FUNDAMENTAL AND APPLIED FUNDMENTAL RESEARCH·Radiochemistry and Nuclear Chemistry 173
Radiochemistry and Nuclear Chemistry
Extraction of U, Pu, Am, Eu and Sr With TODGA-DHOA/OK
ZHU Wen-bin, JIANG De-xiang, YE Guo-an, YE Yu-xing
The extraction of U(Ⅵ), Pu(Ⅳ), Am(Ⅲ) Eu(Ⅲ) and Sr(Ⅱ) with N,N,N’,N’-tetraoctyl-3-oxapentane diamide (TODGA) and N, N-dihexyl-octanamide (DHOA)/kerosene (OK) as extractants from nitric acid solutions has been studied. The results show that the value of D(M) (there, M are U, Pu, Am and Eu) increase with the increasing HNO3 concentration, while the value of D(Sr) reaches the maximum at
3 mol/L HNO3.
The value of D(Pu), D(Am), D(Eu) and D(Sr) decrease with the increasing DHOA concentration, while the D(U) slightly increase with an increase of DHOA concentration.
Study on Catalyzed Electrolytic Plutonium Oxide Dissolution
LIU Li-sheng, GUO Jian-hua, CHANG Li, LI Rui-xue,
CHANG Shang-wen, OUYANG Ying-gen
The dissolution of PuO2 prepared or calcinated at high temperature has been a difficult task. It is shown that crystalline PuO2 is very difficult to dissolve in nitric acid solution, and insoluble in nitric acid solution below about 4 mol/L. Now the electrochemical method is frequently used in the dissolution of PuO2.
The cell for catalyzed electrolytic Plutonium oxide dissolution (CEPOD) is a 2-compartment cell, and the anode and cathode compartments are separated from each other. PuO2 is oxidized in anode compartment:
PuO2PuO2＋＋e－ E0=1.58 V (1)
PuO2PuO22＋＋2e－ E0=1.24 V (2)
The final product of oxidative dissolution will be PuO22+. Ag+ added in anode electrolyte will be oxidized into Ag2+ which is a strongly oxidizing ion.
Ag+Ag2+ + e－ E0=1.98 V (3)
Based on the above potentials, it is possible for the dissolution of PuO2.
A new H-model cell is designed, 2 compartments of which are separated by a porous sintered glass (pore diameter is 2.5-3.5 μm). The capacity of each compartment is 10 mL. Pt plate is used as working electrode (area is 1 cm2), Pt wire is used as counter electrode and reference electrode, respectively. The potential of reference electrode is 0.7 V in 6 mol/L HNO3 solution.
The use of catalyzed electrolytic Plutonium oxide dissolution was studied in the cell. PuO2 can be oxidized into PuO22+ with Ag+ in anode compartment, and the dissolution rate is higher than 99%. The dissolution velocity increases with increasing Ag+ concentration and current density. The effect of HNO3 acidity in the range of 4-8 mol/L on dissolution velocity can be ignored. The current efficiency of dissolution increases with increasing Ag+ concentration and decreases with increasing current density. There is no definitely difference between the dissolution rates of Pu and Am contained in PuO2 powder. The electro- migration of Ag+ from anode compartment to cathode compartment is slow.
Study on Method for Separating Micro Plutonium
From Abundant Uranium
LI Hui-bo, WANG Xiao-rong, LIN Can-sheng, SONG Feng-li, GAO Yu-lan
Extraction-chromatography has not only the selectivity of solvent extraction but also high perform- ance character of chromatography, so it has significant advantage on the separation supermicroelements, especially actinides. In present research micro plutonium was separate from abundant uranium by extrac- tion-chromatography and ion exchange. Firstly extraction-chromatography was use to remove most U and fission elements, then ion exchange was performed to refine and purify Pu.
Based on a series of static experiments, the quaternary ammonium and TBP extraction-chromato- graphy were selected and the adsorption acidity are 4 and 2 mol/L, respectively. Type 256 anion exchange resin was selected and the adsorption acidity is 6.5 mol/L. The single column condition experiments and bunch columns demonstration experiments also were studied. The result shows that the Pu recovery attains to near 70% and the purification coefficient to U is 107 by using the program.
Study on Extraction of Pu(Ⅳ) by Tri-iso-Amyl Phosphate
CHENG Qi-fu, LUO Fang-xiang, LIU Xie-chun, YE Guo-an, XIAO Songt-ao, LI Gao-liang,
ZHANG Hu, HUANG Xiao-hong, ZHU Wen-bin, JIANG De-xiang
The extraction performance of Pu(Ⅳ) with tri-iso-amyl phosphate (TiAP) were studied. The effects of the concentration of nitric acid and the ratio of phase on the extraction efficiency of Pu(Ⅳ), and on the formation of second organic phase were investigated. The experimental results indicate that the distribution ratios of Pu(Ⅳ) increase obviously with increasing aqueous nitric acid concentration, and it is not found the formation of second organic phase when the concentration of Pu(Ⅳ) in organic phase is reached 77 g/L and the concentration of nitric acid in aqueous phase is 3.5 mol/L. In addition, the reduction back-extraction condition of Pu(Ⅳ) from 30% TiAP/OK was also studied.
The results show that Pu(Ⅳ) loaded in the organic phase could be effectively back-extracted into aqueous phase by using 0.8 mol/L DMHAN-0.3 mol/L MMH-0.3 mol/L HNO3 as the stripping agent; at 20 ℃, the stripping percentage of Pu(Ⅳ) is over 90% while the concentration of Pu(Ⅳ) in the organic is approached 25 g/L at phase ratio (O/A) 2.
Kinetic Studies on Reactions Between Monomethylhydrazine and Fe3+
as Well as N,N-Dimethylhydroxylamine and Fe3+
by Measuring Potential of Fe3+/Fe2+
CHEN Hui, ZHANG Hu, HE Hui, LI Gao-liang
The kinetic studies on the reactions between monomethyldrazine and Fe3+ as well as N,N-dimethyl- hydroxylamine and Fe3+ in nitric acid system are performed by measuring open-circuit potential of Fe3+/ Fe2+. The effect of some factors such as the concentration of MMH or DMHAN, the concentration of nitric acid, ionic strength, temperature and the concentration of Fe3+ on the reaction rate is also studied.
The reaction rate equation may be expressed as follows for MMH-Fe3+:
－dc(Fe3+)/dt＝k c1.3(MMH) c－2(H＋)·c(Fe3+) c－0.5(Fe2+)
The rate constant is 1.15×10－3 (mol/L)1.2 s－1 at 55 ℃ and activation energy of the reaction is (94.51±6.1) kJ/mol. The influence of ionic strength on the reaction is negligible.
The reaction rate equation may be expressed as follows for DMHAN-Fe3+:
－dc(Fe3+)/dt＝k c2(DMHAN) c－2.9(H＋) c(Fe3+) c－1(Fe2+)
The rate constant is1.32×10－3 (mol/L)1.9·s－1 at 50 ℃ and activation energy of the reaction is (113.9±2.4) kJ/mol. The influence of ionic strength on the reaction is negligible.
Reaction Between Mono-methylhydrazine and Tc(Ⅶ)
in Nitric Acid Medium
WEI Yan, PAN Yong-jun, JIAO Hai-yang, CONG Hai-feng,
ZHENG Wei-fang, JIA Yong-fen
Methyl hydrazine (MMH) is a supporting reagent used in the Purex process in order to eliminate nitrous acid in the system. The reaction between MMH and Tc(Ⅶ) in nitric acid medium was studied by extraction method. The influences of temperature, acidity, the concentrations of MMH and pertechnetate on the reaction is investigated. The results indicate that the reaction period is composed of three stages, induction period, fast reaction period and the termination of the reaction.
The length of the induction period is related to the acidity, the concentration of MMH, and that of Tc(Ⅶ) in nitric acid solution. The rate equation of the induction period is found as follows:
－dc(Tc(Ⅶ))/dt = k1 c0.64(H+) c0.45(MMH) c(Tc(Ⅶ))
where k1＝(0.029±0.002) (mol/L)－1.09·h－1 at 40 ℃ and 3.0 mol/L of nitrate concentration. The activation energy of this stage Ea1 is (56.5±0.2) kJ/mol.
After induction period the reaction comes into the period of fast reaction. The rate equation in this period is found as follows:
－dc(Tc(Ⅶ))/dt = k2 c0.47(H+) c0.22(MMH) c(Tc(Ⅶ))
where k2＝(0.186±0.002) (mol/L)－0.69·h－1 at 40 ℃. The activation energy of this stage Ea2 is (51.6±0.4) kJ/mol. The ionic strength has no influence on the reaction rate.
From the above results it is seen that the reaction rate between methyl hydrazine and heptavalent technetium is very slow, and the presence of heptavalent technetium has no great influence on the consumption of methyl hydrazine.
Reaction of N, N-Dimethylhydroxylamine and Tc(Ⅶ)
in Nitric Acid Medium
WEI Yan, JIAO Hai-yang, PAN Yong-jun, CONG Hai-feng, ZHU Guo-hui, JIA Yong-fen
N, N-dimethylhydroxylamine (DMHAN) is the reductant used in the Purex process study. The reaction of Tc(Ⅶ) and DMHAN in nitric acid medium was researched by extraction method under different temperature, acidity, the concentrations of DMHAN and Tc(Ⅶ). The results indicate that Tc(Ⅶ) is not reduced by DMHAN under different acidity at temperature of 30 ℃ and 40 ℃ and different concentration of DMHAN at 40 ℃ in 200 h..
From the above results it is seen that the consumption of DMHAN in nitric acid by Tc(Ⅶ) can be ignored.
Stability of N, N-Dimethylhydroxylamine in Nitric Acid Medium
WEI Yan, CONG Hai-feng, JIA Yong-fen
N, N-dimethyl hydroxylamine (DMHAN) is the reductant used in the Purex process study. Its stability directly influences its application in the Purex process. DMHAN was synthesized, the purity of synthesized DMHAN was analyzed to be 99%, and the synthesized DMHAN meets the needs of the experiment. A titration method for determination of the concentration of DMHAN was established based on the potassium dichromate titration after the ferric oxidation.
The ratio of DMHAN to ferric during the oxidation of DMHAN is determined as 1∶4. Methanol, formaldehyde, and formic acid, which are possible oxidized products of DMHAN, do not influence the result of analysis. Using this titration method, the stability of DMHAN in nitric acid was studied. The decomposition of DMHAN in nitric acid depends on temperature and the concentration of nitric acid. The decomposition of DMHAN is lower than 10% within 100 h when the temperature is lower than
35 ℃ and the acidity is lower than 3.0 mol/L. DMHAN is decomposed quickly when the temperature is higher than 35 ℃ and the acidity is higher than 3.0 mol/L. Decomposition of DMHAN produces NO.
Reaction Kinetics Between Mono-methylhydrazine and Nitrous Acid
WEI Yan, CONG Hai-feng, JIAO Hai-yang, PAN Yong-jun, JIA Yong-fen
Mono-methyl hydrazine is one of supporting reagents in the Purex process in order to eliminate nitrous acid in the system. The research on the reaction between them is not found in the literature so far. In order to avoid the possible effect of nitric acid, the oxidation of mono-methylhydrazine by nitrous acid in perchloric acid medium is researched by spectrophotometric method at first. The influences of acidity, concentrations of methyl hrdrazine and nitrous, and temperature on the reaction rate are studied. The rate equation is found as follows:
－dc(HNO2)/dt=k c0.94(H+) c1.11(MMH) c(HNO2)
where k=(46.0±2.7) (mol/L)－2.05×s－1 at 4.5 ℃ and is 0.5 mol/L of perchlorate concentration. The corresponding activation energy of the reaction is Ea=(42.4±0.1) kJ/mol.
Then the reaction between methyl hydrazine in nitric acid medium is also investigated by the similar method. The influences of acidity, temperature, and the concentrations of nitrate, methyl hydrazine, nitrous acid on the reaction is studied. The reaction rate equation in nitric acid medium is as follows:
－dc(HNO2)/dt=k c(H+) c1.14(NO3－) c1.08(MMH) c(HNO2)
where k=(115±2) (mol/L)－3.22×s－1 at 2.6 ℃ and 0.5 mol/L of nitrate concentration. The corresponding activation energy of the reaction is Ea=(37.8±0.1) kJ/mol.
From above mentioned two rate equations, it is seen that NO3－ participates in the reaction in the nitric acid medium. The rate constant in nitric acid medium is higher than that of in perchloric acid medium. Activation energy Ea in nitric acid medium is lower than that of in perchloric acid medium, and it suggests that the presence of nitric acid is advantage to the elimination of nitrous acid by methyl hydrazine. From the research above, we can see that methyl hydrazine can react with nitrous acid very quickly in nitric acidmedium, and the nitrous acid in the system can be eliminated by methyl hydrazine.
Stability of Monomethyl Hydrazine in Water and Nitric Acid
LI Gao-liang, HE Hui, CHEN Hui, TANG Hong-bin
The stability of monomethyl hydrazine in water and nitric acid was studied. The effects of some factors on the spectrophotometric analysis of monomethyl hydrazine were investigated.
The results indicate that little effects were made to the analysis results, when there is a little amount of nitric acid, nitrous acid, methyl alcohol, formic acid, formaldehyde, methylamine, N,N-dimethylhy- droxylamine or ferrous iron in the analysis system. Molar absorption coefficient is found to be about 3.06×103 L·mol－1·cm－1 at 20 ℃, and hydrolysis velocity of monomethyl hydrazine is different under different temperature or concentration of nitric acid. Increasing the concentration of nitric acid or decreasing the temperature is propitious to the stability of monomethyl hydrazine. The stability of monomethyl hydrazine is affected by many factors, which will be studied thoroughly in future.
Synthesis of Dihydroxyurea and Its Possible Application in Purex Process
YAN Tai-hong, ZHU Jian-min, ZHANG Yu, XIAN Liang, ZHENG Wei-fang, YE Guo-an
In the development of advanced Purex process which have been expected to reduce costs and lessen environmental impact, one option for advanced Purex flowsheets is to adopt a new reductant in the U/Pu split. So we synthesized a new reductant-dihydroxyurea (DHU) through the reaction of the nontoxic bis (trichloromethyl) carbonate (BTC) with hydroxylamine (yield: 40%). The product is characterized by elemental anal, FT-IR, 1HNMR, 13CNMR and MS.
Its acid stability and thermic stability experiment results show that at 15 ℃ DHU is stable in 0-
2.5 mol/L HNO3 when being placed for 100 h; At 50℃, DHU decomposed to 91%, 72%, 63%, 31% in 0.5, 1.0, 2.0, 2.5 mol/L HNO3 solution; At 90 ℃, DHU decomposes readily when the concentration of HNO3 is over 2.0 mol/L. DHU was determined colorimentrically with alkali ethanol-water solution. Besides, the reaction between DHU and FeCl3 in water and ethanol is studied, respectively. The results show that DHU can reduce Fe(Ⅲ) to Fe(Ⅱ) quickly, and it means DHU can reduce Pu(Ⅳ) to Pu(Ⅲ) thermodynamically. All the results show that the application of DHU to the U/Pu split in the Purex process is possible.
Synthesis of Zirconyl Pyrophosphate and Study
on Adsorption Property to Cesium
SONG Feng-li, LIN Can-sheng, WANG Xiao-rong, CUI Yu-guo
Zirconyl pyrophosphate and zirconyl molybopyrophosphate were synthesized, and the adsorption property to cesium was experimentally studied for zirconyl pyrophosphate synthesized at different conditions. The synthesized samples with the best adsorption property were analyzed and characterized. The comparison absorption properties between zirconyl molybopyrophosphate with the best adsorption and zirconyl pyrophosphate were performed.
Results show that adsorption properties to cesium have little discrepancy for zirconyl pyrophosphate synthesized in different conditions. The zirconyl molybopyrophosphate shows the best adsorption property when the ratio of pyrophosphate to molybdate is 8 to 1 and zirconyl is enough. Compared with zirconyl molybopyrophosphate, zirconyl pyrophosphate can be used within a larger range when the distribution coefficient is appropriate. The ion exchange capacity of zirconyl pyrophosphate is higher than that of zirconyl molybopyrophosphate, the chemical stability of zirconyl pyrophosphate is similar to that of zirconyl molybopyrophosphate.