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THE IMPACT OF HEXAMETAPHOSPHATE ON COPPER CORROSION AND RELEASE
Citation:
O'Donnell, A. J. THE IMPACT OF HEXAMETAPHOSPHATE ON COPPER CORROSION AND RELEASE. Presented at AWWA Water Quality Technology Conference and Exhibition, Cincinnati, OH, November 16 - 20, 2008.
Impact/Purpose:
to share information
Description:
In 1991, U.S. Environmental Protection Agency (U.S. EPA) promulgated the Lead and Copper Rule, which established a copper action level of 1.3 mg/L in a 1-liter, first-draw sample collected from the consumer’s tap (Federal Register, 1991a, 1991b, 1992). The rule was established due to potential health concerns caused by elevated copper levels in drinking water. Excessive corrosion of copper can lead to elevated copper levels at the consumer's tap, and in some cases, copper corrosion can also lead to pinhole leaks and pipe failure. Water chemistry has a large impact on the type of copper corrosion solubility that takes place. Phosphate-based chemicals (ortho-, poly-, and blended-phosphates) have been used to control lead solubility and iron precipitation in many drinking water systems. The usefulness of orthophosphate to reduce copper release has also been recognized. The relationships between the type of orthophosphate, chemical dosage, water quality and copper solubility are not well defined, nor are the mechanism(s) by which the phosphates work. Some work has shown that polyphosphates can increase metal levels such as lead in water (Holm & Schock, 1991). Polyphosphates are commonly used to stabilize iron particles, and may similarly impact the mobility of copper particles in drinking water in distribution systems. There is also preliminary work being conducted which suggests that polyphosphates may be beneficial in preventing pitting corrosion of copper. The objective of this work was to better understand the effect of phosphates on copper corrosion and release in water.
