A method to produce reduced iron

Abstract

A method to produce reduced iron comprising the step of providing an iron material (1) comprising at least 5% by weight of iron oxides, subjecting this iron material (1) to a thermal treatment at a temperature from 600 to 700°C to reduce the iron oxides to magnetite using a reducing bio-syngas (3), separating magnetite from the remaining part of the iron material using a magnetic separation process to obtain a magnetite concentrate (6), said magnetic separation step being performed at a temperature below 585°C, reducing the magnetite concentrate (6) to iron.

Description

A method to produce reduced iron

[0001] The invention is related to a method to produce reduced iron.

[0002] Iron ore is one of the main materials used in steelmaking production. According to the World Steel Association, on average, it takes around 1.6 tonnes of iron ore to produce one tonne of steel rebar. This amount varies depending on the specific production process and the quality of the iron ore used.

[0003] More and more steel scrap is now being used to reduce the amount of hot metal used in the steelmaking process and thus the environmental footprint of the process, but there is a limit to the production of high-quality steels that require low impurities and therefore still rely on the use of iron reduction processes.

[0004] The quantity of high-grade irons (iron content greater than 62 %) available in the existing mines tends to decrease and thus more and more treatments are needed to get iron ore with the appropriate characteristics for the reduction processes, this is called the beneficiation process. This beneficiation process produces tailings, and the lower the quality of the iron ore, the more tailings are produced.

[0005] Those tailings are usually landfilled and the iron oxides they contain are lost.

[0006] There is so a need for a method allowing to produce reduced iron from low quality iron containing materials, such as low iron grades or iron ore tailings.

[0007] This problem is solved by a method according to the invention, comprising the steps of providing an iron material comprising at least 5% by weight of iron oxides, subjecting this iron material to a thermal treatment at a temperature from 600 to 700°C to reduce the iron oxides to magnetite using a reducing bio-syngas, separating magnetite from the remaining part of the iron material using a magnetic separation process to obtain a magnetite concentrate, said magnetic separation step being performed at a temperature below 585°C and reducing the magnetite concentrate to iron.

[0008] The method of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations: the iron material is chosen among low-quality iron ore, iron mine tailings, run of mine iron, mill sludge and electric arc furnace dust, before the reduction step D, the magnetite concentrate is subjected to an agglomeration step,the agglomeration step comprises the mixing of the magnetite concentrate with a carbon source, the carbon source is a renewable carbon source, the method comprises a step of pyrolyzing biomass to produce a biochar, a reducing bio-syngas and a pyrolysis oil, the reducing bio-syngas being at least partly used in the thermal treatment step, the renewable carbon source is the biochar produced in the pyrolysis step, the biochar and the magnetite concentrate are further mixed with a binder comprising a pyrolysis oil before the agglomeration step, the reducing bio-syngas preferably comprises from 15% to 30% in volume of carbon monoxide CO, from 20% to 45% in volume of H2, remainder being methane CH4, nitrogen N2 and carbon dioxide CO2.

[0009] Other features and advantages of the invention will be apparent from the description of the inventions given below by way of an indication, and which is in no way restrictive, with reference to the appended figures in which:Figure 1 illustrates a first embodiment of a method according to the invention, Figure 2 illustrates another embodiment of a method according to the invention.

[0010] Elements in the figures are illustration and may not have been drawn to scale.

[0011] In the method according to the invention as illustrated in Figure 1 , an iron material 1 comprising at least 5% by weight of iron oxides is provided. By iron content it must be understood content of iron under its various oxidized forms such as hematite Fe2Os, magnetite FesC goethite FeO(OH), limonite FeO(OH)n(H2O) or siderite FeCOs or a mixture of those different oxides.

[0012] This iron material 1 may be low-quality iron ore, run of mine iron, iron tailings, mill sludge. Run Of Mine or "ROM" means ore in its natural, unprocessed state. ROM means ore from source prior to processing. It is the unprocessed mined material which consists of the soil and rock of overburden, minerals, middling, contamination, and impurities.

[0013] The iron material 1 is subjected to a heat treatment step, also called roasting step, in a furnace 2, preferably a Rotary Heart Furnace (RHF). This heat treatment step is performed at a temperature from 600 to 700°C under a reducing atmosphere to reduce iron oxides to magnetite. The reducing atmosphere is created by the injection ofa reducing bio-syngas 3 in the furnace 2. This heat treatment step is preferably performed for a duration of at least 1 hour.

[0014] The heat treatment step is performed at a temperature from 600 to 700°C in order to have the reduction reaction to occur, while remaining at solid state for the subsequent separation step.

[0015] Most present iron oxide present in the iron material is usually hematite which is reduced to magnetite according to following reaction:3Fe2O3 + CO^2Fe3O4 + CO2

[0016] The CO which acts as a reducing agent in the reaction is provided by the reducing bio-syngas 3. A reducing bio-syngas is a syngas produced from renewable sources, such as biomass. Biomass is renewable organic material that comes from plants and animals. Biomass sources for energy include wood and wood processing wastes — firewood, wood pellets, and wood chips, lumber and furniture mill sawdust and waste, and black liquor from pulp and paper mills, agricultural crops and waste materials — com, soybeans, sugar cane, switchgrass, woody plants, and algae, and crop and food processing residues, biogenic materials in municipal solid wastepaper, cotton, and wool products, and food, yard, and wood wastes and animal manure and human sewage.

[0017] It may be produced by pyrolysis of biomass, by reforming of a biomass gasification gas or by steam gasification of biomass-derived oil. The reducing biosyngas has two main components carbon monoxide CO and hydrogen H2.

[0018] Use of this reducing bio-syngas allows reducing the carbon footprint of the process.

[0019] The resulting reduced iron material 4 is then subjected to a magnetic separation step in a magnetic separation device 5 allowing to separate the magnetite from the remaining part of the iron material to get a magnetite concentrate 6. This remaining part 7 mainly consists of silica, and alumina but may also contain heavy metals such as cadmium, chromium, arsenic, and mercury.

[0020] The person skilled in the art is able to determine the intensity of the magnetic force to be applied to separate the magnetite from the other components.

[0021] This magnetic separation step is performed when the resulting reduced iron material 4 has a temperature below 585°C. This temperature is the Curie point of magnetite, above this temperature the magnetite loses its magnetic properties, and the separation is thus not possible.

[0022] The magnetite concentrate 6 thus obtained is then subjected to a further reduction step in a reduction furnace 8 to reduce magnetite to iron and obtain a reduced iron product 9. This reduction step may be performed in a standard DRI furnace such as a Midrex® or HYL® furnace, preferably operated with hydrogen as reducing gas.

[0023] By performing the first reduction step of iron oxides to magnetite and performing the magnetic separation step it is possible to obtain a magnetite concentrate which is suitable for the usual direct reduction processes. This allows to valorize the iron content of the iron material which would have been lost otherwise.

[0024] Depending on the particles size of the magnetite concentrate, an agglomeration step may be necessary before the reduction step.

[0025] This agglomeration step may include the mixing of the magnetite concentrate 6 with a carbon source, preferably a renewable carbon source and the agglomeration of the mixture. Mixing with a carbon source can have two effects. Carbon can participate in the reduction of the magnetite to iron, but it can also be used to enrich the final reduced iron product, a carbon enrichment that may be required for subsequent steelmaking steps.

[0026] The renewable carbon source may be biomass-based Carbon, e.g., biochar, recycled-carbon including graphite refractory, by-products of graphite materials (breeze), coke breeze, petroleum coke. It is preferentially biochar.

[0027] By biochar it is meant a charcoal that is produced by pyrolysis of biomass in the absence of oxygen.

[0028] In another embodiment of the invention, as illustrated in figure 2, biomass 10 is subjected to pyrolysis in a pyrolysis reactor 11. This pyrolysis of biomass produces biochar 14, a reducing bio-syngas 12 and a pyrolysis oil 13.

[0029] The reducing bio-syngas 12 is then injected into the furnace 2 as reducing gas for the thermal treatment step, it may first have been subjected to a treatment step, such as a reforming step or a separation step to increase its reducing capacity. The reducing bio-syngas 12 preferably comprises from 15% to 30% in volume of Carbon monoxide, from 20% to 45% in volume of H2, remainder being methane CH4, nitrogen oxides NOx and carbon dioxide CO2.

[0030] The biochar 14 may be used as renewable carbon source to be mixed with the magnetite concentrate 6 or with the iron material 1. This allows reducing the carbon footprint of the overall process.

[0031] The pyrolysis oil 13 may at least partly used as a binder into the agglomeration process of the biochar 14 and the magnetite concentrate 6 or the iron material 1 . Binders are added to the material mix when the material mix to be agglomerated would not have sufficient compressive and impact resistance, after agglomeration.

[0032] Use of pyrolysis oil 13 as binder allows recycling a byproduct of the pyrolysis process and thus to further reduce the environmental footprint of the overall process. The pyrolysis oil 13 preferably comes from the production of the biochar used in the mix but may come from other biochar production according to availabilities.

[0033] With the method according to the invention it is possible to produce reduced iron from a low-quality iron material.

Claims

CLAIMS1 ) A method to produce reduced iron comprising the step of:A. Providing an iron material (1 ) comprising at least 5% by weight of iron oxides,B. Subjecting this iron material (1 ) to a thermal treatment at a temperature from 600 to 700°C to reduce the iron oxides to magnetite using a reducing bio-syngas (3),C. Separating magnetite from the remaining part of the iron material using a magnetic separation process to obtain a magnetite concentrate (6), said magnetic separation step being performed at a temperature below 585°C,D. Reducing the magnetite concentrate (6) to iron.2) A method according to claim 1 wherein the iron material (1 ) is chosen among low-quality iron ore, iron mine tailings, run of mine iron, mill sludge and electric arc furnace dust.3) A method according to claim 1 or 2 wherein before the reduction step D, the magnetite concentrate (6) is subjected to an agglomeration step.4) A method according to claim 3 wherein the agglomeration step comprises the mixing of the magnetite concentrate (6) with a carbon source (14).5) A method according to claim 4 wherein the carbon source (14) is a renewable carbon source.6) A method according to anyone of the previous claims comprising a step of pyrolyzing biomass (10) to produce a biochar (14), a reducing bio-syngas (12) and a pyrolysis oil (13), the reducing bio-syngas (12) being at least partly used in the thermal treatment step.7) A method according to claim 6 in combination with claim 5, wherein the renewable carbon source is the biochar (14) produced in the pyrolysis step.8) A method according to claim 7 wherein the biochar (14) and the magnetite concentrate (6) are further mixed with a binder comprising a pyrolysis oil (13) before the agglomeration step.9) A method according to anyone of the previous claims wherein the reducing bio-syngas (3,12) preferably comprises from 15% to 30% in volume of carbon monoxide CO, from 20% to 45% in volume of H2, remainder being methane CH4, nitrogen N2 and carbon dioxide CO2.

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