JP5191861B2 - Manufacturing method of slag for cement raw material - Google Patents

Description

  The present invention relates to a method for producing slag for cement raw material from slag generated in a steelmaking process.

  In the steel making process of the iron making process, phosphorus, sulfur, carbon, etc. contained in the hot metal are removed, and the content of trace elements is adjusted according to the use of the steel. In the refining process for that purpose, refining agents such as lime and iron oxide are used, and so-called steelmaking slag is generated as a by-product. This steelmaking slag is broadly classified into hot metal pretreatment slag that is generated in each refining process of desiliconization, dephosphorization, and desulfurization, which is called hot metal pretreatment, and decarburization slag that is generated in the decarburization refining process. These steelmaking slags are used mainly for roadbed materials, earthwork materials, marine earth and lumber, etc., and are also being reused in the steelmaking process.

On the other hand, a cement raw material is considered as one of the uses of steelmaking slag. Regarding such applications, for example, Patent Document 1 proposes a steelmaking slag treatment method suitable for a cement raw material, and Patent Document 2 also proposes a cement production method using steelmaking slag. Patent Document 3 proposes a cement composition containing fine steelmaking slag powder. If steelmaking slag can be used as a cement raw material, CaO contained in a large amount in steelmaking slag can be effectively used for cement, and resource saving can be achieved for natural raw materials such as limestone.
JP 2001-48605 A US Pat. No. 6,491,751 JP 2005-29404 A

  By the way, when manufacturing a Portland cement by baking a cement raw material with a rotary kiln or the like, a small amount of chromium oxide is contained in the cement raw material, and a part of this is treated in an oxidizing atmosphere at a high temperature. It is reported that it is easily formed and contained in cement. For example, according to H.J.M. Bowen's Environmental Inorganic Chemistry (Hakutomo), about 10 mass% of chromium oxide is considered to be hexavalent. Once cooled to room temperature, trivalent chromium is stable under normal conditions, and the change to hexavalent is only in the case of forced oxidation, thus suppressing the formation of hexavalent at high temperatures. It becomes important. There are two methods: (i) suppressing the amount of input chromium oxide, and (ii) maintaining the valence of chromium oxide at 3 by firing in a reducing atmosphere. The most common method is to reduce the amount of input.

  In the case of steelmaking slag, there are cases where chromium oxide is mixed from natural raw materials used. Steelmaking slag itself is in a state in which oxygen is deficient, such as containing metallic iron and divalent iron oxide, so that hexavalent chromium is difficult to generate, and therefore hexavalent chromium is not easily eluted. However, when this is used as a cement raw material, it is exposed to a high-temperature oxidizing atmosphere when it is fired in a kiln or the like, so that chromium is likely to be hexavalent like other cement raw materials. It becomes an obstacle to utilizing steelmaking slag as a raw material for cement.

  Moreover, in order to utilize steelmaking slag as a cement raw material, there also exist the following subjects. That is, in the case of blast furnace slag, it can be used as a mixed cement just by mixing with other raw materials at room temperature, whereas in the case of steelmaking slag, it is necessary to mix with other raw materials and then kiln firing, It cannot fully meet social demands such as reduction of carbon dioxide emissions and energy saving.

The reason why firing is necessary when steelmaking slag is used as a cement raw material is that the CaO-containing mineral contained in the steelmaking slag does not have high activity as a hydration reaction product such as cement. When attention is paid to slag basicity [mass ratio:% CaO /% SiO ₂ ] (hereinafter simply referred to as “basicity”), steelmaking slag generally has a basicity of 1 or more, particularly those having a basicity of 2 or more. It is expected that components that cause a cement reaction such as 2CaO.SiO ₂ (C ₂ S) and 3CaO.SiO ₂ (C ₃ S) are included. C ₂ S in ordinary slag is β-C ₂ S, which is stable with the same crystal structure as general Portland cement. However, since many steelmaking slags contain phosphorus and iron, phosphorus and iron are dissolved in β-C ₂ S, so that the hydration activity is almost lost, and the reaction activity as cement can hardly be expected. . C ₃ S is decomposed into C ₂ S and CaO in the process of cooling from the molten slag, and is not so much contained in the steelmaking slag at room temperature. For this reason, even if steelmaking slag is simply pulverized and mixed at room temperature, the function as a cement raw material is not so much manifested.

Accordingly, an object of the present invention is to solve the problems of the prior art and to provide a production method capable of stably producing cement raw material slag having a low chromium concentration from slag generated in the steelmaking process. is there.
Another object of the present invention is to provide a production method capable of stably producing cement raw material slag having a low chromium concentration and a high hydration reactivity from slag generated in a steelmaking process. .

  When the present inventors investigated about the chromium oxide contained in steelmaking slag, the quantity normally contained as chromium oxide is the range which can be said to be a trace amount of 0.1-1.0 mass%, and if this can be eliminated. It was found that it could be used as a cement raw material. As a conventional research, various methods are known for reducing and recovering chromium in slag, centering on stainless slag. However, there was no knowledge about the processing method considering the use of slag after recovering chromium for cement. This is because stainless slag often has a low basicity (for example, JP-A-2008-81845, JP-A-2002-256323, JP-A-2000-144272, JP-A-2003-301215), and cement. This is because no hydration reaction can be expected. Furthermore, slag from which chromium has been removed is considered to have slightly different characteristics from conventional steelmaking slag as a result of its removal, but there is no knowledge about the processing technology to be used as suitable for cement. This is the actual situation.

  On the other hand, the present inventors examined a method for reducing and removing chromium oxide from steelmaking slag having a high basicity that can be expected to be used as a cement raw material. However, since the basicity is high, the simple melting method stops the reaction, and in order to carry out the reaction while maintaining the molten state, a very high temperature exceeding 1700 ° C. is required, and the separation is effectively performed. I found it impossible. As a result of diligent investigations to solve such problems, it is possible to efficiently remove chromium from the cooled slag by adding a reducing material to a high temperature steelmaking slag containing a considerable amount of Fe and stirring and mixing it. It has been found that low chromization can be realized. It was also found that slag having high hydration reactivity can be obtained as a cement raw material by cooling at a relatively high cooling rate after the reduction treatment.

The present invention has been made on the basis of the above-described findings and has the following gist.
[1] Slag containing chromium oxide generated in the steelmaking process, and reduced to slag having a slag basicity [mass ratio:% CaO /% SiO ₂ ] of 1.5 or more and an Fe content of 10 mass% or more. A method for producing a slag for a cement raw material, comprising adding a material, stirring and mixing at a slag temperature of 1000 ° C. or higher, cooling , and removing magnetic deposits from the cooled slag .
[2] In the production method of [1] above, after adding a reducing material to slag and stirring and mixing, the ratio of the γ phase in the crystal phase of 2CaO · SiO ₂ after cooling is 50% by mass or less. The manufacturing method of the slag for cement raw materials characterized by cooling.
[3] The method for producing slag for a cement raw material, wherein the reducing material is added at a slag temperature of 1200 ° C. or higher in the production method of [1] or [2].
[4] In the production method according to any one of [1] to [3], the slag basicity [mass ratio:% CaO /% SiO ₂ ] generated in the steel making process is reduced to 3.0 or more together with the reducing material. A method for producing a slag for a cement raw material, comprising adding a silicon-containing material so that the slag basicity is 2.0 or more and less than 3.0, and stirring and mixing.

[5] In the production method according to any one of [1] to [4] , the chromium concentration of the slag after removing the magnetic deposit after cooling is 0.1% by mass or less. Manufacturing method.
[6] The cement according to any one of [1] to [5] , wherein the slag generated in the steel making process is slag generated in the decarburization process or slag generated in the dephosphorization process. A method for producing raw material slag.
[7] A method for producing slag for a cement raw material, wherein the reducing material is a carbonaceous material in the production method of any one of [1] to [6] .

[8] Production of cement raw material slag according to any one of [1] to [7] , wherein the slag to which the reducing agent is added is agitated and mixed in a rotating cylindrical processing vessel. Method.
[9] In the production method according to any one of [1] to [8 ] above, the slag to which the reducing material is added is stirred and mixed in a treatment container maintained in a reducing atmosphere. A method for producing slag.
[10] In the method for producing Portland cement using a rotary kiln, the cement raw material slag obtained by any one of the production methods [1] to [9] above is charged into the rotary kiln as a part of the cement raw material. And a method for producing Portland cement.
[11] The cement raw material slag obtained by the production method of any one of [1] to [9] is pulverized to a particle size having a specific surface area of 3000 cm ² / g or more, and the pulverized product is mixed with Portland cement. The manufacturing method of the mixed cement characterized by doing.

  In the present invention, the slag temperature refers to the temperature of the “maximum temperature portion of the slag”. The slag temperature is calculated by (i) directly measuring the slag internal temperature with a temperature probe, (ii) calculating from the slag surface temperature measured by a radiation thermometer (for example, molten steel temperature, slag amount, refining during refining) Taking into account factors such as the elapsed time after the completion, the correspondence between the slag surface temperature and the slag internal temperature (the temperature of the maximum temperature portion) is obtained in advance, and is measured by a method such as be able to.

According to the present invention, high-temperature steelmaking slag having a specific slag composition is subjected to a reduction treatment using slag sensible heat in which a reducing material is added and stirred and mixed, whereby chromium is cooled from the cooled slag. Separation and removal can be performed efficiently, thereby realizing low chromization.
In addition, by cooling under a predetermined condition after the reduction treatment, it is possible to obtain a cement raw material slag having a high hydration reactivity, and even when the cooling under the predetermined condition is not performed, Portland cement can be produced without special component adjustment by charging the cement raw material slag into a rotary kiln as part of the cement raw material and firing it.
Moreover, mixed cement can be manufactured by mixing the pulverized material which grind | pulverized the slag for cement raw materials obtained by this invention to the predetermined particle size with Portland cement.

In the method for producing slag for a cement raw material of the present invention, slag containing chromium oxide generated in a steelmaking process, and slag basicity [mass ratio:% CaO /% SiO ₂ ] (hereinafter simply referred to as “basicity”). ) Is 1.5 or more, Fe content is 10 mass% or more, a reducing material is added, and after performing the reduction process which stirs and mixes at slag temperature of 1000 degreeC or more, it cools. In calculating the Fe content here, the iron content present in the oxide is converted to Fe. Moreover, it is preferable that the slag which performs a reduction process by this invention is a slag in a high temperature state by the sensible heat which it has when it generate | occur | produces in a steelmaking process.
In the present invention, preferably, the slag after the reduction treatment is cooled under conditions (cooling rate) such that the ratio of the γ phase in the crystal phase of 2CaO · SiO ₂ is 50% by mass or less.

In the present invention, a cement raw material slag with less chromium can be produced by the following mechanism. That is, when a reducing material is added to steelmaking slag in a high temperature state and stirred and mixed, chromium oxide in the slag reacts with the reducing material and is reduced to metallic chromium. By this reduction, the metallic chromium is separated from the slag into fine particles, but since the metallic chromium is fine and small in amount, it is difficult to take out (separate and remove) from the cooled slag. On the other hand, in the present invention, the Fe content of the slag is set to a predetermined amount or more, and a reducing material is added to the slag and stirring is performed at a high temperature. Thus, metallic iron and metallic chromium are physically aggregated by the stirring action. For this reason, the metal component containing chromium is in a form that can be easily separated and removed from the slag, and the slag is recovered and removed by magnetic separation after cooling (the granular material containing metal iron and metal chromium aggregated and adhered to it). Chromium can be efficiently removed from
In addition, since unreduced chromium, iron (chromium oxide, iron oxide), and phosphorus (phosphorus oxide) are dissolved in 2CaO.SiO ₂ and 3CaO.SiO ₂ , the crystal phase of slag containing them is hydration-reactive. Is low. In contrast, in the present invention, chromium or iron (chromium oxide, iron oxide) is reduced to a non-solid solution state by reduction treatment, and the cooling conditions after the treatment are optimized to obtain water as a cement raw material. The sum reactivity can be increased.

In the present invention, the slag generated in the steelmaking process to be treated (hereinafter referred to as “steelmaking slag”) may be of any type as long as the steelmaking slag has a basicity of 1.5 or more. Examples include desiliconization slag, dephosphorization slag, desulfurization slag and other hot metal pretreatment slag generated in the treatment process (for example, desiliconization process, dephosphorization process, desulfurization process), decarburization slag generated in the decarburization process, etc. Can do. Of these, decarburized slag and dephosphorized slag are high in iron oxide (FeO, Fe ₂ O ₃ ) content and CaO content, and appropriate amounts of SiO ₂ even if the operation varies to some extent depending on the steel type. Therefore, it is a particularly suitable slag from the viewpoint of both separation of reduced chromium and cementation. If these slags are used, the necessary amount of Fe is usually secured, but if necessary (for example, when the amount of Fe in the slag is insufficient), an Fe source such as metallic iron or iron oxide is added, The amount of Fe in the slag may be increased.
If the basicity of the steelmaking slag is less than 1.5, Ca ₃ Si ₂ O ₇ , CaSiO ₃ , melilite, melvinite and the like are precipitated from the reduced slag, and the activity as a cement raw material cannot be ensured. Even when the cement kiln is charged and refired, it is necessary to add lime, which impairs the economic advantages. From this viewpoint, the basicity of the more preferable steelmaking slag is 2.0 or more.

On the other hand, the basicity of the steelmaking slag is preferably less than 3.5, particularly preferably less than 3.0. Basicity of 3.0 or more, especially of 3.5 or higher, CaO is excessive than _{2CaO · SiO 2, 3CaO · SiO} 2 is the main mineral of a cement. In the case of unreduced steelmaking slag, CaO reacts with FeO and Cr ₂ O ₃ to form a compound and stabilizes it. However, when reduction treatment is performed, FeO and Cr ₂ O ₃ are reduced to become metal, so free-CaO Free CaO called is generated. As a result, it is difficult to ensure volume stability when used as cement. Table 1 shows the results of reducing volume stability of steelmaking slag with different basicity, mixing this with Portland cement at 50:50. The volume stability was evaluated according to the physical test method for cement according to JIS-R-5201. According to Table 1, when the basicity is 3.0 or more, the volume stability tends to decrease, and in 3.5, it is judged that the application method of simply mixing is difficult to apply.

From the points described above, when the basicity of the steelmaking slag is 3 or more, along with the reducing material, the silicon-containing material is added so that the slag basicity is 2.0 or more and less than 3.0, It is preferable to perform a reduction process (stir mixing). As the silicon-containing material, for example, coal ash, silica sand, silica sand powder, glass powder and the like can be used.

  The steel oxide slag preferably has a chromium oxide concentration of 2% by mass or less. Although it is possible to reduce chromium oxide in slag exceeding 2% by mass, when used as a cement raw material, it is necessary to suppress the chromium oxide concentration after the reduction treatment to be low, and the chromium concentration after the reduction treatment Is preferably 0.1% by mass or less. When the chromium concentration is 0.1% by mass or less, even when reheated as a cement raw material, the amount of hexavalent chromium generated can be suppressed to a level causing no environmental problems. When the chromium oxide concentration in the steelmaking slag before the reduction treatment exceeds 2% by mass, it is necessary to carry out the reduction treatment at a higher temperature or for a longer time in order to surely carry out the reaction, resulting in an increase in the processing cost. From this viewpoint, the more preferable chromium oxide concentration of the steelmaking slag is 1.5% by mass or less.

  In addition, the Fe content of the steelmaking slag is 10% by mass or more. When considering only the chemical reaction for removing chromium, it is not necessary to consider the content of Fe and its content, but as described above, in the present invention, iron oxide in slag is reduced by reduction treatment. Is reduced together with chromium oxide, metal iron and metal chromium are physically aggregated by a stirring action, and the metal component containing chromium can be easily separated and removed from the slag (separated and removed by magnetic separation). Therefore, the steelmaking slag needs to contain Fe content (metallic iron, iron oxide). If the Fe content is 10% by mass or more, the chromium content can be stably removed from the slag as the metallic iron on which the metallic chromium is aggregated and adhered by magnetic separation after cooling. In addition, as described above, an iron source such as metallic iron or iron oxide may be added to the steelmaking slag, and the Fe content in the slag is 10% by mass or more including the added Fe source. I just need it.

  In the present invention, a reducing material (reducing material of oxide in the slag) is added to the steelmaking slag as described above, and a reduction treatment is performed in which the slag temperature is 1000 ° C. or higher and stirred. Here, the steelmaking slag is a high-temperature slag generated by a refining process in the steelmaking process. In the present invention, the reduction process is performed by effectively utilizing the sensible heat of such a high-temperature slag. In particular, in order to advance the reduction reaction by effectively using slag sensible heat, it is preferable to add a reducing material to the slag at a stage where the slag temperature is 1200 ° C. or higher, preferably 1300 ° C. or higher. In this way, it is efficient to effectively use the sensible heat of high-temperature slag, but when the slag is lower than this temperature, Joule heat and oxygen supplied from an electric furnace etc. are slightly depleted. It is possible to make up for the shortage by heating the burner.

There are no particular restrictions on the type of reducing material added to steelmaking slag, for example, Fe-Si, Fe-Al, aluminum ash, charcoal (coke, carbon powder, carbon-based dust, charcoal, coal dust, etc.), waste plastic One or more types such as wood can be used, but it is particularly preferable to use a carbonaceous material. By using the carbon material, it is possible to promote the mixing of the slag and the reaction with the reducing material by the generated CO gas while suppressing the decrease in the slag temperature.
The addition amount of the reducing material is not particularly limited, but iron oxide (FeO, Fe ₂ O ₃₎ contained in the steelmaking slag is used in order to ensure that the reduction reaction proceeds and that no excessive reducing material remains. ), About 80 to 120% by mass of the amount of reducing material necessary for reducing the total amount of chromium oxide and phosphorus oxide.

Moreover, in order to effectively advance the reduction reaction of chromium oxide or iron oxide, it is preferable to perform stirring and mixing of slag at 1000 ° C. or more for 5 minutes or more. The reduction of iron oxide is mainly a reduction reaction via CO gas or the like at 1000 ° C. or less, but if it is 1000 ° C. or more, a direct reaction between solids can proceed.
In addition, simply adding a reducing material does not provide sufficient contact between solids and the reaction does not proceed easily. Therefore, the above temperature conditions are insufficient, and an additional amount of heat is required for the reduction reaction to proceed. Although it is necessary to input, if the method of stirring and mixing as in the present invention, sufficient progress of the reaction can be realized. In addition, as described above, by stirring and mixing, reduction proceeds, metal iron and metal chromium are physically aggregated, and the metal component containing chromium is easily separated and removed from the slag (separation removal by magnetic separation). It can be made into a form that can.

There is no particular restriction on the method and means for stirring and mixing the steelmaking slag and the reducing material. Examples include ii) a method in which molten iron, a reducing material, and steelmaking slag are put in an electric furnace and stirring, and (iii) a method in which a rotary kiln type cylindrical processing vessel is used. In particular, in the case of (iii) above, it is easy to control the atmosphere inside the processing vessel, and the steelmaking slag in a semi-molten state and the reducing material can be reliably stirred and mixed at a temperature of 1000 ° C. to 1200 ° C. preferable.
In addition, it is preferable to perform stirring and mixing of the steelmaking slag and the reducing material in a reducing atmosphere. Thereby, progress of reduction by solid-gas reaction and prevention of reoxidation can be achieved. As the reducing atmosphere, an N ₂ or Ar atmosphere is most desirable, but an atmosphere of exhaust gas in which a propane burner is burned under a condition that O ₂ does not become excessive may be used.

FIG. 1 shows an embodiment of the above method (iii). A rotary kiln-type cylindrical processing container 1 includes a cylindrical body 10 that is driven to rotate, and both ends of the cylindrical body 10 are rotatable. The support 11 is provided with a support 11 and 12, and the support 11 is provided with an inlet 2 for the material to be processed, and the support 12 is provided with an outlet 3 for the material to be processed. The cylindrical processing container 1 is inclined downward from the horizontal state toward the outlet 3 side.
In such a cylindrical processing vessel 1, steelmaking slag and reducing material are introduced from the inlet 2 while the cylindrical body 10 is rotating, and the steelmaking slag and reducing material are stirred while moving in the longitudinal direction of the processing vessel. It is mixed and finally taken out from the outlet 3.

Although the steelmaking slag subjected to the reduction treatment by stirring and mixing as described above is cooled, the ratio of the γ phase in the crystal phase of 2CaO · SiO ₂ after cooling is set so that it can be used as a cement raw material as it is. Cooling is preferably performed under cooling conditions (cooling rate) such that the amount is 50% by mass or less. If the ratio of the γ phase in the 2CaO · SiO ₂ crystal phase after cooling is 50% by mass or less, the cement activity of the slag is ensured and it can be directly used as a cement admixture.

Here, the method for measuring the γ phase of 2CaO · SiO ₂ is not particularly limited, but a typical method includes a calibration / evaluation method by XRD. Here, the β phase and the γ phase have many similar peak positions, but the β phase has a single peak near the crystal lattice spacing of 2.28, and the γ phase has a single peak near 4.35. A calibration curve can be created by performing XRD on the powder whose mixing ratio has been changed in advance, and the ratio of the γ phase can be determined based on the calibration curve.
As a cooling condition of the slag for obtaining the crystal phase as described above, it is preferable to cool the slag temperature from 1000 ° C. or more to an average cooling rate of 10 ° C./min or more, preferably from 15 ° C./min or more to 400 ° C. or less. . When the average cooling rate is low, the above crystal phase is hardly obtained stably, and the cement activity of the slag cannot be sufficiently increased. Moreover, since it becomes difficult to produce the phase transformation of a crystal phase in a temperature range lower than 400 degreeC, arbitrary cooling rates may be sufficient.

Steelmaking slag having a basicity of 2.5 was subjected to reduction treatment under the conditions of the present invention, and then cooled from a temperature of 1000 ° C. or higher to 400 ° C. or lower at various average cooling rates. Then, the 28-day compressive strength of the mixed cement which grind | pulverized to the brane value 4000cm < ² > / g in the ratio of 70 mass% of normal Portland, and 30 mass% of slag was investigated. FIG. 2 shows the relationship between the 28-day compressive strength and the average cooling rate after the reduction treatment. According to this, it can be seen that the strength is greatly improved at an average cooling rate of 10 ° C./min or more, and that a high strength is stably developed especially at 15 ° C./min or more.

There is no special limitation on the method for cooling the slag after the reduction treatment under the above cooling conditions. For example, (b) a method of spraying water on the slag, and (b) a method of cooling by blowing a large amount of air on the slag. (C) A rotatable horizontal cooling drum having a refrigerant passed through it is cooled, and the molten slag comes into contact with the outer peripheral drum surface to be cooled, and the cooled slag is separated from the drum surface and discharged. A method of cooling the slag using the molten slag cooling processing apparatus as described above can be applied.
In the cooling method (a), a large cooling rate can be obtained by the latent heat of vaporization of the sprinkled water. In the cooling method (b), a large amount of air is required, but the cooling rate can be secured while suppressing partial progress of the hydration reaction with water. In the method (c), since the slag is cooled by contacting the drum surface in a relatively thin state, a large cooling rate can be obtained in this case as well, and contact with water can be avoided. Become.

In addition, the cooling method (c) includes, for example, a cooling mode using the following cooling processing apparatus.
(A) A cooling processing apparatus (single-drum cooling processing apparatus) including a single horizontal cooling drum and a rod for supplying molten slag to the horizontal cooling drum.
(B) Cooling provided with a pair of horizontal cooling drums arranged in parallel, each of which has a rotating direction in which opposing outer peripheral portions rotate upward, and molten slag is supplied from above between the upper outer peripheral surfaces of the pair of horizontal cooling drums Processing device (double drum type cooling processing device).
(C) A pair of horizontal cooling drums (rolling rolls) having a rotation direction in which the outer peripheral portions facing each other with a gap are rotated downward are provided between the upper outer peripheral surfaces of the pair of cooling drums. The cooling processing apparatus (rolling roll type cooling processing apparatus) to which the molten slag is supplied from.
In addition, when performing a baking process (usually kiln process) in a post process, the cooling after a reduction process may be what kind of conditions.

  The cooled slag is usually crushed to a size suitable for magnetic separation (magnetic separation). The size of the crushing is not particularly limited, but generally the particle size is about 40 mm or less. Next, the magnetic deposit is recovered and removed by magnetic separation (magnetic separation). The main magnetic deposit recovered and removed is a granular material containing metallic iron and metallic chromium aggregated and adhered thereto. Thereby, chromium can be removed from the slag with high efficiency.

In the present invention, cooling of the slag after the reduction treatment is performed under the specific conditions as described above (cooling conditions in which the ratio of the γ phase in the 2CaO · SiO ₂ crystal phase after cooling is 50% by mass or less). If not, it is preferable to perform a baking treatment (usually a kiln treatment) that is performed when the cement clinker is manufactured in order to enable use as a cement raw material. This calcination treatment may be performed on the slag alone, but it is preferable from the viewpoint of treatment efficiency and quality of the cement raw material that the slag is charged into the rotary kiln as a part of the cement raw material and the cement clinker is fired. That is, when manufacturing Portland cement using a rotary kiln, the slag (slag for cement raw materials) obtained by the present invention is charged into a rotary kiln as a part of the cement raw material and fired. When the cement clinker is fired, it becomes an oxidizing atmosphere, but the slag for cement raw material obtained in the present invention has a low chromium content, so if it is such a slag (use other cement raw material having a high chromium content). The amount of hexavalent chromium generated can be maintained at a low level. That is, Portland cement can be manufactured without special component adjustment by charging the slag for cement raw material obtained in the present invention into a rotary kiln as a part of the cement raw material and firing it.

In the present invention, cooling after the reduction treatment is performed under the specific conditions as described above (cooling conditions in which the ratio of the γ phase in the crystal phase of 2CaO · SiO ₂ after cooling is 50% by mass or less). Since the cement raw material slag is mainly composed of β-2CaO · SiO _2, it becomes a material having delayed hydration activity. Therefore, although it is not as hard as ordinary Portland cement, it has a function that can be used for mass concrete materials that are desired to suppress the heat of the initial hydration reaction, like the medium heat Portland cement and the low heat Portland cement. In this case, the slag for cement raw material can be used as an admixture for cement. That is, a mixed cement can be produced by mixing a pulverized product obtained by pulverizing cement raw material slag obtained by the present invention into a predetermined particle size with Portland cement. Generally, about 20 to 100 parts by mass of cement raw material slag is mixed with 100 parts by mass of Portland cement.

The particle size of the slag for cement raw material is not particularly limited, but considering the use as part of the mixed cement, the particle size is similar to that of ordinary cement raw materials (ordinary Portland cement, granulated blast furnace slag, etc.) well for it to have a stable quality, a specific surface area of 3000 cm ² / g or more, and more preferably it is preferred to 4000 cm ² / g approximately.
In the present invention, chemical analysis in general conforms to JIS-K-0050 (general rules for chemical analysis), and slag component analysis conforms to JIS-M-8205 to JIS-M-8224 (quantitative method for iron ore). Complies with.

Dephosphorization slag (slag basicity: 2.5 or less) and decarburization slag (slag basicity: more than 2.5) were used as steelmaking slag, and cement raw material slag was produced therefrom. Carbon powder was used as the reducing material, and silica sand was used as the silicon-containing material.
Steelmaking slag is melted in an electric furnace, and this slag is put together with a reducing material into a rotary kiln type processing container (stirring and mixing apparatus) as shown in FIG. 1, and further a silicon-containing material is added as required. The mixture was stirred and mixed for reduction treatment. The slag thus reduced was discharged from the processing container, and air was blown into the slag to be solidified by changing the cooling rate. In addition, in the case of the comparative example which does not stir and mix after charging the reducing material, the slag was put in a slag pan, and the reducing material was charged from there and held as it was.
The slag after cooling was crushed to a particle size of 40 mm or less with a jaw crusher, and then magnetically selected with a permanent magnet-type suspended magnetic separator to remove magnetic deposits from the slag.
In Tables 2 and 3, the composition of the steelmaking slag used, the production conditions of the slag for cement raw material, and the ratio of γ phase (ratio of γ-C ₂ S) in the 2CaO · SiO ₂ crystal phase of the slag after cooling are shown. Show.

The obtained cement raw material slag was finely pulverized and then mixed with ordinary Portland cement as an admixture at a mass ratio of 30 mass%. The compressive strength was measured. In addition, the mortar after 28 days was crushed to 2 mm or less, subjected to a dissolution test specified by the Ministry of the Environment Notification No. 46 method, the dissolution amount of hexavalent chromium was measured, and evaluated according to the following criteria. Also, the finely pulverized cement raw material slag is put into a rotary kiln as a part of the cement raw material (ratio in the cement raw material: 30% by mass) and fired, and the obtained cement raw material is subjected to the same elution test as above. The elution amount of hexavalent chromium was measured and evaluated according to the following criteria. The results are shown in Table 4 together with the chromium concentration of the slag after removing the magnetic deposit.
○: Less than 0.03 mg / L Δ: 0.03-0.05 mg / L
X: More than 0.05 mg / L

Explanatory drawing which shows one Embodiment in the case of implementing the reduction | restoration process of this invention using a cylindrical kiln of a rotary kiln type. After reducing steelmaking slag having a slag basicity of 2.5 under the conditions of the present invention, slag obtained by cooling from a temperature of 1000 ° C. or higher to 400 ° C. or lower at various average cooling rates is used. Showing the relationship between the 28-day compressive strength of mixed cement and the average cooling rate after reduction treatment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylindrical processing container 2 Input port 3 Outlet 3
10 Tubular body 11, 12 Support body

Claims (11)

A slag containing chromium oxide generated in a steelmaking process, wherein a slag basicity [mass ratio:% CaO /% SiO ₂ ] is 1.5 or more and a reducing material is added to a slag having an Fe content of 10 mass% or more. Then, after stirring and mixing at a slag temperature of 1000 ° C. or higher, cooling , and removing the magnetic deposit from the slag after cooling , a method for producing a slag for a cement raw material. _2. The method according to claim 1, wherein after the reducing material is added to the slag and stirred and mixed, the cooling is performed so that the ratio of the γ phase in the crystal phase of 2CaO · SiO ₂ after cooling is 50 mass% or less. Of producing slag for cement raw materials.   The method for producing a slag for a cement raw material according to claim 1 or 2, wherein the reducing material is added at a slag temperature of 1200 ° C or higher. Slag basicity has occurred in the steelmaking process: the mass ratio% CaO /% SiO _2] is 3.0 or more slag, together with a reducing material, slag basicity of 2.0 or more, silicon to be less than 3.0 The method for producing a slag for a cement raw material according to any one of claims 1 to 3, wherein the containing material is added and stirred and mixed. The method for producing a slag for a cement raw material according to any one of claims 1 to 4 , wherein the chromium concentration of the slag after removing the magnetic deposit after cooling is 0.1 mass% or less. The method for producing a slag for a cement raw material according to any one of claims 1 to 5 , wherein the slag generated in the steel making process is slag generated in the decarburization process or slag generated in the dephosphorization process. The method for producing a slag for a cement raw material according to any one of claims 1 to 6 , wherein the reducing material is a carbon material. The method for producing a slag for a cement raw material according to any one of claims 1 to 7 , wherein the slag to which the reducing material is added is stirred and mixed in a rotary cylindrical processing container. The method for producing a slag for a cement raw material according to any one of claims 1 to 8 , wherein the slag to which the reducing material is added is stirred and mixed in a treatment container maintained in a reducing atmosphere. In a method for producing Portland cement using a rotary kiln,
A method for producing Portland cement, wherein the cement raw material slag obtained by the production method according to any one of claims 1 to 9 is charged into a rotary kiln as a part of the cement raw material and fired. The cement raw material slag obtained by the production method according to any one of claims 1 to 9 is pulverized to a particle size having a specific surface area of 3000 cm ² / g or more, and the pulverized product is mixed with Portland cement. A method for producing a mixed cement.

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