Methods and apparatus for recovery of silicon and silicon carbide from spent wafer-sawing slurry

Abstract

Methods, systems, and apparatus are disclosed herein for recovery of high-purity silicon, silicon carbide and PEG from a slurry produced during a wafer cutting process. A silicon-containing material can be processed for production of a silicon-rich composition. Silicon carbide and PEG recovered from the silicon-containing material can be used to form a wafer-saw cutting fluid. The silicon-rich composition can be reacted with iodine containing compounds that can be purified and/or used to form deposited silicon of high purity. The produced silicon can be used in the photovoltaic industry or semiconductor industry.

What is claimed is: 
     
         1 . A process for recovering silicon comprising:
 a) separating iron-containing particles from a cutting slurry using at least one physical separation device, thereby producing a slurry product;   b) removing liquid from said slurry product, thereby producing a powder mixture of silicon carbide and silicon;   c) providing said powder mixture to a first vessel containing silicon tetra-iodide, thereby producing a vapor comprising silicon di-iodide; and   d) providing said vapor comprising silicon di-iodide to a second vessel, wherein said deposited silicon is formed from the silicon di-iodide.   
     
     
         2 . The process of  claim 1  further comprising purifying and recycling remaining silicon tetra-iodide from said second vessel. 
     
     
         3 . The process of  claim 1  further comprising e) recovering said iron-containing particles from step a). 
     
     
         4 . The process of  claim 1  further comprising f) adding a carrier gas to said first vessel in step d) to adjust the flow rate of the vapor-gas mixture. 
     
     
         5 . The process of  claim 1  further comprising recovering silicon carbide particles from said first vessel. 
     
     
         6 . The process of  claim 1  further comprising recovering at least one of glycol, oil or water from said slurry product. 
     
     
         7 . An apparatus for recovering silicon comprising:
 a) a physical separation device, wherein said physical separation device removes iron-containing particles from a cutting slurry to produce a silicon and silicon carbide rich stream;   b) a cyclone separator for producing a silicon rich stream from the silicon and silicon carbide-rich stream; and   c) a vessel for producing deposited silicon from the silicon-rich stream, wherein said vessel comprises a fluidized bed seeded with pure silicon particles.   
     
     
         8 . The apparatus of  claim 7 , wherein said cyclone separator separates silicon carbide from a silicon carbide and silicon mixture within a vapor-gas phase allowing for reaction between silicon and silicon tetra-iodide. 
     
     
         9 . The apparatus of  claim 7  further comprising a hydro-cyclone, wherein said hydro-cyclone is configured to separate silicon carbide particles between 10 and 20 micrometers from a solid-liquid slurry. 
     
     
         10 . The apparatus of  claim 7  further comprising a high-temperature filter, wherein said high-temperature filter is configured to prevent silicon carbide particles of between 1 and 10 micrometers from entraining with silicon di-iodide gas vapor into said vessel. 
     
     
         11 . A system for recovering silicon comprising:
 a) a physical separation device, wherein said device creates a magnetic field for separating iron-containing particles from a silicon-containing product;   b) a separator, wherein said separation device is a hydro-cyclone or a air-cyclone for separating silicon carbide particles of greater than about 10 micrometers in diameter from said silicon-containing product;   c) a drying device for drying said silicon-containing product;   d) a first vessel configured to receive said silicon-containing product, wherein said first vessel is maintained at a temperature of at least 1000° C.; and   e) a second vessel configured to receive said silicon-containing product, wherein said second vessel comprises a fluidized bed seeded with pure silicon particles.   
     
     
         12 . A process for recovering silicon comprising:
 a) providing a silicon-containing material and iodine to a first vessel, thereby producing a silicon tetra-iodide rich composition comprising silicon tetra-iodide;   b) providing the silicon tetra-iodide rich composition to a distillation process to form an increased purity silicon tetra-iodide rich composition; and   c) providing the increased purity silicon tetra-iodide rich composition to a second vessel, wherein deposited silicon is formed from the silicon tetra-iodide.   
     
     
         13 . The process of  claim 12 , wherein the silicon-tetra-iodide rich composition comprises silicon iodides and greater than about 70% of the silicon iodides are in the form of silicon tetra-iodide. 
     
     
         14 . The process of  claim 12 , wherein the silicon-containing material is prepared by one or more of the following steps: a solid-liquid separation step, a magnetic separation step, a filtration step, a leaching step, and a drying step. 
     
     
         15 . The process of  claim 12 , wherein the silicon-containing material comprises metallurgical-grade silicon. 
     
     
         16 . The process of  claim 12 , wherein the increased purity silicon tetra-iodide rich composition has a purity of at least 99.99999-99.99999999% (7-10N). 
     
     
         17 . The process of  claim 12 , wherein the deposited silicon has a purity of at least 99.999999%. 
     
     
         18 . The process of  claim 12 , wherein the first vessel is operated at a temperature between about 600° C. to 900° C., the second vessel is operated at a temperature between about 900 to 1300° C., and the distillation process is operated at a pressure less than about 101.3 kPa. 
     
     
         19 . A process for recovering a wire-saw cutting slurry comprising:
 a) subjecting a mixture comprising silicon carbide and PEG to a solid-liquid separation to form a silicon carbide rich composition and a silicon carbide depleted composition;   b) subjecting the silicon carbide depleted solution to a filtration separation to form a PEG rich composition; and   c) combining the silicon carbide rich composition and the PEG rich composition to form the wire-saw cutting slurry.   
     
     
         20 . The process of  claim 19 , wherein the filtration separation forms a silicon rich composition,
 wherein the silicon rich solution is reacted with iodide to form a silicon tetra-iodide rich composition,   wherein the silicon tetra-iodide rich composition is separated using a distillation process to form an increased purity silicon tetra-iodide rich composition, and   wherein the increased purity silicon tetra-iodide rich composition is used to form a deposited silicon.   
     
     
         21 . The process of  claim 19 , wherein the deposited silicon has a purity of at least 99.999999%. 
     
     
         22 . An apparatus for recovering silicon comprising:
 a) a first vessel configured for reacting a silicon-containing material with iodide to form an iodide mixture comprising silicon tetra-iodide;   b) a distillation column configured to receive the iodide mixture and produce a high-purity silicon tetra-iodide rich composition; and   c) a second vessel configured to form a deposited silicon from the silicon tetra-iodide rich composition.   
     
     
         23 . The apparatus of  claim 22 , wherein the first vessel is a fast fluidized bed reactor and the second vessel is a fluidized bed reactor. 
     
     
         24 . The apparatus of  claim 22 , wherein a cyclone is attached to the first vessel. 
     
     
         25 . The apparatus of  claim 22 , wherein the second vessel, the distillation column, and/or the second vessel comprise an inner ceramic shell. 
     
     
         26 . A system for recovering silicon comprising: a device for separating silicon from a cutting slurry, wherein said system recovers about 50 to about 5,000 tons of PV-grade silicon per year. 
     
     
         27 . A system for recovering silicon comprising: a device for separating silicon from a cutting slurry, wherein said system recovers about 90% of said silicon from said slurry.