Theoretical and experimental study of Au(III)-containing wastewater treatment using magnetotactic bacteria

A magnetotactic bacterial isolate was found a good biosorbent for removing Au(III) from wastewater in our preliminary studies. In this study, the process and the mechanism of biosorption were investigated from several aspects, including surface complexation, ion exchange, electrostatic attraction, and oxidation-reduction reaction. According to the water treatment experiments, these bacteria were confirmed to quickly purify the wastewater-containing Au(III). The results showed that the role of ion exchange was a secondary mechanism in the biosorption process. The molecular dynamics simulation revealed that electrostatic attraction and thermal motion had effects on the motion of Au(III), and the electrostatics of different functional groups was dissimilar. Using chemical modified and unmodified biomass as absorbents, it was found that the functional groups (including carboxylate, hydroxyl, and phosphoryl groups present on cell wall) were the main reason for the adsorption. The experimental data could be well fitted with the surface complexation model. The analyses from X-ray photoelectron spectroscopy indicated that the reduction of Au(III) to Au(I) and Au(0) on the biomass surface occurred. Comprehensive analysis of the above, a two-stage process model was built: (1) in the electric field of charged cells, metal ions were attracted. This process was the physical adsorption of multimolecular layer; (2) the metal ions arrived the cell surface were chelated or complexed with functional groups, accompanied by ion exchange and reduction reactions.