A high-efficiency process for the separation of chromium and aluminum from waste aluminum sludge with a high chromium content using a combined oxidation and dispersion process

Abstract

Waste aluminum sludge (WAS) contains an abundance of Cr(III), which restricts the potential for recycling of Al resources in WAS. The oxidation process is a potentially effective method for the separation of Cr and Al from solid waste. However, many challenges restrict the application of oxidation treatments for WAS, including their low oxidative efficiency and their inability to handle sludge with high Cr concentration. This study proposes a highly efficient combined oxidative and dispersive process for the separation of Al and Cr from high Cr(III) content WAS. The effects of varying solid–liquid mass ratios and Ca(OCl)2 concentrations in the oxidation process and Na2SO4 concentrations in the dispersion process were investigated. Using single factor experiments, the optimal conditions were found to be a solid–liquid mass ratio of 1:14 and Ca(OCl)2 dosage of 280 mg/g dry WAS in the oxidative process, allowing the Cr(III) oxidative efficiency to reach 93.83%. After treatment using the combined processes, the total Cr removal efficiency reached 95.54% and the aluminum content exhibited almost no loss. Characterization by FTIR, XRD, and SEM-EDS indicated that Ca(OCl)2 destroyed the colloidal structure of WAS, resulting in the release of Cr(III) which could subsequently be oxidized to soluble Cr(VI) by Ca(OCl)2. In the dispersion process, Na2SO4 destroyed the colloidal stability of WAS, resulting in the release of Cr(VI) and improving the Cr removal efficiency. The combined processes were found to have a significantly synergistic effect, indicating that this method is suitable for the separation and collection of Cr and Al from WAS. Furthermore, the economic analysis showed that the combined processes have cost advantage over traditional treatment.