Department of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri, 63130, United States.
Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri, 63130, United States.
Water Res. 2020 Jun 15;177:115764. doi: 10.1016/j.watres.2020.115764. Epub 2020 Apr 6.
This study explored the ability of orthophosphate addition to limit lead release from lead service lines delivering high pH, low alkalinity water. We built pipe loop reactors with lead pipes harvested from Providence, RI, and we operated them with high pH and low alkalinity water of a composition similar to that in Providence. Orthophosphate addition decreased the release of both dissolved and particulate lead to the water. The most substantial decreases in total lead concentrations occurred after 15 weeks of orthophosphate addition, which was associated with the formation of calcium-lead-phosphorus (Ca-Pb-P) solids as part of the pipe scale. Pre-existing hydrocerussite (Pb(CO)(OH)) in the scale of the lead pipe appeared to promote the formation of a Ca-Pb-P solid similar to phosphohedyphane (CaPb(PO)(Cl,F,OH)). Continuous orthophosphate addition was also associated with the formation of a calcium phosphate solid with features like those of fluorapatite (Ca(PO)F) on the outermost layer of the scale. Through promoting the formation of these new solids within and on top of the scales, orthophosphate addition limited release of dissolved and particulate lead. These results demonstrate the ability of orthophosphate to control lead release at higher pH conditions than those for which it has typically been used. In addition to the formation of phosphate solids, PbO, which was not present on the as-received pipes, was formed due to the constant supply of free chlorine in the laboratory-scale experiment.
这项研究探讨了添加正磷酸盐来限制输送高 pH 值、低碱度水的铅供水管线中铅释放的能力。我们使用从罗德岛州普罗维登斯市采集的铅管建造了管道回路反应器，并在与普罗维登斯市水质相似的高 pH 值和低碱度水中运行这些反应器。正磷酸盐的添加减少了水中溶解态和颗粒态铅的释放。在添加正磷酸盐 15 周后，总铅浓度的下降幅度最大，这与钙-铅-磷（Ca-Pb-P）固体的形成有关，这些固体是管道结垢的一部分。铅管结垢中预先存在的羟硅铅矿（Pb(CO)(OH))似乎促进了类似于磷硅钙石（CaPb(PO)(Cl,F,OH)）的 Ca-Pb-P 固体的形成。连续添加正磷酸盐也与在结垢的最外层形成具有氟磷灰石（Ca(PO)F）特征的磷酸钙固体有关。通过在结垢内部和表面促进这些新固体的形成，正磷酸盐的添加限制了溶解态和颗粒态铅的释放。这些结果表明，正磷酸盐能够在比其通常使用的 pH 值更高的条件下控制铅的释放。除了磷酸盐固体的形成外，由于实验室规模实验中不断供应游离氯，在接收的管道上不存在的 PbO 也形成了。
