JPS6053731B2 - Production method of highly reduced chromium ore pellets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing pre-reduced pellets of chromium ore, and particularly aims to increase the reduction rate of the pellets.

The reduction rate here means the proportion (%) of oxygen atoms that are removed by the reduction roasting treatment among the oxygen atoms bonded to valuable metal atoms in the ore, and is calculated by the following formula. It will be done.

However, TotalCr and TotalFe are the total amount of chromium and total amount of iron contained in the roasted ore.

RedCr) RedFe is soluble in acid depending on the amount of reduced chromium and iron.

The following method is generally used to manufacture ferrochrome.

In other words, chromium ore and carbon reducing agent (hereinafter referred to as carbon material)
Chromium ore is charged into an electric furnace and smelted to produce it, or chromium ore is partially reduced in advance by a heating method other than an electric furnace,
In this method, this material is charged into an electric furnace and finally turned into ferrochrome. The latter manufacturing method can reduce costs by replacing part of the electrical energy with energy from liquid fuel such as heavy oil. Partially reduced chromium ore is called pre-reduced pellets, and various reduction methods have been proposed, but the method that has been practically industrialized is is a method of reduction roasting using a rotary kiln.

The disadvantage of this method is that since it uses a combustion flame of heavy oil or the like, it requires mixing of air and blowing in secondary air, which inevitably creates a partially oxidizing atmosphere inside the kiln. In an oxidizing atmosphere, (1) the carbon material blended into the pellets (hereinafter referred to as internal coal) burns, and this combustion reaches about 30% of the internal coal. For this reason, the reducing action of the chromium ore by the inner charcoal is inhibited, and if extra inner charcoal is added to the pellet in anticipation of the amount of combustion mentioned above, the strength of the pellet will be weakened.Furthermore, if the pellet is burned, the pellet becomes breathable. Therefore, when exposed to an oxidizing atmosphere, even what has been reduced is susceptible to oxidation. (2) Normally, in a rotary kiln, pellets are charged from the side opposite to the burner and transferred to the burner side while being reduced, but since the atmosphere on the burner side is particularly oxidizing, the pellets are oxidized in this area. Therefore, at present, most of the pellet surface is oxidized. For the above reasons, the total reduction rate of the pre-reduced pellets is at most 65%. Despite such a reduction rate, there is currently no choice but to use a rotary kiln because no industrial reduction method other than a rotary kiln has been found. The present invention improves the conventional manufacturing method of reduced chromium ore pellets, prevents oxidation as much as possible by using a rotary kiln, increases the reduction rate, and has high pellet strength to prevent the pellets from disintegrating during heating. It was developed with the intention of effectively utilizing ferronickel slag, which is treated as waste, as a raw material for the realization of the material, thereby saving resources.

The present invention is characterized in that, in the conventional production of pre-reduced pellets, the surface of the pellets is coated with slag obtained during ferronickel smelting or a mixture of this slag with a low melting point substance added.

The idea of obtaining pre-reduced pellets whose surfaces are coated with a coating material was already developed by the applicant in
6-43695, Cr. ．． Fe. ．． We have proposed a technology in which the pellet surface is coated with an oxide such as Mgl-.

In addition, carbonaceous substances are added to the CaO-SiO2 system as a coating material, and during firing, the combustion of the carbonaceous substances causes CaO-
Methods for curing SiO2-based films are also known. However, in the former invention, the oxide must be adjusted to a desired range during smelting in the next electric furnace process, and in the latter invention, when the carbonaceous material is burned, the strength of the remaining film becomes weaker. However, it also improves air permeability, but has disadvantages such as lowering the reduction rate. The present invention coats the pellet surface with a coating material different from the concept of the above-mentioned coating method.

That is, the present invention uses ferronickel slag, which is produced in large quantities as a by-product when ferronickel is produced by smelting nickel ore in an electric furnace, as a main material as a coating material.

Ferronickel slag is partially used as a raw material for ferrochrome, but it is difficult to process most of it.

It is extremely meaningful to make effective use of this slag, and as a result of using this slag as a coating material for pre-reduced pellets of chromium ore, it has been found that good results can be obtained as shown in the examples below. . Although ferronickel slag has recently been proposed for use as a binder in the sintering of iron ore powder, it has never been used as a coating material for reduced chromium ore pellets.
The composition of ferronickel slag varies depending on the grade of the raw material nickel ore, and an example of the composition range is shown in the table below.

It is desirable to use ferronickel slag by pulverizing it into a fine powder of 90% or more in a 200 mesh bath, and the slag is used alone or as a mixture of the slag and a fine powder of a low-melting substance.

This low-melting-point substance controls the action of promoting sintering of the ferronickel slag, making it easier to sinter the film, and a dense sintered film can be obtained at low temperatures. It can be added to the slag in an amount of 40% or less. Examples of the above-mentioned low melting point substance include sodium silicate and fluorite.

Further examples include dust generated when smelting substances such as ferrochrome and ferromanganese in an electric furnace, which mainly contain low melting point oxides.

As an example, the dust composition of ferrochrome is listed in the table below.
The selection of the low melting point substance is determined in consideration of the firing temperature of the coated pellets. Next, the manufacturing method of the present invention will be described.

First, chromium ore and carbonaceous material (for example, petroleum coke, coal coke, force-burned anthracite, etc.) are crushed into a predetermined mesh (approximately 100 mesh or less), and the amount of carbon is 0.7 to 1.1 according to the following reaction formula. Blend so that the amount of C is doubled, and granulate to about 10 to 30 m using a granulator.

The granulator is not particularly limited, but examples include an inclined dish granulator, a rotating drum granulator, and a pricket machine, to which a binder is added to increase pellet strength. Binders include inorganic binders such as bentonite, cement, and water glass, and organic binders such as CMCl valve waste liquid. Ferronickel slag powder or a low-melting substance is added to this on the surface of the formed pellet, and
Coat with the mixed powder coating material.

Coating is carried out by spraying a predetermined amount of water or solution binder while rolling the pellets in a granulator, and adding the above-mentioned coating material to form a film layer (a) of a predetermined thickness. 5-1T
n). A water or solution film is formed on the pellet surface by rolling, and coating material powder adheres to the film to form a dense film. A viscous solution binder is used as necessary to increase the bonding force between particles of the coating material. After the coated pellets are dried, they are fired at a predetermined firing temperature (1200-1500 C dry).
At the same time as reduction roasting in a rotary kiln,
Increases strength by fusion bonding between coating particles.

Therefore, even in an oxidizing atmosphere, combustion of the internal coal and reoxidation of the reduced pellets are suppressed, and the reduction rate is increased. As mentioned above, it is desirable to roll the pellets during the process of applying the coating material to the pellet surface and the process of reducing and roasting the coated pellets in order to densify the saw layer film and increase the pellet strength.

The reason for using ferronickel slag as a coating material in the present invention can be understood from the above explanation, but it can be summarized as follows.

(b) To make effective use of slag; (c) Slag has a history of melting, so during firing,
A stable coating film that does not change physically or chemically can be obtained, and (iii) the slag composition is similar to the slag composition produced during ferrochrome smelting using reduced pellets, which is convenient for operation. This is due to the following.

Next, examples will be shown to clarify the effects of the present invention.

In the following examples, parts indicate parts by weight. Example 1 Analytical values of raw materials used (%) Chrome ore (produced in Akohe) Coal-based powder = Nix A mixture of 100 parts of the above chromium ore fine powder (100 mesh or lower) and 31 parts of coke powder (100 mesh or lower) ,
Bentonite (SlO273%, AI2O3l4%)5
% and the amount of water necessary for granulation to make 10 to 2
It was granulated into pellets of 57 mφ.

The pellets were placed in a tilted dish granulator, and fine powder of ferronickel slag having the composition shown in the table below was supplied while spraying valve waste liquid as a binder to obtain a 1Tn thickness! A coating film of n was formed.

Ferotskels. La. Group composition (%). −． ,,,
．． 、． The coated pellets were dried at 500 ± 50°C, and after further preheating, they were charged into a rotary kiln, passed through a temperature range of 1200 to 1450°C about 6 times while rolling, and discharged from the outlet of the kiln for preliminary reduction. Obtained pellets. The film layer of the obtained pellet was dense and strong with an average ugliness of 0.8.

The reduction rate of this product was 78% (n=10). Incidentally, the reduction rate of the pre-reduced pellets which were subjected to reduction roasting without coating with ferronickel slag was 61%.

・Example 2 Dust generated during ferrochrome smelting (Na2Ol5.8%, K2
Ol7.6%, SlO2l2.3%, CaO3.2%,
MgOl3.8%) and 10% in ferronickel slag.
The resulting mixture was coated according to Example 1, dried (500 ± 5 generations), and roasted and reduced in a rotary kiln at 1200-1400°C for about 6 minutes.

The coating film of the obtained reduced pellets was dense and strong despite the low temperature, and the reduction rate of the pellets was 75.
It was %. As shown by the results of the above examples, the method according to the present invention can increase the reduction rate.

Next, the results of producing high carbon ferrochrome using the reduced pellets obtained by the method of the present invention will be shown.

The reduced pellets and lump coke obtained in Example 1 were charged into an electric furnace (23000 KVA), and small amounts of limestone and silica stone were added.

During the smelting process, no disintegration phenomenon of the reduced pellets was observed and the pellets were uniformly chugged. The basic unit was as shown below. As a comparative example, high carbon ferrochrome was produced using reduced pellets obtained by reducing and roasting granulated pellets in the same manner as in Example 1. According to the present invention, ferronickel slag can be used effectively, and SiO7 and MgO in ferronickel slag can be substituted for silica stone and limestone, which are fluxes added when smelting ferrochrome, resulting in cost reduction. It will be done.

Claims (1)

[Claims] 1. In a method for producing pre-reduced pellets of chromium ore, chromium ore powder and a carbon reducing agent are mixed and formed, and on the surface of the pellets, slag obtained during ferronickel smelting or a low melting point substance is added to the slag. A method for producing highly reduced chromium ore pellets, characterized by coating a mixture.