Rock-water interaction was studied between goethite and arsenite to understand the mobilization of arsenic from goethite, a major constituent of the Bengal Delta Plain (BDP) matrix. Goethite was synthesized following standard methods of ferrihydrite precipitation and further transformation to goethite. Characterization was carried out using FT-IR, XRD and TEM. As (III) adsorption broadly follows both Langmuir and Freundlich isotherms. As (III) adsorption on goethite was found to be pH dependant. Optimum As (III) loading on goethite has been estimated at 8.93 mg/g for an initial As (III) concentration of 1.04 mg/L