Adsorption And Desorption Of Silver Using The Deep-sea Bacterial Biogenic Manganese Oxides

Marinobacter sp. MnI7-9 was a highly efficient manganese-oxidizing bacterium isolated from the deep-sea manganese nodules in Indian Ocean. Manganese(Ⅱ) is oxidized to manganese(Ⅳ) oxides by its metabolic process. The biogenic manganese oxides generated by MnI7-9 were of special crystal form with more octahedron voids in the structure and larger surface area compared with chemistry synthetic manganese oxides. Therefore, the biogenic manganese oxides have high chemical reaction activity and great adsorption capacity. At different conditions, the adsorption of Ag+by the biogenic manganese oxides produced by MnI7-9, in comparison with the chemical synthesized manganese oxides, was studied in this project. Then a method to desorption was found and the mechanism of adsorption was discussed.The results of this study showed that the biogenic manganese oxides generated from strain MnI7-9 had a stronger adsorption capability for Ag+ compared to chemical synthesized manganese oxides especially at high concentrations of Ag+. The adsorption using both of the materials were suited for pseudo-second-order and Langmuir models. Based on the models, the maximum adsorption capacity of biogenic manganese oxides and chemical synthesized manganese oxides were 8.097 mmol/g and 0.787 mmol/g at 28 ℃, respectively. Both adsorption reactions were endothermic (ΔHθ>0), occured spontaneously (ΔGθ<0) and were driven by entropy (ΔSθ>0). The ΔHθ of the biogenic manganese oxides was 56.69 kJ/mol which showed the adsorption mainly belonged to chemical adsorption, while that of chemical synthesized manganese oxides was 2.287 kJ/mol which indicated the process was close to physical adsorption.Manganese oxides played an important role in the adsorption of Ag+. The adsorption ratio of the biogenic manganese oxides was higher than that of bacterium without manganese oxides under different conditions in the experiments. The results of XRD/FT-IR/SEM/XPS all suggested that the shape and components of biogenic manganese oxides have changed after adsorption. The Ag(0) appeared and P-H bond disappeared. Whereas after adsorption there was little change in the image of the bacterial cells without manganese oxides and chemical synthesized manganese oxides. The above indicated the mechanism of adsorption on biogenic manganese oxides was different from that of bacterium only and chemical synthesized manganese oxides. Through the analysis of XPS, Ag(I) and Ag(0) existed on the surface of biogenic manganese oxides. And Ag(0) took up 15.29%。In addition, Na2S and nitric acid could desorb the adsorbed silver. The desorption ratio was close to 100%. Cu2+、Fe2+、Ca2+ and 2-anthraquinone sulfonate were added in the culture medium to accelerate the efficiency of manganese oxidation and the adsorption ratio of products have grew up which was close to 99%.This study provides basic knowledge and valuable applications of biogenic manganese oxides produced by a deep sea bacterium for the removal of Ag+ from wastewater.