Insight into a novel circulation system combined with coordination leaching and biosorption for Cu(II) efficient recycling from electroplating sludge

A novel circulation system combined with coordination leaching and biosorption process was successfully used for the direct recycling of Cu2+ from the electroplating sludge. Cu2+ was firstly efficiently leached out from the sludge by the choosing organic acid, and then it was selectively adsorbed onto a modified sorbent from the lixivium containing other co-ions including Zn2+, Ca2+, Fe3+, Cr3+, and Mg2+ under dynamic adsorption condition. The results of static leaching experiments and DFT calculations showed that citric acid showed the best leaching performance for Cu2+ among the studied organic acids and the traditional inorganic acid (HCl). To selective recovery of Cu2+ from the lixivium, ethylenediamine tetraacetic acid dianhydride (EDTAD) modified bagasse was prepared, and it had high adsorption capacity, selectivity, and good reusability toward Cu-citric acid complex. The adsorption isotherm for Cu matched with the Langmuir model with a maximum adsorption capacity of 52.2 mg/g. XPS and EXAFS analysis illustrated that the Cu-citric acid complex was broken by EDTA on the modified bagasse, and Cu2+ enriched on the sorbent while citric acid was released into the lixivium again. In the combined leaching and sorption circulation system, Cu2+ was simultaneously absorbed on the modified bagasse fixed bed column once it was leached out. Benefitting the recycling of citric acid and the continuous adsorbing of Cu of the circulation system, the leaching efficiency could be increased from 75.0 % to 92.4 %, even in the very dilute citric acid solutions (concentration of 0.01 mol/L). The combined methods could increase Cu recovery efficiency from the sludge at a low concentration of the leaching agent, which had great potential in the practical application.