The occurrence of arsenic is frequently observed in groundwaters around the world and harshly affects several million people. Although different technologies have been proven to be efficient to face this environmental threat, adsorption with functionalized magnetic nanomaterials is one of the best alternatives, due to its flexibility and efficient energy use. However, the presence of competing ions typically found in natural waters might affect the arsenic removal efficacy. This paper reports the effect of the presence of carbonate, sulphate, nitrate, silicate, phosphate, chloride, fluoride and iron ions on the arsenate adsorption onto magnetic SiO2/Fe3O4 functionalized with aminoalkoxysilane groups incorporating Fe3+. The adsorption equilibrium of arsenate in the concentration range 50-1000 mu g L-1 was satisfactorily described by linear isotherms with values of the equilibrium parameter KH,298K = 278.8 L g(-1) in monocomponent systems and K-H,K-298K = 1.80 L g(-1) in the presence of competing ions. Carbonate and especially phosphate are demonstrated to be the main species affecting the process with contributions to the loss of efficacy around 70%. Finally, the material reuse after five adsorption cycles and one regeneration stage with NaOH was assessed under several composition scenarios reaching adsorption yields similar to those obtained with fresh materials. (C) 2015 Elsevier B.V. All rights reserved.