US3437474A - Method of making ore agglomerates - Google Patents

Description

United Patent US. Cl. 75-3 8 Claims ABSTRACT OF THE DISCLOSURE A method is provided for producing lump metal ores by admixing the finely divided ore with an alkaline earth oxide or hydroxide and a carbonaceous material, forming the mixture into lumps and reacting it with carbon dioxide in the presence of moisture to form alkaline earth carbonates in situ in the lumps.

This application is a continuation in part of my copending application Ser. No. 374,191, filed June 10, 1964, now Patent No. 3,382,063.

This invention relates to ore agglomerates and methods of making the same and particularly to a high strength and at least partially self-reducing iron ore agglomerates and methods of making such agglomerates.

The need for a satisfactory method of agglomerating iron and other ores, particularly oxide ores, has long been recognized. As the high purity, lumpy ores of the Mesabi and other ranges have been exhausted it has been necessary to turn to ore concentrates recovered from less pure ore deposits and to fine ores not heretofore considered suitable for steel making. In order to make these ores suitable for handling and use in steel melting furnaces it has been necessary to agglomerate these ores into larger pieces. This has conventionally been done by pelletizing or briquetting the fine ores and sintering or fusing the pellets or briquettes to form the solidified agglomerates. Sintering requires extremely high temperatures and large capital outlays in temperature resistant equipment.

I have invented an ore agglomerate and method of making such agglomerates which is much less expensive than these sintered agglomerates and is at least partially selfreducing.

In the preferred practice of my invention I admix ore fines with an oxide or hydroxide of an alkaline earth metal, a finely divided carbonaceous material of the group consisting of coal (both bituminous and anthracite), coke, graphite, charcoal, coke breeze and optionally with a small amount of a mineral acid salt of an alkali metal, or an alkaline earth metal and/or a small amount of an alkali hydroxide together with suificient water to permit the formation of agglomerates such as pellets, briquettes or blocks. These agglomerates are then subjected to an atmosphere of carbon dioxide for a time sufficient to convert a major portion of the alkaline earth oxide or hydroxide to carbonate.

I have found that the moisture level for most effective operation of my process is below 10% by weight of the total admixture and preferably in the neighborhood of 5% or less.

Preferably the carbonaceous material used in my process is finely divided bituminous coal and I shall hereafter discuss the invention in terms of iron ores and bituminous coal. I prefer the size range of 4 mesh and under for the coal used and good results have been attained at both ends of the range as well as with mixtures of varying particle size coal. I have found that amounts between about 1% 3,437,474 Patented Apr. 8, 1969 ice to 15% of coal by weight are most satisfactory for my purposes, although larger amounts up to 25% have been satisfactorily used in practicing my process. I have found that the use of minus mesh coal makes it possible to ball or pelletize conventional as received specular hematite concentrate without the addition of reground hematite or without the addition of any other fine ore. Prior to my invention, it had been impossible to form balls or pelletize specular hematite by usual balling or pelletizing methods without regrinding or adding another fine ore. This has been one of the very real problems in the heat indurated types of pellets heretofore made and is a very distinct advantage to be gained by the practice of this invention. I have found that this can be accomplished within the range of coal concentration set out hereinabove, although I prefer to use about 10% minus 100 mesh coal when forming specular hematite balls or pellets.

The amount of alkaline earth oxide or hydroxide, e.g. lime, preferably lies in the range from about 5% to 20% by weight of the admixture.

I prefer to add a small amount (up to about 2%) of a solubilizing agent for calcium and magnesium, as disclosed in my Patent No. 2,996,372, such as a sugar containing material, e.g. blackstrap molasses, glucose, fructose, dextrose, syrups, or the like together with a small amount of a mineral acid salt of an alkali or alkaline earth metal such as calcium chloride in an amount less than about 1%. I may also add a small amount of an alkali metal oxide or hydroxide such as sodium hydroxide, preferably in the range of about 0.1% to about 1.5%.

The practice of my invention produces a resulting product which has high strength after being subjected to elevated temperatures, e.g. l6001900 F., and which shows a high percentage of reduced iron after such heating indicating that the product is self-reducing. Both of these properties are highly sought after and difiicult to achieve.

The practice of my invention can perhaps best be explained by reference to the following examples which show the significances of the practice of my invention.

EXAMPLE I A series of test were made on pellets produced by balling specular hematite as received and reground with high volatile coal and low volatile coal and mixtures of the two types of coal, with lime and with 0.5% blackstrap molasses and 0.4% calcium chloride, The coal was used as received in which condition its size was minus 4 mesh and reground to 100 mesh (100 M). The lime was a mono hydrated dolomitic lime powder known in the trade as Ohio Super spray hydrate.

A series of tests to determine the green ball strength and characteristics were performed as follows:

Drop test A representative sample of twenty carefully sized green Wet balls are dropped individually from a height of eighteen inches onto a steel plate and the number of consecutive drops required for failure is used to determine an arithmetical average.

Green ball compression test An identical sample as just previously described is used and a compressive load is applied to individual balls and the load required to fracture is used to determine the arithmetical average.

The resulting data appear in Table I.

TABLE L-GREEN BALL STRENGTHS Specular Specular Drop Compression, Coal, type Coal, Hematite Hematite Lime, test, lbs. to failure percent cone. as cone. repercent drops to recd, ground, failure percent percent None 71. 24. 00 5. 00 6 2. 2 High volatile coal, as rec'd 9. 48 64. 10 21. 30 5. 12 13 3. 3 High volatile coal, as rec'd 100 M 4. 75 67. 60 22. 54 5. 12 14 3. 3 DC- 9. 48 64. 10 21. 30 5. 12 16 4.1 18. 96 56. 96 18. 96 5. 12 24 3. 4 D0 25. 00 52. 42 17. 46 5. 12 40 3. 2 Low volatile coal, as rec d 9. 48 64. 10 21.30 5. 12 16 3. 1 Low volatile coal, as rec'd -100 M 9. 48 64. 10 21. 30 5. 12 18 4. 1 High volatile coal, 100 M 11. 00 83. 88 None 5. 12 13 3. 1 High volatile coal, 100 M 8.00 85.00 None 7. 00 19 3.6

EXAMPLE II Open flame test The pellets of Example I were treated with carbon dioxide at room temperature to harden and convert the lime to carbonate in situ. These hardened pellets were tested as follows:

Tumble test A five pound charge of the completed pellets are tumbled in an A.S.T.M. coke tumbler and the residue remaining on a A" screen after 280 revolutions is recorded as a percentage of the original five pounds and noted as the tumble strength index.

Compression test A representative sample of twenty pellets are drawn and a compressive load is applied to individual pellets and the load required to fracture is used to determine the arithmetical average.

The results of these tests are tabulated in Table II.

Selected specimens are placed on a nichrome wire mesh screen which is located (10) ten millimeters above the grid of an ignited Fisher burner and the resultant flames are allowed to envelop the sample for a period of two hours after which the specimens are removed and a qualitative observation of their condition is noted.

Crucible test Carefully sized pellets are placed four at a time in a coal filled crucible, covered and then heated by an ignited Fisher burner for a predetermined period after which the pellets are removed and allowed to return to room temperature before being subjected to a compressive test to destruction. This cycle is repeated for various time/temperature cycles as noted for each run.

TABLE IL-ROOM TEMPERATURE STRENGTH DATA Specular Hematite Lime Tumble Coal, Coals, type c0nc., percent Taeonlte, Hydrate, Compression test, percent percent percent test, lbs. 0+}4' Reed. Reground 0 Rev.

4. 74 High volatile 100 M. 67. 60 5. 12 320 99 9. 48 .-d0 64. 10 5. 12 225 99 18.96 56. 92 5. 12 105 96 25. 00 do 52. 42 5.12 96 9. 48 Low volatile -100 M 64. 10 5. 12 170 99 9. 48 High volatile, as recd 64.10 5. 12 250 99 9. 48 Low volatile, as recd- 64. 10 5. 12 225 98 10. 00 High volatile -100 M. 84.00 6.00 260 98 0 6. 30 343 96 0 9. 10 445 5 High volatile --100 M 5. 00 205 5 6.00 255 99 5 ...do 7.00 323 9. 48 50/50 --100 high volatile] -100 low volatile 64. 10 21. 30 5. 12 205 99 9. 48 50/50 as rec'd. high volatile and low volatile 64. 10 21.30 5. 12 240 98 EXAMPLE III The carbonated pellets of Example II were tested at elevated temperatures and in reducing atmospheres as Reduction test Pellets which had been heated in the above described crucible test are placed in a magnetic field and the degree follows and compared to a commercial taconite heat inof attraction is recorded as a qualitative observation.

durated pellet.

The results appear in Table III.

TABLE III.-CRUCIBLE TEST DATA Crucible test, load to Specular Hematite Lime failure, lbs. Coal percent-type conc., percent Taconite, hydrate,

---- percent percent After tlmeln minutes Ree'd Reground None 72 23 5.00 410 23 14 9 8 11 12 4.74 high volatile M 67.6 22.54 5 12 320 30 30 29 29 29 27 Heat indurated taconite pellet 500 23 15 16 19 12 18 9.48 -high volatile as rec'd. 64. 1 21.3 250 27 27 24 22 22 19 9.48 high volatile 100 M- 64. 1 21.3 5.12 225 30 30 30 30 29 21 Do 34.2 51.20 5.12 180 30 30 30 30 30 27 9.48 --low volatile as recd. 64. 1 21.3 5. 12 30 25 21 20 20 17 18.96 high volatile 100 M. 56.96 18.96 5. 12 30 23 23 17 15 10 11.00 high volatile 100M 83.88 5.12 30 28 23 20 19 12 13.00 high volatile 100M 81.88 5.12 135 30 30 29 25 22 16 None 70.0 23.5 6.50 500 30 26 23 16 19 17 10.00 hlgh volatile -100 M- 84.0 6.00 30 30 30 30 26 18 D 83.0 7.00 178 30 3O 30 30 28 22 57.00 38.00 5.00 11 5 8 8 8 9 0 51.2 34.2 5.12 5 5 3 2 2 3 3 60 40 None 10 2 2 2 2 2 2 l Non-carbonated. l N on-carbonated, 0.75 bentonlte.

6 EXAMPLE IV EXAMPLE VII Pellets were made as in Example II by carbonation sub- A series of tests were made on pellets produced by stituting taconite concentrates for the specular hematite. mixing together lime hydrate, specular hematite ore These pellets were subject to the same tests as Examin both the as received and the reground" forms ple III and the data tabulated in Table IV. 5

TABLE IV Crucible testload to Specular hematite Lime iailure, lbs. Coal percent-type conc., percent Taconite, hydrate,

percent percent Aiter time in minutes Recd Reground None 93. 7 6. 3 343 30 30 30 3O 30 30 5.00 -high volatile -100 M- 88. 0 7. 0 323 50 4O 30 30 3O 30 None 93. 28 l 6. 72 10 16 25 28 13 19 9.48 high volatile 100 M. 83. 80 1 6. 72 7 8 7 9 7 6 8 1 N on-carbonated.

EXAMPLE V Pellets were made by admixing lime hydrate, coal and or as in Example I, The resulting pellets were subjected as Example I but .Substltutmg vanous P to carbon dioxide suificient to form recrystallized limeof carbonaceous i for coal and omlttmg stone in situ. The carbonated pellets were then divided 99 and chloride The resulthngpenets. were into two Parts one heated to 16000 F. and the other to sub ected to an atmosphere of carbon d10x1de as in Ex- 17000 R in an atmosphere containing carbon monoxide ample I to form recrystallized limestone 1n s1tu. These such as would be encountered in a blast furnace or like hardened pellets were tested as were the P m Exiron handling furnacl The pellets were removed and 30 ample II. The results of the tests appear in Table VII. analyzed for'reduced iron. The results are tabulated in Table V.

TABLE Vr-CARBONATE BONDED PELLET SUMMARY Percent Reduction 'Iaconite Concentrate 6% Lime Hydrate 38. 7 44. 8 6% Lime Hydrate Plus 5% High Volatile Goal (-100 M) 49. 1 31, 5 Specular Hematite Concentrate 23.5% Reground (-325 M) Specular Hematite Plus 5% Lime Hydrated" 39. 3 45. 6

23% Reground Specular Hematite (-325 M) 50. 6 74. 1

Plus 5% Lime Hydrate Plus 5% High Volatile Coal 39. 8

As Received Specular Hematite Plus 5% Lime Hydrate Plus 10% High Volatile CoaL 49. 1 87. 1

TABLE VII.-ROOM TEMPERATURE STRENGTH DATA.

Pellet Composition: Specular Hematite as received, 17%; Specular Hematite reground, 70%; Lime Hydrate, 9%; Carbonaceous Materials,

EXAMPLE VI An addilional series of pellets were made as in Example V and after removal from the heating furnace at Tumble Test, 1600" F. and 1700 F., respectively, were screened to %g egp eg wn 048433 determine the amount above 4 mesh and the amount Coke Breeze 161 96 below 20 mesh. They were then jarred for 15 minutes in Anthmeitm 113 89 Graphite. 119 89 a container and again screened The test results appear n Charcoal 173 96 Table VI.

TABLE VI Screen Test From Furnace Screen Test Alter .larring 'Taconite 1,600 F. 1,700 F. 1,600 F. 1,700 F.

+4 20 +4 20 +4 20 +4 20 M M M M M M M M 6% Lime Hydrate 96. 7 1. 67 96. 9 1. 48 43. 7 51. 8 9% Lime Hydrate. 0. 1 90. 87 0. 13 77. 82 21. 96 78. 28 21. 62 12% Lime H drate 0.3 99. 5 0. 2 83.9 15. 9 82. 8 16. 8 9% Lime Hydrate plus 10% High Vola le Coal (minus 8 M) 99. 2 0.38 97. 6 0. 13 80. 64 17. 30 80. 09 15. 0 9% Lime Hydrate plus 8% High Volatile Coal (minus 8 M) and 2% Low Volatile Coal (minus 8 M) 98. 62 0. 61 99. 47 0 23 81.00 16. 98 84. 17 14. 24 9% Lime Hydrate plus 8% High Volatile Coal (minus 8 plus 150 M) and 2% Low Volatile Coal (minus 8 plus 150 M) 96. 69 0. 56 98. 57 0 42 81. 77 14. 23 78 77 17.37 Specular Hematite:

25% Reground (minus 325 M) plus 5% Lime Hydrate plus 15% High Volatile Coal (minus 100 M) 99. 0.35 96. 80 2 54 76. 77 20.17 57. 12 36.61 Venezuelan Ore:

Plus 4.76 Lime Hydrate 97. 59 0.87 60. 43 32. 41 6% Lime Hydrate-t-I5% High Volatile Coal (minus 100 M) 98.0 1.0 95.4 2 0 85. 11. 79 84. 12. 82

3,437,474 7 8 EXAMPLE VIII to about 1% of mineral acid salt of a member from the group consisting of alkali metals and alkaline earth metals and about 0.1% to about 1.5% of a member from the group consisting of alkali metal oxides and hydroxides,

Pellets made for Example VII were then treated in the heated furnace as in Examples V and VI. The test results appear in Table VIII.

TABLE VIII Pellet Composition: Specular Hematite as received, 17%; Specular Hematite regound, 70%; Lime Hydrate, 9%; carbonaceous Materials, various, 4%.

Screen Test From Furnace Screen Test After Jar-ring carbonaceous Materials, types 1,600 F. 1,700 F. 1,600 F. 1,700 F.

+4 M 20 M +4 M -20 M +4 M 20 M +4 M -20 M Coke Breeze 99. 6 0.30 23. Anthracite 99. 8 0. 19 26. 2 Graphite 0 26 24. 6 Charcoal 0 39 21.2

Heat, Indurated Taconite Pellet... ill. 67 1. 37 93. 41 1. 37 72. 24 15. 35 68. 17 20. 03

It will be evident from the foregoing tables and exforming the mixture into lumps and reacting the lumps amples that a high strength pellet capable of a high level with carbon dioxide in the presence of moisture to form of self-reduction can be achieved by the practice of my alkaline earth carbonates in situ in the lumps.

invention. 5. The method as claimed in claim 4 wherein the mois- While I have described certain preferred practices ture level in the mixture is less than about 10% by weight and products according to my invention, it will be under- On the total admixture. stood that this invention may be otherwise embodied Th method of producing a high strength, self within the scope of the following claims. 25 reducing lump ore from finely divided iron containing I claim: materials comprising the steps of admixing the finely di- 1. The method of producing a high strength, self revided iron containing material with about 5% to 20% ducing lump ore from finely divided iron containing of at least one of the group Consisting of the oXideS and materials comprising the steps of admixing the finely dihydroxides of alkaline earth metals and with between vided iron containing material with at least one of the about t f a a mus material from the group consisting of the oxides and hydroxides of alkaline the g oup consisting of coal, eoke, coke breeze, graphite earth metals and with a carbonaceous material from the and charcoal, forming the mixture into lumps and reactgroup consisting of coal, coke, graphite, coke breeze and g the l mp W t a n di Xid in the presence of charcoal, forming the mixture into lumps and reacting moisture to form alkaline earth carbonates in situ in the lumps with carbon dioxide in the presence of moisture the psto form alkaline earth carbonates in situ in the lumps. The m d as C aimed in Claim 6 wherein up to 2. The method as claimed in claim 1 wherein up to about 2% of a Solubililihg agent for Calcium and gabout 2% by weight of the total mixture of a solubilizing heeium is incorporated ihlo the tur agent for alkaline earth metals is added. The method of Producing a high Strength p 3. The method as claimed in claim 1 wherein a mineral iron Ore as C a in cla m 6 wherein the mixture conacid salt from the group consisting of alkali and alkaline m ne up to about 10% moisture. earth metals is added in an amount up to about 1% on the weight of the admixture. References Cited 4. The method of producing a high strength, self reducing lump ore from finely divided metal containing UNITED STATES PATENTS materials comprising the steps of admixing the finely 145462 12/1873 Taylor 75 3 divided metal containing material with at least one of 2,823,109 2/1058 Sudo 753 2,996,372 8/1961 Imperato 753 the group consisting of the oxides and hydroxides of alkaline earth metals and with a carbonaceous material 3,205,063 9/1965 Frankhn et a] 75' 3 from the group consisting of coal, coke, graphite, coke breeze and charcoal, adding thereto up to about 2% D EWAYNE RUTLEDGE Pr'mary Exammer of a solubilizing agent for magnesium and calcium, up ERNEST L. WEISE, Assistant Examiner.