Bacteria affect Sb(III, V) adsorption and oxidation on birnessite

Abstract

The adsorption-oxidation of Sb on manganese oxide plays an important role in controlling Sb mobility and fate in soils and sediments. Widespread organic substances such as microbes may greatly affect this process, and deserve a careful investigation. This study examines the adsorption and oxidation of Sb(III, V) on birnessite, a typical manganese oxide, with and without Bacillus cereus cells. Adsorption isotherms were conducted to explore the adsorption capacity of Sb to the birnessite–bacteria composite. X-ray photoelectron spectroscopy (XPS) was applied to determine the valence state of Mn and the adsorbed Sb species. The SEM results show that birnessite adheres to the outer surface of bacterial cells, and the aggregation of minerals occurs to a lesser extent in the presence of cells. Batch adsorption results show a much larger Sb adsorption on individual birnessite than on bacteria, and the measured Sb adsorption to the birnessite–bacteria composite is larger than that predicted assuming additive, i.e., the sum of the end-member metal adsorptivities. On birnessite, Sb(III) is predominately oxidized to Sb(V) according to the XPS analysis, and the presence of bacteria hinders this oxidation reaction. We propose that microbe−birnessite association favors the immobilization of Sb on solid phases, but can inhibit the oxidation of Sb(III) to Sb(V), which is of great significance for evaluating the toxicity, bio-availability, and mobility of Sb in both natural and contaminated environments.