JP4808655B2 - Method of stabilizing powdered steel slag - Google Patents

Description

Since the present invention contains a large amount of powdered slag in the hot metal pretreatment slag or secondary refining slag of ordinary steel generated in the steelmaking process of steelworks, etc., it is difficult to perform normal steam aging treatment, etc. It relates to the stabilization process how to achieve low expansion of slag showing the expansion behavior over a long period of time.

  Steelmaking slag generated from various smelting furnaces such as ordinary steel converters, hot metal pretreatment furnaces, or secondary smelting furnaces at steelworks, etc., is a component that cannot be completely melted during the smelting process, or crystallizes during cooling after smelting. Contains ingredients to Among these components, when a hydratable component such as CaO or MgO (hereinafter referred to as free CaO or free MgO) hydrates in contact with moisture, the volume increases approximately twice. This causes the slag to expand.

  Among these steelmaking slags, powdery slag having a particle size of 1 mm or less generally contains more free CaO and free MgO than the bulk slag, and has a large specific surface area. The sum reaction is more likely to proceed, and as a result, a severe expansion phenomenon is likely to occur.

  In order to suppress the expansion phenomenon of such steelmaking slag, as a stabilization treatment method to reduce the free CaO and free MgO that are the cause, it is exposed to the atmosphere for several months to several years and fully hydrated. An “atmospheric aging” process that proceeds, a “steam aging” process that promotes a hydration reaction by forcibly reacting with water vapor at atmospheric pressure or under pressure, and a “pressurized aging” process are widely known.

  However, the “atmospheric aging” process requires a large processing area for processing a large amount of steelmaking slag, and at the same time, powdered slag is difficult to process due to problems such as dust, and free CaO. In general, there is a problem that the hydration reaction is generally slow, and the free MgO cannot be sufficiently hydrated.

  Compared with the “atmospheric aging” process, the “steam aging” process can greatly reduce the number of processing days from several days to a few dozen days, but the process requires a large amount of water vapor, which increases the processing cost. is there. In addition, the powdered slag becomes difficult to permeate water vapor depending on the degree of filling, and it is difficult to perform uniform treatment in the apparatus, and the hydration reaction of free MgO is slow, and compared with the bulk slag. It is not easy to perform a stable treatment. Furthermore, the “pressurized aging” treatment requires a dedicated container, so that the cost of the treatment equipment is high, the equipment management is difficult, and it is not suitable for the treatment of a large amount of slag, especially powdery slag.

  As a method for eliminating the disadvantages of these general treatment methods and suppressing the expansion of steelmaking slag, for example, the method disclosed in Patent Document 1 and the method disclosed in Patent Document 2 are shown.

  The method according to Patent Document 1 forms a mixture mainly composed of granular steel slag and gypsum in which particles having a particle size of 5 mm or less occupy 50% by mass or more, and in the presence of hot water at 80 to 120 ° C. or these and carbon dioxide. It is a method of curing by autoclave curing. This method is a very effective method for hydration and carbonation of free CaO. However, it is difficult to obtain a granular steelmaking slag after processing in order to form a solid, and the processing is complicated. There is a disadvantage that it is not suitable for processing a large amount of slag.

  In the method according to Patent Document 2, molten or semi-molten slag in which converter slag and blast furnace slag or desulfurized slag are received in the same receiving pan is discharged into a pit or yard, and immediately after that, the slag is cultivated. To roll. This method is a method of suppressing the formation of free CaO itself by mixing slag with low basicity in the molten state or semi-molten state into the converter slag, but the slag after production becomes a lump and powdery slag is removed. There is a disadvantage that it cannot be obtained.

On the other hand, as a method of stabilizing the steelmaking slag by supplying carbon dioxide, for example, free CaO or the like by flowing carbon dioxide like the method disclosed in Patent Document 3 or the method disclosed in Patent Document 4 A method of stabilizing by changing free MgO to CaCO ₃ or MgCO ₃ is shown.

  In the method disclosed in Patent Document 3, a massive steelmaking slag having a particle size of 40 mm or less is first aged in a steam atmosphere at atmospheric pressure to stabilize the expansibility, and then in a mixed atmosphere of steam and carbon dioxide gas. And carbonating by holding for 1 hour or longer.

  The method disclosed in Patent Document 4 is less than the moisture value at which free water begins to exist in the steelmaking slag that has been subjected to the aging treatment in an air atmosphere, a pressurized atmosphere, or a water vapor atmosphere. In this method, after adjusting the amount of water added so as to be in a range of 10% by mass or less, a gas containing carbon dioxide gas and having a relative humidity of 75 to 100% is flowed.

  In the methods described in these, free CaO and free MgO contained in the slag are reduced, but since the carbonation reaction of free MgO requires a longer time than free CaO, this free MgO is hydrated. In order to sufficiently suppress the long-term expansion phenomenon caused by it, an aging treatment for several days is required in advance before the treatment with carbon dioxide gas, and the process is multistage and takes a long time and requires a large treatment cost. .

  In addition to the above-mentioned patent documents, various methods for stabilizing slag using carbon dioxide gas have been disclosed, both of which are methods for promoting the consolidation of slag and alkali components from slag to water. It is only used as a method for suppressing the increase in pH due to elution of slag, and a method for stably suppressing the expansion of slag is not disclosed.

JP 2000-327396 A JP-A-6-329451 JP-A-8-259282 JP 2005-97076 A

  The object of the present invention is to make a powdery slag of ordinary steel made of a large amount of powdered slag, which has been difficult with the conventional aging treatment method (hereinafter simply referred to as “powdered steel slag”). Focusing on the fact that the steelmaking slag contains a relatively large amount of free CaO and free MgO, and that the formation reaction of carbonates by carbon dioxide gas is effective in reducing free CaO and free MgO, stable and low expansion is achieved. The purpose is to obtain a measuring method.

  The inventors of the present invention have conducted a laboratory-level experiment and desktop study on grasping various factors affecting the carbonation treatment method for reducing the expansion of powdered steelmaking slag. Through experiments at the actual machine level, the inventors have obtained knowledge that the above-mentioned problems can be solved by the following invention.

The stabilization method of powdered steel slag according to the first invention includes T-Fe 2.0 mass% or more and MgO 4.0 mass% or more, and the particle size distribution is 30 mass with a particle size of 1 mm or less. About% or more in a powdery steel-making slag, the water content of the slag was adjusted to 20 mass% or less 8 mass% or more, 20 Nm ³ / hr or more 100 Nm ³ / hr or less in slag per ton of the net amount of carbon dioxide a stabilization processing method for supplying powdery steel slag the carbon dioxide gas-containing gas, the supply amount of the carbon dioxide-containing gas is less slag per ton of 100 Nm 3 / ^hr, containing a particle diameter less than 1mm slag It is characterized by adjusting the pure amount of carbon dioxide supplied per ton of slag according to the rate .

The method for stabilizing a powdered steel slag according to the second invention is characterized in that, in the first invention, a carbon dioxide-containing gas having a relative humidity of 75% or more and 100% or less is supplied.

  According to the method for stabilizing pulverized steelmaking slag of the present invention, the low expansion of the pulverized steelmaking slag does not require a long period of time as in the conventional aging treatment method, and the treatment is performed at a room temperature and in a short time. It becomes possible stably. In addition, carbon dioxide contained in gas discharged from factories, etc. can be used as the carbon dioxide-containing gas used for processing, which contributes to the suppression of greenhouse gas emissions from factories. There is also an effect.

  This stabilized powdery steelmaking slag has low expansion and does not cause a problem that free CaO and free MgO are eluted to raise the pH of groundwater, rivers and seawater. It can be used as a substitute for natural sand or as a civil engineering material such as crushed sand. Moreover, it becomes possible to use it also for various aggregates and roadbed materials by mixing and using with other aggregates.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  In developing an efficient stabilization treatment method for reducing the expansion of powdered steel slag, the present inventor grasped the influence of various factors on the reaction rate of carbonation and the relationship between the carbonation reaction amount and the volume expansion coefficient. In order to clarify the above, we conducted basic experiments on carbonation treatment under various conditions using about 5 kg of powdered steelmaking slag collected from the hot metal pretreatment furnace in the steelmaking process of steelworks, and carbonation. The volume expansion coefficient of the slag after treatment was also measured.

  Here, the measurement conditions of the volume expansion rate are the same as those in the test sample carbonation-treated slag, according to “Water immersion expansion test method for road steel slag” defined in JIS A5015 Annex 2. As for the curing method, in order to more accurately grasp the long-term expansion due to free MgO, the above-mentioned JIS stipulated condition of “repeating holding for 6 hours in 80 ° C. warm water for 10 days” is not necessarily sufficient. Therefore, it is more severe than this, applying the condition of “continuously holding slag after treatment for 10 days during steam saturation at 110 ° C.”, and the ratio of slag volume before and after curing treatment under this strict condition It is defined as the volume expansion coefficient specified in.

  First, the carbonation reaction behavior for each particle size of steelmaking slag was investigated. The steelmaking slag collected from the hot metal pretreatment furnace and measured for the components and the particle size distribution after the collection is a nominal size of a screen sieve specified in JIS Z8801, 26.5 mm, 4.75 mm, 2.36 mm and 1 .Sieving with 18 mm sieves (hereinafter referred to as 30 mm, 5 mm, 2 mm, and 1 mm sieves for convenience), causing carbonation reaction for each particle size, mass change with progress of reaction Was measured. The average composition of this slag is as shown in Table 1, and the slag content with a particle size of 1 mm or less immediately after collection was about 40% by mass.

Here, as the carbonation reaction processing conditions, the water content of each slag is adjusted to about 15% by mass, and the carbon dioxide-containing gas supplied to the slag is a laboratory-level basic experiment, so it is commercially available. Using pure carbon dioxide gas (purity 99% by volume or more) and bubbling it into water in advance to adjust the relative humidity to 100%, supplying it at a flow rate of 50 Nm ³ / hr per ton of slag for 10 hours Retained. Moreover, the mass change amount of slag was measured every arbitrary time, and the value divided by the slag amount at the start of the experiment was determined as the mass change rate accompanying the carbonation reaction.

  FIG. 1 shows the change over time of the mass change rate measured for each particle size. From FIG. 1, it was confirmed that the smaller the particle size, the larger the mass change rate and the earlier the carbonation reaction was completed. Therefore, when the volume expansion coefficient of the slag for each particle size after the reaction was measured by a method of continuously holding for 10 days in the water vapor saturation at 110 ° C., the particle size of 1 mm or less was 0.1% by volume. More than 1 mm and 2 mm or less were 1.2 volume%, more than 2 mm and 5 mm or less were 2.0 volume%, and more than 5 mm to 30 mm or less were 3.0 volume%. In addition, the volume expansion coefficient measured about the slag before a carbonation process had the difference in a particle size, and was in the range of 5-12 volume%.

  When the carbonation state of the slag cross section after the experiment was investigated by EPMA (Electron Probe Micro-Analysis), when the particle size was 1 mm or less, the carbonation of CaO and MgO components progressed to the center of the particle, but the particle size was large. Accordingly, it was confirmed that a phase of CaO and MgO that was not yet carbonated was present in the center of the grain. From this, it was estimated that the carbonation reaction progressed from the surface of the grain toward the inside, and the larger the particle diameter, the more difficult the carbonation progressed to the inside.

  That is, the powdered steel slag having a particle size of 1 mm or less has a characteristic that the above-mentioned hydration reaction is more likely to proceed and a severe expansion phenomenon is likely to occur, but the carbonation reaction is likely to proceed when the carbonation treatment is performed. Newly found that it has.

Next, based on the new knowledge obtained by the above experiment, paying attention to the fact that slag having a particle size of 1 mm or less greatly contributes to the carbonation reaction, the content of slag having a particle size of 1 mm or less is The effect on the volume expansion rate of slag after carbonation was investigated. Content of slag having a particle size of 1 mm or less by mixing a required amount of slag having a particle size of 1 mm or less prepared by sieving the slag shown in Table 1 with a 1 mm sieve beforehand. Prepared powdery steelmaking slag, and after adjusting the water content under various conditions, a commercially pure carbon dioxide gas whose relative humidity was adjusted to 75 to 100% was adjusted to 50 Nm ³ / Hr per ton of slag. While being supplied at a flow rate, the carbonation treatment was performed by holding for 10 hours. Moreover, the volume expansion coefficient of the slag after carbonation treatment was measured under conditions more severe than those of the conventional method of continuously holding for 10 days in water vapor saturation at 110 ° C. as described above.

  FIG. 2 shows the relationship between the moisture content of the slag and the volume expansion coefficient for each slag content having a particle diameter of 1 mm or less. From FIG. 2, if the content of slag having a particle diameter of 1 mm or less is higher within the range of the experimental results of this time, the volume expansion coefficient is lower, and in order to lower the volume expansion coefficient, Not only the water expansion rate of 1.5% by volume or less as defined in JIS A5015 “steel slag for roads”, which can be used as a civil engineering material, is confirmed to have an appropriate value. In order to ensure a volume expansion coefficient of 1.5% by volume or less stably even under a condition of continuously maintaining for 10 days in water vapor saturation at 110 ° C., the slag having a particle size of 1 mm or less is 30% by mass or more, and It has been found that the water content should be 8% by mass or more and 20% by mass or less. In the present invention, the moisture content of the slag is measured in accordance with JIS A1203 “Soil moisture content test method”.

  When the slag content is less than 30% by mass with a particle size of 1 mm or less, the ratio of slag in which uncarbonated CaO and MgO phases are present in the center of the particle is high, so the volume expansion coefficient after the carbonation reaction is high. turn into.

  As for the moisture content, as described in the prior art, a smooth carbonation reaction proceeds due to the presence of a certain amount of moisture, but slag having a particle size of 1 mm or less, which is within the scope of the present invention, is used. In the case of slag containing 30% by mass or more, it was found that controlling the moisture content to 8% by mass or more and 20% by mass or less is an appropriate condition for reducing the expansion. That is, when the amount of water is less than 8% by mass, the slag tends to dry due to the heat generated by the carbonation reaction, and the carbonation reaction does not proceed smoothly. This is because it is considered that the carbon dioxide-containing gas is difficult to be supplied uniformly. In addition, about the water added in order to adjust the moisture content of this slag, even if it uses so-called carbonated water in which the carbon dioxide gas melt | dissolved from the beginning, it does not care. Incidentally, as a method for adding moisture, for example, spraying or the like can be performed.

  In order to keep the slag in a proper wet state during the carbonation reaction, it is effective to supply carbon dioxide gas having a high relative humidity. It is sufficient to supply a gas having a relative humidity of 75% or more and 100% or less. It was also confirmed that a carbonation reaction can be performed. Here, when the gas has a relative humidity of less than 75%, it is difficult to supply sufficient moisture from the gas to the slag. On the other hand, the higher the relative humidity, the better, so the upper limit may be 100%.

  Thirdly, the relationship between the supply amount of carbon dioxide pure per ton of slag and the volume expansion coefficient of slag after carbonation reaction was investigated. Using the components shown in Table 1, powdered steel slag having a content of slag having a particle size of 1 mm or less adjusted to 40% by mass and a moisture content of about 15% by mass is used, and the relative humidity is 100% as the carbon dioxide-containing gas. Using commercially available pure carbon dioxide gas (purity 99% by volume or more) adjusted to%, the pure carbon dioxide amount supplied per ton of slag was variously changed and maintained for 48 hours. Since pure carbon dioxide was used in this experiment, the pure amount of carbon dioxide supplied per ton of slag coincides with the total amount of gas supplied per ton of slag. In addition, the holding time was set to 48 hours in the preliminary experiment, when the content of slag having a particle size of 1 mm or less is 40% by mass, regardless of the supply amount of carbon dioxide pure per ton of slag, This is because it was confirmed that the carbonation reaction sufficiently progressed and reached an equilibrium state after 48 hours of carbonation treatment. Incidentally, in the steam aging treatment actually performed to promote the hydration reaction of these slags described in the prior art, the suppression of expansion is insufficient in the treatment time of 48 hours. Processing time is needed.

  Furthermore, in this experiment, when the mass change amount of each slag after the carbonation reaction is 100% (hereinafter referred to as total mass change amount), the time required to reach 80% is obtained. It was. The reason for setting the time to reach 80% of the total mass change is that if the mass change is 80% or more of the total mass change, the particle size is 1 mm or less regardless of the properties of the powdered steel slag. The volume when the mass change amount is 80% with respect to the volume expansion coefficient when the mass change amount is 100% in the range where the slag is 30 mass% or more and the water content is 8 mass% or more and 20 mass% or less. The present inventor has confirmed by experiments that the difference from the expansion coefficient is extremely small. If the amount of mass change is 80% or more, it can be evaluated that the entire slag is carbonized almost uniformly. Because.

  Incidentally, in evaluating that the entire slag is carbonized almost uniformly, the amount of mass change is not limited to 80% or more, and may be set appropriately by experimentation or the like. However, in this experiment, a case where the mass change amount is 80% or more and the entire slag can be evaluated to be carbonized almost uniformly will be described as an example.

FIG. 3 shows the supply amount of carbon dioxide pure per ton of slag and the time until the mass change amount of slag accompanying the carbonation treatment reaches 80% of the total mass change amount (hereinafter, “carbonation time”). ) Is exemplified. From this figure, if the supply amount of carbon dioxide pure is within a range of 100 Nm ³ / Hr or less with respect to 1 ton of slag, the total amount of mass change over a predetermined time (about 5 hours in the example of FIG. 3) It can be seen that the change amount can be 80% or more.

Further, when the supply amount of the carbon dioxide pure amount exceeds 100 Nm ³ / Hr per ton of slag, that is, when the total amount of gas supply per ton of slag exceeds 100 Nm ³ / Hr, the mass change amount It was found that slag that does not reach 80% was partially generated, and as a result, uniform carbonization of slag could not be performed.

  This is because when the gas supply amount becomes excessive, a so-called blow-through phenomenon occurs in which the gas selectively flows in a portion where the ventilation resistance in the slag is low. In such a state, a carbonation reaction of the slag occurs. This is because there is no part.

  Here, the lower limit value of the supply amount of the pure carbon dioxide amount per ton of slag is not particularly defined, and may be set as appropriate according to the required carbonation time. Therefore, the upper limit of the carbonation time is not particularly specified. However, practically, as described later, it is preferable to set the carbonation time to be within 24 hours.

  In addition, in the treatment of slag on an actual scale at an ironworks, etc., in order to use pure carbon dioxide gas as in this basic experiment, a dedicated large container is required. It is thought that it is realistic to effectively use various by-product gases such as this, and in some cases, carbon dioxide in which commercially pure carbon dioxide gas and argon gas are mixed and the volume concentration of carbon dioxide gas is adjusted to various ratios. An experiment was also performed in which the gas-containing gas was used to change the supply amount of carbon dioxide-containing gas per ton of slag.

  As a result, the supply amount per ton of slag as the carbon dioxide gas pure amount converted from the volume concentration of carbon dioxide and the supply amount of carbon dioxide-containing gas per ton of slag and the mass change amount of slag accompanying carbonation treatment are the total. It has been found that the time relationship until reaching 80% of the mass change amount is almost the same as the relationship shown in FIG.

In addition, when the carbon dioxide supply amount exceeds 100 Nm ³ / Hr per ton of slag regardless of the volume concentration of carbon dioxide, a blow-through phenomenon occurs, and there is a portion where the carbonation reaction of slag does not occur. There was found.

Accordingly, it has been found that in order to carbonize the entire slag almost uniformly, it can be managed by controlling the supply amount per ton of slag as the pure carbon dioxide content. Accordingly, the pure carbon dioxide amount per ton of slag can be adjusted by either or both of the volume concentration of carbon dioxide gas and the supply amount of the carbon dioxide-containing gas per ton of slag. However, it has been found that it is necessary to carry out the supply amount of the carbon dioxide-containing gas per ton of slag within a range of 100 Nm ³ / Hr or less.

  In addition, the lower limit value of the carbon dioxide-containing gas supply amount per ton of slag is not particularly specified, and the volume concentration of carbon dioxide gas is taken into account when setting the supply amount of the pure carbon dioxide amount per ton of slag. It may be set as appropriate.

  Furthermore, when the supply amount of carbon dioxide containing gas per ton of slag is constant, the lower limit of the volume concentration of carbon dioxide in the carbon dioxide containing gas is 10% by volume or more considering the equipment configuration such as piping of the gas supply system. Needless to say, the concentration is preferably 20% by volume or more, and the concentration is preferably higher in order to shorten the carbonation treatment time.

  As described above, the case of using powdered steel slag having a content of slag having a particle size of 1 mm or less adjusted to 40% by mass and a moisture content of about 15% by mass has been explained. As for the relationship between the supply amount and the carbonation time, the content of slag having a particle diameter of 1 mm or less is 30% by mass or more, and the content of slag is 8% by mass or more and 20% by mass or less. It has also been confirmed that it shows a trend.

  Moreover, since the content rate of slag with a particle size of 1 mm or less is 30 mass% or more has a high carbonation reaction rate as described above, the content rate of slag with a particle size of 1 mm or less is less than 30 mass percent. Then, the carbonation time corresponding to the supply amount of the carbon dioxide gas pure amount can be remarkably shortened. This is because the content rate of slag having a particle size of 1 mm or less is 30% by mass or more, and as a result of increasing the surface area of slag per unit volume, the carbonation reaction rate can be increased. This is considered to be because the carbonation reaction was efficiently promoted up to the part.

  Fourthly, the composition of the slag to be subjected to the stabilization treatment of the present invention, that is, the composition of the powdered steel slag that easily causes long-term expansion was examined. In general, powdered slag having a particle size of 1 mm or less contains more free CaO and free MgO than massive slag, and its specific surface area is large. It was mentioned above that it is easy to produce. However, among them, the hydration reaction of free MgO is slower than the hydration reaction of free CaO, and it is generally said that this hydration reaction proceeds slowly over a long period of time. It was important to accurately grasp the composition of steel slag.

Steelmaking slag that is an object of the present invention is generated from various refining furnaces such as a converter of normal steel, a hot metal pretreatment furnace, or a secondary refining furnace, and the mass ratio CaO / SiO _{2 in} these slags is CaO / SiO ₂ (hereinafter referred to as basicity) is generally in the range of 1.5 to 3.0. Therefore, in this basicity range, MgO precipitates without forming a mineral phase with other components, and the limit concentration at which it becomes free MgO causing hydration reaction can be determined using commercially available thermodynamic software (for example, When calculated using an integrated thermodynamic calculation system “Thermocalc-Software & Database” (manufactured by Thermo-Calc Software AB), a result of about 2% by mass or more was obtained.

On the other hand, metal oxides such as FeO and Fe ₂ O ₃ are generally present at the same time in the steelmaking slag of these ordinary steels at the same time. Generally, free MgO is present in these metal oxides. It is known to dissolve. Therefore target ordinary steel steelmaking slag results components were widely detailed investigation made, the iron oxide component such as FeO and Fe ₂ O ₃ were summarized in iron terms, the total iron concentration (the present invention, wherein the T-Fe In this condition, the concentration at which the free MgO precipitates is increased to about 4.0% by mass. I found out.

From the above examination, the invention according to (1) described above is an effective stabilization method for powdered steelmaking slag, including 2.0% by mass or more of T-Fe and 4.0% by mass or more of MgO, For powdered steelmaking slag with a particle size of 1 mm or less as a particle size distribution of 30% by mass or more, the water content of the slag is adjusted to 8% by mass or more and 20% by mass or less, and the pure carbon dioxide gas amount per ton of slag 100 Nm 3 / ^hr of the following carbon dioxide gas-containing gas to a stabilization treatment method for supplying powdery steel slag, and the supply amount of the carbon dioxide gas-containing gas is defined as that less slag per ton of 100 Nm 3 / ^hr .

Here, the upper limit of the slag content with a particle size of 1 mm or less can be processed even at 100% by mass as shown in the experimental results in FIG. 1, and there is no particular limitation. From the viewpoint of uniform supply of the gas-containing gas, the amount is preferably less than 60% by mass in order to ensure voids. As for the upper limit of the T-Fe and MgO content of a component of the slag, but no particular limitation, the first place because steel slag is CaO or SiO ₂ is the main component, 40 mass% or less as a T-Fe However, MgO is generally 20% by mass or less even when actively added from the viewpoint of refractory protection.

In addition, in FIG. 3 shown above, when the second plot from the left side in the figure (the supply amount of carbon dioxide pure per ton of slag is less than 5 Nm ³ / Hr), the carbon dioxide pure is simply Since the carbonation treatment time is remarkably long as 24 hours or more due to the small amount of supply, the actual treatment conditions are not so preferable, and it contains a large amount of powdered steel slag that is the subject of the present invention and is likely to expand for a long time. In the case of carbonation of slag, it is effective to supply a larger amount of carbon dioxide gas per ton of slag, and the amount of carbon dioxide gas to be 5 Nm ³ / Hr or more per ton of slag. Is preferred. (Invention pertaining to (2))

If there is a need to shorten the carbonation time, the supply amount of carbon dioxide per ton of slag is 10 Nm ³ / Hr (fourth plot from the left side of FIG. 3) or more, and about half a day And more preferably 20 Nm ³ / Hr (the fifth plot from the left side of FIG. 3) or more, since it can be about 8 hours.

  Furthermore, from FIG. 2 shown earlier, it can be inferred that the higher the content of slag with a particle size of 1 mm or less, the higher the carbonation reaction rate. From FIG. 3, the content of slag with a particle size of 1 mm or less is shown. In certain cases, the amount of time required to reach 80% of the total mass change (that is, the time until the carbonation reaction is considered to be almost complete) varies depending on the supply amount of pure carbon dioxide. I understand that From these relationships, when the content of slag with a particle size of 1 mm or less is large, the treatment time is shortened by increasing the supply amount of the carbon dioxide gas supplied per ton of slag to match the amount of slag. And a more efficient stabilization method can be obtained. (Invention pertaining to (3) above)

  In addition, adjustment of the supply amount of the pure amount of carbon dioxide gas to be supplied per ton of slag corresponding to the content rate of slag having a particle diameter of 1 mm or less is scheduled to be performed with respect to the relationship of FIG. 2 and FIG. Although it may be carried out in advance for each property of the powdered steel slag, the average value when there is not much difference with respect to the relationship of FIG. 2 and FIG. 3 of the powdered steel slag of various properties Or it can also implement using a representative value.

  Thus, the stabilized steelmaking slag obtained by the treatment of the present invention has almost no change in the slag content with a particle size of 1 mm or less before and after the carbonation treatment, and the content of T-Fe is 2.0% by mass. From the above, since MgO is contained in an amount of 4.0% by mass or more, the particle size distribution is a particle size of 1 mm or less of 30% by mass or more, and the volume expansion coefficient is 1.5% by volume or less. It can be effectively used as a civil engineering material. (Invention pertaining to (4) above)

  The experimental results shown in FIG. 1 to FIG. 3 were the results of a small-scale experimental apparatus with a steelmaking slag amount of about 5 kg, but based on these relationships, the actual experimental site was used. Similar results could be obtained even with carbonation treatment at the actual machine level of several tons to hundreds of tons.

  At a steelworks, about 50 tons of steelmaking slag of ordinary steel generated in the hot metal pretreatment furnace in the steelmaking process is recovered in a hot metal state, naturally cooled in the atmosphere, and then sieved with a 30 mm sieve. Components and particle size distribution before slag treatment were measured. The average composition of this slag was as shown in Table 1 above, and the content of slag having a particle size of 1 mm or less was about 40% by mass.

  The slag is subdivided by about 2 tons, and the slag having a particle diameter of 1 mm or less prepared by sieving the slag with a 1 mm sieve in advance is mixed with the slag before sieving in a necessary amount and shown in Table 2. Under such conditions, the content of slag having a particle diameter of 1 mm or less was adjusted, and water content was adjusted by adding water by spraying. Moreover, the slag with low content of T-Fe and MgO was also prepared for the comparison. These slags are installed in a 2m long, 2m wide, 1.5m high bucket with a gas supply pipe at the bottom, covered with a sheet, and the relative humidity is adjusted to 100%. Then, a carbon dioxide-containing gas in which the volume concentration of carbon dioxide was changed by adding a part of argon gas to pure carbon dioxide was also supplied under the conditions shown in Table 2.

  Thus, about the post-process slag which processed on various conditions, the particle size distribution, the moisture content, and the volume expansion coefficient were measured. Regarding the volume expansion rate, in accordance with “Water immersion expansion test method for steel slag for roads” prescribed in JIS A5015 Annex 2, only for the curing of the specimen, it is 10 days under 110 ° C. steam saturation condition. Strict conditions of continuous retention were used.

These measurement results are shown in Table 3. In Examples 1 to 8 of the present invention and Reference Example 1 , the volume expansion rate of the slag was stably 1.5% by volume or less, and a low expansion that can be used as a civil engineering material was achieved. Incidentally, the volume expansion coefficient of the slag before treatment was in the range of 8 to 10% by volume. On the other hand, in Comparative Examples 1 to 3 in which the slag content rate with a particle size of 1 mm or less falls outside the conditions of the present invention, and in Comparative Example 4 in which the supply amount of carbon dioxide deviates from the conditions of the present invention, the volume expansion coefficient of the slag after treatment is all It exceeded 1.5 volume% and was difficult to use as a civil engineering material.

Moreover, about the slag after a process, although the measurement of the slag content rate of a particle size of 1 mm or less was performed, in 1-8 of the Example of this invention , and the reference example 1 , compared with the slag of a particle size of 1 mm or less compared with before a process. The rate is slightly reduced and there is no noticeable caking phenomenon between fine slag particles, and it can be recovered as powdery slag that can be used as a substitute for natural sand or as a civil engineering material such as crushed sand. It was.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  As described above, according to the method of the present invention, powdered steelmaking slag can be stabilized at a low cost and in a large amount in a much shorter time than before without adjusting the temperature. The powdered steelmaking slag stabilized in this way has low expansion and does not cause the problem that the free CaO or free MgO elutes and raises the pH of groundwater, rivers and seawater, and makes use of the powdery characteristics. Therefore, it can be used as a substitute for natural sand or as a civil engineering material such as crushed sand. Moreover, it becomes possible to use it also for various aggregates and roadbed materials by mixing and using with other aggregates. Furthermore, since the carbon dioxide gas discharged from the factory can be used in the method of the present invention, a secondary environmental effect that the emission of carbon dioxide to the atmosphere can be suppressed is also obtained.

It is a figure which shows the relationship between carbonation time at the time of changing slag particle size, and mass change rate. It is a figure which shows the relationship between the moisture content at the time of changing the slag content rate of a particle size of 1 mm or less, and a volume expansion coefficient. It is a figure which shows the relationship between the supply amount per 1 ton of slag and the time until the mass change amount of slag reaches 80% of the total mass change amount per pure carbon dioxide.

Claims (2)

For powdered steel slag containing 2.0% by mass or more of T-Fe and 4.0% by mass or more of MgO and having a particle size distribution of 1 mm or less and 30% by mass or more, the moisture content of the slag is thereof was adjusted to 8 to 20 mass%, the stabilization method of processing powdery steel slag supplies 20 Nm ³ / hr or more 100 Nm ³ / hr or less of carbon dioxide-containing gas into the slag per tonne as net amount of carbon dioxide a is, the supply amount of the carbon dioxide-containing gas is less slag per ton of 100 Nm 3 / ^hr, depending on the content of the particle diameter of less than 1mm slag, net amount of carbon dioxide supplied to the per ton slag A method for stabilizing a powdered steel slag, characterized by adjusting the slag. The method for stabilizing a powdered steelmaking slag according to claim 1, wherein a carbon dioxide-containing gas having a relative humidity of 75% or more and 100% or less is supplied.