Synthesis of Al–Zr master alloy in KF–AlF3–ZrO2 melts by aluminothermic reduction–molten salt electrolysis

Abstract

The synthesis of an Al–Zr master alloy in KF–AlF3–ZrO2 molten salt by combining aluminothermic reduction and molten salt electrolysis processes was studied. The effects of reduction parameters such as stirring, reaction time, Al/ZrO2 mass ratio and temperature on the Zr content and Zr recovery rate were studied and optimized. Under the optimal conditions of stirring, reaction time of 4 h, Al/ZrO2 mass ratio of 3 and temperature of 960 °C, an Al–Zr master alloy can be obtained with a Zr content of 6.78 wt% and Zr recovery rate of 29.85%. The characterization results of the alloy show that the main phases contain Al and Al3Zr. And the Al3Zr appears as long rod-shaped or tetragonal shapes, which influenced by the Zr content and cooling rate. In addition, the reduced molten salt is electrolyzed to further extract Zr from the molten salt. The results show that the Zr remaining in the molten salt is completely recovered with a Zr recovery rate up to 94.72%. This two-step process is feasible for the large-scale extraction of Zr in molten salts to produce Al–Zr master alloys.