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CRYSTAL AND MORPHOLOGICAL PHASE TRANSFORMATION OF LEAD IN THE PRESENCE OF ORTHOPHOSPHATE
Citation:
White, C., D. A. LYTLE, AND J. Conover. CRYSTAL AND MORPHOLOGICAL PHASE TRANSFORMATION OF LEAD IN THE PRESENCE OF ORTHOPHOSPHATE . Presented at Fifth Annual EPA Drinking Water Workshop, , Cincinnati, OH, August 05 - 07, 2008.
Impact/Purpose:
Information
Description:
The use of phosphates in the drinking water industry is well known. Orthophosphate is used to reduce lead levels at the consumer’s tap by forming a relatively insoluble divalent lead orthophosphate compounds on the surface of the lead source (e.g., lead service line, brass fixture, soldered joint, etc.) in the drinking water distribution system. Water utilities are required to meet the United States Environmental Protection Agency’s (U.S. EPA’s) Lead and Copper Rule (LCR )that sets a 90th action level for lead at 0.015 mg/L at the consumer’s tap (Federal Register 1991; Federal Register 1991; Federal Register 1992). Polyphosphates (e.g. pyrophosphate, tripolyphosphate, hexametaphosphate, etc.) have been used to prevent the undesirable precipitation of manganese, calcium, iron, and magnesium through the treatment plant and in the drinking water distribution system. The mechanisms by which polyphosphates function are based on colloidal stabilization and chemical complexation interactions (Manahan 1991; Lytle et.al. 2005; Stumm and Morgan 1996). There is evidence that some polyphosphates may actually increase lead levels in the distribution system by the same interactions and thereafter potentially increase lead exposure to the consumer (Holm and Schock 1991). Therefore, the objective of this study was to observe and report morphological transformations of lead particles in the presence and absence of phosphate corrosion inhibitors.