US2412217A - Froth flotation of chromite with fluoride - Google Patents

Description

Patented Dec. 10, 1946 FROTH FLOTATION OF CHROMITE WITH FLUORIDE Richard Havens, Salt Lake City, Utah, assignor to the United States of America, as represented by the Secretary of the Inter-lor- No Drawing. Application December 19, 1944,

' Serial'No. 568,908

' Claims. (01. zo9 166) (Granted under .the act of March 3, 1883, as

amended April 30,1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions 'of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467).

This invention relates to the beneficiation of chromium ores, and more particularly to the production of a chromite ore concentrate. Heretofore, attempts have been made to beneficiate chromium ores by magnetic separation, gravity concentration, and flotation methods but in the case of gravity or magnetic methods very expensive equipment is required and the flotation methods have not been particularly satisfactory from the standpoint of yields and quantities of reagents employed.

Accordingly, this invention has as an object the provision of a practical and economical process for the beneficiation of chromium ores. Another object is to provide a mineral concentrating treatment for the beneficiation of chromium ores involving selective filming of a desired mineral and the production of a high-grade chromium containing concentrate. A further object is the provision of a flotation process or other mineral filming treatment wherein a high grade of concentrate is produced with maximum recovering of chromium-bearing material with a very low consumption of reagents. Other and further objects will be apparent or will appear hereinafter as this specification proceeds.

These objects are accomplished in accordance with this invention wherein chromium ores are beneficiated by subjecting them to a mineralconcentrating treatment involving selective filming under acidic conditions in the presence of a soluble fluoride. Desirably, a soluble fluorine compound capable of yielding fluoride ions under acidic conditions is employed. 1 While agglomeration tabling concentrating treatments, bulk flotation and similar mineral concentrating treatments involving selective filming of one or more ore constituents can be employed, it is preferred to employ a froth flotation concentration involving agitation and aeration of an aqueous pulp of a comminuted chromium-bearing ore, and the ensuing description will largely be directed to this type of mineral concentrating treatment.

Suitable chromium ores for employment in accordance with this invention include any of the usual ores from which chromium is derived such as for example Oregon beach sands containing chromite, the residues from gravity separation plants formerly discarded, and other similar chromite-containing ores.

Suitable soluble fluorides for employment in accordance with this invention include any fluorine compound which is soluble in an aqueousmenstruum or pulp, or which becomes soluble therein under acidic conditions ranging from the strongly acid to the moderately acid pH range. Examples of suitable fluorine compounds are hydrofluoric acid, the alkali metal fluorides such as sodium, potassium and lithium fluoride, the soluble silicofluorites such as sodium and potassium and ammonium silicofluorite, and similar ionizable fluorine compounds which are appreciably soluble in water at a pH range between about pH 1.5 and pH 5.5.

- The beneficiation of chromium ores for example chromites, is carried out under acidic conditions in order that the acidity cooperate to best advantage with the soluble fluoride to accomplish a good recovery of high-grade chromite concentrate, While the exact function of the soluble fluoride in this method for beneficiating chromium ores is not entirely understood, and therefore it is not desired to limit this invention to any particular theory of reaction, nevertheless it is thought that the soluble fluoride under acidic conditions accomplishes several things among which may be mentioned the cleaning of the mineral surface, the dispersion of slimes, the ,depression of undesired gangue materials such as garnet, ilmenite, quartr and the like, and the selective activation of the chromite particles enabling them to be readily floated away from gangue constituents.

In carrying out the beneficiation, of chromium ores, the ores are preferably ground by customary means to provide liberation of the chromite or other chromium-bearing material from the gangue constituents, and generally the chromiumbearing ore is comminuted to particle size between 3 minus 20-mesh and minus SOO-mesh; preferably the particle size of the ore is maintained within the more restricted range of between minus 48-mesh and minus zoo-mesh.

By the expression "minus ---mesh" is meant a particle size which passes through a standard Tyler screen having the stated number of meshes per linear inch.

In general, it has been found that superior results are secured when the selected chromium ore is stage ground and when it is deslimed, that is to say freed from particles having diameters less than microns, prior to the treatment of this invention. In desliming the ore, treatment with a small amount of sodium silicate appears to facilitate dispersion of the slimes and their subsequent removal. as by washing of the desired sands with a large excess of water. A suitable amount of sodium or other soluble silicate is from 1 to 10 pounds of soluble silicate per ton of ore.

In the practice of this invention, it has been found that the employment of along chain fatty acid having from 8 to 18 carbon atoms-as a collector or collecting agent results in a superior grade and recovery of chromium concentrate when employed in conjunction with the acidic pulp and the soluble fluoride of this invention. Suitable long chain fatty acids, generally employed in amounts of from 0.5 to 5 pounds per ton of ore and preferably within the more restricted range of from about 1 to 4.5 pounds of fatty acid per ton of ore, include the fatty acids derived from vegetable, animal, marine and synthetic sources having from-8 to 18 carbon atoms in the molecule, examples being the fatty acids derived from olive oil, palm oil, coconut oil, castor oil, sunflower seed oil, sesame oil, linseed oil, whale oil, sardine oil, menhaden oil, and the synthetic fatty acids produced in the oxidation of petroleum and similar hydrocarbons. Lauric acid, palmitic acid, stearic acid and preferably oleic acid have been found eminently suitable for employment in this invention.

Highly efficient results and considerable reagent economy have been effected in the practice of this invention when the fatty acid collector employed is incorporated in the form of a stabilized emulsion or dispersion with the ore pulp, and to this end it is preferred to employ a small amount of a dispersing agent together with the fatty acid, a suitable dispersing agent being the ammonium salt of lauryl diethylene glycol sulfate sold by the Emulsol Corporation of Chicago, Illinois, under the trade name Emulsol X-l. Other dispersing agents stable to acidic conditions can, of course, be employed to achieve the same and, representative examples being starch, salts of long chain amines, and alkylol amine salts of the fatty acids themselves. Emulsol X-l as above defined however constitutes apreferred dispersing agent for use. The dispersing agent, generally employed in amounts of from .1 to 2.5 pounds per ton of ore and preferably in an amount within the more restricted ores from 0.2 to 2.0 pounds per ton of ore, is preferably incorporated with a suitable amount of water and with the selected long chain fatty acid such as oleic acid prior to its incorporation with the ore pulp for greatest reagent economy.

To achieve the desirable acidic pulp conditions in accordance with this invention, one may employ hydrofluoric acid itself to supply both the soluble fluoride and the necessary pH range as above discumed, but in general it has been found equally satisfactory to employ other strong mineral acids, generally in amounts of from 1 to 11 pounds of acid per ton of ore, and preferably from about 3 to about 7 pounds of acid per ton of ore, such as for example nitric acid, hydrochlorlc acid, and preferably the cheap and readily available sulfuric acid. Sulfuric acid has the additional advantage in this invention of removing soluble calcium salts from the pulp and thereby preventing any interference with the mineral concentrating treatment which might result from the presence of soluble calcium salts in the pulp.

In carrying out this invention in accordance with the foregoing principles, the selected chromium ore is ground in a suitable device such as a ball mill, then preferably although not necessarily deslimed by washing with an excess of water to remove colloidally dispersed material, and thereafter the sands are diluted to a pulp consistency of generally about 25 percent solids. Thereafter, the pulp is conditioned by agitating with an amount of strong mineral acid suflicient to bring the pH range of the pulp within the desired acidity, and the fatty acid collector (preferably emulsifled or dispersed with the dispersing agent selected), is incorporated with the pulp. Thereafter, the soluble fluoride is incorporated in the selected amount, the pulp is conditioned for a suitable length of time, and flotation is initiated. Any suitable flotation machine can be employed, such as for examplethe Denver Cell or the Callow type of flotation machine. The usual rougher and cleaner procedures are employed and this invention can well be utilized in a cyclic process wherein the tailing water and middling ore fractions are returned to the process.

The following illustrative examples show how the invention may be carried out, but it is not limited thereto. Parts and percentage compositions are by weight unless otherwise designated.

EXAMPLE I ORE: MoUAr Crmomrr:

Table 1 REAGENTS, POUNDS PER TON or ORE Cond. Rougher Cleaner Recleaner H SO4 5.8 3.33 1.66 1.66 NaF 3.33 1.66 1.66' Oleic acid l. 33 50 25 Emulsol X-l 27 10 .05

METALLURGICAL DATA Distribution Per Assay, per cent per cent Product cent ClzOa F0 siol CHO: F8

Chromite conct. 1.. 37. 9 41.4 22. 0 l. 8 62. 2 50. 3 Chromite conct. 2 r 9. 5 39. 4 2o. 8 5. 2 14. 8 ll. 9 Recleaner tailing. 4. 3 22. 3 17. 2 3. 9 4. 5 Cleaner tailing- 9. 3 16. 3 14. 6 6. 0 8. 2 Rougher tailing- 31. 0 7. 0 9. 9 8. 6 18. 5 Slimes 8. 0 l4. 0 13. 8 4. 5 6. 6

Calculated heads 100.0 25. 2 l6. 6 100. 0 100.0

Combined concts 47 4 41. 0 21. 8 2. 5 77.0 62. 2

5 EKAMPLEII On: Casno Cmonrrr Burns Table 2 REAGENTS, POUNDS PER TON OF ORE Desliming Rougher Cleaner Recleaner Sodium silicate 3. 7 l. 8

NaF 4. 6 0. 9

H2801 6. 8 2.6 1.8 Emulsol X-l" 2 .02 .02

METALLURGICAL DATA Assay, per cent 'ggg Product per pe cent CHO] Fe CnOl Fe Chromite conct. 1 9. 33 40. 8 11. 85 37. 3 18. 6 Chromite oonct. 2 2.19 34. 1 1O. 25 7. 3 3. 7 Recleaner tail. 2 3. 84 19. 3 7. 2 7. 2 4. 7 Recleaner tail. 1... 11.33 18. 1 7. 2 20. 13.8 Cleaner tail 7. 31 ll. 4 6. 0 8. 1 7. 4 Rougher tail 39. 86 1. 8 4. 1 7. 1 27. 3 Slimes 28. 14 5. 1 6. 6 13. 0 24. 6

Calculated heads 100. (X) 10. 2 6. 0 100. 0 1(1). 0

Combined eoncts 11. 52, 39. 6 ll. 44. 6 22. 3

Remarka slimes as received contained 73.0 percent minus 200-mesh and sands floated contained 73.5 percent minus 200-mesh.

6 EXAMPLEIII Scum Amman The unconsolidated sands as received were screen sized and results are given in Table 3.

Table 3 SCREEN ANALYSIS OF HUMPHREYS GOLD CORPORATION OONCENDRA'IES Lake City tap water to about percent solids and an emulsion of oleic acid stabilized with Emulsol X-l was added until flocculation was fairly complete. Sodium fluoride was added in stages until some depression of the garnet was noted. The pulp was then diluted to about 25 percent solids and dilute sulfuric acid was added untllflocs were clean of garnet and gangue. The flocculated chromite then floated rapidly and usually no additional collector was required.

Results of flotation tests on Humphreys Gold Corporation primary concentrates are given in Tables 4, 5, and 6, except that magnetic separation was employed on the chromite cleaner concentrates in the test recorded in Table 4.

ram.

CHROMITE FLOTATION USING LARGE AMOUNTS OF FATTY ACID Assay, percent Distribution, percent P duct Wt.. Ratio percent Cr/Fe CHO: F6 5101 Ono] SiO Chromite cleaner concentrate 1 49. 4 43. 10 21. 0 l. 0 S4. 4 54. 9 2. 9 Chromite cleaner concentrate 2- 3. 1 3a. 32 21.0 3. 6 4. 3 3. 4 0. 6 Chromite cleaner tailing 11. 4 23. 80 22. 0 9. 0 10. 8 13. 3 .6. 0 Rougher tailing 36. 1 0. 32 14. 8 42. 8 0. 5 28. 4 90. 5

Calculated head 100. 0 25. 10 18. 9, 17. 1 100. 0 100. 0 100. 0

Nonmagnetic from chromite cleaner concentra 44. 0 46. 7 19. 8 0. 8 79. 8 45. 2 2. 6 1.62 Magnetic from chromite cleaner concentrate l... 5. 4 22. 0 34. 1 0. 6 4. 6 9. 7 0. 3

Calculated head chromite cleaner concentrate 49. 4 8 21. 4 0.8 84. 4 54. 9 2. 9

REAGENTS, POUNDS PER TON 0 F ORE Oleic acid k i lw NaF also. pH

Rougher "MANN! 4. 12 0. 82 11. 8 11. 8 2. 7 Cleaner l. 0. 36 4. 7 5. 9

The results recorded in Table 4 show that 09.5 percent 01' the chromium was recovered in a rougher concentrate that assayed 39.3 percent C1301. Final cleaner flotation concentrate showed a recovery of 88.4 percent of the chromium, assayed 43.1 per cent C1'2O3, 21 percent lron, 1.0 percent S102, and had a chromium to iron ratio of 1.40.

By using low intensity magnetic separation to reject magnetite and iimenite from the chromite cleaner concentrate, 79.8 percent of the total chromium was recovered in a nonmagnetic product that assayed 46.7 percent CrzOa, 19.8 percent Fe, 0.8 percent 8102 and had a chromium to By flotation, 05.0 percent or, the chromium was.

recovered in a rougher concentrate that assayed 38.8 percent CraOa. The flnai chromite cleaner concentrate represented an 84.2 percent recovery oi the chromium. and assayed 41.50 percent CraQs, 23.0percent Fe and 1.0 percent 810:. Resuits were comparable to those given in Table and reagent consumption wasiower.

EXAMPLE 1v Proms: Mun-Sums A The following flotation tests recorded 111' Tables 7, 8, 9, and were made on sands from the Pioneer mine. Procedure for flotation onthese sands iron ratio of 1.62 to 1. difiers somewhat from procedure used in the flo- Table 5 Assay, percent Distribution, percent Product Ratio percent Cr/Fe C1101 Fe B10: CHO Fe SlO Chromite cleaner concentrate 1 46. 6 42.00 20. 8 1. 0 80. 6 44. 8 3. l Chromite cieaner concentrate 2 4. 5 33. 72 28. 4 1. 6 6. 2 5. 8 0. 5 Chromite cleaner tailing 8. 8 21. 25. 8 9. 0 7. 7 l0. 5 5. 2 Rougher tailing 40. 1 3. 33 20. 9 34. 3 5. 5 38. 8 I 91. 2

Calculated heads 100. 0 24.32 21. 6 15. 0 100. 0 100. 0 100. 0

REAGENTS, POUNDS PER TON 0F ORE Oleic acid l ly NaF H 801 pH Rougher flotation 1. 49 0. 30 2. 98 2. 19 3. 8 Cleaner flotation 25 0.05 2. 39 1.00

The results given in Table 4 show a recovery of 94.5 percent of the chromium in a rougher concentrate that assayed 38.4 percent C12O3. However, 80.6 percent of the chromium was recovered in the final chromite cleaner concentrate that contained 42.00 percent CraOa, 20.8 percent Fe and 1.0 percent S101. Smaller amounts of re- CHEMICAL ANALYSES, PER CENT agents were used in this test than in the one rec1101 1:. s10. MgO 111,01 c110 2101 T10, corded in Table 4, but recovery of chromium was not quite as good. Pioneer-Mine 21.00 201 11.4 5.3 1.4 23 210 1.01

Table 6 Assay, percent Distribution, percent Product Ratio percent Cr/Fe C1301 Fe 810; C1101 Fe S10;

Chromite cleaner concentrate 1 50.1 41. 21.0 1. 0 84.2 53. 3 3 1 1. z; Chromite cleaner concentrate 2 2.9 34. 26 25. 0 2. 8 4. 0 3. 3 0. 5 94 Chromite cleaner 7.6 22.40 19.8 11.4 8.8 7.0 5.4 Rougher tailing Y 30.4 3.10 10.0 31.3 5.0 304 91.0

' Calculated heads 100.0 24.7 21.0 10.1 100.0 100.0 100.0

REAGENTS, POUNDS PER TON 0F ORE Oleic acid 5 511 35 No!" mso. pH

Rougher flotation 0. 97 0. 2) 2. 28 3. 04 3. 1 Cleaner flotation 25 05 1. 97 99 Table 7 I SCREEN ANALYSIS 0N PIONEER MINE HIGH CHROMITE SAND Assay, percent Distribution, percent we, Product mt 01-101 Fe 010, 01,0. Fe 8101 +48-meah 58 12.3 30.5 20. 3.0 5.1 103 oli-muh 20.3 18.6 21.3 21.0 203 30.1 301 53.3 241 20.1 143 51.0 525 400 100-mesh 10.0 20.9 21.0 7.2 100 11.1 4.1

Calculatedhcads" 1000 22.7 201 100.0 1000 100.0

The screen analysis given in the table shows an increase in chromite grade in the finer sizes with silica tending to remain in the coarser sizes. Only a very small amount of minus 200-mesh material was present in the ore.

The procedure-for flotation of chromite from the Pioneer mine sands recorded in Table 8 was as follows:

1. Sands as received were pulped with tap water to about 50 percent solids and an emulsion of oleic acid stabilized with Emulsol X--1 was added until flocculation waspronounced.

2. A dilute solution of 10 percent HF was added until the flocs were clean of garnet and gangue.

3. Flotation was carried out until all recoverable chromite had been removed in the froth.

Table 9 CHROMITE FLOTATION EMPLOYIN G HYDRO GEN FLUORIDE IN PLACE OF FLUORIDE-AO:ID

1 Assay percent Distribution, percent Product Ratio percent Cr/Fe Ono: Fe SiO Ono: Fe Slog Chromite cleaner concentrate 53.0 41.0 2o. 3 a 7 19. e 46. a c. e 1.38 Chromite cleaner tailing 7. 2 23. 6 3 14. 6 7. 6 7. 8 6. 0 Rougher 49. B 5. 7 17. 0 3 12. 8 45. 4 i 87. 4

Calculated heads 100. 0 22. 2 18. 7 17. 8 100. 0 100. 0 100. 0

REAGENTS, POUNDS PER TON OF ORE Olelo acid i-11 9 HF pH Rongher flotat 1. 94 0. 39 0. 62 3. 9 Cleaner flotatiom- ..50

1. Sands as received were pulped with tap water to about percent solids, equal amounts of sodium fluoride and sulfuric acid were added and the pulp was conditioned for 2 minutes.

2. An emulsion of oleic acid stabilized with Emulsol X-l was added until all the chromite was well fiocculated.'

3. The pulp was diluted with tap water to about 25 percent solids and all recoverable chromite was floated.

Table 8 CHROMITE FLO'IATION EMPLOYIN G FLUORIDE-AOID TREATMENT AHEAD OF FATTY ACID Assay percent Distribution percent Product Wt., Ratio percent I Cr/Fe Ono: Fe S10, CHO: Fe Bio:

Chromite cleaner concentrate 41.3 41. 5 2o. 9 1. s 77. 5 4e. 4 3. c 1. 3c Chromite cleaner tailing 12. 7 25. 2 18. 4 13. 1 14. 4 12. 6 i 9. 5 Bonghertailing 46.0 3.9 16.6 32.9 &1 41.0 sec Calculated heads 100. 0, 22. 1 18. 6 17. 4 100. 0 100. 0 100- 0 REAGENTS, POUNDS PER TON OF ORE Oleic acid kifw NaF mso. pH

Roughflnfaflnn 4. m 0. 84 2. 0 2. 0 4. 4 Cleaner flflmfifln 25 05 1. 0 1. 6

Results show that 91.9 percent of the chromium was recovered in the rougher chromite concentrate at a grade at 38.4 percent CrzOc. By cleaning the rougher concentrate, 77.5 percent of the chromium was recovered at 41.5 percent cated consumption in the fluoride-sulfuric acid circuit.

EXAMPLE V Locxnn Tnsrmc A locked rougher flotation test was run on Pioneer mine sands to determine the effect of returning middlings and flotation water to the circuit. Six rougher tests were run, each of which produced a clean rougher concentrate, a-scavenger concentrate, and a rougher tailing. The scavenger concentrate, together with tailing water from each test, was added to the feed in 76 each succeeding test. Combined rougher tailings were later reground for minutes in a laboratory ball mill and refloated to produce a concentrate and a clean tailing. The combined flotation products were further cleaned by removing magnetite and ilmenite on a disc-type high intensity magnetic separator. The results are given in Tables and 11..

Various changes can be made in the invention since many apparently widely diflerin: embodiments thereof will occur to one skilled in the art.

5 What is claimed is:

1. A process for the beneflciation of chromium ores which comprises agitating and aerating an Table 10 LOOKED TEST 0N PIONEER MINE BANDS Assay percent Distribution percent P duct I Ratio percent Cr/Fe CnOt Fe 5101 C110: Fe BiO:

A. Combined rougher chromite concentrate-..-. 43. 8 41.4 no 5 3. 0 81. 1 48. 6 D. Scavenger its conet. irom No. 8 of .7 23.0 18.8 0 .7 .7 Combined rougher tailings 55. 5 7. 8 17. 0 29 4 18. 2 50. 7

Calculated heads 100. o 22. 4 1a 4 17 a 100.0 100.0

B. Regrind cleaner chromite concentrate 5. 4 36. 2 19. 2 4. 6 8. 7 5. 6 1. 4 1. 29 C. Regrind cleaner chromite taiiings'n'n 7. 0 20. 9 16. 3 17. 0 6. 5 5. 1 6. 7 88 Regrind rougher tailings 43. l l. 5 16. 8 34. 6 3. 0 39. 0 84. 0

Calculated rougher tailings I 55. 5 7. 3 17.0 29 4 i8. 2 50. 7 92. 1

TOTAL REAGENTS, POUNDS PER TON OF ORE Oleic acid 5i??? NaF mso. 5

R0 her flnfmflnn 2. 38 0- 8 0. 59 1. 60 3- 6 Reg! (1 rougher flotation 66 14 54 l. 32 3. 3 Regrind cleaner flotation 04 13 33 3. 4

The results of the locked flotation tests indicated that the middlings would not build up 35 aqueous pulp of such an ore in the Presence of hydrofluoric acid, and a long-chain fatty acid at a pulp acidity of between pH 1.5 and pH 5.5, and separating a chromium-containing froth as a concentrate.

2. In a process for the beneiiciation of chromium ores the steps which comprise agitating and aerating aqueous pulp of a comminuted chromite ore in the presence of a long-chain fatty acid, and an acidic fluorine compound at a pulp acidity between pH 2.5 and pH 4.5, and recovering a froth containing a chromite concentrate.

Table 11 I MAGNETIC SEPARATION OF FLOTATION CONCENTRATEB [OBTAINED FROM LOCKED TEST Assay percent Distribution percent Product Wt., Ratio percent Cr/Fe CHO: F8 S10: CHO: Fe 5104 Nonm etlc from rodnct A 38. 8 45. 3 18. 9 2. 0 77. 1 39. 6 0. 3 Magnet 0 from pro not A 5. 0 18. 2 33. 4 0. 8 4. 0 9. 0 7. 0

Calculated heads product A 43. 8 42. 2 20. 6 1. 9 B1. 1 48. 0 7. 3

Nonmagnetic from products A and B 43. 1 44. 5 18.4 2. 4 84. 7 43. 2 0.8 Magnet 0 from products A and B 6.1 18. 8 33.0 1. 6 5. 1 11. 0 7. 9

Calculated head products A and B 49. 2 41. 3 20. 2 2. 3 89. 8 54. 2 8. 7

N onmagnetic from (Products A, B, C, D 50.0 41. 9 18.0 4. 4 91. 4 49. 0 0. 8 Magnetic from pro note A, B, C, D 6. 9 19.0 32.2 1.6 5. 6 12.0 15. 2

Calculated head products A, B, C, D 56. 9 39. 1 19. 7 4. 1 97. 0 61. 0 16.0

The use of magnetic separation to remove '3. Ina process for the beneflciation of chrosmall amounts of magnetite and ilmenite from mium ores, the improvement which comprises flotation concentrates would permit plus 90 percent recoveries at 41.9 percent CrzOa grade or grades up to 45.0 .percent CrzOa with lower recoveries.

Asshgwn in the foregoing examples, the flotation procedure can be followed by a agnetic concentration further to remove magnetic iron compounds from the concentrate s cured by tfzlrottation to yield a still higher grad concenagitating and aerating an aqueous pulp of a comminuted chromite ore in the presence of a long-chain fatty acid, a dispersing agent, and a soluble fluoride at a pulp acidity between pH 1.5

and pH 5.5, and recovering a froth containing a chromite concentrate.

4. In a process for the beneflciation of chromium ores, the improvement which comprises agitating and aerating a chromite ore pulpcomminuted to a particle size between minus 20- mesh and minus 800-mesh in the presence 01.,

per ton of ore, from 0.1 to 10 pounds of a. soluble fluoride, from 0.5 to 5 pounds of a long-chain fatty acid having from 8 to 18 carbon atoms,

and an amount of a strong mineral acid sufficient to maintain the pulp acidity between pH 2.5 and pH 4.5, and recovering a chromite concentrate as a floated product.

5. In a process for the beneflciation oi chromium ores, the improvement which comprises 10 and aerating an aqueous pulp or a RICHARD HAVENS.