Isotherm and Thermodynamical Studies of Arsenic Adsorption from Water using Laterite

Abstract

This study investigates the removal of arsenic (As) from polluted water using laterite. Three different particle sizes 425, 850, and 106 μm of laterite were prepared, characterised and utilised as an adsorbent to remove As from polluted water. The highest removal efficiency was 94.90% and was associated with the particle size of 106 μm. The adsorption data can best be described by Langmuir Isotherm model, which had a superior R-square value of 0.99 to that of Freundlich adsorption model from the Isotherm modelling fitting. The results indicated that metal ion absorption occurs on a homogenous surface via monolayer adsorption and that the adsorption process may be controlled by chemisorption processes. The removal efficiency values were found to be increasing with increasing temperature. The enthalpy (ΔH°) and entropy (ΔS°) for the thermodynamical process at 308.15 K were 32.2 kJ/mol and 206.0 J/K mol, respectively, for the optimum particle size (106 μm) of the laterite. Gibb’s Free Energy (ΔG°) was determined to be -31.70, -33.54, and -35.85 kJ/mol at temperatures 308.15, 318.15, and 328.15 K respectively. The negative ΔG° values reflect the feasibility and spontaneity of the adsorption process. The adsorption process can, thus, be described as endothermic. Lateritic soil adopted has a promising ability in arsenic adsorption.