JPS5811761A - Raw material for alloy iron - Google Patents

Abstract

PURPOSE:To utilize Cr ore effectively as a raw material for production of Fe-Cr alloys contg. no Cr (VI) by pelletizing the residues produced after roasting of the Cr ore with soda ash and leaching of sodium chromate with water together with a reducing agent and a binder and calcining the pellets. CONSTITUTION:The residues produced after oxidation roasting of mixed raw materials of Cr ore, soda ash, lime, etc. and leaching of water soluble sodium chromate with water contain Cr oxides including Cr(VI), Fe oxides and soda components. Such residues are ground, and are mixed with a reducing agent such as coke and an org. binder such as sodium lignin sulfonate. The mixture is pelletized and the pellets are heated to 1,000-1,300 deg.C. The contained Cr(VI) is reduced to CrIII), and further part of the oxides of Cr and Fe are reduced to metallic substances, whereby the pellets contg. >8% Cr2O3, >20% R2O3 (R; total content of Cr and Fe), <7% Na2O are obtained. The pellets are utilizable as a raw material for Fe-Cr alloys and Cr is recovered in high yields.

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, as a raw material for producing chromium-containing ferroalloys. 3 Regarding effective utilization Generally, industrial production of sodium chromate involves blending chromium ore with alkali agents such as soda ash and caustic soda, and further adding lime and inert fillers as necessary. The mixture is oxidized and roasted at high temperature,
Next, 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 generated as a by-product, and its composition varies depending on the roasting conditions, the type of ore, whether lime is added, etc., but in most cases it falls within the following range.

Weight% Of these, the 0r20B component mainly exists as trivalent chromium, but hexavalent chromium also exists in the range of 3000 to 15000 PPM.
Contains some degree. 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. Until now, such chromium slag has been found to have almost no practical utility after chromate has been recovered by increasing the leaching efficiency. Therefore, the hexavalent chromium in the slag is
Normally, it is reduced to trivalent chromium using a reducing agent such as iron and disposed of in a landfill, but active and effective use of chromium-containing slag has not yet been considered, and the following are typical examples: 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 high temperature to form a granular porous silicate, which is used as a lightweight aggregate for civil engineering. use for purposes. (Japanese Patent Publication No. 52-10094) Second, some of the components such as Fe2O3, Al2O3, and MgO are dissolved by applying acid to chromium-containing slag, and an aqueous solution of these salts is used as a sewage water treatment agent. . (Japanese Patent Application Laid-open No. 11010/1983).

However, among these usage methods, the former method of using lightweight aggregate has the disadvantage of adding a large amount of silicic acid and requiring a large amount of energy. Since the value added is low and it is not necessarily used, it is difficult to call it an industrial method.

In addition, the latter method of applying chromium-containing slag as a water treatment agent is not a rational method since only one component in the chromium-containing slag is utilized.

In any case, chromium-containing slag has not been actively utilized to its full potential.

In view of this situation, the inventors of the present invention have conducted various research and studies on more effective and efficient utilization methods that utilize the characteristics of chromium slag, and as a result, they have decided to apply chemical treatment to the chromium slag. The present invention has been completed based on the discovery that the processed product having a specific composition obtained by the method is extremely suitable as a raw material for producing chromium-containing iron alloys. That is, the present invention is a product in which a reducing agent (such as coke) and an organic binder (sodium lignin sulfonate or calcium, etc.) are blended with chromium-containing slag, which is a by-product during the production of sodium chromate from chromium ore, and then fired. At least the chromium component is Cr2O
8% by weight or more as 3, and the i-value components of iron and chromium are 20% as R203 (R represents the total amount of Fe and Cr).
The present invention relates to a raw material for a ferroalloy, characterized in that the content of each component is 7% by weight or more as Na2O, and the soda content is 7% by weight or less as Na2O. The reason why the sintered product of the present invention must have the above-mentioned component content is that the raw material for ferroalloy according to the present invention can be effectively used by itself or in combination with other raw materials for iron manufacturing. If the slag component is outside this range, there may be too much slag component or damage to the furnace material may occur.
This is because it becomes impossible to use it in large quantities. According to the study results of the present inventors, chromium-containing slag, coke, and an organic binder are mixed and made into pellets in a heating furnace such as a rotary kiln under a reducing atmosphere at a maximum temperature of 900 to 13
At 00°C, preferably from 1000 to 1300°C, an average residence time of 05 to 10 hours was appropriate;
Of course, valent chromium was reduced to trivalent chromium, but it was also found that in some raw materials, chromium and iron were reduced to metallic chromium and metallic iron.

In this case, the reduction firing temperature may be 800°C or higher when only hexavalent chromium is reduced, but if solid phase reduction of chromium and iron is also taken into account, it is preferably 900°C or higher, preferably 1000-1000°C.
300°C is desirable.

Further, as the reducing agent of the present invention, those commonly used as reducing agents can be used, but solid reducing agents such as coke, coal, and charcoal are mainly preferred. When coke is used as a reducing agent, it has been found that the amount of coke added to chromium-containing slag and the amount of metallic chromium and metallic iron produced in the fired product are almost proportional. In this case, if the amount of coke as a reducing agent is small, the reduction reaction cannot be carried out, so the effective amount is preferably 5% by weight or more, preferably 10% by weight, based on the chromium-containing slag.

In this case, it has also been found that the amount of the reducing agent added to the chromium-containing slag is approximately proportional to the amount of metallic chromium and metallic iron produced in the fired product. In this way, chromium compounds and iron formation in chromium-containing slag are reduced.

If the chromium content and iron content of the raw materials fed into the electric furnace for producing ferroalloys are in the state of metallic chromium or metallic iron when the compound is effectively used as a valuable component for producing ferroalloys, This will reduce the electricity consumption rate and lead to energy savings.

As described above, the fired product of the present invention not only detoxifies hexavalent chromium in chromium-containing slag, but also can be effectively used to recover valuable components as part of raw materials for ferroalloys, which is an important resource saving feature. It can be said that it has great industrial significance today.

Next, examples of the present invention will be shown.

Example 1 100 chromium-containing slag powder (particle size 175μ) shown in Table 1
Parts by weight and 30 parts by weight of coke powder (particle size 175μ) are uniformly mixed, granulated using an organic binder as a binder, and then pre-dried at about 50° C. for 1 hour. The dried material is placed in a rotary kiln at a maximum temperature of 1250°C and an average residence time of 5.
It was fired for 0 minutes under reducing atmosphere conditions.

After mixing 100 parts by weight of the above-mentioned fired product with 5 parts by weight of silica stone 2 parts by weight of quicklime and 10 parts by weight of coke, an organic binder is mixed,
Form into briquettes about 20m long.

This briquette is melted at about 1650° C. in an electric furnace. The products obtained by the treatment and the chromium recovery rate are shown in Table 3.

As is clear from the above results in Table 3, most of the chromium in the chromium-containing slag was recovered as ferrochrome, and it was found to be effective as a raw material for steelmaking.

Sender: Nippon Chemical Industry Co., Ltd. Agent Yutaka 1) Yoshio

Claims (2)

[Claims] (1) A fired product obtained by heating and firing a mixture of chromium-containing slag produced as a by-product when producing sodium chromate from chromium ore and a reducing agent to reduce the hexavalent chromium content in the slag, which contains at least chromium. Cr2O, 8% by weight or more, iron and chromium valuable valve R20, (R is Fe and Cr
) is 20% by weight or more and the soda content is N
A raw material for a ferroalloy characterized by having a content of each component of 7% by weight or less as a2O. (2) The raw material for a ferroalloy according to claim 1, wherein the fired product is in the form of pellets.