US3154403A - Process for pelletizing ores - Google Patents

Description

United States Patent C) 3,5 %,403 PROCESS FOR hELLlETiZiNG GEES Edward S. ticliley, Edwin Gritiith, and Evan W. Wiiiiams, Dodge ity, Karts, assignors to Grain Products, inc, Dodge City, Karts, a corporation of Kansas No Drawing. Filed Sept. 24, 1962, Ser. No. 225,855 illaims. (Cl. 75-3) This invention relates to a process for pelletizing granular and pulverulent ores and, more particularly, to a process for pelletizing finely divided oxidic iron concentrates.

Until recently, much of the iron for the steel industry has been obtained from the rich iron ore deposits found primarily in the northern United States around the Great Lakes region, and Canada. Because such ores, containing 50% iron, are being steadily depleted, the industry has recently been turning its attention to lean ore deposits such as taconite, which contain approximately to iron. Heretofore, these ores have never been exploited to the extent of the rich 50% ores because they must first undergo beneficiation to render them suitable for charging into a blast furnace. Growing interest in such low grade ores is readily apparent when it is noted that in 1961 16,000,000 tons of taconite pellets were consumed by the steel industry compared to the 1,000,000 tons consumed in 1955. Use of such pellets, along with higher top pressure, better coke and sinter, can almost double the production capacity of the blast furnace.

Many processes are known for beneficiating ores and then pelletizing the resulting beneficiated ore particles. Such processes include crushing or pulverizing the ore into granular or powder form, and then separating the ore granules or particles from the gangue particles, such as silica and the like. The beneficiated ore, while richer in metallic content, is unsuitable for use in a blast furnace in its granular or powdered form and must be first pelletized into masses of from one-eighth to an inch or more in size. The pellets, preferably uniform in size, when charged into a blast furnace, become loosely packed therein and permit the furnace blast to pass upwardly therethrough during the smelting operations.

A suitable process for pelletizing ores is disclosed in the Firth Patent 2,411,873, wherein initially moist particles of oxidic iron are first rolled into ball-like masses, commonly referred to as green compacts, Within a rotating drum. The moistened compacts, after being subjected to a thermal hardening or indurating treatment, have a high degree of mechanical strength imparted thereto. However, when the initially moist compacts are subjected to this thermal indurating treatment, the heat of the process causes the compacts to first undergo dehydration and, when largely dehydrated and prior to being indurated, the dry compacts have the least mechanical strength, so that they are susceptible to being fractured and even powdered, during the normal handling thereof prior to induration.

To avoid such fracturing and powdering of the fragile, friable dry compacts, binders of various types have been utilized by the art. The binder material is preferably i11- corporated into the moistened particles before or during the balling operation and, being admixed therewith, forms an integral part of the green compact. Upon being dehydrated, during the initial phase of the induration treatment, the mechanical strength of the dry compact is materially improved by the binder, and the compact passes through this transition phase to form a hard, indurated pellet suitable for shipment and subsequent use in a blast 3,l5i,d3 Patented Get. 27, 1964 "Ice furnace. Bentonite is the binder which has been preferred by the industry and it is normally used in an amount of about 12 to 18, and preferably about 12 to 14, pounds per long ton of ore. Other binders which are known or have been suggested for pelletizing ores include sodium silicate, gum arabic, sugar, starch, and the like. None of these binders, with the exception of bentonite, have proved satisfactory for commercial purposes. Since bentonite is a clay, use thereof as a binder means that the amount of silica in the indurated pellets is proportionately increased, and since the pellets must be shipped to the mills, part of the shipping cost is attributable to the added silica.

It is known that starch is more effective as a binder than bentonite, and impartes a greater strength to the dry compacts during the transitional phase from dry compact to indurated pellet. However, when commercially available starch, including raw starch and pregelatinized starch, is used as the binder and admixed with the moistened finely divided ore, the starch material, without exception, causes aglomeration of the ore particles and clustering of the partially formed compacts in the balling apparatus, to such an extent that control of the process on a commercial scale is lost. One-half pound of starch per long ton of ore was the maximum that could be tolerated, and a considerable amount of bentonite had to be used at this level. Clustering of the green compacts as they are being formed prevents the formation of uniform pellets during the pelletizing operation. Since the balling process is a continuous process in which a constant amount of material is kept within the drum, and considering that the balling apparatus commercially being used can form anywhere from 30 to 50 tons of green compacts per hour, the importance of inhibiting the clustering of the green compacts and the consequent loss of control of the process becomes obvious. Since high production rates reduce the operating costs per ton of finished pellets, and cost is of critical importance in such a highly competitive industry where production volume is huge and profit margins per ton of product are small, starch has not been used successfully on a commercial scale because of its tackiness and aforesaid disadvantages.

Accordingly, it is an object of this invention to obviate the difficulties which occur when starch is used as a binder for finely divided ores during the balling process.

Another object of this invention is to take advantage of the improved bonding properties of starch as the binder for dry compacts of finely divided ores.

A further object of this invention is to provide a process for producing indurated pellets from finely divided oxidic iron concentrates which pellets have the proper composition and physical characteristics suitable for use in a blast furnace.

It is another object of this invention to provide a process for facilitating the pelletizing of finely divided oxidic iron concentrates, such as those obtained from taconite and consisting primarily of magnetite or hematite, while maintaining high production rates so as to reduce the overall cost per ton of indurated pellets.

In attaining the objects of this invention, one feature resides in using as a binder for the compacts a particular expanded cereal grain having properties which render it non-tacky and thus prevent it from causing clustering of the partially formed green compacts while at the same time substantially improving the mechanical strength of the dry compacts.

Another feature resides in the use of a mixture of C9 bentonite and the expanded cereal grain product as the binder wherein the amount of bentonite in the mixture and, in fact, the total amount of the binder mixture, is considerably less than the bentonite which ordinarily would be used to produce the same results.

Other objects, features, and advantages of the invention will become more apparent from the following disclosure thereof.

It has been discovered that if an expanded cereal product made in accordance with the process described in copending application Serial No. 37,765, filed June 21, 1960, which process is wholly incorporated herewith by reference and is to be considered a part of this disclosure, is used as a binder for the finely divided ore, the green compacts which are formed in the rotary drum during the compacting or balling process do not cluster together as normally occurs with other starches but, instead, the spherical green compacts remain separated as they increase in mass during the rolling operation. When the moist green compacts are subjected to the normal thermal induration treatment, they become dehydrated and, while in this transitory stage, the finely divided concentrates in each pellet are tightly held together by the binder. As the dry compacts are subjected to further heat, they become indurated and are referred to as pellets or pelletized merchantable ore, suitable for shipment to steel mills for use in the blast furnaces.

While the invention will be discussed in terms of pelletizing finely divided oxidic iron concentrates, and particularly in terms of taconite which consists primarily of magnetite or hematite, it is to be understood that the binder of the present invention can be used in the pelletizing process for ores in general, if a binder is necessary in order to maintain the ore masses or compacts in their particular configuration pending further treatment thereof.

The expanded cereal products which have given excellent results as binders for taconite ore have been those produced from starch-bearing cereal material, and examples of such material include whole grains, decorticated grains and/or separates thereof, and particularly corn, Wheat, rye, barley, sorghum and other grains. The cereal material is first conditioned by blending with water and steam until the moisture content is about 15 to by weight of the material, while the temperature of the moistened material is maintained below that at which the starch would turn to paste. The heated, moistened material is then compressed and sheared into a compacted plastic mass within a suitable expander apparatus, while maintaining the mass at a temperature of at least C. and a pressure sufficient to maintain the water in a condensed state therein. By then rapidly decreasing the pressure to vaporize the water within the plastic mass, usually by extruding the mass into the atmosphere, the mass is caused to rapidly expand. The expanded cereal product which forms is then granulated, and the granulated product has been found to be a binder suitable for the purposes of the present invention. One form of expander apparatus suitable for mechanically compressing and shearing the cereal material into a compacted plastic mass is disclosed and illustrated in the aforesaid copending application Ser. No. 37,765, which apparatus also is incorporated into the present application by reference.

The expanded cereal product thus formed, when examined under a microscope, has the starch granules discernible as entities. The granules are greatly distended or swollen and completely disorganized internally so as to have their polarization crosses removed. Thus, the granules, having been freed from the cellular structure of the cereal tissue and having been disorganized internally but not ruptured, can separate readily from each other when wetted, and may swell but will not disgorge their starch contents. Thus, the expanded cereal material is dispersible, in a granular sense, as distinguished from dispersible in a molecular sense, i.e., the cellular tent of 18-20%.

and granular structures have been destroyed and starch and protein have been freed and fragmented so as to allow a high degree of solubility in water and permit the formation of pastes and sols having desirable properties.

Besides being dispersible in the granular sense defined above, the cereal product binders of the present invention have the following properties:

Cold water solubles "percent" Less than 25 Consistency (Water sorptive properties) ccs 7-11 10% cold paste viscosity cps 50-500 10% cooked paste viscosity:

Hot cps SOD-2,500 Cold (24 hours) cps 3,000-10,000

Excellent cereal binders for finely divided metallic ores, such as taconite, have been prepared and used wherein these binders have had. the aforementioned granular dispersibility and also properties coming within the following ranges:

Cold water solubles percent 10-25 Hot water solubles ccs 25-60 Consistency (water sorptive properties) ccs 7-11 Fat percent 1.0-2.5 Bulk density lb./cu. ft 38-45 10% cold paste viscosity:

Initial cps 50-500 Final (24 hours) cps 50-1,500 10% hot paste viscosity:

Hot cps 5002,500 Cold cps 3,000-10,000

The following examples are to be considered as being illustrative of the processes for forming the cereal binders of the invention:

EXAMPLE 1 Whole sorghum grain was first ground to produce a flour of a fineness such that essentially all would pass through a US. No. 20 sieve and no more than 10% would ride on a US. No. 30 sieve.

The granulated flour having a 12% moisture content was fed into an expander at the rate of 6000 pounds per hour and water was immediately added thereto at a rate of from 360 to 400 pounds per hour, together with a sufiioient quantity of steam to raise the moisture content to from 16 to 19%, and to raise the temperature of the flour to within a range of from 49-75 0., thus permitting conditioning of the flour as it moved downstream in the expander. After flowing downstream for approximately 15-20 seconds, more steam was intro duced into the conditioned flour, and the steam in combination with the mechanical forces within the expander, ruptured the cereal tissue structure and gelatinized the starch, as the flour was compressed and sheared into a plastic mass by the expander. The tempeiature of the plastic mass was raised by the steam to within a range of from to C. at the point immediately adjacent to the die plate of the expander. The mass was discharged through tapered dies having a minimum diameter of /2" and the extruded mass immediately expanded and was pelletized in the manner described in co-pending application Serial No. 37,765. The pellets, after expansion and the flashing off of steam, had a moisture con- The pellets were dried in a gas-fired drier at a temperature around 120 C. until a final moisture content in the range of 11-13% was. attained. The dried pellets were then ground to a fine powder, all of which passed through a US. No. 50 sieve. The ground cereal product had the properties set forth in Table I, infra.

EXAMPLE 2 A whole grain sorghum flour was prepared by grinding sorghum grain in a hammer mill so that all of it passed through a No. 20 U.S.B.S. sieve, and approximately 88% passed through a No. U.S.B.S. sieve. The flour was then fed into an expander, such as that illustrated in copending application SN. 37,765, .at a rate of 1800 pounds per hour, together with water at a rate of 95 pounds per hour, and steam which raised the moisture content of the flour to from 2024%, and increased the emperature of the mass. As the mass passed downstream in the expander, it was compressed and sheared into a compact plastic mass which reached a maximum temperature of 143 C. at a point just before being ex panded through dies of A" diameter. The expanded pellets were dried, crushed, and ground so that all passed through a No. U.S.B.S. sieve.

Other cereal binders were made in accordance with processes such as described above in Examples 1 and 2, with the exception of certain minor differences in operating conditions, such as rate of feed, water content, and the like.

All of the expanded cereal products had the starch granules freed from the cellular structure of the cereal tissue and, while disorganized internally, the granules were not ruptured. When wetted, the granules readily separated from each other and while they swelled, they did not disgorge their starch contents. The properties of the products of the examples are as follows:

Table 1 Examples Properties I II III IV V Moisture Content percent 4. 4 5.0 6. 8 7. 8 9. 2 Cold Water Solubles percent 18. 1 17. 4 13. 7 10. 7 18.3 Hot Water Solubles percent 52.7 51. 6 39. 5 27. 9 35. 2 Reducing Power (R.C.U.) 90 79 66 62 Fat percent 1. 88 1. 26 2. 04 1. 21 Consistency (ccs Water Sorp Capacity 9 8 8 8 10 Bulk Density (lbs/cu. 40. 8 40. 3 10% Cold Paste Viscosity:

(a) Initial (cps.) 260 80 60 140 (11) Final (24 hr.) (cps) 1,250 80 10% Cooked Paste Viscosity:

(a) Hot (cps) 2,070 540 1, 660 1,830 1, 600

' (0) Cold (cps) i 9, 100 3, 880 6, 550 6,900 4, 400

EXAMPLE A The cereal product of Example I was added to moistened, finely divided taconite ore in a amount of 4 lbs. per long ton of ore and the mixture was readily balled into green compacts which when dehydrated to dry compacts at the beginning of the induration treatment had excellent mechanical strength and, more importantly, no clustering of the green compacts occurred during the balling operation.

EXAMPLE B A mixture of 3 pounds of the expanded cereal product of Example 1 and 7 pounds of bentonite per long ton of ore was fed in a continuous stream onto the conveyed stream of moist taconite ore during a commercial operation without any auxiliary mixing being required. The balling drum was 9 ft. in diameter and 30 ft. in length, and had a feed rate of approximately 46 long tons of ore per hour. Spherical green compacts were formed in the normal manner without any clustering occurring and the compacts readily underwent the normal indurating treatment without any ditficulty. The dry compacts which formed prior to indurating had excellent strength and withstood the normal handling encountered in a commercial pelletizing process.

EXAMPLE C A mixture of 4 pounds of the expanded cereal product of Example 1 and 6 pounds of bentonite per long ton of taconite ore was used as the binder and also fed into a continuous stream onto the conveyed stream of moist ore. The agitation of the moist ore in the rotary balling drum of the type described in the Firth Patent 2,411,873 was 6 sufficient to insure adequate mixing of the binder with the ore as balling occurred. Sufficient binder was present in each green compact to impart the necessary strength to the dry compact during its critical transitory dehydrated phase prior to induration.

EXAMPLE D A mixture of 3 /2 pounds of the expanded cereal product of Example 2 and 4 pounds of bentonite per long ton of ore was used satisfactorily as a binder for taconite ore to produce dry compacts of sufficient mechanical strength to resist fracturing during the pelletizing process. When a mixture of 3 /2 pounds of the Example 2 product was admixed with 6 pounds of bentonite, similarly good results were obtained.

Each of the expanded cereal products of Table I were found to be suitable for use as binders in the pelletizing process for finely divided oxidic iron concentrates. None of these binders caused any clustering of the raw green compacts as they were being formed during the balling operation. While the binders of the present invention are suitable, per se, they can also be admixed with other binders, if desired. Thus, while it has been the practice of the industry to use anywhere from 12 to 18 lbs., and preferably from 12-14 lbs., of .bentonite per long ton of taconite ore, and as much as 30 lbs. has been used, by use of applicants invention the amount of silica introduced into the pellets by the bentonite may be considerably reduced by either (1) reducing the amount of ben-tonite required to less than half by the addition of a small amount of the expanded cereal product of the invention, or (2) substituting the expanded cereal product for the bentonite or other binder which has heretofore been used.

Throughout the specification Where reference is made to the normal pelletizing operation for finely divided ore, it is intended to refer to the balling and indurating processes which result in the final indurated pellets. In the balling process the finely divided ore is moistened with from 6 to 30 percent by weight of water, and preferably from 8 to 12 percent if the process of Firth Patent 2,411,- 873 is followed. Enough water is present to give the balls of ore or green compacts sufiicient wet strength to permit a limited amount of handling. However, when the green compacts are subjected to the normal thermal indurating treatment, the ore particles are heated to a temperature just below the melting temperature of the ore, permitting the particles to frit together and form pellets of high mechanical strength which may be handled, shipped and used in blast furnaces. It is at the beginning of the indurating treatment that the green compacts lose their moisture and become friable, and it is at this transitory stage of the process that the binders render the necessary service of holding the dry compacts intact.

The expanded cereal products of the invention may be used as binders in amounts of from 0.5 to about 6 pounds per long ton of finely divided ore. If desired, from about 2 to 8 pounds of another binder, such as bentonite, may .be used with the expanded cereal product so that the amount of such binder is less than would ordinarily have been used, resulting in a decrease in the amount of silica which would otherwise have been added to the pellets.

In the foregoing application, the properties of the expanded cereal products have been described in terms obtained by several methods of analysis, and while such methods are fully described in co-pending application Ser. No. 37,765, they are being set forth herein as follows:

(1) Cold Water Solubility 1 Cold water solubility determinations are made as folows:

A twenty gram sample of the product, together with approximately 7 grams of a diatomaceous earth filter aid, is placed in a one-quart glass Waring Blendor jar. Five hundred ml. of distilled water at 77:2" F. are added; and the resulting slurry is mixed with the Blendor at high speed for 30 seconds, removed from the Blendor and shaken for seconds, and finally mixed for another 30 seconds with the Blendor. The slurry is filtered through a fluted crepe-surfaced filter paper of medium porosity, such as a Reeve Angel No. 230 paper. A 50 ml. sample of the filtrate is pipetted into a tared glass evaporating dish and is evaporated to dryness on a sand bath with occasional stirring to avoid bumping. The residue is dried to constant weight in an oven at 105 C., and is finally cooled and weighed. The percent of cold water soluble material, on dry basis, is calculated by the following equation:

Residue WeightX 1000 Sample WeightX (D.S.)

where (D.S.) is the proportion of dry solids in the original sample.

Percent solubles (D.B.)

(2) Hot Water Solubility Hot water solubility determinations are made as follows:

A gram sample of the product is dispersed to form a smooth paste with 50 to 75 ml. of distilled water in a 500 ml. Erlenmeyer flask; then, more water is added to bring the total volume to approximately 300 ml. The slurry thus prepared is adjusted to pH of 7.0 to 7.5 by the use of either dilute ammonium hydroxide or dilute hydrochloric acid as required. The slurry is then heated with occasional stirring to a temperature of 190 F., preferably in a water bath, with the heating so regulated that the time required to attain that temperature is 10 to 12 minutes; and the slurry is thereafter allowed to remain at 190 F. for one minute, and is then cooled quickly to around 75 F. The cooked and cooled paste is transferred to a 500 ml. volumetric flask, water is added to fill the flask to the mark, and the diluted paste is thorough- 1y mixed. The paste is then transferred to a one-quart Waring Blendor jar containing approximately 14 grams of a diatomaceous earth filter aid. The contents of the jar are mixed at high speed for 15 seconds, and are then filtered upon a fluted crepe-surfaced filter paper. A 50 ml. sample of the filtrate is evaporated to dryness and weighed in the same manner as described above for the determination of cold water solubility. Calculation of the percent of hot water solubles is made by means of the equation given above.

(3) Reducing Sugars Reducing sugars are determined in accordance with the procedure of Lane and Eynon, as reported in Sugar Analysis by Browne and Zerban, 3rd edition, page 753, published by Wiley and Sons, New York (1941). This procedure is applied to the filtrates prepared for the determination of cold water solubility as described above; and usually said filtrates are found to require no further clarification. When clarification is considered beneficial, it is accomplished by means of dry neutral lead acetate followed by deleading with potassium oxalate. The reducing sugar values thus obtained are herein reported as percent dextrose based upon the dry weight of the product.

(4) Cold Water Paste Viscosity Cold water paste viscosity determinations are made as follows:

A 10 percent paste or dispersion is made by dispersing a sample of material containing 36.0 grams of dry solids in sufiicient distilled water at C. to give a total weight of paste of 360 grams. Dispersion is accomplished by means of moderate mechanical agitation to break up lumps of material and provide a smooth paste. Viscosity is determined with a Brookfield Synchroelectric Model LVF viscometer, with a No. 2 spindle rotating at 6 r.p.m. Viscosity is expressed as centipoise, as calculated from calibration charts provided by the manufacturer of the viscometer.

a K.) (5) Bulk Density Bulk density is determined as follows:

The material is packed lightly into a container of known weight and volume until said container is level full. The preferred method of filling the container is to add the material in increments of such size as to provide successive layers of approximately one-half inch depth, packing after the addition of each increment with a pressure of 0.225 pound per square inch. Said pressure is best applied by placing lightly upon the surface of the material a flat bottom weighted object fitting loosely into the container and having a proper ratio of weight to surface area. After the final packing, the material is struck off level with the top of the container with a straightedged knife or spatula. The container and the contents are then weighed, and the density of the contents is calculated as pounds per cubic foot.

(6) Water Sorptive Capacity Water sorptive capacity (or water sorption) by the effect upon consistency of a plaster slurry is determined as follows:

Thoroughly admix 50 grams of US. No. 1 moulding plaster and one gram of starch product by rolling the mixture on a piece of heavy paper about 12" x 12" in size. Run a measured volume of water from a buret into a glass evaporating dish of about 60 mm. diameter. Sift the plaster mixture from the paper into the water, and allow the mixture to stand for 30 seconds so that the whole mass of plaster becomes moistened. Stir briskly with a spatula for complete revolutions, reversing direction of the stirring after each tenth revolution. Quickly pour the plaster slurry onto a clean glass plate, starting with the rim of the evaporating dish /2 inch above the plate and ending 3 /2 inches above the glass plate. Measure two diameters of the resulting plaster patty at right angles to each other, and take the arithmetic average of those two measurements. Repeat the test varying the quantity of water, until a patty is obtained with a standard diameter of 3 inches.

Make a blank determination in the same manner as directed above, excepting that no starch material is added, until a patty with a standard diameter of 3 /2 inches is obtained. Water sorption is calculated by the following equation:

Water sorption=2 (vol. Ivol. II)

where vol. I=volume of water required to make 3 /2 inch patty in the presence of starch product, and vol. II=volume of water required for the 3 /2 inch patty blank.

Determinations of moisture content were made in an air oven at C., following the established procedure recognized by the trade.

(7) Cooked Paste Viscosity Cooked paste viscosity determinations are made as follows:

A 10% paste or dispersion is made by dispersing a sample of material containing 36.0 grams of dry solids in sutficient distilled water at 25 C. to give a total weight of paste of 360 grams. The dispersion is accomplished by means of moderate mechanical agitation to break up the lumps of material and provide a smooth paste.

The cold water paste thus prepared is placed in a beaker which is then immersed in a boiling water-bath to such depth that the level of paste in the beaker is below the level of water in the water bath. The paste is allowed to cook for -16 minutes. The paste is stirred constantly with .a spatula for the first 5 minutes of this cooking period; it is then allowed to cook without agitation for the next 4 minutes and 45 seconds, during which time the beaker is covered with a watch-glass; it is then stirred for 15 seconds and finally covered and cooked without agitation for another 5 minutes.

When this final stage of cooking is completed, the measuring element of a model LVF Brookfield Synchroelectric Viscorneter is placed in the paste. The viscometer motor is turned on and the spindle is allowed to rotate for 1 minute before the viscosity reading is taken. This hot viscosity is thus read 16 minutes after the start of the cooking period. The reading is taken with a No. 2 spindle rotating at 6 r.p.m.; and the viscosity is expressed as centipoise as calculated from calibration charts provided by the manufacturer of the viscometer.

The beaker containing the cooked paste is then removed from the water bath, is covered again with a Watch-glass, and is allowed to stand at room temperature for approximately 24 hours. The aged paste is then stirred vigorously with a spatula for one minute to break up the gel structure; and determination is made of the cold viscosity. The same viscometer is used but with the No. 4 spindle rotating at 6 r.p.m.; and the spindle is allowed to rotate within the paste for one minute before the reading is taken. Viscosity is expressed as centipoise, calculated as before from the calibration chart.

Having fully described the invention, what is claimed 1. In the process for producing pellets of finely divided oxidic iron concentrates comprising mixing said finely divided oxidic iron concentrates, water and a starch binder for said concentrates to form a plastic mixture, balling said mixture into green compacts and subjecting said green compacts to a thermal hardening treatment during which said compacts are dried and then indurated to pellet form, the improvement which comprises mixing said finely divided oxidic iron concentrates with a sufficient amount of a starch binder consisting of an expanded cereal product having starch granules which are discernible as unruptured entities, and are greatly distended and swollen, said starch granules being completely disorganized internally and having all remnants of polar crosses removed when viewed under polarized light, said starch granules being readily separable from one another when moistened by the water available from the moistened oxidic iron concentrates, whereby clustering of partially formed green compacts during the balling process is inhibited.

2. The process as defined in claim 1 wherein said expanded cereal product has the following properties:

Cold water solubles percent Less than 25 Water sorptive capacity ccs 7 to 11 cold paste viscosity cps 50 to 500 10% cooked paste viscosity:

Hot cps 500-2500 Cold (24 hours) cps 300010,000

3. The process as defined in claim 1 wherein said finely divided oxidic iron concentrate is finely divided taconite ore.

4-. The process as defined in claim 1 wherein said expanded cereal product is derived from whole sorghum grain.

5. In the process for producing pellets of finely divided oxidic iron concentrates comprising mixing said finely divided oxidic iron concentrates, water and a binder for said concentrates to form a plastic mixture, balling said mixture into green compacts and subjecting said green compacts to a thermal hardening treatment during which said compacts are dried and then indurated to pellet form, the improvement which comprises mixing said finely divided oxidic iron concentrates with a sufiicient amount of a binder which is a mixture of bentonite and an expanded cereal product having starch granules which are discernible as unruptured entities and are greatly distended and swollen, said starch granules being completely disorganized internally and having all remnants of polar crosses removed when viewed under polarized light, said starch granules being readily separable from one another when moistened by the water available from the moistened oxidic iron concentrates.

6. The process as defined in claim 1 wherein said expanded cereal product is present in the amount of from 0.5 to 6 pounds per long ton of said oxidic iron concentrates.

7. The process as defined in claim 5 wherein said expanded cereal product is present in the amount of from about 0.5 to 6 pounds and said bentonite is present in an amount of from about 2 to 8 pounds per long ton of said oxidic iron concentrates.

8. in the process for producing pellets of finely divided ore, comprising mixing said finely divided ore, water, and a starch binder for said ore to form a plastic mixture, balling said mixture into green compacts and subjecting said green compacts to a thermal hardening treatment during which said compacts are dried and then indurated to pellet form, the improvement which comprises mixing said finely divided ore with a suilicient amount of a starch binder consisting of an expanded cereal product having starch granules which are discernible as unruptured entities, and are greatly distended and swollen, said starch granules being completely disorganized internally and having all remnants of polar crosses removed when viewed under polarized light, said starch granules being readily separable from one another when moistened by the water available from the moistened finely divided ore, said expanded cereal product having the following properties:

Cold water solubles "percent" Less than 25 Water sorptive capacity ccs.. 7to 11 10% cold paste viscosity cps 50 to 500 10% cooked paste viscosity:

Hot cps 500-2500 Cold (24 hours) cps 300010,000

9. A dry compact comprising finely divided oxidic iron concentrates held together with a binder consisting of an expanded cereal product having starch granules which are discernible as entities, and which are greatly distended and swollen and completely disorganized internally, said granules being unruptured and having all remnants of polar crosses removed when viewed under polarized light.

10. A dry compact as defined in claim 9 wherein said expanded cereal product has the following properties:

Cold water solubles percent Less than 25 Water sorptive capacity ccs 7-11 10% cold paste viscosity cps 50-500 10% cooked paste viscosity:

Hot cps 500-2,500 Cold (24 hours) cps 300010,000

References Cited in the file of this patent UNITED STATES PATENTS 1,239,221 Rodman Sept. 4, 1917 1,933,158 Bohn et al Oct. 31, 1933 2,833,642 Barker et al May 6, 1958 2,838,401 Gates June 10, 1958 3,054,677 Graham et al Sept. 18, 1962 OTHER REFERENCES Kenworthy, H: Report of Investigations 4829, US. Department of Interior, Bureau of Mines, December 1951, pp. 1-13.

Claims (1)

1. IN THE PROCESS FOR PRODUCING PELLETS OF FINELY DIVIDED OXIDIC IRON CONCENTRATES COMPRISING MIXING SAID FINELY DIVIDED OXIDIC IRON CONCENTRATES, WATER AND A STARCH BINDER FOR SAID CONCENTRATES TO FORM A PLASTIC MIXTURE, BALLING SAID MIXTURE INTO GREEN COMPACTS AND SUBJECTING SAID GREEN COMPACTS TO A THERMAL HARDENING TREATMENT DURING WHICH SAID COMPACTS ARE DRIED AND THEN INDURATED TO PELLET FORM, THE IMPROVEMENT WHICH COMPRISES MIXING SAID FINELY DIVIDED OXIDIC IRON CONCENTRATES WITH A SUFFICIENT AMOUNT OF A STARCH BINDER CONSISTING OF AN EXPANDED CEREAL PRODUCT HAVING STARCH GRUNULES WHICH ARE DISCERNIBLE AS UNRUPTURED ENTITIES, AND ARE GREATLY DISTENDED AND SWOLLEN, SAID STARCH GUANULES BEING COMPLETELY DISORGANIZED INTERNALLY AND HAVING ALL REMMANTS OF POLAR CROSSES REMOVED WHEN VIEWED UNDER POLARIZED LIGHT, SAID STARCH GRANULES BEING READILY SEPARABLE FROM ONE ANOTHER WHEN MOISTENED BY THE WATER AVAILABLE FROM THE MOISTENED OXIDIC IRON CONCENTRATES, WHEREBY CLUSTERING OF PARTIALLY FORMED GREEN COMPACTS DURING THE BALLING PROCESS IS INHIBITED.