Sodium silicate impacts on lead release in a blended potable water distribution system

Abstract

The effects sodium silicate corrosion inhibitor doses (ranging from 3 to 12 mg/L-SiO₂) on lead release were investigated during a pilot study. Samples were taken from a system of copper loops within a pre-existing pilot drinking water distribution system. The source of lead for the loop system was 50/50 lead/tin coupons. Variations in water quality were implemented through blending differing proportions from 3 different source waters; groundwater, surface water, and desalinated water, and studied in four specifi c blending phases. The study analyzed both total and dissolved lead release while monitoring several other water quality parameters. A non-linear regression model was developed to describe total lead release in terms of dose and water quality. The model suggested that the dose, temperature, alkalinity, chlorides, and pH had an effect on lead release (R² = 0.60). The response of total lead to silicate suggested that increasing dose signifi cantly decreased lead release. Solubility modeling suggested that hydrocerussite would theoretically exist as the predominant lead solid. The solubility model was compared to lead release data from samples that were given months to approach equilibrium.

Keywords:

• Sodium silicate
• Silica
• Corrosion inhibitor
• Lead release
• Lead and Copper rule