The adsorption of Cd(II) ion from aqueous solutions by Bacillus subtilis and Escherichia coli immobilized in agarose gel was studied in a batch system. The adsorption experiments were performed under various conditions such as different initial concentrations, pH, contact time and temperature. It was found that the equilibrium of the process was reached after 60 min. The optimum pH value was found to be 6. The adsorption capacity of the adsorbent were found to increase with temperature. Bacillus subtilis immobilized in agarose gel was found to posses relatively high sorption capacity than Escherichia coli immobilized in agarose gel. The data obtained from the equillibrium experiment were analyzed using Langmuir, Freundlich and Temkin isotherm models. The Langmuir equation describe adsorption isotherm of Cd(II) with high correlation coefficients, and better than Temkin and Freundlich model. According to the Langmuir model, the maximum uptake capacities of Bacillus subtillis for Cd(II) at 450C was 2.94 mg/g and that of Escherichia coli at 450C was 2.84 mg/g. Various thermodynamic parameters, such as G, H, S were calculated and the negative value of G obtained indicate the process was spontaneous, positive value of H confirms the reaction to be endothermic and positive value of S show that the degree of freedom increase at the solid-liquid interface during the adsorption process . The pseudo first order and pseudo second order and intra-particle kinetic models were used to describe the kinetic data. The kinetic data fitted with the pseudo second order kinetic model with high correlation coefficient and better than the pseudo-first order and the intraparticle diffusion model.
