Removal of chromium(vi) from wastewater using weakly and strongly basic magnetic adsorbents: adsorption/desorption property and mechanism comparative studies

Abstract

Two novel strongly basic magnetic adsorbents, quaternary ammonium-modified polystyrene and chitosan magnetic microspheres (Pst–MIMCl and CTS–GTMAC), were prepared using the in situ coprecipitation and emulsion cross-linking methods under mild conditions, with features of strong magnetic responsiveness and high quaternary ammonium group contents. The Cr(VI) adsorption/desorption properties and mechanisms of strongly and weakly basic magnetic adsorbents were compared through simulated wastewater. The strongly basic adsorbent exhibited low pH dependence, and the main adsorption mechanism was ion exchange. The weakly basic adsorbent exhibited high pH dependence, and the major adsorption mechanism was electrostatic attraction. Besides, the strongly basic adsorbent required higher desorption conditions than the weakly basic adsorbent owing to the difference of the desorption mechanisms. Furthermore, the removal selectivity of the strongly and weakly basic magnetic adsorbents was estimated by the chromium plating wastewater. The results demonstrated that the strongly basic magnetic adsorbents exhibited higher selectivity than the weakly basic magnetic adsorbents. In addition, the Pst–MIMCl was selected as the optimal magnetic adsorbent for Cr(VI) recovery from wastewater, with the advantages of strongly magnetic responsiveness, wide pH applicable range, high removal efficiency, high adsorption selectivity and good reusability.