Patent ID: 7931883

Claim:
A method for the production of a solar grade silicon feedstock from a metallurgical grade silicon comprising: a) treating a molten, metallurgical grade silicon produced in an electric arc furnace by carbothermic reduction and containing up to 300 ppma boron and up to 100 ppma phosphorus with a calcium-silicate slag to reduce the boron content of the silicon to between 0.2 and 10 ppma; b) solidifying the treated silicon obtained from step a); c) leaching the solidified silicon obtained from step b) in at least one leaching step by an acid leach solution to remove impurities; d) melting the leached silicon obtained from step c) to form molten silicon; e) solidifying the molten silicon obtained from step d) by directional solidification to form a solid ingot; and f) removing an upper part of the solid ingot obtained from step e) where p-type changes to n-type, to provide a silicon ingot containing 0.2 to 10 ppma boron and 0.1 to 10 ppma phosphorus.