EA024243B1 - Method for reduction of ores and metal oxides - Google Patents

Abstract

The invention is related to metallurgy, in particular, to reduction of metal oxides in solid state. The method comprises production of a reducing mixture consisting of: metal oxides, solid hydrocarbon and limestone; placing the reducing mixture into a solid protective shell made of heat-resistant material; heating and holding the reducing mixture at a temperature lower than the metal melting temperature. A briquette with a protective shell of heat-resistant material in plastic state is formed from the reducing mixture and subjected to heat pre-treatment until the protective shell acquires the required strength. The technical result includes lower costs and higher automation of the sponge iron production process.

Description

The invention relates to metallurgy, in particular to the reduction of metal oxides in the solid state.

There is a known method for the reduction of metal oxides (ore or concentrate, scale) used by Heganas when producing sponge iron with a solid hydrocarbon (coal, coke, charcoal, etc.), according to which the crushed iron oxide and solid hydrocarbon are loaded into heat-resistant containers (capsules, crucibles) made of silicon carbide with immiscible layers and restored at a temperature of 900-1300 ° C (Pokhvistev A.N., Kozhevnikov I.Yu., Spektrov A.N., Yarkho E.N. Instantaneous iron production abroad Metallurgical Publishing House, 1964, p. 22-31). Filled containers installed on technological trolleys are transported through a tunnel furnace, where heat treatment is performed. Then sponge iron pipes are removed from the cooled capsules, and the spent recovery mixture is sucked out of the containers and transported to the dump.

Closest to the invention is a method for reducing ores of metal oxides in a solid state, characterized in that, together with iron oxide, briquetted reducing agent mixed with limestone and a binder is loaded into heat-resistant containers with immiscible layers. The compaction of the reducing agent and flux allows you to increase the amount of iron oxide loaded into the capsules, which gives an increase in productivity [a.s. USSR No. 1209478 / 22-2 A1 (Foreign company Hoganas), 12/22/1970, Bulletin No. 2 of 1971].

The disadvantage of this method is that the expensive heat-resistant refillable containers made of silicon carbide used in it have increased fragility and require careful and careful handling both during the loading of capsules and their subsequent unloading after firing, as well as when installing capsules. on top of each other in tiered rows on trolleys for firing in a tunnel kiln and then removing them from the trolley after firing. The resistance of containers made of silicon carbide reaches 120-150 heat exchange. If the tank breaks and fails at an early stage of its use, then its replacement entails a significant increase in the cost of sponge iron. Therefore, all these operations are distinguished by the use of a large share of manual labor and do not allow to automate to a large extent the process of producing sponge iron.

In the proposed method for the reduction of metal oxides, this disadvantage is partially or completely eliminated by the use of a disposable cheap heat-resistant protective shell, inside which a reducing mixture of crushed metal oxide, solid hydrocarbon, limestone is placed. The shell will fulfill the function of a container preventing contact of the reducing mixture with atmospheric oxygen, and the entire structure is a briquette.

The shape of the briquette is determined by the geometry of the mold. It is most simple to make briquettes cylindrical.

When forming a briquette, the heat-resistant material of the shell, for example of ceramic masses, is in a plastic state and acquires the necessary strength during drying and regenerative firing.

After re-firing, the briquette is crushed, crushed, and the reduced oxide powder is extracted from the mixture using one of the enrichment methods, for example, magnetic or gravitational.

To obtain a mechanically stronger briquette, a binder is introduced into the reduction mixture. In the drying process, due to the presence of a binder, the reducing mixture also acquires additional strength and, together with the hardening hardening during drying, a briquette is created that is resistant to subsequent mechanical and thermal loads during the preparation and conduct of thermal re-firing.

Used in known methods for the reduction of metal oxides, solid carbon, as a rule, contains sulfur. Therefore, for desulfurization, i.e. sulfur absorption; limestone is used for firing.

In the proposed method, a lime-based binder is introduced into the reduction mixture, which eliminates the need for limestone addition.

Press briquette is offered in one or two steps.

In the first embodiment, a loose structure briquette is formed from a reducing mixture with a binder, enclosed in a shell of a heat-resistant material in a plastic state, and then pressing the briquette gives the necessary strength, which increases when the briquette is dried.

In the second embodiment, at the first stage, the briquette is formed from a reducing mixture, which is then dried to give it strength. Then on the outer surface of the briquette put a shell of heat-resistant material in a plastic state, for example in the form of a slip. The shell is applied, for example, by dropping the briquette into the clay solution or by passing the briquette placed on the grate through the incident stream of such a solution.

Since, while pressing the briquette, the air remaining inside it creates elastic stresses, when the load is removed, the reverse reaction of elastic forces can lead to the formation of cracks. The lateral surface of the containment is most susceptible to cracking. Practice shows that the protective layers of the base and cover of the briquette, as a rule, remain intact or often cracks on them are a continuation of cracks in the protective shell of the side surface. Resilient compression

- 1,024,243 material is proportional to the pressing force. Therefore, the condition for maintaining the integrity of the briquette limits the magnitude of the pressing pressure. To eliminate this negative phenomenon, vacuum is usually recommended.

An alternative to such an approach may be another briquette manufacturing option, when in the first stage only the core of the briquette is pressed from a reducing mixture with a base and a lid of heat-resistant material in a plastic state. After removing the load and the reverse elastic reaction, the dimensions of the briquette preform are stabilized. At this stage, the formation of cracks on the side surface of the workpiece from the recovery mixture is allowed. If necessary, the preform is pre-dried. Then, on the outer side surface of the briquette preform, a shell of heat-resistant material in a plastic state is formed. The resulting briquette is dried and subjected to reduction firing.

The choice of material for the briquette protective shell depends on the temperature of reduction firing, which in the case of iron is 900–1300 ° С. Such material can be various types of ceramic masses, for example clay (brick, refractory clay and others). It is convenient to use them in a wet ground state to facilitate the formation of a multilayer briquette.

In order to increase the useful volume of the briquette, it is necessary to strive for the minimum thickness of its protective shell. The thickness of the shell depends on its strength properties: during drying and firing, large cracks should not occur in the shell. Microcracks are allowed through which the gases forming inside are released.

Thinning additives can be added to the shell material, which reduce the ductility and shrinkage of clays during drying and roasting. This can be, for example, sand, calcined clay, waste obtained after extraction of the reduced oxide from the crushed calcined briquette, ore dressing waste, in particular the non-magnetic fraction of iron ore formed during the preparation of the concentrate, and other materials.

To increase the strength of the briquette during firing and cooling, it is preferable that part of the material entering the shell is melted. This can be achieved by the additional introduction of fluxes of additives contributing to such a process, for example, by adding the metal oxides of the initial ore, which are present in the waste formed during ore dressing; alkali metal oxides or concentrate.

Preferably, to increase the strength of the briquette, a small amount of a binder is additionally introduced into the shell material.

Since the protective shell is quite thin, it maintains integrity at high heating and cooling rates. In particular, it is possible to cool the hot briquette with water. The high cooling rate with water allows the destruction of the shell and significantly limits the proportion of reverse metal oxidation, which can further control the acidity of the aqueous medium, i.e. pH value.

The advantage of the proposed method for the reduction of oxides is also to increase the productivity of furnaces, since compaction of the reducing mixture during briquette pressing, on the one hand, increases the specific load of the furnace, and on the other hand, increases its thermal conductivity, which leads to an increase in the heating rate of the inner areas of the briquette, t. e. recovery speed increases.

Claims (9)

CLAIM 1. The method of recovery of ores and metal oxides in the solid state, including obtaining a mixture for the recovery of metals, consisting of metal oxides, solid carbon and limestone; placing this mixture in a solid protective sheath of heat-resistant material; heating and holding the mixture at a temperature below the melting point of the metal and sufficient to reduce the metal, characterized in that a briquette with a protective sheath of a heat-resistant material in a ductile state is formed from this mixture, and the briquette with a protective sheath is subjected to preliminary heat treatment prior to its acquisition by a protective sheath required strength. 2. The method according to claim 1, characterized in that different types of clays and other ceramic masses are used as a heat-resistant shell material. 3. The method according to p. 2, characterized in that in the heat-resistant material of the shell add emaciated additives, fluxes and a binder. 4. The method according to p. 3, characterized in that the emaciated additives choose any or a mixture of any of the following: sand; burnt clay; the waste obtained after extraction of the reduced oxide from the crushed burnt briquette; waste rock is a product of ore dressing. 5. The method according to claims 1-4, characterized in that the binder is added to the mixture. 6. The method according to claim 5, characterized in that they add a binder on a lime basis. 7. The method according to claims 5 and 6, characterized in that the briquette from the mixture and the binder is subjected to preliminary heat treatment prior to the application of the protective heat-resistant shell. 8. The method according to PP.1-7, characterized in that a briquette is formed with the upper and lower layers of the protective shell of the heat-resistant material, and then the protective heat-resistant material, which is in a plastic state, is applied only on the lateral surface of the briquette. 9. The method according to claim 8, characterized in that the briquette with the upper and lower layers of the protective sheath of heat-resistant material in a plastic state, before applying a protective heat-resistant material on the side surface is subjected to preliminary heat treatment.