Methods and apparatus for processing of rare earth metal ore
In one aspect, the present invention is directed to methods for extracting rare earth metals from ores comprising reduction of rare earth metal oxyfluorides. In another aspect, the invention relates to an apparatus for extracting rare earth metals from ores comprising reduction of rare earth metal oxyfluorides. The methods and apparatuses described herein generate rare earth metals from ores with reduced requisite pre-removal of metal oxides found as natural impurities in ores.
1. A method of extracting rare earth metal from mixtures comprising rare earth metal compounds, the method comprising:
providing a first molten salt mixture comprising a group II fluoride and a rare earth metal fluoride present in a first ratio;
continuously providing a feedstock mixture comprising a rare earth metal oxyfluoride and a group II oxide present in a second ratio, the second ratio being such that chemical conversion of the rare earth metal oxyfluorides and group II oxides to rare earth oxides, group II fluorides, and rare earth fluorides generates group II fluorides and rare earth metal fluorides in about the same ratio as the first ratio;
combining the first molten salt mixture and the feedstock mixture to form a reaction mixture, the reaction mixture comprising oxide ions;
providing a first cathode in electrical contact with the reaction mixture;
providing an anode, wherein the anode is in ion-conducting contact with an oxide ion-conducting membrane, and the oxide ion-conducting membrane is in ion-conducting contact with the reaction mixture;
generating a potential between the anode and the first cathode to reduce the metallic species of the rare earth metal oxyfluoride at the first cathode, transport oxide ions across the oxide ion-conducting membrane, and oxidize the oxide ions at the anode; and
collecting the reduced rare earth metallic species.
2. The method of claim 1 , further comprising providing a second molten salt, the second molten salt being in ion-conducting contact with the oxide ion-conducting membrane and the anode, the second molten salt not being in physical contact with the first molten salt.
3. The method of claim 2 , wherein the first molten salt mixture is at least about 90% liquid.
4. The method of claim 3 , wherein the first molten salt is at least about 95% liquid.
5. The method of claim 1 , wherein the first molten salt further comprises lithium fluoride.
6. The method of claim 1 , wherein the group II fluoride and the rare earth fluoride are at the eutectic composition.
7. The method of claim 1 , wherein the rare earth metal oxyfluoride and at least a portion of the group II oxide is present in a same ore.
8. The method of claim 1 , further comprising providing a second cathode to reduce a second rare earth metallic species.
9. The method of claim 8 , wherein a first potential is applied between the anode and the first cathode, followed by application of a second potential between the anode and the second cathode.
10. The method of claim 1 , wherein the rare earth metal oxyfluoride includes calcined bastnäsite.
11. The method of claim 1 , wherein the group II oxide comprises calcium oxide, barium oxide, or strontium oxide, or any combination thereof.
12. The method of claim 1 , wherein the group II fluoride comprises calcium fluoride, barium fluoride, or strontium fluoride, or any combination thereof.
13. The method of claim 1 , wherein the ion-conducting membrane comprises zirconia.
14. The method of claim 1 , wherein the providing a feedstock mixture comprises:
determining a third ratio of a rare earth metal oxyfluoride to a group II oxide present in a raw metal source mixture; and
adjusting the third ratio of the rare earth metal oxyfluoride to the group II oxide present in the raw metal source mixture to obtain the second ratio.
15. The method of claim 14 , wherein the adjusting includes adding material comprising group II oxides.
16. The method of claim 14 , wherein the adjusting includes removing at least a portion of group II oxides.