离子液皂化在稀土分离工艺中应用的基础研究

Rare earth elements (REEs) are critical materials, the development of novel REEs separation technology has aroused worldwide attention. The industrial RREs extractants, such as P507 and naphthenic acid, have been used in China for 30 years. Some disadvantages of the traditional extractants need to be ameliorated. The pollution from saponification wastewater is a prominent problem. To control the pollution, some laws and regulations have been continuously issued by Chinese government. To develop novel REEs separation method, ionic liquid type saponification is proposed in this program. Our primary research results have indicated the novel saponification method may reveal some advantages for industrial extractants, i.e., (1) increasing the extraction abilities. (2) no multiple saponification procedure is needed, no saponification wastewater is produced. (3) selectivities of REEs can be increased. (4) stripping properties can be improved. In this program, thermodynamic properties, kinetic properties and extraction mechanisms of the ABC-BILs for REEs will be studied. Some basic scientific problems of ionic liquid type saponification for REEs separation industry will be resolved. The countercurrent experiments will be conducted to evaluate the potential applications of optimized ABC-BIL extractants in rare earth minerals separation engineering. This program contributes to provide scientific basises for developing efficient and environment-friendly rare earth separation technologies.

稀土是重要的战略元素，新型稀土分离技术的研发已在全球引起广泛关注。我国的P507、环烷酸等工业稀土萃取剂已应用三十余年，存在一系列问题急需改进，其中萃取剂皂化废水污染已成为一个突出问题。针对皂化废水污染问题，国家近年连续颁布法规，要求治理。面向新型稀土分离工艺研发的需要，本申请提出了离子液皂化的方法。我们的初步研究结果表明，这种新型皂化方法对工业萃取剂可以具备如下优势：（一）提高萃取能力。（二）不需多次皂化，无皂化废水产生。（三）增强选择性。（四）改善反萃性能。本申请将对酸碱耦合型双功能化离子液（ABC-BIL）萃取稀土的热力学性质、动力学性质及机理开展研究。着力解决离子液皂化在稀土分离工艺中应用的一些基本科学问题，对优化出来的ABC-BIL通过串级实验进行工艺应用的可行性评估。上述研究有助于为开发高效、环境友好的稀土分离新工艺提供科学依据。

本项目针对我国传统工业萃取剂的皂化废水污染问题，面对新型稀土分离工艺研发的需要，提出了离子液皂化的方法。按照项目计划书，采用酸碱中和法合成了多种ABC-BIL离子液体，采取多种表征手段对基于ABC-BIL的新型稀土分离体系开展了深入研究，阐明了萃取机理。研究表明ABC-BIL离子液体的离子缔合型的萃取机理，有助于避免传统皂化过程中往复式的酸碱消耗及皂化废水。我们在设计和合成新型ABC-BIL萃取剂时，发现某些苯氧羧酸可以定量萃取低浓度稀土，与稀土形成固体萃合物，并且苯氧羧酸可以反萃和循环使用。根据此类萃取剂的特性，集合溶剂萃取法和化学沉淀法的特点，我们开拓了新型萃取-沉淀法，特征是萃取过程不使用有机溶剂，可定量萃取金属离子生成萃合物沉淀，萃取剂能够反萃及循环使用。这不仅是分离体系的创新，更是一种全新的分离方法，国内外未见相关报道。上述研究有助于为开发高效、环境友好的稀土分离新工艺提供科学依据。