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The Inhibitation of Pb(IV) Oxide Formation in Chlorinated Water by Orthophosphate
Citation:
LYTLE, D. A. AND M. R. SCHOCK. The Inhibitation of Pb(IV) Oxide Formation in Chlorinated Water by Orthophosphate. Crystal Growth and Design. American Chemical Society, Washington, DC, 43(17):6624-6631, (2009).
Impact/Purpose:
to present information
Description:
Previous work showed that PbO2 can form in water in the absence of phosphate. The analysis of many pipe scales and deposits removed from real DWDS has shown that PbO2 is present in some cases and absent in others. High ORP has been shown to favor PbO2 formation, but some drinking waters have high chlorine levels and presumably high ORP, and no PbO2 in the distribution system. Similarly, anecdotal observations of some water systems at the time of the Washington D.C. lead problem did not observe lead increases following a similar switch from free chlorine to chloramines for disinfection. In such situations, the addition of orthophosphate for corrosion control was thought to prevent PbO2 formation. By preventing the formation of PbO2, orthophosphate would reduce the vulnerability to destabilization and dissolution of PbO2 with treatment changes that result in an ORP drop in the distribution system. Hence, this work provides an explanation for the observations of many water systems of the varying impact of disinfectant change on lead release.
