Methods to recover and purify silicon particles from saw kerf
AssigneeMEMC Electronic Materials, Inc.
InventorsAlexis Grabbe, Tracy M. Ragan
Life of this patent
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Abstract
The present disclosure generally relates to methods for recovering silicon from saw kerf, or an exhausted abrasive slurry, resulting from the cutting of a silicon ingot, such as a single crystal or polycrystalline silicon ingot. More particularly, the present disclosure relates to methods for isolating and purifying silicon from saw kerf or the exhausted slurry, such that the resulting silicon may be used as a raw material, such as a solar grade silicon raw material.
Claims36
A method for separating and recovering silicon particles from silicon saw kerf resulting from slicing silicon wafers from a silicon ingot, the saw kerf comprising a lubricating fluid and a mixture of solid particulate comprising abrasive grains, silicon particles, metal particles and oxide particles, the method comprising:
- separating at least a portion of the lubricating fluid from the solid particulate mixture;
- washing the solid particulate mixture with an acidic solution in which (i) the silicon particles are substantially insoluble, and (ii) the metal particles and oxide particles are soluble, metal particles and oxide particles being dissolved from the solid particulate mixture;
- collecting the washed solid particulate mixture, the washed mixture comprising silicon particles and abrasive grains;
- and,
- separating the silicon particles from the abrasive grains in the washed solid particulate mixture, wherein the separated silicon particles have a carbon content of less than about 50 ppma and have a content of metal contaminants of less than about 150 ppma.
A method for separating and recovering silicon particles from silicon saw kerf resulting from slicing silicon wafers from a silicon ingot, the saw kerf comprising a organic lubricating fluid and a mixture of solid particulate comprising abrasive grains, silicon particles, metal particles and oxide particles, the method comprising:
- contacting the saw kerf with a chelating agent soluble in the organic lubricating fluid to form a complex with one or more metals present in the saw kerf;
- mixing the chelated saw kerf solution with an aqueous acid solution and allowing the mixture to separate into an aqueous phase and an organic phase, the aqueous phase comprising silicon particles and the organic phase comprising the complex formed between chelating agent and the metals;
- collecting the aqueous phase comprising the silicon particles;
- and,
- recovering at least a portion of the silicon particles from the aqueous phase, wherein the recovered silicon particles have a carbon content of less than about 50 ppma and have a content of metal contaminants of less than about 150 ppma.
A method for slicing a silicon ingot, the method comprising contacting a surface of the silicon ingot with a reciprocating wire saw and a slurry comprising an organic lubricating fluid, an abrasive particulate, and a metal chelating agent soluble in the organic lubricating fluid.
A method for preparing solar grade silicon from silicon particles recovered from silicon saw kerf resulting from slicing silicon wafers from a silicon ingot, the saw kerf comprising a organic lubricating fluid and a mixture of solid particulate comprising abrasive grains, silicon particles, metal particles and oxide particles, the method comprising:
- separating and recovering silicon particles from the saw kerf by one of the following methods (A) or (B):
- (A)
- (i) separating at least a portion of the lubricating fluid from the solid particulate mixture;
- (ii) washing the solid particulate mixture with an acidic solution in which the silicon particles are substantially insoluble, and the metal particles and oxides particles are soluble, metal particles and oxide particles being dissolved from the solid particulate mixture;
- (iii) collecting the washed solid particulate mixture, the washed mixture comprising silicon particles and abrasive grains;
- and,
- (iv) separating the silicon particles from the abrasive grains in the washed solid particulate mixture, wherein the separated silicon particles have a carbon content of less than about 50 ppma and have a content of metal contaminants of less than about 150 ppma;
- or,
- (B)
- (i) contacting the saw kerf with a chelating agent soluble in the organic lubricating fluid to form a complex with one or more metals present in the saw kerf;
- (ii) mixing the chelated saw kerf solution with an aqueous acid solution and allowing the mixture to separate into an aqueous phase and an organic phase, the aqueous phase comprising silicon particles and the organic phase comprising the complex formed between chelating agent and the metals;
- (iii) collecting the aqueous phase comprising the silicon particles;
- and,
- (iv) recovering at least a portion of the silicon particles from the aqueous phase, wherein the recovered silicon particles have a carbon content of less than about 50 ppma and have a content of metal contaminants of less than about 150 ppma;
- melting the separated and recovered silicon particles;
- and,
- forming the melted silicon particles into silicon pellets.
Dependencies are inferred from the claim text.