THE MINERALOGY OF PB SCALES IN DRINKING WATER DISTRIBUTION SYSTEMS AS REVEALED BY COMBINED XRD AND MICRO-RAMAN SPECTROSCOPY
One lead pipe and its scales, provided by Utility X, was used for this study. This pipe was examined with a stereomicroscope to identify the spatial arrangements of the mineral phases. The scale minerals displayed a great deal of variation both vertically and horizontally. Scale deposits from portions of the pipe were harvested as a single sample for pressed-powder XRD analyses. The mineralogy determined by XRD included: hydrocerussite, (Pb3(CO3)2(OH)2), cerussite (PbCO3), litharge (PbO), and massicot (PbO). Minor amounts of plattnerite (PbO2) were also detected. Plumbonacrite (Pb10O(CO3)6(OH)6) and/or quartz may also be present. Micro- Raman spectra confirmed the presence of these same minerals. In addition it showed that these minerals occur in radial patterns, with hydrocerussite at the center, followed by massicot, then litharge all of which is surrounded by plattnerite. The large number of Pb phases shows that these pipes do not constitute an equilibrium system. The Raman mapping suggests the evolution in Pb chemistry with time that may reflect changes in water treatment practices.