基于共存阳离子竞争吸附的稀土萃取过程界面盐效应

Interface salt effect based on competition adsorption of co-existing cations in process of rare earth solvent extraction

萃取过程的界面盐效应影响目标待萃离子与萃取剂分子间相互作用的微观机理一直是争论的焦点。本文采用LB膜、动态界面张力表征和分子动力学模拟等手段,研究了水溶液中与稀土离子共存的NH_(4)^(+)、K^(+)、Na^(+)、Mg^(2+)、Ca^(2+)、Al^(3+)、Fe^(3+)等阳离子竞争扩散和界面吸附行为对目标稀土Er^(3+)离子的影响规律,探讨了界面盐效应的微观机制。结果表明:各种共存阳离子的水化能力及其竞争吸附行为差异是影响P507萃取剂分子与Er^(3+)离子间相互作用的重要因素。共存阳离子及其浓度变化不仅影响Er^(3+)离子向界面的扩散速率,而且影响其与P507分子的相互作用强度。在低盐浓度区,各种共存阳离子的影响服从NH_(4)^(+)>K^(+)>Na^(+)>Mg^(2+)>Ca^(2+)>Al^(3+)>Fe^(3+)顺序。共存阳离子的竞争水化效应是决定Er^(3+)离子向界面扩散速率的关键因素。在高盐浓度区,共存阳离子的影响与上述相反,服从Fe^(3+)>Al^(3+)>Mg^(2+)>Na^(+)>K^(+)>NH_(4)^(+)顺序。高浓度共存阳离子具有更强的竞争吸附效应,对Er^(3+)离子的扩散速率及其界面吸附产生明显的抑制作用。

The microscopic mechanism of the interaction between the target ions and the extractant molecules affected by the interfacial salt effect in the extraction process has always been the focus of controversy.In this paper,LB film,dynamic interfacial tension characterization,molecular dynamics simulation was used to study the effects of competitive diffusion and interfacial adsorption of coexisting cations,NH_4~+,K~+,Na~+,Mg~(~(2+)),Ca~(2+),Al~(3+),Fe~(3+),on target rare earth Er~(3+)ions in aqueous solution.Meanwhile,the microscopic mechanism of the interfacial salt effect was also discussed.The results indicate that the hydration ability and competitive adsorption kinetics of various coexisting cations have a significant impact on the interaction between P507 molecules and Er~(3+)ions.The change in the type of coexisting cations and their concentrations have an influence not only on the diffusion rate of Er~(3+)ions towards the interface but also the strength of intermolecular interaction between Er3+ions and P507molecules.In the lower salt concentration region,such an influence follows the order of NH4+>K+>Na+>Mg~(2+)>Ca~(2+)>Al~(3+)>Fe~(3+).The competitive hydration of various coexisting cations plays an important role in determining the diffusion and adsorption rates of Er~(3+)ions.However,the influence is opposite to the above mentioned when the coexisting cations have a higher concentration.A reverse order of Fe~(3+)>Al~(3+)>Mg~(2+)>Na+>K+>NH4+can be observed for their influence on Er~(3+)ion adsorption.A higher concentration of the coexisting cations has a stronger competitive adsorption effect,which significantly inhibits the diffusion and adsorption of Er~(3+)ions towards the interface.