Adsorption of lead and cadmium ions from aqueous solutions using manganoxide minerals

Removal of lead and cadmium ions from aqueous solutions by adsorption process was investigated. Low cost and locally available natural mineral of manganoxide mineral was used as an adsorbent. The kinetics of adsorption process data was examined using the pseudo-first-order, pseudo-second-order kinetics and the intra-particle diffusion models. The rate constants of adsorption for all these kinetics models were calculated and compared. The adsorption kinetics was best described by the pseudo second-order model. The Langmuir and Freundlich adsorption isotherm models were applied to the experimental equilibrium data at different temperatures. The experimental data well fitted to Langmuir isotherm model. The maximum adsorption capacities of manganoxide mineral for lead and cadmium ions were calculated from the Langmuir isotherm and were 98 and 6.8 mg/g, respectively. Thermodynamic parameters such as the change of Gibbs free energy, enthalpy and entropy of adsorption were also calculated and it was found that the lead and cadmium uptake reactions by manganoxide mineral were endothermic and spontaneous in nature. Therefore, manganoxide mineral can be used as adsorbents for lead and cadmium ions removal processes as an alternative natural mineral among the others.