Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/242—Binding; Briquetting ; Granulating with binders
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/2406—Binding; Briquetting ; Granulating pelletizing
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/242—Binding; Briquetting ; Granulating with binders
  • C22B1/243—Binding; Briquetting ; Granulating with binders inorganic
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/242—Binding; Briquetting ; Granulating with binders
  • C22B1/244—Binding; Briquetting ; Granulating with binders organic

Definitions

• the invention relates to a process for producing iron ore agglomerates.
• a process for producing iron ore agglomerates is known from US 6,293,994, which discloses a process of making fired mineral pellets by mixing particulate mineral material with moisture and binder comprising substantially water-soluble organic polymer and alkali metal silicate in a dry weight amount which is either (a) above 0.13% based on moist mix or (b) above 0.08% based on moist mix and at least three times the dry weight of substantially water-soluble organic polymer.
• the preferred polymer is a synthetic polymer formed of water-soluble ethylenically unsaturated monomer or monomer blend.
• the high amount of alkali metal silicate in the pellets described in US 6,293,994 generally is undesirable, because silicates can slow down the reduction process in steel making operations by blocking the pathways the reducing gases use to permeate the pellet, which leads to an increase in energy costs. Furthermore, the use of such high amounts of alkali metal silicate results in green pellets that have a high tendency to deform, which in turn may lead to pellets of different size and shape, resulting in an inefficient process for preparing fired 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 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.
• the process of the invention leads to iron ore agglomerates with increased cold compression strength, preheat strength, and dry crush strength relative to the use of conventional binder systems comprising the same binder.
• alkali metal silicate small amounts are already sufficient to obtain a significant improvement in the physical properties of the agglomerates.
• the specified amount of alkali metal silicate causes the agglomerates obtained with the process of the invention to have a similar or only slightly higher degree of deformation than binder systems where alkali metal silicate is absent.
• binder systems comprising a larger amount of alkali metal silicate exhibit a significant increase in the degree of deformation, which is undesirable.
• the use of alkali metal silicate in accordance with the invention may enable a reduction of the amount of binder without a significant loss in physical properties of the obtained agglomerates.
• the amount of alkali metal silicate preferably is at most 0.07 percent by weight (wt%), and most preferably at most 0.06 wt%, based on the total weight of dry iron ore agglomerate.
• dry iron ore agglomerate is meant the total of all ingredients used in the formation of the iron ore agglomerate except water.
• the amount of alkali metal silicate is at least 0.02 wt%, and most preferably at least
• pellets prepared using a binder system comprising at least 0.04 wt% of alkali metal silicate generally have a smooth surface and a higher resistance to abrasion
• pellets prepared using a binder system comprising less than 0.04 wt% of alkali metal silicate generally exhibit a rough surface, which can lead to the generation of fines or debris during processing of the formed pellets, e.g. during transport of the pellets.
• the alkali metal silicate usually is a sodium silicate, but other alkali metal silicates can be used.
• sodium silicates are sodium metasilicate and the commercially available water glass.
• the molar ratio Na 2 O:SiO 2 generally is 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 generally is at least 1 wt%, preferably at least 10 wt%, and most preferably at least 15 wt%, and generally it is at most 99 wt%, preferably at most 85 wt%, and most preferably at most 75 wt%, based on the total weight of the binder system.
• the alkali metal silicate preferably is 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, etc.
• 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.
• inorganic binders are bentonite and hydrated lime.
• alkali metal silicate is not considered to be an inorganic binder.
• organic binders are polymers including:
• Water-soluble natural polymers such as guar gum, starch, alginates, pectins, xanthan gum, dairy wastes, wood related products, lignin, and the like;
• 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, carboxymethylhydroxyethyl cellulose, methyl cellulose, lignin derivatives (e.g. carboxymethyl lignin), and the like.
• guar derivatives e.g. hydroxypropyl guar, carboxymethyl guar, carboxymethylhydroxypropyl guar
• modified starch e.g. anionic starch, cationic starch
• starch derivatives e.g. dextrin
• cellulose derivatives such as alkali metal salts of carboxymethyl cellulose, hydroxyethyl
• the aforesaid polymers may be used alone or in various combinations of two or more polymers.
• the binder system is free of synthetic polymers.
• 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 carboxymethyl cellulose or a salt thereof and an alkali metal silicate.
• the binder system comprises carboxymethyl cellulose or a salt thereof and an alkali metal silicate.
• carboxymethyl cellulose and alkali metal silicate leads to agglomerates with increased physical properties, such as cold compression strength, preheat strength, and dry crush strength.
• the reducibility of the iron in the agglomerates generally is higher than is observed when a binder system comprising an inorganic binder is used in the agglomeration process.
• the invention further concerns a binder system comprising carboxymethyl cellulose and an alkali metal silicate.
• the amount of alkali metal silicate in the binder system generally is at least 1 wt%, preferably at least 10 wt%, and most preferably at least 15 wt%, and generally it is at most 99 wt%, preferably at most 85 wt%, and most preferably at most 75 wt%, based on the total weight of the binder system.
• the carboxymethyl cellulose or the salt thereof preferably is substantially 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 (the average number of carboxymethyl ether groups per repeating anhydroglucose chain unit of the cellulose molecule) of at least 0.4, preferably at least 0.5, and most preferably at least 0.6, and at most 1.5, more preferably at least 1.2, and most preferably at most 0.9.
• the average degree of polymerization of the cellulose furnish is at least 50, preferably at least 250, and most preferably at least 400, and generally it is at most 8,000, preferably at most 7,000, and most preferably at most 6,000. It is more preferred to use sodium carboxymethyl cellulose having a Brookfield viscosity in a 1% aqueous solution of more than 2,000 cps at 30 rpm, spindle #4. Still 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, spindle #4.
• a series, of commercially available binders containing sodium carboxymethyl cellulose especially useful in the present invention is available from Akzo Nobel, under the trademark PeridurTM.
• 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 results.
• 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 results desired.
• the amount of binder may range from 0.0025 to 0.5 wt.%, based on the weight of the iron ore particles, with a preferred range being 0.005 to 0.2 wt.%.
• the amount of binder may range for example from 0.1 to 3 wt.%, 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, etc. This is not critical, so long as care is taken to ensure that when the agglomeration takes place, the binder and the additive are present to perform.
• the process of the invention is useful in agglomerating fine iron ore particles.
• the invention is not limited to iron ores and is also useful in the agglomeration of fine particles of other metal ores.
• This invention is particularly well adapted for the agglomeration of materials containing iron, including iron ore deposits, ore tailings, cold and hot fines from a sinter process, iron oxides from dust collected in systems, or aqueous suspensions of 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, goethite, siderite, franklinite, pyrite, chalcopyrite, chromite, ilmenite, and the like.
• the size of the material being agglomerated varies according to the desired results.
• 100% of the particles may be less than 80 mesh, preferably, 90% are less than 200 mesh, and most preferably, 75% are less than 325 mesh.
• additives for instance a base such as sodium hydroxide, soda, or other additives such as sodium citrate, sodium oxalate, etc.
• base such as sodium hydroxide, soda, or other additives such as sodium citrate, sodium oxalate, etc.
• a binding agent is added to the wetted mineral ore concentrate and the binder/mineral ore composite is conveyed to a balling drum or other means for pelletizing the ore.
• the binding agent serves to hold or bind the mineral ore together, so that the individual agglomerates can be transported without losing their integrity en route to further processing and induration.
• the pellets are formed, but they are still wet. These wet pellets are commonly referred to as “green pellets” or “green balls”. These green pellets are thereafter transported to a kiln and heated in stages to an end temperature of about 1, 300-1 ,350°C. In the pelletizing process, the wet green pellets are loaded into the furnace for further processing. The moisture in the pellets is removed by induration at temperatures normally between 400-600°C. Following drying in the furnace, the pellets are transported to the preheat zone. This is an additional heating stage to further increase the pellets' hardness before they are transported to the kiln and/or final firing stage. Heating generally occurs at 900-1 ,200°C to bind the pellets together (e.g.
• the pellets are dropped 10-15 feet from the grate to the kiln. This is where the preheat strength is needed to prevent the pellets from chipping and breaking apart into dust particles. Finally, the preheated pellets are fired at a temperature of between 1 ,300 and 1 ,350°C.
• the ability of the pellets to withstand breakage throughout processing can be approximated by performing standard tests that measure the strength the pellets will need at each stage of processing, (e.g. wet crush strength, dry crush strength, preheat strength, and cold compressive strength).
• the present invention is illustrated in the following Examples.
• green pellets of iron ore comprising various compounds in the amounts indicated in Table 1 were prepared.
• the green 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 percent by weight) shown in Table 1 are based on the total weight of the iron ore concentrate.
• the iron ore concentrate employed in the Examples of Table 1 was Brazilian hematite ore.
• the binder is Peridur 330 (ex Akzo Nobel), which comprises sodium carboxymethyl cellulose and sodium carbonate, and the sodium silicate (Na 2 O:SiO 2 is 1 :3.3) used in these experiments is supplied by PQ Corporation.
• the binder was mixed into the dry concentrate and homogenized. Then, the alkali metal silicate was mixed with the required amount of water (moisture content between 8 and 9 wt%) and subsequently thoroughly mixed with the concentrate and the binder (using a Mullen Mixer model No. 1 Cincinnati Muller, manufactured by National Engineering Co. or the like). Pellet "seeds” were formed by placing a small portion of the concentrate in the rotating tire and adding atomized water to initiate pellet growth. Seed pellets with a size between 3.5 and 4 mm were retained and kept apart for the formation of pellets with the desired size of 11.2 and 12.5 mm. Finished green pellets were produced by placing 165 grams of seed pellets described above in the rotating tire and adding a portion of the remaining concentrate mixture over a 3-minute growth period. Atomized water was added if necessary.
• the moisture content, the drop number, and the wet and dry compressive strengths of the obtained green pellets were measured.
• Wet drop number The Wet drop number was determined by repeatedly dropping a green pellet having a size between 11.2 and 12.5 mm from a height of 46 cm onto a horizontally placed steel plate until a visible crack formed in the pellet surface. The number of times the pellet was dropped up to the point of fracture/cracking was determined. The average number of times averaged over 20 green pellets is referred to as the "Wet drop number”.
• Wet compressive strength 20 wet green pellets having a size of between 11.2 and 12.5 mm were stored in an airtight container. One by one the pellets were removed and placed in a standard measuring device in which a plunger of a scale was lowered onto the green pellet at a speed of 25 mm per minute. The maximum applied force at which the pellet cracked was determined. The average force averaged over 20 green pellets is referred to as the Wet compressive strength.
• a minimum of 20 wet green pellets having a size of between 11.2 and 12.5 mm were stored in an airtight container. One by one the pellets were removed and placed in a standard measuring device in which a plunger of a scale was lowered onto the green pellet at a loading rate of 25 mm per minute.
• the machine (Model Lloyd Texture Analyser TA-Plus, controlled by PC with Nexygen version 4.5 software) is equipped with a 50 N load-cell and has a probe diameter of 10 mm.
• the deformation/deflection of the green pellet is recorded while increasing the force. The deformation is defined as the change in diameter of the green pellet at a force of 1 N, provided that the pellet is not ruptured at this point.
• 20 green pellets having a size of between 11.2 and 12.5 mm were dried in an oven at 105°C for a minimum of two hours. Following drying, the dried pellets were placed one by one in a standard measuring device in which a plunger of a scale was lowered onto the green pellet at a speed of 25 mm per 10 seconds. The maximum applied force at which the pellet cracked was determined. The average force averaged over 20 green pellets is referred to as the Dry compressive strength.
• the appearance of the green pellets of Examples 2-4 is smooth and non-sticking, whereas the green pellets of Comparative Example 1 are rough.
• the pellets of Examples 2-4 will generate a lower amount of fines or debris, e.g. during transport of these pellets, compared to the pellets of Comparative Example 1.
• the green pellets of Comparative Example 2 are smooth, they are sticky, causing undesirable clustering of the pellets during processing.

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• Chemical & Material Sciences (AREA)
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• General Life Sciences & Earth Sciences (AREA)
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• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)

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• 2004
  • 2004-08-12 UA UAA200607787A patent/UA86959C2/uk unknown
  • 2004-12-08 CA CA2548395A patent/CA2548395C/en not_active Expired - Fee Related
  • 2004-12-08 EP EP04820426A patent/EP1692319B1/de not_active Not-in-force
  • 2004-12-08 MX MXPA06006655A patent/MXPA06006655A/es active IP Right Grant
  • 2004-12-08 EA EA200601137A patent/EA011259B1/ru not_active IP Right Cessation
  • 2004-12-08 BR BRPI0417529-8A patent/BRPI0417529B1/pt not_active IP Right Cessation
  • 2004-12-08 US US10/582,451 patent/US20070119563A1/en not_active Abandoned
  • 2004-12-08 WO PCT/EP2004/014017 patent/WO2005059186A1/en active Application Filing
  • 2004-12-08 CN CNA2004800368959A patent/CN1890391A/zh active Pending

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