JP3379642B2 - Hazardous substance stabilization method using zeolite - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of stabilizing harmful substances using porous minerals, especially zeolite.

[0002]

2. Description of the Related Art As a known stabilization treatment method for harmful heavy metal-containing substances, radioactive substances and other harmful substances, conventionally known are melt vitrification, cement solidification and chemical treatment. Is. The features and problems of these methods are as follows.

(1) Molten vitrification: A method of stabilizing a vitrified body by melting a substance containing a harmful heavy metal at a high temperature of 1500 ° C. or higher and then cooling it. Although this method has a very low elution property, it has a problem that a large amount of energy is required for vitrification and that a volatile harmful heavy metal is vaporized and diffused during the high temperature melting process.

(2) Cement solidification: A method in which harmful heavy metal-containing substances and the like are kneaded into cement mortar and stabilized.
This method is problematic in that the volume of harmful substances is not reduced so much and that the effect of suppressing dissolution is not guaranteed over a long period of time due to deterioration of cement mortar over time.

(3) Chemical agent treatment: A method of treating harmful chemicals with a chemical such as a chelating agent to solidify harmful heavy metals into a chemically stable form with little elution. This method has a problem in that the cost of the drug is high, and the chemical stability is impaired in a relatively short period of time, and the effect of suppressing the dissolution is not continued.

[0006]

The method of the present invention for solving the above-mentioned problems is as follows. First, a state in which a harmful substance is incorporated into pores in the crystal structure of zeolite and the internal structure of the crystal is retained. The toxic substance is enclosed in the zeolite pores by closing the opening of the pores.

Secondly, the opening is closed by heating and calcining the zeolite surface.

Third, heating and baking is performed at about 800 ° C to 1000 ° C.
It is characterized in that it is performed in a relatively low temperature range.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, harmful heavy metals are taken into the pores in the crystal structure of zeolite by an ion exchange action or the like, and the zeolite is heated to, for example, 800 ° C to 1 ° C.
It is heated and baked at a relatively low temperature of about 000 ° C. As a result, only the entrance and exit of the pores are closed while maintaining the pore structure of the zeolite inside the crystal, and harmful heavy metals are enclosed in the pores of the zeolite to render it harmless in a stable form.

In general, a large number of pores having a diameter of several angstroms are present in a zeolite due to the crystal structure, and the pores have functions such as ion exchange, gas adsorption, molecular sieving and catalytic action. Is known to be expressed.

Among the zeolites, natural zeolites generally have tunnel-shaped pores extending in the same direction and arranged in parallel, and there is no lateral communication path between the tunnels. On the other hand, in synthetic zeolite, there is a lateral connecting path between the tunnels. Therefore, it can be said that the natural zeolite is more suitable from the viewpoint of stabilization by closing the entrance and exit of the pores peculiar to this method.

The stabilization treatment in the present invention means a state in which harmful substances such as harmful heavy metals do not elute even when immersed in water, a high-concentration salt solution, or an acid or alkali solution. Once stabilized, landfill disposal at a managed waste treatment plant becomes possible.

[0013]

EXAMPLES Next, a detailed description will be given of a case where Pb is stabilized by using mordenite, which is a natural zeolite produced in Shimane Prefecture.

First, a glass cylindrical column (diameter 30 m
m, length 300 mm) and N of 0.75-1.5 mm particle size
a-type mordenite (zeolite weight 85g, filling volume 9
0 ml).

Subsequently, the Pb content in this column was 1035 m.
After passing through the solution of g / l, the Pb content of the solution after passing through the column was continuously measured. The column temperature at this time is room temperature,
The flow rate of the solution is 30 ml / min.

The Pb content in the solution after passing through the column is below the detection limit up to about 30 CV (30 times the column volume CV = 2700 ml) of the cumulative solution delivery volume, and about 60 CV (column volume CV). Up to 60 times = 5400 ml), it was 1/20 or less of the Pb content of the stock solution (see Fig. 1).

From the above, it was confirmed that Pb in the solution was trapped in the mordenite by the ion exchange action. It was also confirmed that it is possible to capture harmful heavy metals in the solution phase in the zeolite by such a method. Also,
The harmful heavy metals in the powdery solid can be captured in the zeolite by a method of passing the extract solution by the acid through a zeolite column, or a method of adding a small amount of water and kneading and stirring the heavy metal-containing powder and the zeolite particles. It is possible.

As shown in Table 1, the results of confirming the elution properties of the zeolite particles trapped with Pb as described above by heat treatment in an electric furnace (see FIGS. 8 and 9). However, the results in Table 1 are shown as the elution rate (%) with respect to the Pb content in the zeolite.

[0019]

[Table 1] Change in Pb elution rate due to change in heat treatment temperature (unit:%) Elution conditions: temperature = room temperature, elution time = 96 hours solid / liquid ratio = 1/50 (g / ml), continuous shaking and stirring

The P in the zeolite used for the dissolution test
b content is 10.63 wt% in the non-heat treated product, 90
The 0 ° C. heat-treated product was 10.69 wt%. Therefore, volatilization and diffusion of the Pb component was not observed in the process of heating and baking.

From the above, it was confirmed that the elution of Pb from the zeolite that has captured Pb by the ion exchange action is extremely reduced by the heat treatment at about 1000 ° C. and the stabilization treatment can be achieved.

Next, the description of the drawings and the evaluation thereof for various data in the individual embodiments will be described in detail. [FIG. 1] Pb exchange breakthrough curve The adsorption capacity of Pb was evaluated using octazeo (octazeolite) and Izcalite, which are zeolites produced in Shimane Prefecture, as samples. A column experiment was conducted under the conditions of Pb solution concentration = 1035 ppm, temperature = room temperature, and solution flow rate = 30 ml / min.

If the Pb concentration in the solution after passing through the column is 1/20 (C / C0 = 0.05) or less of the original solution, Pb is added to the zeolite.
Was determined to be adsorbed and removed. 2 according to this criterion
Evaluating the Pb removal capacity of each type of zeolite, octazeo can treat a solution with a volume 30 times the column volume and Izcalite with a volume 60 times the column volume. Was there.

[FIG. 2] Cs exchange breakthrough curve As in FIG. 1, the adsorption capacity was evaluated when the heavy metal in the solution was Cs. Cs solution concentration = 2125 ppm, temperature =
A column experiment was conducted under the conditions of room temperature and solution flow rate = 30 ml / min. Both octazeo and Izcalite were capable of treating a solution having a volume of about 50 times the column volume, and all the zeolites had a high adsorption capacity for the Cs solution.

[FIG. 3] Sr exchange breakthrough curve Similar to FIGS. 1 and 2, the adsorption capacity when the heavy metal in the solution was Sr was evaluated. A column experiment was conducted under the conditions of Sr solution concentration = 769 ppm, temperature = room temperature, and solution flow rate = 30 ml / min. Octazeo can treat 10 times the column volume and Izcalite can treat 20 times the column volume.
All the zeolites had a certain adsorption capacity for the Sr solution.

[Fig. 4] Change in X-ray diffraction pattern due to heating of Izucarite [0027] Fig. 4 shows a change in X-ray diffraction pattern when Izucarite adsorbing Cs is heat-treated. As the heat treatment temperature increases, the peak intensity of the mordenite crystal, which is a zeolite mineral, gradually decreases. The heat treatment temperature is 10
The mordenite peak remains at 00 ° C or lower, but the mordenite peak disappears by the heat treatment at 1100 ° C or higher. In other words, Izcalite that adsorbed Cs is
When heated to 1000 ° C or higher, the crystal structure of zeolite is completely destroyed.

[Fig. 5] Change in X-ray diffraction peak intensity due to heating The change in peak intensity of X-ray diffraction of zeolite crystals due to heating is shown for octazeo and Izcalite adsorbing Pb, Cs, and Sr. All are 800-1000 ℃
Zeolite crystal peak intensity is 0 by heat treatment before and after
And the zeolite structure collapses completely. However, the temperature of crystal collapse differs slightly depending on the type of zeolite and the type of heavy metal ions adsorbed.

[Fig. 6] Change in pore distribution of Cs-adsorbed Izcalite by heating The change in the distribution of zeolite pores due to heat treatment of Cs-adsorbed Izucarite is shown. The measurement was performed by the argon gas adsorption method.

The amount of zeolite pores having a diameter of about 7 angstroms decreases with heating, and becomes almost zero in the heat treatment at 900 ° C. or higher. However, according to the result of X-ray diffraction shown in FIG. 4, the peak of the zeolite crystal still remains after the heat treatment at 900 ° C., and the crystal is not completely collapsed. That is, the amount of pores in the zeolite becomes 0 at a temperature lower than the temperature at which the zeolite crystals collapse.

It is presumed that, as a result of the heat treatment closing the entrances and exits at both ends of the zeolite pores, the zeolite remained in terms of crystal structure, but the pore amount became 0. It is considered that the both ends of the pores in the zeolite are closed and the heavy metal adsorbed inside the pores is in a state of being enclosed in the ampoule-shaped pores.

[FIG. 7] Changes in CEC and the like due to heating of Pb-adsorbed zeolite For octazeo and Izcalite adsorbed Pb, CEC and N due to changes in heat treatment temperature
The change of H ₄ exchangeable Pb and Pb amount in solid zeolite is shown. Although the amount of Pb in the solid zeolite hardly changes by heating, the CEC and NH ₄ exchangeable Pb gradually decrease to 0.

That is, Pb in the zeolite is not volatilized even by the heat treatment, is hard to elute, and is stably encapsulated in the zeolite pores. As a result of precise measurement of the amount of Pb in the solid zeolite, the difference in the amount of Pb between the non-heat-treated product and the 1100 ° C heat-treated product was within 0.2% of the content.

[Fig. 8] Dissolution of Pb-adsorbed zeolite to acid The dissolution of the zeolite when immersed in an acid solution of pH 4 is shown. Almost no Pb elutes even if originally untreated, but 10
By subjecting to a heat treatment at about 00 ° C, the elution property becomes extremely small.

[FIG. 9] Dissolution of Pb-adsorbed zeolite to alkali The dissolution of the zeolite when immersed in an alkaline solution having a pH of 10 is shown. When untreated, some Pb elutes, but 900 ° C
The elution property becomes almost 0 by performing a heat treatment to a degree. [Figure 10] CEC accompanying heating of zeolite adsorbed with Cs
Etc. [Fig. 11] Elution of Cs-adsorbed zeolite to acid [Fig. 12] Elution of Cs-adsorbed zeolite to alkali

Results obtained when the target heavy metal is Cs in FIGS. Cs is 1/10 even if it is heat-treated
It has a% order of dissolution and is difficult to completely stabilize. [Figure 13] CEC with heating of Sr-adsorbed zeolite
Etc. [Fig. 14] Dissolution of Sr-adsorbed zeolite to acid The dissolution of Sr-adsorbed zeolite to alkali is
Both octazeo and Izcalite were below the detection limit for all samples, so illustration is omitted.

Results when the target heavy metal is Sr in FIGS. When Sr is heat-treated at about 800 ° C., the dissolution property disappears and it can be completely stabilized.

[Applicable Fields and Ripple Effects] In addition to the harmful heavy metals exemplified above, the method of the present invention is not limited to various harmful or stable metals having a certain stability against heat of 800 ° C. to 1000 ° C. It can stabilize unnecessary elements, can be applied to the treatment of radioactive elements that are dangerous or harmful, and can be used in the specific fields described below. Further, in the above-mentioned examples, the uptake of harmful substances by the ion exchange action was mainly described, but application to adsorption without ion exchange is also possible as long as the size of the molecule can be enclosed in the pores of zeolite.

(1) Since heavy metals in waste liquid containing harmful heavy metals can be concentrated and stabilized, it can be applied to the field of wastewater treatment. (2) It can be applied to the industrial waste treatment industry because it can stabilize fly ash and incineration ash generated in the process of incineration of industrial waste, which contains harmful heavy metals in high concentration. . (3) Since various radioactive nuclides in radioactive liquid waste can be concentrated and stabilized, they can be applied to the nuclear industry.

[0039]

According to the present invention configured as described above, the following concrete effects are exhibited.

(1) Since it is sufficient to close only the entrances and exits of both ends of the pores in the zeolite crystal, the temperature of treatment of harmful substances is much lower than that of the molten vitrification treatment.
Stabilization of harmful heavy metals is possible by heat treatment at 0 ° C to 1000 ° C.

(2) Energy cost can be reduced because of low temperature treatment.

(3) Since it is a low-temperature treatment, vaporization and diffusion of volatile harmful heavy metals and the like in the treatment process, which is a problem in the existing stabilization treatment method of molten vitrification, can be suppressed to an extremely low level. .

(4) Since harmful heavy metals and the like are encapsulated in the pores in the crystal structure of zeolite, they are contained in a strong capsule at the atomic level, and a high dissolution inhibiting effect can be achieved.

(5) Since the zeolite pores are ultrafine with a diameter of several angstroms, there is no possibility that the pores will be exposed due to mechanical damage such as normal pulverization operation, and semipermanent stabilization is expected. it can.

(6) By combining this method with the existing stabilization treatment method, a higher degree of stabilization can be achieved. In other words, applying this method to stabilize zeolite that has adsorbed harmful heavy metals, etc. by heat treatment, and further subjecting the zeolite to glass melting treatment or concrete solidification treatment, which is an existing stabilization treatment method, it is possible to chemically shape it. A stable form can be obtained.

[Brief description of drawings]

[Figure 1] (A) and (B) are measurement range and concentration (C / Co)
The Pb exchange breakthrough curve displayed by changing the scale magnification of the axis is shown.

[Figure 2] (A) and (B) are measurement range and concentration (C / Co)
The Cs exchange breakthrough curve displayed by changing the scale magnification of the axis is shown.

[FIG. 3] (A) and (B) are measurement range and concentration (C / Co)
The Sr exchange breakthrough curve displayed by changing the scale magnification of the axis is shown.

FIG. 4 is a diagram showing a change in X-ray diffraction pattern due to heating of Izucarite.

5 (A) and 5 (B) are charts showing changes in X-ray diffraction peak intensity due to heating of octazeolite and Izcalite.

FIG. 6 is a chart showing changes in pore distribution due to heating of Cs-adsorbed iscalite.

7A and 7B are diagrams showing changes in CEC and the like accompanying heating of Pb-adsorbed octazeolite and Izcalite.

8 (A) and 8 (B) are diagrams showing the elution properties of Pb-adsorbed octazeolite and Izcalite for acids.

9 (A) and 9 (B) are diagrams showing the elution properties of Pb-adsorbed octazeolite and Izcalite to alkali.

10 (A) and (B) are charts showing changes in CEC and the like due to heating of Cs-adsorbed octazeolite and Izcalite.

11 (A) and (B) are diagrams showing the elution properties of Cs-adsorbed octazeolite and Izcalite for acids.

12 (A) and (B) are diagrams showing the elution properties of Cs-adsorbed octazeolite and Izcalite to alkali.

13A and 13B are diagrams showing changes in CEC and the like due to heating of Sr-adsorbed octazeolite and Izcalite.

14 (A) and 14 (B) are diagrams showing the elution properties of Sr-adsorbed octazeolite and Izca zeolite with respect to acids.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoto Imakaka 219 Izumogo, Higashi Izumo-cho, Yatsuka-gun, Shimane Prefecture Shimane Prefectural Industrial Technology Center (56) Reference JP-A-11-76981 (JP, A) JP-A 8-10739 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) A62D 3/00 ZAB B01J 20/18 B09B 3/00 301

Claims (2)

(57) [Claims] 1. A harmful substance is incorporated by incorporating a harmful substance into the pores in the crystal structure of zeolite, and heating and calcining the surface of the zeolite while maintaining the internal structure of the crystal to block the openings of the pores. A method for stabilizing a harmful substance by using a zeolite in which the substance is enclosed in zeolite pores. 2. Heating and baking at a temperature of about 800 ° C. to 1000 ° C.
The method for stabilizing a harmful substance using the zeolite according to claim 1, which is carried out in a relatively low temperature range .