Method for producing porous nanocrystalline silicon

A method of forming porous silicon particles from a silicate source, comprising:

• removing contaminants comprising organic contaminants and heavy metals and alumina from the silicate source by treating with first and second acidic leaching solutions, the first acidic leaching solution comprising sulfuric acid and hydrogen peroxide, and the second acidic leaching solution comprising an aqueous solution of perchloric acid, wherein the organic contaminants and alumina react with the first acidic leaching solution and heavy metals react with the second acidic leaching solution such that the contaminants are removed from the silicate source with a decanting of the first and second acidic leaching solutions thereby forming a first intermediate product, wherein the first intermediate product comprises silica and a reduced amount of aluminum and sodium as compared to the silicate source;
• reducing the first intermediate product to form a second intermediate product by reacting the first intermediate product with magnesium vapor at a temperature of about 700° C. to about 750° C. to reduce silica present in the first intermediate product to produce porous magnesiated silicon particulates;
• removing magnesium and magnesium containing compounds from the second intermediate product to form a third intermediate product by treating the second intermediate product with a third leaching solution comprising one or more of hydrochloric acid, nitric acid, and perchloric acid at a temperature of about 10° C. to about 30° C. and removing the third leaching solution to leave a third intermediate product;
• and
• treating the third intermediate product with a fourth leaching solution comprising hydrofluoric acid (HF) at a temperature of about 10° C. to about 30° C. to remove remnant silica from the third intermediate product and thereby provide the porous nanocrystalline silicon particles, wherein reducing the first intermediate product comprises placing the first intermediate on a porous divider above the magnesium and/or magnesium containing compounds and heating the first intermediate product and the magnesium and/or magnesium containing compounds to a temperature of about 700° C. to 750° C. in an Ar atmosphere to produce a magnesium vapor having a vapor pressure of about 3 Torr (0.05 Psi) and which is capable of interacting with first intermediate product to reduce the first intermediate product to form the second intermediate product, or wherein reducing the first intermediate product comprises exposing the first intermediate product to a magnesium vapor under vacuum while maintaining a temperature of about 700° C. to about 750° C. and a magnesium vapor pressure of about 10 Torr to 17 Torr.