School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, 28 Xianning West Road, Xi'an, Shaanxi, 710049, PR China; Department of Civil and Resource Engineering, Dalhousie University, 1360 Barrington Street, Halifax, Nova Scotia, B3H 4R2, Canada.
Department of Civil and Resource Engineering, Dalhousie University, 1360 Barrington Street, Halifax, Nova Scotia, B3H 4R2, Canada.
J Environ Manage. 2022 Nov 1;321:115947. doi: 10.1016/j.jenvman.2022.115947. Epub 2022 Aug 14.
Orthophosphate is widely used to control lead (Pb) release in drinking water distribution systems, but phosphorus addition is not sustainable. Alternative corrosion control treatments are needed, and sodium silicate is one possibility. Here, pre-corroded Pb coupons-with and without free chlorine-were used to examine early-phase corrosion scale development after silicate addition, with orthophosphate as a reference corrosion inhibitor. Scale development was evaluated in terms of total Pb release, phase transformation, electrochemical impedance, morphological changes, Pb dissolution kinetics, and short-term Pb-Cu galvanic corrosion. Elevated Pb release occurred for approximately one month after silicate addition, and total Pb release peaked at 1968.1 μg/L and 1176.9 μg/L from systems with and without free chlorine, respectively. In contrast, orthophosphate-treated coupons exhibited fewer, less pronounced spikes in Pb release. By day 354, the median total Pb release from orthophosphate-treated coupons with and without free chlorine had decreased to 3.7 and 5.0 μg/L, respectively, while the median total Pb release from corresponding silicate-treated coupons was much higher, at 44.9 μg/L and 34.3 μg/L. Calcium lead apatite (CaPb(PO)OH) was identified in orthophosphate-treated scales, with hydroxylpyromorphite (Pb(PO)OH) present in the absence of free chlorine. Plattnerite occurred on coupons in all chlorinated systems. Pb silicate compounds were not detected, but CaSiO and NaCa(SiO) were identified by X-ray powder diffraction. The charge transfer: film resistance ratio characterizing the orthophosphate-treated coupons decreased slowly while that of the silicate-treated coupons increased after silicate was added. These variations suggest orthophosphate provided better corrosion control than silicate did. Silicate treatment generally caused degradation of the top Pb scale layer, resulting in elevated Pb release, while orthophosphate encouraged the growth of more structured, generally thicker, corrosion scales that were effective in limiting Pb release.
正磷酸盐被广泛用于控制饮用水分配系统中的铅（Pb）释放，但磷的添加并不可持续。需要替代的腐蚀控制处理方法，硅酸钠就是一种可能性。在这里，使用预腐蚀的 Pb 试片-有和没有游离氯-来研究硅酸盐添加后早期腐蚀层的发展情况，以正磷酸盐作为参考腐蚀抑制剂。通过总 Pb 释放、相转化、电化学阻抗、形态变化、Pb 溶解动力学和短期 Pb-Cu 电偶腐蚀来评估结垢的发展。硅酸盐添加后约一个月内 Pb 释放量升高，且无游离氯系统中的总 Pb 释放量峰值为 1968.1μg/L 和 1176.9μg/L，而有游离氯系统中的总 Pb 释放量峰值为 1968.1μg/L 和 1176.9μg/L。相比之下，用正磷酸盐处理的试片的 Pb 释放量则较少且不明显。到第 354 天，有和无游离氯的正磷酸盐处理试片中的总 Pb 释放量中位数分别降低至 3.7μg/L 和 5.0μg/L，而相应的硅酸盐处理试片中的总 Pb 释放量则高得多，分别为 44.9μg/L 和 34.3μg/L。在正磷酸盐处理的结垢中发现了钙铅磷灰石（CaPb(PO)OH），而在无游离氯的情况下则存在羟基磷氯铅矿（Pb(PO)OH）。在所有加氯系统中的试片上都发现了锌尖晶石。未检测到 Pb 硅酸盐化合物，但通过 X 射线粉末衍射鉴定出了 CaSiO 和 NaCa(SiO)。在添加硅酸盐后，表征正磷酸盐处理试片的电荷转移：膜电阻比缓慢降低，而硅酸盐处理试片的电荷转移：膜电阻比则增加。这些变化表明正磷酸盐提供的腐蚀控制优于硅酸盐。硅酸盐处理通常会导致顶层 Pb 结垢层降解，从而导致 Pb 释放量升高，而正磷酸盐则鼓励生长更具结构、通常更厚的腐蚀层，从而有效限制 Pb 释放。
