Selective removal of copper from heavy-metals-containing acidic solution by a mechanochemical reduction with zero-valent silicon

Abstract

It is always a challenge to deal with industrial wastewater containing heavy metals. Selective removal and recovery of valuable metals such as copper particularly from acidic solutions are very important from both stances of resource supplying and environmental purification. Among all the divalent heavy metals, copper has the potential of being reduced to monovalent state. A new approach was proposed to ball mill zero-valent silicon (ZVS) in CuSO4 solution and the solutions containing multi-metal ions to serve the purpose. In this study, both quantitative and qualitative data were reported on the induced mechanochemical reduction reaction to convert Cu2+ into Cu2O by ball milling with ZVS. Experimental parameters such as milling time and Si to Cu ratio were found to play important role in stimulating the reaction, and as a result, 97.32% Cu2+ was removed from the solution under Si/Cu molar ratio of 100. Even at a high concentration of sulfuric acid up to 4.6 mol/L, the copper removal percentage maintained a high value of 82.57%. Furthermore, in the sulfate solutions containing several other heavy metals of Zn, Mn, Ni, Cd, Co, Fe etc., the reduction reaction by zero-valent silicon occurred only on Cu2+ with other heavy metal ions remaining in the solutions. The feasibility of this technology has been verified by treating a leaching solution of NiS mineral, from which copper has been removed selectively from nickel, iron etc. This research may serve another purpose for applying waste silicon from the solar energy devices after lifetime in the future.