Abstract: Silicon-containing products, such as silicon, silicon carbide and silicon nitride, containing less than 0.01 weight percent total mineral impurities and selectively determined carbon-to-silicon ratios. The products are derived from plant matter, such as rice hulls and rice straw, containing at least three weight percent silica. Methods are provided for making such high purity silicon-containing products by leaching silica-containing plant matter with aqueous sulfuric acid under controlled temperatures, pressures and reaction times to remove minerals and metals while adjusting the mole ratio of fixed carbon to silica, and then thermally treating under controlled conditions to produce the desired product.

Abstract: A method for producing carbon-silica products from silica-containing plant matter such as rice hulls or straw by leaching with sulfuric acid to remove non-silica minerals and metal while adjusting the mole ratio of fixed carbon to silica in the resultant product. The carbon and silica are intimately mixed on a micron or submicron scale and are characterized by high purity and reactivity, small particle size, high porosity, and contain volatile carbon that can be used as a source of energy for the production of silicon-containing products from the carbon-silica products. High purity silicon-containing products made from the carbon-silica products of the invention are also disclosed.