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. 
     
     
         21 . The method according to  claim 1 , in which the voltage increases at a rate of less than 0.2 mV/s, and preferably at a rate of less than 0.1 mV/s. 
     
     
         22 . The method according to  claim 1 , in which:
 the fused-salt electrolyte comprises a second salt in solution in a first salt, the second salt but not the first salt comprising an anion which is the same as the substance; and   the concentration of the second salt in solution in the first salt is greater than zero, and preferably greater than 1 mol %, during the application of the voltage.   
     
     
         23 . The method according to  claim 22 , in which the concentration of the second salt in solution in the first salt during the application of the voltage is sufficient to enable transport of the substance through the electrolyte from the cathode to the anode. 
     
     
         24 . The method according to  claim 22 , in which the removal of the substance from the solid compound to produce the metal involves the formation of an intermediate compound comprising a cation and/or an anion of the second salt, and the fused-salt electrolyte contains a sufficient quantity of the second salt both to enable formation of the intermediate compound and to retain the concentration of the second salt in solution in the first salt greater than zero, and preferably greater than 1 mol %, during the application of the voltage. 
     
     
         25 . The method according to  claim 24 , in which the fused-salt electrolyte contains a sufficient quantity of the first salt to retain the sufficient quantity of the second salt in solution. 
     
     
         26 . The method according to  claim 22 , in which the substance comprises oxygen, the compound comprises an oxide, and the anion in the second salt comprises oxygen. 
     
     
         27 . The method according to  claim 26 , in which the first salt is calcium chloride and the second salt is calcium oxide. 
     
     
         28 . The method according to  claim 26 , in which the compound comprises a titanium oxide. 
     
     
         29 . The method according to  claim 1 , in which the electrolyte comprises calcium oxide; and,
 the voltage applied between the cathode and the anode is such that the potential at the cathode is insufficient to cause continuous decomposition of the calcium oxide.   
     
     
         30 . The method according to  claim 29 , in which the potential at the cathode, as measured with respect to a carbon reference electrode, is less than about (1541-116 log C) mV, where C is the normalised concentration of calcium oxide in the fused-salt electrolyte. 
     
     
         31 . The method according to  claim 29 , in which the potential at the cathode, as measured with respect to a carbon reference electrode, is less than 1.7 V, and preferably less than 1.6 V. 
     
     
         32 . The method according to  claim 29 , in which the metal compound comprises a titanium oxide, the anode is a carbon anode, and the voltage applied between the cathode and the anode is such that the potential at the cathode, as measured with respect to a carbon reference electrode, is more than 1.1 V, and preferably more than 1.3 V. 
     
     
         33 . The method according to  claim 1 , in which the solid metal compound comprises a titanium oxide, and the voltage applied between the cathode and the anode is such that the potential at the cathode is more than 1.1 V, and preferably more than 1.3 V. 
     
     
         34 . 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 comprising a second salt in solution in a first salt, the second salt but not the first salt comprising an anion which is the same as the substance;   b) contacting an anode with the electrolyte; and   c) applying a voltage between the cathode and the anode such that the potential at the cathode is less than a potential for deposition of cations from the electrolyte; the concentration of the second salt in solution in the first salt being greater than zero, and preferably greater than 1 mol %, during the application of the voltage.   
     
     
         35 . The method according to  claim 34 , in which the concentration of the second salt in solution in the first salt during the application of the voltage is sufficient to enable transport of the substance through the electrolyte from the cathode to the anode. 
     
     
         36 . The method according to  claim 34 , in which the removal of the substance from the solid compound to produce the metal involves the formation of an intermediate compound comprising a cation and/or an anion of the second salt, and the fused-salt electrolyte contains a sufficient quantity of the second salt both to enable formation of the intermediate compound and to retain the concentration of the second salt in solution in the first salt greater than zero, and preferably greater than 1 mol %, during the application of the voltage. 
     
     
         37 . The method according to  claim 36 , in which the fused-salt electrolyte comprises a sufficient quantity of the first salt to retain the sufficient quantity of the second salt in solution. 
     
     
         38 . The method according to  claim 34 , in which the substance comprises oxygen, the compound comprises an oxide, and the second salt comprises an oxide. 
     
     
         39 . The method according to  claim 38 , in which the first salt is calcium chloride and the second salt is calcium oxide. 
     
     
         40 . The method according to  claim 38 , in which the compound comprises a titanium oxide. 
     
     
         41 . A method for removing a substance from a solid metal compound comprising the substance and a metal, comprising the steps of:
 a) contacting a cathode comprising the solid metal compound with a fused-salt electrolyte, the electrolyte comprising a corresponding salt which contains the substance as an anion;   b) contacting an anode with the electrolyte; and   c) applying a voltage between the cathode and the anode which is insufficient to cause continuous decomposition of the corresponding salt.   
     
     
         42 . The method according to  claim 41 , in which the solid metal compound comprises a metal oxide and the corresponding salt comprises an oxide. 
     
     
         43 . The method according to  claim 42 , in which the corresponding salt is calcium oxide, the anode is a carbon anode and the potential at the cathode, as measured with respect to a carbon reference electrode, is less than about (1541-116 log C) mV, where C is the normalised concentration of calcium oxide in the fused-salt electrolyte. 
     
     
         44 . The method according to  claim 42 , in which the corresponding salt is calcium oxide, the anode is a carbon anode and the potential at the cathode, as measured with respect to a carbon reference electrode, is less than 1.7 V, and preferably less than 1.6 V. 
     
     
         45 . The method according to  claim 41 , in which the metal oxide comprises a titanium oxide, the anode is a carbon anode, and the voltage applied between the cathode and the anode is such that the potential at the cathode, as measured with respect to a carbon reference electrode, is more than 1.1 V, and preferably more than 1.3 V. 
     
     
         46 . A method for removing oxygen from a solid titanium oxide, comprising the steps of:
 a) contacting a cathode comprising the solid titanium oxide with a fused-salt electrolyte;   b) contacting a carbon anode with the electrolyte; and c) applying a voltage between the cathode and the anode such that the potential at the cathode, as measured with respect to a carbon reference electrode, is more than 1.1 V, and preferably more than 1.3 V.   
     
     
         47 . 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 such that the potential at the cathode increases with time.   
     
     
         48 . The method according to  claim 47 , in which the potential at the cathode increases continuously with time. 
     
     
         49 . The method according to  claim 47 , in which the potential at the cathode increases stepwise with time. 
     
     
         50 . (canceled) 
     
     
         51 . A method for forming an alloy comprising two or more metal components, comprising the steps of forming a precursor material containing mixed solid compounds of each of the metal components with a substance or substances, and processing the precursor material to remove the substance or substances as defined in:
 i) 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; or 
   ii) 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 comprising a second salt in solution in a first salt, the second salt but not the first salt comprising an anion which is the same as the substance; 
 b) contacting an anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode such that the potential at the cathode is less than a potential for deposition of cations from the electrolyte; the concentration of the second salt in solution in the first salt being greater than zero, and preferably greater than 1 mol %, during the application of the voltage; or 
   iii) a method for removing a substance from a solid metal compound comprising the substance and a metal, comprising the steps of:
 a) contacting a cathode comprising the solid metal compound with a fused-salt electrolyte, the electrolyte comprising a corresponding salt which contains the substance as an anion; 
 b) contacting an anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode which is insufficient to cause continuous decomposition of the corresponding salt; or 
   iv) a method for removing a substance from a solid metal compound comprising the substance and a metal, comprising the steps of:
 a) contacting a cathode comprising the solid metal compound with a fused-salt electrolyte, the electrolyte comprising a corresponding salt which contains the substance as an anion; 
 b) contacting an anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode which is insufficient to cause continuous decomposition of the corresponding salt; or 
   v) a method for removing oxygen from a solid titanium oxide, comprising the steps of:
 a) contacting a cathode comprising the solid titanium oxide with a fused-salt electrolyte; 
 b) contacting a carbon anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode such that the potential at the cathode, as measured with respect to a carbon reference electrode, is more than 1.1 V, and preferably more than 1.3 V; or 
   vi) 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 such that the potential at the cathode increases with time. 
   
     
     
         52 . A metal or alloy formed using the method of  claim 51 . 
     
     
         53 . An apparatus for carrying out a method selected from:
 i) 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; or 
   ii) 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 comprising a second salt in solution in a first salt, the second salt but not the first salt comprising an anion which is the same as the substance; 
 b) contacting an anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode such that the potential at the cathode is less than a potential for deposition of cations from the electrolyte; the concentration of the second salt in solution in the first salt being greater than zero, and preferably greater than 1 mol %, during the application of the voltage; or 
   iii) a method for removing a substance from a solid metal compound comprising the substance and a metal, comprising the steps of:
 a) contacting a cathode comprising the solid metal compound with a fused-salt electrolyte, the electrolyte comprising a corresponding salt which contains the substance as an anion; 
 b) contacting an anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode which is insufficient to cause continuous decomposition of the corresponding salt; or 
   iv) a method for removing a substance from a solid metal compound comprising the substance and a metal, comprising the steps of:
 a) contacting a cathode comprising the solid metal compound with a fused-salt electrolyte, the electrolyte comprising a corresponding salt which contains the substance as an anion; 
 b) contacting an anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode which is insufficient to cause continuous decomposition of the corresponding salt; or 
   v) a method for removing oxygen from a solid titanium oxide, comprising the steps of:
 a) contacting a cathode comprising the solid titanium oxide with a fused-salt electrolyte; 
 b) contacting a carbon anode with the electrolyte; and 
 c) applying a voltage between the cathode and the anode such that the potential at the cathode, as measured with respect to a carbon reference electrode, is more than 1.1 V, and preferably more than 1.3 V; or 
   vi) 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 such that the potential at the cathode increases with time; or 
   vii) a method for forming an alloy comprising two or more metal components, comprising the steps of forming a precursor material containing mixed solid compounds of each of the metal components with a substance or substances, and processing the precursor material to remove the substance or substances as defined in method (i), (ii), (iii), (iv), (v), or (vi).   
     
     
         54 . An apparatus for removing a substance from a solid compound comprising the substance and a metal, comprising;
 a) a cathode assembly for holding the solid compound;   b) an anode;   c) a reference electrode of carbon;   d) a receptacle for holding a fused-salt electrolyte in contact with the cathode assembly, the anode and the reference electrode;   e) a voltage source for applying a voltage between the cathode and the anode; and   f) a means for monitoring the voltage between the cathode and the reference electrode and controlling the voltage source in response to the monitored voltage.