US20190337847A1 - Method for Manufacturing Briquettes Containing a Calcium-Magnesium Compound and an Iron-Based Compound, and Briquettes Obtained Thereby - Google Patents

Method for Manufacturing Briquettes Containing a Calcium-Magnesium Compound and an Iron-Based Compound, and Briquettes Obtained Thereby Download PDF

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US20190337847A1
US20190337847A1 US16/309,204 US201716309204A US2019337847A1 US 20190337847 A1 US20190337847 A1 US 20190337847A1 US 201716309204 A US201716309204 A US 201716309204A US 2019337847 A1 US2019337847 A1 US 2019337847A1
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calcium
weight
briquettes
iron
composition
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Guillaume Criniere
Michael Nispel
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Lhoist Recherche et Developpement SA
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    • 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
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B18/02—Agglomerated materials, e.g. artificial aggregates
    • C04B18/021—Agglomerated materials, e.g. artificial aggregates agglomerated by a mineral binder, e.g. cement
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B14/02—Granular materials, e.g. microballoons
    • C04B14/30—Oxides other than silica
    • C04B14/308—Iron oxide
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators, shrinkage compensating agents
    • C04B22/06—Oxides, Hydroxides
    • C04B22/062—Oxides, Hydroxides of the alkali or alkaline-earth metals
    • C04B22/064—Oxides, Hydroxides of the alkali or alkaline-earth metals of the alkaline-earth metals
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators, shrinkage compensating agents
    • C04B22/06—Oxides, Hydroxides
    • C04B22/066—Magnesia; Magnesium hydroxide
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/10—Lime cements or magnesium oxide cements
    • C04B28/105—Magnesium oxide or magnesium carbonate cements
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2683—Other ferrites containing alkaline earth metals or lead
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • C21C7/0645—Agents used for dephosphorising or desulfurising
    • 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
    • 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
    • C22B1/245—Binding; Briquetting ; Granulating with binders organic with carbonaceous material for the production of coked agglomerates
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00732—Uses not provided for elsewhere in C04B2111/00 for soil stabilisation
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00758—Uses not provided for elsewhere in C04B2111/00 for agri-, sylvi- or piscicultural or cattle-breeding applications
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/0087—Uses not provided for elsewhere in C04B2111/00 for metallurgical applications
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/0087—Uses not provided for elsewhere in C04B2111/00 for metallurgical applications
    • C04B2111/00887—Ferrous metallurgy
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
    • C04B2235/3206—Magnesium oxides or oxide-forming salts thereof
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
    • C04B2235/3208—Calcium oxide or oxide-forming salts thereof, e.g. lime

Definitions

  • the present invention relates to a method for manufacturing a composition in the form of briquettes containing a “quick” calcium-magnesium compound and an iron-based compound, to green briquettes containing the “quick” calcium-magnesium compound and iron oxide, to thermally treated briquettes containing the “quick” calcium-magnesium compound and calcium ferrites, and to the use thereof.
  • the term “quick” calcium-magnesium compound means, in the sense of the present invention, a solid mineral material whose chemical composition is mainly calcium oxide and/or magnesium oxide.
  • the “quick” calcium-magnesium compounds in the sense of the present invention therefore comprise quicklime (calcium lime), magnesium quicklime, dolomitic quicklime or “quick” calcined dolomite.
  • the “quick” calcium-magnesium compounds contain impurities, namely, compounds such as silica, SiO 2 or alumina, Al 2 O 3 , etc., at the level of a few percent. It is to be understood that these impurities are expressed in the aforementioned forms but may in reality appear as different phases.
  • Quicklime means a solid mineral material, whose chemical composition is mainly calcium oxide, CaO.
  • Quicklime is commonly obtained by calcination of limestone, mainly consisting of CaCO 3 .
  • Quicklime contains impurities, namely compounds such as magnesium oxide MgO, silica SiO 2 , or alumina Al 2 O 3 , etc., at a level of a few percent. It is to be understood that these impurities are expressed in the aforementioned forms but may in reality appear as different phases. It also generally contains a few percent of residual CaCO 3 , called underburned, and a few percent of residual Ca(OH) 2 , owing to partial hydration of calcium oxide CaO during the phases of cooling, handling and/or storage.
  • briquette means a compact of oblong shape, weighing about 5 to 100 g per briquette, inscribed in a flattened or elongated ellipsoid of revolution (“oblate ellipsoid of revolution” or “prolate ellipsoid of revolution”).
  • briquettes have the shape of a bar of soap or are described as “egg briquettes”.
  • tablets which are typically in the form of pellets, such as those produced with the “Titan” presses from the company “Eurotab”.
  • tablets for industrial use are of regular shape, more particularly in the form of a cylinder with a small height.
  • Briquettes are known from the prior art, see for example document WO2015007661. According to this document, compacts (i.e. briquettes or tablets) are described comprising particles of calcium-magnesium compound comprising at least 50% of “quick” calcium-magnesium compound.
  • the compacts (in the form of briquettes or tablets) disclosed may also contain additives, in particular iron oxide.
  • drop strength (drop mechanical strength) is measured in a Shatter test.
  • the compacts described generally have a Shatter test index below 10%.
  • Stress test index means, in the sense of the present invention, the percentage by weight of fines under 10 mm generated after 4 drops from 2 m starting from 10 kg of product. These fines are quantified by sieving through a screen with square mesh of 10 mm after 4 drops from 2 m.
  • Calcium-magnesium compounds are used in many industries, for example iron and steel metallurgy, treatment of gases, treatment of water and sludge, agriculture, the building industry, public works etc. They may be used either in the form of pebbles or lumps, or in the form of fines (generally smaller than 7 mm). However, the pebble form is preferred in certain industries.
  • Lubricants and binders are additives that are often used in methods of agglomeration in the form of briquettes or similar.
  • Lubricants may be of two types, internal or external. Internal lubricants are mixed intimately with the materials to be briquetted. They promote on the one hand the flowability of the mixture during feed of the briquetting machine and on the other hand rearrangement of the particles within the mixture during compression. External lubricants are applied on the surfaces of the rollers of the briquetting machine and mainly aid mould release. In both cases they reduce friction on the surface and therefore wear.
  • the lubricants may be liquids such as mineral oils, silicones, etc., or solids such as talc, graphite, paraffins, stearates, etc. In the case of compositions based on “quick” calcium-magnesium compounds, stearates are preferred, and more particularly calcium stearate or magnesium stearate.
  • Binders are substances having the property of agglomerating the particles together, either by forces of adhesion, or by a chemical reaction. They may be of mineral origin (cements, clays, silicates, etc.), of plant or animal origin (celluloses, starches, gums, alginates, pectin, glues, etc.), of synthetic origin (polymers, waxes, etc.). In many cases they are used together with water, which activates their agglomeration properties.
  • a composition of “quick” calcium-magnesium compounds such as quicklime and/or “quick” dolomite as well as scrap iron, are added to a converter to control the kinetics and chemistry of the slag forming reaction, thus facilitating removal of impurities and protecting the refractory lining of the furnace against excessive wear.
  • the “quick” calcium-magnesium compounds introduced float on the bath of hot metal, thus forming an interface.
  • molten metal is introduced into the vessel, to which scrap iron may also be added.
  • the molten metal resulting from the fusion of metal compounds has an initial carbon content typically from 40 to 45 kg per tonne of molten metal and an initial phosphorus content from 0.7 to 1.2 kg per tonne of molten metal.
  • the “quick” calcium-magnesium compounds are charged and float above the bath of molten metal. Oxygen is blown in for a predetermined period of time, in order to burn off the carbon and oxidize, directly and/or indirectly, the phosphorus-containing compounds, and silicon. During blowing, the calcium-magnesium compounds are immersed in the bath of molten metal and dissolve/melt slightly at the interface with the molten metal, the calcium-magnesium compounds always floating.
  • Slag is the layer of oxides floating on top of the bath and results from the formation of SiO 2 due to oxidation of the silicon, from formation of other oxides (MnO and FeO) during blowing, from addition of “quick” calcium-magnesium compounds for neutralizing the action of SiO 2 on the refractory lining and for liquefying and activating the slag, and from MgO from wear of the refractory lining.
  • a metal/slag reaction takes place, which is intended to remove phosphorus from the molten metal.
  • the phosphorus content is about 0.1 kg or less per tonne of molten metal, i.e. about 100 ppm or less.
  • the chemical reaction is as follows:
  • the FeO (iron oxide) and the phosphorus are derived from the hot metal, whereas the CaO is added in the converter. This reaction is exothermic and the aim is to shift the equilibrium to the right-hand side. This may be achieved by lowering the temperature, fluidizing the slag as much as possible, homogenizing the metal bath (carried out by blowing argon and/or nitrogen from the bottom in most cases), maintaining the CaO/SiO 2 basicity index between 3 and 6 (the weight ratio of calcium oxide to silica, which is acidic), maintaining the level of magnesite at less than 9% in the slag, and creating sufficient quantities of slag.
  • Magnesite is typically present in the slag and is derived from wear of the refractory lining, which may be reduced by controlled addition of “quick” dolomite. However, to favour the kinetics of the reaction in the slag, the level of magnesite should be kept below 9%.
  • refining of the hot metal is not so easy, and it would need to be optimized to obtain a given amount of liquid metal, by action on the mass equilibrium of the metal, a given chemical analysis, by action on the mass equilibrium of oxygen (oxidation reaction), and a given temperature at the end of blowing (action on the thermal equilibrium).
  • the complexity of improving dephosphorization during refining of hot metal is due, among other things, to simultaneous observation of the three equilibria.
  • This patent focuses on improvement of dephosphorization during a process in a converter by cooling the slag in the second half of the process
  • the present invention aims to solve these drawbacks, at least partly, by supplying a method allowing a considerable reduction in the loss of lime and improvement of the efficacy of the lime in slag formation.
  • a method for making a calcium-magnesium composition in the form of briquettes comprising the following steps:
  • a pulverulent mixture comprising at least one “quick” calcium-magnesium compound, said mixture comprising at least 40 wt % of CaO+MgO equivalent relative to the weight of said composition and having a Ca/Mg molar ratio greater than or equal to 1, preferably greater than or equal to 2, more particularly greater than or equal to 3 and an iron-based compound having a very fine granulometric distribution characterized by a median size d 50 below 100 ⁇ m, preferably below 50 ⁇ m as well as a size d 90 below 200 ⁇ m, preferably below 150 ⁇ m, preferably below 130 ⁇ m, more preferably below 100 ⁇ m;
  • said at least one “quick” calcium-magnesium compound comprising at least 40 wt % of CaO+MgO equivalent comprises a fraction of particles of calcium-magnesium compound having a particle size ⁇ 90 ⁇ m having at least 20 weight % CaO equivalent with respect to the weight of said pulverulent mixture, and wherein said iron-based compound is present at an amount of at least 20 wt %, preferably at least 25 wt %, more preferably at least 30 wt %, in particular at least 35 wt % relative to the total weight of the pulverulent mixture.
  • said pulverulent mixture comprises at most 97 wt %, preferably at most 90 wt %, preferably at most 88%, in certain embodiments at most 60 wt % of CaO+MgO equivalent relative to the weight of said composition.
  • step i. is carried out in the presence of a binder or a lubricant, preferably in the form of powder or concentrated aqueous suspension, more particularly selected from the group consisting of binders of mineral origin such as cements, clays, silicates, binders of vegetable or animal origin, such as celluloses, starches, gums, alginates, pectin, glues, binders of synthetic origin, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate and mixtures thereof, preferably calcium stearate and/or magnesium stearate, at a content between 0.1 and 1 wt %, preferably between 0.15 and 0.6 wt %, more preferably between 0.2 and 0.5 wt % relative to the total weight of said briquettes.
  • a binder or a lubricant
  • the percentages by weight of CaO+MgO equivalent, but also Fe 2 O 3 are determined by X-ray fluorescence spectrometry (XRF) as described in standard EN 15309.
  • XRF X-ray fluorescence spectrometry
  • Semiquantitative chemical analysis by XRF for determining the relative concentration by weight of the elements whose atomic mass is between 16 (oxygen) and 228 (uranium) is carried out starting from samples ground to 80 ⁇ m and formed into pellets. The samples are introduced into PANalytical/MagiX Pro PW2540 apparatus, operating in wavelength dispersion mode. The measurement is performed with a power of 50 kV and 80 mA, with a Duplex detector.
  • the present invention it was in fact found that in contrast to the known compositions, in the briquettes according to the present invention, on the one hand owing to the fact that the mixture formed is homogeneous, but on the other hand also owing to the amount of the iron-based compound present in the form of iron oxide with a very fine particle size distribution, together with the presence of a fraction of particles of calcium-magnesium compound having a particle sizes ⁇ 90 ⁇ m in the “quick’ calcium-magnesium compound, which latter comprises further at least 20 weight % CaO equivalent with respect to the weight of said pulverulent mixture, a large amount of iron oxide was converted to calcium ferrite, after thermal treatment.
  • the amount of the iron-based compound, more particularly of iron-based compound with a very fine granulometric distribution is of at least 20 wt % relative to the total weight of the pulverulent mixture, but also the presence of CaO in the calcium-magnesium compound in the form of very fine particles (d 30 ⁇ 90 ⁇ m) is of at least 20 wt %, not only the formation of calcium ferrite is improved and has a yield of conversion of iron oxide to calcium ferrite of about 90%, but also the balance between the formation of monocalcium ferrites and dicalcium ferrites is in favour of forming dicalcium ferrites, particularly when the content of very fine CaO and Fe 2 O 3 equivalent is balanced. It has been identified that it can be interesting at an industrial point of view to be able to control the proportion of dicalcium ferrites with respect to the proportion of monocalcium ferrite depending on the needs and vice versa.
  • the granulometric distribution of the iron-based compound that is used in the method is determined by laser granulometry. Measurement is therefore based on the diffraction of light and follows the theories of Fraunhofer and Mie.
  • the particles are spherical, non-porous and opaque. Measurement is carried out according to standard ISO 13320 in methanol, without sonication.
  • iron-based compound “iron-based compound of very fine particle size distribution” means for example a compound based on iron, preferably based on iron oxide, characterized by a median size d 50 below 100 ⁇ m, preferably 50 ⁇ m as well as a size d 90 below 200 ⁇ m, preferably below 150 ⁇ m, preferably below 130 ⁇ m, more preferably below 100 ⁇ m.
  • this iron oxide as active iron, which implies in particular that it relative to the total amount of iron oxide present in the iron-based compound, at least 40% of this iron oxide is present in the peripheral layer of the grains of the iron-based compound, said peripheral layer being defined by a thickness of 3 ⁇ m. This thus defines a volume fraction of iron oxide at the surface of the iron oxide particles that is able to react, to be converted to ferrite during thermal treatment or else directly in situ in the converter.
  • the iron-based compound is in the form of a mixture of iron-based compounds, wherein said mixture of iron-based compounds may comprise one or more iron oxides, which may in their turn comprise 50 wt %, preferably 60 wt %, preferably 70 wt % of active iron oxide relative to the total weight of said iron-based compound.
  • the granulometric distribution of the iron-based compound in the composition in the form of briquettes is determined by scanning electron microscopy and X-ray mapping, coupled to image analysis.
  • Measurement is based on the property of the particles of the iron-based compound of emitting X-rays of specific energy (6.398 keV) when they are submitted to high-energy radiation (for example, a high-intensity electron beam). Detection of this radiation, combined with precise knowledge of the position of the electron beam for each point observed, makes it possible to map specifically the particles of the iron-based compound.
  • high-energy radiation for example, a high-intensity electron beam
  • Each particle identified is then characterized by its particle diameter at equivalent surface area (X a,i ), as defined in standard ISO 13322-1.
  • the particles are then classified by granulometric fraction of particle size.
  • the fraction of active iron in the sense of the invention is in the peripheral layer of each particle of the iron-based compound, in the outer layer with a thickness of 3 ⁇ m.
  • V ext is the volume of the particle of the iron-based compound and V int is the volume at the core of the particle at more than 3 ⁇ m from the surface, i.e. the volume corresponding to a spherical particle having a radius reduced by 3 ⁇ m.
  • D ext is the diameter of the particle expressed in ⁇ m, or the size of the particle in the sense of laser granulometry.
  • the fraction of total active iron in the sense of the invention is therefore the sum of all the granulometric fractions of the fraction of active iron multiplied by the percentage by volume of each granulometric fraction obtained by laser granulometry
  • % Fe active ⁇ % volume/particle ⁇ % Fe active/particle
  • the percentage of active iron must be at least 40%.
  • said active iron oxide did not have an adverse effect on the mechanical strength of the briquettes formed, even at a high content of 60 wt % relative to the total weight of the green briquettes.
  • the method according to the present invention therefore makes it possible to obtain briquettes of calcium-magnesium compounds whose mechanical strength is not mandatorily impaired by adding fluxes, even without thermal treatment for contents of iron oxide below 40 wt % of the composition of the green briquette, in which the iron oxide has a very fine granulometric distribution characterized by a median size d 50 below 100 ⁇ m, preferably below 50 ⁇ m as well as a size d 90 below 200 ⁇ m, preferably below 150 ⁇ m, preferably below 130 ⁇ m, more preferably below 100 ⁇ m, and which moreover is very flexible and has good performance, without the aforesaid constraints.
  • said iron-based compound may be formed from one or more iron-based compounds, together totalling a content in the composition of at least 3 wt %, preferably at least 12 wt %, more preferably at least 20 wt %, preferably at least 25 wt %, preferably at least 30 wt %, more preferably at least 35 wt %.
  • said iron-based compound has a granulometric distribution characterized by a d 50 less than or equal to 80 ⁇ m, preferably less than or equal to 60 ⁇ m.
  • the notation d x represents a diameter expressed in ⁇ m, measured by laser granulometry in methanol without sonication, relative to which x vol % of the particles measured are less than or equal.
  • the method according to the present invention further comprises thermal treatment of the green briquettes at a temperature comprised between 900° C. and 1200° C., preferably comprised between 1050° C. and 1200° C. included, more preferably between 1100° C. and 1200° C. included.
  • the thermal treatment is carried out preferably for a predetermined time between 3 and 20 minutes, preferably greater than or equal to 5 minutes and less than or equal to 15 minutes, with formation and production of thermally treated briquettes, in which said iron oxide has been converted to calcium ferrite, in particular under the form of monocalcium ferrites, i.e. thermally treated briquettes comprising a “quick” calcium-magnesium compound and an iron-based compound comprising at least calcium ferrite, the iron-based compound comprising at least calcium ferrite, which is present at a content of at least 3%, preferably at least 12%, more preferably at least 20%, preferably at least 30%, more preferably at least 35% in Fe 2 O 3 equivalent.
  • thermal treatment When the thermal treatment is carried out in “multilayer” conditions, i.e. when the briquettes are in the form of a static bed of briquettes of a certain thickness, it will be understood that the thermal treatment time can be increased to allow time for the heat to penetrate to the centre of the bed of briquettes.
  • thermal treatment makes it possible to obtain thermally treated briquettes comprising a calcium-magnesium compound and an iron-based compound containing calcium ferrite, with little or no change in its porosity and specific surface area, and whose mechanical strength has been improved. In other words, the phenomenon of sintering of the briquettes is avoided at these temperatures.
  • briquettes obtained by the method according to the present invention not only have a sufficiently high content of calcium ferrite, but the briquettes have particularly interesting mechanical strength represented by the Shatter test index.
  • the composition in the form of green briquettes comprises said “quick” calcium-magnesium compound comprising at least a fraction of particles of calcium-magnesium compound having a particle size ⁇ 90 ⁇ m, which latter comprises at least 20 wt % CaO equivalent relative to the weight of the pulverulent mixture as well as the iron-based compound present at an amount of at least 20 wt %, preferably at least 25 wt %, more preferably at least 30 wt %, in particular at least 35 wt % relative to the total weight of the pulverulent mixture, a calcium ferrite matrix is formed.
  • Said matrix is to be understood as being a continuous phase based on calcium ferrite, in which particles of “quick” calcium-magnesium compound, in particular quicklime, are dispersed.
  • particles of “quick” calcium-magnesium compound are of small size, so that they melt visibly in the matrix based on calcium ferrite, and the case when particles of “quick” calcium-magnesium compound are of larger size, appearing as inclusions of “quick” calcium-magnesium compound in said matrix.
  • the aforesaid distinction is made concrete on the basis of a section of a briquette according to the invention, applying scanning electron microscopy coupled to energy dispersive analysis.
  • This provides visualization in two dimensions (the surface of the section) of an object initially in three dimensions (briquette), but also of the particles that make up the briquette.
  • the particles of calcium-magnesium compound also appear in two dimensions on the section plane.
  • the cut surface of the particle is likened to an equivalent disk and its “two-dimensional” size to the equivalent diameter of this disk.
  • the two-dimensional sizes are calculated with a program that finds, for each particle of “quick” calcium-magnesium compound dispersed in the continuous matrix of calcium ferrite, the sum of the smallest and the largest dimension of its cut surface divided by two. This sum divided by two represents the diameter of the equivalent disk.
  • the particles of “quick” calcium-magnesium compound melt or merge in said matrix (continuous phase) of calcium ferrite when said particles of “quick” calcium-magnesium compound have a two-dimensional size under 63 ⁇ m, observable by scanning electron microscopy coupled to energy dispersive analysis, in a section of the briquette.
  • the thermally treated briquettes have a Shatter test index below 8%, sometimes below 6%, below 4%, below 3%, or even around 2%.
  • said “quick” calcium-magnesium compound is a soft- or medium-burned calcium-magnesium compound, preferably soft-burned.
  • the calcium-magnesium compound supplied in the form of a homogeneous mixture is itself also sufficiently reactive, so as to form cohesive briquettes with the iron-based compound after thermal treatment.
  • the “quick” calcium-magnesium compound is advantageous for use in converters for forming slag.
  • the “quick” calcium-magnesium compounds are produced industrially by baking natural limestones in various types of kilns, such as shaft kilns (dual-flow regenerative kilns, annular kilns, standard shaft kilns, etc.) or else rotary kilns.
  • the quality of the calcium-magnesium compound, such as quicklime for example, notably its reactivity with water, and the consistency of this quality, are partly linked to the type of kiln used, the operating conditions of the kiln, the nature of the limestone from which the “quick” calcium-magnesium compound is derived per se, or else the nature and the amount of fuel used.
  • said “quick” calcium-magnesium compound is quicklime.
  • This overburned quicklime is moreover more expensive to produce than a milder quicklime as it requires the use of higher temperatures, but also because, unless dedicated kilns are used, production of this overburned quicklime leads to pauses in production campaigns to alternate with the production of mild quicklimes, which are more commonly used, which is not without problems in stabilization of the calcination conditions and therefore problems in stabilization of quality.
  • Quicklimes obtained by mild baking generally have specific surface areas measured by nitrogen adsorption manometry after vacuum degassing at 190° C. for at least 2 hours, calculated by the multiple-point BET method as described in standard ISO 9277:2010E, above 1 m 2 /g whereas the overburned quicklimes generally have surface areas well below 1 m 2 /g.
  • the reactivity of quicklime is measured using the water reactivity test of European standard EN 459-2:2010 E.
  • 150 g of quicklime is added with stirring to a cylindrical Dewar of 1.7 dm 3 capacity containing 600 cm 3 of deionized water at 20° C.
  • the quicklime is supplied in the form of fines with a size between 0 and 1 mm. Stirring at 250 revolutions per minute is carried out with a specific paddle.
  • the temperature variation is measured as a function of time, making it possible to plot a curve of reactivity.
  • the value of t 60 which is the time taken to reach 60° C., can be found from this curve.
  • the reactivity of burned dolomite is measured using this same reactivity test.
  • 120 g of burned dolomite is added with stirring to a cylindrical Dewar of 1.7 dm 3 capacity containing 400 cm 3 of deionized water at 40° C.
  • the burned dolomite is supplied in the form of fines with a size between 0 and 1 mm.
  • Stirring at 250 revolutions per minute is carried out by means of a specific paddle.
  • the temperature variation is measured as a function of time, making it possible to plot a curve of reactivity.
  • the value of t 70 which is the time taken to reach 70° C., can be found from this curve.
  • composition according to the present invention comprises a soft- or medium-burned calcium-magnesium compound, preferably soft-burned, which is therefore necessarily relatively reactive, thus supplying reactive briquettes.
  • a soft- or medium-burned calcium-magnesium compound preferably soft-burned
  • the method comprises, before said supplying of a pulverulent mixture:
  • said fraction of particles of calcium-magnesium compound present a particle size ⁇ 90 ⁇ m, which latter comprises at most 60 wt % equivalent CaO with respect to the weight of the pulverulent mixture.
  • a binder or lubricant may be added directly at the level of feeding the roller press, said binder or lubricant is added to the mixer, wherein said binder or lubricant is included in said pulverulent mixture, preferably homogeneous.
  • said calcium-magnesium compound contains at least 10 wt % of quicklime in the form of ground particles relative to the weight of said composition.
  • said calcium-magnesium compound according to the present invention contains at least 40 wt %, preferably at least 50 wt %, preferably at least 60 wt %, particularly at least 65 wt %, in particular at least 70 wt %, preferably at least 80 wt %, advantageously at least 90 wt %, or even 100 wt % of quicklime in the form of ground particles relative to the weight of said composition.
  • “Quicklime in the form of ground particles” refers to the lime fines resulting from grinding quicklime and therefore corresponding to a size reduction of the limestone. Grinding may be carried out either starting from the ungraded material leaving the furnace and/or leaving the storage bin or starting from the ungraded material leaving the furnace and/or leaving the storage bin, screened beforehand. Grinding may be carried out using different types of grinding mills (impact crusher, hammer crusher, double roll crusher, cone crusher, etc.), either in open circuit (no recycling loop), or in closed circuit (recycling loop).
  • Quicklime in the form of ground particles differs from screened lime.
  • Screened lime means the lime fines resulting from screening of lime. The granulometry is defined by the size of the screen. For example, a lime screened at 3 mm gives a 0-3 mm screened lime. Thus, screening of the ungraded material leaving the furnace leads to a “primary” screened lime. Screening of the ungraded material leaving the storage bin leads to a “secondary” screened lime.
  • quicklime in the form of ground particles means lime fines generally containing more very fine particles than the lime fines from screening.
  • quicklime fines in the form of ground particles will typically contain at least 30 wt %, most often at least 40 wt %, or even at least 50 wt % of very fine particles under 100 ⁇ m, whereas screened lime fines will often contain at most 25 wt %, or even at most 15 wt % of very fine particles under 100 ⁇ m.
  • the chemical composition of the fines of ground lime is generally more uniform than that of the screened lime fines.
  • an ash-generating fuel such as coal (lignite, hard coal, anthracite, etc.) or else petroleum coke, and characterize the 0-3 mm fines resulting from grinding or screening of this limestone, it will be found that the 0-200 ⁇ m fraction of the 0-3 mm fines resulting from grinding has a similar chemistry to that of the 200 ⁇ m-3 mm fraction, whereas the 0-200 ⁇ m fraction of the 0-3 mm fines resulting from screening contains more impurities than the 200 ⁇ m-3 mm fraction.
  • the fines of ground lime are in general more reactive than the screened lime fines.
  • the fines from grinding typically have values of t 60 below 5 min whereas the fines from primary screening often have values of t 60 above 5 min.
  • said quicklime in the form of ground particles is a soft-burned or medium-burned quicklime, preferably soft-burned, said quicklime in the form of ground particles being characterized by a value of t 60 below 10 min, preferably below 8 min, preferably below 6 min, and more preferably below 4 min.
  • the method further comprises a pre-treatment step of the briquettes under modified atmosphere containing at least 2 vol % CO 2 and at most 30 vol % CO 2 , preferably at most 25 vol % CO 2 , preferably at most 20 vol % CO 2 , more preferably at most 15 vol % CO 2 , even more preferably at most 10 vol % CO 2 with respect to the modified atmosphere.
  • said pulverulent mixture comprises less than 10% of particles of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m and ⁇ 5 mm relative to the total weight of the pulverulent mixture.
  • the briquettes obtained by the method according to the present invention have a relative particle size homogeneity, i.e. that when the briquette is cut, it has a granular composition in the major fraction of its volume.
  • a continuous phase made by calcium ferrite, by calcium-magnesium compound, such as for example of quicklime and optionally of iron-based compound, such as iron oxide, depending on the initial content in the green briquette of calcium-magnesium compound, of calcic component in this latter, of iron-based compound.
  • the particles of “quick” calcium-magnesium compound melt or merge in said matrix (continuous phase) of calcium ferrite when said particles of “quick” calcium-magnesium compound have a two-dimensional size under 63 ⁇ m, observable by scanning electron microscopy coupled to energy dispersive analysis, in a section of the briquette.
  • inclusions of “quick” calcium-magnesium compound are present in the matrix based on calcium ferrite, when particles of “quick” calcium-magnesium compound having a two-dimensional size above 63 ⁇ m, observable by scanning electron microscopy coupled to energy dispersive analysis in a section of the briquette, cover at least 20% of the area of said section.
  • Briquettes of calcium ferrites without significant presence of inclusions of “quick” calcium-magnesium compounds are therefore usable in iron and steel metallurgy, notably in a converter for refining molten metal, to facilitate slag formation. Such briquettes therefore clearly offer an advantage in accelerating the formation of slag and increasing its fluidity.
  • said pulverulent mixture comprises between 10 and 60% of particles of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m and ⁇ 5 mm relative to the total weight of the pulverulent mixture.
  • An advantageous alternative according to the invention is to provide inclusions of “quick” calcium-magnesium compounds, in particular of quicklime, dispersed in the continuous phase (matrix) of calcium ferrite, as described above.
  • the “quick” calcium-magnesium compound is then available in situ at the place where the calcium ferrites have promoted slag formation, acting as flux to allow the “quick” calcium-magnesium compound to act immediately.
  • the section plane contains spread inclusions of calcium-magnesium compound and/or quicklime, which allows to have those latter under the form of quicklime having not reacted to form calcium ferrites under quicklime and which are still available for a use under the form of quicklime, such as for example in the steelmaking, such as for slag formation.
  • the content of those inclusions of calcium-magnesium compound can be more or less important such as explained here above in the section related to thermally treated briquettes according to the present invention.
  • said at least one iron-based compound is present at an amount higher or equal to 20 wt %, preferably of at least 25 wt %, more preferably of at least 30 wt %, in particular of at least 35 wt % relative to the total weight of the pulverulent mixture.
  • the wt % of CaO equivalent in the fraction of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m with respect to the total of the wt % of quicklime in the fraction of calco-magnesium compound having a particle size ⁇ 90 ⁇ m and the % Fe 2 O 3 equivalent of the iron-based compound having a very fine particle size distribution is ⁇ 30%, preferably ⁇ 32%, preferably ⁇ 34%, in a particularly preferred manner ⁇ 36%.
  • the wt % of CaO equivalent in the fraction of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m with respect to the total of the wt % of quicklime in the fraction of calco-magnesium compound having a particle size ⁇ 90 ⁇ m and the % Fe 2 O 3 equivalent of the iron-based compound having a very fine particle size distribution is ⁇ 40, preferably ⁇ 38, more preferably ⁇ 36% %, and higher than 20%, preferably higher than 22%, preferably 24%.
  • P1 represents the percentage, in the pulverulent mixture intended for briquetting, of the particles of the “quick” calcium-magnesium compound whose size is under 90 ⁇ m (fraction of calcium-magnesium compound having a particle size ⁇ 90 ⁇ m),
  • P2 represents the percentage, in the pulverulent mixture intended for briquetting, of the particles of the “quick” calcium-magnesium compound whose size is above 90 ⁇ m
  • C1 represents the percentage of CaO equivalent in the particles of “quick” calcium-magnesium compound whose size is under 90 ⁇ m
  • C2 represents the percentage of CaO equivalent in the particles of “quick” calcium-magnesium compound whose size is above 90 ⁇ m
  • C3 represents the percentage of Fe 2 O 3 equivalent in the iron-based compound
  • the weight ratio “P1/(P1+P3)” is a key parameter that must be controlled for forming either predominantly monocalcium ferrites or predominantly dicalcium ferrites, and more generally the weight ratio “P1.C1/(P1.C1+P3.C3)” is one of the possibilities for predominant formation of monocalcium ferrite or else predominant formation of dicalcium ferrite.
  • said thermal treatment is preferably a thermal treatment with a temperature higher than or equal to 1100° C., preferably higher than or equal to 1150° C., more particularly less than or equal to 1200° C., preferably according to the relationship (predefined period)/(temperature of thermal treatment ⁇ 1000° C.)>5.
  • the percentage P2 is a key parameter that must be controlled for forming briquettes with or without inclusions of “quick” calcium-magnesium compound having a two-dimensional size above 63 ⁇ m.
  • the iron-based compound comprises at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, more preferably at least 80 wt % and in a particular manner more than 95 wt % iron oxide under the form of magnetite Fe 3 O 4 relative to the total weight of the iron based compound expressed in Fe 2 O 3 equivalent.
  • the wt % of said particles of quicklime having a particle size ⁇ 90 ⁇ m and or said iron based compound is ⁇ 40, preferably ⁇ 38, more preferably ⁇ 36% in order to influence the formation of monocalcium ferrites during thermal treatment.
  • said thermal treatment is a thermal treatment at a temperature lower or equal to 1150° C., preferably lower or equal to 1100° C., more particularly higher or equal to 900° C., preferably according to the relationship (predetermined duration)/(thermal treatment temperature ⁇ 1000° C.)>5, which allow to still further promote the formation of monocalcium ferrites.
  • the iron-based compound comprises at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, more preferably at least 80 wt % and in a particular manner more than 95 wt % iron oxide under the form of hematite Fe 2 O 3 relative to the total weight of the iron based compound expressed in Fe 2 O 3 equivalent.
  • the invention also relates to a composition in the form of green briquettes comprising at least one “quick” calcium-magnesium compound and an iron-based compound, characterized in that the composition comprises at least 40 wt % of CaO+MgO equivalent relative to the weight of said composition, said composition having a Ca/Mg molar ratio greater than or equal to 1, preferably greater than or equal to 2, more preferably greater than or equal to 3 and characterized in that said iron-based compound is present at a content of at least 20 wt %, preferably at least 25 wt %, in a preferred manner at least 30 wt %, more preferably at least 35 wt % of Fe 2 O 3 equivalent relative to the weight of said composition, said iron-based compound having a very fine granulometric distribution characterized by a median size d 50 below 100 ⁇ m, preferably below 50 ⁇ m and a size d 90 below 200 ⁇ m, preferably below 150 ⁇ m, preferably below 130 ⁇ m, more preferably
  • said “quick” calcium-magnesium compound comprises one or more “quick” calcium-magnesium compounds.
  • the “quick” calcium-magnesium compound is selected from the group consisting of quicklime (calcium lime), magnesian lime, dolomitic quicklime, calcined dolomite and mixtures thereof, preferably in the form of particles, such as particles resulting from screening, from grinding, dusts from filters and mixtures thereof.
  • Said “quick” calcium-magnesium compound may hence be regarded as a calcium-magnesium component of the composition under the form of briquettes, which latter may also comprise other compounds.
  • said composition under the form of green briquettes according to the present invention comprises at most 97 wt %, preferably at most 90 wt %, preferably at most 88%, in certain embodiments at most 60 wt % of CaO+MgO equivalent relative to the weight of said composition.
  • the composition under the form of green briquettes according to the present invention comprises less than 10% of particles of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m and ⁇ 5 mm relative to the total weight of the pulverulent mixture.
  • the composition under the form of green briquettes according to the present invention comprises between 10% and 60% of particles of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m and ⁇ 5 mm relative to the total weight of the pulverulent mixture.
  • the wt % of CaO equivalent in the fraction of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m with respect to the total of the percentage in weight of quicklime in the fraction of calcium-magnesium compound having a particle size ⁇ 90 ⁇ m and the % Fe 2 O 3 equivalent of the iron-based compound having a very fine particle size distribution is ⁇ 30%, preferably ⁇ 32%, more preferably ⁇ 34% and in a particularly preferred manner ⁇ 36%.
  • the composition under the form of green briquettes according to the present invention comprises at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, more preferably at least 80 wt % and in a particular manner more than 95 wt % iron oxide under the form of magnetite Fe 3 O 4 relative to the total weight of the iron based compound expressed in Fe 2 O 3 equivalent.
  • the wt % of CaO equivalent in the fraction of “quick” calcium-magnesium compound having a particle size ⁇ 90 ⁇ m with respect to the total of the percentage in weight of quicklime in the fraction of calcium-magnesium compound having a particle size ⁇ 90 ⁇ m and the % Fe 2 O 3 equivalent of the iron-based compound having a very fine particle size distribution is ⁇ 40, preferably ⁇ 38, more preferably ⁇ 36%.
  • the composition under the form of green briquettes according to the present invention comprises at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, more preferably at least 80 wt % and in a particular manner more than 95 wt % iron oxide under the form of hematite Fe 2 O 3 relative to the total weight of the iron based compound expressed in Fe 2 O 3 equivalent.
  • the present invention also relates to a composition in the form of thermally treated briquettes, comprising at least one iron-based compound, said composition comprising at least 40 wt % of CaO+MgO equivalent relative to the weight of said composition and having a Ca/Mg molar ratio greater than or equal to 1, preferably greater than or equal to 2, more preferably greater than or equal to 3, characterized in that said iron-based compound is present at a content of at least 20 wt %, preferably at least 25 wt %, in a preferred manner at least 30 wt %, more preferably at least 35 wt % of Fe 2 O 3 equivalent relative to the weight of said composition, said iron-based compound comprising at least 60%, preferably at least 80%, and even more preferably at least 90% of calcium ferrite, expressed by weight of Fe 2 O 3 equivalent, relative to the total weight of said iron-based compound expressed by weight of Fe 2 O 3 equivalent, wherein at least 20 wt % calcium ferrite with respect to the weight of the composition
  • Calcium ferrite is represented by the following formulae: CaFe 2 O 4 (monocalcium ferrite) and/or Ca 2 Fe 2 O 5 (dicalcium ferrite).
  • Said matrix is to be understood as being a continuous phase based on calcium ferrite in which particles of “quick” calcium-magnesium compound, in particular quicklime, are dispersed.
  • particles of “quick” calcium-magnesium compound are of small size so that they melt visibly in the matrix based on calcium ferrite, and the case when particles of “quick” calcium-magnesium compound are of larger size and appear as inclusions of “quick” calcium-magnesium compound in said matrix.
  • the aforesaid distinction is made concrete on the basis of a section of a briquette according to the invention, applying scanning electron microscopy coupled to energy dispersive analysis.
  • This provides visualization in two dimensions (the surface of the section) of an object initially in three dimensions (briquette), but also of the particles that make up the briquette.
  • the particles of calcium-magnesium compound also appear in two dimensions on the section plane.
  • the cut surface of the particle is likened to an equivalent disk and its “two-dimensional” size to the equivalent diameter of this disk.
  • the two-dimensional sizes are calculated with a program that finds, for each particle of “quick” calcium-magnesium compound dispersed in the continuous matrix of calcium ferrite, the sum of the smallest and the largest dimension of its cut surface divided by two. This sum divided by two represents the diameter of the equivalent disk.
  • the particles of “quick” calcium-magnesium compound melt or merge in said matrix (continuous phase) of calcium ferrite when said particles of “quick” calcium-magnesium compound have a two-dimensional size under 63 ⁇ m, observable by scanning electron microscopy coupled to energy dispersive analysis, in a section of the briquette.
  • said pulverulent mixture comprises at most 97 wt %, preferably at most 90 wt %, preferably at most 88 wt %, in certain embodiments at most 60 wt % of CaO+MgO equivalent relative to the weight of said composition.
  • said “quick” calcium-magnesium compound comprises at least 10 wt %, preferably 20 wt %, more preferably 30 wt %, in a more preferable manner 40 wt % CaO+MgO equivalent, relative to the total weight of said composition.
  • said “quick” calcium-magnesium compound contains fine particles rejected in screening in the production of pebbles of said calcium-magnesium compound, calcium-magnesium dust from filter at a concentration from 0 to 90 wt % relative to the total weight of said “calcium-magnesium” and from 10 to 100 wt % of quicklime in the form of ground particles, relative to the total weight of said “quick” calcium-magnesium compound.
  • said “quick” calcium-magnesium compound contains from 0 to 100 wt % quicklime in the form of ground particles from pebbles of said calcium-magnesium compound.
  • said “quick” calcium-magnesium compound contains from 0 to 90 wt % of fine particles rejected in screening in the production of pebbles of said calcium-magnesium compound and from 10 to 100 wt % of quicklime in the form of ground particles, relative to the total weight of said “quick” calcium-magnesium compound.
  • said quicklime in the form of ground particles is present at a concentration of at least 15 wt %, in particular at least 20 wt %, more preferably at least 30 wt %, especially preferably at least 40 wt % relative to the weight of the composition.
  • said “quick” calcium-magnesium compound is a soft- or medium-burned calcium-magnesium compound, preferably soft-burned.
  • said quicklime in the form of ground particles is a soft-burned or medium-burned quicklime, preferably soft-burned.
  • composition when the composition is in the form of green briquettes, said composition has a BET specific surface area greater than or equal to 1 m 2 /g, preferably greater than or equal to 1.2 m 2 /g, more preferably greater than or equal to 1.4 m 2 /g.
  • said composition when the composition is in the form of green briquettes, said composition has a porosity greater than or equal to 20%, preferably greater than or equal to 22%, more preferably greater than or equal to 24%.
  • porosity of the composition in the form of briquettes means, in the sense of the present invention, the total mercury pore volume determined by mercury intrusion porosimetry according to part 1 of standard ISO 15901-1:2005E, which consists of dividing the difference between the skeletal density, measured at 30000 psia, and the apparent density, measured at 0.51 psia, by the skeletal density.
  • porosity may also be measured by kerosene intrusion porosimetry.
  • the density and the porosity of the briquettes are determined by kerosene intrusion, according to a measurement protocol derived from standard EN ISO 5017. The measurements are performed on 5 briquettes.
  • the density of the briquettes is calculated according to the formula m1/(m3 ⁇ m2) ⁇ Dp and the percentage porosity according to the formula (m3 ⁇ m1)/(m3 ⁇ m2) ⁇ 100.
  • m1 is the weight of these 5 briquettes
  • m2 is the weight of these 5 briquettes immersed in kerosene
  • m3 is the weight of these 5 “wet” briquettes, i.e. impregnated with kerosene.
  • Dp is the density of the kerosene.
  • the composition when the composition is in the form of green briquettes and the calcium-magnesium compound is mainly quicklime, said composition has a value of reactivity t 60 below 10 min, preferably below 8 min, preferably below 6 min and even more preferably below 4 min.
  • a little more than 150 g of said composition is added in the reactivity test, to have the equivalent of 150 g of quicklime added.
  • said composition when the composition is in the form of green briquettes and the calcium-magnesium compound is mainly burned dolomite, said composition has a value of reactivity t 70 below 10 min, preferably below 8 min, preferably below 6 min and even more preferably below 4 min.
  • reactivity t 70 below 10 min, preferably below 8 min, preferably below 6 min and even more preferably below 4 min.
  • a little more than 120 g of said composition is added in the reactivity test to have the equivalent of 120 g of burned dolomite added.
  • composition when the composition is in the form of thermally treated briquettes, said composition has a BET specific surface area greater than or equal to 0.4 m 2 /g, preferably greater than or equal to 0.6 m 2 /g, more preferably greater than or equal to 0.8 m 2 /g.
  • said composition when the composition is in the form of thermally treated briquettes, said composition has a porosity greater than or equal to 20%, preferably greater than or equal to 22%, more preferably greater than or equal to 24%.
  • the composition when the composition is in the form of thermally treated briquettes and the calcium-magnesium compound is mainly quicklime, said composition has a value of t 60 below 10 min, preferably below 8 min, preferably below 6 min and even more preferably below 4 min.
  • t 60 below 10 min, preferably below 8 min, preferably below 6 min and even more preferably below 4 min.
  • a little more than 150 g of said composition is added in the reactivity test to have the equivalent of 150 g of “free” quicklime added.
  • “Free” quicklime means quicklime that has not reacted with iron oxide to give calcium ferrites CaFe 2 O 4 and/or Ca 2 Fe 2 O 5 .
  • said at least one calcium-magnesium compound is formed from particles under 7 mm.
  • said at least one calcium-magnesium compound is formed from particles under 5 mm.
  • said at least one calcium-magnesium compound is formed from particles under 3 mm.
  • said at least one calcium-magnesium compound is a mixture of particles under 7 mm and/or of particles under 5 mm and/or of particles under 3 mm.
  • the composition in the form of green or thermally treated briquettes further comprises a binder or a lubricant, more particularly selected from the group consisting of binders of mineral origin such as cements, clays, silicates, binders of vegetable or animal origin, such as celluloses, starches, gums, alginates, pectin, glues, binders of synthetic origin, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate and mixtures thereof, preferably calcium stearate and/or magnesium stearate, at a content between 0.1 and 1 wt %, preferably between 0.15 and 0.6 wt %, more preferably between 0.2 and 0.5 wt % relative to the total weight of the composition.
  • binders of mineral origin such as cements, clays, silicates
  • the composition according to the present invention is a composition of green or thermally treated briquettes produced in industrial volumes and packaged in types of containers having a volume of contents greater than 1 m 3 such as big bags, containers, silos and the like, preferably sealed.
  • the briquettes of the composition in the form of green briquettes have a Shatter test index below 10%, for contents of iron oxide below 20 wt % of the composition.
  • the briquettes of the composition in the form of thermally treated briquettes have a Shatter test index below 8%, more particularly below 6%, regardless of the content of iron-based compound.
  • said briquettes have a largest dimension of at most 50 mm, preferably at most 40 mm, more preferably at most 30 mm.
  • the briquettes of the composition in the form of briquettes pass through a screen with square mesh with side of respectively 50 mm, preferably 40 mm, and in particular 30 mm.
  • said green or thermally treated briquettes have a largest dimension of at least 10 mm, preferably at least 15 mm, more preferably at least 20 mm.
  • a largest dimension means a characteristic dimension of the green or thermally treated briquette that is largest, whether it is the diameter, length, width, thickness, preferably in the longitudinal direction of the briquette of oblong shape.
  • said at least one calcium-magnesium compound is “quick” dolomite.
  • said at least one calcium-magnesium compound is quicklime.
  • said green or thermally treated briquettes have an average weight per briquette of at least 5 g, preferably at least 10 g, more preferably at least 12 g, and in particular at least 15 g.
  • said green or thermally treated briquettes have an average weight per briquette less than or equal to 100 g, preferably less than or equal to 60 g, more preferably less than or equal to 40 g and in particular less than or equal to 30 g.
  • said green or thermally treated briquettes have an apparent density between 2 g/cm 3 and 3.0 g/cm 3 , advantageously between 2.2 g/cm 3 and 2.8 g/cm 3 .
  • the thermally treated briquettes according to the present invention comprise particles of “quick” calcium-magnesium compound, preferably particles of “quick” calcium-magnesium compound of two-dimensional size lower than 63 ⁇ m, observable by scanning electron microscopy coupled to energy dispersive analysis, in a section of said briquette and covering at least 20% of the area of said section.
  • the thermally treated briquettes according to the present invention further comprise particles of “quick” calcium-magnesium compound, preferably particles of “quick” calcium-magnesium compound of two-dimensional size above 63 ⁇ m and under 5 mm, observable by scanning electron microscopy coupled to energy dispersive analysis, in a section of said briquette and covering at most 20% of the area of said section and preferably at most 10% of the area of said section.
  • the thermally treated briquettes further comprises particle of “quick” calcium-magnesium compound, preferably particles of “quick” calcium-magnesium compound of two-dimensional size above 63 ⁇ m and under 5 mm, observable by scanning electron microscopy coupled to energy dispersive analysis, in a section of said briquette and covering at least 20% of the area of said section and preferably at most 60% of the area of said section.
  • the thermally treated briquettes according to the present invention comprise at least 40 wt %, preferably at least 50 wt % of the calcium ferrite are in the form of monocalcium ferrite CaFe 2 O 4 .
  • the thermally treated briquettes according to the present invention comprise at least 40 wt %, preferably at least 50 wt % of the calcium ferrite are in the form of dicalcium ferrite Ca 2 Fe 2 O 5 .
  • compositions in the form of green or thermally treated briquettes according to the invention are presented in the accompanying claims.
  • the invention also relates to use of a composition in the form of green briquettes or in the form of thermally treated briquettes according to the present invention in iron and steel metallurgy, in particular in oxygen converters or in electric arc furnaces.
  • the green or thermally treated briquettes according to the present invention are used in oxygen converters or in arc furnaces, mixed with briquettes of “quick” calcium-magnesium compounds or with pebbles of “quick” calcium-magnesium compounds.
  • composition according to the present invention i.e. doped with fluxes, which melts more quickly than limestone, helps to form a liquid slag earlier at the start of the process, in comparison with the conventional methods, owing to homogeneous mixing and shaping of this homogenized mixture, which makes it possible to accelerate the slag forming process even more and minimize the formation of slag components of high melting point, such as the calcium silicates that usually form in the aforementioned method of the prior art.
  • the invention also relates to the use of a composition in the form of green briquettes or in the form of thermally treated briquettes in a process for refining molten metal, in particular the dephosphorization of molten metal and/or desulphurization of molten metal and/or reduction of losses of refined metal in the slag.
  • compositions in the form of green briquettes or in the form of thermally treated briquettes according to the present invention in a process for refining molten metal comprises
  • the use according to the present invention further comprises a step of adding quicklime, preferably quicklime in lumps or quicklime compacts, especially quicklime tablets or briquettes.
  • FIG. 1 is a graph of the BET specific surface area and of kerosene intrusion porosity as a function of the content of Fe 2 O 3 equivalent in the briquettes according to the present invention.
  • FIG. 2 is a graph of the Shatter test index (STI) as a function of the content of Fe 2 O 3 equivalent in the thermally treated and green briquettes according to the present invention.
  • STI Shatter test index
  • FIG. 3 is a graph of the percentage of Fe 2 O 3 converted to calcium ferrites as a function of the content of Fe 2 O 3 equivalent in the thermally treated briquettes according to the present invention.
  • FIG. 4 is a graph of the variation of the content of calcium ferrites expressed as Fe 2 O 3 equivalent in the thermally treated briquettes as a function of the iron oxide content expressed in Fe 2 O 3 equivalent in the green briquettes before thermal treatment.
  • FIG. 5 shows photographs of sections of the briquettes according to examples 9 to 16.
  • the present invention relates to a method for briquetting fine particles of calcium-magnesium compounds and iron-based compound, said iron-based compound having a very fine granulometric distribution characterized by a median size d 50 below 100 ⁇ m, preferably below 50 ⁇ m as well as a size d 90 below 200 ⁇ m, preferably below 150 ⁇ m, preferably below 130 ⁇ m, more preferably below 100 ⁇ m.
  • the method of briquetting according to the invention comprises supplying an approximately homogeneous pulverulent mixture comprising at least 40 wt % of CaO+MgO equivalent of a “quick” calcium-magnesium compound and at least 20 wt %, preferably at least 25 wt %, in a preferred manner of at least 30 wt %, more preferably at least 35 wt % of an iron-based compound expressed in Fe 2 O 3 equivalent relative to the weight of said composition, in which said quick calcium-magnesium compound comprising at least 40 wt % CaO+MgO equivalent further comprises at least a fraction of particles of calcium-magnesium compound having a particle size ⁇ 90 ⁇ m, which latter further comprises at least 20 wt % CaO equivalent with respect to the weight of the pulverulent mixture.
  • said pulverulent mixture comprises at most 97 wt %, preferably at most 90 wt %, preferably at most 88%, in certain embodiments at most 60 wt % of CaO+MgO equivalent relative to the weight of said composition.
  • the homogeneous mixture in which the iron-based compound is uniformly distributed is fed into a roller press, also sometimes called a tangential press, for example a Komarek, Sahut Konreur, Hosokawa Bepex, or Köppern press.
  • a roller press also sometimes called a tangential press, for example a Komarek, Sahut Konreur, Hosokawa Bepex, or Köppern press.
  • the approximately homogeneous pulverulent mixture is compressed, optionally in the presence of a binder or a lubricant, more particularly selected from the group consisting of binders of mineral origin such as cements, clays, silicates, binders of vegetable or animal origin, such as celluloses, starches, gums, alginates, pectin, glues, binders of synthetic origin, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates
  • the rollers of the roller press develop linear speeds at the periphery of the rollers between 10 and 100 cm/s, preferably between 20 and 80 cm/s, and linear pressures between 60 and 160 kN/cm, preferably between 80 and 140 kN/cm, and even more preferably between 80 and 120 kN/cm.
  • the surface pressure can be calculated, which is equal to the linear pressure divided by (1 ⁇ 2. ⁇ .D)/360, where D is the diameter of the hoops in cm.
  • the surface pressure is between 300 and 500 MPa, preferably between 300 and 450 MPa, and more preferably between 350 and 450 MPa.
  • the calcium-magnesium composition is obtained in the form of green briquettes, which are collected.
  • the green briquettes collected are treated thermally at a temperature between 900° C. and 1200° C., preferably between 1050° C. and 1200° C., more preferably between 1100° C. and 1200° C. inclusive.
  • the thermal treatment is carried out preferably for a predetermined time of between 3 and 20 minutes, obtaining thermally treated briquettes in which said iron oxide is converted to calcium ferrite, i.e.
  • thermally treated briquettes comprising a “quick” calcium-magnesium compound and a calcium ferrite compound present at a content of at least 3%, preferably at least 12%, more preferably at least 20%, preferably at least 30%, more preferably at least 35% of Fe 2 O 3 equivalent.
  • said thermal treatment of the green briquettes is carried out in a rotary kiln at high temperature.
  • the rotary kiln is used for thermal treatment of briquettes whose iron oxide content is below 40%.
  • the thermal treatment is carried out in a horizontal kiln, for example a tunnel kiln, a through-type kiln, a car-type kiln, a roller kiln or a mesh band kiln.
  • a horizontal kiln for example a tunnel kiln, a through-type kiln, a car-type kiln, a roller kiln or a mesh band kiln.
  • any other type of conventional kiln may be used, provided it does not cause a change in the integrity of the compacts, for example through excessive attrition.
  • Cooling may either be performed conventionally in the downstream part of the kiln, or outside the kiln, for example in a vertical cooler in countercurrent for the cooling air or else in a fluidized-bed cooler with cooling air in the case of quenching.
  • cooling at the end of the thermal treatment is carried out quickly, in less than 15 min, preferably in less than 10 min, in a fluidized bed with cooling air.
  • the method comprises, before said supplying of a homogeneous pulverulent mixture,
  • a powder mixer with at least 40 wt % of CaO+MgO equivalent of a “quick” calcium-magnesium compound and with at least 20 wt %, preferably at least 25 wt %, more preferably at least 30 wt %, more preferably at least 35% of an iron-based compound expressed in Fe 2 O3 equivalent having a very fine granulometric distribution characterized by a median size d 50 below 100 ⁇ m, preferably below 50 ⁇ m as well as a size d 90 below 200 ⁇ m, preferably below 150 ⁇ m, preferably below 130 ⁇ m, more preferably below 100 ⁇ m; said quick calcium-magnesium compound comprising at least 40 wt % CaO+MgO equivalent further comprises at least a fraction of particles of calcium-magnesium compound having a particle size ⁇ 90 ⁇ m, which latter further comprises at least 20 wt % CaO equivalent with respect to the weight of the pulverulent mixture.
  • the calcium-magnesium compound comprises at least 10 wt % of ground quicklime particles, preferably at least 20 wt %, more particularly at least 30 wt % and at most 100 wt % relative to the total weight of said calcium-magnesium compound.
  • the “green” briquettes are based on quicklimes (optionally dolomitic) and ultrafine particles of iron oxide. They are characterized by an iron content by weight of at least 20 wt %, preferably at least 25 wt %, in a preferred manner of at least 30 wt %, more preferably at least 35 wt % expressed in Fe 2 O 3 equivalent.
  • the green briquettes are also characterized by a content by weight of calcium and magnesium of at least 40 wt %, expressed in CaO and MgO equivalent. Chemical analysis is performed by X-ray fluorescence spectrometry (XRF) according to standard EN 15309.
  • XRF X-ray fluorescence spectrometry
  • XRF Semiquantitative chemical analysis by XRF for determining the relative concentration by weight of the elements whose atomic mass is between 16 (oxygen) and 228 (uranium) is carried out starting from the samples ground to 80 ⁇ m and formed into pellets.
  • the sample is excited by a high-energy source (primary X-rays), and on recovering its original state of excitation, the sample emits secondary X-rays, characteristic of the chemical elements making up the sample.
  • the samples are put in a PANalytical/MagiX Pro PW2540 apparatus, operating in wavelength dispersion mode. Measurement is performed with a power of 50 kV and 80 mA, with a Duplex detector.
  • iron-based compounds iron oxides Fe 2 O 3 , Fe 3 O 4 , calcium ferrites CaFe 2 O 4 , Ca 2 Fe 2 O 5 .
  • This method consists of simulating a diffraction pattern using a crystallographic model of the sample, then adjusting the parameters of this model so that the simulated diffraction pattern is as close as possible to the experimental diffraction pattern.
  • the total amount of iron expressed in Fe 2 O 3 equivalent does not differ by more than 10% relative to the values obtained by XRF.
  • the percentage of total iron in the form of calcium ferrites is obtained by simple division (Fe in the ferrites divided by Fe in all of the iron-based compounds).
  • the green briquettes are also characterized by a BET specific surface area greater than or equal to 1 m 2 /g, preferably 1.2 m 2 /g, preferably 1.4 m 2 /g.
  • the porosity of the green briquettes is greater than or equal to 20%, preferably 22%, preferably 24%.
  • the green briquettes have an apparent density between 2.0 and 3.0 and preferably between 2.2 and 2.8.
  • the briquettes have good resistance to ageing. Thus, when they are exposed to a humid atmosphere containing for example 5 to 15 g/m 3 of absolute humidity, degradation of their mechanical properties (STI) only occurs beyond 1.5% of weight increase, preferably 2% of weight increase, and more preferably 2.5% of weight increase, following the reaction of hydration of quicklime CaO to slaked lime Ca(OH) 2 .
  • STI mechanical properties
  • the thermally treated briquettes comprise a calcium-magnesium compound, for example quicklimes (dolomitic) and an iron-based compound, containing ultrafine particles of iron oxide and calcium ferrites CaFe 2 O 4 and/or Ca 2 Fe 2 O 5 .
  • the thermally treated briquettes are characterized by an iron content by weight of at least 20 wt %, preferably at least 25 wt %, in a preferred manner of at least 30 wt %, more preferably at least 35 wt % expressed in Fe 2 O 3 equivalent. They are also characterized by a content by weight of calcium and magnesium of at least 40 wt % expressed in CaO and MgO equivalent. Chemical analysis is carried out by XRF, as mentioned above.
  • At least 40%, preferably at least 50%, preferably at least 60% and more preferably at least 70% of the total iron is in the form of calcium ferrites.
  • Quantification of the calcium ferrites is performed by XRD/Rietveld analysis after grinding the briquettes, as for the green briquettes.
  • the thermally treated briquettes of the present invention have a Shatter test index (“STI”, i.e. percentage by weight of fines below 10 mm after 4 drops from 2 m) below 6%, regardless of the content of iron-based compounds.
  • STI Shatter test index
  • the porosity is greater than or equal to 20%, preferably 22%, preferably 24%.
  • the thermally treated briquettes have an apparent density between 2.0 and 3.0 and preferably between 2.2 and 2.8.
  • the thermally treated briquettes have good resistance to ageing. Thus, when they are exposed to a humid atmosphere containing for example 5 to 15 g/m 3 of absolute humidity, degradation of their mechanical properties (STI) only occurs beyond 4% of weight increase, preferably 4.5% of weight increase, and more preferably 5% of weight increase, following the reaction of hydration of quicklime CaO to slaked lime Ca(OH) 2 .
  • STI mechanical properties
  • Quicklime fines from grinding were prepared from a soft-burned lump lime produced in a parallel-flow regenerative kiln. Grinding is performed in a hammer mill equipped with a 2-mm screen and a recycling loop for sizes above 2 mm. These quicklime fines from grinding contain 29% of particles having a particle size lower than 90 ⁇ m (d 30 ⁇ 90 ⁇ m), 71% of particles above 90 ⁇ m, 37% of particles above 500 ⁇ m, 21% of particles above 1 mm and 1% of particles between 2 and 3 mm. The value of t 60 of the water reactivity test is 0.9 min. The BET specific surface area (measured by nitrogen adsorption manometry after vacuum degassing at 190° C. for at least two hours and calculated by the multipoint BET method as described in standard ISO 9277:2010E) is 1.7 m 2 /g. These quicklime fines from grinding contain 95.7% of CaO and 0.8% of MgO by weight.
  • a Gericke GCM450 powder mixer is used, with a capacity of 10 dm 3 , equipped with standard paddles with radius of 7 cm, rotating at 350 revolutions per minute (i.e. 2.6 m/s).
  • This mixer is used in continuous mode for preparing a mixture consisting of:
  • the total flow rate of powder is 300 kg/h and the residence time is 3.5 s.
  • the mixture obtained is very homogeneous. This signifies that the Fe content for different 10 g samples taken from the final mixture is always plus or minus 5% of the mean value.
  • a tangential press is used, equipped with hoops with a diameter of 604 mm and width of 145 mm for producing briquettes with a theoretical volume of 7.2 cm 3 in the shape of a bar of soap (4 arrays of 67 pockets per hoop, or 268 pockets per hoop), capable of developing a linear pressure of up to 120 kN/cm.
  • the tangential press is supplied and compaction is performed at a speed of 12 revolutions per minute (i.e. a linear speed of 38 cm/s) at a linear pressure of 120 kN/cm (or a calculated surface pressure of 455 MPa for an angle of 0.5 degree).
  • briquettes having an average volume of 8.4 cm 3 , an average weight of 21.4 g and an average density of 2.4. These briquettes have a length of about 36 mm, a width of about 26 mm and a thickness of about 15.8 mm. These briquettes develop a total mercury pore volume (determined by mercury intrusion porosimetry according to part 1 of standard ISO 15901-1:2005E, which consists of dividing the difference between the skeletal density, measured at 30000 psia, and the apparent density, measured at 0.51 psia, by the skeletal density).
  • the water reactivity of the briquettes is determined by adding a predetermined amount of these briquettes, previously ground to fines with a size between 0 and 1 mm, to 600 ml of water at 20° C. to correspond to 150 g of quicklime.
  • a Shatter test is carried out with 10 kg of these briquettes, performing 4 successive drops from 2 m. The amount of fines under 10 mm generated at the end of these 4 drops is weighed.
  • the granulometric distribution of the iron-based particles in the composition in briquette form is determined by scanning electron microscopy and X-ray mapping, coupled to image analysis.
  • the briquettes are also characterized by carrying out a thermal treatment (hot charge/discharge) on several of these briquettes, at the end of which a powder with granulometry under 80 ⁇ m is prepared.
  • the latter is characterized by X-ray diffraction, and phase quantification is performed by Rietveld analysis.
  • Green briquettes are prepared according to the invention with ground quicklime containing particles with sizes between 0 and 2 mm, but having different granulometric profiles and contents of iron oxide of the hematite type expressed in Fe 2 O 3 equivalent ranging from 10% to 60 wt %.
  • the iron oxide used in these examples is characterized by a d 10 of 0.5 ⁇ m, d 50 of 12.3 ⁇ m and d 90 of 35.7 ⁇ m.
  • the particles of ground quicklime with size between 0 and 2 mm have at least 30% of particles that are under 90 ⁇ m.
  • the preparation protocol is described at example 1.
  • Green briquettes of identical composition were treated thermally at 1100° C. or at 1200° C. for 20 minutes to obtain thermally treated briquettes having different contents of quicklime and iron-based compounds.
  • the composition of the briquettes and the thermal treatments carried out are presented in Table 2. Several tests were carried out on these green and thermally treated briquettes, and are described below with the aid of FIGS. 1 to 4 .
  • FIG. 1 is a graph showing:
  • FIG. 2 is a graph showing:
  • the Shatter indices are below 20% for green briquettes having contents of iron-based compound expressed in Fe 2 O 3 equivalent below 40%, whereas for the thermally treated briquettes, all the Shatter tests are below 10%, or even 6%.
  • FIG. 3 is a graph showing the variation of the yield of iron-based compound (iron oxide) converted to calcium ferrite, as a function of the iron oxide content expressed in Fe 2 O 3 equivalent as well as the amount of iron oxide converted in monocalcium ferrite and dicalcium ferrite.
  • the thermal treatment is done in static bed during 20 min at 1100° C. in a tunnel furnace on a 100 mm thickness of briquettes.
  • the yield in conversion to calcium ferrite begins to decrease for contents of iron oxide expressed in Fe 2 O 3 equivalent above 40%.
  • the percentage in monocalcium ferrites go through a maximum for amount of iron oxide of 40%.
  • the percentage of the formation of dicalcium ferrites reduced with the iron oxide content.
  • FIG. 4 shows the variation of the content of calcium ferrites expressed in Fe 2 O 3 equivalent in the thermally treated briquettes as a function of the iron oxide content expressed in Fe 2 O 3 equivalent in the green briquettes before thermal treatment.
  • the contents of calcium ferrites in the thermally treated briquettes increase with the iron oxide content in the green briquettes.
  • this variation passes through a maximum at 50% content of calcium ferrites for contents of iron oxide in the green briquettes in the range from 40 to 45%, and then decreases to contents of calcium ferrites of about 40% for contents of iron oxide in the green briquettes of 60%.
  • thermally treated briquettes having a yield in conversion to calcium ferrite of 98% and containing 55.3 wt % of monocalcium ferrite relative to the amount of calcium ferrites are produced after thermal treatment at 1200° C. for 20 minutes on green briquettes containing about 40 wt % of hematite and 60 wt % of quicklime having a d 97 equal to 2 mm and a d 30 equal to 90 ⁇ m, except for the presence of 0.25 wt % of calcium stearate, relative to the total weight of the green briquettes.
  • thermally treated briquettes having a yield in conversion to calcium ferrite of 90% and containing 69.9 wt % of monocalcium ferrite relative to the amount of calcium ferrites are produced after thermal treatment at 1100° C. for 20 minutes on green briquettes containing about 50 wt % of hematite and 25 wt % of quicklime having a d 97 equal to 2 mm and a d 30 equal to 90 ⁇ m and 25 wt % of quicklime having a d 97 equal to 90 ⁇ m, except for the presence of 0.25 wt % of calcium stearate, relative to the total weight of the green briquettes.
  • thermally treated briquettes having a yield in conversion to calcium ferrite of 96% and containing 47.2 wt % of monocalcium ferrite relative to the amount of calcium ferrites are produced after thermal treatment at 1100° C. for 20 minutes on green briquettes containing about 50 wt % of hematite and 50 wt % of quicklime having a d 97 equal to 90 ⁇ m.
  • thermally treated briquettes having a yield in conversion to calcium ferrite of 99% and containing 43.9 wt % of monocalcium ferrite relative to the amount of calcium ferrites are produced after thermal treatment at 1200° C. for 20 minutes on green briquettes containing about 50 wt % of hematite and 25 wt % of quicklime having a d 97 equal to 2 mm and a d 30 equal to 90 ⁇ m, except for the presence of 0.25 wt % of calcium stearate, relative to the total weight of the green briquettes.
  • the yield of monocalcium ferrite can be increased by reducing the thermal treatment temperature to 1100° C., except for the presence of 0.25 wt % of calcium stearate, relative to the total weight of the green briquettes.
  • thermally treated briquettes having a yield in conversion to calcium ferrite of 61% and containing 82.6 wt % of monocalcium ferrite relative to the amount of calcium ferrites are produced after thermal treatment at 1100° C. for 20 minutes on green briquettes containing about 50 wt % of hematite and 50 wt % of quicklime having a d 97 equal to 2 mm and a d 30 equal to 90 ⁇ m.
  • the yield of monocalcium ferrite can be increased by increasing the amount by weight of quicklime having a d 100 equal to 90 ⁇ m, except for the presence of 0.25 wt % of calcium stearate, relative to the total weight of the green briquettes.
  • FIG. 5 shows photographs of the sections of the briquettes from examples 9 to 16.
  • the textures of the thermally treated briquettes from examples 9 to 16 were analysed by scanning electron microscopy coupled to energy dispersive analysis, by preparing a section of these briquettes, by encapsulating these briquettes in a resin, and by polishing the surface of the section.
  • These analyses make it possible to construct a map of the distribution of each element in a section of the briquettes.
  • image analysis software it is possible to combine the maps obtained for each element and measure the size distribution and the relative coverage of each element.
  • calcium ferrite forms a matrix (or continuous phase) in which particles of quicklime (discontinuous phase) are dispersed.
  • a calcium ferrite matrix can be obtained after thermal treatment for 20 minutes at temperatures between 900° C. and 1200° C., preferably between 1050 and 1200° C., of green briquettes containing at least 20 wt % of particles of calcium-magnesium compound, preferably in the form of quicklime and at least 20 wt % of iron oxide having a d 90 under 200 ⁇ m, preferably under 150 ⁇ m, more preferably under 100 ⁇ m and a d 50 below 50.
  • the two-dimensional sizes of the particles of lime dispersed in the matrix are calculated by a program that finds the average of the smallest and largest dimension of each particle of quicklime in the calcium ferrite matrix.
  • the particles are classified in a first group of particles whose two-dimensional size is under 63 ⁇ m and above the limit of detection of the measuring equipment, and a second group of particles whose two-dimensional size is above 63 ⁇ m.
  • Table 2 shows, for the briquettes from examples 2 to 9, the relative coverage of the calcium ferrite matrix, of the particles of quicklime under 63 ⁇ m and of the particles of quicklime above 63 ⁇ m in the cut section from each briquette.
  • the percentages of surface coverage of the particles of quicklime above 63 ⁇ m are less than 25% for thermally treated briquettes having contents of calcium ferrites above 60 wt % of the composition.
  • green briquettes were prepared with 38.85 wt % of iron oxide in the form of magnetite Fe 2 O 4 having a d 97 of 150 ⁇ m and a d 50 of 40 ⁇ m with 60.9 wt % of quicklime having a d97 below 2 mm and a d 30 below 90 ⁇ m as well as 0.25 wt % of calcium stearate, relative to the weight of the briquette.
  • Thermal treatment was carried out on a static bed of three layers of briquettes for 20 min at 1100° C. in order to obtain thermally treated briquettes and the percentage by weight of iron converted to monocalcium ferrite is 8% whereas the percentage of iron converted to dicalcium ferrite is 82%.
  • green briquettes were prepared with 39.9 wt % of iron oxide in the form of hematite Fe 2 O 3 characterized by a d 10 of 0.5 ⁇ m, d 90 of 12.3 ⁇ m and d 90 of 35.7 ⁇ m and with 59.85 wt % of quicklime having a d 97 below 2 mm and a d 30 below 90 ⁇ m and 0.25 wt % of calcium stearate relative to the weight of the briquette.
  • the green briquettes obtained were treated thermally in the same conditions as in example 17 in order to obtain thermally treated briquettes. In this case, the percentage of iron converted to monocalcium ferrite is 65 wt % and the percentage of iron converted to dicalcium ferrite is 24 wt %.
  • the concentrations by volume of H 2 O in the gas are between 3.9 and 20.1%.
  • the concentrations by volume of CO 2 in the gas are between 0.9 and 9.1%.
  • the Shatter indices were compared with the compressive force for several samples of green briquettes to establish the correlation between the Shatter index and the compressive force.
  • the green briquettes tested comprised quicklime with particle size between 0 and 3 mm with different contents of iron oxide, from 0 to 60 wt % and different contents of lubricant, ranging from 0.125 to 0.5 wt %, relative to the total weight of the briquettes.
  • the parameters of the briquetting process were also altered to ensure that the population was large enough for establishing the correlation.

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  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
  • Carbon Steel Or Casting Steel Manufacturing (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
  • Compounds Of Iron (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
  • Magnetic Ceramics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Manufacture Of Iron (AREA)
  • Solid Fuels And Fuel-Associated Substances (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Magnetic Treatment Devices (AREA)
  • Lubricants (AREA)
US16/309,204 2016-07-08 2017-07-07 Method for Manufacturing Briquettes Containing a Calcium-Magnesium Compound and an Iron-Based Compound, and Briquettes Obtained Thereby Abandoned US20190337847A1 (en)

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PCT/EP2017/067176 WO2018007637A1 (fr) 2016-07-08 2017-07-07 Procede de fabrication de briquettes contenant un compose calco-magnesien et un compose a base de fer, et briquettes ainsi obtenues

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US16/309,044 Abandoned US20190345066A1 (en) 2016-07-08 2017-07-07 Method for Manufacturing Briquettes Containing a Calcium-Magnesium Compound and an Iron-Based Compound, and Briquettes Obtained Thereby
US16/308,735 Abandoned US20190144336A1 (en) 2016-07-08 2017-07-07 Method for Manufacturing Briquettes Containing a Calcium-Magnesium Compound and an Iron-Based Compound, and Briquettse Obtained Thereby
US16/308,293 Active US10851017B2 (en) 2016-07-08 2017-07-07 Thermally treated briquettes containing a “quick” calcium-magnesium compound and calcium ferrites, and method of manufacture thereof
US16/309,204 Abandoned US20190337847A1 (en) 2016-07-08 2017-07-07 Method for Manufacturing Briquettes Containing a Calcium-Magnesium Compound and an Iron-Based Compound, and Briquettes Obtained Thereby

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US16/308,735 Abandoned US20190144336A1 (en) 2016-07-08 2017-07-07 Method for Manufacturing Briquettes Containing a Calcium-Magnesium Compound and an Iron-Based Compound, and Briquettse Obtained Thereby
US16/308,293 Active US10851017B2 (en) 2016-07-08 2017-07-07 Thermally treated briquettes containing a “quick” calcium-magnesium compound and calcium ferrites, and method of manufacture thereof

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