非皂化P507体系萃取分离镧和锕元素

Extraction and Separation of Lanthanum and Actinium by Non-Saponification P507 System

由于稀土生产过程中锕元素未被有效分离去除,导致我国部分稀土产品的放射性超出豁免值(α和β总放射性小于1 Bq/g)。本工作以非皂化的2-乙基己基磷酸单-2-乙基己基酯(P507)为萃取剂,二乙基三胺五乙酸(DTPA)或N-(2-羟乙基)乙二胺-N,N',N'-三乙酸(HEDTA)为水相掩蔽剂,乳酸为酸度缓冲剂,分别在盐酸和硝酸体系中研究了对镧和锕两种元素的萃取分离。结果显示,弱酸试剂可有效缓冲稀土料液的酸度,使萃取反应向有利于生成有机配合物的方向进行。在pH为3.0、初始La^(3+)浓度为0.2 mol/L的盐酸溶液中,该体系对La^(3+)的萃取效果较单一的皂化P507有显著提高,D(La)可达5.0。在pH为2.0~2.5的硝酸体系中,恒定DTPA/HEDTA和乳酸的浓度分别为0.02 mol/L和1.0 mol/L,此时Ac^(3+)被有效掩蔽,D(Ac)的最大值仅有0.46,SF(La/Ac)值较盐酸体系的3~4可提高至5~7。此外,该非皂化P507体系也可以优先去除稀土低酸废水中的放射性Ac^(3+),其SF(Ac/La)值随乳酸浓度的增加可提高至14,这一现象能够用于实现有效控制稀土工业废水中放射性物质的目标。

Due to the ineffective separation and removal of actinium during the production process of rare earths,the radioactive of some products in China exceed the exemption values(the total activity ofαandβless than 1 Bq/g).Using non-saponified 2-ethylhexyl phosphate mono-2-ethylhexyl ester(P507)as an extractant,diethylenetriamine-N,N,N',N'',N''-pentaacetic acid(DTPA)or N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid(HEDTA)as aqueous masking agent,lactic acid as acidity buffer,the extraction and separation of lanthanum-actinium elements was studied respectively in hydrochloric acid and nitric acid media in this work.The results show that the weak acid can effectively buffer the acidity of the aqueous phase and promote the coordination reaction to form organic chelates favorably.The extraction properties of La^(3+)in the above system is better than in the single saponified P507 system.When pH is 3.0 and the initial La^(3+)concentration is 0.2 mol/L in hydrochloric acid solution,D(La)can reach 5.0 and SF(La/Ac)value is 3-4.Compared with that,SF(La/Ac)can increase to 5-7 in nitric acid system under the fixed conditions of pH as 2.0-2.5,the DTPA/HEDTA and lactic acid concentrations as 0.02 mol/L and 1.0 mol/L,respectively.In this case,Ac^(3+)is effectively masked and the maximum D(Ac)is only 0.46.Furthermore,the non-saponification P507 system can also preferentially remove the radioactive Ac^(3+)from the acidic rare earth wastewater,and SF(Ac/La)value can reach 14 with the increase of lactic acid concentration.The phenomenon can be used to achieve the goal of effective control of radioactive substances in the wastewater of rare earth industry.