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LEAD AND COPPER CONTROL WITH NON-ZINC ORTHOPHOSPHATE
Citation:
Schock*, M R. AND J. A. Clement. LEAD AND COPPER CONTROL WITH NON-ZINC ORTHOPHOSPHATE. JOURNAL OF THE NEW ENGLAND WATER WORKS ASSOCIATION. New England Water Works Association, 112(2):20-42, (1998).
Description:
Successful application of orthophosphate formulations not containing zinc for achieving control of copper and lead corrosion requires careful consideration of the background water chemistry, particularly pH and DIC. Inhibitor performance is extremely dependent upon dosage and pH, and frequently pH must be adjusted with inhibitor addition. Many issues remain to be resolved about the mechanism of corrosion inhibition afforded, but there are clear differences between the conditions that are optimum for reducing lead solubility and those for minimizing copper solubility, producing a situation where a trade-off is necessary. Consideration of the redox chemistry at the surfaces of new and old metal piping reveals that the positive effects of zinc-containing formulations are magnified on new surfaces, which may not represent many realistic distribution system conditions. This is important when extrapolating pipe loop, coupon or electrochemical screening test data to full-scale application. Equivalent control of plumbosolvency and cuprosolvency while still maintaining good performance of cast iron materials and disinfection may be achieved in most cases without the unwanted side-effects accompanying zinc addition. This is shown both from theoretical considerations and also evidence from a variety of full-scale treatment implementations in the United States and Europe.