JP2010207672A - Method of disposing of waste containing chromium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a disposal method which enables disposing of waste containing chromium without using a special disposal device and recovering the chromium as a steel material component. <P>SOLUTION: This method of disposing of waste containing chromium involves the following procedures: First, the waste 4 containing the chromium is put into a molten slag 3 of a ladle 1 in which a secondary refining is caaried out. After that, a reducing agent is added, and hence the chromium contained in the waste 4 is reduced and thus, the disposal of the waste 4 is accomplished. That is, the chromium can be recovered directly as a molten steel component by melting and reducing the waste 4 containing the chromium. Further, the concentration of chromic acid contained in the waste 4 is set at not more than 0.5% and therefore is below the hexavalent Cr elution criterion to soil, 0.05 mg/l, so that the same disposal procedures as applied to the ordinary slag can be applied to the slag under this disposal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of recovering chromium in waste containing chromium as a molten steel component by a reduction reaction and treating the waste in a harmless state.

Since bricks containing magnesium oxide and chromium oxide such as magcro brick are excellent in fire resistance and high temperature corrosion resistance, they are used as lining refractories for cement rotary kilns and secondary steelmaking furnaces. Chromium contained in such bricks is stable as trivalent Cr ₂ O ₃ at the time of production, and has low risk because it is insoluble in water. However, the waste material after use is changed to hexavalent CrO ₃ due to high-temperature oxidation or the like, so that the brick scraps at the time of furnace disassembly contain hexavalent chromium. Hexavalent chromium is water-soluble, so it is treated by burying a barrier sheet at the bottom of the landfill and reclaiming it on top of it, but the barrier sheet cannot be completely waterproofed. There have been some environmental problems such as the contamination of groundwater.

  Here, in JP-A-6-269964, solid waste containing hexavalent chromium is pulverized to a diameter of 10 mm or less, a reducing agent mainly composed of aluminum refining ash and tin oxide or antimony oxide are mixed, and this mixture is added to 800 There has been disclosed a technique for detoxifying hexavalent chromium in solid waste by heating to a temperature of ℃ or higher. Japanese Patent Application Laid-Open No. 10-174955 discloses a method for removing hexavalent chromium contained by firing waste magcro bricks at 500 ° C. or higher in a reducing atmosphere. Japanese Patent Application Laid-Open No. 2002-249811 discloses a technique of using a vertical smelting reduction furnace to recover a chromium component in a brick waste material as a chromium-containing metal and render it harmless.

Japanese Unexamined Patent Publication No. 6-269964 Japanese Patent Laid-Open No. 10-174955 JP 2002-249811 A

  However, in the methods disclosed in JP-A-6-269964 and JP-A-10-174955, the hexavalent chromium contained therein is rendered harmless by reduction, and it is considered as a technology that enables the treatment of waste refractories containing chromium. The amount of reducing agent necessary for reduction and the amount of processing are not clarified, and the economics of processing large-scale waste refractories such as cement kiln furnaces and secondary refining equipment for ironmaking Etc. are unknown and difficult to apply. In addition, the method disclosed in Japanese Patent Application Laid-Open No. 2002-249811 can obtain a molten metal based on chrome-iron, but it is rare that such a furnace is installed in a normal ironworks. It is necessary to construct a new construction for the treatment of contained waste, which increases the processing cost.

  In consideration of such circumstances, the present invention provides a processing method for processing waste containing chromium without using a special processing apparatus and recovering chromium as a steel material component.

  In order to solve the above problems, according to the present invention, in a molten slag of a ladle where secondary refining is performed, waste containing chromium is melted and added with a reducing agent. A method for treating chromium-containing waste is provided in which chromium is reduced to recover chromium in molten steel. Add reducing agents such as Al and Si so that the composition of the molten slag in the ladle is, for example, T.Fe + MnO ≤ 2.5 mass%, and reduce chromium contained in the waste in the molten slag with strong reducing power. By doing so, chromium is recovered in the molten steel.

  According to the present invention, the slagging material is put into the ladle, and a reducing agent such as Al, Si, etc. is added so that T.Fe + MnO ≦ 2.5% by mass in the molten slag in the ladle. In molten steel ladle refining for reduction refining, chromium-containing waste is put into molten slag before or during refining treatment, and the waste is melted by melting reduction treatment to directly add chromium to the molten steel component. As recovered. After the refining process, the chromic acid concentration in the slag is reduced to 0.5 mass% or less, so that the hexavalent Cr elution standard of 0.05 mg / l in the soil will be reduced, and the same treatment as normal slag will be possible. .

It is explanatory drawing of the processing method of the waste concerning embodiment of this invention. It is a graph showing the amount of elution of the relationship Cr ₂ O ₃ concentration and Cr ⁶⁺ in the slag. And T.Fe + MnO in the slag after the ladle refining, a graph illustrating the results of Cr ₂ O ₃ concentration in the slag. It is a graph which shows the relationship of Si mass% in the molten steel after ladle refining, and T.Fe + MnO in slag. It is a graph which shows the relationship of Al mass% in the molten steel after ladle refining, and T.Fe + MnO in slag.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram of a waste processing method according to an embodiment of the present invention.

  As shown in FIG. 1A, molten steel 2 is extracted from a converter or an electric furnace, for example, into a ladle 1, and secondary refining is performed in the ladle 1. In addition, as a secondary refining method performed in the ladle 1, LF, RH, DH, VAD, VOD, AOD etc. are illustrated. For example, a reducing agent such as Al or Si is added to the molten steel 2 in the ladle 1 to perform deoxidation. A reducing agent such as Al or Si is added so that T.Fe + MnO ≦ 2.5 mass% in the molten slag 3 is satisfied. At that time, the refining efficiency is increased by charging the ladle 1 with a flux mainly composed of quicklime, alumina or the like, stirring the mixture using gas bubbling or the like, and kneading.

  In the ladle 1 where secondary refining is performed in this way, as shown in FIG. 1 (b), the waste 4 containing chromium is put into the molten slag 3 of the molten steel 2. The waste 4 is, for example, a refractory brick (MgCr brick) used as a lining refractory for a cement rotary kiln or a secondary steelmaking refining furnace. The waste 4 may be directly fed into the molten slag 3, but when receiving the molten steel 2 in the ladle 1, various alloy irons for component adjustment, Al, Si and the like as reducing agents are used. At the same time, waste 4 containing chromium may be added.

  And in the ladle 1, the secondary refining using LF, for example is performed. Thus, the waste 4 containing chromium is put into the molten slag 3, so that the waste 4 is dissolved by being mixed with the molten slag 3, and as shown in FIG. The contained chromic acid is reduced by a strong reducing agent such as Al or Si added to the molten steel 2 and recovered as a molten steel component (chromium).

  Thus, by utilizing the powerful reduction function of the molten steel ladle refining, the waste 4 containing chromium is melted and reduced, the chromium content is separated into the molten steel 2, and the other components are separated into the slag 3. In this treatment method, it is not necessary to construct a new treatment facility for hexavalent chromium contained in waste 4 that is difficult to dispose of as it is, and ladle smelting that is widely used by many steel companies. Since it can be processed in normal production activities using equipment, it can be said that it is a very low cost processing method. In addition, since it is not necessary to construct a new facility, it can be processed in large quantities in normal production activities, and at the same time, Cr can be recovered as a molten steel component.

Put the chromium oxide contained in the brick waste into the ladle after the converter / electric furnace steel, and then add the slagging material and the reducing agent and smelt the ladle to melt the brick waste. The chromium oxide is reduced and chromium is recovered as a molten steel component. As an example, a case where LF is used for ladle refining will be described. When receiving molten steel from a 280t converter into a ladle, 400 kg of chromium-containing bricks (MgCr bricks) with the components shown in Table 1 are added together with various alloy irons for component adjustment and Al as a reducing agent. did. Next, the ladle was transported to LF, and while performing bottom blowing bubbling with an inert gas, 2200 kg of quicklime and 600 kg of alumina were added, and the electrode was heated to slag. At the same time, Al was added as a deoxidizer (reducing agent). Table 2 shows the slag component after about 50 minutes of LF treatment. The chromium-containing brick melted and the Cr ₂ O ₃ concentration in the slag decreased to 0.02%. T.Fe + MnO in the slag was 0.6% by mass (≦ 2.5% by mass).

Here, the relationship between the Cr ₂ O ₃ concentration in the slag and the elution amount of Cr ⁶⁺ is shown in FIG. When the Cr ₂ O ₃ concentration in the molten slag is 0.5% by mass or less, the dissolution amount of Cr ⁶⁺ will be 0.05 mg / l or less, which is the soil dissolution standard amount, and the molten slag should be disposed of in landfills. Is possible.

In this example, it can be seen that the Cr ₂ O ₃ concentration in the slag is reduced to 0.02% by mass and reduced to a sufficiently low value. Moreover, the elution amount of hexavalent chromium of 0.05 mg / l or less when using slag as civil engineering materials was greatly cleared. On the other hand, as shown in Table 3, the Cr concentration in the molten steel increased by 0.029% by mass from 0.030% by mass (before LF treatment) to 0.059% by mass (after LF treatment). It can be seen that it is completely recovered as a molten steel component. Moreover, the chromium recovery rate to the molten steel component was 94%.

As in this example, the Cr ₂ O ₃ concentration in the slag decreased to 0.02% by mass or less, while the reduction of Cr ₂ O ₃ resulted in the recovery of 0.029% by mass of Cr in the molten steel. This is because the chromium-containing brick (MgCr brick) put into the ladle was dissolved and a reduction reaction occurred. If the chrome-containing brick was not dissolved and remained in the slag, it would be an event that did not occur. When the chromium-containing brick is put into the ladle during the LF treatment, the molten steel specific gravity≈7 and the MgCr brick specific gravity≈3.0, so the chromium-containing brick floats between the molten steel surface and the slag. In this state, the processing proceeds, the melting of the chromium-containing brick progresses, and almost all of the Cr component added as the chromium-containing brick moves into the molten steel. By performing the treatment by this method, Cr content moves from the slag to the molten steel, and the slag becomes harmless. As a result, the chromium-containing brick is processed into a harmless state.

FIG. 3 is a graph showing the analysis results (actual values) of T.Fe + MnO (mass%) in the slag and the Cr ₂ O ₃ concentration in the slag after ladle refining. In addition, T.Fe is the mass% of Total Fe (total iron). From FIG. 3, in order to satisfy the condition for clearing the Cr ⁶⁺ elution limit, “Cr ₂ O ₃ concentration in slag ≦ 0.5 mass%”, T.Fe + MnO ≦ 2.5 mass% If it is, you know that it is enough.

  FIG. 4 shows the relationship between Si mass% in molten steel and T.Fe + MnO (mass%) in slag after ladle refining (at the end of LF). FIG. 5 shows the relationship between Al mass% in molten steel and T.Fe + MnO (mass%) in slag after ladle refining (at the end of LF). In order to obtain T.Fe + MnO (mass%) in the slag after ladle refining, when Si is added as a reducing agent to the ladle, Si ≧ 0. What is necessary is just to set it as 10 mass%. Moreover, what is necessary is just to set it as Al> = 0.012 mass% in the molten steel after ladle refining (after LF), when throwing Al as a reducing agent in a ladle.

  The present invention can be applied to the treatment of waste containing chromium such as bricks used as lining refractories for cement rotary kilns and steelmaking secondary refining furnaces.

1 Ladle 2 Molten steel 3 Molten slag 4 Waste

Claims (2)

Chromium is contained in molten slag in a ladle where secondary refining is performed and melted. By adding a reducing agent, the chromium in the waste is reduced and recovered in the molten steel. A method for treating waste containing chromium. The processing method of the waste containing chromium of Claim 1 whose composition of molten slag is T.Fe + MnO <= 2.5 mass%.

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