Experimental Study On Extraction Of Zirconium And Hafnium By Fluoride Chloride Mixed Salt System

Zirconium is the important core structural and nuclear fuel cladding material for nuclear reactor,with a small thermal neutron capture surface,which is contrary to Hafnium.Zirconium and hafnium are general symbiosis in natural environment,and the content of hafnium in zirconium is about 2%,but the requirement of hafnium concentration in nuclear grade zirconium is less than 0.01%.Therefore,the separation of zirconium and hafnium is very important.However,they have quite similar chemical property,which makes it difficult to separate them from each other.Currently,the separation methods of zirconium and hafnium mainly include hydrometallurgical method and pyrometallurgical method.Solvent extraction is mainly used in industry,but involves complex processing steps and heavy environmental burden.In this study,zirconium and hafnium were separated by molten salt extraction,which has the advantages of short process and high efficiency.Our experiment mainly contained three parts: preparation of master alloys,preparation of master molten salts and separation of Zr-Hf.Master alloy is composed of 72.8%Cu-18.2%Sn-8%Zr-1%Hf and master molten salt is constituted of 5%CuF₂-32%NaCl-63%CaCl2.The effects of CuF₂/Hf molar ratio,reaction temperature,reaction time and the content of CuF₂ in salt on the separation of zirconium-hafnium were investigated.The appropriate separation conditions were explored and the separation results were compared with the pure chlorine salt system.Experimental results show that: 1)CuF₂/Hf molar ratio has complicated influence on separation process.In general,the loss rate of Zr???and the removal rate of Hf???both increase with the increasing of the molar ratio,especially when the temperature is low.However,a high molar ratio will lead to a quite high value of?,and the suitable molar ratio is 4/1;2)Temperature has a great influence on the separation process.In the temperature range of 905 970?,the loss rate of Zr???decreased with the increase of temperature,which was dominated by the thermodynamic factors.At 1010?,the loss rate of Zr???improved,which was dominated by the dynamical factor — diffusion of ions.The removal rate of Hf is maintained at a high level?97 99.6%?at 905 1010?.On the whole,the separation coefficient???increased with the increase of temperature;3)the effect of time: the appropriate reaction time is 4h,which can not only ensure high Hf removal rate,butalso maintain the loss of Zr at a low level;4)the separation effect of Zr-Hf increased slightly with the decrease of the content of CuF₂ in salt,but the effect was not obvious;5)in general,under the same conditions,the separation effect of the mixed chlorine system is better than that of the pure chlorine salt system,whose separation coefficient is up to 79.353 and 85.200.The optimum conditions for the separation of zirconium and hafnium from the mixed molten salt were as follows: reaction temperature 1010?,CuF₂ / Hf molar ratio 4/1,reaction time 4h.Under this condition,the content of hafnium separated from zirconium is 0.107%,which is lowest.Through the further optimization of the experimental conditions,it is expected to obtain the required nuclear grade zirconium.