Redox-driven recrystallization of metal oxides is an environmental phenomenon that can influence biogeochemical cycles of both nutrients and contaminants. Lead(IV) oxides (PbO2) have been observed as a component of scales on the surface of lead pipe used for water supply. Two polymorphs of PbO2, scrutinyite (α-PbO2) and plattnerite (β-PbO2), can be formed from the reaction of Pb(II) species with the free chlorine (HOCl/OCl-) in drinking water. On the one hand, PbO2 has a much lower solubility than other lead-containing solids found pipe scales and hence can be a sink for Pb(II) in drinking water. On the other hand, PbO2 is only stable in the presence of free chlorine, and many chemical species can chemically reduce it to release Pb(II) back to the water. Recrystallization can alter the inherent stability with respect to reductive dissolution of PbO2, which will influence drinking water quality by causing the incorporation/release of aqueous Pb(II). At pH 5.5, the reductive dissolution of PbO2 was significantly higher compared with dissolution at pH 6.5 to 9.5. Higher dissolution yielded less net adsorption aqueous Pb(II) and possibly inhibited recrystallization process. We also examined mineral phase, average particle size, crystallinity, and reactivity of PbO2 after reaction with aqueous Pb(II). Different inhibitory effects of Pb(II), Cu(II), and Zn(II) on α-PbO2 and β-PbO2 reductive dissolution were observed, which may be caused by different strengths of adsorption to the PbO2 surface. We have also measured the extent of Pb atom exchange between aqueous Pb(II) and PbO2 by reacting isotopically “normal” PbO2 with aqueous 207Pb(II). This approach allowed us to calculate the fraction of structural Pb(IV) in PbO2 that reacted with aqueous 207Pb(II) in solution.

Lead-catalyzed redox-driven recrystallization of lead oxide

2019 Spring National Meeting

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