In this study, the removal of heavy metal ions from acid mine drainage (AMD) using natural zeolite (clinoptilolite), obtained from the Gordes region of Turkey, and synthetic zeolite (Na-4A) under different experimental conditions was investigated in an agitated vessel. The efficiency of zeolite as an adsorbent for the removal of heavy metals such as Zn (II), Cu (II), Mn(II) and Fe(III) from AMD has been determined at the different initial concentrations, zeolite amount, speed impeller and pH. Adsorption data have been interpreted in terms of Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich (DKR) equations. The results straightforwardly showed that the adsorption phenomena of heavy metals into clinoptilolite and synthetic zeolite are well described by the Langmuir isotherm in most of the cases. The agitated batch adsorber method was employed in order to find a correlation wherein the adsorption percentage was function of experimental conditions. The selectivity of the studied metals was determined as Fe>Mn>Zn>Cu using synthetic zeolite and Cu>Fe>Mn>Zn using natural zeolite. Synthetic zeolite exhibited about 10 times greater sorption capacities than natural zeolite. The sorption kinetics was tested for the first order reaction, intra-particle diffusion, pseudo-first order, and pseudo-second order reaction at different experimental conditions. The rate constants of sorption for all these kinetic models were calculated. Good correlation coefficients were obtained for the pseudo-second order kinetic model showing that metal ions uptake processes followed the pseudo-second order rate expression.
The batch sorption model, based on the assumption of a pseudo-second order mechanism, has been developed to predict the rate constant of sorption and the equilibrium capacity with the effect of initial metal ions concentration, mass of zeolite used, speed impeller and initial solution pH.