Method for electrolytic production and refining of metals

Abstract

The present invention relates to a method for electrolytic production and refining of metals having a melting point above about 1000 0C, particularly silicon, where there is provided a first electrolytic cell having an upper molten electrolyte layer of a first electrolyte, a lower molten alloy layer of an alloy of the metal to be refined and at least one metal more noble than the metal to be refined. The lower alloy layer is the cathode in the first cell and an anode is positioned in the upper molten electrolyte layer. A second electrolytic cell is also provided with an upper molten metal layer of the same metal as the metal to be refined, said layer constituting a cathode, a lower molten alloy layer, said lower layer constituting an anode, said alloy having a higher density than the metal to be refined, and an intermediate molten electrolyte layer having a density between the density of the upper and lower molten layers. Both electrolytes are oxide based electrolytes containing oxide of the metal to be refined, and the electrolyte is in molten state and has a melting point below the operating temperature of the process. Raw material comprising an oxide of the metal to be refined is added to the first cell and direct electric current is passed through the anode to the cathode such that the metal to be refined is moved from the anode and deposited in molten state at the cathode. The two cells can be operated in two separate steps. One to produce an alloy and the other to refine metal from the alloy.

Description

Technical field [0001] The present invention relates to a method for electrolytic production and refining of metals with a high melting point higher than about 1000°C, especially silicon. Background technique [0002] There is a growing demand for high-purity metals, especially high-purity solar grade and electronic grade silicon. Solar-grade silicon raw materials for solar cells have been based on electronic-grade silicon scraps / scraps from the semiconductor industry. Electronic grade silicon is produced by silane production from metallurgical silicon and gas phase reduction of silane to silicon. However, this method is very expensive. In addition, the available amount of scrap / scrap in the semiconductor industry is now small and cannot supply the rapidly growing solar cell market. [0003] From U.S. Patent No. 3,219,561, it is known that the production is produced by passing a direct current between an anode in contact with a molten salt bath containing fluoride and silicon or ...

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Problems solved by technology

[0006] However, the above-mentioned process disclosed in U.S. Patent No. 1,534,318 cannot be used for electrolytic refining of metals having a high melting point above 1000° C., because a large amount of chloride vapor is formed in a chloride-based molten electrolyte at this high temperature, thereby destroy the properties of the electrolyte

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