Patent Number: 042345553
Section: summary

This invention was developed in response to a need for a simple but effective method for decreasing the uranium content of a large volume of by-product aqueous hydrofluoric acid contaning uranium in the parts-per-million range. The acid solution comprised about 20 wt-% HF and 76 ppm uranium (uranium species in solution not known). Sale of the solution on the open market required that its uranium concentration be decreased below 10 ppm by some technique which would not introduce additional impurities into the product solution. An attempt was made to decrease the uranium content of the solution by passing it over amorphous carbon maintained at 350.degree.-450.degree. C. This decreased the uranium content by only 64%. In another approach, the solution was passed through an anion exchange column of the hydroxide type. This decreased the uranium concentration by only 32%. Various other removal techniques were considered but rejected as impractical. Various publications describe the adsorption of uranium from solutions by selective adsorption. The following is an example of such a publication: Minhai Dai and Shaw-Chii Wu, "Adsorption of Uranium from Dilute Aqueous Solution on Inorganic Adsorbents," Separation Science, 10(5), pp. 633-638 (1975). That paper described recommends adsorbing uranium with a mixture of aluminum hydroxide, ferric hydroxide, and activated carbon. It also describes experiments conducted with various alkaline earth oxides, hydroxides, and sulfates as adsorbents. OBJECTS OF THE INVENTION Accordingly, it is an object of this invention to provide a novel method for decreasing the uranium content of aqueous hydrofluoric acid containing trace amounts of uranium in solution. It is another object to provide a simple and effective method for decreasing the uranium content of a uranium-bearing aqueous HF solution without introducing a contaminant into the product solution. Other objects will be made evident hereinafter. SUMMARY OF THE INVENTION This invention may be summarized as being a method of decreasing the uranium content of an aqueous HF solution containing uranium, said method comprising mixing particulate calcium fluoride with said solution to form uranium-bearing particulates; permitting said particulates to sediment from said solution; and separating the resulting solution from the sedimented particulates. BACKGROUND OF THE INVENTION This invention is generally applicable to the recovery of uranium from aqueous HF solutions containing the same. It is based on our finding that intimately contacting such solutions with particulate CaF.sub.2 and then sedimenting the particulates effects removal of much of the uranium. That is, uranium is carried down out of solution by the sedimented CaF.sub.2 particles. The resulting solution then is separated from the sedimented, uranium-bearing particulates by any suitable technique. The mechanism by which the uranium is carried down is not yet well understood. So far as is known, this process has not been reported previously. It is clear from the very low solutility of CaF.sub.2 in aqueous solutions that the well-known common-ion effect is not involved here. If the uranium is in solution as UF.sub.4 and no ionization has occurred, then the solubility-product principle would not be governing the carry-down of uranium. If the uranium is present as UO.sub.2 F.sub.2, the solubility of this species is too high to account for the carry-down of uranium when present in trace quantities.