JP4751181B2 - Sand-capping method - Google Patents

Description

  The present invention covers the bottom sediment of the water area with blast furnace granulated slag and steelmaking slag, and further consolidates these so as to contain the pollutants contained in the bottom sediment and prevent the pollution from spreading into the water area. It relates to the sand method.

  Eutrophication that causes red tide and blue tide, such as phosphorus and hydrogen sulfide, in sediments such as riverbeds, lakes and marine areas in the bottom of public water bodies and sediments. It may contain contaminants such as substances, toxic heavy metals, dioxins.

  As one method for preventing water pollution caused by the diffusion of pollutants in the bottom sediment, a method of covering the bottom sediment with natural sand such as sea sand and mountain sand, a so-called sand covering method is known. Conventionally, a technology that uses blast furnace granulated slag, which is a steel byproduct, instead of natural sand has also been developed (see, for example, Patent Documents 1 and 2).

  The blast furnace slag is a component other than iron in the iron ore melted in the blast furnace for producing pig iron, and is a by-product separated and recovered together with the lime in the auxiliary material and the ash in the coke, and generates about 300 kg per ton of pig iron. Although the slag taken out from the blast furnace is in a molten state of about 1500 ° C., it is separated into blast furnace granulated slag and blast furnace gradually cooled slag by the cooling method. The granulated blast furnace slag is a vitreous (amorphous) granular slag that is generated by cooling rapidly by, for example, injecting pressurized water into the molten blast furnace slag. On the other hand, blast furnace slow cooling slag is either discharged directly into the dry pit, or transferred to a torpedo car from the dredging and transported to a distant outdoor yard where it is discharged and then naturally cooled and moderately sprinkled. This is a crystalline rock-like slag.

  Patent Document 1 discloses a method for preventing water pollution, in which a sediment containing dioxins is coated with a mixture obtained by adding steelmaking slag and / or natural sand to blast furnace granulated slag. In the method described in Patent Document 1, steelmaking slag is used as an alkali stimulating material that improves the hydraulic properties of blast furnace granulated slag, but when steelmaking slag is mixed and the pH is raised excessively, white turbidity occurs in the surrounding water area. Sometimes. Therefore, Patent Document 1 describes that blast furnace slow cooling slag may be used to avoid cloudiness.

  Patent Document 2 proposes a technique in which the latent hydraulic properties of granulated blast furnace slag are expressed by alkali stimulation and consolidated, and the sediment is covered with a consolidated layer having a low water permeability coefficient. In addition, latent hydraulic property refers to the property of hardening by causing a hydration reaction in the presence of alkali, sulfate, etc., although it does not have the self-hardening property that is solidified only by mixing with water like cement. .

JP 2004-195456 A JP 2004-285560 A

  However, in the case of the method described in Patent Document 1, by using the blast furnace slow cooling slag as described above, it is possible to avoid white turbidity that occurs at the time of charging into the water and thereafter, but when using the blast furnace slow cooling slag, There is a problem that the consolidation promoting action becomes insufficient and the consolidation force becomes weak.

  In addition, in the case of the method described in Patent Document 2, since the granulated blast furnace slag has insufficient caking strength due to its own alkalinity, the caustic force is weakened when the blast furnace granulated slag is used alone. is there. Moreover, in patent document 2, nothing is examined about the white turbidity prevention at the time of throwing in water.

  Furthermore, in any of the above-described techniques, when steelmaking slag is used as an alkali stimulating material for blast furnace granulated slag, white turbidity due to pH increase during charging into water is avoided, and blast furnace granulated slag is firmly consolidated. It is difficult. That is, conventionally, there has not been realized a sand-capping method that does not become cloudy when thrown into water and can reliably solidify blast furnace granulated slag.

  Therefore, the present invention has been devised in view of the above-described problems, and the object of the present invention is to provide sand-covering sand that can solidify sand-covering without causing white turbidity in the surrounding water area. To provide a construction method.

The sand-capping method according to the present invention is a sand-capping method in which the bottom material is covered with a sand-capping material to prevent the diffusion of contaminants contained in the bottom material. A granulated blast furnace slag having a particle content of 1.5% by mass or less, and a fine particle having a maximum particle size of 5 mm or less and granulated or carbonated in advance and having a particle size of 75 μm or less. The steel slag having a content of 1.5% by mass or less, and the mass ratio of the blast furnace slag to the steel slag (blast furnace granulated slag / steel slag) is (3/7) to (7/3). What is mixed is used , and the bottom sediment is covered with the sand covering material by introducing the sand covering material onto the bottom sediment .

  In the present invention, as an alkali stimulating material for granulated blast furnace slag, since steelmaking slag whose surface is stabilized and granulated is added by granulation treatment or carbonation treatment, a rapid increase in pH and Suspension caused by fine powder is suppressed.

  In this sand-capping method, as the carbonation treatment, untreated steelmaking slag is put into a rotating mixer, and carbon dioxide gas is blown into the inside while rotating the rotating mixer for 0.5 to 24 hours. Can do.

  In addition, as the granulation treatment, untreated steelmaking slag: 10 parts by mass, blast furnace granulated slag, blast furnace slag fine powder, fly ash, construction sludge, clay and silica fume Substance: 2 to 5 parts by mass and water: 0.5 to 2 parts by mass are charged into a rotating mixer, and these are stirred and mixed for 3 to 10 minutes by the rotating mixer, followed by curing for 1 week or more. Can do.

  According to the sand-capping method of the present invention, since sand-clad material in which granulated slag or carbonated slag is mixed with granulated blast furnace slag is used, white turbidity in surrounding water areas can be avoided and A desired consolidated state can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described.

  In the sand-capping method of the present invention, a sand-capping material, which is a mixture of steel by-product blast furnace granulated slag and steel slag, is put on the bottom sediment, and blast furnace granulated slag is consolidated by alkali stimulation of the steel slag. Thus, the bottom material is covered with a consolidated layer having a low water permeability coefficient. And in the sand-capping method of the present invention, the granulated steel granulated slag and / or carbonated carbonated steel slag is used as the steel slag, and in the sand-clad material of these steel slags The content is 30 to 70% by mass.

  The ground granulated blast furnace slag used in the sand-capping method of the present invention is weak in its self-hardness that reacts with water and solidifies, but in the presence of highly alkaline steelmaking slag, etc. The pre-furnace granulated slag produced by quenching the molten slag separated from pig iron in the molten state of the blast furnace immediately after the separation and the outside of the furnace produced by carrying it to the outside and quenching it Any of granulated slag may be used.

  Moreover, about the processing method after the granulation process of blast furnace granulated slag, an unprocessed thing may be used after granulation manufacture, or what adjusted the particle size by crushing may be used. There is no special provision for the aging period. Furthermore, the maximum particle size of the granulated blast furnace slag is preferably 5 mm or less in order to prevent sinking into the floating mud at the time of injecting into the water, and in order to prevent suspension when injecting into the water with fine powder, The content of fine particles having a diameter of 75 μm or less is desirably 1.5% by mass or less of the whole.

  On the other hand, steelmaking slag used by mixing with granulated blast furnace slag in the sand-capping method of the present invention is a steelmaking process in which unnecessary components are removed from pig iron produced in a blast furnace and steel having toughness and workability is obtained. There are converter slag to be produced, hot metal pretreatment slag and converter secondary refining slag, or electric furnace oxidation slag and electric furnace reduction slag produced when steel is produced by directly melting scrap in an electric furnace. Such a steelmaking slag has a function as an alkali stimulating material for promoting consolidation of blast furnace granulated slag.

  These steelmaking slags generally have a high content of fine particles having a particle size of 75 μm or less in a state where they are classified by sieving, and may be suspended when thrown into water. For example, when steelmaking slag containing such fine particles is thrown into seawater, the pH rapidly rises when thrown, magnesium ions present in large quantities in the seawater precipitate as magnesium hydroxide, and the surrounding water area becomes cloudy. Therefore, in the sand-capping method of the present invention, a steelmaking slag that has been subjected to stabilization treatment that stabilizes the surface and enlarges the fine particle component is used. Specifically, steelmaking slag subjected to granulation treatment or carbonation treatment is used as the stabilization treatment. Thereby, the rapid raise of pH of the surrounding water area at the time of submerged injection can be suppressed. In addition, as for the steelmaking slag used in this invention, it is desirable to make the maximum particle diameter into 5 mm or less similarly to the above-mentioned blast furnace granulated slag.

  The granulation treatment is a treatment in which a pozzolanic substance and a small amount of water are added to steelmaking slag, and the mixture is stirred and mixed, and then the mixture is cured for a desired period of time, and this treatment is referred to as granulated steelmaking slag. At that time, examples of the polyazone substance used include blast furnace granulated slag, blast furnace slag fine powder, fly ash, construction sludge, clay, and silica fume. When this granulation process is performed, the steelmaking slag reacts with the pozzolanic substance to form a hydrate, and the surface of the steelmaking slag is partially covered and stabilized by the hydrate, and also due to the hydrate. Due to the binder effect, the fine particles mainly contained in the steelmaking slag are enlarged or bonded to the surface of the large particles. Thereby, even if added to the sand-capping material, it is possible to prevent a sudden increase in pH due to reaction with the surrounding water area and the occurrence of suspension due to fine powder.

  As a specific method of the granulation treatment, for example, with respect to 10 parts by mass of steelmaking slag classified into a self-rotating mixer such as a mixer with a stirring blade or a concrete mixer so that the maximum particle size is 5 mm or less. Blast furnace granulated slag, ground granulated blast furnace slag, fly ash, construction sludge, 2-5 parts by mass of pozzolanic material selected from the group consisting of clay and silica fume, 0.5-2 parts by mass of water And then stirring and mixing for 3 to 10 minutes, and then curing these mixtures for one week or more.

  At this time, when the pozzolanic material added to 10 parts by mass of the steelmaking slag is less than 2 parts by mass or the water is less than 0.5 parts by mass, the reaction becomes immature and the steelmaking slag is sufficiently covered with the hydrate. It may not be done. Therefore, it is preferable that the addition amount of the pozzolanic material with respect to 10 parts by mass of the steelmaking slag is 2 parts by mass or more and the addition amount of water is 0.5 parts by mass or more. Moreover, reaction may be saturated when the addition amount of a pozzolanic substance exceeds 5 mass parts with respect to 10 mass parts of steelmaking slag, or when the addition amount of water exceeds 2 mass parts. Therefore, it is preferable that the addition amount of the pozzolanic material with respect to 10 parts by mass of the steelmaking slag is 5 parts by mass or less and the addition amount of water is 2 parts by mass or less. Furthermore, when stirring time is less than 3 minutes, it may not fully stir, and when stirring time exceeds 10 minutes, reaction may be saturated. Therefore, the stirring time is desirably 3 to 10 minutes. The curing period of the mixture is desirably 1 week or longer, and thereby, a coating effect by a sufficient hydration reaction can be obtained.

  In addition, the steelmaking slag after performing the granulation treatment, that is, the granulated steelmaking slag has a particle content of 75 μm or less, which is 1.5% by mass or less of the whole, like the blast furnace granulated slag. It is desirable.

  On the other hand, the carbonation treatment is a treatment in which a steelmaking slag adjusted to a desired water content ratio is kept stationary or stirred and blown with carbon dioxide, and what is subjected to such treatment is called carbonated steelmaking slag. . When carbonation treatment is performed, calcium hydroxide eluted from steelmaking slag reacts with carbonate ions generated by the dissolution of carbon dioxide in water to produce stable calcium carbonate. This calcium carbonate produces steelmaking slag. The surface is partially stabilized and the fine powder contained in the steelmaking slag is aggregated. Thereby, even if added to the sand-capping material, it is possible to prevent a sudden increase in pH due to reaction with the surrounding water area and the occurrence of suspension due to fine powder.

  As a specific method of carbonation treatment, for example, steelmaking slag is put into a rotating mixer such as a rotary concrete mixer, and carbon dioxide gas is introduced into the inside while rotating the mixer for about 0.5 to 24 hours. Steelmaking slag that has been blown or adjusted so that the water content ratio is 5 to 15% by mass is put into a rotating mixer such as a rotary concrete mixer, and the mixer is rotated for about 0.5 to 24 hours. There is a method of blowing carbon dioxide into the inside.

  At this time, when the treatment time (rotation time) is less than 0.5 hours, the surface of the steelmaking slag cannot be partially stabilized, or the fine powder contained in the steelmaking slag can be aggregated. There may be no. Therefore, the processing time is desirably 0.5 hours or longer. If the treatment time exceeds 24 hours, the stabilization of the steelmaking slag surface is saturated and the cost is not appropriate, so the upper limit of the treatment time is preferably 24 hours.

  And in the sand covering method of this invention, the sand covering material which mixed the blast furnace granulated slag mentioned above, granulated steelmaking slag, and / or carbonation steelmaking slag is used. At that time, the ratio (blast furnace granulated slag / steel slag) between the amount of blast furnace granulated slag and the amount of steel slag in the sand-capping material is set within the range of (3/7) to (7/3). That is, the steelmaking slag content in the sand-capping material (the total content in the case where both the granulated steelmaking slag and the carbonated steelmaking slag are included) is adjusted to 30 to 70% by mass. When the steelmaking slag content of the sand-capping material exceeds 70% by mass or less than 30% by mass, the compaction at the stage before consolidation at the initial stage of charging becomes poor, and the gap between the steelmaking slag particles becomes large. For this reason, the water permeability coefficient increases. As a result, the containment effect at the initial stage of charging is lowered. Even if the steelmaking slag content of the sand-capping material is out of the above-mentioned range, a higher containment effect than natural sand may be obtained by consolidation, but even in that case, the containment effect at the initial stage of charging is inferior. Therefore, it is out of the scope of the present invention.

  When throwing this sand-capping material into the seabed, blast furnace granulated slag and granulated steel slag and / or carbonated steel slag are mixed in advance at a ratio within the range of the present invention. It can be thrown into the water by a ship of the type or a tremy pipe.

  In the sand-capping method of the present invention, granulated steel slag and / or carbonated steel slag having a surface that is more stable than that of untreated steel slag and containing less particulate components is used. While being able to reduce the rate of pH increase, suspension by fine particle components can be prevented. Moreover, since pH rises gradually after throwing in water, sand covering sand can be made into a desired solidified state. As a result, the sand covering can be solidified without causing white turbidity in the surrounding water area.

  In particular, dioxins are not dissolved in the form of ions, but are mainly adsorbed on suspended particles, so the contamination route is the raising of sediment and fishery products on which dioxins are adsorbed. It is thought that it begins with ingestion by species and propagates through the food chain. The sand cover as the countermeasure method is positioned as an inexpensive method for confining in-situ, but the sand cover method of the present invention can further solidify the sand covering material covering the low quality. Compared to the sand-capping method, safety can be further improved.

  Examples of the present invention will be described below. In addition, this invention is not limited to the following Example.

  As a first example of the present invention, granulated steelmaking slag (Example 1), carbonized steelmaking slag (Example 2) or untreated steelmaking slag (Comparative Example 1) is used as an alkali stimulating material for granulated blast furnace slag. A mixed sand-capping material and a sand-capping material to which blast furnace slag was not added (Comparative Example 2) were prepared, and the pH increase and white turbidity phenomenon were confirmed when solidifying blast furnace granulated slag in seawater. Fig. 1 is a graph showing the time after the addition on the horizontal axis and the pH of the seawater on the vertical axis, showing the change over time of the pH after the sand-capping material was added. Fig. 2 shows the number of days of curing. It is a graph which shows the time-dependent change of the consolidation strength of a sand cover layer, and a water permeability coefficient, taking uniaxial compressive strength on the vertical axis. In addition, the mass ratio (blast furnace granulated slag: each steelmaking slag) of blast furnace granulated slag and each steelmaking slag in the sand covering material of Example 1, Example 2, and Comparative Example 1 was 7: 3.

  The white turbidity of seawater occurs when the pH becomes 9.5 to 9.6 or more. As shown in FIG. 1, the sand covering material of Comparative Example 2 using blast furnace granulated slag alone has a pH of Almost no increase was observed, and no cloudiness occurred. On the other hand, in the sand-capping material of Comparative Example 1 in which untreated steelmaking slag and blast furnace granulated slag were mixed, the pH in seawater increased rapidly immediately after the addition, and magnesium ions in the seawater precipitated and white turbidity occurred. . In contrast, the sand covering material of Example 1 in which granulated steel slag was mixed with granulated blast furnace slag and the sand covering material of Example 2 in which carbonated steel slag was mixed had a slow increase in pH of seawater after charging. Thus, no cloudiness was generated even 24 hours after the construction. That is, in the sand covering materials of Examples 1 and 2, a sand covering layer was formed within 24 hours after charging, and white turbidity immediately after charging was prevented.

  Moreover, as shown in FIG. 2, the sand covering layer formed with the sand covering material of Example 1, Example 2 and Comparative Example 1 in which steelmaking slag is added to the granulated blast furnace slag is uniaxially compressed as the curing days elapse. Although the strength increased and the solidification proceeded sufficiently, the sand-capping layer formed by the sand-capping material of Comparative Example 2 used alone with the blast furnace granulated slag was insufficiently consolidated even after 28 days. It was.

  Next, as a second embodiment of the present invention, blast furnace granulated slag and granulated steelmaking slag or carbonated steelmaking slag were mixed at different mixing ratios within the scope of the present invention, and the sand-clad sand of Examples 11-16. The sand-covered material of Comparative Example 13 in which the sand-covered material of Comparative Example 1 alone, mountain sand alone, the sand-covered material of Comparative Example 12 of blast furnace slag alone, and blast furnace slag and untreated steelmaking slag mixed at 5: 5, The content of granulated steel slag or carbonated steel slag in Comparative Example 15 with a content of less than 30% by mass, of Comparative Example 15 with a content of granulated steel slag or carbonated steel slag in excess of 70% by mass A sand-capping material was prepared and applied to the bottom sediment (dioxin concentration: 100 pg-TEQ / kg) contaminated with dioxin, and the white turbidity phenomenon, the consolidated state, and the water quality after 28 days were investigated. The results are shown in Table 1 below.

  As shown in Table 1 above, the sand covering materials of Examples 11 to 16 were compared with the sand covering material of Comparative Example 11 using mountain sand and the sand covering material of Comparative Example 12 using blast furnace granulated slag alone. High containment performance. Moreover, the sand-covering material of Examples 11 to 16 was confirmed to have a confining performance comparable to the sand-covering material of Comparative Example 13, which is a mixture of blast furnace granulated slag and untreated steelmaking slag, Like the sand covering material of Comparative Example 13, white turbidity did not occur immediately after charging. Furthermore, the sand-capping material of Comparative Examples 14 and 15 in which the blending ratio of the granulated blast furnace slag and granulated steel slag or carbonated steel slag deviates from the scope of the present invention does not cause white turbidity immediately after charging, and after 28 days. Consolidation was also confirmed, but because the compaction at the initial stage of injection was poor, the containment effect was low, and compared to the case of using the sand-capping material of Examples 11 to 16, the SS in the surrounding water area, the dissolved dioxin concentration and Suspended dioxin concentration was high. Therefore, only the Examples 11 to 16 within the scope of the present invention were the sand-capping materials that achieved both white turbidity prevention immediately after the addition and consolidation of the product after 28 days from the addition, and further had an excellent effect of containing the pollutants. .

It is a graph which shows the time-dependent change of pH of the surrounding water area after taking elapsed time on a horizontal axis and taking pH on a vertical axis | shaft and throwing sand-covering material into. It is a graph which shows a time-dependent change of the consolidation strength of a sand-capping layer and a water permeability coefficient, taking a curing day on a horizontal axis and taking uniaxial compressive strength on a vertical axis.

Claims (3)

In the sand-capping method for covering the bottom with a sand-capping material and preventing the diffusion of contaminants contained in the bottom,
As the sand-capping material, a granulated or carbonized maximum blast furnace granulated slag having a maximum particle size of 5 mm or less and a content of fine particles having a particle size of 75 μm or less and 1.5% by mass or less is previously applied. Steelmaking slag having a particle size of 5 mm or less and a particle content of 75 μm or less is 1.5 mass% or less, and a mass ratio of the blast furnace granulated slag to the steelmaking slag (blast furnace granulated slag / steel slag). ) Is used so that it becomes (3/7) to (7/3), and the bottom sand material is covered with the sand covering material by introducing the sand covering material onto the bottom material. The sand cover method.   The carbonation treatment is characterized in that untreated steelmaking slag is put into a rotating mixer, and carbon dioxide gas is blown into the rotating mixer while rotating the rotating mixer for 0.5 to 24 hours. Item 10. The sand-capping method according to item 1.   As the granulation treatment, untreated steelmaking slag: 10 parts by mass, blast furnace granulated slag, blast furnace slag fine powder, fly ash, construction sludge, clay and silica fume, at least one kind of polazone substance: 2 to 5 parts by mass and water: 0.5 to 2 parts by mass are charged into a rotating mixer, and after stirring and mixing for 3 to 10 minutes by the rotating mixer, a treatment for curing for 1 week or more is performed. The sand-capping method according to claim 1.

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