Magnetic nanoparticles (maghemite gamma-Fe2O3) functionalised with citrate ions were synthesised and characterised. These highly dispersible particles are stable in aqueous media and have a large surface area (170 m(2) g(-1)), which confers them a high number of active sites leading to a large ion loading capacity. The adsorption of Eu3+, La3+, Co2+ and Ni2+ ions from aqueous solution by these citrate-coated magnetic nanoparticles was studied. The maximum adsorption capacities determined by fitting experimental data with Langmuir model were close to 0.5 mmol g(-1) for the 4 cations studied. The kinetic study showed a rapid adsorption due to the presence of active sites on the external surface of the magnetic nanoparticles. The equilibrium time is 15 min at most and at least 83% of cations are adsorbed after 1 min. The effect of pH was also investigated. The adsorbed amount of cations increases drastically with pH from pH 2 to 3.5 and remains constant over pH 3.5. In addition, competitive adsorption was investigated. The adsorption capacity of the citrate-coated magnetic nanoparticles for both cations together (Eu3+/La3+ or Co2+/Ni2+) is similar to those obtained when each type of ion was present alone. These results show that these nanoparticles could be used in water treatment process for removal of pollutants. Indeed, this magnetic adsorbent is efficient and easily removed from the aqueous solution by applying a magnetic field. (C) 2011 Elsevier B.V. All rights reserved.