Magnetic Fe3O4-chitosan@bentonite (Fe3O4-CS@BT) composites using natural materials were synthesized and used to remediate acid mine drainage (AMD) for heavy metal removal. It was found that the composites had a good magnetism, high stability and good performance in removal of Cr(VI) in the synthetic aqueous solutions. The thermodynamic parameters showed that Cr(VI) adsorption onto Fe3O4-CS@BT was an exothermic and spontaneous process. The adsorption kinetics was well described by a pseudo-second-order model, and the adsorption isotherms fit the Langmuir model with a maximum adsorption capacity of 62.1 mg/g at 25 degrees C. Solution pH was a key factor for adsorption and the optimized pH was 2.0. Fe3O4-CS@BT could be easily recycled through an external magnetic field and the adsorption capacity reduced by only 3% after five consecutive adsorption-desorption processes. In addition, Fe3O4-CS@BT was found to be an excellent adsorbent for actual AMD remediation containing Cd, Cr, Cu, Fe Zn, Ni and Pb, suggesting that the Fe3O4-CS@BT was an effective and economical adsorbent for the treatment of AMD. (C) 2018 Elsevier Inc. All rights reserved.