Removal of hexavalent chromium from aqueous solution using low-cost magnetic microspheres derived from alkali-activated iron-rich copper slag

The utilization of iron-rich copper smelting waste residues is a promising method to treat chromium (Cr(VI)) contaminated wastewater. Improving its recoverability and adsorption efficiency in the adsorption process is the key to their effective utilization. Based on this, magnetic copper slag-based alkali-activated microspheres (CS-AAMs) with controllable particle size were prepared under the activation of sodium silicate by mechanical dispersion-suspension solidification method and used as an efficient low-cost magnetic adsorbent for Cr(VI) removal. The capability of CS-AAMs for Cr(VI) removal was investigated under different conditions. A maximum adsorption capacity of 32.5 mg/g was achieved at the pH of 1. The adsorption capacity can keep 89.25% after four cycles adsorption-desorption experiments. The adsorption process follows pseudo-first-order kinetics and occurs spontaneously with an endothermic nature. Both intraparticle diffusion and chemical complexation controlled the adsorption process. Notably, the electrostatic attraction between Cr(VI) and CS-AAMs played a key role in the adsorption of Cr(VI). The adsorbed Cr(VI) was complexed and partially reduced under the action of active Fe(II) species in CS-AAMs. The findings indicate that the CS-AAMs prepared in this study can efficiently adsorb Cr(VI) from industrial effluents.