Electro-deoxidation method, apparatus and product

Abstract

The subject invention concerns an electro-decomposition process wherein a cathode comprising a metal compound is contacted with a fused salt electrolyte in an electrochemical cell. The metal compound is a compound between a metal and another substance, and a voltage is applied between the cathode and an anode such that the substance is removed from the metal compound. In the improved method, the applied voltage increases with time, either continuously or stepwise, up to a predetermined maximum voltage. In addition, or in the alternative, the fused salt composition is selected so as to maintain a predetermined concentration of the substance in the fused salt during electro-decomposition.

1 . A method for removing a substance from a solid compound comprising the substance and a metal, comprising the steps of:
 a) contacting a cathode comprising the solid compound with a fused-salt electrolyte;   b) contacting an anode with the electrolyte; and   c) applying a voltage between the cathode and the anode which increases with time.   
     
     
         2 . The method according to  claim 1 , in which the voltage increases substantially continuously with time. 
     
     
         3 . The method according to  claim 1 , in which the voltage increases stepwise with time. 
     
     
         4 . The method according to  claim 1 , in which the electrolyte comprises a cation and the voltage is applied such that the potential at the cathode increases to a potential which is less than a potential for continuous deposition of the cation from the electrolyte at the cathode. 
     
     
         5 . The method according to  claim 1 , in which the voltage is applied such that the effective potential between the cathode and the anode increases to a potential which is less than a potential sufficient to cause continuous decomposition of the electrolyte. 
     
     
         6 . The method according to  claim 1 , in which the voltage is applied such that the potential at the cathode increases from a potential which is insufficient to cause removal of the substance from the compound. 
     
     
         7 . The method according to  claim 1 , in which the voltage is applied such that the potential at the cathode increases from a potential of approximately 0 V. 
     
     
         8 . The method according to  claim 1 , in which, after the increasing voltage has been applied, a substantially constant voltage is applied between the cathode and the anode. 
     
     
         9 . The method according to  claim 8 , in which the electrolyte comprises a cation and the substantially-constant voltage is such that the potential at the cathode is less than a potential for continuous deposition of the cation from the electrolyte at the cathode. 
     
     
         10 . The method according to  claim 8 , in which the substantially-constant voltage is insufficient to cause continuous decomposition of the electrolyte. 
     
     
         11 . The method according to  claim 1 , in which, after the increasing voltage has been applied, a voltage is applied between the cathode and the anode such that the potential at the cathode is substantially constant. 
     
     
         12 . The method according to  claim 11 , in which the electrolyte comprises a cation and the substantially-constant potential is less than a potential for continuous deposition of the cation from the electrolyte at the cathode. 
     
     
         13 . The method according to  claim 11 , in which the substantially-constant potential is insufficient to cause continuous decomposition of the electrolyte. 
     
     
         14 . The method according to  claim 1 , in which the potential at the cathode is monitored using a reference electrode. 
     
     
         15 . The method according to  claim 1 , in which the reference electrode comprises a carbon electrode. 
     
     
         16 . The method according to  claim 1 , in which the fused-salt electrolyte comprises a second salt in solution in a first salt, the first and second salts containing different anions, and in which the increasing voltage increases at a rate sufficiently slow to favour discharge of anions from the second salt rather than anions from the first salt at the anode. 
     
     
         17 . The method according to  claim 16 , in which the substance comprises oxygen, the solid compound comprises an oxide and the electrolyte comprises calcium chloride containing calcium oxide in solution therein, and in which the increasing voltage increases at a rate sufficiently slow to favour discharge of oxygen anions rather than chlorine anions at the anode. 
     
     
         18 . The method according  claim 1 , in which the increasing voltage increases at a rate sufficiently slow to suppress precipitation of the substance removed from the solid metal compound, or of a material comprising the substance removed from the solid metal compound, in the region of the cathode. 
     
     
         19 . The method according to  claim 18 , in which the substance comprises oxygen, the solid compound comprises an oxide and the electrolyte comprises calcium chloride containing calcium oxide in solution therein, and in which the increasing voltage increases at a rate sufficiently slow to suppress precipitation of calcium oxide at the cathode. 
     
     
         20 . The method according to  claim 1 , in which removal of the substance from the solid compound to produce the metal involves the formation of an intermediate compound comprising the substance and the metal, and in which the increasing voltage increases at a rate sufficiently slow to favour formation of the intermediate compound before formation of the metal.