Kinetics of lead(IV) oxide (PbO2) reductive dissolution: Role of lead(II) adsorption and surface speciation

Abstract

Lead(IV) oxide (PbO2) is a corrosion product on lead pipes used for drinking water distribution, and its dissolution can control lead release to drinking water. This study evaluated the adsorption of Pb(II) to PbO2 and its impact on the dissolution rate of PbO2. The dissolution rate of PbO2 was determined as a function of pH in the absence and presence of free chlorine using continuously-stirred tank reactors. Pb(II) adsorption was examined as a function of pH and initial Pb(II) concentrations. The dissolution rate of PbO2 increased with decreasing pH. The presence of free chlorine inhibited PbO2 dissolution. The dissolution of PbO2 involves a coupled reduction–detachment process, and a model was developed that accounts for the adsorption of Pb(II) from the reduction. The extent of Pb(II) adsorption to PbO2 increased with increasing pH and Pb(II) concentrations until reaching a plateau. Adsorption was interpreted with a surface complexation model using the diffuse double-layer model and a single surface complex. The dissolution rate of PbO2 was directly related to the distribution of the PbO2 surface species predicted by the surface complexation model. The dissolution rate was predominantly controlled by >Pb(IV)OH2+ for acidic conditions and by>Pb(IV)OH and>Pb(IV)O− at neutral to basic conditions.