JP2008247690A - Method for treating slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating slag, which is used for producing a slag material, which hardly solidifies, exhibits an excellent effect when used for restraining a pH rise and is suitable as an environment improving material or a civil engineering and construction material, from blast furnace slag and steelmaking slag inexpensively by using simple equipment. <P>SOLUTION: The method for treating slag comprises a step of bringing carbon dioxide, a microbe and nutriment or carbon dioxide and nutriment into contact with the slag coexisting with water. It is preferable that carbon dioxide is brought into contact with the slag all the time for ≥0.5 hours, a gas having ≥1 vol% carbon dioxide concentration is brought into contact with the slag and the slag to be used is blast furnace slag and/or steel slag. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a slag processing method for producing a slag material that is hard to consolidate and has an excellent effect of suppressing pH increase from blast furnace slag and steelmaking slag.

  As a method of purifying the bottom of the sea, rivers, lakes, etc., cover the bottom of the water, i.e. cover the bottom with a granular material, and remove hydrogen sulfide and nutrients eluted from the bottom that cause red tide and blue tide. There is a known method of containment, and the material used for the sand cover covers the bottom like lime in addition to the material intended only to cover the bottom like natural sand such as sea sand and mountain sand. In addition, those having the function of chemically adsorbing eutrophication components in the bottom have been used. However, there is a concern that a material that does not have chemical reactivity such as natural sand will not provide a sufficient sand covering effect, while a material that has chemical reactivity such as lime will be expensive. In addition, there is a problem that the pH is difficult to control and the water quality may become highly alkaline.

  Therefore, as a means for solving the above-described problems, a technique for purifying water quality and bottom of water using blast furnace slag or steelmaking slag as sand-capping material has been proposed (for example, see Patent Document 1).

However, blast furnace slag and steelmaking slag have the property of solidifying (consolidating) in water, and when consolidated, as a habitat for the main benthic organisms such as shellfish and sandworms that inhabit the sand mud. There was a problem that it became unsuitable and the roots of the eel were not able to be established. This consolidation occurs due to a hydration reaction in which calcium ions eluted in the interstitial water between the slag particles (hereinafter referred to as “Ca ²⁺ ions”) precipitate to form hydrates and bind the slag particles.

In addition, blast furnace slag and steelmaking slag are used not only for the above sand-capping material but also for various applications. For example, steelmaking slag is used for soil improvement materials, roadbed materials, ground improvement materials, cement and concrete aggregates, etc. It is effectively used as a civil engineering building material. However, steelmaking slag has hydratable components (free CaO and free MgO) including a CaO component and the like, and in particular, a pH increase phenomenon caused by the elution of free CaO into water, The pH increases and the turbidity is caused by precipitation of Mg (OH) ₂ , so civil engineering and building materials such as roadbed materials, aggregates, and stones, and submarine materials in the ocean, etc. It was an impediment when using it as a civil engineering building material.

  Furthermore, the consolidation of the slag described above is not only in water, but also blast furnace slag or steelmaking slag that has been crushed and prepared to a predetermined size, for example, stacked in the field, temporarily placed, and if the temporary placement period is prolonged, However, if they are consolidated and cannot be crushed again, there is a problem that they cannot be used as environmental improvement materials or civil engineering and building materials.

  Therefore, many means for preventing consolidation of blast furnace slag and steelmaking slag and suppressing pH increase have been proposed.

  For example, Patent Document 2 discloses an anti-caking agent for granulated blast furnace slag, which includes 80 units in total of the structural units of the crosslinked structure portion of acrylamide, acrylic acid, acrylic acid derivatives and acrylic acid derivatives in all the structural units. Containing at least mol%, and 14 to 48 mol% of acrylamide, 1 to 42 mol% of acrylic acid, 10 to 84 mol% of acrylic acid derivative, and 0.05 to An anti-caking agent composed of a water-insoluble and highly water-absorbing acrylic cross-linked polymer containing 1 mol% has been proposed.

  Patent Document 3 proposes a method of covering the slag surface with an organic substance having a hydroxyl group or a carboxyl group, such as a fatty acid, or a metal salt thereof. In Patent Document 4, a powder containing 0.1 to 2 parts by mass of aluminum oxide and at least 5 parts by mass of an aqueous solvent are added to 100 parts by mass of slag particles, and the three are crushed and mixed. By the metathesis reaction occurring at this time, a modified layer made of an aluminum-containing compound is formed on the particle surface of the slag particle group, and dewatering treatment is performed as necessary, so that the water elution pH value is 5.8 to 8.6. A method of neutralization has been proposed.

In Patent Document 5, ground granulated blast furnace slag is ground into ground granulated blast furnace slag, and this ground ground blast furnace slag contains either an inorganic acid or a mixed acid mainly containing an inorganic acid and partially containing an organic acid. A method of reducing the content of alkali by adding and stirring and mixing to neutralize the alkali eluted from the ground blast furnace slag has been proposed.
JP 2003-286711 A JP 2006-188381 A JP 2002-104848 A JP 2006-290713 A JP 2006-282432 A

  However, the above prior art has the following problems.

  In the production of the anti-caking agent according to Patent Document 2, it is necessary to perform a polymerization reaction at a maximum temperature of 90 ° C. in a pressure atmosphere of 300 kPa, and a special pressure vessel is required. There is a problem of becoming. In addition, when the granulated blast furnace slag to which this anti-caking agent is added is used in water, it does not necessarily cover the active sites of calcium elution, and thus is not necessarily an effective anti-caking measure.

  In Patent Document 3, the surface of the slag is coated with an organic substance or a metal salt thereof. However, in order to coat the organic substance over the entire slag particles, it is necessary to add the organic substance in excess of the amount used, which causes an increase in manufacturing cost. . In addition, when the slag particles are large, it is difficult to mix with organic matter, which is an obstacle to uniform coating. According to the example of Patent Document 3, heating at 90 ° C. is necessary, which also causes high costs.

  In Patent Document 4, after adding an iron-containing compound as a capture component to an aluminum salt compound as a basic component, a mixing contact, a granulating step, a curing step at room temperature to 80 ° C, and a dehydrating step at room temperature to 190 ° C are necessary. The process is complicated and causes an increase in manufacturing cost. The reaction of Ca—Si—Al—H also occurs at the time of aluminosilicate formation, and calcium elution may occur from the reaction product, and there is a possibility that the alkali elution suppression effect over a long period may not be maintained. Moreover, there also exists a fault that an object is restricted to blast furnace slag.

Patent Document 5 discloses a technique of sequestering Ca ²⁺ ions in an alkali with an inorganic acid while neutralizing the alkali eluted from the slag with an inorganic acid such as sulfuric acid. It adheres to the equipment and causes equipment troubles, while nitric acid and hydrochloric acid are expensive, and the slag treated accordingly becomes expensive. In addition, when slag is dissolved with an acid, an active site for calcium elution appears newly, which is insufficient as a complete pH suppression measure. Furthermore, there is a drawback that the object is limited to blast furnace slag.

  The present invention has been made in view of the above circumstances, and the object of the present invention is from blast furnace slag and steelmaking slag, etc., inexpensive and simple equipment, hardly caking, and excellent in the effect of suppressing pH increase, and the environment. It is providing the processing method of the slag which can produce a slag material suitable as an improvement material or a civil engineering building material.

The inventors of the present invention have conducted intensive studies and studies to solve the above problems. As a result, after a calcium carbonate (CaCO ₃ ) film is formed on at least a part of the surface of the slag, the microorganisms are grown on the surface of the slag or in the vicinity of the surface so that the microorganisms are formed at the site where the calcium carbonate film is formed. The surface of at least a part of the slag particles is coated with an organic coating called biofilm, which grows preferentially and is formed by these microorganisms, and contact between the slag particles is physically hindered to suppress slag consolidation. And elution of Ca ²⁺ ions from the slag was suppressed by the biofilm, and the increase in pH was also prevented.

  The present invention has been made on the basis of the above knowledge, and the method for treating slag according to the first invention is to bring carbon dioxide, microorganisms and nutrients, or carbon dioxide and nutrients into contact with slag coexisting with moisture. It is characterized by this.

  The slag treatment method according to the second invention is characterized in that, in the first invention, carbon dioxide gas is brought into contact with the slag for 0.5 hour or longer.

  The slag treatment method according to the third invention is characterized in that, in the first or second invention, a gas having a carbon dioxide gas concentration of 1 vol% or more is brought into contact with the slag.

  A slag treatment method according to a fourth invention is characterized in that, in any one of the first to third inventions, the slag is blast furnace slag and / or steelmaking slag.

According to the present invention, a calcium carbonate film is formed on the surface of the slag by contact with carbon dioxide gas, and microorganisms are grown on or in the vicinity of the surface of the slag by contacting the microorganisms with nutrients or nutrients. Microorganisms proliferate preferentially at the site, and the organic coating formed by the microorganisms and consisting of a collection of microorganisms called biofilm covers at least a part of the surface of the slag particles. Even if placed or laid on the water or on the beach, the contact between the slag particles is hindered, and slag consolidation is suppressed. In addition, since the slag has a biofilm, Ca ²⁺ ions eluted from the slag also remain in the biofilm, so the Ca ²⁺ ions themselves that cause slag consolidation are reduced, and the consolidation is further suppressed. The By reducing Ca ²⁺ eluted from the slag, the pH is lowered and the cloudiness phenomenon when laid in the sea can be prevented.

  Since this biofilm can be easily formed into one slag particle by simply contacting microorganisms and nutrients or nutrients with slag, it can be formed very easily and inexpensively. Further, since the biofilm itself contains nutrients such as phosphorus and nitrogen, when a slag material having a biofilm is used as an environmental improvement material for an ammo base material, it can also serve as a nutrient replenishment. Furthermore, since it has a biofilm, that is, an organic substance in advance, natural microorganisms are also likely to adhere when settling on the seabed and the like, and it becomes easier to approach the state of natural stone and sand already existing in the sea. Furthermore, by having an organic substance in advance, the affinity of living organisms in the sea area, for example, is increased, and bottom organisms such as shellfish and sandworms are liable to live.

  Hereinafter, the present invention will be specifically described.

In the present invention, when producing a slag material that can be used as an environmental improvement material or a civil engineering building material from blast furnace slag or steelmaking slag, carbon dioxide (CO ₂ gas), microorganisms and nutrients, or slag coexisting with moisture, Treat slag with carbon dioxide and nutrients in contact. In this case, carbon dioxide and microorganisms and nutrients, or carbon dioxide and nutrients may be brought into contact with the slag at the same time, or may be brought into contact with each other separately. However, when contacting separately, it is necessary to contact with carbon dioxide gas first.

By bringing carbon dioxide gas into contact with the slag, a calcium carbonate film is formed on at least a part of the slag surface. Moreover, since microorganisms and nutrients or nutrients are brought into contact with the slag, the microorganisms proliferate preferentially at the site where the calcium carbonate coating is formed on the slag surface. This is because the formation of a calcium carbonate coating suppresses the elution of Ca ²⁺ ions at that site, lowers the pH, and facilitates the growth of microorganisms. And the surface of at least one part of slag particle | grains is coat | covered with the biofilm formed by this propagated microorganism. By this biofilm, the contact between slag particles is physically hindered to suppress slag consolidation, and Ca ²⁺ ions eluted from the slag remain in the biofilm, causing slag consolidation. Ca ²⁺ ions themselves are reduced, and solidification is further suppressed, and at the same time, the pH increase phenomenon is prevented. In this case, even if only nutrients are brought into contact without contacting microorganisms, various microorganisms exist in nature, and these microorganisms grow to form a biofilm on the surface of at least a part of the slag particles. The

When carbon dioxide, microorganisms and nutrients, or carbon dioxide and nutrients are brought into contact with the slag, the slag needs to coexist with moisture. This is necessary for eluting Ca ²⁺ ions on the surface of the slag, as well as for dissolving carbon dioxide to form carbonic acid (H ₂ CO ₃ ). And for the formation of biofilms. The ratio of slag to moisture is preferably such that the moisture content (moisture mass x 100 / (slag mass + moisture mass)) is 1 to 15 mass%, more preferably 2 to 10 mass%.

When a gas containing carbon dioxide gas is brought into contact with the slag containing moisture in this way, Ca ²⁺ ions eluted from the slag surface react with carbon dioxide formed by dissolving the carbon dioxide gas, and calcium carbonate is formed on the slag surface. Is formed. In the present invention, this treatment is defined as “carbonation treatment”.

  Usually, the pH of the slag surface containing moisture often exceeds 10, and in normal microorganisms that have not been subjected to a high pH tolerance treatment, the cells are killed and no biofilm is formed. By carbonizing, the pH between the slag particles is less than 10 even in the state of containing moisture, so that normal microorganisms not subjected to high pH resistance treatment grow and biofilm formation becomes possible. When a biofilm is formed on a part of the slag surface, the cell growth starts from the site, and a biofilm is formed on the slag surface. Therefore, even if the carbonized film on the surface of the slag does not occur on the entire surface of the slag, there is no problem. However, since the growth of microorganisms is promoted as the proportion of the carbonated coating on the slag surface increases, the proportion of the carbonated coating is preferably as high as possible.

  That is, the minimum carbonation ratio on the slag surface is necessary for the growth of microorganisms, and it is difficult to measure the carbonation ratio on the slag surface. For the growth of the slag, the carbonation ratio of the slag particles is preferably 0.05% by mass or more, more preferably 0.1% by mass or more. However, in order to carbonize the entire surface of the slag, corresponding equipment and processing time are required, resulting in high costs, and even if the carbonation rate of the slag particles exceeds about 5% by mass, the growth of microorganisms is saturated. Therefore, the carbonation ratio of the slag particles may be about 5% by mass as the upper limit value. The carbonation ratio of slag particles of 0.05% by mass corresponds to a state in which a 10 μm thick calcium carbonate coating is uniformly formed on the surface of slag having a particle diameter of 10 cm.

  The carbonation ratio of the slag particles can be determined by thermal analysis (thermal mass measurement) of the slag after the carbonation treatment, or by SEM photography and EDX analysis. In the case of thermal analysis, it can be determined from the decrease in mass when heated to 600 to 800 ° C.

For example, (1) a method of filling a mold with slag containing water and supplying a gas containing carbon dioxide from below, (2) carbon dioxide gas. A method of laying a gas-conducting pipe containing slag, stacking slag containing water on the pipe, and gradually circulating a gas containing carbon dioxide from the conducting pipe; (3) downward using a fluidized bed apparatus Various methods such as a method of blowing a gas containing carbon dioxide from (4) a method of blowing a gas containing carbon dioxide from a gas pipe provided inside while stirring with a mixer such as a concrete mixer . Moreover, the method of spraying the water which melt | dissolved the carbon dioxide gas to slag is also applicable. When water in which carbon dioxide gas is dissolved is used, the amount of carbon dioxide dissolved in the standard state (25 ° C., 1 atm) is sufficient in the range of 0.1 to 1.713 L / L—H ₂ O. In short, any method may be used as long as the slag surface can be carbonated.

  Examples of the carbon dioxide or carbon dioxide-containing gas to be brought into contact with the slag include exhaust gas (usually around carbon dioxide concentration = about 25 vol%) generated at a lime firing plant of a steelmaking integrated steel works, and exhaust gas from a heating furnace (usually carbon dioxide concentration) = 6.5 vol%) is preferable, but is not limited thereto. If the carbon dioxide concentration in the gas is low, the carbonation reaction tends to be slow, but there are no other special problems, so the carbon dioxide concentration in the gas containing carbon dioxide is specified. Although not necessary, considering the efficiency of the carbonation treatment, the concentration of carbon dioxide in the gas containing carbon dioxide is preferably 1 vol% or more, preferably 3 vol% or more, more preferably 5 vol% or more. If the carbon dioxide gas concentration is less than 1 vol%, the carbonation efficiency of the slag surface decreases, which is not preferable.

The flow rate of the gas containing carbon dioxide is not particularly limited, but as a general guideline, a supply amount of about 0.004 to 0.5 Nm ³ / min · ton can be ensured as pure carbon dioxide. The temperature of the gas containing carbon dioxide gas to be supplied may be room temperature, but higher temperatures are advantageous because the reactivity increases. However, if the temperature becomes too high, the slag is dried and the calcium carbonate is decomposed. Therefore, it is necessary to control the temperature within a range where such a phenomenon does not occur.

  The contact time between the moisture-containing slag and the carbon dioxide-containing gas varies depending on the carbon dioxide concentration in the gas, the ambient temperature, etc., but is preferably 0.5 hours or more, more preferably 1 hour or more, and even more preferably Is more than 3 hours. If the contact time is less than 0.5 hour, it is difficult to form a carbonized film on the slag surface, which is not preferable.

  The slag targeted by the present invention is a slag from which alkaline components are eluted when immersed in water, and is not limited by the composition or production process. Particularly, a suitable slag is a steel production process. Blast furnace slag and steelmaking slag generated as by-products (hereinafter collectively referred to as “steel slag”).

  Also in steel slag, (1) molten steel slag is poured into a slag processing yard and air-cooled, and cooled and solidified bulk slag is crushed by a crusher, and (2) molten steel slag is abundant. The particle size is approximately 6 mm obtained by a method of quenching by jetting, mixing and agitating water or by quenching by pouring molten steel slag into a large amount of water and quenching (these cooling methods are referred to as “water granulation methods”). The following granular slag (referred to as “granulated slag”), (3) obtained by blowing a molten steel slag together with a gas such as air into the air for rapid cooling (this cooling method is called “wind crushing method”). In addition, although there is a spherical slag having a particle size of approximately 6 mm or less (referred to as “winding slag”), it may be a slag obtained by any method. Further, if the composition is so-called “blast furnace slag” and so-called “steel slag”, there may be some difference in composition. Here, blast furnace slag is slag discharged from the blast furnace together with hot metal, and steelmaking slag is desiliconized slag, desulfurized slag, dephosphorized slag generated in the hot metal pretreatment process, and hot metal in the converter. Decarburization slag generated during decarburization refining (referred to as “converter slag”).

  Bacteria, actinomycetes, molds such as gonococci contained in the fungal kingdom, mushrooms and yeasts such as white rot fungi, etc. can be used as microorganisms for forming a biofilm on the slag surface by contacting with slag. Among these, aerobic bacteria are preferable for the formation of biofilms, and Bacillus bacteria are particularly preferable from the viewpoint that they can grow even in an environment of about pH 8. Bacteria belonging to the genus Bacillus are common bacteria that are present in soil and withered grass, and are also present in foods such as natto, miso, and soy sauce.

  Examples of bacteria belonging to the genus Bacillus include Bacillus cohnii, Bacillus alcalophilus, Bacillus agaradhaerens sp., Bacillus clarkii sp., Bacillus clarkii sp. clausii sp.), Bacillus gibsonii sp., Bacillus halmapalus sp., Bacillus halodurans comb., Bacillus horikosii sp., Bacillus horikosii sp. Examples include Calophyllus (Bacillus pseudoalcalophilus sp.), Bacillus pseudofirmus (Bacillus pseudofirmus sp.), Bacillus vedderi sp. Bacillus subtilis natto also belongs to this genus and can be effectively used because of its high growth rate and ease of culturing in large quantities.

  Moreover, it is preferable to use together 2 or more types chosen from said microorganisms. By using 2 or more types together, the effect that a biofilm is easily formed or a firm biofilm is formed can be obtained. This is because when considering the microflora in biofilms formed in various places, many of them exist in complex systems. For example, Furukawa et al. (See Furukawa et al., Proc. ASM Biofilm Conf., P. 93, 2003.), for the elucidation of the formation mechanism of complex microbial biofilm, As a result of examining the biofilm formation in the culture system, it was found that the biofilm formation amount increased with 30.6% combination and the biofilm formation amount decreased with 9.7% combination among all 903 patterns. Reporting.

  In general, microorganisms take in inorganic or organic dissolved substances from their surroundings, and use them to acquire energy or synthesize cell components in the process of metabolic degradation. These dissolved substances are called nutrient sources, and nutrient sources are divided into energy sources, carbon sources, nitrogen sources, inorganic salts, and micronutrients (or growth factors (vitamins, etc.)).

  Therefore, in order to grow the above microorganisms, this nutrient source is necessary. As nutrients to be added to slag as this nutrient source, glucose solution (glucose concentration: 0.5 to 10% by mass), protein hydrolysis Food, meat and yeast extracts, blood and eggs, shochu and beer squeezed sugar, sugar cane squeezed sucrose, molasses, waste molasses, pruning materials, seaweed, plant waste, and fermentation products thereof are preferred. Among these, it is more preferable that the pH is lower than neutral, such as waste molasses and waste liquid generated in the alcohol production process. This is because when the pH is lower than neutral, even if an alkaline component is eluted from the slag, it is possible to suppress an increase in pH and maintain an environment favorable for the growth of microorganisms. From this point, it is preferable to add organic acids such as formic acid and acetic acid to the nutrients.

  The supply of microorganisms and nutrients to the slag may be performed simultaneously or separately, but it is more economically preferable to perform them simultaneously.

  In order to form a biofilm on the slag surface, for example, the above-mentioned microorganisms and nutrients or nutrients are sprayed on the slag accumulated in the slag yard, preferably stirred and grown for about one week to grow and grow the microorganisms. Let In this case, since microorganisms do not grow or grow in a dry state, the outflow and drying of nutrients may be prevented by forming a bank around the slag or covering the slag with a sheet. When dried, it is preferable to add moisture. In the present invention, the treatment for forming a biofilm with microorganisms is defined as “microbe treatment”.

Further, the number of days until biofilm microorganisms are formed in the slag is affected by the number and amount of nutrients of microorganisms to be added, to thereby form a biofilm about one week, to the slag 1 m ³ It is preferable to add about 0.15 m ³ of 5 mass% glucose solution containing about 10 ⁷ cells (hereinafter referred to as “cells / mL”) per mL. Usually, the cultured microorganisms are present at 10 ⁶ to 10 ⁸ cells / mL, and therefore the above-described relationship may be maintained according to the number of microorganisms present. Similarly, the relationship may be maintained according to the concentration of the glucose solution. In this case, it is not necessary to deposit slag in the slag yard, and the microbial treatment can be performed in a container having a closed bottom. In addition, water is added when dried. In this case, microorganisms and nutrients may be added again together with water. The reason why the unit of the number of microorganisms is described as “cells” is that the microorganism is a single cell, and the number of cells and the number of individual microorganisms match.

  The timing of supplying microorganisms and nutrients or nutrients to the slag may be the same as the timing of contacting carbon dioxide with the slag, or may be performed after contacting the carbon dioxide with the slag.

  When carbon dioxide is supplied from below the slag filled in the mold, or when slag is piled up on the conducting pipe and supplied from the conducting pipe, microorganisms and nutrients or nutrients are simultaneously supplied with the carbon dioxide. In the case of supplying carbon dioxide gas from the gas pipe provided inside while stirring the slag with a mixer such as a concrete mixer, from the viewpoint of increasing the operating rate of the mixer, After carbonation with carbon dioxide gas is completed, it is preferable to discharge slag from the mixer, deposit the slag in a slag yard, etc., and then supply microorganisms and nutrients or nutrients to the slag. Of course, when supplying slag in a pile and supplying carbon dioxide gas from a conducting pipe, microorganisms and nutrients or nutrients may be supplied to the slag after carbonation with carbon dioxide gas is completed.

  Biofilm adhesion identification on the slag surface can be performed by a method of measuring the area of the cells stained by Gram staining with a microscope. In order to judge organic matter derived from microorganisms, it can be identified from the fact that the amount of carbon and nitrogen are clearly larger than the content of slag itself in elemental analysis. Moreover, if the form of microorganisms is clear, it can be identified. If a part of the slag surface is carbonated and a biofilm adheres to 5% or more of the slag particles, alkali elution from the slag particles and consolidation of the slag are prevented.

  Moreover, there is a counting board method as a method of counting the number of microorganisms present in the slag regardless of the life or death of the microorganisms. The counting plate method uses a lattice glass made by carving a small groove on the lower part of the surface of the slide glass, and put 5 g of slag in 10 mL of physiological saline. Remove the microorganisms from the slag by sonication for about 2 minutes, drop the physiological saline containing the detached microorganisms, cover the glass so that a certain gap is filled with the solution, and place it on the slide glass with a microscope In this method, the number of microorganisms in the lattice-like minimum compartment is counted, and the number per unit volume is obtained by calculation. Further, it is also possible to use a technique for extracting genes from slag and measuring the number of genes by using a gene analysis technique called a real-time PCR method to determine the number of microorganisms. Specifically, it is a method of extracting DNA by charging 0.5 g of slag into an extraction kit.

  It is preferable that after a predetermined amount of biofilm is formed on the slag, the biofilm is adhered to the surface of the slag particles by drying. Although the effect is enhanced by drying and closely contacting, it is not always necessary to dry. The slag can be dried by leaving the slag as it is in the slag yard, or scraping it out from the slag yard and storing it in a container. By drying the slag, most of the microorganisms are killed, but they are present in the slag as a biofilm, which prevents the slag particles from consolidating and alkaline elution.

  The slag material obtained in this way is suitable as an environmental improvement material for improving the environment and water quality of the bottom of the sea, rivers, lakes, etc., and is also a roadbed material, soil improvement material, ground improvement material, cement It is also suitable for civil engineering and construction materials such as aggregates, concrete aggregates, stones, and submerged dike materials, lining materials, backfill materials, embankment materials, sand compactions, SCP sand mats, and shallow-field materials.

Blast furnace granulated slag having a volume of 10 m ³ and converter slag crushed after being cooled and solidified are deposited in a slag yard, and water is firstly sprinkled to contain water, and a gas containing carbon dioxide is deposited at the bottom of the deposited slag. The slag surface was carbonized by supplying it to the slag deposited through a conduction pipe installed in the slag. The carbon dioxide gas concentration was adjusted to 4.8 to 5.1 vol%, the contact time between carbon dioxide gas and slag (blowing time of carbon dioxide-containing gas) was 30 minutes, and the temperature of the gas containing carbon dioxide gas was adjusted to 25 ° C.

  After the supply of the gas containing carbon dioxide gas was completed, natto bacteria as microorganisms and glucose or molasses as nutrients were added to the slag, and the microorganism treatment was carried out. However, when the microorganism treatment was carried out, a treatment in which only glucose was added without adding the microorganism was also carried out (Example 13 of the present invention). The microbial treatment was continued for 7 or 11 days with watering as necessary to prevent the slag from drying. After the completion of the microorganism treatment, a sample was collected from the slag, and the number of bacterial colonies present in the slag was measured, and the pH of the slag pore water was measured.

  The number of bacterial colonies present in the slag was determined as follows. 3 g of surface-slag slag (referred to as “wet-slag”) is placed in 30 mL of a phosphate buffer solution, and the cells present in the slag are extracted into the phosphate buffer solution while applying ultrasonic vibration, and the extracted cells are heterotrophic bacteria. The number of colonies after 24 hours was counted and converted into the number of colonies per 1 g of wet-slag.

  For comparison, air from which carbon dioxide has been removed is supplied to the deposited slag for 30 minutes or 20 minutes through a conducting pipe installed at the bottom of the deposited slag, and then the microorganisms and their nutrients are supplied. 30 minutes to the deposited slag through the conduction pipe installed at the bottom of the deposited slag with the example (Comparative Examples 1 to 10) in which the slag was supplied to the slag and the gas containing carbon dioxide gas Then, examples (Comparative Examples 11 to 14) in which only watering was performed as necessary to prevent slag from drying without adding microorganisms and nutrients were also performed.

  Table 1 shows the processing conditions and processing results of the inventive examples and the comparative examples.

As shown in Table 1, in Comparative Examples 1 to 10, the number of bacterial colonies after the treatment was zero, and the pH of the slag pore water remained as high as 11 to 12. This is because the carbonation treatment was not performed on the slag surface, and the pH around the slag was increased by Ca ²⁺ ions eluted from the slag, and the added microorganisms were killed. When this slag material is used as an environmental improvement material or a civil engineering / building material, it is predicted that consolidation and alkali elution cannot be prevented.

  In Comparative Examples 11 to 14, the pH of the slag pore water was about 11, but the number of bacterial colonies after the treatment was zero. This is because the microorganisms could not grow because the nutrients of the microorganisms were not supplied. Even when this slag material is used as an environmental improvement material or a civil engineering / building material, it is predicted that caking and alkali elution cannot be prevented as in Comparative Examples 1-10. It can be seen that carbonation of the slag surface is not sufficient and microbial treatment is necessary.

On the other hand, in Examples 1 to 20 of the present invention, the number of fungal colonies was 10 ⁶ or more, and the pH of the slag pore water was 10 or less. When this slag material is used as an environmental improvement material or a civil engineering and building material, caking and alkali elution are prevented, and long-term application is possible.

  In the slag containing water, the pH around the slag often exceeds 10, and it is not an environment in which microorganisms can easily grow. Therefore, as shown in Comparative Examples 1 to 10, even if microorganisms were present at the beginning, it was impossible to grow and form a biofilm. In the present invention, carbon dioxide gas is brought into contact with moisture-containing slag, and microorganisms and nutrients or nutrients are supplied to the slag to grow the microorganisms, thereby preventing alkali elution from the slag and preventing solidification of the slag. It becomes.

Claims (4)

  A method for treating slag, comprising bringing carbon dioxide, microorganisms and nutrients, or carbon dioxide and nutrients into contact with slag coexisting with moisture.   The method for treating slag according to claim 1, wherein carbon dioxide gas is brought into contact with slag for 0.5 hour or longer.   The slag treatment method according to claim 1 or 2, wherein a gas having a carbon dioxide gas concentration of 1 vol% or more is brought into contact with the slag.   The slag treatment method according to any one of claims 1 to 3, wherein the slag is blast furnace slag and / or steelmaking slag.