Mn-substituted iron oxyhydroxide (Mn0.13Fe0.87OOH) was prepared by the oxidation of ferrous carbonate precipitated from ferrous sulfate and sodium carbonate solutions. X-ray diffraction analysis led to the conclusion that the sample was basically iron manganese hydroxide with bixbyite structure. The sample exhibited a surface area of 101 m(2) g(-1) and a pore volume of 0.35 cm(3) g(-1). Batch experiments were conducted to study the adsorption of arsenite and arsenate species onto Mn-substituted iron oxyhydroxide (MIOH) and adsorption equilibrium time was evaluated. The temperature of adsorption was varied from 30 to 60 degrees C. The maximum uptake of arsenite and arsenate was found to be 4.58 and 5.72 mg g(-1), respectively. Zeta potential measurements and FT-IR spectral studies were also conducted to study the nature of adsorption. In both cases. adsorption was best described by Langmuir isotherm and activation energies as calculated from a model-free isoconversional method were found to be on the order of 15-24 and 45-67 kJ mol(-1) for arsenate and arsenite, respectively. (c) 2006 Elsevier Inc. All rights reserved.