US2570120A - Process for recovery of pitchblende and similar uranium minerals from ores of same by special flotation practice - Google Patents

Description

Watenteci Oct. 2, 1953 WED STATES FATE 25min FF i CE PROCESS FOR RECOVERY OF PITCHBLENDE AND SIMILAR URANIUM MINERALS FROM ORES OF SAME BY SPECIAL FLOTATION PRACTICE NB Drawing. Application February a, 1949, Serial No. 74,486

Claims.

This invention relates to methods for separating pitchblende from its ores and more particularly to flotation procedures which are effective for recovering pitchblende from siliceous ores of this mineral.

The pitchblende ore which was employed in connection with the development of the present invention came from the Reboleiro mine at Trancoso in the District of Guarda, Portugal. This ore analyzed 7.29% in UaOa. The gangue minerals in this ore consist chiefly of quartz, with about 5% of muscovite, less than 1% of pyrite, about 1% of limonite, and traces of other minerals including apatite. Uranium containing minerals constitute from to 20% of this ore, and about 90% of the uranium occurs as pitchblende, the balance being principally autunite, with small amounts of uranophane and traces of meta-torbernite also being present. Most of the quartz grains are colored black due to pitchblende surface coatings and fine dissemination in the quartz, but an appreciable quantity of the quartz seems to have been colored b emanation effects.

The problem of obtaining a concentrate of pitchblende from this ore by flotation was a problem the solution of which was not easy as can be appreciated from the next two paragraphs.

In attempting to concentrate pitchblende from the ore described in the preceding paragraph various flotation reagents and techniques were tried. When large amounts of various amine flotation reagents were used, the flotation was non-selective, the recovery of quartz being accentuated with a definite degree of rejection of pitchblende. Attempts were made to recover pitchblende from this ore by using a flotation reagent comprising a long chain fatty acid, such as oleic acid, and a high molecular weight aliphatic amine, such as dodecylamine. This flotation reagent which contains a long chain fatty acid and a long chain aliphatic amine has been successfully employed in separating carnotite from its siliceous ores. This latter procedure for separating carnotite from its ores is more fully described and claimed in our copending application, Serial No. 74,485 filed February 3, 1949. This fatty acid and amine reagent was found to be of no value in recovering pitchblende from this Reboleiro ore since little, if any, of the black pitchblende was drawn into the flotation froth produced. It was visibly apparent that the results were so poor that it was not considered worth while to run chemical analyses on the concentrates or tailings. Numerous other flotation reagents were tested and found to be of no value in obtaining a froth concentrate of pitchblende.

collectors.

Despite the foregoing failures applicants ultimately succeeded in developing and perfecting the present invention which satisfies the purposes of the present research which are hereinbelow set forth.

An object of the present invention and the research leading up to it is to provide a suitable flotation process for separating pitchblende from its siliceous ores. A further object is to provide a process for recovering pitchblende from its siliceous ores which makes use of relatively inexpensive flotation reagents. A still further object is to provide a procedure for concentrating pitchblende from its siliceous ores which will maximize the amount of the uranium values of the ore appearing in the flotation concentrate and minimize the amount of gangue carried by the flotation concentrate. Other objects will appear hereinafter.

These objects are accomplished in accordance with the present invention by converting a siliceous ore of pitchblende to an aqueous ore pulp, giving said ore pulp a preliminary treatment with ferric chloride and then subjecting said ore pulp to flotation in the presence of a flotation reagent which comprises a long chain fatty acid and an aliphatic amine. It is often considered advisable to dry crush the ore and deslime it before converting it to an aqueous ore pulp. After the ferric chloride treatment it is often desirable to condition the ore pulp with sodium silicate and soda ash before adding the flotation reagent thereto. The flotation concentrate may be cleaned one or more times, if desired, in order to obtain a concentrate'containing a high amount of uranium values.

The following examples illustrate but do not limit the invention.

Example I parts by weight of pitchblende ore from the Reboleiro mine which analyzed 7.29% in U308 was mixed with 35 parts by weight of water and wet ground in a ball mill for 12 minutes to a particle size or -65 mesh. While the ore was being ground there was added thereto 10 pounds or FeCla-GHsO pereach ton of ore. To the pulp of ground ore which had been treated with ferric chloride there were then added 0.5 pound of 40% f sodium silicate and 3 pounds of soda ash per ton oi ore in said ore pulp, and the pulp was then conditioned with these added reagents for 10 minutes. The addition of these reagents brought the pH 01' the ore pulp up to 6.9. To the ore pulp there were then added 0.7 pound or linseed oil acids and 2.1 pounds of castor oil acids emulsified with 1.5 pounds of 2-amino-2-methyl- 1,3-propanediol tor each ton of ore in said ore pulp. and the ore pulp was then agitated in a flotation machine for 5 minutes at 23 C. A further addition of 0.: pound of linseed oil acids and 0.7 pound of castor oil acids emulsified with 0.75 pound of 2-ainino-2-methyl-1,3-propanediol per ton of original ore treated was then made and flotation continued for 5 minutes longer. The total rougher concentrate thus secured contained 41.6% by weight of the solids and 78.9% of the uranium values of said ore. This rougher concentrate analyzed 13.66% in UaOa. The rougher tailings contained 58.4% by weight of the solids and 21.1% of the uranium values of said ore. These rougher tailingsanalyzed 2.59% in U308.

The rougher concentrate was then treated in a cleaning operation without any additional reagents. There was thereby obtained a cleaner concentrate which contained 19.6% by weight of the solids and 56.2% of the uranium values of the ore being treated. This cleaner concentrate analyzed 20.65% in UaOa. By refloating this cleaner concentrate in the recleaner cell of the flotation machine a recleaner concentrate was obtained that contained 8% by weight of the solids and 42.1% of the uranium values of the ore being treated and that analyzed 38.04% in UsOa. The tailings from the cleaner and recleaner cells together constituted what was called cleaner middlings. These cleaner middlings contained 33.6% by weight of the solids and 36.8% of the uranium values of the ore being treated and analyzed 7.88% in U308- These cleaner middlings had a uranium content which was only slightly greater than that of the ore being treated, and therefore they were added to new batches of ore which were about to undergo concentration treatment.

The recleaner concentrate obtained in this way comprised principally relatively coarse quartz and pitchblende. Most of the pitchblende grains Pitchblende ore from the Reboleiro mine which analyzed 7.29% in UaOa was dry crushed to pass 10 mesh, and the primary slimes were removed therefrom by decantation without use or deflocculating agents. These primary slimes included 7.2% by weight of the solids and 13.4% of the uranium values of the ore being treated. These primary slimes analyzed 13.17% in UaOa.

This procedure 0! desliming was adopted because it had been round that the major part of the uranium values which went into the flotation tailings was in the ultra-slime portion 01' said tailings. This indicated that the finest slimes of pitchblende were difiicultly recovered by flotation. Fortunately, this slime removal really constituted a step of concentration, since such slimes contained uranium values equivalent to about twice the uranium content of the original ore.

The deslimed ore was then diluted with an equal weight 01 water and wet ground for 8 minutes in a ball mill to a particle size or mesh. While the grinding was going on. 15 pounds of FeCh-6Hz0 per ton of original ore was added thereto in order to accomplish the necessary resurfacing with ferric chloride. The ground ore Dulp which had been treated with ferric chloride was then transferred to a flotation machine where it was conditioned for about 5 minutes with additions of sodium silicate and soda ash. 5 pounds of 40% sodium silicate and 8 pounds of soda ash per ton of ore in the original ore pulp were used to efiect this conditioning. The conditioned ore pulp had a pH of 8,-and therefore any residual ferric chloride must have been precipitated as ferric hydroxide.

There were then added to the ore pulp 0.8 pound of linseed oil acids emulsified with 0.2 pound of technical dodecyl amine and 0.4 pound of 2-amino-2-methyl-1,3-propanediol per each ton of are in the original .ore pulp. The ore pulp was then agitated in the flotation machine for 5 minutes at 24 C. A further addition of 1.0 pound of linseed oil acids emulsified with 0.1 pound of technical dodecyl amine and 0.4 pound of 2-amino-2-methyl-1,3-propanediol per ton of original ore was made and flotation continued for 5 minutes longer. A rougher concentrate was thereby obtained which contained 30.7% by weight of the solids and 69.6% of the uranimn values of the ore being treated. This rougher concentrate analyzed 16.11% in (1301;.

Taken together the primary slimes and the rougher concentrate contained 37.9% by weight of the solids and 83% of the uranium values of the ore being treated and analyzed 15.55% in UaOa. The overall recovery of 83% of the uranium values in the combined flotation rougher concentrate andprimary slimes in a composite product analyzing 15.55% in U30; showed how very effective this concentration technique actually was.

62.1% by weight of the solids and 17% of the uranium values of the ore being treated went into the rougher tailings which analyzed 1.94% in U308. These rougher tailings comprised a "san portion that analyzed 1.18% in U308 and a deflocculated slimes portion that analyzed 5.4% in 'UaOa. The presence of this slimes portion in the rougher tailing showed that the so-called secondary slimes of pitchblende were also difllcultly floatable even after ferric chloride activation.

The total rougher concentrate was then agitated for 2 minutes at 24 C. in the ole -er cell of the flotation machine without any additional reagents. A cleaner concentrate was thereby obtained which included 17% by weight of the solids and 47.1% of the uranium values of the ore being treated and which analyzed 19.68% in UaOa.

The cleaner concentrate was agitated for 2 minutes in the recleaner cell of the flotation machine, and a recleaner concentrate was thereby obtained that analyzed 29.96% in U30; and that contained 7.1 by weight of the solids and 29.8% of the uranium values of the ore being treated.

When attempts were made to repeat the procedure described in this example but omitting the ferric chloride treatment of the ore it was found that the selectivity of the flotation was so deplorable that a great deal of gangue was floated and substantially no concentration of the pitchblende was accomplished.

In all pitchblende ore flotation it is essential that the wet grinding in a ball mill prior to actual flotation be such as to free the mineral and gangue with the least possible production of slimed material. Such separation is effected at about 65 mesh with ore from the Reboleiro mine, although at that grinding there are still grains of quartz carrying a very thin adhering film of pitchblende on part of the grain surface.

The preliminary treatment of the ore with ferric chloride is preferably carried out during the usual wet ball mill grindin that normally precedes flotation. The water-soluble commercial salt, F'eCh-GHZO, has been found to be quite suitable as a source of ferric chloride. The amount of such salt necessary to obtain the required acti vation of pitchblende for subsequent flotation need not exceed 1% of the weight of the ore and may be considerably less in the case of siliceous ores containing little or no water-soluble basic constituents. The ferric chloride used in this preliminary treatment should have very little or no free acidity, and the ore pulp should be substantially neutral. The ore pulp should not be modified b alkaline reagents which will react with the ferric chloride which is to be subsequently added. The surface activation of pitchblende by ferric chloride is best secured in an aqueous medium having a pH varying between 6.0 and 7.5. In the case of basic ores where the normal ball mill grinding and classification results in an ore pulp with a pH in excess of 7.5 which contains water-soluble basic constituents that will react with ferric chloride, it is preferable. in order to economize on the amount of ferric chloride required, to add an acid, such as hydrochloric, to reduce the pH to 6.5-7.0 before the addition of the ferric chloride. It is advisable that the acid used for changing the pH of the pulp be added in the grinding circuit and that conditioning with ferric chloride should promptly follow.

In the case of a siliceous ore of pitchblende the optimum degree of surface activation by ferric chloride is best obtained by making the initial feed of ferric chloride into the ball mill circuit. It may be advantageous to continue such conditioning of the ground ore in an auxiliary agitation tank to continue the contact between the mineral particles and the activating agent during an additional period of conditioning after grinding and prior to modification of the pulp in preparation for flotation. The treatment with ferric chloride results in an increase of the acidity of the pulp which may accordingly attain a pH of 5.2-5.6. It is presumed that the action of ferric chloride is to produce at the grain surface of the pitchblende an alteration or resurfacing which is reactive with the combination of fatty acids and aliphatic amines that is used as the collector agent for the flotation.

After the pitchblende ore has received the preliminary ferric chloride treatment, the ore pulp is suitably treated in order to soften the water used in flotation, to deflocculate the gangue slimes, and to adjust the pH so that the subsequent flotation operation may be carried out under optimum conditions. The desired relative fcrmate or acetate.

softness of the water is best secured by the addition of soda ash to the ore pulp. The interference to flotation by the presence of gangue slimesisbestminimizedbytheuseofasmall amount of sodium silicate, although other agents of similar deflocculating character, such as sodium lignin sulfonate, may be used. The proportions and amounts of such alkaline agents should be such as to produce a pulp with a pH of 7.5-8.0. in which dispersion of gangue slime is definitely evident after some few minutes of conditioning.

. After the ore pulup has been suitably modified by the addition of soda ash and sodium silicate there is added thereto the flotation collector agent. This flotation collector agent comprises a long chain fatty acid containing 10 or more carbon atoms and a primary aliphatic amine containing 4 or more carbon atoms.

The long chain fatty acid used as a collector agent contains over 10 carbon atoms and may be a relatively pure individual fatty acid, such as lauric or oeic. For reasons of economy it is preferable to use technical mixtures of fatty acids that are obtained by hydrolyzing suitable fats and oils. The fatty acid mixtures obtained by hydrolizing castor oil, linseed oil, palm oil. corn oil. cottonseed oil, peanut oil, and coconut oil are good flotation reagents for use in the present invention. The castor oil acids and linseed oil acids have been found to be particularly efficacious collection agents for pitchblende. Other suitable fatty acid reagents which may be used include the technical fatty and resin acid mixtures derived from tall oil that are marketed under the trade names Indusoil and Liqro," which are respectively described in greater detail on pages 361 and 401 of thethird edition of The Condensed Chemical Dictionary.

The amine reagent used in the flotation contains 4 or more carbon atoms. The amine may be used as such or in the form of one of its watersoluble salts such as the hydrochloride, nitrate,

Suitable amines include 2- amino-2-rnethyl-1,3-propanediol and the primary hexyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl and octadecyl amines. It is convenient to use mixtures of normal primary amines such as the technical dodecyl amine derived from coconut oil wherein the alkyl radicals present in this amine mixture correspond in chain length to the various fatty acids produced by hydrolyzing coconut oil. This technical dodecyl amine may contain only 47% of dodecyl amine and the remaining 53% is made up of a mixture of normal primary hexyl, octyl, decyl, tetradecyl, cetyl and octadecyl amines. Mixtures of amines derived from coconut oil may be used from which practically all of the amines containin less than 12 carbon atoms have been removed. Only small amounts of these amines are used. In view of the presence of gangue slimes it is doubtful if these amines function as cationic collectors for pitchblende. It is quite possible that the chief function of the amine rea ent is as an emulsifying agent for the fatty acid collectors. The amine reagent also has incidental value in the maintenance of adequate froth volmne and stabili y.

It has been found that the best recoveries in flotation and frothing characteristics are secured when the fatty acid agents and aliphatic amine compounds are carefully emulsified in the ore pulp prior to flotation. Emulsification of the fatty acid reagent may be achieved by adding it to an ore pulp containing a suitable emulsifying agent for the fatty acid. Good results in pitchblende flotation are obtained by emulsifying the fatty acid agents either by agitation in water made slightly alkaline with soda ash or by agitation in a' dilute aqueous solution of the amine reagent. Satisfactory flotation is secured with reactivity between the fatty acids and the min-' eral surfaces.

Satisfactory flotation results can be attained when the water temperature is about 55 E, if the fatty acid agents and aliphatic amines are properly emulsified at the selected temperature. The temperature of the flotation circuit is of importance when fatty acid compounds which have fusion points much above the temperature of the water are used. Unless the temperature of the pulp is maintained above the fusion point of the organic flotation reagent with the highest melting point, said reagent may be poorly emulsified in the ore pulp thereby causing poor efficiency of flotation. This factor influences the choice of fatty acid and amine to be used if pulp heating is to be avoided.

"The theories underlying the present invention whereby treatment of a pitchblende ore with ferric chloride activates the pitchblende so that it may be floated by a flotation reagent comprising a higher fatty acid and an aliphatic amine are not thoroughly understood at the present time. Therefore, it is to be understood that the following attempted theoretical explanations of the ferric chloride activation of pitchblende do not limit the invention even if they are subsequently proven to be erroneous, since the invention may be successfully prac.iced by one skilled in the art of ore flotation without any knowledge of a reason for the ferric chloride activation of pitchblende. It is considered possible that the ferric chloride treatment of pitchblende ore may result in a slight alteration or cleaning of the surface of the .mineral grains whereby the reactivity between the amine of the flotation reagent combination and .he uranium ion of the mineral may be sufficiently emphasized to cause production of an insoluble uranium amine salt at the mineral surface.

It is thought that the ferric chloride treatment of pitchblende ore results in the formation of a coa ing of goethite upon the grains of pitchblende. This at present constitutes our preferred theoretical explanation for the ferric chloride activation of pitchblende. This explanation is predicated upon studies made of the reactivity of pitchblende win a practically neutral ferric chloride solution. Viewed under a microscope. this reactivity is shown by the formation of a brown coating on the mineral grain which is attended by the production of small gas bubbles at the mineral surface. This coating increases in dimensions with a lessened amount of gas production. Then .he thickened coating appears to detach itself from the mineral surface and can be disintegrated by slight movement into a fine coating has been definitely removed from the pitchblende grain surface, there seems to be a sort of tarnish to such surface which again builds up into a similar brown coating but more slowly and with less evolution of gas. The slowing down of the reaction is accompanied by an increase in the acidity of the aqueous ferric chloride solution and a decrease in the production of the amount of the fine brown precipitate. Chemical analyses of solution and residue show that ferrous chloride, hydrous iron oxide and free hydrochloric acid are produced and that gaseous oxygen is evolved. From the point of view of flotation the most interesting aspect of this reactivity is the production at the mineral grain surface of a coating of freshly precipitated goethite under the proper conditions of acidity.

In order that this reactivity may be effective for the activation of pitchblende by resurfacing, it must be able to take place under conditions of relatively low ferric chloride concentration. Furthermore, such resurfacing must be of such a nature that it will be insoluble in the nearly neutral or alkaline ore pulps that are utilized in the subsequent flotation operations. These conditions are fulfilled, as the microscopic study shows that the reactivL-y at the surface of the pitchblende is optimum at nearly neutral stages, and the resulting coating or "tarnish of goethite is insoluble in nearly neutral or alkaline solutions. Upon the foregoing evidence it has been tentatively concluded that the activation of pitchblende by ferric chloride is predica.ed upon the formation of a goethite coating upon the grains of pitchblende.

Resort may be had to such modifications and variations as fall within the spirit of the invention and the scope of the appended claims.

We claim:

1. A process of recovering pitchblende from a siliceous ore thereof, in which uranium minerals constitute from 10 to 20% of the ore, about 90% of the uranium occurs as pitchblende, the balance being principally autunite, with small amouns of uranophane and traces of meta-torbernite also being present and in. which the gangue minerals consist chiefly of quartzwith about. 5% of muscovite, less than 1% of pyrite, about 1% of limonite, and traces of other minerals including apatite, which comprises giving said ore in a wet ground sta.e a preliminary treatment with ferric chloride, adding a long chain fatty acid containing at least 10 carbon atoms and a primary aliphatic amine containing at least 4 carbon atoms to an aqueous pulp of said ore, and subjecting said ore pulp to fiotation at a pH of 7.5 to 8.

2. A process of separating pitchblende from a siliceous ore thereof in which uranium minerals constitute from 10 to 20% of the ore, about 90% I of the uranium occurs as pitchblende, the halance being principally autunite, with small amounts of uranophane and traces of meta-torbernite also being present and in which the gangue minerals consist chiefly of quartz with about 5% of muscovite, less than 1% of pyrite,

about 1% of limonite, and traces of other minbrown fiocculent-material. When this built-up (6 containing at least 4 carbon atoms to said con- 0 ditioned ore pulp, and then subjecting said ore pulp to flotation at a pH of 7.5 to 8.

3. A process of separating pitchblende from a siliceous ore thereof in which uranium minerals constitute from 10 to 20% of the ore, about 90% of the uranium occurs as pitchblende, the balance being principally autunite, with small amounts of uranophane and traces of meta-torbemite also being present and in which the gangue minerals consist chiefly of quartz with about 5% of muscovite, less than 1% of pyrite, about 1% of limonite, and traces of other minerals including apatite, which comprises dry crushing said ore, separating the primary slimes from the dry crushed ore, converting the deslimed ore to a ground aqueous ore pulp, giving the aqueous ore pulp a preliminary treatment with ferric chloride, then conditioning said pulp by adding soda ash and sodium silicate thereto, adding a fatty acid containing at least 10 carbon atoms and a primary aliphatic amine containing 10 at least 4 carbon atoms to said conditioned ore pulp, and then subjecting said ore pulp to flotation at a pH of 7.5 to 8.

4. A process in accordance with claim 1 in which the preliminary treatment with ferric chloride is carried out at a pH below 7.5.

5. A process in accordance with claim 1 in which the primary aliphatic amine is 2-amino- 2-methyl-1,3-propanedio1.

ROBERT W. HANDLEY. CARL W. SAWYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,979,324 Gaudin Nov. 6, 1934 2,000,656 Armstrong et a1. May 7, 1935 2,014,406 Weed et al. Sept. 17, 1935

Claims (1)

1. A PROCESS OF RECOVERING PITCHBLENDE FROM A SILICEOUS ORE THEREOF, IN WHICH URANIUM MINERALS CONSTITUTE FROM 10 TO 20% OF THE ORE, ABOUT 90% OF THE URANIUM OCCURS AS PITCHBLENDE, THE BALANCE BEING PRINCIPALLY AUTUNITE, WITH SMALL AMOUNTS OF URANOPHONBE AND TRACES OF META-TORBERNITE ALSO BEING PRESENT AND IN WHICH THE GANGUE MINERALS CONSIST CHIEFLY OF QUARTZ WITH ABOUT 5% OF MUSCOVITE, LESS THAN 1% OF PYRITE, ABOUT 1% OF LIMONITE, AND TRACES OF OTHER MINERALS INCLUDING APATITE, WHICH COMPRISES GIVING SAID ORE IN A WET GROUND STATE A PRELIMINARY TREATMENT WITH FERRIC CHLORIDE, ADDING A LONG CHAIN FATTY ACID CONTAINING AT LEAST 10 CARBON ATOMS AND A PRIMARY ALIPHATIC AMINE CONTAINING AT LEAST 4 CARBON ATOMS TO AN AQUEOUS PULP OF SAID ORE, AND SUBJECTING SAID ORE PULP TO FLOTATION AT A PH OF 7.5 TO 8.