【作者】 叶国安；

【导师】 何建玉； 林漳基；

【作者基本信息】 中国原子能科学研究院 ， 核燃料循环与材料， 2002， 博士

【摘要】 本文研究了Purex流程共去污槽中镎的走向控制和新型萃取剂酰胺荚醚的萃取热力学及其从模拟高放废液中回收锕镧元素。镎走向控制研究中通过调价阶段加入亚硝酸、而萃取前清除亚硝酸的独特办法可以将大于95％的镎赶入1AW。合成了三种酰胺荚醚萃取剂，研究了它们对锕系和裂片元素的萃取热力学，通过条件实验选择了其中一种荚醚TBOPDA（N，N，N’，N’—四丁基—3—氧戊二酰胺），进行了从模拟高放废液中分离锕镧系元素的工艺研究，锕系的回收率大于99.99％，并且基本上实现了锕镧元素的组分离。其要点如下： 1．Np（Ⅴ）在1～3mol/LHNO₃溶液中的歧化很慢，在1.0和2.0mol/LHNO₃中17天内仍未达到平衡，3.0mol/LHNO₃中12天后可认为基本达到平衡，计算出K_c=（3.60±0.45）×10^-4，K_混=（3.22±0.40）×10^-6。 2．在2.0～3.0mol/LHNO₃体系中加入尿素(使其浓度达到10^-2mol/L)，可以有效地抑制Np（Ⅴ）的氧化反应，Np（Ⅳ）和Np（Ⅵ）仅由Np（Ⅴ）歧化生成，17天内，可以使95％以上的镎稳定在5价。萃取过程中加入尿素可以有效地抑制镎的萃取。但随萃取时间的延长，镎可以不断被萃入有机相，同时随酸度增加，Np（Ⅴ）的氧化平衡向生成Np（Ⅵ）的方向移动。 3．实验结果表明HNO₂催化HNO₃氧化Np（Ⅴ）的浓度上限可高至5×10^-3mol/L。求出氧化反应的平衡常数值为K_混=（3.50±1.50）×10^-8。HNO₂浓度在5×10^-3—5×10^-5mol/l之间时，随着萃取时间的延长，镎不断被萃入有机相，HNO₂在5×10^-2mol/L时，萃入有机相的镎量相对少。 4．1AF料液用NO气体预调价可使进料液中的Np（Ⅴ）＞95％。在不同条件下的试管串级实验、微型混合澄清槽实验和全流程台架温实验结果表明，在选定的工艺条件下，多数情况下可使98％的Np进入高放废液（1AW）中，最低也使大于95％的Np进入1AW。实验结果还说明提高温度会加速Np（Ⅴ）氧化至Np（Ⅵ）。如果进料液中含有Np（Ⅳ），则会引起Np（Ⅳ）在1A萃取器中的积累。 5．实验结果表明，酰胺荚醚对金属离子的萃取属于中性络合萃取，萃取方程式为： 萃取不同金属离子时的i值见下表（i即为萃合物中萃取剂的分子数）： 6．以40％辛醇/煤油为稀释剂，酰胺荚醚萃取金属离子时有以下萃取规律；对不同价态的锕镧离子萃取分配比大小顺序为：Ln（Ⅲ）≥An（Ⅲ）＞An（Ⅳ）＞An（Ⅵ）＞An（Ⅴ），且三种萃取剂的萃取顺序为TBOPDA＞TiBOPDA＞TBDOODA；对阴离子TcO₄^-有一定的萃取分配比，萃取顺序为TBOPDA～T旧OPDAtoTBDOODA；对 Sr ＄取顺序为：TIBOPDA＞TBOPDAThTBDOODA。7．革取以上金属离子时，自由能变化（凸G）均小于零，革取过程可以自发进行。三价媚的凸G变化最大，因此三种荚醚对三价用系的革取分配比最高。对同一种金属离子，一般有TBOPDA的自由能变化高于另两种革取剂，因此TBOPDA的宰取分配比在三种茬取剂中是最高的。苯取腮时，T旧OPDA的革取自由能变化高于TBOPDA和TBDOODA的，T旧OPDA对锡的苹取分配比最高，TBOPDA次之，TBDOODA最低。苹取缉时，TBOPDA与TBOPDA在相同酸度卜臼由能变化相差不大，两者对锡的革取分配比基本相同。8．TBDOODA的苹取摘变最大，TIBOPDA的嫡变次之，这反应了构型嫡在苹取反应的嫡变中贡献最人。苹取四价锋钎时，单醚键荚醚嫡变反常，即革取后体系嫡变增加。9．苹取硝酸后，碳基吸收峰位移大，成键作用明显；单醚键荚醚的醚键吸收峰位移也较人，有成键作用，而双醚键荚醚的醚键峰位则没有发生位移变化。三种荚醚苹取EU、U、Th后，级基都发生了较大的位移，而醚键的峰位置则基本没有改变，因此荚醚对不同价态硼祸元素的苹取上要是以碳基的作用为主；奉取稀土时，碳基位移最大。荚醚革取锯时，碳基和醚键都发生了程度不同的位移，这一点是与革取其他金属离于的不同点，但两类峰的位移都不大，说明实际成键情况可能较复杂。IO．以 TBOPDA与 Eu形成的革合物为例，测定了成革合物的 EXAFS（Extended X－my AbsorptionFine Structure，扩展 X射线吸收精细结构储，拟合计算结果表明：TBOPDA和 TIBOPDA ％合物中中心金属原于周围有11个氧原子；第一配位层氧原子数在8—9之间，金属原于与氧原子之间的距离为0二40urn，第二层氧原子数为3，原于间距为0．257urn。11．TBDOODA不宜用于从高放废液中分离钢系和饶系元素，因为它对 U仰）的分配比相对较低。TIBOPDA／辛醇＋煤油与HLLW混合后易形成界面污物和三相。只有TBOPDA适宜于从HLLW中问收分离钢系和澜系元素，对三价崩谰苹取分配比高。选择的稀释剂为 40％煤油＋辛醇。12．川选定的苹取体系革取新配制的模拟高放废液料液时，易生成界面污物，将模拟料液放置一年后，界面污物消失。进行混合革取槽实验时，配制后模拟高放废液需放置一年。13．采用0．ZmolMBOPDAj40％辛醇一煤油为革取剂，用设计的流程，三四价钢系回收率人于99．99％，并且基本实现了 U（VI）／Pn（IV）＄11 Am（Ill）iu（Ill）之间的组分离。 本工作中求出的Np（V）在低酸下歧化平衡常数未见文献报道，对IAF料液中的锋在调价后用加入尿?更多还原

【Abstract】 The path-way controlling of neptunium in co-decontamination step of Purex process,the extraction thermodynamics of amido podand and its usage in recovery of actinides from simulated HLLW have been investigated.More than 95% Np were maintained in Np( V) in 1A extractor and flowed into 1 AW,if enough amount of HNO2 was added in feed adjustment and then HNO2 scavenger(urea) was added before extraction.Three kinds of amido podand were synthesized,and the extraction of lanthanides,actinides and some fission products were studied.One of them (TBOPDA,N,N,N’,N’ -tetrabutyl-3-oxa-pantenadiamide) was used as extractant to recover actinides from HLLW.The results of experiments show that more than 99.99% actinides were recovered from HLLW and separated basically in groups.The main digests are as follows:1. The rate of Np(V) disproportionate in 1.0-3.0mol/L HNO3 solutions is very slow. The reaction does not achieve equilibrium state after 12 days in 3.0mol/L HNCh solution.The disproportionation constant is Kc=(3.60+0.45)x10-4,Kmix=(3.22+0.40)x10-6,which has not been reported in literature before.2. The oxidation of Np(V) can be restrained effectively if urea was added into Np(V) solution,and more than 95% Np remained in Np(V) state for 17days.The extraction of Np can be neglected if there is urea in the solution.When increasing the acidity of solution.the equilibrium of Np( V) oxidation shifts towards Np(VI).3. The experimental results show that HNO2 catalyzes the oxidation reaction of Np(V) by HNO3.lts concentration can rech as high as 5X10 3mol/L.The equilibrium constant of the oxidation reaction of Np(V) is Kmix=(3.50+1.50) x10-8.When HNO2 concentration is in the range of 5x10-3-5x10-5mol/l,Np can be continuously extracted into organic phase. If HNO2 concentration is 5x10-2mol/L,the fraction of Np extracted in to organic phase become less.4. More than 95% Np can be adjusted to Np(V) if NO was bubbled into 1AF feed solution. Various experiments (tube cascade test,mini-mixsettler test,and bench scale warm test)show that,95%-98% Np flows into 1AW under the selected process parameters. Warm test results show that increasing temperature accelerates the oxidation of Np( V ).Small amount of Np(IV) in 1AF can cause accumulation of Np in the extraction sector of 1A extractor.5. Experiment results show that the extraction of metal ions by amido podand belongs to neutral complex extraction,which can be written as:Mn+ + nNO3- + iSM(NO)niS,(o)The numbers of extractant molecule in the extracted complexes (i) are given in the above table.6. The order of distribution ratio of actinides and lanthanides is:Ln(III)>An(III)>An(IV)>An(VI) > An( V ),the extraction order of three kinds of amido podand is:TBOPDA > TiBOPDA > TBDOODA.The extraction order is:TBOPDA-TiBOPDA>TBDOODA for the extraction of TcO4-,and TiBOPDA>TBOPDA>TBDOODA for the extraction of Sr.7. The free energy change of all extraction reactions is negative (AG<0),it means that the reaction can occur spontaneously. The AG of Am(III) extraction by any kind of amido podand is biggest in all metals,which can explain the fact that its distribution ratio is greatestFor a certain metal ion,the AG of TBOPDA is bigger than that of other two kinds of extractant,so distribution ratio of TBOPDA is higher.But for Sr extraction,TiBOPDA possesses highest free energy change,and its distribution ratio is highest.8. Among three kinds of extractant,the entropy of TBDOODA extraction is biggest,that of TBOPDA is least.lt means that configuration entropy makes the greatest contribution to the whole entropy change of extraction. When tetravalent actinides are extracted by TBOPDA or TiBOPDA.their entropy change is positive.At present this abnormal phenomenon cannot be explained.9. The extraction of nitric acid with TiBOPDA and TBOPDA causes great shifts for the absorption peaks of both carboxyl group and ether group of the complex compound in IR spectrum.For the complex compound of Eu,U and Th,graet shift occurs only in the wave range of carboxyl g更多还原