Separating rare earth metal oxalates

1. A method of separating at least one light rare earth metal oxalate that includes at least one of La through Sm of the Periodic Table from at least one other metal oxalate comprising at least one of a transition metal oxalate and a heavy rare earth metal oxalate that includes at least one of Gd though Lu of the Periodic Table without using mineral acid, wherein the method comprises providing the at least one light rare earth metal oxalate and the at least one other metal oxalate in an aqueous solution comprising oxalic acid and an organic base that is selected from the group consisting of N-containing organic base, P-containing organic base, and S-containing organic base and having a pH of 6 to 8 without inorganic base present to form an aqueous separation solution in which the at least one light rare earth metal oxalate is insoluble and selectively separates out of the aqueous separation solution as an insoluble residue and the at least one other metal oxalate is soluble and remains in the aqueous separation solution, thereby separating the at least one light rare earth metal oxalate from the at least one other metal oxalate in the aqueous separation solution without use of mineral acid.

2. The method of claim 1 wherein the at least one other metal oxalate includes different heavy rare earth metal oxalates wherein the heavy rare earth oxalates include at least two of Gd through Lu of the Periodic Table of Elements.

3. The method of claim 2 wherein the different heavy rare earth metal oxalates include at least one of Gd, Tb, and Dy and at least one of Tm, Yb, and Lu.

4. The method of claim 1 wherein said at least one other metal oxalate comprises a transition metal oxalate.

5. The method of claim 4 wherein the transition metal oxalate comprises at least one of cobalt oxalate, nickel oxalate, iron oxalate, copper oxalate, zirconium oxalate, and zinc oxalate.

6. The method of claim 1 wherein the said at least one light rare earth metal oxalate comprises Sm oxalate and the said at least one other metal oxalate comprises Co oxalate.

7. The method of claim 1 wherein the oxalic acid comprises 30 to 40 mole % and the organic base comprises 60 to 70 mole % of the aqueous solution.

8. The method of claim 1 wherein the organic base comprises 1-methylimidazole.

9. A method of purifying an impure oxalate mixture, comprising providing at least one rare earth metal oxalate and at least one transition metal oxalate impurity and in a mineral acid-free aqueous solution comprising oxalic acid and an organic base that is selected from the group consisting of N-containing organic base, P-containing organic base, and S-containing organic base and having a pH of 6 to 8 without inorganic base present to form an aqueous separation solution in which the at least one rare earth metal oxalate is insoluble and selectively separates out of the aqueous separation solution as an insoluble residue and the at least one transition metal oxalate impurity is soluble in the aqueous separation solution and remains in the aqueous separation solution, wherein the insoluble residue as dried consists essentially of at least 98% purity by weight of said at least one rare earth metal oxalate, thereby separating the at least one rare earth metal oxalate and the transition metal oxalate impurity in the aqueous separation solution without use of mineral acid.

10. The method of claim 9 wherein the at least one rare earth metal oxalate comprises an oxalate including at least one of La, Ce, Pr, Nd, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y.

11. The method of claim 9 wherein the at least one transition metal oxalate impurity comprises at least one of cobalt oxalate, nickel oxalate, iron oxalate, copper oxalate, zirconium oxalate, and zinc oxalate.

12. The method of claim 9 wherein the at least one transition metal impurity comprises 8 weight % or less of the impure mixture.

13. The method of claim 9 wherein the impure oxalate mixture is obtained from at least one of waste material from production of permanent magnets, waste material from the production of electrical components, ore containing a rare earth metal and a transition metal, and ore tailings containing a rare earth metal and a transition metal.

14. In a solvent extraction method of rare earth metals wherein rare earth metal oxalates are preformed as a mixture comprising at least one light rare earth metal oxalate that includes at least one of La through Sm of the Periodic Table and at least one other metal oxalate that comprises at least one of a transition metal oxalate and a heavy rare earth metal oxalate that includes Gd through Lu of the Periodic Table the subsequent step of separating the at least one light rare earth metal oxalate from the mixture by a mineral acid-free one-step separation process comprising mixing the mixture and an aqueous solution of oxalic acid and organic base that is selected from the group consisting of N-containing organic base, P-containing organic base, and S-containing organic base and having a pH of 6 to 8 without inorganic base present to form an aqueous separation solution in which the at least one light rare earth metal oxalate is insoluble and selectively separates out of the aqueous separation solution as an insoluble residue and the at least one other metal oxalate is soluble and remains in the aqueous separation solution, thereby separating the at least one light rare earth metal oxalate from the at least one other metal oxalate in the aqueous separation solution without use of mineral acid.

15. The method of claim 14 wherein the heavy rare earth metal oxalate includes at least two of Gd through Lu of the Periodic Table of Elements.

16. The method of claim 15 wherein the heavy rare earth metal oxalate includes at least one of Gd, Tb, and Dy and at least one of Tm, Yb, and Lu.

17. The method of claim 14 wherein the oxalic acid comprises 30 to 40 mole % and the organic base comprises 60 to 70 mole % of the aqueous solution.