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US 8,475,758 B2Granted
Low cost routes to high purity silicon and derivatives thereof
AssigneeMayaterials, Inc.
InventorsRichard M. Laine, David James Krug, Julien Claudius Marchal, Andrew Stewart Mccolm
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Abstract
The present invention is directed to a method for providing an agricultural waste product having amorphous silica, carbon, and impurities; extracting from the agricultural waste product an amount of the impurities; changing the ratio of carbon to silica; and reducing the silica to a high purity silicon (e.g., to photovoltaic silicon).
Claims19
A method for providing high purity silicon comprising the steps of:
- providing an agricultural waste product having amorphous silica, carbon, and impurities;
- extracting from the agricultural waste product an amount of the impurities;
- changing the ratio of carbon to silica to form a cleaned agricultural waste product (AWPcl);
- and
- reducing the silica to photovoltaic silicon;
- wherein the agricultural waste product is a product of burning a raw agricultural waste product, and
- in the step of extracting the impurities, the impurities are extracted from the agricultural waste product with an aqueous acidic solution so as to form an extracted agricultural waste product.
4 more elements
A method for producing high purity silicon comprising the steps of:
- providing an agricultural waste product that includes amorphous silica, carbon and impurities, the agricultural waste product having a ratio of carbon to silica ranging from about 5:95 to about 60:40;
- extracting from the agricultural waste product an amount of the impurities using one or more applications of an aqueous acidic solution so as to form an extracted agricultural waste product, wherein the one or more applications includes a first application of the aqueous acidic solution having hydrochloric acid in distilled water;
- changing the ratio of carbon to silica by contacting the extracted agricultural waste product with an ammonium hydroxide to increase the carbon to silica ratio to a ratio that ranges from about 1:1 to about 5:1 so as to form a cleaned agricultural waste product, AWPcl, while at least partially extracting silica as an ammonium silicate;
- re-crystallizing the ammonium silicate in electronic grade water, electronic grade alcohol, or both;
- applying a second application of an aqueous acidic solution to the AWPcl after the step of contacting with an ammonium hydroxide to further reduce or eliminate impurities from the AWPcl;
- combining electronic grade colloidal silica and the AWPcl;
- compacting the combined electronic grade colloidal silica and AWPcl;
- and
- reducing the compacted electronic grade colloidal silica and AWPcl so as to form photovoltaic grade silicon by thermal heating, plasma heating, or a combination of both at a temperature of at least about 1300° C.
6 more elements
A method for producing high purity silicon comprising the steps of:
- providing rice hull ash that includes amorphous silica, carbon and impurities, the rice hull ash having a ratio of carbon to silica ranging from about 5:95 to about 60:40;
- extracting from the rice hull ash an amount of the impurities in an aqueous acidic solution of hydrochloric acid so as to form an extracted rice hush ash;
- changing the ratio of carbon to silica by reacting the extracted rice hull ash with a tetraalkylammonium hydroxide to increase the carbon to silica ratio to a ratio that ranges from about 1:1 to about 5:1 so as to form a cleaned rice hull ash, RHAcl;
- and
- carbothermally reducing the silica from the RHAcl to photovoltaic grade silicon by heating in an inert atmosphere at a temperature of at least about 1300° C.
2 more elements
Dependencies are inferred from the claim text.