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THE FORMATION OF PB(IV) OXIDES IN CHLORINATED WATER
Citation:
LYTLE, D. A. AND M. R. SCHOCK. THE FORMATION OF PB(IV) OXIDES IN CHLORINATED WATER. In Proceedings, 2005 AWWA WQTC Conference CD-ROM, Quebec, QC, CANADA, November 06 - 10, 2005. AWWARF, Denver, CO, 15 p., (2005).
Impact/Purpose:
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Description:
Recent research has shown that Pb(IV) oxides can play an important geochemical role in drinking water distribution systems. The basis of most guidance for lead control in drinking water, however, presumes that Pb(II) solids control lead solubility. Therefore, it is important that a better understanding of the chemistry of Pb(IV) in water is gained. Long-term lead precipitation experiments were conducted in chlorinated (1 to 3 mg Cl2/L) water at pH 6.5, 8, and 10, with and without sulfate. Results showed that two Pb(IV) dioxide polymorphs, plattnerite (β-PbO2) and scrutinyite (α-PbO2) formed over time as long as high suspension redox potential was maintained with free chlorine. Neither mineral formed spontaneously, and the rate of formation increased with increasing pH. Hydrocerrusite and/or cerrusite initially precipitated out and with time either disappeared or coexisted with PbO2. Water pH dictated mineralogical presence; high pH favored hydrocerrusite and scrutinyite. Low pH favored cerrusite and plattnerite. Along with a transformation of Pb(II) to Pb(IV) came a change in particle color from white to a dark shade of red to dark grey (differing with pH) and a decrease in lead solubility. If free-chlorine was permitted to dissipate, the aging processes (i.e., mineralogy, color, and solubility) was reversible.