Multi-scale structural regulation of a low-grade mixed-dimensional attapulgite clay intergrowth for site-synergistic Pb2+ capture

Low-grade attapulgite clay intergrowths, composed mainly of attapulgite, illite, calcite and quartz, are abundant. The intimate intergrowth among these phases buries active surfaces under inert components, limiting performance and hindering value-added utilization. Herein, a multi-scale structural regulation strategy was employed. Sieving and water washing removed inert components for compositional regulation. High-speed shearing and ultrasonic treatment broke soft agglomerates and exposed active surfaces, achieving aggregation state regulation. Controlled thermal treatment removed channel water, activated exchangeable sites and enhanced negative surface charge, thereby regulating structural and surface chemistry. These steps progressively modified the material from its macroscopic composition down to its atomic-level surface properties. After the regulation, Pb2+ adsorption capacity increased from 153.1 to 237.5 mg g–1. The material remained effective even at pH 1 and reduced Pb2+ from 1000 to 0.83 μg L–1, well below the World Health Organization (WHO) guideline of 10 μg L–1. X-ray diffraction, X-ray photoelectron spectroscopy and quantitative cation release analysis were performed to elucidate the adsorption mechanism. Ion exchange dominated by Ca-rich mineral serves as the primary pathway. Cation exchange on silicate surfaces, forming PbSiO3, provides a key supplementary contribution. Electrostatic attraction and in situ precipitation participate synergistically. This work establishes a theoretical foundation and offers a reagent-free, industrially feasible route for the value-added utilization of low-grade intergrown clay resources in environmental remediation.