Bioleaching and selective biorecovery of zinc from zinc metallurgical leach residues from the Três Marias zinc plant (Minas Gerais, Brazil)

Abstract

BACKGROUND Gradual depletion of high-grade ores for heavy metals has encouraged industries to search for alternative methods to recover metals. Wastes generated from metallurgical industries can be used as a secondary resource as it contains high concentrations of metals. RESULTS The bioleaching kinetics and biorecovery of zinc from Zn-plant leach residues (ZLR), collected from a currently operating Zn-plant in Tres Marias (Minas Gerais, Brazil) were investigated using sulfuric acid producing Acidithiobacillus thiooxidans (A. thiooxidans). Response surface methodology (RSM) with full factorial central composite design (CCD) was applied to optimize Zn bioleaching by A. thiooxidans. The experiments were performed by varying the initial elemental sulfur concentration (5–30 g L−1), pulp density (5–50 g L−1) and initial pH (3.0–4.0 pH units). More than 75% of Zn was extracted from ZLR by A. thiooxidans under optimized conditions (sulfur concentration 25.1 g L−1, pulp density 21.5 g L−1 and initial pH 3.3). The leaching efficiencies of culture supernatant (biogenic sulfuric acid) and chemical sulfuric acid were compared to understand the leaching kinetics. The Zn leaching kinetics of ZLR followed the shrinking core diffusion model. Zn was selectively recovered from the Fe-rich acidic bioleachate by biogenic sulfide precipitation. Fe was first removed (more than 85% of total Fe in the leachate) by adjusting the initial pH to 5.0, followed by selective Zn biorecovery. CONCLUSIONS Zn (>95%) was selectively recovered from Fe-depleted ZLR by biogenic sulfides (with 1:1, Zn:biogenic sulfide mass ratio). Biohydrometallurgy can be a potential alternative resource recovery strategy for the selective recovery of Zn from ZLR. © 2016 Society of Chemical Industry