US2965440A - Method of beneficiating uranium ores by forming ferromagnetic uranium values and magnetically separating same - Google Patents

Description

l4 1 MAGNE'I lC S EPARATION ES BY URANIUM VALUES PARATING SAME AQ/T MAGNETIC SEPARATION R. M. TRIPP FICIATING URANIUM OR ETIC Fig.

FORMING FERROMAGN AND MAGNETICALLY SE Filed Jan. 11, 1957 ROAST METHOD OF BENEI De c. 20, 1960 AIR OR WATER 300 ROASTI'NG TEMPERATURE- DEGREES CENTIGRADE R m. N H ET V mm w 0 W H 5 w R ATTORNEYS ROASTING TEMPERATURE- DEGREES CENTIGRADE Fly. 3

United States Patent l METHOD OF BENEFICIATING URANIUM ORES BY FORMING FERROMAGNETIC URANIUM gADI JlUES AND MAGNETICALLY SEPARATING Russell Maurice Tripp, Dallas, Tex., assignor to Tripp Research Corporation, Dallas, Tex., a corporation of Delaware Filed Jan. 11, 1957, Ser. No. 633,674

Claims. (Cl. 23-145) This invention relates to new and useful improvements in methods for beneficiation of uranium ores.

This invention is particularly concerned with new and useful improvements in methods for beneficiation of low grade deposits of uranium minerals or uraniumcontaining rock.

In many uranium deposits and especially in the occurrences of uranium minerals known at this time, uranium is present in very small amounts, and therefore the processing of inordinately large volumes of rock for the recovery of a relatively small amount of the valuable mineral is required. Since the cost of processing the rock by presently known methods to recover the small amount of the valuable element may be equal to or :exceed the value of the mineral recovered, various methods have been attempted in the past for preconcentrating the desired mineral by a relatively low cost procedure. These procedures are usually based upon differences in certain physical characteristics of the valuable mineral and gangue material such as magnetic susceptibility, density, electrical conductivity, surface energy, and so forth. In many instances the usability of simple physical methods of preconcentration is rather limited due to the fact that the uranium may be present in a variety of minerals or compounds having different physical properties, and therefore the efiiciency in recovering all of the uranium in its different compounds or forms and free of gangue is very poor.

Most of the known occurrences of uranium have concentrations of less than 0.5% of U 0 yet to be salable, the ore must have a U 0 concentration of 0.1% or more. Thus, those deposits having concentrations of less than 0.1% U 0 are not presently marketable although they constitute the bulk of the present uranium ore discoveries. Further, the uranium bearing material may occur in a sandstone or arkose in the form of several minerals or compounds, and these uranium minerals may be distributed throughout the deposit or gangue as interstitial particles, as coatings on individual grains of gangue, or partial coatings, and/or as small bodies of mineral present or held in re-entrant cavities in the gangue particles. Accordingly, the recovery of uranium from a relatively high grade ore or deposit is at best a difiicult and costly process and usually involves some type of chemical leaching method. In the absence of a usable preconcentration process, large quantities of reagents are expended on non-valuable constituents, and ineffective and ineflicient recoveries are encountered. In the case of low grade ores, vast quantities of ore must be carried through lengthy and involved processes in order to recover the relatively small quantity of uranium which is present, and consequently, such low grade deposits have not heretofore been commercially exploitable.

It is, therefore, one object of this invention to pro- 2,965,440 Patented Dec. 20, 1960 vide an improved process for uranium ore beneficiation in which by means of relatively simple steps the uranium content of the ore may be brought into such condition that it may be readily separated from the bulk of the rock so as to produce a concentrate containing as much as 8% to 10% of the desired mineral.

A further object of the invention is to provide an improved process for the beneficiation of uranium ores in which the ore is roasted to bring the uranium into such condition that it lends itself readily to magnetic sorting from the balance of the ore.

A still further object of the invention is to provide an improved process for beneficiating low grade uranium deposits in which the uranium minerals may be physically separated from the worthless mineral grains of the host rock and then sorted from the bulk of these worthless grains so that a concentrate is obtained containing as much as five to ten percent of the desired uranium when the original rock may have contained less than one-tenth of one percent.

Yet another object of the invention is to provide an improved process for beneficating low grade uranium deposit having marked elfectiveness for sorting the valuable mineral from the waste by converting all of the different minerals containing the uranium into a compound or mixture having a physical property distinctly differently from that of the associated gangue minerals.

Other and more specific objects will be apparent from a reading of the following description and the claims appended thereto.

As employed herein, the word ore includes those commercially-usable mineral deposits normally termed ore," as well as those low-grade deposits which are often designated as mineral-bearing rock due to the low concentration of minerals which may be present.

A construction designed to carry out the invention will be hereinafter described, together with other features of the invention.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawing, wherein an example of the equipment for carrying out the processes of the invention is shown, and wherein:

Fig. l is a schematic diagram illustrating the processing of an ore in accordance with this invention,

Fig. 2 is a graph illustrating the concentrating of uranium in the ferro-magnetic fraction of the ore, and

Fig. 3 is a graph illustrating the production within the ore of a ferro-magnetic fraction, in both Figs. 2 and 3, the curves being plotted against roasting temperature.

The first step in obtaining a concentrate of the valuable mineral present in the rock requires a physical separation of the uranium mineral from the gangue mineral, and is followed by the utilization of some physical property, such as magnetic susceptibility, electrical conductivity, density, or surface energy which differs considerably between the valuab e mineral and the gangue mineral to effect a sorting thereof into different bins.

The process of preconcent-rating therefore includes l) employing a means for grinding the rock in such a manner as to liberate the interstitial particles, scour the film coating from certain grains, and free as much mineral contained in re-entrant crevices as possible with a minimum of crushing of the gangue particles, and (2) passing the finely ground mixture through a suitable force field which acts selectively on the valuable mineral and the waste minerals. The first step can be successfully carried out in commercially available attrition grinding equipment of the types well known in this art. The second step, however, is complicated by the fact that the uranium may be present in a variety of minerals or compounds which do not necessarily have comparable characteristics that contrast with those of the gangue materials. This latter problem can be overcome by providing means whereby all the uranium bearing minerals present are converted to one compound or mixture exhibiting a contrasting physical characteristic. It has been demonstrated that this is possible to achieve under the proper conditions of roasting.

I have discovered that if rock bearing uranium minerals and also containing iron pyrites is ground to a degree sufficient that no aggregates are left in the gangue and whatever minerals that may be present are thus exposed and freed of attachment to gangue particles, and if the ore is then subjected to roasting at certain temperatures, there will result an optimum conversion of the pyrites which are present into a ferro-magnetic fraction, or a new mineral having ferro-magnetic properties, which may be readily separated from the balance of the ore and gangue material. I have also discovered that this process results in a bringing of the uranium values of the ore into such condition that such uranium values may be recovered along with the highly magnetic fraction for further processing. Further, I have discovered that this phenomenon of conditioning the uranium values for recovery with the ferro-magnetic fraction reaches an optimum within approximately the same temperature range as that required for optimum conversion of pyrites to the ferro-magnetic fraction, and hence, the simple steps of grinding, followed by roasting of the ground ore under certain conditions and temperatures, and a selective sorting step, will remult in the extraction of a concentrate containing 5% to uranium from a body of ore which may contain only as much as 0.1% U 0 or uranium.

This can be accomplished by converting the uranium present into a quadrivalent oxide which has a high magnetic susceptibility, or better still by forming a uraniumiron compound having a high magnetic susceptibility. These aims can be carried out by roasting the ground rock in a neutral to slightly reducing atmosphere at a temperature of 450 to 550 centigrade, and in the presence of an excess of iron pyrites. Normally, the naturally-occurring uranium ore contains a suflicient quantity of iron pyrites due to the fact that during the time of deposition of the naturally-occurring uranium minerals, reducing conditions prevailed locally in the rocks and this also favored the formation and deposition of iron sulphide. When the ore-bearing rock is finely ground and subsequently roasted Within the specified temperature range the iron sulphide apparently decomposes and combines with the uranium mineral to form a uranium-iron complex having a high magnetic susceptibility.

This process is illustrated schematically in the flow diagram of Fig. 1 of the drawings in which ore is fed from a chute or point of supply 10 into a conventional grinding apparatus 11 within which the ore is ground and abraded to the point at which no aggregates or no appreciable quantity of aggregates remain. The degree of grinding will, of course, vary between various ores, but the grinding should be carried to the point at which substantially all of the uranium or other minerals present will be exposed and liberated from the gangue material for further processing.

Following the grinding step, the ore is subjected to a heating or roasting process in the unit 12, this being an oven or muifle, a fluo-solids furnace, or any other suitable type of equipment or apparatus capable of attaining the required temperatures and of subjecting the ore to the desired atmospheric conditions. The roasting need not be prolonged, but only need be sufficient to bring all parts of the ground ore to the required temperature, although longer heating or roasting will not impair the results obtained if the proper temperature is maintained. The roasting must be carried out in a neutral to slightly reducing atmosphere and at a temperature of 450 to 550 centigrade. The optimum temperature may vary with different mineral deposits, but it will be that temperature at which a maximum percentage of the pyrites are converted to the ferro-magnetic fraction, or a maximum formation of the ferromagnetic product is obtained, usually a temperature of 480 to 510 C. The neutral to slightly reducing atmosphere may, of course, be maintained in the roasting step by utilization of flue gases, natural or hydrocarbon gases, or other of the conventional and well-known steps employed for maintenance of such an atmosphere.

Following the roasting and conversion step, the ore is conveyed to a pair of magnetic filters which are operated alternately, one filter 13 receiving the finely ground and roasted ore in a stream of air or water, or other fluid, while the second filter 14 is being cleaned of the magnetic fraction which has accumulated therein. Obviously, this magnetic filtration may be carried out in a number of fashions, there being illustrated in the drawings a simple switching valve 15 through which the flow of ore may be directed to either of the filters 13 or 14. The ground and roasted ore may be carried from the roasting unit 12 by means of a conveyor or conductor 16 to a point 17 at which it is commingled with a flow of air or water or other fluid supplied through a conductor 18, the combined flow of air or water with the finely ground ore suspended or dispersed therein passing through the valve 15 to Whichever of the filters is in operation at that moment.

Magnetic filters of this type are commercially available and include in general means for establishing a high magnetic flux density and means for causing all the particles of the ore to pass through that field. The nonmagnetic material passes on through the filters and is removed through the outlets 19, while the magnetic particles, and the uranium minerals associated therewith, are retained within the magnetic fields within the filters for ultimate recovery. After one filter has operated a period of time suflicient to accumulate a load of magnetic material, the flow of the ore is switched to the alternate filter, and the first filter relieved of its accumulated load by dumping, flushing, back-washing with air or water, or the like. This filter is then again ready to receive the ore stream when the second filter has accumulated a load of retained material.

A commercially available filter of this type is known as a Ferro-filter, and is manufactured by S. G. Frantz Corporation of Camden, New Jersey.

Although the invention is not to be limited in any way to its theory of operation, it is presently demonstrable that rock bearing quadrivalent uranium or minerals containing uranium that can readily be converted to the four valence state and also small amounts of the ubiquitous iron pyrite will, upon roasting at the proper temperature and oxidation-reduction potential, result in the dissociation of the sulfide, vaporization of much of the organic matter which is normally present with the uranium and a formation of a uranium-iron complex having a high magnetic susceptibility. It is not known definitely whether this is a substitution of uranium for iron in a magnetic sulfide or in a partially reduced oxide such as Fe O The best evidence at present suggests that the dissociation and oxidation of the sulfide favors the reduction of the uranium to the U+ state and the formation of FeO-Fe o the magnetic oxide of iron. The quadrivalent uranium ion is almost identical in size With the divalent iron ion and therefore could occupy its site in the magnetic structure. The electric charge requirements could be satisfied by one U+ substituting for two Fe and tying two FeO-Fe O molecules together.

Structurally the reaction may be represented as follows:

In the case of an oxidized uranium mineral containing uranium of six valence the entire reaction might be represented as:

in which the Fe UO is a ferromagnetic compound containing quadrivalent uranium replacing ferrous iron.

Thus, maximum conversion by means of the roasting has been found to take place in a'relatively narrow temperature range. Further, it appears that the uranium values of the ore tend to concentrate in the Fe O fraction, and that such concentration reaches an optimum or maximum in a narrow temperature range substantially coinciding with that at which maximum conversion of the pyrites occurs. The reason for the concentration of the uranium values in the Fe O fraction is not important except that it has been observed to occur, and accordingly, it is possible to obtain a quite considerable concentrating of the uranium values from a given uranium ore by the carrying out of a relatively few and simple, inexpensive process steps. The roasting must take place in a neutral to a slightly reducing atmosphere and must be carried out at a temperature at which a maximum of the pyrites are converted to the Fe O fraction. Further, the roasting must be continued only sufficiently long to convert the pyrites, following which, the simple magnetic separation step results in the recovery of a relatively high concentration uranium product.

In a particular instance, a uranium ore irom the Big Indian Wash mining district near Moab, Utah, was ground to a particle size of minus 150 microns and smaller, and subjected to the present beneficiation process. Various heating or roasting temperatures were employed and determinations of conversion and recovery made. The curves or graphs of Figs. 2 and 3 illustrate the specific results obtained with this ore at various roasting temperatures, it being observed that the graph of Fig. 2, which represents a plotting against roasting temperature in degrees centigrade of the percentage of total uranium, calculated as U originally present in the sample which was recovered with the ferro-magnetic fraction, peaks sharply at approximately 490 C. and falls ofi rapidly on either side of this temperature. Fig. 3 represents a plotting against the roasting temperature of the ferro-magnetic fraction obtained in percent of the total sample. Thus, Fig. 3 is a graph illustrating the degree of conversion of the pyrites to the magnetic fraction and shows that a clearly-defined maximum was obtained at 500 C. These two graphs illustrate forcefully that maximum conversion of pyrites to ferro-magnetic material occurs at a roasting temperature closely adjacent that temperature at which a maximum recovery of uranium with the ferro-magnetic fraction was also observed, and from the results obtained on this particular ore an optimum roasting temperature of 480 to 510 C. should be employed, and preferably, a temperature of 490 to 500 C. As mined, this ore contained less than 0.10% uranium, while the recovered concentrates contained 5% to 8% uranium.

The various uranium ores differ considerably, however, and the roasting should be carried out at a temperature at which a maximum of conversion of pyrites, or formation of the ferro-magnetic fraction, occurs, although, in

general, this temperature will fall within the range of- 450 to 550 C., and most usually, in the range of 475 to 525 C.

In some instances, it may be necessary or desirable to introduce additional iron pyrites with the ore into the roasting step to make certain the proper formation of the ferro-magnetic fraction in sufiicient quantities for efiective recovery of the uranium values. This, however, along with control of the temperature, atmosphere, and other conditions obtaining within the roasting enclosure, involves routine process control operations which are conventional and readily carried out by normal control and testing procedures.

Various changes in the steps of the process, the materials employed and the concentrations thereof, as well as in the controlling of the various conditions obtaining throughout the process, may be made, within the scope of the appended claims, without departing from the spirit of the invention.

What I claim and desire to secure by Letters Patent is:

1. The method of uranium ore beneficiation including, grinding the ore, roasting the ore at a temperature at which occurs maximum conversion of uranium present in the ore to a terro -magnetic fraction containing greater uranium values than the ore and having magnetic permeability, sorting the ferro-magnetic fraction from the balance of the ore by means of a direct-current magnetic field, and recovering the enriched ferro-magnetic uranium fraction.

2. The method of uranium ore beneficiation including, grinding the ore, roasting the ore at a temperature at which occurs maximum conversion of uranium present in the ore to a non-magnetized ferro-magnetic fraction containing greater uranium values than the ore and having magnetic permeability, sorting the ferromagnetic fraction from the balance of the ore by means of a direct-current magnetic field, and recovering the ferromagnetic fraction enriched with uranium values.

3. The method of uranium ore beneficiation including, grinding the ore, roasting the ore in a neutral to slightly reducing atmosphere at a temperature at which occurs maximum conversion of uranium present in the ore to a ferro-magnetic fraction containing greater uranium values than the ore and having magnetic permeability, separating the ferro-magnetic fraction from the balance of the ore by means of a direct-current magnetic field, and recovering the ferro-magnetic fraction enriched with uranium values.

4. The method of uranium ore beneficiation including, grinding the ore, roasting the ore at 450 to 550 C. to form a ferro-magnetic uranium fraction containing greater uranium values than the ore and having magnetic permeability, separating the ferro-magnetic uranium fraction from the balance of the ore by means of a directcurrent magnetic field, and recovering the ferro-magnetic uranium fraction.

5. The method of uranium ore beneficiation including, grinding the ore, roasting the ore at 480 to 510 C. to form a term-magnetic uranium fraction containing greater uranium values than the ore and having magnetic permeability, separating the ferro-magnetic uranium fraction from the balance of the ore by means of a directcurrent magnetic field, and recovering the ferro-magnetic uranium fraction.

6. The method of uranium ore beneficiation including, attrition grinding the ore, roasting the ore at 450 to 550 C. to form a ferro-magnetic uranium fraction containing greater uranium values than the ore and having magnetic permeability, dispersing the ore and the ferrm magnetic uranium fraction in a fluid stream, and passing the ore and said fraction in said stream through a directcurrent magnetic field for recovery of the ferromagnetic uranium fraction.

7. The method of beneficiation of uranium ore containing FeS including, attrition grinding the ore, forming a uranium-iron complex having the formula Fe UO through converting the FeS to the uranium-iron complex by roasting, separating the uranium-iron complex from the balance of the ore by means of a direct-current magnetic field, and recovering the uranium-iron complex.

8. The method of beneficiation of uranium ore containing FeS including, grinding the ore, forming a uranium-iron complex having magnetic permeability and having the formula Fe UO through converting the FeS to the uranium-iron complex by roasting the ore in a neutral to slightly reducing atmosphere at a temperature of 480 to 510 C., separating the uranium-iron complex from the balance of the ore by means of a direct-current magnetic field, and recovering the uranium-iron complex.

'9. The method of beneficiation of uranium ore containing iron sulphide including, grinding the ore, converting the iron sulphide to a non-magnetic uranium-iron complex having magnetic permeability by means of roasting, separating the uranium-iron complex from the balance of the ore by means of a direct-current magnetic field, and recovering the uranium-iron complex.

10. The method of beneficiation of uranium ore containing iron sulphide including, grinding the ore, converting the iron sulphide to a non-magnetized uranium-iron complex having magnetic permeability by roasting the ore in a neutral to slightly reducing atmosphere at a temperature of 480 to 510 C., separating the uraniumiron complex from the balance of the ore by means of a direct-current magnetic field, and recovering the uraniumiron complex.

References Cited in the file of this patent UNITED STATES PATENTS 1,001,536 Lilja Aug. 22, 1911 1,478,295 Perkins Dec. 18, 1923 2,132,404 Dean et a1. Feb. 17, 1934 OTHER REFERENCES Davis: Report of Investigation 3370, Bureau of Mines,

20 US. Dept. of Interior, February 1938, pp. 85-92. (Copy in Scientific Library.)

Claims (1)

1. THE METHOD OF URANIUM ORE BENEFICIATION INCLUDING, GRINDING THE ORE, ROASTING THE ORE AT A TEMPERATURE AT WHICH OCCURS MAXIMUM CONVERSION OF URANIUM PRESENT IN THE ORE TO A FERRO-MAGNETIC FRACTION CONTAINING GREATER URANIUM VALUES THAN THE ORE AND HAVING MAGNETIC PERMEABILITY, SORTING THE FERRO-MAGNETIC FRACTION FROM THE BAL-

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