KR101038790B1 - Steelmaking Slag with Reduced Fluorine Dissolution and pH and Manufacturing Method Thereof - Google Patents

Abstract

In the present invention, when manufacturing the steelmaking slag by cooling the molten steelmaking slag, fluorine (F) is concentrated in the steelmaking slag by spraying or spraying a cooling gas or a cooling solution while adjusting the oxygen partial pressure inside the slag, and 2CaO · Fe on the surface thereof. Steelmaking slag with capsule layer formed by mixing phase of ₂ O ₃ , 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ solid solution or 2CaO · Fe ₂ O ₃ and 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ solid solution It provides a manufacturing method. In this case, fluorine (F) is formed in the grain boundary of 2CaO.SiO ₂ and concentrated inside the steelmaking slag, and the surface is protected by the capsule layer, so that fluorine elution is suppressed and its own pH is low, thereby providing environment-friendly steelmaking slag.

According to the present invention, it is possible to supply eco-friendly steelmaking slag economically and stably so that steelmaking slag can be effectively recycled in the field of civil engineering.

Steelmaking slag, fluorine, pH, eco-friendly, capsule layer

Description

Steelmaking slag with reduced pH of fluorine elution and eluate and its manufacturing method {of Steelmaking Slag with Reduced Fluorine Dissolution and pH and Manufacturing Method Thereof}

The present invention relates to a method for stably recycling steelmaking slag for road slab, landfill, landfill cover, and other civil works, and more specifically, fluorine (F) component is eluted from steelmaking slag used as a civil engineering material. It is to provide a method of using environmentally friendly steelmaking slag by reducing the amount.

Conventionally, a method of forming a coating layer of calcium carbonate on the surface of the slag by continuously reacting the solidified slag with a high temperature carbon dioxide gas in order to prevent elution of fluorine from the slag has been proposed. There is a problem that the coating layer is formed to be slow to a thickness of several micrometers or less, so that the coating layer can be easily broken to use slag for civil engineering. In addition, carbon dioxide gas must be blown for a long time of 120 hours or more in order to produce a calcium carbonate coating layer, which is very uneconomical.

In addition, conventionally, a method of reducing the fluorine leaching amount of the slag without adding a foreign material or surface modification by adding oxygen to the molten slag to increase the oxidation state of the slag by increasing the slag oxidation state. However, considering the form of fluorine in the slag, this method is expected to have a minimal effect of inhibiting fluorine elution. Also, when oxygen is injected into the molten steel slag, 2CaO · Fe ₂ O ₃ (hereinafter referred to as C ₂ F) in the crystal phase of steelmaking slag There is a problem that the ratio of the phase increases, but there is a lack of a description of the mechanism for suppressing the fluorine elution or the oxygen partial pressure and cooling method of the slag.

    Furthermore, the technology to reduce the fluorine content of steelmaking slag by smelting fluorine in advance by sprinkling hot water on steelmaking slag after crushing steelmaking slag to the size actually used, but this is about the method of reducing fluorine and basically This is different from the method for reducing fluorine elution.

The present invention is to improve the above problems and to provide a method for stably recycling the steelmaking slag by reducing the amount of fluorine eluted from the slag itself without the crushing and other processes for the slag.

The present invention provides a method for manufacturing steelmaking slag that cools the molten steelmaking slag and injects or sprays a cooling gas or a cooling solution while adjusting the oxygen partial pressure inside the slag. In this case, one kind of the cooling gas may be oxygen, air, and one or two or more kinds of gas selected from the group consisting of CO ₂ gas, the cooled solution is selected from the group consisting of oxygen, air or CO ₂ gas Alternatively, a solution in which two or more gases are dissolved may be used.

Furthermore, in the present invention, fluorine (F) is concentrated in the steelmaking slag, and 2CaO · Fe ₂ O ₃ , 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ solid solution or 2CaO · Fe ₂ O ₃ and 4CaO · Al on the surface thereof. Steelmaking slag with a capsule layer formed by a mixed phase of a ₂ O ₃ · Fe ₂ O ₃ solid solution is provided. In this case, fluorine (F) is formed at the grain boundaries of 2CaOSiO ₂ and concentrated inside the steelmaking slag, and the grain size of the steelmaking slag may be 40 mm or less. It is preferable that the fluorine elution amount of the steelmaking slag which concerns on this invention is 0.6 mg / L or less, and pH is 11.7 or less.

According to the present invention, it is possible to supply eco-friendly steelmaking slag economically and stably to effectively recycle steelmaking slag in the field related to civil engineering.

First, an abbreviation used to refer to a substance in the present specification will be described.

As used herein, C ₂ F means 2CaO · Fe ₂ O ₃ , and C ₄ AF ss means 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ solid solution. And C ₂ S means 2CaO.SiO ₂ . For reference, 'F' in C ₂ F and C ₄ AF ss does not mean fluorine (F).

Hereinafter, the present invention will be described in more detail.

In the steelmaking process, fluorite (CaF ₂ ) is often used in the converter steelmaking process to reduce the melting point and viscosity of the steelmaking slag. Therefore, in such a case, a small amount of fluorine (F) is present in the steelmaking slag, and there is a fear that fluorine will be eluted when the slag is used for civil engineering. Fluoride elution can lead to serious problems such as environmental pollution. In Japan, fluoride leaching standards for slag are less than 0.8 mg / L, and in Korea, when used as rovan ash, soil contamination around roads due to fluoride leaching It is recommended that there is no concern.

The inventors observed through electron microscopic analysis that the position of fluorine present in the steelmaking slag was determined by the grain boundaries of 2CaOSiO ₂ (hereinafter referred to as C ₂ S) and C ₂ F or C ₄ AF ss, which are the major crystalline phases of steelmaking slag. (grain boundary). Therefore, the inventors of the present invention use the C ₂ S and C ₂ F or C ₄ AF ss phases, which are the main crystalline phases of the steelmaking slag, to show the C ₂ F or C ₄ AF ss phase and C ₂ F or C _{4 which} appear during slag cooling. A method of suppressing the dissolution of fluorine has been proposed using the difference in the solidification rate between the AF ss phase and the C ₂ S mixed phase.

In order to reduce or replace the use of fluorspar in the steelmaking process, secondary refining slag with high Al ₂ O ₃ content may be used in the converter steelmaking process, but even in this case, fluorspar is contained in the secondary refining slag. This secondary refining slag is a small amount when reused in the converter steelmaking process, but the fluorine component is eventually contained in the steelmaking slag.

Therefore, the present inventors applied the following method to reduce the fluorine leaching amount of steelmaking slag. That is, 1) cooling gas, preferably oxygen, air, or CO ₂ gas is injected into the molten slag to directly cool by spraying the oxygen partial pressure in the molten slag to be at least logPo ₂ = -2.0 Pa, or ② cooling solution, preferably oxygen , By cooling and solidifying by spraying a solution in which air or CO ₂ gas is dissolved (it is economical to use as an aqueous solution), the cooling rate is increased during solidification of molten slag and the slag particle size after cooling is 40 mm or less, preferably 10 mm or less. Adjust the particle size as much as possible (see Figure 1).

Injecting a cooling gas such as oxygen, air, or CO ₂ gas into the molten steel slag increases the equilibrium oxygen partial pressure in the molten slag. In this case, the content of Fe ^{3+ in the} slag increases, and the particle size of the slag is solidified by directly injecting a gas or the like during cooling the molten slag or by spraying a cooling solution containing a cooling gas such as oxygen, air, or CO ₂ gas to solidify the molten slag. It can manufacture small. If the oxygen partial pressure during cooling is lower than logPo ₂ = -2.0 Pa, Fe ³⁺ is not sufficiently formed, and a large amount of Fe and FeO phases are present in the slag, thereby preventing CaO from forming a compound. Therefore, since CaO inside the slag is present as free CaO, the pH of the steelmaking slag may rise to a level that may cause environmental pollution. Therefore, the cooling rate should be adjusted to a level capable of appropriately maintaining the oxygen partial pressure.

In addition, if the cooling rate is too fast, the process economy is inferior. If the cooling rate is slow, the grain size of C ₂ S and C ₂ F and / or C ₄ AF ss, which constitute the steel slag, becomes larger than that of the quenching treatment, but the fluorine There is a problem that the inside of the slag and the outside of the slag are almost the same as the probability of exposure to the surface increases.

Through the cooling process, fluorine is concentrated in the steelmaking slag, and C ₂ F and / or C ₄ AF ss forms capsules on the slag surface in a short time. At this time, C ₂ F and / or C ₄ AF ss is to form a capsule by the following principle.

That is, C ₂ F or C ₄ melting point on the AF ss is C ₂ F or C ₄ AF ss-phase and C higher than the ₂ S eutectic melting point (eutectic temperature) on, which results main crystal phase constituting the steel-making slag when solidified molten slag quench The relatively high content of C ₂ F or C ₄ AF ss phase is first solidified to form a capsule layer on the surface of the slag. The remaining non-solidified C ₂ F or C ₄ AF ss and C ₂ S components are then moved into the slag and both phases solidify simultaneously within the slag when the cooling temperature reaches the eutectic point of the two phases. See 3).

As a result, a capsule can be formed on the surface of the slag by using the principle that the C ₂ F or C ₄ AF ss phase is first solidified, and the C ₂ S grains are concentrated in the direction of the center of the produced slag particles. Fluorine in steelmaking slag is naturally concentrated to the center of slag where C ₂ S grains are located. Elution of fluorine can be suppressed by the capsule layer formed on the slag surface.

Furthermore, in the present invention, even when a small amount of fluorine is exposed to the surface, fluorine ions are substituted in the OH ^- site of the hydride by the hydration reaction of C ₄ AF ss, so that the fluorine can be immobilized and stabilized, and the amount of fluorine released from the slag is increased. It has the advantage that it can be reduced.

(Example)

Hereinafter, the present invention will be described in more detail with reference to the following examples.

Synthetic steel slag was prepared by mixing the components shown in Table 1 to carry out this example.

ingredient CaO Fe ₂ O ₃ Al ₂ O ₃ CaF ₂ FeO SiO ₂ P ₂ O ₅ MgO Content (wt%) 46.6 23.0 6.2 2.0 4.7 14.2 0.3 3.0

As a raw material for preparing the synthetic slag as shown in Table 1, high purity CaCO ₃ , Al ₂ O ₃ , Fe ₂ O ₃ , FeO, CaF ₂ , SiO _2, P ₂ O ₅ and MgO were used. The CaCO ₃ was used for 24 hours heat treatment at 1000 ℃, other samples were used in a sufficiently dry state. These samples were uniformly mixed and molded at the mixing ratio shown in Table 1 above, placed in a dense MgO crucible and dissolved at 1550 ° C. for 1 hour, followed by cooling the molten steel slag by various methods as shown in Table 2 below. Each fluorine elution amount and pH were measured.

division Slag Melting Temperature and Time Oxygen partial pressure
logPo ₂ (Pa) Cooling method Comparative Example 1 1550 ℃, 1hr -2.5 Slow cooling
(air) Comparative Example 2 1550 ℃, 1hr -4.1 Quench
(air) Inventive Example 1 1550 ℃, 1hr -1.8 Quench
(CO ₂ gas) Inventive Example 2 1550 ℃, 1hr -1.8 Quench
(CO ₂ saturated solution) Inventive Example 3 1550 ℃, 1hr -1.0 Quench
(air) Honorable 4 1550 ℃, 1hr -1.0 Quench
(Oxygen gas) Comparative Example 3 1550 ℃, 1hr -1.8 Slow cooling
(air)

In this embodiment, the CO ₂ / CO ratio control was used as the gas for controlling the atmosphere, thereby controlling the equilibrium oxygen partial pressure in the molten state of the synthetic slag. This is a method for controlling the oxygen partial pressure by the method taken to accurately control the oxygen partial pressure, and does not limit the scope of the present invention only by the CO ₂ gas blowing method.

Fluorine elution test of steelmaking slag was used as the size of the cooled form without crushing or crushing the slag. For dissolution test, the solid / liquid ratio was 1/10 and the mixture was shaken at 200rpm for 6 hours and filtered. A method of analyzing the solution by ion chromatography was used.

In the method of measuring the pH of steelmaking slag, the solid / liquid ratio was set to 1/10 and the mixture was shaken at 200 rpm for 6 hours, and the filtered solution was analyzed using a pH meter.

The measurement results are shown in Table 3 below.

division F elution amount
(mg / L) Slag pH Remarks Comparative Example 1 3.2 12.3 High F Elution,
High pH Comparative Example 2 1.6 12.0 High F Elution,
High pH Example 1 0.6 11.2 Low f,
Low pH Example 2 0.5 11.0 Low F Elution,
Low pH Example 3 0.6 11.7 Low F Elution,
Low pH Example 4 0.5 11.5 Low F Elution,
Low pH Comparative Example 3 0.9 12.1 High F Elution,
High pH

Comparative Example 1 is formed by a general steelmaking slag manufacturing method, the oxygen partial pressure during melting is lower than logPo ₂ = -2.0 Pa Fe 2 or FeO phase in the slag crystal structure is present by C ₂ F and / or Grains on the C ₄ AF ss are uniformly present throughout the slag (see FIG. 3). Therefore, the probability of CaF ₂ on the surface of slag increases, and as expected, the fluorine elution rate is 3.2 mg / L. In addition, since the oxygen partial pressure is low and a large amount of Fe and FeO phase remains, a portion of CaO in the slag does not form a compound and exists as free CaO. Therefore, the pH of steelmaking slag is 12.3, which is undesirable for the environment.

Comparative Example 2 is a sample in which the oxygen partial pressure is also low as logPo ₂ = −4.1 Pa and is air-quenched by spraying air. The fluorine elution amount of Comparative Example 2 was 1.6 mg / L and the slag pH was still high at 12.0. This is because the partial pressure of oxygen in the production of molten slag is low and the quenching process is not sufficiently oxidized in Fe and FeO, so that the capsule layer, which is a C ₂ F and / or C ₄ AF ss coating layer on the surface of the slag, was not sufficiently formed. do.

In Comparative Example 3, the oxygen partial pressure was maintained at logPo ₂ = -1.8 Pa while the molten steelmaking slag was manufactured, but the cooling method was performed by slow cooling in air. If not, the fluorine content in the slag is high and the cooling rate is low, so the fluorine is uniformly distributed in the slag.

On the other hand, Examples 1 and 2 produced molten steel slag by the method of the present invention, the fluorine elution amount was observed to 0.6mg / L and 0.5mg / L. This result was significantly reduced compared to the existing steelmaking slag of Comparative Example 1 and the pH of the slag was found to be sufficiently reduced to 11.2 and 11.0. It is used for the production of C ₂ F or C ₄ AF ss due to the large oxidation of Fe and FeO in the steelmaking slag with high oxygen partial pressure in the production of molten steel slag, through which the fluorine component is concentrated inside the grains and C ₂ F and / or C ₄ It is expected that the AF ss phase forms a slag cross-sectional structure (Fig. 3 (1)) that forms a capsule layer.

This may be applied to the fact that low fluorine elution and pH levels can be obtained by the same principle in Examples 3 and 4 using air and oxygen gas, unlike Examples 1 and 2.

According to this embodiment, it is expected to provide an environment-friendly and economical steelmaking slag by maintaining the oxygen partial pressure above a certain level as in the method of the present invention and managing the cooling rate.

1 is a flow-chart showing a series of processes of the present invention.

Figure 2 is a state showing a higher than C ₂ F or C ₄ AF ss melting point of C ₂ F or C ₄ AF phase ss and C ₂ S eutectic melting point (eutectic temperature) on the on the.

Figure 3 is a schematic diagram showing the structure (1) of the slag layer produced by the present invention and the structure (2) of the slag layer which appears during slow cooling.

Claims (7)

In the method of manufacturing the steelmaking slag by cooling the molten steelmaking slag, The cooling step is a method of manufacturing a steelmaking slag with a reduced pH of fluorine elution and eluate characterized in that the spraying or spraying a cooling gas or a cooling solution so that the oxygen partial pressure logPo ₂ in the slag is more than -2.0 Pa. The method of claim 1, wherein the cooling gas is one or two or more gases selected from the group consisting of oxygen, air, and CO ₂ gas. The method of claim 1, wherein the cooling solution is a solution of one or two or more gases selected from the group consisting of oxygen, air and CO ₂ gas dissolved fluorine elution and the pH of the steelmaking slag is reduced Manufacturing method. Fluorine (F) is concentrated inside the steelmaking slag, On the surface of the steelmaking slag, a mixed phase of 2CaO · Fe ₂ O ₃ , 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ solid solution or 2CaO · Fe ₂ O ₃ and 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ solid solution Steelmaking slag, the pH of the fluorine elution and eluate is reduced, characterized in that the capsule layer formed by. The steelmaking slag of claim 4, wherein the fluorine (F) is formed at a grain boundary of 2CaO.SiO ₂ . The steelmaking slag according to claim 4 or 5, wherein the grain size of the steelmaking slag is 40 mm or less. The steelmaking slag according to claim 4 or 5, wherein the fluorine elution amount of the steelmaking slag is 0.6 mg / L or less and the pH is 11.7 or less.

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