Method for purifying silicon

Abstract

The present invention provides for methods of purifying silicon, methods for obtaining purified silicon, as well as methods for obtaining purified silicon crystals, purified granulized silicon and/or purified silicon ingots.

1 . A method for purifying silicon to provide metallurgical grade (MG) silicon, the method comprising:
 (a) forming a first molten liquid from silicon and a solvent metal comprising aluminum, or an alloy thereof;   (b) contacting the first molten liquid with a first gas to provide a second molten liquid and dross, wherein the first gas comprises chlorine (Cl 2 ), oxygen (O 2 ), nitrogen (N 2 ), helium (He), argon (Ar), hydrogen (H 2 ), sulfur hexafluoride (SF 6 ), phosgene (COCl 2 ), carbon tetrachloride CCl 4 , water vapor (H 2 O), oxygen (O 2 ), carbon dioxide (CO 2 ), carbon monoxide (CO), tetrachlorosilane (SiCl 4 ), tetrafluorosilane (SiF 4 ), or a combination thereof;   (c) heating the second molten liquid;   (d) separating the dross and the second molten liquid;   (e) cooling the second molten liquid to form first silicon crystals and a first mother liquid;   (f) separating the first silicon crystals and the first mother liquid;   (g) heating the first silicon crystals to form a first molten bath;   (h) directionally solidifying the first molten bath to form second silicon crystals and a second mother liquor;   (i) heating the second silicon crystals to provide a second molten bath;   (j) contacting the second molten bath with a second gas to form a stag that forms on the surface of a third molten bath, wherein the second gas comprises chlorine (Cl 2 ), oxygen (O 2 ), nitrogen (N 2 ), helium (He), argon (Ar), hydrogen (H 2 ), sulfur hexafluoride (SF 6 ), phosgene (COCl 2 ), carbon tetrachloride CCl 4 , water vapor (H 2 O), oxygen (O 2 ), carbon dioxide (CO 2 ), carbon monoxide (CO), tetrachlorosilane (SiCl 4 ), tetrafluorosilane (SiF 4 ), or a combination thereof;   (k) separating the slag and the third molten bath;   and at least one of steps (l)-(o):   (l) cooling the second molten bath to form silicon ingots;   (m) contacting the second molten bath with water to form granulized silicon;   (n) introducing the third molten bath into a mold and cooling the third molten bath to form a second silicon; and   (o) directionally solidifying the third molten bath below the melting point, thereby forming a third silicon crystals, and separating the upper portion and the lower portion; wherein the upper portion comprises a third mother liquor and the lower portion comprises a third silicon.   
     
     
         2 . The method of  claim 1 , wherein the second molten bath contacts the second gas employing a rotary degasser, such that the rotary degasser effectively introduces the second gas into the second molten bath. 
     
     
         3 . The method of  claim 1 , wherein the second molten bath contacts the second gas employing a rotary degasser, such that the rotary degasser effectively introduces the second gas into the second molten bath, and the rotary degasser effectively agitates the second molten bath while the second gas is introduced into the second molten bath. 
     
     
         4 . The method of  claim 1 , wherein the first gas comprises water vapor (H 2 O). 
     
     
         5 . The method of  claim 1 , wherein the second gas comprises water vapor (H 2 O). 
     
     
         6 . The method of  claim 1 , wherein in step (a), the first molten liquid is formed by heating above the liquidus temperature. 
     
     
         7 . The method of  claim 1 , wherein in step (b), the dross forms on the surface of the second molten liquid. 
     
     
         8 . The method of  claim 1 , wherein after step (b) and before step (c), the second molten liquid is heated. 
     
     
         9 . The method of  claim 1 , wherein after step (b) and before step (c), the second molten liquid is heated above the liquidus temperature. 
     
     
         10 . The method of  claim 1 , wherein after step (b) and before step (c), the second molten liquid is heated to within about 20° C. above the liquidus temperature. 
     
     
         11 . The method of  claim 1 , wherein in step (c), the dross is removed from the surface of the second molten liquid. 
     
     
         12 . The method of  claim 1 , wherein in step (d), the second molten liquid is cooled to above the solidus temperature and below the liquidus temperature. 
     
     
         13 . The method of  claim 1 , wherein at least one of steps (a)-(e) is carried out multiple times. 
     
     
         14 . The method of  claim 1 , wherein each of steps (a)-(e) is carried out multiple times. 
     
     
         15 . The method of  claim 1 , wherein each of steps (a)-(e) is carried out multiple times, and the first mother liquid obtained in step (e) is employed as the solvent metal in subsequent step (a). 
     
     
         16 . The method of  claim 1 , wherein at least about 45 kg of purified silicon is obtained. 
     
     
         17 . The method of  claim 1 , wherein the purified silicon is used to grow a multicrystalline or monocrystalline ingot or boule. 
     
     
         18 . The method of  claim 1 , wherein the purified silicon is employed in the manufacture of a solar panel or an integrated circuit. 
     
     
         19 . A method for purifying silicon to provide metallurgical grade (MG) silicon, the method comprising:
 (a) forming a first molten liquid from silicon and a solvent metal comprising aluminum, or an alloy thereof;   (b) contacting the first molten liquid with a first gas, employing a rotary degasser, to provide a second molten liquid and dross, wherein the first gas comprises water vapor (H 2 O);   (c) heating the second molten liquid;   (d) separating the dross and the second molten liquid;   (e) cooling the second molten liquid to form first silicon crystals and a first mother liquid;   (f) separating the first silicon crystals and the first mother liquid;   (g) heating the first silicon crystals to form a first molten bath;   (h) directionally solidifying the first molten bath to form second silicon crystals and a second mother liquor;   (i) heating the second silicon crystals to provide a second molten bath;   (j) contacting the second molten bath with a second gas, employing a rotary degasser, to form a slag that forms on the surface of a third molten bath, wherein the second gas comprises water vapor (H 2 O);   (k) separating the slag and the third molten bath;   and at least one of steps (l)-(o):   (l) cooling the second molten bath to form silicon ingots;   (m) contacting the second molten bath with water to form granulized silicon;   (n) introducing the third molten bath into a mold and cooling the third molten bath to form a second silicon; and   (o) directionally solidifying the third molten bath below the melting point, thereby forming a third silicon crystals, and separating the upper portion and the lower portion; wherein the upper portion comprises a third mother liquor and the lower portion comprises a third silicon.   
     
     
         20 . A method for purifying silicon to provide metallurgical grade (MG) silicon, the method comprising:
 (a) forming a first molten liquid from silicon and a solvent metal comprising aluminum, or an alloy thereof;   (b) contacting the first molten liquid with a first gas to provide a second molten liquid and dross, wherein the first gas comprises water vapor (H 2 O);   (c) heating the second molten liquid;   (d) separating the dross and the second molten liquid;   (e) cooling the second molten liquid to form first silicon crystals and a first mother liquid;   (f) separating the first silicon crystals and the first mother liquid;   (g) heating the first silicon crystals to form a first molten bath;   (h) directionally solidifying the first molten bath to form second silicon crystals and a second mother liquor;   (i) heating the second silicon crystals to provide a second molten bath;   (j) contacting the second molten bath with a second gas to form a slag that forms on the surface of a third molten bath, wherein the second gas comprises water vapor (H 2 O);   (k) separating the slag and the third molten bath;   and at least one of steps (l)-(o):   (l) cooling the second molten bath to form silicon ingots;   (m) contacting the second molten bath with water to form granulized silicon;   (n) introducing the third molten bath into a mold and cooling the third molten bath to form a second silicon; and   (o) directionally solidifying the third molten bath below the melting point, thereby forming a third silicon crystals, and separating the upper portion and the lower portion; wherein the upper portion comprises a third mother liquor and the lower portion comprises a third silicon.