Modification and Application of Natural Clinoptilolite and Mordenite from Almaty Region for Drinking Water Purification

In this paper the modification of natural clinoptilolite and mordenite zeolites from Almaty using acid treatment is addressed for the purposes of improving adsorption performance and for drinking water purification. Structural chemical transformation was characterized by the use of XRD, FTIR, and SEM techniques. Acid treatment led to a partial dealumination that was responsible for the increase in number of surface defects and micropores, improvement in ion exchange capacity and selectivity toward heavy metals. Additionally, modifications greatly enhance the uptake capacities of Pb2+, Cd2+ and As3+. The clinoptilolite post-modification removal efficiencies reached 94%, 86%, and 84% respectively, while mordenite zeolites achieved 95%, 90%, and 87% removal efficiencies respectively. The enhancement of performance was related to the increase of surface area and active sites for ion exchange, verified from analysis of BET surface area. The use of different Bhatt and Kothari methods has revealed that adsorption processes followed Langmuir isotherm models for Pb²⁺ and Cd²⁺, whereas As³⁺ adsorption was better described by the Freundlich isotherm model. However, second-order kinetics indicate that chemisorption was the dominant mechanism. Such evidence indicates spontaneity and an endothermic process, as shown from thermodynamic studies. Results showed that modified zeolites indeed had a high degree of reusability, with over 80% of the adsorption capacity retained even after five cycles. Acid-modified zeolites can provide cheaper, greener methods of purification, generating only negligible secondary waste when compare to conventional methods of water purification, for example, activated carbon and membrane filtration. Results from this study proved that modified clinoptilolite and mordenite zeolites have the potential for sustainable heavy metal treatment in drinking water purification systems.