Study of the composition of the KCl – AlCl₃ – ZrCl₄ – HfCl₄ melt in relation to extractive rectification of zirconium and hafnium chlorides

Abstract

In 2021, Chepetsk Mechanical Plant SC put into operation the production of a zirconium sponge of nuclear purity for the production of nuclear fuel components. The purification of zirconium from hafnium is carried out by extractive rectification in a KCl–AlCl3 melt. The experience of the plant operation has shown that the elemental analysis of the melt for the content of K, Al, Zr, Hf is not enough to determine its operational properties. During the operation of the plant at various points of the technological scheme, the composition of the melt KCl–AlCl3–ZrCl4–HfCl4 was studied by a complex of independent methods using specially developed methods. The content of the phases ZrCl4, K2ZrCl6 and AlCl3 against the background of the matrix phase KAlCl4 was studied in frozen melts by X-ray diffractometry. The regularities of changes in the content of ZrCl4, AlCl3 and K2ZrCl6 according to the technological scheme of the installation are established. The content of the X-ray amorphous component, which contains up to 1.5 wt% aluminum and up to 3.5 wt% zirconium, has been established in frozen melts. By the method of reducing melting in the presence of carbon in frozen melts, the oxygen content of up to 1.8 wt% was determined, which is part of the X-ray amorphous component, presumably consisting of AlOCl and ZrOCl2. A method for determining the AlCl3/KCl ratio based on the difference in the physicochemical properties of the melt components has been developed. Based on the results obtained, the melt composition was adjusted during the operation of the zirconium and hafnium chloride separation unit at ChMP JSC.