Isotherm Studies of Arsenic Adsorption on Natural Adsorbents: Laterite, Sandstone, and Shale

Abstract

Arsenic contamination of drinking water has been an increasing concern worldwide because of toxicity. In Côte d'Ivoire, high concentrations of arsenic are increasingly being found in the water around mining operations. Identifying and determining the modes of arsenic retention on geological matrices is essential for designing adsorption systems. In this study, the adsorption process of an aqueous arsenic solution on laterite, sandstone, and shale was examined. Under optimized conditions of pH, contact time, initial arsenic concentration, and temperature, batch adsorption isotherms were performed. Thermodynamic parameters such as ΔH◦, ΔS◦, and ΔG◦ were calculated. The Langmuir, Freundlich, Temkin, Elovich, and Dubinin–Radushkevich (D–R) models were explored. Isotherms are classified as type L. The Langmuir isotherm was highly favorable at all temperatures with maximum monolayer capacities of 1.627 for laterite, 0.539 for sandstone, and 0.135 for shale. The correlation coefficient R² was closest to 1. Temkin’s binding energy values (22.101–67.977 KJ/mol) chemisorption is suggested, while Dubinin-Radushkevich energies below 8 KJ/mol point to physical adsorption. Both types of adsorption appear to be involved. This study recommends the applicability of laterite first, followed by sandstone and shale, for removing arsenite ions from water.