US3041161A - Pelletizing metallic ore - Google Patents

Description

vided metallurgical ores.

' grade ores.

3,041,161 PELLETIZING METALLIC ORE Walter E. Heinz, Roxana, and Ralph E. Dodd, Bethalto,

llll., assignors to Shell Oil Company, a corporation of Delaware No Drawing. Filed June 1, 1959, Ser. No. 817,035 7 Claims. (Cl. 75-3) This invention relates to the agglomeration of subdi- More particularly, it relates to a process for agglomerating finely ground beneficiated ferruginous ores for use in refining furnaces, such as blast furnaces.

One of the problems encountered in the handling and treating of metallic ores comprises the losses due to improper handling of the finely ground material or the fines which generally occur in association with more coarsely ground ores. The advent of the commercial exploitation of low grade ferruginous ores, such as taconite and jasper, necessitates the preparation of the ore in finely ground condition for the initial beneficiation thereof. Also, once the beneficiation has been accomplished, it is necessary to agglomerate the fine dust so that it can be properly handled in metallurgical furnaces, such as blast furnaces. The problems of beneficiation and handling of such low grade ores are reviewed in the publication, Business Week, October 12, 1957.

Several means have been proposed and tested for the agglomeration of finely ground ores, such as oxides and sulfides, for the purpose of overcoming the problems referred to above. One of the chief limitations on such means comprises the necessity for holding costs at a minimum so that the processing of the ores may compete with'the processing costs entailed in the refining of higher At the present time, one of the common means of producing pellets of finely ground ores comprises the addition of clay to damp ore, rolling the mixture into pellets and sintering them at temperatures in the order of 2300-2500 F. While this has provided some improvement in the handling of finely ground ores, a number 'of limitations are inherent in the use of the clay. One of the expensive aspects of its use is the high temperature required in the sintering process. The green pellets (by which is meant pellets containing appreciable amounts of water) have low crushing strength and tend to abrade.

Heating of these green clay-containing pellets to moderately high temperatures in the order of 500 F. does not appreciably improve their physical properties.

Other means have been proposed for the production of pellets'which either entail the use of a complicated mixture of materials or inherently possess shortcomings and disadvantages which should be avoided. For example,

. it has been proposed to introduce finely powdered ore into a blast furnace and to spray water or an emulsion at the top of the furnace to prevent the dust from blowing out the stack. While this may reduce the number of fines leaving the stack from the surface of the charge, it does not cure the problem of plugging of the rest of the furnace with a finely ground charge nor prevent such a charge when it is sufiiciently agitated from blowing out the stack in the form of a fine gas-containing dust.

The spraying of finely ground ore with an asphalt emulsion has been proposed but it has been necessary in past processes to modify such atreatment by the addition of supplementary materials for the improvement in the mechanical strength of the pellets. For example, one variation on such pelletizing composition has been an asphalt emulsion modified by powdered hard asphalt combined with a hydrated cementing agent, such as limestone or hydraulic cement. The use of such a complicated mixture naturally increases the cost of the pelletizing procedure and requires high sintering temperatures.

3,041,161 Patented June 26, 1952 Moreover, it is uneconomical to include more than the absolute minimum of components in the pellets since, under normal conditions, the pelleted ore is prepared at the beneficiation site, which is usually removed a substantialdistance from the blast furnace or other refining locality. Consequently, any transportation charges for the inclusion of supplementary materials adds to the cost of the finally produced product. I

One of the disadvantages which is normally inherent in the use of ores which have been beneficiated in a flotation process comprises the effect of residual amounts of flotation agents which remain on the surfaces of the ore particles. The oleophilic materials utilized in flotation are not compatible with hydrophilic pelletizing agents such as clays. Therefore, clays do not properly agglomerate the ore particles and result in pellets having relatively low crushing strengths.

It is an object of the present invention to provide an improved ore treating process. It is a particular object of this invention to improve the refining processes for the production of metals from relatively low grade ores. It is a special object of this invention to provide an improved process for the pelletizing of subdivided metalliferous ores. It is a special object of the invention to provide pellets of finely subdivided ores having improved crushing strength. Other objects will become apparent from the detailed description of this invention.

Now, in accordance with the present invention, an improved process for agglomeratin-g subdivided metallic ores is provided which comprises commingling the subdivided ore and an oil-in-water bituminous emulsion under such conditions of agitation that pellets are formed which contain 5-20% by weight of Water and then baking the pellets so formed at a temperature between about 400 and about 650 F. for a period between about 0.5 and about 24 hours, whereby Water is removed from the pellets and the crushing strength thereof is substantially increased, the dry pellets so formed having uniformly distributed throughout the entire body of each pellet between about 1.5% and about 10% by weight of bitumen.

A still further improvement in the process of agglomerating ores is obtained by the additional step of treating the surfaces of pellets formed as described with a hydrophobic coating material, such as asphalts and the like, so that the pellets not only have increased crushing strength but also resist abrasion to a much greater degree and exhibit substantially improved resistance to the absorption of moisture.

A preferred aspect of the present invention comprises the use of asphalt emulsions wherein the asphalt contained therein has a penetration value from about 60 to about 200 while the baking time and temperature is such as to not only drive ofi Water contained in the pellet but also is suificient to convert this relatively soft asphalt to one having a penetration value between about 0 and about 25 at 77 F.

The metallic ores with which this invention is especially concerned include particularly the oxides and sulfides of iron, aluminum, copper, zinc, tin, and other allied metals. The invention will be particularly described with respect to low grade ores and more particularly with respect to low grade iron ores, such as jasper and taconite. iron ores which may. be utilized in the process include siderite, limonite, goethite, magnetite and hematite. The ores are preferably beneficiated prior to application of the agglomeration process but may be utilized in their crushed form without previous beneficiation, if the metallic content is sufiiciently high to make their use in a refining process economical. Generally, the prior processing steps comprise blasting the ore from its mine site, crushing and fractionating the crushed ore particles, washing the ore to remove, insofar as possible, dolomite or other undesir- Other benefit rather than a detriment as they have been inthe past. This is due to the fact that the asphalts employed in the agglomeration technique described are oleophilic and actually their adhesion characteristics are enhanced by the presence of such oleophilic surfactants rather than degraded.

Preferably the ore particles are previously ground by one or another of the techniques known in the art so that they have particle sizes between about 50 and minus 325 mesh and may be utilized in either dry or wet conditions. It is preferred that the amount of water present, if any, be small enough that, together with the water incorporated by means of the form of the asphalt emulsion, the pellet formed therefrom contains between about and about 20% by Weight of water.

The asphalt emulsions utilized in this agglomerating process are preferably of the oil-in-water type and still more preferably are of the so-called slow setting? type. Various asphalt emulsions well known in the art are useful in the process. The preferred emulsions comprise those having at least 30% by weight of asphalt and normally are supplied as emulsions containing at least about 55% by weight of asphalt. The water present in the emulsion may be adjustedduring or prior to incorporation with the subdivided ore with supplemental Water so as to coordinate with any water which may be present in the core, thus giving a final green (wet) pellet having the desired water content, which is in the order of 5-20%. 7 Preferred dispersing agents for slow setting asphalt emulsions include inorganic hydroxides, clay and other water insoluble dispersing agents.

The rate of breaking of the emulsion may be modified by the presence of soaps, including sodium tallate and the like and may be further modified by the presence of stabilizing materials such as petroleum hydrocarbon-insoluble pine wood resins and their alkali metal salts or by sodium petroleum sulfonates, sodium ligno sulfonates, and the like. It is preferred that a relatively soft asphalt be utilized since it is difiicult to form stable emulsions of asphalt out of the harder variety. The preferred asphalts have penetrations of 60-200 DMM at 77 F. and softening points of 80-125 F.

The asphalts employed for the purpose of this invention may be straight-run, propane precipitated, cracked or oxidized asphalts preferably obtained from residual petroleum fractions. They may be modified by the presence of oxidation catalysts, such as ferric chloride, Friedel Crafts catalyst, aluminum chloride, phosphorus pentaoxide, or phosphoric acid. The aqueous phase may contain thickening agents, such as water dispersible ethers including hydroxy ethyl cellulose, methyl cellulose, carboxy methyl cellulose, sodium carboxy methyl cellulose, clays, gums, such as gum arabic or agar or inorganic salts such as sodium chloride for the purpose of viscosity regulation. While fast cure and medium cure emulsions may be utilized under some conditions, it is perferred that slow curing emulsions be employed. This is due to the fact that such emulsions provide suflicient time for the asphalt and subdivided ore to become commingled before the emulsion breaks and water is released thereform.

The subdivided ore and bituminous emulsion are commingled under conditions of agitation such that agglomerates are formed wherein the bituminous material is uniformly distributed throughout particles of the ore.

This,is preferably done under the conditions obtained in a rotating drum wherein the subdivided ore and the emulsion are separately injected into the drum in such proportions as to cause pellet formation to commence, after which either or both ore and emulsion are injected in supplementary amounts to increase the size of the pellets. lt is not necessary to agitate the powdered ore at any great speed, since rotation of thedrum in the order of l5l00 rpm. has been found to be sufficient. This will vary, of course, with the size of the drum and the precise nature of the ore both in identity and particle size as well as in the Water content thereof and the proportion of asphalt emulsion being utilized. Temperature conditions have not been found to be critical, although it is necessary to conduct the pelletizing operation at temperatures above the freezing point and below the boiling point of the water and preferably at such temperatures that the asphalt contained in the emulsion is in sufficiently plastic condition that it will adhere to the ore particles; For example, it is preferred that the temperature of pelletizing be no more than about 5G F. below the softening point of the asphalt since below such temperatures the asphalt becomes too stiff for ready adherence to the ore. In addition to the injection or ore particles and asphalt emulsion, it is possible to :modify the procedure by the further incorporation of water coordinatedwith the water content of the ore and emulsion so that the entire mixture contains an optimum predetermined proportion of moisture designed to promote the ready formation of pellets having the maximum plastic strength possible in the green (wet) condition. Normally, the amount of water derived either from damp ore, emulsion or supplementary addition is adjusted so that the water present in the green I pellets is in the order of 5-20% based on the weight of the pellets, preferably between about 12 and 15%.

As will be seen by the data contained in the working examples, the green pellets possess only a limited amount of structural strength. Consequently, they cannot be piled in any substantial depth when in this condition. This is due apparently not only to the water content but also to the softness of the asphalt employed. However, as pointed out previously, the relatively soft asphalt utilized in the first step of the pelletizing process is required and highly desirable, since it forms the most effective.

agglomeration matrix for the subdivided ore particles. However, the problem then remains to so treat the pellets that not only is the water removed but the strength of the pellet is further improved by an alteration in the properties of the asphalt binder. Consequently, the second essential step in the pelletizing process comprises heating the green pellets for about 0.5 hour to about 24 hours, preferably between about 1 and about 2 hours. The temperature of heating is also important, optimum crushing strengths being obtained by heating at temperatures between about 400 and 650 F, preferably between about 450 and 550 F. for periods between about 1 and 2 hours. This heating process may be carried out in an oven or in heated pipelines wherein the pellets are being transported from the pelletizing site to either a shipping point or a metallurgical furnace site. Preferably, the

green pellets are not stack-ed in depths greater than between about one and about two feet, at least during the initial baking stages. As the pellets become drier and the asphalt content becomes harder during the baking, the depth of the pellets may be correspondingly increased.

The baking may be done in the presence or absence of air. It is accelerated by the presence of oxygen (air), which, at the temperatures employed, tends to oxidize the asphalt to a harder and higher melting product. Some of the metallurgical ores being treated according to this process, such as iron ores particularly, may act as catalysts for this oxidation. Hence, there is a cooperative effect in the baking process wherein the metallurgical ore actually tends to catalyze the strengthening process of the baking so that the pellets containing both the ore and bitumen attain their maximum crushing strength more rapidly especially in the'presence of oxygen. However, the baking may be conducted in the absence of oxygen or in the presence of reducing atmospheres such as hydrogen and the like, such as is utilized in many of the so-called direct reduction processes. In some of these processes, particularly the H-iron process, the refining temperatures are relatively low, the maximum temperature in the H-iron process being in the order of 900 F. Under these conditions and in the presence of hydrogen the green pellets may be introduced into a lowertemperature end of such a furnace and be gradually raised in temperature, although it is preferred that for at least the initial half-hour of baking the temperature be maintained between about 400 and 650 F. until at least a major portion of the wateris expelled and the asphalt has been given a chance to harden substantially.

The bakiugprocess is an essential part of the pelletizing process and constitutes the step in which the pellets reach their maximum strength, this strength increase being a combination of water reduction and bitumen hardening. Baking of the pellets can be carried out, for

example, in a continuous traveling bed oven. The hardening process of the bitumen is due eitherto volatiliza tion of low boiling components or due to thermal and oxidative hardening of the remaining components to such an extent that the bitumen at the end of the baking period has a penetration between about 0 and 25 at 77 F. The pellets attain strengths in the order of 100 pounds crushing strength and higher and usually in the order of 150- 300 pounds crushing strength. Such strengths are more than sufiicient for deep piling of the pellets either during transportation to a refining site or during storage periods.

Subsequent to the baking process the pellets either may be utilized immediately in a metallurigcal refining furnace or may be transported or stored. Under such conditions, the pellets may be subjected to weathering, including snow or rain or other conditions wherein they may be attacked by water. Even with the presence of a hydrophobic binder and support such as hardened bitumen, the pellets are deleteriously effected by Water, their crushing strength being sharply reduced thereby. During the handling and storage of pellets even in the absence of water, they may be subjected to abrasion upon each other or from the sides of containers, such a freight car gondolas and the like. Therefore, it may be advisable to so treat the pellets as to make them weather impervious and abrasion resistant as well as to increase their crushing strength. Such a treatment comprises superficial surface treatment with an asphalt cutback.

Cutback asphalts comprise asphalts thinned with relatively volatile solvents, such as naphtha, kerosenes, or other relatively volatile oils. In the present process where superficial coating of the baked pellets is desired, the rapid curing cutbacks may be employed or a medium curing type. In the rapid curing cutbacks various naphthas are the ordinary solvent while in the medium curing type hydrocarbons oils in the kerosene boiling range are utilized.

Cutback asphalt, preferably of the rapid cure (RC) or medium cure (MC) types, is produced by fluxing the asphalt with a suitable solvent such as a naphtha or a similar hydrocarbon. The latter makes the asphalt more fluid and easier to apply to the pellets. It may be applied in the cold or at room temperature, except in cutback asphalt having a small amount of solvent, which may be war-med. 'llhe cutback asphalts must be free from water and conform to certain ASTM requirements. (See for instance, ASTM- 1944, pages 432-433.) As illustrative of a typical cutback asphalt, the following is the analysis of the MC-3, which is described \more particularly hereinafter.

Viscosity at 140 F., Saybolt Furol -Q 435 Specific gravity at 60 0.9548 IBP, F 438 45%, F 500 74%, F '600 78.5%, F 680 Penetration at 77 F. (on residue) 171 Crude source-Illinois.

The application of cutback to the baked pellet may be by means of dipping or spraying, preferably the latter. The protective supplementary cutback treatment may be performed on only the pellets occurring on the surface of a piled amount or may 'be uniformly carried out so that all of the pellets are so treated. Ordinarily, the superficial coating should be such that the asphalt remaining on the surface of the pellets after evporation of the cutback solvent is in the order of between about 0.1 and 5% based on the total weight of the pellet, preferably 05-25%.

It has been found that this superficial coating improves the abrasion resistance of the pellets and their crushing strength as well as their water repellency. in all three respects, therefore, the pellets are materially improved by the cutback treatment following the baking process. The examples which follow illustrate the use of the process described:

Reground jasper iron ore having a particle size distribution of 70% minus 325 mesh was treated with a slow setting asphalt emulsion in a rotating drum rotating at a speed of '24- r.p.m. The powdered ore was placed in the drum.

and asphalt emulsion was sprayed into the drum as small pellets were formed, ore and emulsion were gradually added. This was continued at approximately room temperature until the pellets had achieved the size of /2-% oh an inch. Enough water was present or added to the emulsion so that the final water content of the green pellets was approximately 13% and the pellets, after dehydration, contained 3.5% asphalt. The green pellets (before drying) withstood 15-20 drops of 12 inches and had a crushing strength of about 2 pounds. After these pellets were baked for 1 /2 hours at 500 F. they could be ropped 36 inches about 45 times before fracturing and their crushing strength was 200-250 pounds.

The baking time and temperature as well as the asphalt content of pellets was investigated utilizing the same process of pellet formation and baking as described above. Table I of data was obtained on the products so prepared.

TABLE I Crush Strength 1 of One-Half Inch Diameter Pellets From Reground Iron Ore Baking Temperature, F. 400

Asphalt Content Asphalt Content Asphalt Content 1 As measured on a Biehle Testing Machine/load applied at 0.5 in. per minute.

The asphalt emulsion utilized in the preparation of the above pel-lets was a type 88-2 and had the following compositions:

Asphalt: 60%, 60/70 pen. Water: 40% containing 2% petroleum hydrocarbon-in- Sintered, clay bound pellets 1. 4 Baked, asphalt bound pellets 14.0 Baked, cutback coated, asphalt bound pellets 2.

soluble pine wood resin saponified with a small excess of sodium hydroxide.

Pellets prepared and baked as described above were improved still further by spraying them with 1.5 by weight of an asphalt, applied in the form of a cutback comprising 65% naphtha and 35% asphalt. Tables ll and iii demonstrate the improvements in both water repellency and abrasion resistance achieved by this treatment.

TABLE 11 Improvement of Water Repellency of Pellets by Czitback Coating.

TABLE III Improvement of Abrasion Resistance of Pellets by Cntback Coating [Pellets tumbled 30 minutes with Vi inch limestone chips] Weight Loss Percent We claim as our invention:

1. The process of agglomerating powdered mineral ore prior to introduction into a metallurgical furnace which comprises uniformly commingling ore and bituminous emulsion with agitation of a type and sufficiency to cause pellet formation, said emulsion being an oil-in-water emulsion comprising major proportions of asphalt as the sole binder for the ore, water and a minor emulsifying amount of an emulsifying agent, said agitation being the sole agglomerating action and being conducted at a temperature above 50 F. below the softening point of the asphalt, said pellets containing 20% by weight of water, and baking the pellets at a temperature of 400-650 F. for a period of /224 hours, whereby Water'is removed and the crushing strength of the pellets is substantially increased, and the dry pellets comprising ore particles consisting essentially of particles of sizes between 50 and minus 325 mesh having uniformly distributed throughout the entire body thereof between about 1.5% and about by weight of bitumen.

2. The process of producing high crushing strength pellets of subdivided mineral ore which comprises uniformly commingling with agitation said ore and a bituminous emulsion, said emulsion being an oil-in-water emulsion comprising major proportions of asphalt as the sole binder for the ore, water and a minor emulsifying proportion of an emulsifying agent, said agitation being the sole agglomerating action and being conducted at a temperature above 50 F. below the softening point of the asphalt, whereby the ore and bitumen agglomerate to form pellets containing 520% by weight of Water, and baking the pellets at a temperature of 450-550" F. for a period of /2-24 hours, whereby water is removed and the crushing strength of the pellets is substantially increased, the dry pellets comprising ore particles consisting essentially of particles of sizes between 50 and minus 325 mesh having uniformly distributed throughout the entire body thereof between about 1.5% and about 10% by Weight of bitumen, thereafter coating the pellets with an asphalt cutback and evaporating the cutback solvent whereby an D or asphalt coating is formed on the surfaces of the pellets, said coating comprising 0.l-5'% by weight of the pellets.

3. The process of producing high crushing strength pellets of subdivided mineral ore which comprises uniformly 5 commingling with agitation said material with a bituminous emulsion, said emulsion being an oil-in-water emulsion comprising major proportions of asphalt as the sole binder for the ore, water and a minor emulsifying proportion of an emulsifying agent, said agitation being the sole agglomerating action and being conducted at a temperature above 50 F. below the softening point of the asphalt, whereby the ore and asphalt agglomerate to form pellets containing 520% by weight of water free of hydraulic binders and baking the pellets at a temperature of 400650 F. for a period of /2-24 hours, whereby water is removed and the crushing strength of the pellets is substantially increased, said pellets comprising ore particles consisting essentially of particles of sizes between 50 and minus 325 mesh, the dry pellets having uniformly distributed trroughout the entire body thereof between about 1.5 and about 10% by weight of asphalts, thereafter coating the pellets with cutback and evaporating the cutback solvent whereby an asphalt coating is formed on the surfaces of the pellets, said coating comprising 0.1-5 by weight of the pellets.

4. The process of agglomerating powdered iron ore prior to introduction into a metallurgical furnace which comprises uniformly commingling ore and asphalt emulsion with agitation of a type and suificiency to cause pellet formation, said emulsion being an oil-in-water emulsion comprising major proportions of asphalt as the sole binder for the ore, water and a minor emulsifying proportion of an emulsifying agent, said agitation being the sole agglomerating action and being conducted at a temperature above 50 F. below the softening point of the asphalt, said pellets containing 5-20% by weight of water and baking the pellets at a temperature of 400650 F. for a period of /2-24 hours, whereby Water is removed and the crushing strength of the pellets is substantially increased, said pellets comprising ore particles consisting essentially of particles of sizes between 50 and minus 325 mesh having uniformly distributed throughout the entire body thereof between about 1.5 and about 10% byweight of asphalt, thereafter coating the pellets with an asphalt cutback and evaporating the cutback solvent whereby an asphalt coating is formed on the surfaces of the pellets, said coating comprising 0.1-5% by weight of the pellets.

5. The process of agglomerating powdered iron ore prior to introduction into a metallurgical furnace which comprises uniformly commingling ore and asphalt emulsion with agitation of a type and sufliciency to cause pellet formation, said emulsion being an oil-in-water emulsion comprising major proportions of asphalt as the sole binder for the ore, water and a minor emulsifying proportion of an emulsifying agent, said agitation being the sole agglomerating action and being conducted at a temperature of 50 F. below the softening point of the asphalt, said pellets containing 1215% by weight of water and baking the pellets at a temperature of 400-650 F. for a period of /224 hours whereby the Water is removed and the crushing strength of the pellets is substantially increased, the dry pellets comprising ore particles consisting essentially of particles of sizes between 50 and minus 325 mesh having uniformly distributed throughout the entire body thereof of between about 3 and 7.5% by weight of asphalt, thereafter coating the pellets with an asphalt cutback and evaporating the cutback solvent whereby an asphalt coating is formed on the surfaces of the pellets, said coating comprising 0.1-5 by Weight of the pellets.

6. A process according to claim 1 wherein, subsequent to the baking step, the pellets are superficially coated with asphalt, whereby water'resistance is increased.

7. The process of agglomerating subdivided beneficiated iron ore prior to introduction into a metallurgical furnace which comprises uniformly commingling ore and an oil in Water asphalt emulsion comprising major proportions of asphalt as the sole binder for the ore, water and a minor emulsifying proportion of an emulsifying agent, said asphalt having a penetration between about 50 and 150 DMM at 77 F., said commingling being effected by agitation of a type and sufficiency to cause pellet formation, said agitation being the sole agglomerating action and being conducted at a temperature above 50 F. below the softening point of the asphalt, said pellets containing 5-2()% by weight of water, and baking the pellets at a temperature of 450550 F. in the presence of oxygen for %4 hours, whereby water is removed, the asphalt is hardened to 0-25 DMM at 77 F. penetration and the crushing strength of the pellets is substantially increased, the dry pellets having uniformly distributed therethrough 10 between about 3 and 7.5% by weight of asphalt, thereafter coating the pellets with an asphalt cutback and evaporating the cutback solvent whereby an asphalt coating is formed on the surfaces of these pellets, said coating comprising O.15% by weight of the pellets.

References Cited in the file of this patent UNITED STATES PATENTS 2,127,632 Najarian Aug. 23, 1938 2,164,950 Schulze July 4, 1939 2,494,420 Wells Jan. 10, 1950 2,808,325 Subervie Oct. 1, 1957 FOREIGN PATENTS 14,356 Great Britain of 1900

Claims (1)

1. THE PROCESS OF AGGLOMERATING POWDERED MINERAL ORE PRIOR TO INTRODUCTION INTO A METALLURGICAL FURNACE WHICH COMPRISES UNIFORMLY COMMINGLING ORE AND BITUMINOUS EMULSION WITH AGITATION OF A TYPE AND SUFFICIENCY TO CAUSE PELLET FORMATION, SAID EMULSION BEING AN OIL-IN-WATER EMULSION COMPRISING MAJOR PROPORTIONS OF ASPHALT AS THE SOLE BINDER FOR THE ORE, WATER AND A MINOR EMULSIFYING AMOUNT OF AN EMULSIFYING AGENT, SAID AGITATION BEING THE SOLE AGGLOMERATING ACTION AND BEING CONDUCTED AT A TEMPERATURE ABOVE 50*F. BELOW THE SOFTENING POINT OF THE ASPHALT, SAID PELLETS CONTAINING 5-20% BY WEIGHT OF WATER, AND BAKING THE PELLETS AT A TEMPERATURE OF 400-650*F. FOR A PERIOD OF 1/2-24 HOURS, WHEREBY WATER IS REMOVED AND THE CRUSHING STRENGTH OF THE PELLETS IS SUBSTANTIALLY INCREASED, AND THE DRY PELLETS COMPRISING ORE PARTICLES CONSISTING ESSENTIALLY OF PARTICLES OF SIZES BETWEEN 50 AND MINUS 325 MESH HAVING UNIFORMLY DISTRIBUTED THROUGHOUT THE ENTIRE BODY THEREOF BETWEEN ABOUT 1.5% AND ABOUT 10% BY WEIGHT OF BITUMEN.