In situ synchrotron X-ray diffraction investigation of the evolution of a PbO₂/PbSO₄ surface layer on a copper electrowinning Pb anode in a novel electrochemical flow cell

This paper describes the quantitative measurement, by in situ synchrotron X-ray diffraction (S-XRD) and subsequent Rietveld-based quantitative phase analysis and thickness calculations, of the evolution of the PbO₂ and PbSO₄ surface layers formed on a pure lead anode under simulated copper electrowinning conditions in a 1.6 M H₂SO₄ electrolyte at 318 K. This is the first report of a truly in situ S-XRD study of the surface layer evolution on a Pb substrate under cycles of galvanostatic and power interruption conditions, of key interest to the mining, solvent extraction and lead acid battery communities. The design of a novel reflection geometry electrochemical flow cell is also described. The in situ S-XRD results show that β-PbO₂ forms immediately on the anode under galvanostatic conditions, and undergoes continued growth until power interruption where it transforms to PbSO₄. The kinetics of the β-PbO₂ to PbSO₄ conversion decrease as the number of cycles increases, whilst the amount of residual PbO₂ increases with the number of cycles due to incomplete conversion to PbSO₄. Conversely, complete transformation of PbSO₄ to β-PbO₂ was observed in each cycle. The results of layer thickness calculations demonstrate a significant volume change upon PbSO₄ to β-PbO₂ transformation.