Methods and apparatuses for increasing energy efficiency and improving membrane robustness in primary metal production

Abstract

The invention relates to apparatuses and methods for increasing energy efficiency and improving membrane robustness in primary metal production. In some aspects, the methods and apparatuses comprise interrupting a first current flow from the cathode to the anode and permitting a second current flow from the anode to the cathode. In some aspects, the methods and apparatuses comprise a solid oxygen ion-conducting membrane disposed in ion-conducting contact with the molten electrolyte, wherein the membrane has an electronic resistance less than about 200 ohms/cm 2

1 . A method for reducing a metal oxide comprising:
 (a) providing a cathode in ion-conducting contact with a molten electrolyte, the molten electrolyte containing a metal oxide;   (b) providing an anode in ionic communication with the molten electrolyte;   (c) providing a power supply disposed between the cathode and the anode;   (d) using the power supply to cause a first current flow from the cathode to the anode, thereby reducing at least a portion of the metal oxide; and   (e) from time to time, interrupting the first current flow and electrically coupling the anode and the cathode, thereby permitting a second current flow from the anode to the cathode and thereby oxidizing at least a portion the metal in the molten electrolyte.   
     
     
         2 . The method of  claim 1 , further comprising:
 (f) providing a solid oxygen ion-conducting membrane disposed to be in ion-conducting contact with the molten electrolyte and in electrical contact with the anode, the solid oxygen ion-conducting membrane separating the anode from the molten electrolyte.   
     
     
         3 . The method of  claim 1 , further comprising providing an electronic conductor disposed in electrical contact with the anode. 
     
     
         4 . The method of  claim 2 , further comprising providing oxygen to the anode. 
     
     
         5 . The method of  claim 3 , wherein the oxygen is provided through a second solid oxygen ion-conducting membrane. 
     
     
         6 . The method of  claim 1 , wherein the first current flow is run from about 3 to about 20 times as long as that of the second current flow. 
     
     
         7 . The method of  claim 1 , wherein the second current flow is run for about 1 second to about 60 seconds. 
     
     
         8 . The method of  claim 1 , wherein the second current flow is run for about 30 seconds to about 60 minutes. 
     
     
         9 . The method of  claim 2 , wherein the solid oxygen ion-conducting membrane has a corrosion rate of less than about 1 micron per hour at current density of at least 0.1 amperes/sq. cm and at temperatures greater than about 700° C. 
     
     
         10 . The method of  claim 2 , wherein the solid oxygen ion-conducting membrane comprises zirconia, ceria, or copper oxide. 
     
     
         11 . The method of  claim 2 , wherein the solid oxygen ion-conducting membrane is doped with an n-type oxide. 
     
     
         12 . The method of  claim 2 , wherein the solid oxygen ion-conducting membrane is doped with an oxide of cobalt, manganese, iron, cerium, titanium, or praseodymium. 
     
     
         13 . The method of  claim 2 , wherein the solid oxygen ion-conducting membrane comprises a two-phase material. 
     
     
         14 . The method of  claim 13 , wherein the two-phase material comprises cerium and strontium. 
     
     
         15 . The method of  claim 13 , wherein the two-phase material comprises samarium-doped cerium oxide, gadolinium-doped cerium oxide, samarium-doped zirconium oxide, or gadolinium-doped zirconium oxide. 
     
     
         16 . The method of  claim 1 , wherein the metal oxide comprises and oxide of magnesium, aluminum, silicon, calcium, titanium, copper, tantalum or a rare earth. 
     
     
         17 . The method of  claim 15 , wherein the metal oxide comprises magnesium oxide. 
     
     
         18 .- 46 . (canceled) 
     
     
         47 . A method for recovering metal from a molten electrolyte comprising:
 (a) providing a cathode in ion-conducting contact with a molten electrolyte, the molten electrolyte containing the metal oxide;   (b) providing a solid oxygen ion-conducting membrane disposed to be in ion-conducting contact with the molten electrolyte, wherein the product of membrane electronic resistance and its active area is less than about 200 ohms·cm 2 ;   (c) providing an anode in electrical contact with the solid oxygen ion-conducting membrane, the solid oxygen ion-conducting membrane separating the anode from the molten electrolyte;   (d) providing a power supply disposed between the cathode and the anode; and   (e) applying a current flow from the cathode to the anode.   
     
     
         48 . (canceled) 
     
     
         49 . The method of  claim 47 , wherein the product of membrane electronic resistance and active area is less than about 20 ohms·cm 2 . 
     
     
         50 .- 53 . (canceled) 
     
     
         54 . The method of  claim 47 , wherein the solid oxygen ion-conducting membrane is doped with an n-type oxide. 
     
     
         55 .- 64 . (canceled)