Binding of Sb(III) by Sb-tolerant Bacillus cereus cell and cell-goethite composite: implications for Sb mobility and fate in soils and sediments

Abstract

Adsorption onto mineral and bacterial surfaces can profoundly affect the mobility and fate of dissolved ions in soils; however, currently, there is a poor understanding of antimony (Sb) adsorption onto mixture of these two sorbents. This study aims at investigating the adsorption of Sb(III) to an antimony-tolerant soil bacterium Bacillus cereus and cell-goethite binary composite under anaerobic condition. Adsorption isotherms and adsorption edges (pH 3–10) were conducted to explore the adsorption capacity of Sb(III) to goethite, bacteria, and the cell-goethite composite. X-ray photoelectron spectroscopy (XPS) was applied to determine the surface functional groups that are responsible for Sb adsorption. Scanning electron microscope shows that nano-particulate goethite is strongly adsorbed onto the cell surfaces to give a mineral film. The cell-goethite composite displays an additive Sb adsorption behavior, i.e., composite adsorptivity is the sum of the individual end-member metal adsorptivities (i.e., the additivity rule). Sb(III) adsorption to goethite, Bacillus cereus cells, and the cell-goethite composite is independent of pH. Using high-resolution XPS spectra, we identify the ferric hydroxyl functional groups of goethite and the carboxyl and amino/amide groups of bacteria responsible for Sb binding to the binary solid products. Moreover, the molecular binding mechanisms are very similar between the composite and the isolated end-member bacteria and mineral phases. Sb(III) adsorption to the bacteria-goethite conforms to a component-additive rule. Goethite component plays a more important role in Sb binding to the bacteria-mineral composite. New findings of this research suggest that it should be careful to use the universal adsorption rule for cations as previously suggested, to simulate anion adsorption to organo-iron oxide composite.