Removal of Zinc from Aqueous Solution by Metal Resistant Symbiotic Bacterium Mesorhizobium amorphae

Abstract

Biosorption of zinc by living biomasses of metal resistant symbiotic bacterium Mesorhizobium amorphae CCNWGS0123 was investigated under optimal conditions at pH 5.0, initial metal concentrations of 100 mg L−1, and a dose of 1.0 g L−1. M. amorphae exhibited an efficient removal of Zn2+ from aqueous solution with maximum biosorption capacity of 120.85 mg g−1. Moreover, more than 70% Zn2+ could be recovered from Zn-loaded biomass at pH 1.0. Both the Langmuir and Freundlich isotherms provided a better fit to experimental data for Zn2+ sorption with correlation coefficients of 0.9885. Kinetics models suggested there was more than one step involved in the Zn2+ sorption process, while a pseudo-second-order model was more suitable to describe the kinetic behavior accurately, indicating a chemisorption process. Carbonyl, amino, carboxyl, and aromatic groups were responsible for the biosorption of Zn2+ by M. amorphae. Cellular deformation, precipitate, and damage were found after Zn2+ treatment. Competitive sorption revealed Cu2+, Cd2+, and Ni2+ were competed with Zn2+ for adsorption sites with the order: Cu2+ > Cd2+ >> Ni2+.