基于气泡支撑有机油膜萃取的气助动力学推拉体系分离相邻稀土元素机理研究

Separation of adjacent rare-earth elements with similar physicochemical properties by traditional liquid-liquid phase equilibrating solvent extraction is very difficult. Generally, thermodynamic separation factors and selectivity coefficients between adjacent rare-earth elements are extremely low. Therefore, to explore feasible methods for separation process intensification of rare earths remain being one of the most challenged tasks in rare-earth’s solvent extraction and hydrometallurgical processes. The aim of present proposal is to develop a promising novel strategy by gas-bubble supported organic liquid membrane extraction to achieve gas-assisted kinetic push-pull separation of adjacent rare-earth elements, so that to enlarge their separation factors. We suggest to disperse and cover organic extractant onto surface of gas bubbles to form a layer of organic liquid membrane, so called oil bubbles, to conduct extraction processes so that to intensify interfacial mass transfer of rare earth ions. Based on the differences in reaction rate of rare-earth ions with organic extractants on surface of ascending oil bubbles and the differences in complexation and dissociation rate of rare-earth ions in aqueous solution with water-soluble complexing agents, kinetic separation of adjacent rare-earth elements can be achieved. In this work, we will focus on some crucial scientific problems relevant to that proposed new method: The kinetic difference of rare-earth ions reacted with organic extractant on surface of oil-covered gas bubbles. The essential reasons why differences in reaction rates of rare-earth ions can be enhanced in gas-assisted push-pull extraction processes. Why the microscopic effect resulting from molecular and ionic interfacial non-linear dynamic behavior, such as adsorption, aggregation and orientated arrangement of extractant molecules and rare-earth ions on surface of oil bubbles have impact on reaction rates and could enlarge kinetic differences? The main purpose of current research is to reveal microscopic mechanism of kinetic separation of rare-earth ions, to explore intrinsical rules why interfacial molecular dynamic behaviors and changes in interaction between extractant molecules and rare-earth ions could result in kinetic push-pull effect, the crucial influence factors for controllable kinetic separation, and to provide relevant mathematic models for interfacial non-equilibrium mass transfer and gas-assisted kinetic separation. The present works want to provide scientific fundament to develop our suggested new method for kinetic non-equilibrium extraction and separation of adjacent lanthanide elements based on differences in interfacial kinetic behaviors, so as to obtain practical instructions for future industrial application in process intensification for kinetic group separation of adjacent rare-earths from various complicated low-content leaching solutions.

相邻稀土元素物化性质极其相近，萃取分离系数小。如何实现相邻稀土元素离子对的萃取分离过程强化是稀土萃取冶金的难题。本项目提出基于气泡支撑有机萃取剂油膜萃取的气助动力学推拉体系分离相邻稀土创新思想，放大其分离系数。利用气泡表面包覆有机萃取剂油膜(亦称油泡)上升过程萃取稀土的速率差异以及水溶液中稀土络合解离速率差异产生推拉效应实现动力学分离。重点研究稀土离子在上浮油泡表面油膜层推拉萃取动力学行为差异，研究动力学推拉体系对相邻稀土元素离子分离系数的放大效应，研究界面分子/离子吸附、聚集、取向排布等非线性动态行为对萃取反应速率的影响规律。揭示萃取剂分子与稀土离子界面相互作用变化导致动力学推拉分离的微观机制。阐明相邻稀土元素动力学分离的界面机理、关键控制因素及调控方法，建立数学预测模型。从调控相邻稀土气助推拉萃取界面动力学行为差异出发，为实现多稀土溶液中相邻稀土元素离子动力学分离过程强化提供理论依据。

相邻稀土元素离子对的萃取分离是稀土萃取冶金的难题。本项目提出基于气泡支撑有机萃取剂油膜萃取的动力学推拉分离相邻稀土元素新方法，利用气泡表面包覆有机萃取剂油膜(亦称油泡)上升过程萃取稀土的速率差异以及水溶液中络合剂与稀土离子络合/解离速率的差异产生推拉效应，实现相邻稀土元素动力学分离过程强化。针对拟解决的关键科学问题，本项目重点考察了气助动力学推拉萃取过程有机萃取剂分子在上浮油泡分散相表面吸附、聚集、取向排布等动态行为影响稀土离子萃取反应速率的作用机制，阐明了性质相似相邻稀土元素离子在上浮油泡表面与有机萃取剂分子相互作用、以及与水相中添加的水溶性氨酸络合剂竞争相互作用差异导致相邻稀土元素离子萃取反应速率产生差异的微观机理。研究揭示了气助动力学推拉效应强化分离相邻稀土元素的本质原因、关键控制因素和界面传质调控规律，建立了描述动力学推拉萃取分离行为的相关数学预测模型。发现：油泡表面有机萃取剂分子的活性官能基团取向角变化将导致其反应活性位点在水油两相界面处的“有效浓度”发生相应变化。有机萃取剂分子在油膜层界面的取向吸附行为以及稀土离子的界面吸附能力对萃取反应速率均具有重要影响。由于上浮油泡表面引发的Marangoni对流效应对不同的稀土离子具有选择性，当气泡表面有机萃取剂薄层油膜萃取不同稀土离子的速率大小与水溶液中添加的络合剂竞争络合稀土离子的速率大小变化趋势相反时，利用“动力学推拉效应”可实现难分离相邻稀土元素萃取分离过程强化。本项目的研究提出了一种从萃取反应相间界面微观分子动态深入认识萃取反应动力学行为的新视角，解决了性质相似相邻稀土元素萃取分离系数小的瓶颈难题。相邻稀土元素的非平衡态动力学分离系数远远大于其平衡态热力学分离系数。从调控相邻稀土元素气助推拉萃取过程的界面传质动力学行为差异出发，为实现多稀土共存复杂溶液中相邻稀土元素对的动力学分离过程强化提供了理论依据。