JPS5840112B2 - Post-treatment method for dephosphorization slag - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention consists mainly of calcium carbide and alkaline earth metal halide used for dephosphorization and desulfurization treatment of molten metals or alloys, and calcium oxide is added as necessary. The present invention relates to a method for stabilizing slag.

The present inventors first used a slag made of carbon-unsaturated metal or alloy molten calcium carbide (CaC2) whose main component is an alkaline earth metal fluoride, and in some cases CaO is added. Invented a method of refining in a non-oxidizing atmosphere.

(Japanese Patent Application No. 50-2943, Japanese Patent Application No. 50-99143) According to this method, not only sulfur but also phosphorus can be removed from metals or alloys at the same time. Stabilizing and rendering the slag harmless is a technology that should be developed from the viewpoint of improving the working environment and working.

That is, the basic reaction of the invention is as follows: Slag phase Slag phase Metal phase (CaC2)-+(Ca) +2 Metallic calcium is generated in the slag phase by [C], and phosphorus in the metal phase is removed by this metallic calcium. Ru.

That is, slag phase metal phase slag phase 3 (Ca) +2 (P, l −+(Ca3P2
) reaction causes dephosphorization of the metal or alloy, and phosphorus is absorbed in the slag phase in the form of Ca3P2.

Therefore, the slag phase inevitably contains metallic calcium and Ca3.
Contains P2.

When the slag separated from the metal or alloy after the completion of the reaction (hereinafter referred to as slag after metal treatment) is left at room temperature, it reacts with water vapor or water in the atmosphere to generate phosphine (PH3).

That is, (Ca3P2) + 3)L! Q-+3
A reaction of Cao + 2 PH3 (1) takes place.

At room temperature and in an atmosphere containing water vapor, calcium phosphide (Ca3P2) in the slag phase is unstable and may generate phosphine.

Therefore, it is necessary to convert the calcium phosphide in the slag into a stable compound without generating phosphine in the slag after metal treatment, thereby stabilizing the slag.

The generation of phosphine is caused by the reaction between calcium phosphide contained in the slag and water, and the amount generated varies depending on the concentration of calcium phosphide contained in the slag.

As a result of various studies, the present inventors have found that generation of phosphine from the slag can be prevented by reducing the concentration of phosphorus as calcium phosphide contained in the slag to 0.05% or less ( Example 1, Figure 2).

The present inventors succeeded in stabilizing the slag after metal treatment without generating phosphine by the following method.

That is, the present invention stabilizes the slag by subjecting the slag separated from the metal phase to an oxidation treatment to reduce the concentration of phosphorus as calcium phosphide in the slag to 0.05% or less. The method for post-treatment of the dephosphorization slag is characterized in that:

The fundamental technical idea of the present invention is that the calcium phosphide contained in the slag is converted into CaC2+502+ 2CaO+4CO□ (2) Ca
The purpose is to fix it in the slag phase as a stable phosphoric acid compound by the reaction of 3P2+402=)3CaO-P2O3 (3).

The details of the present invention will be described below.

The oxidation treatment of the slag after metal treatment must be performed after separating the dephosphorized metal from the slag.

When the slag oxidation treatment is performed in the presence of refined metal,
This is because metallic calcium and calcium carbide in the slag phase are oxidized and lost, the slag loses its ability to absorb or retain phosphorus, and the phosphorus absorbed in the slag phase returns to the metal phase. be.

The slag after metal treatment is separated from the metal in various states (molten state, semi-molten state, solid state, or a mixture of the above states).

The first method for stabilizing the slag in such a state is to perform a melt oxidation treatment on the slag, or to oxidize the slag in an oxidizing atmosphere at high temperature for a long period of time even if the slag has solidified. This is a method of converting calcium phosphide into a stable phosphoric acid compound and reducing the concentration of phosphorus as calcium phosphide in the oxidized slag to 0.05φ or less.

Furthermore, a second method of stabilizing the slag is to solidify the slag separated from the metal phase at a temperature of 200°C or higher,
200℃ in slag air or oxidizing gas atmosphere
The oxidation treatment is performed at the above temperature to convert the calcium phosphide in the slag free surface layer into a stable phosphoric acid compound, and the concentration of phosphorus as calcium phosphide in the slag free surface layer is reduced to 0.
A stable slag layer with a diameter of 05φ or less is 0.511LIIL.
This is a method of forming and stabilizing the above.

Furthermore, if necessary, the slag may be stabilized by the first method or other methods.

This will be explained in detail in the following examples.

First, the first method of stabilization will be described.

When melted and oxidized in the slag air or oxidizing gas (gas in which the sum of one or more oxidizing gases such as oxygen gas or CO2 gas is 20 or more) atmosphere after metal processing, (Through the 3X reaction, phosphorus as calcium phosphide is oxidized and fixed in the slag phase as a stable phosphoric acid compound (Example 2, Figure 3).

However, in the melting process under neutral gas or reducing gas, the reactions shown by equations (2) and (3) do not occur, and the calcium phosphide in the slag remains in the slag and the slag is stabilized. (Example 2, Figure 3).

In addition, when melting and oxidizing the slag, (2), (
3) Spraying or blowing air or the above-mentioned oxidizing gas onto the slag by a known method increases the oxidation rate of calcium phosphide as shown in Example 2, and increases the oxidation rate of the slag. It is very effective for promoting stabilization (Example 2, FIG. 3).

Furthermore, in melting and oxidizing the slag, (2)
In order to accelerate the reaction of formula (3) or to lower the melting point of the slag, mill scale, SiO
It is also effective to oxidize calcium phosphide to add oxides such as converter slag, fluorides of alkaline earth metals such as CaF2, or mixtures thereof during the slag treatment.

FIG. 1 shows one example of the apparatus used in the method of the present invention, in which 1 is a container containing slag 2, 3 is an electrode for arc heating, and 4 is a lance for blowing gas.

In addition, if the temperature of the slag should not be lowered during the slag melt oxidation treatment, a known heating method such as oxidation flame heating using an arc heating burner (not shown) using the arc heating electrode 3 may be used for the melt oxidation treatment. good.

By subjecting the slag after metal treatment to melt oxidation treatment, the concentration of phosphorus as calcium phosphide in the slag can be easily reduced to 0.05φ or less, and stabilization of the slag can be achieved. .

The slag separated from the metal phase after metal treatment can be stabilized in the solid state by the following method.

That is, by maintaining the temperature at 200° C. or higher in the slag air or oxidizing atmosphere, the calcium phosphide contained in the slag mass is transferred to the gas blowing muzzle 4.
The slag is oxidized by an oxidizing gas blown into the slag and converted into a stable phosphoric acid compound in the slag mass, and the concentration of phosphorus as calcium phosphide in the slag mass is reduced to 0.05% or less. This is a method of stabilization.

FIG. 5 shows a schematic diagram of a cross section of the slag during the oxidation treatment.

The atmosphere during the oxidation treatment of the slag needs to be air or an oxidizing gas for the following reasons.

That is, by the reaction of formula Q) and (3) above, the free surface (surface in contact with the atmosphere) layer of the slag is converted into a stable layer (calcium phosphide is converted into a stable phosphoric acid compound, and the concentration of phosphorus as calcium phosphide is increased. is 0.05% or less.

The same applies hereafter) It is essential for forming a.

In a neutral or reducing gas atmosphere, the calcium phosphide in the slag surface layer is not oxidized and a stable layer a is not formed, but the slag surface layer a treated in an air or oxidizing gas atmosphere is The concentration of phosphorus as calcium phosphide is 0.05φ or less, and the slag surface layer is stabilized.

(Example 4, FIG. 7) The thickness of the stabilized layer a of the slag increases as the oxidation treatment temperature increases and the oxidation treatment time increases (Example 4, FIG. 6).

By such oxidation treatment, the slag after metal treatment can be stabilized to the inside by oxidation treatment at high temperature for a long time without the need for melt oxidation treatment.

In carrying out this invention, the slag after metal treatment is
In order to increase the surface area for reaction with oxidizing gas and shorten the oxidation treatment time, it is desirable to crush the slag into appropriate sizes, and the finer the slag lumps, the shorter the time required for stabilization.

In FIG. 5, C is an unreacted phase: brownish color, and C is an intermediate black color.

The oxidation treatment temperature for stabilizing the slag lump here is important for the following reasons.

It has already been mentioned that calcium phosphide contained in slag after metal treatment generates phosphine through the reaction shown by equation (1) at room temperature.As a result of various studies, the present inventors and others It has been found that if the temperature is maintained above C, no phosphine is generated even if water vapor is present in the atmosphere (Example 3).

Therefore, when oxidizing the slag mass, the temperature must be 200°C to stabilize the slag without generating phosphine.
must be processed at higher temperatures.

The slag lump can be stabilized by oxidizing it with an oxidizing gas at a high temperature of 200°C or more, but when actually oxidizing the slag lump, it is necessary to speed up the formation of the stabilized slag layer a. Preferably, the oxidation treatment is performed at a temperature of 600°C or higher.

In order to stabilize the slag, the oxidation treatment described above may be performed separately from the melt oxidation treatment and the solid oxidation treatment, or may be performed simultaneously in the same treatment furnace.

As described in the first method, the second method for stabilizing the slag is to temporarily form a stable slag layer a of 0.5 mJ1 or more on the slag surface layer at a high temperature of 200° C. or higher. After that, the slag is reoxidized as necessary to reduce the concentration of phosphorus as calcium phosphide contained in the slag to 0.
．． This is a method to reduce the amount to 0.5% or less.

The stabilized layer a of the slag is dense and plays the role of protecting the inner layer and preventing the inner layer from reacting with water vapor and water (formula (1)). It also prevents the generation of phosphine.

The layer a to be stabilized here needs to have a thickness of 0.51 u1 or more in order to prevent the inner layer from reacting with water vapor and water.

The slag mass obtained by such treatment does not generate phosphine even when left at room temperature in the presence of water vapor.

Further, as a method for stabilizing the inner layer, the slag lump may be stabilized by the first method, or the slag lump may be charged into a converter or the like and subjected to melt oxidation treatment in the molten pig iron oxidation refining process. It's okay.

Example 1 5 kg of slag having the composition shown below was added to about 100 Ky of molten ferrochrome 7[polyC)-63C%Cr]-Fe melted in the refining container of an induction melting furnace, and the above alloy was melted in an argon atmosphere. was refined to obtain alloys and slag with the compositions shown in the table below.

Added slag: Granular CaC2 (purity 85%, remainder ■ is almost Ca0) 3.5Kg Powdered CaF2 (purity 99% or more) IKIi Powdered Cab (
Purity: 98% or higher) 0.5 kg unit (%) Almost all of the phosphorus in the obtained slag after metal treatment exists as calcium phosphide.

The amount of phosphorus other than calcium phosphide was only 0.002.

Such slag was melted and oxidized in a slag melting furnace as shown in FIG. 1, and several slags were collected during the treatment to obtain slags with various calcium phosphide concentrations.

The amount of phosphine generated from the obtained slag was examined under the following conditions.

Atmosphere: air at 25°C, saturated steam at 20'C Contains slag 10v1 The concentration of phosphine is the concentration of IAI' in air.

The results are shown in Figure 2.

Example 2 Almost the same as Example 1, the compositions were 45.1 (%CaC2), 19 (%CaF2), 24
A metal-treated slag with (%Cab), 4.1 (%Ca), and 0.37 (%P) was obtained.

Almost all of the phosphorus in the metal-treated slag was present as calcium phosphide, and the amount of phosphorus other than calcium phosphide was only 0.002.

The obtained slag is melted in a slag melting furnace as shown in Figure 1.
The slag was subjected to melting treatment in an argon atmosphere and melting oxidation treatment in an air atmosphere by blowing air and oxygen gas.

The amount of dissolved slag is approximately I kg.

The results are shown in Figure 3. When the slag is melted in an argon atmosphere, the calcium phosphide in the slag remains in the slag.

On the other hand, calcium phosphide in the slag is oxidized by melt oxidation treatment in an air atmosphere and fixed to the slag as a phosphoric acid compound, thereby stabilizing the slag.

Example 3 In almost the same manner as in Example 1, the compositions were 46.0 (%CaC2), 20 (%CaF2), 24 (
A metal-treated slag with %Ca0) of 0.38 (%P) and 3.5 (%Ca) was obtained.

The slag is approximately 5imj6'-10vta! ! The amount of PH3 generated at each temperature was examined.

The atmosphere is air and contains moisture equivalent to the saturated water vapor pressure at 20°C.

The results are shown in Figure 4.

Example 4 5 kg of slag having the composition shown below was added to about 104 molten ferrochrome (7,0φC-63% Cr-Fe) melted in the refining container of an induction melting furnace, and the above alloy was refined in an argon atmosphere. , alloys and slags with the compositions shown in the table below were obtained.

Added slag: Granular CaC2 (purity 85%, remainder is mostly Ca0) 3.5 kg Powdered CaF2 (purity 99% or more) IKy Powdered Ca cotton content 98% or more) 0.5 kg unit (%) obtained Almost all of the phosphorus in the slag after metal treatment exists as calcium phosphide.

The amount of phosphorus other than calcium phosphide was only 0.002.

The obtained slag was crushed into approximately 5 crrLf, and the slag was oxidized at temperatures ranging from 300°C to 1200°C in an air atmosphere.

A replica of the oxidized slag is shown in FIG.

Figure 6 shows the change over time in the thickness of the surface layer that turned white.

Furthermore, the concentrations of phosphorus in the form of calcium phosphide in the surface layer and phosphorus present in forms other than calcium phosphide are shown in FIG.

As explained above, according to the present invention, stabilization treatment of slag after dephosphorization treatment of molten metal or alloy can be easily carried out, and therefore, its effects are incomparable to those often used.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the method of the present invention;
Figure 2 shows phosphorus and P as calcium phosphide in slag.
Figure 3 is a diagram showing the relationship with H concentration; Figure 3 is a diagram showing changes over time due to oxidation treatment of phosphorus in slag; Figure 4 is a diagram showing changes in PH3 concentration due to slag treatment temperature;
The figure is a schematic cross-sectional view of solid slag after oxidation treatment, Figure 6 is a chart showing changes in the thickness of the stabilizing layer over time due to oxidation treatment, and Figure 7 is a diagram showing the phosphorus content in the slag surface layer before and after treatment by the method of the present invention. It is a figure showing a form. 1... Container containing slag, 2... Slag, 3.
... Electrode for arc heating, 4... Lance for gas injection.

Claims (1)

[Claims] 1. A molten metal or alloy is dephosphorized using a slag whose main components are calcium carbide and an alkaline earth metal halide, and then the molten metal and the slag are separated, and then the slag is oxidized. The above method for post-treatment of slag for dephosphorization of molten metal or alloy, characterized in that the concentration of phosphorus as calcium phosphide contained in the slag is reduced to 0.05% or less. 2 Dephosphorizing the molten metal or alloy using slag whose main components are calcium carbide and alkaline earth metal halides, then separating the molten metal from the slag, and heating the slag at 200°C or higher in an oxidizing atmosphere. The free surface of the slag is oxidized by oxidation treatment at a temperature of A method for post-treatment of slag for dephosphorization of molten metal or alloy, characterized by reducing the concentration to 0.05% or less, and further subjecting the slag to reoxidation treatment as necessary.