JP2006076825A - Method for utilizing carbon dioxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attempt effective utilization of carbon dioxide for reducing discharge amount of the same. <P>SOLUTION: Magnesium carbonate is prepared from carbon dioxide and a magnesium oxide-containing substance. The magnesium carbonate is utilized as a cement admixture together with silica and a setting retarder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for using carbon dioxide for reducing the amount of carbon dioxide that is one of the global warming gases.

  In recent years, global warming has attracted attention as a serious issue facing humanity. Various methods are being studied for reducing the emission of carbon dioxide, which is one of the global warming gases. Specifically, carbon dioxide is stored in the ocean or underground, or carbon dioxide is fixed to industrial waste or natural minerals.

  Here, as an example of the fixation of carbon dioxide gas to industrial waste, cement fine powder discharged as waste when producing recycled aggregate from concrete waste is mixed with water to form a slurry, and the calcium component in water Is dissolved, and carbon dioxide gas is blown into the slurry to react with the calcium component to obtain calcium carbonate (see Non-Patent Document 1).

  Among the carbon dioxide immobilization methods, ocean storage and underground storage are unclear on the effects of high-concentration carbon dioxide on the natural world and require a long time for verification.

  Furthermore, in any method, simply storing and fixing only costs processing, and if it is not used effectively, incentives are difficult to work. Therefore, a technique that enables effective utilization of carbon dioxide gas by immobilization treatment and provides cost incentives is desired.

  As an industrially effective technology, carbon dioxide is immobilized on industrial waste or natural minerals to produce carbonate, that is, magnesium carbonate, and use it as a cement admixture.

  Examples of application of magnesium carbonate to cement admixtures include magnesium carbonates as setting accelerators, and one or more components α selected from the group consisting of aluminum sulfates, thickeners and water reducing agents, There is a cement admixture containing as an active ingredient (see Patent Document 1).

Japanese Patent No. 3171879 Iizuka et al., "New carbon dioxide fixation process using waste concrete," Chemical Engineering, Vol.28, No.5, (2002)

  The inventor tried to apply the method of Patent Document 1. As a result, there was a problem that the strength was reduced when magnesium carbonate was added.

  In the present invention, when this problem is solved and magnesium carbonate is applied to a cement admixture, it is possible to effectively use as cement construction and civil engineering materials by suppressing the strength reduction, and the fixation rate of carbon dioxide gas. An object of the present invention is to provide a method for immobilizing carbon dioxide gas, which improves the above.

  The outline of the present invention is as follows.

  (1) Cement is 10 to 20% by mass, fine aggregate is 35 to 45% by mass, coarse aggregate is 40 to 55% by mass, and water is added to a total of 100% by mass of cement mixture to produce concrete. In addition, the carbon dioxide gas and the magnesium carbonate produced from the magnesium oxide-containing substance are added in place of 15% by mass or less exceeding 0% by mass of the cement, and 0.3 to 1.2% by mass of the fine aggregate. In addition, silica is added, and 0.05 to 0.15% by mass of a setting retarder is added to the total amount of cement and magnesium carbonate.

  According to the present invention, carbon dioxide, which is a global warming gas, can be used safely and economically. Magnesium carbonate can be effectively used as a cement admixture.

  Hereinafter, the present invention will be described in detail.

  The present invention is a method for effectively using carbon dioxide to reduce the amount of carbon dioxide that is one of the global warming gases. Carbon dioxide gas is contained in various combustion exhaust gases, blast furnace gas, converter gas, and the like. Its content is generally at least 2% by volume.

  As an example of an embodiment of the present invention, first, magnesium carbonate is generated from a gas containing carbon dioxide and a magnesium oxide-containing substance.

  Here, the magnesium oxide-containing substance contains 10% by mass or more of MgO, and examples include serpentinite, olivine, talc, chlorite, asbestos, and ferronickel slag. As a method for producing magnesium carbonate, for example, a blast furnace gas as a gas containing carbon dioxide gas is passed through an ammonia solution, and carbon dioxide gas and ammonia are reacted to obtain an ammonium carbonate solution.

  Further, serpentine as a magnesium-containing substance is brought into contact with a hydrochloric acid solution, and MgO in the serpentine is reacted with hydrochloric acid to obtain a magnesium chloride solution. The magnesium chloride solution and the unreacted portion of serpentinite are separated by filtration.

  Next, the ammonium carbonate solution and the magnesium chloride solution are reacted. Then, magnesium carbonate precipitates and ammonium chloride is generated in the solution. The ammonium chloride solution is sent to a distillation column and separated into hydrochloric acid and ammonia. Magnesium carbonate can be obtained by collecting the solution by filtration.

  Next, this magnesium carbonate is utilized as a cement admixture. That is, ordinary concrete is produced by adding water or water and an admixture to cement, fine aggregate (sand, etc.) and coarse aggregate (andesite, etc.). It is possible to effectively use magnesium carbonate in which carbon dioxide gas is fixed by adding the above magnesium carbonate instead of part, adding silica instead of a part of fine aggregate, and further adding a setting retarder. it can.

  The ratio of the amount of each substance added is 10-20% by mass of cement, 35-45% by mass of fine aggregate, 40-55 of coarse aggregate, when the total of cement, fine aggregate and coarse aggregate is 100% by mass. A preferred range is based on mass%.

  The addition amount of magnesium carbonate is preferably more than 0% by mass and 15% by mass or less with respect to the cement amount. Even if the substitution rate with respect to the cement is small, the carbon dioxide gas fixing effect can be obtained. Therefore, it is sufficient to exceed 0% by mass.

The form of magnesium carbonate, magnesium carbonate (MgCO _3), magnesium positive carbonate _{(MgCO 3 · 3H 2 O)} , basic magnesium carbonate _{{aMgCO 3 · Mg (OH)} 2 · bH 2 O, (a, b) = Any of (3, 3), (4, 4), (1, 3), (4, 5), (4, 8)} may be used.

  The addition amount of silica is preferably replaced with 0.3 to 1.2% by mass with respect to the amount of fine aggregate. If the amount is less than 0.3% by mass, the strength development effect is insufficient, and if it exceeds 1.2% by mass, the filling property is deteriorated and the strength is lowered. As silica, crystalline silica fine powder, amorphous silica fine powder, silica fume and the like can be used.

  The addition amount of the setting retarder is preferably 0.05 to 0.15 mass% with respect to the total amount of cement and magnesium carbonate. If it is less than 0.05% by mass, the setting delay effect is insufficient, and if it exceeds 0.15% by mass, the setting of cement is inhibited. As the setting retarder, gluconate, lignin sulfonate, etc. can be used.

  Examples of the present invention are shown (see Table 3).

  The gas containing carbon dioxide in this example was blast furnace gas. The chemical composition is shown in Table 1. Serpentinite was used as the magnesium-containing material. The chemical composition is shown in Table 2.

  Blast furnace gas was passed through the ammonia solution to absorb the carbon dioxide gas to obtain an ammonium carbonate solution. In addition, you may use the ammonia solution obtained from the low water generated from a coke oven.

  Further, the serpentine was crushed and brought into contact with a hydrochloric acid solution, and MgO in the serpentine and hydrochloric acid were reacted to obtain a magnesium chloride solution. Next, the ammonium carbonate solution and the magnesium chloride solution were reacted. Magnesium carbonate precipitated and ammonium chloride formed in the solution.

The ammonium chloride solution was sent to a distillation column and separated into hydrochloric acid and ammonia. Ammonia was used again to absorb carbon dioxide in the blast furnace gas, and hydrochloric acid was used again to react with serpentine. Magnesium carbonate was recovered by filtration and used as a cement admixture in the proportions shown in Table 3. Here, the magnesium carbonate is MgCO ₃ . As the setting retarder and silica, sodium gluconate and amorphous silica fine powder were used, respectively.

  The compressive strength of the concrete was measured after curing for 28 days. The results are shown in Invention Examples 1 to 7 in Table 3. In Table 3, the water cement ratio was 55%. Here, the water cement ratio is the mass ratio of water to be added when the cement mass is 100.

  On the other hand, the conventional method was confirmed by the following method. Conventional method 1 is a standard test condition in which no admixture or the like is blended. As shown in Patent Document 1, the conventional method 2 effectively uses one or more components α selected from the group consisting of magnesium carbonates and aluminum sulfates, a thickener and a water reducing agent. It relates to a cement admixture as a component. For the conventional methods 1 and 2, the material age 28-day compressive strength was measured. The results are shown in Conventional Methods 1 and 2 in Table 3.

  When the result of Table 3 was seen, regarding the material age 28-day compressive strength, the conventional method was 29 to 34 MPa, and the present invention example was 40 to 57 MPa, and all of them could exhibit higher strength than the conventional method. The comparative examples in Table 3 are cases where the manufacturing conditions are outside the scope of the claims. The comparative example has a slightly lower compressive strength than the inventive example. However, the value is higher than that of the conventional method.

  According to the present invention, as described above, since carbon dioxide, which is a global warming gas, can be used safely and economically, the present invention has a great applicability as a global environmental conservation technology. is there.

Claims (1)

When cement is produced by adding water to a cement mixture of 10 to 20% by mass, fine aggregates of 35 to 45% by mass, and coarse aggregates of 40 to 55% by mass and a total of 100% by mass, Add the carbon dioxide-containing gas and magnesium carbonate produced from the magnesium oxide-containing substance to 0 to 15% by mass over the cement, and replace it with 0.3 to 1.2% by mass of fine aggregate. A method for using carbon dioxide, comprising adding silica and further adding 0.05 to 0.15 mass% of a setting retarder with respect to the total amount of cement and magnesium carbonate.