You are here:
Orthophosphate Interactions with Destabilized PbO2 Scales
Citation:
DeSantis, Mike, M. Schock, J. Tully, AND C. Bennett-Stamper. Orthophosphate Interactions with Destabilized PbO2 Scales. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 54(22):14302–14311, (2020). https://doi.org/10.1021/acs.est.0c03027
Impact/Purpose:
This research presents two case studies in which a change in disinfection from free chlorine to chloramine caused an issue with lead corrosion. In both systems the predominant Pb(IV) scale destabilized as a result of the disinfection change. Orthophosphate was used in both systems as corrosion control, and the effect of this treatment chemical on the destabilized Pb(IV) scales was examined. This research confirms that P does not interact with legacy Pb(IV) scales. Instead, P and Ca were found to permeate through the destabilized Pb(IV) material and react with Pb(II) at the surface of a basal PbO layer. This reaction precipitated a crystalline lead phosphate in both utilities which could not be specifically identified by any known powder diffraction files. Further analysis suggests that the compound formed is not the typically modeled hydroxypyromorphite, but rather a calcium-substituted hydroxypyromorphite. Results of this study illustrate the longevity of legacy scales and how disequilibrium compounds persist long after treatment changes have been made.
Description:
This research presents two case studies in which a change in disinfection from free chlorine to chloramine caused an issue with lead corrosion. In both systems the predominant Pb(IV) scale destabilized as a result of the disinfection change. Orthophosphate was used in both systems as corrosion control, and the effect of this treatment chemical on the destabilized Pb(IV) scales was examined. This research confirms that P does not interact with legacy Pb(IV) scales. Instead, P and Ca were found to permeate through the destabilized Pb(IV) material and react with Pb(II) at the surface of a basal PbO layer. This reaction precipitated a crystalline lead phosphate in both utilities which could not be specifically identified by any known powder diffraction files. Further analysis suggests that the compound formed is not the typically modeled hydroxypyromorphite, but rather a calcium-substituted hydroxypyromorphite. Results of this study illustrate the longevity of legacy scales and how disequilibrium compounds persist long after treatment changes have been made.
URLs/Downloads:
DOI: Orthophosphate Interactions with Destabilized PbO2 Scales
Free Access through PubMed Central