Minimising oxygen contamination through a liquid copper-aided group IV metal production process

Abstract

This paper demonstrates for the first time the fabrication of Zr-Cu alloy ingots from a Hf- free ZrO2 precursor in a molten CaCl2 medium to recover nuclear-grade Zr. The reduction of ZrO2 in the presence of CaO was accelerated by the formation of Ca metal in the intermediate stage of the process. Tests conducted with various amounts of ZrO2 indicate that the ZrO2 was reduced to the metallic form at low potentials applied at the cathode, and the main part of the zirconium was converted to a CuZr alloy with a different composition. The maximum oxygen content values in the CuZr alloy and Zr samples upon using liquid Cu were less than 300 and 891 ppm, respectively. However, Al contamination was observed in the CuZr during the electroreduction process. In order to solve the Al contamination problem, the fabrication process of CuZr was performed using the metallothermic reduction process, and the produced CuZr was used for electrorefining. The CuZr alloy was further purified by a molten salt electrorefining process to recover pure nuclear-grade Zr in a LiF-Ba2ZrF8-based molten salt, the latter of which was fabricated from a waste pickling acid of a Zr clad tube. After the electrorefining process, the recovered Zr metal was fabricated into nuclear-grade Zr buttons through arc melting following a salt distillation process. The results suggest that the removal of oxygen from the reduction product is a key reason for the use of a liquid CaCu reduction agent.