Adsorption equilibrium of zinc ions from aqueous solution by using modified clinoptilolite

Adsorption of Zn(II) ions from aqueous solution onto clinoptilolite has been investigated to evaluate the effects of initial concentration, initial pH and contact time on the removal of Zn2+. Experimental data obtained from batch equilibrium tests have been analyzed by four two-parameter (Freundlich, Langmuir, Temkin and Dubinin-Radushkevich) isotherm models. It was found that the optimum concentration of solution is about 500 ppm and the optimum pH value of water to be treated for adsorption was found to be 7. In adsorption studies, residual heavy metal ion concentration reached equilibrium in short duration of 2.0 h for initial Zn2+ concentration of 300 ppm. Maximum adsorption capacity, 9.43 mg Zn2+/g zeolite, showed that this adsorbent was suitable for zinc removal from aqueous media. The process of metal ions uptake by natural zeolite is best described by the equation for adsorption and can be easily carried out with a satisfactory rate. The correlation found between the Zn2+ uptake and the amount of Na+, Ca2+ and K+ released into solution by zeolite showed that the ion exchange sorption plays the basic role in metal ions uptake by natural zeolite. Adsorption phenomena appeared to follow two-parameter isotherms. The results showed that there is a good fit between the experimental data and empirical isotherms.