Importance of Pb and Cu Particulate Species for Corrosion Control

Abstract

This paper examines the important, and oftentimes dominant, role of particles in lead and copper corrosion by-product release from stagnant pipes. For copper pipes, orthophosphate generally reduced soluble copper levels compared to pipes with no inhibitor but had little effect on particulate copper, while pipes dosed with polyphosphate generally had higher levels of particulate copper, probably due to the formation of a less durable copper–phosphate solid. For lead, the vast majority of lead by-products were particulate, and particulate release in low pH and low alkalinity waters was associated with hydrocerrusite scales. Orthophosphate and polyphosphate tended to decrease particulate lead species, possibly due to the formation of a lead–phosphate solid. For both lead and copper pipes, zinc orthophosphate did not show any significant advantages compared to orthophosphate alone, generally due to the increased release of particulate lead or copper species which may be associated with a zinc–phosphate precipitate. Finally, the occurrence of particulate and colloidal species, especially lead, was confirmed by utility tap water sampling.