Adsorption of 60Co radionuclides from aqueous solution by raw and modified bentonite

Bentonite and formaldehyde modified-bentonite (MF-bentonite) were tested for removal of the radioactive isotope Co-60. The two adsorbents were characterized (FTIR spectroscopy and scanning electron microscope) before and after modification. Some enhancement was obtained in the mesopore region due to impregnating the bentonite with 35% of formaldehyde solution and the modified sample had better adsorption performance. Furthermore, the adsorption capacity of MF-bentonite increased by increasing the quantity of formaldehyde deposited on the surface. The adsorption potential of bentonite and MF-bentonite for the removal of Co-60 radionuclide from radioactive waste solutions has been investigated. The influence of pH, contact time, adsorbent dosages and temperature is reported. Pseudo first-order and pseudo second-order kinetic models were used to analyze the adsorption rate data. The pseudo second-order model was found to best correlate the kinetic data. Adsorption isotherms were determined to assess the maximum adsorption capacity of bentonite and MF-bentonite. The Langmuir model fitted the data reasonably well in terms of regression coefficients. Adsorption studies were also performed at different temperatures to obtain the thermodynamic parameters. The numerical value of Delta G(0) decreased with an increase in temperature, indicating that the adsorption is more favorable at higher temperature. The positive values of Delta H-0 corresponded to the endothermic nature of adsorption processes. (C) 2008 Elsevier B.V. All rights reserved.