97% of copper leaching were achieved under these optimum conditions. While gold leaching could not be obtained with the same reagents, 91.02% of silver leaching was obtained under optimum leach conditions as ChCl-urea, 95 oC of leaching temperature, 48 hours of leaching time, and 1/10 g/mL solid/liquid ratio. After the leaching experiments with BmimBF4 in the presence of tetrafluoroboric acid (HBF4), the optimum leaching conditions for selective copper leaching was determined as 40% BmimBF4 concentration, 95 oC leaching temperature, 12 hours leaching time, and 1/25 g/mL solid/liquid ratio and 98.36% of copper leaching efficiency was obtained under determined optimum leaching conditions. The optimum working conditions for copper leaching with BmimCl were found out as ionic liquid concentration: 80% BmimCl, leaching temperature: 95 oC, leaching time: 2 hours, and solid/liquid ratio: 1/25 g/mL. Under these conditions, 83.50% of copper leaching was obtained. Optimum leaching conditions for gold leaching using BmimCl were determined as 80% ionic liquid concentration, 50 oC leaching temperature 1 hour leaching time, 1/20 g/mL solid/liquid ratio and 63.34% of gold leaching was attained. Silver leaching with BmimCl ionic liquid could not be performed. After the leaching experiments, 98.10% of copper recovery was achieved after 120 minute cementation test at 95 oC using two lead plates from the DES leaching solution. As a result of the studies carried out with DES, 95% of copper recovery was obtained from the copper anode slime under the specified conditions. After the 120 minute cementation experiments with copper-loaded BmimBF4/HBF4 leaching solution at 45 oC, 93.33% copper recovery was obtained and the total copper recovery rate was calculated as 98.20% from copper anode slime. As a result of this study, the usability of ionic liquids and DESs for precious metal recovery from copper anode slime has been demonstrated.