Application of sulfate reduction for the biological conversion of anglesite (PbSO4) to galena (PbS)

In a bench scale trial biological sulfate reduction was applied to convert anglesite (PbSO4) to galena (PbS). Anglesite is a main constituent in waste fractions such as lead paste from spent car batteries or residues from (in)direct leaching processes. The goal of this study was to develop a technology to decrease lead (Pb) emissions by converting PbSO4 from a waste fraction to PbS, which can be recovered using electrochemical processes. The conversion of PbSO4 to PbS is based on the biological reduction of sulfate and the consequent precipitation of PbS. 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-containing influent. The reactor was seeded with biocatalyst from several full-scale reactors. PbSO4-containing residue was added batch-wise when the formation of sulfide started. The residue contained mainly PbSO4 (51.7%), sulfate (SO42−, 19.9%) and elemental sulfur (S0, 15.1%). PbS precipitates in the bioreactor due to the near-neutral pH at which the sulfate reduction process is carried out. From the electron balance and chemical analyses it was concluded that both sulfate and sulfur present in the residue were biologically reduced. The formation of PbS was confirmed by the increased Pb:O ratio in the sludge (1:0.1) relative to the Pb:O ratio in the PbSO4-containing residue (1:3.3). A potential large-scale application is proposed.