Dissolution characteristics of black aluminum dross in Na3AlF6-AlF3-Al2O3 molten salt system

Abstract

The dissolution performance of black aluminum dross (BAD) in cryolite electrolyte is key to its recovery by molten salt electrolysis. The stable operation of the electrolyzer depends mainly on the rapid dissolution of BAD in Na3AlF6-AlF3-Al2O3 electrolyte system. In this paper, the dissolution performance and behavior of BAD and its main components in the cryolite system were studied, and the saturation solubility of aluminum nitride in this system was determined. The dissolution performance of BAD in cryolite electrolyte before and after denitration was compared, and the effects of temperature, cryolite ratio, and the doping ratio of BAD and alumina on the dissolution rate were investigated. The obtained results showed that aluminum nitride was the main factor affecting the dissolution performance of BAD in the electrolyte. Aluminum nitride was partly converted to a-Al2O3 after addition to the electrolyte, and the converted a-Al2O3 was partially dissolved in the cryolite electrolyte, while the remaining precipitated and accumulated at the bottom with aluminum nitride. Aluminum nitride was almost insoluble in the cryolite electrolyte, with 0.0022% solubility. A higher proportion of a-Al2O3 in BAD was negatively influenced its solubility in the cryolite electrolyte. The dissolution rate of BAD in cryolite electrolytes was effectively improved by mixing BAD with ?-Al2O3.