JPH0623397A - Treatment of calciferous sludge - Google Patents

Abstract

PURPOSE:To reutilize calciferous sludge as water-resistant porous lightweight aggregate without decomposing the same in contact with moisture. CONSTITUTION:The sludge generating in the mining and industrializing process of limestone is dehydrated and a foaming agent is mixed with the dehydrated sludge and the resulting mixture is baked at 900-1200 deg.C. Calcium carbonate contained in the sludge generates carbon dioxide at the time of baking and the baked matter is property made porous.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating sludge generated during the process of mining limestone and its industrialization, and a porous lightweight aggregate obtained by this treatment.

[0002]

2. Description of the Related Art Generally, in the lime industry, mined limestone (CaCO ₃ ) and dolomite rock (CaCO ₃ .MgCO
It is well known to produce calcium carbonate, slaked lime, and quick lime from ₃ ) through steps such as washing with water, crushing, classification, and calcination.

The sludge generated in the lime industry has a high water content mainly generated in the limestone washing process. As a general treatment method, sludge coagulated and precipitated in water is filtered by a press machine. The so-called dehydrated cake was made by and was disposed of.

[0004]

However, although the above dehydrated cake is solidified in a dried state, when it comes into contact with water again, it decomposes into a red sludge, which contaminates the area around the waste treatment plant. It has drawbacks. Therefore, an effective treatment method has been demanded to reuse the sludge.

Therefore, the present invention solves the above-mentioned problems and makes it possible to reuse calcareous sludge as a water-resistant, porous, lightweight aggregate without decomposing even when it comes into contact with moisture. It is an issue.

[0006]

In order to solve the above problems, the present invention employs a means for dehydrating calcareous-containing sludge and then firing it.

The calcined sludge containing calcareous material can be used as a porous lightweight aggregate.

[0008]

In the method for treating calcareous sludge of the present invention, calcium carbonate contained in the sludge itself generates carbon dioxide gas during firing, and the fired product is appropriately made porous.

The porous calcinated product is insolubilized by heat denaturation and becomes an inorganic porous material having excellent mechanical strength, water retention and water permeability, and has particularly suitable physical properties as a lightweight aggregate.

[0010]

Examples Examples of calcareous-containing sludge used in the present invention include those generated when a raw material such as limestone and dolomite is washed with water, or those generated in the step of digesting and separating quicklime after that, particularly Any mud-like substance containing at least calcium carbonate can be widely used without limiting the generation factors and the chemical composition.

The above sludge is dehydrated before firing to enhance its shape-retaining property, and is shaped as necessary. As a method of dehydration,
Pressure dehydration is performed with a filter press or the like, and the water content is preferably 30 to 40%.

Further, in order to obtain a uniform porosity at the time of firing the sludge, a foaming agent may be mixed in advance and preliminarily foamed at a required temperature. The foaming agent is not particularly limited in the kind of the generated gas and the foaming temperature, and for example, CO ₂ , NH ₂ , N ₂ , H ₂ when heated.
Examples thereof include sodium hydrogen carbonate, ammonium carbonate, and azide compounds that generate O gas, and a surfactant such as alkylbenzene sulfonic acid (hereinafter referred to as ABS) may be used.

The term "calcination" as used in the present invention means that calcium carbonate and the like in sludge are thermally decomposed to exceed the decomposition pressure of CO ₂ of 1 atm (so-called calcination), and further, impurities are generated in the ordinary lime industry process. Such as SiO ₂ ,
It means that components such as Al ₂ O ₃ , FeO, MgO, CaO, and Na ₂ O are appropriately melted and consolidated or sintered. As a specific firing temperature, 900 to 1200 ° C, and practically about 1100 ° C, is sufficient.

[Experimental Example] 3 g of ABS as a foaming agent was added to 10 kg of a dehydrated cake obtained by pressurizing and dehydrating calcareous-containing sludge with a filter press to a water content of 30 to 40%, and biaxially forced. After kneading with a stirrer, the mixture was crushed into a rectangular form (4 cm x 4 cm x 16 cm) and naturally dried for 24 hours. Then, store this in a baking furnace and
It was fired at 0 ° C. for 10 minutes to obtain a prismatic porous test piece.

In order to confirm the practicality of the obtained test piece as a porous lightweight aggregate, a pressure strength test, a water retention test and a water permeability test were carried out below.

(1) Pressure Strength Test According to the mortar strength test method (JIS K102), a uniaxial crush test (pressing in the axial direction) was performed to determine the pressure (kg / cm ² ) at the time of breaking.

The above test was repeated 3 times, and the pressure strength measured was 105 kg / cm ² 105.5 kg / cm ² 104.
It was found to be kg / cm ^2, which is a preferable strength as a lightweight aggregate.

(2) Water retention test The test piece obtained in the above experimental example was crushed into particles having a diameter of about 5 mm,
50 g thereof was placed in a 200 ml graduated cylinder, 150 ml of water was poured into the graduated cylinder from the top, and after dipping for 10 minutes, it was taken out. Then, the change in the weight of the test piece was examined immediately after taking out and after naturally drying at room temperature of 20 ° C. for 48 hours.

As a result, the weight of the test piece immediately after being immersed in water and taken out was 63.0 g, and after 48 hours was 58.8 g. Therefore, within this elapsed time, it was found that the amount of evaporation was 4.5 g, which was an extremely small amount (water holding amount of 8.5 g), and that there was sufficient water holding property. (3) Water permeability test The test piece obtained in the experimental example was crushed to 100 mesh or less, 100 g of which was stored in a 200 ml graduated cylinder, 100 g of water was poured, and the time until the water reached the bottom of the graduated cylinder. Was measured.

As a result, it was found that the arrival time was about 7 seconds and the water permeability was excellent.

[Comparative Example] A dehydrated cake obtained by drying calcareous-containing sludge at a low temperature (100 ° C) was pulverized to 100 mesh or less, and this was subjected to the water permeability test of the above (3).

As a result, it was confirmed that water did not reach the bottom of the May cylinder even after 1 hour, and the water permeability was extremely low.

[0023]

[Effect] As described above, the present invention makes the calcareous-containing sludge produced in the lime industry insoluble in water and makes it porous, so that it can be used as a water-resistant lightweight general-purpose material. Since the fired product obtained by this treatment method has sufficiently improved water permeability, water retention, and mechanical strength, it can be effectively reused as a lightweight aggregate, for example, as a building material and as a soil improvement material. There are advantages available.

Claims (2)

[Claims] 1. A method for treating calcareous sludge, which comprises calcining after dehydrating calcareous-containing sludge. 2. A porous lightweight aggregate comprising a calcined product of calcareous sludge.