In situ speciation studies of copper in the electroplating sludge under an electric field

Speciation of copper in the electrokinetic treatments of an industrial sludge was studied by in situ extended X-ray absorption fine structural (EXAFS) and X-ray absorption near-edge structural (XANES) spectroscopies in the present work. The least-square fits (LSF) of the XANES spectra indicated that the main copper species in the sludge were Cu(NO)₃ (82%) and adsorbed copper (Cu/SiO₂) (17%). Copper in the sludge possessed a Cu-O bond distance of 1.97Å with a coordination number (CN) of 3.8. In the second shells, the bond distance of Cu-(O)-Si was 3.03Å with a CN of 1.5. Most of Cu/SiO₂ was dissolved in the aqueous phase since little Cu-(O)-Si species in the sludge was found after 180min of the electrokinetic treatments. About 69% of total Cu(II) was dissolved into the aqueous phase and 51% of which was migrated to the cathode under the electric field (5Vcm^-1) for 180min.