A Thesis on the Interactions between Lead Pipe Scales and Dissolved Silica from the Addition of Sodium Silicate as a Corrosion Inhibitor
Ingestion of lead-contaminated drinking water is one of the major pathways for human exposure to lead. Addition of sodium silicate can potentially control lead release from lead service lines (LSLs) to the water that they convey, but the mechanism of silica uptake and corrosion control have not been reported. Knowledge of variables which affect the uptake of dissolved silica and the consumption rate of added sodium silicate by scales of corrosion products that are present on lead service lines will be useful to water utilities and distribution systems. This study investigated the effects of pH, initial silica concentration and mass of scales on the rates and extents of silica uptake by real scales removed from lead service lines and by hydrocerussite, which is one of the dominant lead-containing solids found in such scales. The study used batch experiments with these solid phases at environmentally relevant water chemistry conditions. Statistic models were built for different conditions to fit experimental data, a biphasic model was found to fit the data well. Adsorption is a potential process of silica uptake, and adsorption isotherms were plotted in this study to observe the behavior of hydrocerussite and Buffalo scales during the uptake of dissolved silica. Other processes and possible reactions were also hypothesized to evaluate their role in the uptake of silica.
Sodium silicate, adsorption, lead pipe scales, hydrocerussite, corrosion inhibition, Engineering
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