Method for treating an iron ore

Abstract

The invention relates to a method for treating an iron ore to increase its mass concentration of magnetic compounds, the method comprising in particular a step / E3 / of calcining an iron ore in a calciner (5) to obtain a calcined iron ore containing iron III oxides, a step / E4 / of reducing the iron III oxides present in the calcined iron ore, a step / E5 / of cooling the reduced iron ore to lower its temperature below a threshold temperature making it possible to avoid reoxidation of the iron II oxides and / or of the triiron tetroxides.

Description

METHOD FOR PROCESSING IRON ORE

[0001] The technical field of the invention relates to methods for treating iron ore, more particularly methods for enriching iron ore intended to increase the mass concentration of magnetic compounds in said iron ore.

[0002] Magnetic compounds include, for example, iron (II,III) oxide or so-called triiron tetroxide (Fe3O4), iron (II) oxide or so-called ferrous oxide (FeO), or iron or so-called metallic iron (Fe).

[0003] For the purposes of the present invention, iron ore means all ores which contain iron in different forms, such as sulfides, carbonates or oxides, and which themselves can be hydrated. The mass concentrations of iron in the different forms can be between 20% and 75%, preferably between 30 and 70%, by weight relative to the total weight of the ore. Background to the invention

[0004] For ecological and economic reasons in particular, processes for treating such iron ores exist in order to obtain phases enriched in iron atoms and / or in mineral species containing iron atoms.

[0005] Conventionally, the processes for obtaining phases enriched in iron atoms and / or in mineral species containing iron atoms comprise a grinding step then a step of separating the ground iron ore so as to extract a maximum of elements not containing iron.

[0006] Today, the processes for obtaining enriched phases are carried out largely using the wet method. This results in disadvantages such as the generation of numerous mineral wastes and the increase in environmental and human risks, for example during mudflows, particularly in the event of a mine tailings reservoir failure.

[0007] Furthermore, the processes currently implemented are not optimal and can still be improved in order to increase the concentration of iron atoms and / or mineral species containing iron atoms in the enriched phases obtained and to reduce waste.

[0008] There is therefore a need to overcome these drawbacks.

[0009] In order to overcome the technical problems and limitations encountered by the methods of the prior art, the invention proposes a method for treating an iron ore to increase its mass concentration of magnetic compounds, the method comprising the following steps: / E1 / providing an iron ore containing particles having a particle size of less than 2 mm, / E3 / calcining the iron ore in a calciner to obtain a calcined iron ore containing iron III oxides, the calcination step / E3 / being carried out under stoichiometric or oxidizing conditions, / E4 / reducing the iron III oxides present in the calcined iron ore, the reduction step / E4 / being carried out by injection, into a reduction reactor separate from the calciner,of a reducing gas containing hydrogen atoms and brought into direct contact with the calcined iron ore to obtain a reduced iron ore comprising iron II oxides and / or triiron tetroxides, / E5 / cooling, under a reducing or neutral atmosphere, said reduced iron ore to lower its temperature below a threshold temperature making it possible to avoid reoxidation of the iron II oxides and / or triiron tetroxides.,

[0010] By reducing or neutral atmosphere, within the meaning of the present invention, is meant an atmosphere defined by a volume concentration of dioxygen less than 2%, and preferably substantially equal to 0%.

[0011] Such a process makes it possible to obtain calcined, reduced and cooled iron ore which is concentrated in magnetic compounds in order to facilitate subsequent dry magnetic separation so as to obtain a phase enriched in iron atoms and / or in mineral species containing iron atoms. Indeed, applying such a process makes it possible to make the iron oxides contained in the supplied iron ore magnetic and thus facilitate its selection. In particular, the reduction step makes it possible to transform the most widespread iron oxides in the natural state, those which are found in the form of Fe2O3, into Fe3O4 and FeO which are magnetic.

[0012] Furthermore, this process advantageously makes it possible to obtain an iron ore defined by a high concentration of magnetic compounds using a small amount of reducing agent. Furthermore, this process makes it possible to improve the reduction of iron III oxides because the contact of the iron ore with the reducing gas is maintained for a prolonged period during a large number of the process steps.

[0013] It should be noted that the particle size distribution of the particles contained in the iron ore is such that 90% by mass of the particles have a diameter less than or equal to 2 mm, preferably less than 1 mm.

[0014] Advantageously, the invention comprises the following characteristics, taken alone or in combination:

[0015] the iron ore supplied in supply step / E1 / comes from prior grinding carried out in a grinding device, and preferably drying, during a grinding step / E0 / , and preferably drying;

[0016] the method further comprises, between the supply step / E1 / and the calcination step / E3 / , a step / E2A / of drying the iron ore in a drying device during which the humidity level of the supplied iron ore is reduced to a humidity level of less than 5%, preferably less than 1%;

[0017] the method further comprises, between the supply step / E1 / and the calcination step / E3 / , a step / E2B / of preheating the iron ore in a preheater during which the temperature of the iron ore is increased to a preheating temperature of between 400°C and 700°C;

[0018] during the calcination step / E3 / , the temperature of the iron ore introduced into the calciner is increased to a calcination temperature equal to 950°C, preferably between 700°C and 900°C;

[0019] the reducing gas comprises dihydrogen and / or carbon monoxide;

[0020] the reducing gas contains dihydrogen and carbon monoxide, or dihydrogen;

[0021] the quantity of reduction gas injected in the reduction step / E4 / corresponds to a quantity of between 0.33 and 3, preferably 0.4 to 1, moles of reactants per mole of iron III oxide present in the calcined iron ore;

[0022] step / E5 / of cooling said reduced iron ore, the temperature of the reduced iron ore is lowered below a threshold temperature of between 200°C and 600°C, preferably between 350°C and 500°C;

[0023] the method further comprises, after the cooling step / E5 / , a final cooling step / E6 / in an air cooling device during which the temperature of the reduced iron ore is lowered to a temperature below 150°C, preferably below 60°C;

[0024] the method further comprises, after the cooling step / E5 / , a step / E7 / of magnetic separation of the reduced iron ore in a magnetic separation system to remove magnetic molecules containing iron atoms or magnetic mineral species containing iron atoms from the reduced and cooled iron ore;

[0025] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. Brief description of the figures

[0026] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which:

[0027] This is a schematic representation of an installation capable of implementing an example of the method according to the invention.

[0028] This is a schematic representation of a reduction reactor connected to a cooling device implemented for carrying out the cooling step / E5 / according to an embodiment of the method according to the invention.

[0029] This is a schematic representation of a reduction reactor connected to a cooling device implemented for carrying out the cooling step / E5 / according to an embodiment of the method according to the invention.

[0030] This is a schematic representation of a reduction reactor connected to a cooling device implemented for carrying out the cooling step / E5 / according to an embodiment of the method according to the invention. Detailed description

[0031] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0032] Shown is an iron ore processing unit 1. The purpose of this processing unit 1 is to increase the mass concentration of magnetic compounds in the iron ore introduced into processing unit 1.

[0033] The treatment unit 1 comprises: - a grinding / drying device 2, - a preheater 3, - a filter 4, - a calciner 5, - a reduction reactor 6, - a cooling device 7, - a final cooler 8, - a magnetic separation system 9.

[0034] The path of the gases and iron ore in the production unit 1 shown in the is first described. Hot gases 15 are sent to the calciner 5, then the preheater 3 and finally to the grinding / drying device 2. These hot gases are then discharged through the filter 4. In parallel, the iron ore moves from the grinding / drying device 2 to the magnetic separation system 9, passing respectively through the preheater 3, the calciner 5, then the calcined iron ore 10 is sent to the reduction reactor 6, then circulates in the cooling device 7. A reduction gas 11 is injected into the reduction reactor 6 to reduce the iron ore, then the reduced iron ore mixed with reduction gas, preferably in the form of a suspension of reduced iron ore 12 in the reduction gas, then circulates in the cooling device 7.In this cooling device 7 circulates, among other things, a flow of cooling gas, as well as the reduced iron ore. A gaseous part 13 of this flow of cooling gas is extracted from the cooling device 7 and is sent to the calciner 5. After passing through the cooling device 7, the reduced and cooled iron ore 14 is extracted from the cooling device 7 and is conveyed to a final cooler 8 before being sent to a magnetic separator 9.

[0035] In the following, examples of the method according to the invention will be described with reference to the figures.

[0036] In the figure, the solid lines represent the path of the iron ore and the dotted lines indicate the path of the gas flows.

[0037] According to an exemplary embodiment, the method then firstly comprises, preferably, a grinding step / E0 / , and advantageously a drying step, in which iron ore is ground, and can be dried, at least in part, in the grinding / drying device 2. Preferably, the ground iron ore contains particles having a particle size of less than 2 mm, it is then this ground iron ore which is supplied, during a supply step / E1 / , to the method which will be described below.

[0038] Preferably, when the iron ore has not been sufficiently dried in the grinding / drying device 2 and its moisture content is greater than 5%, a step / E2A / of drying the iron ore in a drying device is implemented. During this drying step, the moisture content of the supplied iron ore is decreased to a moisture content of less than 5%, preferably less than 1%. For example, this drying step / E2A / can be implemented with a flash drying means or using a rotary tube type dryer.

[0039] Then, the crushed and dried iron ore is sent to the preheater 3, except for the finest fraction which is carried to the filter 4 by the flow of hot gases. Thus, during a preheating step / E2B / , in the preheater 3, the crushed and dried iron ore is preheated by the hot gases coming from the calciner 5 to a preheating temperature between 400°C and 700°C.

[0040] The preheated iron ore is then directed to the calciner 5. Thus the method comprises a step / E3 / calcining the iron ore in the calciner 5 to obtain a calcined iron ore containing iron III oxides. Preferably, the temperature of the iron ore introduced into the calciner 5 is increased to a calcination temperature equal to 950°C, preferably between 700°C and 900°C. The calcination is carried out under stoichiometric or oxidizing conditions. For example, the hot gases 15 sent into the calciner 5 have been generated by the combustion of the mixture of an oxidizer and a fuel in stoichiometric proportions for complete combustion or with an excess of oxidizer for oxidizing combustion.

[0041] The calciner 5 may be of any type, for example it may be a fluidized bed calciner. Preferably, the calciner 5 is configured to implement suspension calcination in which the residence time of the iron ore is between 0.1 and 10 seconds and subjected to a set temperature between 800 and 1100°C. The suspension calcination process, or flash calcination used, may be any type of suspension calcination process known from the state of the art. As a non-limiting example, reference is made to the technology described in patent application EP498731.

[0042] The calcined iron ore 10 is then introduced, through a material inlet 61, into the reduction reactor 6 which is separate from the calciner 5, and in which a step / E4 / of reducing the iron III oxides present in the calcined iron ore is implemented. The reduction step / E4 / is carried out by injecting, into the reduction reactor 6 through a gas inlet 62, a reduction gas 11 containing hydrogen atoms. This reduction gas 11 is brought into direct contact with the calcined iron ore.

[0043] Reducing gas 11 containing hydrogen atoms allows the reduction of iron III oxides according to the following formulas to obtain mainly triiron tetroxides and possibly iron II oxides FeO:

[0044]

[0045]

[0046] and according to the following formulas, carbon monoxide, when present, reacts with iron III oxides:

[0047]

[0048]

[0049] Using a gas containing hydrogen atoms rather than diesel or any other liquid fuel as a reducing agent significantly reduces the amount of reducing agent in the reduction step / E4 / . The calcined and reduced iron ore is therefore produced at a significantly lower cost. In addition, the environmental impact of iron ore processing is reduced.

[0050] Preferably, the reducing gas 11 comprises dihydrogen and / or carbon monoxide. Advantageously, the reducing gas 11 contains, among the aforementioned gases, both dihydrogen and carbon monoxide, or only dihydrogen. It should be noted that these gases can be mixed with other gases, mainly nitrogen and / or carbon dioxide.

[0051] Preferably, the quantity of reduction gas injected into the reduction reactor 6, during the reduction step / E4 / , corresponds to a quantity substantially between 0.33 and 3, preferably 0.4 to 1, moles of reactants per mole of iron III oxide present in the calcined iron ore. By respecting this dosage, a reduced iron ore is obtained by minimizing the gas supply, which makes it possible to reduce the costs of processing the iron ore and its impact on the environment.

[0052] According to an exemplary embodiment of the invention, the reduction gas 11 contains a reagent of the dihydrogen type. This gas makes it possible to avoid the production of carbon oxides during the reduction step / E4 / .

[0053] According to another exemplary embodiment of the invention, the reduction gas 11 contains a mixture of reagents of the dihydrogen and carbon monoxide type. This gas has the advantage of being easy to synthesize in situ in a dedicated reactor, either in an “endogas generator” or in an “exogas generator”.

[0054] According to the embodiments illustrated in Figures 2 and 3, the reduction step / E4 / is implemented in a reduction reactor 6 which is a reactor of the static reactor, fluidized bed reactor or rotary reactor type. Reduced iron ore 12 containing iron II oxides and / or triiron tetroxides leaves the reduction reactor 6. Under these conditions, the reduced iron ore 12 leaves the reduction reactor 6 in two parts. The coarsest part of the reduced iron ore 12 leaves through a material outlet 64 of the reduction reactor 6 in the form of particles 12'', and the finest part leaves through a gas outlet 63 in the form of dust entrained in a reduction gas flow to be treated 12'.The calcined iron ore is preferably maintained in the reduction reactor 6 for a residence time greater than 10 seconds and up to 10 minutes, preferably up to 5 minutes, or even up to 2 minutes, under optimal reduction conditions. The reduction reactor 6 comprises in particular a reduction gas inlet 62 through which reduction gas 11 is injected.

[0055] According to the exemplary embodiment illustrated in, the reduction step / E4 / is initiated in a reduction reactor 600 which is a suspension reactor. Reduced iron ore containing iron II oxides and / or triiron tetroxides suspended in a reduction gas flow leaves the reduction reactor 600 via the outlet 603. The calcined iron ore is preferably maintained in the reduction reactor 600 for a residence time of less than 10 seconds, under optimal reduction conditions. The reduction reactor 600 comprises in particular a reduction gas inlet 601 through which reduction gas 11 is injected and a material inlet 602 through which the calcined iron ore 10 enters.

[0056] Then, during a cooling step / E5 / under a reducing or neutral atmosphere, the reduced iron ore 12 is cooled to a threshold temperature of between 200°C and 600°C, preferably between 350°C and 500°C. This makes it possible to avoid reoxidation of the iron II oxides and / or the triiron tetroxides. At the end of the cooling step / E5 / , reduced and cooled iron ore 14 is then obtained.

[0057] By cooling the reduced iron ore in a reducing or neutral atmosphere, the energy efficiency of processing unit 1 can be improved. The heat energy from cooling is used for other applications, either in the same process or for another use. This is made possible by using a gas containing hydrogen atoms as a reducing agent, which allows reduction of iron III oxides at lower temperatures than in a process using a liquid reducing agent, for example.

[0058] Preferably, the method further comprises, after the cooling step / E5 / which preferably takes place in the cooling device 7, a final cooling step / E6 / in an air cooling device 8 during which the temperature of the reduced and cooled iron ore is lowered to a temperature below 150°C, preferably below 60°C. Achieving such a temperature facilitates the subsequent use of the calcined, reduced and cooled iron ore.

[0059] Advantageously, the method further comprises, after the final cooling step / E6 / , a step / E7 / of magnetic separation of the reduced iron ore in a magnetic separation system 9. Such magnetic separation is carried out with conventional separation means of the prior art. Such separation aims to remove the magnetic molecules containing iron atoms or the magnetic mineral species containing iron atoms from the reduced and cooled iron ore 14 leaving the cooling device 7.

[0060] Finally, the enrichment process can be followed by a well-known pelletization step / E8 / .

[0061] With reference to Figures 2 and 3, exemplary embodiments of cooling devices 7 will be described, each of these exemplary cooling devices 7 being connected to a reactor of the static reactor type, fluidized bed reactor or even rotary reactor as indicated above. According to these exemplary embodiments, the reduced iron ore 12 is sent to the cooling device 7. In particular, each portion 12' and 12'' of the reduced iron ore 12 is conveyed and introduced via a fluid conduit into a cooling reactor 77 in which the reduced iron ore is suspended in a cooling gas which is obtained as indicated below.

[0062] The reduced iron ore then exits, in the form of a suspension in a cooling gas, through an outlet 774 of the cooling reactor 77 and is sent to an inlet 712 of a first gas / particle separation device 71. The reduced iron ore is then cooled. This first gas / particle separation device 71, for example a cyclone-type separator, is configured to implement an operation / O1 / of separation of the gas with the reduced iron ore in suspension to obtain: a gas separated from the reduced iron ore, and reduced iron ore. The reduced and cooled iron ore exiting through the material outlet 716 of the first gas / particle separation device 71 is recovered and possibly stored in a suitable storage means. Advantageously, the recovered reduced iron ore is at a temperature of between 200°C and 600°C, preferably between 350°C and 500°C.

[0063] After this operation / O1 / , a cooling operation / O2 / is carried out, in a first cooling means 72, of the gas separated from the reduced iron ore to obtain a cooled gas. To do this, an inlet 722 of the first cooling means 72 is connected by a pipe to an upper part of the first gas / particle separation device 71. The cooled gas then leaves through an outlet 724 of the first cooling means 72. For example, the first cooling means 72 may be a recovery boiler or an air cooler.

[0064] Preferably, during the operation / O2 / of cooling the gas separated from the reduced iron ore, the temperature of the gas is lowered below a threshold temperature of between 100°C and 450°C. This is referred to as indirect cooling since the gas separated from the reduced iron ore is not in direct contact with the cooling fluid. It is thus possible to connect, to the outlet 724 of the cooling means 72, a ventilation device 73 without it being damaged by excessively hot gas flows. The ventilation device 73 promotes the circulation of the gas flow in the aforementioned elements of the unit and also in those which will be described below. Furthermore, to the extent that the gas has been cooled, the opportunity is left to use a wide range of ventilation devices 73 which would then be adapted to such gas flow temperatures.Furthermore, the / O2 / operation of cooling the gas separated from the reduced iron ore makes it easier to implement the subsequent / O3 / operation.

[0065] According to the embodiment illustrated in, an operation / O5 / of introducing the cooled gas into the cooling reactor 77 is carried out. This allows the flow of cooling gas which enters the cooling reactor 77 via the inlet 772 to be at least partly, or entirely (), made up of the cooled gas obtained in the cooling operation / O2 / . It should be noted that the introduction operation / O5 / induces the creation of a cooling loop.

[0066] However, to optimize the cooling of calcined and reduced iron ore, in particular to improve the energy efficiency of their cooling, it is appropriate to carry out cooling in several stages, for example in two stages using two separate cooling means 72 and 75. Carrying out cooling in several stages allows energy optimization of the entire reduction process.

[0067] This is why, according to the embodiment illustrated in, before implementing the operation / O5 / of introducing the cooled gas into the cooling reactor 77, the cooled gas leaving the first cooling means 72 is used to cool the reduced iron ore which leaves through the material outlet 716 of the first gas / particle separation device 71. Advantageously, an operation / O3 / of cooling the reduced iron ore which leaves through the material outlet 716 of the first gas / particle separation device 71 is then carried out.

[0068] This cooling operation / O3 / is implemented using a second cooling means 75 configured to further cool the reduced and cooled iron ore in the cooling reactor 77. This cooling operation / O3 / comprises bringing the reduced iron ore into contact with the cooled gas exiting the first cooling means 72. This also makes it possible to further reduce, in an economical and ecological manner, the temperature of the reduced iron ore in order to avoid reoxidation of the iron II oxides and / or the triiron tetroxides of the reduced iron ore which exits the reduction reactor 6 via its material outlet 64.

[0069] As can be seen in the, the second cooling means 75 comprises a gas inlet 752 through which the cooled gas is introduced, this gas inlet 752 being indirectly connected to the outlet 724 of the first cooling means 72, via the ventilation device 73, and a material inlet 754, connected to the lower outlet, or material outlet 716, of the first gas / particle separation device 71, through which the reduced iron ore separated during the separation operation / O1 / is introduced. The second cooling means 75 further comprises an outlet 756 through which a gaseous suspension of reduced iron ore exits. It should be noted that during this cooling operation / O3 / , the cooled gas heats up in contact with the reduced iron ore which is hotter than the cooled gas.

[0070] Preferably, as can be seen in the, the ventilation device 73 of the cooled gas is arranged between the first cooling means 72 and the second cooling means 75. In this way, the circulation of the gas flows in the cooling loop is easily maintained.

[0071] Advantageously, the cooling operation / O3 / is carried out by placing the cooled gas in direct contact with the reduced iron ore to the extent that the cooled gas contains less than 2% oxygen by volume to the extent that it is largely derived from the reduction gas 11 injected into the reduction reactor 6.

[0072] Advantageously, during the cooling operation / O3 / , the temperature of the reduced iron ore is lowered below a threshold temperature of between 200°C and 600°C, and preferably between 350°C and 500°C. This makes it possible to reduce, in an economical and ecological manner, the temperature of the reduced iron ore in order to avoid the reoxidation of the iron II oxides and / or the triiron tetroxides of the reduced iron ore which leaves the reduction reactor 6 via its outlet 63, for example during the final air cooling and handling and storage. For example, this contacting is carried out using direct contacting of the cooled gas with the reduced iron ore.

[0073] Advantageously, an operation / O4 / of separating the gaseous suspension of reduced iron ore is carried out. This produces a gas separated from the reduced and cooled iron ore, and the reduced and cooled iron ore 14. This separation operation / O4 / is carried out using a second gas / particle separation device 76 configured to separate the reduced and cooled iron ore from the gaseous suspension.

[0074] The gaseous suspension of reduced iron ore is then introduced into the second gas / particle separation device 76 via an inlet 762 connected to the outlet 756 of the second cooling means 75. The second gas / particle separation device 76 further comprises, on the one hand, a gas outlet 764 for a cooling gas separated from the reduced and cooled iron ore and, on the other hand, a material outlet 766 for reduced and cooled iron ore. This second gas / particle separation device 76 may, for example, be of the same type as the first gas / particle separation device 71. The reduced and cooled iron ore leaving via the material outlet 766 of the second gas / particle separation device 76 is conveyed into a final cooler 8 in which a final cooling step is carried out, for example in air, to obtain reduced and cooled iron ore at a temperature of between 100°C and 150°C.At this temperature, iron ore is easily stored and packaged.

[0075] Advantageously, the operation / O5 / of introducing, into the cooling reactor 77, the cooling gas, which corresponds to the gas separated from the reduced and cooled iron ore, leaving the second gas / particle separation device 76, is now carried out. Thus, the cooling gas in which the reduced iron ore is suspended in the cooling reactor 77 is at least partly made up of the gaseous suspension of reduced iron ore.

[0076] It should be noted that the cooling gas flow is the flow of gas which loops in the cooling device 7 and which is introduced through the inlet 772 of the cooling reactor 77.

[0077] It is advantageous to ensure thermal balance and pressure balance so that the cooling loop circulating in the cooling device 7 is sustainable.

[0078] Thus, it is advantageous, once the cooling loop is produced, i.e. after the introduction operation / O5 / , to implement an operation / O6 / of extracting from the cooling device 7 a portion of the cooled gas to maintain the pressure in the cooling device 7 at a value lower than the ambient pressure, i.e. to maintain a depression in the cooling device 7. The implementation of such an extraction operation / O6 / also makes it possible to compensate, for example, the volume of gas 11 introduced into the reduction reactor 6 and / or the volume of gas introduced into the cooling device 7, in the form of false air, resulting from possible sealing defects in the pipes or equipment.

[0079] The extraction flow rate of the cooling device 7 during the extraction operation / O6 / is regulated via the use of a valve-type member 74, so as to maintain a constant depression in the cooling loop.

[0080] Preferably, this valve-type member 74 is configured to extract cooled reduction gas at the outlet of the ventilation device 73, in the direction of circulation of the gas flows.

[0081] Preferably, an operation / O7 / of sending the extracted cooled gas portion 13 into the calciner 5 is preferably carried out. Thus, the energy released during the combustion of gases such as dihydrogen, carbon monoxide or even gaseous hydrocarbons contained in the cooling gas flow is recovered.

[0082] It is, furthermore, advantageous to implement an operation / O8 / of supplying thermal energy and / or fuel into the cooling loop of the cooling devices 7 as illustrated in figures 2 and 3. This supply is a localized supply in the cooling loop and carried out punctually. By proceeding in this way, an increase in oxygen in the gas flows circulating in the cooling loop is avoided.

[0083] Furthermore, such an operation / O8 / of supply makes it possible to consume oxygen contained in the gas flow circulating in the cooling loop and mainly supplied by the false airs. Advantageously, as can be seen in figures 2 and 3, the cooling loop then comprises a means 78 for supplying thermal energy and / or fuel in the cooling loop arranged between the first gas / particle separation device 71 and the first cooling means 72. Preferably, the outlet 1204 of the first gas / particle separation device 71 is then connected to the inlet 782 of the supply means 78 and the outlet 784 of the supply means 78 is connected to the inlet 722 of the first cooling means 72. It should be noted that the quantity of fuel introduced into the supply means 78 is higher according to the embodiment illustrated in laque in that illustrated in.For example, through a specific inlet 784 of the supply means 78, a thermal supply in the form of a flame or an electric heater, or possibly an additional supply of fuel, is introduced into the supply means 78 so as to raise the temperature of the cooling gas, with a view to consuming the oxygen present in the gaseous flows by reaction with the carbon monoxide (CO) and the dihydrogen (H2) present in this cooling gas. Thus, the oxygen present in the gaseous flows circulating in the cooling loop is consumed. This ensures that the volume concentration of dioxygen in the cooling gas is maintained at a value of less than 2%, and preferably substantially equal to 0% to obtain a neutral atmosphere in the cooling loop.

[0084] According to another exemplary embodiment as illustrated in the, the reduction step / E4 / is initiated in a reduction reactor 600 which is, preferably, a suspension reactor type reactor in which the calcined iron ore is maintained within it for a duration of less than 10 seconds. The reduction reactor 600 comprises in particular a reduction gas inlet 601 through which reduction gas is injected. After passing through the suspension reduction reactor 600, reduced iron ore containing iron II oxides and / or triiron tetroxides suspended in a reduction gas flow is obtained at the outlet 603 of the reduction reactor 600. The iron ore suspended in the reduction gas flow then enters the first gas / particle separation device 71.

[0085] As can be seen in the, before the implementation of the operation / O3 / of cooling the reduced iron ore which leaves through the material outlet 716 of the first gas / particle separation device 71, the separated reduced iron ore obtained after the operation / O1 / which then leaves through the material outlet 716 of the first gas / particle separation device 71 is sent to a complementary reduction reactor 79.

[0086] The complementary reduction reactor 79 is configured to maintain the reduced iron ore for residence times greater than 10 seconds and up to 10 minutes, preferably up to 5 minutes or even up to 2 minutes, under optimal reduction conditions. For example, the complementary reduction reactor 79 may be of the static reactor type, a fluidized bed reactor or even a rotating reactor. The complementary reduction reactor 79 makes it possible to process iron ore defined by high iron contents or to work at lower temperatures while reducing the consumption of reduction gas.

[0087] The inlet 792 of the complementary reduction reactor 79 is then connected to the material outlet 716 of the first gas / particle separation device 71. In this complementary reduction reactor 79, a complementary reduction operation is then implemented, further comprising a complementary operation of bringing the reduced iron ore into contact with a complementary reduction gas which contains hydrogen atoms. This complementary reduction operation makes it possible to complete step E4) of reducing the iron ore. The complementary reduction gas is injected into the complementary reduction reactor 79 via a gas inlet 796. Preferably, the complementary reduction gas is identical to the reduction gas injected into the reduction reactor 6. In another exemplary embodiment, the reduction gas and the complementary reduction gas are different but are both configured to reduce the iron ore.

[0088] It should be noted that during the additional reduction operation, a portion of the additional reduction gas injected into the additional reduction reactor 79 can naturally flow towards its inlet 792. According to an exemplary embodiment, the portion of the gas which flows towards its inlet 792 is then introduced into the first gas / particle separation device 71 via its material outlet 716 to mix in the first separation device 71. Thus, additional reduction gas from the additional reduction reactor 79 can then mix with the reduction gas introduced into the first gas / particle separation device 71 via its inlet 712, this mixture then being sent to the first cooling means 72.According to another exemplary embodiment, the part of the gas which heads towards its inlet 792 is sent upstream of the first gas / particle separation device 71 in the reduction gas flow leaving the reduction reactor 600. According to yet another exemplary embodiment, the part of the gas which heads towards its inlet 792 is sent into a complementary gas / particle separation device, of the cyclone type, the separated part of the particles which emerges therefrom is sent into the reduction gas flow separated from the reduced iron ore leaving the first gas / particle separation device 71, while the reduced iron ore is sent into the second cooling means 75.

[0089] Then, according to the embodiment illustrated in the, the iron ore leaving the additional reactor 79 is introduced into the second cooling means 75 via its material inlet 754 in the same way as in the embodiments described above.

[0090] As can be seen in the embodiment illustrated in, the gas leaving through the gas outlet 764 of the second gas / particle separation device 76 passes into a heating means 78, in particular which passes through it from its inlet 782 to its outlet 784. The heating means 78 is configured to heat the gas flow leaving the second gas / particle separation device 76 before introducing it into the reduction reactor 600. The heating means 78 is preferably arranged at the level of the fluidic conduit which connects the gas outlet 764 of the second gas / particle separation device 76 and the gas inlet 604 of the reduction reactor 600. For example, as heating means, mention may be made, without being limited to this example, of an electric heating device which is capable of being arranged on the periphery of the fluidic conduit connecting the second gas / particle separation device 76 to the reduction reactor 600.

[0091] The units and processes described above advantageously make it possible to obtain an iron ore defined by a high concentration of magnetic compounds, in particular triiron tetroxide, using a small quantity of reduction gas because a portion of this reduction gas is recycled. Furthermore, this installation and this process make it possible to improve the reduction of iron III oxides because the contact of the calcined iron ore with the reduction gas is maintained for a prolonged period during certain steps of the process implemented in the unit described above. In addition, this process makes it possible to increase the energy efficiency of the reduction process because the reduction step is carried out at lower temperatures compared to those of a process using liquid reagents.

[0092] Furthermore, the unit and process described above make it possible to optimize natural resources by processing all types of iron ores with high ignition loss. They also make it possible to reduce waste by improving magnetic separation thanks to the reduction of hematite in favor of magnetic compounds, for example triiron tetroxide, and to improve the strength of the pellets by reducing porosity, this reduction in porosity being induced following the implementation of the calcination step.

Claims

A method of treating an iron ore to increase its mass concentration of magnetic compounds, the method comprising the following steps: / E1 / providing an iron ore containing particles having a particle size of less than 2 mm, / E3 / calcining the iron ore in a calciner (5) to obtain a calcined iron ore containing iron III oxides, the calcination step / E3 / being carried out under stoichiometric or oxidizing conditions, / E4 / reducing the iron III oxides present in the calcined iron ore, the reduction step / E4 / being carried out by injecting, into a reduction reactor (6) separate from the calciner (5), a reduction gas (11) containing hydrogen atoms and brought into direct contact with the calcined iron ore to obtain a reduced iron ore comprising iron II oxides and / or triiron tetroxides, / E5 / cooling, under a reducing or neutral atmosphere,said reduced iron ore to lower its temperature below a threshold temperature to prevent reoxidation of iron II oxides and / or triiron tetroxides., Method according to claim 1, in which the iron ore supplied in supply step / E1 / comes from prior grinding carried out in a grinding device (2), and preferably from drying, during a grinding step / E0 / , and preferably from drying. Method according to one of claims 1 or 2, further comprising, between the supply step / E1 / and the calcination step / E3 / , a step / E2A / of drying the iron ore in a drying device during which the humidity level of the supplied iron ore is reduced to a humidity level of less than 5%, preferably less than 1%. Method according to one of claims 1 to 3, further comprising, between the supply step / E1 / and the calcination step / E3 / , a step / E2B / of preheating the iron ore in a preheater (3) during which the temperature of the iron ore is increased to a preheating temperature of between 400°C and 700°C. Method according to one of claims 1 to 4, in which during the calcination step / E3 / , the temperature of the iron ore introduced into the calciner is increased to a calcination temperature equal to 950°C, preferably between 700°C and 900°C. Method according to one of claims 1 to 5, in which the reducing gas (11) comprises dihydrogen and / or carbon monoxide. A method according to claim 6, wherein the reducing gas (11) contains:- dihydrogen and carbon monoxide, or- dihydrogen. Process according to claim 7, in which the quantity of reduction gas injected in the reduction step / E4 / corresponds to a quantity of between 0.33 and 3, preferably 0.4 to 1, moles of reactants per mole of iron III oxide present in the calcined iron ore. Method according to one of claims 1 or 8, wherein during step / E5 / of cooling said reduced iron ore, the temperature of the reduced iron ore is lowered below a threshold temperature of between 200°C and 600°C, preferably between 350°C and 500°C. Method according to one of claims 1 to 9, further comprising, after the cooling step / E5 / , a final cooling step / E6 / in an air cooling device (8) during which the temperature of the reduced iron ore is lowered to a temperature below 150°C, preferably below 60°C. Method according to one of claims 1 to 10, further comprising, after the cooling step / E5 / , a step / E7 / of magnetic separation of the reduced iron ore in a magnetic separation system (9) to remove the magnetic molecules containing iron atoms or the magnetic mineral species containing iron atoms from the reduced and cooled iron ore (14).

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