Efficient removal of Sr²⁺, V⁵⁺, and Rb⁺ ions from groundwater using a hybrid Mg-MCM-41/Talc composite; Siwa Oasis in Egypt as case study

This study presents the development and application of a hybrid inorganic adsorbent composed of mesoporous Mg-MCM-41 integrated with exfoliated talc nanosheets (MCM/talc composite)-for the efficient removal of Sr²⁺, V⁵⁺, and Rb⁺ ions from contaminated water sources. The composite exhibited a mesoporous architecture (9.6 nm) and a specific surface area of 123.6 m²/g, combining the high reactivity of MCM-41 with the layered structure of talc. Batch adsorption experiments revealed exceptional saturation capacities (Q_sat) of 229.9 mg/g (Sr²⁺), 188.8 mg/g (V⁵⁺), and 137.2 mg/g (Rb⁺). Kinetic data followed a pseudo-first-order model, while Langmuir isotherms confirmed monolayer adsorption. Critically, statistical physics modeling provided deep mechanistic insights into the adsorption process. The number of ions per active site (n) exceeded 2 for all ions, indicating multi-ionic vertical stacking at single adsorption sites. The adsorption energies (ΔE), derived from advanced monolayer modeling, were all below 8 kJ/mol. These values confirm a physisorption-dominant mechanism, governed by weak interactions such as van der Waals forces, hydrogen bonding, and electrostatic attractions. Fixed-bed column studies further validated the material's dynamic performance, achieving removal efficiencies of 79.7% (Sr²⁺), 73.4% (V⁵⁺), and 68.6% (Rb⁺). Application to real groundwater from Egypt's Siwa Oasis resulted in final concentrations of 1.3 mg/L (Sr²⁺), 0.46 mg/L (V⁵⁺), and 0.03 mg/L (Rb⁺) after two treatment cycles-meeting global health standards. This work demonstrates that the MCM/talc composite is a highly promising, low-cost, and reusable adsorbent for environmental remediation and selective recovery of critical metals, combining advanced theoretical modeling with field-relevant practicality.