In situsynchrotron X-ray diffraction investigation of the evolution of a PbO2/PbSO4surface layer on a copper electrowinning Pb anode in a novel electrochemical flow cell

Abstract

This paper describes the quantitative measurement, byin situsynchrotron X-ray diffraction (S-XRD) and subsequent Rietveld-based quantitative phase analysis and thickness calculations, of the evolution of the PbO2and PbSO4surface layers formed on a pure lead anode under simulated copper electrowinning conditions in a 1.6 MH2SO4electrolyte at 318 K. This is the first report of a trulyin situS-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. Thein situS-XRD results show that β-PbO2forms immediately on the anode under galvanostatic conditions, and undergoes continued growth until power interruption where it transforms to PbSO4. The kinetics of the β-PbO2to PbSO4conversion decrease as the number of cycles increases, whilst the amount of residual PbO2increases with the number of cycles due to incomplete conversion to PbSO4. Conversely, complete transformation of PbSO4to β-PbO2was observed in each cycle. The results of layer thickness calculations demonstrate a significant volume change upon PbSO4to β-PbO2transformation.