Role of Aluminosilicate deposits in Lead and Copper Corrosion

Abstract

Aluminosilicates frequently deposit onto plumbing materials in distribution systems. Such solids were previously believed to provide some degree of corrosion protection to pipes—although at the expense of increased head loss, reduced flow, and consumer complaints related to postprecipitation. However, this work demonstrates that new copper and lead pipe sections did not benefit from the deposition of aluminosilicate solids. In fact, in most situations the presence of solids actually caused the release of more metal to drinking water compared with solutions without solids. Final pH played a key role in determining the extent of copper corrosion, and the aluminum deposits prevented increases in pH during stagnation through a buffering action.

Role of iron and aluminum coagulant metal residuals and lead release from drinking water pipe materials

“…Collectively, there is evidence to suggest that residual aluminum (or iron), from coagulation processes, could be a factor contributing lead release at the tap. Furthermore these relationships are limited to the conditions used in this study, they corroborate the relationships and trends noted elsewhere for residual aluminum effects on elevated lead [1] and linkages between elevated iron and lead. [15,17] …”

“…[10][11][12][13][14] One prior research article also attempted to quantify possible secondary benefits of aluminum from coagulation passing through water treatment (i.e., residual aluminum) in reducing lead release, but instead demonstrated that the aluminum tended to increase mobilization of lead. [1] It was speculated that the aluminum deposits sorbed lead from the plumbing material, causing excess lead to slough or dissolve into the water. Recent work has also highlighted similar relationships between iron in water and lead release.…”

“…[1] Changing the coagulant type and dose has been recognized to produce a variety of secondary impacts on corrosion control in some systems. For example, higher chloride:sulfate mass ratios (CSMR) resulting from switches from sulfate-containing coagulant to chloride-containing have triggered several instances of elevated lead release from galvanic corrosion in service lines and premise plumbing.…”

Secondary effects of implementing arsenic removal treatment—focus on corrosion and microbial regrowth

“…Nonuniform corrosion of iron. Iron corrosion is one of the most important economic and aesthetic problems facing public utilities (McNeill & Edwards, 2001). Numerous attempts have been made to empirically describe waters in which iron corrosion problems occur.…”

“…Column operation can increase residual aluminum concentrations if aluminum hydroxides are used. These aluminum residuals coat pipes, influence lead and copper corrosion, cause consumer complaints, and initiate copper pitting (Rushing & Edwards, 2004; Snoeyink et al, 2003; Kvech & Edwards, 2002; 2001). High levels of silica in crease dissolution of aluminum from columns (Smith & Edwards, 2005), so the concentration of soluble residual aluminum is a function of water quality and is sometimes above the USEPA secondary maximum contaminant level.…”