AU2014364667B2 - Method for pelletizing fine-grained ores - Google Patents

Abstract

The present invention relates to a pelletization of fine-grained ore particles with the following steps: a) mixing the ore particles with water to which surface-active sub¬ stances have been added, b) adding a binder and at least one aggregate for preparing a pelletizing mixture, c) supplying the pelletizing mixture to a pelletizing device, and d) processing the pelletizing mixture in the pelletizing device to obtain pellets by addition of water to which surface-active substances have been added.

Description

Method for Pelletizing Fine-Grained Ores

This invention relates to the pelletization of fine-grained ore particles.

Fine-graind ore particles are obtained in a multitude of processes. On the one hand, larger ore lumps are ground for the production of pig iron, wherein finegrained ore particles are obtained. On the other hand, fine-grained ore particles also are obtained as dusts in the metallurgy. The fine-grained ore material only can be handled with difficulty and therefore is agglomerated, in particular pelletized. For pelletizing, the ore powder is mixed with water on rotating plates or in rotating drums. The moist ore spherules formed thereby are referred to as green pellets. They are dried subsequently and fired at a temperature between 1000 and 1400 °C, before the actual ore reduction is effected.

From EP 1 263 995 B1 a method for agglomerating and sintering iron and zinc ores is known. In this method, finely divided solids are mixed with a fuel and a sinter agglomerating agent and subsequently supplied to a sintering means, wherein for sintering the solids the sinter bed formed is ignited. As sinter agglomerating agent water-soluble polyethers and/or oil emulsions are used. For producing the oil emulsions, surface-active substances are added. DE 25 01 636 C2 describes a method for producing briquettes by mixing anhydrous solids with an aqueous emulsion of an organic, bituminous binder. As emulsifiers, soaps or other surface-active agents can be used. The solids used for briquetting have particle sizes of 0.1 mm to 10 mm. DE 692 30 809 T2 discloses a binder composition and a process for agglomeration of iron containing material. Potassium hydroxide is sprayed onto iron ore concentrate for agglomeration of the same. Subsequently, a polymeric binder is added and the resulting composition is mixed. Finally, the resulting mixture is pelletized to green pellets in a pelletizing device, while atomized water is added. US 4 751 259 A also describes a binder composition for agglomeration of wet, metal ores comprising a water/oil emulsion, a polysaccharide, a surface-active substance and borax. US 5 294 250 A concerns a binder composition suitable for application in a pelletizing device for ore concentrates. The composition comprises a carrier material having a high surface area and a water soluble organic enhancer, in particular a polysaccharide. EP 0 376 713A2 discloses a process and a composition for agglomerating particulate material, wherein a polymeric binder is utilized, which includes polymer particles having a mean particle diameter of more than 100 pm. The polymeric particles are entrained in an aqueous liquid, which is submitted to the materials to be pelletized. The aqueous liquid comprises water or a water/oil emulsion.

In DE 21 09 086 as well, an organic binder is admixed for briquetting fine solids, wherein as binder carbohydrates, in particular sugars, are used. For activation, in particular for increasing the permeativity, of the binders surface-active substances are pre-mixed with the binder. In addition, water can be added to the mixture of solids and binder, which increases the kneadability of the mixture and the moisture content to about 16%.

In contrast to the sintering of fine solids, an accretion of the ore particles to each other is not intended during the pelletization, as otherwise no separate pellets would be formed. Therefore, the demands on the sinter mixture, for example with regard to the addition of fuels or the used binder, are different from those on a pelletizing mixture.

Pellets mostly are more suitable for the further metal processing than sintered materials, since pellets have a higher porosity and hence a larger surface. Due to the larger surface, the succeeding physical and/or chemical processes, for example the reduction of the ores at elevated temperature, proceed distinctly more efficiently.

In some ores, in particular in some iron ores or nickel ores, a green pelletizabil-ity is difficult, since due to the ore properties the agglomeration of the fines is so poor that no pellets are formed, but small and/or shapeless agglomerates with a diameter of few millimeters. Pellets of sufficient quality with a desired diameter of e.g. > 9 mm, round shape, sufficient strength and smooth surface are not obtained.

From the literature described above it is known, for example, to add surface-active substances, in order to increase the wettability of the particles. This addition, however, reduces the strength of the green pellets produced and therefore is avoided in practice as far as possible.

It is also known that the effectiveness of the surface-active substances is decreased by a high water content. This is explained by the fact that the binding of the surface-active substances to the particles competes with the binding of the surface-active substances to the water molecules. Therefore, surface-active substances have been used only in connection with a relatively low water content, in particular of < 20%.

The pelletization of fine-grained ore particles is effected with the following steps: a) mixing the ore particles with water to which surface-active substances have been added, wherein that the amount of surface-active substances in the water is 0.2% to 2%, b) adding a binder and at least one aggregate for preparing a pelletizing mixture, c) supplying the pelletizing mixture to a pelletizing device, and d) processing the pelletizing mixture in the pelletizing device to obtain pellets by addition of water to which surface-active substances have been added, and wherein the amount of surface-active substances in the water is 0.2% to 2%.

In the sense of the present invention, surface-active substances (surfactants) are referred to as substances which decrease the interfacial tension between two phases.

Surprisingly, it has been found that by the two-stage addition of water and surface-active substances pellets with a sufficient size and strength are produced from ores which up to now were regarded as non-pelletizable.

It is assumed that as a cause for the poor pelletizability undesired van der Waals' adhesive forces of the particles among each other primarily are responsible, which are decreased by the use of the surface-active substances.

According to the invention, the amount of surface-active substances in the added water is 0.2% to 2% and preferably about 0.5% to about 1%. The amount of surface-active substances in the water during the first addition of water (to the ore particles) and during the second addition of water (in the pelletizing device) can be the same, but also different. However, the amount always lies within the indicated limits.

In the context of the present invention, all percentages are understood to be mass percent.

According to the invention, cationic, anionic, non-ionic or amphoteric surfactants are considered as surface-active substances. In particular, it was found to be advantageous to use commercially available detergents and preferably dishwashing detergents as surface-active substance.

In accordance with a development of the invention, the added binder is bentonite which preferably is added in an amount of up to 2.5%, preferably of 1.5 to 2.5%, in particular about 2% of the finished pelletizing mixture. Said amounts of bentonite can be used for all fine-grained ore particles.

Particularly preferably, however, amounts of bentonite of 1.5 to 2.5%, in particular about 2%, are used during the pelletization of nickel ores. For iron ores, the amount of bentonite particularly preferably is adjusted to values of 0.5% to 1%, in particular 0.7%.

As aggregate limestone preferably is added, preferably in an amount of up to 10%, preferably 3 to 10%, in particular about 8% of the pelletizing mixture. Other aggregates such as dolomite, anthracite or olivine can, however, also be added.

The second addition of water can be designed particularly effectively, when the water mixed with surface-active substances is sprayed onto a pelletizing plate or into a pelletizing drum of the pelletizing device. This ensures a uniform distribution of the water during the pelletization, whereby particularly uniform pellets are formed.

For the method according to the invention in particular iron ores, for example hematite, magnetite, pyrite, siderite or limonite, but also nickel ores, for example garnierite, kamacite, saprolite ortaenite are suitable as educt.

The water content of the pelletizing mixture should be adjusted to values up to 30%, preferably greater than 15%, preferably between 20% and 30%, and in particular to about 25%. When this water content of the fine-grained ore already is quite high, the addition of water according to the invention can be reduced. The above-mentioned water contents are suitable for all fine-grained ore particles.

It is particularly preferred, however, to adjust the water content during the pelletization of nickel ores to values between 20% and 30%, in particular to about 25%. Among other things, this is due to the fact that nickel ores inherently have a relatively high moisture. For iron ores, water contents greater than 5%, in particular of 8 to 10%, are used particularly preferably.

With the method according to the invention, fine-grained ore particles can be processed, which for at least 50%, preferably for at least 80% have a particle diameter of < 1 mm, preferably < 150 pm, and particularly preferably < 100 pm. Ores which have a mean particle diameter of < 45 pm are particularly preferred, wherein in particular about 80% of the material show a mean diameter of < 45 pm.

For a good further processing, the formed pellets have a mean diameter of > 9 mm, and preferably 16 to 25 mm. Furthermore, the pellets have an almost spherical, in particular round shape, sufficient strength and a smooth surface. Said mean diameters can be used for all fine-grained ore particles.

Particularly preferably, pellets with a mean diameter of 16 to 25 mm are obtained during the pelletization of nickel ores. During the pelletization of iron ores, mean diameters of 12.5 to 16 mm are obtained particularly preferably.

The invention will subsequently be explained in detail with reference to exemplary embodiments. All features described form the subject-matter of the invention per se or in any combination, also independent of their inclusion in the claims or their back-references.

Pelletizing operation

For pelletizing, fine-grained ore particles (about 80% < 45 pm) initially are mixed with water (first addition of water), wherein 0.5 to 1% of surface-active substances, e.g. dishwashing detergents or other surfactants, were added to the water. The amount of added water substantially depends on the water content of the ore used. Subsequently, up to 2.5%, preferably about 1 to 2% of bentonite are admixed as binder, and at least one aggregate, in particular limestone, is admixed in an amount of up to 10%, preferably about 8% (preparation of the pelletizing mixture).

The pelletizing mixture then is supplied to a pelletizing device, in particular onto a pelletizing plate or into a pelletizing drum, and processed there by addition of further water (second addition of water), which in turn contains 0.5 to 1% of surface-active substances, to obtain pellets with a size of up to 25 mm. The added amount of water substantially is determined by the pelletizing operation.

It was found out that an addition of water and surfactants before the pelletization alone is not sufficient, in order to produce satisfactory pellets from the ores according to the invention. Rather, water mixed with surface-active substances also must be supplied again during the pelletization.

Contrary to the prejudice existing in the prior art that an addition of surface-active substances reduces the strength of the pellets, the invention also allows to produce pellets with the desired size, sufficient strength (green strength about 1 to 2 kg/pellet, dry strength up to about 20 kg/pellet), uniform shape and smooth surface from the pelletization of ores not accessible so far. The inventors have refrained from adding organic binders, for example bitumen or carbohydrates, as it is recommended in the prior art.

In the following examples, 17 green pelletizing experiments with 35 kg of green pellets each were carried out. As binder 2% bentonite and as aggregates 4 to 8% limestone as well as 0 to 2% anthracite were added. 0.5% dishwashing detergent containing surfactants were added to the water. After the pelletization, the obtained green pellets were fired at 1000 to 1400 °C.

Example 1: Pelletization of an iron ore

The pelletization was carried out as described above. There was used finegrained limonite (iron ore), wherein the mean diameter of 100% of the particles was <315 pm, and 64% of the particles had a mean diameter of < 45 pm.

Example 2: Pelletization of a nickel ore

The pelletization likewise was carried out as described above. Other than in Example 1, however, fine-grained saprolite (nickel ore) was used, wherein the mean diameter of 100% of the particles was <315 pm, and 54% of the particles had a mean diameter of < 45 pm.

The green pellets produced according to the Examples 1 and 2 had a mean diameter of 16 to 20 mm and their moisture was 23 to 25%. The moisture according to the invention hence was distinctly above the values used in the prior art and surprisingly does not decrease the effectiveness of the added surface-active substances. This was revealed in particular by the fact that without the addition of the surface-active substances no pellets were obtained. The green strength of the pellets was 1.3 to 2.0 kg/pellet and the dry strength 12 to 21 kg/pellet.

After firing, the mean diameter of the fired pellets was 12.5 to 16 mm and the cold compressive strength was 77 to 327 kg/pellet.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims (14)

1. Claims:

   1. A method for pelletizing fine-grained ore particles, with the following steps: a) mixing the ore particles with water to which surface-active substances have been added, wherein that the amount of surface-active substances in the water is 0.2% to 2%, b) adding a binder and at least one aggregate for preparing a pelletizing mixture, c) supplying the pelletizing mixture to a pelletizing device, and d) processing the pelletizing mixture in the pelletizing device to obtain pellets by addition of water to which surface-active substances have been added, and wherein the amount of surface-active substances in the water is 0.2% to 2%.
2. 2. The method according to claim 1, wherein the amount of surface-active substances in the water ranges from 0.5% to 1%.
3. 3. The method according to claim 1 or 2, wherein the surface-active substances are selected from a group consisting of cationic, anionic, non-ionic or amphoteric surfactants.
4. 4. The method according to any one of the preceding claims, wherein the binder is bentonite.
5. 5. The method according to claim 4, wherein up to 2.5% bentonite is added.
6. 6. The method according to any of the preceding claims, wherein the aggregate is limestone.
7. 7. The method according to claim 6, wherein up to 10% limestone is added.
8. 8. The method according to any one of the preceding claims, wherein the water is sprayed onto a pelletizing plate or into a pelletizing drum of the pelletizing device.
9. 9. The method according to any one of the preceding claims, wherein as finegrained ore particles iron ores and/or nickel ores are used.
10. 10. The method according to any one of the preceding claims, wherein the water content of the pelletizing mixture is up to 30%. 11 The method according to any one of the preceding claims, wherein at least 50% of the fine-grained ore particles have a particle diameter of < 100 pm.
11. 12. The method according to any one of the preceding claims, wherein at least 80% of the fine-grained ore particles have a particle diameter of < 100 pm.
12. 13. The method according to any one of the preceding claims, wherein at least 50% of the fine-grained ore particles have a particle diameter of <45 pm.
13. 14. The method according to any one of the preceding claims, wherein at least 80% of the fine-grained ore particles have a particle diameter of <45 pm.
14. 15. The method according to any one of the preceding claims, wherein the size of the pellets produced is > 9 mm.