Enhancement of arsenic mobility by Fe(III)-reducing bacteria from iron oxide minerals

Batch bioleaching experiments were conducted using the Fe(III)-reducing bacteria, Shewanella putrefaciens CN32, to determine the effect of the Fe(III) reduction on As mobilization. For this purpose, Fe(III) reduction experiments were also performed to deduce the optimum conditions of the bioleaching experiment. In the Fe(III) reduction experiment, insoluble Fe(III), such as synthesized poorly and well crystalline hydrous ferric oxide (HFO), was rarely used as electron acceptor by S. putrefaciens. However, the addition of a humic substance (2,6-anthraquinone disulfonate, AQDS) greatly increased iron reduction capacity (5–10 times) under the same conditions. For the poorly and well crystalline HFO, the effective carbon sources as electron donor were acetate and lactate, respectively. In bioleaching experiments using the two types of synthesized Fe(III) oxide minerals bearing As (poorly crystalline HFO and well crystalline HFO), S. putrefaciens enhanced the As mobilization, with 1,870 and 1,460 mg kg−1 of As released in the poorly and well crystalline HFO, respectively. From a correlation coefficient analysis between reduced Fe and released As, the R2 values were 0.8612 and 0.9115, respectively. These results indicated that the reduction of Fe(III) can enhance the As mobilization. Therefore, bioleaching using the Fe(III)-reducing mechanism can be useful for remediation of As contaminated soil.