Effects of pH and Carbonate Concentration on Dissolution Rates of the Lead Corrosion Product PbO_2

摘要

Lead(Ⅳ) oxide is a corrosion product that can develop on lead pipes and affect lead concentrations in drinking water. Continuously stirred flow-though reactors were used to quantify the dissolution rates of plattnerite (β-PbO_2) at different pH values and dissolved inorganic carbon (DIC) concentrations. Organic pH buffers were not used, because several were found to be reductants for PbO_2 that accelerated its dissolution. Most plattnerite dissolution rates were on the order of 10~(-10) mol/ min-m~2. The rate of dissolution increased with decreasing pH and with increasing DIC. The effect of DIC is consistent with a reductive dissolution mechanism that involves the reduction of Pb(Ⅳ) to Pb(Ⅱ)atthe plattnerite surface followed by the formation of soluble Pb(Ⅱ)-carbonate complexes that accelerate Pb(Ⅱ) release from the surface. Under the experimental conditions, dissolved lead concentrations were controlled by the dissolution rate of plattnerite and not by its equilibrium solubility. A dissolution rate model was developed and can be used to predict dissolution rates of plattnerite as a function of pH and DIC.