JP6835117B2 - Steel slag processing method and steel slag recycled product manufacturing method - Google Patents

Description

The present invention relates to a method for treating steel slag, and more particularly to a method for suppressing the amount of boron eluted from steel slag. Furthermore, the present invention relates to a method for producing a recycled steel slag product using this treatment method.

Steel slag is a by-product of the steel manufacturing process. Also, during the production of ferroalloys such as ferromanganese and ferrosilicon, ferroalloy slag having substantially the same composition as steel slag is produced. In recent years, interest in the global environment has increased, and the shift from the conventional mass production, mass consumption and mass disposal society to a zero emission society has been emphasized. In particular, technological developments for weight reduction, recycling, and intermediate treatment of steel slag and ferroalloy slag, which are generated in large quantities at pig iron integrated steelworks, are continuing.

Although steel slag is expected to be reused for roadbed materials and cement raw materials, there is a possibility that substances that pollute the environment may elute from steel slag into rainwater. Since steel slag is heated at a high temperature of 1200 to 1600 ° C. in the production process, it contains almost no organic compounds or heavy metals having a low melting point such as mercury, arsenic, and cadmium. Therefore, heavy metals with a low melting point are not detected in the elution test of steel slag. However, other substances may elute. For example, the Building Materials Testing Center standard "JSTMII 8001: 2008 (steel crushed stone for earthwork)" stipulates five environmental items: lead, hexavalent chromium, selenium, fluorine, and boron. These elution standards are similar to the environmental quality standards for soil contamination (Notification No. 46 of the Environmental Agency, 1991) (hereinafter referred to as "soil environmental quality standards"). Of the five substances, methods for suppressing elution of selenium, fluorine, etc. have been proposed in Patent Documents 1 and 2, for example.

Patent Document 3 describes incineration ash such as lime ash, sewage sludge incineration ash, paper sludge ash, steel slag, and garbage incineration ash using an elution inhibitor that combines calcium aluminate, aluminum sulfate, and alkali metal phosphate. A method has been proposed to reduce the amount of fluorine, boron, arsenic and slag elution from slag below the soil environmental standard.

Japanese Unexamined Patent Publication No. 2013-234111 JP-A-2009-67646 Japanese Unexamined Patent Publication No. 2014-133856

In Patent Document 3, a composition combining calcium aluminate, aluminum sulfate and alkali metal phosphate as an elution inhibitor of fluorine, boron, arsenic and selenium is used, and calcium aluminate, aluminum sulfate and It is described to use a composition that combines a reducing component and / or slaked lime in addition to the alkali metal phosphate. However, the use of an elution inhibitor that uses such an expensive drug not only increases the cost, but may also cause salt damage due to the alkali metal salt. That is, Patent Document 3 does not propose an elution inhibitor suitable for treating slag reused as a material for civil engineering work such as roadbed materials and embankments, and a method for treating steel slag using the same. Further, Patent Document 3 does not describe a method for calculating the amount of an elution inhibitor required in order to effectively suppress the elution amount of boron in the case of treating steel slag containing boron.

Steel slag may contain a large amount of boron depending on the components contained in the hot metal raw material. When steel slag is treated with the selected anti-eluting agent and the steel slag is reused without calculating the amount of anti-eluting agent required to effectively suppress the amount of boron elution, the steel slag is used as soil. Boron that exceeds the specified value of the environmental standard may be eluted. Therefore, in order to improve the reusability of steel slag, when treating steel slag containing boron, a process of calculating the amount of elution inhibitor required in order to effectively suppress the amount of boron elution. A method is sought.

In view of the above circumstances, the present invention is a method for treating steel slag and a method for treating steel slag, which makes it possible to calculate the amount of an elution inhibitor required in order to suppress the amount of boron eluted from steel slag below a desired standard. An object of the present invention is to provide a method for producing recycled slag products.

As a result of diligent studies to solve the problem, the present inventors have found that by mixing a steel slag containing boron and a substance containing a calcium aluminate component, boron is eluted from the mixture containing the steel slag. We have found that the amount can be effectively reduced, and that a predetermined relationship is established between the mixing ratio representing the mass ratio of the substance to the steel slag and the amount of boron eluted from the steel slag. The invention was completed. That is, the present invention is as follows.
(1) A method for treating steel slag in which a substance containing calcium aluminate is mixed with steel slag containing boron, and a mixing ratio representing the mass ratio of the substance to the steel slag and boron from the steel slag. A method for treating steel slag in which a mixing ratio of less than or equal to the target amount of boron eluted is determined from a relationship obtained in advance with the amount of elution of the steel slag, and the substance is mixed with the steel slag in an amount of the determined mixing ratio or more.
(2) The method for treating steel slag according to (1), wherein the relationship is a regression line between the natural logarithmic value of the mixing ratio and the elution amount.
(3) The substance is at least one of a desulfurization flux containing calcium aluminate, desulfurization slag generated by hot metal desulfurization treatment, desulfurization slag generated by molten steel desulfurization treatment, and cast slag remaining on a pan after casting. The method for treating steel slag according to (1) or (2), which comprises one.
(4) The method for treating steel slag according to any one of (1) to (3), wherein the substance is mixed with the steel slag so that the mixing ratio is 10% by mass or more.
(5) A method for manufacturing a recycled steel slag product, wherein the steel slag is treated by the steel slag treatment method according to any one of (1) to (4) to manufacture a recycled steel slag product. A method for manufacturing recycled steel slag.

According to the present invention, the elution amount of boron from steel slag is desired on the premise that a substance containing calcium aluminate is used as an elution inhibitor capable of effectively reducing the elution amount of boron from steel slag. It is possible to calculate the amount of the required substance in order to keep it below the standard of. As a result, the amount of the elution inhibitor for treating the steel slag is determined, and the steel slag whose elution amount of boron meets the environmental standard can be easily reused. Therefore, it becomes easier to reuse steel slag as a roadbed material or a raw material for cement.

It is a graph which shows the relationship between the mixing ratio Ws [mass%], and the elution amount B [mg / l] of boron from a mixture. It is a graph which shows the relationship between the natural logarithmic value of the mixing ratio Ws [mass%] of the data in the graph shown in FIG. 1 and the elution amount B [mg / l] of boron. It is a graph which shows the relationship between the mixing ratio Ws [mass%] and the elution amount B [mg / l] of boron in Example 2. FIG. It is a graph which shows the relationship between the natural logarithmic value of the mixing ratio Ws [mass%] of the data in the graph shown in FIG. 3 and the elution amount B [mg / l] of boron.

The method for treating steel slag of the present invention is to mix a substance containing calcium aluminate and steel slag to allow calcium aluminate to absorb boron in the steel slag. Thereby, even when the mixture of the steel slag and the substance is immersed in water, the amount of boron eluted from the steel slag in the mixture can be reduced. It is expected that boron in the steel slag will be incorporated into the structure of calcium aluminate, making it difficult for boron to elute from the steel slag.

The compound of CaO and Al ₂ O ₃ is called calcium aluminate, and depending on the abundance ratio of _{CaO and Al 2} O _{3 , CaO · 6Al 2} O ₃ , CaO · 2Al ₂ O ₃ , CaO · Al ₂ O ₃ , 12 CaO · 7Al ₂ O ₃ , 3 CaO, Al ₂ O _{3 and the} like are contained in calcium aluminate. The existence state of CaO and Al ₂ O ₃ can be confirmed by XRD measurement described later. Among these, substances containing calcium aluminate component used in the present invention, desirably contains calcium aluminate 12CaO · _7Al 2 O _3. This is because 12CaO ・ 7Al ₂ O ₃ has a tetrahedral structure, and by confining boron inside the structure, boron can be confined in the substance and elution of boron can be suppressed.

[Mixing process of substances containing calcium aluminate and steel slag]
At steelworks, slag is in a solid-liquid coexisting state at high temperatures, and becomes lumpy or powdery after cooling. The present invention assumes that both the substance containing calcium aluminate and the steel slag are in a lumpy or powdery state, and an example of a mixing step performed in a steel mill will be described below.

The steel slag to be treated is placed in a slag transport container, the container is transported to a slag processing plant, and the steel slag is transferred from the container and stored in a pit surrounded by side walls on three sides. Several cups of steel slag for slag transport may be stored in one pit. It is desirable to flatten the steel slag after containment in order to effectively use the capacity of the pit and / or to facilitate the mixing operation of the steel slag.

Next, a predetermined amount of the substance containing calcium aluminate is stored in a pit, and the mixture is stirred and mixed with a heavy machine. Although the mixture of the steel slag stored in the pit and the substance is cooled in the atmosphere, water may be sprayed on the steel slag or the mixture in the pit to cool the steel slag or the mixture and prevent dust generation. ..

The method of adding a substance containing calcium aluminate to the steel slag stored in the pit of the slag treatment plant and then mixing both of them has been described. However, both are stored in the slag transport container and the container is used. May be agitated and mixed in the container after being transported to the slag treatment plant. For example, steel slag is placed in a transport container containing a substance containing calcium aluminate in advance, and the mixture is stirred and mixed in the transport container. At this time, the steel slag may be stored first.

Another method is to add steel slag to a processing container in which slag (substance) containing calcium aluminate is generated in the refining process, and then remove the refined hot metal (molten steel) to remove the slag on the hot metal. May be housed in a slag transport container and then the slag may be stirred and mixed. Further, both may be mixed at a high temperature, or may be mixed after cooling.

As described above, an example of the mixing process in a steel mill has been described, but the present invention does not have any special mixing conditions, and only mixes a substance containing calcium aluminate and steel slag containing boron. Good.

[Method for measuring the elution amount of substances and slag components and boron according to the present invention]
The measuring method will be described.
(I) Method for measuring the amount of boron elution After preparing a test solution by the method specified in the 1991 Environmental Agency Notification No. 46 Appendix, the boron concentration in the prepared test solution is measured by ICP emission spectroscopy (JIS K0102: 2008). It can be measured according to 47.3). Using this analytical method, boron-containing steel slag is sieved to 2 mm or less, and the amount of boron eluted in the test solution [mg / l] is measured with respect to 100 g of slag under the sieve. Thereby, the amount of boron eluted from the steel slag alone and the amount of boron eluted from the mixture of the steel slag and the substance containing calcium aluminate can be measured.
(II) Method for measuring the component content of a substance By XRD measurement, the morphology of the compound present in the substance containing calcium aluminate is confirmed, and the amount of _{CaO and Al 2} O _{3 obtained from the component analysis is XRD.} The amount of calcium aluminate can be calculated on the assumption that the obtained compound is formed. Here, the XRD measurement is possible with a powder X-ray diffractometer. Examples of the powder X-ray diffractometer include SmartLab manufactured by Rigaku Co., Ltd.

The substances containing calcium aluminate include desulfurization flux containing calcium aluminate, desulfurization slag generated by hot metal desulfurization treatment, desulfurization slag generated by molten steel desulfurization treatment, and cast slag remaining on the pan after casting. In addition, slag produced in the ironmaking or steelmaking process can also be used. For example, slag is collected, roughly pulverized, molded by the glass bead method (the sample is melted together with anhydrous sodium tetraborate at 1050 ° C. for about 10 minutes to quench vitrification), and fluorescent X-rays are obtained. The content of the components in the slag can be measured using an analyzer.

[Experimental method for determining the mixing ratio of substances containing calcium aluminate to steel slag]
If the relationship between the mixing ratio, which represents the mass ratio of the substance to the steel slag, and the amount of boron eluted from the mixture when the substance is mixed with the steel slag is required, the elution amount is less than or equal to the target amount. It is possible to determine the mixing ratio to be used.

The present inventors have discovered that a substance containing calcium aluminate and steel slag can be mixed to reduce the amount of boron eluted from the mixture even when the mixture is immersed in water. In the process, the present inventors prepare a plurality of steel slags having different boron elution amounts, mix the substance with the steel slag, and measure the boron elution amount B [mg / l] from the mixture. Experiments were conducted. In the experiment, the mixing ratio Ws [mass%] representing the mass ratio of the substance to the steel slag was changed, and the amount B of boron eluted from the mixture was measured.

From the results of the experiment, the present inventors have observed that the amount of boron eluted from the mixture tends to decrease exponentially as the amount of the substance mixed in the steel slag increases. The relationship between the mixing ratio Ws representing the mass ratio of the substance to the steel slag and the elution amount B of boron from the mixture is shown in the graph of FIG. From the graph of FIG. 1, when the mixing ratio Ws is 0, the mixing ratio Ws, which is the mass ratio of the substance to the mass of the steel slag having an elution amount of boron of 20 [mg / l], is 10% by mass. When a substance containing calcium aluminate is mixed with the above, the amount B of boron eluted from the mixture is 9.5 [mg / l]. Further, when the substances are mixed so that the mixing ratio Ws is 20% by mass, the elution amount B of boron is 5.5 [mg / l].

When the mixing ratio Ws is 10% by mass, the amount of decrease in the amount of boron elution is 10.5 (= 20-9.5) [mg / l], but even if the mixing ratio Ws is 20% by mass, the amount of decrease is Is 14.5 (= 20-5.5) [mg / l]. That is, it can be read from FIG. 1 that the decrease in the amount of boron elution decreases as the amount of the substance mixed in the steel slag increases. From this, it can be inferred that the amount of boron eluted from the mixture tends to decrease exponentially as the amount of the substance mixed in the steel slag increases.

Next, FIG. 2 shows a graph showing the relationship between the natural logarithmic value of the mixing ratio Ws of the data in the graph shown in FIG. 1 and the elution amount B of boron. In this graph, since the natural logarithmic value of the mixing ratio Ws is displayed, the data in which Ws is 0 cannot be displayed and is omitted. From the graph of FIG. 2, it can be seen that the amount of boron elution B decreases linearly as the natural logarithmic value of Ws increases. Multiple points indicated by ▲ when a substance containing calcium aluminate is mixed with steel slag having a boron elution amount of 20 [mg / l] when the mixing ratio Ws is 0 while changing the mixing ratio Ws. From this, a calibration curve showing the relationship between the mixing ratio Ws and the boron elution amount B can be derived, and from this calibration curve, the mixing ratio Ws to be equal to or less than the target boron elution amount can be obtained.

In the example of FIG. 2, the equation (B = -4.1 ln (Ws) + 17.5) representing the calibration curve can be derived by the least squares method. From this formula, if the target elution amount B is 1.0 [mg / l] that satisfies the soil environmental standard, ln (Ws) can be obtained as 4.1. Ws which becomes this value is 58.8 mass%. Therefore, when the mass of the steel slag having a boron elution amount of 20 [mg / l] is 100 g when the mixing ratio Ws is 0, 58.8 g or more of a substance containing calcium aluminate is mixed with the steel slag. Then, it can be expected that the amount of boron eluted from the mixture (steel slag contained in the mixture) satisfies the environmental standard.

In the example of FIG. 2, the equation of the calibration curve is derived from the least squares method, but the equation may be derived by drawing the calibration curve by hand. Further, from the graph shown in FIG. 1, an equation may be derived by performing an approximation by the least squares method using an exponential function instead of a straight line. That is, the relationship obtained in advance between the mixing ratio Ws and the elution amount B of boron is a regression line between the natural logarithmic value of the mixing ratio Ws and the elution amount B.

From the relationship obtained as described above, determine the mixing ratio so that the amount of boron elution is less than the target amount.
It is possible to mix substances in steel slag in a determined mixing ratio or more. It should be noted that the subject to be mixed and the subject seeking the above-mentioned relationship do not necessarily have to be the same. That is, it is also possible for a person other than the mixing subject to obtain the relationship in advance, and the mixing subject can use the relationship prepared by the other person.

As the substance containing calcium aluminate, steelmaking slag and waste products obtained at the iron and steel integrated steel mill can be used, and the substance is generated by the desulfurization flux containing calcium aluminate and the hot metal desulfurization treatment. It is preferable that the amount is at least one of desulfurized slag, desulfurized slag generated by the desulfurization treatment of molten steel, and cast slag remaining on the pan after casting. These contain at least about 45% by mass of calcium aluminate due to the flux and deoxidizer added in the refining treatment. Therefore, they contain a large amount of calcium aluminate without component analysis.

From FIG. 1, when a substance containing calcium aluminate is mixed with steel slag so that the mixing ratio Ws is 10% by mass, the elution amount B of boron from the mixture can be considerably suppressed. When steelmaking slag or waste is used as the substance, since these contain a large amount of calcium aluminate, the steel slag is mixed with steelmaking slag or waste so that the mixing ratio Ws is 10% by mass or more. It can be expected that the elution amount B of boron from the steel slag (mixture) can be considerably suppressed by just doing so.

Although steelmaking slag and waste products can be preferably used as the substance containing calcium aluminate, the substance used in the present invention is not limited to these.

In the above description, steel slag has been mentioned as a substance containing boron, but even if a substance containing calcium aluminate is mixed with slag having a similar component, the amount of boron eluted from the slag. It is possible to suppress. Therefore, steel slag includes slag generated during the production of alloy iron such as ferromanganese and ferrosilicon, molten waste slag, and incineration ash of waste and sludge.

By treating steel slag by the above steel slag treatment method, it is possible to manufacture recycled steel slag products such as roadbed materials and cement raw materials.

A plurality of types of steel slag generated at a steel mill, which are different from those prepared in the above experiment, were prepared, and a plurality of types of steel slag generated at a steel mill were prepared as substances containing calcium aluminate. The relationship between the mixing ratio representing the mass ratio of the substance to the steel slag and the amount of boron eluted from the steel slag was determined. The target elution amount of boron was set to 1.0 [mg / l], and the mixing ratio thereof was determined.

First, it was confirmed whether the amount of boron elution B from the mixture obtained by mixing the steelmaking slag with the steelmaking slag was smaller than the amount of boron elution B of the unmixed steel slag (Comparative Example). 1-3 and Examples 1 to 16).

The prepared steel slag the result of component analysis, the components of a plurality of kinds of iron and steel slag, CaO: 25 to 65 _wt%, SiO 2: 15 to 45 _{wt%, Al} 2 O 3: _5~20 wt%, B: 0 It was .05 to 0.3% by mass. The amount of boron elution of steel slag in a state where a substance containing calcium aluminate was not mixed and a mixture of steel slag and steelmaking slag was measured by ICP emission spectroscopy (JIS K0102: 2008 47.3). .. The calcium aluminate content of the prepared steelmaking slag was measured with a powder X-ray diffractometer. The components of the slag were analyzed using a fluorescent X-ray analyzer on the slag molded by the glass bead method.

In the slag transport container or the pit of the slag treatment plant, only the steel slag alone was agitated, or the steel slag and the steelmaking slag were mixed. In some cases, water was sprinkled during stirring and mixing, but in other cases it was not. In all of the invention examples, the mixing ratio representing the mass ratio of steelmaking slag to steel slag was set to 10% by mass. It was known from the previously obtained relationship that the target elution amount of boron was less than 1.0 [mg / l] when the mixing ratio was 10% by mass.

Table 1 shows the conditions of Comparative Examples 1 to 3 and Invention Examples 1 to 16 and the amount of boron elution B.

Comparative Examples 1 to 3 are examples in which the steelmaking slag is not mixed with the steel slag, and the amount of boron eluted from the steel slag does not change even when only the steel slag is agitated. On the other hand, Invention Examples 1 to 16 are examples in which steelmaking slag is mixed with steelmaking slag. The amount of boron elution from the mixture obtained by mixing the steelmaking slag with the steel slag is 1.0, regardless of the mixing location, the temperature of the mixture at the time of mixing, and the presence or absence of watering. It can be seen that it satisfies less than [mg / l].

A plurality of types of steel slag generated at a steel mill were prepared, and casting slag A, casting slag B, hot metal desulfurization slag, and molten steel desulfurization slag were prepared as substances containing calcium aluminate. Any one of the four calcium aluminate-containing substances was mixed with steel slag, and the mixing ratio Ws, which is the mass ratio of slag to the mass of steel slag, and the amount of boron eluted from the obtained mixture B. Investigated the relationship. ( Plot data Nos. 17 to 41).

The prepared steel slag the result of component analysis, the components of the steel slag, all, CaO: 22-54 _wt%, SiO 2: 15 to 45 _{wt%, Al} 2 O 3: _10~40 wt%, B: 0. It was 05 to 0.3% by mass. The amount of boron elution of steel slag in a state where the calcium aluminate-containing substance is not mixed and the mixture of the steel slag and the calcium aluminate-containing substance is measured by ICP emission spectroscopy (JIS K0102: 2008 47.3). did. The component analysis of the calcium aluminate-containing substance was carried out using a fluorescent X-ray analyzer on the slag molded by the glass bead method.

Steel slag and calcium aluminate-containing material were mixed in a slag transport container or a pit at a slag treatment plant. In some cases, water was sprinkled during stirring and mixing, but in other cases it was not. Plot data No. Table 2 shows the mixed amount of the calcium aluminate-containing substances 17 to 41 and the elution amount B of boron.

When cast slag A, cast slag B, hot metal desulfurized slag, and molten steel desulfurized slag were used as the substances containing calcium aluminate, and when the mixing ratio of the calcium aluminate-containing substance was increased, the mixture was obtained. It was found that the amount of boron eluted B decreased. FIG. 3 shows the relationship between the mixing ratio of the substances and the elution amount B of boron from the obtained mixture for each calcium aluminate-containing substance. Further, FIG. 4 shows a graph showing the relationship between the natural logarithmic value of the mixing ratio Ws and the elution amount B of boron. From the graph of FIG. 4, it can be seen that the amount of boron elution B decreases linearly as the natural logarithmic value of Ws increases.

When the calcium aluminate-containing substance is the casting slag A, the formula (B = -2.4 ln (Ws) + 10.9) representing the calibration curve can be derived by the least squares method. From this formula, assuming that the target elution amount B is 1.0 [mg / l] that satisfies the soil environmental standard, the mixing ratio Ws at which B = 1.0 is 67% by mass. Therefore, when the mass of the steel slag having a boron elution amount of 11 [mg / l] is 100 g when the mixing ratio Ws is 0, if 67 g or more of the casting slag A is mixed with the steel slag, the mixture (the said). It can be seen that the amount of boron eluted from the steel slag contained in the mixture meets the environmental standards.

Similarly, when the calcium aluminate-containing substance is molten steel desulfurized slag, the formula (B = -3.9 ln (Ws) + 13.6) representing the calibration curve can be derived by the least squares method, and 1.0 meets the soil environmental standard. Assuming that the target dissolution amount B is [mg / l], the mixing ratio Ws at which B = 1.0 is 27% by mass. Therefore, when the mass of the steel slag having a boron elution amount of 14 [mg / l] is 100 g when the mixing ratio Ws is 0, if 27 g or more of the casting slag A is mixed with the steel slag, the mixture (the said). It can be seen that the amount of boron eluted from the steel slag contained in the mixture meets the environmental standards.

In this way, regardless of the substance containing calcium aluminate, a calibration curve showing the relationship between the mixing ratio Ws and the elution amount B of boron can be derived from the actual values of the mixing ratio Ws and the elution amount B. From the calibration curve, the mixing ratio Ws to be equal to or less than the target amount of boron eluted can be obtained.

Claims (4)

A method for treating steel slag in which a substance containing calcium aluminate is mixed with steel slag containing boron.
From the previously obtained relationship between the mixing ratio representing the mass ratio of the substance to the steel slag and the amount of boron eluted from the steel slag, the mixing ratio to be equal to or less than the target amount of boron eluted was determined.
The substance is mixed with the steel slag in a determined mixing ratio or more .
The substance is a hot metal desulfurized slag or a molten steel desulfurized slag containing 45% by mass or more of calcium aluminate, and a method for treating steel slag having a mixing ratio of 10% by mass or more. A method for treating steel slag in which a substance containing calcium aluminate is mixed with steel slag containing boron.
From the previously obtained relationship between the mixing ratio representing the mass ratio of the substance to the steel slag and the amount of boron eluted from the steel slag, the mixing ratio to be equal to or less than the target amount of boron eluted was determined.
The substance is mixed with the steel slag in a determined mixing ratio or more .
A method for treating steel slag, wherein the substance is a cast slag containing 74% by mass or more of calcium aluminate, and the mixing ratio is 10% by mass or more. The method for treating steel slag according to claim 1 or 2 , wherein the relationship is a regression line between the natural logarithmic value of the mixing ratio and the elution amount. It is a method of manufacturing recycled steel slag.
The steel slag is treated by the steel slag treatment method according to any one of claims 1 to 3.
Manufacture of recycled steel slag A method for manufacturing recycled steel slag.