Characterization and Aluminum Recovery from Chemical Milling Sludge in Aerospace Industry

The chemical milling process used in the aerospace industry generates substantial metallic residue in the etching bath, referred to as chemical milling sludge (CMS). The direct disposal of CMS into the environment leads to ecological deterioration and economic losses. This study focused on the recovery of aluminum from the aerospace industry CMS, aiming to mitigate environmental harm and enhance resource efficiency. The energy-dispersive X-ray (EDX) analysis revealed that the aluminum content in extracted CMS increased significantly to 95.86%, compared to 28.98% in non-extracted sludge. The XRD analysis of the CMS extracted samples also revealed the presence of increased Al₂O₃. The surface morphology study suggested the irregularly shaped particles with large chunks, and fine granules were observed on CMS. The yield of Al₂O₃ was observed to be 35.9% (wt) prior to the calcination process followed by 12.1% (wt) after calcination. The phytotoxicity study indicated that the CMS inhibited plant growth and disposal of untreated sludge may lead to adverse impact on soil quality and disrupt ecosystem. This work contributes toward the sustainable waste management practices (i.e., waste to value) in the aerospace industry and recovery of valuable aluminum from the CMS.