Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2001-08-08
2003-07-15
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S504000, C075S484000, C075S485000
Reexamination Certificate
active
06592647
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in the technique for obtaining metallic iron by heating and reducing an iron oxide source such as iron ore by carbonaceous reducing agents such as coke, and a method improved so as to efficiently reducing iron oxide to metallic iron by simple treatment, to efficiently separate produced metallic iron from a slag forming component mixed in iron ore or the like as a gangue component, to produce metallic iron particles of high purity with high yield.
2. Description of the Related Art
Recently, many studies have been progressed with respect to a direct iron producing method for forming a raw material mixture containing an iron oxide source (such as iron ore) and carbonaceous reducing agents (such as coke), heating the former to thereby reduce iron oxide in the iron oxide source by the carbonaceous reducing agents, and separating produced metallic iron from a by-produced slag component to produce metallic iron.
The present inventors have also progressed the study on the direct iron producing method of this kind since long ago, and developed the following method as a result of the study, and further progressed study.
This method comprises, in producing metallic iron by heating and reducing a compact containing carbonaceous reducing agents and iron oxide, reduced iron oxide in solid state by heating to thereby produce and grow a metallic iron shell, continuing solid reducing till iron oxide is not substantially present inside, further continuing heating to flow out the produced slag from the metallic iron shell, and afterward separating metallic iron from slag.
In carrying out the above method, a part of the metallic iron shell may be molten to thereby flow out the molten from the metallic iron shell. At this time, for melting a part of or the whole metallic iron shell, carbon resulting from carbonaceous reducing agents which is present inside the metallic iron shell may be dissolved (solution) in metallic iron (this phenomenon is sometimes called “carburizing”) to thereby lower a melting point of the metallic iron shell.
Metallic iron of high purity obtained by the above method and the produced slag are cooled and solidified to crush the slag and the solidified metallic iron particles are subjected to classification by magnetic separation or a sieve, or metallic iron is separated from slag by heating and melting and due to a difference in specific gravity to thereby enable obtaining a material having high purity in excess of 95 mass %, or in excess of 98 mass %. Moreover, the disclosed invention provides a method for proceeding reducing of iron oxide in solid state, which can reduce molten FeO amount in the produced slag as less as possible, in which erosion and/or corrosion of refractories of a processing furnace caused by molten FeO is hard to occur, and which is expected that the above method be realized as a practical application from a viewpoint of maintenance of equipment.
Among the above methods, the method for cooling and solidifying the produced metallic iron and the produced slag, crushing the produced slag and thereafter obtaining metallic iron particles by magnetic separation or the sieve seems to be suitable for the application to an industrial scale as compared with a method for separating them by a difference in specific gravity after melting. That is, in the melting and separating method, it is necessary to heat at high temperature for melting, because of which a great heat energy is required, and in addition, when both are separated, a part of molten iron is entrained in molten slag at an interface to possibly lower yield of metallic iron. On the other hand, in the method for obtaining metallic iron particles by crushing, magnetic separation or a sieve, heat energy is unnecessary, and in addition, design of a continuous separating system according to a scale of iron-manufacturing equipment are easy, and iron loss can be also minimized.
The above disclosed invention has stressed that in the heating and reducing step, the metallic iron shell is produced, and a high-degree reducing atmosphere is formed within the shell whereby metallizing is progressed efficiently. However, according to later study, it has been confirmed that when the neighborhood of a raw material compact is kept in a higher reducing atmosphere by a large amount of CO gas generated by combustion of carbonaceous reducing material included in the raw material compact, such a metallic iron shell is not always necessary.
On the other hand, with respect to the method for controlling a producing slag composition to accelerate separation of metallic iron when the direct iron manufacturing method as described above, several methods have been proposed.
For example,, there is a method for using ironmaking dust as a iron oxide source, mixing it with carbonaceous material (carbonaceous reducing agents) and additional material (slag forming agent), controlling a producing slag composition in a range of 1.4 to 1.6 at CaO/SiO
2
ratio (basicity), subjecting it to heating and reducing at 1250 to 1350° C. to produce metallic iron, and separating metallic iron particles from slag having a low melting point containing FeO.
However, this method is a method for using ironmaking dust as an iron oxide source, and control of basicity used in this method is at the time of initial raw material preparation. In this method, there is no recognition on the behavior of slag produced during heating and reducing, that is, behavior when the product slag turns to a molten state in a solid-liquid co-existing state affects on acceleration of separation of produced metallic iron. Further, In this method, the slag having a low melting point containing FeO is used to accelerate separation of metallic iron, but the method using the molten slag containing FeO has many problems noted below from a viewpoint of actual operation:
1) the molten slag containing molten FeO greatly damages fire brick of a hearth;
2) molten FeO comes in contact with carbonaceous material to produce reducing reaction, which reaction is endothermic reaction to make temperature control difficult; and
3) since metallic iron produced by contact reaction between molten FeO in slag and carbonaceous material is scattered in a fine granular form in slag, work for cooling and solidifying it together with slag after recovering becomes extremely complicated.
Accordingly, it is desirable to recover metallic iron efficiently while suppressing the production of molten FeO in the by-product slag.
There is a further method for, in charging a raw material mixture containing fine iron ore and solid reducing agents onto a moving hearth and heating and reducing it to produce metallic iron, previously laying fine solid reducing agents on the hearth, progressing heating and reducing in a state that the raw material iron ore is placed in a small-section on it not to contact directly with the hearth, and melting reduced iron at least once on the hearth. According to this method, the reason why “placed in a small section” as termed herein is to prevent the molten substance containing produced metallic iron by heating and reducing and by-product slag from being fused or stuck on the hearth surface to corrode the hearth. However, for carrying out the method as described above, not only complicated equipment is necessary in order to form the small section or to charge raw material into the small section but also a large quantity of fine solid reducing substances are necessary, which method is not to be considered as a practical method in view of efficiency of raw material. Moreover, in this method, formation of the small section rather accelerates fusion and sticking of the molten substance on the hearth surface to disturb the discharge of produced substances.
Further, the above invention takes measures for preventing the damage on the assumption that the molten substance produced by heating and reducing could give the damage to the hearth refractor. However, it is rather important, in terms of a
Hino Mitsutaka
Kikuchi Shoichi
Kobayashi Isao
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