State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, NanjingUniversity, 210023, PR China.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, NanjingUniversity, 210023, PR China.
Chemosphere. 2019 Mar;218:860-868. doi: 10.1016/j.chemosphere.2018.11.192. Epub 2018 Nov 28.
Fluoride (F) pollution is a worldwide issue. Coagulation with aluminum (Al) salts is an efficient and economical method for the removal of F. However, due to the strong complexation between Al and F, the residual F and Al after coagulation usually exceed the limits. Zirconium (Zr) coagulants have drawn increasing attention due to their excellent flocculation ability for organic matter. In this work, the performance and mechanism of ZrCl coagulation for F removal were investigated with the widely used Al(SO) as a reference. The optimum pH range is 4.0-6.0 for ZrCl and 8.0-10.0 for Al(SO). ZrCl was superior to Al(SO) for F removal as the initial F concentration was less than 30.0 mg L. Coexisting substances at environmental concentration levels showed negligible effects on F removal by ZrCl. Besides the better F removal, another advantage of ZrCl over Al(SO) was the much lower residual metal concentration in the pH range of 4.0-11.0. The hydrolysis of Al(SO) was significantly inhibited due to the formation of Al-F complexes while the hydrolysis of ZrCl was not influenced even under strongly acidic conditions. Therefore, F removal by Al(SO) was mainly achieved by preliminary complexation between Al and F and subsequent hydrolysis and polymerization of these complexes, while adsorption onto hydrolysates and ion exchange with surface hydroxyl groups were the main ways of F removal by ZrCl. The work here provides a new method for F removal and may shed light on the application of Zr coagulants for other pollutants.
氟（F）污染是一个全球性问题。用铝（Al）盐进行混凝是去除 F 的一种有效且经济的方法。然而，由于 Al 与 F 之间的强络合作用，混凝后残留的 F 和 Al 通常会超过限制。由于其对有机物的出色絮凝能力，锆（Zr）混凝剂越来越受到关注。在这项工作中，以广泛使用的 Al(SO)作为参考，研究了 ZrCl 混凝去除 F 的性能和机理。ZrCl 的最佳 pH 范围为 4.0-6.0，而 Al(SO)的最佳 pH 范围为 8.0-10.0。当初始 F 浓度小于 30.0 mg/L 时，ZrCl 比 Al(SO)更有利于 F 的去除。共存物质在环境浓度水平下对 ZrCl 去除 F 的影响可以忽略不计。除了更好的 F 去除效果外，ZrCl 相对于 Al(SO)的另一个优点是在 pH 范围为 4.0-11.0 时残留金属浓度要低得多。由于 Al-F 配合物的形成，Al(SO)的水解受到显著抑制，而即使在强酸性条件下，ZrCl 的水解也不受影响。因此，Al(SO)去除 F 主要是通过 Al 与 F 之间的初步络合以及随后这些配合物的水解和聚合来实现的，而吸附到水解产物上和与表面羟基的离子交换则是 ZrCl 去除 F 的主要方式。本工作为 F 的去除提供了一种新方法，可能为 Zr 混凝剂在其他污染物中的应用提供启示。
