在金属离子的溶剂萃取分离过程中，共存盐离子对金属离子的萃取行为有着重要的影响，这种现象称之为盐离子效应。目前，人们对于萃取过程中盐离子效应作用机理的认识还比较缺乏，特别是微观层次。从界面分子层次来研究萃取行为是当前萃取化学研究的前沿，这也为理解萃取过程中盐离子效应的微观机理提供了新方向。本文从离子的界面行为出发，分别针对阴离子（钒、铬）和阳离子（稀土）萃取过程盐离子效应中阴离子的作用机理进行了研究。在理解阴离子微观作用机理的基础上，提出了新方法用于强化碱性介质钒、铬的萃取分离、稀土与过渡金属间的萃取分离以及相邻稀土Pr/Nd的萃取分离。具体研究内容和结果如下：通过搭建全内反射紫外可见吸收光谱装置研究了碱性条件下盐离子在有机溶液/水溶液界面的竞争吸附行为。发现不同盐离子对界面的亲和力存在差异，而且其大小服从SCN- > ClO4- > I- > NO3- > Br- >Cl- > SO42-的顺序，即Hofmeister序列。通过实验验证了离子在隐埋的液/液界面吸附行为中的Hofmeister序列。进一步，通过分子动力学模拟研究了盐离子在有机溶液/水溶液界面的竞争吸附行为，从分子层次揭示了离子在界面竞争吸附行为中的Hofmeister序列。这为理解盐离子与钒、铬离子在界面的竞争吸附行为提供了理论基础。采用衰减全反射红外光谱研究了碱性条件下硫酸根离子与钒、铬离子在界面的竞争吸附行为。发现在硫酸根离子浓度增加过程中，铬离子的表面红外特征峰的强度发生明显的降低，而钒离子的表面红外特征峰则几乎不发生变化。为了进一步阐明钒、铬离子这种界面吸附行为的差异，采用分子动力学模拟研究了硫酸根离子与钒、铬离子在界面的竞争吸附行为。研究结果表明，可以通过硫酸根离子调控钒、铬离子在界面的选择性吸附行为，从而为发展碱性介质分离钒、铬的新方法提供了理论基础。根据离子在界面竞争吸附行为的研究结果，提出了一种新方法用于强化碱性介质中钒、铬的萃取分离。在酸化伯胺-硫酸钠萃取体系中，通过调控水溶液中硫酸钠的浓度，选择性抑制铬的萃取，从而实现钒、铬在碱性介质中的有效分离。研究表明，钒在有机相中的萃取机理为阴离子交换反应，其中钒以HVO42-的形态与有机相中的NO3-发生阴离子交换反应。热力学研究表明，钒的萃取为放热反应。反萃实验表明，采用硝酸钠溶液可以将负载有机相中的钒有效地反萃下来，反萃后得到的有机相具有较好的循环使用性能。研究了中性膦类萃取剂萃取稀土过程中特殊的盐离子效应。与传统的盐析效应理论不同，本文发现盐离子促进稀土萃取的能力还与盐的浓度密切相关。在低盐浓度条件下，不同盐离子促进稀土萃取的能力服从SCN- > ClO4- > NO3- > Br- > Cl-的顺序，即Hofmeister序列。而在高盐浓度条件下，不同盐离子促进稀土萃取的能力不再服从Hofmeister序列，而变成NO3- > SCN- > ClO4- > Br- > Cl-的顺序。采用分子动力学模拟研究了TOPO与稀土离子在界面的相互作用机理。结果表明，低盐浓度条件下，盐阴离子的界面亲和力主导稀土萃取过程中的盐离子效应。高盐浓度条件下盐阴离子的界面亲和力和盐析能力将共同主导TOPO萃取稀土过程中的盐离子效应。研究了非功能离子液体萃取稀土过程中的盐离子效应。结果表明，盐离子促进稀土在非功能离子液体中萃取效率的能力服从SCN- >NO3- > Br- > Cl- > ClO4-的顺序。通过分子动力学模拟结果分析，发现萃取配合物中盐离子作为桥梁连接着稀土离子与离子液体。进一步，通过分析不同盐离子的水化能力及其与稀土离子的配位能力，提出非功能离子液体萃取稀土过程中的盐离子效应可以归因于盐离子的水化行为和盐离子与稀土离子间配位能力的协同作用。这为进一步利用盐离子的配位能力调控不同金属离子的萃取分离行为提供了理论基础。提出了一种新的离子液体基双水相萃取体系，用于从过渡金属中萃取分离稀土。研究发现，利用硝酸根离子与稀土离子和过渡金属离子间配位能力的差异，可以选择性地从溶液中萃取Nd，从而实现Nd与Fe、Co、Ni之间的有效分离。结合核磁共振氢谱和分子动力学模拟发现，硝酸根离子在Nd3+的内配位层，而离子液体则在Nd3+的外配位层，硝酸根离子作为桥梁连接了离子液体与Nd3+。不仅如此，由于该离子液体基双水相体系中液/液界面两侧具有相似的微观环境，导致该体系具有极低的粘度和超低的界面张力。这些特征有利于稀土离子在界面的传质动力学，从而提高其萃取动力学。提出了一种由P507有机相、离子液体富集相和硝酸钠水溶液相组成的三液相萃取体系，用于强化相邻稀土Pr/Nd间的萃取分离。研究发现，相比于有机-水溶液两相体系和离子液体基双水相体系，Pr、Nd在三液相体系中的分离效率得到了显著的提高。这可以归因于P507有机上相和离子液体富集中相对Pr、Nd具有相反的萃取选择性，即存在“外推拉效应”。通过分析发现，离子液体富集相对稀土的反序萃取可以归因不同稀土离子与硝酸根离子配位能力的差异。全稀土萃取实验结果表明，有机上相易于萃取重稀土，而离子液体富集中相易于萃取轻稀土。因此，所提出的三液相萃取体系可以同时实现轻稀土与重稀土的分离富集。;The study on the interface behaviors during the extraction is a new area in the extraction chemistry. It provides a new direction to understand the micro-mechanism of salt effect in the extraction. In this thesis, the specific salt effect on the extraction of anions (vanadium, chromium) and cations (rare earths) were studied from the viewpoint of interfacial behavior of salt ions. Based on the knowledge obtained from the mechanistic study, the salt effect was then used to strengthen the extraction and separation of vanadium, chromium, separation of rare earth from transition metal and separation of adjacent rare earth praseodymium/neodymium. The main research content and results are given as follow:Total internal reflection UV-visible absorption spectroscopy (TIR-UV) was employed to investigate the competitive adsorption behavior of salt ions at the organic/aqueous solution interface. It was found that salt anions exhibited different affinity to the interface. In addition, the affinity of salt ions to the interface followed the order of SCN– > ClO4– > I– > NO3– > Br– >Cl– > SO42–, which was consistent with the Hofmeister series. It provided the first evidence for the Hofmeister series in the adsorption behavior of ion at the buried liquid/liquid interface. The molecular level knowledge on the competitive adsorption behavior of ions at the organic/aqueous solution interface was also obtained from molecular dynamic simulations. It provided a basis for the further understanding into the competitive adsorption behavior of salt ion with V(V), Cr(VI) ions at the interface.The competitive adsorption behavior of SO42– ions with V(V), Cr(VI) ions at the interface was studied by using attenuated total reflection infrared spectroscopy (ATR-IR). It was found that the intensity of ATR peak of Cr(VI) ions would decrease gradually during the increase of SO42– concentration. While the intensity of ATR peak of V(V) ions would not be affected by the addition of SO42– ions. Furthermore, molecular dynamic simulations were employed to elucidate the different adsorption behaviors of V(V) and Cr(VI) ions. The selective adsorption behaviors of V(V) and Cr(VI) ions could be regulated by the introduction of SO42– ions. It provided a fundamental basis for the development of new methods for the separation of V(V), Cr(VI).According to the competitive adsorption behavior of V(V), Cr(VI) at the interface, Na2SO4 was used as additive to strengthen the extraction and separation of V(V), Cr(VI) in the alkaline solutions. It was found that the extraction of Cr(VI) could be inhibited by regulating the concentration of SO42– in the aqueous solutions. In addition, the extraction mechanism of V(V) in the organic phase was suggested to be anion exchange reaction between HVO42– in the aqueous solution and NO3– in the organic phase. Thermodynamic studies demonstrated that the extraction of V(V) was an exothermic reaction. Besides, the results indicated that V(V) could be stripped effectively by NaNO3 aqueous solution. The organic phase also exhibited excellent regeneration performance.The specific salt effect on the extraction of rare earth in the neutral phosphine extractant-organic phase was studied. Unlike the traditional salting-out effect theory, we found that salt effect was also closely related to the concentration of salts in the aqueous solution. When the concentration of salt was low, the ability of salt ions in enhancing the extraction of rare earth followed the order of SCN– > ClO4– > NO3– > Br– > Cl–, which was consistent with Hofmeister series. When the concentration of salt was high, the ability of salt ions in enhancing the extraction of rare earth followed the order of NO3– > SCN– > ClO4– > Br– > Cl–, which was not consistent with Hofmeister series. To obtain the fundamental mechanism behind the specific salt effect, molecular dynamic simulations was employed to study the interaction of TOPO molecules with rare earth ions at the interface. The result indicated that the interface propensity of salt anions dominated the specific salt effect on the extraction of rare earth in the TOPO organic phase when the concentration of salt was low. While the interface propensity and salting-out ability of salt anions would co-dominate the extraction of rare earth in the TOPO organic phase when the concentration of salt was high. The specific salt effect on the extraction of rare earth in the non-functional ionic liquids was also studied. The experimental results indicated that the ability of salt ions in enhancing the extraction of rare earth followed the order of SCN– >NO3– > Br– > Cl– > ClO4–. Furthermore, the results of molecular dynamic simulations demonstrated that salt anions act as the bridge to connect rare earth ion with ionic liquids. Combining the experiments and simulation, the specific salt effect on the extraction of rare earth in the non-functional ionic liquids could be attributed to the synergism of complexation and hydration behavior of salt anions. The experimental results of extraction behavior of rare earth in four kinds of typical non-functional ionic liquids further verified the mechanism proposed above. It provided a fundamental basis for regulating extraction behavior of metal ions by using their different complexation behaviors.According to the mechanism of salt effect on the extraction of rare earth in the non-functional ionic liquids, we constructed an ionic liquids-based aqueous two phase system to separate rare earth from transition metal based on the different complexation ability of NO3– with rare earth and transition metal ions. The results indicated that the efficient separation of Nd from Fe、Co、Ni could be achieved by regulating the experimental parameters. In addition, the structure of extraction complex in the ionic liquid-rich phase was elucidated by NMR and molecular dynamic simulations. The result indicated that NO3– ions were in the inner coordination shell of Nd3+ ions, while ionic liquids were in the outer coordination shell of Nd3+ ions. In addition, similar micro-environment was existed across the liquid/liquid interface in the ionic liquids-based aqueous two phase system, which resulting the extra-low viscosity and interfacial tension. These characters of ionic liquids-based aqueous two phase system was in favour of transfer kinetics of metal ions across the liquid/liquid interface, and then enhanced the extraction kinetic of rare earth ions.A three-liquids phase extraction system consisting of P507 organic phase, ionic liquid-rich phase and NaNO3 aqueous solution was constructed to strengthen the separation efficiency of adjacent rare earth Pr/Nd. It was found that the separation efficiency of Pr/Nd in the three-liquid-phase extraction system could be enhanced compared to that in the organic-aqueous two phase and ionic liquids-based aqueous two phase system. The enhanced separation efficiency of Pr/Nd could be attributed to the external push-pull effect on the extraction of Pr/Nd in the P507 organic phase and ionic liquid-rich phase. The extraction experimental result of total rare earths demonstrated that the organic phase preferred to extract heavy rare earths, while ionic liquid-rich phase preferred to extract light rare earths. Therefore, the separation and enrichment of light rare earths and heavy rare earths could be simultaneously achieved in the three-liquids phase extraction system