PRODUCTION OF SOLAR-GRADE SILICON FROM SILICON DIOXIDE

摘要

Disclosed herein is a process for preparing pure silicon, comprising the reduction of purified silicon oxide with one or more pure carbon sources, wherein the pure carbon sources are selected from the group consisting of carbohydrate, graphite, coke, coal, carbon black and thermal black, the purified silicon oxide has a content of other polyvalent metals of less than or equal to 300 ppm, based on the silicon oxide, and wherein the purification of the silicon oxide comprises the following steps a to d): providing silicates dissolved in an aqueous phase; contacting with a strongly acidic cation exchange resin of the hydrogen type, in an amount which is sufficient for the ion exchange of essentially all other metal ions in the aqueous phase, the temperature of the aqueous phase being in the range from 0 DEGREE C to 60 DEGREE C, obtaining the aqueous phase of an active silica with an SiO2 concentration of from 2 to 6% by weight and a pH of from 0 to 4, obtaining purified silicon oxide, and wherein further silicon carbide is added in a formulation comprising the purified silicon oxide and at least one pure carbon source silicon or the purified silicon oxide or at least one pure carbon source and wherein pure silicon means a material displaying ? 5 ppm of aluminium, ?10 ppm to 0.0001 ppt of boron, ? 2 ppm of calcium, ? 20 ppm of iron, ? 10 ppm of nickel, < 10 ppm to 0.0001 ppt phosphorus, ? 2 ppm of titanium and ? 3 ppm of zinc, purified silicon dioxide means a material displaying ? 5 ppm of aluminium, < 10 ppm to 0.0001 ppt of boron, ? 2 ppm of calcium, ? 20 ppm of iron, ? 10 ppm of nickel, < 10 ppm to 0.0001 ppt of phosphorus, ? 2 ppm of titanium and ? 3 ppm of zinc and pure carbon means a material displaying between 4 and 0.000001 ppm aluminium, 5 and 0.000001 ppm boron, 5 and 0.000001 ppm phosphorus, 100 and 0.000001 ppm iron, 20 and 0.000001 ppm sodium, 30 and 0.000001 ppm potassium, 4 and 0.000001 ppm nickel, 4 and 0.000001 ppm chromium.