Tungsten and vanadium separation

1. A method of separating vanadium and tungsten, comprising:

treating an aqueous solution comprising vanadium and tungsten with a reducing agent to reduce pentavalent vanadium to give a treated aqueous solution,

wherein the reducing agent is selected from the group consisting of zinc, oxalic acid, iron, and sulfur dioxide, and

mixing the treated aqueous solution with an organic solvent to form a loaded organic layer comprising 50% by weight or more of the tungsten in the aqueous solution and an aqueous raffinate having an equilibrium pH of less than about 3 and comprising 50% by weight or more of the vanadium in the aqueous solution,

wherein the organic solvent comprises a diluent and an extractant, wherein the extractant comprises a tertiary or secondary amine; and

separating the loaded organic layer and the aqueous raffinate.

2. The method of claim 1 , wherein the aqueous solution is acidic.

3. The method of claim 1 , wherein the pH of the treated aqueous solution is 0 to 5 or 0 to 3.

4. The method of claim 2 , further comprising adjusting the pH of the aqueous solution or the treated aqueous solution by adding an acid to the aqueous solution or the treated aqueous solution.

5. The method of claim 1 , wherein the aqueous solution comprises spent deNOx catalyst leach solution.

6. The method of claim 1 , wherein the concentration of vanadium in the aqueous solution is 0.1 g/L or greater and the concentration of tungsten in the aqueous solution is 1.5 g/L or greater; or the concentration of vanadium in the aqueous solution is 0.5 g/L or greater and the concentration of tungsten in the aqueous solution is 7.5 g/L or greater, or the concentration of vanadium in the aqueous solution is 0.1 to 10 g/L and the concentration of tungsten in the aqueous solution is 1.5 to 150 g/L tungsten.

7. The method of claim 1 , wherein the organic solvent further comprises a phase modifier.

8. The method of claim 1 , wherein the extractant is selected from the group consisting of trioctylamine, tri-isooctylamine, and combinations thereof.

9. The method of claim 1 , wherein the diluent comprises a hydrocarbon.

10. The method of claim 1 , wherein the diluent comprises kerosene.

11. The method of claim 7 , wherein the phase modifier is an alcohol or a phosphate.

12. The method of claim 1 , further comprising subjecting the loaded organic layer to further purification treatment to give a tungsten-enriched material.

13. The method of claim 12 , wherein the further purification treatment comprises stripping the loaded organic layer by contacting the loaded organic layer with an aqueous stripping solution to give a strip raffinate comprising the tungsten.

14. The method of claim 13 , wherein the aqueous stripping solution comprises ammonium hydroxide.

15. The method of claim 13 , wherein the further purification treatment further comprises scrubbing the loaded organic layer prior to stripping by mixing the loaded organic layer with an aqueous scrubbing solution to give a scrubbed organic comprising the tungsten.

16. The method of claim 15 , wherein the aqueous scrubbing solution comprises hydrochloric acid, sulfuric acid, or a combination thereof.

17. The method of claim 12 , wherein, following the further purification treatment, the tungsten-enriched material comprises 25% by weight or less of the vanadium in the aqueous solution; 15% by weight or less of the vanadium in the aqueous solution; or 5% by weight or less of the vanadium in the aqueous solution.

18. The method of claim 12 , wherein the further purification treatment comprises removal of at least a portion of any impurities in the loaded organic layer, wherein the impurities are selected from the group consisting of zinc, molybdenum, aluminum, calcium, chromium, iron, magnesium, manganese, sodium, phosphorus, sulfur, silicon, titanium, zirconium, and combinations thereof.

19. The method of claim 18 , wherein the further purification treatment further comprises a concentrating step to give the tungsten-enriched material, wherein the tungsten-enriched material comprises 15% by weight or less of the impurities or 5% by weight or less of the metal impurities.

20. The method of claim 1 , further comprising treating the aqueous raffinate to give a vanadium-enriched material.

21. The method of claim 20 , wherein the treating comprises mixing the aqueous raffinate with a phosphoric acid-containing extractant to give the vanadium-enriched material.

22. The method of claim 21 , wherein the phosphoric acid-containing extractant comprises diethylhexyl phosphoric acid.

23. The method of claim 1 , wherein the aqueous solution comprises:

an aqueous pregnant leach solution arising from the alkaline digestion of spent DeNOx catalyst, comprising vanadium and tungsten;

and wherein the method comprises:

modifying the pH of the aqueous solution to provide an acidic aqueous solution;

treating the acidic aqueous solution with a reducing agent to reduce pentavalent vanadium, giving the treated aqueous solution;

mixing the treated aqueous solution with an organic solvent to give the loaded organic layer and the aqueous raffinate;

separating the loaded organic layer and the aqueous raffinate;

contacting the loaded organic layer with an aqueous scrubbing solution to give a scrubbed organic;

contacting the scrubbed organic with an aqueous stripping solution to give a stripping raffinate; and

concentrating the stripping raffinate to provide a tungsten-enriched material, wherein the tungsten-enriched material comprises 50% by weight or more of the tungsten in the pregnant leach solution and 50% by weight or less of the vanadium in the pregnant leach solution.

24. The method of claim 1 , wherein the aqueous solution comprises an aqueous pregnant leach solution arising from the alkaline digestion of spent DeNOx catalyst.

25. The method of claim 1 , wherein the pH of the treated aqueous solution is less than about 0.5.