NaCl-KCl熔盐体系电解制备金属铈工艺研究

为优化熔盐电解还原制备金属铈的工艺条件,开展了NaCl-KCl熔盐体系中CeCl₃的电化学行为及电解工艺研究。结果表明,在830 ℃下,以钼棒为工作电极、石墨棒为对电极、阴极电位高于1.9 V(Ag/AgCl为参比电极,下同)时,Ce³⁺可快速电解,提高Ce3+浓度有利于反应的进行。槽电压为4.41 V、相应的阴极电位为2.27 V时,电流效率最佳。固定阳极面积改变阴极面积的研究结果显示,随着阴极面积的减小,槽电压逐渐升高。实验条件下,槽电压随电极中心距的变化是线性的,与电极中心距的改变相比,电流的变化对槽电压的影响更显著。     

用于高温NaCl-KCl熔盐体系莫来石隔膜Ag/AgCl参比电极的性能研究

制备了用于高温NaCl-KCl熔盐体系的莫来石隔膜Ag/AgCl参比电极,并研究了该参比电极的性能。结果表明,初次于830℃NaCl-KCl熔盐体系中使用时参比电极的活化时间为2 h。在780～880℃范围内,实验所得电位差值与计算值的偏差在±3 mV以内,温度与电位差呈线性关系(r²=0.999)。±10 mA电流极化10 s后电极电势可于10 min内恢复平衡。以上结果表明,莫来石隔膜Ag/AgCl参比电极具有良好的稳定性、平行性和重现性,可用于高温NaCl-KCl熔盐体系的电化学行为研究。     

Electrolysis of Burnup-Simulated Uranium Nitride Fuels in LiCl-KCl Eutectic Melts

The electrochemical behavior of burnup-simulated uranium nitride fuels containing representative solid fission product elements, UN+Mo (Mo = 2.84 wt%), UN+Pd (Pd = 4.6 wt%) and (U, Nd)N (NdN = 8.0 wt%), was investigated in the molten LiCl-KCl eutectic salt with 0.54 wt% UCl₃ in order to clarify the effects of fission products on the dissolution of actinide nitrides and the behavior of FPs in the electrorefining of spent nitride fuel. The rest potentials of burnup-simulated UN pellets were similar to that of pure UN. The electrochemical dissolution of UN began at about _0:75V vs Ag/AgCl reference electrode in all samples as well as that of pure UN. After the electrolyses at the constant anodic potential of ?0:65––0:60V vs Ag/AgCl, most of UN was dissolved into LiCl-KCl as UCl₃ at the anode, and U was recovered in the liquid Cd cathode in all samples. Furthermore, Nd was dissolved at the anode and accumulated into LiCl-KCl as NdCl₃, while Mo and Pd were not dissolved but remained at the anode.     

Separation of plutonium from lanthanum by electrolysis in LiCl–KCl onto molten bismuth electrode

This work presents a study on the electroseparation of plutonium from lanthanum using molten bismuth electrodes in LiCl–KCl eutectic at 733 K. The reduction potentials of Pu³⁺ and La³⁺ ions were measured on a Bi thin film electrode using cyclic voltammetry (CV). A difference between the peak potentials for the formation of PuBi₂ and LaBi₂ of approximately 100 mV was found. Separation tests were then carried out using different current densities and salt phase compositions between a plutonium rod anode and an unstirred molten Bi cathode in order to evaluate the efficiency of an electrolytic separation process. At a current density of 12 mA/cm²/wt% (Pu³⁺), only Pu³⁺ ions are reduced into the molten Bi electrode, leaving La³⁺ ions in the salt melt. Similar results were found at two different Pu/La concentration ratios ([Pu]/[La] = 4 and 10). At a current density of 26 mA/cm²/wt% (Pu³⁺), co-reduction of Pu and La was observed as expected by the large negative potential of the Bi cathode during the separation test.     

用于熔盐体系的莫来石隔膜Ag/AgCl 参比电极的性能研究

以莫来石为隔膜材料，制备了用于高温氯化物(LiCl-KCl)熔盐体系的封闭式Ag/AgCl参比电极。采用LCR法分别测定了参比电极隔膜的电阻。同时，系统研究了参比电极的稳定性和重复使用性及平行性，重点研究了AgCl浓度对参比电极稳定性的影响。表征结果表明隔膜的组成为3Al₂O₃•2SiO₂，具有良好的离子导通性。电化学研究结果表明，AgCl摩尔分数为2.0%时，参比电极可连续稳定使用40 h以上，电位差稳定在±2 mV以内；重复使用4次后(约100 h)，电位变化±5 mV；±5 mA的极化电流5 s后可于15 s内恢复初始开路电位。上述研究结果表明，莫来石隔膜Ag/AgCl具有良好的稳定性、重复使用性、可逆性，可用于熔盐电化学研究及电解工艺中电极电位的控制中。     

LiCl-KCl共晶熔盐的纯化

氯化锂-氯化钾共晶熔盐是电解精炼干法后处理中最常用的电解质,其含有的杂质直接影响电流效率和产物纯度。本研究分别采用高温处理、HCl气体鼓泡和恒电位电解等方法依次去除了熔盐中的易挥发物质、氧离子和金属离子等杂质,获得了较高纯度的熔盐。采用热重分析(TGA)、电化学和电感耦合等离子体原子发射光谱(ICP-AES)等方法对比了纯化前后熔盐中各杂质的含量。研究结果表明:去除易挥发杂质的最佳处理温度范围为450～650℃;去除杂质金属离子时最佳电解电位为-2.3Vvs.Ag/AgCl(摩尔分数2%),恒电位电解800s后杂质金属离子总量低于1.5×10-6 g/g(盐)。以上研究结果表明,采用高温处理、HCl气体鼓入和恒电位电解可获得纯度较高的LiCl-KCl共晶熔盐。     

W/BDD薄膜电极制备及其电化学性能研究

利用化学气相沉积（CVD）法研制了一种钨基硼掺杂金刚石（W/BDD）薄膜电极,通过扫描电镜和Raman光谱考察了W/BDD薄膜电极的性能,通过电化学方法测定了其在LiCl-KCl熔盐中的电化学窗口和电化学性能。结果表明,研制的W/BDD薄膜电极的BDD薄膜有较好的微观结构;W/BDD薄膜电极在LiCl-KCl熔盐中的电化学窗口约为3.5 V(-2.5～1.0 V,相对于Ag/AgCl参比极电位);电解过程中,氧离子不与W/BDD薄膜电极表面BDD薄膜层的碳反应,直接被氧化为氧原子;长时间电解不会改变电极表面薄膜层的形貌和结构。     

稀土氧化物Gd2O3、Nd2O3、Sm2O3和Dy2O3在KCl-LiCl-Li2O熔盐中的电解

采用循环伏安法和计时电位法研究了Li₂O在KCl-LiCl熔盐中的电化学行为,并利用卷积伏安法计算了923 K下O₂^-在KCl-LiCl熔盐中的扩散系数（D),得到D=0.5×10^-5 cm²/s。以Gd₂O₃、Nd₂O₃、Sm₂O₃和Dy₂O₃为阴极,在KCl-LiCl-Li₂O(w=1%)熔盐中进行电解（恒电压3.40 V、电解温度923 K、电解时间25 h）。通过X射线衍射分析(XRD),证实稀土氧化物被部分还原为金属,并分析了电解过程中可能发生的反应。同时利用PRS模型（该模型可将固态阴极内离子的极限扩散速率与固态氧化物孔隙P、金属/氧化物摩尔体积R、阴极还原后的体积收缩率S等参数关联）分析了这些稀土氧化物的电解还原模型,得到Gd₂O₃、Nd₂O₃、Sm₂O₃和Dy₂O₃的最优孔隙率分别为18.7%、24.2%、30.6%、16.7%,最短电解时间分别为133、157、143、119 h,将这些结果与电解实验结果进行对比,发现阴极的孔隙率和电解时间均不满足金属氧化物完全被还原的要求,并给出了相应的解释。     

ThF4浓度对CeF3-ThF4-LiCl-KCl熔盐中Th电解沉积的影响

研究了高ThF4浓度下的CeF3-ThF4-LiCl-KCl熔盐中Th的电化学沉积行为.ThF4的质量分数从3％增加为10％时,Th(Ⅳ)的初始还原电位略微正移(从-1.75 V正移至-1.72 V,vs.Ag/AgCl).熔盐中Th(Ⅳ)浓度的增大会导致其初始还原电位正移,而F浓度的增大则导致其负移.电解沉积时,10...     

LiCl-KCl熔盐中Zr(Ⅳ)于Mo电极上的电化学行为

通过循环伏安法、方波伏安法和计时电位法等研究了LiCl-KCl共晶熔盐中ZrCl_4于Mo电极上的电化学行为。探究Zr(Ⅳ)于Mo阴极的还原机理,并计算Zr(Ⅱ)的扩散系数及Zr(Ⅱ)/Zr(0)的表观标准电势。结果表明:Zr(Ⅳ)在Mo阴极还原机理为:Zr(Ⅳ)+2e=Zr(Ⅱ);Zr(Ⅱ)+2e=Zr(0)或Zr(Ⅱ)+e+Cl~-=ZrCl;ZrCl+e=Zr(0)+Cl~-;金属Zr在阳极的氧化过程为:Zr(0)-2e=Zr(Ⅱ)和Zr(Ⅱ)-2e=Zr(Ⅳ)。Zr(Ⅳ)还原为Zr(Ⅱ)和Zr(Ⅱ)还原为Zr(0)均为可逆反应,且还原过程均为扩散控制。LiCl-KCl熔盐中Zr(Ⅱ)于Mo阴极上的扩散系数与温度的关系为:ln D=-6 724/T-2.95,扩散的活化能Ea=55.9kJ/mol。Zr(Ⅱ)/Zr(0)的表观标准电位与温度的关系为:E_(Zr(Ⅱ)/Zr(0))~(Θ*)=-2.695+9.33×10~(-4) T。     

影响CaCl2-NaCl熔盐电脱氧法制备金属Zr的工艺条件

将氧化物转化为金属是熔盐电解精炼干法后处理氧化物乏燃料流程的关键步骤之一。在等摩尔CaCl₂-NaCl混合熔盐体系中,以石墨棒为阳极,采用高温烧结后的ZrO₂模拟UO₂开展了电脱氧制备金属Zr的FFC剑桥工艺条件优化。研究了工艺条件（槽电压、电解时间、烧结温度和电解温度等）对电脱氧制备Zr的影响。采用场发射扫描电子显微镜(SEM)和X射线衍射(XRD)分别分析了电解前后ZrO₂阴极的微观结构和物相组成。优化后的工艺条件为：电压3.4 V、电解时间12 h、烧结温度900 ℃和电解温度722 ℃。同时,研究结果表明, ZrO₂电脱氧还原为Zr时,存在中间产物CaZrO₃和ZrO。     

Application of a boron doped diamond (BDD) electrode as an anode for the electrolytic reduction of UO2 in Li2O–LiCl–KCl molten salt

A boron doped diamond thin film electrode was employed as an inert anode to replace a platinum electrode in a conventional electrolytic reduction process for UO₂ reduction in Li₂O–LiCl molten salt at 650 °C. The molten salt was changed into Li₂O–LiCl–KCl to decrease the operation temperature to 550 °C at which the boron doped diamond was chemically stable. The potential for oxygen evolution on the boron doped diamond electrode was determined to be approximately 2.2 V vs. a Li–Pb reference electrode whereas that for Li deposition was around ?0.58 V. The density of the anodic current was low compared to that of the cathodic current. Thus the potential of the cathode might not reach the potential for Li deposition if the surface area of the cathode is too wide compared to that of the anode. Therefore, the ratio of the surface areas of the cathode and anode should be precisely controlled. Because the reduction of UO₂ is dependent on the reaction with Li, the deposition of Li is a prerequisite in the reduction process. In a consecutive reduction run, it was proved that the boron doped diamond could be employed as an inert anode.     

LiCl-KCl-LaCl_(3)熔盐体系中La^(3+)的反应动力学机理北大核心CSCD

在LiCl-KCl共晶盐中,研究了在不同温度下La^(3+)的反应动力学机理。首先,在723~873 K范围内,利用循环伏安法(CV)测得La^(3+)的扩散系数D为3.06×10^(-5)~6.08×10^(-5)cm^(2)/s,并根据Arrhenius方程计算了La^(3+)在电解质中的扩散活化能E_(D)=34.51 kJ/mol。随后,利用电化学阻抗谱技术(EIS)研究了La^(3+)在电极上的动力学参数并测得交换电流密度i_(0)为0.48~1.39 A/cm^(2)、反应速率常数k_(0)=2.04×10^(-4)~5.90×10^(-4)cm/s及反应活化能E_(a)=35.04 kJ/mol。通过Nyquist图和拟合的等效电路图研究La^(3+)在W电极上的反应动力学机理,发现在LiCl-KCl共晶盐中La^(3+)的电化学反应速率不仅受扩散控制还受电荷转移控制,且与温度成正相关。     

Investigation of metal matrix systems for cosmogenic Al analysis by accelerator mass spectrometry

We report experiments designed to help optimize accelerator mass spectrometry (AMS) of ²⁶Al (in the form of Al₂O₃) for geochronologic and geomorphologic applications. Analysis times are long and the precision of AMS are restricted by counting statistics for ²⁶Al, which are in turn limited by the intensity of Al⁻ beam currents. We show that ion beam currents are affected by the metal matrix in which Al₂O₃ is dispersed, by the matrix-to-Al₂O₃ mixing ratio, and for at least some matrices, such as Ag, by the depth to which the sample is packed in the AMS cathode. Typical instantaneous Al⁺⁷ currents (μA) produced by the LLNL CAMS Cs sputter ion source and measured in a Faraday cup after the accelerator are 2.26 for samples in Ag, 2.17 in Re, 2.00 in Nb, 1.92 in V and 1.73 in Mo. The AMS counting efficiency (Al⁻ ions detected per Al atom loaded in the target) for a constant analysis time (900 s) and for equimolar mixtures of Al₂O₃ and matrix is in the range of 6 × 10⁻⁵–9 × 10⁻⁵ in the order Ag > Re > Nb > V > Mo. Additionally, we observed a correlation between the ion detection efficiency (Al ions detected per Al atoms loaded) and the matrix work function and inverse vaporization enthalpy of the matrix and beam current. Typical currents (μA) obtained with elemental Al are 13.3 for samples in no matrix, 3.23 in V, 3.14 in Nb, 3.07 in Re, 2.85 in Mo, 1.46 in Ag. The ion detection efficiency for elemental Al correlates strongly with matrix electron affinity. Thus, our data indicate that the current practice of mixing Al₂O₃ with Ag is reasonable until a means is found to produce cathodes of elemental Al.     

LiCl-KCl熔盐中钍的电极过程研究

通过循环伏安法和计时电位法,研究LiCl-KCl熔盐中Th⁴⁺在723～803 K内在Mo电极上的电极过程。结果表明,Th⁴⁺在Mo电极上的电极过程受离子扩散步骤控制,扩散系数D随温度T变化的经验公式为ln D＝33.94-2.879×10⁴/T,形式电位的经验公式为E _vsCl-^0′/Cl²＝-3.45+7.5×10^-4T。     

LiCl-KCl共晶熔盐中氧离子的去除

采用NH₄Cl和HCl气体进行LiCl-KCl共晶熔盐中氧离子的去除。在使用NH₄Cl和HCl气体去除LiCl-KCl共晶熔盐中的氧离子过程中，用钇稳定氧化锆测氧电极对熔盐中的氧离子浓度变化进行测定。结果表明，HCl与熔盐中氧离子反应生成H₂O，并将反应产物水通过HCl载带出去。NH₄Cl去除氧离子的过程也是通过NH₄Cl分解的HCl与氧离子反应除去熔盐中氧离子。NH₄Cl和HCl均能有效地去除LiCl-KCl熔盐中的氧离子，使氧离子浓度降低至10^-5～10^-4 mol/kg。     

LiCl-KCl共晶熔盐中氧离子的去除

采用NH₄Cl和HCl气体进行LiCl-KCl共晶熔盐中氧离子的去除。在使用NH₄Cl和HCl气体去除LiCl-KCl共晶熔盐中的氧离子过程中，用钇稳定氧化锆测氧电极对熔盐中的氧离子浓度变化进行测定。结果表明，HCl与熔盐中氧离子反应生成H₂O，并将反应产物水通过HCl载带出去。NH₄Cl去除氧离子的过程也是通过NH₄Cl分解的HCl与氧离子反应除去熔盐中氧离子。NH₄Cl和HCl均能有效地去除LiCl-KCl熔盐中的氧离子，使氧离子浓度降低至10^-5～10^-4 mol/kg。     

液体阴极法回收盐渣中钚离子的模拟实验

采用液体阴极法电解NaCl-KCl-CeCl_3熔盐,回收熔盐中的铈离子以模拟高温化学工艺废盐渣中钚离子的回收。研究了初始CeCl_3浓度、温度、阴极电流密度对电解指标的影响,确定了初始CeCl_3质量分数为5%、温度750℃、阴极电流密度0.10A/cm~2时,熔盐对Ce的净化系数可达130,盐渣中残留的CeCl_3质量分数可降低到0.04%以下。实验证实了液体阴极法有望应用于废盐渣中钚离子的回收。     

Electrochemical Properties of Uranyl Ion in Ionic Liquids as Media for Pyrochemical Reprocessing

We have proposed a new reprocessing process by using ionic liquids (ILs) instead of molten salts of alkali chlorides in pyrochemical process. In the proposed process, spent nuclear fuels are dissolved in ILs by using Cl₂ as an oxidant, and UO₂ ²⁺ and PuO₂ ²⁺ ions in ILs are recovered as UO₂ and PuO₂ by electrochemical reduction. In order to examine applicability of ILs as media for reprocessing, we have studied electrochemical behavior of UO₂ ²⁺ in 1-butyl-3-methylimidazolium chloride (BMICl), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄), and 1-butyl-3-methylimidazolium nonafluorobutanesulfonate (BMINfO). Electrochemical properties of uranyl chloride dissolved into ILs were examined by cyclic voltammetry. In BMICl, an almost reversible redox couple was observed, and the formal potential and the diffusion coefficient were evaluated as _0:758V vs. Ag/AgCl and 4:8 × 10^?8 cm²s^?1, respectively. On the other hand, the electrochemical reactions of UO₂ ²⁺ in BMIBF₄ and BMINfO were irreversible. In BMINfO, some reduction peaks and one sharp oxidation peak were observed in the range of ?0:6～–0:2V and around 0.85V vs. Ag/AgCl, respectively. The reduction and oxidation peaks were assigned to multi step reduction of UO₂ ²⁺ to U(IV) via U(V) and/or direct reduction of UO₂ ²⁺ to U(IV), and the oxidative dissolution of the resulting U(IV) compounds, respectively. The electrochemical reduction of UO₂ ²⁺ in BMINfO at ?1:0V vs. Ag/AgCl produced the deposits on a carbon electrode as a cathode. Analyses of the deposits with the scanning electron microscope and the energy dispersive X-ray spectrometer indicated that the deposits are compounds containing uranium, oxygen, and chlorine. As a result, it is expected that the UO₂ ²⁺ in IL can be recovered electrolytically as uranium compounds such as UO₂ and uranium oxychlorides.     

Investigation of electrorefining of metallic alloy fuel onto solid Al cathodes

This work concerned the electrorefining of UZr and UPuZr alloys on a solid aluminium cathode, in the LiCl-KCl eutectic melt containing U³⁺, Pu³⁺, Np³⁺, Zr²⁺ or Zr⁴⁺, Am³⁺, Nd³⁺, Y³⁺, Ce³⁺ and Gd³⁺ chlorides. During constant current electrolyses, the use of a cathodic cut-off potential (−1.25 V versus Ag/AgCl) allowed to selectively deposit actinides (mainly U), while lanthanides remained in the salt. The aim was to determine the maximal load achievable on a single aluminium electrode. The total exchange charge was 4300 C, which represents the deposition of 3.72 g of actinides in 4.17 g Al, yielding a composition of 44.6 wt% An in Al. It was shown that the melting of the cathode contributed to increase the total amount of actinides deposited on the aluminium.