Study of Co (II) and Cr (VI) Adsorption from Aqueous Solution by CaCO/sub 3/

Calcium carbonate was synthesized, characterized, and utilized in water purification. The adsorption of Co(II) and Cr(VI) ions from aqueous solutions in CaCO/sub 3/ was studied as a function of different optimal conditions, such as contact time, initial metal ion concentration and temperature, at fixed solid/solution rations by using batch adsorption experiments. Characterization studies confirmed that synthesized CaCO/sub3/ is crystalline with a high phase purity and specific surface area of 9.68 m2/g. The kinetic processes of the systems were described in order to provide a more clear interpretation of the rate of adsorption mechanism. Langmuir, Freundlich and Dubinin-Radushkevich isotherms were used as the model adsorption equilibrium data. The maximum amounts (qmax) of Co(II) and Cr(VI) adsorbed in CaCO/sub 3/ were 2.29 and 1.06 x 10-2 mg/g, respectively. The pseudo-second order kinetic model was found to better fit the experimental data measured for both metallic ions. The adsorption processes of both systems were adjusted by the Freundlich isotherm. The adsorption energies calculated from Dubinin-Radushkevich isotherm show that the adsorption processes were physical in nature. Based on the thermodynamic data of delta H degree, delta S degree and delta G obtained, it can be concluded that the processes of Co(II) and Cr(VI) ion adsorption in CaCO/sub 3/, were endothermic, spontaneous, and are the result of physical adsorption process. These features make the CaCO/sub 3/ a potential adsorbent for both Co(II) and Cr(VI) adsorption from wastewater. (author)