JP2010120782A - Method for producing low alkali elution property slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing low alkali elution property slag where steelmaking slag is efficiently carbonated to the inside thereof without using a special large-sized device and also with reduced energy so as to become the low alkali elution property slag. <P>SOLUTION: Nanobubble-containing water obtained by dispersing CO<SB>2</SB>or a CO<SB>2</SB>-containing gas into water in the form of bubbles with a diameter of ≤1 μm is brought into contact with steelmaking slag. In the carbon dioxide nanobubble-containing water, since the bubbles (nanobubbles) of carbon dioxide can be stably present in the water for a long time, the water comprising carbon dioxide suitably infiltrates to the inside of the slag and is held for a long time, thus free CaO and free MgO at the inside of the slab can be suitably carbonated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a low alkali-eluting slag, in which a steelmaking slag containing free CaO or free MgO is carbonized to form a slag having low alkali elution.

In the steel making process of the steel manufacturing process, CaO is used as a refining agent and becomes part of the slag to be generated. Further, most of the refractory lining the refining vessel contains MgO, and this MgO shifts to slag as the refractory melts. As a result, steelmaking slag such as converter slag contains a large amount of free CaO and free MgO. When such a steelmaking slag is brought into contact with water in a cooled and solidified state, a hydration reaction of free CaO or free MgO occurs, resulting in Ca (OH) ₂ and Mg (OH) ₂ , respectively. Since these hydroxides show strong alkalinity, when they react with rainwater or the like, strong alkaline water is generated, which may adversely affect the environment such as living things.

One effective method for stabilizing free CaO and free MgO is carbonation treatment. Naturally carbonated free CaO exists stably as marble, limestone and the like mainly composed of CaCO ₃ , and it can be easily imagined that the influence on the environment is reduced. MgO is more stable as it is than CaO, but it becomes possible to make it more difficult for alkali to leach out by carbonation. Thus, the idea of stabilizing free CaO and free MgO in slag by carbonation is a natural idea in chemical engineering, and many proposals have been made heretofore.

For example, Patent Document 1 discloses a carbonation method at a high temperature. In this method, molten slag is granulated and solidified, and then a temperature range of 800 to 300 ° C. is maintained in a CO ₂ atmosphere, and free CaO is carbonated to CaCO ₃ . However, in this method, since the slag needs to be held at a high temperature, a special apparatus is required for its implementation.
Patent Document 2 discloses a method in which slag is aged in a water vapor atmosphere, then held in a mixed atmosphere of water vapor and CO ₂ gas, and carbonized. This method is useful because it can use a steam aging technique that is industrially used. On the other hand, there is a problem that the use time of the aging equipment is extended and the processing efficiency is slightly lowered.
In these two methods, although carbonation of the slag surface proceeds, free CaO and free MgO remain in the slag, and it is difficult to suppress long-term alkalization.

Patent Document 3 discloses a method of introducing and carbonating a CO ₂ -containing gas while applying mechanical stirring to slag. According to this method, carbonation proceeds to the inside due to the destruction of the CaCO ₃ layer on the slag surface or the introduction of cracks. This can be said to be an effective carbonation method if the reaction proceeds as described, but a special apparatus is required to treat and carbonize the steelmaking slag that is generated in large quantities. A great deal of energy is required for rotation.
JP-A-52-129672 JP-A-8-259282 JP 2005-200234 A

  Accordingly, the object of the present invention is to solve the above-mentioned problems of the prior art, efficiently carbonize the steelmaking slag to the inside without using a special large-sized apparatus and with less energy, and have a low alkali elution property. It is providing the manufacturing method of the low alkali elution slag which can be used as slag.

One condition for performing slag carbonation without using special equipment is to allow the reaction to proceed in a temperature range close to room temperature. The reaction of free CaO or free MgO contained in slag and the like and carbon dioxide (CO ₂ ) directly reacts at a high temperature range, but proceeds through water existing around each slag particle in a region close to normal temperature. It is considered a thing. That is, CO ₂ flowing around the slag particles dissolves in the adhering water present on the surface of the slag particles, and Ca ions and Mg ions elute from the slag particle side and react with each other, so that carbonation proceeds. It is considered to be.

Since the carbonation reaction proceeds through water as described above, the present inventors studied to promote the carbonation reaction by dissolving carbon dioxide gas in water first. In general, carbon dioxide has a high solubility in water, and this process was expected to function effectively, but was not very effective in practice. The cause of this is not necessarily clear, but when carbon dioxide is simply blown, most of the gas is released as a bubble of millimeter size, and carbon dioxide dissolved in water is also added to the slag particles. It is presumed that it is precipitated as soon as it comes into contact, the reaction proceeds only on the surface portion of the slag particles, and it cannot reach the inside.
Therefore, the present inventors have intensively studied a method of stably dispersing carbon dioxide gas in water and allowing it to react without simply dissolving carbon dioxide gas. It has been found that carbonization can proceed to the inside of the slag by reducing the size to a minimum and bringing the slag into contact with the slag, so that a slag having a low alkali elution can be obtained.

  Japanese Laid-Open Patent Publication No. 2007-186364 discloses a technique for reducing the size of carbon dioxide gas bubbles dispersed in water and bringing the water into contact with blast furnace slag. Blast furnace slag is obtained by cooling molten slag generated from the blast furnace. Blast furnace gradual slag is cooled by slowly discharging water that is cooled rapidly using blast furnace slag, yard, etc. It is called slug. Among them, granulated blast furnace slag has a glassy amorphous structure because it is cooled rapidly, and its shape is sandy, so it is used as an alternative material for concrete fine aggregates, but it has latent hydraulic properties. Therefore, there is a problem that a caking phenomenon occurs before use. As a countermeasure, in JP-A-2007-186364, the surface of the slag particles is carbonated by adding carbon dioxide as microbubbles to the water for rapidly cooling the molten blast furnace slag, and is coated with a carbonation layer. Proposing technology.

However, the steelmaking slag targeted by the present invention, unlike the blast furnace slag, generally contains iron in a molten state, and there is a risk of explosion when directly cooled with water. It is hardly implemented. In other words, the steelmaking slag must be carbonized after cooling, and the proposed method cannot be applied.
In addition, the blast furnace slag targeted by the proposed method has a CaO ratio in the slag of at most 40 mass%, whereas the steelmaking slag may reach 60 mass%, which is completely different from the blast furnace slag. have. Therefore, the pH of contact water is not so high in blast furnace slag, and the above proposal has not been studied at all, whereas steelmaking slag has a high possibility that the contact water will exhibit alkali, and is not considered in the above proposal. It is necessary to study from.

In addition, as mentioned above, granulated blast furnace slag is amorphous and macroscopically high in roughness, but microscopically, it is smooth and almost homogeneous like glass beads, and is carbonated into fine cracks. There is no need to consider. On the other hand, steelmaking slag is crystalline, and its surface is rough both macroscopically and microscopically. In addition, peeling is likely to occur between crystals, and therefore many fine cracks are present. Therefore, in order to suppress alkali, it is important to advance carbonation to the inside.
The present inventors conducted an experiment to carbonize steelmaking slag after cooling using microbubble-containing water in which bubbles of micro-sized carbon dioxide gas were dispersed, and examined alkali elution of the treated slag. Although the pH was temporarily lowered, it was confirmed that the pH immediately increased when immersed in water for a long time. In other words, it has been found that even if the steelmaking slag after cooling is carbonized with water containing microbubbles as disclosed in JP-A-2007-186364, a sufficient effect cannot be obtained.

The present invention has been made on the basis of such findings and has the following gist.
[1] A method for producing a low alkali-eluting slag, characterized in that nanobubble-containing water in which CO ₂ or a CO ₂ -containing gas is dispersed in water in the form of bubbles having a diameter of 1 μm or less is brought into contact with steelmaking slag.
[2] In the production method of the above [1], the nanobubble-containing water is obtained by dispersing 0.1% by volume or more of CO ₂ or CO ₂ -containing gas bubbles having a diameter of 1 μm or less. Method for producing eluting slag.
[3] A method for producing low alkali-eluting slag, wherein the steelmaking slag is immersed in nanobubble-containing water in the production method of [1] or [2].
[4] A method for producing a low alkali-eluting slag, characterized in that, in the production method of [1] or [2], nanobubble-containing water is sprinkled on steel slag.

  According to the method of the present invention, carbon dioxide-containing nanobubble-containing water has carbon dioxide bubbles (nanobubbles) that can be stably present in water for a long time, so that water containing carbon dioxide appropriately penetrates into the slag for a long time. The free CaO and free MgO inside the slag can be appropriately carbonated, and there is an advantage that it can be carried out at a low cost by a simple means without using a special device. For this reason, this invention method can manufacture slag with small alkali elution from steel-making slag efficiently and at low cost. The produced low alkali-eluting slag can be effectively used as a substitute for natural crushed stone or aggregate.

In the present invention, CO ₂ or a CO ₂ -containing gas (hereinafter collectively referred to as “carbon dioxide gas” for convenience of explanation) is dispersed in water in the form of bubbles having a diameter of 1 μm or less to form nanobubble-containing water. The carbonation treatment is performed by bringing the contained water into contact with the steelmaking slag.
In the present invention, carbon dioxide gas is dispersed in water as bubbles (nanobubbles) refined to a size of less than a micron, thereby suppressing the bubble from becoming coarse and rising due to contact between gases or from a gas and a solid. It becomes possible to keep it stably in water for a long time. As a result, water containing carbon dioxide gas appropriately penetrates into the slag and is retained for a long time, and free CaO and free MgO inside the slag can be appropriately carbonated.
Examples of the steelmaking slag to be treated in the present invention include converter slag (decarburization slag), hot metal pretreatment slag (dephosphorization slag, desulfurization slag, desiliconization slag, etc.), but are not limited thereto. Is not to be done.
The particle size of the target slag is not particularly limited, but is preferably crushed to a particle size of 40 mm or less from the viewpoint of reaction efficiency.

  Water containing carbon dioxide bubbles (hereinafter simply referred to as “nanobubbles”) having a diameter of 1 μm or less, that is, nanobubble-containing water may be obtained by any manufacturing method. For example, Japanese Patent Application Laid-Open No. 2005-245817 And a known method and apparatus as disclosed in JP-A-2008-73658. For example, nanobubbles can be generated by generating microbubbles of carbon dioxide in water with a microbubble generator, and applying a physical stimulus to the microbubbles to rapidly reduce them. As a method of applying physical stimulation to microbubbles, for example, (i) a method of discharging into microbubbles using a discharge generator, (ii) putting water containing microbubbles in a container equipped with a rotating body, A method of using water by a rotating body and utilizing compression, expansion and vortex generated during the flow, (iii) Compression, expansion and vortex generated during flow by introducing water and carbon dioxide into a cylindrical container so as to swirl at high speed. (Iv) by circulating water containing microbubbles in a circulation path having an orifice or a porous plate in the flow path, and passing the orifice or the porous plate in the middle, thereby compressing, A method for generating expansion and vortex flow can be applied.

  An example of bubble size distribution is shown in FIG. 1 for nanobubble-containing water in which carbon dioxide nanobubbles are dispersed. In this example, water containing carbon dioxide bubbles is put into a rotating body, and nanobubbles of carbon dioxide are generated in ultrapure water by a method of making bubbles into nanobubbles by eddy current. It was investigated by a scattering type particle size distribution measurement. As shown in FIG. 1, it can be seen that nanobubbles having a diameter of 1 μm or less (particularly, a diameter of 500 nm or less) are appropriately retained in water even after one week has elapsed.

  The nanobubble-containing water used in the present invention is not particularly limited in the amount of carbon dioxide nanobubbles dispersed, but from the viewpoint of the efficiency of carbonation treatment, carbon dioxide nanobubbles in water are 0.1 vol% or more, more preferably It is preferable to disperse 0.35% by volume or more. The amount of nanobubbles dispersed in the water containing nanobubbles should be measured by leaving the nanobubbles to stand for 1 hour or more and then allowing the large bubbles to rise completely by vibration and then examining the specific gravity of the water containing nanobubbles. Can do. In the experiments by the present inventors, when water has a specific gravity of 0.9977, by using nanobubble-containing water having a specific gravity of 0.9966 (nanobubble dispersion amount: 0.1% by volume), the elution of steelmaking slag with alkali is performed. It has been confirmed that the suppression effect can be obtained. In addition, when the amount of nanobubble dispersion was further increased and the specific gravity of the water containing nanobubbles was set to 0.9940 (nanobubble dispersion amount: 0.35% by volume), it was confirmed that a more remarkable alkali elution suppression effect was obtained. ing. For these reasons, the dispersion amount of carbon dioxide nanobubbles in water is preferably 0.1% by volume or more, more preferably 0.35% by volume or more.

The carbon dioxide gas contained in the nanobubble-containing water desirably has a high CO ₂ concentration, but may have an appropriate CO ₂ concentration (preferably a concentration of 10 vol% or more) such as boiler exhaust gas or heating furnace exhaust gas. FIG. 2 shows the results of investigation on the influence of CO ₂ concentration of carbon dioxide contained in nanobubble-containing water. Converter slag (free CaO: 8 mass%) was pulverized to a particle size of 10 mm or less. It shows the results of investigating the pH reached by immersing the slag after treatment in nanobubble-containing water with various CO ₂ concentrations for 24 hours and immersing the treated slag in water having a mass ratio of 10 times. According to FIG. 2, the higher the CO ₂ concentration, the higher the alkali elution suppression effect, but it can be seen that the effect can be obtained even at a concentration of about 10 vol%.

There are no special restrictions on the method of bringing nanobubble-containing water into contact with steelmaking slag,
Usually, it is performed by either (i) a method of immersing steelmaking slag in water containing nanobubbles, or (ii) a method of spraying water containing nanobubbles into steelmaking slag.
In the case of the above immersion method (i), the immersion time is preferably 2 hours or longer, more preferably 6 hours or longer so that carbonation proceeds sufficiently to the inside of the slag. Moreover, in the case of the watering method of said (ii), it is preferable to water so that it may become the water content of 5 mass% or more which is the general water content of steelmaking slag, desirably 10 mass% or more.

In the present invention, by bringing the nanobubble-containing water into contact with the steelmaking slag as described above, water containing carbon dioxide gas appropriately penetrates into the slag and is retained for a long time, and the free CaO and free MgO inside the slag are appropriately retained. Can be carbonated. For this reason, slag with small alkali elution property can be efficiently manufactured from steelmaking slag.
In addition, since water containing nanobubbles has high stability of bubbles (nanobubbles), the bubbles continue to exist stably even when mechanical stress is applied to the water. For this reason, even if it makes it contact with slag, even if it uses simple methods, such as sprinkling, without giving special consideration, the characteristic as nanobubble content water is not lost. Therefore, it is possible to advance the carbonation reaction of slag by a very simple method such as sequentially adding steelmaking slag to nanobubble-containing water or conversely spraying nanobubble-containing water on steelmaking slag. it can.

In particular, nanobubbles have a larger surface area than normal bubbles in the same bubble volume, so that the reaction activity can be increased. In addition, although CO ₂ is nonpolar as a molecule, it is nanosized. By doing so, the influence of the polarity between C = O appears, and the reaction with Ca ²⁺ or Mg ²⁺ easily proceeds. Due to these factors, carbon dioxide-containing nanobubble-containing water is used for carbonation treatment of steelmaking slag, whereby free CaO and free MgO inside the slag can be efficiently carbonated.

Hot metal pretreatment slag (free CaO content: 1.5 mass%) and converter slag (free CaO content: 7.7 mass%) having the component composition shown in Table 1 are carbonized to produce low alkali-eluting slag. did. Any steelmaking slag is discharged into the yard, cooled, and then crushed to a particle size of 10 mm or less.
In this example, water: 25 L and carbon dioxide: 7 L were simultaneously sucked with a mixing pump, and introduced into a cylindrical container so as to swirl at high speed to obtain nanobubble-containing water in which carbon dioxide was dispersed. The bubble volume of this nanobubble-containing water was 0.36%. Carbonation treatment of steelmaking slag was performed by using this nanobubble-containing water under the conditions shown in Table 2 by immersing steelmaking slag in nanobubble-containing water and by spraying nanobubble-containing water into steelmaking slag. In addition, in the method of sprinkling nanobubble containing water, the sprinkling of nanobubble containing water corresponding to 5 mass% of the steelmaking slag mass was repeatedly performed every hour within the treatment time shown in Table 2.

The treated slag was immersed in pure water having a mass ratio of 10 times, and the pH after 6 hours was measured. Moreover, the same pH measurement was performed also about the untreated steelmaking slag for the comparison. The results are shown in Table 2. In Table 2, No. 3 and no. FIG. 3 shows the change over time in pH when 6 (untreated converter slag) was immersed in pure water.
The hot metal pretreatment slag and the converter slag before treatment have pH values of 11.5 and 12.6 after 6 hours of immersion in pure water, respectively. In particular, the converter slag is extremely short as shown in FIG. It can be seen that a high pH has been reached. On the other hand, in the example of the present invention, the pH is lowered by 0.4 to 0.6 by carbonation treatment (immersion or watering) for about 2 hours, and when the treatment time is further extended, the pH is compared with the slag before treatment. Is reduced by about 0.8 to 1.1. Moreover, from the behavior of this pH change, the pH value has almost reached saturation, and it is confirmed that long-term alkali elution can also be reduced.

Graph showing an example of bubble size distribution for nanobubble-containing water in which carbon dioxide nanobubbles are dispersed Graph showing the relationship between the CO ₂ concentration and the alkali dissolution of carbonated treated slag carbon dioxide contained in the nanobubbles containing water The graph which shows the time-dependent change of pH at the time of immersing carbonated slag and untreated slag in a pure water in an Example.

Claims (4)

A method for producing a low alkali-eluting slag, characterized in that nanobubble-containing water in which CO ₂ or a CO ₂ -containing gas is dispersed in water in the form of bubbles having a diameter of 1 μm or less is brought into contact with steelmaking slag. The method for producing a low alkali-eluting slag according to claim 1, wherein the nanobubble-containing water is obtained by dispersing 0.1% by volume or more of CO ₂ or CO ₂ -containing gas bubbles having a diameter of 1 µm or less. .   The method for producing a low alkali-eluting slag according to claim 1 or 2, wherein steelmaking slag is immersed in water containing nanobubbles.   The method for producing a low alkali-eluting slag according to claim 1 or 2, wherein the water containing nanobubbles is sprinkled into the steelmaking slag.

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