Agglomerated iron(III)-aluminum(III) mixed oxide nanoparticles (NIAO)were investigated for their As(V) adsorption performances in the presence/absence of some ions occurring in groundwater. NIAO sample calcined at 250 degrees C (NIAO-250) showed highest As(V) adsorption efficiency at pH = 7.0 (+/- 0.1) and 30 degrees C. The pseudo-second order and the Langmuir isotherm models described, respectively, the kinetic and equilibrium As(V) adsorption data of NIAO-250 very well. The Langmuir monolayer capacity of As(V) adsorption by NIAO-250 estimated in the absence of any other ion (54.55 +/- 2.04 mg g(-1)) was about 15-35% higher than that in the presence of tested ions occurring in groundwater, implying adverse influence on the removal reaction. Adsorption reactions were endothermic and spontaneous, which took place with increasing entropy (Delta S- = +0.072 to +0.158 kJ mol(-1) K-1). Spontaneous nature of reactions increased with increasing temperature. Low regeneration (similar to 40%) of As(V) adsorbed NIAO-250 by 2.0 M NaOH solution and other supporting evidences suggested that As(V) was bound to NIAO-250 surface by chemical interaction. (C) 2011 Elsevier B.V. All rights reserved.