Producing solar cell-grade silicon from rice hulls

Production of high purity solar grade silicon can be made from common rice hulls. A unique process for material purification and reduction includes leaching the rice hulls in acid followed by treatment with high purity water, coking the acid-cleaned hulls in a non-oxidizing ambient, compensating the carbon or silica content of the coked hulls to obtain a desired carbon to silica ratio and reducing the silica to produce high purity silicon. The size of the rice hulls is decreased by grinding or milling, the rice hull is leached in with aqueous hydrochloric acid and rinsing in distilled water to reduce the impurity level in the rice hulls to below about 400 ppm., the leached rice hull is coked by pyrolyzing the rice hulls at a temperature of about 920.degree C in a non-oxidizing atmosphere comprising a gaseous mixture of an inert gas comprising about 1% anhydrous hydrogen chloride and at least one of the group of anhydrous acids consisting of HCl, HBR, and HI to produce a composite of carbon and silica by adjusting the carbon to silica ratio of the coked rice hulls to less than about 2:1 and thermally reducing the adjusted carbon and silica mixture to produce elemental silicon.