氯化物熔盐体系中铀的化学种态研究进展

乏燃料后处理是未来先进核燃料循环体系的中心环节, 基于高温熔盐电解的干法后处理技术具有一定优势. 该技术通常在高温氯化物熔盐体系中进行, 采用电化学技术回收锕系元素, 并实现其与镧系元素的电解分离. 其中铀的分离回收是研究的重点之一. 为更好实现铀在熔盐中的分离与回收, 需要深入理解铀的电化学性质与其在熔盐中的配位化学性质的联系. 因此, 开展铀在氯盐体系中的化学种态研究至关重要. 本Review对国际上氯化物熔盐体系中针对铀化学种态的研究进展进行了总结归纳和提炼, 并对未来锕系元素在高温熔盐介质中的化学种态研究进行了展望.     

熔盐电解法制备镁稀土合金的现状及展望

熔盐电解法是一种高效制备镁稀土合金的方法,工艺流程简便易于连续生产,而且制备的镁稀土合金成分均匀,不偏析。 不同稀土元素的熔盐体系也有所区别,重稀土元素一般采用氧化物电解法,而轻稀土元素则采用氯化物电解法。 针对以上不同的电解方法,本文从电解原料、电解槽结构、电极过程、电解工艺、尾气处理等多方面详细阐述了制备镁稀土合金的现状,并对电解法制备镁稀土合金的未来提出发展方向。     

La和Nd在其氯化物熔体中的电化学腐蚀

稀土金属在其氯化物熔盐中的自腐蚀是导致电解制备稀土金属时电流效率降低的一个重要原因。但由于实验技术上的困难,有关这方面的研究报道不多。本文将在水溶液体系中常用的电化学弱极化测量腐蚀速度及电化学参数的方法用之于La、Nd在其氯化物熔盐体系中的腐蚀,表明同样适用。     

熔盐技术的应用

本文阐述熔盐技术在工业及科技领域中的应用。着重介绍熔盐电解冶金、表面处理，制取半导体、超导体单晶、氟化锆系玻璃，熔盐燃料电池、锂电池，原子能体系中应用的熔盐技术，以及熔盐氟化、氯化等实例和发展动向。     

稀土元素氯化物水合物的脱水过程与水解反应的机理

熔盐电解法制取稀土金属时,所用的无水稀土氯化物是由相应的水合物在减压下加热脱水而制得的。弄清楚脱水过程的机理,避免氯化物水解生成氯氧化物,以期制得纯净的无水氯化稀土,这对于提高电解时的电流效率,降低金属产品中的含氧量,是很重要的。为此我们研究了全部稀土元素氯化物水合物的脱水过程和气相水解反应的机理,确定了一些中间水合     

对电解熔融氯化铝问题的思考

一般认为“氯化铝是分子晶体,熔融的氯化铝不导电,在电解槽中不能电解”,但这不是绝对的,我们可以改变它的环境,比如电解NaCl—AlCl3熔盐制铝[1],这一类似问题在中学教辅材料中早有体现,如电解Al2O3—Na3AlF6制铝,其中Na3AlF6的引入便是问题的关键,近年来Al在NaCl—AlCl3熔盐体系中的电沉积研究已经取得了很多研究成果[2],以下对电解熔融氯化铝问题进行分析。1电解熔融氯化铝问题的理论分析纯的氯化铝是无色的晶体,在通常情况下氯化铝容易挥发,180℃时开始升华,研究其蒸气密度表明在400℃以下氯化铝的分子式为Al2Cl6,氯化铝溶于有机…     

熔盐电解法制备硅纳米线的过程机理

采用FESEM、XRD和EDS分析了纳米二氧化硅烧结片在900℃的CaCl2熔盐中浸泡后结构和组成的变化,结果表明,由于纳米尺寸效应和CaCl2熔盐对二氧化硅的熔融(软化)具有助熔作用,纳米二氧化硅烧结片在900℃的CaCl2熔盐中由固态转变为熔融或半熔融态。根据对900℃的CaCl2熔盐中-1.2V恒电位电解不同时间电极片上反应区的结构和组成分析结果,提出了纳米二氧化硅电极片的硅/熔融二氧化硅/熔盐三相界面沿极片径向方向均匀推进的电解还原过程。通过对900℃的CaCl2熔盐中-1.2V恒电位电解5和15min电解产物的形貌、结构和成份分析,提出了硅纳米线在熔盐中的电化学成核与生长机理。     

LiF-DyF_3-Cu_2O-Dy_2O_3熔盐体系的粘度特性研究

熔体粘度对熔盐电解过程中金属与熔盐的有效分离、炉膛及电极寿命等具有显着影响。因此,运用旋转法对制取Dy-Cu合金的LiF-DyF_3-Dy_2O_3-Cu_2O熔盐体系粘度进行了研究。考察了温度、单一氧化物(Dy_2O_3或Cu_2O)及混合氧化物(Dy_2O_3与Cu_2O)添加对熔盐体系粘度的影响。同时,通过Arrehnius公式验证了熔盐粘度与温度的关系,计算并分析了粘度活化能的变化规律。研究结果表明:在温度为910～1030℃范围内, LiF-DyF_3熔盐体系的粘度均随着温度的升高及单一氧化物(Dy_2O_3或Cu_2O)添加量的增大而降低,随熔盐中Cu_2O与Dy_2O_3质量比的增大而升高;粘度活化能随单一氧化物(Dy_2O_3或Cu_2O)添加量的增大而增大。熔盐电解制备Dy-Cu合金适宜温度为970～1000℃,W_((Cu_2O))+W_((Dy_2O_3))=2.0%(质量分数)且W_((Cu_2O))∶W_((Dy_2O_3))比值为1∶0.5。     

吉林大学化学学院构建“三阶式”教师教学能力发展体系*

吉林大学化学学院注重教师队伍建设,尊重教育规律,在发挥老教师“传帮带”作用的同时,结合时代发展,构建了科学合理高效的“三阶式”教师教学能力发展体系。在培养强化青年教师教学基本功的同时,注重全体教师新型能力的培养,搭建平台促进教师不断钻研教学内容,研究教学方式和方法,将专业知识与先进信息技术和教育教法融合,提高教学能力与水平,实现从“能教书”到“教好书”到“会教书”能力逐步提升的态势。该模式可为探索高校教师教学能力发展体系的建设提供参考和借鉴。     

氯化物熔盐中钕离子在铂电极上的电化学还原

利用极谱,Ⅲ利用电位阶跃研究了轻稀土离子在碱金属氯化物熔盐中的阴极还原。本文作者研究过Sm~(3 )在NaCl-KCl熔盐中的电还原。上述工作分别提出了稀土离子一步还原和分步还原的结论。本文采用线性扫描伏安法和恒电位电解,并配以扫描电子显微镜X射线能谱分析,对Nd~(3 )在Pt电极上的阴极还原过程进行了研究,利     

An analysis of the potassium concentrations of soft drinks by HPGe gamma spectrometry

A pyrochemical processing has become one of the potential technologies for a future nuclear fuel cycle. An integrated multi-physics simulation and electrotransport model of a molten-salt electrolytic process are proposed and discussed with respect to the recovery of pure uranium when using thermochemical data. This study has been performed to provide information for diffusion boundary layers between the molten salt (KCl-LiCl) and electrode. The diffusion-controlled electrochemical model demonstrate a prediction of the electrotransport behaviors of LWR spent fuel as a function of the time up to the corresponding electrotransport satisfying a given applied current based on a galvanostatic electrolysis.     

Electrochemical reduction of UO2 to U in a LiCl–KCl-Li2O molten salt

An electrochemical reduction of UO₂ to U in a LiCl–KCl-Li₂O molten salt has been investigated in this study. A diagram showing equilibrium potentials (relative to Cl₂/Cl^?) plotted versus the negative logarithms of oxide-ion activity (pO^2?) was constructed. The crushed UO₂ pellets in the cathode basket of an electrolytic reducer were successfully reduced to U. The reduction of UO₂ is proved to proceed mainly through chemical reaction with in situ generated Li and K at the cathode. The control of cathode potential is essential to prevent the deposition and subsequent vaporization of K metal at the cathode for the applications of a LiCl–KCl-Li₂O molten salt as an electrolyte for the metal production from its oxide sources.     

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.     

Lanthanides extraction processes in molten fluoride media: Application to nuclear spent fuel reprocessing

This paper describes four techniques of extraction of lanthanide (Ln) elements from molten salts in the general frame of reprocessing nuclear wastes; one of them is chemical: the precipitation of Ln ions in insoluble compounds (oxides or oxyfluorides); the others use electrochemical methodology in molten fluorides for extraction and measurement of the progress of the processes: first electrodeposition of pure Ln metals on an inert cathode material was proved to be incomplete and cause problems for recovering the metal; electrodeposition of Ln in the form of alloys seems to be far more promising because on one hand the low activity of Ln shifts the electrodeposition potential in a more anodic range avoiding any overlapping with the solvent reduction and furthermore exhibit rapid process kinetics; two ways were examined: (i) obtention of alloys by reaction of the electroreducing Ln and the cathode in Ni or preferably in Cu, because in this case we obtain easily liquid compounds, that enhances sensibly the process kinetics; (ii) codeposition of Ln ions with aluminium ions on an inert cathode giving a well defined composition of the alloy. Each way was proved to give extraction efficiency close to unity in a moderate time.     

Characteristics of an integrated cathode assembly for the electrolytic reduction of uranium oxide in a LiCl-Li2O molten salt

Summary Electrochemical behavior of the reduction of uranium oxide was studied in a LiCl-Li₂O molten salt system with an integrated cathode assembly. The mechanism for the electrolytic reduction of uranium oxide was studied through cyclic voltammetry. By means of a chronopotentiometry, the effects of the thickness of the uranium oxide, the thickness of the MgO membrane and the material of the conductor of an integrated cathode assembly on the overpotential of the cathode were investigated. From the voltamograms, the reduction potential of the uranium oxide and Li₂O was obtained and the two mechanisms of the electrolytic reduction were considered with regard to the applied cathode potential. From the chronopotentiograms, the exchange current, the transfer coefficient and the maximum allowable current based on the Tafel behavior were obtained with regard to the thickness of the uranium oxide, and of the MgO membrane and the material of the conductor of an integrated cathode assembly.     

Enhanced electrodeposition and separation of metallic Cr from soluble K_2CrO_4 on a liquid Zn cathode

Carbon contamination and the formation of low-valence oxides limit the preparation of refractory metals by molten salt electrolysis.In this paper,a liquid Zn cathode is adopted for the electrochemical reduction of soluble K_2Cr O_4to metallic Cr in Ca Cl_2-KCl molten salt.It is found that Cr O_4~(2-)can be directly electrochemically reduced to Cr via a six-electron-transfer step and low-valence Cr oxides is hardly produced.The reduction rate is obviously increased from 16.7 mg_(Cr)h~(-1)cm~(-2)on the solid Mo cathode to58.7 mg_(Cr)h~(-1)cm~(-2)on liquid Zn cathode.The electrodeposited Cr is distributed in liquid Zn cathode.Carbon contamination is effectively avoided due to the negligible solubility of carbon in the liquid Zn cathode.Furthermore,Cr can be effectively separated and enriched to the bottom of liquid Zn under supergravity field,realizing the efficient acquisition of metallic Cr and recycling of liquid Zn.The method herein provides a promising route for the preparation of refractory metals with high-purity by molten salt electrolysis.     

Definition and use of an Oxoacidity Function ω for the Comparison of Acidity Levels at Iooo K of Some Chloride Melts Involved in Electrometalluric Processes

Abstract

Many molten chlorides are used in industry for the electrolytic production of metals. In such processes, the oxoacidity level is crucial with respect to the cost and the yield.

The determination and the comparison of the oxoacidic properties of chloride melts then appears to be of practical interest. Such a comaprison is described applying a similar process to that used for pH scales in room temperature solvents. Purification processes of such melts are then explained quantitatively.     

A flow system with an electrochemical reduction cell for spectrophotometric determinations of major constituents in Fe/V alloys

Insertion of an electrochemical cell in a flow injection system to evaluate the on-line reduction of ionic species is presented. The cell comprised Pt electrodes installed in two sections separated by a Nafion membrane. The sample was injected into an acidic carrier stream and passed through the cathode compartment of the electrolytic chamber where the species were reduced as consequence of an applied DC voltage. The sample solution leaving the cell received a confluent reagent stream (1,10-phenanthroline buffered at pH 4.7) and the reacted products were dropped off in an open tube for gas/liquid separation. Efficiency of the Fe(3+) to Fe(2+) reduction in acidic medium was evaluated in the presence of strongly reducing species of V and Mo by monitoring the Fe(II) colored complex. Interferences from Pb(2+), Co(2+), Ni(2+), Zn(2+), Cu(2+), V(5+) and Mo(6+) were evaluated. Production of strongly reducing species of V at the electrolytic cell presented higher efficiency for Fe reduction than the electrolytic chamber itself. Total reduction of Fe(3+) in solutions containing up to 10 mg l(-1) Fe plus 100 mg l(-1) V or 100 mg l(-1) of Mo was achieved by the electrolytic process at 2 A. The quantitative determination of Fe and V in low silicon Fe/V alloys was achieved. Accuracy was assessed with the certified Euro-standard 577-1 ferrovanadium alloy produced by the Bureau of Analysed Samples Limited and no difference at the 95% confident level was found.     

A direct electrochemical route from ilmenite to hydrogen-storage ferrotitanium alloys

An unrecognised but predictable need for a hydrogen-supported society is tens or even hundreds of million tonnes of hydrogen-storage materials, and thus challenges existing technologies in terms of resource and economical realities. Ilmenite is an abundant mineral, and ferrotitanium alloys are among the earliest known hydrogen-storage materials. At present, industrial production of ferrotitanium alloys goes through separate extraction of individual metals, followed by a multistep arc-melting process. In particular, the extraction of titanium from ilmenite is highly energy intensive and tedious, accounting for titanium's high market price and restricted uses. This article reports the electrochemical synthesis of various ferrotitanium alloy powders directly from solid ilmenite in molten calcium chloride. More importantly, it demonstrates, for the first time, that such produced alloy powders can be used without further treatment for hydrogen storage and perform comparably with or better than similar products by means of other methods, but cost just a fraction.