In situ X-ray absorption spectroscopic studies of copper in a copper-rich sludge during electrokinetic treatments

Speciation of copper in a copper-rich chemical-mechanical polishing sludge during electrokinetic treatment has been studied by in situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy. The least-squares-fitted XANES spectra indicate that the main copper species in the sludge are Cu(OH)₂ (74%), nanosize CuO (20-60 nm) (13%) and CuO (>100 nm) (13%). The average bond distance and coordination number (CN) of Cu-O are 1.96 Å and 3.5, respectively. Under electrokinetic treatment (5 V cm^-1) for 120 min, about 85% of the copper is dissolved in the electrolyte, 13% of which is migrated and enriched on the cathode. Notably the copper nanoparticles in the sludge can also migrate to the cathode under the electric field. By in situ EXAFS, it is found that during the electrokinetic treatment the bond distance and CN of Cu-O are increased by 0.1 Å and 0.9, respectively.