Patent ID: 6861040

Claim:
Method for purification of metallurgical grade silicon where a calcium containing compound is added to molten silicon prior to or after the silicon is tapped from the furnace, whereafter the silicon is cast and solidified at a relatively high cooling rate and the solidified silicon is crushed and subjected to a purification process consisting of two leaching steps where the silicon in the first leaching step is treated with an aqueous solution of FeCl 3 or FeCl 3 and HCl which causes disintegration of the silicon, and where the silicon in the second leaching step is treated with an aqueous solution of HF or HF/HNO 3 , characterized in that the calcium-containing compound is added to the molten silicon in an amount necessary to provide between 0.3 and 0.95% by weight of calcium in the molten silicon and that the weight ratio between Al and Fe in the molten silicon is regulated to between 0.5 and 2.0 by addition of aluminum to the molten silicon.