Abstract
This study reports the development of a hierarchically porous material based on natural diatomite, thermally treated diatomite (450 °C), and an activated carbon-modified diatomite composite for saline groundwater treatment in West Kazakhstan, addressing the need for efficient desalination solutions under real environmental conditions. The material was synthesized via sequential thermal activation at 450 °C followed by incorporation of activated carbon, with bentonite used as a binder to improve mechanical stability. Comprehensive physicochemical characterization (SEM, XRD, XRF, BET, DTA, and FTIR) confirmed significant structural and compositional transformations, including silica enrichment, removal of impurities, and the development of a well-defined hierarchical porous network. The specific surface area increased from 8 to 10 m2/g for natural diatomite to 35–40 m2/g for thermally treated diatomite and further to 55–60 m2/g for the activated carbon-modified diatomite composite, accompanied by enhanced pore volume and mesoporosity. Performance evaluation using real groundwater samples demonstrated that thermally treated diatomite (450 °C) improved removal efficiency by approximately 19%, while the activated carbon-modified diatomite composite achieved 35–37% removal of chloride, sulfate, and total dissolved solids under multi-ion competitive conditions. The enhanced adsorption performance is attributed to the synergistic effect of increased surface area, improved pore accessibility, and additional active sites introduced by activated carbon. The adsorption process is governed by ion bridging mediated by multivalent cations, pore filling within the hierarchical pore structure, and surface complexation on silanol and metal–hydroxyl functional groups. Leaching tests confirmed the structural stability of the composite and indicated no significant release of environmentally relevant elements under aqueous conditions. Compared with natural diatomite, the thermally treated and activated carbon-modified materials demonstrate improved adsorption efficiency and stable performance under realistic groundwater conditions. These results highlight their applicability for decentralized water treatment systems in regions affected by saline groundwater contamination.