Removal of Boron from Metallurgical Grade Silicon by Chloride Molten Salt

Removal of boron is one of the greatest barriers in the process of upgrading metallurgical grade silicon (MG-Si) to solar grade silicon (SoG-Si). In this work, a chloride molten salt was used as a new refining reagent for removal of boron from MG-Si. The theoretical supporting for chloride molten salt refining was studied by the thermodynamic analysis at first, which testified that boron could be volatilized and removed from MG-Si melt by generating the gaseous boron chloride species. Then the experiments for the removal of boron were carried out using the chloride molten salt with the different conditions of refining time and the ratio of chloride molten salt to MG-Si. The results showed that the boron content in refined silicon was successfully reduced from 22.0×10-6 to 3.0×10-6 in a medium frequency induction furnace at 1695 K for 2h.