Induced biotransformation of lead (II) by Enterobacter sp. in SO₄-PO₄-Cl solution

Pb is a toxic heavy metal in contaminated soil and water, resulted from industrial activities, mine exploration, etc. Phosphate solubilizing bacteria are able to secrete organic acids and further to enhance the solubility of phosphates. Enterobacter. sp and geological fluorapatite (FAp) were applied to investigate the biotransformation of Pb²⁺ in solution with SO₄^2-, PO₄^3-, and Cl^- species by ICP-OES, ATR-IR, XRD, and SEM. Enterobacter. sp can lower pH of the medium to ∼4. Meanwhile, >90% mobile Pb (declining from 1000 to 30 ppm) was immobilized via the combination of Enterobacter. sp and FAp. With the addition of FAp and Pb, pyromorphite was precipitated, but with relatively low content. In contrast, abundant anglesite mineral was formed in such weakly acidic system. These anglesite crystals can even absorb phosphates particles onto their surface. Additionally, geochemical modeling confirms the formation of anglesite and cerussite under weekly acidic and alkalic condition respectively, especially when H₂PO₄^- concentration <10^-8 mM. Furthermore, the presence of Cl^- in solution leads to the formation of chloropyromorphite when H₂PO₄^- concentration >10^-12 mM, especially under neutral environment. This study explored the biotransformation of Pb in SO₄-PO₄-Cl aqueous system and hence provided guidance on bioremediation of Pb by bacteria and FAp.