摘要
采用自制氟化反应器,以NH_(4)HF_(2)为氟化剂,开展了不同反应温度、氟化剂过量比条件下NH_(4)HF_(2)氟化制备UF;工艺研究,实验获得了反应温度、NH_(4)HF_(2)过量比对氟化效率的影响规律,采用化学分析结合X射线粉晶衍射法对反应产物进行鉴定。研究结果表明:温度为573、673、823 K时,氟化产物中UF_(4)含量随NH_(4)HF_(2)过量比的增加而逐渐增大,当温度为723、773 K时,氟化率随NH_(4)HF_(2)过量比的增加呈先增大后减小的趋势。温度为723 K、NH_(4)HF_(2)过量比为300%时,该反应氟化率最大,为92.53%。反应温度为573~823 K时,该氟化反应氟化产物中包括4NH_(4)F·UF_(4)、NH_(4)F·3UF_(4)、3NH_(4)F·UO_(2)F_(2)、UO_(2)F_(2)、UF_(4)5种形式。采用热力学基本方程对氟化反应的反应热和反应平衡常数进行计算,计算结果表明,研究温度下NH_(4)HF_(2)氟化制备UF_(4)反应为放热反应。
UF_(4)is a key intermediate product that can be converted to UF_(6)for isotope separation or uranium metal used in nuclear fuel elements.The production of UF;includes wet and dry processes.The wet process is of a long process and high cost,along with a large amount of waste liquid.Therefore,the dry process is usually used to prepare UF_(4)in the process of uranium chemical production.In earlier time,UF_(4)was prepared by the method of one-step reaction of CCl_(2)F_(2)and UO_(3).However,Freon has been completely banned as a result of its increasingly apparent damage to ozone.Two-step reaction is usually adopted in the present preparation process of UF_(4),where UO_(3)is reduced to UO_(2)by H_(2)at high temperature and then fluoridated by HF to produce UF_(4).This routine provides a high fluorination efficiency,while hydrogen and hydrogen fluoride gas is flammable,explosive and highly corrosive,presenting high demands on productive conditions,such as structure of the factory and material of equipment.NH_(4)HF_(2)has the advantages of economy,low corrosiveness and low environmental pollution,and is regarded as the most promising fluorination agent.The one-step synthesis of UF_(4)by fluorination of NH_(4)HF_(2)has a complex reaction process and many intermediate products,while there are few reports on the intermediate process of it.Therefore,in this work,preparation of UF_(4)by fluorination of NH_(4)HF_(2)under different reaction temperatures and proportion of fluoride agent were investigated using a self-made fluorination reactor.The influence of reaction temperature and proportion of NH_(4)HF_(2)on the efficiency of fluoride was obtained.The reaction products were identified by the methods of chemical analysis and X-ray powder diffraction.Results show that the content of UF_(4)in products increases gradually with the excess ratio of ammonium hydrogen fluoride at T=573,673 and 823 K,and the fluoride rate increases first and then decreases with the increase of the excess ratio of NH_(4)HF_(2)at T=723 K and 773 K.When the temperature is at 573 K to 823 K,the fluorination products have five forms:4 NH_(4)F·UF_(4),NH_(4)F·3 UF_(4),3 NH_(4)F·UO_(2)F_(2),UO_(2)F_(2)and UF_(4).When the temperature T is not lower than 673 K,there is no double salt 3 NH_(4)F·UO_(2)F_(2)formed,when the temperature is not lower than 723 K,the double salt 4 NH_(4)F·UF_(4)and NH_(4)F·3 UF_(4)disappear,and it only exists in the forms of UO_(2)F_(2)and UF_(4)in the products.Thermodynamic basic equation was used to calculate the reaction enthalpy and the equilibrium constant,and it shows that the process using NH_(4)HF_(2)and UO_(3)to prepare UF_(4)is an exothermic reaction.
作者
王林
王继财
唐菲菲
冯建新
崔韩龙
李小强
王文辉
龚伟
朱盈喜
WANG Lin;WANG Jicai;TANG Feifei;FENG Jianxin;CUI Hanlong;LI Xiaoqiang;WANG Wenhui;GONG Wei;ZHU Yingxi(The Fourth Branch of the 404 Company Limited,CNNC,Lanzhou 732850,China)
出处
《原子能科学技术》
EI
CAS
CSCD
北大核心
2022年第S01期118-129,共12页
Atomic Energy Science and Technology
基金
中核集团“青年英才”项目
