AU656060B2 - Iron-making sintered ore produced from pisolitic iron ore and production thereof - Google Patents

Description

OPI DATE 03/09/93 AOJP DATE 11/11/93 APPLN. ID 35743/93 ~II1111 111 II1111 I PCI NUMBER PCT/JP93/00 184 ilI i if 1111I 1)11ii AU9335743 C22B 1/00, 1/16 Al (4 3) rI 731 ign El 193'1afl19U (19.08,1993) (21)kjM- POT/JP93/00184 (22) fijbA 19934-2,912B(12. 02, 93) %Yc- .9 4/5 881 3 19924:2)13EI(13, 02. 92) IP 6 5 6 0 6 (71) ffiMA ~8~~aNIPPON STEEL CORPORATION) IJP/JP) 71 00-71 Tokyo, (JP) (72) RBA )fI(HIDA, Yukihi ro) RP~ fl(OKAZAKI, Jun) MBtJ1E)HOSOTAN 1, Yo zo) Aichi. (JP) (74) ft31A Tokyo, (JP) AU, JP, KR.

(54) Title :IRON-MAKING SINTERED ORE PRODUCED FROM PISOLITIC IRON ORE AND PRODUCTION

THEREOF

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Is X 0 0 00 oX. X9~c( 00X 0 04 0) 6 IX 40~ X X 0 a" X XO0 0 X 0c 0 X0 I 1 000 .000 a Slag content b Content of fine calcium ferrite with width of 10 umn or less (57) Abstract c Content of SiOa in Iron ore An iron-making sintered ore having a cross section wherein at least 80 of a solid part except for non fused residues of the sintering materials other than pisolitic iron ore is composed of a densified pisolitic iron ore enclosed by Fine calcium ferr ite with a width of 10 gim or less, or of hematite particles and calcium ferrite which bonds the hematite particles together while holding traces of the pisolitic iron ore, or of a mixture thereof. The production process comprises sintering iron-containing starting material such as iron ore, carbonaceous material, water, and the like in a sintering m~achine by using 40-70 mass of pisolitic iron ore and a high-grade iron or containing 1.5 mass or less Of SiO 2 as the iron-containing starting material other than returns.

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DESCRIPTION

Iron Ore Sinter for Ironmaking Using Pisolitic Iron Ore as Raw Material and Process for Producing the Same TECHNICAL FIELD The present invention relates to an iron ore sinter for a blast furnace ironmaking process using a pisolitic iron ore as raw material and a process for producing the same.

BACKGROUND ART A sintered ore as a major raw material for a blast furnace ironmaking process is generally produced as follows. At tie outset, CaO-containing sub raw materials (hereinafter referred to as "CaO sub raw materials"), such as limestone and dolomite and a converter slag, Si02-containing sub raw materials (hereinafter referred to as "SiO 2 sub raw materials"), such as serpentine, silica rock and peridotite, and carbonaceous materials, such as coke breeze and anthracite, and further a suitable amount of water are added and mixed with an iron ore fines having a particle size of about 10 mm or less, and the mixture is granulated. The raw mix in the form of pseudo-particles thus obtained is packed onto a pallet in a sintering machine provided with a movable grate to a height of about 500 mm, and carbonaceous materials on the surface layer portion of the packed bed are ignited. The carbonaceous materials are burnt while drawing air downward, and the raw mix is sintered by taking advantage of combustion heat generated at that time. The resultant sinter cake is crushed and subjected to particle size regulation, and particles of 3 to 5 mm in size are charged as an iron ore sinter into a blast furnace. In this case, sintered ore fines unsuitable as a raw material to be charged into the blast furnace are called

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"return sinter fines" and returned as a raw material for the iron ore sinter.

The use of a high-quality iron ore sinter is necessary for stably operating the blast furnace with a high efficiency, and strict quality control has been effected with respect to cold strength, reducibility, resistance to reduction degradation, etc. Further, a high yield (a sinter product/a sinter cake) has been desired from the viewpoint of the production cost of the sintered ore.

With respect to ore resources in the world, there is a tendency that hematite ores deposits having a good quality, which have been mainly used in the art, are exhausted. It is expected that continuation of current production of the supply of the hematite ores will come to an end early in the next century. On the other hand, there is a kind of an iron ore having an Si02 content of to 6% that belongs to the category of pisolitic iron ores. Representative examples thereof include Robe River and Yandicoojina native to Australia. The deposits thereof are advantageously abundant in reserves, low in mining cost by virtue of a low proportion of a low-grade portion (a soil stripable ratio) to be removed for mining and stable in supply. Therefore, the use of this iron ore in a large proportion in the raw materials is very advantageous from the viewpoint of not only profitability but also of effective use of resources.

Since, however, this iron ore has the so-called "oolitic structure or pisolitic structure" wherein hematite (Fe 2 0 3 particles are surrounded by goethite (Fe 2 0 3

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2 it has several problems.

Specifically, the decomposition of combined water occurs in the course of heating, which gives rise to selective cracking in the goethite portion. This renders the ore brittle. Further, when the iron ore is reacted with a sub raw material to provide a melt, the melt rapidly penetrates into the cracks, so that large pores are

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"n formed, which deteriorates the strength of the sinter.

That is, there occurs a lowering in the yield and cold strength in the sintering operation. Further, the assimilated area (an area where the melt has been reacted with the ore) is composed of small granular hematite grains and glassy silicate, so that the resistance to low-temperature reduction degradation index is deteriorated. For this reason, the present situation is that the proportion of pisolitic iron ore in the raw material cannot be increased. As described above, the development of a sintering process, which enables a large proportion of pisolitic iron ore to be used, is of considerable significance.

The fundamental solution to this problem in pisolitic iron ore is to prevent a large amount of melt from rapidly penetrating into the cracks. In order to inhibit the rapid penetration of the melt, the present inventors have proposed a method described in Japanese Patent Application Nos. 1-184047 and 2-115730 wherein a protective layer having a particular composition is formed on the surface of pisolitic iron ore particles and a method described in Japanese Patent Application Nos. 3- 146481 and 3-303854 wherein a highly viscous melt is formed. These methods, however, disadvantageously need a special flux material and segregated charging equipment for special raw materials.

The present inventors have thought that the penetration of the melt could be inhibited if the amount of the melt present around the pisolitic iron ore particles could be always minimized, and have repeated basic research on requirements to be satisfied for attaining this purpose. As a result, they have found the process of the present invention that is applicable to existing sintering machines.

Accordingly, an object of the present invention is to provide an iron ore sinter, having an excellent

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quality, by using iron ores that are incheap and abundant in reserves, particularly pisolitic iron ores.

Another object of the present invention is to produce a sintered ore having an excellent quality using the above-described iron ores without need of any special equipment.

Disclosure of the Invention According to a first embodiment of this invention there is provided an iron ore sinter for ironmaking, characterised in that, in the iron ore sinter, 80% or more of the iron ore sinter except for pores and particles remaining unmelted other than pisolitic iron ores comprises at least one member selected from the group consisting of densified pisolitic iron ores particles covered with fine calcium ferrites, and granular haematite grains and calcium ferrites bonding said haematite grains to each other with traces of the pisolitic iron ore being present.

According to a second embodiment of this invention there is provided a process for producing an iron ore sinter for ironmaking, comprising sintering iron-bearing materials, such as an iron ore, return sinter fines and so on, sub raw materials, carbonaceous S. materials and water, etc., in a sintering machine, characterized in that high-grade iron ores having a SiO 2 content of 1.5% by mass or less and an A1 2 0 3 /SiO 2 mass ratio of more than 0.3 and pisolitic iron ores are used as the iron-bearing material with the 20 blending ratio of said pisolitic iron ores being 40 to 70% by mass in the iron-bearing materials, except for the return sinter fines, and as a result, the iron ore sinter prescribed by the first embodiment is produced.

According to a third embodiment of this invention there is provided a process for producing an iron ore sinter for ironmaking, comprising sintering iron-bearing materials, 25 such as an iron ore, return sinter fines and so on, sub raw materials, carbonaceous materials and water, etc., in a sintering machine, characterized in that high-grade iron ores having a SiO 2 content of 1.5% by mass or less and an A1 2 0 3 /SiO 2 mass ratio of more than 0.3, low-Al 2 0 3 iron ores having an A1 2 0 3 /SiO 2 mass ratio of 0.3 or less and pisolitic iron ores are used as the iron-bearing material with the blending ratio of said pisolitic iron ores being 40 to 70% by mass in the iron-bearing materials and with the blending ratio of said low A1 2 0 3 iron ores being 60% by mass or less based on the whole the high-grade iron ores and the low A1 2 0 3 iron ores, except for the return sinter fines, and as a result, the iron sinter prescribed by the first embodiment is produced.

In the present invention, in order to attain the above-described objects, an ironbearing raw material comprising a pisolitic iron ore and a high-grade iron ore having a SiO 2 content of 1.5% by mass or less (in the following description means by mass" as a rule) with the amount of blending of the pisolitic iron ore being 40 to 70% is

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used as an iron-bearing raw material except for return sinter fines, and the iron-bearing IN:A\BUU]00450:KEH raw material, together with a sub raw material, carbonaceous materials, water, etc., is sintered in a sintering machine at a temperature of 1,200 0 C or above to provide an iron ore sinter for ironmaking, wherein, in the section of the sintered ore, 80% or more of the solid portion except for particles remaining unmelted of the sintering raw materials other than the pisolitic iron ore comprises, densified pisolitic iron ore particles covered with fine calcium ferrites having a width of 10.im, granular haematite grains bonded to each other with calcium ferrite with a trace of the pisolitic iron ore being present, a mixture of granular haematite grains with calcium ferrite, or a structure comprising a combination of and Further, it is also possible to use, as the iron-bearing raw material except for return ore fines to be provided for the above-described sintering means, such an ironbearing raw materials that 60% or less of a high-grade iron ore having a SiO 2 content of or less has been replaced with an iron ore having an A1 2 0 3 /SiO 2 mass ratio of 0.3 or less. Further, it is also possible to conduct blending in such a manner that the total content g *g *ao o* IN;\LIBUU00450:KEH of the pisolitic iron ore, high-grade iron ore and low- A1 2 0 3 iron ore is 80% or more.

The iron ore sinters thus obtained has a sinter yield and a quality comparable to the sinter from the hematite ores that have been regarded as having a high quality.

A in the following description in connection with the chemical composition is by mass as a rule.

[Brief Description of Drawings] Fig. 1 is a diagram showing the relationship between the Si02 content of the iron ore and the proportions of fine calcium ferrite having a width of pr or less and slag in the iron ore sinter with respect to an iron ore sinter produced in a pot using a single kind of iron ore so that the iron ore sinter has a basicity of 1.6 to 2.2; Fig. 2 is a diagram showing the relationship between the A1 2 0 3 /SiO 2 ratio of the iron ore and the proportions of fine calcium ferrite having a width of jm or less and slag in the iron ore sinter with respect to an iron ore sinter produced in a pot using a single kind of iron ore having a SiO2 content of 1.5% or more so that the sintered ore has a basicity of 1.6 to 2.2; Fig. 3 is a diagram showing a microstructure of the iron ore sinter of the present invention; Fig. 4 is a diagram showing another microstructure of the iron ore sinter of the present invention; Fig. 5 is a diagram showing a further microstructure of the iron ore sinter of the present invention; Fig. 6 is a diagram showing a microstructure of the conventional iron ore sinter; Fig. 7 is a diagram showing the results of a sintering pot test on a raw mix comprising a pisolitic iron ore and an iron ore having a SiOz content of 1.5% or less with the results shown in terms of the relationship between the proportion of the pisolitic iron ore to the total of the two iron ores and the sinter yield and JIS shatter strength; Fig. 8 is a diagram showing the results of a sintering pot test on a raw mix comprising a pisolitic iron ore and an iron ore having a Si0 2 content of 1.5% or less wherein the proportion of the pisolitic iron ore is or 70% and part of the iron ore having a SiO 2 content of 1.5% or less has been replaced with an iron ore having an Al 2 0 3 /SiO 2 mass ratio of 0.3 or less with the results shown in terms of the relationship between the percentage replacement and the sinter yield and JIS shatter index of iron ore sinter; and Fig. 9 is a diagram showing the results of a sintering pot test on a raw mix comprising a pisolitic iron ore and an iron ore having a Si02 content of 1.5% or less wherein the proportion of the pisolitic iron ore is or 70%, 60% of the iron ore having a SiO 2 content of or less has been replaced with an iron ore having an Al 2 0 3 /SiO 2 mass ratio of 0.3 or less and, further, a part of the raw mix has been replaced with an iron ore having an A1 2 0 3 /SiO 2 mass ratio higher than 0.3 with the results shown in terms of the relationship between the percentage replacement and the sinter yield and JIS shatter index of iron ore sinter.

[Best Mode for Carrying Out the Invention] The best mode for carrying out the invention will now be described in detail.

At the outset, the basic principle of the present invention will be described.

As described above, a feature of the present invention is that the kaleidoscopically changing existing melt is minimized. This can be attained under a basic principle that calcium ferrite (an acicular or plate form having a width of 10 tn or less) is produced and grown by a reaction of a solid with a liquid caused after the temperature reaches 1200 0 C in the stage of raising the -temperature during sinteringr. The calcium ferrite is .Y M fCC k

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.i produced upon occurrence of a high CaO/3i0 2 melt, that is, the calcium ferrite is produced by rate determining production of the melt, so that the amount of the actually existing melt becomes very small. The present invention has thoroughly investigated the relationship between the properties of the iron ore and the production of calcium ferrites.

At the outset, the present inventors have made a sintering test on a raw material using a single kind of iron ore adjusted to have a CaO/SiO 2 value range found in the conventional sintered ore, that is, in the range of from 1.6 to 2.2, with an iron ore and limestone. The section of a sinter particle having a size of about 20 mm was polished, and the proportion of fine calcium ferrite having a width of 10 pm or less was quantitatively determined by using an optical microscope equipped with a television camera and an image analyzer. Further, a coke breeze was added in an amount of 4% to the raw mix.

As a result, it has been found that a high-CaO/SiO 2 melt is necessary for producing the fine calcium ferrite and, for this reason, it is important to lower the SiO 2 content of the iron ore, or to prevent the dissolution of quartz (SiO 2 or the Si02 component of clay (Si02-A1 2 0 3 in the melt. Further, the present inventors have made various studies on the solubility of ores having a SiO 2 content of 0.5 to 7.6% and, as a result, have confirmed that the solubility can be summarized using the ratio of A1 2 0 3 to SiO 2 (A1 2 0 3 and Si02 being components of the ore).

Fig. 1 is a diagram showing the relationship between the SiO 2 content of the iron ore and the contents of fine calcium ferrite having a width of 10 pm or less and slag in the iron ore sinter. The contents of calcium ferrite and slag can be regarded as corresponding to the amount of the melt that were actually present.

The results have led to the conclusion that a Si02 content of 1.5% or less in the iron ore has a favorable

I.

effect on the production of fine calcium ferrite. Fig. 2 is a diagram showing the relationship between the A1 2 0 3 /SiO 2 mass ratio of the iron ore and the contents of fine calcium ferrite having a width of 10 pm or less and slag in the iron ore sinter with respect to an iron ore sinter with respect to a conventional imported iron ore having a Si02 content of 0.5 to An iron ore capable of providing an iron ore sinter having a fine calcium ferrite content and a slag content substantially equal to an iron ore sinter provided from an ore having a SiO 2 content of 1.5% or less has an A1 2 0 3 /SiO 2 value of 0.3 or less. The ore having a Si0 2 content of 1.5% or less can be replaced with the ore having an A1 2 0 3 /SiO2 value of 0.3 or less.

Based on the above-described finding, a sintering test was carried out on a raw mix comprising a plurality of iron ores, that is, a pisolitic iron ore adjusted to provide an iron ore sinter having a CaO/SiO 2 value (basicity) range found in the conventional iron ore sinter, that is, in the range of from 1.6 to 2.2, and a low-SiO 2 iron ore having a Si02 content of 1.5% or less.

A coke breeze was added in an amount of 4% as a solid fuel to the raw mix.

As a result of the test, when the proportion of the pisolitic iron ore was 40 to 70%, a characteristic microstructure different from that in the conventional sinter was provided in the resultant iron ore sinter.

The microstructure is shown in Figs. 3 to 5. For comparison, the microstructure of a pisolitic iron ore portion in an iron ore sinter produced by the prior art process is shown in Fig. 6.

The microstructure of the pisolitic iron ore was such that O as shown in Fig. 3 the coarse pisolitic iron ore particles remaining unmelted were densified and the circumference thereof was covered with fine calcium ferrites having a size of 10 pm or less or as shown in Fig. 4 although traces of the original shape of the 9 coarse pisolitic iron ore were observed, the pisolitic iron ore was completely assimilated and granular hematite grains and calcium ferrites bonding said grains to each other were precipitated (see Fig. 4 In some iron ore sinter particles, however, the structure was present together with the structure A fine pisolitic iroi ore powder of about 0.5 mm or less adhering to other raw material particles or intermediate risoliticiron ore particle comprised granular hematite grains and calcium ferrites (grown to 20 to 30 pm in width although this phenomenon was observed in a very small part thereof) as shown in Fig. 5 and had a structure substantially similar to that shown in Fig. 4. That is, it is characterized by a bond structure of the calcium ferrites.

In the production of an iron ore sinter for ironmaking, the whole raw material is not completely melted to avoid clogging of voids in sinter bed for the purpose of ensuring the combustion of coke. Therefore, part of the raw materials remains unmelted. In Fig. ores remaining unmelted were intentionally removed for photographing. Since a coke breeze having a relatively broad particle size distribution and a MgO-bearing sub raw material, such as serpentine, are blended with the iron-bearing raw materials, calcium ferrite is not theoretically formed around these coarse particles.

Accordingly, 20 samples having a size of about 20 mm were selected at random in one sintering experiment, and in the section of each particle, the proportion of each structure was determined and averaged for solid portion Nos. 1 to 6 except for the raw material remaining unmelted other than the pisolitic iron ore. The results are given in Table 1.

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Table 1 Results of experiment for blr -ng and sintering pisolitic iron ore and low-Si iron ore (CaO/Si02 1.6) No. Propor- Struc- Struc- Struc- Struc- Struc- Struction of ture ture ture ture ture ture pisolitic QO iron ore 1 30% 5% 10% 49% 10% 7% 19% 2 40 16 16 50 4 2 12 3 50 16 19 46 5 3 11 4 60 18 20 45 4 2 11 70 19 22 41 5 3 6 80 17 12 33 6 9 23 Note: Structure Densified pisolitic iron ore particles are covered with fine calcium ferrites having a width of 10 pm or less.

Structure Although traces of the pisolitic iron ore particles are observed, the pisolitic iron ore particles are assimilated with granular hematite grains and calcium ferrites.

Structure comprises granular hematite grains and calcium ferrites.

Structure comprises granular hematite grains and glassy silicate.

Structure comprises magnetite particles, calcium ferrites and glassy silicate.

Structure G comprises reoxidized hematite particles, magnetite particles, calcium ferrites and glassy silicate.

As is apparent from Table 1, when the proportion of the pisolitic iron ore is in the range of from 40 to as in Nos. 2 to 5, the percentage areas of the structures ©and are large and amount to more than 80% in total. When the proportion of the pisolitic iron ore is low and 30% as in No. 1, the percentage areas of the structures and are increased because an increase in the amount of addition of the Si02 flux material I 4-I facilitates the assimilation of pisolitic iron ore.

Further, when tie proportion of the pisolitic iron ore is high and 80% as in No. 6, the percentage area of the structure is increased probably because the permeability of the bed is inhibited to give rise to heterogeneous combustion.

In the conventional iron ore sinter, as shown in Fig. 6 large cracks occur in a concentric circle form or from the surface to the center portion in the residual pisolitic iron ore remaining unmelted, and the ore is surrounded with many pores having various indefinite shapes, which renders the wall between pores very thin, so that the structure is very brittle. Further, as shown in Fig. 6 the porous portion surrounding the residual pisolitic iron ore comprises granular hematite grains and glassy silicate bonding the hematite grains to each other, so that such a structure is poor in the resistance to lowtemperature reduction degradation and reducibility. The bond phase shown in the above-described Figs. 3 to comprises calcium ferrites which are known to have excellent resistance to low-temperature reduction degradation and reducibility. In fact, while the lowtemperature reduction degradation index (RDI) was 37 3 for the prior art process, it was greatly improved to 34 2 for the present invention. Further, in the pore structures shown in Figs. 3 to 5, the pores are not indefinite but circular, and the thickness of wall between pores is increased, so that the strength is high. The change in the pore structure is closely related to the fluidity of the melt, and since the calcium ferrite melt has a high fluidity, it has a univocal relationship with the formation of the calcium ferrite bonding phase.

The results of a sintering pot test on a raw material comprising a pisolitic iron ore and iron ores having a Si02 content of 1.5% or less are shown in Fig. 7. It is evident that a significant improvement in the yield of the sinter and cold strength (JIS shatter index) when the proportion of the pisolitic iron ore characterized by the calcium ferrite bond phase is 40 to The reason why a significant lowering in the yield occurs when the proportion of the low-Si02 iron ore is higher than 70% is that the amount of SiO2 is so small that the amount of the melt serving as a bonding phase, as such, is reduced.

Then, a sintering test was carried out wherein the low-Si2 iron ore in the above-described raw mix was replaced with a low A1 2 0 3 ore having an Al 2 0 3 /SiO 2 value of 0.3 or less. Since no change in the tendency was observed when the basicity of the sintered ore was in the range of from 1.6 to 2.2, the results of the test for a basicity of 1.6 are shown in Fig. 8. It is apparent that, even when the low-SiO2 iron ore is replaced with the low-A1 2 0 3 ore, the yield and cold strength can be maintained by limiting the percentage replacement to or less. Further, the structure of the sinter in the case of a percentage replacement of 60% or less was substantially the same as that shown in Figs. 3 to except that the proportion of the fine calcium ferrites having a size of several pm or less was increased.

In the sintering operation on a commercial scale, there is a possibility that the supply of the raw material becomes insufficient due to a strike in the mine or the like.

For this reason, a sintering test was carried out to determine what proportion of the above-described "a blended raw material comprising a pisolitic iron ore and a low-SiO2 iron ore" and "a blended raw material comprising a pisolitic iron ore, a low-SiO 2 iron ore and a low-A1 2 0 3 ore" can be replaced with "an iron ore having an A1 2 0 3 /SiO 2 value larger than The results are shown in Fig. 9. Since the results (tendency) did not significantly vary depending upon the basicity, the results of the test for a basicity of 1.9 is shown in Fig. 9. Also in this test, the amount of addition of the coke bree'ze was As can be seen from Fig. 9, when the percentage replacement is up to 20%, the cold strength can be maintained although the yield is somewhat lowered.

Specifically, the structures Q and could be provided even when blending was effected so that the total amount of a high-grade iron ore having a SiO 2 content of 1.5% or less and an iron ore having a A1 2 0 3 /SiO 2 mass ratio of 0.3 or less was 80% or more.

EXAMPLES

The effect of the present invention will now be described with reference to the following Examples. It has been confirmed that the microstructure comprised a mixture of the structures shown in Figs. 3 and 5 with the total of these structures being 80% or more.

Example 1 Table 2 shows a representative blended raw material (composed mainly of hematite ores) in a conventional process and the results of a sintering operation in a plant test. In Table 3, in condition A, only the pisolitic iron ore is sintered, while in condition B, the proportion of the pisolitic iron ore in the new raw material in the blended raw material specified in Table 2 is 30%. Further, conditions C and D are examples of the results of a sintering operation according to the process of the present invention. In the case of sintering the pisolitic iron ore alone, the yield, productivity and cold strength were remarkably lowered, and when the proportion of the pisolitic iron ore in the new material was 30%, the yield was considerably inferior to that given in Table 2. On the other hand, when a low-Si02 iron ore having a Si02 content of 1.5% or less was blended under conditions specified in the present invention, as shown in conditions C and D, the yield, productivity and cold strength were comparable to the general yield, productivity and cold strength given in Table 2 and obtained at present in the art.

Y r S- Table 2 Representative blending conditions in a conventional process (on dry basis) and results of sintering operation Raw Materials Chemical Composition Blending T.Fe CaO SiO 2 A1 2 0 3 Ratio Proportion of Pisolite iron ore-A 57.1% 0.1% 5.7% 2.7% 21.7% individual raw material High-grade iron ore native to 678 01 .7 0.7 9.6 components in Brazil-B iron-bearing Hematite iron ore native to 62.7 0.0 5.4 2.5 36.2 raw material Australia-C except for Low-A1 2 0 3 /SiO 2 iron ore-D 64.3 0.1 5.2 1.1 24.1 return sinter fines Hematite iron ore native to 63.5 0.0 2.7 1.7 8.4 India-E Blend- New Mixture of the above ironing materi- Iron-bearing raw material bearing raw material components ma- als Limestone 0.2 54.5 0.6 0.2 16 teri- __Serpentine 5.6 1.0 38.4 0.7 1 als Return sinter fines Coke 0.9 0.3 7.1 3.1 3.9* Re- Yield 82.2 sults Production efficiency (t/d/m 2 32.5 of JIS-SI 88.3 oper- JIS-RI 63.3 ation RDI 35.6 Proportion to the new material Results of proportion Table 3 sintering operation using large of pisolitic iron ore Condi- Condi- Condi- Condi- R a w Materials tion A tion B tion C tion D Proportion of Pisolite iron 100.0% 36.1% 70.0% 40.0% individual ore-A raw material High-grade 0 7.8 30.0 0 components in iron ore-B iron-bearing High-gradeiron 0 0 0 60.0 raw material ore-F except for Low-A1 2 0 3 /SiO 2 0 19.6 0 0 return sinter iron ore-D fines Low-A1 2 0 3 /SiO 2 0 0 0 0 iron ore-G Iron ore-C 0 29.6 0 0 Iron ore-E 0 6.9 0 0 Blend-New Iron-bearing 79.40 83.0 84.6 82.7 ing materi- raw material ma- als Limestone 19.0 16.0 13.3 14.8 teri- Serpentine 1.6 1.0 2.1 als Return sinter fines 34.9 22.5 18.9 18.9* Coke 3.9 3.9 3.9 3.8* Re- Yield 70.8 79.9 82.3 82.5 sults Production efficiency 29 1 31.3 32.6 32.9 29-. 1 /31.3 326 32.9 of (t/d/m 2 oper- JIS-SI 88.3 88.5 89.1 89.0 ation JIS-RI 70.5 65.3 68.1 67.2 RDI 39.5 38.2 35.7 34.3 Proportion to the new material Remarks: Chemical composition of iron ore Raw Materials Chemical Composition T.Fe CaO Si0 2 A1 2 0 3 High-grade iron ore native 67.1% 0.1% 1.5% 0.8% to Brazil-F Low-Al 2 0 3 /SiO 2 iron ore-G 65.3 0.0 3.1 0.9 Table 4 shows the results of a sintering operation wherein part of the low-Si02 ore in the raw materials comprising a pisolitic iron ore and low-SiO 2 ores having a SiO 2 content of 1.5% or less have been replaced with iron ores having an A1 2 0 3 /SiO 2 value of 0.3 or less under conditions specified in the present invention. Also in this case, the sintering performance was comparable to that of the conventional process shown in Table 2.

iZI r.

Example of process of Table 4 results of operation according the present invention to the Condi- Condi- Condi- Materials tion E tion F tion G Proportion of tion of Iron ore-A 70.0% 50.0% 40.0% individual raw material rawnmaterl Iron ore-B 12.0 12.5 0 components in iron-bearing iron-bearing Iron ore-F 0 12.5 24.0 raw material except for Iron ore-D 0 12.5 36.0 return sinter fines Iron ore-G 18.0 12.5 0 Blend- New Iron-bearing 84.6 82.3 82.7 ing materi- raw material ma- als Limestone 13.3 15.3 14.8 teri- S__erpentine 2.1 2.4 als Return sinter fines 19.2 18.1 19.2* Coke 3.9 3.9 3.8* Re- Yield 82.2 83.0 82.3 sults Production efficiency 323 33.9 32.5 of (t/d/m 2 oper- JIS-SI 89.0 88.3 89.2 ation JIS-RI 67.0 66.3 66.5 RDI 35.1 35.5 36.0 Proportion to the new material Example 3 Table 5 shows the results of a sintering operation wherein part of the blended iron ore raw materials specified in Table 4 have been replaced with iron ores having an A1 2 0 3 /SiO 2 value greater than 0.3. In this case, although the yield and productivity were somewhat lower than those for the conventional raw material shown in Table 2, they were far higher than those for conditions A and B specified in Table 3. Further, the cold strength was substantially the same as that given in Table 2.

4

C-

Table Example of results of operation according to the process of the present invention Condi- Condi- Condi- __tion H tion I tion J Proportion of Pr tion of Iron ore-A 56.0% 40.0% 36.0% individual raw material components in Iron ore-B 9.7 10.0 0 components in iron-bearing Iron ore-F 0 10.0 21.5 raw material Iron ore-D 0 10.0 32.4 except for Iron ore-G 14.4 10.0 0 return sinter Iron ore-C 19.9 10.0 0 fines Iron ore-E 0 10.0 10.1 Blend New Iron-bearing 3 82 ing materi- raw material ma- als Limestone 13.3 15.3 14.8 teri- Serpentine 2.1 2.4 als Return sinter fines 21.0 20.8 20.3* Coke 3.9 3.9 3.8* Re- Yield 81.0 81.1 81.5 sults Production efficiency 31.8 33.1 32.1 of (t/d/m 2 oper- JIS-SI 88.2 88.4 89.0 ation JIS-RI 65.2 64.5 64.3 RDI 35.8 35.6 36.0 Proportion to the new material [Field of Utilization in Industry] As described above, according to the present invention, a sinter performance comparable to that obtained by the conventional process can be attained using a high proportion of a pisolitic iron ore the use of which has been regarded as unfavorable in the prior art due to the low yield and the low quality of the iron ore sinter. It is self-evident the there is a tendency for hematite ores having a good quality, which have been mainly used in the art, to be exhausted. The process of the present invention that enables a pisolitic iron ore, which is abundant and inexpensive, to be used in a high proportion in the raw mix can solve the resource problem and greatly contributes to a reduction in the cost of ironmaking.

"-i )fti A

Claims (8)

1. An iron ore sinter for ironmaking, characterised in that, in the iron ore sinter, 80% or more of the iron ore sinter except for pores and particles remaining unmelted other than pisolitic iron ores comprises at least one member selected from the group consisting of densified pisolitic iron ores particles covered with fine calcium ferrites, and granular haematite grains and calcium ferrites bonding said haematite grains to each other with traces of the pisolitic iron ore being present.

2. The sinter according to claim 1, which comprises a combination of a structure comprising said iron ore sinter with a structure comprising granular haematite grains and calcium ferrites.

3. A process for producing an iron ore sinter for ironmaking, comprising sintering iron-bearing materials, such as an iron ore, return sinter fines and so on, sub raw materials, carbonaceous materials and water, etc., in a sintering machine, characterized in that high-grade iron ores having a SiO 2 content of 1.5% by mass or less and an A1 2 0 3 /SiO 2 mass ratio of more than 0.3 and pisolitic iron ores are used as the iron-bearing material with the blending ratio of said pisolitic iron ores being 40 to by mass in the iron-bearing materials, except for the return sinter fines, and as a result, the iron ore sinter prescribed by claim 1 or 2 is produced.

4. A process for producing an iron ore sinter for ironmaking, comprising 20 sintering iron-bearing materials, such as an iron ore, return sinter fines and so on, sub raw materials, carbonaceous materials and water, etc., in a sintering machine, characterized in that high-grade iron ores having a SiO 2 content of 1.5% by mass or less and an A 2 0 3 /SiO 2 mass ratio of more than 0.3, low-A1 2 0 3 iron ores having an A1203/SiO 2 mass ratio of 0.3 or less and pisolitic iron ores are used as the iron-bearing 25 material with the blending ratio of said pisolitic iron ores being 40 to 70% by mass in the iron-bearing materials and with the blending ratio of said low A1 2 0 3 iron ores being by mass or less based on the whole the high-grade iron ores and the low A1 2 0 3 iron ores, except for the return sinter fines, and as a result, the iron sinter prescribed by claim 1 or 2 is produced. 30

5. The process according to claim 4, in which blending is effected in such a manner that the total amount of pisolitic iron ores, high-grade iron ores having a SiO 2 content of 1.5% or less and an A1203/SiO 2 mass ratio of more than 0.3 and low A1 2 0 3 iron ores having an A1 2 0 3 /SiO 2 mass ratio of 0.3 or less is 80% or more based on the whole iron-bearing materials except for the return sinter fines.

6. An ore sinter for ironmaking, substantially as hereinbefore described with reference to any one of the Examples.

7. An ore sinter for ironmaking, substantially as hereinbefore described with reference to the accompanying drawings. [N:\LIBUU0045:KEH 19

8. A process for producing an iron ore sinter for ironmaking, substantially as hereinbefore described with reference to any one of the Examples. Dated 7 November, 1994 Nippon Steel Corporation Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON aee* e a ee [N:\LIBUUI00450:KEH ABSTRACT In sintering an iron-bearing raw material, such as iron ores and so on, carbonaceous material, water, etc. in a sintering machine, 40 to 70% by mass of pisolitic iron ores and high-grade iron ores having a SiO2 content of 1.5% by mass or less are used as the iron-bearing raw materials except for sinter return fines to provide an iron ore sinter for ironmaking wherein, in the section of the iron ore sinter, 80% or more of the solid portion except for particles remaining unmelted other than the pisolitic iron ore comprises densified pisolitic iron ore particles covered with fine calcium ferrites having a width of 10 pm or less, or granular hematite grains and calcium ferrites bonding said hematite grains to each other with traces of the pisolitic iron ore being present, or a combination thereof. A'-r Q;