Study of high malachite green adsorption by organically modified clay

Abstract

The removal of the toxic dye malachite green (MG) from aqueous effluents using organically modified clay (OC) was investigated in a batch system. The OC was synthesized by intercalating the cationic surfactant hexadecyltrimethylammonium bromide into Algerian montmorillonite. The study explored the effects of initial dye concentration, temperature, pH, and contact time on dye adsorption. The OC demonstrated high dye removal efficiency (99%) at an initial dye concentration of 100 mg L−1, pH 6, and 20°C. The adsorption capacity was found to be independent of pH but increased with temperature, with maximum adsorption capacities of 350, 380, and 398 mg·g⁻¹ at 20°C, 30°C, and 40°C, respectively. The adsorption process was characterized by rapid initial uptake followed by a slower rate until equilibrium was reached, with a maximum uptake of 49.45 mg·g⁻¹. The experimental data were best described by the Langmuir adsorption model, indicating monolayer adsorption on homogeneous sites. Kinetic studies revealed that the sorption rate followed a pseudo-second-order model, with a high correlation (R² = 0.999), suggesting a chemisorptive nature of the interaction. Thermodynamic analysis indicated that the process was spontaneous and endothermic, with positive enthalpy and negative Gibbs free energy values. Overall, the OC proved to be an effective and environmentally friendly adsorbent for the removal of MG dye from wastewater.