JPS581053A - Raw material for ferroalloy - Google Patents

Abstract

PURPOSE:To provide a raw material which consists of a sintered mixture of chromic slag and silicic acid-contg. materials of specified contents of chromium, valuable components of iron and chromium, and sodium, and which is extremely suitable for production of chromium contg. ferroalloy. CONSTITUTION:Powder of chromium-contg. slag which is byproduced in the stage of producing Na2CrO4 from chromium ore and powder of silicic acid- contg. materials (e.g.; silica, silica sand) are thoroughly mixed. Here, these are so mixed that basicity, that is, molar ratio of (Na2O+CaO+Mg)/SiO2 attains 0.50-3.0. A reducing agent such as coke is added to this mixture or a desired binding agent is added in granulating the mixture according to need, then the mixture is heat-treated at 900-1,300 deg.C max. temps. in a heating furnace such as rotary kiln. As a result, the intended raw material of ferroalloy contg. >=8wt% chromium expressed in terms of Cr2O3, >=20wt% valuable components R2O3 (R is the total amt. of Cr and Fe) of iron and chromium and <=5wt% sodium expressed in terms of Na2O is obtained.

Description

Detailed Description of the Invention The present invention uses raw materials for ferroalloys, particularly chromium-containing slag produced as a by-product when producing sodium chromate from chromium ore, through chemical treatment. related to effective use as

Generally, industrial production of sodium chromate involves blending chromium ore with alkaline agents such as soda ash and caustic soda, and then adding lime and inert fillers as necessary, and then oxidizing and roasting the mixture at high temperatures. Then, a method is adopted in which a sodium chromate aqueous solution is obtained by leaching the roasted product with water. On the other hand, at this time, a large amount of chromium-containing leaching residue, chromium-containing slag, is produced as a by-product, and its composition varies depending on the roasting conditions, type of ore, presence or absence of lime addition, etc., but in most cases it falls within the following range. .

Among these, the Cr2O3 component mainly exists as trivalent chromium, but hexavalent chromium also exists in the form of 3.000 to 15,000.
Contains about ppM. Furthermore, since most of the Na2O component exists as a compound that is poorly soluble or insoluble in water, it is not eluted by normal leaching operations.

Conventionally, such chromium slag has hardly been found to have any practical utility after recovering as much chromate as possible by focusing solely on leaching efficiency. Therefore, although it is normal to reduce the hexavalent chromium in the slag to trivalent chromium using a reducing agent such as ferrous sulfate and dispose of it in a landfill, active and effective use of chromium-containing slag has not been studied. This is not to say that there are no such proposals, but the following typical proposals have been made.

First, after adding and mixing chromium-containing slag with silicic acid and a reducing agent and granulating it, the granulated product is fired at a temperature to form a granular porous silicate, which is used as a lightweight aggregate. Used for civil engineering. (Special Publication No. 52-10094) No. 2,
By applying acid to chromium-containing slag, Fe2O
3. Some of the components such as Al2O and MgO are dissolved and the aqueous solution of these salts is used as a sewage water treatment agent. (Unexamined Japanese Patent Publication No. 47-11010) However, among these usage methods, the former method of using lightweight aggregate requires large-scale facilities to add a large amount of silicic acid and heat it at a high temperature close to the melting point. It has the disadvantage of requiring a large amount of energy and energy, and in addition, even if it requires such economic sacrifice, the added value is low and it is not necessarily used, so it cannot be called an industrial method. hard. In addition, the latter method of providing water treatment agents is not a rational method since only one component in the chromium-containing slag is utilized.

In any case, the characteristics of chromium-containing slag have not been actively used effectively.

In view of this situation, the inventors of the present invention have repeatedly conducted various studies and studies on a more effective and efficient usage method that takes advantage of the characteristics of chromium slag, and have found that by applying chemical treatment to the chromium slag, The present invention was completed by discovering that the resulting treated product having a specific composition is extremely suitable as a raw material for producing chromium-containing iron alloys. That is, the present invention is a sintered product of a mixture consisting essentially of chromium-containing slag and silicic acid-containing material produced as a by-product during the production of sodium chromate from chromium ore, the chromium component being at least 8% by weight as Cr203.
As mentioned above, the valuable components of iron and chromium are R203 (R is Or
The raw material for the ferroalloy is characterized by having a content of each component of 20% by weight (expressing the total amount of iron and Fe) and 5% by weight BF (as Na2O and the soda content). According to the study results of the present inventors, chromium-containing slag generally contains significant amounts of hexavalent chromium and Na2O components, causing environmental pollution, and may also contain large amounts of CaO components. , itself is not suitable as a raw material for ferroalloys. Also, even if you dare to use it, a large amount of Ca0by
, decreases the content of valuable components such as chromium and iron, which results in the production of more slag than necessary in the steelmaking process, leading to an increase in energy requirements.

However, even with such slag, CaO and Na2
It has been found that chromium slag with a low O content can be effectively used as a raw material for ferroalloy by making use of the characteristics of chromium slag by mixing it with a silicic acid-containing material and converting it into a sintered body. Preferably, the sintered body has reduced hexavalent chromium, so that it is rendered harmless and substantially free of hexavalent chromium.

In the present invention, among the sintered bodies of mixtures consisting essentially of chromium-containing slag and silicic acid-containing substances, those which can be particularly applied as raw materials for ferroalloys have a chromium content of F18 as Cr2O3.
By weight, the valuable components of iron and chromium are about 20% by weight or more, preferably about 25% by weight or more as R203 (R has the same meaning as above), and the soda content is about about 10% by weight or more by weight as Na2O. It has been found that it is necessary to have a content of each component of at least about 5 to 5 parts by weight, preferably about 3 parts by weight.

The chromium-containing slag used in the present invention should preferably have as low a soda and calcium content as possible, but at most it should have a content of about 10% by weight or less as CaO and 8% by weight or less as Na20, and should contain at most about 10% by weight or less as CaO and 8% by weight or less as Na20. A total amount of about 10% by weight or less is particularly preferred.

In this case, chromium oxide as other auxiliary raw materials.

Hydrous oxides, chromium ore, laterite ore, or by-products such as dust and scale discarded from iron, steel, or metal processing processes can be mixed and used during or after the production of the sintered body.

On the other hand, silicic acid-containing substances are raw materials that are used without T in order to neutralize the alkalinity of chromium-containing slag, such as silica stone, silica sand, silica 2 shale, clays, ferrosilicon dust, etc. can give.

The raw material for a ferroalloy according to the present invention can be industrially produced using the above two types of raw materials as essential starting materials as follows.

That is, the powders of both raw materials are sufficiently mixed to prepare a mixture. It goes without saying that the mixing ratio is set so that the composition of the sintered product has the above content, but the basicity (Na2O+
-CaO+ MgO)/SiC2 molar ratio is 0.5
It is necessary that it is 0-30, preferably 07-20.

In this case, if necessary, a reducing agent such as coke or an organic substance or a desired binder for granulation can be appropriately selected and used, and at most 10% by weight based on the chromium-containing slag. That's fine.

The mixture is heat treated in a heating furnace such as a rotary kiln, and the conditions are such that the maximum temperature is 900-1300'C, preferably 1000-1250'C, and the average residence time is 0.
5-2 hours is Jg.

The mixture is obtained as a hard sintered body by heat treatment as described above. Also, if necessary, the sintered product is granulated into pellets. This is thought to be due to a portion of the alkali and silicic acid in the raw material being vitrified, but the hexavalent chromium has been substantially reduced and no dust is generated, making it extremely safe to handle.

Therefore, the raw material for the ferroalloy according to the present invention can be obtained as a granulated hard sintered body of a desired size.
In its use, there is an advantage that it is not necessarily necessary to pelletize it together with other original materials, and it can be directly charged into an electric furnace.

As described above, the sintered body of the present invention can be used not only to detoxify hexavalent chromium, but also to effectively recover valuable components as part of raw materials for ferroalloys, which is an important consideration in today's world of resource conservation. Next, examples of the present invention, which can be said to have great industrial significance, will be shown.

Example Chromium-containing slag powder (particle size 175μ) shown in Table 1 100
Part by weight and 20 overlapping parts of shale powder (particle size 175μ) were mixed uniformly, and heated in a rotary kiln at a maximum temperature of 1250°C.
When fired under conditions of an average residence time of 1 hour, a tightly sintered granulated product was obtained, the composition of which was as shown in Table 1.

Basicity in the formulation (Na20 +CaO+ MgO)
The molar ratio of /5jO2 was 37, and the fired product was a dark brown hard spherical body. By the above treatment, 18 parts by weight of silica stone, 10 parts by weight of quicklime and 17 parts by weight of coke are added and mixed to 100 parts by weight of the above sintered material, and the mixture is charged into a Soederberg electric furnace and melted at about 1650°C. The treated products and recovery rates obtained are shown in Table 2.

As is clear from the above results, most of the chromium in the chromium-containing slag was recovered as ferrochrome, which was found to be effective as a raw material for ferroalloys.

Sender: Nippon Chemical Industry Co., Ltd.

Claims (2)

[Claims] (1) A sintered product of a mixture consisting essentially of chromium slag produced as a by-product when producing sodium chromate from chromium ore and a silicic acid-containing substance, in which at least the chromium content is Cr.
8 weight X or more as 2O3, evening value R of iron and chromium
A raw material for a ferroalloy, characterized in that 2O3 (R represents the total amount of Or and Fe) is 20% by weight or more, and the soda content is 5% or less F as Na2O. (2) Raw material 0 for a ferroalloy according to claim 1, wherein the sintered product is in the form of pellets.