A 12 days laboratory study on potential desorption of Lanthanum (La) from a commercial La modified clay (Phoslock) was conducted using lake water from 17 Danish lakes with alkalinities between 0.02 and 3.7 meq L⁻¹ and varying concentrations of DOC and humic acids (HA's). A similar study was conducted in artificial lake water with alkalinities from 0 to 2.5 meq L⁻¹in order to exclude interference from dissolved HA's. To test if La in solution (FLa) was associated with fine particles, the water samples were filtered sequentially through three filter sizes (1.2 μm, 0.45 μm and 0.2 μm), and finally, ultracentrifugation was used in an attempt to separate colloidal La from dissolved La. The study showed that higher FLa (up to 2.5 mg L⁻¹ or 14% of the total La in the Phoslock) concentrations were found in soft water lakes compared to hard water lakes, probably due to dispersion of the clay at low alkalinities. In addition, this study showed that HA's seem to increase the FLa concentrations in soft water lakes, most likely through complexation of La retained in the Phoslock matrix. In summary, we conclude that elevated La concentrations in lake water after a Phoslock treatment should only be expected in soft water lakes rich in DOC and HA's.

中文翻译：

---

湖泊水碱度和腐殖质对镧改性膨润土颗粒分散和镧解吸的影响

使用来自17个丹麦湖的碱度在0.02和3.7 meq L ^-1之间且浓度不同的DOC和腐殖酸（已）。在碱度为0到2.5 meq L ^-1的人工湖水中进行了类似的研究，以排除溶解的HA的干扰。为了测试溶液（FLa）中的La是否与细颗粒相关，将水样品依次通过三种尺寸（1.2μm，0.45μm和0.2μm）的过滤器进行过滤，最后，通过超速离心从胶体中分离胶体La。研究表明，较高的FLa（高达2.5 mg L ^-1与硬水湖泊相比，在软水湖泊中发现了总磷浓度（占Phoslock中总La的14％），这可能是由于粘土在低碱度下的分散所致。此外，这项研究表明，HA似乎增加了软水湖中FLa的浓度，这很可能是通过保留在Phoslock基质中的La的络合而引起的。总而言之，我们得出的结论是，仅在充满DOC和HA的软水湖泊中，经过Phoslock处理后，湖水中的La浓度会升高。