BRPI0417529B1 - process for producing iron ore agglomerates using sodium silicate containing binder. - Google Patents

Description

Report of the Invention Patent for "PROCESS FOR PRODUCTION OF IRON ORE AGGLOMERATES USING SODIUM CONTAINING CONTAINER".

The invention relates to a process for producing iron ore agglomerates.

Such a process is known from US 6,293,994, which describes a process of producing mineral pellets cooked by mixing moisture-particulate particulate material and binder comprising substantially water-soluble organic polymers and alkali metal silicate in a amount of dry weight which is either (a) above 0.13% based on the wet mixture or (b) above 0.08% based on the wet mixture and at least three times the dry weight of the organic soluble polymer. Water. The preferred polymer is a synthetic polymer formed of a water soluble ethylenically unsaturated monomer or a combination of monomers. The large amount of alkali metal silicate in the pellets described in US 6,293,994 is generally undesirable because silicates can slow down the process of steelmaking operations by blocking the pathways that reducing gases use. to permeate the pellet, which leads to an increase in energy costs. In addition, the use of such large amounts of alkali metal silicate results in crumbly pellets that tend to deform, which in turn can lead to pellets of different sizes and shapes, resulting in an inefficient process for preparing pellets. cooked pellets.

The object of the present invention is to provide iron ore agglomerates with improved physical properties.

The present invention provides 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 an alkali metal silicate binder and a silicate. wherein the alkali metal silicate is present in an amount of from 0.0001 to 0.08 weight percent, based on the total weight of the dry iron ore agglomerate, where the binder system is free of synthetic polymer. The process of the invention leads to iron ore agglomerates with increased cold compressive strength, preheat resistance and dry compressive strength over the use of conventional binder systems comprising the same binder. In addition, small amounts of alkali metal silicate are already sufficient for a significant improvement in the physical properties of the agglomerates. In addition, the specific amount of alkali metal silicate causes agglomerates obtained with the process of the invention to have a similar or slightly higher degree of deformation than binder systems where alkali metal silicate is absent. In contrast, binder systems comprising a larger amount of alkali metal silicate show a significant increase in the degree of deformation which is undesirable. Additionally, the use of alkali metal silicate according to the invention may allow the reduction of the amount of binder without a significant loss of the physical properties of the obtained agglomerates.

The amount of alkali metal silicate preferably is at most 0.07 weight percent (wt.%), And more preferably at most 0.06 weight percent, based on the total weight of dry iron ore agglomerate. By "dry iron ore agglomerate" is meant the total of all ingredients used in the formation of the iron ore agglomerate except water. Preferably the amount of alkali metal silicate is at least 0.02 wt%, and more preferably at least 0.04 wt% based on the total weight of the dry iron ore agglomerate. It has been found that pellets prepared using a binder system comprising at least 0.04% by weight of alkali metal silicate generally having a smooth surface and higher abrasion resistance, while pellets prepared using a binder system comprising less than 0.04% by weight of alkali metal silicate generally exhibit a rough surface which may lead to the generation of debris fines during processing of shaped pellets, for example during pellet transport.

Alkali metal silicate is usually a sodium silicate, but other alkali metal silicates may be used. Examples of sodium silicates are sodium metasilicate and commercially available soluble glass (sodium metasilicate). In sodium silicates, the molar ratio Na20: Si02 is generally in the range 2: 1 to 1: 5, preferably in the range 1: 1 to 1: 4. The amount of alkali metal silicate in the binder system is generally at least 1 wt%, preferably at least 10 wt%, and more preferably at least 15 wt%, and is generally at most 99 wt%. preferably at most 85% by weight, and more preferably at least 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 may be added to the iron ore particles as a dry powder, an aqueous suspension, an aqueous solution, etc. Preferably the alkali metal silicate is added as an aqueous solution.

The binder in the binder system of the invention may be a bentonite inorganic binder and hydrated lime. In the context of this application alkali metal silicate is not considered to be an inorganic binder. Examples of organic binders are polymers including:

(1) water-soluble natural polymers such as guar gum, starch, alginates, pectins, xanthan gum, dairy residues, wood products, lignin, and the like.

(2) modified natural polymers such as guar derivatives (e.g., hydroxypropyl guar, carboxymethyl guar, carboxymethylhydroxypropyl

guar), modified starch (e.g. anionic starch, cationic starch), starch derivatives (e.g. dextrin), and cellulose derivatives such as alkali metal salts of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl hydroxyethyl cellulose, methyl cellulose, lignin derivatives (e.g. carboxymethyl lignin), and the like.

The aforementioned polymers may be used alone or in various combinations of two or more polymers. The binder system is free of synthetic polymers. Examples synthetic polymers are polyacrylamides. Such as partially hydrated polyacrylamides, methacrylamide and polymethacrylamide, polyacrylates and their copolymers, polyethylene oxides and the like.

Another aspect of the present invention is a process for

production of iron ore agglomerates comprising the agglomeration of fine iron ore particles in the presence of a binder system wherein the binder system comprises carboxymethyl cellulose or one of its salts and an alkali metal silicate. The use of the combination of carboxymethyl cellulose and alkali metal silicate leads to agglomerates with increased physical properties such as cold compressive strength, preheat resistance and dry compressive strength. In addition, the reducibility of iron in the agglomerate is generally greater than that observed when a binder system comprising an inorganic binder is used in the agglomeration process.

The invention also relates to a binder system comprising carboxymethyl cellulose and an alkali metal silicate. The amount of alkali metal silicate in the binder system is generally at least 1 wt%, preferably at least 10 wt%, and more preferably at least 15 wt%, and is generally at most 99 wt%, preferably at most 85 wt%, and more preferably at most 75 wt% based on the total weight of the binder system.

Carboxymethyl cellulose or its salt (both are referred to as "CMC") is preferably water soluble. Preferred salts of carboxymethyl cellulose are alkali metal salts of carboxymethyl cellulose. Of these alkali metal salts the sodium salt is preferred. The CMC used in the present invention generally has a degree of substitution (average number of carboxymethyl ether groups per cellulose molecule anhydroglucose repeat chain unit) of at least 0.4, preferably at least 0.5, and most preferably at least at least 0.6, and at most 1.5, more preferably at least 1.2, and most preferably at most 0.9. Generally, the average degree of polymerization of the pulp composition is at least 50, preferably at least 250, and more preferably at least 400, and generally it is at most 8,000, preferably at most 7,000 and most preferably at most. 6,000. Sodium carboxymethyl cellulose having a Brookfield viscosity in a 1% aqueous solution of more than 2,000 cps at 30 rpm, axis 4 is most preferred. Even more preferred is sodium carboxymethyl cellulose having a Brookfield viscosity. in a 1% aqueous solution of more than about 4,000 cps at 30 rpm, axis # 4.

A range of commercially available sodium carboxymethyl cellulose binders 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 being agglomerated, the type of binder being used, and the desired result. For example, the binder may be added as a dry powder, an aqueous suspension, an aqueous solution, an aqueous gel, an aqueous sol (colloidal system), etc.

The amount of binder employed also varies with the desired results. For example, when an organic binder is used, the amount of binder may range from 0.0025 to 0.5% by weight, based on the weight of the iron ore particles, with a preferred range being 0.005 to 0, 2% by weight. In the case of an inorganic binder, the amount of binder may vary for example from 0.1 to 3% by weight based on the weight of the iron ore particles.

Binder and alkali metal silicate may be added to the iron ore particles together, one after the other, etc. This is not critical as long as care is taken to ensure that when agglomeration occurs, the binder and additives are present for execution.

The process of the invention is useful in the agglomeration of fine iron ore particles. The invention, however, is not limited to iron ores and is also useful in agglomerating fine particles of other metal ores. This invention is particularly well suited for the agglomeration of iron-containing materials, including iron ore deposits, ore waste, hot and cold fines from a sintering process, iron oxides from dust collected in systems, or aqueous suspensions. iron ore concentrates from natural sources or recovered from various processes. Iron ore or any of a wide variety of the following minerals may form a part of the material to be agglomerated: taconite, magnetite, hematite, limonite, gohetite, sankanite, franklinite, pyrite, chalcopyrite, chromite, limenite, and the like.

The size of the material being agglomerated varies according to the desired results. For example, when the particulate material being agglomerated is iron ore, 100% of the particles should be less than 80 mesh, preferably 90% have less than 200 mesh and more preferably 75% have less than 325 mesh.

Also considered is the use of conventional additives, for example a base such as sodium hydroxide, or other additives such as sodium citrate, sodium oxalate, etc. These additives, their purpose and their use are known to those skilled in the art.

Many processes for particle agglomeration, especially metal-based particles, are known in the art. Examples of such processes are pelletizing, briquetting, sintering, etc. The binder system used according to the invention is particularly suitable for pelletizing. In the mining industry it is common practice to agglomerate or pellet finely ground beneficiated mineral ore concentrate to facilitate ore processing and handling / transportation. After the mineral ore has been mined, it is often processed by wet grinding to release and separate unwanted mineral groups from the desired material, eg iron in the case of iron ore. Moisture-processed ore is sieved to remove large particles that can be recycled for later grinding. The screened fines are then vacuum filtered to reduce the moisture content to an acceptable pelletizing range. Filtered mineral ore is known in the art as "concentrate". A second process involves "dry milling" and beneficiation of mineral ore, in which case the moisture required for pelletizing is added later.

After beneficiation, a binder is added to the moistened mineral ore concentrate and the binder / mineral ore compound is transported to a pellet drum or other ore pelletizing media. The binding agent serves to hold or bind together the mineral ore so that individual agglomerates can be transported without losing their integrity on the way for further processing and hardening. 1 o After the operation of the pellet drum, the pellets

they are formed but still moist. These wet pellets are commonly referred to as "raw pellets" or "rough balls". These raw pellets are then transported to an oven and heated in stages to a final temperature of about 1300-1350 ° C. In the pelletizing process, the damp raw pellets are loaded in the oven for further processing. Moisture in the pellets is removed by hardening at temperatures typically between 400-600 ° C. After drying in the oven, the pellets are transported to the preheat zone. This is an additional heating stage to also increase the hardness of the pellets before they are transported to the oven and / or to the final cooking stage. Heating generally occurs at 900-1200 ° C to agglutinate the pellets together (eg to oxidize magnetite or crystallize hematite). From the preheat zone, the pellets are dropped 10 to 10 feet (3.05 - 4.57 m) from the net to the oven. This is where the preheat resistance is necessary to prevent the pellets from chipping or breaking into dust particles. Finally the preheated pellets are cooked at a temperature between 1,300 and 1,350 ° C.

The ability of pellets to withstand breakage throughout processing can be approximated by performing standard tests that measure what strength the pellets will need at each stage of processing (eg wet compressive strength, dry compressive strength, preheat resistance, and cold compressive strength).

The present invention is illustrated in the following examples.

Examples

In the following examples, crude iron ore pellets comprising various compounds in the amounts indicated in Table 1 were prepared. Crude pellets were prepared by agglomerating iron ore concentrate in the presence of a binder and a binder additive. . The amounts of binder and / or sodium silicate (in weight percent) shown in Table 1 are based on the total weight of the iron ore concentrate. The iron ore concentrate concentrated in the Examples in Table 1 are Brazilian hematite ores. The binder is Peridur 330 (from Akzo Nobel), which comprises sodium carboxymethyl cellulose and sodium carbonate, and the sodium silicate (Na20: Si02 is 1: 3.3) used in the experiments is provided by PQ Corporation. . Agglomerate production processes are generally co-

the person skilled in the art. The process is described in detail in US 6,071,325, which describes a process of producing 2,500 gram agglomerates on a rotary airplane tire (approximately 40 cm in diameter).

First the binder was mixed in the dry concentrate and

homogenized. Then the alkali metal silicate was mixed with the required amount of water (moisture content between 8 and 9% by weight) and subsequently thoroughly mixed with the concentrate and binder (using a model Mullen Mixer). No. 1 Cincinnati Muller, produced by National Engineering Co. or similar). The seed pellets were formed by placing a small portion of the concentrate in the spinneret and adding water spray to begin pellet growth. Seed pellets with a size between 3.5 and 4 mm were retained and kept separate for pellet formation with the desired size of 11.2 and 12.5 mm. Finished raw pellets were produced by placing 165 grams of seed pellets described above into the spinneret and adding a portion of the remaining concentrate mixture for a growth period of over 3 minutes. Water spray was added if necessary.

Table 1

Comparative Example Peridur ™ (% by weight) Sodium Silicate 1 0.03 - 2 0.03 0.20 Example 1 0.03 0.03 2 0.03 0.05 3 0.03 0.06 4 0.03 0.08

Moisture content, number of drops and resistance to

Wet and dry compressions of the obtained raw pellets were measured. Number of Wet Falls

The number of wet falls was determined by repeatedly dropping a rough pellet having a size between 11.2 and 12.5 mm from a height of 46 cm on a horizontally placed steel plate until a visible crack formed on the surface of the pellet. . The number of times the pellet has been dropped to the point of fracture / rupture has been determined. The average number of times measured in more than 20 raw pellets is referred to as the "Number of Wet Falls". Wet Compressive Resistance

Damp raw pellets having a size between 11.2 and 12.5 mm were stored in an impermeable container. One by one the pellets were removed and placed in a standard measuring device in which a plunger of a ruler was lowered onto the raw pellet at a speed of 25 mm per minute. The maximum applied force at which the pellet cracked was determined. The average force measured on the 20 raw pellets is referred to as wet compressive strength. Deformation

A minimum of 20 wet gross pellets having a size between 11.2 and 12.5 mm were stored in an impermeable container. One by one the pellets were removed and placed in a standard measuring device in which a plunger of a ruler was lowered onto the raw pellet at a loading rate of 25 mm per minute. The machine (Model Lloyd Texture Analyzer TA-PIus1 PC controlled with Nexygen software version 4.5) is equipped with a 50 N load cell and has a test diameter of 10 mm. The deformation / deflection of the raw pellet is recorded as the force increases. Deformation is defined as the change in diameter of the raw pellet at a force of 1 N, provided that the pellet is not fractured at this point. Dry Compressive Resistance

Raw pellets having a size between 11.2 and 12.5 mm were dried in an oven at 105 ° C for a minimum of two hours. After drying, the dried pellets were placed one by one in a standard measuring device in which a plunger of a ruler was lowered onto the raw pellet at a speed of 25 mm for 10 seconds. The maximum applied force at which the pellet cracked was determined. The average force measured over the 20 gross pellets is referred to as Dry Compressive Resistance.

The values obtained for the above parameters are tabulated in the Table below. Table 2

Example Comparative Resistance Number of Depression Appearance moisture drops raw pellet compressi- (%) wet va dry 1 8.6 2.7 0.22 Rough, non-sticky 1.0 2 8.6 8.3 0.28 Smooth, sticky 2.0 Example 1 8.2 3.1 0.20 Rough, non-sticky 1.2 2 8.3 4.4 0.24 Smooth, sticky 1.9 3 8.3 5.6 0.23 Smooth, sticky 2.9 4 8.1 4.9 0.24 Smooth, sticky 3.3

From the table above it can be deduced that the pellets of the Examples

1-4, which are in accordance with the invention, show increased dry compressive strength compared to pellets obtained using a binder system comprising only the Peridur binder (Comparative Example 1). At the same time, the pellets of Examples 1-4 show an improvement in the number of wet falls and only a slight increase in deformation, while the pellets of Comparative Example 2 show significantly greater deformation and number of wet falls. Accordingly, the pellets of Comparative Example 2 will be deformed in the steelmaking process to a greater extent than the pellets of the invention, making the process for preparing cooked pellets less efficient compared to the processes using the pellets of the invention. It is also noted that the appearance of the crude pellets of Comparative Example 1 is rough. The pellets of Examples 2-4 will generate less fines or leftovers, for example during the transport of such pellets, compared to the pellets of Comparative Example 1. Although the crude pellets of Comparative Example 2 are smooth, they are small. gudges, causing undesirable grouping of the pellets during processing.

Claims (4)

A process for producing iron ore agglomerates, which comprises agglomerating fine iron ore particles in the presence of a binder system wherein the binder system comprises a binder selected from the group of inorganic binders, water soluble natural polymers and natural polymers. and an alkali metal silicate, characterized in that the alkali metal silicate is present in an amount of between 0.0001 and 0.07 weight percent, based on the total weight of the iron ore agglomerate. in which the binder system is free of synthetic polymers. Process according to Claim 1, characterized in that the binder is carboxymethyl cellulose. Process according to Claim 1 or 2, characterized in that the amount of alkali metal silicate is between 0.04 and 0.07 weight percent, based on the total weight of dry iron ore agglomerate. . Process according to any one of Claims 1 to 3, characterized in that the alkali metal silicate is sodium silicate.