The aim of this study was to investigate the adsorption potential of heat treated lepidocrocites (gamma-FeOOH) towards As(III) and As(V) ions in aqueous solutions. Initially, mesoporous lepidocrocite was synthesized, treated at different temperatures, and characterized using various analytical techniques. During the heating, transformation of lepidocrocite into hematite was observed. The adsorption of As(III) and As(V) was studied by batch experiments and the effects of different operational parameters e.g., adsorbent dose, solution pH, contact time, and the initial concentration of As(III)/(V) (isotherms) were studied. Lepidocrocite treated at 250 degrees C exhibited >99% and 94% adsorption from 50 mg/L As(V) and As(III) solutions, respectively with an adsorbent dose of 2.5 g/L. The highest uptake capacity was obtained for As(III) (55 mg/g) on lepidocrocite without the heat treatment and for As(V) (38 mg/g) on lepidocrocite treated at 250 degrees C, which was assigned to be a mixture of maghemite and hematite. The adsorption kinetic data fitted well with the pseudo-second-order model and the BiLangmuir isotherm had the best applicability to describe the adsorption equilibrium. (C) 2011 Elsevier B.V. All rights reserved.