Enhancing Cr(VI) removal by regulating Fe/Al bimetal adsorption and reduction properties: kinetic and mechanistic studies

In the study, a novel Fe/Al bimetal with a high specific surface area and electron transfer capacity was synthesized through ball milling Fe and Al powder. Importantly, this synthesis process did not consume Al powder and did not generate by-products that required treatment. Compared with Fe or Al powder and the ball-milled Fe or Al powder, Fe/Al could rapidly remove Cr(VI) through adsorption–reduction under near-neutral conditions. Nevertheless, the removal efficiency of Cr(VI) by Fe/Al was influenced by the initial pH of the solution and dissolved oxygen (DO). Kinetic studies and adsorption isotherm analysis demonstrated that the pseudo-second-order adsorption kinetic model and the Freundlich model could better describe the Cr(VI) removal data, and the maximum removal amount of Cr(VI) was 6.25 mg/g. Furthermore, based on the characterization analysis of XPS, the adsorbed Cr(VI) was reduced to Cr(III). SEM-EDS analysis revealed that Cr mainly overlapped with the Fe elemental distribution on the surface of Fe/Al particles, suggesting that Fe was the main reaction site. Consequently, the results indicated that highly active Fe/Al could be prepared by solid–solid blending for pollutant removal, which provided technological concepts for the waste utilization of scrap iron and aluminum.