Definition of a first process window for purification of aluminum via “cooled finger” crystallization technique

Abstract

Aluminum ultra-purification is commonly realized through a combination of three-layer electrolytic refining and fractional crystallization, mostly using zone melting. In order to achieve a purity over 6N with the aid of zone melting, many passes have to be performed, taking several days to be accomplished. This paper focuses on a fractional crystallization methodology using a rotating and internally gas cooled crystallizer (“cooled finger”), based on a Japanese patent from the 1980s, about which no scientific investigation or publication has yet been found. This paper focuses on the impact of process conditions (mainly cooling gas flow and rotation velocity) on the growth rate of the crystallized material as well as on the reduction factor of the impurities Fe, Si, Pb, and Zn in aluminum in relationship to their initial concentration and their interaction in a multi-component system. This technique can be considered as a promising alternative for purification of aluminum as well as other metallic systems.