A novel adsorbent of CaFe2O4 magnetic nanoparticles (MNPs) which was synthesized by sol-gel process, showed an excellent high affinity to anionic congo red (CR), and could be employed to selectively adsorb CR from ternary dye system with a high separation factor. The mechanism of the selectivity was revealed in detail. The effects of various parameters such as pHs, ionic strengths and coexisting ions on the selective adsorption were investigated. The CR adsorption followed pseudo-second-order kinetic model. The sorption data could be well interpreted by the Langmuir model. The thermodynamic parameters showed the spontaneous, exothermic and physical nature of the adsorption process. The selectively adsorbed CR dye could be recovered rapidly by ethanol/Na3PO4 (2 mM) (1/1, v/v) with the recovery percentage of 96.6%. The regenerated adsorbent still showed a highly selective adsorption capacity for CR after five regeneration-removal cycles and a strong anti-interference ability, confirming the potential of the CaFe2-O4 MNPs as practical selective adsorbent for treatments of dye containing effluents. (C) 2014 Elsevier B.V. All rights reserved.