Identification and Distribution of Vanadinite (Pb[subscript 5](V[superscript 5+]O[subscript 4])[subscript 3]Cl) in Lead Pipe Corrosion By-Products

This study presents the first detailed look at vanadium (V) speciation in drinking water pipe corrosion scales. A pool of 34 scale layers from 15 lead or lead-lined pipes representing eight different municipal drinking water distribution systems in the Northeastern and Midwestern portions of the United States were examined. Diverse synchrotron-based techniques, including bulk XANES (X-ray absorption near edge spectroscopy), {mu}-XANES, {mu}-XRD (X-ray diffraction), and {mu}-XRF (X-ray fluorescence) mapping were employed along with traditional powder XRD, SEM-EDXA (scanning electron microscopy-energy dispersive X-ray analysis), and ICP-OES (inductively coupled plasma-optical emission spectrometry) to evaluate vanadium speciation and distribution in these deposits. Vanadinite (Pb{sub 5}(VO{sub 4}){sub 3}Cl) was positively identified, and occurred most frequently in the surface layers. Low V{sub tot} in these waters is likely the limiting factor in the abundance of vanadinite in the pipe scales, along with the existence of divalent lead. The occurrence of V in these samples as a discrete mineral is important because it is formed in the presence of very low concentrations of V in the finished water, it provides a mechanism to concentrate {mu}g{center_dot}L{sup -1} amounts of V from the water to near-percent levels in the pipe scales, and the robustness of V accumulation and release in response to water chemistry changes is likely different than it would be with a sorption accumulation mechanism. Extrapolation from limited existing water chemistry data in this study provides an estimate of {Delta}G{sub f}{sup o} for vanadinite as approximately -3443 kJ{center_dot}mol{sup -1}, or less, leading to a log K{sub s0} value of approximately -86 for the reaction Pb{sub 5}(VO{sub 4}){sub 3}CI{sub (s)}{r_reversible} {l_brace}Pb{sup 2+}{r_brace}{sup 5} + {l_brace}VO{sup 3-}{sub 4}{r_brace}{sup 3} + {l_brace}Cl{sup -}{r_brace}, in which {l_brace}{r_brace} denotes activity.