DE2151911A1 - Process for the production of cold-bound agglomerates from particulate iron ore concentrate - Google Patents

Description

AB Oold-Pound Pellets Djursholm / Sweden

Process for the production of cold-bound agglomerates from particulate iron ore concentrate

The invention relates to a method for the production of cold-bound agglomerates from particulate iron ore concentrate, wherein the iron ore concentrate with an additive containing a binder which is in the It is able to harden to form an embedding compound or matrix in which the iron particles are embedded, mixed before agglomerates are formed from the mixture of ore concentrate and additive and the binding agent is brought to harden. In particular, it is a process for the production of cold-bonded Agglomerates or pellets that have little or no tendency to plating.

Usual agglomerates of particulate iron ore concentrate, such as sintered pellets and lump ore, can usually not economical due to direct reduction

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processes are reduced, i.e. processes in which the iron oxide is reduced without melting at the same time using hot reducing gases rich in carbon monoxide. As a result of the tendency to split or plating tendency of lump ore and agglomerates, i.e. the tendency or tendency of the pieces and agglomerates to cake together, it is when using the Wieberg-Söderfors process for example, it has been necessary to work at temperatures too low to achieve the To make the process economically satisfactory, while still resulting in a low capacity the sponge iron oven results. The plating slopes made of lump ore and common agglomerates it is still impossible to obtain carbon monoside-rich hot gas to reduce lump ore and common agglomerates using the more effective direct reduction processes that have emerged recently, such as for example the so-called fluidized bed processes, in which the Agglomerates are reduced while they are suspended in a fluidized bed. For economic Therefore, directly reduced material can only be used for more theoretical purposes within the steel industry can be used, although for quality reasons it is desirable that directly reduced material be used for mixing with or to replace scrap, e.g. such scrap as it is used in electrical steelmaking processes, in larger than is currently used.

Heretofore, the plating of the agglomerates or lump ore, when this material has been reduced with hot reducing gases rich in carbon monoxide, has been considered inevitable, being particularly troublesome during the reduction step between the wustite phase and the iron phase, especially when this step was carried out at temperatures below 1000 ⁰ O and in particular at temperatures around 925 ⁰ O, ie at temperatures that have hitherto normally been used in practice

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became. It was believed that plating at these temperatures would occur during the reduction step or steps Reduction stage between the wüstite phase and the iron phase is caused in particular by the fact that on the iron oxide particles in the lump ore or the agglomerates protruding iron layers are formed in particular as a result of the permeability of the particles to that during the reduction process formed carbonic acid gas is only very low, and that the nucleus or crystal nucleus formation is uneven during the precipitation of iron, whereby the partially reduced iron oxide particles one rough, fissured, burr-like surface preserved, often accompanied by excessive swelling or swelling Particle growth.

The invention is based on the object of a new and economical process for the production of agglomerates create from particulate iron ore concentrate, removing the iron oxide particles during the reduction process should be so permeable to carbon dioxide, and such a finely divided nucleus or crystal nucleus formation when reducing pure iron should have that the agglomerates are free from plating tendencies or only show extremely slight plating tendencies, so that they thereby in an advantageous manner directly by means of hot reducing gases can be reduced, and even those gases that are rich in carbon monoxide.

To achieve this object, the method according to the invention is characterized in that an additive is used which comprises a substance which contains at least one of the metal compounds MgO, MnO, Al ₂ O, and TiO ₂ in such amounts and in such a form that at the reduction of iron oxide in the agglomerates in one does not

below SOO ⁰ C lying temperature at least a part of the

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metal present in the metal compound can diffuse into the iron oxide.

The agglomerates can be calf bonded using the method according to the invention by three different methods, namely a) by using essentially Ca (OH) ₂ as a binder, the agglomerates being hardened by carbonic acid saturation of the slaked lime with COp-containing gases, b ) by essentially using cement or blast furnace slag as a binder, the agglomerates being formed by self-hardening of the cement or the blast furnace slag at relatively low temperatures, such as ambient temperatures, and c) by essentially using a binder which, when the agglomerates treated with steam at elevated temperature and under elevated pressure, forms a solid embedding mass or matrix that embeds the iron oxide particles in the agglomerates, for example such binders as slaked lime, slaked slag, cement or mixtures thereof are used, preferably with additives v on gait and finely divided silica.

Despite the fact that any of the three above-mentioned cold bonding methods can be used in the present context, the last-mentioned cold bonding method is preferred when carrying out the method according to the invention, ie the method according to which the uncured agglomerates with the hydratable binder constituents are in the slaked state and preferably after pre-drying of the agglomerates with steam normally at a temperature of about 160 - 23O ⁰ C at a pressure of about 10-70 atm about 1-20 hrs are treated for.. Both the self-hardened agglomerates bound by carbonic acid saturation and those by the cement or

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The agglomerates bound to the blast furnace slag have a much lower mechanical strength at higher temperatures, for example temperatures in the range of 700-1000 ⁰ O, than the steam-hardened agglomerates. In the case of steam-hardened agglomerates, a smaller amount of binding agent is also required, since the gangue contained in the iron ore concentrate and also a certain amount of the iron oxide in the additive, if iron oxide is present in it, and a certain amount of the iron ore concentrate especially if the starting material for the agglomerates have been strongly ground, can be made to react chemically with the binder and dissolve therein, namely during the steam hardening process, in order to provide an active part of the binding phase with regard to the binding aspect in the form of, for example, iron calcium hydrosilicate, iron hydrosilicate and calcium ferrate contain. In other words, this means that part of the binder substance comes from the material to be agglomerated. Magnetite and partially reduced iron oxide, such as wustite, have a particularly pronounced tendency to react in a finely divided state with the binder, so that for this reason they are preferably used as constituents of the additive.

Those selected from the group MgO, MnO, AloO * and TiOp Metal compounds that are used according to the present invention can be in the additive in proportion in small amounts, provided that they are in a suitable reactive form. So can the necessary amount in the very small one On the order of 0.1 - 1 #, based on the dry weight of the additive, provided that these compounds are present as a solid solution in a finely divided

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th iron oxide material is present, which reads with the additive and preferably also with the egg ore concentrate was married together. The mentioned metal compounds also provide the desired anti-plating properties Effect when in a free form and in a hydrate or hydrosilicate bound Form and finely divided in the additive, although in this case the required one The amount of these compounds is usually ten millimeters greater, as if the compounds mentioned as a solid solution

P are present in a finely divided iron oxide material, which is attached to the additive. Silicate-bonded metal compounds of the type mentioned, for example MgO in Blast furnace and steel furnace slag, as well as AIpO, in cement, do not lead to the desired anti-plating effect because they are stably bound. In this context it should be mentioned that the anti-plating Effect, of course, cannot be obtained in sintered agglomerates, as in the case of sintered agglomerates all reactions that affect the surface of the iron oxide particles and the crystal lattice, already during of the sintering process have taken place and therefore no influence on the reduction process of the agglomerates

When carrying out the process according to the invention, the metal compounds MgO, MnO, AlpO, and TiO ₂ should therefore either alone or in a mixture, preferably in the form of a solid solution in finely divided iron oxide, preferably in magnetite or partially reduced iron oxide, such as wustite, or be present in the free, hydrated or hydrosilicate-bound form, or in a combination of these forms. When the metal compounds are present in these forms, they are capable of reducing the agglomerates with carbon monoxide-rich gas and at elevated temperatures to the ferric oxide particles penetrate, whereby these compounds etch the surface of the iron oxide particles or form pores therein, at the same time the finely distributed

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Nucleus or crystal nucleus formation is increased when the iron oxides are reduced to pure iron. So far it is not yet known whether the metal compounds MgO, MnO, AlpO, and TiOp penetrate into the iron oxide particles in their entirety or whether it is only the metals of these compounds that penetrate these particles. It is probable that the metal compounds mentioned _{diffuse in magnetite as MgO, HnO, Al 2} O ₅ and IDiO ₂ , while the situation is even more in the dark when the iron oxide has reached the wustite phase. The agglomerates produced by the process according to the invention have a high reducing power.

The required amount of the metal compounds mentioned depends to a certain extent on the composition of the additive in general and on the composition of the iron ore concentrate and the composition and temperature of the gas used to reduce the hardened agglomerates, the amount of metal compounds decreasing with increasing reduction temperature. The amount of metal compounds required to achieve the desired effect can, however, be determined for the individual case by experiments on a small industrial scale. The ability of the metal compounds mentioned to penetrate the iron oxide in the agglomerates at reduction ^{temperatures below 800 °} C. is of secondary importance, since it can be assumed that plating problems as a result of a burr-provided surface of the partially reduced iron oxide particles do not occur below this temperature. Furthermore, there are no surfaces provided with burrs with the resulting plating problems on the ferrous oxide particles in the agglomerates when they are reduced with gases which are rich in carbon monoxide and at very high reduction temperatures of, for example

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over 11üü ° C.

Since the agglomerates produced by the method according to the invention are primarily by means of hot reducing gases should be reduced, for which a low gas resistance together with a large contact area between Reduction gas and agglomerates in the furnace used for the reduction process "are advantageous, have the agglomerates or pellets, preferably a substantially spherical shape of substantially uniform size.

In order to ensure that the agglomerates are sufficiently firm for transport so that they do not disintegrate when they are transferred from the agglomeration plant to the reduction plant and also have sufficient strength during the reduction so that they do not disintegrate during the reduction process, it is often necessary to take certain measures. The particle size of the starting material from which the agglomerates are produced should preferably be selected in such a way that a close packing of the particles is obtained in the agglomerates, specifically in such a way that the porosity of the agglomerates is below 0.3. Thus, a suitable degree of compaction may, for example be obtained by using as the starting material is about 50-80 wt .- ^ is used a * normal, coarse-grained iron ore concentrate from which, for example, 80 wt .- ^ a core size of less than 0.2mm, while the remaining additive , comprising iron oxide material, binder and at least one of the metal compounds MgO, MnO, Al ₂ O ₅ and TiO _{2 is present} with a finer grain size than the mineral concentrate, for example 80 wt .- $ below 0.06 mm or even more fine-grained is. The best degree of compaction is obtained when the additive makes up about 25-35 # of the total particle volume of the starting material.

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The binder may preferably be in an amount of about 3-10 percent by _e - #, or about 6-20 vol .- # of the starting material to be present, while, as already mentioned, the minimum amount in which the metal compounds MgO, mho, Al ₂ O, and! DiO ₂ are present, depends on their shape. From the point of view of mechanical strength and reduction resistance, it is also advantageous to ensure that the binder is firmly adhered to the surfaces of the iron oxide particles in the iron ore concentrate and the additive. With regard to the heat resistance of the binder matrix which surrounds the iron ore concentrate particles in the agglomerates, it is also advantageous to add a relatively high proportion of magnesium, for example free or silicate-bound MgO, to the binder. In addition, finely divided gangue and finely divided SiO ₂ , in particular extremely finely divided silicon dioxide, such as silicon dust from silicon iron production processes, can advantageously be added to the binder in order to improve the adhesion of the binder to the surfaces of the iron oxide particles.

As already mentioned, it is essential that the metal compounds MgO, MhO, Al ₂ O, and TiO ₂ and, in the case of steam-hardened agglomerates, the binder are present in the additive in such a reactive form that the reaction with the iron oxide particles is facilitated . Such a reactive form is obtained to a certain extent that these substances are finely ground either alone or in a mixture, a joint, preferably intensive joint grinding of the constituents in the additive is preferable, since in this case a relatively extensive chemical reaction between the Components in the additional

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substance takes place. The extent to which the mentioned chemical reaction takes place can be increased if the mixture or the mixture by means of a high-energy comminution or grinding process of the constituents is produced, vibrating mills being found to be particularly advantageous for this purpose to have; the mill should preferably be supplied with an amount of energy of about 10-40 kWh per ton of additive. The constituents that are ground together in this way and form the additive are then mixed with the iron ore concentrate preferably entered mixed in a rod mill.

The quenching of the hydratable constituents of the binder can take place at any point in time prior to the hardening of the agglomerates be carried out, although it is advantageous that the quenching takes place during the co-grinding of the Ingredients in the additive is carried out, at least when difficult to use in the binder quenching material such as MgO is present. A certain amount of post-erasing can after the common The grinding process may be allowed by keeping the additive in a moist state for a period of for example stored for a few days or more.

The plating tendency of the agglomerates can also be reduced by coating the agglomerates with a powdery Material rich in MgO can be coated. This coating or dusting should preferably be in a final stage of the agglomeration process or immediately afterwards, while the uncured Agglomerates are moist. The coating material in which the hydratable constituents are in the extinguished state should be present, can be dusted on the uncured agglomerates, or the agglomerates can be in

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the coating material are rolled. When the agglomerates are subsequently steam cured, the coating material adheres adheres to the agglomerates and forms an essential refractory layer around them.

1-3 each show a small section of a steam-hardened agglomerate of particulate iron ore concentrate, which is partially reduced ^{at about 95O 0 G, to illustrate the method according to the invention.}

I ¹ Ig. 1 shows the typical appearance of a partially reduced iron oxide particle that is embedded in a conventional binder which does not contain the additive described in connection with the method according to the invention. The central portion of the particle comprises wustite and is surrounded by protruding layers of pure iron which give the particle a rough, burr-like surface and give rise to plating problems.

Figures 2 and 3 show a number of particles and give the typical appearance of partially reduced Iron ore particles in agglomerates again, which are produced by the method according to the invention. the bright surface sections of the in Pig. Particles shown in Figure 2 comprise pure iron and have a porous and gas-permeable form, while the darker central areas of the particles are in the form of a desert. In Fig. 3 »at which the larger particles a light colored outer layer of pure iron in a porous gas-permeable Form that surround a darker central section made of wüstite, the reduction has already progressed further, creating a larger part of the central section of the largest partially reduced iron oxide particle has been reduced to iron in a similar porous form

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is. The partially reduced iron oxide particles according to FIGS. 2 and 5 have no plating tendencies that originate from rough or burr-like surfaces.

The advantages achieved by the process according to the invention are described below with the aid of two examples.

example 1

A starting material intended for the production of agglomerates from particulate iron ore concentrate was produced by adding 80% by weight of hematite ore concentrate, 80% by weight of which has a grain size of less than 0.2 mm, and 20% by weight of additive in a rod mill were mixed, which consisted of a jointly intensively ground mixture of equivalent parts by weight of slaked lime and hematite ore concentrate. The particle size of the additive was 80 wt .- # below 0.04 mm. The starting material was pelletized and the pellets were cured by placing them were treated 6 hrs. In an autoclave with steam at a temperature of about 200 ⁰ O. After reducing the pellets at about 95O ⁰ O with a gas having a composition substantially simulating a blast furnace, the pellets showed pronounced plating tendencies and were swollen to an extent well above the normal swelling of about 15 vol. $ as is inevitable in the transition from hematite to magnetite.

Example 2

The pellets were produced according to the procedure described in Example 1, but with the difference that that the iron oxide material in the additive is a magnetic

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Iron ore concentrate containing about 0.2 wt% MgO and about 0.3 wt% TiO ₂ in solid solution. When the pellets were reduced in the manner described in Example 1 ", they showed only a very slight tendency towards plating. No swelling or enlargement could be observed which was greater than that caused by the transition of the hematite to magnetite. The reduction strength of the pellets obtained exceeded the reduction strength of the conventional sintered pellet several times, and its reduction strength was also considerably higher than that of the sintered pellets.

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Claims (6)

Claims 1. Process for the production of cold-bonded agglomerate en from particulate iron ore concentrate, where the Iron ore concentrate with an additive that contains a binder that is capable of making an embedding compound or to harden matrix in which the iron ore particles are embedded, is mixed before the Mixture of ore concentrate and additive agglomerates are formed and the binding agent hardened is, characterized in that an additive is used which comprises a substance the at least one of the metal compounds MgO, MnO, AlgO, and IiOg in such amounts and in such amounts Form contains that in the reduction of the iron oxide in the agglomerates at a temperature not below 800 ° 0 at least some of the metal present in the metal compound can diffuse into the iron oxide. 2. The method according to claim 1, characterized in that the additive by intensive joint grinding of the binding agent, iron oxide material and the additional substance is produced. 3. The method according to claim 1, characterized in that that for the production of the additive, the binder and the iron oxide material in which this If the substance is present as a solid solution, it must be grinded together intensively. - 15 209817/0987 4. Method according to claim 2 or 3, characterized in that that the joint grinding process in a high-energy crushing stage, is preferably carried out in a vibrating mill. 5. The method according to any one of claims 1-4, characterized in that the agglomerates with a material rich in MgO. 6. agglomerates which are produced by the method according to any one of claims 1-5. 209817/0987 Blank page