Lead oxide (PbO₂) has the lowest solubility with free chlorine among Pb corrosion products, but depletion of free chlorine or a switch from free chlorine to monochloramine can cause its reductive dissolution. We previously reported that Cu(II) and Zn(II) inhibited PbO₂ reductive dissolution within 12 h. Here, we expanded on this work by performing longer duration experiments and further exploring the underlying mechanisms. Between 12 and 48 h, Cu(II) and Zn(II) had no discernible effect on PbO₂ reductive dissolution. From 48 to 192 h, Cu(II) and Zn(II) enhanced PbO₂ reductive dissolution. Dissolved oxygen (DO) concentrations followed the same trends as PbO₂ reductive dissolution, indicating that the DO was produced by PbO₂ reductive dissolution. On the basis of extended X-ray absorption fine structure spectra, we hypothesize that the inhibitory effect of Cu(II) and Zn(II) on PbO₂ reductive dissolution (<12 h) is caused by decreasing abundance of protonated sites on the PbO₂ surface. The enhanced dissolution (>48 h) may be caused by competitive adsorption of Cu(II) and Zn(II) with Pb(II), which could limit the adsorption of Pb(II) onto PbO₂ that could otherwise inhibit reductive dissolution. This study indicates that stagnation time plays a vital role in determining cations’ effects on the stability of Pb corrosion products.

中文翻译：

---

Cu(II)和Zn(II)对饮用水条件下PbO2还原溶解的影响：短期抑制和长期增强

在 Pb 腐蚀产物中，氧化铅 (PbO ₂ ) 与游离氯的溶解度最低，但游离氯的消耗或从游离氯转换为一氯胺会导致其还原溶解。我们之前报道过，Cu(II) 和 Zn(II)在 12 小时内抑制 PbO ₂还原溶解。在这里，我们通过进行更长时间的实验并进一步探索潜在机制来扩展这项工作。在 12 和 48 小时之间，Cu(II) 和 Zn(II) 对 PbO ₂还原溶解没有明显影响。从 48 到 192 小时，Cu(II) 和 Zn(II) 增强了 PbO ₂还原溶解。溶解氧 (DO) 浓度遵循与 PbO ₂相同的趋势还原溶解，表明溶解氧是由 PbO ₂还原溶解产生的。基于扩展的 X 射线吸收精细结构光谱，我们假设 Cu(II) 和 Zn(II) 对 PbO ₂还原溶解（<12 h）的抑制作用是由于 PbO 上质子化位点丰度的降低引起的₂表面。溶解增强（>48 小时）可能是由于 Cu(II) 和 Zn(II) 与 Pb(II) 的竞争吸附引起的，这可能会限制 Pb(II) 吸附到 PbO _{2 上}，否则会抑制还原溶解。该研究表明，停滞时间在确定阳离子对 Pb 腐蚀产物稳定性的影响方面起着至关重要的作用。