High-purity recycling of hematite and Zn/Cu mixture from waste smelting slag

In this study, Zn/Cu-bearing smelting slag was recycled via an integrated acid dissolution and hematite precipitation method. The slag was dissolved in nitric acid to generate an acid solution containing 23.5 g/L Fe, 4.45 g/L Zn and 2.81 g/L Cu, which was subjected to hydrothermal treatment with the addition of levulinic acid (LA). More than 99.95% of the initial Fe content was removed as hematite particles with diameters of approximately 200 nm, and the residual Fe concentration in the acid was 0.43 mg/L. The generated hematite contained 97.3% Fe2O3, 0.64% ZnO and 0.58% CuO. Greater than 99% of the initial Zn and Cu was retained in the acid and further precipitated as Zn/Cu-bearing solids by adjusting the solution pH to 9. The precipitated Zn/Cu-bearing solids contained 33.6% Zn and 21.7% Cu, whereas the Fe content was less than 0.2%. This paper is the first report of an environmentally friendly approach for recycling smelting slag without generating any hazardous waste.