JPS62256938A - Reducing method for chromium ore - Google Patents

Abstract

PURPOSE:To reduce chromium ore at a low cost and high degree by adding a binder to a pulverized powder mixture composed of the chromium ore and carbonaceous reducing agent, molding the mixture to a lump shape, forming a protective film on the surface and subjecting the molding to a heating treatment in a tunnel kiln. CONSTITUTION:The pulverized powder mixture preferably sized about <=100mesh is prepd. by mixing the chromium ore powder and carbonaceous reducing agent powder such as coke and coal. The compounding ratio of the above-mentioned carbonaceous reducing agent is specified to the theoretical ratio or the ratio slightly in excess thereof. The binder such as bentonite or CMC is added to the pulverized powder mixture and the mixture is molded to the lump shape sized about 10-300mm. The protective film which prevents the intrusion of an oxidizable combustion gas is formed by using pulverized powder such as Cr2O2, SiC and fly ash on the surface of the resulted molding. The coated molding is heated to 1,200-1,500 deg.C and reduced in the tunnel kiln. The reduced chromium ore having high reducibility of about >=80% is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for reducing romite ore, which is suitable as an additive for metallurgy.

(Prior Art) Generally, steel containing chromium is manufactured by a method of adding chromium in the form of ferrochrome to steel. The method for producing ferrochrome involves charging chromium ore together with a carbonaceous reducing agent and a slag-forming agent into an electric furnace and melting and smelting it. Methods have also been adopted to reduce the amount of kerosene used and to use inexpensive heavy oil or coal energy for smelting.

That is, as seen in Japanese Patent Publication No. 413-43895, a binder is added to a fine powder mixture of chromium ore and a carbonaceous reducing agent, granulated into pellets, and the granulated material is loaded into a rotary kiln. A method of reducing and roasting in a solid phase state in an oxidizing combustion air stream is used.

In this method, a fuel with a low energy unit price such as heavy oil or pulverized coal is selected and used, but in order to completely burn the fuel and obtain a high temperature, excess combustion air is used and oxidizing combustion air is used. directly heating the pellets. Carbon gas (CO2), water vapor (H
2O), oxygen (02), and other gases that are oxidizing to chromium/iron carbide or carbonaceous reducing agents, which are reduction products, are contained in large quantities. Therefore, the oxidation reaction proceeds on the surface of the pellet, and the reduction of chromium and iron does not proceed to a high degree, so that the actual reduction rate of the pellet as a whole reaches only about 80% at most. In particular, the reduction rate of chromium is limited to about 75%. If such pellets are to be used as raw material for steelmaking, expensive electrical energy must be used to reduce the remaining portion.

On the other hand, as a solid-phase reduction method that avoids heating in an oxidizing combustion stream, a mixture of chromium ore and a carbonaceous reducing agent is charged into a vacuum furnace and heated while introducing argon (Ar) gas. A method of solid-phase reduction is known (Special Publication No. 1973-
1959 etc.).

In addition, in the method of solid phase reduction in a rotary kiln, the inner charcoal pellets of chromium ore are charged into the rotary kiln together with a large amount of carbon material, and the inner charcoal pellets are kept buried in the carbon material while oxidizing combustion is carried out. A solid-state reduction method is also known in which the pellet is isolated from the air flow and in an atmosphere of monomorphic carbon (CO) generated substantially by reduction of the pellet (
(See USP 2,869,850, etc.).

(Problems to be Solved by the Invention) As described above, when charcoal pellets of chromium ore are charged into a rotary kiln and roasted for reduction in an oxidizing combustion air stream, the reduction rate is about 80% at most.

In recent years, attempts have been made to make steel by directly charging chromium ore, rather than in the form of ferrochrome, into a steelmaking furnace and using it as a chromium source. Reduction requires a large amount of energy, and there are limits to reduction in steelmaking furnaces.

Therefore, if we use the combustion energy of cheap fuel to perform solid phase reduction to the highest possible degree and add this highly reduced product to the steelmaking furnace, we can shorten steelmaking time, reduce energy consumption, and prevent damage to refractories. It will have a huge effect. That is, the main objective of the present invention is to obtain highly reduced chromium ore with a reduction rate of 80% or more using energy from inexpensive fuel.

To avoid the disadvantages of reductive roasting in an oxidizing combustion stream,
As mentioned above, attempts have been made to reduce and roast the method in an inert air stream, but there are problems with equipment to make it an industrial standard, and it has not yet been realized.

That is, in the method using a vacuum furnace such as the above-mentioned Japanese Patent Publication No. 38-195i3, a batch operation is required, which inevitably leads to a decrease in productivity.

Further, in the reduction roasting method in a rotary kiln together with a large amount of exterior carbon material as in USP 2,868,850, the pellets after reduction roasting and the carbon material are mixed.

In this state, it is impossible to obtain anything that can be used directly in the steelmaking process, and it is substantially difficult to separate the reduced roasted material from the exterior carbonaceous material.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems, and includes forming a fine powder mixture of chromium ore and a carbonaceous reducing agent into a lump, After forming a protective film on the surface to prevent the intrusion of oxidizing gases, the molded body is heated to 1200 to 1500°C using a tunnel kiln, and the molded body is thermally reduced to obtain highly reduced chromium ore. The present invention provides a method.

The present invention will be explained in detail below.

The chromium ore of the present invention is chromium oxide (Cr2 03
) with a content of 40 to 60%. The chromium ore may be a fine ore.

Carbonaceous reducing agents include metallurgical coke, petroleum coke,
Those containing fixed carbon (FC) such as anthracite, coal, and charcoal can be used. The mixing ratio of chromium ore and carbonaceous reducing agent is determined according to the following formula.

7Cr2 03 +27G = 2Cr7 C3+2L
CO(1)7FeO+ IOC→Fe7 C3+ 70
0 (2) In other words, the amount of carbonaceous reducing agent required to reduce the chromium oxide and iron oxide in the chromium ore to carbide may be blended. 0 In the present invention, the oxidative depletion of the carbonaceous reducing agent by the oxidizing air flow is sufficient. Since this does not occur, the blending ratio of the carbonaceous reducing agent may be a stoichiometric amount or a slight excess of the stoichiometric amount.

Since the chromium ore and the carbonaceous reducing agent are brought into intimate contact for solid phase reduction, they are mixed into a fine powder and then formed into a lump using an appropriate binder.

The particle size of the mixed fine powder is 100 mesh or less, preferably 2
It is better to set it to 00 meshes or less.

In addition, as a binder, an inorganic material (for example, bentonite) can be used.
However, organic substances (for example, CMC) may also be used.

There is no particular restriction on the amount of the binder used, and it may be sufficient to obtain a formed body, and there is no problem in using water in combination.

The molding method is not particularly limited either, and ordinary pellets, briquettes, etc. can be used as long as the chromium ore powder particles and carbonaceous reducing agent particles are in close contact with each other.

The size of the molded body is also not particularly limited, and the diameter is 1
It is possible to use cylindrical or spherical ones with a diameter of about 0 mm to about 300 mm in diameter, and the selection may be made in consideration of the tunnel kiln equipment to be used.

Next, a protective film is formed on the surface of the chromium ore compact to prevent infiltration of oxidizing combustion air in the tunnel kiln. Materials suitable for the protective film include: 1) It must not soften or flow at temperatures below 1200°C, 2) It must not be consumed by oxidation, and 3) Its expansion and contraction are not significantly different from those of chromium ore. is required. Substances useful as protective films include Cr203-FeO, ZrO,
It may be a single substance or a mixture of oxides such as MgO, CaO, Al2O'3, and Sio2, carbides and nitrides such as SiC, Si3N, and AIN, or a substance containing two or more of the above components, such as fly ash. ,Also,
Mixing these substances with a carbonaceous reducing agent is convenient because it protects the interior by releasing carbon monoxide gas in an oxidizing gas flow.

These protective film-forming substances are made into fine powder of 50 ml or less, and coated on the surface of the chromium ore compact using a binder.

As a binder, water, water glass, and molasses are used.

Organic solvents such as CMC and phenol can be used.

The coating method may be spray coating, brush coating, dipping, etc., or a double granulation method using a pelletizer may be used.

The chromium ore compact with the protective film formed thereon is placed in a tunnel kiln and heated and reduced.

The tunnel kiln is not a special one, and can be one that has been used conventionally.It is 30 to 100 meters long, and a trolley runs inside, and chromium ore molded bodies are loaded on each truck and fed into the kiln one after another. From the entrance, it passes through three zones: a pre-preparation zone, a reduction zone, and a cooling zone.

The heating required for reduction is performed using the combustion energy of various fuels.

In this case, all types of fuel can be used, including heavy oil, coal, natural gas, smelting furnaces, and waste gas.

What is necessary is to select the most economically advantageous fuel for the plant, and also to select the most efficient combustion conditions without being restricted by the reduction reaction.

Even when such a state of complete combustion of fuel is utilized, in the case of the present invention, no oxidation phenomenon occurs on the surface of the compact, and a reduced chromium ore product with a high reduction rate can be obtained.

What is the temperature at which chromium oxide in chromium ore is reduced?

Since the temperature is 1200°C or higher under normal pressure, the temperature of the molded product is 1200°C or higher.
It is necessary to adjust the processing speed so that the residence time in the temperature range of 00° C. or higher is at least 30 minutes or more.

The chromium ore reduced sintered compact obtained in this way is
Because it is not affected by oxidizing combustion air currents.

The condition is almost uniform from the inside of the compact to the surface, and the reduction rate of the entire compact reaches 90% or more.

Next, the present invention will be explained with reference to Examples.

Example 30 parts of coke powder was mixed with 100 parts of chromium ore from South Africa, dried in a rotary dryer and ground in a ball mill to obtain a mixed fine powder with a 200 mesh pass of 90%.

Table 1 shows the grades of the chromium ore and coke breeze used.

(Margins below) Table 1 (Add 3.5% bentonite as a binder to the above-mentioned mixed fine powder, mix it in a pug mill while adding water, and put this mixed raw material in a hydraulic extrusion molding machine. Accordingly, 250■φ,
Table 2 shows the composition of the extruded product formed into a 500 m layered cylinder.

Table 2 (The surface of wt Chiko's molded body was coated with an anti-oxidation coating agent as shown in Table 3 to a thickness of around 1 mm using a sprayer, and the coated molded body was lined up bare on a trolley and transported through a tunnel. It was placed in a kiln and heated and reduced.

Table 3 The tunnel kiln used had a total length of 24 m, a pre-heating zone length of 12 m, an effective cross-sectional area of 1.2 m', a reduction zone length of 10 m,
The effective cross section was [3, Orn'. One side lO in the reduction zone
A total of 20 heavy oil burners were installed. There is 1 in the kiln.
Six carts were arranged and the carts were moved at a speed of 3.5 m/hour. The temperature inside the reduction zone at this time is 1400 + 50℃
was controlled. Table 4 shows the composition of the reduced pellets thus obtained.

Table 4 Here, Sol, Cr, Sol, and Fe are Cr and Fe that are soluble in 10% sulfuric acid. Also, (Cr, Fe)
The reduction rate means the proportion (%) of oxygen atoms that are removed by reduction treatment among the oxygen bonded to (Cr, Fe) atoms in the ore, and is determined by the following formula.

As is clear from Table 4, the chromium ore compact obtained by the method of the present invention was highly reduced, and both the inside and surface of the compact were uniformly highly reduced.

In particular, the reduction rate of chromium exceeds 90%, and a reduced product with such a high chromium reduction rate could not be obtained by the conventional rotary kiln method.

In addition, when using the method of the present invention, there was no abrasion of the molded bodies into powder, and each molded body was strongly sintered, so it was sufficiently durable to be used in the subsequent smelting process and steelmaking process.

Claims (1)

[Claims] A binder is added to a mixed raw material of chromium ore powder and carbonaceous reducing agent powder, which is then molded, a protective film is formed on the surface of the molded product, and then reduced by heating to 1200 to 1500°C in a tunnel kiln. A method for reducing chromium ore, which is characterized by: