MXPA06006655A - Process for producing iron ore agglomerates with use of sodium silicate containing binder. - Google Patents

Abstract

The present invention relates to a process for producing iron ore agglomerates comprising agglomerating fine iron ore particles in the presence of a binder system wherein the binder system comprises a binder and an alkali metal silicate and wherein the alkali metal silicate is present in an amount of between 0.0001 to 0.08 percent by weight, based on the total weight of dry iron ore agglomerate, wherein the binder system is free of synthetic polymer, and preferably comprises carboxymethyl cellulose as binder.

Description

PROCEDURE FOR PRODUCING AGGLOMERATES OF IRON MENA BY THE USE OF AN AGGLUTINANT CONTAINING SODIUM SILICATE DESCRIPTIVE MEMORY The invention relates to a process for producing agglomerates of iron ore. Said procedure is known from the document of E.U.A. 6,293,994, which discloses a process for producing pellets of incinerated ore by mixing particulate mineral material with moisture and binder comprising a substantially water-soluble organic polymer and an alkali metal silicate in a dry weight amount which is either: (a) ) above 0.13% based on the wet mix, or (b) above 0.08%, based on the wet mix and at least three times the dry weight of the substantially water-soluble organic polymer. The preferred polymer is a synthetic polymer that is formed of a water-soluble ethylenically unsaturated monomer or a combination of monomers. The high amount of alkali metal silicate in the nodes described in the document E.U.A. 6,293,994 is generally undesirable, because silicates can slow down the process of reduction in steelmaking operations by blocking the pathways of use of reducing gases to permeate the nodule which generates an increase in energy costs. In addition, the use of said high amounts of alkali metal silicate results in untreated nodules that have a high tendency to deform, which in turn can generate nodules of different size and shape, resulting in an inefficient process for preparing incinerated nodules. The aim of the present invention is to provide iron ore agglomerates with improved physical properties. The present invention provides a process for producing agglomerates of iron ore which comprises agglomerating fine particles of iron ore in the presence of a binder system wherein the binder system comprises a binder and an alkali metal silicate and wherein the silicate The alkali metal is present in an amount between 0.0001 and 0.08 weight percent, based on the total weight of the dry iron ore agglomerate, wherein the binder system is free of synthetic polymer. The process of the invention generates iron ore agglomerates with an increased resistance to cold compression, resistance to preheating and resistance to dry grinding in relation to the use of conventional binder systems comprising the same binder. In addition, small amounts of the alkali metal silicate are insufficient in advance to obtain a significant improvement in the physical properties of the agglomerates. In addition, the specified amount of alkali metal silicate causes the agglomerates obtained with the process of the invention to have a degree of deformation similar or only slightly higher in comparison with binder systems where silicate is absent. alkali metal cato. In contrast, binder systems comprising a larger amount of alkali metal silicate show a significant increase in the degree of deformation, which is undesirable. In addition, the use of the alkali metal silicate according to the invention may allow a reduction in the amount of binder without a significant loss in the physical properties of the agglomerates that are obtained. The amount of alkali metal silicate is preferably at most 0.07 weight percent (% by weight), and most preferably at most 0.06 weight%, based on the total weight of the ore agglomerate. of dry iron. By the term "dry iron ore agglomerate" is meant all or all of the ingredients used in the formation of the iron ore agglomerate, except water. Preferably, the amount of alkali metal silicate is at least 0.02% by weight, and more preferably at least 0.04% by weight, based on the total weight of dry iron ore agglomerate. It has been found that nodes prepared using a binder system comprising at least 0.04% by weight alkali metal silicate generally has a smooth surface and increased abrasion resistance, whereas nodes prepared using a binder system comprising less 0.04% by weight alkali metal silicate generally have a rough surface which can lead to the generation of fines or residues during the processing of the formed nodules, for example, during the transport of the nodules.

The alkali metal silicate is usually a sodium silicate, but other alkali metal silicate can be used. Examples of sodium silicates are sodium metasilicate and liquid sodium silicate (water crystal) commercially available. In sodium silicates, the molar ratio Na 2+: SiO 2 is generally in the range of 2: 1 to 1: 5, preferably in the range of 1: 1 to 1: 4. The amount of alkali metal silicate in the binder system is generally at least 1% by weight, preferably at least 10% by weight, and much more preferably at least 15% by weight, and so general, at most 99% by weight, preferably, at most, 85% by weight, and much more preferably, at most, 75% by weight, based on the total weight of the binder system. The alkali metal silicate is preferably well dispersed in the particles to be agglomerated. The silicate can be added to the iron ore particles in the form of a dry powder, an aqueous suspension, an aqueous solution, and the like. Preferably, the alkali metal silicate is added in the form of an aqueous solution. The binder in the binder system of the invention can be an inorganic binder or an organic binder, or a mixture thereof. Examples of inorganic binders are bentonite and hydrated quicklime. In the context of the present application, the alkali metal silicate is not considered to be an inorganic binder. Examples of organic binders are polymers and include: (1) Water-soluble natural polymers such as guar gum, starch, alginates, pectins, xanthan gum, dairy wastes, wood-related products, lignin and the like; (2) Modified natural polymers such as guar gum derivatives (for example hydroxypropyl guar, carboxymethyl guar, carboxymethyl hydroxypropyl guar), modified starch (for example anionic starch, cationic starch), starch derivatives (for example dextrin) and derivatives of cellulose such as alkali metal salts of carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, methylcellulose, lignin derivatives (for example carboxymethyl lignin) and the like. The polymers mentioned above can be used alone or in various combinations of two or more polymers. The binder system is free of synthetic polymers. Examples of synthetic polymers are polyacrylamides such as partially hydrated polyacrylamides, methacrylamide and polymethacrylamide, polyacrylates and copolymers thereof, polyethylene oxides and the like. A further aspect of the present invention is a process for producing iron ore agglomerates comprising agglomerating fine iron ore particles in the presence of a binder system wherein the binder system comprises carboxymethylcellulose or a salt thereof and an alkali metal silicate. . The use of the combination of carboxymethylcellulose and alkali metal silicate generates agglomerates with increased physical properties, such as compressive strength in cold, resistance to preheating and resistance to dry grinding. In addition, the susceptibility to reduction of the iron in the agglomerates is generally greater than that which is observed when a binder system comprising an inorganic binder is used in the agglomeration process. The invention further relates to a binder system comprising carboxymethylcellulose and an alkali metal silicate. The amount of alkali metal silicate in the binder system is generally at least 1% by weight, preferably at least 10% by weight and much more preferably at least 15% by weight, and generally is, at most 99% by weight, preferably at most 85% by weight and much more preferably at most 75% by weight, based on the total weight of the binder system. The carboxymethylcellulose or a salt thereof (both referred to as "CMC") are preferably substantially water soluble. The preferred salts of carboxymethylcellulose are alkali metal salts of carboxymethylcellulose. Of these alkali metal salts, the sodium salt is preferred. The CMC used in the present invention generally has a degree of substitution (the average number of carboxymethylether groups per repeating anhydroglucose chain unit of the glucose molecule) of at least 0.4, preferably at least 0.5, and more preferably by at least 0.6, and at most 1.5, more preferably at least 1.2 and, much more preferably, at most 0.9. Generally, the average degree of polymerization of the cellulose supply is at least 50, preferably at least 250, and much more preferably at least 400, and generally is at most 8,000, preferably, at most, 7,000, and much more preferably, at most, 6,000 . In some preferred embodiment for using sodium carboxymethyl cellulose having a Brookfield viscosity in a 1% aqueous solution of more than 2,000 cps at 30 rpm, with a # 4 rod. Sodium carboxymethylcellulose having a Brookfield viscosity in a 1% aqueous solution greater than about 4,000 cps at 30 rpm, with a # 4 rod is further preferred. A series of commercially available binders containing sodium carboxymethyl cellulose especially useful in the present invention are available from Akzo Nobel under the trademark Peridur ™. The manner in which the binder is added to the particulate material depends on the type of material that is agglomerated, the type of agglutinant that is used in the desired results. For example, the binder can be added as a dry powder, an aqueous suspension, an aqueous solution, an aqueous gel or an aqueous sol (colloidal system), and so on. The amount of binder used varies with the desired results. For example, when an organic binder is used, the amount of binder can vary from 0.0025 to 0.5% by weight, based on the weight of the iron ore particles, wherein a preferred range is 0.5 to 0.2% by weight. In the case of an inorganic binder, the amount of agglutinating The amount may vary, for example, from 0.1 to 3% by weight, based on the weight of the iron ore particles. The binder and the alkali metal silicate can be added to the iron ore particles together, one after the other, and so on. This is not critical insofar as care is taken to ensure that when agglomeration is carried out, the binder and the additive are present to function. The process of the invention is useful for agglomerating fine iron ore particles. However, the invention is not limited to iron ore and is also useful in the agglomeration of fine particles of other metal ores. This invention is particularly adapted for the agglomeration of iron-containing materials, which include iron ore deposits, fine, cold and hot ore residues from a sintering process, iron oxide from fine powders collected in systems, or aqueous suspensions from iron ore concentrates from natural sources or recovered from various processes. The iron ore or any of a wide variety of the following minerals may be part of the material to be agglomerated: taconite, magnetite, hematite, limonite, goethite, siderite, franklinite, pyrite, chalcopyrite, chromite, ilmenite and the like. The size of the material that is agglomerated varies according to the desired results. For example, when the particulate material that is agglomerated is iron ore, 100% of the particles may be smaller 80 mesh, preferably 90% are less than 200 mesh and much more preferably 75% are less than 325 mesh. The use of conventional additives, for example a base such as sodium hydroxide, soda, or other additives is also considered. such as sodium citrate, sodium oxalate, and the like. These additives, their purpose and their use are known to those skilled in the art. Many methods for the agglomeration of particles, especially metal-based particles, are known in the art. Examples of such procedures are pelleting, briquetting, sintering, 10. etc. The binder system used according to the invention is particularly suitable for pelleting. In the mining industry it is a common practice to agglomerate or pellet finely mined beneficiated mineral ore concentrate to facilitate ore processing and handling / transportation. After the mineral ore has been extracted, frequently wet milled to release and remove unwanted gangue minerals from the desired material, for example iron in the case of iron ore. The processed wet milled ore is screened to remove large particles, which can be recycled for subsequent grinding. The fine sieves are then filtered under vacuum to reduce the moisture content to an acceptable pelletization range. The filtered mineral ore is known in the art as "concentrate." A second procedure involves "dry milling" and benefit of mineral ore, in which case the moisture required for pelleting is added later.

After the benefit, a binding agent is added to the moistened mineral ore concentrate and the binder / mineral ore composite is transported to an agglomeration drum or other means for pelleting the ore. The bonding agent serves to hold or bind together the mineral ore, so that the individual agglomerates can be transported without loss of their integrity in the way for further processing and induration. After the operation in drum agglomeration, nodules are formed, but they are still wet. These moist nodules are commonly referred to as "untreated nodules" or "untreated spheres." These untreated nodules are then transported to a homo and heated in stages to a final temperature of about 1, 300-1, 350 ° C. In the pelleting process, the wet untreated nodules are loaded in the furnace for further processing. The moisture in the nodules is extracted by induration at temperatures normally between 400-600 ° C. After drying in the oven, the nodules are transported to the preheating zone. This is an additional heating step to further increase the hardness of the nodules before they are transported to the furnace and / or a final incineration stage. Heating generally occurs at 900-1,200 ° C to bond the nodules together (for example, to oxidize magnetite or crystallize hematite). Starting from the preheating zone, the nodules are dropped 3-4.6 m (10-15 feet) from the grill from the hearth to the furnace. This is when the preheating resistance is necessary to prevent the nodules from splinter and break into fine dust particles. Finally, the preheated nodules are incinerated at a temperature between 1, 300 and 1, 350 ° C. The ability of the nodules to resist rupture during the procedure can be approximated by performing standard tests that measure the strength of the nodules they will need at each stage of processing (for example resistance to wet grinding, resistance to dry grinding, resistance to preheating and cold compressive strength). The present invention is illustrated in the following examples.

EXAMPLES In the following examples, untreated iron ore nodules are prepared which are constituted of various compounds in the amounts indicated in table 1. The untreated nodules are prepared by agglomeration of iron ore concentrate in the presence of a binder and a binder additive. The amounts of binder and / or sodium silicate (in percent by weight) shown in Table 1 are based on the total weight of the iron ore concentrate. The iron ore concentrate used in the examples in Table 1 is a Brazilian hematite ore. The binder is Peridur 330 (from Akzo Nobel), which comprises sodium carboxymethylcellulose and sodium carbonate, and the sodium silicate (Na20: SiO2 is 1: 3.3) used in these experiments is supplied by PQ Corporation.

The method of making agglomerates is generally known to a person skilled in the art. The procedure is described in detail in the document of E.U.A. 6,071, 325, which describes a process of producing agglomerates of 2,500 grams in a rotary airplane tire (approximately 40 cm in diameter). First, the binder is mixed in the dry concentrate and homogenized. The alkali metal silicate is then mixed with the required amount of water (moisture content between 8 and 9% by weight) and then mixed thoroughly with the concentrate and the binder (using a Mullen Model No. 1 Cincinnati Muller mixer, manufactured by National Engineering Co. or similar). "Seeds" of the nodule are formed by placing a small portion of the concentrate in the rotating tire and adding atomized water to initiate the growth of the nodules. The seeds of nodules with a size between 3.5 and 4 mm are retained and kept separate from the formation of the nodules with the desired size of 11.2 and 12.5 mm. The finished untreated nodules are produced by placing 165 grams of pellet seed described above on the rotating tire and adding a portion of the remaining concentrate mixture during a growth period of 3 minutes. Atomized water is added, if necessary.

TABLE 1 The moisture content, the fall number and the wet and dry compressive strength of the untreated nodules obtained are measured.

Wet fall number The wet fall number is determined by repeatedly dropping an untreated nodule having a size of 11.2 and 12.5 mm from a height of 46 cm onto a horizontally placed steel plate until a fracture is formed visible on the surface of the nodule. The number of times the nodule is dropped to the point of fracture / cracking is determined. The average number of times averaged out of 20 untreated nodules is termed the "wet drop number".

Wet compressive strength Twenty untreated, moist nodules having a size between 11.2 and 12.5 mm are stored in an airtight container. One by one, the nodules are removed and placed in a standard measuring device in which a plunger of a scale is lowered onto the untreated nodule at a speed of 25 mm per minute. The maximum force applied at which the nodule breaks is determined. The averaged strength of 20 untreated nodules is termed as the wet compressive strength.

Deformation A minimum of 20 wet untreated nodules measuring between 11.2 and 12.5 mm are stored in an airtight container. One by one, the nodules are removed and placed in a standard measuring device in which a plunger of a scale is lowered onto the untreated nodule at a loading speed of 25 mm per minute. The machine (Model Lloyd Texture Analyzer TA-Plus, controlled by a PC with Nexygen software version 4.5) is equipped with a 50 N load cell and has a probe diameter of 10 mm. The deformation / deflection of the untreated nodule is recorded while the force is increased. The deformation is defined as the load in diameter of the untreated nodule at a force of 1 N, with the condition that the nodule does not break at this point.

Dry compressive strength An amount of 20 untreated nodules that are between 11.2 and 12.5 mm in size are dried in an oven at 105 ° C for a minimum of two hours. After drying, the dry nodules are placed one by one in a standard measuring device in which a plunger of a scale is lowered onto the untreated nodule at a speed of 25 mm for 10 seconds. The maximum force applied at which the nodule is broken is determined. The average force is averaged over 20 untreated nodules and is termed as the dry compressive strength. The values obtained from the above parameters are tabulated in Table 2 below.

TABLE 2 From the previous table 2, it can be deduced that the nodule of examples 1-4, which are made according to the invention, show an increased resistance to dry compression, in comparison with the nodules obtained using a binder system comprising only the Peridur binder (Comparative Example 1). At the same time, the nodes of examples 1-4 show an improvement in wet fall number and only a slight increase in strain, while the nodes of Comparative Example 2 show a deformation and a wet fall number. significantly higher Accordingly, the nodes of Comparative Example 2 will be deformed in a steelmaking process to a much greater degree compared to the nodes of the invention, which makes the process to prepare less efficient incinerated nodules as compared to a process that uses the nodes of the invention. It is further noted that the appearance of the untreated nodes of Examples 2-4 is smooth and non-adherent, while the untreated nodes of Comparative Example 1 are rough. The nodes of Examples 2-4 will generate a smaller amount of fines or residues, for example during transport of these nodules, compared to the nodes of Comparative Example 1. Although the untreated nodes of Comparative Example 2 are smooth, they are sticky , which causes an undesirable grouping of the nodules during processing.

Claims (5)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for producing iron ore agglomerates characterized in that it comprises agglomerating fine iron ore particles in the presence of a binder system, wherein the binder system comprises a binder and an alkali metal silicate and wherein the alkali metal silicate is present in an amount of between 0.0001 and 0.08 weight percent, based on the total weight of the dry iron ore agglomerate, wherein the binder system is free of synthetic polymer.

2. The process according to claim 1, further characterized in that the binder is carboxymethylcellulose.

3. The process according to any of claims 1 and 2, further characterized in that the amount of alkali metal silicate is between 0.04 and 0.08 weight percent, based on the total weight of the dry iron ore agglomerate.

4. The process according to any of the preceding claims, characterized in that the alkali metal silicate is sodium silicate.

5. A binder system comprising carboxymethylcellulose and an alkali metal silicate, with the proviso that the binder system is not an aqueous suspension comprising an alkali metal silicate, carboxymethyl cellulose and particulate impurities originating from impure silica powder used to prepare the alkali metal silicate, or a combination of 18 kg of liquid sodium silicate, kg of carboxymethylcellulose and 40 kg of water.