Montmorillonite modification and chromate adsorption mechanisms of organo-montmorillonite: A multiscale study

Cetyltrimethylammonium bromide modified montmorillonite (CTMAB-Mt) demonstrates effective removal of hexavalent chromium. It is crucial to understand the mechanisms by which changes in the microstructure of montmorillonite affect its adsorption capacity. This study combines molecular dynamic simulation, microscopic detection, and column/batch tests to reconstruct the microstructure of CTMAB-Mt at various loading levels and to investigate its chromate adsorption behavior. The results indicate that the primary modification mechanism of CTMAB-Mt involves ligand binding between the head group N(CH₃)₃ of the organic modifier and the surface oxygen of the siloxane layer in the clay. Compared to capture by CTMA⁺, CrO₄²⁻ prefers to form aqueous complexes, resulting in limited enhancement of CTMAB-Mt's adsorption capacity at low loading levels (<1.00 CEC). Notably, Molecular dynamics simulations reveal that the adsorption capacity of 1.00 CTMAB-Mt is exceptionally high, reaching 7.87 mg/L. This finding is consistent with results from column and batch tests, providing a novel method for calculating the heavy metal adsorption capacity. The enhanced adsorption capacity is primarily due to electrostatic attraction and van der Waals forces between the head groups of CTMA⁺ and CrO₄²⁻. A comprehensive understanding of chromate adsorption by modified montmorillonite is essential for developing modified clay and preventing chromium pollution.