Theoretical Study on the Mechanism of Super-stable Mineralization of Heavy Metal Cations by Ternary Layered Double Hydroxides for Soil Remediation

Abstract

The long-term stabilization of heavy metals in contaminated soils remains a critical research focus in the field of environmental remediation. Layered double hydroxides (LDHs), owing to their structural tunability and favorable mineralization stability, have demonstrated great potential for the super-stable immobilization of heavy metal ions. In this work, Mg₂CaMᴵᴵᴵ-CO₃-LDHs (M = Al, Fe, Mn) models were constructed to systematically investigate the adsorption, co-adsorption, and isomorphic substitution behaviors of Pb²⁺, Cd²⁺, and Cu²⁺, thereby elucidating the super-stable mineralization mechanism from both thermodynamic and kinetic perspectives. Based on density functional theory (DFT) calculations coupled with ab initio molecular dynamics (AIMD) simulations, the results reveal that ternary LDHs exhibit lower activation barriers for adsorption and isomorphic substitution, alongside more stable adsorption configurations, more favorable thermodynamics, and superior co-adsorption capability compared to binary LDH systems. Meanwhile, the coexistence of Mg²⁺ and Ca²⁺ provides two distinct substitutable sites within the layers, enabling heavy metals to replace either cation and thus enhancing site selectivity. In addition, in ternary LDHs with Fe as the trivalent cation, increasing the proportion of Ca²⁺ in the layers enhances the adsorption strength toward all three heavy metal ions, while the introduction of Ca vacancies significantly reduces the energy barriers for isomorphic substitution. Overall, multi-cation synergistic regulation within the layered structure optimizes substitution kinetics while preserving thermodynamic stability, diversifying the mineralization pathways and providing theoretical guidance for the rational design of LDH-based materials for complex remediation systems.