Electrostatic Origin of Element Selectivity during Rare Earth Adsorption
Electrostatic Origin of Element Selectivity during Rare Earth Adsorption
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DOI：
10.1103/physrevlett.122.058001
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发表时间：
2019-02-08
影响因子：
8.6
通讯作者：
Dutta, Pulak
中科院分区：
文献类型：
--
作者：
Miller, Mitchell;Liang, Yihao;Dutta, Pulak
稀土是现代技术的基本成分，通常在油水界面使用表面活性剂从水溶液中提取。较重的稀土元素更容易提取，尽管所有的稀土元素在化学上都非常相似。通过X射线荧光测量和理论论证，我们发现在含Er3+或Nd3+的水溶液中，阳离子在与浮动单分子膜接触的界面吸附过程中存在明显的随浓度变化的跃迁。Er(Z=68)的阈值体积浓度比Nb(Z=60)低一个数量级，当溶液中同时含有这两种离子时，Er优先被吸附。这意味着分离过程中的元素选择性起源于表面活性剂界面。界面介电失配、离子相关性和离子大小引起的静电效应解释了尖锐的吸附曲线和选择性。
Rare earths, which are fundamental components of modern technologies, are often extracted from aqueous solutions using surfactants at oil-water interfaces. Heavier lanthanides are more easily extracted, even though all lanthanides are chemically very similar. Using x-ray fluorescence measurements and theoretical arguments, we show that there is a sharp bulk-concentration-dependent transition in the interfacial adsorption of cations from aqueous solutions containing Er3+ or Nd3+ in contact with a floating monolayer. The threshold bulk concentration of erbium (Z = 68) is an order of magnitude lower than that of neodymium (Z = 60), and erbium is preferentially adsorbed when the solution contains both ions. This implies that elemental selectivity during separation originates at the surfactant interface. Electrostatic effects arising from the interface dielectric mismatch, ionic correlations, and sizes of the ions explain the sharp adsorption curve and selectivity.