Removal of copper from industrial sludge by traditional and microwave acid extraction

This work elucidates the removal of copper from industrial sludge by traditional and microwave acid extraction. The effects of acid concentration, extraction time, sludge particle size and solid/liquid (S/L) ratio on copper removal efficiency were evaluated. Leaching with more concentrated acid yielded greater copper content from the industrial sludge. The experimental findings reveal that the most economical traditional extraction conditions were the use of 1N sulfuric or nitric acid for 60 min at an S/L ratio of 1/20; however, at an S/L ratio of 1/6, the extraction time needed to achieve the same copper removal efficiency was increased to 36 h. Increasing the microwave power and reducing the S/L ratio increased the copper extraction efficiency and the effect in the larger S/L ratio system was more significant. A comparison of the results of microwave-assisted (microwave only) and microwave-enhanced (microwave with addition of active carbon) acid extraction demonstrated that under both conditions, S/L ratio=1/6 and 1/20; adding active carbon shortened the extraction time required to achieve 80% copper extraction efficiency from 20 to 10 min. These experimental results indicate that the most important factors that most strongly affected microwave acid extraction were the addition of a microwave absorber, the microwave power input and the S/L ratio. The sludge particle size did not significantly affect the copper extraction. The results reveal that sulfuric acid was an effective extractant and that the copper fraction in the extracted sludge shifted from being mostly bound to the Fe-Mn oxides and organic matter, to being mostly bound to organic matter and remaining as a residue during acid extraction.