Adsorption behavior of ruthenium ions on activated charcoal from nirtic acid medium

The adsorption behavior of ruthenium ions onto activated charcoal has been studied in relation to equilibration time, ruthenium ions concentration and temperature from nitric acid solutions of 0.001, 0.01 and 0.1 M concentration as adsorptive medium. It was observed that low acid concentration favors the adsorption and the extent of ruthenium ions adsorption on activated charcoal lie in the order of: 0.001 M > 0.01 M > 0.1 M nitric acid solutions. The general ruthenium ions adsorption process is essentially independent of nitric acid solution concentration. However, variation in nitric acid solution concentration influences the amount of ruthenium ions adsorbed, which decreases with the increase in nitric acid solution concentration. The adsorption equilibrium is attained within 70 min and the ruthenium ions adsorption process is predominately by diffusion. The overall rate process appears to be influenced by both boundary layer diffusion and intraparticle diffusion, and the calculated values of intraparticle diffusion rate constant are 3 x 10(-5) 4 x 10(-5) and 5 x 10(-5) at 0.001, 0.01 and 0.1 M nitric acid solution, respectively. The adsorption isotherms for ruthenium ions are L2 type and the experimental adsorption data obtained were found to correlate well with the Langmuir and the Dubinin-Radushkevich isothermal equations. Values of adsorption energy, E-a, calculated from the DR isotherm, lies in the range of 5.27-5.50 kJ mol(-1) indicate that the ruthenium ions adsorption process on activated charcoal is physical in nature and the change in nitric acid solution concentration does not influence the nature of the adsorption process. Increase in temperature induced a positive effect on ruthenium ions adsorption indicating an endothermic adsorption process. Thermodynamic parameters Delta G, Delta H and Delta S were computed from the equilibrium constant, K-C and is interpreted. (c) 2006 Published by Elsevier B.V.