Montmorillonite and amino acid composites for heavy metal ion adsorption

This study explores the interactions between montmorillonite (MMT) and selected amino acids (lysine, arginine, serine, and aspartate), as well as their complexes with heavy metal ions. Multi-technique characterization (e.g., XRD, FT-IR, XPS, SEM, TEM, and ICP-MS) revealed that MMT exhibits high affinity for basic amino acids, with the adsorption capacity following the order: amino > carboxyl > hydroxyl. The adsorption kinetics of lysine were well described by pseudo-second-order, Elovich, and Weber-Morris models, indicating a chemically controlled, two-stage process involving initial surface diffusion and subsequent internal diffusion. In contrast to the adsorption of amino acids, that of Cu²⁺ exhibited a higher initial rate and greater adsorption energy. Furthermore, amino acid-MMT composites effectively immobilized metal ions via coordination and electrostatic interactions. These findings enhance the understanding of mineral-organic interactions and suggest potential applications in biocatalysis, biopharmaceuticals, and environmental remediation.