Biosorption of Cd, Cu, Ni, Mn and Zn from aqueous solutions by thermophilic bacteria, Geobacillus toebii sub. sp. decanicus and Geobacillus thermoleovorans sub.sp. stromboliensis: Equilibrium, kinetic and thermodynamic studies.

Biosorption of each of the ions Cd(2+), Cu(2+), Ni(2+), Zn(2+) and Mn(2+) on Geobacillus toebii sub.sp. decanicus (G1) and Geobacillus thermoleovorans sub.sp. stromboliensis (G2) in a batch stirred system was investigated. The equilibrium adsorptive quantity was determined to be a function of the solution pH, contact time, biomass concentration, initial metal concentrations and temperature. The results obtained from biosorption experiments are used to understand the driving forces that govern the interaction between metal ions and a biosorbent. The experimental results were fitted well to the Scatchard plot, Langmuir, Freundlich, Dubinin-Radushkevich (D-R) isotherms. According to the parameters of the Langmuir isotherms, the maximum biosorption capacities of Cd(2+), Cu(2+), Ni(2+), Zn(2+) and Mn(2+) for G2 were 38.8, 41.5, 42, 29 and 23.2 mg/g, respectively, while 29.2, 48.5, 21, 21.1 and 13.9 mg/g for G1, respectively. The mean free energy values evaluated from the D-R model indicated that the biosorptions of studied heavy metal ions onto bacteria were taken place by physical interaction. The biosorption mechanisms of studied metal ions on to the biosorbents were analysed by FT-IR spectra of G1 and G2 with and without metal ions. The first order and second order coefficients were obtained at 298, 308, 318 and 343 K. The experimental results were used to calculate the thermodynamic parameters.