JP2016117592A - Magnetized zeolite, method for manufacturing the same, and selective and specific capturing method of cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide zeolite and a method for manufacturing thereof by which radioactive cesium in soil or in liquid containing soil can be efficiently captured selectively and specifically.SOLUTION: Alkali solution 7 is added to zeolite raw material 5 containing burned ash of coal or burned ash of papermaking sludge to soften the surface of burned ash. The zeolite raw material 5 in which the surface of burned ash is softened and magnetite nano fine particles are mixed and heated. Thus, magnetized zeolite 13 which is a composite material of magnetite nano fine particles 11 and Na-P1 type zeolite 9 is obtained. The magnetized zeolite 13 has a structure that the magnetite nano fine particles 11 are confined in boundaries of a polycrystal body of the Na-P1 type zeolite 9 or a structure that the magnetite nano fine particles 11 are partially substituted in a crystal of the Na-P1 type zeolite 9 to form a nano composite body, or both of the structures.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetized zeolite, a method for producing the same, and a method for selectively capturing cesium.

  There is a demand for a decontamination method for removing radiocesium, one of the radionuclides, from soil contaminated with radionuclides due to accidents at nuclear power plants and the like. As one of the methods for decontaminating radioactive cesium, it is considered to use zeolite. It is known that zeolite has an adsorbing action on cesium due to electric affinity (see, for example, Patent Documents 1 to 3).

  Zeolite is an aluminosilicate having an infinite number of pores in its crystal structure, and is a substance composed of M-Al-Si-O (M is an alkali metal or alkaline earth metal). With respect to zeolite, the smaller the Si / Al ratio, the more negatively charged the zeolite skeleton is due to isomorphous substitution, and M plus ions are required to compensate for it. In addition, the cation exchange capacity (CEC) of zeolite increases as the Si / Al ratio decreases.

  Further, as a method for recovering zeolite mixed in a fluid, a method is known in which an adsorbent containing zeolite and magnetic particles is used and the adsorbent is recovered by magnetic separation (see, for example, Patent Documents 4 to 6). ).

Japanese Patent Laid-Open No. 10-15401 JP-A-8-271692 JP-A-6-186396 JP 2005-177709 A JP 2005-137773 A JP 2007-234097 A

Inada Miki, Hokujo Junichi, “Zeolite Synthesis from Coal Ash”, Materials Science and Engineering, Japan Society for Materials Science, 2006, Vol. 43, No. 1, p. 14-19

  However, a general zeolite such as natural zeolite is weak because the capturing ability of cesium ions depends only on electric affinity. Moreover, since a general zeolite captures regardless of a kind if it is a cation, it cannot selectively capture a cesium ion. Moreover, general zeolite does not have the ability to attract cesium taken in between clay layers in soil until it is drawn out from the clay layers.

There are two possible reasons why the cesium ion capture ability of a general zeolite is low.
One is that, since general zeolites can be captured regardless of the type if they are cations, the cation exchange capacity (CEC value), which is a standard for the capture capacity of zeolites, will soon fill the capacity value. It does not work well against cesium ions.

  The other is that general zeolite is weak because the trapping ability of cesium ions relies only on electric affinity, and the zeolite pores of physical shape are about the diameter of cesium ions (3.6 angstroms). ) Is too large or too small to meet the capture conditions.

For example, mordenite (Si / Al ratio is about 5), which is one of natural zeolites, has a large CEC of 120 to 150 meq / 100 g (SI unit is cmol (+) · kg ⁻¹ ), which is a cation capture capacity. However, since the crystal pores are 5.5 to 8.0 、 and larger than the diameter of cesium ions (3.6 Å), the capture and fixing ability of radioactive cesium is weak.

  In addition, the soil in Fukushima, where there is concern about contamination by radioactive cesium, is “masa soil” that is mainly weathered granite. The CEC of the “masa soil” is about 20, and the CEC of the clay mineral kaolinite derived from feldspar weathered from the “masa soil” is 3 to 15 meq / 100 g. The mica-derived clay mineral illite has a CEC of 10 to 40 meq / 100 g. Furthermore, the clay mineral vermiculite with altered illite has a relatively large CEC value of 100 to 150 meq / 100 g, which is a measure of the adsorption capacity, and also expands the interlayer, which is a characteristic of 2: 1 type clay minerals. It has the property of easily incorporating cesium ions between layers. Therefore, it was difficult to capture cesium free from such soil.

  An object of the present invention is to provide a magnetized zeolite capable of efficiently capturing radioactive cesium in soil or a liquid containing soil, a method for producing the same, and a method for capturing cesium.

  Among the various types of zeolites, including natural and artificial, the inventors of the present application have innumerable crystal pores having the same size as that of cesium ions (diameter: 3.6 mm) in the Na-P1 type zeolite. It was found that it has the ability to selectively capture and fix ions selectively. Na-P1 type zeolite is disclosed in Non-Patent Document 1, for example.

  A method for producing a magnetized zeolite according to the present invention comprises mixing a zeolite raw material containing coal incineration ash or paper sludge incineration ash with an alkali solution to soften the surface of the incineration ash and magnetite nanoparticles. The magnetized zeolite, which is a composite material of magnetite nanoparticles and Na-P1 type zeolite, is obtained by heat treatment.

  In the method for producing a magnetized zeolite of the present invention, the zeolite raw material may be an example in which the Si / Al ratio is adjusted to 2 or less using one or more of sodium aluminate and an aluminum compound. .

  The magnetized zeolite according to the present invention is a magnetized zeolite obtained by the method for producing a magnetized zeolite of the present invention, and magnetite nanoparticles are confined at the grain boundary of the Na-P1 type zeolite polycrystal, or Na- A magnetite nanoparticle is partially substituted in a P1-type zeolite crystal to form a nanocomposite, or is a composite material of a magnetite nanoparticle and Na-P1-type zeolite having both structures. To do.

  The method for capturing cesium according to the present invention is a method for selectively treating radioactive cesium in soil or liquid containing soil by collecting the magnetized zeolite of the present invention in soil or liquid containing soil and recovering it by magnetic separation. It is characterized by capturing.

  The magnetized zeolite and the production method thereof of the present invention can provide a magnetized zeolite which is a composite material of magnetite nanoparticles and Na-P1 type zeolite capable of efficiently capturing radioactive cesium in soil or in a liquid containing soil.

  The method for capturing cesium of the present invention can efficiently capture radioactive cesium in soil or in a liquid containing soil using the magnetized zeolite of the present invention. Furthermore, since the Na-P1 type zeolite mixed in the soil or the liquid containing the soil is recovered by magnetic separation, the method for capturing cesium according to the present invention facilitates the recovery of the zeolite capturing cesium.

It is a schematic diagram for demonstrating one Example of the manufacturing method of a magnetized zeolite. It is a figure which shows the frame | skeleton structure model of Na-P1 type | mold zeolite. It is a figure which shows the result of having investigated the capture ability of the cesium ion and strontium ion of Na-P1 type | mold zeolite in a solution. It is a figure which shows the result of having investigated the capture ability of the Na-P1 type | mold zeolite with respect to the cesium in soil. It is a conceptual diagram for demonstrating the collection | recovery method of the magnetized zeolite which captured the cesium. It is a figure which shows the change of the radioactive cesium density | concentration in soil when the magnetic separation using the magnetized zeolite of this invention is performed in multiple times.

FIG. 1 is a schematic diagram for explaining one embodiment of a method for producing magnetized zeolite.
For example, 2 mol / L (mol / liter) sodium hydroxide solution 3 is added to iron salt solution 1 containing iron (II) chloride or iron (III) chloride or both, and mixed at 100 ° C., A dispersion of magnetite nanoparticles was obtained by coprecipitation. The average particle size of the obtained magnetite nanoparticles is about 30 nm (nanometers).

  For example, zeolite raw material 5 was obtained by mixing coal incinerated ash whose Si / Al ratio was previously examined by fluorescent X-ray analysis with aluminum hydroxide so that the Si / Al ratio was 2. A 2 mol / L sodium hydroxide solution 7 was added to the zeolite raw material 5 and allowed to stand at room temperature for 24 hours. Thereby, the zeolite raw material containing the incinerated ash whose surface was softened was obtained.

  Magnetite nanoparticles and a zeolite raw material containing incinerated ash whose surface was softened were mixed and heated to reflux (heat treatment) at 100 ° C. for 24 hours. Thereby, the magnetized zeolite 13 which is a composite material of the Na-P1-type zeolite 9 and the magnetite nanoparticle 11 was obtained.

  In the magnetized zeolite 13, the molar ratio of Na-P1 type zeolite 9 and magnetite nanoparticle 11 (Na-P1 type zeolite: magnetite) was about 7: 3. The particle size of the Na-P1 type zeolite 9 was about several tens of micrometers (micrometers). The particle size of the magnetite nanoparticle 11 was about several tens of nm.

In the magnetized zeolite 13, the magnetite nanoparticle 11 is partially substituted in the crystal of the Na—P1 type zeolite 9 to form a nanocomposite. In addition, magnetite nanoparticles 11 are confined in the grain boundaries of the polycrystalline Na-P1-type zeolite 9.
Thus, the structure of the magnetized zeolite 13 is different from that obtained by simply mixing Na-P1-type zeolite particles and magnetite nanoparticles.

  In this embodiment, before the magnetite nanoparticles and the zeolite raw material 5 are mixed and heat-treated, a pretreatment for softening the surface of the incinerated ash contained in the zeolite raw material 5 is performed. By performing this pretreatment, when the Na-P1 type zeolite 9 is synthesized by mixing and heat treatment, the magnetite nanoparticles 11 are added to the crystals of the Na-P1 type zeolite 9 as compared with the case where the pretreatment is not performed. The fine particles are easily taken up.

  In addition, when the Si / Al ratio using aluminum hydroxide is not adjusted for the coal incineration ash, a magnetized zeolite containing a large amount of impurities such as mullite in addition to the composite material of magnetite nanoparticles and Na-P1 type zeolite is obtained. It was. Omission of the Si / Al ratio adjustment work for the zeolite raw material has advantages such as simplification of the manufacturing method and the absence of the addition of an aluminum compound, which can reduce the manufacturing cost of the magnetized zeolite. .

FIG. 2 is a diagram showing a framework structure model of Na—P1 type zeolite.
The chemical formula of the Na-P1 type zeolite 9 is described as Na ₆ Al ₆ Si ₁₀ O ₃₂ · 12H ₂ O in Non-Patent Document 1. The basic unit of the structure of the Na—P1 type zeolite 9 is the same tetrahedral structure of SiO ₄ or AlO ₄ . Therefore, the Na-P1 type zeolite 9 can maintain the Na-P1 type zeolite structure even if the Si / Al ratio changes to some extent.

  The crystal pores of the Na-P1 type zeolite 9 are about 3.6 cm, which is almost the same as the diameter of cesium ions. Therefore, the Na-P1-type zeolite 9 has a particularly excellent selective capture characteristic with respect to cesium ions.

  Moreover, the Si / Al ratio of the Na—P1 type zeolite 9 is smaller than 2. That is, the Na-P1 type zeolite 9 has a high CEC. The CEC of Na-P1 type zeolite 9 is 250 meq / 100 g or more. In addition, when the Si / Al ratio is further lowered in the Na—P1 type zeolite, the CEC of the Na—P1 type zeolite can be 400 to 500 meq / 100 g.

FIG. 3 is a diagram showing the results of examining the capturing ability of cesium ions (Cs ⁺ ) and strontium ions (Sr ²⁺ ) of Na—P1 type zeolite in a solution. In FIG. 3, the horizontal axis indicates the amount of zeolite charged (g) in 50 ml (milliliter) of the solution. The vertical axis represents the removal rate (%) of cesium ions or strontium ions.

  In 50 ml of a solution containing cesium ions or strontium ions at a concentration of 10 mmol / L, 0.1 g or 0.2 g of Na-P1 type zeolite was added, and cesium ions or strontium ions were adsorbed on the Na-P1 type zeolite. Thereafter, the concentration of cesium ion or strontium ion was measured by atomic absorption analysis for the supernatant from which Na-P1 type zeolite was removed by centrifugation.

  The removal rate of cesium ions was 99%. The removal rate of strontium ions when 0.1 g of Na-P1 type zeolite was added to 50 ml of the solution was 95%, and the removal rate of strontium ions when 0.2 g of Na-P1 type zeolite was added was 96%. Met.

  Thus, the Na-P1 type zeolite showed a high capturing ability for cesium ions. Moreover, it turned out that Na-P1 type | mold zeolite shows high capture ability also with respect to strontium ion.

FIG. 4 is a diagram showing the results of examining the capture ability of Na-P1 type zeolite for cesium in soil. In FIG. 4, the horizontal axis indicates the amount of zeolite mixed with the soil (% by weight). The vertical axis represents the cesium ion elution amount (mmol · kg ⁻¹ ). As cesium-fixed soil, granitic soil mixed with vermiculite (CEC: 3 to 15 meq / 100 g) at 10% by weight was used. Cesium capture ability was determined by mixing cesium-fixed soil mixed with a predetermined amount of Na-P1-type zeolite for 2 hours, and then measuring the amount of cesium ions eluted from the soil.

  Compared to the case where the mixing amount of Na-P1 type zeolite is 0% (Cs saturated soil), the mixing amount of Na-P1 type zeolite is 0.1%, 23%, the case of 1% is 74%, 10%. In the case of, 85% of cesium could be captured. This means that Na-P1 type zeolite can capture cesium from soil with a large CEC.

  With reference to FIG. 3 and FIG. 4, the capturing ability of unmagnetized Na—P1 type zeolite with respect to cesium and strontium has been described. In the magnetized zeolite of the present invention, the magnetite nanoparticles are confined in the grain boundary of the Na-P1 type zeolite polycrystal, or the magnetite nanoparticles are partially substituted in the Na-P1 type zeolite crystal to form a nanocomposite. It is a composite material of magnetite nanoparticles and Na-P1-type zeolite formed or having both structures. Since the magnetized zeolite of the present invention contains Na-P1 type zeolite crystals, it has the same trapping ability with respect to cesium and stronium as Na-P1 type zeolite which is not magnetized.

FIG. 5 is a conceptual diagram for explaining a method for recovering magnetized zeolite capturing cesium.
Granular magnetized zeolite 13 is mixed with cesium-contaminated soil containing cesium (Cs) 21 captured by the soil particles 19, and a water-containing shake is added by adding a release agent such as potassium chloride. To capture.

  For example, using a magnetic separator equipped with a magnet pulley 23 and a drum separator 25, the magnetized zeolite 13 capturing the cesium 21 and the soil particles 19 from which the cesium has been removed are separated. Thereby, the purified soil particle 19 is obtained. The magnetic separator is not limited to the one provided with the magnet pulley 23 and the drum separator 25, and may have any structure.

  FIG. 6 is a diagram showing a change in the concentration of radioactive cesium in the soil when magnetic separation using the magnetized zeolite of the present invention is performed a plurality of times. In FIG. 6, the horizontal axis indicates the number of magnetic separations. The vertical axis represents the radioactive cesium concentration (%).

  As the soil, soil having a radioactivity concentration of 12000 to 16000 Bq / kg (becquerel / kilogram) was used. The four types of samples A, B, C, and D show the difference in the types of release agents such as an aqueous potassium salt solution and an aqueous ammonium salt solution that are necessary for once releasing radioactive cesium from the soil.

  Sample A release agent is a solution containing 0.1% potassium chloride and 4% oxalic acid. Sample B release agent is a solution containing 0.1% potassium chloride, 4% oxalic acid and 4% ammonium oxalate. Sample C release agent is a solution containing 0.1% potassium chloride, 2% oxalic acid and 2% ammonium oxalate. The release agent for Sample D is a solution containing 0.1% potassium chloride and 4% ammonium oxalate. Each sample is obtained by mixing 2 kg of soil with 200 g of magnetized zeolite and 2 L (liter) of a release agent and stirring for 10 minutes.

  Each sample was magnetically selected three times. The addition of magnetized zeolite and release agent is only the first time, and the second and subsequent times are only magnetic separation operations. In each sample, the concentration of radioactive cesium decreased as the number of magnetic separations increased. About 80% of the radioactive cesium was successfully removed by three magnetic separation operations.

  In addition, since a radioactive cesium is once released from soil, a releasing agent is not limited to what was used for the said samples A, B, C, and D.

  The method of capturing cesium of the present invention is an innovative method that can recover only radioactive elements such as cesium in the current situation where there is no true decontamination technology against soil contamination by radionuclides caused by an accident at a nuclear power plant in Fukushima. Technology. Furthermore, the method for capturing cesium according to the present invention is a technology that can be readily adapted to the current decontamination around Fukushima as a technology that is suitable for widespread use with a large amount, low cost, and ease of use. Furthermore, it can be expected to be useful even in areas where decontamination is not sufficiently advanced, such as Chernobyl.

  In the above embodiment, coal incineration ash is used as a zeolite raw material for synthesizing magnetized zeolite, but even if paper incineration ash is used instead of coal incineration ash, a composite of magnetite nanoparticles and Na-P1 type zeolite is used. It is possible to synthesize magnetized zeolite as a material. Also, magnetized zeolite, which is a composite material of magnetite nanoparticles and Na-P1 type zeolite, is synthesized using a mixture of water glass, sodium aluminate, and aluminum compound and having a Si / Al ratio adjusted to 2 or less. You can also.

  In the method for producing a magnetized zeolite of the present invention, the Si / Al ratio of the zeolite raw material may be adjusted to a desired value. The material for adjusting the Si / Al ratio is a compound containing silicon or aluminum, preferably water glass, sodium aluminate, or an aluminum compound. Moreover, the value of Si / Al ratio is 2 or less, for example, 2. The value of the Si / Al ratio of the synthesis material may be any value as long as the composite material of magnetite nanoparticles and Na-P1 type zeolite is synthesized and is 2 or less.

Moreover, in the method for producing a magnetized zeolite of the present invention, the particle size of the magnetite nanoparticles mixed with the zeolite raw material containing the incinerated ash whose surface has been softened is, for example, 5 to 200 nm, preferably 30 nm or less.
In the method for producing a magnetized zeolite of the present invention, the magnetite nanoparticles may be commercially available.

  In the method for producing a magnetized zeolite of the present invention, the alkaline solution is not limited to sodium hydroxide, and may be another alkaline solution such as potassium hydroxide.

  As mentioned above, although the Example of this invention was described, this invention is not limited to these, A various change is possible within the range of this invention described in the claim.

5 Zeolite raw material 7 Sodium hydroxide solution (alkali solution)
9 Na-P1-type zeolite 11 Magnetite nanoparticle 13 Magnetized zeolite 19 Soil particle 21 Cesium

Claims (4)

  Magnetite nanoparticles and Na by mixing an alkali solution to a zeolite raw material containing coal incineration ash or papermaking sludge incineration ash to soften the surface of the incineration ash, and mixing and heating the magnetite nanoparticles. A method for producing a magnetized zeolite, comprising obtaining a magnetized zeolite which is a composite material of P1 type zeolite.   2. The method for producing a magnetized zeolite according to claim 1, wherein the zeolite raw material has a Si / Al ratio adjusted to 2 or less using one or more of sodium aluminate and an aluminum compound.   Magnetized zeolite obtained by the method for producing a magnetized zeolite according to claim 1 or 2, wherein magnetite nanoparticles are confined at the grain boundary of the Na-P1 type zeolite polycrystal, or Na-P1 type Magnetization characterized in that a magnetite nanoparticle is partially substituted in a zeolite crystal to form a nanocomposite, or a composite material of a magnetite nanoparticle having both structures and a Na-P1 type zeolite. Zeolite.   It is possible to selectively capture radioactive cesium in the soil or the liquid containing the soil by collecting the magnetized zeolite described in claim 3 in the soil or the liquid containing the soil and then collecting the magnetized zeolite by magnetic separation. A selective and specific method for capturing cesium.