In the cup type precipitator, Ce2(C2O4)3 was used to simulate Pu(C2O4)2 for continuous precipitation experiments. Keeping other conditions unchanged, process conditions including temperature at 30.0-50.0 ℃, Ce(NO3)3 concentrations of 0.084 mol/L and 0.167 mol/L, crystal seed addition ratios in the range of 0-2.0×10-1 and seed feeding position were investigated respectively, to find out their effects on the particle size distribution and morphology of Ce2(C2O4)3 particles. When the concentration of Ce(NO3)3 is 0.167 mol/L at 50.0 ℃, the D50 maximum values(D50 is the value of the particle diameter at 50% in the cumulative distribution) of Ce2(C2O4)3 particles can increase by 62.2 μm compared with that without crystal seeds. When the concentration of Ce(NO3)3 is 0.167 mol/L and the crystal seeds are added in the peripheral vortex region and the central vortex region at 50.0 ℃, the corresponding D50 maximum values are 154.1 μm and 120.7 μm respectively. When the temperature changes from 30.0 ℃ to 50.0 ℃, the maximum value of precipitated particles D50 increases with temperature. Under various process conditions, and when D50 reaches the maximum, the shape of Ce2(C2O4)3 particles is dominated by regular flaky long strips, the proportion of fragmented and irregular flaky aggregates is small. The grain growth mode of Ce2(C2O4)3 belongs to the spiral growth mechanism, and the thickness of the single layer of grain is about 16 nm.

在核燃料后处理过程钚尾端处理中,通常利用草酸制备草酸钚沉淀然后进一步煅烧获得氧化钚颗粒、用于M OX燃料的制造,因此掌握草酸钚热分解机制、控制氧化钚产品颗粒的形貌和粒度具有实际意义.针对草酸盐的热分解机理和沉淀在煅烧后颗粒形貌遗传性问题,本工作选用草酸铈和草酸铀作为研究对象,系统研究了草酸铈、草酸铀的热分解反应,结合同步热分析仪(TG/DSC)与X射线衍射仪(XRD)的表征,获得了草酸铈和草酸铀的热分解数据;制备了不同粒度的草酸铈和草酸铀,用激光粒度仪考察了煅烧前后颗粒的粒度,并用扫描电镜(SEM)观察颗粒聚集状态、粒度和形貌,结果表明煅烧分解会导致粒径有规律地下降,但形貌得以保留.

Abstract The effects of feeding location on crystals size and distribution, precipitation percentage of Pu(IV) oxalate were investigated in a vortex continuous precipitator when the apparent average residence time was 25 min at 50 °C. The results showed that when oxalic acid was into the free vortex zone and Pu(IV) nitrate solution was into the forced vortex one, the VMD of the particles near the outlet of the precipitator increased from 36.8 ± 1.2 µm to 45.8 ± 2.1 µm, the precipitation percentage of Pu(IV) oxalate from 97.90% ± 1.0–99.79% ± 0.05%, compared with another feeding location, both oxalic acid and Pu(IV) nitrate solution into the forced vortex zone. The two feeding methods could both prevent Pu(IV) oxalate nuclei contacting the inner wall of the precipitator during nucleation. The results showed agglomeration happened during crystals growth even under stirring. Both local supersaturations and agglomeration decided particles size distribution and the average size of Pu(IV) oxalate.

Abstract A new method is developed to calculate the dilution ratio N of the two reactant solutions during nucleation rate determination. When the initial apparent supersaturation ratio S N = f(N) in the dilution tank is controlled between 1.66 and 1.67, the counted nuclei is the most, both nuclei dissolving and secondary nucleation avoided satisfactorily. Based on this methoed, Plutonium(IV) oxalate is precipitated by mixing equal volumes of tetravalent plutonium nitrate and oxalic acid solutions. Experiments are carried out by varying the supersaturation ratio from 8.37 to 22.47 and temperature from 25 to 50 °C. The experimental results show that the nucleation rate of plutonium(IV) oxalate in the supersaturation range cited above can be expressed by the equation R N = A N exp(−E a /RT)exp[−B/(ln S)2], where A N = 4.8 × 1023 m−3 s−1 , and E a = 36.2 kJ mol−1, and B = 20.2. The crystal growth rate of plutonium(IV) oxalate is determined by adding seed crystals into a batch crystallizer. The crystal growth rate can be expressed by equation G(t) = k g exp(−E’ a /RT) (c − c eq) g , where k g = 7.3 × 10−7 (mol/L)−1.1(m/s), E’ a = 25.7 kJ mol−1, and g = 1.1.

The ammonium ions produced by the reactions of relatively excessive dimethylhydroxylamine(DMHAN) with Fe3+, Ce4+ and Pu4+ in dilute nitric acid solutions at room temperature were determined by ion chromatographic method. The results show that the reactions between DMHAN and Fe3+, Ce4+ and Pu4+ all produce a certain amount of ammonium ramifications under acidic conditions, which includes (CH3)2NH+2, NH+4 and CH3NH+3. The reaction mechanism is as follows. When DMHAN reacts with Fe3+, Ce4+ and Pu4+ respectively, it can be oxidized and reduced simultaneously in the acidic solution for the -1 valence of N atom in DMHAN. Then part of DMHAN is reduced to (CH3)2NH+2, and it is further converted into NH+4 and CH3NH+3 partly. With the increase of redox potential of Fe3+, Pu4+ and Ce4+, the conversion ratio of DMHAN into amine ions increases and the proportion of (CH3)2NH+2 in total amine ions decreases, while the proportion of NH+4 in total amine ions increases.

研究了磷酸三丁酯(TBP)辐解产物磷酸二丁酯(HDBP)和磷酸一丁酯(H2 MBP)对U(Ⅳ)-肼以及乙异羟肟酸(AHA)反萃Pu(Ⅳ)的影响,考察了相接触时间、相比(o:a)、还原剂浓度、HNO3浓度、肼浓度、TBP辐解产物HDBP和H2 MBP浓度等条件对含有HDBP或H2 MBP的30％(体积分数)TBP/煤油中Pu(Ⅳ)反萃率的影响.结果表明:U(Ⅳ)对Pu(Ⅳ)有很强的还原反萃能力,降低相比、HNO3浓度、肼浓度有利于U(Ⅳ)对Pu(Ⅳ)的反萃,并且U(Ⅳ)可以快速有效地破坏HDBP、H2MBP与Pu(Ⅳ)的络合,将Pu(Ⅳ)反萃到水相.乙异羟肟酸对Pu(Ⅳ)有很强的络合反萃能力,通过降低酸度、延长相接触时间和增大AHA浓度能够有效降低HDBP和H2 MBP对AHA络合反萃Pu(Ⅳ)的影响.

用草酸铈代替草酸钚,在一种新型连续沉淀反应器——沉淀脉冲柱中进行沉淀研究.利用MSMPR结晶器的数学模型对沉淀脉冲柱在特定条件下的草酸铈结晶动力学进行研究,指导放大反应器的结构设计,确定了有利于制备大颗粒沉淀的结构参数,用草酸铈产品的粒度分布对反应器的结构参数进行验证,并考察了不同结构参数对沉淀颗粒形貌的影响规律.研究结果表明,MSMPR结晶器的数学模型适用于沉淀脉冲柱,求解的动力学数据可以很好的指导反应器的结构设计,优化的制备大颗粒沉淀的反应器结构为:折流板上部进料,板间距为32 mm,脉冲强度为0.5×2.65 cm/s.

为研究草酸盐沉淀动力学,本研究用草酸铈代替草酸钚对成核和晶体生长动力学进行了研究,并提出了一种在测定成核动力学时确定稀释倍数的有效方法.在25～50℃时,在硝酸铈浓度为0.030～0.400 mol/L、草酸浓度为0.250～0.800 mol/L、母液草酸浓度0.100 mol/L的条件下,分别研究了草酸铈成核和晶体生长动力学方程.结果表明:成核时稀释倍数对成核速率的测量影响很大,定义的稀释过饱和比Sn值为1.65时得到的稀释倍数最佳.草酸铈成核过程可分为均相成核和异相成核,成核速率方程可表示为:RN=AN0·exp[-Ea/RT]·exp[-BN/(ln S)2],其中均相成核时:AN0=3.86×1030/(m3·s),Ea=67.4 kJ/mol,BN=55.3;异相成核时:A N0=3.10×1020/(m3·s),Ea=19.1 kJ/mol,BN=11.5.晶体生长速率方程可表示为:G=kg0·exp[-Ea/RT]·δg(t),其中kg0=4.81×105 m/s,Ea=80.3 kJ/mol,g=2.09,草酸铈的晶体生长受界面反应过程控制.该装置和沉淀动力学测量方法可用于其他草酸盐成核和晶体生长动力学的研究.

Abstract The effects of feeding location, stirring speed and apparent average residence time on oxalate crystals size and distribution, tackiness of the product on the walls of reactor and stirring paddle were investigated in a vortex continuous precipitator at 45 °C. The results showed agglomeration happened during nucleation and crystals growth of U(IV) oxalate. Both local supersaturations and agglomeration maked the particles size distribution of U(IV) oxalate from 10–100 µm and the average sizes 35–45 µm. On the other hand, when the nucleation process were controlled to happen in the forced vortex zone, two feeding locations: (a) both oxalic acid and U(IV) nitrate solution into the forced vortex zone, (b) oxalic acid into the free vortex and U(IV) nitrate solution into the forced vortex, tackiness of the crystals on the wall of the precipitator could be effectively avoided.

Abstract A series of single stage trials were conducted using six reducing reagents to investigate the rate determining step during Np(VI) reduction back-extraction from 30%TBP/Kerosene to HNO3 solution under the same conditions. The six reducing reagents included: acetohydroxamic acid, N,N-dimethylhydroxylamine, N,N-diethylhydroxylamine, 2-hydroxyethylhydrazine, methylhydrazine and N,N-dimethylhydrazine. Moreover, the back-extraction of Np(V) from 30%TBP/Kerosene to HNO3 solution without reducing reagent was conducted with the same concentrations of Np and HNO3. The experimental results indicate the rate of Np(VI) reduction in the two-phase system is determined mainly by the rate of Np(V) mass transfer from 30%TBP/Kerosene to HNO3 solution, whose mass transfer kinetics is far slower than previously estimated. The rate determining step is a slow chemical reaction as: NpO2NO3·TBP = NpO2 + + NO3 − + TBP.

采用着色法研究了杯式连续沉淀器中流场形状与性质,并采用加入颗粒、即时沉淀反应生成颗粒两种方式考察了沉淀颗粒在中心涡流区域的分布与扩散情况.在26℃时,采用杯式连续沉淀器研究了料液的加料方式、搅拌速率、表观反应时间等因素对生成的草酸亚铁沉淀颗粒粒径分布和平均粒径、对连续沉淀器和搅拌桨表面颗粒粘结的影响.当草酸料液与硫酸亚铁料液均从杯式连续沉淀器中心涡流区域加入时,可以有效避免沉淀器内壁产生颗粒粘附、结块现象,且所生成的颗粒平均粒径较大,其中生成的粒径为2～5 μm和小于10μm的颗粒所占比例较小.当搅拌速率在500～800 r/min时,提高搅拌转速不利于生成粒径为2～5 μm和小于10μm的沉淀颗粒,而草酸亚铁连续沉淀反应的表观反应时间大于30.0 min时,沉淀颗粒的生长速率逐渐变缓.

The thermal stability of N, N-dimethylhydroxylamine (DMHAN) in the HNO3 solution was studied using microcalorimeter. The influence of concentration of HNO3, DMHAN, methylhydrazine (MH), atmosphere (air and nitrogen), and metals was investigated. The kinetic parameters and self-accelerating decomposition temperature (SADT) of the feed in process (stripping reagents 1BX, scouring agent 2DS, stripping reagents 2BX, and waste aqueous phase 2DW) were calculated by Advanced Kinetics and Technology Solutions (akts) thermokinetics software. The molar enthalpy of the reaction of NaNO2 with DMHAN and MH was also determined. The results show that the initial reaction temperature (T0) of DMHAN/HNO3 (HNO3: 1.5–3.0 mol/L, DMHAN: 0.05–0.8 mol/L) is increased as the acidity is reduced or the concentration of DMHAN is increased. Holding reductant MH made the induction period of the autocatalytic reaction longer. The air, nitrogen atmosphere, Fe, and the fission products (Zr, Ru) do not affect the decomposition of DMHAN, but the stainless steel made the T0 of DMHAN/HNO3 become lower. The SADT of 1BX/2DS, 2BX, and 2DW is 56 °C, 52 °C and 47 °C, respectively. The molar enthalpies of formation of the reaction of NaNO2 with DMHAN and MH are −411.3 kJ/mol, −246.0 kJ/mol, respectively.

An improved apparatus is used for nucleation measurements according to Nielsen's method. A new method is proposed to calculate the dilution ratio N of the reaction solution during nucleation rate determination. With the rule, when the initial apparent supersaturation ratio S’=f(N) in the dilution tank is controlled from 1.3 to 3.0, crystal nucleus dissolving and secondary nucleation can be avoided satisfactorily. Experiments are realized by varying the supersaturation ratio from 15.6 to 93.3 and temperature from 15 °C to 50 °C. Ferrous oxalate is precipitated by mixing equal volumes of ferrous sulfate and oxalic acid solution. The experimental results showed that the nucleation rate of ferrous oxalate in the supersaturation range above is characterized by the primary homogeneous mechanism and can be expressed by the equation RN = ANexp(-Ea/RT)exp[-B/(ln S)2], where AN = 3.9×1013 m−3 s−1, Ea = 33.9 kJ mol−1, and B =13.7. The crystal growth rate can be expressed by equation G(t)=kgexp(-E'a/RT) (c-ceq)g, where kg = 3.6 × 1013 m/s, E'a = 58.0 kJ mol−1, and g = 2.4.

建立了Fe(II)-邻菲啰啉显色法测定HNO3体系中氨基羟基脲(HSC)的方法.在乙酸/乙酸钠缓冲体系中,HSC与Fe(III)反应生成的Fe(II)能与邻菲啰啉形成稳定的络合物,该络合物的最大吸收波长在510 nm.考察了缓冲溶液用量、反应时间等条件对吸光度(A)的影响.结果表明:HSC浓度在5～60μmol/L范围内遵循比尔定律,线性回归方程为:A=0.0292cHSC(μmol/L),相关系数R2=0.9993.方法用于实际样品测定,加标回收率在100.1％ ～104.4％之间,检出限为3.8×10-2μmol/L,相对标准偏差0.04％ ～0.12％,满足HSC分析的需求.

Formaldehyde methyl hydrazine,the secondary reaction product of MMH in DMHAN-MMH solution was detected and verificated by gas chromatography-mass spectrometry(GC-MS) in this research.DMHAN-MMH nitrate solution stored for a long time will be changed yellow.The main reason is that part of MMH is oxidized to be HCHO by oxygen in the air,and then HCHO and MMH is to be methyl hydrazone by condensation reaction.Low temperature,closed environment and dark is conducive to the preservation of DMHAN-MMH nitric acid solution.At room temperature,10-3 mol/L MMH has no significant effect on the stripping ratio of macroconcentration Pu(Ⅳ) in 30％TBP-dodecyl hydride,but it has obvious effect on the stripping ratio effect of low concentration of Pu(Ⅳ) (＜0.5 g/L) and the lower the concentration of plutonium,the more obvious the effect.

Device and process of oxidization, degassing, acidity adjustment of 1BP (The Pu production feed from U/Pu separation section) from APOR process (Advanced Purex Process based on Organic Reductants) were improved through rational design and experiments. The device was simplified and the process parameters, such as feed position and flow ratio, were determined by experiments. Based on this new device and process, the reductants N,N-dimethylhydroxylamine (DMHAN) and methylhydrazine (MMH) in 1BP solution could be oxidized with much less N2O4 consumption. (C) 2015 Elsevier B.V. All rights reserved.

The thermal stability of N,N-dimethylhydroxylamine (DMHAN)in the nitric acid solution was studied using micro calorimeter.The main influence factors including the nitric acid concentration,the concentration of DMHAN,MMH,atmosphere(air and nitro-gen)and metals were studied and compared the thermal stability of DMHAN with HAN under the same conditions.The results show that the initial reaction temperature (t0 )of DMHAN/HNO3 (HNO3:1.5-3.0 mol/L,DMHAN:0.05-0.8 mol/L)is improved as the acidity reduces or the concentration of DMHAN increases.The reaction heat of DMHAN/HNO3 is 865.5 kJ/mol and 683.4 kJ/mol respectively when the mole concentration ratios of HNO3 to DMHAN are 2.5-10 and 12.5-20.This indicates the different ratio of HNO3 to DMHAN makes the scale of reactions different in the DMHAN/HNO3 ,so it makes the different reaction heat.Holding reductant MMH make the induction period of the autocata-lytic reaction become longer.The air,nitrogen atmosphere,Fe and the fission products (Zr, Ru)do not affect the decomposition of DMHAN,but the stainless steel make the DMHAN/HNO3 show higher reactivity.

The reaction kinetics of N,N-dimethylhydroxylammonium ion(DMHAN)with nitrous acid were studied by spectrophotometerly in 0.1-0.4 mol/L nitric acid media.Influ-ences of temperature,ion strength,nitric acid concentration,nitrous acid concentration and DMHAN concentration were investigated.The reaction rate equation is obtained as:-dc(HNO2 )/dt=kc1.26 (HNO2 )c0.85 (DMHAN)c0.45 (H+) The reaction rate constant and the reaction activation energy are 3.09 (mol/L)-1.56 ·s-1 and 55.1 kJ/mol at 20 ℃,μ=0.50 mol/L,respectively.The stoichiometric ratio of nitrous acid to DMHAN is observed by 2.5:1 .

The high specific activity of fast reactor MOX spent fuel will leads to serious solvent degradation ,so the contact time needs to be shorten .A rig trial of U and Pu co‐recovery process was performed in centrifugal contactor .The results show that when contact time in single stage is 20 s ,the yields of U and Pu in extraction‐scrub process are higher than 99.99% , respectively , and the yields of U and Pu in co‐stripping process are 99.99% and 99.94% ,respectively .The risk of the third phase generation and polymerization and precipitation of Pu can be prevented .