Recovery of uranium from a mixture of western uranium ore and phosphate rock

An otherwise unusable western sandstone uranium ore is blended with uranium-containing phosphate rock. The mixture is then digested with sulfuric acid to produce a wet process phosphoric acid solution containing higher levels of uranium. Recovery of the uranium values from this solution can be effected by various known processes such as solvent extraction.

The mining of phosphate rock such as that found in Florida and many 
countries of the world, e.g., Morocco has as its prime objective the 
production of phosphate-containing fertilizer. In one widely used process, 
the phosphate values are recovered from the rock by digestion with 
sulfuric acid to produce a phosphoric acid solution (called wet process 
phosphoric acid) and an insoluble calcium sulfate (gypsum). Phosphate rock 
may contain significant quantities of uranium, e.g., on the order of from 
about 0.1 to 0.5 pounds of uranium per ton of phosphate rock mined and 
more generally within the range of about 0.2 to about 0.4 pounds per ton. 
During the digestion step the uranium values are solubilized resulting in 
a uranium concentration (expressed as U.sub.3 O.sub.8) in the wet-process 
phosphoric acid of from about 0.05 to about 0.3 grams per liter and more 
generally from about 0.15 to about 0.25 grams per liter. 
Attempts to recover uranium values from wet-process phosphoric acid have 
centered on the use of solvent extraction processes in which the uranium 
values are transferred to an organic phase, stripped from the organic 
phase and subsequently recovered as a uranium precipitate. The 
uranium-free wet-process phosphoric acid is then processed conventionally 
to form various phosphate-containing fertilizer products. 
The uranium solvent extraction process which has generated the most 
commercial interest is the so-called reductive stripping extraction 
process developed by Oak Ridge National Laboratories (ORNL). See Hurst, 
U.S. Pat. No. 3,711,581; Hurst, et al, "Recovery of Uranium from 
Wet-Process Phosphoric Acid", I & EC Process Design and Development, Vol. 
II, p. p. 122-128, January 1972; Hurst et al, "Recovering Uranium from 
Wet-Process Phosphoric Acid", Chemical Engineering, Jan. 3, 1977, p. 
56-57; See also, Hurst et al, ORNL-TM-2522 (1969) and Hurst et al, 
ORNL-2952 (1960). The ORNL process as described in the Hurst '591 patent 
employs a synergistic extraction mixture of di(2-ethylhexyl)phosphoric 
acid (DEPA) and trioctylphosphine oxide (TOPO) dissolved in an organic 
diluent. This extraction mixture is known to have a high affinity for 
uranium in the hexavalent oxidation state. 
A more widely utilized uranium source is western uranium ores. These ores 
are primarily sandstone in nature and contain uranium in various mineral 
forms. Western sandstone ores may contain as much as 1.0% uranium 
(expressed as U.sub.3 O.sub.1) but generally contain from about 0.1% to 
about 0.3% uranium oxide. Most large deposits of these ores are processed 
on or near the mine site to minimize transportation of the sandstone 
gangue. In some instances, however, sandstone ore deposits may be either 
too small or too remotely located to justify the construction of a full 
scale recovery system. Moreover, some otherwise high grade ore deposits 
cannot be processed in the conventional western uranium mills because of 
high impurity levels. Ores with high humate or carbonate concentrations 
are particularly troublesome in these systems. 
The present invention is based on the discovery that uranium can be more 
efficiently and economically recovered by blending a small amount of high 
U.sub.3 O.sub.8 western sandstone ore with phosphate rock and processing 
the resulting blend in a conventional phosphoric acid facility having a 
uranium recovery operation. The use of such an approach not only markedly 
improves the economics of uranium recovery from phosphate rock, but also 
provides for the recovery of uranium from western sandstone ores which for 
various reasons were not previously utilized at all. 
The process of the present invention comprises the steps of forming a 
mixture comprising uranium-containing phosphate rock and western uranium 
ore; digesting the mixture with a sulfuric acid solution to produce a 
uranium-containing solution of phosphoric acid; and recovering the uranium 
values from the phosphoric acid solution. 
In the practice of the present invention any of the conventional western 
sandstone uranium ores may be employed. As indicated above, the preferred 
sources of western ores are deposits which are either too small or too 
remote for on-site processing, or which cannot be easily processed via 
western ore techniques due to high impurity levels. 
The first step of the process of the present invention comprises blending 
the uranium ore with phosphate rock. The components of this blend can be 
sized, e.g., by grinding, before or preferably after the blending step to 
a particle size normally employed in conventional phosphate rock 
processing. Phosphate rock feed material is generally ground to a particle 
size of about 60%-200 mesh with up to about 5% plus 35 mesh. Rock 
comprising a majority of particles in the -100 to -200 mesh range can be 
employed. The amount of U.sub.3 O.sub.8 ore added to the mixture can vary 
widely depending on the particular ore being processed, the nature and 
capacity of the phosphoric acid recovery facility, the economic incentives 
present and numerous other factors such as regulatory limits. Any 
proportion of uranium ore which is suitable under the specific processing 
conditions being utilized can be employed according to the present 
invention. In most circumstances it is preferred to employ a blend 
comprising a major portion of phosphate rock and a minor portion of 
uranium ore. In a typical phosphate acid facility of the type found in 
Florida, amounts of up to about 200 lbs of U.sub.3 O.sub.8 ore per ton of 
phosphate rock generally may be employed. The practical upper limit of 
U.sub.3 0.sub.8 or content it these plants as presently constituted is 
largely dependent on the filtration capacity of the facility. Preferred 
are U.sub.3 O.sub.8 ore additions in the range of from about 10 to about 
100 lbs per ton of phosphate rock. Most preferred is an ore addition of 
about 50 lbs/ton of phosphate rock. 
The next step in the process of the present invention is digestion of the 
U.sub.3 O.sub.8 -phosphate rock mixture with sulfuric acid. The presence 
of a minor amount of U.sub.3 O.sub.8 ore in the phosphate rock feed does 
not interfere with any of the digestion methods employed in typical 
phosphoric acid facilities. Therefore the parameters of digestion such as 
contact time, temperature, acid concentration, etc. are not critical and 
those values normally employed for phosphate rock alone may be utilized. 
Typically the acid concentraion is adjusted to give a P.sub.2 O.sub.5 
content in the filtrate of about 28-32%. Digestion temperatures will 
usually run from about 170.degree.-180.degree. F. and normal contact times 
run from about 10 to 16 hours. It is preferred to operate the digestion 
step under oxidizing conditions to ensure the oxidation of uranium values 
present. 
After the mixture of U.sub.3 O.sub.8 ore and phosphate rock has been 
completely digested, the resulting P.sub.2 O.sub.5 solution, which 
contains most of the uranium values, is separated from the reaction 
solids--i.e., gypsum. Conventional phosphoric acid filtration systems may 
be employed to effect the separation. 
The resulting crude wet process phosphoric acid stream will contain a 
higher amount of uranium per ton of P.sub.2 O.sub.5 than that normally 
associated with wet-process phosphoric acid. The increased concentration 
of uranium in the phosphoric acid stream results in higher uranium yields 
than presently possible from phosphate rock and, therefore, makes the 
economics of uranium recovery from phosphoric acid more attractive. 
Typically, phosphoric acid solutions processed according to the preferred 
embodiments of the process of the present invention can contain from about 
0.25 to about 0.5 g/l of U.sub.3 O.sub.8 or more depending on the amount 
of U.sub.3 O.sub.8 ore added and the concentration of U.sub.3 O.sub.8 in 
the ore. 
The uranium may be recovered from the wet process phosphoric acid by any of 
the known techniques. The preferred manner of recovery is based on solvent 
extraction techniques. A particularly preferred process is that described 
in commonly assigned U.S. patent application Ser. No. 22,079 entitled 
"Recovery of Uranium from Wet-Process Phosphoric Acid" filed on March 19, 
1979 in the names of the Berry and Henrickson. 
The following example is intended to illustrate more fully the nature of 
the present invention without acting as a limitation on its scope.

EXAMPLE 
The uranium ore used in this example was a western sandstone ore having the 
following approximate analysis: 
______________________________________ 
Weight Percent 
______________________________________ 
U.sub.3 O.sub.8 
0.151 
V.sub.2 O.sub.5 
1.00 
Cu 0.0006 
CO.sub.2 1.9 
______________________________________ 
This ore was ground to 60%-200 mesh and blended with ground phosphate rock 
at the rate of 20 lbs of ore per ton of phosphate rock. The blended 
mixture was then digested with a mixture of H.sub.2 SO.sub.4 and water 
sufficient to produce a filtrate of approximately 28% P.sub.2 O.sub.5, 
with a free H.sub.2 SO.sub.4 content of about 2%. Air was sparged through 
the digestion slurry to ensure uranium oxidation. The temperature during 
the reaction was maintained in the range of about 80.degree.-90.degree. F. 
After the reaction was complete the slurry was filtered to remove gypsum 
and the first filtrate was collected for uranium recovery. This phosphoric 
acid solution has a uranium content, expressed as U.sub.3 O.sub.8, of 
about 0.2 g/l. Results indicate that generally, over 90% of the U.sub.3 
O.sub.8 added to the acid via the sandstone is dissolved into the 
phosphoric acid stream. 
While certain specific embodiments of the invention have been described 
with particularity herein, it will be recognized that various 
modifications thereof will occur to those skilled in the art. Therefore, 
the scope of the invention is to be limited solely by the scope of the 
appended claims.