JP2002068740A - Method for manufacturing anhydrous gypsum for cement composition from gypsum waste material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing anhydrous gypsum suitable as a raw material for cement composition from gypsum waste material. SOLUTION: The method for manufacturing the anhydrous gypsum by calcining the gypsum waste material in a kiln is characterized by manufacturing the anhydrous gypsum containing II anhydrous gypsum of >=80 wt.%, a total of hemihydrate and III anhydrous gypsum of <=5 wt.%, CaO of <=5 wt.% and carbon of <=0.3 wt.% by controlling the calcination temperature to be at 600-1200 deg.C, calcination period to be 10 minutes or longer, charge ratio of the gypsum waste material in the kiln to be <=15 vol.% and oxygen concentration in combustion gas at the inlet of the kiln to be >=5 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering anhydrous gypsum suitable for a cement composition from waste gypsum. Specifically, when firing gypsum waste material in a kiln, the combustion environment in the furnace is controlled so that the content of type II anhydrous gypsum is high, and the total carbon content is significantly lower than that of cement compositions suitable for cement compositions. The present invention relates to a method for producing gypsum.

[0002]

BACKGROUND ART Gypsum board waste can be effectively used as a cement raw material. However, various papers and organic admixtures are used in gypsum board, and gypsum board waste is directly used as a gypsum raw material. Incorporation into cement causes problems such as lowering the manifestation of cement strength
(JP-A-10-36149). Therefore, it is necessary to collect and use gypsum suitable for the raw material of the cement composition from gypsum board waste so as not to cause such a problem.

[0003] Against this background, several methods for recovering gypsum from gypsum board waste have been proposed.
One example is a method in which waste gypsum board is heated to about 300 ° C. to recover hemihydrate gypsum or soluble type III anhydrous gypsum (Japanese Patent Laid-Open No. 06-142633). Another example is a method of recovering mainly type II anhydrous gypsum by firing waste gypsum board at a higher heating temperature (Japanese Patent Laid-Open No. 10-36149).

[0004]

However, in the former method, since the firing temperature is low, the paper and organic admixture contained in the waste gypsum board easily carbonize and remain, and are suitable as gypsum for cement compositions. Absent. On the other hand, the latter method is based on the proposal of the present applicant, and paper and organic admixtures are burned and vaporized to burn the gypsum board waste material at a higher temperature, and the cement composition is removed from the burned material. A type II anhydrous gypsum suitable for water can be recovered. However, in the actual operation using a rotary kiln, even if firing at a sufficient temperature and time, carbides (inorganic carbon) may remain without being sufficiently removed due to differences in the amount of paper contained in the waste material. For a while. Therefore, it is not always easy to collect the type II anhydrous gypsum suitable for the cement composition simply by controlling the heating temperature and time.

More specifically, for example, when gypsum waste is fired at a temperature higher than 1200 ° C. in order to promote the removal of inorganic carbon, type I anhydrous gypsum or calcium oxide (quick lime: CaO)
Is generated. Type I anhydrous gypsum has little effect on adjusting the setting time of the cement, and if the amount of CaO is large, it adversely affects the setting and strength development of the cement. Therefore, it is not preferable to increase these amounts. On the other hand, even if the firing temperature is lower than 1200 ° C., if the combustion environment in the kiln is not appropriate, local overheating or insufficient combustion occurs and carbon remains, and in this case, it is possible to collect gypsum suitable for the cement composition. Can not.

[0006]

The present invention is a further improved method for recovering type II anhydrous gypsum from waste gypsum waste previously proposed. In the case of firing gypsum waste using a rotary kiln, the method is simply performed in a kiln. Not only by controlling the temperature and residence time of the gypsum, but also by controlling the filling rate of the gypsum waste material in the kiln and the oxygen concentration in the combustion gas, more desirably a lifter is provided in the furnace, making it suitable for papers and organic admixtures. It is intended to stably produce anhydrous gypsum suitable for cement raw materials by preparing a suitable combustion environment.

That is, the present invention relates to a method for producing anhydrite having the following constitution. (1) In a method for producing anhydrous gypsum by calcining waste gypsum in a kiln, a calcining temperature of 600 to 1200 is used.
℃, firing time 10 minutes or more, filling rate of gypsum waste material in the kiln 15 volume% or less, oxygen concentration in combustion gas at kiln inlet 5 volume%
By controlling as described above, the content of type II anhydrous gypsum is 80
5% by weight or more, total content of hemihydrate gypsum and type III anhydrous gypsum 5
A method for producing an anhydrous gypsum having a content of not more than 5% by weight, a content of not more than 5% by weight of CaO, and a content of not more than 0.3% by weight of carbon from waste gypsum. (2) Anhydrite having a content of type II anhydrous gypsum of 90% by weight or more, a total amount of hemihydrate gypsum, type III anhydrous gypsum and CaO of 5% by weight or less, and a carbon content of 0.2% by weight or less is gypsum The method according to the above (1), which is manufactured from waste materials. (3) The carbon content and the CaO content are reduced by providing a lifter in the kiln and firing.
Or the manufacturing method of (2).

[0008] The anhydrous gypsum obtained by the present invention is II
Contains 80% by weight or more, preferably 90% by weight or more, of anhydrous gypsum, and organic carbon such as organic admixture and paper contained in gypsum waste material sufficiently burns, so that substantially no organic carbon remains and combustion Since the gasified carbon is removed outside the system, the amount of inorganic carbon is also significantly reduced, and the carbon content is 0.3% by weight.
The content is preferably 0.2% by weight or less, and is suitable as a raw material for building materials and civil engineering materials. In particular, there is an advantage that the strength is not reduced even when blended in the cement composition.
Also, air entrainers (AE agents) are generally added to entrain air into concrete, but inorganic carbon adsorbs air entrainers, as does unburned carbon in fly ash. It impedes air entrainment to concrete. However, since the anhydrous gypsum obtained by the present invention has an extremely small amount of inorganic carbon, there is an advantage that the performance of the air entraining agent is not impaired even when mixed with concrete.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. The present invention relates to a method for producing (recovering) anhydrous gypsum by calcining waste gypsum in a kiln, and to a method for producing anhydrous gypsum suitable for a cement composition by controlling a calcination environment. In particular,
By controlling the firing temperature to 600 to 1200 ° C., the firing time to 10 minutes or more, the filling rate of the gypsum waste material in the kiln to 15% by volume or less, and the oxygen concentration in the combustion gas at the kiln inlet to 5% by volume or more,
More than 80% by weight of type II anhydrous gypsum, hemihydrate gypsum and III
A method for producing an anhydrous gypsum having a total content of anhydrous gypsum of 5% by weight or less, a content of CaO of 5% by weight or less, and a carbon content of 0.3% by weight or less from waste gypsum, Preferably, the carbon content and the CaO content are further reduced, and the content of type II anhydrous gypsum is 90% by weight or more,
Total content of hemihydrate gypsum, type III anhydrous gypsum and CaO 5
This is a method for producing anhydrous gypsum having a carbon content of 0.2% by weight or less from gypsum waste material.

In the present invention, gypsum waste refers to waste mainly composed of gypsum, and includes gypsum board waste and other gypsum product waste. In particular, gypsum board waste materials with a large amount of generation are exemplified, and the generation place and the form of the gypsum waste materials are not limited. It may be one having a gypsum board base paper or a cosmetic material such as vinyl chloride resin, or may be a plate-like, lump-like, or powder-like one. Further, the form and the water content of the gypsum contained in the gypsum waste material are not limited, and may be made of gypsum dihydrate, gypsum hemihydrate or anhydrous gypsum or a mixture thereof.

In the present invention, the anhydrous gypsum means a type mainly containing anhydrous type II gypsum, and a small amount of hemihydrate gypsum or Ca
It may contain O, ash, charcoal and the like. The production method of the present invention, the content of type II anhydrous gypsum is 80% by weight or more,
Total content of hemihydrate gypsum and type III anhydrous gypsum of 5% by weight or less,
CaO content of 5% by weight or less, and carbon content of 0.3
A method for producing an anhydrous gypsum of less than 5% by weight from gypsum waste material, preferably a content of type II anhydrous gypsum of 90% by weight or more, a total content of hemihydrate gypsum and type III anhydrous gypsum and CaO of 5% by weight or less, And a method for producing anhydrous gypsum having a carbon content of 0.2% by weight or less from waste gypsum. In addition,
This carbon content is obtained by heating anhydrous gypsum at 1250 ° C. for 2 minutes, converting the value obtained by quantifying the generated carbon dioxide by an infrared absorption method into the amount of carbon (C), and measuring the amount of carbon (C). In the weight of the anhydrous gypsum used in the above is shown in% by weight, and is a reduced amount of the total of organic carbon and inorganic carbon.

[0012] The type II anhydrous gypsum, when incorporated into a cement composition such as mortar or concrete, effectively acts to prevent flashing. On the other hand, if the amount of hemihydrate gypsum or type III anhydrous gypsum is large, false setting is likely to occur. In addition, when the content of CaO is large, the setting time (initial and final) is likely to be shortened, the strength of organic carbon is reduced, and the inorganic carbon adsorbs an admixture for concrete such as an AE agent and a water reducing agent. As a result, the air content and the fluidity of the concrete are reduced. Type I anhydrous gypsum has almost no setting effect. Therefore, in the present invention, the content of type II anhydrous gypsum is 80% by weight or more, the total content of hemihydrate gypsum and type III anhydrous gypsum is 5% by weight or less,
The content of CaO is set to 5% by weight or less, and the content of carbon is set to 0.3% by weight or less. Preferably, the content of type II anhydrous gypsum is 90% by weight or more, the total content of hemihydrate gypsum, type III anhydrous gypsum and CaO is 5% by weight or less, and the carbon content is 0.2% by weight or less.

According to the production method of the present invention, when calcining waste gypsum using a kiln or the like to produce anhydrous gypsum, the calcining temperature is 600 to 1200 ° C. and the calcining time (residence time in the kiln) is 10 minutes or more. This is a method for producing anhydrous gypsum having the above composition by controlling the gypsum waste material filling rate in the kiln to 15 vol% or less and the oxygen concentration in the combustion gas at the kiln inlet (kiln tail) to 5 vol% or more.

If the firing temperature in the furnace is lower than 600 ° C., even if the firing time is extended, the waste gypsum will be insufficiently fired, making it difficult to reduce the carbon content of the anhydrous gypsum to 0.3% by weight or less. If the sintering temperature is higher than 1200 ° C., the carbon content is 0.1.
Although it is reduced to 3% or less, on the other hand, gypsum is thermally decomposed to generate sulfur trioxide (SO ₃ ) and quicklime (CaO), and a transition from type II anhydrous gypsum to type I anhydrous gypsum is preferable. Absent. In the range of the firing temperature, when operating at the upper firing temperature, the firing time should be as short as possible within the above range, and when operating at the lower firing temperature, the firing time should be increased. desirable.

The firing time (residence time in the kiln) is preferably 10 minutes or more. If the firing time is less than 10 minutes, the firing of the gypsum waste material becomes insufficient even when the firing temperature is within the above range, the base paper and the organic admixture contained in the gypsum board waste material and the like do not completely burn, and this carbon content is anhydrous. It remains in the gypsum and has a carbon content above 0.3% by weight. Further, hemihydrate gypsum and type III anhydrous gypsum may remain.

Further, in order to stably recover the anhydrous gypsum having the above composition in the actual operation using the kiln, it is necessary to not only control the kiln temperature and the firing time but also to sufficiently remove carbon from the system. It is necessary to prepare a firing environment so as to increase the content of type II anhydrous gypsum. That is, it is preferable to control the gypsum waste material filling rate in the kiln to 15% by volume or less and the oxygen concentration in the combustion gas at the kiln inlet (kiln tail) to 5% by volume or more. If the gypsum waste material filling rate in the kiln is more than 15% by volume and the oxygen concentration in the combustion gas is less than 5% by volume, the combustion of the gypsum waste material becomes insufficient, and the carbon content of the anhydrous gypsum is 0.3 weight. %. On the other hand, by controlling the firing temperature and time, the filling rate of the gypsum waste material in the kiln, and the oxygen concentration in the combustion gas within the range of the present invention, the carbon content of the anhydrous gypsum is 0.3% by weight or less, preferably It can be reduced to 0.2% by weight or less. Incidentally, as shown in the Examples below, those fired under the firing conditions of the present invention (No. 3, 6,
11,14,17,20,23,26), the carbon content contained in the recovered anhydrite was less than 0.3% by weight, and some (No.
0,23,26) has a carbon content of not more than 0.2% by weight.

Further, in order to reduce the carbon content of the anhydrous gypsum, it is necessary to promote the burning of paper and combustibles and the removal of inorganic carbon contained in gypsum waste material. It must be removed outside the system. Therefore, it is preferable to provide a lifter on the inner wall of the kiln and sufficiently agitate the waste gypsum in the furnace by rotating the kiln to increase the permeability of combustion gas and carbon dioxide to the waste gypsum in the furnace. As a result, the combustion gas is supplied to the entire gypsum waste material and uniformly burned, and the carbon source is gasified and removed out of the system, so that the carbon content of the anhydrous gypsum can be significantly reduced. Further, by providing a lifter in the furnace to promote agitation of the gypsum waste material, the carbon content of the anhydrous gypsum can be reduced even when firing at a lower temperature than in the case where no lifter is provided. Therefore, by-products of CaO due to high-temperature calcination are less, and anhydrous gypsums suitable for cement compositions can be obtained.

The anhydrous gypsum of the present invention obtained as described above is suitable as a raw material for anhydrous gypsum to be added to the cement composition. Here, the cement composition refers to a hydraulic composition mainly composed of cement, for example, mixed cement such as ordinary Portland cement, early-strength cement, low heat cement, fly ash cement, blast furnace cement, and Irwin (3CaO3).・ 3Al ₂ O ₃・ CaSO ₄ ) -based cement, calcium fluoroaluminate (11CaO ・ 7Al ₂ O ₃・ CaF ₂ ) -based cement, expanded cement, etc., mainly as a solidifying material, injection material, backing material, ground improvement material Including those used for various applications. The anhydrous gypsum of the present invention is suitable as an anhydrous gypsum raw material to be added to a cement composition used for such mortar, concrete and the like.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples. In addition, these are illustrations and do not limit the scope of the present invention.

Example 1 Waste gypsum board (thickness 21 mm, paper content 7 to 25 wt%) was coarsely crushed by a roll crusher and sieved to a diameter of 100 mm or less using a vibrating sieve. The crushed material of the gypsum board waste material (adhered to the base paper) is
(1.3 m in diameter, 20 m in length) and fired under the conditions shown in Table 1. The form of the obtained anhydrous gypsum is identified and quantified by powder X-ray diffraction, and the content of CaO is subjected to a standard test (CAJS I
01: Cement Institute Standard Test Method). Further, the carbon content was measured by a carbon analyzer. The results are summarized in Table 1.

At a calcination temperature of 500 ° C., even if the oxygen concentration in the furnace and the filling ratio of the gypsum waste material are adjusted to appropriate ranges, the carbon content of the recovered anhydrous gypsum is independent of the paper amount of the gypsum waste material and the calcination time. The amount is greater than 0.3% by weight (Nos. 1, 2). Further, when the firing temperature is 600 ° C., when the gypsum waste material having a large amount of paper is used, the carbon content of the material controlled at a filling rate of 15% by volume or less and an oxygen concentration of 5% by volume or more is 0.1%.
It could be 3% by weight or less (Nos. 3, 6). in this case,
There was no significant effect even if the firing time was lengthened (No. 10).
When the firing temperature rises to 700 ° C. to 1000 ° C., the carbon content contained in the anhydrous gypsum gradually decreases, but the same tendency is observed for the oxygen concentration in the furnace and the gypsum waste material filling rate. Those with a high filling ratio of gypsum waste material have a carbon content exceeding 0.3% by weight (No. 12, 13, 15, 16, 18, 18,
19,21,22).

At a firing temperature of 1100 ° C., the carbon content of the anhydrous gypsum is reduced to 0.3% by weight or less even if the oxygen concentration is relatively low, but if the firing time is longer than 15 minutes,
The amount of type II anhydrous gypsum decreases and the amount of CaO increases (No. 2
Four). When the firing temperature is 1250 ° C., the carbon content is 0.1.
Although it is reduced to 3% by weight or less, the amount of type II anhydrous gypsum decreases and the amount of CaO increases even when the calcination time is 10 minutes (No. 29).
If the firing time is less than 10 minutes in the kiln firing, stable operation is extremely difficult. From the above, the content of type II anhydrous gypsum is 80% by weight or more, the total content of hemihydrate gypsum and the type III anhydrous gypsum is 5% by weight or less, the content of CaO is 5% by weight or less, and the carbon content is 0.3. In order to obtain an anhydrous gypsum having a weight percentage of not more than 1, a firing temperature of 600 to 1200 ° C., a filling ratio of gypsum waste material of 15% by volume or less, and an oxygen concentration of combustion gas of 5% by volume or more are suitable (No. 3). , 6,11,14,17,20,
23,26).

[0023]

[Table 1]

[Embodiment 2] As shown in FIG.
The lifter 2 was attached to the kiln 1 used in the above, and the waste gypsum was fired under the same conditions as in Example 1 to collect anhydrous gypsum. The results are shown in Table 2 (lifter distance 4
m). Table 2 shows the results of Example 1 in which firing conditions were almost the same except for the presence or absence of a lifter (No. 41).
No.6 for No.42, No.3 for No.42, No.1 for No.43
0). As shown in this example, the carbon content contained in the recovered anhydrous gypsum is relatively low when the lifter is installed to increase the agitation of the waste gypsum in the kiln. From this, by providing a lifter to the kiln, there is no problem such as decomposition of gypsum, a sufficient calcining effect is obtained even when calcined at a lower temperature, and the carbon content contained in anhydrous gypsum is efficiently reduced. Instead, it can be reduced.

[0025]

[Table 2]

Example 3 The anhydrous gypsum obtained in Example 1 (N
o.9,11,14,17,20,28) is mixed with the ordinary Portland cement clinker (grain size 1.2 mm or less) so that the SO ₃ content in the cement is 2.0% by weight. Was ground with a ball mill to a Blaine specific surface area of 3250 cm ² / g to produce a cement. For comparison, a cement was produced in the same manner as described above, using natural dihydrate gypsum alone (hereinafter, standard gypsum). Using these cements, concrete was kneaded with the indicated composition shown in Table 3 and various concrete tests were performed. Table 4 shows the results. During the preparation of the concrete, 0.02% of an air regulator (AE auxiliary agent: Pozzolith 303A, a product of NMB) was dissolved in the kneading water and added to the cement. Slump, air volume, coagulation and strength tests are based on standards (JISA1101, JIS A1116, JIS A6204, J
IS A1108).

[0027]

[Table 3]

[0028]

[Table 4]

As shown in Table 4, concrete prepared using cement mixed with anhydrous gypsum (No. 11, 14, 17, 20) having the composition range of the present invention is natural gypsum (standard gypsum).
The test results were almost the same as those in the case of using the cement using the gypsum, and had a sufficient effect as a gypsum raw material for cement. On the other hand, the concrete prepared using a cement containing a low anhydrous gypsum containing the type II anhydrous gypsum and having a high CaO content of anhydrous gypsum (No. 28) has significantly reduced both the initial setting and the final setting time, Low compressive strength. In addition, in concrete using anhydrite with a high carbon content (No. 9), it is not possible to secure a sufficient amount of air in spite of the addition of a predetermined air amount regulator, which is desirable as anhydrite for cement. It turns out there is no. The amount of air is regulated according to the purpose of securing the freeze-thaw resistance of concrete.
(JIS A5308) specifies an allowable amount of 4.5 ± 1.5%. Therefore, it is not preferable that the amount of air varies depending on the cement, since it makes it extremely difficult to control the quality of concrete. Also, if the carbon content of the anhydrous gypsum is high, the carbon powder floats on the concrete surface and causes color spots.

Example 4 The anhydrous gypsum obtained in Example 1 (N
o.14) was evaluated for its performance when used as an additive for cement-based solidification materials. Specifically, the anhydrous gypsum is added to ordinary Portland cement clinker so that the amount of SO ₃ in the solidified material becomes 7.5% by weight, and the mixture is pulverized by a ball mill to a Blaine specific surface area of 4500 cm ² / g to obtain a cement system. A solidified material was prepared. This solidified material was used for cohesive soil (water content 87.3% by weight), loam soil (water content 86.4% by weight) and organic soil (water content 87.3% by weight). The test method was as follows: 100 kg of the solidified material was added to 1 m ³ of the solidified material and the target soil, and the mixture was stirred for 5 minutes.
(Height: 10 cm), molded, and subjected to a uniaxial compression strength test in accordance with the standard (JIS A 1216). The results are shown in Table 5. As is clear from the results, when anhydrous gypsum belonging to the range of the composition of the present invention is used as an additive of the solidifying material, it is almost equivalent to the case where standard gypsum is used for any target soil. , Indicating that it can be sufficiently used as an additive for a solidifying material.

[0031]

[Table 5]

[0032]

According to the production method of the present invention, using gypsum waste as a raw material, the content of type II anhydrous gypsum is 80% by weight or more, the total content of hemihydrate gypsum and type III anhydrous gypsum is 5% by weight or less,
Anhydroplasters having an aO content of 5% by weight or less and a carbon content of 0.3% by weight or less, preferably 90% by weight or more of type II anhydrous gypsum, hemihydrate gypsum, type III anhydrous gypsum and CaO Anhydroplasters having a total content of 5% by weight or less and a carbon content of 0.2% by weight or less can be obtained. This anhydrous gypsum has significantly reduced total content of hemihydrate gypsum and type III anhydrous gypsum, CaO content and carbon content,
It is suitable as a gypsum raw material for a cement composition. Further, according to the present invention, an effective method for treating gypsum waste material is provided, and the effective use of gypsum waste material can also be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an installed state of a lifter according to a second embodiment.

[Explanation of symbols]

 1-kiln, 2-lifter

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G012 MB12 4G076 AA14 AB08 BA38 BD02 BD06 BH01 CA29 CA36 DA30

Claims (3)

[Claims] 1. A method for producing anhydrous gypsum by calcining waste gypsum in a kiln, wherein the calcining temperature is 600 to
By controlling the temperature at 1200 ° C., the firing time at least 10 minutes, the filling rate of the gypsum waste material in the kiln at 15% by volume or less, and the oxygen concentration in the combustion gas at the kiln inlet at 5% by volume or more, the content of type II anhydrous gypsum is 80% by weight. As described above, anhydrous gypsum having a total content of hemihydrate gypsum and type III anhydrous gypsum of 5% by weight or less, a CaO content of 5% by weight or less, and a carbon content of 0.3% by weight or less is produced from waste gypsum. And how. 2. A type II anhydrous gypsum content of at least 90% by weight;
Total content of hemihydrate gypsum, type III anhydrous gypsum and CaO 5
2. The method of claim 1 wherein an anhydrous gypsum having a carbon content of 0.2% by weight or less and a carbon content of 0.2% by weight or less are produced from waste gypsum. 3. The method according to claim 1, wherein a carbon content and a CaO content are reduced by providing a lifter in the kiln and firing the kiln.