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.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority to and the benefit of Korean Patent Application No. 10-2012-133845, filed on Nov. 23, 2012, the disclosure of which is incorporated herein by reference in its entirety.BACKGROUND[0002]1. Field of the Invention[0003]The present invention relates to a method for recovering elemental silicon from silicon sludge by electrolysis in a non-aqueous electrolyte.[0004]2. Discussion of Related Art[0005]Cutting slurry containing silicon carbide of 20 μm in size and the like is used in a process of cutting wafers from a silicon ingot. In this process, sludge containing silicon, silicon carbide, metal powder, cutting oil, etc. is discharged and effective separation and recovery of waste sludge for reuse or recycling as a useful resource has a significant meaning in terms of efficient use of resources as well as in terms of environmental protection.[0006]In general, the refinement of silicon can be obtained by reacting co...

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Benefits of technology

[0014]The present inventors have studied on a method for recovering silicon from silicon sludge by electrolysis and found that elemental silicon could be directly reduced in a conductive non-aqueous electrolyte prepared from silicon tetrachloride and, and through subsequent heat treatment, the efficiency of electrolysis of silicon and the stabilizing efficiency of silicon could be significantly improved, thus completing the present invention.

Problems solved by technology

In general, the refinement of silicon can be obtained by reacting concentrated silicon dioxide (SiO2) with a reductant such as carbon at high temperature, and the refined silicon has a purity of about 98% and thus has limitations on its use.

Moreover, in the refinement process, a lot of energy is used, a large amount of carbon dioxide is emitted, and impurities are contained, which are very problematic.

The purification of silicon yields a purity of 99.9% or higher by conversion into halogen compounds, fractional distillation, and reduction, but the process is complicated, energy-consuming, and uses toxic substances.

However, no alternative process has yet been suggested.

This process is performed under high vacuum and is difficult to be carried out as a continuous process, which involves a lot of expenses.

Over the past few decades, extensive research has been conducted on processes for easily manufacturing silicon thin films, but there is no alternative yet.

However, the electrolytic reduction of silicon is very difficult to achieve in a typical aqueous electrolyte due to low oxidation-reduction potential and high reduction overpotential.

Moreover, even a very small amount of reduced silicon is reoxidized with oxygen in an aqueous solution, and thus it is impossible to achieve the electrolytic reduction of elemental silicon.

They studied electrodeposition using a molten salt at high temperatures of 500 to 1,400° C., which requires a complicated process and a high temperature process, resulting in significant cost and energy.

They all reported a study on the electrolytic reduction of silicon at room temperature but did not solve the problem that the reduced silicon is oxidized.

Moreover, it is not yet determined whether the electrodeposited silicon oxide is reduced along with dissolved oxygen in the electrolyte or whether the electrodeposited porous silicon is exposed to the air and oxidized.

Furthermore, a study aimed at stabilizing the electrodeposited silicon by annealing before being exposed to the air has been partially performed, but this problem has not yet been solved.

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