JPH0123531B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing high strength agglomerates from finely divided iron oxide-containing materials containing sufficient internal carbon to reduce all iron oxide therein to metallic iron. When fine iron oxide-containing materials, such as fine iron concentrate and waste dust from steel mills, are charged into a steelmaking furnace, they contain carbon to speed up the reduction of iron oxide to metallic iron. It is well known to form pellets into pellets. This method is covered by a US patent.
No. 2793109 (Huebler, etc.),
No. 2806779 (Case), No. 3264092 (Ban), No. 3333951 (Ban), No. 3386816 (English), No. 3770416 (Goksel), No. 3938987 (Ban) and Canadian Patent No. 844,592 (Volin et al.). The presence of carbonaceous materials in sufficient quantities to reduce all iron oxides to metallic iron has an adverse effect on the crushing resistance or compressive strength of the pellets. It is generally accepted that there is a tendency to
No. 2,806,779 and Bang's Patent No. 3,264,092 disclose the use of coal in agglomerated form and then heating the pellets to a temperature of about 871-1260°C (1600-2300°) to carbonize the coal, thereby making it possible to produce coal for the pellets. It teaches making bonds. Bang's patent No. 3,938,987 states that when non-agglomerated coals such as lignite, subbituminous coal, anthracite, and coke breeze are used as carbonaceous materials, the amount is sufficient to form pellets with sufficient strength for steelmaking furnaces. It teaches that the amount needed to reduce iron oxide to metallic iron must be about 40 to 80%. English Patent No. 3386816 is
Pellets containing only 8% coke have a compressive strength of 26.3 kg (58 lbs), which is generally considered too low to be acceptable for most steelmaking processes. The primary object of the present invention is to form fine, iron oxide-containing materials into inexpensive, hardened masses containing at least sufficient carbonaceous material to reduce all iron oxides to metallic iron, yet having high compressive strength. The purpose is to provide a method. Another object of the invention is to provide a method for producing such a mass suitable as a charge for a steelmaking furnace. Other aspects, benefits, and objects of the invention will become apparent to those skilled in the art from the following detailed description and appended claims. According to the invention, the compressive strength is at least 45.4Kg
(100 lbs) of hardened mass containing the majority of iron oxides and sufficient carbonaceous material to reduce all iron oxides to metallic iron: bituminous coal char, anthracite coal, lignite char, coke, Manufactured by utilizing native or pyrolyzed carbonaceous materials having a volatile content (dry basis) of about 20% by weight or less, such as charcoal, graphite, and the like. Hydrothermally cured iron oxide agglomerates containing carbonaceous material with high volatile content and sufficient to reduce total iron oxide to metallic iron have low crushing resistance or compressive strength for many applications. Not acceptable. Quite unexpectedly, it appears that the compressive strength of such a mass is reduced by the amount of volatile matter (dry basis).
It has been found that significant increases can be achieved by using up to 20% by weight of native or pyrolyzed carbonaceous material. More specifically, the method of the present invention provides a method for preparing finely divided iron oxide-containing materials, which are naturally occurring, having an amount of volatile content (dry weight basis) of about 20% by weight or less, at least sufficient to reduce all iron oxides to metallic iron. or about 1 to about 30% by weight of a binder selected from the group consisting of pyrolyzed carbonaceous materials, calcium and magnesium oxides, hydroxides, carbonates, and mixtures thereof, and siliceous materials (available SiO ₂ 0 to 3% by weight of)
forming the resulting mixture into individual green masses; and contacting with steam for a sufficient period of time to form a hardened, fully bonded mass. The process includes the step of hot-hydrolytically curing the raw mass. This method uses so-called "steel mill waste oxides" recovered as by-products from iron concentrate and steel-making processes, or
Iron-rich (e.g. 30-80% iron) solid particles or fines, including dust collected from BOF, open hearth, blast furnace and electric furnace flue gases, mill scale powder, settling chamber dust, and fines separated from iron pellets. It can be used to produce hardened masses from. As used herein, the term "iron oxide-containing material" includes iron concentrate, steel mill waste oxides, or mixtures thereof. The process produces high strength agglomerates from iron ores such as hematite or magnetite, preferably in the form of high grade ores or concentrates with an iron content of about 45-70% and the balance comprising gangue and oxides. Particularly suitable for Therefore, this method will refer to the iron concentrate used as starting material. The starting mixture is first thoroughly mixed with iron concentrate, carbonaceous material, binder, siliceous material, and sufficient water to form a hydrated mixture that can be formed into individual agglomerated masses or pellets. Manufactured by. The carbonaceous material may be naturally produced or thermally decomposed as long as its volatile content (on a dry weight basis) is about 20% by weight or less, preferably about 10% by weight or less. Pyrolyzed carbonaceous materials are generally preferred due to their low volatile content. Typically suitable natural carbonaceous materials include low volatile anthracite, graphite and the like. As used herein, the term "pyrolyzed carbonaceous material" refers to naturally occurring high carbonaceous materials that are heated to high temperatures in the absence of oxygen to drive off most of the volatiles, primarily organic materials. means a solid product made by Typical suitable pyrolyzed carbonaceous materials include char made from non-caking bituminous, subbituminous and anthracite coals, lignite char, charcoal, coke made from bituminous coal, and coke breeze. , petroleum or coal tar pitch, and mixtures thereof. Among these, bituminous coal char, lignite char and coke powder are preferred because of their low cost. Suitable binders include calcium and magnesium oxides, hydroxides, carbonates and mixtures thereof. Quicklime (CaO) and slaked lime (Ca
(OH) ₂ ) are preferred because, in addition to acting as a binder, they aid in slag formation and desulfurization when the agglomerates are used in steelmaking processes. The amount of binder used is from about 0.1 to about 30% by weight, based on the total weight of dry solids in the starting mixture. Below about 0.1% by weight, the hardened pellets do not have sufficient crush resistance or compressive strength to withstand the loads commonly imposed during handling, storage, and transportation. On the other hand, an excess of more than 30% by weight of binder will not significantly increase the compressive strength, will dilute the iron oxide grade in the final mass to an undesirable level, and will create an excessive amount of slag during melting. become. The preferred amount of binder is about 2
from about 10% by weight. If the iron oxide-containing material reacts with the binder during hydrothermal curing conditions to form silicate or hydrosilicate bonds, some amount (e.g., greater than about 0.5% by weight)
of available _SiO2 , approximately 90.7Kg (200lbs) without adding any siliceous material to the starting mixture
Hardened pellets are obtained with a compressive strength of up to . 3% by weight based on total dry solids weight for high grade iron concentrates with relatively low amounts of available _SiO2 .
A natural or processed siliceous material containing up to available SiO ₂ is added to the starting mixture. The total available _SiO2 in this mixture, either as part of the iron oxide-containing material or added with the siliceous material, should be at least 0.5% by weight. Typically suitable siliceous materials include finely ground quartz, silica sand, bentonite, diatomaceous earth, Fuller's earth, sodium, calcium, magnesium and aluminum silicates, and mixtures thereof. Among these, finely ground quartz and silica sand are preferred. In addition to the binder and siliceous material, other reinforcing additives can be included in the starting mixture to further increase the strength of the cured mass. For example, oxides, hydroxides, carbonates, bicarbonates, sulfates, bisulfates of alkali metals (e.g. potash and sodium);
Borate salts and mixtures thereof can be added in amounts up to 3% by weight. Among these, sodium hydroxide, soda carbonate and sodium bicarbonate are preferred. The presence of some of these reinforcing additives may be considered undesirable when the hardened mass is used as a charge to a blast furnace. In such cases, omitting such additives will not significantly reduce the strength of the mass. If used, the preferred amount of reinforcing additive is approximately
0.15 to about 1% by weight. The amount of water contained in the starting mixture will vary depending on the physical properties of the materials and the particular agglomeration technique used. When a pelletizing process using, for example, a boring drum or disc is used for spherical pellets, the total water content in the hydrated starting mixture will generally range from about 5 to about 20% by weight, preferably from about 10 to 15% by weight. Should. On the other hand, when a briquette press is used, the amount of water in the hydrated starting mixture should be about 3 to about 15% by weight, preferably about 5 to 10% by weight. The average particle size of the various solid materials included in the starting mixture may normally range from about 10 meshes to about 325 meshes, preferably all of less than about 200 meshes. Particle sizes coarser than about 100 mesh do not provide a homogeneous mixture of ingredients and, in some cases, do not provide sufficient surface area to provide the necessary high strength bonding in the hardened mass. Furthermore,
It is difficult to form pellets from mixtures containing coarse pellets. Preferably, the average particle size of at least half of all solid materials in the starting mixture is less than or equal to 200 mesh for pelletizing. Briquettes can be made with very coarse particles. Many low-volatile, naturally occurring and pyrolyzed carbonaceous materials have small capillary-like pores or cavities that tend to absorb water during the mixing process. This free internal moisture, if in excess quantity in the pores or cavities, tends to convert to steam during the hydrothermal curing process, resulting in a loss in compressive strength and sometimes cracking or spalling. This can be minimized by allowing the hydrated mixture to sit or stand for a sufficient period of time for a substantial portion of the free internal water in the carbonaceous material to migrate from the pores or cavities to the surface. The time and conditions for this holding or resting step can vary significantly depending primarily on the particular type of carbonaceous material and binder used. Removal of excess internal moisture from the pores or cavities in the carbon material can be facilitated by heating the hydrated mixture to high temperatures. When quicklime and/or magnesium oxide are used as binders, they react with the moisture present to form hydroxides. This exothermic hydration reaction tends to hasten the movement of free internal moisture to the particle surface, thereby reducing the required standing time without external heating. As a general guideline, the hydrated mixture prior to agglomeration is allowed to stand at a temperature of about 60 to 90°C for about 0.5 to 48 hours, preferably about 2 to about 3 hours. Higher temperatures and pressures can be used but are undesirable due to higher operating costs. When quicklime or magnesium oxide is used as a binder, the hydrated mixture is placed in a closed, insulated container to take advantage of the exothermic hydration reaction. The hydrous mixture is then formed into a green mass of the desired size and shape for the intended end use by conventional agglomeration techniques such as molding, briquettes, pelletizing, extrusion and similar methods. be done. Pelletizing by boring discs or boring drums is preferred because of its low operating costs. When formed into spherical pellets, the green mass generally has a diameter of about 5 to about 25 mm, preferably about 10 to about 20 mm. When briquettes are used, the agglomerates are preferably spherical-like or oval-shaped with a larger diameter ranging up to about 75 mm. Larger pellets and briquettes can be used if desired. The crush resistance or compressive strength of the cured mass can be increased by drying the green mass to a free moisture content of less than about 5% by weight, preferably less than about 3% by weight, prior to the hydrothermal curing step. . This drying is
Using the drying temperature as the decomposition temperature of the carbonaceous material,
This can be accomplished by conventional means such as placing the green mass in a furnace or blowing heated gases over it. The time required to reduce free moisture to about 5% by weight or less depends on the drying temperature used, the moisture content of the green agglomerates, the flow rate of the drying gas, the level of moisture content reduction, the size and shape of the green agglomerates, etc. Depends on. The raw mass is placed in a reaction chamber or pressure vessel, such as an autoclave, in which the mass is heated to high temperatures in the presence of moisture to harden and bond the individual particles into a complete, high-strength mass. put in. The compressive strength of the cured mass produced by this hot water curing process depends to some extent on the temperature, time, and humidity of the atmosphere used. Application of heat to the raw mass can be accomplished in any of a number of ways. The use of steam is preferred because it simultaneously provides the source of heat and moisture necessary for the hydrothermal reaction. Either saturated steam or substantially saturated steam is used. Superheated steam tends to create hardened masses with reduced strength. Therefore, saturated steam or steam at a temperature and pressure close to saturated steam is preferred. Generally, temperatures in the range of about 100 to about 250°C, preferably 200 to about 225°C, are sufficient to achieve the desired hardening of the green mass within a reasonable time. Autoclave pressures substantially above atmospheric pressure are preferred to reduce curing time and improve the strength of the cured mass. In general economic conditions, the maximum pressure should not exceed about 35 atmospheres and about 10
Pressures of from to about 25 atmospheres are preferred. The length of time a pellet is held in a reaction chamber or pressure vessel depends on various process variables such as reaction chamber pressure, temperature, atmosphere, pellet size, and composition. In all cases, this holding time must be sufficient for the binder to create silicate and/or hydrosilicate bonds in the active SiO ₂ and bond the individual particles into a hardened, high-strength state. When higher temperatures and pressures are used, the time required for hydrothermal curing is generally from about 5 minutes to about 15 hours, preferably from 30 to 60 minutes. The hardened mass is removed from the reaction chamber and is ready for use after cooling. High temperature hardened mass is usually about 1.5
% free moisture and has compressive strength properties suitable for most applications. The compressive strength of the hardened mass is improved by rapid drying, preferably immediately after removal from the reaction chamber and before substantial cooling has occurred, to remove substantially all of the free water from the mass. Can be increased. This drying can be carried out in a convenient manner. The minimum compressive strength of the hardened mass produced by the method of the invention varies depending on the size of the mass. For example, spherical pellets with a diameter of 12 to 15 mm have a compressive strength of at least 100 lbs. and the diameter is approx.
The compressive strength of the 30mm one is around or above about 90.7Kg (200lbs). Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following examples are intended to illustrate the invention and should not be construed as limiting the invention thereby. EXAMPLE A series of tests were conducted to evaluate the crushing resistance or compressive strength of hardened magnetite pellets containing discrete carbonaceous materials in amounts sufficient to reduce all of the iron oxide to metallic iron. The ingredients formulated into the starting mixture were mixed together in a roller or high-intensity mixer for a sufficient time to obtain a homogeneous moisture mixture.
Green, spherical pellets (15 mm) were produced from the mixture in a conventional boring machine. The raw pellets were dried to about 0-3% moisture by weight and then transferred to a high pressure steam autoclave. The autoclave was heated and maintained at a temperature of 210°C and a pressure of 22 atmospheres for 1 hour. After cooling, the compressive strength of the pellets was measured using a Dillon tester. The results of these tests are summarized in Table 1.

[Table] (a) Dicalite, diatomaceous earth from General Refractory Co. From these results, it is clear that dicalite contains low volatile (anthracite) or pyrolyzed (bituminous coal coal, lignite coal and coke) carbonaceous materials. It can be seen that the pellets have a compressive strength of 45.4 kg (100 lbs) or more. Those containing carbonaceous materials with high volatile content (bituminous coal and lignite) have substantially lower compressive strength. The use of char from non-caking bituminous coal, brown coal and other lower carbonaceous materials is because these materials are low cost and the volatiles expelled during the pyrolysis process can be burned and used as a heat source. It is particularly advantageous because it can be used. From the foregoing description, those skilled in the art can easily ascertain the essential features of the present invention and can apply the present invention to various uses and situations by making various changes and modifications without departing from the spirit and scope of the invention. can.

Claims (1)

[Claims] 1. In producing a self-reducing mass having a compressive strength of at least 45.4 Kg (100 Lbs) from a fine iron oxide-containing material: (a) an iron oxide-containing material; 20% by weight (dry basis); ) finely-grained carbonaceous materials, either native or pyrolized, in amounts sufficient to reduce at least all iron oxides to metallic iron, having a volatile content of: oxides, hydroxides, carbonates of calcium and magnesium; and 1 to 30% by weight of a finely divided binder selected from the group consisting of _: (b) preparing said hydrated starting mixture consisting of a finely divided siliceous material in such an amount as to be capable of reacting with said binder to form silicate or hydrosilicate bonds; (b) of said carbonaceous material; (c) forming individual green agglomerates from the starting mixture for a sufficient period of time for a substantial amount of the free internal water present in the pores to migrate to its surface; (d) drying the raw mass to reduce the moisture content to 5% by weight;
and (e) a period of time sufficient for the binder to form silicate or hydrosilicate bonds with the available SiO ₂ and to form a hardened, fully bonded mass.
A method for producing a self-reducing mass, comprising the step of: hydrothermally curing the green mass by contacting it with steam at a temperature of 100 to 250°C. 2. The method according to claim 1, wherein the binder is calcium oxide or calcium hydroxide. 3. The method according to claim 2, wherein the siliceous material is silica. 4. The method of claim 1, wherein the carbonaceous material is selected from the group consisting of bituminous coal, anthracite, brown coal, charcoal, coke, graphite, and mixtures thereof. 5 The carbonaceous material is bituminous coal char, lignite char,
or a mixture thereof, the method according to claim 4. 6. The method according to claim 4, wherein the amount of volatile matter in the carbonaceous material is 10% by weight or less. 7 alkali metal oxides, hydroxides, carbonates, bicarbonates, sulfates, in which the water-containing mixture contains not more than 3% by weight, based on the total weight of dry solids in the starting mixture;
bisulfate, borate, quaternary ammonium hydroxide,
5. The method of claim 4 including a reinforcing additive selected from the group consisting of quaternary ammonium chloride, quaternary ammonium amines, and mixtures thereof. 8. The method of claim 7, wherein said reinforcing additive is selected from the group consisting of sodium hydroxide, soda carbonate, and soda bicarbonate. 9. The method of claim 4, wherein the iron oxide-containing material is iron concentrate. 10. The method of claim 1, wherein step (b) is carried out at a temperature of 60 to 90°C for 0.5 to 48 hours.