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The electrochemical dissolution of galena Brodie, John Buchan

Abstract

The electrochemical oxidation and reduction of galena (PbS) was studied in aqueous solutions of perchloric acid between pH 0 and 4. The wide variation of rest potential as reported in the literature was explained on the basis of stoichiometric variations of this material as well as the activities of ionic and molecular species involved in the PbS equilibria. The stoichiometry of the anodic and cathodic reactions was determined to be primarily PbS ↦ Pb⁺⁺+ S° + 2e⁻ and PbS + 2H⁺ + 2e⁻↦ Pb° + H₂S respectively. The irreversibility of anodic oxidation to lead sulphate was observed, with no sulphate produced below about 0.7 to 1.0 volt, depending on the pH. Polarization experiments revealed that ohmic, concentration, and activation polarization effects all contributed to the non-equilibrium behavior of PbS. Reaction of Pb0₂ and MnO₂ with PbS was rapid and interpreted as a "galvanic" effect, relying on the conductivity of the reactants as a necessary condition for its success.

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