Role of Manganese in Accelerating the Oxidation of Pb(II) Carbonate Solids to Pb(IV) Oxide at Drinking Water Conditions

Journal Article · Thu May 23 00:00:00 EDT 2019 · Environmental Science and Technology

DOI:https://doi.org/10.1021/acs.est.8b07356· OSTI ID:1650427

Pan, Weiyi ^[1]; Pan, Chao ^[2]; Bae, Yeunook ^[1]; Giammar, Daniel ^[1]

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1. Washington Univ., St. Louis, MO (United States). Dept. of Energy, Environmental & Chemical Engineering
2. Washington Univ., St. Louis, MO (United States). Dept. of Energy, Environmental & Chemical Engineering; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physical & Life Sciences

Pb(II) carbonate solids are corrosion products that form on the inner surfaces of lead service lines (LSLs) and can be oxidized by free chlorine to form Pb(IV) oxide (PbO₂). The formation of PbO₂ can maintain low dissolved lead concentrations in drinking water, but PbO₂ can dissolve if a free chlorine residual is not maintained. Experiments demonstrated that the oxidation of Pb(II) carbonate by free chlorine was faster with manganese (Mn). Without Mn(II), the oxidation of Pb(II) carbonate was an autocatalytic process. With Mn(II), the overall oxidation rate was 2 orders of magnitude faster than without Mn(II). X-ray diffraction and free chlorine consumption profiles indicated that δ-MnO₂ was formed within several minutes of the reaction of Mn(II) with free chlorine, and δ-MnO₂ catalyzed the oxidation of Pb(II) carbonate by free chlorine. Free chlorine consumption profiles for Pb(II) carbonate with and without Mn(II) were interpreted based on the kinetics and stoichiometry of the underlying chemical reactions. These findings highlight the importance of Mn in accelerating the formation of PbO₂ in water with Pb(II) carbonate solids and free chlorine, and it may help explain why PbO₂ is observed on LSLs of some but not all water systems that use free chlorine.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1650427
• Report Number(s): LLNL-JRNL--789697; 988185
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 12 Vol. 53; ISSN 0013-936X
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
chlorine
contamination
environmental sciences
inorganic carbon compounds
oxidation
transition metals