Adsorption characteristics of lead (Pb2+) and cadmium (Cd2+) by an isolated bacterium from soil samples obtained from a tungsten mine

Eight bacterial strains were isolated from lead-cadmium contaminated soil samples obtained from a Tungsten mine. Pb ²⁺ and Cd ²⁺ adsorption abilities of the isolated strains were screened. One isolate, referred to as Strains S, was selected for further study because of its relatively high adsorption ability. Five factors affecting adsorption of Pb ²⁺ and Cd ²⁺ were studied, namely, the initial concentration of Pb ²⁺ or Cd ²⁺, temperature, pH, biomass of Strains S, and adsorption time. Results indicated that Strains S best adsorbed Pb ²⁺ when the initial concentration of Pb ²⁺ was 100 mg/L, temperature was 35°C, pH was 6.5, dosage was 0.1 g, and adsorption time was 20 min. In contrast, Strain S best adsorbed Cd ²⁺ at an initial Cd ²⁺ concentration of 100 mg/L, temperature of 40°C, pH 6.5, dosage of 0.1 g, and adsorption time of 20 min. The experimental data were fitted to the Langmuir and Freundlich adsorption isotherm models, and the results indicated that the Langmuir model better fitted the experimental data. The results of infrared spectroscopy revealed that the functional groups involved in adsorption of Cd ²⁺ and Pb ²⁺ were -OH, -NH ₂, -S=O and -P=O. Using 16S rDNA sequencing and phenotypic properties test, Strains S was identified as Enterobacter sp.