Patent ID: 8480991

Claim:
A method for purifying metallurgical grade silicon with a phosphorous level below 60 ppmw and boron level below 15 ppmw, the method comprising: (a) forming a first molten liquid from a source silicon and a solvent metal selected from the group of copper, tin, zinc, antimony, silver, bismuth, aluminum, cadmium, gallium, indium, magnesium, lead, an alloy thereof, and combinations thereof; (b) contacting the first molten liquid with a first gas, such that a vortex is formed in the melt, to provide dross and a second molten liquid, wherein the first gas is selected from the group consisting of oxygen (O 2 ), nitrogen (N 2 ), helium (He), argon (Ar), hydrogen (H 2 ), sulfur hexafluoride (SF 6 ), water vapor (H 2 O), oxygen (O 2 ), carbon dioxide (CO 2 ), carbon monoxide (CO), tetrafluorosilane (SiF4), and combinations thereof; wherein the contacting the first molten liquid with the first gas employs a gas rotary degasser, thereby creating a vortex of the second molten liquid, which effectively mixes the dross in the second molten liquid; (c) separating the dross and the second molten liquid; (d) cooling the second molten liquid to form first silicon crystals and a first mother liquor; (e) separating the first silicon crystals and the first mother liquor; (f) contacting the first silicon crystals with an acid to provide washed silicon crystals and used acid; and (g) separating the washed silicon crystals and the used acid; wherein the washed silicon crystals have a boron level below 3 ppmw and a phosphorous level below 9 ppmw.