Title of Invention

A METHOD FOR PRODUCING METALLIC IRON

Abstract The present invention provides a method for producing metallic iron in which metallic iron, in either solid or molten form, having very high iron purity, is made from iron ore. The iron ore may have relatively low iron content, or relatively high iron content. A metallic iron shell is generated and grown via reduction through -the application of heat, and the reduction is continued until substantially no iron oxide is present within the shell, during which slag aggregates within the shell. Alternatively, heating may he further continued to melt the shell to allow molten slag to flow out from inside the shell, thereby separating the slag from metallic iron.
Full Text



The present invention relates to a method f.or producing metallic iron by subjecting iron oxides contained in iron ore or the like to reduction through the application of heat using a carbonaceous material as a reductant. More specifically, the invention relates to a method of efficiently making high purity metallic iron in which iron oxides are efficiently reduced into metallic iron while slag components including gangue and the like contained in an iron oxide source, such as iron ore, are melted and separated properly from metallic iron.
Description of the Related Art:
A conventional direct iron-making method is where iron ore or pellets which contain iron oxide are directly reduced using a reducing gas to obtain reduced iron. An example is a shaft furnace method represented'by the Midrex process . In this type of direct iron-making method, a reducing gas made from natural gas or the like, is forced into a shaft furnaae from a tuyere located at the bottom portion thereof to reduce iron oxides, thereby obtaining reduced iron.
In recent years, of particular interest has been a process of manufacturing reduced iron in which a

carbonaceous material, such as coal, is used as a reductant in place of natural gas. Such a method has already been put into practice a.id is referred to as an SL/RN method in which sintered pelTets manufactured from iron ore are subjected to reduccion through the applicc'ition of heat using pulverized coal as a. reductant.
Another reducing iron-making process is disclosed in U.S. Patent No. ',443,931, in which a mixture of pulverized iron ore and pulverized Coal are agglomerated, and the agglomerated ma.3s is subject to reduction through the application of heat on a rotary hearth, in a high temperature "tmosphere, yielding reduced iron.
Reduced iron obtained using the above-mentioned method? .'. i charged directly into an electric furnace
direc-Ij as source iron or in the form of briquette^. With
I 1
thf. i-icreasing trend of recycling scrap in recent years, t.'.ij reduced iron is of particular interest, since it may je used as a diluent of impurities contained in the scrap.
A conventional method, however, does not involve separating slag components such as SiOa, AI2O3, and CaO contained in the iron ore or the like and in the carbonaceous material (coal or the like), from the reduced
iron produced. Therefore, the resultant reduced iron has a
t
relatively low iron content (iron purity of metallic iron). In actual practice, these slag components are separated and removed durincr a subseauent refinincr orocess . However, an

increase in the amount of slag not only decreases yield of refined molten iron, but significantly increases the running cost of an electric furnace. Therefore, reduced iron is required to be iron rich and have a relatively low content of slag components. In order to meet this requirement, it is necessary for the above-mentioned conventional reducing iron-making methods to use iron-rich iron ore, which narrows the choice of source materials for making iron.
Furthermore, a goal of the conventional methods
described above is to obtain a reduced solid product as an
I intermediate product in an iron making process. ' Therefore,
additional step such as conveyance, storage, forming
briquettes, and cooling are required before reduced iron is
sent to the next refining process. These steps involve a
large energy loss, and a briquetting step requires excess
energy and a special apparatus. ^
In addition, a smelting reduction process such as the
DIOS method is known in which iron oxides are directly
reduced to obtain reduced iron. In this method, iron
oxides are pre-reduced to an iron purity of approximately
3 0 to 50%, and then molten iron in an iron bath is
subjected to a direct reducing reaction with carbon, to
obtain metallic iron. However, this method has problems;
since two steps are required, pre--reduction and final

reduction within an iron bath, the work is complicated, and in addition, due to direct contact between molten iron oxide (FeO) present in an iron bath and the refractory of a furnace, the refractory is significantly damaged.
Thus, it is quite important to realize a method of making metallic iron having a relatively low content of of slag components, since such a method adds more value to a metallic iron product, reduces the running cost of an electric furnace, and provides a flexible choice of source materials.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the foregoing. An object of the present invention is to provide a method of making metallic iron in which metallic iron, in either solid or molten form, having a very high purity, is readily and efficiently made from iron o^e having a relatively low iron content or having a relatively high iron content, without' damaging the refractory of a furnace via direct contact with molten iron oxide.
In the method of making metallic iron according to the present invention, iron oxide compacted with a carbonaceous reductant is subjected to reduction through the application of heat to yield metallic iron, the method having the following aspects:

(1) A shell containing metallic iron is generated and
grown via reduction through the application of heat. The
reduction normally is continued until substantially no iron
oxide is present within the shell, during which sl^g
aggregates within the shell.
(2) A metallic iron shell is generated and grown via
reduction through the application of heat, the reduction is
continued until substantially no iron oxide is present
within the shell, and heating ia further continued to allow
slag generated within the shell to f],ow out from inside the
shell.
(3) A metallic iron shell is generated and grown via
reduction through the application of heat, the reduction is
continued until substantially no iron oxide is present
within the shell, and heating is further continued to allow
molten metallic iron to separate from molten slag.
(4) A metallic iron shell is generated and grown via
reduction through the application of heat, and the
reduction is continued until substantially no iron oxide is
present within the shell, during which slag aggregates
within the shell, and then the aggregated slag is separated
from metallic iron.
In order to embody aspect (2) descrilsed above, part of the metallic iron shell may be melted to allow molten slag to flow out from inside the shell. In this case or in order to embody aspect (3) described above, carburization

may be continued within the metallic iron shell in the presence of a carbonaceous reductant so as to reduce the melting point of the metallic iron shell, thereby readily melting part or the entirety of the metallic iron shell.
When any of aspects (1) to (4) described above is embodied, a maximum temperature of heating for reduction may be controlled to be not less than the melting point of the accompanying slag and not more than the melting point of the metallic iron shell, so as to more efficiently conduct the reaction of generating metallic iron. This reducing step may be solid phase reduction, through which an iron oxide is reduced, and liquid phase reduction which is continued until substantially no iron oxide, composed mainly of FeO, is present, whereby the purity of the metallic iron obtained can be efficiently improved.
As used herein, the term "reduction is continued until substantially no iron oxide is present within the metallic iron shell" means, on a quantitative basis, that the reduction through the application of heat is continued until the content of iron oxide, composed mainly of FeO, is preferably reduced to 5% by weight or less, more preferably to 2% by weight or less. From a different point of view, this means that the reduction through the application of heat is continued until the content of iron oxide, composed mainly of FeO in the slag separated from metallic iron, is

preferably not more than 5% by weight, more preferably 2% by weight or less.
The thus-obtained metallic iron having a high iron purity and accompanying slag may be melted by further heating so as to separate one from the other through differences in their specific gravities. Alternatively, they may be solidified by chilling, and then crushed to separate the metallic iron from the slag magnetically, or by any other screening method. Thus, it is possible to obtain metallic iron having a high iron purity, with a metallization ratio of not less than 95%, or in some cases of not less than 98%.

Accordingly, the present invention provides a method fdr producing metalhc iron comprising heating a first compact, thereby forming a reduced compact; wherein said first compact comprises (i) iron oxide, and
(ii) a carbonaceous reducing agent; and said reduced compact comprises (iii) a shell, comprising metallic iron and
(iv) molten slag, inside said shell wherein the heating is at temperature such that the iron oxide is reduced to metallic iron, wherein said heating is performed at an ultimate temperature of from 1350-1540°C.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same become better understood by reference to the following detailed description when considered in connection with reference to the accompanying drawings, wherein:
Figs. 1(A) to (F) are cross-sectional views of a compact schematically illustrating the progress of a reducing reaction when a method of the present invention is carried out;
Fig.2 is a set of photographs showing cross-sections of pellets subjected to reduction through the application of heat at different temperatures;

Fig. 3 is a set of photographs showing a change in the appearance of a reduced pellet observed when the reducing time is varied at a reducing temperature of 1500°C;
Fig. 4 is a graph showing a change in the metallization ratio of reduced pellets with reducing time at a reducing temperature of 1500°C;
Fig. 5 is a graph showing a change in the content of
slag constituents with reducing time at a reducing
1 temperature of 1500°C;
Fig. 6 is a graph showing a change in. the FeO content of reduced pellets with reducing time at: a reducing temperature of 1500°C;
Fig. 7 is a graph showing a change in the carbon content of reduced pellets with reducing time at a ^■educing lemperature of 1500°C; and
Fig. 8 is a schematic flow chart illustrating a reducing iron-making process according to an embodiment of ■.he present invention.
DETAILED DESCRIPTION OF THE INVENTION A method of making metallic iron according to the resent invention, involves compacting the pulverized ixture, composed of iron ore which contains iron oxides nd coal or the like acting as a carbonaceous reductant/ to rains, pellets, or to any other forms. A feature of the 2thod is that a metallic iron shell is generated and grown

via reduction through the application of heat. The reduction is continued until substantially no iron oxide is present within the shell.
In the process of studying a new method of making metallic iron, which may replace both indirect iron making methods such as a method using a blast furnace, and direct iron making methods such, as the heretofore mentioned SL/RN method, the present inventors found tliat when cc|>mpacts, in grains, pellets, or in any other form, of pulverized iron oxides and carbonaceous reductant are heated in a non-oxidizing atmosphere, the following phenomenon occurs. When a compact is heated, the carbonaceous reductant contained in the compact reduces iron oxides in the following manner: the reduction continues from the periphery of the compact, and metallic iron generated during the incipient stage of the reduction diffuse and join together on the surface of the compact to form a metallic iron shell on the. periphery of the compact. Subsequently, reduction of iron oxides by the carbonaceous reductant progresses efficiently within the shell, so that
a state is established within a very short period of time
I such that substantially no iron oxide is present within the
shell. The thus generated metallic iron adheres to the.
.nner surface of the shell, and the shell grows
iccordingly. On the other hand, most of the by-product
ilag, which is derived from both gangue contained it an

iron oxide source, such as iron ore, and the asl^ content of a carbonaceous reductant, aggreg^ites within the metallic iron shell. Thus, metallic ix'on having a relatively high iron purity and constituting the shell can be efficiently, separated from the aggregated slag.
This phenomenon, which occurs during reduction and will be described later with reference to photos, is believed to occur in the following manner. Figs. 1(A) to 1(F) show cross-sectional views of a compact schematically illustrating the phenomenon which occurs when the method of the present invention is carried out. When a compact 1 composed of an iron oxide-containing material and a carbonaceous reductant and having a form shown in Fig. 1 (A) is heated, for example, to a temperature of 1450 to 1500°C in a nonoxidizing atmosphere, the reduction of iron i oxides progresses from the periphery of the compact 1, and metallic iron generated diffuses and joins together to form a metallic iron shell la (Fig. 1 (B)). Subsequently, as heating continues, iron oxides within the shell la are quickly reduced, as shown in Fig. 1 (C), through reduction by the carbonaceous reductant present within the shell la and reduction by CO generated by a reaction between the carbonaceous reductant and iron oxides. The thus generated metallic iron Fe adheres to the inner surface of the shell, and the shell grows accordingly. On the other hand, as shown in Fig. 1 (D), most of the by-product slag Sg derived

from the above-mentioned gangue and the like aggregates within the cavity defined by the shell la.
The reduction through the application of heat is represented by the f ollov/ing schemes:
FeO^ + xC -> Fe + xCO (1)
FeO^ + (x/2)C -> Fe + (x/2) CO2 (2)
Y = y, + y^ (3)
where Y: chemical equivaleuit (mol) of carbon required for reduction y^: amount (mol) of carbon required for
reaction represented by scheme (1) Yz'. amount (mol) of carbon required for. reaction represented by scheme (2) When compacts are prepared using an iron oxide, containing material and a carbonaceous reductant, the mixing ratio between iron oxides and the carbonaceous reductant is adjusted such that the amount of the carbonaceous reductant is not less than a theoretical equivalent expressed by scheme (3). This allows reduction through the application of heat to progress efficiently.
As described above, according to the present invention, the metallic iron shell la is formed on the periphery of the compact 1 during the incipient stage of reduction through the application of heat, and the reduction progresses further within the cavity defined by the shell la, thereby significantly improving the

efficiency of the reduction. Preferably, an ultimate temperature of heating for reduction may be controlled so as to be not less than the melting point of the accompanying slag and not m.ore than the melting point of the metallic iron shell la. If the ultimate temperature of heating is equal to or greater than the melting point of the metallic iron shell la, generated metallic iron will immediately fuse and aggregate; consequently, the metallic iron shell la will not form and the subsequent reducing reaction will not progress efficiently. Also, if non-reduced molten iron oxide flows out from inside the metallic iron shell la, it may be highly likely to damage the refractory of the furnace. On the other hand, when the ultimate temperature of heating for reduction is controlled so as to be not less than the melting point of the accompanying slag, the by-product slag fuses and aggregates, and metallic iron diffuses and joins together intensively; consequently, the metallic iron shell la grows accordingly while slag Sg is separating from the shell la as shown in Figs. 1 (C) and (D).
As described above, a key feature of the present invention is that "a metallic iron shell is formed within which a reducing reaction progresses efficiently," which 'is not employed in conventional indirect and direct iron-making methods and which significantly enhanced reduction through the application of heat. The metallic iron shell

la grows as a carbonaceous reductant: contained m tne compacts progressively reduces the compacts. Once the metallic iron shell la is formed, the carbonaceous reductant and the generated CO continue reduction within the shell la. Hence, the atmosphere for reduction through the application of heat does not need to be reducing, but may be a non-oxidizing atmosphere such as a nitrogen gas atmosphere. This is a significant difference from the conventional methods.
All the reducing agent necessary for reducing the iron oxide is present in the pellet. No external reducing agent is needed; neither solid nor gaseous reducing agents need to be added during the reduction process. The reducing agent used in the process may be only the carbonaceous reductant present in the compact. Furthermore, the metallic iron shell may be in contact with the atmosphere in the furnace; there is no need to coat or cover the shell.
Basically, the above-stated reduction through the application of heat progresses in the form of a solid phase reduction, which does not cause the metallic iron shell la to melt. Conceivably, liquid phase reduction also progresses at the latter or end stage of the reducing reaction for the following reason. The interiox- of the metallic iron shell la is believed to maintain a highly reducing atmosphere because of the presence of a

carbonaceous reductant and CO generated by the reducing reaction of the reductant, resulting in a significant rise in reduction efficiency. In such a highly reducing atmosphere, metallic iron generated within the shell la is subjected to carburization, so that its melting point gradually reduces. As a result, at the latter or end stage of the reducing reaction, part of the compacts melt, so that iron oxides undergo liquid phase reduction. By setting a relatively low reducing temperature, reduction can be carried out entirely in the solid phase. However, since the higher the reducing temperature, the higher the reaction ratio of reduction, and so a relatively high reducing temperature is advantageous to complete the reducing reaction within a short period of time. Hence, it is desirable that the reducing reaction ends with liquid phase reduction.
Whether or not the above-mentioned reducing reaction is completed can be confirmed by measuring the concentration of CO or CO2 contained in the atmosphere of gas produced by the reduction through the application of heat. In other words, the gas generated is extracted at appropriate intervals of time from inside the furnace of the reducing reaction. When no CO or CO^ is detected from the gas, it indicates the completion of the reducing reaction. This method uses the fact theit the reduction through the application of heat involves a. reducing

reaction carried out by a carbonaceous reductant itself and a reducing reaction carried out by the CO gas which is generated by the reaction between the carbonaceous reductant and iron oxides. After the iron oxides are all reduced, CO and CO2 are no longer generated.
In actual practice, there is no need to continue the reaction until the release of the CO and CO2 gasps terminates completely. The present inventors have confirmed that it depends on the inner volume of the furnace used for the reaction, but when the concentration= of the CO and CO2 gases in the furnace gas drops to approximately 2 volume % or less, not less than 95% by weight of iron oxides are reduced; when the gas concentration drops to about 1 volume % or less, not less than 98% by weight of iron oxides are reduced.
In the state shown in Fig. 1 (D), iron oxides composed mainly of FeO and contained in the compact are substantially all reduced to metsillic iron (iron oxide content, indicative of the progress of,the reduction, is usually not more than 5% by weight and is experimentally confirmed to be not more than 2% by weight or not more than 1% by weight), and some iron oxides composed mainly of FeO and fused into the internal aggregate of molten slag Sg are also mostly reduced (content of iron oxides composed mainly of FeO contained in the slag, indicative of the progress of the reduction, is usually not more than 5% by weight and is

experimentally confirmed to be not more than 2% by weight or not more than 1% by weight). Accordingly, metallic iron having a relatively high iron purity can be efficiently obtained by chilling compacts in the state of Fig. 1 (D), crushing their metallic iron shell la with a crusher, and magnetically selecting metallic iron from slag. Alternatively, heating at the same temperature or a higher temperature may be continued subsequently to the establishment of the state of Fig. 1 (D), whereby part or all of the metallic iron shell la is melted so as to separate the slag from metallic iron, which v/ill^ be described below.
When heating is continued at a slightly higher temperature, as needed, subsequent to the establishment of the state of Fig. 1 (D), part of the metallic iron shell la melts, for example, as shown in Fig. 1 (E). This allows the accompanying slag Sg to flow out from inside the shell la, thereby facilitating the separation of metallic iron from the slag. Alternatively, heating may be continued to establish the state shown in Fig. 1 (E) , whereby the entire' metallic iron shell la melts and aggregates, in order to be separated from the slag Sg which had previously melted and aggregated. Then, the thus prepared mass in the state shown in Fig. 1 (E) or (F) is processed by a crusher or the like to crush the fragile slag only, leaving metallic iron in agglomerates. The crushed mass is then subjected to

screening using a screen having an appropriate mash or to magnetic separation, thereby readily obtaining metallic iron having a relatively high iron purity. In addition, the difference in specific gravity between metallic iron and slag may be used to separate molten metallic iron from molten slag.
The metallic iron shell can be melted not only by heating at a higher temperature subsequently to the completion of the reducing reaction but also by reducing the melting point of the metallic iron shell through carburization. At the last stage of the reduction progressing within the metallic iron shell, the internal atmosphere, which is strongly reducing, causes reduced iron to be carburized with a resultant reduction in the melting point of the reduced iron. Hence, even by maintaining the
reducing temperature, the metallic iron shell can be melted
I due to the reduction in its melting point. '
Carbonaceous reductants usable with the present
invention include coal, coke or other similar carbonaceous
materials treated by dry distillation, petroleum coke, and
any other form of carbonaceous materials. In actual use,
mined coal is pulverized and screened to obtain coal powder
for use, and coke is also pulverized. In addition, for
example, blast furnace dust may be used which is collected
as waste which contains carbonaceous materials. However,
in order to efficiently progress the reaction of reduction

through the application of heat, a carbonaceous reductant to be used contains carbon preferably not less than 70% by weight, more preferably not less than 80% by weight. In
addition, in order to increase the specific surface area of
1
I
the carbonaceous reductant, its grain size is preferably not more than 2 mm, more preferably not more than 1 mm. Likewise, in order to improve the efficiency of a reducing reaction through an increase in the specific surface area of iron ore or iron oxide-containing materials, its grain size is preferably not more than 2 mm, more preferably not more than 1 mm.
In the present embodiment, an iron oxide and a carbonaceous reductant and, as needed, a binder, are homogeneously mixed and then formed into agglomerates, grains, briquettes, pellets, bars, or other forms of compacts, and the resulting compacts are subjected to reduction through the application of heat. The amount of the carbonaceous reductant to be mixed in is not less than a theoretical chemical equivalent required for a reducing reaction represented by the aforesaid schemes (1) to (3). Preferably, the carbonaceous reductant is used in excess, in consideration of the amount consumed or carburization to lower the melting point of the metcillic iron shell.
As heretofore mentioned, preferably, an ultimate temperature during reduction through the application of heat is not less than the melting point of the by-product

slag and not more than the melting point of the metallic iron shell. However, it is not necessarily adequate to absolutely predetermine the ultimate temperature because the temperature of slag varies depending on the amount gangue contained in iron ore or other iron oxide sources and depending on the amount of iron oxide contained in the slag. Nevertheless, the reducing temperature falls preferably in the range of 1400 to 1540°C, more preferably in the range of 1430 to 1500°C. Such a temperature range, of reduction provides metallic iron having as high an iron purity of not less than 95% by weight in, metallization ratio, usually not less than 98% by weight, and in excellent cases not less than 99% by weight.
As for the by-product slag, its content of iron oxides composed mainly of FeO can be reduced to not more than 5% by weight, usually not more than 2% by weight, or under more adequate conditions of reduction through the application of heat, not more than 1% by weight. This \ feature is advantageous to prevent damage to the refractory wall of a furnace caused by direct contact with molten iron oxide. According to the heretofore mentioned conventional reducing iron-making methods, when iron oxides contained in iron ore or the like are subjected to reduction through the application of heat using a carbonaceous material, or when metallic iron obtained through reduction is separated from accompanying slag, a considerable amount of iron oxides

composed mainly of FeO is left unreduced in the slag, causing damage to the refractory of the furnace. Accotding to the present invention, iron oxides composed mainly of FeO contained in slag are mostly reduced, so that almost no iron oxide or only a very small amount of iron oxide, if any, is left unreduced in the slag. Thus, the problem of damage to the refractory of a furnace does not occur, not only at the reducing step, but also at the subsequent slag separating step.
Since the thus obtained metallic iron has a relatively high iron purity and does not contain constituents of slag, it can be used intact as long as it is used as a diluent in a steel making process. However, since the metallic iron contains a considerable amount of impurities such as S and P, it needs to be refined so as to reduce the impurities, if the impurities raise any problems. In addition, the metallic iron allows its carbon content to be adjusted.
The metallic iron may form a continuous closed shell. In this form, most, if not all, of the reduced iron is in a single piece or mass, separate from the slag. Even after the shell has been partially or completely melted most of the reduced iron is in the form of a single piece dr mass.
When the present invention is carried out, preferably, a grown metallic iron shell is not allowed to melt while molten"slag is aggregating, and also at the subsequent step of separating slag from metallic iron, the metallic iron is

not allowed to melt. This practice minimizes the amount of S and P contained in the obtained metallic iron. The mechanism of this practice is described below. After completion of reduction, if metallic iron, together with slag, is melted, part of the S and P contained in the molten slag may mingle with the molten metallic iron. However, if at the reducing step and the subsequent slag separating step, metallic iron is held in the solid state and only slag is melted for separation from the metallic iron, S and P contained in the cai:bonaceous reductant, such as coal, melt into the molten slag and are removed together with the slag, thereby minimizing entry of S and P into the metallic iron.
EXAMPLES
The present invention will next be described in detail by way of example, which should not be construed as limiting the invention. .Variations and modifications are possible without deviating from the gist of the jinvention. Example:
Coal powder (carbonaceous reductant), iron ore (iron-containing material), and binder (bentonite), each having a composition shown in Table 1 and an average grain diameter of not more than 45 J-LVX, were mixed in the mixing ratio shown in Table 1. The resulting mixture was 'formed into substantially spherical pelletsy. The thus formed

pellets were subjected to reduction through the application of heat in a non-oxidizing atmosphere (nitrogen gas atmosphere) for 20 minutes at 1400°C, 1450°C, and 1500°C, followed by cooling. The cross-sections of the reduced pellets were observed. Fig. 2 shows typical photographs of their cross-sections. In the tables "T." stands for ' "total", and "M." stands for "metallic".

As seen from Fig. 2, in pallets subjected to reductio through the application of heat at a temperature of 1400°C and 1450°C, a metallic iron shell is formed on their surface while metallic iron adheres to the internal surfac of the shell as it accumulates, and slag agglomerates separately from the shell in an internal space defined by the shell. In a pellet subjected to reduction through the
application of heat at a temperatvire of 1500°C, it seems
1

that once formed, the metallic iron shell melted after the reducing reaction had completed, and then the m(|)lten metallic iron and molten slag solidified to mutually separated metallic iron having metallic luster, and a vitreous mass, respectively (the corresponding photograph' in Fig..2 show only metallic iron obtained by removing slag after crushing). Table 2 shows the chemical composition of the reduced pellets, and Table 3 shows the chemical composition of the vitreous slag.


Table 3 Chemical Composition of Vitreous Matter
Unit: % by weight

As seen from Table 2, in pellets subjected to reduction at a temperature of 1500°C, solidified metallic iron (see Fig, 2) having an elliptical shape and metallic luster contains almost no slag constituents, and the reduced metallic iron having a metallization ratio of not less than 99% by weight is substantially completely
separated from the slag. On the other hand, in,pellets
I subjected to reduction at a temperature of 1400'C or
1450°C, a metallic iron shell still remains, and their
chemical compositions seem to indicate that reduction of ,
iron oxide is insufficient. However, as seen from Fig. 2,
in those pellets, a metallic iron shell is already
separated from aggregated slag within the shell. This
implies that granular metallic iron having a relatively
high iron purity can be obtained by: crushing reduced
pellets and collecting metallic iron through magnetic
separation; continuing heating at a higher temperature to
melt part of the metallic iron shell to thereby allow
molten slag to flow out from inside the shell, followed by
separation of metallic iron from slag; or continuing
heating at a higher temperature to melt the entire metallic■

iron shell and then allowing molten metallic iran and molten slag to aggregate separately lirom each other. Fig. 3 shows a change in appearance of a pellet observed when reducing time is varied from 3 minutes through 15 minutes at a reducing temperature of 1500°C. Table 4 shows the chemical composition of each reduced pellet corresponding to each i-educing time. Figs. 4 to 7 show a change in metallization ratio, content of slag constituents, iron oxide content, and carbon content, respectively, with reducing time.
Table 4
Effect of Reducing Time on Chemical
Composition of Reduced Pellet

As seen from Fig. 3, 3 minutes after heating has started, no particular change in appearance is observed

with the pellet. However, as seen from Table 4, reduction of iron oxide is considerably progressed in the pellet. 5 minutes after heating has started, the pellet surface exhibits an apparent metallic luster indicative of a metallic iron shell being formed. In addition, the T. Fe content of the metallic iron is in excess of 90% by weight. 6 minutes
later, the T. Fe content of the metallic iron is as high as not less than 98% by weight as shown in Table 4.
At this point of time, it is observed that part of the metallic iron shell melts to allow molten slag to flow out from inside the shell. 9 minutes later, most o^ the metallic iron shell melts and aggregates in a fried egg like shape, in which metallic iron agglomerates in the position corresponding to the yolk, and vitreous slag aggregates around the metallic iron in the position corresponding to the white of the egg. After this point of time, the shape of the metallic iron and slag varies somewhat, but as seen from Table 4, the T. Fe concentration in the metallic iron shows almost no further increase. This indicates that the reducing reaction of iron oxides contained in a pellet progresses quickly and is almost completed while the metallic iron shell is formed and, once the metallic iron shell is formed, under an enhanced reducing condition established within the shell, after which the separation of the metallic iron from slag

I progresses with time. As seen from Table 4 and Figs. 4 to
7, 6 minutes after reduction through the application df
heat starts, the slag and FeO content of the obtained
metallic iron is reduced to a very low level, whereby
i metallic iron having a metallization ratio of not less than
99% is obtained.
As will be easily understood, if the compact composed
of an iron oxide-containing material and a carbonaceous
reductant contains as much carbonaceous reductant as equal
to or greater than the equivalent required for reducing
iron oxides contained in the compact, then v;hen the compact
is heated at a temperature of about 1400°C or higher, a
metallic iron shell will form on the periphery of the
compact at the incipient stage of heating, and subsequently
iron oxide will be quickly reduced within the metallic iron
shell, while molten slag is separated from metallic iron.
When the reducing temperature is increased to 1500°C, a
reducing reaction and the separation of metallic iron from
slag progress within a very short pei-iod of time, whereby
metallic iron having a very high iron purity is obtained at
a relatively high yield.
Fig. 8 shows a flow chart illustrating an embo^iiraent
of the present invention. Pulverized iron oxide-containing
material and pulverized carbonaceous reductant, together
with binder, are mixed and formed into pellets or other
forms of compacts. The thus formed pellets or the like are

I.' subjected to reduction through the application of heat at a
temperature of not less than 1400°C in a furnace. During
the reducing step, a metallic iron shell is formed during
the incipient stage of reduction, and then a reducing
reaction progresses within the shell while molten slag
aggregates within the shell. At the separating step,
reduced masses are chilled to solidify, and then the
resulting solidified masses are crushed, followed by
collection of metallic iron through magnetic separation or
the like. Alternatively, heating may be furthei:} continued
to melt metallic iron so as to separate molten metallic
iron from molten slag utilizing a difference in the
specific gravity between them. IE needed, the collected
metallic iron may be refined to remove impurities such as S
and P, and in addition, the carbon content of the metallic
iron can be adjusted.
As has been described above, according to the present
invention, compacts of iron oxide containing a carbonaceous
reductant are subjected to reduction through the
application of heat, at the incipient stage of which a
metallic iron shell is formed. Once the metallic iron
shell is formed, iron oxides are reduced under an enhanced
reducing condition which is established within the metalli
iron shell, whereby the reducing reaction progresses
quickly and efficiently. Therefore, the method of the .
invention can efficiently produce, via reduction through

the application of heat and in a short period of time, metallic iron having such a high iron purity, with a metallization ratio of not less than 95%, or in some cases of not less than 98%, which cannot be attained by-conventional direct iron making methods. The thus obtained metallic iron having a relatively high iron purity and accompanying slag may be solidified by chilling and then crushed to separate metallic iron from slag magnetically or by any other screening method or may be melted by further heating so as to separate one from the other through a difference in their specific gravities.
Further, the method of the present invention can make the iron oxide content of slag relatively small, so that it does not do damage to the refractory of a furnace^ which would normally result from contact of molten iron oxide with the refractory.


WE CLAIM:
A method for producing metallic iron comprising heating a first compact,
thereby forming a reduced compact; wherein said first compact comprises
(i) iron oxide, and
(ii) a carbonaceous reducing agent; and said reduced compact comprises
(iii) a shell, comprising metallic iron and
(iv) molten slag, inside said shell wherein the heating is at temperature such that the iron oxide is reduced to metallic iron, wherein said heating is performed at an ultimate temperature of from 1350-1540°C.
The method as claimed in claim 1, wherein substantially no iron oxide is present within said shell.
The method as claimed in claim 1, wherein the method additionally comprises further heating, thereby allowing said slag to flow out from inside said shell.
The method as claimed in claim 3, wherein during said further heating part of said shell is melted, thereby separating molten slag from said metallic iron.
The method as claimed in claim 4, wherein during said further heating said metallic iron is carburized, thereby reducing the melting point of said metallic iron.
The method as claimed in claim 1, wherein the method additionally comprises further heating, thereby melting said metallic iron and separating said metallic iron from said slag.

The method as claimed in claim 6, wherein during said further heating said metallic iron is carburized, thereby reducing the melting point of said metallic iron.
The method as claimed in claim 1, wherein the method additionally comprises allowing said slag to form aggregates, and separating said aggregates from said metallic iron.
The method as claimed in claim 1, wherein said heating is performed at a maximum temperature of not less than the melting point of said slag, and not more than the melting point of said metallic iron.
The method as claimed in claim 1, wherein during said heating said iron oxide is reduced first by solid phase reduction, followed by liquid phase reduction, and said heating is continued until substantially no iron oxide is present.
The method as claimed in claim 1, wherein said reduced compact comprises 5% by weight or less of FeO.
The method as claimed in claim 11, wherein said reduced compact comprises 2% by weight or less of FeO.
The method as claimed in claim 1, wherein said slag comprises 5% by weight or less of FeO.
The method as claimed in claim 13, wherein said slag comprises 2% by weight or less of FeO.

The method as claimed in claim 1, wherein said shell is closed and continuous.
The method as claimed in claim 1, wherein said heating is performed at a temperature of 1400-1540°C.
A method for producing metallic iron substantially as herein described with reference to the accompanying drawings.


Documents:

1006-mas-1996 abstract.pdf

1006-mas-1996 claims.pdf

1006-mas-1996 correspondence others.pdf

1006-mas-1996 correspondence po.pdf

1006-mas-1996 description (complete).pdf

1006-mas-1996 drawings.pdf

1006-mas-1996 form-2.pdf

1006-mas-1996 form-26.pdf

1006-mas-1996 form-4.pdf

1006-mas-1996 form-6.pdf

1006-mas-1996 others.pdf

1006-mas-1996 petition.pdf


Patent Number 193833
Indian Patent Application Number 1006/MAS/1996
PG Journal Number 13/2007
Publication Date 30-Mar-2007
Grant Date 19-Feb-2007
Date of Filing 10-Jun-1996
Name of Patentee KABUSHIKI KIASHA KOBE SEIKO SHO
Applicant Address 3-18 WAKINOHAMA – CHO, 1-CHOME, CHUO-KU, KOBE 651,
Inventors:
# Inventor's Name Inventor's Address
1 TAKUYA NEGAMI C/O. KOBE STEEL, LTD 8-2, MARUNOUCHI 1-CHOME, CHIYODA-KU, TOKYO 100,
2 KAZUO KUNII C/O. KOBE STEEL, LTD 8-2, MARUNOUCHI 1-CHOME, CHIYODA-KU, TOKYO 100,
3 ISAO KOBAYASHI C/O OSAKA BRANCH OFFICE IN KODE STEEL, LTD. 1-3, BINGO-MACHI, 4-CHOME, CHUO-KU, OSAKA-SHI, OSKA 541,
4 TOSHIHIDE MATSUMURA C/O. KAKOGAWA WORKS IN KOBE STEEL, LTD. 1, KANAZAWA-CHO, KAKOGAWA-SHI, HYOGO 675-01,
5 YOSHIMICHI TAKENAKA C/O. KAKOGAWA WORKS IN KOBE STEEL, LTD. 1, KANAZAWA-CHO, KAKOGAWA-SHI, HYOGO 675-01,
6 MASATAKA SHIMIZU C/O. KAKOGAWA WORKS IN KOBE STEEL, LTD. 1, KANAZAWA-CHO, KAKOGAWA-SHI, HYOGO 675-01,
7 SHINICHI INABA C/O. KAKOGAWA WORKS IN KOBE STEEL, LTD. 1, KANAZAWA-CHO, KAKOGAWA-SHI, HYOGO 675-01,
PCT International Classification Number C21B11/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 8-59801 1996-03-15 Japan