Claims
- 1. A method of electrochemically reducing a metal oxide to the metal in an electrochemical cell in which each of the anode and cathode operate at their respective maximum reaction rates depending on cell operating conditions including applied voltage and cell materials and cell geometry, said method comprising providing a molten salt electrolyte having a cation selected from one or more of the alkali metals, the alkaline earth metals, the eutectics and mixtures thereof, providing an anode at which oxygen can be evolved, providing a cathode including a metal oxide to be reduced, providing a third electrode of an alkali metal or an alkaline earth metal or mixtures or alloys thereof, providing a power supply connecting the anode and the third electrode, and providing a power supply connecting the cathode and the third electrode, whereby establishing and independently controlling voltage potentials between the third electrode and each of the anode and the cathode permits reduction of the metal oxide the metal without either the anode reaction rate or the cathode reaction rate being limited by the other, resulting in substantially complete reduction of the metal oxide.
- 2. The method of claim 1, wherein the anode during cell operation operates at maximum reaction rate at substantially constant voltage with respect to the third electrode.
- 3. The method of claim 1, wherein the cathode during cell operation operates at maximum reaction rate at substantially constant voltage with respect to the third electrode.
- 4. The method of claim 1, wherein each of the anode and cathode operate at their maximum reaction rate with each being at substantially constant voltage with respect to the third electrode.
- 5. The method of claim 1, wherein the third electrode operates as an anode at the start of cell operation and as a cathode at the end of cell operation.
- 6. The method of claim 4, wherein the metal oxide is an oxide of one or more of the actinides.
- 7. The method of claim 6, wherein the metal oxide is an oxide of one or more of uranium and the transuranics.
- 8. The method of claim 4, wherein the metal oxide is an oxide of one or more of the rare earth oxides selected from the group consisting of the oxides of Eu Gd, Nd, Pr, Yb, La and Ce.
- 9. The method of claim 8, wherein the metal oxide is one or more of the rare earth oxides selected from the group consisting of the oxides of Dy, Sc and Er.
- 10. A method of electrochemically reducing an actinide oxide to the actinide in an electrochemical cell in which each of the anode and cathode operate at their respective maximum reaction rates depending on cell operating conditions including applied voltage and cell materials and cell geometry, said method comprising
providing a molten salt electrolyte having a cation selected from one or more of the alkali metals, the alkaline earth metals, the eutectics and mixtures thereof and a low concentration of oxide ion, providing an anode at which oxygen can be evolved, providing a cathode including actinide oxide to be reduced, providing a third electrode of an alkali metal or an alkaline earth metal or mixtures or alloys thereof, providing a power supply connecting the anode and the third electrode, and providing a power supply connecting the cathode and the third electrode, whereby establishing and independently controlling voltage potentials between the third electrode and each of the anode and the cathode permits reduction of the actinide oxide to the actinide without either the anode reaction rate or the cathode reaction rate being limited by the other, resulting in substantially complete reduction of the actinide oxide while maintaining a low concentration of oxide ion in the electrolyte.
- 11. The method of claim 10, wherein the cation is an alkali metal ion.
- 12. The method of claim 10, wherein the cation is Li.
- 13. The method of claim 10, wherein the molten salt is a halide.
- 14. The method of claim 10, wherein the molten salt is a chloride.
- 15. The method of claim 10, wherein during cell operation the anode produces anode products and the anode is substantially chemically unreactive with the anode products and the electrolyte at the conditions of cell operation.
- 16. The method of claim 10, wherein the anode is gold or an alloy thereof.
- 17. The method of claim 15, wherein the anode is an electronically conductive ceramic substantially chemically unreactive with the anode products and the electrolyte at the conditions of cell operation.
- 18. The method of claim 17, wherein the anode is an oxide.
- 19. The method of claim 10, wherein the cathode includes one or more of uranium and the transuranic oxides.
- 20. The method of claim 10, wherein the voltage of the anode is maintained substantially constant with respect to the third electrode during the reduction of the actinide.
- 21. The method of claim 10, wherein the voltage of the cathode is maintained substantially constant respect to the third electrode during the reduction of the actinide.
- 22. The method of claim 10, wherein the voltage of each of the cathode and the anode is maintained substantially constant respect to the third electrode during the reduction of the actinide.
- 23. The method of claim 22, wherein the third electrode acts as an anode at the start of cell operation and as a cathode at the end of cell operation.
- 24. The method of claim 22, wherein the third electrode is a metal of a cation in the electrolyte.
- 25. The method of claim 10, wherein the third electrode is intermediate the cathode and the anode.
- 26. The method of claim 10, wherein the anode is intermediate the third electrode and the cathode.
- 27. The method of claim 10, wherein the cathode is intermediate the third electrode and the anode.
- 28. The method of claim 10, wherein the actinide includes uranium and the oxide ion concentration at the end of the reduction is less than about one ppm.
- 29. The method of claim 28, wherein the actinide oxide includes one or more of the transuranic oxides.
- 30. A method of electrochemically reducing one or more of a rare earth oxide and/or an actinide oxide to the metal in an electrochemical cell in which each of the anode and cathode operate at their respective maximum reaction rates depending on cell operating conditions including applied voltage and cell materials and cell geometry, said method comprising providing a molten halide salt electrolyte having an alkali metal cation and a low oxide ion concentration, providing an anode at which oxygen can be evolved, providing a cathode including one or more of a rare earth oxide and an actinide oxide to be reduced, providing a third electrode of an alkali metal in the salt electrolyte, providing a power supply connecting the anode and the alkali metal third electrode, and providing a power supply connecting the cathode and the alkali metal third electrode, whereby establishing and independently controlling voltage potentials between the alkali metal third electrode and each of the anode and the cathode permits substantially complete reduction of the selected rare earth and/or actinide oxides to the corresponding rare earth and/or actinide without either the anode reaction rate or the cathode reaction rate being limited by the other.
- 31. The method of claim 30, wherein the molten halide salt electrolyte includes LiCl.
- 32. The method of claim 30, wherein the third electrode includes Li.
- 33. The method of claim 32, wherein the anode and the cathode are each operated at a constant voltage during the reduction of the actinide oxide and/or the rare earth oxide.
- 34. The method of claim 30, wherein the actinide oxide includes one or more of uranium and the transuranics and the oxide ion concentration at the end of the reduction is less than about one ppm.
- 35. The method of claim 34, wherein the rare earth oxide if present is one or more of Eu, Gd, Pr, Yb, Nd, La and Ce.
- 36. The method of claim 35, wherein the actinide oxide if present is one or more of the uranium and the transuranic oxides.
- 37. The method of claim 36, wherein each of the anode and cathode operate at their maximum reaction rate with each being maintained at substantially constant voltage with respect to the third electrode.
- 38. The method of claim 37, wherein the third electrode is Li and the electrolyte includes LiCl.
- 39. The method of claim 38, wherein the third electrode operates as an anode at the start of cell operation and as a cathode at the end of cell operation.
- 40. An electrochemical cell comprising an anode at which oxygen evolves during cell operation; a metal oxide cathode; a halide salt electrolyte molten during cell operation having a cation selected from one or more of the alkali metals, the alkaline earth metals, the eutectics and mixtures thereof; a third electrode of an alkali metal or an alkaline earth metal or mixtures or alloys thereof wherein at least one constituent of the third electrode is the same as at least one cation in the electrolyte; and independent power supplies connecting said anode and said third electrode and connecting said cathode and said third electrode, whereby upon cell operation the third electrode operates sequentially as an anode and as a cathode during reduction of the metal oxide cathode to produce the metal while said independent power supplies maintain substantially constant voltage between said anode and said third electrode and between said cathode and said third electrode.
- 41. The electrochemical cell of claim 40, wherein the anode is gold.
- 42. The electrochemical cell of claim 40, wherein the metal oxide is one or more of the oxides of the actinides.
- 43. The electrochemical cell of claim 40, wherein the metal oxide is one or more of the rare earth oxides.
- 44. The electrochemical cell of claim 40, wherein the electrolyte includes LiCl and the third electrode includes lithium.
- 45. The electrochemical cell of claim 40, wherein the third electrode is a metal sponge having an alkali metal contained therein.
- 46. The electrochemical cell of claim 40, and further including a gas sparging device for transmitting evolved oxygen out of said cell.
- 47. An electrochemical cell comprising an anode at which oxygen evolves during cell operation; a gas sparging device associated with said anode to conduct evolved oxygen away from the cell; a metal oxide cathode including one or more oxide of the actinides and rare earths; a salt electrolyte containing lithium chloride molten during cell operation; a spacially confined third electrode including lithium; and independent power supplies connecting said anode and said third electrode and connecting said cathode and said third electrode, whereby upon cell operation the third electrode operates sequentially as an anode and as a cathode during reduction of the metal oxide cathode to produce the metal while said independent power supplies maintain substantially constant voltage between said anode and said third electrode and between said cathode and said third electrode and oxygen is conducted out of said cell.
- 48. A method of electrochemically reducing a metal oxide to the metal in an electrochemical cell in which each of the anode and cathode operate at their respective maximum reaction rates depending on cell operating conditions including applied voltage and cell materials and cell geometry, said method comprising providing an electrolyte that will support the anodic and cathodic reactions, providing an anode at which oxygen can be evolved, providing a cathode including a metal oxide to be reduced, providing a third electrode that substitutes for either the metal oxide cathode or the oxygen evolving anode as required, providing a power supply connecting the anode and the third electrode, and providing a power supply connecting the cathode and the third electrode, whereby establishing and independently controlling voltage potentials between the third electrode and each of the anode and the cathode permits reduction of the metal oxide the metal without either the anode reaction rate or the cathode reaction rate being limited by the other, resulting in substantially complete reduction of the metal oxide.
CONTRACTUAL ORIGIN OF THE INVENTION
[0001] The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S. Department of Energy (DOE) and The University of Chicago representing Argonne National Laboratory.