| 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...
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