The influence of some groundwater occurring ions was investigated on As(V)-sorption by agglomerated nanoparticles (40-50 nm) of synthetic hydrous iron(III)-chromium(III) mixed oxide (NHICO). Solubility tests of NHICO suggested that it could be used safely for As(V) removal at pH = 6.4 ± 0.1 by agitation (speed: 350 ± 5 rpm) for an hour. Kinetic data obtained in the presence of applied ions for this reaction were well described by the pseudo-second order equation (0.98 < r2 <1.00, 0.04 < x2 < 0.18). Good agreement of the equilibrium data with the Freundlich isotherm (0.96 < r2 <1.00, 0.41 < x2 < 6.30) suggested that the NHICO surface was heterogeneous. Adequate fitting of the data with the Redlich-Petterson (0.96 < r2 <1.00, 0.65 < x2 < 7.83) isotherm with g < 1.0 confirmed the conclusion drawn. The positive enthalpy (ΔH0) and entropy (ΔS0) changes indicated that the endothermic As(V)-sorption reaction in the absence/presence of ions was driven by an entropy increase at the solid-liquid interface. Negative values of free energy change (ΔG0) indicated that the reaction spontaneity increased with increasing temperature. The sorption of As(V) by NHICO occurred via an ion-exchange mechanism (mean sorption energy, EDR = 8.98 to 11.47 kJ. mol-1) involving surface M-OH groups.