Acid Resistance and Ion Exchange Capacity

This study investigates the acid resistance and ion-exchange performance of natural mixtures of heulandite (HEU) and chabazite (CHA) intended for use as filter materials in heavy metal removal and water disinfection. Two zeolitic rocks were examined: a heulandite-dominant tuff from the Dzegvi–Tedzami deposit (Rkoni, Georgia; HEU/CHA ≈ 8) and a heulandite–chabazite rock from the Chankanay deposit (Kazakhstan; HEU/CHA ≈ 1, with significant quartz). Samples were treated with hydrochloric acid solutions of varying concentration under controlled conditions. Changes in chemical composition, structure, and textural properties were characterized by XR-EDS, XRD, and adsorption measurements (water, benzene, nitrogen; BET and BJH analysis). Acid treatment induced dealumination, decationization, partial dissolution, and reorganization of micro- and mesoporous systems, with the extent strongly dependent on the initial composition and framework characteristics. Georgian heulandite exhibited pronounced dealumination (Si/Al increased from 3.6 to 9.5; aluminum reduced to 44% of the original), whereas Kazakhstani zeolite underwent milder modification and showed higher acid resistance. Acid treatment increased specific surface area and improved accessibility of zeolite micropores to larger molecules while decreasing mesopore volume and favoring pores <4 nm. Under acidic conditions, Kazakhstani zeolite retained high ion-exchange capacity, while mildly acid-treated Georgian heulandite displayed enhanced uptake of valuable Ag⁺, Cu²⁺, and Zn²⁺ ions, relevant for bactericidal applications. The results identify conditions under which natural HEU/CHA mixtures combine improved structural stability with enhanced ion-exchange performance in acidic wastewater environments.