JPH0632676A - Light porous aggregate and its production - Google Patents

Abstract

PURPOSE:To produce light porous aggregate free from environmental pollution and excellent in strength, water permeability and water retention while effectively utilizing resources by blending a prescribed sludge with bentonite sludge, kneading the resultant mixture and then calcining it for generation of carbonic acid gas. CONSTITUTION:A sludge generated when digging limestone is coagulated, precipitated and subsequently dehydrated so as to obtain a limestone-containing dehydrated sludge (A) exhibiting 20 to 40wt.% water content and containing SiO2, Al2O3, FeO, etc., in addition to limestone. The resultant (A) component is then blended with a bentonite sludge (B) composed mainly of montmorillonite, etc., and exhibiting 70 to 90wt.% water content in a weight ratio of (A):(B)=1:(0.1 to 0.2) on solid matter base so as to obtain a mixture (C). To the component (C), as necessary, a foaming agent (D) such as sodium bicarbonate is added in an amount of 0.03 to 0.7wt.% based on the solid matter of the component (A) and the resultant mixture is kneaded, formed and subsequently calcined at 900 to 1200 deg.C, thus producing the objective light porous aggregate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a sludge generated in limestone mining and industrial processes and a lightweight aggregate made of sludge generated from a construction site by a bentonite method and the like, and a method for producing the same. Holds uniform pores,
The present invention relates to a porous lightweight aggregate having excellent strength, water permeability and water retention and capable of effectively utilizing resources, and a method for producing the same. INDUSTRIAL APPLICABILITY The present invention is widely used as a building material, soil improvement material for agriculture, golf course, greenhouse cultivation, landscaping, water purifying agent, and the like.

[0002]

2. Description of the Related Art Generally, in the lime industry, calcium carbonate, slaked lime or quick lime is produced from mined limestone (CaCO ₃ ) and dolomite rock (MgCO ₃ ) through steps such as washing with water, crushing, classification and calcination. . The sludge generated in such a lime industry has a high water content generated in the limestone washing step, and as a general treatment method thereof, the sludge coagulated and sedimented by a thickener is dehydrated by dehydration with a filter press or the like. It is landfilled as cake. Bentonite sludge is an excess sludge mainly used to protect the side walls of foundation piles by taking advantage of the high swelling properties of bentonite, which is sludge mixed with mud and has a high water content. Is. As a method for treating this sludge, it is dried with quick lime or cement, and then landfilled after drying. On the other hand, as a method of producing a porous lightweight aggregate, a method of mixing a carbon component during firing and burning the carbon component is known.

[0003]

However, although the above dehydrated sludge has a self-hardening property and appears to be solidified when dried, once it comes into contact with water, it is decomposed by water to give a red mud, which is landfilled. Environmental damage such as polluting the surrounding area. Further, the bentonite sludge that has been dried and solidified also decomposes and becomes sludge-like when it comes into contact with water, and there is a similar problem of environmental pollution. Therefore, an effective treatment method for this sludge has been demanded. Further, in the case of the above-mentioned landfill disposal, since useful resources are discarded, it is not possible to effectively utilize the resources, and the disposal time and labor are great. Furthermore, in the above-mentioned conventional method for producing a lightweight aggregate, when firing is insufficient, the porosity is insufficient, and it is difficult to produce a stable and homogeneous aggregate, and the aggregate itself Also affects the strength of.

The present invention solves the above problems and is a porous lightweight bone that does not pollute the environment, is excellent in strength, water permeability, water retention, etc. and can effectively utilize resources. An object is to provide a material and a manufacturing method thereof.

[0005]

Means for Solving the Problems The inventors of the present invention have earnestly studied a method for producing a lightweight aggregate using limestone mining sludge as a raw material. As a result, bentonite or a foaming agent was mixed and kneaded to burn the sludge. However, the present invention has been completed based on the finding that a porous lightweight aggregate having excellent strength and little change in strength can be produced. That is, the method for producing the porous lightweight aggregate of the present invention is to coagulate and precipitate sludge generated when limestone is mined, and then mix limestone-containing dehydrated sludge and bentonite sludge obtained by dewatering, kneading, then, It is characterized by firing to generate carbon dioxide gas.

[0006] Usually, this "limestone-containing dehydrated sludge" usually has a water content of 20 to 40 (particularly 30)% by weight, in which SiO ₂ and Al ₂ are contained as components other than limestone.
Components such as O ₃ , FeO, MgO, and Na ₂ O are contained alone or in a combined form, and the amount of these other components varies depending on the type of sludge. The "bentonite sludge" may be any sludge containing montmorillonite as a main component, and is not limited to those generated in the civil engineering industry, and may be those generated in the pigment manufacturing process or the like,
Further, the bentonite thus produced may be dispersed in water or the like and can be widely adopted. Furthermore, as this sludge, what is usually settled and concentrated, or dehydrated or dehydrated dehydrated sludge (or concentrated sludge) is used. Usually, the water content of this sludge is 70 to 90 (particularly 85)% by weight. The mixing ratio of the limestone-containing dehydrated sludge and bentonite sludge is
Usually, it is 1: [0.2 or less (especially 0.1
.About.0.2)]. Bentonite sludge is 0.2
If it exceeds the above range, the mechanical strength is lowered and becomes brittle, and if it is less, the mechanical strength is improved, but the bentonite sludge, which is difficult to treat, cannot be effectively utilized, which is not preferable.

As shown in the second invention, a foaming agent can be further added to the raw material of the first invention. As the "foaming agent", a material that generates a predetermined gas by heating or a surfactant can be used. As the former, there is no particular limitation on the type of generated gas, foaming temperature, etc., for example, a gas such as carbon dioxide gas, nitrogen, ammonia gas, water vapor, etc. when heated, specifically, carbon dioxide. Examples include sodium hydrogen, ammonium carbonate, azide compounds and the like. The latter surfactant also has a function of foaming the entire mixture by mechanical stirring, and can be sufficiently utilized as a foaming agent. This foaming agent is 0.03 to 0.7 parts by weight (hereinafter, simply referred to as "parts.", More preferably 0.05 parts) with respect to 100 parts by weight of the solid content of the dehydrated sludge.
˜1.0 part) is preferably added. This is 0.0
If it is less than 3 parts, it is difficult to obtain a sufficient foaming effect.
If it exceeds 0.7 parts, the strength tends to decrease, which is not preferable. Further, as in the third invention, the bentonite sludge in the second invention may be manufactured in the same manner without using it.

The porous lightweight aggregate according to the fourth invention is an oxide thereof containing at least calcium, silicon, aluminum, iron, magnesium and sodium.
It is manufactured by firing limestone-containing sludge and bentonite sludge, and is characterized by having a water permeable structure, and can be manufactured by the first and second inventions. At the time of the above "firing", it is usually granulated or molded into a predetermined shape, and then,
Dry (natural drying or preliminary drying). The firing temperature is usually 900 to 1200 ° C, and practically about 1100 ° C is sufficient.

[0009]

In this production method, since calcium carbonate is contained in the dehydrated sludge containing limestone, carbon dioxide gas is generated during firing, which makes the fired product porous and has a water-permeable structure (open cell structure). Also, in this sludge,
As other components, SiO ₂ , Al ₂ O ₃ , FeO, MgO,
CaO, Na ₂ O and the like are contained alone or in a combined form. Further, the mixed bentonite sludge contains a large amount of montmorillonite whose main component is silica-alumina. Therefore, these silica and alumina components are melted by firing, united and sintered to form a strong bond. Therefore, unlike the case where only limestone (or substantially limestone) is heated and calcined, solid strength can be maintained without being dissolved even when contacted with water.

When a foaming agent is further added to the raw material of the first invention (particularly in the case of a water-soluble inorganic substance), this is easily dissolved or dispersed in sludge (water). Therefore, this foaming agent generates a predetermined gas by heating, and this gas is added to the carbon dioxide gas generated by the decomposition of calcium carbonate, so that a more uniform foamed porous body can be manufactured. Furthermore, when a surfactant is used, the foam generated by mechanically stirring the mixture is stabilized, and each raw material component is dispersed more uniformly, so that a more uniform foamed porous body can be produced in this case as well. .

[0011]

EXAMPLES The present invention will be specifically described below with reference to examples. (1) Preparation of test piece Example 1 A dehydrated cake of lime sludge and bentonite sludge were mixed in equal proportions by weight, and 3 g of sodium alkylbenzenesulfonate was added to 10 kg of the kneaded mixture, and a forced biaxial mixer ( Product name: “Sludge mixer”, manufactured by Nippon Evatry Co., Ltd. was used for further kneading. The dehydrated cake of this lime sludge has a water content of 30% (solid content in the dehydrated cake;
3.5 kg). In terms of oxide composition, this solid content contains CaO, MgO, SiO ₂ , Al ₂ O ₃ , iron oxide and the like. Bentonite sludge has a water content of 85.
% (Solid content in this sludge; 750 g), this solid content is mainly composed of silica-alumina, and the content ratio of each composition component is SiO ₂ ; about 70 to 71%, Al
₂ O ₃ ; about 17%, Fe ₂ O ₃ ; about 3-4%, Na
₂ O: about 4%, and CaO + MgO + K ₂ O: about 3%.

A square formwork (4 × 4 × 16 m
It was compacted in m) and naturally dried for 24 hours. Then, this was housed in a firing furnace and fired at 1100 ° C. for 10 minutes to obtain a prismatic porous test piece. When this cut surface was observed with magnifying glass (about 5 times), it was about 0.4-0.6 mm
The bubbles were distributed almost uniformly over the entire surface.

Example 2 A test piece was prepared in the same manner as in Example 1 except that the sodium alkylbenzenesulfonate used in Example 1 was not used. When this test piece was similarly observed with a magnifying glass, it was confirmed that numerous innumerable fine holes (what can be seen as dots) were densely packed. Example 3 A test piece was prepared in the same manner as in Example 1 except that only the dehydrated cake and the surfactant used in Example 1 were used and bentonite sludge was not used. When this test piece was observed in the same manner, as in Example 1, bubbles of about 0.4 to 0.6 mm were uniformly distributed over the entire surface.

Comparative Example The same mixture of the dehydrated sludge containing limestone and the bentonite sludge used in Example 1 was molded into the same shape as in Example 1
A test piece having the same shape was obtained by drying at 0 ° C. When this test piece was observed in the same manner, fine pores (dots) were not observed, and the surface became viscous when touched with water.

(2) Performance test and its evaluation In order to confirm the practicality of each of the above test pieces as a porous lightweight aggregate, the following strength test, water retention test and water permeability test were carried out. Strength Test A uniaxial crush test was performed on the three test pieces of Example 1 described above according to the mortar strength test method (JISK102) to determine the pressure at the time of breaking. The pressure intensity is
75.0 kg / cm ² , 74.5 kg / cm ² , 7
It was found to be 5.0 kg / cm ^2, which is a strength suitable as a lightweight aggregate. When the test piece of Example 2 was also tested in the same manner, the pressure strength was almost the same as above, 75.2 kg / cm ² , 74.9.
kg / cm ^2, it was 75.1kg / cm ^2. still,
In the test piece of the above-mentioned comparative example, when it was left to stand after drying, cracks occurred as it dried. Furthermore, when the test piece of Example 3 was also tested in the same manner, the pressure strength thereof was larger than that of Example 1 (that is, 10).
^{5.0kg / cm 2, 105.5kg / cm} 2, 1
It was 04.0 kg / cm < ² >.

Water retention test The test pieces of the above-mentioned Example 1 were made into granular particles of about 5 mm, and No. 5
0 g was put into a 200 ml graduated cylinder, 150 ml of water was injected, and after soaking for 10 minutes, it was taken out. And
Immediately after being taken out and after being naturally dried at room temperature of 20 ° C. for 48 hours, the change in weight of the test piece was examined. As a result, the test piece immediately after being immersed in water and taken out was 63.0 g (water retention amount: 13.0 g).
g), and 58.5 g after 48 hours. Therefore, it was proved that the amount of evaporation was 4.5 g, which was a very small amount (water retention amount of 8.5 g) within this elapsed time, and that there was sufficient water retention. When the test piece of Example 2 was tested in the same manner, the water retention amount was slightly small, but the evaporation amount was small. That is, the test piece immediately after being taken out was 57.0 g (water retention amount 7.0 g), after 48 hours was 55.0 g, and the evaporation amount was 2.
It was 0 g (water retention amount 5.0 g). This is a bubble (hole)
Is probably too small. Further, when the test piece of the above-mentioned Example 3 was tested in the same manner, it was exactly the same as that of Example 1. That is, the test piece immediately after taking out is 63.0 g.
(Water retention amount 13.0 g), 48 hours later, 58.5 g, and evaporation amount was 4.5 g (water retention amount 8.5 g).

Water Permeability Test The test piece obtained in Example 1 was crushed to 100 mesh or less, 100 g of which was placed in a 200 ml graduated cylinder, and 100 g of water was poured from above to reach the bottom of the graduated cylinder. The time was measured. This arrival time was about 7 seconds, and this test piece was found to have excellent water permeability. Since it has water permeability, it can be said that it has an open cell structure. Further, regarding the test piece of Example 2 described above,
A similar test showed that the size of the hole was about 7-8, even though the hole was small.
It showed almost the same performance as seconds. Further, when the test piece of Example 3 was tested in the same manner, the same result as that of Example 1 was shown for about 7 seconds, and it was similarly shown that the water permeability was excellent.

On the other hand, the test pieces obtained in the above comparative examples were also tested by using a crushed product having a mesh size of 100 mesh or less. As a result, water did not reach the bottom of the graduated cylinder even after 1 hour, and the water permeability was extremely high. It was recognized as low. From the above results, the test pieces of Examples 1 to 3 sufficiently satisfied the characteristics as a lightweight aggregate excellent in strength, water retention and water permeability, as compared with those of Comparative Examples. In particular, Examples 1 and 3
Shows excellent water retention and water permeability, and Example 2 shows excellent mechanical strength. The present invention is not limited to the specific examples described above, and various modifications may be made within the scope of the present invention depending on the purpose and application.

[0019]

INDUSTRIAL APPLICABILITY As described above, the lightweight aggregate produced by the method of the present invention is excellent in mechanical strength, water permeability, and water retention, and therefore can be used as a lightweight general-purpose material. It can be widely used as an improving agent. In addition, the problem of securing a disposal site for sludge and water treatment can be solved at the same time, and moreover, resources can be effectively used, which can contribute to the lime industry as a new production business.

Claims (4)

[Claims] 1. A method of coagulating and sedimenting sludge generated when limestone is mined, and then dehydrating limestone-containing dehydrated sludge and bentonite sludge to be mixed and kneaded, followed by firing to generate carbon dioxide gas. A method for producing a porous lightweight aggregate characterized by: 2. A sludge produced during mining of limestone is coagulated and precipitated, and then dehydrated limestone-containing sludge and bentonite sludge obtained by dehydration are kneaded by adding a foaming agent and then calcined to produce carbon dioxide gas. A method for producing a porous lightweight aggregate, which comprises: 3. A sludge produced during mining of limestone is coagulated and precipitated, and then dehydrated limestone-containing sludge obtained by dehydration is added with a foaming agent and kneaded, followed by firing to generate carbon dioxide gas. A method for producing a porous lightweight aggregate characterized by the following: 4. Calcium, silicon, aluminum, iron,
A porous lightweight aggregate characterized by being an oxide thereof containing at least magnesium and sodium, produced by firing limestone-containing sludge and bentonite sludge, and having a water-permeable structure.