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  Electrochemical reduction of metal oxidesUSPTO Application #: 20070193877Title: Electrochemical reduction of metal oxides Abstract: An electrolytic cell (1) for reducing metal oxide powders and/or pellets in a continuous or semi-continuous manner, the cell includes a cathode (25) in the form of a plate that has an upper surface for supporting metal oxide powders and/or pellets. The plate is supported for movement so as to cause the metal oxide on the upper surface to move toward a forward end of the plate while immersed in a molten electrolyte (21). The cell includes multiple anodes (23) and support structures (63,65) that separately support the cathode and the anodes from above the cell. In a preferred embodiment the anode support structure enables adjustment of the spacing of the anodes above the upper surface of the cathode. (end of abstract) Agent: Brinks Hofer Gilson & Lione - Chicago, IL, US Inventors: Gregory David Rigby, Andrew Arthur Shook USPTO Applicaton #: 20070193877 - Class: 204243100 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Cells, Fused Bath The Patent Description & Claims data below is from USPTO Patent Application 20070193877. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to electrochemical reduction of metal oxides. [0002] The present invention relates particularly to continuous and semi-continuous electrochemical reduction of metal oxides in the form of powder to produce metal having a low oxygen concentration, typically no more than 0.2% by weight. [0003] The present invention was made during the course of an on-going research project on electrochemical reduction of metal oxides being carried out by the applicant. The research project has focused on the reduction of titania (TiO.sub.2). [0004] During the course of the research project the applicant carried out experimental work on the reduction of titania using electrolytic cells that included a pool of molten CaCl.sub.2-based electrolyte, an anode formed from graphite, and a range of cathodes. [0005] The CaCl.sub.2-based electrolyte was a commercially available source of CaCl.sub.2, namely calcium chloride dihydrate, that decomposed on heating and produced a very small amount of CaO. [0006] The applicant operated the electrolytic cells at a potential above the decomposition potential of CaO and below the decomposition potential of CaCl.sub.2. [0007] The applicant found that at these potentials the cell could electrochemically reduce titania to titanium with low concentrations of oxygen, i.e. concentrations less than 0.2 wt. %. [0008] The applicant operated the electrolytic cells on a batch basis with titania in the form of pellets and larger solid blocks in the early part of the work and titania powder in the later part of the work. The applicant also operated the electrolytic cells on a batch basis with other metal oxides. [0009] Whilst the research work established that it is possible to electrochemically reduce titania (and other metal oxides) to metals having low concentrations of oxygen in such electrolytic cells, the applicant has realised that there are significant practical difficulties operating the electrolytic cells commercially on a batch basis. [0010] In the course of considering the results of the research work and possible commercialisation of the technology, the applicant realised that it was possible that commercial production could be achieved by operating an electrolytic cell on a continuous or semi-continuous basis with metal oxide powders and pellets being transported through the cell in a controlled manner and being discharged in a reduced form from the cell. [0011] International application PCT/AU2003/001657, which claims priority from Australian provisional application 2002953282 lodged on 12 Dec. 2002, in the name of the applicant describes this invention in broad terms as a process for electrochemically reducing a metal oxide, such as titania, in a solid state in an electrolytic cell that includes a bath of molten electrolyte, a cathode, and an anode, which process includes the steps of: (a) applying a cell potential across the anode and the cathode that is capable of electrochemically reducing metal oxide supplied to the molten electrolyte bath, (b) continuously or semi-continuously feeding the metal oxide in powder and/or pellet form into the molten electrolyte bath, (c) transporting the powders and/or pellets along a path within the molten electrolyte bath and reducing the metal oxide as the metal oxide powders and/or pellets move along the path, and (d) continuously or semi-continuously removing reduced metal oxide powders and/or pellets from the molten electrolyte bath. [0012] The International application defines the term "powder and/or pellet form" as meaning particles having a particle size of 3.5 mm or less. The upper end of this particle size range covers particles that are usually described as pellets. [0013] The term "powder" and "pellets" as used herein is understood to mean particles that are less than 5 mm in a major dimension. [0014] The term "powder" and "pellets" as used herein is not intended to limit the scope of patent protection to a particular procedure for producing the particles. [0015] The term "semi-continuously" is understood in the International application and herein to mean that the process includes: (a) periods during which metal oxide powders and/or pellets are supplied to the cell and periods during which there is no such supply of metal oxide powders and/or pellets to the cell, and (b) periods during which reduced material is removed from the cell and periods during which there is no such removal of reduced material from the cell. [0016] The overall intention of the use of the terms "continuously" and "semi-continuously" in the International application and herein is to describe cell operation other than on a batch basis. [0017] In this context, the term "batch" is understood in the International application and herein to include situations in which metal oxide is continuously supplied to a cell and reduced metal builds up in the cell until the end of a cell cycle, such as disclosed in International application WO 01/62996 in the name of The Secretary of State for Defense. [0018] After making the initial invention described above, the applicant carried out further research into the possibility of commercial production based on operating an electrolytic cell on a continuous or semi-continuous basis. [0019] The applicant realised that a commercial production cell should include a cell cathode in the form of a member, such as a plate, having an upper surface for supporting metal oxides in pellet form, as described herein, that is horizontally disposed or slightly inclined and has a forward end and a rearward end and is immersed in the electrolyte bath and is supported for movement, preferably in forward and rearward directions, so as to cause metal oxide pellets to move toward the forward end of the cathode. [0020] The applicant proposed that, with this arrangement, in use, metal oxides in powder and/or pellet form could be supplied onto the upper surface of the cathode, preferably near the rearward end thereof, and moved forward by the movement of the cathode and fall off the upper surface at the forward end of the cathode and ultimately be removed from the cell. With this arrangement, the metal oxides would be reduced as the metal oxides moved over the upper surface. [0021] International application PCT/AU2004/000809, which claims priority from Australian provisional application 2003903150 lodged on 20 Jun. 2003, in the name of the applicant describes this so-called "shaker table" cathode invention in broad terms. [0022] The applicant has carried out further research and development work on the "shaker table" invention and has now designed a particular electrolytic cell in accordance with the invention. The invention of the particular electrolytic cell design is the subject of this patent specification. [0023] The particular electrolytic cell design of the present invention is characterised by multiple anodes and by support structures that separately support the "shaker table" cathode and the anodes from above the cell, and preferably with the anode support structure enabling adjustment of the spacing of the anodes above the upper surface of the "shaker table" cathode. [0024] According to the present invention there is provided an electrolytic cell for electrochemically reducing metal oxide powders and/or pellets (as described herein), which electrolytic cell includes (a) a bath of a molten electrolyte, (b) a cathode in the form of a member, such as a plate, having an upper surface for supporting metal oxide powders and/or pellets that is horizontally disposed or slightly inclined and has a forward end and a rearward end and is immersed in the electrolyte bath, (c) a cathode support means for supporting the cathode from above the electrolyte bath and for moving the cathode in the cell so as to cause metal oxide powders and/or pellets on the upper surface of the cathode to move toward the forward end of the cathode while in contact with molten electrolyte whereby electrochemical reduction of the metal oxide can occur as the powders and/or pellets move toward the forward end, (d) a plurality of anodes extending into the electrolyte bath, (e) an anode support means for supporting the anodes from above the electrolyte bath, (f) a means for applying a potential across the anodes and the cathode, (g) a means for supplying metal oxide powders and/or pellets to the electrolyte bath so that the metal oxide powders and/or pellets can deposit onto the upper surface of the cathode, and (h) a means for removing at least partially electrochemically reduced metal oxides from the electrolyte bath. 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