Effectiveness of Sodium Silicates for Lead Corrosion Control: A Critical Review of Current Data

Orthophosphate is commonly used to control lead release to drinking water, but it is a potential source of nutrient pollution and can increase the concentration of particulate and colloidal lead. Given these drawbacks, there is considerable interest in alternative corrosion control treatments. While less common than orthophosphate, sodium silicate is recognized as a treatment for controlling lead release to drinking water. But there is no consensus in the scientific literature as to whether it is effective. Here, we conduct a data summary of the peer-reviewed literature pertaining to silicate-based corrosion control of lead. We find that silicate treatment generally accompanied higher lead release than the equivalent (pH-matched) system without sodium silicate (0.5–21.5 times higher). Moreover, silicate treatment was inferior to orthophosphate treatment; sodium silicate accompanied 1.0–65 times more lead release than the equivalent orthophosphate-treated system. Sodium silicate’s positive effect on pH, then, appears to be the main driver of lead release control. While it is possible that under some circumstances silicate treatment promotes formation of a solid phase that either limits equilibrium solubility or slows lead release, the mechanism has not been described precisely.