US3228763A - Agglomeration of finely divided minerals in thin-walled metal containers - Google Patents

Description

United States Patent 3,228,763 AGGLOMERATION 0F FINELY DIVIDED MINER- ALS IN THIN-WALLED METAL CONTAINERS Earl C. Herkenhoft and Phillip R. Porath, Los Altos, Calif., assignors to Utah Construction & Mining Co., San Francisco, Calif., a corporation of Delaware No Drawing. Filed Apr. 1, 1963, Ser. No. 269,798 3 Claims. (Cl. 75-5) The present invention relates to a process for agglomerating fine particles of mineral ores by the use of thinwalled metal containers.

As it is well known, mineral ores are generally concentrated before they are reduced to metal. In the case of iron ore for instance, such concentration or beneficiation increases the proportion of iron, by removing inert materials (gangue) which are usually in the form of silica and silicates. This concentration is generally effected prior to shipment of the ore, and in any case prior to its introduction in a blast furnace.

Among the numerous known methods of beneficiation, crushing and magnetic separation is one of the most effective. In order to separate the excess inert materials, the ore is crushed and magnetically separated thereby breaking away and removing the adherent gangue. While the gangue is thus removed, the process causes much of the ore to be crushed or ground into sizes which are relatively difiicult to handle in blast furnace operations.

It has, therefore, been the practice either to sinter or to pelletize the fine ore particles, so that they may be used as a charge in a blast furnace without excessive formation of dust. These processes, however, have their limitations due to the fact that they can only be successfully practiced with fines within relatively narrow ranges of size. Thus, it has been found that for sintering, generally not more than 20% of the particles can be minus 100 mesh, while for pelletizing, on the other hand, at least 70% of the particles must be minus 325 mesh.

There is thus a considerable range of particle sizes (between 100 and 325 mesh) where neither sintering nor pelletizing is very practical. Moreover, it is costly and uneconomical to employ several different agglomerating processes depending upon the size of the particles involved. Also, thereis considerable expense in grinding coarser material to a size suitable for pelletizing. A uniform process for agglomerating mineral ore fines which would yield consistently successful results with particles of a widely varying range of sizes would, therefore, be highly desirable.

It is accordingly an object of this invention to provide a process for agglomerating fine ore particles so that they may thereafter be reduced or otherwise processed without the formation of excessive quantities of dust.

Another object of the invention is to provide an agglomerating process which is usable with ore fines having a wide range of sizes, including fines which are too small to be sintered, and too large to be pelletized.

Still another object of this invention is to provide a relatively simple and economical process of agglomerating ores to prevent excessive dust losses during agglomeration and damage to equipment attributable to dust.

A further object of the invention is to provide a method for agglomerating ores which is usable with a wide variety of mineral ores, and in particular iron ores.

Still a further object of the present invention is to provide a process by which ore is agglomerated by the use of heat without any substantial chemical change taking place in the ore in the course of such agglomeration.

Other objects and features of this invention will become more clearly apparent upon a review of the following description.

3,228,763 Patented Jan. 11, 1966 In accordance with the present invention, dry or slightly moist ore particles having dimensions between and including those of particles adaptable for pelletizing and sintering are packed into thin-walled (about 0.01 inch) metal containers of convenient size. The metal containers include one or more small openings for the release of moisture which may be present in the fines, and which expands in the form of steam as the temperature is raised. The particular measurements, either for the openings or for the containers themselves, are not criti cal. By way of example, ordinary uncoated fruit juice cans may be used and one or more holes of approximately one-sixteenth inch diameter may be punched in the cans.

After the containers have been filled, they are sealed with a lid, using, .if desired, conventional can sealing equipment, or the container may be crimped shut. The holes may have been punched into the containers either prior to or after either filling or sealing. If desired, the filled and sealed containers may then be handled by lift magnets, or by standard conveying equipment.

The filled containers then are heated to an agglomerating temperature (in the case of cans filled with iron ore, about 2200" F.) in a neutral or slightly reducing atmosphere. This can be accomplished in various types of furnaces, such as oil or gas-fired, and of vertical shaft or rotating kiln construction. Because there are no dangers of dust losses and the unagglomerated fines are completely enclosed, high velocity heating gases may be employed, and good distribution of heat throughout the mass of containers can thereby be obtained. No damage from dust adhering to or slagging on the refractory brick can result, permitting use of high temperature heating gases. These advantages result in high furnace capacities and output. This heating may also be accomplished in an oxidizing atmosphere without oxidizing the ore since the openings in the container are small. Thus, the gas pressure within the containers is slightly higher than outside due to the vaporization of moisture in the ores. However, in an oxidizing atmosphere the metal containers themselves may oxidize, react with the contents or disintegrate.

The con-tainers may be made of any low-cost material which is capable of withstanding the temperatures of the process such as thin sheets of ordinary black iron plate. The moisture present may be added to the ore at any time prior to the heating step or may even be a residue of some earlier treatment.

When the ore and container are so heated, the ore progressively agglomerates into a mass determined by the shape and size of the container. It is necessary only that the metal containers be strong enough to withstand the stress imposed when being filled with fine ore, handling into the furnace and during initial heating. After heating the contents become durable masses capable of withstanding heavy loads and abrasion. The container openings, as will be seen hereinafter, are sufficiently small that they are capable only to permit the passage of gases out of the container, and the entrance of atmosphere from the furnace is thus prevented. Since the container openings are small enough to prevent passage of the furnace atmosphere into the container, the ore remains in its original chemical state. No further oxidation takes place. Thus, if magnetite iron ore (Fe O is agglomerated by the inventive process, it remains as magnetite throughout the process. As a result, the agglomerate at the end of the process has retained its magnetic properties, and may even be handled with electromagnets to the same extent as before processing.

It may be said in summary that as a result of the process above described, the ore principally changes its physical, granular structure, without undergoing any substantial change in its chemical composition.

As examples of the practical application of the above invention, the following may be given:

(1) 4.4 pounds of Erie taconiate iron concentrate containing 5% moisture was placed into an American Can Co. black iron container having a wall thickness of 0.0085 inch, :a diameter of 4 /8 inches and a height of 6% inches. The ore particle size was 65 mesh. The composition was 64% Fe. The container had sever-a1 openings of A diameter. After capping the container it was placed in an electric furnace with a reducing atmosphere and having a temperature of 2200 F. It was held in the furnace for four hours. After withdrawing and cooling it was determined by analysis that the hardened, agglomerated mass had substantially the same chemical characteristics as prior to agglomeration. The only change was the physical one from a fine state to a hard agglomerated mass, resistant to shock and abrasion and yet retaining a high percentage of microporosity which is desirable in subsequent blast furnace reduction.

(2) 321 grams of Peruvian magnetite concentrate with about 6% moisture was placed into a black iron container having a wall thickness of 0.012 inch, a diameter of 2% inches and a height of 2 inches. The ore particle size was 32% 325 mesh with top size of 20 mesh. The composition was magnetite, with an overall analysis of 68% Fe. The container had several openings of about inch diameter. After capping the container, it was placed in an electric muflle furnace with a non-oxidizing atmosphere at a temperature of 2200 F. It was held in thefurnace for four hours. After cooling, a strength analysis and tumbling test was performed on the resultant hardened mass. After 20 minutes of severe tumbling in a lab rod mill, 34% of the material was abraded from the surface. (This may be compared to other tests wherein moisture was not employed and with the other conditions similar wherein 69% of the concentrate slufled off.) From chemical analysis, it was determined that the mass had substantially the same chemical characteristics as prior to agglomeration. The only change was the physical one from a fine state to durable agglomerated mass.

It will, therefore, be seen that a practical process has been disclosed, whereby small mineral particles and in particular, ore fines may be agglomerated to make them usable in further treatment without the costly, deleterious and wasteful formation of large amounts of dust. The process may be used with particles of a wide range of different sizes, and greatly simplifies the machinery and furnaces required for ore processing and agglomeration as compared with prior art processes.

We claim:

1. In a process of agglomerating iron containing mineral ore fines of varying particle sizes, the steps of introducing fine, moist particles consisting essentially of ore into thin-walled, vented metal containers, heating said containers and contents to a temperature capable of gradually vaporizing the moisture in said ore so that the gas pressure within the containers is slightly higher than outside the containers, whereby the outside atmosphere is at least partially excluded, and continuing the heating of said containers until the ore is substantially agglomerated into a microporous mass without any substantial chemical change taking place in the ore in the course of such agglomeration.

2. A process as in claim 1 wherein said ore is iron ore and said agglomerating temperature is of the order of 2200 F.

3. A process for agglomerating iron containing mineral ore fines, consisting essentially of crushing said ore to reduce it to fine moist particles, removing the gangue, filling thin-walled metal containers with fine particles consisting essentially of the remaining gangue-free ore, sealing and venting said containers, heating said containers and contents to a temperature of about 2200 F. to vaporize said moisture and cause agglomeration of the ore with substantial exclusion of the outside atmosphere, simultaneously maintaining an atmosphere ranging from neutral to slightly reducing about said container and contents, and continuing to heat said containers until the ore is agglomerated into a microporous mass without any substantial chemical change taking place in the ore in the course of such agglomeration.

References Cited by the Examiner UNITED STATES PATENTS 52,149 1/1866 Dupuy 7s 3 65,473 6/1867 Chubb 3 194,340 8/1877 Dupuy 75 3 2,331,074 10/1943 Jones 75 3 2,336,618 12/1943 Jones 75 -3 2,346,034 4/1944 Kraner 75-3 DAVID L. RECK, Primary Examiner. BENJAMIN HENKIN, Examiner.

Claims (1)

1. IN A PROCESS OF AGGLOMERATING IRON CONTAINING MINERAL ORE FINES OF VARYING PARTICLE SIZES, THE STEPS OF INTRODUCING FINE, MOIST PATICLES CONSISTING ESSENTIALLY OF ORE INTO THIN-WALLED, VENTED METAL CONTAINERS, HEATING SAID CONTAINERS AND CONTENTS TO A TEMPERATURE CAPABLE OF GRADUALLY VAPORIZING THE MOISTURE IN SAID ORE SO THAT THE GAS PRESSURE WITHIN THE CONTAINERS IS SLIGHTLY HIGHER THAN OUTSIDE THE CONTAINERS, WHEREBY THE OUTSIDE ATMOSPHERE IS AT LEAST PARTIALLY EXCLUDED, AND CONTINUING THE HEATING OF SAID CONTAINERS UNTIL THE ORE IS SUBSTANTIALLY AGGLOMERATED INTO A MICROPOROUS MASS WITHOOUT ANY SUBSTANTIAL CHEMICAL CHANGE TAKING PLACE IN THE ORE IN THE COURSE OF SUCH AGGLOMERATION.