Abstract
Pb(IV)O2(s, plattnerite) nanoparticle aggregrates in aqueous suspension are readily reduced by Mn2+(aq) and Fe2+(aq) between pH 3.0 and 8.5, yielding pb2+(aq) and adsorbed Pb". Fe2+(aq) oxidation generates Fe(III) (hydr)oxides that impede Pb(IV) reduction, especially at pH > or =5. Under acidic conditions, production of dissolved Fe(III) may also be significant. Mn2+(aq) oxidation generates mixed Mn(III)/Mn(IV) (hydr)oxides that are less of an impediment to Pb(IV) reduction. Adding both Fe2+(aq) and Mn2+(aq) can set in motion a Mn redox cycle that catalyzes PbO2(s) reduction by Fe2+(aq). Reaction with Fe2+(aq) and Mn2+(aq) can affect subsequent reactions with natural organic matter. Hydroquinone was employed as a representative organic reductant. Both hydroquinone and its two-electron oxidation product p-benzoquinone are readily quantified by HPLC. Adding Fe2+(aq) before hydroquinone greatly diminishes p-benzoquinone production. Adding Mn2+(aq) before hydroquinone has little effect on p-benzoquinone production. Free chlorine residual variations in premise plumbing can setthe stage for the reactions documented here.
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