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

Lead(IV) oxide (PbO(2)) 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 PbO(2) and its impact on the dissolution rate of PbO(2). The dissolution rate of PbO(2) 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 PbO(2) increased with decreasing pH. The presence of free chlorine inhibited PbO(2) dissolution. The dissolution of PbO(2) 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 PbO(2) 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 PbO(2) was directly related to the distribution of the PbO(2) surface species predicted by the surface complexation model. The dissolution rate was predominantly controlled by >Pb(IV)OH(2)(+) for acidic conditions and by>Pb(IV)OH and>Pb(IV)O(-) at neutral to basic conditions.