US2992891A - Treatment of uranium containing carbonaceous materials - Google Patents

Description

United States Patent Ofice Patented July 18, 1961 2,992,891 TREATMENT OF CONTAINING CA'RBONACEOUS MATERIALS Frederick B. Sellers, Tarrytown, N.Y., assignor to Texaco Development Corporation, New York, N.Y., a corporation of Delaware a No Drawing. Filed Dec. 22, 1958, Ser. No. 781,899

7 Claims. (Cl. 2314.5)

This invention relates to the recovery of uranium from carbonaceous fuels containing uranium. In one of its more specific aspects, it is directed to a process for the generationof a gas comprising carbon monoxide and hydrogen and concomitantly recovering uranium from a uranium containing carbonaceous fuel wherein said carbonaceous fuel is incompletely reacted with an oxygen containing gas under reducing conditions, a composite solid comprising noncombustible solid and unconverted carbon is separated, said solid composite is treated under oxidizing conditions with an ammonium fluoride efiecting formation of volatile uranyl ammonium pentafluoride, and separating vapor comprising uranyl ammonium pentafluoride from a solid residue.

Various uraniferous fossil carbonaceous fuel deposits are known, notable among which are those occurring in the Black Hills section of the Dakotas and Montana where ore grade uraniferous lignite exists in commercial quantities. The US. Atomic Energy Commission has defined commercial quality uranium ore as a material with a minimum uranium content of A of 1 percent U 0 Uranium concentrations in lignite deposits are known in which the concentration of uranium is several times the minimum set by ABC. Some coal deposits, particularly in the western part of the United States, contain com mercial quantities of uranium. These coals generally are low grade bituminous coals. Certain oil shales are also known'to contain commercial quantities of uranium. Some of the oil shales in Sweden, for example, are reported to contain on the order of 0.5 percent uranium.

The process of this invention is applicable to therecovery of uranium from various carbonaceous materials, for example coal, lignite and oil shale, which contain a suificient fuel value to support combustion. Although the occurrence of uranium in liquid carbonaceous fuels, for

example petroleum, is less common, the process of this invention is applicable to liquid fuels which may containilranium. In accordance with this invention, the carbonaceous material is reacted with a limited amount of free oxygen at a temperature above about 1800 F. in proportions elfective for the conversion of a major portion of the carbon content of the material to carbon monoxide. Hydrogen is usually present 'in the fuel, and moisture or steam is naturally present or may be added thereto. As a result, hydrogen is'also produced with the carbon monoxide.

The reaction of the carbonaceous content of the fuel with a controlled amount of oxygen results in concen tration of uranium in the solid residue. Partial oxidation of carbonaceous fuel is effected by reacting the fuel, in disperse phase or suspension, with oxygen in an unpacked, "compact reaction zone at an au-togenous temperature therange of about 1200 to 3500 F. and preferably within the range of 22100 to 3200 Air, oxygen enriched air, or substantially pure oxygen may be used; substantially pure oxygen is preferred; In addition'to oxygen or air, an endothermitireactant, such as stream or carbon dioxide, may be added 'to control' the temperature. Steam is generally preferable if an .endothermiereactant is required. The amount of steam required to maintain the temperature within the desired range depends upon the particular fuel supplied tothe combustion zone and the concentration of oxygen in the oxygen-containing gas stream. With some of the lower grade carbonaceous minerals, it may be necessary to add supplemental amounts of fuel. In such cases, it is preferable to employ as an auxiliary fuel a hydrocarbon gas 5 or oil although high carbon low ash content solid fuels may also be used, as for example petroleum coke.

The streams of reactants supplied to the reaction zone preferably are preheated. In general, substantially pure oxygen may be preheated to a temperature up to about 600 F. whereas air may be preheated without difficulty to a considerably higher temperature, for example to a temperature as high as 1200 F. by indirect heat exchange, and to temperatures on the order of 2000 F. by direct heat exchange, e.g., by means of ceramic pebbles. General-1y no preheat is required when substantially pure oxygen is employed, and satisfactory results may often be obtained without preheat of the air, although preheat increases gasification efiiciency and permits operation with lesser amounts of fuel than required without preheat. The steam, mineral and auxiliary fuel, if present, are also preferably preheated, preferably to a temperature within the range of, for example, 600 to 1200 F. The temperatures mentioned as preheat temperatures are illustrative only and are not to be construed as limiting temperatures.

The particle size of the mineral supplied to the reaction zone should be finer than 100 mesh and preferably at least 95 percent through 200 mesh (U.S. standard screen scale). Pulverization of the mineral may be effected by any of the conventional grinding methods. A preferred method of pulverizing the mineral is by fluid energy pulverization, for example as described in U .8. 2,735,787, issued to Du Bois Eastman and Leon P. Gaucher on Process for Pulverizing Solid Materials, dated February 21, 1956. According to the preferred method of pulverizing, the mineral in moderately pulverized form, i.e., particles smaller than about $4" average diameter, are mixed with a vaporizable liquid, suitably water, and passed through an elongated tubular heating zone wherein the liquid is vaporized forming a dispersion of solid panti cles in vapor. The dispersion is subjected to a high degree of turbulence suitably by impingement of. two streams upon one another at velocities above about 60 feet per second and preferably above 300 feet per second effecting disintegration of the particles to powder. Although water is generally the preferred vaporizable liquid, in some instances, for example, those in which the mineral is deficient in fuel value, hydrocarbon liquid may be employed as the sole medium or as a supplement with water. The dispersion of solid particles in vapor may be subjected to a separation step to remove any desired part of the vapor from the solid particles or the entire dispersion may be fed directly into the reaction zone.

Solid particles dispersed in vapor are introduced into the reaction zone wherein they are intimately admixed with oxygen, preferably relatively pure oxygen. Thereaction zone is maintained at a pressure within the range of atmospheric pressure to "1000 p.s.i.g., preferably 100 to 600 p.s.i.g. The resulting gaseous products of partial oxidation and residual solids are cooled substantially instantaneously to a temperature below 1000 F., preferably below 500 F., by direct contact with liquid water. The product gas is separated from the solid residue and may be employed as a source of hydrogen oras a source of synthesis feed gas, for example, for synthesis of hydrocarbons, methanol or ammonia. Preferably, the quantity of water employed in the quench cooling of the gas and residual solid is in excess of the amount vaporized in reducing the temperature from that of the gen erator to the desired quench temperature. Water efiectively removes solid particles from the gas stream. Conventional gas-liquid contact apparatus, or scrubbers, may

be employed to insure complete removal of solid particles from the gas stream. When the residue is in molten form, the generator is preferably arranged to permit the molten residue to drop directly into a pool of quench water. A suitable arrangement of apparatus of this type is shown in the patent to Strasser, 2,701,755, and in the copending application of Du Bois Eastman, Serial No. 525,240, filed July 29, 1955. Under the conditions prevailing in the partial oxidation of carbonaceous fuels to produce carbon monoxide described above, uranium contained in the fuel is reduced to a tetravalent oxidation state and appears in the solid residue in this form.

Uranium is advantageously separated from other'solids by forming a volatile or sublimable uranium compound and separating the uranium as a vapor from a solid residue. 7 Uranium, in hexavalent form may be reacted with an ammonium fluoride, for example ammonium fluoride per se, ammonium bifluoride or reaction mixtures of ammonia and hydrogen fluoride, to form uranyl ammonium pentafluoride (U (NH F which may be readily sublimed.

As noted above, uranium in the solid residue produced by partial oxidation of uranium containing fuels is largely in tetravalent form whereas separation by formation of uranyl ammonium pentafluoride requires the uranium be in hexavalent form. I have found that partial oxidation and uranium recovery by sublimation may be integrated by operating the partial oxidation process with relative proportions of oxygen and fuel such that unconverted carbon appears in the solid residue forming a composite solid comprising non-combustibles and unconverted carbon. The foregoing solid is passed to a kiln or furnace in contact with air and an ammonium fluoride. The carbon in the composite is burned with an excess of air heating the reactants to a temperature of at least 1000 F. and oxidizing the uranium values of the composite to a hexavalent form. At the foregoing temperature, the ammonium fluoride and hexavalent uranium react forming uranyl ammonium pentafluoride in vapor form. The vapor is separated from the solid residue and uranyl ammonium pentafluoride is separated therefrom.

In accordance with the process of this invention the relative proportions of oxygen and fuel for partial oxidation are selected such that the unconverted carbon content of the composite solid residue is within the range of about 2 to about 80 percent, preferably within the range of 5 to 50 percent. The separated composite solid from the generator may be pumped to the oxidizing treating furnace as a slurry of solids in quench Water. The ammonium fluoride may be added to the slurry or may be introduced separately into the oxidizing-treating furnace. Although the composite granules may be passed dlrectly from the partial oxidation to the treating step, if desired, the granules may be subjected to an interposed grinding step.

The treating-oxidizing step is efiected at a temperature of at least 1000" F. preferably at a temperaturewithin the range of about 1000 to 1200 F. although iti t oibe understood that the upper temperature limit may be considerably higher and is defined only" by the operating limitations imposed by the materials of construction of the apparatus employed. Air is employed in an amount sufficient to consume substantially all of the carbon of the solid composite and provide an oxidizing atmosphere containing at least 0.5 percent oxygen and preferably 2.0 to 10.0 percent oxygen.

An advantage of the process of this invention is that uranium containing carbonaceous fuels are convertedto a gas comprising carbon monoxide andhydrogenand' a solid adapted for separate recovery and purification of the uranium valuesby sublimation means. The reduc: ingconditions of the partial oxidation step, which are inimical to the formation of hexavalent uranium;' are employed to composite carbon with the u'ranium eontain ing solids, which carbon is" employed in a; subsequent oxidation step to provide heat to effect oxidation and sublimation of the uranium values.

In accordance with the process of this invention, a Dakota lignite containing 0.1 percent uranium is processed for the generation of carbon monoxide and hydrogen and for recovery of the uranium values. The lignite has a proximate analysis of about 30 percent moisture, 29 percent volatile matter, 29 percent fixed carbon and 12 percent ash. The lignite is reacted with steam and oxygen in relative proportions of 530 pounds of lignite (dry basis), 340 pounds of steam and 3610 standard cubic feet of substantially pure oxygen at a pressure of 205 pounds per square inch gauge and at an autogenous temperature of 2050 F. Gas of the following composition is obtained:

Additionally, 106 pounds of slag comprising 0.72 weight percent uranium as U 0 and 14.3 weight percent carbon is withdrawn from the gas generation zone as a slurry in water. Ammonium fluoride is dissolved in the slag slurry and the slurry is then passed into a heating zone where the water is vaporized forming a dispersion of slag particles in vapor. Air is introduced with the slag dispersion to provide an oxidizing atmosphere and further heats the slag dispersion to a temperature of about 1100 F. by burning the carbon constituent of the slag. Under the high temperature oxidizing conditions of the kiln, the ammonium fluoride reacts with the uranium values of the slag forming volatile uranyl ammonium pentafluoride. The slag is separated from the vapor products which are separately cooled and solid uranyl ammonium pentafluoride is precipitated therefrom.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for the-generation of a gas comprising carbon monoxide and hydrogen and concomitantly recovering uranium values from lignite containing naturally occurring uranium values which comprises reacting said lignite by partial oxidation with a free oxygen containing gas at a temperature above about 1800 F. in relative proportions such that a part of the carbon content of said lignite is converted to carbon monoxide and a part of said lignite is unconverted to gaseous products and is liberated as acomposite solid with non-combustible solid containing uranium values, separating said composite solid from the resulting gaseous products of reaction, contacting said composite solid with a free oxygen containing gas inan amount in excess of that required to completely oxidize all of the carbon contained in said composite solid at a temperature above1000 F. thereby effecting conversion of uranium values contained in said composite to a hexa: valent form, reacting said uranium in hexavalent form with an ammonium fluoride forming uranyl ammonium pentafluoride in vapor form, and separating vaporcomprising uranyl ammonium pentafluoride from a solid residue. 7 a 1 2. The processof claim 1 wherein said lignite and free oxygenare contacted at at autogenous temperature .within the range of about 2200 to 3200 F. 7 3. .The process of claim 1 wherein said composite solid comprising uraniurn values, non-combustible solid and 'unconverted carbon comprises about 2 to percentfcarbon.

4. The process of claim 1 wherein said composite solid comprising uranium values, non-combustible solid and 5 6 unconverted carbon comprises about 5 to 50 percent Kirk and Othmer Encyclopedia of Chemical Technolcarbon. ogy, vol. 8, pp. 765-772, 777-783 (1952), Interscience 5. The process of claim 1 wherein said solid com- Publishers, Inc., New York. (Copy in Scientific Library.) posite is ground before contacting with said oxygen con- Katz et al.: Chemistry of Uranium, page 365 (1951), taining gas. 5 McGraw-Hill Book Co., New York. (Copy in Scientific 6. The process of claim 1 wherein said composite solid Library,) is contacted with a free oxygen containing gas at a tem- -I Chem, Eng. Progress, vol. 50, N0. 5, pp. 230- perature within the range of 1000 to 1200 F. 234, May 5 (Copy in S i tifi Library 7. The process of claim 1 wherein said composite solid Ewing et aL: BMI 237 July 31, 5 (date d l ifi d is contacted with a free oxygen containing gas in an 0 April 11 1956) (Copy in Scientific Library) amount effective to provide an oxidizing atmosphere conwnsoll et BMI 274, Jam 14, 1954 (date dec1assi ammg Percent fied 0a. 17, 1955 pp. 12-36. (Copy in Scientific References Cited in the file of this patent Library) AEC Document BMI-JDS-175, pages 14 and 15, Pitmon et al.: WIN-81, Oct. 18, 1957, pp. 7-10, 18-36.

March 15, 1949 (declassified March 5, 1956). (Copy in 15 (Copy in Div. 46.) Scientific Library.)

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,992,891- 7 July 18 1961 Frederick Ba Sellers It is hereby certified that error appears in the above nun pe d pstent requiring correction and that the said Letters Patent ShOui'dj eades corrected below.

Column 1, line 62, for "l200" read 1800 line 67,, for "stream" read steam Signed and sealed this 5th day of December 1961'. I

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2 992, 891- Frederi ck B. Sellers It is hereby certified that error appears in the above ent requiring correction and t hat the said Letters Patent shoui' as corrected below.

Column 1 line 62, f0r" "l2OO" read 1800 line 67, for "stream" read steam Signed and sealed this 5th day of December 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents July 18 1961 USCOMM-DC C

Claims (1)

1. A PROCESS FOR THE GENERATION OF A GAS COMPRISING CARBON MONOXIDE AND HYDROGEN AND CONCOMITANTLY RECOVERING URANIUM VALUES FROM LIGNITE CONTAINING NATURALLY OCCURRING URANIUM VALUES WHICH COMPRISES REACTNG SAID LIGNITE BY PARTIAL OXIDATION WITH A FREE OXYGEN CONTAINING GAS AT A TEMPERATURE ABOVE ABOUT 1800*F. IN RELATIVE PROPORTIONS SUCH THAT A PART OF THE CARBON CONTENT OF SAID LIGNITE IS CONVERTED TO CARBON MONOXIDE AND A PART OF SAID LIGNITE IS UNCONVERTED TO GASEOUS PRODUCTS AND IS LIBERATED AS A COMPOSITE SOLID WITH NON-COMBUSTIBLE SOLID CONTAINING URANIUM VALUES, SEPARATING SAID COMPOSITE SOLID FROM THE RESULTING GASEOUS PRODUCTS OF REACTION, CONTACTING SAID COMPOSITE SOLID WITH A FREE OXYGEN CONTAINING GAS IN AN AMOUNT IN EXCESS OF THAT REQUIRED TO COMPLETELY OXIDIZE ALL OF THE CARBON CONTAINED IN SAID COMPOSITE SOLID AT A TEMPERATURE ABOVE 1000*F. THEREBY EFFECTING CONVERSION OF URANIUM VALUES CONTAINED IN SAID COMPOSITE TO A HEXAVALENT FORM, REACTING SAID URANIUM IN HEXAVALENT FORM WITH AN AMMONIUM FLUORIDE FORMING URANYL AMMONIUM PENTAFLUORIDE IN VAPOR FORM, AND SEPARATING VAPOR COMPRISING URANYL AMMONIUM PENTAFLUORIDE FROM A SOLID RESIDUE.