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Publication numberUS3660073 A
Publication typeGrant
Publication dateMay 2, 1972
Filing dateMay 21, 1969
Priority dateMay 21, 1969
Publication numberUS 3660073 A, US 3660073A, US-A-3660073, US3660073 A, US3660073A
InventorsSandri Joseph M, Youngs Roger W
Original AssigneeNalco Chemical Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Ore pelletizing aid
US 3660073 A
The invention relates to an organic ore pelletizing aid, to a method for making it, and to a method for pelletizing ore using the pelletizing aid. The pelletizing aid comprises coal which has been treated with an alkali metal hydroxide. A particular advantage is the provision of good ore "ballability," even at relatively high moisture content. The pelletizing aid may be coated with a high molecular weight, water dispersible organic polymer to further improve its performance.
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Description  (OCR text may contain errors)

United States Patent Youngs et al.

[451 May 2,1972

[54] ORE PELLETIZING AID [72] Inventors: Roger W. Youngs, Hinsdale; Joseph M.

Sandri, Flossmor, both of 111.

[51] Int. Cl. ..C2lb 1/22,C21b 1/26 [58] Field of Search ..208/8; 23/2099; 1 17/100 B; 75/3 5 [56] References Cited UNITED STATES PATENTS 3,387,941 6/1968 Murphy et al. ..23/209.9

1,923,803 8/1933 Trent 2,894,851 7/1959 Booth et al. ..l17/10O B X 3,180,723 4/1965 McCauley.... ..75/5 3,214,346 10/1965 Mason et all ...23/209.9 3,304,168 2/1967 Ban ..75/3 3,393,978 7/1968 Murphy et al. ..23/209.9 3,418,237 12/1968 Booth et a1 ..75/3 X Primary ExaminerA1len B. Curtis Attorney-Hume, Clement, Hume & Lee, John G. Premo, Charles W. Connors and Morando Berrettini [5 7] ABSTRACT The invention relates to an organic ore pelletizing aid, to a method for making it, and to a method for pelletizing ore using the pelletizing aid. The pelletizing aid comprises coal which has been treated with an alkali metal hydroxide. A particular advantage is the provision of good ore bal1ability," even at relatively high moisture content. The pelletizing aid may be coated with a high molecular weight, water dispersible organic polymer to further improve its performance.

8 Claims, 1 Drawing Figure PATENTEDmz I972 lfl M 1 W 9 #0 9M M m M! M 4 m y M w W M M w w W w MWH MZM M M r r14 r l ma m m m m mum a, {r as; I i if! t 74 flfl 4 W? M M y MMM Mm MM w. fl M a M w M one PELLETIZING AID The present invention relates to an improved ore pelletizing aid, and more specifically to an ore pelletizing aid that contributes improved ballability, yet is consumed in a blast furnace.

In recent years, the metal refining industry has undergone striking changes in processing ores. In particular, emphasis has been placed upon production of ore concentrate pellets. The use of these pellets as part or all of the ore charge to a blast furnace has resulted in immense increases in efficiency. In particular, the reduction of such pellets in a blast furnace can be achieved at increased rates, with concurrent decrease in emission of small particles of flue dust, which for most efficient operation must be collected and reused. Also, a permeable bed of pellets allows rapid transfer of the hot reducing gases through its entire dimension. In many instances, up to percent increases in efficiency have been noted when ore pellets are used in a blast furnace. The rate of reduction of iron ore is particularly improved through use of such pellets.

In some instances relatively pure ores containing a high percentage of valuable mineral constituents have been pelletized after minor prior processing such as crushing. Of more importance is the production of pellets from relatively impure ores, such as ores having a low content of iron oxide. Many of these ores must be beneficiated, that is, increased in relative proportion of desired metal content. After such process of beneficiation the purified mineral is already in the wetted particulate state, therefore a pelletization process is particularly suitable. The ore mass then can be easily and conveniently made into pellets for subsequent blast furnace use.

The lower grade ore deposits such as finely divided hematite iron ore deposits are more useful in such pelletizing process. Tailings" from prior ore processing, which have heretofore been discarded and stockpiled, can also be made into convenient pellet size. In the case of these relatively impure minerals or by-product fines, not only is pelletizing desirable, but in many instances it is also essential. For example, some low grade iron ores cannot be fed directly into a blast furnace due to the fact that the high content of impurities causes excessive slag and decreased efficiency of operation.

After beneficiation many ore concentrates are in such a fine state of aggregation that they would be lost through the flue of a blast furnace long before any liquification into a fluid state could take place. The same result occurs through use of flue dust, which, while it could be collected and reused, nevertheless in subsequent reuse without further processing would again be lost through the flue. Therefore, these fine particles must be processed into larger dense masses such as small integral units or pellets. It can be seen that the pelletizing process is admirably suited to use of the above type materials.

As is mentioned above, in the case of impure mineral deposits the valued or desired metal constituent in the mineral must be concentrated prior to pelletization. For example, many impure iron ore deposits have an iron content as low as 30 percent or less-These deposits must be increased in iron content to above about 60 percent in order for them to be economically and efficiently employed in a blast furnace as pellets.

In general, impure ore deposits are processed to the desired wetted particulate state prior to pelletization as follows:

The first step normally involves crushing or comminution of the raw ore as mined or in the presence of a liquid media, most generally water. By means of successive reduction steps the ore is reduced to the final particulate stage. In the crushing operation, in which the final particles are usually ground to a fine or intermediate state, two general types of mechanisms are employed to apply gradual pressure to the particles. The first mechanism involves reciprocating breakers, that is, alternate approach and withdrawal of the crushing surfaces in the crushing zone to a substantially fixed predetermined minimum spacing. Reciprocating pressure breakers include such mechanisms as jaw, gyratory, cone and gyrasphere crushers. The continuous pressure breakers include rolls, single roll crushers and roller mills. Of lesser importance are impact crushers such as stamps, hammer mills and tumbling mills.

In order to concentrate the valuable or desired metal in the mineral, now in a particulate state, it is necessary to separate it from the impurities or gangue which normally contains a substantial amount of silica, which is later discarded. One means by which the mineral may be separated from the gangue is by gravity concentration since the desired metal portion of the mineral and gangue difier appreciably in specific gravity. The theory of gravity separation depends upon a diflerence in movement in response to joint simultaneous actions upon the mineral and impurity or gangue by gravity and one or more other forces. This type concentration may be carried out by means of pulsated, shaken, or stirred beds, water impulse separators, pneumatic concentration, etc. Normally, water is employed as the impregnating fluid.

Another method of concentration of the valuable mineral constituent is by means of flotation processes. Normally these consist either of froth flotation or agglomerate or table flotation. Another excellent method of concentrating the desired constituent is by magnetic means. This is effective only with magnetic iron oxide ores. In particular, magnetic iron ores such as taconite are admirably suited to beneficiating by treatment of the ores with electromagnets or magnets.

After the desired mineral content has been increased to a relatively high content via any of the above means, the material must normally be partially dewatered either by draining or thickening. For best pellet formation, the mass of the particulate mineral substance to be processed must be in a damp or wetted condition. Normally from 5-15 percent by weight of water content is required for efficient pellet formation. In conjunction with the dewatering process, normally the beneficiated ore must be filtered to give a wet ore mass having water in the above range. This filtration may be carried out by use of continuous vacuum, sand, pressure, vacuum-leaf, centrifugal, etc., filters. After such processing, the mineral is now in the desired state for pellet formation.

The concentrated, dewatered ore may be pelletized alone or flue dust may be added thereto and the resultant mixture pelletized. Likewise, moist flue dust may be pelletized singly. Generally, prior to the pellet forming step, coke or coal is added as a fuel-media for use in the subsequent step of firing or setting the formed pellets to a hard mass suitable for mechanical handling and shipping. In some instances a small amount of calcium carbonate-containing material, preferably limestone, may be used as a flux. This flux, intermingled in the pellet, causes ore such as iron ore to melt more readily by dissolving the outside or surface impurities, thereby increasing the fluidity of the impure ore in bringing all of its components to a more intimate contact during the liquification step at the blast furnace.

In addition to low grade ores which have been processed as generally outlined above, ore flue dust or sludges may also be used. In the case of iron ore a convenient source is found in the use of sludge which is obtained in an aqueous suspension or slurry, from flue dust which has been collected from blast furnace stacks, wetted in gas washers and then concentrated. Other iron ore sludges may be found, for example, in holds of iron barges or around iron ore shiploading areas. In addition to use of flue dust as a by-product from the blast furnace melting process, cold and hot fines falling from a sinter process, mill scale and tailings from various iron ore processing operations may be used. For convenience sake, these finely divided dry iron bearing materials, generally in the form of impure iron oxides, may be referred to as iron oxide dust. Again, these may be used alone, in combination with each other or with the beneficiated ore concentrate and/or the ore sludge.

In order to form an ore pellet of sufficient strength to hold its shape prior to the firing step, it is necessary, as mentioned above, that it contain sufficient water to form a damp mass suitable for formation of a cohesive pellet. Normally, in the case of impure ore deposits which have been processed by the above stated steps, sufficient water remains after the filtration step so that no additional water need be added. In some cases it may be necessary to add water to the material to be pelletized in order to improve its pellet-forming properties. The water may be added directly to the material at any point prior to the pelletizing, and/or it may be introduced into the system by use of ore sludge. A burden from material to be pelletized is then available in a form for ready pelletization by means of known machinery.

The pelletization step itself may be carried out by such machinery as a disc or drum pelletizer. This machinery is comprised of a rotating inclined surface, which agglomerates the burden material composite into pellets when the burden is flowed upon the revolving inclined surface. Multiple-cone drum pelletizers are particularly desirable for the pelletizing operation. Another type of machinery available for this use is a pug mill, which in its simplest form is a long trough containing two parallel counter-rotating paddle-bearing shafts, horizontally mounted in side by side relationship so that the paddles are moving upwardly and away from each other in the center of the trough. This paddle action kneads burden mix and causes the dampened mass to be joined into cohesive particles.

Particular problems in the pelletization of ores have been the provision of adequate ballability together with adequate green strength and dry strength. Ballability is the ability of an ore to form satisfactory pellets in the environment involved, and presents a particular problem with organic pelletizing aids when the ore contains any significant amount of moisture. Green strength refers to the strength of the pellets immediately after formation, while dry strength refers to their strength after they have been dried.

At the present time, Bentonite, a naturally occurring clay, is the additive primarily used to provide ballability in moist ores, and also to improve green strength, dry strength, and shock temperature. However, Bentonite has the disadvantages that it is effective only at relatively high dosages, and also adds silica to the burden. The addition of silica is, of course, exactly contrary to the result desired, since a large portion of the ore refining process has been directed to the removal of silica. In addition, when Bentonite is employed, additional amounts of limestone are required to remove the silica contained in the Bentonite during the blast furnace operation, resulting in increased amounts of undesirable slag.

It would therefore be desirable and advantageous to the art if an additive could be produced which provides good ballability, while also contributing adequate green strength, dry strength, and shock temperature to an ore. Another advantage would be realized if this additive were relatively inexpensive, would not adversely affect any desired pellet properties, and would be consumed during the blast furnace operation.

Accordingly, it is the object of the present invention to provide an improved ore pelletizing aid, a process for making it, and improved ore pellets having the above-mentioned desirable characteristics.

Generally, the present invention relates to a method for preparing an improved organic ore pelletizing aid, to the ore pelletizing aid obtained by this method, and to a method for pelletizing ore utilizing the ore pelletizing aid. In its broad aspects, the preparation of the organic ore pelletizing aid comprises contacting finely divided raw (unoxidized) coal with an alkali metal hydroxide in aqueous solution. Ore to be pelletized is contacted with this pelletizing aid, and then formed into pellets. These pellets are then fired to a hardened state.

Also in accordance with the present invention, it has been discovered that the ballability properties of the ore pelletizing aid may be further improved by coating the ore pelletizing aid with a suitable high molecular weight, water-dispersible organic polymer. The most preferred polymer is an alkali metal polyacrylate, particularly sodium polyacrylate. Other polymers that are suitable include both natural and synthetic polymers, such as polyacrylamides, polyvinyl alcohols, watersoluble gums, vinyl acetate-maleic anhydride copolymers, etc.

A particularly important feature of these polymers is that they impart increased viscosity to water. Accordingly, polymers of high molecular weights are most preferred. In the case of sodium polyacrylates, the preferred molecular weight is in excess of 1 million, and may run as high as 50 million or even higher.

The polymer is applied to the coal preferably after treatment with the alkali metal hydroxide by any suitable method that will distribute the polymer over the surface of the coal. Suitable methods include spraying, ball milling, immersing, etc., although spraying is preferred. The amount of polymer to be applied is determined primarily by economic factors, since the amount of benefit derived is dependent upon the amount of polymer employed. However, below about 0.1 percent, relatively little benefit is derived, while above about 1.0 percent polymer, based on the total weight of the ore pelletizing aid, the increased benefits derived are not in proportion to the increased cost. In the case of high molecular weight sodium polyacrylate, about 0.5 percent is preferred.

The processing of impure mineral ores into their final hardened pellet stage generally includes the steps of comminution of a mineral ore to a particulate size and concentrating from this impure ore the valued or desired mineral constituent thereof to any desired increased purity by treating the mineral such as by gravity concentration, flotation, or magnetic separation, in order to obtain a wetted particulate mass. This wetted mass is then pelletized into integral or individual pellets and the formed pellet units fired into a hardened fused state for use in blast furnace operations. The particular improvement in this method, comprising the invention, is the addition of a pelletizing aid comprising finely divided coal that has been treated in aqueous solution with an alkali metal hydroxide.

Almost any type of ore to be pelletized may be advantageously acted upon by the pelletizing aid of the present invention. For example, the metal constituent of the ore chosen may be lead, copper, nickel, zinc, uranium, iron, etc. Mixtures of these metals, or any other metal occurring in the free or molecularly combined state as a mineral, which are capable of pelletization, may be acted upon by the pelletizing aids of the present invention.

As mentioned above, the burden or material to be pelletized may contain iron ore deposits coming directly from the mining site, from ore tailings, flue dust, cold and hot fines from a sinter process or iron ore which may be found in a sludge condition as aqueous iron ore concentrates from natural sources or recovered from various processes. For example, flue gases containing fine flue dust particles may be caught, wetted in gas washers and then concentrated by coagulation-type clarifiers into a relatively concentrated wet sludge which may be employed in the pelletizing operation. Any one of these sources of iron or any possible combination thereof may be employed according to their availability and particular process set-up of the pelletizing unit, normally existing at the mine site itself. Iron ore of any of a wide variety of the following minerals may form a part of the burden: magnetite, hematite, limonite, goethite, siderite, franklinite, ilmenite, chromite, pyrrhotite, cholcopyrite, pyrite, etc.

The burden to be pelletized may include a flux material chosen from a number of substances if such a flux is added. A calcium carbonate-containing substance is generally employed because of availability and relatively low cost. Among these, limestone or an impure source of limestone, such as calcite are suitable. Calcite is also known as calspar which is a hexagonal, normally colorless, rock-forming mineral composed of both crystalline species, such as Iceland spar, corn spar, satin spar, and amoiphous varieties including chalk, marble, limestone, stalactite, and baryte. Also spongy and flakelike calcium-containing mineral forms, such as mountain milk and schifer spar may be employed.

Another element in the burden, normally essential in order to fire and fuse the formed burden pellets after pelletization, is a source of fuel. Generally, coke or coal is employed, but any other inexpensive source of fuel may be included in the operation. A particular advantage in the use of the pelletizing aid of the present invention is that concurrent with its action in increasing pellet ballability, wet strength, and dry strength is its ability to burn and thereby enhance the fuel value of coke or any other fuel used in the firing step. The pelletizing aid not only helps to form pellets of requisite size and strength, but also volatilizes in the firing step, thereby acting as a minor source of fuel.

As outlined above, in order to promote compactness and adhesiveness of the pellets so that they may withstand handling subsequent to their formation and prior to the firing step, it is necessary that they be moist and in condition for ready and efficient pellet formation. It is necessary, then, that water in some form be added to the burden prior to the pelletization. In the wet processing of impure ores, whereby the desired metal constituent is increased to a usable amount, sufficient water for good compaction generally remains after the completion of this beneficiation. However, in some cases water may be conveniently added by use of aqueous ore sludge, or may itself be added at any point in the overall pelletizing process.

As previously mentioned, a particular problem in the pelletization of ores has been the provision of adequate ballability" so that suitable pellets are formed when the ore contains significant amounts of moisture. That is, when the moisture content is too high, excessive surface moisture leads to uncontrolled agglomeration, which makes proper pellet formation impossible. While other factors such as particle size are also important, the overall moisture content is most significant. Some ores, such as taconite concentrate, require a pelletizing aid regardless of the moisture content. Generally, above about 9 percent moisture, a pelletizing aid is required for most ores. Moistures above about 13-15 percent are rarely encountered in commercial operations.

Any coal may be used in the preparation of a pelletizing aid in accordance with the present invention. Included are anthracite, bituminous, sub-bituminous, lignite and peat. Lignite coals are preferred, and have been found to produce particularly satisfactory results. It is important, however, that the coal be in the raw, unoxidized state. Both artificially oxidized coal and weathered" or naturally oxidized coal are unsatisfactory for use in preparing the pelletizing aid of the present invention. These weathered coals contain large amounts of humic acids which are solubilized by the action of alkali metal hydroxides. Alkali metal humates were found to impart ineffective ballability to ore burdens with high moisture contents such as encountered in pelletizing taconite concentrates.

For economic reasons, the preferred alkali metal hydroxide for use in the present invention is sodium hydroxide. The best pelletizing aid is obtained by treating the coal in the presence of about 12-18 percent sodium hydroxide, based on the dry weight of the coal and the dry weight of the sodium hydroxide. Below this range, ballability of the ore falls off, while above this range the pellet dry strength begins to drop. The concentration of the alkali metal hydroxide is not critical, but should be maintained high enough to insure that the sodium hydroxide is in intimate contact with the coal. Although reaction conditions are not critical, in the preferred embodiment the alkali metal hydroxide treatment is carried out by contacting the finely pulverized coal in the form of a -25 percent slurry with a solution of the alkali metal hydroxide, preferably at elevated temperatures of around 75-l00 C. At these temperatures, the reaction is very rapid, and is complete within about 1 to 3 minutes. The reaction is observable by a swelling of the coal particles.

The amount of pelletizing aid to be added to the burden may be varied over a wide range. Broadly, anywhere from 1 to 100 pounds of pelletizing aid per long ton of ore may be employed. More preferably, about 1 to 30 pounds of pelletizing aid are employed, with the most preferable results, from a standpoint of efiiciency and cost, being obtained in the range of about 8-16 pounds of pelletizing aid per long ton of ore.

The primary factors influencing the amount of pelletizing aid required are the ore particle size and moisture content. These factors are interrelated, since finer ores have more surface area, and therefore contain more moisture. Generally, the higher the moisture and surface area, the more pelletizing aid that is required. The amount of pelletizing aid required also depends upon whether or not the aforementioned polymer is applied to the pelletizing aid. For example, without any polymer added, satisfactory results are generally obtained in the range of about 12-16 pounds of pelletizing aid per long ton of ore on a dry basis. When the ore is coated with sodium polyacrylate, about 8-12 pounds per long ton, dry basis, are sufficient.

The pelletizing aid may be added at any place during or prior to the pelletization operation. In the normal operating procedure, the finely divided iron ore in any of its various forms and the coke, and, if necessary, flux material, which components when combined with the above required amounts of water comprise a mixture known as a burden, are mixed together first. The pelletizing aid may be added at any point in the operation, before, during, or after addition of any of the components of the burden. It is preferred, however, that the burden be prepared first and that the pelletizing aid be added subsequently.

Any of the well-known types of pelletizing apparatus may be employed in the present invention, but the preferred embodiment involves the use of what is known as a revolving disc or revolving drum-type pelletizing machine. In this type of operation, the composite comprising the burden and pelletizing aid flow over revolving surfaces, and are retained thereon for a sufiicient amount of time, generally only a few seconds or so, to impart a centrifugal force to the composite and form or ball it into numerous agglomerates or pellets. These pellets spinning off the surface of the revolving drum or disc are then caught on a conveyor belt for transfer to the firing furnace. In the case of revolving discs, the surfaces are normally set at an angle of inclination ranging from 40 to 60. Additional water may be added to the rotating pelletizing disc in order to promote better pellet formation.

Subsequent to pelletization, the pellets are dried and fired" by heating them in a furnace to about 2,000-2,500 R, which renders the pellets quite hard. The drying and firing may be performed either together or as separate steps.

EXAMPLE In order to obtain comparative data on the ballability of ore pelletizing aids, a standard test was devised, wherein taconite concentrate was used as the standard ore. This ore was first dried at C. in a forced draft oven. The dry ore was then mixed with various dosages of the pelletizing aid. Water was added to give a final ore moisture of 11.4 percent. Pelletization was accomplished in a sealed drum pelletizer of the type previously described operated at 31.5 r.p.m. for 500 revolutions. The drum was then stopped, and the pellets were screened from ii-inch down to i s-inch at Va-inch intervals. The weight of the pellets on each screen was recorded, and the average pellet diameter was calculated by plotting the accumulated weight per cent of pellets on each screen against the screen size and taking the 50 percent level as an average diameter. The smaller pellet diameter was indicative of more controlled pellet formation, and therefore of superior ballability.

Pellet dry strength was determined by placing the ore and additive, at about 11 percent moisture, in a small mixermuller, and mixing for 5 minutes. The ore was then pelletized on a 39-inch disc, from which the ore bed was first removed. The pellets were screened to a size that would pass a %-inch screen but would not pass a v-inch screen. The pellets were removed, dried at C. for at least 4 hours, and cooled for 30 minutes. The dry strength is represented by the amount of force required to crush the pellets in an unconfined compression tester.

Finely ground lignite coal was suspended in a 20-25 percent aqueous slurry, heated to 90 C., and a solution of 50 percent sodium hydroxide was added in an amount to give an amount of sodium hydroxide of about 15 percent, based upon the dry sodium hydroxide and the dry weight of the lignite coal. After remaining in the slurry for 1 minute, the lignite was removed and dried according to procedures previously described. The lignite was then added to portions of a taconite ore sample in various dosages, and the ballability was measured in accordance with the techniques described above. In addition, varying amounts of a high molecular weight sodium polyacrylate were added to the pelletizing aid by spraying in an aque ous solution. Sufficient sodium polyacrylate solution was applied to give an overall concentration of 0.1 percent, 0.5 percent, and 1.0 percent, based upon the total dry weight of the pelletizing aid. Dry strength was also measured for some of the samples. Bentonite was employed as a control. The results are shown in the following table, and are plotted in the drawing.

As the drawing illustrates, outstanding results are obtained in each instance, these results being comparable to, and in some instances superior to, those obtained with Bentonite. Furthermore, the use of increasing amounts of sodium polyacrylate produced a steady improvement in the results obtained. In each case where dry strength was measured, it was comparable to the values obtained with Bentonite.

Obviously, many modifications and variations of the present invention as hereinbefore set forth will occur to those skilled in the art, and it is intended to cover in the appended claims all such modifications and variations as fall within the true spirit and scope of the invention.

We claim:

1. In a method for pelletizing ore comprising pelletizing a wetted particulate mass of mineral ore to form integral pellet units, and fuing said pellet units to a hardened state, the improvement comprising: incorporating into said wetted particulate mass a pelletizing aid, said pelletizing aid prepared by the method comprising contacting coal with an alkali metal hydroxide at temperatures of up to about C.

2. The method as defined in claim 1 wherein said coal is lignite.

3. The method as defined in claim 1 wherein said alkali metal hydroxide is sodium hydroxide, and is present in an amount of about l2-l8 percent, based on the dry weight of said coal and the dry weight of said sodium hydroxide.

4. In a method for pelletizing ore comprising pelletizing a wetted particulate mass of mineral ore to form integral pellet units, and firing said pellet units to a hardened state, the improvement comprising: incorporating into said wetted particulate mass a pelletizing aid, said pelletizing aid prepared by the method comprising contacting coal with an alkali metal hydroxide at temperatures of up to 100 C. and subsequently coating said coal with a water-dispersible organic polymer of relatively high molecular weight.

5. The method as defined in claim 4 wherein said polymer is an alkali metal polyacrylate.

6. The method as defined in claim 5 wherein said polymer has an average molecular weight of at least about 1 million.

7. The pelletizing aid as defined in claim 6 wherein said coal is lignite.

8. In a method for pelletizing ore comprising pelletizing a wetted particulate mass of mineral ore to form integral pellet units, and firing said pellet units to a hardened state, the improvement comprising: incorporating into said wetted particulate mass a pelletizing aid, said pelletizing aid prepared by the method comprising contacting finely divided lignite coal with sodium hydroxide at temperatures of up to 100 C., said sodium hydroxide being present in an amount of about 12-18 percent based on the dry weight of said lignite coal and the dry weight of said sodium hydroxide, and subsequently coating said lignite coal with sodium polyacrylate having a molecular weight of at least about 1 million.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 g 55 07 Dated May 9 I 1 Q77 Invent0r(s) Roger W. Youngs and Joseph M. Sandri It: is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 34, "NaDH-treated" should be "NaOH-treated".

Column 7,, line 30, under Ballability "NaOH-treated" should be "0.43".

Signed and sealed this 26th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETC1E1E3R,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM PO-IOSQ (10-69) USCOMM-DC 60376-P69 U 5. GOVERNMENT PRINTING OFFICE v I969 0*366-334

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U.S. Classification75/766, 252/1, 524/65, 75/771
International ClassificationC22B1/242, C22B1/14
Cooperative ClassificationC22B1/242
European ClassificationC22B1/242