Physicochemical characterization of manganese-nodule leached residues was carried out by chemical analyses, XRD, TG-DTA, surface area measurement, and FTIR techniques. The material is very fine-grained (<75 pm), is cryptocrystalline to amorphous in nature, and contains mainly of delta-MnO2, quartz (alpha-SiO2), and zeolite/feldspar minerals. Physically adsorbed sulfates in the leached residue are removed by repeated water washing and the washed sample shows an appreciable increase in surface area. This is indicated by the absence of 1387 and 1099 cm(-1) peaks in the IR spectrum of the washed sample. The adsorption behavior of the washed sample toward Ni2+ was recorded as a function of time, pH, temperature, and concentrations of adsorbent and adsorbate. (C) 2004 Published by Elsevier Inc.