有机含磷及含氮萃取剂萃取分离锆铪研究进展

Progress in Extraction and Separation of Zirconium and Hafnium with Organic Phosphorus and Nitrogen Extractants

锆和铪是两种性质接近、分离困难的稀有金属,主要应用于核工业。目前,针对湿法分离锆铪,工业上多采用溶剂萃取法。从有机含磷(膦)萃取剂、有机含氮萃取剂、协萃体系三方面,分别综述溶剂萃取法分离锆和铪的研究进展。发现对有机磷(膦)萃取剂研究较多,分离效果较好。对于新型萃取剂和萃取工艺的开发,如萃取剂二(2-乙基己基)-1-(2-乙基己基氨基)磷酸丙酯(BEAP)和超分子溶剂萃取法和膜渗透萃取工艺,在分离锆铪方面有很好的应用前景。以有机磷(膦)萃取剂为基础的协同萃取体系,在工艺开发和优化、萃取机制、动力学和热力学理论分析上作了大量研究,在进一步研究和工业应用上具有指导意义。最后,分析溶剂萃取法在分离锆铪方面的研究现状,对未来研究和工业应用给出合理建议。

Zirconium(Zr)and hafnium(Hf)are rare metals with similar properties and difficult to separate;they are mainly used in the nuclear industry.In this study,the extraction properties of extractants were analyzed by expounding the principles of the separation of Zr and Hf by different extractants,thus providing an existing theoretical basis for researchers regarding the separation of Zr and Hf.Through an analysis and summary of relevant scientific research,the latest research progress of Zr and Hf was reported to a vast number of researchers to aid in the development of the Zr and Hf separation industry in China.This work was also expected to provide new ideas and views for solving the"stuck neck"problem in the field of Zr and Hf separation in China.Through a comprehensive review of recent research progress in the field of Zr and Hf separation via solvent extraction,the separation of Zr and Hf by solvent extraction was introduced in this paper from three aspects,namely,organic phosphorus(phosphine)extractant,organic nitrogen extractant,and co-extraction system.The principles,conditions,and characteristics of the separation of Zr and Hf by solvent extraction and the various extractants and extraction separation methods were introduced.The internal relationship between extractants and extraction separation methods was explained,and current research problems,deficiencies,and future research directions were identified.The tributyl phosphate(TBP)-HNO3 system with kerosene as the diluent was used to separate Zr and Hf.When the TBP concentration was 2.5 mol·L-1,the H+concentration was 7.0 mol·L-1,and the NO3-concentration was 9.2 mol·L-1,91.6%of Zr and 12%of Hf were extracted,and the separation factor was 16,which denoted nuclear-grade Zr and nuclear-grade Hf.In the sulfuric acid medium,the new Zr and Hf separation extractant BEAP was used to separate Zr selectively.With heptane as the diluent,the BEAP extractant was utilized for countercurrent extraction of Zr,with a separation coefficient of 6.8.If further extraction and washing sections were added,then nuclear-grade Zr products would be obtained.The mechanism of several organic phosphorus-containing extractants in separating Zr and Hf was also studied.The extractants had the properties of dimerization and cation exchange due to the activity of the acid=P(O)OH group.Compared with D2 EHPA,Ionquest 801,and Dio-PA,DPPA produced a softer Lewis base extractant because of the electron attraction of phenoxy,which was beneficial to the extraction of Hf.Therefore,DPPA’s"solventized"cation exchange mechanism was a favorable extraction method,and because of the electron-withdrawing substituents,the affinity for Hf and Zr was increased,resulting in a reduced concentration of the required extractant and high economic efficiency.Among the extractants Aliquat 336,TEHA,Alamine 336,Alamine 308,and Alamine 300,Alamine 308 and Alamine 300 had good potential for separating Zr and Hf.Under similar extraction conditions,the extraction rate of Alamine 300 was higher than that of Alamine 308;the separation factor of Alamine 308 was also higher at 12.4.In the medium of 0.5~4.0 mol·L-1 nitric acid,Lix 63 exhibited high extraction efficiency for Zr and Hf,which was within the best initial concentration ratio of Zr and Hf(1~50).The maximum extraction separation factor of Lix 63 was 186.In the concentrated sulfuric acid solution,Lix 63 could not separate Zr and Hf.In the process of the DIBK-phosphorus extractant(P204,P350,TBP and TOPO)synergistic extraction system’s separation of Zr and Hf,the performance of the DIBK-TOPO system in separating Zr and Hf was higher than that of DIBK-TBP and DIBK-P350 and better than that of the traditional MIBK extraction system.The use of an organophosphorus(phosphine)extractant to extract and separate Zr and Hf was the main research direction at present.Kerosene was a good choice as a diluent,and nitric,sulfuric,and hydrochloric acids made up the main acidic system for the extraction of Zr and Hf.The majority of extractants extracted Zr selectively.Many processes for the extraction and separation of Zr and Hf had been reported,but the theoretical research on the equipment for extracting Zr and Hf was minimal.A synergistic extraction system could extract Zr and Hf and obtain a high separation coefficient.However,it needed a high pH and precise control of the acidity of the system,making it difficult to implement.An analysis of current references indicated that the theoretical research on relevant factors was relatively scarce and immature,and the following aspects needed to be further explored.(1)The emulsification phenomenon,corrosion of extraction equipment,and loss of extractant due to different reasons in the existing extraction process needed to be addressed.(2)New extraction methods,such as supramolecular solvent extraction and membrane permeation extraction,exerted a good extraction separation effect and had a good application value,but they were not mature.The stability of the extraction process needed to be improved,the separation coefficient and distribution ratio needed to be increased,basic theoretical research should be deepened,and the combination of extraction methods and extractants should be explored.Moreover,the combination of multiple extraction methods and new ideas for combining extraction and anti-extraction research needed to be investigated.(3)A systematic and in-depth study of the extractant structure,extraction mechanism,thermodynamics,and kinetic theory of the extraction reaction of different extractants in the extraction process must be conducted to establish a solid theoretical foundation for the development of superior extractants.The new extractant BEAP performed well in separating Zr and Hf and had a good application prospect.Further in-depth research on structure and process optimization could be the focus of future research.(4)Among existing co-extraction systems,the DIBK series had better extraction and separation effects.DIBK,with its MIBK-like properties and minimal toxicity,was a superior extractant and expected to replace MIBK in the future.Therefore,further research was required to improve the extraction separation coefficient of THEK,develop anti-extractants with a small extraction loss,and design industrialized extraction equipment.