Purification of metallurgical silicon through directional solidification in a large cold crucible

A large cold crucible has been used to purify metallurgical silicon in an induction heating furnace. Melt and directional solidification of more than 200kg metallurgical silicon melt are realized by controlling down speed of the cold crucible relative to an induction coil. Metal impurity content in metallurgical silicon is reduced to a very low level, typically below 0.05ppmw for transition metals like iron. The total processing time is within 30h, and the mass ratio is higher than 70%. A numerical model is set up to reveal the electromagnetic field, the temperature distribution and the flow field. This purifying method could remove metal impurities effectively and has advantages of low contamination and low cost by avoiding use of graphite and quartz crucibles. ► More than 200kg metallurgical silicon is melted and purified in a batch using a large size cold crucible. ► Reduction ratio of metal impurities is over 99%. ► Process time is within 30h and the silicon yield is over 70%.