Comparative Study of Sulfide Precipitation Methods for Zinc Recovery from Sulfuric Acid Leach Solutions of Oxidized Zinc Ores

Selective zinc recovery from pregnant leach solutions obtained by sulfuric acid leaching of oxidized zinc ores is an important task in hydrometallurgy. This study comparatively evaluated zinc sulfide precipitation using gaseous H2S and Na2S solution and investigated the effects of pH and temperature on zinc recovery and precipitate characteristics. The thermodynamic feasibility of ZnS formation was assessed using Eh–pH diagrams of the Zn–S–H2O system at 25, 40, and 60 °C. The diagrams showed a ZnS stability region throughout the investigated temperature range. Using gaseous H2S at a final pH of 1.25 and 25 °C resulted in 96.8% zinc precipitation, a residual Zn concentration of 1.0 g/L, and a precipitate containing 57.2 wt.% Zn, corresponding to a calculated ZnS content of 85.3 wt.%. Using 20 wt.% Na2S at pH 2.25–2.30 and 50–60 °C resulted in 98.1% zinc precipitation, a residual Zn concentration of 0.028 g/L, and a precipitate containing 49.8 wt.% Zn, corresponding to a calculated ZnS content of 74.2 wt.%. Na2S provided more complete zinc recovery, whereas H2S produced a higher-grade sulfide precipitate with better filtration properties. These results provide a basis for selecting the sulfidizing reagent and operating conditions for zinc recovery from oxidized zinc ore leach solutions.