A porous and efficient arsenic adsorbent (specific surface area, 181 +/- 4 m(2)/g; pore volume, 0.35 +/- 0.01 mL/g) is prepared from raw laterite by acid followed by alkali treatment. FTIR, XRD, SEM-EDAX, HRTEM, and a surface area analyzer are used for detailed characterization of treated materials. Adsorption of arsenic on treated laterite (TL) using arsenic spiked distilled water and contaminated groundwater (CGW) is studied in the batch and fixed-bed column modes. The Langmuir isotherm fits better to the experimental data compared to the Freundlich isotherm. The Langmuir maximum capacities of As(V) and As(III) on the best-performing treated material are found to be 24.8 +/- 3.9 and 8.0 +/- 1.4 mg/g, respectively. Arsenic adsorption on TL follows pseudo-second-order kinetics. The Langmuir maximum adsorptions of arsenic on raw laterite and TL using CGW as the total arsenic are found lobe 0.11 +/- 0.01 and 7.5 +/- 0.4 mg/g, respectively. In the fixed-bed column run, the 6.5 cm TL bed is capable to produce similar to 3000 times the bed volume of treated water with an effluent arsenic concentration <10 mu g/L using CGW as an influent. The arsenic adsorption capacity of TL is found to be 30 to 40 times higher compared to that of raw laterite.