Zirconium had good mechanical properties and processing properties, excellent corrosion resistance in high temperature and high pressure water at 300~400 ℃, low thermal neutron absorption cross section (0.18×10-28 m2). Due to the good compatibility with uranium fuel, it was often used as a reactor fuel cladding material. In addition, zirconium hydride was the most ideal neutron moderator material. Therefore, zirconium was an indispensable strategic metal material in the nuclear industry. The main method for preparing metallic zirconium was the Kroll method. The process was mainly divided into two steps: zirconium oxide was coked and chlorinated with chlorine and petroleum coke in a high-temperature furnace to prepare zirconium tetrachloride, and then zirconium tetrachloride was replaced and reduced by magnesium to obtain zirconium sponge. The method had high equipment maintenance cost, used dangerous gas chlorine, could not realize the cycle of magnesium chloride, had poor economy, and the quality of the mass-produced zirconium sponge could not meet the nuclear-level requirements. The metal thermal method for direct reduction of zirconia had simple process, low cost, was clean and efficient, and had high product quality. Therefore, it was of great significance to study and improve the metal thermal reduction method to directly reduce ZrO2 to produce nuclear-grade metal zirconium. At present, the reduction of zirconia by the metal thermal reduction method needs to solve two core problems: one is to provide sufficient heat to reach a higher reaction temperature, and the other is to realize the separation of product slag and gold. The research idea in this paper was to add KClO3 to the raw material to make a strong exothermic reaction with Al during the preparation of Al-Zr master alloy by thermite reduction of zirconia to provide sufficient heat source for the system; at the same time, CaO and CaF2 were also added to assist Al2O3 production. Slaging to improve the separation effeciency of slag-gold; then through the electron beam furnace smelting Al-Zr master alloy, dealumination and refining, to prepare metal zirconium with higher purity. In this paper, the process of preparing nuclear-grade zirconium metal by metal thermal reduction was improved. First, Al-Zr master alloy was prepared by direct reduction of zirconia by aluminothermic method, and then Zr was obtained by vacuum dealumination in vacuum electron beam melting furnace. The theoretical feasibility of preparing Al-Zr master alloy was determined by differential scanning calorimetry (DSC). It was found that the reaction could begin at about 945 ℃. By adding KClO3 as heating agent, controlling the heat of reaction of 3000 kJ∙kg-1 and adding 34% CaO and 8% CaF2 as slagging agent, a good slag-gold separation product was obtained, and the optimum alloy yield was 73.4%. The Al-Zr master alloys were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical composition analysis. The results showed that the Al-Zr master alloys could be successfully prepared by aluminothermic reduction. Its internal microstructure was lamellar and consists of al-rich phase and Zr-rich Al3Zr phase, and the optimum oxygen content was 0.044%. Vacuum dealumination of master alloys was carried out in an electronic smelting furnace taking advantage of the difference of saturated vapor pressure between Al and Zr. XRD patterns and elemental analysis showed that the product of electron beam refining was Zr, in which Zr content was 97.44%, main impurity gas elements were O content of 0.23%, N content of 0.14%. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
