JP2002211970A - How to recycle used chromium-containing refractories - Google Patents

Abstract

(57) [Problem] To provide a chromium-containing refractory in which hexavalent chromium is reduced in recycling chromium-containing refractory waste after use. SOLUTION: In the production of refractory bricks, in the production of fired refractories composed of a combination of used chromium-containing refractories and other refractory raw materials, the use of carbon-containing raw materials and / or other reducing agents makes the fired refractories smaller.
How to use chromium-containing refractories and used chromium-containing refractories with reduced valent chromium. [Effect] A waste disposal problem can be solved by using a used chromium-containing refractory containing hexavalent chromium which is harmful to the human body as a refractory raw material by reducing hexavalent chromium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to recycling of used chromium-containing refractories.

[0002]

2. Description of the Related Art Chromium-containing refractories widely used in rotary kilns for cement firing and the like have become indispensable in fields requiring high corrosion resistance. However, as a result of reacting with alkali salts, there is a disadvantage that hexavalent chromium which is easily water-soluble and harmful to the human body is produced. Therefore, measures to treat the waste of used chromium-containing refractories have a significant social problem due to their environmental impact.

As a countermeasure, there is a method of making the waste harmless or reusing it. This is a method in which the generated hexavalent chromium compound is chemically treated to render it harmless, or solidified and reused, but at present it is costly.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to recycle the waste of used chromium-containing refractories and to eliminate the problem of environmental pollution caused by harmful hexavalent chromium.

[0005]

According to the present invention, there is provided a method for reusing a used chromium-containing refractory according to the present invention. A method for producing a refractory, characterized in that hexavalent chromium is reduced by adding a starting material and / or another reducing agent.

The used chromium-containing refractories used as a raw material in the present invention include iron and steel, non-ferrous metals, chromium-containing refractories used in various types of chemical furnace incineration ash melting furnaces, rotary kilns for cement firing, and the like.

[0007] The purpose of adding the carbon-containing raw material and other reducing agents is to make the hexavalent chromium component harmless by reducing it during firing. The carbon-containing raw material may be carbon black, tar, pitch, scale graphite, artificial graphite, earthy graphite, pulverized magnesia-carbon brick, or an organic substance such as phenolic resin that can be carbonized after firing. As other reducing agents, powdered aluminum, powdered silicon, powdered aluminum magnesium alloy, powdered aluminum silicon alloy and the like are used. The carbon-containing raw material and other reducing agents may be used alone or in combination. These raw materials tend to decrease the amount of hexavalent chromium component in the fired brick as the added amount increases (FIG. 1).

However, the carbon in these raw materials is burned out in the brick firing step, so if added in an excessive amount, the porosity of the brick increases, and the strength decreases.
Since the original performance of the refractory brick is reduced, the carbon-containing raw material should be kept at 5% by weight or less in terms of carbon. In addition, as an addition method, in order to prevent a reduction in strength after firing, it is desirable to use as little as possible intermediate grains.

[0009] The particle size of the used chromium-containing refractory used is not particularly limited, and is used in the form of coarse, intermediate or fine powder.

[0010] The refractory according to the present invention is composed of the above-described raw materials, and can reduce the content of the residual hexavalent chromium component after firing, thereby reducing the problem of environmental pollution due to harmful hexavalent chromium. It became possible to reduce.

[0011]

The method for recycling used chromium-containing refractories according to the present invention is to use used chromium-containing refractories as a part of raw materials in the process of producing refractory bricks, and further use raw materials containing carbon and / or other materials. This is a refractory manufacturing method in which a hexavalent chromium component is reduced and fired to make it harmless during firing by adding a reducing agent to the raw materials. Table 1 shows an example of the chemical composition of the used chromium-containing refractory. Mainly MgO,
It is composed of Cr ₂ O ₃ etc., but contains Na ₂
An alkaline component such as O or K ₂ O reacts with Cr ₂ O ₃ to produce K
Hexavalent chromium, such as ₂ CrO ₄ is produced. When the hexavalent chromium component and carbon coexist and are calcined appropriately, the hexavalent chromium component is reduced to trivalent chromium and rendered harmless as shown in the following formula. Further, since the alkali component evaporates during firing, trivalent chromium is not reoxidized to hexavalent chromium during cooling in the refractory brick firing step.

4K ₂ CrO ₄ + 3C → 3CO ₂ + 4K ₂
O + 2Cr ₂ O ₃

[Table 1]

EXAMPLES Table 2 shows that a fired brick and a refractory containing used chromium containing 30% by weight of carbon in the refractory containing 100% by weight of used refractory containing used chromium were used as raw materials.
It is the result of measuring the amount of the residual hexavalent chromium component of the calcined bricks added by weight% and 10 weight%. It is shown that the content of hexavalent chromium is reduced to 1/10 or less by the addition of the raw material containing carbon.

[0013]

[Table 2] Note 1) Hexavalent chromium elution condition Burned brick was crushed to 4.0
200 g of the sample classified to ９9.5 mm
The extract was immersed at room temperature in 39 ml for 39 hours, and the extract was subjected to measurement of hexavalent chromium. The measurement was performed by atomic absorption analysis.

[0014]

In the refractory brick production process, used chromium-containing refractory is used as a part of the raw material, and a carbon-containing raw material and / or another reducing agent is added to the refractory material and fired. The content of the chromium (VI) component can be reduced, and the used refractory containing chromium can be reused.

[0015]

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a carbon-containing raw material and the content of a hexavalent chromium component in a fired brick.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 35/00 W

Claims (3)

[Claims] 1. A combination of one or more of magnesia-chromia-based, chromia-based, chromia-magnesia-based, chromia-alumina-based, and chromia-alumina-zirconia-based refractories containing 5 to 100% by weight. And one or more combinations of magnesia clinker, chromite, alumina, alumina-silica system, chromium oxide, zirconia and zircon 0 to 95% by weight
In the production of a fired refractory using as a main material, 0.3 to 5% by weight of carbon-containing raw material and / or fine particles or powder metal of 0.5 to 3% in terms of carbon with respect to 100% by weight of the above main material at the time of kneading. A method for producing a fired refractory by recycling a used chromium-containing refractory that reduces hexavalent chromium by using a combined amount of 6% by weight. 2. Various furnaces using the refractory obtained in claim 1. 3. A method for producing a refractory wherein the fired product obtained in claim 1 is pulverized, classified into particles and reused as a raw material.