Chiang Mai Journal of Science

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Surface structure of the Pb-0.5%Ag plate after used as anode in zinc electrowinning for 15 days and effect of pretreatment by dipping the lead alloy plate in a hot acidic potassium permanganate solution on the surface structure were studied by scanning electron microscopy and x-ray diffractometry. Formation of compound layers including PbO_n, PbSO₄ and MnOOH-MnO₂ were observed on the lead alloy plate after used in zinc electrowinning for 15 days, with a thickness ratio of about 1:100:900. The observation supports the Pavlov’s model of Pb/PbO_n/PbSO₄, where 1<n<2, and the ECE reaction model proposed by Paul and Cartwright for the formation of MnO₂ via an insulating intermediate MnOOH. Treatment by dipping the lead alloy plate in the hot acidic potassium permanganate solution resulted in the formation of a compound layer containing PbSO₄ and Pb₂MnO₄. This layer could act as a barrier layer decreasing a dissolution rate of lead ions and reducing the contamination of Pb at the cathode during zinc electrowinning.

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