The stability of Pb(IV) corrosion product PbO2 has been found associated with lead contamination in drinking water when the changeover of disinfectant from free chlorine (HOCl/OCl-) to monochloramine (NH2Cl) is practiced.The work by Lin and Valentine (2008) discovered that auto-decomposition of NH2Cl can lead to reductive dissolution of PbO2. A mysterious intermediate was proposed to be responsible for the reaction. Bromide (Br-) is a known catalyst for NH2Cl decomposition. In this study, we investigated whether Br--catalyzed NH2Cl decomposition could further enhance lead release from PbO2 via the same mechanism. Our results showed that Br--catalyzed NH2Cl decomposition accelerated the reduction of PbO2 and the rate was enhanced by the lower pH value, higher Br- and NH2Cl concentrations. A single linear correlation was found between the amount of NH2Cl decomposed and the amount of total Pb(II) released either in the absence or presence of Br-, suggesting that Br--catalyzed NH2Cl decomposition and NH2Cl auto-decomposition may generate the same intermediate toward PbO2 reduction. The kinetics of total Pb(II) release can be successfully modelled by considering the overall rate of NH2Cl decomposition with NOH as the reactive intermediate responsible for PbO2 reduction. Our findings suggested that special attentions on lead contamination should be paid to systems with PbO2 scales and high Br--containing source waters when switching disinfectant from free chlorine to monochloramine.

Linking chloramine decomposition to lead release from tetravalent lead corrosion product PbO<sub>?2</sub>

248th National Meeting (2014)

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Linking chloramine decomposition to lead release from tetravalent lead corrosion product PbO?2

Linking chloramine decomposition to lead release from tetravalent lead corrosion product PbO_?2