Removal of hexavalent chromium ion from aqueous solution using the light fraction of padma river sand adsorbent: Studies on equilibrium, kinetics, and thermodynamics

This study investigates the removal of hexavalent chromium (Cr(VI)) from aqueous solutions using the light fraction of Padma River sand as a low-cost natural adsorbent. The adsorbent was characterized through FTIR, XRD, FESEM, and WD-XRF analyses, confirming its composition to be primarily quartz and muscovite, with no hazardous components. Batch adsorption experiments were performed to examine the influence of pH, contact time, adsorbent dosage, and temperature. Optimal Cr(VI) removal occurred at pH 2, with an adsorption capacity of 4.9128 mg/g. Adsorption kinetics followed the pseudo-second-order model, while equilibrium data best fitted the Langmuir isotherm, indicating monolayer adsorption. Thermodynamic analysis revealed that the process is spontaneous and exothermic, with a negative Gibbs free energy (ΔG° = –4.02 kJ/mol) and enthalpy change (ΔH° = –19.62 kJ/mol). WD-XRF confirmed chromium deposition on the adsorbent post-treatment. Comparative assessment with other sand-based adsorbents highlights the superior performance of the light fraction of Padma River sand. These findings suggest its potential as an efficient, sustainable material for Cr(VI) removal in water treatment systems, especially in resource-constrained settings.