Removal of chromium [Cr(VI)] from contaminated solutions by using biogenic ferrous iron in bioreduced minerals

Abstract

Abiotic reduction of Cr(VI) by ferrous iron was investigated in the presence of bioreduced goethite, hematite and two types of nontronites (NAU-1 and NAU-2). Bioreduction experiments were performed with structural Fe(III) in the minerals as sole electron acceptor, lactate as sole electron donor, Shewanella putrefaciens CN32 cells as a mediator and anthraquinone-2,6-disulfate (AQDS) was added as an electron shuttle. The results showed that bioreduction of Fe(III) occurred in all the studied minerals and the reduction increased with the application of AQDS. The maximum (21%) and minimum (3%) bioreduction of Fe(III) occurred in the nontronite (NAU-2) and hematite, respectively. The removal of Cr(VI) for all studied minerals was increased with decreasing pH. Most of the abiotic reduction of Cr(VI) by biogenic Fe(II) at pH 7 was observed in the bioreduced NAU-2 treatment with a maximum efficiency about 75%.