在LiCl-KCl-ZnCl_2熔盐体系中电化学共还原提取钕

针对镧系元素钕,本文通过循环伏安、开路计时电位、方波伏安等方法研究了773 K时Nd(III)在钼电极上在LiCl-KCl-ZnCl2熔盐体系中的电化学行为及Zn-Nd合金的形成过程.结果表明:在LiCl-KCl-ZnCl2熔盐中,Nd(III)在预先沉积的Zn阴极上欠电位沉积形成三种Zn-Nd金属间化合物.基于电化学行为研究,采用恒电位电解提取Nd并用方波伏安曲线测量来检测Nd(III)离子浓度的变化,然后通过电解前后Nd(III)离子浓度变化评估了Nd的电解提取效率.实验结果表明:-1.84 V恒电位电解进行50 h后,Nd(III)离子浓度接近于零,提取效率为99.67%.在973 K时通过恒电流电解提取Nd并获得了Zn-Nd合金,通过X射线衍射(XRD)和扫描电子显微镜(SEM)附带能量散射谱(EDS)对合金的相组成和微观形貌进行了分析.XRD分析表明在Zn-Nd合金中存在Nd2Zn17,LiZn和Zn相,EDS能谱分析表明Nd在合金中的原子分数高达14.99%.     

氯化物体系中La的电化学提取及共沉积Zn-La合金

通过循环伏安、方波伏安和开路计时电位等方法研究了723 K时,La(Ⅲ)在LiCl-KCl和LiCl-KClZnCl_2熔盐体系中Mo电极上的电化学行为.结果表明,La(Ⅲ)还原为金属La是一步扩散控制的不可逆还原反应.在LiCl-KCl-ZnCl_2熔盐中,La(Ⅲ)在预先沉积的Zn阴极上欠电位沉积形成4种Zn-La金属间化合物.在923 K时通过恒电流电解获得Zn-La合金,通过X射线衍射(XRD)和扫描电子显微镜(SEM)以及附带的能谱仪(EDS)对合金的相组成和微观形貌进行了分析.采用恒电位电解提取La并用方波伏安曲线检测La(Ⅲ)离子浓度的变化,电解50 h后,La(Ⅲ)离子浓度接近于零,提取效率达到99.55%.     

Dy(Ⅲ)离子在LiCl-KCl熔盐中的电化学行为及Dy-Ni金属间化合物的选择性制备

采用循环伏安、方波伏安和开路计时电位等电化学方法研究了Dy(Ⅲ)离子在LiCl-KCl 共晶盐中的电化学行为及Dy-Ni 合金形成的电化学机理. 循环伏安和方波伏安法研究表明, Dy(Ⅲ)离子的电化学还原过程为三个电子转移的一步反应. 与惰性W电极相比, Dy(Ⅲ) 离子在Ni 电极上的循环伏安曲线多出了三对氧化还原峰,是由于Dy与Ni 形成了合金化合物, 导致Dy(Ⅲ)离子在活性Ni 电极发生了欠电位沉积. 采用X射线衍射(XRD)和扫描电子显微镜(SEM)附带能量散射谱(EDS)对恒电位(-1.6, -1.8 和-2.0 V)电解制备的Dy-Ni 合金进行分析, 分别获得了DyNi₅, Dy₂Ni₇和DyNi₂金属间化合物. 实验结果表明, 通过控制电位进行恒电位电解可以有选择性地制备不同的金属间化合物.     

在LiCl-KCl共晶熔体中电化学制备钬镍金属间化合物

采用循环伏安、方波伏安和开路计时电位等研究了Ho(Ⅲ)离子在LiCl-KCl共晶熔体中的电化学行为及Ho-Ni合金化机理。在惰性W电极上,Ho(Ⅲ)离子在-2.06 V(vs Ag/AgCl)发生电化学还原,该还原过程为3个电子转移的一步反应。与惰性W电极上的循环伏安相比,Ho(Ⅲ)离子在活性Ni电极的循环伏安曲线上还出现了3对氧化还原峰,是Ho与Ni形成了金属间化合物,导致了Ho(Ⅲ)离子在活性Ni电极发生了欠电位沉积。在不同的电位进行恒电位电解制备的3个不同的Ho-Ni合金,采用X-射线衍射(XRD)和扫描电子显微镜-能谱仪(SEM-EDS)等测试手段进行表征,结果表明:制备的3种合金分别是Ho₂Ni₁₇,HoNi₅ 和 HoNi₂ 3种合金化合物。     

Dy（III）离子在LiCl-KCl熔盐中的电化学行为及Dy-Ni金属间化合物的选择性制备

采用循环伏安、方波伏安和开路计时电位等电化学方法研究了Dy(III)离子在LiCl-KCl共晶盐中的电化学行为及Dy-Ni合金形成的电化学机理.循环伏安和方波伏安法研究表明, Dy(III)离子的电化学还原过程为三个电子转移的一步反应.与惰性W电极相比, Dy(III)离子在Ni电极上的循环伏安曲线多出了三对氧化还原峰,是由于Dy与Ni形成了合金化合物,导致Dy(III)离子在活性Ni电极发生了欠电位沉积.采用X射线衍射(XRD)和扫描电子显微镜(SEM)附带能量散射谱(EDS)对恒电位(-1.6,-1.8和-2.0 V)电解制备的Dy-Ni合金进行分析,分别获得了DyNi5, Dy2Ni7和DyNi2金属间化合物.实验结果表明,通过控制电位进行恒电位电解可以有选择性地制备不同的金属间化合物.     

在LiCl-KCl-AlCl3熔盐中直接电化学还原Sm2O3及Al-Sm合金的形成

在803 K LiCl-KCl熔盐中, 研究了通过添加助剂AlCl₃直接电化学还原Sm₂O₃和Al-Sm合金的形成。以SmCl₃为原料作为参照, 采用循环伏安和方波伏安方法, 研究了Sm₂O₃在LiCl-KCl-AlCl₃熔盐体系中的电化学行为。通过对比发现在两个体系中, 峰的数量和位置基本一致, 这说明在LiCl-KCl熔盐中, 加入AlCl₃之后, 可以将Sm₂O₃有效氯化。计时电位结果表明, 当阴极电流比-139.8 mA·cm^-2更负时, Al和Sm共同还原。为了提取Sm, 采用恒电流从LiCl-KCl-AlCl₃-Sm₂O₃熔盐中电解得到Al-Sm合金样品, 并进行XRD表征, 结果表明可以通过调节AlCl₃和Sm₂O₃的浓度得到不同相的Al-Sm合金。     

KCl-LiCl-MgCl2熔盐体系中共电沉积制备Mg-Li合金及理论分析

在670 ℃的KCl-LiCl-MgCl₂熔盐体系中通过共电沉积方法制备了Mg-Li合金,并进行了理论分析。循环伏安表明：670 ℃时,锂在镁上(镁预先沉积到钼丝上)的欠电位沉积形成了液态的Mg-Li合金;当MgCl₂质量分数为10%时,出现了Mg-Li合金成核。极化曲线表明：在含有5% MgCl₂的熔盐中,MgCl₂的极限电流密度为0.35 A·cm^-2,超过此值时,Mg和Li就能产生共电沉积。对沉积物进行X射线衍射和电感耦合等离子体发射光谱(ICP)分析表明：通过恒电流电解得到了3种不同相的Mg-Li合金。在电流密度为6.21 A·cm^-2电解2 h条件下,只有当MgCl₂质量分数小于10%时,才能得到Mg-Li合金。并通过Nernst和浓差极化方程讨论了MgCl₂浓度对于Mg-Li合金形成的影响。Mg-Li合金中锂的含量能够通过熔盐中的MgCl₂浓度配比和电解参数来控制。实验证明这种直接从原料入手,通过共电沉积制备Mg-Li合金的新方法是可行的。     

MgCl2在LiCl-KCl熔盐中的电化学特性

研究了温度范围在723-908 K的LiCl-KCl 熔盐体系中MgCl₂的电化学行为和热力学性质. 循环伏安和方波伏安法研究表明镁离子的电化学还原过程为包含了两个电子转移的一步反应. 利用Berzins 和Delahay 方程计算了不同温度下的镁离子的扩散系数, 并通过Arrhenius 公式计算了镁离子在LiCl-KCl 熔盐体系中的扩散活化能. 采用开路计时电位法得到了不同温度下的Mg(II)/Mg(0)体系的平衡电位, 并结合电动势法计算了在LiCl-KCl 熔盐体系中Mg(II)/Mg(0)体系的标准形式电位. 根据不同温度下的标准形式电位, 计算得到了MgCl₂在LiCl-KCl 熔盐体系中的熵变和焓变以及不同温度下的活度系数.     

Pr(Ⅲ)离子在LiCl-KCl熔体中Bi膜W电极上的电化学行为

采用循环伏安、方波伏安、计时电位和开路计时电位等电化学方法研究了Pr（Ⅲ）离子在LiCl-KCl-BiCl₃熔体中W电极上的电化学行为。循环伏安和方波伏安的研究表明,Pr在预先沉积的Bi膜电极上发生欠电位沉积是由于生成了Pr-Bi金属间化合物,导致Pr（Ⅲ）在Bi膜电极上的还原电位比在W电极上还原电位更正。从开路计时电位曲线可以观察到两相共存的Pr-Bi金属间化合物的两个平台。利用开路计时电位计算了723-873 K温度范围内Pr在Pr-Bi合金中的活度和偏摩尔Gibbs自由能以及Pr-Bi金属间化合物的生成Gibbs自由能。通过恒电位电解,在液态Bi电极上得到了Pr-Bi合金,并采用X射线衍射（XRD）和扫描电子显微镜（SEM）附带能量散射谱（EDS）对样品进行了表征,结果表明所得到的Pr-Bi金属间化合物为PrBi₂和PrBi。     

NaCl-KCl熔盐体系中AlF3氟化Tb4O7电化学制备Al-Tb合金

在NaCl-KCl-Tb₄O₇-AlF₃体系中为了制备Al-Tb合金,首先对熔盐中的上清液和沉淀物进行了分析,X射线衍射（XRD）结果确定了Tb₄O₇能被AlF₃氟化生成TbF₃。采用一系列的电化学方法对NaCl-KCl-AlF₃-Tb₄O₇体系在Mo电极上的电化学行为进行了研究。循环伏安、方波伏安、计时电位和开路计时电位等电化学方法的研究结果表明Tb（III）在预先沉积的Al电极上发生欠电位沉积。在不同条件下进行恒电流电解制备了Al-Tb合金,并对所得合金样品进行XRD和扫描电镜-能量散射谱（SEM-EDS）表征。结果表明在-2.5 A进行恒电流电解得到的Al-Tb合金是由Al和Al₃Tb两相组成。采用电感耦合等离子体-原子发射光谱仪（ICP-AES）对实验所得沉积物的组成进行分析,研究了电解条件对合金组成和电流效率的影响。在电流强度为-1.5 A进行恒电流电解2 h,电流效率可达76.5%。     

Electrochemical co-reduction of Y(III) and Zn(II) and extraction of yttrium on Zn electrode in LiCl-KCl eutectic melts

This work presents an electrochemical study of Y(III) ions on W electrode and liquid Zn electrode and co-reduction mechanism of Y(III) and Zn(II) on W electrode in LiCl-KCl eutectic melts. Cyclic voltammogram and current reversal chronopotentiogram revealed that the electrochemical reaction of Y(III) on W electrode proceeds a single step mechanism of Y(III) to Y(0). On liquid Zn electrode, the deposition potential of Y(III) is more positive than that on W electrode due to the formation of Y-Zn solution and the reduction process was found to be a diffusion controlled and quasi-reversible at lower scan rate of 0.1 V/s. Based on the results of cyclic voltammometry, square wave voltammetry, and chronopoteniometry, the Y-Zn intermetallics could be formed by co-reduction process of Y(III) and Zn(II) on W electrode in LiCl-KCl-ZnCl₂-YCl₃ molten salts. Moreover, the electrochemical extracting metallic Y was conducted by galvanostatic and potentiostatic electrolysis on liquid Zn electrode. Electrolysis products consisted of Zn and YZn₁₂ phases characterized by scanning electron microscopy with energy dispersive spectrometry and X-ray diffraction. Meanwhile, the change of Y(III) concentration in LiCl-KCl eutectic melts was detected by inductive coupled plasma atomic emission spectrometer and the extraction efficiency could be estimated.     

Electrochemical Behaviour of Magnesium(II) on Ni Electrode inLiCl-KCl Eutectic

The electrochemical behaviour of magnesium(II) and the formation mechanism of Mg-Ni alloys on Ni electrode were studied in LiCl-KCl eutectic using various electrochemical techniques. Cyclic voltammogram and square-wave voltammogram revealed that under-potential deposition of magnesium occurred on Ni electrode because Mg-Ni alloy compounds were formed. The thermodynamic properties of the Mg-Ni intermetallics, Mg₂Ni and MgNi₂, were determined using open circuit chronopotentiometry in the temperature range of 818―893 K. Moreover, the Mg-Ni alloys were produced by potentiostatic and galvanostatic electrolysis under different conditions and characterized by means of scanning electron microscopy(SEM) equipped with energy dispersive spectrometry(EDS) and X-ray diffraction(XRD). The experimental results indicate that Mg-Ni intermetallic compounds can be selectively produced by potentiostatic electrolysis.     

Extraction of neodymium from other fission products by co‐reduction of Sn and Nd

High temperature processing is an important method for recovering long‐lived elements from spent nuclear fuel. Electrolysis is the key technology for high temperature processing. The electrochemical behaviors of Sn²⁺, Nd³⁺ and the mechanisms of Sn‐Nd alloy formation were investigated on a Mo electrode at 873 K by conducting a series of electrochemical techniques. The results showed the deposition of Nd on inert electrode is a two‐step process in LiCl‐KCl‐SnCl₂ (2.0 wt.%) melt system. Subsequently, the electrochemical extraction of Nd from molten chlorides were carried out on the Mo electrode at temperature of 873 K by the potentiostatic electrolysis at ?1.2 V for 40 hr. Besides, the extraction efficiency is 97.6%. A series of potentiostatic electrolysis were carried out at potential range between ?1.0 and ? 1.4 V. The NdSn₃ alloy was obtained by electrolysis at ?1.2 V. This deposition potential is consistent with the predicted results of the mathematical model. The micro‐chemical analysis and morphology analysis of the deposits was characterized by energy dispersive spectrometry (EDS) with scanning electron microscopy (SEM) equipped. The composition of the deposits was analyzed by X‐ray diffraction (XRD) and inductive coupled plasma atomic emission spectrometer (ICP‐AES).     

Electrochemical behaviour of lanthanum fluoride in molten fluorides

The electrochemical behaviour of lanthanum fluoride dissolved in molten lithium fluoride and in eutectic mixture LiF-CaF₂ was investigated by cyclic voltammetry and laboratory electrolysis. The cyclic voltammetry experiments were carried out at 900°C and 800°C, respectively, in a graphite crucible (counter electrode). Several types of working electrodes (Mo, W, Ni and Cu) were used. Ni/Ni(II) was used as a reference electrode. Laboratory electrolysis was carried out in the system LiF-CaF₂-LaF₃ at 800°C in galvanostatic (j _c = −0.21 A cm⁻²) and potentiostatic (E = 0.87 V) regimes. In both cases, nickel served as the cathode and graphite as the anode. It was found that no new separate reduction peak occurred on the molybdenum or tungsten electrodes in the investigated systems. When copper or nickel electrodes were used, new peaks corresponding to the reduction of lanthanum(III) to lanthanum metal appeared. This can be explained by the formation of alloys or intermetallic compounds of lanthanum with copper or nickel. X-ray microanalysis showed that lanthanum was electrodeposited together with calcium under formation of intermetallic compounds with the electrode materials in the galvanostatic regime. In the potentiostatic regime, mainly lanthanum was deposited, which enabled its separation.     

铝电极在LiNO3-KNO3熔盐中的电化学行为

采用循环伏安和恒电位电解法考察了铝电极在LiNO3-KNO3熔盐中的电化学行为. 实验结果表明, 在该熔盐中, 锂离子在铝电极上的电还原过程伴随着新生态的锂原子向电极内部的随后扩散步骤; 锂原子进入铝电极后与铝发生合金化, 形成β-LiAl合金和γ-LiAl合金; 锂离子在铝电极上的还原过程受还原态锂在铝基体内的扩散步骤控制. 循环伏安实验发现, 铝电极在该熔盐中的氧化和还原峰电流都先随循环次数增加而增大, 最后基本上趋于稳定. 这表明铝电极在该熔盐体系中具有较好的电化学稳定性.     

Electrode process of Nd-Fe alloy formed on iron electrode in molten chlorides

The cyclic voltammetry, convolution voltammetry and chronopotentiometry were used to study the electrode process of Nd (III) reduced on iron electrode in molten NaCl-KCl-NdCl₃ from 700 to 850°C. The electrodeposited products were analysed by X-ray diffraction. The results indicate that the intermetallic compound Fe₂Nd forms first, and then the metallic neodymium deposits when Nd (III) is reduced on iron electrode. The Nd-Fe alloys rich in neodymium can be obtained by electrolysis with iron cathode in molten chlorides. The Nd-Fe alloys are composed of Fe₂Nd and Nd.     

Electrochemical Co-reduction of Bi(Ⅲ)and Y(Ⅲ)and Extracting Yttrium from Molten LiCl-KCl Using Liquid Bi as Cathode

The electrochemical reaction of Bi(Ⅲ)and co-reduction behaviour of Bi(Ⅲ)and Y(Ⅲ)ions were researched in molten LiCl-KCl on a ttmgsten(W)electrode employing a range of electrochemical teclmiques.Cyclic voltammetric and square-wave voltanunetric results revealed that the reduction of Bi(Ⅲ)was a one-step process,with the exchange of three electrons on a W electrode,and diffusion-controlled.The electrochemical curves showed two reduction peaks pertaining to the formation of Bi-Y alloy compounds,because of the co-reduction of Bi(Ⅲ)and Y(Ⅲ) by metallic Y deposited on the pre-deposited Bi-coated W electrode and reacting with Bi metal in molten LiCl-KCl. Furthermore,galvanostatic electrolysis was conducted using liquid Bi as cathode to extract yttrium at different current intensities,and the extractive products were analyzed by SEM,EDS and XRD.The results indicated that BiY intermetallic compotmd was formed in the molten LiCl-KCl-YCl3 system.