An unconventional approach for the efficient recovery of iron, cobalt, copper and silicon from copper slag

High-grade heavy metal elements in copper slag (CS) are worth recovering. Unfortunately, the high viscosity of leaching solution, low leaching efficiency, difficult filtration and low separation efficiency of valuable components exist in the traditional sulfuric acid leaching process. In this study, the above problems are solved by sulfuric acid pretreatment + curing + water leaching. Moreover, iron, cobalt and copper ions in solution are separated by stepwise precipitation. The final iron, cobalt, copper and silicon recoveries are 99.01 %, 98.45 %, 93.13 % and 99.52 %, respectively. Thermodynamic calculations show that H₄SiO₄ can be converted to insoluble SiO₂ to improve filtration properties under curing conditions of sulfur dioxide partial pressures of 10^-20∼0 atm, oxygen partial pressures of 10^-20∼0 atm and 400-600k. Simulation studies of the phase equilibria of the components of the leach solution by Visual MINTEQ showed that the oxidation of Fe²⁺ to Fe³⁺ is necessary for the removal of Fe²⁺ from the solution by precipitation. This study provides a new idea for the efficient utilization of CS.