CAS OpenIR
酸性有机磷类萃取剂与稀土离子的气-液界面相互作用研究
高振
Subtype硕士
Thesis Advisor刘会洲
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工程
KeywordP507,单分子膜,稀土离子,界面红外反射吸收光谱,布儒斯特角显微镜
Abstract

目前,酸性有机磷类萃取剂因其优异的萃取性能被广泛应用于稀土元素的萃取分离。萃取剂分子对不同稀土离子的分离选择性一般取决于其与目标离子的结合能力以及有机相中萃合物的性质差异。镨钕元素性质相近,体相中萃合物结构相同,常规方法萃取分离镨钕,分离系数一般在1.5左右。由于萃取是萃取剂分子与稀土离子的界面相互作用过程,从界面层次探究镨钕离子与萃取剂分子间相互作用的差异,可以为分离镨钕元素新方法的研究奠定一定基础。萃取剂分子在体相中主要以二聚体形式存在,但在界面处其存在状态会发生改变。为了更清楚地了解萃取剂分子界面存在状态改变引起其与稀土离子间相互作用变化的微观机制,本论文根据气-液界面具有类似液-液界面的特点,借助Langmuir膜技术,通过界面红外反射吸收光谱(IRRAS)和布儒斯特角显微镜(BAM),研究萃取剂分子界面存在状态变化对其与镨、钕离子间相互作用的影响。将萃取剂P507铺展在纯水表面,研究P507分子的气-液界面行为。以极性溶剂二氯甲烷和非极性溶剂正己烷作铺展溶剂时,得到表面压-分子面积(π-A)等温线存在显著差异。通过IRRAS和BAM进一步表征,证实了铺展溶剂极性改变,会引起P507分子在气-液界面存在状态的变化,铺展溶剂极性增强,界面P507分子主要以单体形式存在,而正己烷溶剂铺展的单分子膜中含有更多的P507分子聚集体。在纯水pH降低,单分子膜完全质子化时,正己烷铺展的P507单分子膜中更容易形成聚集体。该研究从气-液界面的角度,分析萃取剂分子在相界面上存在状态的变化规律,有助于理解实际萃取过程中萃取剂分子的油-水界面行为。在NdCl3水溶液表面铺展P507单分子膜,分析P507分子极性端离子化状态和界面形态变化对其与Nd3+离子间相互作用的影响。P507分子结合Nd3+离子后,π-A曲线出现“平台区”,而降低NdCl3溶液pH,“平台区”会逐渐消失。BAM表征显示,“平台区”的P507单分子膜经历由二维结构向三维结构转变的过程;“平台区”消失时,单分子膜内有萃合物聚集体形成。以二氯甲烷和正己烷溶剂改变P507分子界面存在状态,IRRAS表征显示,P507分子与Nd3+离子结合的基团发生变化:界面P507主要以聚集体形态存在时,Nd3+离子仅与P507分子的P-OH基团结合;P507分子主要以单体形态存在时,P-OH和P=O基团皆会与Nd3+离子发生相互作用。采用傅里叶变换红外光谱和界面红外反射吸收光谱,对比分别在体相和气-液界面时镨钕离子与P507分子间相互作用的差异。傅里叶红外光谱表征显示,体相中镨钕离子与P507分子的作用相同。IRRAS光谱显示,气-液界面P507分子与镨钕离子相互作用的差异受铺展溶剂和溶液pH影响,二氯甲烷做铺展溶剂时,钕离子结合P507分子后,νas PO2–的峰位处于更低的波数,表明钕离子结合P507分子的能力强于镨离子;溶液pH降低,会增强镨离子与P507分子的配位能力。以正己烷作铺展溶剂,P507分子结合镨离子出现νas PO2–吸收峰,说明镨离子与P=O基团的配位能力略强于钕离子。该研究发现P507分子界面聚集状态显著影响镨钕离子与P507分子的相互作用。这对从界面层次增大镨钕离子萃取行为差异性的研究提供了一定的理论基础。;The acidic organophosphorus extractants are widely employed in the industrial production of extracting and separating rare earth elements. The separation selectivity of extractant molecules for different rare earth ions depends on their ability to bind the target ions and the difference in the properties of rare earth complexes in the organic phase. While the properties of praseodymium and neodymium elements are so similar that the separation coefficient is generally about 1.5 through the conventional extraction method. Due to the solvent extraction is the result of the interaction of extractant molecules with metal ions at oil-water interface, exploring the difference in the interaction between Pr3+ ions and Nd3+ ions with extractant molecules at interface is helpful to the development of new separating methods. The extractant molecules, mainly in the form of dimers in the bulk phase, change their existing forms when they enter the interface. In order to understand the interaction between the extractant molecules and rare earth ions, Langmuir monolayer technique was used to imitate extractant molecules adsorbed at oil-water interface. The effect of extractant molecules existing forms on their interaction with Pr3+ and Nd3+ ions were investigated by infrared reflection absorption spectroscopy (IRRAS) and Brewster angle microscope (BAM).The existing forms of extractant molecules at air-water interface were studied by spreading P507 molecules on the surface of water without metal ions. It was found that the π-A isotherms of P507 monolayers spread by n-hexane and dichloromethane are different. The characterization by IRRAS and BAM confirmed that the existing forms of P507 molecules in the monolayer changed with the spreading solvent polarity. And P507 molecules mainly exist in the form of monomers at interface as the spreading solvent polarity increased. Moreover, when the monolayer is completely protonated, P507 aggregates are more likely to form in the monolayer spread by n-hexane. This work investigated the existing forms of P507 molecules at air-water interface, which would help to understand their interfacial behavior at oil-water interface during solvent extraction.The interaction between P507 molecule and Nd3+ ions was analyzed by spreading P507 monolayers on the surface of NdCl3 solution. The plateau region in the π-A isotherms appeared when P507 molecules bind to Nd3+ ions and the plateau gradually disappeared as NdCl3 solution pH decreased. The characterization of BAM microscopy showed that the plateau region indicated the transition process of P507 monolayer from a two-dimensional monolayer to the three-dimensional structure. And when the plateau region disappeared, the aggregates of P507-Nd complexes formed in the monolayer. As the existing forms of P507 molecules at interface changed with n-hexane and dichloromethane, the IRRAS spectra confirmed the binding sites of P507 molecules with Nd3+ ions were changed with their existing forms. When P507 monolayer was spread by n-hexane, Nd3+ ions only bound to P=O groups. And as the dichloromethane was spread solvent, P=O and P-OH groups both bound to Nd3+ ions.Fourier transform infrared spectroscopy (FTIR) and IRRAS were used to compare the difference between Pr3+ ions and Nd3+ ions in the interaction with P507 molecules in bulk phase and at the interface, respectively. FTIR spectra showed that there was little difference between Nd3+ ion and Pr3+ ions in bulk phase. IRRAS spectra showed that the difference between Pr3+ ions and Nd3+ ions in the interaction with P507 molecules at air-water interface depended on spreading solvent and subphase pH. The Nd3+ ions had the stronger interaction with P507 molecules than Pr3+ ions in monolayer spread by dichloromethane, which was indicated by the band of νas PO2– at a lower wavenumber. The decrease in solution pH could enhance the coordination ability of Pr3+ ions with P507 molecues. But when the monolayer was spread by n-hexane, Pr3+ ions were slighter stronger than Nd3+ ions in combination with P507 molecules. The difference in the interaction of P507 molecules with Pr3+ and Nd3+ ions at interface will provide a theoretical basis for the study of extraction behavior of them from the interface level.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40693
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
高振. 酸性有机磷类萃取剂与稀土离子的气-液界面相互作用研究[D]. 中国科学院大学,2019.
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