Redox-Driven Recrystallization of PbO.

Lead(IV) oxide (PbO) is one of the lead corrosion products that forms on the inner surface of lead pipes used for drinking water supply. It can maintain low dissolved Pb(II) concentrations when free chlorine is present. When free chlorine is depleted, PbO and soluble Pb(II) will co-occur in these systems. This study used a stable lead isotope (Pb) as a tracer to examine the interaction between aqueous Pb(II) and solid PbO at conditions with no net change in dissolved Pb concentration. While the dissolved Pb(II) concentration remained unchanged, significant isotope exchange occurred that indicated that substantial amounts (24.3-35.0% based on the homogeneous recrystallization model) of the Pb atoms in the PbO solids had been exchanged with those in solution over 264 h. Neither α-PbO nor β-PbO displayed a change in mineralogy, particle size, or oxidation state after reaction with aqueous Pb(II). The combined isotope exchange and solid characterization results indicate that redox-driven recrystallization of PbO had occurred. Such redox-driven recrystallization is likely to occur in water that stagnates in lead pipes that contain PbO, and this recrystallization may alter the reactivity of PbO with respect to its stability and susceptibility to reductive dissolution.