A critical review of natural clay minerals: Structural characterization, textural properties, and adsorption mechanisms for sustainable wastewater treatment

The escalating crisis of water pollution necessitates the development of sustainable, low-cost, and globally accessible treatment technologies. Natural clay minerals have emerged as highly promising adsorbents due to their widespread availability, favorable physicochemical properties, and demonstrated effectiveness in removing a broad spectrum of aqueous pollutants. This review provides a comprehensive and critical assessment of the use of natural clay minerals for sustainable wastewater treatment. We first establish the fundamental structure-property-performance relationships of key clay types, including smectite, kaolinite, illite, vermiculite, and palygorskite. The review then outlines a rigorous framework for their characterization and critically evaluates the application of equilibrium and kinetic models to describe adsorption processes. A central focus is placed on the physicochemical modification strategies—such as acid/base activation, pillaring, organophilization, and composite formation—used to enhance adsorption capacity, selectivity, and regeneration. We synthesize performance data for the removal of heavy metals, anions, and organic pollutants, critically analyzing the underlying mechanisms and the influence of environmental factors. Finally, we identify persistent challenges for real-world deployment and propose a translational roadmap from laboratory research to pilot-scale application. This includes a critical discussion of regeneration, end-of-life options, and the need for transparent techno-economic and life-cycle assessments benchmarked against incumbent technologies. This review concludes that natural clays represent a viable and scalable platform for water remediation, provided that key challenges in material processing, regeneration, and data standardization are systematically addressed. • Explores adsorption mechanisms of natural clay minerals for wastewater treatment. • Links surface area, porosity, and CEC to pollutant removal performance in engineered systems. • Elucidates physisorption and chemisorption pathways using quantitative thermodynamic and spectroscopic evidence. • Highlights regeneration, scalability, and multi-contaminant treatment potential of clay-based systems. • Offers research roadmap for optimizing clay modification and integration in wastewater technologies.