JP5824718B2 - Method for producing solidifying agent - Google Patents

Description

  The present invention relates to a method for producing a solidifying agent for solidifying and improving soil, and more particularly to a method for producing a solidifying agent using steelmaking slag.

  Cement-based solidification materials are widely used as a solidifying agent for solidifying and improving soft soil, but cement-based solidification materials that are highly alkaline can adversely affect the improved soil ecosystem when run out with rainwater. In addition, the elution of fluorine and heavy metals derived from the cement material has a problem of adversely affecting the surrounding environment. For this reason, various non-cement solidifying agents have been proposed.

For example, Patent Document 1 describes a solidifying agent using steelmaking slag generated in a steelmaking process of stainless steel, and this solidifying agent is produced by mixing gypsum and a polymer flocculant with steelmaking slag.
In patent document 1, the steelmaking slag which grind | pulverized the coarse-grained or lump-shaped steelmaking slag in the roller mill, and was collected with the collector, the solidification promoter containing the collected finely powdered steelmaking slag and hemihydrate gypsum, Are mixed with a mixer to produce a solidifying agent.

JP 2010-120987 A

  However, since the solidifying agent produced as described in Patent Document 1 is a mixture of gypsum and fine powder steelmaking slag having different particle sizes, the uniformity during mixing is not high. Therefore, there is a problem that the soil cannot be improved with uniform solidification strength, that is, there is a problem that the solidification performance of the solidifying agent varies. Furthermore, in the case of producing a solidifying agent as described in Patent Document 1, in order to carry out the treatment of mixing the steelmaking slag with the solidification accelerator after pulverizing the steelmaking slag into a fine powder, the material is used in a series of production steps of the solidifying agent. There is also a problem that the number of transporting processes and processing processes increases and the manufacturing cost increases.

  This invention was made in order to solve such a problem, and it aims at providing the manufacturing method of the solidification agent of the soil which secures the stable solidification performance and reduces cost.

  In order to solve the above-described problems, a method for producing a solidifying agent according to the present invention is a method for producing a solidifying agent for solidifying and improving soil, in which steelmaking slag and gypsum hydrated more than dihydrate are mixed together. A solidifying agent is produced by heating while pulverizing, and the steelmaking slag has a basicity (calcium oxide content / silicon dioxide content) of 0.8 to 1.6, a composition of mass%, and fluorine. Less than 0.4%, calcium oxide 35-65%, silicon dioxide 20-55%, alumina 1-15%, and the elution amount of fluorine with respect to water is less than 0.8 mg per liter of water, The elution amount of valent chromium to water is less than 0.05 mg per liter of water.

Moreover, the fineness of the mixture of steelmaking slag and gypsum after crushing becomes 2300-4500 branes, and the mixture is crushed so that the content of hemihydrate gypsum in the gypsum contained in the mixture after heating is 50% by mass or more. Heating may be controlled.
Furthermore, steelmaking slag and gypsum may be mixed at a mixing ratio of 80:20 to 50:50.

Moreover, the steelmaking slag mixed with the gypsum may be at least one of a massive steelmaking slag and a granular steelmaking slag after the beneficiation treatment is performed from the stainless steel slag and the metal is collected.
On the other hand, the gypsum mixed with the steelmaking slag has an elution amount of fluorine with respect to water of 8 mg or less per liter of water, and may be at least one selected from waste gypsum, desulfurized gypsum, and chemically synthesized gypsum.
Moreover, you may add a polymer flocculent to steelmaking slag and gypsum.
Moreover, you may implement mixing, grinding | pulverization, and heating of steelmaking slag and gypsum with the grinder which can control the particle size which grinds steelmaking slag and gypsum, and the amount of heat added to steelmaking slag and gypsum.
Further, the pulverizer is a vertical roller mill that discharges an object pulverized by an air flow introduced into the interior from the introduction port, and introduces an air current by hot air from the introduction port into the vertical roller mill. The steelmaking slag and gypsum may be heated.

  According to the method for producing a solidifying agent according to the present invention, it is possible to secure stable solidification performance and reduce costs.

It is a schematic diagram which shows the flow which manufactures a solidification agent. It is a figure which classifies and shows each process which manufactures a solidifying agent.

Hereinafter, the manufacturing method of the solidifying agent 10 for improving the soil in the embodiment of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 2, the process for producing the solidifying agent 10 is roughly classified into a steelmaking process 1 for producing steelmaking slag as a raw material, a slag beneficiation treatment process 3 for collecting metal from the steelmaking slag, and a steelmaking slag and It is comprised by three processes of the solidification agent manufacturing process 8 which produces | generates the solidification agent 10 from the raw material of gypsum.

Referring also to FIG. 1, in the steelmaking process 1, steelmaking slag is generated when stainless steel is melted, and the generated steelmaking slag is collected. Steelmaking slag is produced in the process of desulfurizing molten stainless steel that is melted in an electric furnace, and in the process of secondary refining of the molten stainless steel after desulfurization, such as a converter or vacuum degassing process. There is something.
The collected steelmaking slag is transferred to the cooling step 2 and cooled and solidified. And since steel manufacture slag contains comparatively many useful metal components, the metal which is a metal component contained at the following slag beneficiation processing process 3 is collect | recovered.

The steelmaking slag that has been cooled and solidified is transferred to the crushing step 31 of the slag beneficiation treatment step 3 and subjected to crushing treatment by two types of rod mills that crush to different particle sizes, and then subjected to crushing treatment to be roughly sized. The
The steelmaking slag that has been subjected to the pulverization process is transferred to a sieve classification step 32, and those having a predetermined size or less are selected, that is, classified by the sieve. The steelmaking slag that has not passed through the sieve is returned again to the crushing step 31 and subjected to crushing and crushing treatment.

The classified steelmaking slag is moved to the magnetic separation process 33, and the metal 4 contained in the steelmaking slag is recovered by the magnetic separation machine. Further, the steelmaking slag is transferred to a specific gravity separation step 34 in which the difference in specific gravity of minerals is used to collect the bullion 4 contained therein.
The steelmaking slag from which the metal 4 has been collected is transferred to the Akins classification process 35, and is classified by the Akins classifier to select massive and coarse-grained steelmaking slag 6 having a specific particle size (approximately 5 mm) or more. The
The steelmaking slag classified by the steelmaking slag 6 is transferred to a thickener / dewatering step 36, where the finely powdered steelmaking slag is separated by the thickener, and the separated finely powdered steelmaking slag is subjected to a dehydration treatment, thereby producing powdery steelmaking slag. Collected as 5.

  As described above, the slag beneficiation treatment process 3 is completed from the crushing process 31 through the thickener / dehydration process 36, and the obtained massive and coarse-grained steelmaking slag 6 is supplied to the solidifying agent production process 8 as a raw material of the solidifying agent 10. used. In addition, the powdery steelmaking slag 5 is often soft among the steelmaking slags, and due to the wet treatment by the thickener, the reaction due to moisture has already progressed to some extent compared to the massive and coarse-grained steelmaking slag 6. . For this reason, since the powdery steelmaking slag 5 is not suitable for expressing sufficient long-term strength in the soil after the solidification improvement, the powdered steelmaking slag 6 is not used as a raw material of the solidifying agent 10, and the massive and coarse-grained steelmaking slag 6 is Used as a raw material for the solidifying agent 10.

In the solidifying agent production process 8, a roller mill pulverization / mixing process 81 is first performed, and a drying process 82 is performed in parallel with the roller mill pulverization / mixing process 81.
In the roller mill crushing / mixing step 81, the steelmaking slag 6 and the gypsum raw material 7 made of dihydrated gypsum (dihydrate gypsum: CaSO ₄ .2H ₂ O) are put into the conveying device 81c of the vertical roller mill 81a. Is done. That is, the steelmaking slag 6 and the gypsum raw material 7 are simultaneously fed into the vertical roller mill 81a.

The gypsum raw material 7 includes waste gypsum regenerated from waste building materials such as gypsum board, desulfurized gypsum generated when the exhaust gas from the power generation boiler is desulfurized, and chemically synthesized gypsum which is a by-product in chemical synthesis at a chemical factory. A raw material containing any gypsum such as natural gypsum can also be used. However, the gypsum used as a raw material has an elution amount of fluorine (F) with respect to water of less than 8 mg (8 mg / L) per 1 liter of water in order to suppress the elution amount to the soil to be solidified and improved. Use as low a quantity as possible. Furthermore, the gypsum raw material as shown above is usually hydrated and contains water that is dihydrated or higher (having a crystal structure of CaSO ₄ .2H ₂ O and adhering moisture). And when hemihydrate gypsum (CaSO ₄ · 1 / 2H ₂ O) having the property of easily causing a hydration reaction is mixed with the steelmaking slag 6, it comes into contact with moisture contained in the steelmaking slag 6 to cause a hydration reaction. On the other hand, the gypsum raw material composed of gypsum of two or more hydrates does not cause a hydration reaction and does not harden even if it comes into contact with moisture contained in the steelmaking slag 6 by mixing. By the way, in this embodiment, the gypsum raw material 7 made of dihydrate gypsum is used, but gypsum raw material in which various gypsums more than trihydrate or various dihydrates are mixed may be used. Good.

The steelmaking slag 6 and the gypsum raw material 7 that have been charged are transported into the main body 81b of the vertical roller mill 81a by the transport device 81c, and are moved together between the horizontally rotating table 81e and the roller 81f at the bottom of the main body 81b. Into fine powder. Since the gypsum raw material 7 does not cure and harden during mixing and crushing, the steelmaking slag 6 and the gypsum raw material 7 are crushed by the conveying device 81c and by the roller 81f. And evenly mixed.
At the same time, hot air is introduced into the main body 81b from an inlet 81d provided on the lower side of the main body 81b so that the temperature inside the main body 81b is about 120 ° C. to 160 ° C. Forcibly supplied by. At this time, ascending airflow is generated inside the main body 81b by the supplied hot air, and the pulverized mixture of steelmaking slag and gypsum is dried by the hot air and is transported upward, and more uniformly when transported upward. To be mixed.

In addition, the moisture contained in the steelmaking slag in the mixture is removed by the drying action at about 120 ° C. to 160 ° C. The moisture hydrated in the dihydrate gypsum is removed, and the dihydrate gypsum At least partly changes to hemihydrate gypsum. The produced hemihydrate gypsum has a property of causing a hydration reaction and is easy to harden. However, since moisture is removed from the surrounding steelmaking slag 6, it causes a hydration reaction and hardens. Without being lost.
Here, drying with hot air constitutes a drying step 82.

A mixture of steelmaking slag and gypsum carried upward in the main body 81b is sorted and collected by a separator 81g provided on the upper portion of the main body 81b, and discharged together with air from the discharge port 81h. Is done.
The discharged fine powder of the steelmaking slag and gypsum mixture moves to the collection step 83, is collected from the air by the powder collector, and is stored in the silo as the solidifying agent 10. Then, the solidifying agent 10 stored in the silo is shipped to the market as a soil improving agent.

When the solidifying agent 10 is mixed with soft soil containing a large amount of water, the hemihydrate gypsum itself hydrates by using the water of the soil to precipitate needle-shaped crystals of dihydrate gypsum and condense. Also, the steelmaking slag itself is cured by hydration using soil moisture. Furthermore, using the moisture of the soil, calcium oxide (CaO) and alumina (Al ₂ O ₃ ) contained in the steelmaking slag react with a hydrated gypsum, and ettringite (3CaO · Al ₂ O · 3CaSO) ₄ · _32H 2 O) condenses by precipitating needle crystals. Then, the water is removed and the strength is increased, that is, the soil is solidified by the hydrated hemihydrate gypsum, the hydrated steelmaking slag and ettringite.
Hemihydrate gypsum develops strength in the soil in a relatively short time when hydrated using water in the soil, so it has a rapid solidification of the soil and expresses the initial strength of the soil. To do. Steelmaking slag has a delayed reaction to harden and solidify the soil by hydration reaction, so that it takes a long time to develop sufficient strength in the soil and develops the long-term strength of the soil. Ettlingite expresses strength by itself, and reacts quickly with highly reactive hemihydrate gypsum to produce the initial strength of the soil.

  In addition, when the solidifying agent 10 is manufactured so as to satisfy the following conditions, the solidifying agent 10 can effectively improve the solidification performance such as improved strength of the soil and suppress the elution of heavy metals and the like. It has been confirmed that this can be achieved.

First, as a first condition, the steelmaking slag 6 used as a raw material for the solidifying agent 10 has a basicity (mass ratio of CaO [calcium oxide] content to CaO / SiO ₂ : SiO ₂ [silicon dioxide] content). Is 0.8 to 1.6, the composition is mass%, fluorine (F) is less than 0.4%, calcium oxide is 35 to 65%, silicon dioxide is 20 to 55%, alumina (Al ₂ O ₃ ) Is 1 to 15%, the elution amount of fluorine to water is less than 0.8 mg (0.8 mg / L) per liter of water, and the elution amount of hexavalent chromium (Cr ⁶⁺ ) to water is 1 Less than 0.05 mg (0.05 mg / L) per liter is used. And the reason for the said range limitation is demonstrated below.

The reason why the basicity (CaO / SiO ₂ ) is set to 0.8 to 1.6 is to suppress adverse effects on the desulfurization of molten stainless steel. Basicity has a great effect on the desulfurization of molten stainless steel. If it is less than 0.8, sufficient desulfurization reaction cannot be obtained with steelmaking slag, and if it exceeds 1.6, the fluidity of steelmaking slag decreases. The contact interface between the molten stainless steel and the steelmaking slag is reduced, and the desulfurization reaction by the steelmaking slag is not promoted. In addition, in order to compose steelmaking slag with fluorine (F) described below of less than 0.4 mass%, the use of fluorite (CaF ₂ ) that has been used to improve the fluidity of slag is limited. Therefore, it is necessary to adjust the basicity to ensure the fluidity of the steelmaking slag.

The reason for making fluorine (F) less than 0.4 mass% in the composition of steelmaking slag is to satisfy the content of less than 0.4 mass% defined in the soil environment standard.
The reason for making calcium oxide (CaO) 35-65 mass% in the composition of steelmaking slag is to implement effective desulfurization of molten stainless steel. Calcium oxide is an essential component for the desulfurization reaction, and in order to sufficiently desulfurize molten stainless steel, it is necessary to contain 35% by mass or more in the steelmaking slag. On the other hand, when the content of calcium oxide is excessive with respect to the content of silicon dioxide (SiO ₂ ) in the steelmaking slag, the basicity becomes too high and the fluidity of the slag deteriorates, and the desulfurization reaction by the steelmaking slag is accelerated. Therefore, the content of calcium oxide needs to be 65% by mass or less.

The reason why silicon dioxide (SiO ₂ ) is 20 to 55% by mass in the composition of the steelmaking slag is to carry out effective desulfurization of molten stainless steel. Silicon dioxide is generated from the raw material and is also generated as a deoxidation reaction product by a reducing agent. When the content of silicon dioxide in the steelmaking slag is less than 20% by mass, the basicity becomes too high and the desulfurization reaction by the steelmaking slag is not promoted. When the content exceeds 55% by mass, the basicity becomes too low and sufficient desulfurization is performed. No reaction is obtained. For this reason, silicon dioxide shall be 20-55 mass%.

Why alumina _(Al 2 _{O 3)} 1 to 15 wt% in the composition of the steelmaking slag, is to ensure the fluidity of the steel slag. Alumina is mixed from refractory bricks and raw materials, and if the content of alumina in the steelmaking slag is too low or too high, the melting point of the slag rises and the fluidity of the slag decreases.
The reason why the amount of elution of fluorine (F) with respect to water is less than 0.8 mg / L and the amount of elution of hexavalent chromium (Cr ⁶⁺ ) with respect to water is less than 0.05 mg is to satisfy the soil environmental standards. .
And steelmaking slag 6 is based on the rule of thumb about the compounding ratio of a raw material, and the element distribution ratio between slag and stainless steel molten steel, and adjusting the kind and compounding ratio of a slag raw material for every steel type to melt. Basicity and composition can be adjusted as described above.

As a second condition, for the steelmaking slag and gypsum mixture discharged from the discharge port 81h of the vertical roller mill 81a, 50% by mass or more of the gypsum contained in the mixture is hemihydrate gypsum, and The fineness of the mixture is 2300-4500 branes. In addition, a brane value is also called a brane specific surface area, and is a fineness calculated | required by a specific surface area test, The unit is cm < ² > / g.

  The ratio of hemihydrate gypsum in the gypsum of the mixture discharged from the discharge port 81h is adjusted by adjusting the temperature and flow rate of hot air supplied to the vertical roller mill 81a to adjust the outlet temperature at the discharge port 81h. Can be controlled. For example, the ratio of hemihydrate gypsum can be increased by increasing the temperature of the hot air, and the residence time of gypsum in the vertical roller mill 81a can be increased by decreasing the flow rate of the hot air. The percentage of can be increased. Furthermore, the fineness of the mixture can be controlled by adjusting the pressing force that presses the roller 81f of the vertical roller mill 81a against the table 81e. For example, the fineness of the mixture can be increased by increasing the pressing force of the roller 81f.

Moreover, the ratio of the hemihydrate gypsum to the gypsum of 50 mass% or more is because of the reason explained below.
Steelmaking slag affects the development of long-term strength of the soil, and hemihydrate gypsum affects the development of the initial strength of the soil. For this reason, the proportion of hemihydrate gypsum in the gypsum of 50% by mass or more is set in order to secure the amount of hemihydrate gypsum that expresses the initial strength of the soil and promote the solidification reaction to the soil. . Moreover, the ratio of the said hemihydrate gypsum is also set so that the used gypsum raw material 7 may be efficiently utilized for soil solidification improvement.

  Moreover, about the fineness of the mixture of 2300-4500 branes, the lower limit 2300 brane ensures a contact surface area between the soil particles, the steelmaking slag particles, and the gypsum particles, so that the hydration reaction between each other is sufficiently performed. This is the value to be implemented. Moreover, when the mixture of steelmaking slag and gypsum is heated by grinding | pulverizing to the fineness of 2300 branes or more, the removal efficiency of the water | moisture content from dihydrate gypsum improves. On the other hand, the upper limit 4500 brane for fineness is a value for suppressing the operation of the vertical roller mill 81a for a long time by pulverizing the mixture excessively finely and ensuring the productivity of the solidifying agent 10. .

As a third condition, the mixing ratio of the steelmaking slag 6 and the gypsum raw material 7 (steelmaking slag 6 / gypsum raw material 7) to be put into the vertical roller mill 81a is 80:20 to 50:50 (mass ratio). 80/20 to 50/50).
As described in the second condition, it is necessary to increase the content of hemihydrate gypsum in the solidifying agent 10 in order to develop sufficient initial strength in the solidified and improved soil. However, if the content of hemihydrate gypsum in the solidifying agent 10 exceeds 50% by mass, solidification rapidly proceeds during the solidification treatment of the soil, so the solidifying agent 10 cannot be uniformly mixed with the soil. , Improve solidification of uniform soil. On the other hand, if the content of hemihydrate gypsum in the solidifying agent 10 is too low, the initial strength at the time of soil solidification treatment is not sufficiently developed, and the workability of soil handling cannot be improved.
Furthermore, as shown in the second condition, the vertical roller mill 81a is controlled such that 50% by mass or more of the gypsum discharged from the vertical roller mill 81a is semi-water gypsum.

  For this reason, in order to obtain sufficient initial strength of the soil at the time of solidification improvement while suppressing the content of hemihydrate gypsum in the solidifying agent 10 to 50% by mass or less, the steelmaking slag 6 to be introduced into the vertical roller mill 81a. And the mixing ratio of the gypsum raw material 7 that produces hemihydrate gypsum is selected from the range of 80:20 to 50:50.

  Further, when the steelmaking slag content in the mixture is less than 50% by mass, the long-term strength expressed in the solidified and improved soil is lowered, and the content of gypsum increases, so that the fluorine contained in gypsum There is also a problem that the amount of elution of (F) increases. Also from this point, it is necessary that the mixing ratio of the steelmaking slag 6 and the gypsum raw material 7 does not become larger than 50:50.

When the solidifying agent 10 manufactured according to the first to third conditions described above improves the soil, the steelmaking slag and the hemihydrate gypsum react with each other by utilizing the moisture contained in the soil, ettringite to produce a _{(3CaO · Al 2 O · 3CaSO} 4 · 32H 2 O) and the like. Further, the generated ettringite is fixed by replacing the chromate ion (CrO ₄ ²⁻ ) of the steelmaking slag and the fluorine ion (F ⁺ ) eluted from the gypsum with the sulfate ion (SO ₄ ²⁻ ) of the ettringite, Suppresses the elution of fluorine (F) and chromium (Cr) into the soil. In addition, when the soil is improved, the steel slag generates a calcium silicate hydrate aggregate by the hydration reaction using the moisture of the soil, and the generated calcium silicate hydrate aggregate Due to the heavy metal adsorption action, elution of heavy metals such as chromium is suppressed. And the elution inhibitory effect of heavy metals etc. improves remarkably by the above-mentioned two inhibitory action.

Further, in the solidifying agent production step 8, the steelmaking slag 6 and gypsum raw material 7 which are put into the vertical roller mill 81a, or the steelmaking slag discharged from the vertical roller mill 81a and collected by the powder collector and A step of adding a polymer flocculant to the gypsum mixture can be added.
As the polymer flocculant, acrylic chloride polymer, natural water-soluble polymer calcium salt and the like can be used. These polymer flocculants are almost neutral, do not become highly alkaline even when contained in a steelmaking slag and gypsum mixture, react with moisture in the soil, harden in a relatively short time, and are soft. The initial strength is expressed in the soil.

(Example)
Hereinafter, the Example of the solidification agent 10 manufactured using the manufacturing method of this Embodiment is demonstrated. In this example, soft soil was solidified with the solidifying agent of each example, and the properties of the treated soil were evaluated.
Table 1 shows the basicity, composition and elution amount of the steelmaking slag used as a raw material for the solidifying agent of the examples.

Steelmaking slag and dihydrate gypsum shown in Table 1 were mixed, pulverized and dried in a vertical roller mill 81a to produce seven types of solidifying agents so as to satisfy the above three conditions. These solidifying agents are referred to as Examples 1-7, respectively.
Table 2 shows the blending amounts of the solidifying agents of Examples 1 to 7 used with respect to 1 m ³ of the soil to be solidified.

The solidifying agent of Example 1 has a steelmaking slag / gypsum mixing ratio (mass) of 80/20.
The solidifying agent of Example 2 has a steelmaking slag / gypsum mixing ratio (mass) of 70/30.
The solidifying agent of Example 3 has a steelmaking slag / gypsum mixing ratio (mass) of 60/40.
All of the solidifying agents of Examples 4 to 7 have a steelmaking slag / gypsum mixing ratio (mass) of 50/50 and a brazing value of the solidifying agent of 3900 (cm ² / g). The percentage of plaster is different.

Furthermore, the solidification process of the sludge was performed using the solidification agent of Examples 1-7. And about the sludge after a solidification process, strength, PH, and the elution amount of various elements were measured. In addition, about the intensity | strength, the cone index was measured by the cone index test method of the compacted soil according to JISA1228 standard. The corn index indicates that the larger the value, the higher the strength of the soil. For example, in the case of sludge before solidification improvement, the corn index is 200 kN / m ² or less.
Table 3 shows the measurement results of each measurement item for real施例1-7.

The corn index was measured 1 day after solidification to confirm initial strength and 7 days after solidification to confirm long-term strength. Soil having a corn index of 400 kN / m ² or more can be applied to banking, embankment construction, and residential land development in construction work, and is easy to handle and has good workability. That is, it can be evaluated that soil having a corn index of 400 kN / m ² or more has sufficient initial strength. Furthermore, soil having a corn index of 800 kN / m ² or more can be applied to all types of work such as roadbeds in construction work, and can be evaluated as having sufficient permanent strength (long-term strength).
In any of the solidifying agents of Examples 1 to 7, the corn index one day after the solidification treatment is 500 kN / m ² or more, and a sufficient initial strength is expressed. Further, after 7 days from the solidification treatment, the corn index is 1300 kN / m ² or more in any of the solidifying agents of Examples 1 to 7, and a sufficient long-term strength is expressed.

PH was measured 1 day after the solidification treatment to confirm the effect immediately after the solidification treatment and 7 days after the solidification treatment to confirm the effect over a long period of time. When PH is in the range of 5.0 to 9.0, it can be evaluated as neutral. Moreover, the drainage standard of the Water Pollution Control Law stipulates that the pH of drainage must be in the range of 5.8 to 8.6.
The pH after 1 day of the solidification treatment is less than 9.0 in the solidifying agents of Examples 4, 6 and 7, and can be evaluated as neutral. In the solidifying agents of Examples 1 to 3 and 5, 9. Although it exceeds 0, it shows 9.2 to 9.3 in the vicinity of 9.0, and can be evaluated as being almost neutral.
In addition, the pH after 7 days from the solidification treatment shows a value in the range of 8.0 to 8.4 in all the solidifying agents of Examples 1 to 7, and can be evaluated as neutral. Meets legal wastewater standards. Therefore, it can be said that acidic or alkaline water is prevented from flowing out from the improved soil in the long term.

The amount of elution was measured for fluorine (F), hexavalent chromium (Cr ⁶⁺ ), lead (Pb), cadmium (Cd) and arsenic (As). In Table 3, the column indicated by ND indicates that the elution amount for each element was not more than the detection limit value. In any solidifying agents of Examples 1 to 7, the elution amount of all elements was ND, and there was no problem.

Moreover, in order to compare with the solidification agent of Examples 1-7, 12 types of solidification agents were prepared. These 12 kinds of solidifying agents are referred to as Examples 8 to 11 and Comparative Examples 1 to 8 , respectively.
Table 4 shows the blending amounts of the solidifying agents of Examples 8 to 11 and Comparative Examples 1 to 8 used for 1 m ^{3 of} soil that is the target of the solidification treatment.

In Examples 8 to 11 , steelmaking slag and dihydrated gypsum shown in Table 1 are mixed, pulverized, and dried in a vertical roller mill 81a so that only the first and third conditions described above are satisfied. It is a solidifying agent manufactured as described above. For this reason, in the solidifying agents of Examples 8 to 11 , the proportion of hemihydrate gypsum in the gypsum contained in the solidifying agent is less than 50% by mass.
Further, the solidifying agent of Example 8 has a steelmaking slag / gypsum mixing ratio (mass) of 80/20, which is the same mixing ratio as Example 1.
The solidification agent of Example 9 has a steelmaking slag / gypsum mixing ratio (mass) of 70/30, which is the same mixing ratio as Example 2.
The solidifying agent of Example 10 has a steelmaking slag / gypsum mixing ratio (mass) of 60/40, which is the same mixing ratio as Example 3.
The solidifying agent of Example 11 has a steelmaking slag / gypsum mixing ratio (mass) of 50/50, which is the same mixing ratio as Example 4.
Comparative Examples 1-3 are cement-type solidification materials, and the addition amount with respect to soil is different, respectively.

In Comparative Examples 4 to 8 , the steel making slag shown in Table 1 was pulverized by a vertical roller mill 81a, and the hydrated steel slag was simply mixed with dihydrate gypsum, and the mixed solidified was produced by heating. The manufacturing process of the solidifying agent is different from the examples.
All the solidifying agents of Comparative Examples 4 to 8 have a steelmaking slag / gypsum mixing ratio (mass) of 50/50, which is the same mixing ratio as in Examples 5 to 7. In addition, as for the solidification agent of Comparative Examples 4-6 , the ratio of the half-water gypsum in the gypsum to be contained is less than 50 mass%, and all the solidification agents of Comparative Examples 7 and 8 are half in the gypsum to contain The ratio of water gypsum is 50% by mass or more.

Next, the solidification process of sludge was performed using the solidification agent of Examples 8-11 and Comparative Examples 1-8 . About the sludge after a solidification process, the intensity | strength by corn index, PH, and the elution amount of various elements were measured.
Table 5 shows the measurement results of the measurement items for Examples 8 to 11 and Comparative Examples 1 to 8 .

The corn index was measured 1 day and 7 days after the solidification treatment as in Examples 1 to 7.
In any of the solidifying agents of Examples 8 to 11 and Comparative Examples 1 to 8 , the corn index after one day of the solidification treatment is 400 kN / m ² or more, and a sufficient initial strength is expressed. In particular, Comparative Examples 1 to 3 , which are cement-based solidified materials, exhibit a cone index of 750 kN / m ² or more. However, in Examples 8 to 11 and Comparative Examples 4 to 8 , the initial strength is slightly lower as compared with Examples 1 to 7 as a whole. In particular, in Examples 8, 10 and 11 and Comparative Examples 4 to 6 , the proportion of hemihydrate gypsum in the gypsum as a solidifying agent is low, and in Example 8 , the proportion of gypsum in the solidifying agent is also low. The initial strength of is low.

In addition, after 7 days from the solidification treatment, Comparative Examples 4 and 6 showed a corn index of less than 800 kN / m ² , but in all Comparative Examples except Comparative Examples 4 and 6 , a corn index of 800 kN / m ² or more was obtained. It shows a sufficient long-term strength.
Moreover, long-term intensity | strength is significantly low in Examples 8-11 and Comparative Examples 4-8 compared with Examples 1-7 as a whole. On the other hand, Comparative Examples 1 to 3 , which are cement-based solidified materials, exhibit a very high cone index of 3050 kN / m ² or more. In Examples 8 to 11 , since the proportion of hemihydrate gypsum in the gypsum contained in the solidifying agent is low, the amount of hemihydrate gypsum itself contained in the solidified and improved soil is small, and the soil caused by the hemihydrate gypsum A small increase in strength lowers the expression strength in the improved soil. Moreover, in Comparative Examples 4-8 , it is not mixed uniformly between the steelmaking slag and the gypsum which differ greatly from each other, and the strength of the soil in which the steelmaking slag is expressed is not uniform. It is low.

Therefore, in the production of the solidifying agent using steelmaking slag and gypsum, the ratio of hemihydrate gypsum in the gypsum of the solidifying agent and the difference in the production process of the solidifying agent between Examples 1-7 and Comparative Examples 4-8 . All affect both the initial strength and long-term strength of the solidified soil, and it can be seen that the method for producing the solidifying agent in Examples 1 to 7 is excellent in terms of expression strength.

PH was measured 1 day and 7 days after the solidification treatment, as in Examples 1-7 .
PH after solidification day, for Examples 8-11, can be evaluated as neutral in the range of 5.0 to 9.0 in Example 11, greater than 9.0 In Examples 8-10 However, 9.1-9.4 in the vicinity of 9.0 is shown, and it can be evaluated as almost neutral as in Examples 1-4.

About Comparative Examples 4-8 , PH has exceeded all 9.0, and it is as high as 9.6-10.1 especially in Comparative Examples 4-6 . In Comparative Examples 4 to 6 , the amount of steelmaking slag added to the soil is large, but the ratio of hemihydrate gypsum in the gypsum as a solidifying agent is low, and steelmaking slag and gypsum having different degrees of fineness are uniformly mixed. Therefore, there is little steelmaking slag that reacts with hemihydrate gypsum to become ettringite, and the amount of steelmaking slag that hydrates with moisture in the soil and becomes alkaline increases. Under the influence, the value of PH is high.
Moreover, PH of the comparative examples 1-3 which is a cement-type solidification material has shown especially high numerical value with 11.8 all.

The pH after 7 days from the solidification treatment is within the range of 8.0 to 8.8 in any of Examples 8 to 11 and Comparative Examples 4 to 8 in which the solidifying agent was produced from steelmaking slag and gypsum. Can be evaluated. Furthermore, PH in Examples 8 to 11 and Comparative Examples 4, 7, and 8 also satisfies the drainage standards of the Water Pollution Control Law. Moreover, PH in Examples 8 to 11 and Comparative Examples 4 to 8 is close to the measurement results in Examples 1 to 7 . The decrease in PH after 7 days from the solidification treatment is due to the progress of the delayed steelmaking slag reaction.
Moreover, PH of the comparative examples 1-3 which is a cement-type solidification material has exceeded 11.0, and is still maintaining the high state.

Regarding the amount of elution, in Examples 8 to 11 , fluorine (F) at the upper limit of the reference value was detected in Example 11 . Further, in Comparative Examples 1 to 3 , hexavalent chromium (Cr ⁶⁺ ) exceeding the reference value in Comparative Example 1 and lead (Pb) at the upper limit of the reference value are detected, and in Comparative Example 3 , hexavalent chromium ( Cr ⁶⁺ ) was detected. In Comparative Examples 4 to 8 , lead (Pb) and arsenic (As) at the upper limit of the reference value are detected in Comparative Example 4 , and arsenic (As) exceeding the reference value is detected in Comparative Examples 5, 6 and 8 , In Comparative Example 7 , arsenic (As) at the upper limit of the reference value was detected. In Examples 8-11 and Comparative Examples 1-8 , about other elements, the elution amount was below the reference value.

In Examples 8 to 11 , the amount of ettringite produced is small and the amount of elution of fluorine and hexavalent chromium is large in Example 11 in which the amount of hemihydrate gypsum contained in the solidified and improved soil is very small.
In Comparative Examples 1 to 3 , which are cement-based solidified materials, the amount of hexavalent chromium eluted is large overall due to the properties of the cement-based solidified material.
In Comparative Examples 4 to 8 , the amount of arsenic eluted is large as a whole.
And in Examples 1-7 compared with a comparative example, the elution amount of all the elements is suppressed low.

  As described above, the method for producing the solidifying agent 10 according to the present invention is a method for producing a solidifying agent for solidifying and improving the soil. The steel making slag 6 and the gypsum raw material 7 for gypsum hydrated to dihydration or more are used. It is a method of producing a solidifying agent by mixing and heating while pulverizing together. The steelmaking slag 6 used in this production method has a basicity (calcium oxide content / silicon dioxide content) of 0.8 to 1.6, a composition of mass%, and fluorine of less than 0.4%. Calcium oxide is 35 to 65%, silicon dioxide is 20 to 55%, alumina is 1 to 15%, and the elution amount of fluorine to water is less than 0.8 mg per liter of water, and hexavalent chromium to water The elution amount is less than 0.05 mg per liter of water.

  At this time, by mixing the steelmaking slag 6 and the gypsum raw material 7, these can be pulverized at the same time and heated at the same time, so that the manufacturing process of the solidifying agent 10 can be shortened and the cost can be reduced. It becomes possible. Moreover, since the steelmaking slag 6 and the gypsum raw material 7 of the gypsum hydrated to more than two hydrates are mixed and pulverized together, the gypsum does not cause a hydration reaction due to moisture contained in the steelmaking slag at the time of pulverization. Can be mixed. Furthermore, because the steelmaking slag and gypsum are heated while uniformly mixed and pulverized, the water is removed from gypsum that is more than dihydrated. The occurrence of a hydration reaction that hardens can be suppressed. Therefore, it is possible to produce the solidifying agent 10 having stable solidification performance.

  Moreover, in the manufacturing method of the solidifying agent 10, the mixing, pulverization, and heating of the steelmaking slag 6 and the gypsum raw material 7 are controlled, and the amount of heat applied to the steelmaking slag 6 and the gypsum raw material 7 is controlled. It implements with the vertical roller mill 81a which is a possible grinder. Furthermore, the steelmaking slag 6 and the gypsum raw material 7 are heated by introducing an air flow by hot air into the vertical roller mill 81a from the inlet 81d of the vertical roller mill 81a. Thereby, since the solidifying agent 10 can be manufactured only by the vertical roller mill 81a, the cost can be reduced.

Further, the vertical roller mill 81a has a fineness after grinding of the mixture of the steelmaking slag 6 and the gypsum raw material 7 to 2300-4500 branes, and the content of hemihydrate gypsum in the gypsum contained in the mixture after heating is 50 mass. By controlling so that it may become more than%, it becomes possible to manufacture the solidification agent 10 with high reactivity. That is, by setting the fineness to 2300 to 4500 branes, the efficiency of producing hemihydrate gypsum from hydrated gypsum is improved, and the contact area between the soil particles and the solidifying agent 10 particles is ensured to react with each other. It becomes possible to improve the property. Moreover, it becomes possible to accelerate | stimulate the expression of the solidification intensity | strength in the improved soil by making the content rate of hemihydrate gypsum in the gypsum of the solidification agent 10 into 50 mass% or more.
Furthermore, in the manufacturing method of the solidifying agent 10, the steelmaking slag 6 and the gypsum raw material 7 are mixed at a mixing ratio of 80:20 to 50:50. As a result, the content of hemihydrate gypsum in the solidifying agent 10 becomes too high, and it is possible to suppress abrupt solidification during the solidification improvement.

  Moreover, in the manufacturing method of the solidifying agent 10, the steelmaking slag 6 mixed with the gypsum raw material 7 is at least one of a massive steelmaking slag and a granular steelmaking slag after the mineral processing is recovered from the stainless steel slag and the metal is recovered. It is. Steel slag, which is a byproduct of stainless steel, has been diminished in use due to the inclusion of fluorine due to recent environmental regulations, but can be effectively reused as a resource without being discarded.

Moreover, in the manufacturing method of the solidifying agent 10, the gypsum raw material 7 mixed with the steelmaking slag 6 has an elution amount of fluorine with respect to water of 8 mg or less per liter of water, and is selected from waste gypsum, desulfurized gypsum, and chemically synthesized gypsum. It can be at least one selected. By suppressing the fluorine elution amount of the gypsum raw material 7 low, it becomes possible to suppress the fluorine elution amount in the soil solidified and improved by the solidifying agent 10. In addition, it becomes possible to effectively reuse waste and gypsum as a by-product as resources.
In the method for producing the solidifying agent 10, a polymer flocculant may be added to the steelmaking slag 6 and the gypsum raw material 7. This makes it possible to develop sufficient initial strength more quickly with respect to the solidified and improved soil.

In the embodiment, in the vertical roller mill 81a, the steelmaking slag 6 and the gypsum raw material 7 are mixed, pulverized, and heated at the same time. However, the present invention is not limited to this. After the steelmaking slag 6 and the gypsum raw material 7 are mixed and pulverized, hot air may be supplied from the introduction port 81d to the inside of the main body 81b. This makes it possible to reliably prevent the hemihydrate gypsum produced from dihydrate gypsum from being heated and reacting with the moisture of the steelmaking slag 6 in the process of being mixed or pulverized.
Moreover, in this Embodiment, although the vertical roller mill 81a was used for mixing, grind | pulverizing, and heating the steelmaking slag 6 and the gypsum raw material 7, it is not limited to this, The steelmaking slag 6 and the gypsum raw material 7 As long as they can be mixed and pulverized and heated at the same time.

  6 Steelmaking slag, 7 Gypsum raw material, 8 Solidifying agent production process, 10 Solidifying agent, 81 Roller mill grinding / mixing process, 81a Vertical roller mill, 81d Inlet, 82 Drying process, 83 Collection process.

Claims (8)

In the method for producing a solidifying agent for solidifying and improving soil,
Producing the solidifying agent by mixing steelmaking slag and gypsum hydrated more than dihydrate and heating together while pulverizing together,
The steelmaking slag is
Basicity (calcium oxide content / silicon dioxide content) is 0.8 to 1.6,
The composition is mass%, fluorine is less than 0.4%, calcium oxide is 35 to 65%, silicon dioxide is 20 to 55%, alumina is 1 to 15%,
A method for producing a solidifying agent, wherein the elution amount of fluorine with respect to water is less than 0.8 mg per liter of water, and the elution amount of hexavalent chromium with respect to water is less than 0.05 mg per liter of water.   The mixture so that the fineness after grinding of the steel slag and the mixture of gypsum becomes 2300-4500 branes and the content of hemihydrate gypsum in the gypsum contained in the mixture after heating is 50% by mass or more. The manufacturing method of the solidification agent of Claim 1 which controls the grinding | pulverization and heating of a solid.   The method for producing a solidifying agent according to claim 2, wherein the steelmaking slag and the gypsum are mixed at a mixing ratio of 80:20 to 50:50.   The steelmaking slag mixed with the gypsum is at least one of massive steelmaking slag and granular steelmaking slag after beneficiation treatment from stainless steel slag and recovery of the metal. A method for producing the solidifying agent according to item.   The gypsum mixed with the steelmaking slag has an elution amount of fluorine with respect to water of 8 mg or less per liter of water, and is at least one selected from waste gypsum, desulfurized gypsum, and chemically synthesized gypsum. The manufacturing method of the solidification agent as described in any one of -4.   The method for producing a solidifying agent according to any one of claims 1 to 5, wherein a polymer flocculant is added to the steelmaking slag and the gypsum.   The mixing, pulverization, and heating of the steel slag and the gypsum are performed by a pulverizer capable of controlling a particle size for pulverizing the steel slag and the gypsum, and a heat amount applied to the steel slag and the gypsum. The manufacturing method of the solidification agent as described in any one. The pulverizer is a vertical roller mill for discharging an object pulverized by an air flow introduced into the inside from an introduction port,
The manufacturing method of the solidification agent of Claim 7 which heats the said steelmaking slag and the said gypsum by introduce | transducing the airflow by a hot air into the inside of the said vertical roller mill from the said inlet.

Images