Study On The Separation Of Zirconium And Hafnium By Molten Salt Extraction

Zirconium(Zr)and hafnium(Hf)have attracted great attention because of the excellent nuclear properties.Zr and Hf are quite different in nuclear perpromances: zirconium has a low thermal neutron absorption area(0.18b),and it is very suitable for nuclear reactor cladding material.On the contrary,hafnium has a high thermal neutron absorption area(105b),can effectively control the speed of the nuclear reaction.And it is suitable for nuclear reactor control rod material.Hafnium content should be less than 0.01% while use nuclear-grade zirconium to build nuclear reactors.And zirconium content should be less than 2% in the nuclear-grade hafnium.However,zirconium and hafnium are always symbiotic in nature.There is no zirconium ore without hafnium.What's more,the chemical properties of Zr and Hf are significantly similar owing to lanthanide contraction effect.As a result,the separation of Zr and Hf is a global problem.Currently,Zr-Hf is separated via hydrometallurgical technology in an industrial scale,which involves long procedure,much materials loss and serious environmental pollution.Molten salt extraction present in this paper is a pyrometallurgical technology with the advantages of environmental-friendly and more convenient.It uses Cu-Sn-Zr alloy as the alloy phase(zirconium is industrial-grade zirconium,contains a small amount of hafnium),and uses the CuCl2-NaCl-CaCl2 salt as the salt phase.Then,the alloy phase and the salt phase were mixed in the MgO crucible with Ar atmosphere.Hafnium in alloy phase will be oxidized by Cu2+ in salt phase selectively and preferentially,then hafnium ions move into the molten salt phase.As a result,Zr-CuSn alloy without Hf is obtained,namely Zr and Hf can be separated effectively.The effects of extraction temperature and time,the molar ratio of CuCl2 and hafnium,and CuCl2 content in salt phase on Zr-Hf separation were investigated.It is concluded that when the CuCl2 content in salt phase is higher,the thermodynamics plays a key role in Zr-Hf separation,and the Zr and Hf would be efficiently separated at lower temperature.In contrast,the separation of Zr and Hf mainly depends on the dynamics when CuCl2 content is lower,and the efficient separation of Zr and Hf would be observed at longer time and higher temperature.When the CuCl2 content in salt phase is 2.105%,the temperature is 1000?,the time is 4 hours and the molar ratio of CuCl2 and hafnium is 4,the experimental result is the best: the loss rate of zirconium is 44.293%,the removal rate of hafnium is 99.516%,the Zr-Hf separation rate is 115.128,hafnium content in zirconium is 0.0668%.