Solid-phase controls on lead partitioning in laboratory bioleaching solutions

The purpose of the work was to examine the co-precipitation of Fe(III) and Pb(II) in Acidithiobacillus ferrooxidans cultures under ambient temperature conditions. The competitive formation of plumbojarosite (PbFe6(SO4)4(OH)12) and anglesite (PbSO4) was of particular interest with respect to defining the phase(s) controlling Pb solubility. The medium contained no K+ and a low level of 6.06 mM NH4+. Precipitates were prepared in two phases. In the first phase (8 days), A. ferrooxidans cultures oxidized ferrous iron to ferric iron (pH 2.4), which partially precipitated as schwertmannite (Fe8O8(OH)5.5(SO4)1.25). In the second phase, lead nitrate (up to 100 mmol Pb/l) was added to the schwertmannite-containing culture solutions, and the suspensions were held for an additional 22 days. X-ray diffraction analysis indicated that lead precipitated as anglesite, and ferric iron was associated with schwertmannite and hydronium jarosite. No characteristic X-ray diffraction peaks for plumbojarosite were evident.