Patent Number: 
Section: claims

1. A method of immobilizing uranium (VI) in a subsurface environment, comprising: adding a solution containing a monovalent or divalent cation and vanadium (V) to a subsurface environment contaminated with uranium (VI), wherein a precipitate comprising said uranium (VI) is formed in the subsurface environment. 2. The method of claim 1, further comprising the step of removing the precipitate from the subsurface environment. 3. The method of claim 1, wherein the precipitate comprises a uranyl vanadate. 4. The method of claim 1, further comprising the step of adjusting the pH of the subsurface environment to between about pH 5.5 and 6.5. 5. The method of claim 1, further comprising the step of removing the precipitate from the subsurface environment. 6. The method of claim 1, further comprising the step of adjusting the pH of the subsurface environment to between about pH 4.5 and 8.5. 7. The method of claim 6, wherein the cation solution comprises a monovalent cation selected from the group consisting of potassium, lithium, rubidium and cesium. 8. The method of claim 6, wherein the cation solution comprises the monovalent cation potassium. 9. The method of claim 8, wherein the pH of the subsurface environment is adjusted to between about 5.5 and 6.5. 10. The method of claim 8, wherein the pH of the subsurface environment is about 6, the ratio of the concentration of vanadium to uranium is greater than or equal to about 50:1, and the ratio of the concentration of potassium to uranium is greater than or equal to about 10000:1. 11. The method of claim 8, wherein the pH of the subsurface environment is about 8 and the ratio of vanadium concentration to uranium concentration is greater than 5:1. 12. The method of claim 6, wherein the cation solution comprises a divalent cation selected from the group consisting of calcium, strontium and barium. 13. The method of claim 6, wherein the cation solution comprises the divalent cation calcium. 14. The method of claim 13, wherein the pH of the subsurface environment is adjusted to between about 5.5 and 6.5. 15. The method of claim 6, wherein the subsurface environment is also contaminated with vanadium and wherein the ratio of the concentration of vanadium to uranium in the subsurface environment is less than or equal to about 1:1. 16. The method of claim 15, wherein the cation solution comprises a monovalent cation selected from the group consisting of potassium, lithium, rubidium and cesium. 17. The method of claim 15, wherein the cation solution comprises a divalent cation selected from the group consisting of calcium, strontium and barium. 18. A method of treating sediment contaminated with U(VI) and V(V) comprising:(a) providing a sediment comprising uranium and vanadium; and,(b) mixing said sediment with an aqueous solution comprising a monovalent or divalent cation, wherein a precipitate comprising uranyl vanadate is formed; and,(c) further comprising mixing the sediment with a solution comprising vanadium prior to mixing the solution comprising a monovalent or divalent cation, wherein the ratio of the concentration of vanadium to uranium in the sediment is less than or equal to about 1:1.