Preparation of ZnSO₄·7H₂O and Separation of Zinc from Blast Furnace Sludge by Leaching-Purification-Crystallization Method

抄録

Blast furnace sludge (BFS) is an industrial waste generated during ironmaking, which contains approximately 10% Zn, 25% Fe and 24% C and is a valuable secondary resource of zinc. In this study, ZnSO₄·7H₂O was produced using BFS by the combination of acid leaching, iron and calcium precipitation, concentration and crystallization. The effects of different factors and operation steps on zinc recovery were investigated, and the optimum parameters of the treatment process were obtained as follows: Acid leaching was carried out at 60°C for 10 min using sulfuric acid with the concentration of 150 g/L and a liquid to solid ratio at 3 mL/g; Iron precipitation was performed at 25°C using the liquid solution with pH value in a range of 4.0–4.4 and the H₂O₂ dosage of 60 mL/L; Calcium precipitation was conducted at 60°C for 40 min with the ZnF₂ dosage of 7.5 g/L. The recovery efficiency of zinc was approximately 95% and the purity of ZnSO₄·7H₂O in the product reached 99.57%. The obtained results indicate that the proposed process in this work can successfully recover Zn from BFS with high efficiency and short production route.