Stability of Lead(IV) Oxide in a Lead Pipe Scale and Its Potential Role in Corrosion Control

Lead(IV) oxide (PbO₂) is an important component of the scale in many lead pipes used for water supply. Promoting conditions that maintain its stability could be an effective method for limiting lead release. In this study, we applied a method that combined electrochemical and free chlorine conditioning to form PbO₂ scales on coupons. Lead coupons were then used to investigate the impacts of water stagnation time and residual free chlorine on PbO₂ stability. Free chlorine depletion and associated lead release were investigated from 30 min to 5 days for different initial free chlorine concentrations (0.5-3.0 mg/L as Cl₂). There was a lag time of up to 24 h between free chlorine depletion and observed lead increases. With daily readjustment of free chlorine to 0.2 mg/L or higher, the stability of the PbO₂ scale on the lead coupon was maintained and dissolved lead remained consistently below 10 μg/L. This study provides information on key factors affecting reductive dissolution of PbO₂ present in lead scales. It bridges the theoretical threshold free chlorine to maintain PbO₂ stability with experimental results and provides implications for actual water quality monitoring and household drinking water use.