Citrate-Mediated Hydrometallurgical Lead Extraction and Integrated Electrochemical Recovery from Zinc Leaching Residue

Abstract

The treatment and hydrometallurgical recovery of Pb from zinc leaching residue (ZLR), a waste stream generated by the zinc refining process, is proposed in this work. Leaching achieved complete extraction of Pb (140 mg/g) within 24 h contact time using a 0.8 M sodium citrate solution. The batch leaching process that operates at ambient temperature results in a pregnant leachate solution of dissolved lead citrate. Pb is recovered from the dissolved organometal complex as a precipitate of PbSO4 after chemical reaction in acidic conditions that are maintained through continuous membrane electrolysis. In addition, an alkaline buffer is generated at the cell cathode to regenerate the leachate, so that the recycled lixiviant can be used in consequent leaching steps. Characterization of the final product by XRD, ICP-AES, and Raman spectroscopy identified an amorphous PbSO4 phase with traces of lead citrate. The overall purity of Pb is 46 ± 4%, representing a 3.3 fold concentration of ZLR. The integrated process is capable to treat ZLR sustainably. It can resolve the need for landfilling the mineral tailing and treat historic dump sites, respecting the zero-waste rationale, while also recovering raw material from a secondary source.