Heavy metal adsorption with biogenic manganese oxides generated by Pseudomonas putida strain MnB1

Abstract

Biogenic Mn oxides (BMO) have attracted a great attention recently, due to their high heavy metals adsorption capacity. However, the characteristics of the heavy metals adsorption by BMO have not been explored in depth. In this study, nano-sized and poorly crystalline BMO was generated by Pseudomonas putida MnB1, and the heavy metals adsorption by BMO was investigated based on isotherm and kinetic studies. The adsorption capacities of BMO for Pb(II), Cd(II), and Zn(II) were 7–8 times higher than abiotic Mn oxide (i.e., birnessite). The results of the equilibrium adsorption study using several isotherm models showed that adsorption of Pb(II), Cd(II), and Zn(II) on BMO surfaces is a chemical adsorption. The adsorption of Pb(II) and Zn(II) was homogeneous but that of Cd(II) was heterogeneous, probably due to the contribution of ion exchange. Among three heavy metals, Pb(II) was preferentially adsorbed and the adsorption was faster than others. The adsorption capacity of heavy metals by BMO increased as pH increased and ionic strength decreased. It also increased as the temperature increased, indicating the adsorption is endothermic. The results of this study indicate that BMO is an excellent adsorbent due to the abundant vacancies in its amorphous structure.