Cr(VI) adsorption on red mud modified by lanthanum: Performance, kinetics and mechanisms

Abstract

Water pollution caused by the highly toxic metal hexavalent chromium (Cr(VI)) creates significant human health and ecological risks. In this study, a novel adsorbent was used to treat Cr(VI)-containing wastewater; the adsorbent was prepared using red mud (RM) generated from the alumina production industryand the rare earthelement lanthanum. This study explored adsorptionperformance, kinetics, and mechanisms. Results showed that the adsorptionkinetics of the RM modified by lanthanum (La-RM), followed the pseudo-second-order model, with a rapid adsorption rate. Cr(VI) adsorption was positively associated with the absorbent dose, pH, temperature, and initial Cr(VI) concentration; coexisting anions had little impact. The maximum Cr(VI) adsorptioncapacity was 17.35 mg/g. Cr(VI) adsorption on La-RM was a mono-layer adsorptionpattern,following the Langmuir isotherm model. Thermodynamicparameters showed the adsorptionwas spontaneous and endothermic.The adsorptionof Cr(VI) on La-RM occurred as a result of LaOCl formation on the RM surface, which in turn furtherreacted with Cr(VI) in the wastewater. This study highlighted a method for converting industrial waste into a valuable material for wastewater treatment. The novel absorbent could be used as a potential adsorbent for treating Cr(VI)-contaminating wastewater, due to its cost-effectiveness and high adsorption capability.