Surface interactions of Cs+ and Co2+ with bentonite and perlite

Abstract

During nuclear weapon tests, any accidents in the nuclear power plants or nuclear fuel cycle generating, considerable amounts of radioactive waste can release very hazardous radionuclides such as137Cs and 60Co to the geosphere. Both 137Cs and 60Co have long half- lives as 30.2 and 5.27 years, respectively, and these radiotoxic elements can give hazards to biota or human being in the environment. The isolation of radiotoxic elements from environment is efficiently and low-costly achieved by the adsorption of these radionuclides onto the clay or oxide surfaces. In this study, bentonite and perlite was used as adsorbents for the removal of Cs+ and Co2+ from aqueous solution. In this concern, the adsorption behavior of Cs+ and Co2+ onto either bentonite or perlite as a function of pH, time, initial metal concentration, temperature, ionic strength and humic acid (HA) concentration was studied by batch adsorption technique. The adsorption isotherm data were interpreted by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Bentonite attained maximum adsorption capacity for Cs+ as 83.3 mgg-1 and for Co2+ mgg-1 as 15.9 whereas perlite attained capacity values for Cs+ as 1.22 mgg-1 and for Co2+ as 1.83 mgg-1. HA had little influence on adsorption capacity of bentonite for Cs+, but it greatly affected the adsorption capacity of perlite for Cs+. Furthermore, HA increased the adsorption capacity of bentonite for Co2+, whereas it decreased adsorption capacity of perlite for Co2+. Thermodynamic parameters, standard enthalpy (ΔHo), standard entropy (ΔSo) and standard free energy (ΔGo), for the adsorption of Cs+ and Co2+ were determined at four different temperatures of 288 K, 298 K, 318 K and 338 K. All adsorption processes, except Cs+ adsorption onto bentonite, showed the endothermic nature with the positive ΔHo values. The negative values of ΔGo and the positive values of ΔSo indicated the feasibility and spontaneous nature for all adsorption processes and more disordered form after adsorption.