Kinetic, Isothermal and Equilibrium Studies of the Biosorption of Pb(II) from Solution by a Moss (Stereophyllum radiculosum).

In this work, biosorption of Pb(II) ions on Stereophyllum radiculosum, a moss, was investigated in batch mode. The equilibrium adsorptive quantity was determined to be a function of the solution pH, contact time, initial concentration of lead ions, and temperature. The study on pH showed that the biosorption is pH dependent. The optimum pH for the biosorption was pH 6. Maximum biosorption was obtained within the first 50 min. of the process. The kinetic study showed that the pseudo-first-order model correlated with the experimental data better than the pseudo-second-order model examined. The biosorption isotherm obtained fitted well into the Freundlich and Langmuir isotherms. The free energy change obtained for the biosorption of Pb(II) at 21 o C, initial Pb(II) concentration of 100mgL -1 and pH 6 is –9.09 kJmol -1 . The high negative value of the standard free energy change (ΔG ) indicates spontaneous nature of the process. The calculated values of ΔH and ΔS are negative, showing that the process is exothermic and the degree of disorder reduces with increase in temperature, respectively.