Secondary resource utilization of exhausted copper slags (ECSs): Efficient removal of Cr (VI) from aqueous solutions and removal mechanism

Abstract

Exhausted copper slags (ECSs) are secondary slags produced in the reusing process of copper smelting fly ashes and have the potential to synthesize adsorbent for the elimination of toxic elements. This study focuses on the potential of the original ESCs for the detoxication and removal of Cr(VI) from aqueous solutions. Batch adsorption experiments showed that ESCs present an excellent performance on Cr(VI) eliminate, and the maximum adsorption capacity is 110.50 mg∙g−1 at acid solutions (pH = 2) with a mild temperature condition (308 K). Furthermore, the adsorption efficiency of Cr was barely effected by the comment co-existing elements, such as NO3– and SO42-, indicating its specific adsorption capacity for Cr. The elimination of Cr onto ESCs fits well with the Langmuir adsorption model, indicating that the adsorption process was controlled by monolayer adsorption. Moreover, Cr(VI) adsorption onto ESCs also followed the Pseudo-second-order kinetics with the adsorption rate constant k at 2.65 × 10-3 g·mg−1·min−1. Mechanistic analysis indicated that ECSs eliminated Cr(VI) by electrostatic adsorption and flocculation precipitation, and reduced Cr(III) by Fe2+, Mo2+, S2-, and SO32-. The environmental risks during its adsorption implication process were also accessed and the toxic elements, such as Cu, As, and Pb in the materials were barely detected in the residue solutions. Thus, ECSs could be used as a facile and cost-effective adsorbent for Cr(VI) removal, even without any further pre-treatment process, which is meaningful to the disposal of this typical industrial waste.