Full Description

Lead concentrations in drinking water distribution systems are influenced by the dissolution,precipitation, and transformation of lead corrosion products that are present as scale indistribution system pipe. Changes in treatment processes that influence the distribution systemwater chemistry can induce the dissolution or transformation of the lead-containing corrosionproducts. The addition of orthophosphate as a corrosion inhibitor has been demonstrated inprevious work to limit the dissolved concentrations of lead to below the action level establishedby the Lead and Copper Rule. In this research, the role of orthophosphate in controllingthe dissolution rates of the lead carbonate hydrocerussite and the lead phosphatehydroxylpyromorphite were evaluated in controlled laboratory-scale experiments usingcontinuous-flow stirred tank reactors. Dissolution rates are interpreted within a reaction-basedapproach that considers the overall thermodynamic driving force for dissolution as part of afundamental dissolution rate equation. The solid phases remaining at the conclusion of selectedexperiments were characterized by scanning electron microscopy and X-ray diffraction to assesstransformations in the solid phases that may have been induced by orthophosphate. Lowintrinsic solubility and dissolution rates were observed for hydroxylpyromorphite. Theseobservations suggest that the formation of hydroxylpyromorphite can decrease dissolved leadconcentrations in distribution system waters. The presence of orthophosphate during thedissolution of hydrocerussite dramatically decreased the rate of lead release to solution. Includes 9 references, figures.

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Edition: Vol. - No. Published: 11/01/2008 Number of Pages: 7File Size: 1 file , 780 KB