JP7303989B2 - Method for modifying boron-containing substance and method for producing civil engineering and construction material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for modifying a boron-containing substance and a method for producing a material for civil engineering and construction.

With the development of industry, the amount of industrial by-products generated in various industries is steadily increasing. In recent years, effective utilization of such industrial by-products has been carried out from the viewpoint of global environment conservation. For example, steel slag such as blast furnace slag and steelmaking slag generated from steel plants, coal ash generated from thermal power plants, and molten slag obtained by melting, cooling, and solidifying waste and sewage sludge incineration ash at high temperatures, After proper particle size adjustment, it is reused as a civil engineering and construction material such as roadbed material and ground improvement material.

When reusing industrial by-products, it is necessary to suppress the emission of harmful substances contained therein into the environment. Typical hazardous substances include heavy metals such as cadmium, mercury, chromium and lead. In addition to these heavy metals, for example, fluorine, selenium, arsenic and boron are also harmful to the environment. , the emission (elution) into the environment is strictly regulated.

Among the components that adversely affect the environment, methods for suppressing the elution of boron include, for example, a method of adding and mixing magnesium oxide in the form of powder or slurry to incineration ash containing boron (Patent Document 1 ), a method of humidifying and curing coal ash discharged from a thermal power plant for a predetermined period (Patent Document 2), and controlling the cooling rate of a boron-containing substance, specifically from a temperature state having a liquid phase to 900 ° C. It is known to increase the cooling rate up to (Patent Document 3).

Japanese Patent Application Laid-Open No. 2004-298741 JP 2007-90155 A Japanese Unexamined Patent Application Publication No. 2020-32343

However, in the method described in Patent Document 1, the magnesium oxide used as the boron elution inhibitor is expensive, and the mixture (final product) to which the elution inhibitor is added hardens and has a relatively high strength. Since it becomes a lump of this, there is a problem that it takes time and effort to adjust the particle size for using this as a material. In addition, in the method described in Patent Document 2, long-term humidification curing is required in order to suppress the elution of boron. Low productivity is a problem because it requires long-term moisturizing and curing.

The method described in Patent Document 3 can reduce the amount of boron eluted by a simple operation, but the amount of boron eluted from the boron-containing substance may increase through this method, and is more reliable. A method for reducing the amount of eluted boron has been desired.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a simple and highly reliable treatment method that can suppress the elution of boron from boron-containing substances such as industrial by-products.

The present inventor conducted various studies to solve the above problems, and found that when cooling a high-temperature boron-containing substance, by more strictly controlling the cooling rate to a lower temperature, The inventors have found that the amount of eluted boron satisfies environmental standards, and have completed the present invention.

Embodiments for solving the above problems are as follows.
[1] A method for treating a boron-containing substance, in which a boron-containing substance containing a liquid phase and having a temperature of 1100°C or higher is cooled from 1100°C to 750°C at an average cooling rate of 25°C/min or higher. A method for treating a boron-containing substance, characterized by:
[2] The method for treating a boron-containing substance according to [1], wherein the cooling is performed on the boron-containing substance poured out in the form of a thin plate.
[3] The method for treating a boron-containing substance according to [1] or [2], wherein the boron content of the boron-containing substance is 0.1% by mass or more.
[4] Any one of [1] to [3], wherein the basicity ((% by mass CaO)/(% by mass SiO ₂ )) of the boron-containing substance is adjusted to 1.20 or less prior to the cooling. 3. A method for treating a boron-containing substance according to .
[5] The above-mentioned [4], wherein the adjustment of the basicity is performed by adding a modifier containing SiO ₂ to the boron-containing substance while the temperature of the boron-containing substance is 1250 ° C. or higher. method of treating boron-containing materials in.
[6] The above [1] to [5], wherein the cooling is performed by forcibly cooling the boron-containing substance during the entire period or part of the period until the temperature of the boron-containing substance reaches 1100 ° C. to 750 ° C. ] The method for treating a boron-containing substance according to any one of the above.
[7] A method for producing a material for civil engineering and construction, characterized in that a boron-containing substance obtained by the method for treating a boron-containing substance according to any one of [1] to [6] is used as a raw material. , a method for manufacturing materials for civil engineering and construction.

According to the present invention, it is possible to provide a simple and highly reliable treatment method capable of suppressing elution of boron from boron-containing substances such as industrial by-products.

Hereinafter, each embodiment of the present invention will be described in detail, but the present invention is not limited to each embodiment. In addition, the mechanism of action described below includes presumptions, and its correctness does not limit the present invention. It should be noted that the description of a numerical range (a description in which two numerical values are connected by "-") is meant to include numerical values described as lower and upper limits.

In the process of studying to solve the above-mentioned problems, the present inventors, in order to confirm the distribution of boron in the boron-containing substance, determined the glass phase ratio based on the X-ray diffraction (XRD) measurement results for the boron-containing substance. Calculation, confirmation of uneven distribution of boron with an electron probe microanalyzer (EPMA), and observation of boron distribution in the glass phase with an electron energy loss spectrometer (TEM-EELS) attached to a transmission electron microscope were carried out. As a result, it was found that boron in the boron-containing material was mainly concentrated in the glass phase region.

The inventors also confirmed that the glass phase produced by rapid cooling of the boron-containing substance in a liquid phase crystallizes by slow cooling in a temperature range of less than 900°C.

According to these results, when cooling the boron-containing substance in the state of having a liquid phase, if the cooling rate in the temperature range of 900 ° C. or less is slow, the glass phase will crystallize and the amount will decrease. It can be said that the boron concentration in the glass phase relatively increases, and the amount of boron eluted from the boron-containing substance after cooling increases. If so, by continuing high-speed cooling down to a low temperature of less than 900° C., crystallization of the glass phase is suppressed, and a boron-containing substance with a small amount of eluted boron can be obtained.
Each embodiment of the present invention to be described later is based on such a technical idea.

[Method for treating boron-containing substances]
A method for treating a boron-containing substance according to one embodiment of the present invention is a boron-containing substance containing a liquid phase of 1100 ° C. or higher, from 1100 ° C. to 750 ° C., at an average cooling rate of 25 ° C./min or more. It is characterized by cooling at

The boron-containing substance is not particularly limited as long as it contains boron and can be placed in an environment where elution of boron poses a problem. Examples of boron-containing substances include steel slag such as blast furnace slag and steelmaking slag generated from steel plants, coal ash generated from thermal power plants, and incinerated ash of waste and sewage sludge, etc., which are melted at high temperatures, cooled, and solidified. Various slags such as slag, and paper sludge incineration ash, etc., can be mentioned.

The boron-containing material is cooled from a temperature above 1100° C. and containing a liquid phase. The boron-containing substance in this state may be obtained by heating a substance at normal temperature, or may be used as it is produced in a molten state. If the boron-containing material is slag, it may be cooled and solidified and reheated to a molten state.

Cooling of the boron-containing substance is carried out at an average cooling rate of 25°C/min or more from when it reaches 1100°C to 750°C. Here, the average cooling rate is a value obtained by dividing 350°C, which is the temperature difference between 1100°C and 750°C, by the required time t (min) for the boron-containing substance to reach 1100°C and reach 750°C. (350/t (°C/min)). By setting the average cooling rate to 25° C./min or higher, crystallization of the crystal phase can be suppressed and the ratio of the glass phase after cooling can be increased. The average cooling rate is preferably 30° C./min or higher, more preferably 35° C./min or higher, in order to enhance the effect of suppressing crystallization of the crystal phase. The average cooling rate is preferably as fast as possible within an industrially achievable range, so the upper limit is not limited. If the average cooling rate is less than 25° C./min, the effect of suppressing the crystallization of the crystal phase is small, so the ratio of the glass phase after cooling is low, and the elution amount of boron increases. Regarding the temperature range in which high-speed cooling is performed, even if the cooling rate of the boron-containing substance at a temperature exceeding 1100°C is increased, the effect of suppressing the crystallization of the crystal phase is limited. On the other hand, at temperatures below 750°C, the amount of crystalline phase that can be crystallized is small, and in order to achieve high-speed cooling, it is necessary to introduce expensive equipment or use a large amount of refrigerant, so the high-speed Cooling becomes less cost effective.

The temperature measurement position of the boron-containing substance for calculating the average cooling rate is the point where the cooling rate is the slowest and the temperature is the highest during the cooling period. In order to identify the location and determine the cooling conditions for obtaining the above-mentioned average cooling rate, the shape and dimensions of the boron-containing material during cooling are measured in advance, and the initial temperature of the boron-containing material in the molten state , and the temperature change over time at each position in the boron-containing substance during cooling is measured and recorded by temperature measuring means such as a thermocouple, and the time until the highest temperature point reaches 750 ° C. or less is grasped. Good. Alternatively, a heat transfer calculation may be performed in advance to predict a location where the cooling rate is expected to be the slowest and a time-dependent change in temperature at that location. The boron-containing material is cooled by a cooling means until the highest temperature part reaches 750 ° C. or less, and an average cooling rate of 25 ° C./min or more is secured at any point in the boron-containing material. to For example, when pouring a boron-containing substance from a molten state into a cooling vessel for cooling, the thickness of the boron-containing substance should be reduced so as to obtain a desired average cooling rate.

The method for cooling the boron-containing substance is not limited as long as it satisfies the above average cooling rate, and natural cooling may be used. However, as the temperature of the boron-containing substance decreases, the cooling rate tends to decrease. It is preferable to allow the solid substance to cool naturally as a coolant. For example, when pouring a boron-containing substance onto an iron plate to cool it, the boron-containing substance is poured into the iron plate while the temperature of the iron plate is low so that the iron plate has sufficient cooling power for the heat of the slag, or the iron plate is thick. It is better to take measures such as using In addition, if the above measures are difficult to take, forced cooling such as air cooling or water cooling may be performed. Specific methods of forced cooling include a method of cooling the surface of the poured boron-containing substance by blowing air with a blower such as a rotary cooler, a method of spraying water mist from a mist nozzle, and a container into which the boron-containing substance is poured. is exemplified by water cooling. These methods may be used in combination. The forced cooling described above can be performed during the entire period or part of the cooling period until the temperature of the boron-containing substance reaches 750°C. In particular, it is more effective to perform forced cooling at a low temperature side where the temperature of the boron-containing substance is close to 750° C., because a high cooling rate can be maintained even if the temperature of the boron-containing substance drops.

The shape of the boron-containing substance during cooling is not particularly limited, either. preferably. A thin plate-like boron-containing substance can be formed by pouring a boron-containing substance containing a liquid phase onto a metal plate such as an iron plate or a refractory such as alumina. The thickness of the thin plate-like boron-containing substance is exemplified by 100 mm or less from the viewpoint of increasing the cooling rate. The thickness is preferably 80 mm or less, more preferably 60 mm or less.

The method for treating a boron-containing substance according to one embodiment of the present invention is more effective when applied to a boron-containing substance having a boron content of 0.1% by mass or more. This is because such a boron-containing substance has a high possibility of exceeding the environmental standard because the amount of elution of boron increases remarkably when crystallization of the glass phase occurs. The upper limit of the boron content is not limited, but is usually at most 0.5% by weight in boron-containing substances occurring as industrial by-products.

In the method for treating a boron-containing substance according to one embodiment of the present invention, it is preferable to adjust the basicity to 1.20 or less prior to cooling the boron-containing substance. Thereby, the elution of boron from the boron-containing substance after cooling can be further suppressed. Here, the basicity of the boron-containing material means the ratio of the CaO content in mass % to the SiO ₂ content in mass % ((mass % CaO)/(mass % SiO ₂ )). The lower limit of basicity is not particularly limited. Therefore, a boron-containing substance that contains almost no CaO and has a basicity of almost zero can also be treated.

The aforementioned basicity adjustment may be performed by adding a modifier containing SiO ₂ to the boron-containing substance while the temperature of the boron-containing substance is 1250° C. or higher. By adding the modifier while the temperature of the boron-containing substance is 1250° C. or higher, the modifier is sufficiently dissolved in the liquid phase of the boron-containing substance, and the basicity of the boron-containing substance is uniformly lowered. When adding the modifier containing SiO ₂ , it may be added after heating and melting. Thereby, it is possible to suppress the temperature drop of the boron-containing substance due to the addition of the modifier containing SiO ₂ . As the modifier containing SiO ₂ , it is preferable to use a material having a SiO ₂ content of 30% by mass or more and being dissolved in the liquid phase of the boron-containing substance. This can effectively suppress the elution of boron from the boron-containing substance after treatment. The SiO ₂ content in the modifier is more preferably 50% by mass or more, and even more preferably 70% by mass or more. Examples of specific modifiers include silica sand, waste glass, and pyrophyllite.

The boron-containing substance treated as described above is cooled to room temperature, crushed and sieved by a conventional method to a particle size of 2 mm or less, and the elution of boron is evaluated by the Environment Agency Notification No. 46 test.

[Manufacturing method for civil engineering and construction materials]
A method for producing a material for civil engineering and construction according to another aspect of the present invention is characterized by using, as a material, the modified slag obtained by the above-described method for treating a boron-containing substance.

In this embodiment, it is preferable to adjust the particle size of the boron-containing substance whose boron elution satisfies the environmental standard according to the use of the civil engineering and construction materials such as roadbed materials and soil improvement materials. An example of particle size adjustment is crushing or sieving the boron-containing material to a size of 40 mm or less when the boron-containing material is used as a roadbed material.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the examples.

[Examples 1 to 4]
Four types of slag (A to D) having the compositions shown in Table 1 were prepared as boron-containing substances. These slags are normally generated in metal smelting processes. The composition of slag shown in Table 1 is estimated from normal operating conditions.

Immediately after being generated in the refining process, the slag A to D in a molten state of about 1450 ° C. was poured onto an iron plate, spread thinly so that the thickness was 50 mm or less, and cooled, Examples 1 to 4. We processed the slag related to. The iron plate was selected so that (the heat capacity of the iron plate)>{1.5×(the heat capacity of the slag to be poured out)} to ensure the cooling performance. Also, the temperature of the iron plate before receiving the slag was 500° C. or lower. When pouring out the slag, a thermocouple was placed in the central portion of the thinly spread slag in the thickness direction to measure and record changes in temperature over time, and the average cooling rate was calculated based on the results. As a result, the average cooling rate at 1100 to 750° C. was 25° C./min or higher in any of the examples.

For each slag after cooling, the elution amount of boron was evaluated by the Environment Agency Notification No. 46 test. As a result, the amount of eluted boron in all slags was below the voluntary standard value, and the slag was determined to be acceptable (○).

[Examples 5-7]
Executed in the same manner as in Examples 1 and 2 above, except that several mass % of silica sand was added to each of slags A and B that were in a molten state of about 1450 ° C. immediately after being generated in the refining process. Slag treatments according to Examples 5 and 6 were performed. In addition, for the slag C which was in a molten state of 1450° C. immediately after being generated in the refining process, the waste glass was heated and melted in advance and then added to the slag C in the same manner as in Example 3. The slag according to Example 7 was treated. The addition of silica sand or waste glass increased the _SiO2 content in the slag and decreased the basicity of the slag. The average cooling rate at 1100 to 750°C in each example was 25°C/min or more.

For each slag after the treatment, the elution of boron was determined in the same manner as in Examples 1 to 4 described above. As a result, the amount of eluted boron in all slags was below the voluntary standard value, and the slag was determined to be acceptable (○).

[Comparative Examples 1 to 4]
Each slag poured out on the iron plate was removed from the iron plate during cooling, deposited on the slag that was similarly cooled on the iron plate, and further the slag during cooling was deposited on it and sandwiched. Treatments according to Comparative Examples 1 to 4 were performed in the same manner as in Examples 1 to 4 described above. In addition, even after sandwiching with slag, the temperature measurement was continued at the central portion in the thickness direction when it was first poured onto the iron plate. In each comparative example, it was confirmed that the average cooling rate at 1100 to 750°C was less than 25°C/min.

For each slag after the treatment, the elution of boron was determined in the same manner as in Examples 1 to 4 described above. As a result, the amount of eluted boron exceeded the voluntary standard value for all slags, and they were judged to be unacceptable (x).

Table 2 summarizes the conditions and boron elution determination results for the treatment of slag according to Examples 1 to 7 and Comparative Examples 1 to 4.

From Table 2, in the example in which the slag was cooled from 1100 ° C. to 750 ° C. at an average cooling rate of 25 ° C./min or more, the elution amount of boron was the voluntary standard value. It turns out that it can be suppressed as follows. On the other hand, in the comparative examples in which the average cooling rate at 1100° C. to 750° C. is less than 25° C./min during cooling, the boron elution amount exceeds the voluntary standard value.

[Examples 8 to 11]
As the boron-containing substance, the same as in Examples 1 to 4 above except that slag A to D that was generated in the refining process and left to cool and then reheated in an electric furnace to a molten state of 1450 ° C. was used. The method was used to treat the slag according to Examples 8-11.

For each slag after treatment, the amount of eluted boron was evaluated in the same manner as in Examples 1 to 4 described above. As a result, it was confirmed that if the slag had the same composition, there was no difference in the amount of eluted boron from the molten slag immediately after being generated from the refining process.

According to the present invention, there is provided a simple and highly reliable method capable of reducing the amount of elution of boron from a boron-containing substance for which the amount of elution of boron exceeds the environmental standard by a conventional treatment method. For this reason, it is possible to reuse boron-containing substances that could not be reused only because the amount of eluted boron exceeds environmental standards, and for the same reason, boron that had to be treated separately at the time of final disposal. The present invention is useful in that the contained substance can be simply disposed of by omitting the treatment.

Claims (7)

A method for treating a boron-containing material, comprising:
Cooling a boron-containing substance containing a liquid phase of 1100° C. or higher from 1100° C. to 750° C. at an average cooling rate of 25° C./min or more (excluding 100° C./min or more) characterized by
A method for treating boron-containing substances. 2. The method for treating a boron-containing substance according to claim 1, wherein the cooling is performed on the boron-containing substance poured out in the form of a thin plate. 3. The method for treating a boron-containing substance according to claim 1, wherein the boron content of said boron-containing substance is 0.1% by mass or more. The boron-containing according to any one of claims 1 to 3, wherein the basicity of the boron-containing substance ((mass% CaO) / (mass% SiO2)) is adjusted to 1.20 or less prior to the cooling. How to handle substances. The boron-containing substance according to claim 4, wherein the adjustment of the basicity is performed by adding a modifier containing SiO ₂ to the boron-containing substance while the temperature of the boron-containing substance is 1250 ° C. or higher. How to handle. 6. The method according to any one of claims 1 to 5, wherein the cooling is performed by forcibly cooling the boron-containing substance during the entire period or part of the period until the temperature of the boron-containing substance reaches 1100°C to 750°C. 3. A method for treating a boron-containing substance according to . A method for producing a material for civil engineering and construction, characterized in that the boron-containing substance obtained by the method for treating a boron-containing substance according to any one of claims 1 to 6 is used as a raw material. How the material is made.