US2586545A - Beneficiation of nonmetallic ores - Google Patents

Description

Patented Feb. 19, 1952 r 2,588,545 nanarrcm'rlon or NONMETALLIC ORES 1 in: Milton Le Baron, Lakeland, Walter 0. McClintock, Mulberry, and James E. Lawvcr,

Lakeland, Fla., assignors to International Minerals and Chemical Corporation, a corporation of New York No Drawing. Application June 3 1947,

Serial No. 752,272

5 Claims. (01. 209-8) The present invention relates to the beneficiation of non-metallic ores and is applicable in particular to phosphate ores such as those found in Tennessee and Montana. The novel process hereinafter described is applicable for the beneficiation of any phosphatic ores in which the iron values are differentially associated either with the gangue or with the phosphate values as the case may be. I

The phosphate industry requires, for the production of superphosphate and for the production of triple superphosphate, a phosphatic rock of relatively high B. P. L. (bone phosphate of lime) value and imposes penalties where impurities, such as iron compounds, alumina, etc., are present in excess of minimum fixed percentages. Previous processes of beneficiating non-metallic ores in which group phosphate rock is commonly classified have resulted in successfully meeting these standards of B. P. L. content, but it has been found that such processes as tabllng and flotation, while successful in a large number of cases, are nevertheless quite expensive to operate because of the initial cost of machinery and because of the subsequent operating and maintenance costs. Also, in these previously used processes of beneficiating, the required chemical reagents employed for pretreating the phosphatic ores are quite expensive. In cases where the ores are associated with large quantities of slimes, the consumption of these expensive reagents is likewise materially increased over that required with ores having a relativelysmall amount of slime. In flotation and tabling processes as now conventionally employed, the increased amounts of these costly reagents used may be not only required because of large quantitles of slime which may be originally present in the ores processed, but also required because in the process of working the ores from step to step to beneficiate the same, further amounts of slime are inherently produced. Because of this, an additional quantity of costly reagents must be added to compensate for the increased production of slimes. In addition these reagents must be added at the proper stages in the processing if they are to be efilcaciously utilized.

It is an object of the present invention to produce beneflciated phosphatic ores of high B. P. L. content and with relatively low iron compounds, alumina, etc. content from relatively low grade phosphate ores containing undesirable amounts of iron compounds, alumina and other impurities.

It is a. further object of the present invention to obviate the necessity for using expensive reagents in the beneflciation of phosphatic ores while at the same time producing concentrates of such ores which meet the accepted requirements of purity for the phosphate and fertilizer industries.

It is a further object of the invention to produce high grade phosphatic ore concentrates ,while avoiding the use of excessive amounts of electrical power, machinery, maintenance and other operating costs heretofore considered necessary to accomplish this result.

It is a still further object of the invention to beneficiate the non-metallic ore, such as phosphatic ore, having undesirable amounts of iron compounds, alumina and other impurities to meet the required standardsregardless of the particular particle size or the uniformity of the ore particles processed so long as the individual particles are sufficiently comminuted to give separation of the desired values.

Other objects will be apparent upon a fuller understanding of the invention as hereinafter more completely described.

It has been discovered that any non-metallic I ore containing iron compounds disproportionally associated with the various components of the ore may be subjected to a segregation treatment so that various values of the ore may be beneficiated or concentrated with respect to one another by passing such an ore which has been previously roasted in a reducing atmosphere through a magnetic field, one or more times. In so doing, the non-magnetic and magnetic portions so separated are found to be beneflciated with respect to the phosphatic content. In some ores the greater part of the phosphatic content is magnetically associated with the iron compound. In other ores the magnetic impurities are differentially separated from the greater part of the phosphatic values. The roasting and subsequent magnetic treatment may be varied considerably. If more than one passage is carried out, the intensity of the magnetic field is generally increased, though not necessarily so, as between the first magnetic field and subsequent fields.

In the case of such treatment of a Tennessee phosphate rock (brown rock), whichhas been roasted in a reducing atmosphere, a marked beneficiation of the ore may be effected by passing the reduced ore through a magnetic field of relatively low intensity which gives a separation of the ore into a product which is high in iron compounds, alumina and other impurities and somewhat higher in phosphatic values. This second assaus product in turn may then be passed through a magnetic field of much higher intensity than the first field used which results in. a second substantially non-magnetic product being quite low in iron compounds, alumina, and in other impurities and quite low in phosphatic values with the magnetic product, having intermediate amounts of iron compounds, alumina and other impurities, but containing high phosphatic values.

A similar treatment of iron-containing Montana phosphate ore indicates that .it behaves somewhat differently from the Tennesseephosphate ore. However, the principle of operation involved is the same. The Montana ore has the same disproportionate association of iron values with respect to the other constituents of the ore so that it is possible to remove iron and at the same time beneficiate the phosphatic values. Montana phosphate rock, upon being roasted in a reducing atmosphere and subjected to a magnetic field, yielded after a first passage ata relatively low intensity of magnetism a first product quite high in iron compounds, alumina and other impurities,

and quite low in phosphate content with the nonattracted portion being of increased phosphatic value and decreased impurity content. This nonattracted portion may he then subjected to a magnetic field of relatively higher intensity resulting in a magnetically attracted product having intermediate amounts of iron compounds, alumina and other impurities and a. substantially non-magnetically attracted portion of very low iron content, alumina and other impurities but of very high phosphatic content.

Various modifications of the above described process are possible. For example in processing Montana phosphate ore, the magnetically reduced ore may be initially subjected to a relatively high intensity magnetic field to give a separation or segregation of an attracted portion of high iron compounds, alumina and other impurities and relatively low desired non-attracted product of low iron compounds, alumina and other impurities but having a very high phosphate content. If desired this attracted portion may be resubjected to a magnetic field of lower intensity and a non-attracted, portiontherefrom admixed with the non-attracted portion first produced. Although the once-through magnetic treatment may be advantageously employed with reference to Montana rock, this type of treatment, while it may be employed for Tennessee phosphate rock. is not generally advantageous because itgives poor results so far as phosphatic beneficiation is concerned. Depending upon the properties of any particular phosphate iron-containing ore, one or several passages through the magnetic field at the same or varying magnetic intensities may be employed. Still a further variation in the procedure involves subjecting the roasted ore. the originally attracted fractions and/or the originally non-attracted ores to subsequent magnetic fields which may be of either higher or lower intensities than that employed in the next preceding-magnetic treatment, with the exception that little advantage is to be gained, generally speaking, in subjecting the fraction previously attracted under a low intensity magnetic field to a subsequent higher magnetic field without some intermediate treatment.

As previously indicated, in order to successfully practice the novel'process herein outlined, the particular phosphatic ore processed must contain iron compound impurities disproportionately associated with the various other chemical constituents, and in addition, this ore, prior to its actual beneficiation, must be roasted in a reducing atmosphere. Generally speaking, the particular temperature, time of reaction, and other roasting conditions used, depend upon the average particle size of the ore, the physical characteristics of the ore particle, the chemical content of-the ore, and in addition, depend upon the ore being sumciently comminuted to free the particles containing the impurities from the particles of the desired phosphatic values. In general, it has been found that a phosphate rock containing substantially free particles may be successfully processed according to the novel process, if the sizing is between "1" in diameter and about plus 200 mesh. Such an ore generally will require between about 15 and about '70 minutes roas time at a temperature between about 750 and 1350" F. A reducing atmosphere is employed d g the roasting so as to insure the conversion 0 substantlally all of the iron-bearing compounds present in the ore into a magnetic iron oxide. A reducing atmosphere is insured if the roasting chamber contains a reducing agent such as carbon, carbon monoxide, hydrogen or any other convenient material of similar reducing properties. These reducing materials may be added in any convenient form, that is, as gases, liquids or solids.

It is desirable, though not absolutely necessary, to efiect a pre-treatment of the ore with a. dilute mineral acid such as hydrochloric or sulfuric acid before subjecting the ore to the reducing roast. The ore treatment with dilute acid effects a desliming, in which case there is also an upgrading of the B. P. L. content of the ore with an incidental removal of considerable amounts of aluminum oxide. As previously mentioned, it is also desirable, at times, to grind or otherwise comminute the ore particles so as to free the particles insofar as possible into individual units for efficiently processing prior to the acid desliming or reducing roast treatments.

The ore, after roasting under reducing conditions, is then subjected to the action of a magnetic field. In the manner previously explained,

being varied between about 1" and about 54;".

It is obvious, of course, that magnets and magnetic fields of various sizes, strengths, and spacings between the magnetic poles of varied distances outside the figures stated, may be employed with the proper a fiustments being made for the particular ore particles being processed. Although direct current magnets were employed in the specific runs hereinafter described, alternating magnets may also be used if desired. Various commercially-available magnetic separators may be employed. These are already marketed and available for ore dressing operations, in connection with the beneficlation' of the metallic ores.

The following specific examples are only illustrative of the nature and character of the invention, and it is not intended that the invention be limited hereo.

Example 1.A sample of a Tennessee brown phosphate rock was washed with concentratedv was added in the amount corresponding to about 3 lbs. of 100% sulfuric acid per ton of rock fed. Alternatively, up to 4 lbs. per ton of feed of any suitable mineral acid such as, for example, hydrochloric acid or sulfuric acid also could be used though not in all instances is it necessary to employ a pre-acid treatment. The acidified rock was agitated for about 5 minutes and then deslimed by water washing and draining. The ma terial was then dried and subjected to a roasting operation under a reducing atmosphere at a temperature of about 1000 F. for about one hour. The reducing atmosphere was provided using wood charcoal. The roasted product was then cooled and subjected to a magnetic separation using a magnetof 3000 ampere turns. The material contacted the poles of the magnet. The magnetic product was 25 weight per cent. of the material treated and had about 61.25% Bf P. L., about 11.7% insoluble and about 12.6% iron oxide and alumina. The non-magnetic portion of the material constituted about 75 weight per cent of the material treated and contained about 70.36% B. P. L., about 10.8% insoluble and about 5.03% iron oxide and alumina. The original feed contained about 68.0% B. P. L., about 11.02% insolubles and about 6.92% iron oxide and alumina. Even in the presence of such a weak magnet the non-magnetic portion of the product showed an upgrading of B. P. L. content with a marked lowering of iron compounds and alumina. In the following examples, a much stronger magnetic field was employed.

Example 2.A Tennessee brown phosphate rock was treated with sulfuric acid in accordance with the description shown in Example 1. The washed ore analyzed as follows:

Weight per cent B. P. L. 63.69 Insolubles 20.26 Iron oxide and alumina 5.60

Per Cent Iron 6:

Weight P- Ins1 Alumina Feed to Magnet 100. 0 63. 69 20. 26 5. 60 Highly Magnetic Product 12. 2 62.54 12. 95 14. 02 Weakly Magnetic Product. 46. 2 72. 86 9.32 i 4. 68 Non-Magnetic Product. 40. 6 54. 92 33. 54 2. 07

An inspection of the data shows that the weakly magnetic product was beneficiated in B. P. L. content from 63.69 weight per cent up to 72.86 weight per cent, the acid insolubles dropped from 20.26 weight per cent to 9.32 weight per cent and the iron oxide and alumina content dropped from an original value of 5.6 weight per cent to 4.68 weight per cent. The product so produced is acceptable to the trade for use in the phosphate industry whereas the original material processed is not so accepted.

Example 3.A sample of Montana phosphate rock was crushed and then ground in a ball mill to minus 48 mesh and the minus 150 mesh portion Per cent Iron 6:

weight Insol' Alumina Feed to Magnet 100.0 63. 61 14.41 3. 23 Highly Magnetic Product 41. 6 50. 72 25. 5. 54 Weakly Magnetic Product 15. 7 68. 26 13.10 2.00 N on Magnetie Product 42. 7 74. 57 7. 60 i. 20

In contrast to the results obtained in magnetically beneficiating Tennessee phosphate rock wherein the weakly magnetic fraction was the desired portion of the feed as indicated in Examples 1 and 2, in the instant example wherein Montana phosphate rock was similarly processed, the desired portion of the feed was isolated as the non-magnetic fraction. Thus it is clear from the data shown in this example that the weight per cent B. P. L. was increased from 63.61% to 74.57%, the acid insolubles dropping from a weight per cent of 14.41% to 7.60% and the iron oxide and alumina dropping from a weight per cent of 3.23% to 1.20%. This product likewise is readily saleable to the phosphate rock industry.

Example 4.Another sample of Montana phosphate rock was preliminarily processed in similar manner to that described in Example 3, similarly roasted under reducing conditions and subjected to magnetic separation using the same magnet employed in Examples 2 and 3. The fraction and analysis thereof were as follows:

Per cent Iron (in weight B. P. L. Insol. Alumina Feed to Magnet 100.0 75.07 9.30 3.02 Highly Magnetic Product 2. 0 46. 55 23. 75 15. 20 Weakly Magnetic Product ll. 0 63. 28 20. 56 5. 06 Non-Magnetic Product 87. 0 81. 12 6. 22 1.48

In the run, the non-magnetic portion constituted about 8'7 weight percent of the feed with the weight percent of B. P. L. rising from 75.07% to 81.12%, the acid insoluble portion weight percent decreasing from 9.3% to 6.22% and the weight percent of iron oxide and alumina decreasing from 3.02% to 1.48%. This is a high grade product readily saleable to the phosphate stars in the range oi between about 750 F. and about 1350 FL, and subjecting the roasted ore to magnetic separation to produce at least a phosphate traction low in iron content.

2. A process for beneficiation of iron compound-containing Tennessee phosphate rock having the iron compounds unevenlydispersed through the phosphate material as a component which economical comminution methods fail to liberate, which comprises desliming the comminuted ore, roasting the comminuted ore in areducing atmosphere at a temperature in the range of between about 750 F. and about 1350 F., and subjecting thev roasted ore to magnetic separation to produce at least a phosphate traction low in iron content. 4

3. A process for beneflciation of iron compound-containing Montana phosphate rock having the iron compounds unevenly dispersed through the phosphate material as a component which economical comminution methods fail to liberate, which comprises desliming the comminuted ore, roasting the comminuted ore in a reducing atmosphere at a temperature in the range of between about 750 F. and about 1350 F., and subjecting the roasted ore to magnetic separation to produce at least a phosphate fraction low in iron content. c

4. A process of beneflciating iron compoundcontaining Tennessee brown phosphate ore which comprises desliming comminuted ore with dilute sulfuric acid, roasting said deslimed ore under reducing conditions at a temperature of between about 750 F. and about 1350 F., subjecting said ore to mild magnetic separation, subjecting the non-attracted fraction to a magnetic separation or increased magnetic intensity over that of the first magnetic separation and recovering a fraca I tion in the second instance as a desired phosphate traction low in iron content.

5. A process 0! beneflciating iron compoundcontaining Montana phosphate rock which comprises desliming comminuted ore with dilute sulfuric acid, roasting said deslimed ore under reducing conditions at a temperature of between about 750 F. and about 1350 F., subjecting said ore to mild magnetic separation, subjecting the non-attracted fraction to a magnetic separation 01 increased magnetic intensity over that of the first magnetic separation and recovering a fraction in the second instance as a desired phosphate traction low in iron content.

I. MILTON LE BARON. WALTER O. McCLIN'I'OCK. JAMES E. LAWVER.

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

UNITED STATES PATENTS Number Name Date 1,914,695 Lange June 20, 1933 2,373,688 Keck Apr. 17. 1945 FOREIGN PATENTS Number Country Date 274,889 Great Britain Apr. 12, 1928 OTHER REFERENCES Publication by F. Y. Fe'rney in Chemical and Metallurgical Engineering," vol. 43 (1936), pages 23, 24, copy of which is found in the Scientific Library of this oifice.

The American Institute 01' Mining and Metallurgical Engineers T. P. 1074 found in Mining Technology."

Claims (1)

1. A PROCESS FOR BENEFICIATION OF IRON COMPOUND-CONTAINING PHOSPHATE ROCK SELECTED FROM THE GROUP CONSISTING OF MONTANA AND TENNESSEE PHOSPHATE ROCK HAVING THE IRON COMPOUNDS UNEVENLY DISPERSED THROUGH THE PHOSPHATE MATERIAL AS A COMPONENT WHICH ECONOMICAL COMMINUTION METHODS FAIL TO LIBERATE, WHICH COMPRISES DESLIMING THE COMMINUTED ORE, ROASTING THE COMMINUTED ORE IN A REDUCING ATMOSPHERE AT A TEMPERATURE IN THE RANGE OF BETWEEN ABOUT 750* F. AND ABOUT 1350* F., AND SUBJECTING THE ROASTED ORE TO MAGNETIC SEPARATION TO PRODUCE AT LEAST A PHOSPHATE FRACTION LOW IN IRON CONTENT.