Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore , Singapore 117576.
Environ Sci Technol. 2013 Oct 1;47(19):10931-8. doi: 10.1021/es402733e. Epub 2013 Sep 10.
The stability of Pb(IV) corrosion product PbO2 has been linked to lead contamination in chloraminated drinking water. Recent studies have shown that autodecomposition of monochloramine (NH2Cl) can cause lead release from PbO2 via reductive dissolution. 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. Our results showed that Br(-_)catalyzed NH2Cl decomposition did accelerate 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 autodecomposition may generate the same intermediate toward PbO2 reduction. The kinetics of total Pb(II) release can be successfully modeled 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.
Pb(IV)腐蚀产物 PbO2 的稳定性与氯胺消毒饮用水中的铅污染有关。最近的研究表明，一氯胺（NH2Cl）的自动分解会导致 PbO2 中的铅通过还原溶解释放出来。溴化物（Br(-)）是 NH2Cl 分解的已知催化剂。在这项研究中，我们研究了 Br(-)催化 NH2Cl 分解是否会进一步增强 PbO2 中的铅释放。我们的结果表明，Br(-)催化 NH2Cl 分解确实加速了 PbO2 的还原，并且较低的 pH 值、较高的 Br(-)和 NH2Cl 浓度会增强还原速率。在没有 Br(-)或存在 Br(-)的情况下，NH2Cl 分解的量与总 Pb(II)释放量之间存在单一的线性相关性，这表明 Br(-)催化的 NH2Cl 分解和 NH2Cl 的自动分解可能会生成相同的中间产物来还原 PbO2。考虑到 NH2Cl 总分解速率，总 Pb(II)释放的动力学可以成功地建模，其中 NOH 是作为 PbO2 还原的反应中间体。我们的研究结果表明，当从自由氯切换到一氯胺作为消毒剂时，对于含有 PbO2 结垢和高 Br(-)含量水源的系统，应特别注意铅污染。
