Electrolytic reducion of metal oxides

Abstract

A method of electrolytically reducing a metal oxide (such as aluminium and magnesium oxides) to produce a metal in an electrolytic call is disclosed. The method includes electrolytically reducing the metal oxide in an electrolytic cell that includes a pool of molten metal, the metal being the metal of the metal oxide to be reduced, and the molten metal pool forming a cathode of the cell. The electrolytic cell also includes a pool of molten electrolyte in contact with the molten metal, the electrolyte containing alkali and/or alkaline earth halides. The electrolytic cell also includes an anode extending into the electrolyte and a body of metal oxide to reduced in contact with the molten metal and the electrolyte.

1 . A method of electrolytically reducing a metal oxide to produce a metal in an electrolytic cell, which method includes electrolytically reducing the metal oxide in an electrolytic cell that includes a pool of molten metal, the metal being the metal of the metal oxide to be reduced, the molten metal pool forming a cathode of the cell, a pool of molten electrolyte in contact with the molten metal, the electrolyte containing alkali and/or alkaline earth halides, an anode extending into the electrolyte, and a body of metal oxide to be reduced in contact with the molten metal and the electrolyte.  
     
     
         2 . The method defined in  claim 1  wherein the metal oxide body has a geometric shape that maximises contact between (i) the molten metal, (ii) the metal oxide, and (iii) the electrolyte.  
     
     
         3 . The method defined in  claim 1  including feeding the metal oxide body into the electrolytic cell to maintain contact of the metal oxide and the molten metal.  
     
     
         4 . The method defined in  claim 1  wherein the metal oxide body includes one or more of rods, plates and blocks that can be readily immersed into the electrolyte and brought into contact with the molten metal.  
     
     
         5 . The method defined in including maintaining the cell temperature above the melting points of the electrolyte and the metal of the metal oxide to be reduced.  
     
     
         6 . The method defined in including operating the cell at a potential that is above a decomposition potential of at least one constituent of the electrolyte so that there are cations of a metal other than that of the cathode metal oxide in the electrolyte.  
     
     
         7 . The method defined in  claim 1  wherein the metal oxide is an aluminium oxide or a magnesium oxide.  
     
     
         8 . The method defined in  claim 7  wherein the electrolyte is a CaCl 2 -based electrolyte that includes CaO as one of the constituents.  
     
     
         9 . The method defined in  claim 8  including maintaining the cell potential above the decomposition potential for CaO.  
     
     
         10 . The method defined in  claim 8  including maintaining the cell potential below the decomposition potential for CaCl 2 .  
     
     
         11 . The method defined in  claim 10  including maintaining the cell potential less than 3.0V.  
     
     
         12 . The method defined in  claim 10  including maintaining the cell potential less than 2.5V.  
     
     
         13 . The method defined in  claim 10  including maintaining the cell potential less than 2.0V.  
     
     
         14 . The method defined in  claim 8  including maintaining the cell potential to be at least 1.5V.  
     
     
         15 . The method defined  claim 1  wherein the cell includes at least one tap hole for molten metal and the method includes removing molten metal continuously or periodically via the tap hole.