Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2019)

Lead-containing plumbing materials are widely used in drinking water systems across the globe. Being a toxic heavy metal, the release of lead within the drinking water distribution systems poses a major threat to public health. This study examined lead(II) mineral phases present in typical drinking water distribution systems by utilizing chemical equilibrium modeling. The predominant lead(II) minerals were exposed to free chlorine, a residual disinfectant, to study their oxidative transformation. In the absence of phosphate, cerussite PbCO3(s) and hydrocerussite Pb3(CO3)2(OH)2(s) are the predominant phases, dependent on pH. The addition of phosphate induced the precipitation of pyromorphite Pb5(PO4)3Cl(s), lowering the total dissolved lead concentrations. The lead phosphate minerals resisted oxidation by chlorine, but the lead carbonate minerals reacted readily. The resulting solids were analyzed with XAS and revealed the generation of plattnerite -PbO2(s) as the dominant Pb(IV) mineral, with trace amounts of scrutinyite -PbO2(s). Bromine oxidation of these Pb(II) minerals resulted in oxidation rate constants up to an order of magnitude greater than with chlorine. Using the derived rate constants, models of drinking water distribution systems were developed to show in the impact of bromide contamination. Although the lead(IV) phosphate minerals resisted oxidation, the presence of bromide indicated these systems would be oxidized within a century. Next, the mobility of toxic metals in an oxidized system was investigated. Vanadinite Pb5(VO4)3Cl is present in systems with vanadium contamination and has the potential to release both vanadium and lead if oxidation occurs. Like the lead(II) phosphates, vanadinite resists chlorine oxidation but can be oxidized by bromine. This oxidation causes to the release of both lead and vanadium over time. Vanadium is very mobile, as almost 80% that passes through the 0.2 µm filter also passes through the 0.025 µ m filter. Lead is release occurs in the 0.2 µm filter but is effectively removed by the 0.025 µ m filter. This study provides fundamental understanding of lead surface chemistry in drinking water as well as strategies to prevent toxic metal release in drinking water distribution systems.

    Cover page: The Effects of Changing Water Chemistry on the Stability of Lead Service LinesCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2021)
    This study investigated the reaction kinetics on the oxidative transformation of lead(ii) minerals by free chlorine (HOCl) and free bromine (HOBr) in drinking water distribution systems. According to chemical equilibrium predictions, lead(ii) carbonate minerals, cerussite PbCO3(s) and hydrocerussite Pb3(CO3)2(OH)2(s), and lead(ii) phosphate mineral, chloropyromorphite Pb5(PO4)3Cl(s) are formed in drinking water distribution systems in the absence and presence of phosphate, respectively. X-ray absorption near edge spectroscopy (XANES) data showed that at pH 7 and a 10 mM alkalinity, the majority of cerussite and hydrocerussite was oxidized to lead(iv) mineral PbO2(s) within 120 minutes of reaction with chlorine (3 : 1 Cl2 : Pb(ii) molar ratio). In contrast, very little oxidation of chloropyromorphite occurred. Under similar conditions, oxidation of lead(ii) carbonate and phosphate minerals by HOBr exhibited a reaction kinetics that was orders of magnitude faster than by HOCl. Their end oxidation products were identified as mainly plattnerite β-PbO2(s) and trace amounts of scrutinyite α-PbO2(s) based on X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. A kinetic model was established based on the solid-phase experimental data. The model predicted that in real drinking water distribution systems, it takes 0.6-1.2 years to completely oxidize Pb(ii) minerals in the surface layer of corrosion scales to PbO2(s) by HOCl without phosphate, but only 0.1-0.2 years in the presence of bromide (Br-) due the catalytic effects of HOBr generation. The model also predicts that the addition of phosphate will significantly inhibit Pb(ii) mineral oxidation by HOCl, but only be modestly effective in the presence of Br-. This study provides insightful understanding on the effect of residual disinfectant on the oxidation of lead corrosion scales and strategies to prevent lead release from drinking water distribution systems.
      Cover page: Effects of residual disinfectants on the redox speciation of lead( ii )/( iv ) minerals in drinking water distribution systems
      Top