Redox Reactions Influencing Lead Concentrations in Drinking Water: Formation and Dissolution of Lead(IV) Oxide and Impact of Galvanic Corrosion
Energy, Environmental and Chemical Engineering
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Daniel E Giammar
Two approaches have been used to mitigate lead release to drinking water are optimizing water chemistry to form stable lead corrosion products and replacing lead service lines with lead-free materials. The present study investigated the effects of water chemistry on the formation and dissolution of the lead corrosion product lead(IV) oxide: PbO2). The impact of galvanic corrosion on lead release following simulated partial lead service line replacements: PLSLRs) was also determined.
The extent and identity of PbO2 formation was determined as a function of pH, the presence of dissolved inorganic carbon: DIC), and free chlorine concentrations with different lead(II) starting phases. PbO2 formed both with and without DIC. The intermediate solids formed affected the identity of the PbO2: scrutinyite versus plattnerite) product. When no intermediate solids formed, scrutinyite formed from hydrocerussite, and mixtures of scrutinyite and plattnerite formed from lead(II) chloride and massicot.
The dissolution rates of PbO2 were quantified at various pH values and concentrations of DIC, free chlorine, and iodide using continuously stirred tank reactors: CSTRs). Increasing the pH decreased the dissolution rate. The presence of free chlorine inhibited PbO2 dissolution, while the presence of iodide greatly accelerated PbO2 dissolution. The reductive dissolution of PbO2 was proposed to be a coupled process involving chemical reduction of Pb(IV) to Pb(II) at the PbO2 surface followed by detachment of Pb(II) to solution. The dissolution rate was directly correlated with the surface species of PbO2 that participated in the reaction.
The impact of galvanic corrosion on lead release was investigated with aged lead pipes harvested from two different distribution systems connected to copper tubing by four types of couplings: brass, brass dielectric, plastic, and plastic with external electric wires. Experiments were performed in a recirculating flow mode with intermittent stagnation periods. Relative to the plastic-coupled pipe assemblies, which always had the lowest lead release, the lead release increased in the order of the systems coupled with plastic with external wires, brass dielectric, and brass. The enhancement of lead release was attributed to galvanic corrosion. Galvanic corrosion primarily caused release of particulate lead. It is a localized effect with much higher lead release in the region closest to the coupling.
Wang, Yin, "Redox Reactions Influencing Lead Concentrations in Drinking Water: Formation and Dissolution of Lead(IV) Oxide and Impact of Galvanic Corrosion" (2012). All Theses and Dissertations (ETDs). 1023.
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Permanent URL: http://dx.doi.org/10.7936/K70G3H63