Method for recovering elemental silicon from silicon sludge by electrolysis in non-aqueous electrolyte

Abstract

The present invention relates to a method for recovering elemental silicon from silicon sludge by electrolysis in a non-aqueous electrolyte. The recovery method of silicon according to the present invention can achieve direct reduction of silicon by electrolysis at a low temperature (below 200° C.), control the structure of silicon by a simple process and a change in electrolysis conditions, and perform a continuous process by adding a silicon salt.

What is claimed is: 
     
         1 . A method for recovering elemental silicon, the method comprising the steps of:
 (a) mixing waste silicon sludge and an organic solvent to separate cutting oil from the silicon sludge;   (b) separating iron (Fe) from the silicon sludge, from which the cutting oil is removed, using a magnetic separator;   (c) adding chlorine to the silicon sludge, from which the iron is removed, and heating the resulting silicon sludge to prepare silicon tetrachloride (SiCl4);   (d) placing an electrolytic cell provided with conductive electrodes in a conductive non-aqueous solvent, in which the silicon tetrachloride is dissolved, in a high-purity inert gas atmosphere; and   (e) applying an electric power to the electrolytic cell in step (d) such that a reduction of silicon occurs in a negative electrode and a silicon thin film is formed on the surface of the electrode.   
     
     
         2 . The method of  claim 1 , wherein in step (a), the organic solvent comprises chloroform, ethyl acetate, tetrahydrofuran (THF), or dichloromethane (CH 2 Cl 2 ). 
     
     
         3 . The method of  claim 1 , wherein in step (b), the magnetic separator has a magnetic flux density of 500 gauss. 
     
     
         4 . The method of  claim 1 , wherein in step (c), the heating is performed at 800 to 1,200° C. for 30 to 90 minutes. 
     
     
         5 . The method of  claim 1 , wherein in step (d), the electrodes comprises at least two selected from the group consisting of gold, platinum, and copper. 
     
     
         6 . The method of  claim 1 , wherein in step (d) the inert gas comprises at least one selected from the group consisting of nitrogen, helium, argon, neon, and xenon. 
     
     
         7 . The method of  claim 1 , wherein in step (d), the conductive non-aqueous solvent is a conductive non-aqueous solvent containing a bis(trifluoromethylsulfonyl)imide (TFSI) anion and comprises at least one selected from the group consisting of (1-Butyl-3-methyl-pyridinium bis(trifluoromethylsulfonyl)imide) [BMPy]TFSI, (1-methyl-propylpiperidinium bis(trifluoromethylsulfonyl)imide) PP13TFSI, and (1-Ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide) [EMIM]TFSI. 
     
     
         8 . The method of  claim 7 , wherein the conductive non-aqueous solvent further comprises propylene carbonate (PC), dichloromethane (DCM), tetrahydrofuran (THF), dicyanamide (DCA), or N-methylpyrrolidone (NMP). 
     
     
         9 . The method of  claim 1 , further comprising, before step (d), the steps of:
 (d′) cleaning the electrodes and the cell with a mixture solution of sulfuric acid and hydrogen peroxide; and   (d″) drying the non-aqueous solvent at 80 to 120° C. for 20 to 30 hours.   
     
     
         10 . The method of  claim 1 , further comprising, after step (e), the step of performing heat treatment in an inert gas atmosphere at 800 to 900° C. for 30 to 90 minutes. 
     
     
         11 . The method of  claim 10 , wherein the inert gas comprises at least one selected from the group consisting of nitrogen, helium, argon, neon, and xenon.