CA1332286C - Method of refining oxide nickel ore or the like - Google Patents

Abstract

ABSTRACT

A method of refining nickel oxide ore or the like by crushing the ore, then forming briquettes of the crushed ore, and drying, pre-heating and sintering the briquettes in a rotary kiln to reduce metal components contained in the ore and also cause growth of luppe, in which large amounts of a reducing agent and a slag formation agent are preliminarily uniformly incorporated in the briquettes, the water content of the briquettes are adjusted to an optimum amount, and the briquettes are then sintered in a rotary kiln, thus promoting the reduction of metal components and slag formation, greatly increasing the operation efficiency, widely reducing heat energy for drying and pre-heating and reducing the amount of scattered dust so that it is possible to improve the productivity of the kiln.

Description

; 1 332286 METHbD OF REFINING OXIDE NICKEL ORE OR THE LIKE

Background of this invention Field of the invention This invention is related to method of producing a ferro-nickel luppe containing iron and nickel by using a rotary kiln with a drying and pre-heating means, such as a grate, a shaft furnace or the like. This method comprises steps of dividing the nickel oxide ore into two groups, dry crushing the first group nickel oxide ore, while wet crushing the second group nickel oxide ore, mixing and kneading the dry crushed and the wet curshed nickel oxide ores, together with a solid reducing agent, such as cokes or the like, forming the resultant mixture into briquettes, drying and preheating the briquettes using the grate or shaft furnace of the rotary kiln, and sintering the resultant preheated briquettes using the rotary kiln, thereby and other metal compronents contained in the nickel oxide ore and simulataneously causing growth of nickel and other metal component as luppe or growth of nickel and other metal component as luppe or particles and obtaining the luppe containing iron and nickel. In detail, in the briquette formatlon step, large amounts of the solid reducing agent such as cokes and slag formation agent such as limestone are preliminarily uniformly incorporated in the ~ ~ :

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1 3~2~86 briquettes and also the water con-tent of the brique-ttes is optimized to a modera-te quantity. As a result, the reducing reaction of the nickel or other metal compornents is promoted and the slag formation has a remarkable increase during sintering step of the briquettes. Furthermore, a large reduction of heat energy consumption and dust scattering is carried out during drying and pre-heating step using the grate or shaft furnace.

Description of the prior art Nickel is an essential component of the austenitic stainless steel. Usually, nickel silicate ores, such as garnierite or the like, are improted to Japan as nickel ore, which is to be used as a raw material for nickel. Nickel silicate ores are refined, thereby obtaining nickel ~ -;
component as ferro-nickel. Nickel silicate ore to be used as a raw material is usually powdery and has a large amount of water therein. Consequently, nickel silicate ores are usually refined as followed.
Generally, the main material, such as nickel silicate ore and the auxiliary material, such as cokes, limestone, etc., are respectively subjected to an addition of large amount of water, thereby forming respective slurry materials. Each of slurry materials is subjected in sequence to steps, such as wet crushing and mixing and kneading.

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~ 332286 The resultant mixture is dehydrated and then pelle-tized, into pellets or the like, which do not contain cokes in an amount necessary to reduce nickel or other metal components contained therein. Owing to, effecting steps, such as drying, pre-heating and sintering of the pellets or thelike using the rotary kiln, an addition of the cokes to the pellets or the like is necessiated at the instance of feeding the rotary kiln with the pellets or the like.
Namely, furnishing the rotary kiln with excessive cokes effects a good sintering process, in which arises a reduction of nickel or other metal components, and a growth of reduced nickel or metal as luppe.
The luppe is combined with slag to produce clinker to be discharged. In a subsequent process, ferro-nickel is separated and obtained from the discharged clinker.
In this method, since large amounts of water are required to be added to the main and auxiliary materials to form the slurry materials before wet crushing, step, water removal from the slurry mix-ture using a filter or the like is necessiated after mixing with slurry materials. However, the conventional drum filter or the like can not effect a sufficient dehydration of the slurry mixture. In addition, since the individual slurry materials are mixed in the form of slurry, it is difficult to uniformly mix the materials.
Particularly, it is difficult to uniformly disperse cokes, which has a large specific gravity difference, in a large ','. ' ' ~ ' 1 33228~

amount and uniformly.
"Nippon Kogyo Kaishi" (Japanese Mining Industry Bulletin) No. 97-1122 issued in August, 1981, p-p. 792-794.
discloses a prior art method of refining nickel oxide, which is shown in Fig. 3 as a flow sheet. Nickel ore as the main material and cokes and limestone as the auxiliary material are separately crushed by wet crushing in tube mills with addition of large amounts of water to obtain slurries with water content of about 50%. The individual slurries are collected in a storage tank and mixed. Then, a desired polymer coagulant is added to the mixture, and the mixture with the polymer is supplied to a drum filter for dehydration. The degydrated material is then rendered in-to cakes. The cakes are then supplied to a briquette former to form briquettes, which are then fed to a rotary kiln with a grate. In the rotary kiln, briquettes, are subjected in sequence to steps, such as drying on the grate, preheating and sintering. However, with a dehydration of some nickel ores having very inferior dehydration property, by using a conventional drum filter or the like, the nickel ores can not reduce their water content upto about 30% or lower. In the dehydrated nickel ores remains a great amount of water, and the w&ter content of the dehydrated nickel ores varies greatly. Consequently, it is very difficult to form the dehydrated nickel ores in a briquette with a good shape.
Additionally, drying and pre-heating the dehydrated r : ' 1 33228~

nickel ores necessiates a great quantity of heat energy.
In a further aspect, the main and auxiliary materials are mixed in the form of slurry in the storage tank. In this case, however, segregation of the cokes and so forth is liable to result and it is difficult to obtain uniform mixing. This is because the main and auxiliary materials are greatly different in the specific gravity and viscosity.
This lack of uniformity presents problems at the time of the reduction of metal components by sintering. Further, since it is difficult to obtain uniform mixing of materials, only a small quantity of cokes can be incorporated into briqettes or the like. Therefore, the coke content is liable to fluctuate, and the briquettes obtained are fragile and readily liable to crumble. This leads to the problem of generation of the so-called ring on the rotary kiln inner surface. Thus, smooth operation can not be ensured, and it is extremely difficult to improve the productivily.

Summary of the invention The invention has been intended to solve the problems discussed above, and its object is to provide a method of porducing a ferro-nickel luppe by refining nickel oxide ore, in whcih at the time of mi~ing and kneading the main material consisting of nickel oxide ore and the auxiliary material consisting of limestone and cokes after crushing of the material, cokes and solvent can be uniformly dispersed . .
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` 1 332286 and incorporated in amount in excess of an amount necessary for the reduction of nickel and other metal components in the main material, so as to promote a reduction of nickel and metal components and a growth of the reduced nickel or metals as luppe during steps, such as drying step, pre-heating step and reduction step, rotary kiln with grate or shaft furnace, thereby permitting improvement of the operation effeciency and productivity, and by using a high pressure briquette former, the briquettes can get their water content kept up a low level, so as to increase the mechanical strength of the briquettes, and to effect a reduction of heat energy supplied for drying and pre-heating in the rotary kiln.
According to this invention, there is provided a method of producing a ferro-nickel luppe containing iron and nickel, by using a rotary kiln with a grate, a shaft furnace or the like, in which said method comprises steps;
dividing a nickel oxide ore into two groups;
wet crushing one group nickel oxide ore, while dry crushing the other nickel oxide ore;
adding to wet crushed and dry crushed nickel oxide ores and an auxiliary material such as limestone and cokes in an amount in excess of an amount necessary for the reduction of nickel oxide and other metal components;
mixing and kneading informly said wet crushed and dry crushed nickel oxide ores and said auxiliary material;

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~ t332286 forming the resultant mixture into briquettes having a predetermined shape;
drying said briquettes by using said grate, shaft furnace or the like; and sintering said briquettes by using said rotary kiln, thereby reducing nickel oxide and other metal components included in said briquettes by action of said cokes and also promoting a growth of the reduced nickel oxide as luppe.

Further, in the method according to the invention, both the main material such as nickel oxide ore and auxiliary material such as limestone and cokes may be crushed by drying crushing in the crushing step, and the crushed materials may be kneaded together with adequate quantity of added water. -~
The constitution and functions of the invention will now be described in detail with reference to the accompanying drawings.
sRIEF DESCRIPTION OF THE DRAWINGS
Eig. 1 is a flow sheet illustrating an embodiment of the method according to the invention;
Fig. 2 is a view showing an example of arrangement of equipment for carrying out the method according to the invention;
Fig. 3 is a flow sheet illustrating a prior art method 25 of refining nickel oxide ore; and ~;

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Fig. 4 is a graph showing the relation between various mixing/kneading methods and results of fall test on obtained briquettes.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in Figs. 1 and 2, nickel oxide ore as the main material is classified into at least two groups according to the dehydration property. One group of ore, i.e., ore 1a, the dehydration property of which is in~erior, is crushed in a drying crushing step A. The other group of ore, i.e., ore 1b, which has satisfactory dehydration property, is crushed in a wet drying step C.
In the drying crushing step A, the ore 1a is crushed in a dry state. The ore 1a is usually crushed into particles with diameters around 2mm. Usually, this step is performed with an arrangement as shown in Fig. 2, in which a crusher 1, e.g., a crushing mill, a cyclon 2 and a bag filter 3 are coupled together. Dry air is supplied from a hot air furnace 4 to a crusher 1. Part of the ore usually contains 20 to 40 ~ of water and has a diameter of about -300mm. It is crushed in a dry state in a crusher 1, to a grain size of about -2mm, and is then dried until it contains less than 10 % of water. More specifically, hot air is supplied from the hot air furnace 4 to a crushing section of the crusher 1, and the crushed material is discharged together with hot water. By crushing the material in the presence of the hot air stream, it is possible to obtain a uniform grain size, control the grain s~ze according to the amount of hot air supplied and remove water sufficient to obtain satisfactory .~

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, drying.
The dried crushed material is collected in the cyclon 2 and bag filter 3 and temporarily stored in a storage tank 3'.
In the wet crushing step C, ore 1b having satisfactory dehydration property is crushed in the form of a slurry.
This step may be performed using any arrangement. Usually, however, an arrangement as shown in Fig. 2 is used, which comprises a wet tube mill 5 and a plurality of slurry tanks 6, these being coupled to a dry filter 7. The ore 1a having inferior dehydration property, which also usually contains 25 to 40 % of water and has a diameter of about -300mm, is crushed together with added water in the wet tube mill 5 to obtain a slurry containing about 50 % of water. Thus slurry is temporarily stocked in the slurry tanks 6. Subsequently, it is progressively dehydrated in the drum filter 7 to obtain cakes containing 28 to 35 % of water.
The auxiliary material 1c such as cokes and limestone is usually crushed in the dry crushing step B. These crushing materials have differenct crushing properties from that of the ore. Also, they contain less water. Therefore, the dry crushing step B, unlike the drying crushing step A, is performed with an arrangement, in which a tube mill 8 which does not require any screening and a storage tank 9 are coupled together. With this arrangement, the auxiliary material 1c with a diameter of about -100mm is crushed by dry crushing, i.e., in situ, in the tube mill 8 to a grain size of about -2mm. The crushed material is temporarily - 8 ~

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stored in the storage tank 9.
When re-using return dust, it may be added in the next mixing/kneading step. Further, it may be rendered into the form of a slurry in the slurry tank 6 in the wet crushing step C, and the slurry thus obtained may be added to the ore slurry after the wet crushing, the mixture being then dehydrated in the drum filter 7 to obtain cakes.
The grain size of each crushed material may be as small as possible from the standpoint of increasing the crushing strength of briquettes. For this reason, according to the invention the material is crushed to a grain size of about -3mm. If the grain size is above -3mm, briquettes having a predetermined mechanical strength can not be obtained with a high yield (over 90 %) even by taking the crushing in the following mixing/kneading step into consiaerations.
The individual materials with the controlled grain size of about -3mm are mixed together in adequate quantities and kneaded in the mixing/kneading step D. At this time, the water content is adjusted to 10 to 20 %, preferably 15 to 20 %, from the considerations of the moldability of the briquettes or the like and also the saving of heat energy for subsequent drying and pre-heating. Further, the cokes in the auxiliary material should be added in a great amount in excess of the amount necessary for the reduction of nickel and other metal components in the total ore, particularly including an amount of energy which is consumed in combustion.
More specifically, to obtain predetermined moldabllity '~' ' ~ :
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l 332~86 and mechanical strength of briquettes or the like in a subsequent briquette formation step E, a certain amount of water is kneaded. If the amount of water is insufficient, the mechanical strength is reduced.
However, if the amount of water is excessive, the briquette formation property is spoiled. In addition, a great amount of heat energy is required at the time of pre-heating drying, so that sometimes sufficient drying can not be obtained with the exhaust gas produced by reduction combustion. From this standpoint, the upper limit of the water content is preferably about 20 %. Further, it is necessary to incorporate a great amount of cokes in the auxiliary material. More specifically, the cokes should be incorporated in an amount in excess of an amount which is necessary for the reduction of niçkel and other metal components. It is to be appreciated that the method according to the invention, unlike the prior art method, permits formation of briquettes or the like, which contain cokes and solvent in an amount in excess of an amount necessary for the reduction of the metal components and have high mechanical strength. This constitutes one feature of the invention.
If cokes are incorporated only by an amount necessary for the reduction of nickel and other metal components, 50 to 80 % of the incorporated cokes is consumed for the combustion, resulting in the shortage of cokes necessary for the reduction metal components. For this reason, it is necessary to incorporate cokes in an amount in excess of the ~ ' , ~: `" ' ' . . ' . . . ' : .
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' ' .' ' '. '' .' " ~ ' amount necessary for the reduction of nickel and other metal components. Actually, it is necessary to incorpoxate two to five times the amount of cokes necessary for the reduction, although the amount depends on the furnace operating conditions.
In the mixing/keading step D, cokes are incorporated in the great amount as noted above, and the water content is adjusted in the amount noted above. Further, it is necessary to uniformly disperse the great amount of incorporated cokes. If water and incorporated material are not dispersed uniformly, it leads to a reduction of the mechanical strength of briquettes, which are formed as pillow-shaped or armond-shaped briquettes with a diameter of 20 to 30mm after the kneading of the material. This means that the kneading should be carried out more than is done in the case of the prior art method. For this reason, according to the invention a mixer 10, e.g., a pug mill, and kneader 11, e.g., a rod mill, are directly coupled together as shown in Fig. 2. Particularly, it is preferred to provide plural kneaders 11 such as rod mills. The materials are thus preliminarily mixed in the mixer 10 such as a pug mill, and the mixture is kneader while it is slightly coarsely crushed in the kneaders 11 such as rod mills.
During this time, the particles of the materials having already been crushed are further crushed by the rod mill, so that they are uniformly mixed as they are kneaded. That is, water and cokes are uniformly dispersed to enhance the briquette formation property.

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1 33228n The use of rod mills not only for the crushing but also for the kneading is disclosed in Japanese Patent Publication No. 6256/68. ( Date of filing: March 23, 1964 Application No. 15671/64 Applicant: Yahagi Seitetsu Kabushiki Kaisha ) In this technique, however, a ball mill and a rod mill are directly coupled together to prepare pellets from powdery iron ore, and these crushers are provided not only with a function of comminution but also a function kneading. This technique, therefore, is different from the technique of the method according to the invention, in which the kneader and crusher are used for the purpose of dispersing a large amount of cokes in the material. More specifically, the disclosed technique noted above is based on the preparation of pellets by comminuting powdery iron ore and through subsequent steps of kneading, addition of water, granulation, etc. The disclosed technique permits improvement of this process by omitting the comminution step and simultaneously effecting a certain extent of comminution and kneading with the ball mill and rod mill. In other words, while the ordinary pellet preparation process inpcludes a comminution step and a kneading step, in the disclosed technique the comminution and kneading are effected with the ball mill and rod mill without preliminarily comminuting the powdery iron ore. It is a feature of the disclosed technique that the comminution and kneading are carried out in a wet state and without use of a pug mill or like kneader.
In contrast, by the method according to the invention -- . . ,: . :.
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1 3322~6 the materials are preliminarily crushed by drying crushing, wet crushing, etc. be~ore the mixing and kneading. In addition, a large quantity of auxiliary material is incorporated uniformly. Further, as the mixing/kneading equipment a pug mill ~r like mixer is provided, and a rod mill or like kneader is provided after and coupled to the mixer. More specifically, as shown in Fig. 2, kneading is performed to a certain extent in the mixer 10. By this operation, the auxiliary material is uniformly disperesed, that is, the materials are mixed to a considerable extent.
This mixture is further kneaded in the rod mill, which has a function of coarse crushing. In this kneading step, the falling of rod rather promotes the kneading.
The uniformly knead material thus obtained is temporarily stored in a material yard 12 before being supplied to the next briquette formation step E.
In the above description, the material having been crushed by wet crushing and material having been crushed by drying crushing are mixed under the conditions noted above.
However, instead of crushing materials separately by wet crushing and drying crushing, it is possible to crush all the materials in the proportions noted above, and kneading the mixture with10 to 20 % of added water.
In the briquette formation step E, the material is supplied to a briquette formation apparatus 13' for formation of briquettes. In this step, the material may be formed into a pellet-like form. Usually, however, pillow-shaped or almond-shaped briquettes with a diameter of 20 to 1 3322~6 60mm are formed. Pillow-shaped or almond-shaped briquettes may be dried very satisfactorily in the subsequent drying step. In addition, during this drying step no substantial powdering results. Further, heat energy necessary for the drying can be greatly reduced.
After the drying step E, the briquettes or the like are supplied to a sintering step G. The drying step F is carried out in a grate 13 of a grate type rotary kiln as shown in Fig. 2. The sintering step G is carried out in a rotary kiln 15. More specifically, in the grate type rotary kiln shown in Fig. 2, the briquettes are first charged into the grate 13 to be dried with exhaust gas led from the rotary kiln 15 and supplied from above the grate 13. Since the briquettes are of pillow shaped or almond-shaped, they are dried very satisfactorily. Also, since an adequate amount of water is provided, the mechanical strength of the briquettes is further increased when they are dried, and no powdering results. More specifically, the briquettes prepared contain a large amount of cokes as noted above and contain a comparatively small amount, i.e., 10 to 20 %, of water. Therefore, as the briquettes are dried on the grate 13, their temperature can be elevated substantially linearly from normal temperature up to 400 C. In contrast, briquettes prepared in the prior art method contain much water and have inferior molding property, so that their temperature can be elevated only up to about 200 C even when they are dried on a grate. In addition, a long time of pre-heating in a rotary kiln is required.

_ 14 -: . . .- . . . , . - ~ -1 3322~6 After the drying, the briquettes are charged into the rotary kiln 15 from an inlet thereof over a shoot 14. In the rotary kiln 15, the briquettes are pre-heated and sintered. During the sintering, nickel and other metal components in the briquettes are~reduced in a state surrounded by a large amount of cokes. As the briquettes approach an outlet of the rotary kiln 15, the metal components grow as luppe ( i.e., metal particles), which are discharged as clinker contained in slag.
The discharged clinker is cooled and then usually separated by magnetic separation or other separation means to be recovered as an alloy of iron such as ferronickel.
The dust produced during drying of the briquettes on the grate and also during the sintering in the rotary kiln, which is reduced as will be described hereinbelow, is returned for re-use to the wet crushing step C as mentioned before.
The rotary kiln has a conventional construction with a burner 16 provided at the outlet. At the burner 16, fuel, e.g., fine powdery coke, heavy oil, gas, etc., is burnt, and the temperature of the briquettes in the rotary kiln is elevated by the heat energy thus generated.
Further, in the rotary kiln 15, the temperature of the briquettes is gradually elevated as they proceed over the grate 13 from the inlet to the outlet. The briquettes are heated up to about 400 C and to such an extent that they hardly contain water. Their temperature is elevated linearly. When they proceed slightly in the rotary kiln ' : -: ~ :- . : : . .
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~, -: 1 3~2286 (e.g., by 35m from the inlet), the metal components are reduced very satisfactorily mainly because of the presence of a large amount of cokes. As the reduction proceeds in this state, the partial pressure of oxygen in the material 5 layer is reduced, and FeO and the like are increased. When FeO is combined with SiO2, fayalite (2Fe-SiO2) or the like low-melting compound is produced. Such a compound is liable to be attached to and grow as a ring on the inner wall of the rotary kiln. This phenomenon is liable to occur 10 particularly in the presence of a powdery material, and it constitutes a significant problem in the operation of the conventional rotary kiln. In the method according to the invention, the briquettes have a high mechanical strength.
Thus, the generation of powdery material is suppressed, to a 15 small extent if any. The ring thus can be hardly formed, so that very smooth operation can be ensured.
Heretofore, it has been in usual practice, for pellets as source of iron, to incorporate as much cokes as possible and utilize fine powdery coke in place of petroleum system 20 energy. By way of example, "Tetsu-to-Hagane" ( Iron and Steel ) issued in 1982, No. 15, p-p 2231-2237 and p-p 2238-2245 discloses pellets, which contain at most about 1 % of fine powdery coke as means of replacement of petroleum energy with coal energy to cope with the early oil shocks.
25 In these pellets, the incorporated coke does not serve for reducing metal components such as iron, but it only serves as fuel. These pellets are refined as ore in a blast furnace. The amount of coke is determined such that no ... . . . - ::

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powdering results in the furnace, i.e., in a range, in which a crushing strength or falling strength in excess of a predetermined level can be ensured. For this reason, the coke is incorporated in an amount of 1 % at most. In contrast, according to the invention use is made of a rotary kiln, which serves as a reaction furnace corresponding to the blast furnace to promote reduction of nickel and other metal components. In other words, as much cokes as possible are incorporated to provide a state, in which metal components and ore particles are surrounded by cokes to obtain quick and smooth reduction of the metal components by gas reduction.
Next, this invention will be described in connection with its examples.
Example 1 Nickel oxide ores A to D having compositions as shown in Table 1 were each crushed in two groups. At the first group, 380kg, 50kg and 130kg, in dry weight, of the ores A, B and D, respectively, were crushed. The average grain size 20 of the ores was less than 300mm (400mm at the maximum).
This crushing was done by drying crushing in the drying crushing step A shown in Fig. 2. As the second group, 250kg and 200kg of the ores B and C were crushed. The average grain size of the ores was the same as that of the ores in the first group. This crushing was done wet crushing in the wet crushing step C. The crushing of the first group of ores was carried out in a ball mill while supplying hot air supplied from the hot air furnace. The grain size after the -:

~ 332286 crushing was adjusted at this time by hot air to -2mm, and the water content was reduced to about 5 % by drying. The resultant crushed ore was stocked in a stock tank. The crushing of the second group of ores was carried out by adding water such that the total water content isabout 50 %
to obtain a slurry and crushing this slurry in a wet tube mill to a grain size of about -2mm. The resultant slurry was stored in the slurry tank, and 75 kg of return dust (having a composition as shown in Table 4) was added to the slurry. The resultant system was then dehydrated to reduce the water content to 30 %.
As the auxiliary material, cokes and limestone were crushed in the dry crushing step B. 130kg of cokes A
(having the composition shown in Table 2 and water content of 10 %) and 70kg of limestone ~having the composition shown in Table 3 and water content of 3 %) were continuously crushed to obtain a crushed material with a grain size of -2mm and water content of 6.1 %.

Table 1 Composition of nickel oxide ore (wt%) . ' Ore g.loss SiO2 Fe Al23 Ni ~gO Water Content Ore A 8.89 46.48 11.73 1.99 2.32 21.25 27.9 Ore B 10.62 41.68 12.68 0.93 2.47 24.11 25.4 Ore C 10.45 43.12 11.92 0.82 2.50 23.80 24.2 Ore D 10.29 42.50 14.96 0.99 2.28 20.36 30.0 , .. . ~ . ~ , . . . ..
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Table 2 t 332286 Composition of cokes (wt%) Ash Volatile Fixed Phosphorus Sulfur Kcal/kg component component carbon Coke A 13.5 5.9 80.6 0.003 0.16 6500 Coke B 11.7 2.4 85.9 0.030 0.62 7018 * Coke B is a coke sleeve Table 3 Composition of limestone (wt%) Cao Ig.loss 54.6 43.3 Table 4 Composition of return dust (wt%) :
Ig.loss CSiO2 Fe Al23 CaO MgO Ni -~
1.75 11.1736.03 12.00 1.98 2.39 17.08 2.43 The individual crushed materials were mixed and kneaded in the mixing/kneading step D. At this time, the .
composition was set such that the water content was 17 to 19 ;~
96, the cokes were 1 30kg, and the limestone was 70kg. The step D was carried out by coupling together a pug mill and two rod mills, and water and a large amount of cokes were uniformly dispersed.

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t 332286 Subsequently, pillow-shaped briqettes having a diameter of about 40mm were formed by molding in the briquette formation step E using the briquette forming machine. A
fall test was conducted on the briquettes thus formed by causing the briquettes to fall repeatedly five times from a position at a height of 2m. 95% or more briquettes were not cracked.
The briquettes were then dried in the drying step F
using the grate (with a length 17m). The drying was carried out by introducing exhaust gas (at 550 C) as opposed stream from the rotary kiln. At this time, very satisfactory drying could be obtained with the briquette temperature at 390 C at the outlet of the grate. Substantially no powdering due to bursting or like cause resulted, and the amount of recovered return dust was 42kg.
After the drying, the briquettes were charged into a rotary kiln (with a length of 70m) from an outlet thereof to be pre-heated and sintered.
At this time, the briquette temperature was elevated linearly as they proceeded through the rotary kiln. At a position at a distance of 20m from the inlet (and at a distance of 50m from the outlet), the temperature reached 700 C, and decomposition of crystalized water began.
Subse~uently, the reduction proceeded, and the temperature at a position at a distance of 1Om from the outlet was 1,320 C. Further, the same temperature was maintained even in a luppe formation zone covering 1Om from the outlet, and sufficient growth of luppe was recognized. The nickel , . - , ' .' ' ' - ,, .: - , : ,, ,:.

reduction ratio was 96.5 %.
As a contrast, the auxiliary material was added to the ore slurry with the water content of 50 ~ obtained from the second group of ores through wet crushing in a slurry tank such that the coke content was 80kg. However, much segregation occurred in the slurry tank, so that it was difficult to obtain uniform mixing. Accordingly, the slurry was dehydrated in the drum filter to reduce the water content to about 30 % and was then formed into cakes. From these cakes briquettes with a diameter of 12mm were formed.
Since the water content was high at the time of the briquette formation, the briquette formation machine was heated by steam heating to progressively dry the briquettes on the grating. In this case, the moldability of the briquettes was inferior, and the water content was up to 15 %. The briquettes were pre-heated and sintered in the -~
manner as described above in the rotary kiln. Since the amount of incorporated coke was small, 80kg of coke was externally supplied for pre-heating and sintering of the briquettes in the rotary kiln. The status in this case is as shown in Table 5. The nickel reduction ratio was 95.0 : :

Table 5 1 332286 Method according Comparative method to the invention ¦
Amount of incorporated cokes 130kg 80kg :-.
Amount of externally supplied O 80kgcokes Water content in briquette 17 - 19% 29 - 32%
.__ Water content in briquette 1 - 1.5% 15%after drying . _. ., Gas temperature immediately 150 C 220 C
after drying of briquette . . .
20m from inlet Temperature of 700 C 600 C
material (C) Furnace status Deoomposition of Pre-heating _ crystallized water 30m from inlet Tenperature of 820 C 700 C ~:
material (~C) :~
Furnace status Decomposition of Deoomposition of .. _ limestone crystallized water ~:
35m from inlet Temperature of 830 C 820 C :~:
material (C) Furnace status Prcgrees of Deoomposition of :~ :
reduction limestone 50m from inlet Tbmperature of 1060 C 1100 C :~
meterial (C) Furnace status Start of luppe Process of reduction . _ formation (generating of ring) 60m from inlet Temperature of 1320 C 1330 C
material (C) ~ :~
Furnace status Formation of luppe Start of luppe ~:
formation .. .. . . . _ as far as 10m Temperature of 1370 - 1200 C 1370 - 1050 C
from outlet material (C) Furnace status Grcw~l of lupFe Growth of luppe . .

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Further, on the basis of the above results, nickel oxide ore was actually processed by the method according to f the invention and the contrast method, and the operation results per ton of dry ore were as in Table 6 below.

Table 6 Method according toComparative method ;
the invention Amount of cokes130 kg 160 kg Lime as fuel 47 kg 78 kg 10 Amount of return75 kg 300 kg Amount of 262kg 715 kg incorporated water -~
Amount of supplied 1135 X 103 kcal 1575 X 103 kcal 15 heat energy _ Example 2 In this example, unlike Example 1, the second group of ores was crushed by drying crushing like the first group of ores. Auxiliary material was added to crushed materials in the same way as in Exaple 1. Water was added at the time of subsequent kneading to obtain kneaded material as in Example 1. Subsequently, briquette formation, drying, pre-heating and sintering were carried out in the same way as in Example 1. The same results as shown in Table 5 were obtained. ~-ExamPle 3 When kneading the three different crushed materials obtained in Example 1 by ad;usting the water content to 18.5 . .

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1 33228~

and coke amount to 130 kg.
(A) a sole rod mill (B) a sole pug mill (C) three pug mills (D) a combination of pug mill and rod mill were used as kneader, and diffusion of water and cokes and moldability at the time of briquette formation were evaluated.
In the case of a sole mill in (A), both water and cokes could be dispersed uniformly because of a water content of about 18.5 %. However, the yield of briquette formation was insufficient.
In the case of a sole pug mill in (B), cake-like particles remained in the kneaded material due to insufficient kneading. In the case of using three pug mills in (C), the molding yield was inferior due to insufficient kneading due to the same reason.
In the case of use of the combination of pug mill and rod mill in (D), satisfactory diffusion of water and cokes and very satisfactory kneading could be obtained because the materials were mixed in the pug mill and then kneaded in the rod mill.
Subsequently, briquettes with a diameter of 40mm were formed from the kneaded materials (all with water content of 18.5 %) obtained in the cases (A) (C) and (D), and a fall test of these briquettes was made. The results were as shown in Fig. 4. In the test, the briquette was aliowed to fall onto a concrete floor from a position at a height of ~;- - . . ... ~

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1 33228~

2m five times repeatedly. In Fig. 4, shaped portions show rates of generation of cracks and, especially, the cross~
hatched portions show rates of generation of 5 mm and less cracks. ~
From these results, it was found the case of (D) was :
most effective with a yield of 96 % obtained.

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.;

Claims (2)

1. A method of producing a ferro-nickel luppe containing iron and nickel, by using a rotary kiln with a grate, a shaft furnace or the like, in which said method comprises steps:
dividing a nickel oxide ore into two groups;
wet crushing one group nickel oxide ore, while dry crushing the other nickel oxide ore;
adding to wet crushed and dry crushed nickel oxide ores an auxiliary material consisting of a slag formation agent and a reduction agent in an amount in excess of an amount necessary for a reduction of nickel oxide and other metal components;
mixing and kneading uniformly said wet crushed and dry crushed nickel oxide ores and said auxiliary material;
forming the resultant mixture into briquettes having a predetermined shape;
drying said briquettes by using said grate, shaft furnace or the like; and sintering said briquettes by using said rotary kiln, thereby reducing nickel oxide and other metal components included in said briquettes by action of said cokes and also promoting a growth of said ferro-nickel luppe with containment of the reduced nickel.

2. A method of producing a ferro-nickel luppe containing iron and nickel, by using a rotary kiln with a grate, a shaft furnace or the like, in which said method comprises steps:
dry crushing nickel oxide ore;
adding to dry crushed nickel oxide ores and an auxiliary material consisting of a slag formation agent and a reduction agent in an amount in excess of an amount necessary for the reduction of nickel oxide and other metal components;
adding 10 to 20% of water to said crushed nickel oxide ores and the auxiliary material;
mixing and kneading uniformly said crushed nickel oxide ores and the auxiliary material;
forming the resultant mixture into briquettes having a predetermined shape;
drying said briquettes by using said grate, shaft furnace or the like; and sintering said briquettes by using said rotary kiln, thereby reducing nickel oxide and other metal components included in said briquettes by action of said cokes and also promoting a growth of said ferro-nickel luppe with containment of the reduced nickel.