Comparative study of copper extraction by nitric and microwave assisted nitric acid extraction from industrial sludge

Cu was removed from industrial sludge by traditional and microwave assisted acid extraction. The effects of acid concentration, extraction time, sludge particle size and solid/liquid (S/L) ratio on removal of Cu from industrial sludge were investigated. The results indicated that extraction of Cu by 1 N nitric acid for 90 min at an S/L ratio of 1/20 is the most economical traditional extraction conditions; the higher microwave power can increase the Cu extractable fractions; active carbon addition shortened the extraction time required to extract 80% Cu industrial sludge from 15 to 10 min. The addition of a microwave absorber, the microwave power input and the S/L ratio are the most important factors to microwave acid extraction of Cu. The results reveal that sulfuric acid was an effective extractant; Cu fraction bound to the Fe-Mn oxides was extracted. Conversely, the residue fraction remained during acid extraction.