JPH0648727A - Modification of coal ash - Google Patents

Abstract

(57) [Summary] [Objective] To provide a reforming method for effectively utilizing a large amount of coal ash generated in a power plant or the like using coal as an energy source. [Constitution] Add alkali such as caustic soda to coal ash,
A method for reforming coal ash, which comprises controlling the alkali concentration of the alkaline reaction liquid in the range of 1 to 7 N to control the size of the pore diameter when the porous crystalline material is treated by hot water treatment. Hot water treatment of the alkaline reaction liquid in two steps, adding an equivalent amount of alumina source to the amount of silica eluted in the reaction solution before the second step of hot water treatment, hot water treatment method of coal ash . A method for reforming coal ash, wherein the ratio of [(alkaline liquid amount) / (coal ash weight + alumina source weight)] of the second-stage hot water treatment reaction liquid is adjusted to be double or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reforming method for effectively utilizing a large amount of coal ash generated in a power plant or the like using coal as an energy source.

[0002]

2. Description of the Related Art If the size of the pore inlet diameter of zeolite can be adjusted appropriately, its application can be greatly expanded. For example, according to "Latest Zeolite Application Technology" published in 1989, it is said that the effective diameter of pores is changed by introducing a cation having an appropriate valence and size into a synthetic zeolite by ion exchange. It is also known that the inlet diameter can be adjusted by performing secondary processing on the zeolite pores, such as slightly narrowing the inlet diameter by impregnating magnesium, boron or phosphorus into the zeolite pores. ing.

On the other hand, the large amount of coal ash generated in a power plant or the like is industrially mainly used for conventional landfill, used as a raw material for cement, or simply used for roadbed materials. It has come to be directed to the use as a material having the above. As one of them, a method of chemically treating coal ash and using it as an ion-exchange material or an artificial zeolite for an adsorbent is known. For example, JP-A-61-09
No. 0745 describes a method of treating a coal ash with an alkaline solution to produce zeolite.
No. 15 describes a method for producing zeolite by adding caustic soda to a coal ash to which scum-like Al ash is added and boiling the mixture.

[0004]

The method for adjusting the size of the pore entrance diameter of the zeolite by secondary processing is, specifically, to coat the inner surface of the pores of the synthetic zeolite with another substance. In addition to making the secondary processing work complicated, it is difficult to uniformly reduce the inlet diameter of irregularly formed pores. It is accompanied. Therefore, it is desired to generate a desired pore size in the zeolite manufacturing process.

Coal ash is originally understood as a pozzolanic substance, and one characteristic of pozzolan is that it contains alumina-silica which is soluble in alkali content. According to the research conducted by the present inventor, when the soluble alumina / silica content is eluted in an alkaline solution, particularly when the silica content is treated with alkali, soda silicate (so-called water glass) is formed and does not crystallize. It became clear that it remained in the ash and became an impediment factor to the coal ash reforming and hindered the progress of the reforming reaction.

Further, as shown in FIG. 1, when the use ratio of the alkali content is increased for the purpose of improving the reaction efficiency, the soluble silica content is proportionally increased, increasing the viscosity of the reaction solution and increasing the viscosity of the solution. Stirring and solid-liquid separation became impossible, and stable industrial scale reformation became impossible. Further, since the soluble silica content becomes soda silicate, the consumption amount of NaOH increases, which is economically disadvantageous. Further, as shown in FIG. 2, even if the use ratio of the alkali component is increased, the cation exchange capacity indicating the modified crystallinity of the coal ash is not improved and only the elution amount of the silica component to the reaction liquid is increased. I just let it. Therefore, as described in JP-A No. 61-090745 mentioned above, the modification which mainly limits the use at a relatively low alkali concentration was mainly used.

In order to expand the porous crystalline material obtained by modifying coal ash, so-called artificial zeolite, to industrial applications, it is preferable that the above-mentioned cation exchange capacity is large. Here, the present inventors also tried a method of paying attention to amorphous aluminum / silica in coal ash and adding an equivalent amount of Al to it, as shown in JP-A-04-012015. According to this method, the coal ash reforming reaction is accelerated as compared with the above method,
The eluted silica remained in the reaction solution remained, and some coal brands did not reach the target value. It has been found that this is due to the fact that the precipitation of the crystallized substance is deposited on the surface of the coal ash remaining in the reaction solution, thereby hindering the contact between the reaction solution and the coal ash particles. It was also found that the addition ratio of the alumina source added at the time of coal ash reforming was not sufficient just by paying attention to amorphous aluminum / silica.

[0008] An object of the present invention is to reform coal ash, which is an industrial waste, into artificial zeolite having a high utility value.
Adjusting the pore size to the desired size. Thus, the cation exchange capacity of the artificial zeolite can be maximized, and further, the reforming operation can be stably and inexpensively performed on an industrial scale.

[0009]

MEANS FOR SOLVING THE PROBLEMS The present invention is as follows: (1) When alkali such as caustic soda is added to coal ash and treated with hot water to reform into a porous crystalline substance, the alkali concentration of the alkaline reaction liquid is adjusted. A method for reforming coal ash, which is characterized in that the size of the pore diameter of the precipitated porous crystal is adjusted by controlling in the range of 1 to 7 N.

Further, according to the present invention, (2) hot water treatment of an alkaline reaction liquid is carried out in two steps, and an alumina source in an amount equivalent to the amount of eluted silica in the reaction liquid is added before the second hot water treatment, The method for reforming coal ash according to the item (1) is characterized in that hot water treatment is performed.

The present invention also provides (3) [(alkaline liquid amount) of the second stage hot water treatment reaction liquid.
/ (Coal ash weight + alumina source weight)] is adjusted so that the ratio is at least two times, which is the method for reforming coal ash according to the above (1) or (2).

[0012]

The present inventors conducted experiments in which alkali such as caustic soda was added to coal ash, which is a pozzolanic material, and hot water treatment was performed to modify it into a porous crystalline material, depending on the alkali concentration of the alkaline reaction solution. As a result of repeated experiments focusing on the difference in the composition of the porous crystalline substance that precipitates,
The composition of the porous crystal that precipitates when a specified caustic soda is added and reacted under heating at a temperature of 100 ° C. or lower under stirring at atmospheric pressure is a composition mainly composed of phillipsite, and its pore size is It was 4 angstroms. When caustic soda having a concentration of 5N was used, hydroxysodalite was the main component, and the pore size was 2.5 angstrom.

As described above, by selecting the concentration of the alkali source to be added, the composition and the ratio of the porous crystals precipitated by the hydrothermal treatment can be adjusted, so that the pore size produced by the composition can be adjusted. Can be adjusted.

Known alkali sources can be used as the alkali added to the coal ash, but caustic soda is economically suitable. The reason why the alkali concentration is limited to the range of 1 to 7 N is that if the concentration is less than 1 N, the crystallization rate decreases and the quality of the artificial zeolite deteriorates. On the other hand, if the concentration exceeds 7 N, there is almost no difference in the modification effect, which is not economical. As described above, when the concentration of the alkali component is changed in the practice of the present invention, for example, when the alkali concentration is increased, the soluble silica component is proportionally increased, the viscosity of the reaction solution is increased, and the stirring / solid-liquid separation of the solution is performed. become unable. Furthermore,
Since the soluble silica content becomes soda silicate, the consumption amount of NaOH increases. In such a case, by applying the fact that the eluted silica at the time of hot water treatment with an alkali is a so-called water glass form, a primary reaction zone is set in which the eluted amount is sufficiently eluted, After water glass is generated in the reaction solution by the primary hot water treatment, the equivalent amount of alumina source is added to the amount of eluted silica in the reaction solution, and the secondary hot water treatment is performed in the alkaline solution to obtain the water glass. The porous crystalline material,
It is converted to so-called zeolite.

As for the conditions for eluting silica, which is the eluate in the primary hot water treatment, to the extent that it is preferable to carry out the reaction for 2 hours at 100 ° C. under atmospheric pressure as shown in FIG. .

Metal alumina, aluminum hydroxide, and aluminum oxide can be used as the alumina component to which an equivalent amount of alumina source is added to the amount of eluted silica. Further, from an economical point of view, so-called aluminum dross, which is a mixture of aluminum oxide and metallic aluminum produced as a by-product when aluminum is dissolved, is promising.

The alumina content should be added in an amount equivalent to the silica content eluted in the reaction solution. If it is less than the equivalent level, the eluted silica will remain in the reaction solution as water glass, reducing the yield of zeolite formation. In addition, it complicates the final treatment of the reaction solution. On the other hand, if added excessively, the final treatment of the reaction solution in which unreacted alumina intervenes becomes complicated.

In the above-mentioned primary hot water treatment, the silica content eluted in the reaction solution is related to the properties of coal ash and the alkali concentration of the reaction solution. FIG. 1 is a graph showing the relationship between the concentration of caustic soda in the alkaline reaction liquid and the ratio of eluted silica,
As is clear from FIG. 1, it is preferable to set the addition amount of the alumina source by a function of alkali concentration and properties of coal ash. That is, according to the research conducted by the present inventors, the content rate of the mullite contained in the coal ash can be represented as an index showing the properties of the coal ash. For example, the following (1), (2 ) Expression can be set.

Y = α × (normal alkali concentration) -0.041 (1) α = 0.42 × (mullite content ratio) +0.02 (2) Y: Alumina source-kg / kg-Coal ash From the above formula By adding the required amount of alumina source, the silica content eluted in the reaction solution is completely recovered as a porous crystal substance, and no residual eluted silica is present. Modification is achieved.

The addition of the above-mentioned alumina source raises the addition ratio in proportion to the concentration of the reaction solution, but in order to achieve stable operation on an industrial scale, it is necessary to satisfy the following conditions. . That is, the mixture is adjusted so that the ratio of [(amount of caustic soda solution) / weight of coal ash + weight of alumina source)] of the secondary hot water treatment solution is double or more. If the above conditions are not satisfied, reaction stirring becomes insufficient, and at the same time, treatment after the reaction becomes impossible, which is not preferable.

Further, it is preferable to complete the secondary hot water treatment reaction under atmospheric pressure at a temperature of 100 ° C. for 3 hours. It is economically disadvantageous to set the reaction time longer than necessary, and sufficient reforming of coal ash can be achieved in the primary reaction of 2 hours and the secondary reaction of 3 hours.

[0022]

EXAMPLE SiO ₂ : 45.7%, Al ₂ O ₃ : 21.
Caustic soda with different concentrations was added to coal ash having a composition of 0% and mullite: 14% to generate reaction solutions with different alkali concentrations, and the primary hot water treatment was performed at 100 ° C for 2 hours.
After that, Al dross was added to each level amount and secondary hot water treatment was performed at 100 ° C. for 3 hours. Table 1 shows each processing condition.

As comparative examples, an example in which the primary hot water treatment was carried out for a long time using the same coal ash and an example in which the primary dross treatment was performed by adding Al dross to the reaction solution are also shown.

[0024]

[Table 1]

Table 2 shows the cation exchange capacity, the ratio of residual silica in the reaction solution and the pore size as the characteristics of the reaction product obtained by the hot water treatment.

[0026]

[Table 2]

In Comparative Example I, the alkali addition ratio was set to 0.56 mol per mol of silica in the coal ash, and the reaction was carried out at a temperature of 70 ° C. under atmospheric pressure. Was hardly recognized.

In Comparative Example II, coal ash was mixed with Al ash, 2N caustic soda was then added, and the temperature was 100 ° C. under atmospheric pressure.
And reacted for 5 hours. Eluted silica still remained in the reaction solution after completion of the reforming, which was not desirable for industrial scale operation.

In Examples I and II, it is understood that the pore size can be adjusted by controlling the alkali concentration of the present invention.
Further, the cation exchange capacity, which is an index showing the degree of reforming of coal ash, is increased in proportion to the caustic soda concentration, and the present invention shows that the cation exchange capacity can also be controlled by adjusting the alkali concentration. In addition, the eluted silica content remaining in the reaction solution was completely crystallized and disappeared.

[0030]

According to the method for reforming coal ash of the present invention, since the alkali concentration is selected and the treatment with hot water is carried out, the pore diameter of the modified porous crystal can be adjusted. In addition, it is possible to reform coal ash with high crystallinity by performing a secondary hydrothermal reaction by adding an alumina source after performing a primary hydrothermal reaction using an alkali, and its application is on an industrial scale. It can be used as a gas adsorption / separation material, deodorant material, and ion exchange material. In other words, most of them have hitherto been found to be waste disposal, such as landfill, as a main route to the utilization of coal ash as a resource.

In addition, the alkali of the reaction solution is not consumed by the eluted silica and can be completely crystallized, so that the effective utilization of resources can be achieved.

[Brief description of drawings]

FIG. 1 is a graph showing the caustic soda concentration and the elution silica rate of an alkaline reaction liquid.

FIG. 2 is a graph showing the caustic soda concentration of the alkaline reaction liquid and the cation exchange capacity of the coal ash modified product.

FIG. 3 is a graph showing a hot water reaction time and an elution ratio of eluted silica.

Claims (3)

[Claims] 1. When adding an alkali such as caustic soda to coal ash and treating it with hot water to reform it into a porous crystalline material, the alkali concentration of the alkaline reaction liquid is controlled within a range of 1 to 7 N, A method for reforming coal ash, which comprises controlling the size of the pore diameter of the precipitated porous crystalline material. 2. The hot water treatment of the alkaline reaction liquid is carried out in two steps, and the hot water treatment is carried out by adding an equivalent amount of an alumina source to the amount of silica eluted in the reaction liquid before the second hot water treatment. The method for reforming coal ash according to claim 1, which is characterized in that. 3. The ratio of [(alkaline liquid amount) / (coal ash weight + alumina source weight)] of the second stage hot water treatment reaction liquid is 2.
The method for reforming coal ash according to claim 1 or 2, characterized in that the composition is adjusted so as to be double or more.