METHOD FOR OBTAINING AGENCIES OF FINE IRON ORE AND PRESSED PELLETS OBTAINED BY THIS METHOD

Abstract

The invention relates to a method for obtaining agglomerates of fine iron ore, in which polyacrylamide and sodium silicate are used for cold agglomeration of the iron ore, with polyacrylamide acting as both a binder and an activator for the sodium silicate. The invention also relates to pressed pellets obtained by this method.

Description

[0001] SPECIFICATION

[0002] Briquetting and Extrusion of Iron Ore

[0003] Technical Field of the Invention and Prior Art

[0004] Traditionally, cast iron is produced in blast furnaces, by reducing iron ore, by mixing it with coke. The main method is sintering, in which a coke-mineral mixture of low homogeneity is moistened and then dried. Agglomeration by pelletizing using a plate apparatus is also used.

[0005] Coke produces a significant amount of CO2, and the entire steel industry must develop methods that do not use this product.

[0006] The trend is to modify blast furnaces, with ore reduction using gas or hydrogen, to reduce CO2 in cast iron production.

[0007] Additionally, direct reduction methods (DR1) use both electrical energy to heat the ore, and gas or hydrogen to reduce the ore to a relatively low temperature of 900°C, producing solid porous iron.

[0008] To achieve this, it is essential to produce briquettes or extrudates as rich as possible in iron oxide, with high mechanical strength at high temperatures.

[0009] This search for briquettes and extrudates with a high iron oxide content and high mechanical strength at high temperatures requires the following additives:

[0010] 1. A binder for cold forming high-strength pellets or extrudates.

[0011] The best low temperature binders are:

[0012] - Bentonite, which is widely used, but has the disadvantage of increasing impurities in the final product.

[0013] - Organic binders, e.g., starch, molasses, tars, lignosulfonate, polyvinyl alcohol, polyacrylamide, CMC... But these binders do not give high temperature strength.

[0014] - A high-temperature binder has long been known from its use in foundry sands but gives no binding effect at low temperatures. This is sodium silicate.

[0015] 2. A sodium silicate activator. Indeed, for it to play the role of binder, the silicate must be activated:

[0016] -Either by an acid formed after briquetting, and in particular esters, which hydrolyze with the basicity of the silicate, transforming the silicate into colloidal silica, which, on drying, has very high agglomeration power;

[0017] - Or by CO2, widely used in porous foundry sand, but which requires very long processing times on very compact briquettes;

[0018] - Or by lime, which has high agglomeration power in the form of calcium silicate.

[0019] - Or other divalent metal compounds, magnesium oxide, talc, olivine, ...

[0020] But most of these activators have a long reaction time, requiring storage at room temperature for 3 to 20 days.

[0021] 3. Portland cement or aluminous cement, which carries significant impurities.

[0022] 4. Various ingredients with ancillary functions: nanomaterials, such as carbon nanotubes to increase strength, glycerine, triethanolamine, fine iron or oxide dust, ...

[0023] CA3124576A1 discloses a process for the production of iron ore fines agglomerate for metallic load replacement in reduction furnaces using a mixture of nanomaterial and a catalyst to sodium silicate as a binder and fines of fluxes selected from the group consisting of calcium hydroxide, calcitic limestone, dolomitic limestone, calcined magnesite, serpentinite, talc, dunite, and olivine used as activator.

[0024] FR2930265 Al discloses a process for agglomerating industrial dust using a first binder comprising polyacrylamide as a reverse emulsion, and a second binder comprising a sodium silicate at ambient temperature. As mentioned above, sodium silicate does not give binding effect at low temperatures. Additionally, the absence of activators for silicate renders the process non compatible with the production of briquettes or extrudates as rich as possible in iron oxide, with high mechanical strength at high temperatures. Another drawback is that in some cases, the inverse emulsion contains either flammable or combustible solvent which would evaporate on heating, as for example during drying, causing an explosive atmosphere either by an external spark or by reaching the auto-ignition temperature of around 200-250°C (AST ME 659) requiring an ATEX zone below the auto-ignition zone and impossible above.

[0025] Invention

[0026] It has been discovered that polyacrylamide, which is a good cold binder, may also act as an activator for sodium silicate, during the drying and the rise of the temperature of the briquettes. What's more, this method enables very rapid activation of the silicate, with virtually immediate drying and heat treatment. The method can also be applied to scrap from the metallurgical industry, ferroalloys and ores such as nickel, chromium, ...

[0027] The invention therefore relates to the use of only polyacrylamide and sodium silicate for the cold agglomeration of iron ore, characterized in that the polymer acts both as a binder and as an activator for the sodium silicate.

[0028] The invention relates to the use of polyacrylamide as binder and sole sodium silicate activator in a method for the cold agglomeration of iron ore.

[0029] In other words, the invention relates to the use of polyacrylamide both as a binder and as an activator for the sodium silicate in a method for the cold agglomeration of iron ore.

[0030] The polyacrylamides used are either acrylamide homopolymers or copolymers with other monomers.

[0031] Given the variability of iron ore in terms of chemical composition, in particular the impurities, physical composition, in particular the particle size distribution or hydrophilicity, and moisture content, it is necessary to define the most suitable polyacrylamide for each ore by means of compaction, drying, and firing tests.

[0032] In practice, polyacrylamide is chosen from anionic, cationic, amphoteric or non-ionic acrylamide copolymers depending on the variability of the ore to obtain suitable compositions and particle sizes determined by test.

[0033] These polyacrylamides are characterized by their composition, molecular weight and molecular distribution, degree of branching, hydrophilicity or hydrophobicity ... The basic polyacrylamide is a polymer of acrylamide.

[0034] A distinction is then made between:

[0035] - anionic copolymers, in which acrylamide is copolymerized with an anionic monomer: especially acrylic acid or AMPS (acrylamido propane sulfonate), maleic acid, vinylsulfonic acid, itaconic acid, vinylphosphonic acid in the form of sodium, potassium or ammonium salts . . .

[0036] - cationic copolymers containing a cationic comonomer: dimethylamino ethyl (metha)acrylate, dimethylamino propyl acrylamide, DADMAC (dimethyl diallyl ammonium chloride) or similar monomers quatemized with methyl chloride, methyl sulfate or benzyl chloride.

[0037] In addition to anionic monomers, non-ionic monomers can be introduced, which can also impart hydrophilicity or hydrophobicity, e.g., polyoxyethylene glycol acrylate, butyl acrylate ...

[0038] These polymers can also be branched or partially cross-linked by polyvalent monomers such as methylene bis acrylamide, polyethylene glycol diacrylate, etc., or heat-cross-linking monomers such as methylolacrylamide.

[0039] With the option of using amphoteric polymers from anionic and cationic monomers.

[0040] These polymers can have molecular weights ranging from a few thousand to 25 million. The required particle size is determined by tests e.g., 0-300 microns / 0-500 microns / 0-800 microns,.

[0041] In a preferred embodiment, the polyacrylamides used either as acrylamide homopolymers or as copolymers with other monomers, are solid particles having particle size advantageously strictly more than 0 (>) - 300 microns, > 0-500 microns, >0-800 microns. They are in the form of powders or microbeads. These particulate forms are obtained by techniques known to those skilled in the art. It may be obtained by gel polymerization, aqueous solution polymerization followed by drum drying, spray drying, or radiation drying such as microwave drying or fluidized bed drying. The powder form may also be obtained by water-in-oil emulsion polymerization (inverse emulsion), followed by a distillation / concentration step and spray-drying of the resulting liquid. The polymer microbeads are advantageously obtained by reverse suspension polymerization. Method

[0042] The method for producing briquettes or extrudates generally consists of mixing: - the binder,

[0043] - the sodium silicate,

[0044] - the activator,

[0045] - a certain amount of water from the ore or added thereto,

[0046] - and various other ingredients. which are molded in a mechanical press, in the form of "briquettes", at a pressure of around 200 bar, or 35 kN / cm linear, or in vacuum extruders, to avoid the inclusion of air bubbles at high pressure. The extruded product is cut into pieces of various sizes.

[0047] These briquettes and extrudates are then dried at between 150°C and 400°C, at a fairly low speed, to prevent them from exploding due to the vaporization of water.

[0048] According to one embodiment of the invention, the method for obtaining agglomerates of iron ore fines comprises the following steps: a) mixing polyacrylamide, sodium silicate and ore in a mixer under defined conditions; bl) adjust the moisture content for compaction within a range of 2 to 10%, preferably 3 to 8% of the mixture; then agglomerate using a briquetting press (with tangential wheels) and finally dry the agglomerates obtained at a temperature of 100 to 250°C for 30 minutes to 2 hours or, b2) adjust the humidity for extrusion from 5 to 20%, preferably 9 to 18%, then extrude using a vacuum extruder and finally dry the extrudates at a temperature of 100 to 250°C for 30 minutes to 2 hours.

[0049] The test to confirm the quality of the agglomerated product then consists of heating it to 900°C to measure its resistance.

[0050] Current requirements for molding treatments are:

[0051] - cold resistance,

[0052] - resistance after drying,

[0053] - resistance after heating to 900°C.

[0054] In practice, no other activator than polyacrylamide is added to treat the sodium silicate. According to this invention, the silicate is available in solid form as powders, beads or microbeads, or in liquid form by adjusting the amount of water required for mixing.

[0055] In practice, the following dosage ratios are used: 0.01% to 2% by weight of polyacrylamide polymer relative to the total weight of the agglomerate formed, and 0.1 to 5% by weight of active sodium silicate, relative to the total weight of the agglomerate formed.

[0056] In other words, 0.01% to 2% by weight of polyacrylamide polymer are mixed relative to the total weight of the agglomerate formed and 0.1 to 5% by weight of active sodium silicate relative to the total weight of the agglomerate formed.

[0057] In one particular embodiment, a hydrophobic polyacrylamide is added to reduce moisture sensitivity.

[0058] The invention also relates to briquettes obtained by the preceding method, the briquettes having a press recycle of less than 20%, a green briquette burst test of over 80%, a dry briquette burst strength of over 99% and a DCS of over 200 kg.

[0059] According to another characteristic, in contrast to bentonite as a binder or lime as a sodium silicate activator, the briquettes obtained are of very high purity.

[0060] Finally, unlike other activators, briquettes according to the invention are dried and fired without aging.

[0061] Examples

[0062] The purpose of these examples is to illustrate the high quality and good properties of the agglomerated products obtained.

[0063] The concentrated iron ores used in the examples are magnetite concentrate and hematite ores (concentrated and ground).

[0064] Magnetite #1 is a floated concentrate, with Fe content around 68%, particle size less than 100 pm, D80 = 74 pm, Blaine index between 2300 and 2500. The magnetite concentrate comes from Ukrainian deposits. The Blaine index is a unit, expressed in cm2 / g, measuring the specific surface area of particles and powders. Hematite #2 is a crushed hematite, with an Fe content of around 66%, a particle size of less than 300 pm with a D80 = 100 pm, and a Blaine index between 1950 and 2100. Hematite comes from Canadian deposits in particular.

[0065] Hematite #3 is a float hematite, with an Fe content of around 69%, a particle size of less than 100 pm with a D80 = 74 pm, and a Blaine index between 2100 and 2300. Hematite comes from Canadian deposits in particular.

[0066] The tests were carried out by varying the dosages and nature of the organic binders and iron ores, as illustrated in the examples below.

[0067] To prepare these agglomerates, in a first step, the ore and the polymer are mixed with sodium silicate in solid or liquid form and homogenized with the necessary amount of water (moisture content between 2 and 5% by weight). The materials are mixed using a KitchenAid® type mixer (up to 3 kg of concentrate) and Eirich, Lbdige, or Hobart (more than 3 kg of concentrate and up to 40 kg).

[0068] After a mixing time of 4 to 8 minutes, the ore concentrate is fed into the inlet hopper of a tangential wheel compactor (roller press) or vacuum extruder.

[0069] The agglomerates produced with the compactors are called briquettes and have a size of between 30 and 50 mm for volumes of between 5 and 10 cm3. Compactors can be of the Kbppem and affiliated brands (Komarek and Euragglo), or Sahut-Conreur.

[0070] The agglomerates produced with the extruder are called corks and have a size of between 30 and 50 mm for volumes of between 2.5 and 5 cm3. Extruders can be Verdes or JC STEELE and affiliates (Handle).

[0071] These agglomerates are placed in the low-temperature furnace, which is set at 105°C for example, for between 30 minutes and 2 hours to dry them completely.

[0072] Several tests have been carried out to confirm the quality of the agglomerated product, which offers high physical resistance to handling and vibration during transport.

[0073] This involved a series of tests in which various parameters were measured: 1. Briquette appearance test : visual test, the agglomerate must be well formed, shaped like a rectangular pebble or cylinder. We're looking for a smooth exterior and efficient interlocking (no yawning, cracking or mille feuilles).

[0074] 2. Press recycling : The principle of this test is to measure the percentage of fine ore agglomerate required to obtain a complete briquetting process. A 6.3 mm sieve is taken just after leaving the press to check the quality of the pebbles. At this stage, the green agglomerates have a drop height of 1.5 m, which is sufficient to check their strength. The weight of each portion (above and below 6.3 mm) is measured. The proportion of each portion is expressed as a percentage of the total weight of the mix. Results are given in % - good results are between 0 and 20%.

[0075] 3. Shatter Tests: This test measures the strength of the briquettes during transport from the roller press to the furnace. The number of wet drops is determined by repeatedly dropping 500 g of briquettes from a height of 2 m onto a horizontally placed steel plate, through an open, vertical plastic pipe. The diameter of the pipe is 20 cm. After the first drop, all parts of the briquettes (fines, Si, pieces, Si, or briquettes) are removed and put back in place for a second drop. After this second drop, everything is again sampled and weighed. Results are given in % over 10 mm. The limit is 80% good-quality briquettes.

[0076] 4. Low temperature dry hardness: the agglomerates are placed in a furnace at a temperature below 250°C, preferably between 90°C and 150°C, for between 15 minutes and 2 hours to dry completely. After drying, 20 dry agglomerates are placed one by one in a standard hardness tester such as those sold under the SCAINE brand name. The maximum applied force at which the pellet cracks or breaks is determined. The average of these 20 measurements is called "dry compressive strength" (DCS) - results are given in kg / agglomerate. It should be noted that 500 kg is the upper limit of the manual test, this limit being perfectly validated for excellent quality.

[0077] 5. Hardness after 900°C: the agglomerates are placed in a furnace at 900°C for 20 minutes to burn off the organic parts. The burnt pellets are placed one by one in a standard hardness tester such as those sold under the SCAINE brand name. The maximum applied force at which the pellet cracked was determined. The average of these 20 measurements is called "dry compressive strength" (DCS). The results are given in kg / agglomerate. It should be noted that 500 kg is the upper limit of the manual test, this limit being perfectly validated for excellent quality.

[0078] 6. Water Resistance Tests: The agglomeration of certain very fine or more hydrophilic ores can lead to low water resistance of the agglomerates, and therefore possible disintegration of the briquettes during their storage / transport. To compensate for this, we suggest adding, if necessary, a water-repellent agent to make the dry briquettes water-resistant for several weeks. 20 briquettes are then completely immersed in tanks filled with water and left for several days to several weeks. Visual checks are carried out at defined times.

[0079] 7. Tumble and Abrasion Test: Method to provide a relative measurement for the evaluation of the resistance of iron ores to particle size degradation by impact (tumbling in the drum) and abrasion (formation of fines).

[0080] A portion of agglomerates (2 kg or approximately 50 briquettes) is placed in a circular drum for a total of 200 revolutions, at 25 rpm. The drum is opened and all the material present is screened between 6.3 mm and 500 pm. The Tumble Index is expressed as the mass percentage of material above 6.3 mm and the Abrasion Index as the mass percentage of material below 500 pm. The standard values followed here are:

[0081] - Tumble index: 80% > 6.3 mm

[0082] - Abrasion index: 10% < 500 pm.

[0083] Example 1:

[0084] The tests in this example are carried out on a tangential wheel press. We use iron ore concentrate from Ukraine, floated magnetite, with Fe content of 68.1%, particle size less than 100 pm, with D80 = 74 pm, Blaine index between 2300 and 2500. We adjust the moisture content and add our binding formula as shown in Table 1.

[0085] The PAM used is an acrylamide / sodium acrylate copolymer (70-30) with a molecular weight of 18 million and a particle size of V 0 to 800 microns. Sodium silicate is used in powder form, as a silicic acid, sodium salt (MR>3.2). Sodium silicate is a well-known binder for briquetting, mainly used in the recycling of steel fines. It offers good performance for hot processes, allowing agglomerates to withstand the high temperatures of furnaces (blast furnaces, converters, electric arc furnaces).

[0086] [Table 1]

[0087] Table 1 : Example 1

[0088] We mix for 4 minutes in an intensive mixer and leave to rest for 10 to 15 minutes in a covered bucket. We then place the mixture in the press at a pressure of 200 bar, i.e., 30 KN / m linear, and carry out the following measurements (Table 2):

[0089] [Table 2]

[0090] Table 2: Example 1

[0091] Example 1 shows that the use of PAM and sodium silicate gives good results for green briquettes (press recycling and Shatter tests on green briquettes), which was known as a property provided by the PAM.

[0092] The example shows that this formula also gives very good results on dry briquettes: Shatter tests show no breakage or generation of fine particles, and compressive strength is very high, exceeding requirements (200 kg).

[0093] Example 1 shows that the formula is also good for hot testing, where the PAM has disappeared, and the compressive strength shows that the briquettes retain their integrity and strength at a value acceptable to the process. Example 1 shows that the formula gives good results for the Tumble and Abrasion Indices, indicating that the briquettes can be handled and transported without damage to the final process (furnace run).

[0094] Example 2:

[0095] We use the same equipment and iron ore concentrate sample as in Example 1. We adjust the moisture content and add another bonding formula as shown in Table 3. The objective is to determine if the PAM alone can work for cold-agglomerated briquettes.

[0096] [Table 3]

[0097] Table 3: Example 2

[0098] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press at a pressure of 200 bar, i.e., 30 KN / m linear, and carry out the following measurements (Table 4):

[0099] [Table 4]

[0100] Table 4: Example 2

[0101] Example 2 shows that using PAM alone gives good results for green briquettes (press recycling and green briquette Shatter tests), which was known to be a property provided by PAM.

[0102] The example shows that this formula also gives very good results on dry briquettes: Shatter tests show no breakage or generation of fines, but compressive strength is too low to meet requirements after firing at 900°C.

[0103] Example 2 shows that the formula may not be validated due to the poor results obtained during hot testing, during which the PAM disappeared.

[0104] Example 2 shows that the formula gives poor results for Tumble and Abrasion Indices, as the polymer bonds alone are not strong enough to withstand multiple handling and transportation.

[0105] Example 3:

[0106] We use the same equipment and the same iron ore concentrate sample as in Example 1. We adjust the moisture content and add another bonding formula as shown in Table 5. The objective is to determine whether sodium silicate alone may work for cold-bonded briquettes.

[0107] [Table 5]

[0108] Table 5: Example 3

[0109] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 6):

[0110] [Table 6]

[0111] Table 6: Example 3

[0112] Example 3 shows that the use of sodium silicate alone does not give good results, as the green briquettes are too fragile and weak to withstand being dropped and transported from the press to the furnace.

[0113] Example 3 shows that the formula may not be validated due to the poor results of the recycling and Shatter tests (green and dry). Drying, firing and index tests (tumble and abrasion) were therefore not carried out.

[0114] Example 4: We use the same iron ore concentrate sample as in Example 1. We adjust the moisture content and add another binding formula as shown in Table 7. The aim is to determine whether CMC may be used for cold-bonded briquettes.

[0115] CMC, carboxymethylcellulose, is a binder used for iron ore pelletizing, like PAM polymers. It is a cellulose derivative with long carbon chains. It is known to have binding properties comparable to those of PAM polymers, with good pellet plasticity and strength (both green, dry, and fired). We tested CMC at the same dosage as PAM.

[0116] [Table 7]

[0117] Table 7: Example 4

[0118] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the roller press and perform the following measurements (Table 8):

[0119] [Table 8]

[0120] Table 8: Example 4

[0121] Example 4 shows that the use of CMC gives good results for the recycling of green briquettes, and that Shatter tests reveal no breakage or generation of fine particles, which was known to be a given property of CMC.

[0122] Example 4 shows that this formula gives poor results on dry briquettes, with compressive strength too low to meet requirements (200 kg). This binder formula has not been validated, so hot tests (900°C) were not carried out.

[0123] Example 4 shows that the formula gives poor results for Tumble and Abrasion Indices, as the bonds with the CMC are not strong enough to withstand multiple handling and transportation.

[0124] Example 5:

[0125] We use the same equipment and the same iron ore concentrate sample as in Example 1. We adjust the moisture content and add another binder formula as shown in Table 9. The objective is to determine whether other well-known binders can produce cold-bonded briquettes that meet the technical requirements, here we test bentonite.

[0126] Bentonite is a well-known binder for iron ore granulation, which has been used for decades. Bentonite is a montmorillonite clay with a high silicate content, giving the pellets good plasticity properties and good strength (both green, dry and fired).

[0127] [Table 9]

[0128] Table 9: Example 5

[0129] We mix for 5 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 10):

[0130] [Table 10]

[0131] Table 10: Example 5

[0132] Example 5 shows that the use of bentonite gives good results for the recycling of green briquettes and that the Shatter tests reveal no breakage or generation of fines, which was known to be a property provided by bentonite and because we set the moisture level at a higher level to maintain a good binding phenomenon. Example 5 shows that this formula gives poor results on dry briquettes, with compressive strength too low to meet requirements (200 kg). This binder formula has not been validated, so hot tests (900°C) were not carried out.

[0133] Example 5 reveals that the formula gives poor results for Tumble and Abrasion Indices, as the bentonite bonds are not strong enough to withstand multiple handling and transportation.

[0134] Example 6:

[0135] We use the same equipment and the same iron ore concentrate sample as in Example 1. We adjust the moisture content and add another binding formula as shown in Table 11. The objective is to determine whether bentonite at a higher dosage may be used for cold-bonded briquettes.

[0136] [Table 11]

[0137] Table 11 : Example 6

[0138] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 12):

[0139] [Table 12]

[0140] Table 12: Example 6

[0141] Example 6 shows that this formula with a higher bentonite dosage gives poor results on dry briquettes, with compressive strength too low to meet requirements (200 kg). The hot test was therefore not carried out, as the formula was disqualified.

[0142] Example 6 shows that the formula gives poor results for Tumble and Abrasion Indices, as the bentonite bonds are not strong enough, even at higher dosage, to withstand multiple handling and transportation.

[0143] Example 7:

[0144] The tests in this example are carried out on a tangential wheel press. We use an iron ore concentrate from Canada. It is a crushed hematite with an Fe content of 66.8%, a particle size of less than 300 pm with a D80 = 100 pm, and a Blaine index between 1950 and 2100.

[0145] We use the same binding formula as in Example 1. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrates. We adjust the moisture content and add our binding formula as shown in Table 13.

[0146] [Table 13]

[0147] Table 13: Example 7

[0148] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press at a pressure of 200 bar, i.e., 30 KN / m linear, and carry out the following measurements (Table 14):

[0149] [Table 14]

[0150] Table 14: Example 7

[0151] Example 7 shows that the use of PAM and sodium silicate gives good results for green briquettes (press recycling and Shatter tests on green briquettes), which was known as a property provided by the PAM.

[0152] The example shows that this formula also gives very good results on dry briquettes: Shatter tests show no breakage or generation of fine particles, and compressive strength is very high, exceeding the range of requirements (200 kg).

[0153] Finally, Example 7 shows that the formula is also good for hot testing, where the PAM has disappeared. Compressive strength shows that the briquettes retain their integrity and strength, within the required range.

[0154] Example 7 shows that the formula gives good results for the Tumble and Abrasion Indices, indicating that the briquettes can be handled and transported without damage to the final process (furnace run).

[0155] Example 8:

[0156] We use the same equipment and the same iron ore concentrate sample as in Example 6. We adjust the moisture content and add another bonding formula as shown in Table 15. The objective is to determine whether PAM alone may work for cold-bonded briquettes.

[0157] We use the same binding formula as in Example 2. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrates.

[0158] [Table 15]

[0159] Table 15: Example 8

[0160] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 16):

[0161] [Table 16]

[0162] Table 16: Example 8

[0163] Example 8 shows that using PAM alone gives good results for green briquettes (press recycling and green briquette Shatter tests), which was known to be a property provided by PAM.

[0164] The example shows that this formula also gives very good results for dry briquettes: Shatter tests show no breakage or generation of fines, but compressive strength after firing at 900°C is too low to meet requirements (200 kg).

[0165] Example 8 shows that the formula may not be validated due to the poor results obtained during hot testing, where the PAM disappeared.

[0166] Example 8 shows that the formula gives poor results for Tumble and Abrasion Indices, as the polymer bonds alone are not strong enough to withstand multiple handling and transportation.

[0167] Example 9:

[0168] We use the same equipment and the same iron ore concentrate sample as in Example 6. We adjust the moisture content and add another bonding formula as shown in Table 17. The objective is to determine whether alone may work for cold-bonded briquettes.

[0169] We use the same binding formula as in Example 3. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrates.

[0170] [Table 17]

[0171] Table 17: Example 9

[0172] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 18):

[0173] [Table 18]

[0174] Table 18: Example 9

[0175] Example 9 shows that the use of sodium silicate alone does not give good results, as the green briquettes are too fragile and weak to withstand being dropped and transported from the press to the furnace.

[0176] Example 9 shows that the formula may not be validated due to the poor results of the recycling and Shatter tests (green and dry). Drying, firing and index (tumble and abrasion) tests were therefore not carried out.

[0177] Example 10:

[0178] We use the same iron ore concentrate sample as in Example 9. We adjust the moisture content and add another bonding formula as shown in Table 19. The objective is to determine if CMC can be used for cold bonded briquettes with iron ore concentrate type. We test CMC at the same dosage as PAM.

[0179] We use the same binding formula as in Example 6. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrates.

[0180] [Table 19]

[0181] Table 19: Example 10

[0182] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the roller press and perform the following measurements

[0183] (Table 20):

[0184] [Table 20]

[0185] Table 20: Example 10

[0186] Example 10 shows that the use of CMC gives good results for the recycling of green briquettes, and that Shatter tests reveal no breakage or generation of fine particles, which was considered a property provided by CMC.

[0187] Example 10 shows that this formula gives poor results for dry briquettes, as the compressive strength is too low to meet requirements (200 kg).

[0188] Example 10 shows that the formula may not be validated due to poor DCS results at 105°C and poor hot test results. The same bonding phenomenon is not observed as with PAM (high DCS). Compressive strength is very low, making this formula unacceptable.

[0189] Example 10 shows that the formula gives poor results for Tumble and Abrasion Indices, as the bonds with the CMC are not strong enough to withstand multiple handling and transportation.

[0190] Example 11:

[0191] We use the same equipment and iron ore concentrate sample as in Example 6. We adjust the moisture content and add another binder formula as shown in Table 21. The objective is to determine whether other well-known binders can produce cold-bonded briquettes that meet the technical requirements, here we test bentonite.

[0192] We use the same binding formula as in Example 4. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrates.

[0193] [Table 21]

[0194] Table 21 : Example 11

[0195] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 22):

[0196] [Table 22] Table 22: Example 11

[0197] Example 11 shows that the use of bentonite gives good results for the recycling of green briquettes and that the Shatter tests reveal no breakage or generation of fines, which was known to be a property provided by bentonite and because we set the moisture level at a higher level to maintain a good binding phenomenon.

[0198] Example 11 shows that this formula gives poor results on dry briquettes, with compressive strength too low to meet requirements (200 kg). This binder formula has not been validated, so hot tests (900°C) were not carried out.

[0199] Example 11 reveals that the formula gives poor results for Tumble and Abrasion Indices, as the bentonite bonds are not strong enough to withstand multiple handling and transportation.

[0200] Example 12:

[0201] We use the same equipment and the same iron ore concentrate sample as in Example 6. We adjust the moisture content and add another binding formula as shown in Table 23. The objective is to determine whether bentonite at a higher dosage may be used for cold-bonded briquettes.

[0202] We use the same binding formula as in Example 5. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrate.

[0203] [Table 23]

[0204] Table 23: Example 12

[0205] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 24):

[0206] [Table 24]

[0207] Table 24: Example 12

[0208] Example 12 shows that the use of bentonite gives good results for the recycling of green briquettes and that the Shatter tests reveal no breakage or generation of fines, which was known to be a property provided by bentonite and because we set the moisture at a higher level to maintain a good binding phenomenon. The higher dosage makes the briquettes more plastic.

[0209] Example 12 shows that this formula with a higher bentonite dosage gives poor results on dry briquettes, with compressive strength too low to meet requirements (200 kg). The hot test was therefore not carried out, as the formula was disqualified.

[0210] Example 12 shows that the formula gives poor results for Tumble and Abrasion Indices, as the bentonite bonds are not strong enough, even at higher dosage, to withstand multiple handling and transportation.

[0211] Example 13:

[0212] The tests in this example are carried out on an extruder. We use the same iron ore concentrate sample as in Example 1. We adjust the moisture content and add our binding formula as shown in Table 25. The objective is to determine whether bentonite at a higher dosage may be used for cold- bonded briquettes.

[0213] We use the same binding formula as in Example 5. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrate.

[0214] [Table 25]

[0215] Table 25: Example 13 We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the machine and perform the following measurements (Table 26):

[0216] [Table 26]

[0217] Table 26: Example 13

[0218] The use of an extruder requires a much higher moisture content in the mix than with a tangential wheel press. The agglomerates are wetter, so the properties of green agglomerates are improved.

[0219] Example 13 shows that the use of PAM and sodium silicate works well for this equipment, thanks to the plasticity provided by PAM. This binding formula gives good results for green agglomerates (press recycling and Shatter tests on green agglomerates), which was known to be a property provided by PAM.

[0220] The example shows that this formula also gives very good results on dry agglomerates: Shatter tests show no breakage or generation of fine particles, and compressive strength is very high, exceeding requirements (200 kg).

[0221] Example 13 shows that the formula is also good for hot testing, where the PAM has disappeared, and the compressive strength shows that the briquettes retain their integrity and strength at a value acceptable to the process.

[0222] Example 13 shows that the formula gives good results for the Tumble and Abrasion Indices due to the small size of the agglomerates (2.5 to 5 cm3). The agglomerates can be handled and transported without damage for the final process (furnace run).

[0223] Example 14:

[0224] We use the same equipment and the same sample of iron ore concentrate as in Example 13. We adjust the moisture content and add our binding formula as shown in Table 27. The objective is to determine whether bentonite may be used for cold agglomeration.

[0225] [Table 27]

[0226] Table 27: Example 14

[0227] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the roller press and perform the following measurements (Table 28) :

[0228] [Table 28]

[0229] Table 28: Example 14

[0230] Example 14 shows that using bentonite gives results in line with the requirements for burst tests, revealing no breakage or generation of fines, which was known to be a property provided by bentonite and because we set the moisture level at a higher level to maintain a good bonding phenomenon.

[0231] Example 14 shows that passage through the extruder is not optimal, with difficulty in forming structured agglomerates, resulting in a significant proportion of small pieces.

[0232] Furthermore, example 14 shows that this formula performs poorly on dry briquettes, the compressive strength being too low to meet requirements (200 kg). This binder formula has not been validated, so hot tests (900°C) have not been carried out.

[0233] Example 14 reveals that the formula gives poor results for Tumble and Abrasion Indices, as the bentonite bonds are not strong enough, despite the smaller size of the agglomerates, to withstand multiple handling and transportation.

[0234] Example 15: The tests in this example are performed on an extruder. We use iron ore concentrate from Canada. It is a ground hematite, with an Fe content of 66.8%, a particle size of less than 300 pm with a D80 = 100 pm, and a Blaine index between 1950 and 2100.

[0235] We use the same binding formula as in Example 1. The objective is to verify the effectiveness of the formulas on other types of iron ore concentrate.

[0236] We adjust the moisture content and add our binding formula as shown in Table 29.

[0237] [Table 29]

[0238] Table 29: Example 15

[0239] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the machine and carry out the following measurements (Table 30):

[0240] [Table 30]

[0241] Table 30: Example 15

[0242] The use of an extruder requires a much higher moisture content in the mix than with a tangential wheel press. The agglomerates are wetter, so the properties of green agglomerates are improved.

[0243] Example 15 shows that the use of PAM and sodium silicate works well for this equipment, thanks to the plasticity provided by PAM. This binding formula gives good results for green agglomerates (press recycling and Shatter tests on green agglomerates), which was known to be a property provided by PAM.

[0244] The example shows that this formula also gives very good results on dry agglomerates: Shatter tests show no breakage or generation of fine particles, and compressive strength is very high, exceeding requirements (200 kg).

[0245] Example 15 shows that the formula is also good for hot testing, where the PAM has disappeared, and the compressive strength shows that the briquettes retain their integrity and strength at a value acceptable to the process.

[0246] Example 15 shows that the formula gives good results for Tumble and Abrasion Indices due to the small size of the agglomerates (2.5 to 5 cm3). The agglomerates can be handled and transported without damage to the final process (furnace run).

[0247] Example 16:

[0248] We use the same equipment and the same iron ore concentrate sample as in Example 13. We adjust the moisture content and add our binding formula as shown in Table 31. The objective is to determine whether bentonite may be used for cold agglomeration.

[0249] [Table 31]

[0250] Table 31 : Example 16

[0251] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the machine and perform the following measurements (Table 32):

[0252] [Table 32]

[0253] Table 32: Example 16

[0254] Example 16 shows that using bentonite gives results in line with the requirements for burst tests, revealing no breakage or generation of fines, which was known to be a property provided by bentonite and because we set the moisture level at a higher level to maintain a good bonding phenomenon.

[0255] Example 16 shows that passage through the extruder is not optimal, with difficulty in forming structured agglomerates, resulting in a significant proportion of small pieces.

[0256] Furthermore, example 16 shows that this formula gives poor results on dry agglomerates, with compressive strength too low to meet requirements (200 kg). This binder formula has not been validated, so hot tests (900°C) have not been carried out.

[0257] Example 16 reveals that the formula gives poor results for Tumble and Abrasion Indices, as the bentonite bonds are not strong enough, despite the smaller size of the agglomerates, to withstand multiple handling and transportation.

[0258] Example 17:

[0259] The agglomeration of certain very fine or more hydrophilic ores can result in low water resistance of the agglomerates, and therefore possible disintegration of the briquettes during storage / transport. To counter this, we propose adding a water-repellent agent to make dry briquettes water-resistant for several weeks.

[0260] This water-repellent agent is a modified PAM, acrylamide / 2-ethylhexylacrylate copolymer (40 / 60 by weight) with a molecular weight of 2 to 4 million daltons.

[0261] We use iron ore concentrate from Canada. It is a floated hematite, with an Fe content of 69%, a particle size of less than 100 pm with a D80 = 74 pm, and a Blaine index between 2100 and 2300.

[0262] We have chosen this mineral because it has demonstrated a consistent hydrophilic tendency. We use the same binding formula as in examples 1, the objective being to verify the effectiveness of the water-repellent agent (Table 33).

[0263] [Table 33]

[0264] Table 33: Example 17

[0265] We mix for 4 minutes in an intensive mixer and leave to stand for 10 to 15 minutes in a covered bucket. We then place the mixture in the press, still at the same pressure, and carry out the following measurements (Table 34):

[0266] [Table 34]

[0267] Table 34: Example 17

[0268] The results are in line with those of examples 1 and 6, with the water-repellent agent showing no adverse properties to the compaction and physical properties of the briquettes. 20 briquettes are then fully immersed in water-filled tubs and left for several days to several weeks. The results are shown in Table 35 below:

[0269] [Table 35]

[0270] Table 35: Example 17

[0271] These results show that our water-repellent agent makes the briquettes water-resistant for very long periods of time, therefore allowing the briquettes to be transported over long distances.

[0272] The obvious advantages of this method are as follows:

[0273] - allows the necessary agglomeration, drying, and firing resistances to be obtained directly.

[0274] - avoid difficult lime handling. - increases iron ore impurities only marginally. Only silica, from the sodium silicate is included.

[0275] - much lower processing volume than bentonite.

[0276] - processing by drying and firing is virtually immediate, avoiding the need for 3 to 20 days' storage. - allows agglomeration to be financially funded at the metallurgical plant instead of buying more expensive agglomerated products.

[0277] - waterproofing of agglomerated products where necessary.

[0278] - for transport or storage.

[0279] This represents a major simplification of the method for agglomerating iron ore, metallurgical scrap and other ores.

Claims

CLAIMS1. A use of polyacrylamide both as a binder and as an activator for the sodium silicate in a method for the cold agglomeration of iron ore.

2. The use according to claim 1, characterized in that the polyacrylamide is in homopolymer or copolymer form.

3. The use according to the preceding claim, characterized in that the polyacrylamide is selected from anionic, cationic, amphoteric or non-ionic acrylamide copolymers depending on the variability of the ore to obtain suitable compositions and particle sizes determined by testing.

4. The use according to one of the preceding claims, characterized in that the polyacrylamide is solid particles.

5. A method for obtaining agglomerates of iron ore fines comprising the following steps: a) mixing polyacrylamide, sodium silicate and ore in a mixer under defined conditions; bl) adjust- the moisture content for compaction within a range of 2 to 10% preferably 3 to 8% of the mixture; then agglomerate using a briquette press (with tangential wheels)and finally dry the agglomerates obtained at a temperature of 100 to 250°C for 30 minutes to 2 hours or b2) adjust the humidity for extrusion to 5 to 20%, preferably 9 to 18%, then extrude using a vacuum extruder and finally dry the extrudates at a temperature of 100 to 250°C for 30 minutes to 2 hours, characterized in that polyacrylamide is used as an activator of sodium silicate.

6. The method according to claim 5, characterized in that no activator other than polyacrylamide is added to treat the sodium silicate.

7. The method according to claim 5, characterized in that the silicate is in solid form in the form of powders, beads or microbeads or in liquid form by adjusting the amount of water required for mixing.

8. The method according to claim 5, characterized in that the following dosage ratios are used:0.01% to 2% by weight of polyacrylamide polymer, based on the total weight of the agglomerateformed, and 0.1 to 5% by weight of active sodium silicate, based on the total weight of the agglomerate formed.

9. The method according to claim 5, characterized in that a hydrophobic polyacrylamide is added to reduce moisture sensitivity.

10. A briquette obtained by the method according to claim 5, characterized in that they have a press recycle of less than 20%, a green briquette burst test of more than 80%, a dry briquette burst strength of more than 99% and a DCS of more than 200 kg.

11. The briquettes obtained by the method according to claim 5, characterized in that they are of very high purity in contrast to bentonite as binder or lime as sodium silicate activator.

12. The briquettes obtained by the method according to claim 5, characterized in that, unlike other activators, they are dried and fired without aging.