Adsorption of sodium lauryl sulfate onto calcium-phosphate hydroxyl@clay hybrid adsorbents

This work investigated the use of clay (C), calcium phosphate hydroxyl (CPH), and a nanocomposite of calcium phosphate hydroxyl@clay (CPH@C) for the removal of sodium lauryl sulfate surfactant from aqueous solutions. Sorption efficiency was assessed based on parameters like adsorbent dosage, contact time, surfactant concentration, temperature, and pH. Structural elucidation of the adsorbents was performed out using FT-IR spectroscopy, SEM, and XRD. Optimal sodium lauryl sulfate surfactant uptake was achieved under the following conditions: temperature of 55 °C; shaking time of 60 min for clay and CPH, and 80 min for CPH@C; surfactant concentration of 150 mg/L; pH values of 4.0 for clay, 6.0 for CPH, and 5.0 for CPH@C; and adsorbent dosage of 0.7 g for clay and CPH, and 0.5 g for CPH@C. FT-IR survey identified functional groups like OH, Si-Si-OH, Si-O, and PO₄³⁻ as active binding sites involved in the adsorption process. Kinetic studies evaluation indicates that surfactant sorption by clay and CPH obeyed pseudo-first-order kinetics, while CPH@C followed pseudo-second-order kinetics. Adsorption equilibrium data fit the Langmuir isotherm for clay and CPH, and the Freundlich isotherm for CPH@C with maximum adsorption capacities determined to be 47.551 mg/g for clay, 52.335 mg/g for CPH, and 77.321 mg/g for CPH@C. Thermodynamic variables indicated that the adsorption process was spontaneous and endothermic, as evidenced by negative ΔH° and ΔG° values.