56 Chiang Mai J. Sci. 2008; 35(1) Chiang Mai J. Sci. 2008; 35(1) : 56-62 www.science.cmu.ac.th/journal-science/josci.html Contributed Paper Adsorption Equilibrium of Zinc Ions from Aqueous Solution by Using Modified Clinoptilolite Achanai Buasri*, Phetcharat Yongbut, Nattawut Chaiyut and Kittiya Phattarasirichot Department of Materials Science and Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakhon Pathom 73000, Thailand. *Author for correspondence; e-mail: achanai@su.ac.th Received : 18 September 2007 Accepted : 5 October 2007 1. INTRODUCTION Zinc manufacturing and other industries release large quantities of metals, mainly Cd and Zn, during production. The increasing demand for alkaline zinc manganese batteries, instead of mercury based ones, brings serious problems when those batteries are not disposed off properly. Yet, another source of contamination can be due to the flooding of ore mines into the environment. Since heavy metals have toxic effects on the environment and public life, many researchers suggest a cost-effective process, such as ion exchange, for removing dissolved heavy metals from wastewaters by using naturally occurring materials [1]. In the later years, utilization of natural zeolites to control the pollution due to the effluents polluted with heavy metal ions has increased. Natural zeolites have ion exchange capability to remove unwanted metal ions and this prop property makes zeolites favorable for wastewater treatment. Beside this, price ABSTRACT 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 Zn 2+ . 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 Zn 2+ concentration of 300 ppm. Maximum adsorption capacity, 9.43 mg Zn 2+ /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 Zn 2+ uptake and the amount of Na + , Ca 2+ 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. Keywords: Clinoptilolite, Zinc, Removal, Ion Exchange, Adsorption. ENO-003