Abstract
Acid treatment of bauxite residue (BR) has been one of the main approaches to enhance its metal adsorption performance. However, the acid treatment mechanisms remain poorly understood and is complicated by the variable and complex mineralogy of bauxite residue and different test conditions in previous studies. In this study, bauxite residue samples were treated with aqueous HCl solutions, with concentrations ranging from 0 to 0.25 M. The dissolution kinetics of the major elements (Na, Al, Ca, Fe, and Si) and target metals (Pb2+ and Cu2+) for ion exchange and adsorption performance were measured. The solid samples were examined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) cross-sectional elemental mapping to determine the reaction mechanisms. The results revealed that the adsorption performance decreased with increasing acid concentrations, which is related to the structural changes of the sodalite phase. Other mineral phases, such as hematite, boehmite, and quartz, play a minor role in the adsorption. Additionally, different adsorption mechanisms between Pb2+ and Cu2+ were revealed, which were related to surface disruption.
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