Study of Selective Recovery of Lead- and Zinc-Based Products from Leachate After Alkaline Leaching of Copper Shaft Furnace Dust

A leachate from alkaline leaching of copper shaft furnace (CSF) dust as a hazardous waste was used in this study for performing a chemical precipitation experiment of lead, zinc, and copper. The precipitation processes for lead, zinc, and copper were theoretically optimized based on a thermodynamic study. To determine suitable operating conditions, metal phase stability, reaction mechanisms, and precipitation order were analyzed using the Hydra/Medusa and HSC Chemistry v.10 software packages. In the first experimental stage, treatment of the alkaline leachate resulted in the formation of insoluble lead sulfate (PbSO4), while zinc remained dissolved for subsequent recovery. In the second stage, the zinc-bearing solution was treated with Na2CO3, producing a mixed zinc precipitate consisting of Zn5(OH)6(CO3)2(s). This study determined that the optimal conditions for chemically precipitating lead as PbSO4 from alkaline leachate (pH 13.5) are the use of 1 mol/L H2SO4 at pH 3.09 and Eh 0.22 V at 25 °C, while optimal zinc precipitation from this solution (pH 3.02) is achieved with 2 mol/L Na2CO3 at pH 9.39 and Eh –0.14 V at 25 °C. A small amount of copper present in the solution co-precipitated and was identified as an impurity in the zinc product. The chemical composition of the resulting precipitates was confirmed by SEM–EDX analysis.