JPH07145394A - Method for solidifying coal ash - Google Patents

Abstract

PURPOSE:To solidify coal ash simply in a short time. CONSTITUTION:Coal ash is solidified by adding an alkali metal compd. and a hardly sol. alkaline earth metal compd. to it and allowing it to solidify at normal temp. or at 70-100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of further activating the conventional pozzolanic reaction of coal ash generated from a thermal power plant to obtain a solidified product in a short period of time.

[0002]

2. Description of the Related Art Conventional solidification methods for coal ash include those at room temperature and those under heat curing. As a method at room temperature, there is a method by a pozzolanic reaction in which water is present to react with calcium hydroxide, calcium sulfate or the like to form an insoluble substance. On the other hand, as a method under heat curing, there is a method of adding coal ash, slaked lime, and cement or gypsum which are existing solidifying materials, and kneading with water, and steam-treating them.

[0003]

In the above-mentioned conventional solidification method at room temperature, it takes a long period of about one month until the pozzolanic reaction remarkably progresses to solidify. Also,
The solidification method under heat curing is a very complicated process such as curing the kneaded material of cement and gypsum, which are existing solidifying materials, and steam treatment, and it requires a long time to solidify. Was. Therefore,
An object of the present invention is to provide a method for easily obtaining a solidified body of coal ash in a short time.

[0004]

In order to achieve the above object, the solidification method of claim 1 is characterized by adding an alkali metal compound and a sparingly soluble alkaline earth metal compound to coal ash. As the alkali metal compound, sodium hydroxide or sodium carbonate is particularly preferable. Also,
As the sparingly soluble alkaline earth metal compound, calcium hydroxide is particularly preferable. The amount of the alkali metal compound added is determined according to the ratio of soluble SiO ₂ and Al ₂ O ₃ contained in the coal ash, but in order to obtain the effect of the present invention, generally 100 wt. 1 per copy
It is preferable to mix at least parts by weight (0.01 mol or more).

As a mixing method, coal ash powder can be directly mixed in a solid state, or an aqueous solution of an alkali metal compound can be mixed as kneading water. Alternatively, an aqueous solution of an alkali metal compound may be sprayed onto coal ash and dried before use. The sparingly soluble alkaline earth metal compound is mixed in the form of powder in an amount of 5 parts by weight or more (0.068 mol or more) per 100 parts by weight of dry weight of coal ash.

In the present invention, when the addition ratio of the sparingly soluble alkaline earth metal compound is increased, the uniaxial compressive strength of the solidified product increases as a characteristic of the pozzolanic reaction. When the amount of the sparingly soluble alkaline earth metal compound is kept constant and the amount of the alkali metal compound mixed is increased, the uniaxial compressive strength is initially increased, but the amount of the alkali metal compound added is 3% by weight.
It reaches a peak at some degree, and then gradually decreases. In the present invention, the uniaxial compressive strength tends to increase linearly by increasing the addition amounts of both the alkali metal compound and the sparingly soluble alkaline earth metal compound with respect to the dry weight of coal ash.

According to a second aspect of the solidification method of the present invention, a slurry of the same composition as in the first aspect is used under normal pressure at 70 to 1
It is characterized by heating at 00 ° C. Heating temperature is 70 ℃
If it is less than this, a solidified product cannot be obtained in a short time.

By mixing an alkali metal compound and a sparingly soluble alkaline earth metal compound with coal ash and kneading them as a slurry, the silica content in the coal ash immediately reacts with sodium etc. in the alkali metal compound. , The silica structure is cleaved. Ions in the sparingly soluble alkaline earth metal compound are bound to the cut portion, and an insoluble substance of alkaline earth metal silicate is rapidly produced, and strength is developed in a short time. Further, by heating this, the ionization force increases, various reactions become extremely active, and the reaction rate rapidly increases. As a result, the coal ash is solidified in a short time.

[0009]

EXAMPLE An example of the composition according to the solidification method of claim 1 is composition example (c). Composition examples (a) and (b) are comparative examples. Composition Example (a) 10 parts by weight of calcium hydroxide was mixed with 100 parts by weight of coal ash and kneaded with water. The water ratio was 80. Here, the water ratio means the weight of water when the total solid content weight is 100. Composition Example (b) 3 parts by weight of sodium carbonate was mixed with 100 parts by weight of coal ash, and kneaded with water. The water ratio was 80. Composition Example (c) 10 parts by weight of calcium hydroxide and 3 parts by weight of sodium carbonate were mixed with 100 parts by weight of coal ash, and kneaded with water.
The water ratio was 80.

FIG. 1 and Table 1 show the strength development of the above three kinds of compositions by the age of 4 days. In Table 1, the test piece is N. S. , S. N. S. The one in the state of is the uniaxial compressive strength estimated by the cone penetrometer, and the one in the cured state is by the uniaxial compressive strength tester. Composition example (b) exhibited a strength of about 1 kgf / cm ² one day after kneading. At this time, the paste exhibited strength while exhibiting a phenomenon in which the liquid sucked in the liquid by the action of an external force and slightly expanded and solidified (dilatancy phenomenon) for several days. On the other hand, the composition example (c) did not show the above-mentioned dilatancy state after kneading with water, and reached a cured state within a short period of time within 1 to 2 days after kneading.

[0011]

[Table 1]

As an example and a comparative example of the solidification method of claim 2, the strength after heating the reaction slurry at 90 ° C. for 5 hours is shown in FIG.
Shown in. Composition examples (1) and (2) are shown as comparative examples. Composition example (3) is taken as an example of the present invention. Composition Example (1) 100 parts by weight of coal ash was mixed with 30 parts by weight of calcium hydroxide. The water ratio was 50. Composition Example (2) 100 parts by weight of coal ash was mixed with 4 parts by weight of sodium carbonate. The water ratio was 50. Composition Example (3) 100 parts by weight of coal ash and 30 parts by weight of calcium hydroxide,
4 parts by weight of sodium carbonate were mixed. The water ratio was 50. As shown in FIG. 2, in the composition example (3), a solidified body having a high strength can be obtained only by heating at a relatively low temperature for several hours.

In the composition of the present invention, strength is exhibited by changing the mixing ratio and water ratio of an alkali metal compound (eg sodium carbonate, sodium hydroxide) or a sparingly soluble alkaline earth metal compound (eg calcium hydroxide). Is different. FIG. 3 shows the strength development on the 28th day of age under heat curing when the water ratio was kept constant at 30 and the mixing amount of the alkali metal compound or the sparingly soluble alkaline earth metal compound was changed.

As shown in FIG. 3, in the mixing ratio of the alkali metal compound and the sparingly soluble alkaline earth metal compound, high strength is shown in proportion to the increase of both. Also, when the water ratio is reduced,
Naturally, the strength increases. When fine aggregate or coarse aggregate such as sand or gravel is added to this composition, the strength inevitably becomes higher than this.

[0015]

By adding an alkali metal compound and a sparingly soluble alkaline earth metal compound, the pozzolanic reaction in coal ash can be activated and a cured product can be obtained in a short period of time. By heating a slurry in which an alkali metal compound that activates the pozzolanic reaction of coal ash and a sparingly soluble alkaline earth metal compound are heated at a relatively low temperature for several hours, a strong solidified body can be easily obtained. The solidified body prepared by these solidifying methods is relatively stable physically and chemically.

[Brief description of drawings]

FIG. 1 is a graph showing strength development of compositions (a), (b), and (c) up to 4 days of age.

FIG. 2 is a graph of strength development after the compositions (1), (2) and (3) were heated and aged at a temperature of 90 ° C. for 5 hours at normal pressure, and the test pieces were left at room temperature for 1 hour. .

FIG. 3 The water ratio is kept constant at 30 and the mixing amount of the alkali metal compound (sodium carbonate) and the sparingly soluble alkaline earth metal compound (calcium hydroxide) is changed to 7 under normal pressure.
Heat curing at 0-100 ° C for 5 hours, then age 28
It is a three-dimensional graph of strength development of a specimen that has been subjected to underwater curing until day.

Claims (2)

[Claims] 1. A method for solidifying coal ash, which comprises adding an alkali metal compound and a sparingly soluble alkaline earth metal compound to coal ash at room temperature. 2. A method for solidifying coal ash in which the coal ash to which the alkali metal compound and the sparingly soluble alkaline earth metal compound are added is heat-cured at 70 to 100 ° C.