AWWA WQTC69497

Colloidal mobilization of lead particles in drinking water distribution systems is an important, sometimes overwhelming, source for lead release but remains largely unexplored. Prominent random spikes of colloidal release have also been frequently observed. Despite their magnitude, this part of lead release can not be predicted based on the equilibrium plumbosolvency models. Specifically, the role of disinfectants in colloidal release has been examined only sketchily. In this study, colloidal properties and lead release during the oxidation of representative lead (II) solid phases (hydrocerussite, cerussite) by chlorine, along with the colloidal behavior of formed PbO₂, were examined. Zeta-potential measurements show that during lead (II) oxidation, surface charges on lead particles has increased to less negative values before chlorine is consumed. In addition, long before PbO₂ phase is abundant enough to be morphologically distinct, dramatic decrease of colloidal lead in all size factions occurs during hydrocerussite oxidation, whereas lead release increases initially during cerussite oxidation before decreasing eventually. SEM images show that this difference in colloidal mobilization is related to different morphological changes on crystal surfaces. Measurements of zeta-potential of lead solids also suggest formation of a thin oxidized film of PbO₂ or intermediate lead (III) specie controls the colloidal mobility of lead particles, which is important for plumbosolvency. Furthermore, experiments indicate PbO₂ phase can be destabilized and mobilized in the presence of chlorine. Includes 19 references, figures.