JPH0149657B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a new cement that effectively utilizes coal ash, which is an industrial waste. The present invention relates to a method for producing a special cement that can be used for multiple purposes such as stabilization treatment. In recent years, with the increase in thermal power generation, especially coal-fired power generation, a large amount of coal ash has been produced as a by-product, and most of it is discarded as industrial waste. Some of it is used as is, by mixing it with Portland cement to make fly ash cement, or by baking it with other raw materials to form clinker. However, in the case of the former method, not only is there a large amount of unburned carbon in the coal ash, but due to NOx regulations, an even larger amount of unburned carbon is contained, so when using cement, Problems such as adverse effects on the concrete admixtures that were added remained, and there remained room for improvement. On the other hand, in the case of the latter method, if a large amount of coal ash is used as the clinker raw material, the amount of Al ₂ O ₃ will increase too much, and 3CaO.
Too much Al ₂ O ₃ is present to form a cement with the desired chemical composition. Therefore, in the latter method, only a small amount of coal ash could be used, and it was not a very effective use. The present invention was made in view of the above circumstances, and its purpose is to enable coal ash, which is an industrial waste, to be effectively used as a raw material for cement, and to have various excellent properties and to be able to be used for multiple purposes. It is an object of the present invention to provide a method for producing a special cement having the following advantages. That is, the special feature of the special cement manufacturing method of the present invention is that the coal ash produced during coal combustion is
A crushed mixture of 100 parts by weight of coal stone and 200-400 parts by weight of coal stone is calcined to form a clinker containing 15-25% _3CaO.Al2O3 , and then this clinker and _gypsum are mixed and crushed or separated. It is ground and then mixed to form cement. The present invention will be explained in detail below. First, a pulverized mixture of 100 parts by weight of coal ash produced during coal combustion and 200 to 400 parts by weight of coal stone is formed. The milled mixture can be formed by mixed milling or by separate milling followed by mixing.
The fineness of the mixture is preferably similar to that of ordinary Portland cement, for example a Blaine value of 4500 to 6000 cm ² /g. The amount of coal stone used varies depending on the chemical composition of the coal ash and the purpose of use, but if it is 200 to 400 parts by weight per 100 parts by weight of coal ash, a cement with excellent various properties will be formed. On the other hand, if it is outside the range, the desired cement may not be obtained. by the way,
When forming clinker from coal ash and coal stone, it is best to specify the amount of 3CaO・SiO ₂ (C ₃ S), and when trying to increase the strength, C ₃ S
It is desirable to increase the amount as much as possible. However, in this case, if the coal saturation level (LSR) is 1 or more, free CaO will remain in the fired clinker, making it difficult to fire and reducing the strength, so it is desirable that the LSR value is between 0.97 and 0.98. , it is desirable to adjust the amount of C ₃ S so that it falls within this range. Generally, considering the chemical composition of coal ash, if the amount of C ₃ S in clinker is set at about 50-60%, the amount of C ₃ A is 15-25%, and the amount of 2CaO・SiO ₂ (O ₂ S) is 10%. The amount of 4CaO・Al ₂ O ₃・Fe ₂ O ₃ (C ₄ AF) is around 3 to 7%, and excellent strength and coagulation properties can be obtained by reducing the amount of C ₃ S to about 50 to 60%. It is desirable to specify the following. When the amount of C ₃ A is in the range of 15 to 25%, clinker can be formed using two types of clinker raw materials: coal ash and coal stone. This can be seen from the clinker unit consumption calculation results shown in Tables 1 (a) to (d) below.

【table】

【table】

【table】

[Table] Next, as described above, the pulverized mixture consisting of 100 parts by weight of coal ash and 200 to 400 parts by weight of coal stone was heated to 1,350 parts by weight in a normal cement kiln such as a rotary kiln.
~15~25% by firing at a temperature of about 1430℃
Forms a clinker containing 3CaO.Al ₂ O ₃ (C ₃ A). Thereafter, the calcined clinker is mixed and ground with gypsum, or is separated and ground, and then mixed with gypsum to form cement. By the way, it is desirable that the fineness of the clinker powder is between 4,500 and 7,000 cm ² /g.If it is less than 4,500 cm ² /g, the strength may decrease too much, while if it is greater than 7,000 cm ² /g, it may cause abnormal coagulation such as rapid setting. may occur. Also,
By selecting three types of gypsum to be added, gypsum anhydrite, gypsum hemihydrate, and gypsum dihydrate, depending on the purpose of use, various types of multi-purpose cement can be formed. From the viewpoint of strength, the addition of anhydrite is optimal, and the amount of addition is determined by the formula of Lerch, McCay et al. Y = 0.095X _{1 + 1.6364}
amount%), X ₁ = C ₃ A amount % in clinker), X ₂ = (alkali amount in clinker [Na ₂ O + 0.658K ₂ O]
%) is appropriate, and the amount of SO ₃ is preferably about 3 to 7%. If added in excess of this amount, expansion will occur after curing, which will cause a decrease in strength in mortar strength tests. On the other hand, when using it for special purposes such as heavy metal fixation and soil stabilization, the amount of anhydrite added can be greatly increased to 10 to 35%, and various effects can be achieved by increasing the production amount of ettringite. can be expected. Furthermore, adding approximately 0.5 to 5% of gypsum hemihydrate increases expansion after hardening, which is effective when a consolidation effect is expected. In this way, in the present invention, a large amount of ettringite is produced during use in order to obtain excellent effects such as improving the strength of cement and stabilizing the soil by cement, and the maximum amount of ettringite is determined as described above. The amount of anhydrite is 35% of the total amount. The amount of gypsum (CaSO ₄ ) is expressed as the amount of sulfur trioxide (SO ₃ ) used to indicate the composition of cement in the Japanese Industrial Standards (JIS): 35% x (molecular weight of SO ₃ / molecular weight of CaSO ₄ ) ≒35%×0.588=21%, and the upper limit of the amount of gypsum mixed in the present invention is 21% in terms of the amount of SO ₃ based on the total amount. The upper limit of 35% for the gypsum content, which determines the SO ₃ amount of 21%, is based on clinker containing 15 to 25% of 3CaO/Al ₂ O ₃ , which greatly contributes to early strength, heavy metal fixation, soil stability, etc. It is based on the points that are formed. That is, the gist of the present invention is to effectively utilize coal ash, which is an industrial waste, while basically using a large amount of coal ash as a source of Al ₂ O ₃ and coal stone as a source of CaO. By mixing and firing these materials, it is possible to form a clinker containing a large amount of 3CaO and Al ₂ O ₃ , thereby increasing the production amount of ettringite, which has effects on early strength, fixation of heavy metals, and soil stabilization. The purpose is to do so. However,
The amount of gypsum required to produce the maximum amount of ettringite is naturally determined by the upper limit of 25% of 3CaO・Al ₂ O ₃ , and therefore 3CaO・
Corresponding to the upper limit of Al ₂ O ₃ of 25%, the upper limit of SO ₃ amount is 21%. In other words, the SO ₃ amount of 21% as the maximum gypsum addition amount is
The maximum amount of 3CaO.Al ₂ O ₃ of 25% is the amount necessary and sufficient to react with gypsum to produce ettringite. Furthermore, if the amount of SO ₃ is 21% or more, the amount of gypsum that is greater than the amount of gypsum required for the formation of ettringite will be present, and free gypsum will be generated during cement hydration, resulting in a decrease in strength, etc. The purpose of the invention cannot be achieved. On the other hand, the lower limit of the SO ₃ content is sufficient as long as it can achieve the purpose of the present invention, that is, produce more _ettringite than conventional cement during use. The value that exceeds the value will be accepted. As is well known, the addition of gypsum in conventional cement is for the purpose of setting preparation, and the amount of gypsum added is:
According to the 1979 edition of the Japanese Industrial Standards, the amount of SO ₃ in Portland cement, silica cement, and fly ash cement is 3% or less, and adding more than this is not preferable because it reduces long-term strength. On the other hand, in the present invention, SO ₃
By setting the amount to 3% or more, more ettringite can be generated during cement hydration. In this way, in the present invention, by setting the SO ₃ blending amount to 3% to 21% of the total amount, a large amount of ettringite is generated during use, and this increases the strength of the cement itself. It can have excellent effects such as improving and stabilizing the soil in cement. As explained above, in the present invention, a pulverized mixture of coal ash and coal stone is fired to form clinker containing about 15 to 25% _C3A , and this is mixed with gypsum to form cement. is forming. Cement contains a large amount of C ₃ A, which has a faster hydration rate than other calcium aluminate minerals, and also contains gypsum, which adjusts the setting rate, so when cement is used, it can be used at a moderate hydration rate. It can be hydrated and can be set and hardened at a moderate rate without exhibiting rapid setting phenomenon. In addition, when cement is used, a large amount of ettringite, which is a needle-shaped crystal of calcium sulfoaluminate hydrate, is formed due to the three components of coal ash, coal stone, and gypsum, which causes entanglement phenomena, resulting in a short period of time. Strength is achieved over time. Furthermore, since a large amount of ettringite is produced as described above, the following advantages (a) to (b) can be obtained. (a) A large amount of heavy metals can be replaced and fixed in the crystal structure of ettringite, and heavy metals can be contained in cement hydrate by adsorption, etc., and the synergistic effect of these makes it possible to securely fix heavy metals. Therefore, the cement obtained by the method of the present invention can be used for solidifying and fixing harmful heavy metals. (b) Ettringite can take in 32 molecules of water per mole as water of crystallization, and as the amount of gypsum added increases, the expansion coefficient after hardening increases, producing a consolidation effect. Therefore, when the cement obtained by the method of the present invention is used to stabilize soil such as soft ground with a lot of free water, water is reliably fixed and consolidated by expansion, so the soil is reliably stabilized. Ru. As mentioned above, the cement produced by the method of the present invention can be used for multiple purposes such as solidifying and fixing heavy metals and stabilizing soil. Also,
Not only can cement be efficiently formed from the three components of coal ash, coal stone, and gypsum, but since each component is inexpensive, the cost of cement can also be reduced, resulting in practical effects. In addition, C ₃ A is CaO・Al ₂ O ₃ (CA), among calcium aluminate minerals.
2CaO・Al ₂ O ₃ (C ₂ A), 12CaO・7Al ₂ O ₃ (C ₁₂ A ₇ )
It has the advantage that the amount of minerals produced is the largest for the same amount of Al ₂ O ₃ compared to other methods. EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples. Example 1 A pulverized mixture of 100 parts by weight of coal ash produced during coal combustion and 320 parts by weight of coal stone was calcined in a rotary kiln at 1380°C to form clinker. The clinker obtained had the mineral composition shown in Table 2 below. 10 parts by weight of anhydrite was added to 100 parts by weight of this clinker and mixed and ground to form a cement. The compressive strength of the cement obtained by curing was measured, and the results are shown in Table 2 below (No. 1 clinker).
In Table 2, the results for clinkers No. 2 to No. 7 are the measurement results when the above-mentioned blending ratios were changed as appropriate.

[Table] From Table 2 above, No. 1 obtained by the method of the present invention.
1, No. 2, No. 3, No. 5, and No. 6 cements strengthen quickly at the same rate as ordinary early-strength cement, and also have excellent long-term strength growth. I found out that there was. On the other hand, the amount of SO ₃ is 23%, which is higher than the upper limit of 21% according to the present invention.
Cement No. 4, which has a high amount of SO ₃ , has excellent early strength, but its long-term strength growth is significantly inferior to that of the product of the present invention, and the amount of SO ₃ is 2%.
Cement No. 7, in which the amount of SO ₃ was less than the lower limit of 3% according to the present invention, was significantly inferior in early strength, that is, early strength development, compared to the product according to the present invention. Example 2 Anhydrite and hemihydrate were added to the clinker powder of Sample No. 1 of Example 1 to produce cement with an SO ₃ content of 9.4%. This cement was spread at 10% on loamy soft soil with a moisture content of 52.0%, in which allofene was the major component and other components such as montmorillonite-kaolin group, feldspar, and quartz were present, and then mechanical mixing was performed. The loamy soft ground was stabilized. Then, when we measured the uniaxial compressive strength for two types of thrusts: 24 and 55, the third
The results shown in the table were obtained.

[Table] From Table 3 above, it can be seen that when the cement produced by the method of the present invention is used, soft ground is reliably stabilized. Example 3 The amount of SO ₃ in the clinker of sample No. 1 of Example 1 was 21
% of anhydrite was added to form the cement. This cement was used to solidify inorganic sludge having the properties shown in Table 4 below.

[Table] The moisture content of the inorganic sludge used was 80.5.
It was %. Also, what are T・Hg and T・Cr in the table?
Total−Hg and Total−Cr ⁶⁺ are shown, respectively. After the solidification treatment, an elution test was conducted, and the results shown in Table 5 below were obtained. Furthermore, when the compressive strength of the solidified product was measured, the results shown in Table 6 below were obtained. For comparison, the compressive strengths of solidified products obtained by solidification with ordinary early-strengthening cement are also listed in Table 6 below.

【table】

[Table] From Table 5 above, it can be seen that various heavy metals are reliably solidified and fixed when the cement produced by the method of the present invention is solidified. Also, from Table 6,
It can be seen that a solidified product with sufficiently high compressive strength can be obtained compared to ordinary early-strengthening cement.

Claims (1)

[Claims] 1. A clinker containing 15-25% 3CaO Al ₂ O ₃ is formed by calcining a pulverized mixture of 100 parts by weight of coal ash produced during coal combustion and 200-400 parts by weight of coal stone, and then , to this clinker
Either gypsum is mixed and crushed so that the amount of SO ₃ is between 3% and 21%, or it is separated and crushed and then mixed to produce a large amount of acicular crystal ettringite, which is calcium sulfoaluminate hydrate, when used. A method for the production of special cement, characterized in that it obtains a cement that is formed.