Adsorption of 60Co2+ on hydrous manganese oxide powder from aqueous solution

Hydrous manganese oxide (HMO) was synthesized and its ability to sorb 60Co2+ from aqueous solution was studied under static conditions as a function of contact time, cobalt concentration (10-2-10-7 M), temperature (303-333 K) and pH of adsorptive solution (2.2-11.4). X-ray diffraction was used in characterization of synthesized HMO. Low concentration of 60Co2+ solution, high pH and high temperature were the most favorable conditions for the adsorption process. The results show that the removal process is complete in 40 minutes, obeys a first order rate law and can be described using the Freundlich adsorption model. The standard enthalpy of the system was ΔH0 = 12.5 ± 0.2 kJ mol-1 and cobalt desorption indicates that the uptake process proceeds via cation exchange. The removal of cobalt ions by HMO appears to be endothermic and irreversible. The values of calculated ΔG0 and ΔS0 were -17.0 ± 3.0 kJ mol-1 and (9.8 ± 0.2) x 10-2 kJ K-1 mol-1 respectively, this indicates spontaneity of the process and the degree of freedom of ions is increased by adsorption. (orig.)