Application of Sulfate Reduction for the Biological Conversion of Anglesite to Galena

Abstract

In a bench scale trial biological sulfate reduction was applied to convert anglesite (PbSO4) to galena (PbS). Anglesite is a main constituent of waste fractions such as the residue from an indirect leaching process or in lead paste from spent car batteries. The goal of this study was to develop a technology to decrease the lead (Pb) emissions by converting PbSO4 from a waste fraction into PbS, which can be recovered from the waste fraction using a flotation process or an electrochemical process. The conversion of anglesite to galena is based on the biological sulfate reduction process and a metal precipitation process. First sulfate is biologically reduced to sulfide. Secondly, the Pb2+ from the PbSO4 reacts chemically with the sulfide resulting from the first reaction. A bench-scale reactor was started up using sulfate- and sulfur-containing influent. The reactor was seeded with biocatalyst from several full-scale reactors. Anglesite-containing residue was added batch-wise when the formation of sulfide started. The residue contained mainly PbSO4 (51.7%), sulfate (SO4 2-, 19.9%) and elemental sulfur (S0, 15.1%). Galena precipitates in the bioreactor due to the near-neutral pH at which sulfate reduction is carried out. During the experiment a surplus of sulfide relative to Pb was maintained to prevent the formation of PbCO3 and the accompanying pH decrease that would unavoidable result in the inhibition of the biocatalyst. Both sulfate and sulfur present in the residue were biologically reduced. The formation of PbS was confirmed by the increased Pb:O ratio of the sludge (1:0.03) relative to the Pb:O ratio of the residue (1:0.3). A potential large-scale application is proposed.