Abstract Foam (ion and precipitate) flotation is a promising green method of recovery of rare earth elements (REE) from leachates of the primary and secondary resources. However, the capabilities of foam flotation in solutions simulating real leachates are currently poorly understood, especially for green surfactants as collectors. In this work, we report the results of foam flotation of La(III), Ce(III), Gd(III), and Yb(III) ions individually, as a group, and as a group with gangue ions (Al(III), Zn(II), Ca(II), and Mg(II)). These REE represent both light and heavy REE. As the collectors, we test two quintessential synthetic and green anionic surfactants—sodium dodecyl sulfate (SDS) and mono-rhamnolipid, respectively. We find that the floatability of REE with SDS depends considerably on the composition of the REE solution and demonstrate that the recovery kinetics can be used as additional control of the REE separation in the group flotation with gangue ions. Another important finding is that mono-rhamnolipid at a concentration as low as 10 μM can recover up to 100% REE in the group flotation against gangues, except for Al(III) and Zn(II). At pH 9, mono-rhamnolipid selectively removes REE in the group flotation with gangue cations at a surfactant:total cation (excluding Na+) ratio as low as 1:13. We offer an interpretation of the effects observed. Overall, our results demonstrate that foam flotation is capable of selectively recovering an individual REE from a mixture of several REE with gangue ions, provided that the flotation conditions such as surfactant structure, surfactant concentration, solution pH, and flotation time are properly selected. These results are an important milestone toward the commercialization of foam flotation for the recovery and purification of REE.

中文翻译：

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常规和绿色表面活性剂泡沫浮选稀土元素

摘要 泡沫（离子和沉淀）浮选是一种很有前景的从一次和二次资源渗滤液中回收稀土元素（REE）的绿色方法。然而，目前人们对泡沫浮选在模拟真实渗滤液的溶液中的能力知之甚少，尤其是对于作为捕收剂的绿色表面活性剂。在这项工作中，我们分别报告了 La(III)、Ce(III)、Gd(III) 和 Yb(III) 离子的泡沫浮选结果，作为一个组，以及作为一组与脉石离子 (Al(III) )、Zn(II)、Ca(II) 和 Mg(II))。这些 REE 代表轻稀土和重稀土。作为收集者，我们分别测试了两种典型的合成和绿色阴离子表面活性剂——十二烷基硫酸钠 (SDS) 和单鼠李糖脂。我们发现 REE 与 SDS 的可浮性在很大程度上取决于 REE 溶液的组成，并证明回收动力学可用作脉石离子群浮选中 REE 分离的额外控制。另一个重要发现是浓度低至 10 μM 的单鼠李糖脂可以在针对脉石的群浮选中回收高达 100% 的 REE，但 Al(III) 和 Zn(II) 除外。在 pH 值为 9 时，单鼠李糖脂以低至 1:13 的表面活性剂与总阳离子（不包括 Na+）比率选择性地去除与脉石阳离子组浮选中的 REE。我们提供了对观察到的影响的解释。总体而言，我们的结果表明，泡沫浮选能够从多种 REE 与脉石离子的混合物中选择性地回收单个 REE，如果浮选条件，如表面活性剂结构，表面活性剂浓度，溶液pH和浮选时间被适当地选择。这些结果是泡沫浮选用于回收和提纯稀土的商业化的一个重要里程碑。