Patent Number: 042345553
Section: description

EXAMPLE I The invention was tested by mixing selected quantities of particulate CaF.sub.2 in six 0.200-liter samples of an aqueous HF solution containing 120 ppm uranium. The solution comprised 20 wt-% HF. The CaF.sub.2 powder was acid-grade fluorspar, manufactured by Allied Chemical Corporation. This powder had a nitrogen surface area of 1.6 m.sup.2 /g (based on the well-known B.E.T. measurement). Tyler-sieve data for the powder were as follows: 45% of the powder passed through a 325-mesh screen and 15% was retained by the screen; 27% was retained on a 200-mesh screen; 9% was retained on a 100-mesh screen; and 4% was retained on a 65-mesh screen. Each of the samples containing particulate CaF.sub.2 was stirred at room temperature for an hour. Following stirring, the resulting slurries were either filtered promptly or the supernate was separated by decanting. The resulting solutions were analyzed for uranium by gamma-spectrometry and for calcium by atomic absorption. The accompanying table shows the CaF.sub.2 -to-uranium weight ratios employed in each of the six tests, together with the results obtained. It will be noted that removal of 50% of the uranium was accomplished at a CaF.sub.2 /U ratio of 8 and that removal of 92% of the uranium was accomplished at ratios exceeding 37. As shown, the product solutions contained very little calcium--only 9 ppm if the solution was not filtered, and less than 0.2 ppm if it was filtered. Thus, the process was found to remove uranium effectively while avoiding contamination of the product solution. __________________________________________________________________________ Lbs CaF.sub.2 Initial Final Final Sample per 13,500 CaF.sub.2 /U U Conc., U Conc., U Removal, Ca.sup.++ Conc., No. Gal. Solution by Weight ppm ppm % ppm __________________________________________________________________________ 1 56 4 120 72 40 &lt;0.2 2 84 6 120 71 41 &lt;0.2 3 112 8 120 60 50 &lt;0.2 4* 112 8 120 59 51 9 5 500 37 120 10 92 &lt;0.2 6 1000 74 120 10 92 &lt;0.2 __________________________________________________________________________ *Sample 4 was allowed to stand overnight before decanting. All other samples were filtered before analysis. EXAMPLE II A 67,000-pound batch of aqueous 20%-HF solution containing 74 ppm uranium was admitted to a railroad tank car which previously had been used to recover uranium in accordance with this invention. The rubber-linked tank contained a heel of CaF.sub.2 /U slurry remaining from the previous recovery operation. The tank car was provided with means for sparging with air. With the sparging means energized, approximately 400 pounds of particulate CaF.sub.2 (identified in Example I) was added to the solution to provide a total CaF.sub.2 /U weight ratio of 159 to 1. After three days of air agitation and then four hours of sedimentation (both conducted at room temperature), the solution was analyzed. The analysis was as follows: HF, .about.20 wt-%, uranium, 7 ppm; calcium, &gt;0.2 ppm. Following analysis, the solution was decanted for sale. As indicated above, this method for recovery of uranium has significant advantages. For example, it entails comparatively simple process operations and requires only readily available equipment. Again, uranium removal is effected without introducing a contaminant into the product solution. Furthermore, a wide variety of CaF.sub.2 powders may be employed, such as powders having nitrogen surface areas in the range of from about 1 to 200 m.sup.2 /g. The method is believed effective for reducing the uranium content of both dilute and concentrated aqueous HF solutions containing a trace amount of uranium. By "trace amount" is meant in the range of from a few ppm to thousands of ppm. In general, appreciable uranium carry-down may be obtained if the CaF.sub.2 /U weight ratio is in the range of from about 8 to 75. It will be understood that the process parameters cited in Examples I and II, above, are not necessarily the optimum. For example, even higher percentages of uranium might have been removed if the runs had been conducted with (a) higher-surface-area CaF.sub.2, (b) a tank having a more suitable geometry with respect to mixing, or (c) more efficient mixing means--e.g., a propeller-type mixer. Given the teachings herein, one versed in the art will be able to determinne the preferred process parameters (e.g., CaF.sub.2 powder surface areas, CaF.sub.2 /U weight ratios) for a given application of this invention by merely routine experimentation, as by testing on a laboratory scale. The foregoing examples are provided for the purpose of illustration only, and it will be understood that the scope of the invention is to be interpreted in terms of the following claims.