Recovery of valuable elements from copper slag through low-temperature sulfuric acid curing and water leaching

Copper slag, a byproduct of copper smelting, contains valuable metals (Cu, Fe, Zn, and Mn) and harmful elements (As, Cd). Given the annual production of approximately 30 million tons of copper slag, environmentally friendly treatment methods are crucial. This study explored the recovery of valuable elements from copper slag using a low-temperature sulfuric acid curing and water leaching process. Thermodynamic calculations showed that between 25 and 400 degrees C, the Gibbs free energy of reactions between the main components of copper slag and sulfuric acid was negative, indicating that these reactions were thermodynamically favorable and proceed spontaneously. Silicic acid formed during curing decomposes into insoluble SiO2, thereby improving the solution's filtration performance. The sulfuric acid dosage was identified as the key factor affecting leaching efficiency. The optimal conditions were a sulfuric acid dosage of 1.5 times the theoretical amount, curing at 200 degrees C, water addition at 60 % of the slag's dry weight, and 0.5 h curing time. Under these conditions, leaching rates for Co, Cr, Cu, Fe, Mg, Mn, and Ni exceeded 80 %, while Pb and Si had poor leachability (< 3 %). Further water leaching experiments showed minimal influence from leaching time, temperature, liquid-solid ratio, and stirring speed. Microscopic analysis revealed significant structural changes, with FeSO4<middle dot>H2O, FeH(SO4)(2)<middle dot>H2O, and SiO2 as the main phases in the cured products. The water leaching residue mainly consisted of amorphous SiO2 and small amounts of unreacted magnetic black slag (Fe3O4 and other iron oxides). This process effectively recovered valuable elements, offering technical support for the resource recovery and environmental management of copper slag.