Characterization of cadmium biosorption by cadmium-resistant strains: Equilibrium, kinetics, and thermodynamics

Abstract

Abstract In this paper, six cadmium (Cd) resistant strains were used to find the optimal conditions and understand the biosorption process of strains. Influences of pH, temperature, initial Cd2+ content, bacterial dose, and treatment time on Cd2+ biosorption were investigated. The key mechanism of Cd2+ biosorption by selected microbes was preliminarily determined by examining the biosorption process using isothermal biosorption and kinetic models. The strain showed best Cd2+ removal effect at initial Cd2+ content of 50 ~ 100 mg·L-1, pH 7 ~ 9, 30°C temperature, and adsorbent dose of 0.01 g (Cd-6, Cd-7), 0.04 g (Cd-5), and 0.08 g (Cd-1, Cd-2, and Cd-3). The removal efficiency at these conditions was found to be above 90%. The equilibrium state was observed after 120 min of culture time. In six strains, the Cd2+ biosorption obeyed the Langmuir biosorption model, intra-particle diffusion model, and quasi-second-order kinetic model. This suggested that Cd2+ was absorbed by the six strains through monolayer biosorption. Moreover, chemical biosorption was found to be the major restricting factor for the biosorption rate, along with intra-particle diffusion. The six strains Cd2+ biosorption, with spontaneous endothermic reaction below 30°C and spontaneous exothermic reaction above 30°C. This study provides valuable strain resources and data support for the remediation of soil having high concentration of Cd.