Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dr. Clare Robinson

2nd Supervisor

Dr. Jose Herrera

Joint Supervisor

Abstract

Destabilization of lead corrosion scales present in plumbing materials used in water distribution systems results in elevated lead concentrations in drinking water. Lead release caused by changes in water chemistry (e.g., redox conditions) is often due to the destabilization of lead carbonate and oxide solid phases. Although prior studies have examined the effects of varying water chemistry on the stability of β-PbO2 (plattnerite), β-PbO2 stability under depleting chlorine conditions is poorly understood. In addition little is known regarding the mechanisms by which Pb3O4 (minium) dissolves under drinking water conditions. In this thesis, long-term batch dissolution experiments were performed for pure phase β-PbO2 and Pb3O4 under depleting chlorine conditions. Results indicate that the initial availability of free chlorine effectively depresses dissolved lead concentrations released from both solid phases. From the Pb3O4 dissolution experiments, it was found that Pb3O4 was first oxidized by free chlorine to form β-PbO2. After chlorine was depleted, Pb3O4 solvolytic disproportionation resulted in growth of β-PbO2 and an increase in dissolved lead concentrations. The formation of lead carbonates controlled the final lead concentrations (~0.1 mg/L) for Pb3O4 dissolution. In contrast, for the β-PbO2 dissolution experiments, the dissolved lead levels remained low (~0.004 mg/L) even after free chlorine was depleted. Detailed characterization of solid samples collected during the β-PbO2 experiments indicate that Pb2+ impurities present in crystalline β-PbO2 play a dominant role in the stability of this solid phase.

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