JP7132569B2 - Geopolymer solidification material, geopolymer solidification method - Google Patents

Description

The present invention relates to a geopolymer solidifying material and a geopolymer solidifying method for solidifying an object to be solidified.

Concrete, which is obtained by solidifying gravel or sand with cement as a solidifying agent, is widely used in structures such as buildings, bridges, and dams. On the other hand, a large amount of carbon dioxide, which is emitted when manufacturing cement, is required to be reduced as a greenhouse gas.

In recent years, instead of such cement, a geopolymer solidification material has attracted attention as a solidification material with less environmental impact. Conventional geopolymer solidification materials consist of glassy raw materials such as aluminosilicate or volcanic ash made from calcined metakaolin called a highly reactive active filler (filler), and sodium hydroxide to activate the reaction. and various particulate materials called inert fillers are kneaded and dried to form and solidify silicate-based polymers between particles of the particulate materials.

For example, Patent Literature 1 discloses a geopolymer composition made from an active filler, an alkali activator, and an aggregate, that is, an inert filler. The active filler of the geopolymer composition comprises at least one of fly ash, blast furnace slag, and sewage incineration sludge, and the alkali activator comprises at least one of potassium hydroxide, sodium hydroxide, sodium silicate, and potassium silicate. It is said to contain

Further, for example, Patent Document 2 discloses a geopolymer solidification method in which an aqueous solution of sodium silicate and fly ash are mixed, poured into a mold, and solidified as it is at room temperature.

Further, for example, Patent Literature 3 discloses a technology for producing a geopolymer in which temperature control and time control are performed when an active filler and an alkali activator are mixed. Here, materials containing aluminosilicate as an active filler, industrial waste such as fly ash, blast furnace slag, red mud, silica fume, sewage sludge incineration ash, natural aluminosilicate minerals and their calcined materials, volcanic ash, alkali It is described that an aqueous solution exhibiting high alkalinity, that is, an aqueous solution of an alkali hydroxide, an alkali carbonate, or an alkali silicate is used as the activator.

Further, for example, in Patent Document 4, fly ash is used as an active filler, and a pre-mixed mixture of potassium hydroxide solution or sodium hydroxide solution and silicon powder or silica fume is used as an alkali activator to solidify a geopolymer hardened body. is disclosed.

Further, for example, in Patent Document 5, fly ash/blast furnace slag is used as an active filler, sodium hydroxide solution is used as an alkali activator, and these are first mixed, and then silica fume, which is a fine particle powder of silica, is used as a silica source. Disclosed is a method of making a slowly dissolving geopolymer article.

In addition, for example, in Patent Document 6, fly ash, ground granulated blast furnace slag, and silica fume are used as the active filler, and sodium hydroxide solution is used as the alkaline activator, mixed with aggregate (inert filler), and pretreated at room temperature. A production method for producing a hardened geopolymer by curing and steam curing is disclosed.

In Patent Document 6, in order to solve the problems of convenience and versatility, inorganic powder such as active filler fly ash, blast furnace slag, silica fume, sodium hydroxide solution of alkali activator, and inert filler are mixed. It is mixed and two-stage curing is used: pre-curing at room temperature and steam curing. This makes it possible to sufficiently delay the solidification start time while ensuring simplicity and versatility.

Japanese Patent No. 5091519 JP-A-8-301639 Japanese Patent No. 6018682 JP 2016-222528 A Japanese Patent No. 6058474 JP 2017-100905 A

However, in the conventional geopolymer solidifying materials and their manufacturing methods disclosed in the above-mentioned Patent Documents 1 to 6, in order to control the solidification start time, the constituent materials are heated in advance, stirred for a certain period of time or longer, and solidified. There was a problem that the solidification process was complicated and the workability was poor.
In addition, since an aqueous solution is used as the alkali activator in each case, the water content of the mixture cannot be controlled independently, and a separate means for adjusting the concentration is required, which poses the problem of poor handling. rice field.

The present invention has been made in consideration of such circumstances, and a geopolymer solidification material that can control the solidification start time, has a simple solidification procedure, and has excellent workability, and a geopolymer solidification material using the same provide a way.

In order to solve the above problems, the present invention proposes the following means.
That is, the geopolymer solidifying material of the present invention is composed of alkali alumina powder and amorphous silica powder, and the mixing ratio of the amorphous silica powder to the alkali alumina powder is 1.0 in Si/Al molar ratio. It is characterized by being in the range of 0 or more and 2.0 or less .

Since the geopolymer solidifying material of the present invention is a powder (powder) obtained by mixing alkali alumina powder and amorphous silica powder, it has excellent portability compared to conventional geopolymer solidifying materials containing aqueous solutions. , is easy to handle. In addition, since it is a powder (powder), it is possible to easily control the amount of water contained in the kneaded product, compared to the conventional case where an aqueous solution is used as an alkali activator. can improve sexuality. And since it can be solidified only by kneading with the material to be solidified and water at the time of solidification, it is possible to realize a geopolymer solidifying material with excellent workability with less labor involved in solidifying.

Further, in the present invention, the alkali alumina powder may contain sodium aluminate powder.

Further, in the present invention, the sodium aluminate powder may be orthorhombic.

Further, in the present invention, the amorphous silica powder may contain at least one of silica fume powder and fused silica powder.

The geopolymer solidification method of the present invention is a geopolymer solidification method using the geopolymer solidification material described in each of the above items, wherein the geopolymer solidification material, water, and an object to be solidified are kneaded to form a kneaded product. It is characterized by comprising steps.

Further, in the present invention, the mixing ratio of the water to the geopolymer solidifying material may be in the range of 0.5 or more and 1.5 or less in mass ratio.

Further, the present invention may further include a heating step of heating the kneaded material to room temperature or higher.

Further, in the present invention, the material to be solidified may be radioactive waste.

According to the present invention, it is possible to provide a geopolymer solidification material that can control the solidification start time, has a simple solidification procedure, and has excellent workability, and a geopolymer solidification method using the same.

1 is a micrograph showing reaction products of alkali alumina powder and amorphous silica powder. 4 is a photograph showing a solidified product obtained in Verification Example 1. FIG. 10 is a graph showing the results of Verification Example 3; 10 is a graph showing the results of Verification Example 3; 10 is a graph showing the results of Verification Example 3; 10 is a micrograph showing the results of Verification Example 3. FIG. 10 shows a backscattered electron image, an elemental map, and a luminance distribution showing results of Verification Example 4. FIG. 10 is a micrograph and an elemental map showing the results of Verification Example 5. FIG.

Hereinafter, a geopolymer solidifying material and a geopolymer solidifying method using the same according to one embodiment of the present invention will be described with reference to the drawings. It should be noted that each embodiment shown below is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified.

(Geopolymer solidification material)
The geopolymer solidifying material of the present invention is a powdery solidifying material obtained by mixing alkali alumina powder and amorphous silica powder. The alkali alumina powder constituting the geopolymer solidifying material is an alkali activator for the geopolymer solidifying material, and for example, sodium aluminate powder can be used.

In this embodiment, sodium aluminate powder is used as the alkali alumina powder. Sodium aluminate is sodium aluminum dioxide (NaAlO ₂ ), which is a double oxide of sodium and aluminum, is readily soluble in water, and its aqueous solution exhibits strong basicity due to hydrolysis.

The sodium aluminate powder used in the geopolymer solidifying material preferably has an orthorhombic (β phase) crystal structure.

The amorphous silica powder that constitutes the geopolymer solidification material is the active filler of the geopolymer solidification material. Examples of amorphous silica powder that can be used include silica fume powder and fused silica powder. In this embodiment, silica fume powder is used as the amorphous silica powder. Silica fume powder is, for example, amorphous fine particles of high-purity silicon dioxide contained in dust generated during the production of ferrosilicon, metallic silicon, electrofused zirconia, and the like.

The silica fume powder used for the geopolymer solidifying material preferably has an average particle size of 100 nm or more and 45 μm or less, and in this embodiment, 150 nm is used. Further, in the present embodiment, the specific surface area of the silica fume powder (measured by the N2-BET method) is in the range of 15 m ² /g or more and 30 m ² /g or less.

A preferable mixing ratio of the alkali alumina powder and the amorphous silica powder that constitute the geopolymer solidifying material is 1.0 or more in Si/Al molar ratio based on the stoichiometric ratio of minerals that can be produced. It is in the range of 0 or less. If the ratio of the alkali alumina powder is larger than the molar mixing ratio range, a large amount of unreacted alkali alumina remains after solidification, and there is a concern that the highly active alkali alumina may deteriorate the solidified body. On the other hand, if the ratio of the amorphous silica powder is higher than the range of the molar mixing ratio described above, a large amount of unreacted amorphous silica powder remains after solidification, which may lead to a decrease in the strength of the solidified product.

The geopolymer solidifying material of the present invention may further contain magnesium hydroxide powder in addition to alkali alumina powder and amorphous silica powder. By further adding magnesium hydroxide powder, which is stable in a strong alkaline environment, as a geopolymer solidifying material, spherical agglomerates of several tens of μm with outer edges of magnesium silicate are formed, and these aggregates evenly distribute the voids. It is thought that the filling exerts a kind of depletion effect, and the effect of a structural stabilizer that maintains the solidification of the geopolymer more strongly by the electric double layer repulsive force of the aggregates is obtained. Magnesium silicate hydrate progresses at the interfaces of these magnesium hydroxide aggregates, and it is believed that this also strengthens the solidification.
A preferred mixing ratio of the magnesium hydroxide powder is in the range of 0.7 or more and 1.8 or less by mass with respect to the sum of the alkali alumina powder and the amorphous silica powder.
Sodalite, which can be expected to fix seawater components such as chlorine, is produced when excess sodium compounds other than alkaline alumina powder, such as sodium hydroxide (NaOH) and sodium chloride (NaCl), are included.

The geopolymer solidifying material configured as described above is solidified by adding water, kneading the mixture, and allowing the mixture to stand at a predetermined temperature for a predetermined period of time. The chemical reaction during solidification of the geopolymer solidification material is as follows. "Si/Al" indicates the molar ratio between Al contained in the alkali alumina powder and Si contained in the amorphous silica powder.
(1) Si/Al=1.0 2SiO ₂ +2NaAlO ₂ →Na ₂ Al ₂ Si ₂ O ₈ (nepheline)
However, when there is an excess sodium compound 3SiO ₂ + 3NaAlO ₂ +NaOH, Cl=Na ₄ Si ₃ Al ₃ O ₁₂ (OH, Cl) (sodalite)
(2) Si/Al=1.5 3SiO ₂ +2NaAlO ₂ +nH ₂ O→Na ₂ Al ₂ Si ₂ O _{10.nH 2} O (natrolite)
(3) Si/Al=2.0 2SiO ₂ +NaAlO ₂ +nH ₂ O→NaAlSi _{2 O 6.nH 2 O (} analcyme chabazite)

FIG. 1 shows an observed image of the reaction product. In addition, FIG. 1(a) is an optical micrograph of a geopolymer reaction product with a Si/Al molar ratio of 1.0 with crystallization (150 ° C., 23 h), and FIG. 1(b) is a glassy Si/Al An optical micrograph of a geopolymer reaction product (150° C., 26 h) with a molar ratio of 1.4, FIG. Nepheline, NAT: Natrolite), Fig. 1(d) is a scanning electron micrograph of Si/Al molar ratio 1.0, crystalline after addition of tetrabutylamine hydroxide (TBAH), Fig. 1(e) ) is an EPMA backscattered electron image of the cross section of the solidified material with a Si/Al molar ratio of 1.0 (ZEO: zeolum particles, white arrow: crystallized matrix), and FIG. shows backscattered electron beam images of EPMA (ZEO: zeolum particles, white arrows: crystallized matrix) of the cross section of the solidified product after addition of TBAH.

In addition, the reactants generated when the geopolymer solidifying material is solidified are not limited to these, and Na-Al-Si-based oxides with different compositions (amorphous or crystalline silicate) may also be generated.

The amount of water (W) added when solidifying the geopolymer solidifying material of the present invention is 0.5 or more and 1 as a weight mixing ratio (W/GP) of water (W) to the geopolymer solidifying material (GP). .5 or less. If the amount of water is less than these ranges, the dissolution of sodium aluminate becomes incomplete, resulting in the formation of free silanol ions ([Si(OH) ₄ ] ⁴⁻ ) and free four-coordinated structures or Al—O—Al bridges. There is a risk that the tetrahydroxide aluminate ion ([Al(OH) ₄ ] ⁻ , [(OH) ₃ AlOAl(OH) ₃ ] ²⁻ ) component of the structure is insufficient, and solidification of the geopolymer solidifying material does not proceed sufficiently. . For example, when the solubility of sodium aluminate in water is about 500 g/L, the ratio W/NA between water (W) and sodium aluminate (NA) is 2.0. In addition, if the amount of water is too much, free Al that contributes to the solidification reaction will precipitate as gibbsite (Al(OH) ₃ ) first, and it is considered that supersaturation of Si—Al secondary minerals such as zeolite cannot be achieved. .

Examples of objects to be solidified (inactive fillers) to be solidified using the geopolymer solidifying material of the present invention include various aggregates, gravel, sand, etc., which are solidified and used as structures for civil engineering and construction. be able to. It can also be used for the purpose of solidifying and stabilizing industrial waste. For example, it can be used to solidify radioactive waste generated by the accident at the Fukushima nuclear power plant, and to solidify Shirasu (volcanic glass) derived from volcanic ash existing in the stratum in the southern part of Kyushu.

According to the geopolymer solidifying material of the present invention configured as described above, since it is a powder obtained by mixing alkali alumina powder and amorphous silica powder, it is compared with a conventional geopolymer solidifying material containing an aqueous solution. Excellent portability and easy handling. And since it can be solidified only by kneading with the material to be solidified and water at the time of solidification, it is possible to realize a geopolymer solidifying material with excellent workability with less labor involved in solidifying.

In addition, according to the geopolymer solidifying material of the present invention, since it is a mixed powder of alkaline alumina powder and amorphous silica powder, compared to the conventional case where an aqueous solution is used as an alkali activator, The amount of water contained in the kneaded material can be easily controlled, and the workability related to solidification can be improved.

(Geopolymer solidification method)
When solidifying using the geopolymer solidifying material of the present invention described above, first, the geopolymer solidifying material of the present invention and water are added to the material to be solidified (inactive filler) and kneaded to form a kneaded material. (Kneading process). At this time, the weight mixing ratio of the material to be solidified (FL), the geopolymer solidifying material (GP), and the water (W) and GP is FL/GP = 1.0 or more, 3.0 or less, W/GP = preferably within the range of 0.5 or more and 1.5 or less. For kneading, a mixer for cement kneading or the like can be used.

Next, this kneaded product is poured into, for example, a mold. Then, for example, by leaving this kneaded material under sunlight, the alkali alumina powder and the amorphous silica powder react in the presence of water to form a vitreous substance, and then crystalline Na ₂ Al. ₂ Si ₂ O ₈ (nepheline) or the like is generated to form a solidified body together with the object to be solidified.

On the other hand, this kneaded product can be heated to a predetermined temperature above room temperature and held for a predetermined time (heating step) to accelerate the solidification reaction between the alkali alumina powder and the amorphous silica powder. From a practical point of view, the predetermined temperature is preferably 80° C. or lower, for example. Various heaters such as an infrared heater and a hot air heater can be used for heating. By performing such a heating step, the time required for solidification can be shortened and the solidified body can be formed more easily.

Although one embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

The effects of the present invention have been verified.
(Verification example 1)
Zeolite (to-be-solidified), sodium aluminate powder, silica fume powder, and water were mixed at the mixing ratios shown in Table 1 to obtain four types of samples (1) to (4).
- Zeolite: "Tosoh Zeolum A-3 585" was once immersed in water and dried at 60°C to avoid heating due to heat of adsorption during kneading (moisture content: about 20 wt%).
・Sodium aluminate powder: P100 manufactured by Asada Chemical Industry Co., Ltd. is used.
・ Silica fume: Uses “Elkem micro silica 940U”.
After each sample was filled in a mold and removed from the frame, it was heated at 250° C. for 1.5 hours and samples (1-2) and (3-2) for 3.0 hours.
Table 1 shows the results of Verification Example 1. Fig. 2 shows the state of the solidified products of sample 1-2 (sample A) and sample 3-2 (sample B).

According to the results shown in Table 1, a solidified product with a compressive strength of 6 to 13 MPa was obtained after heating for 1.5 hours, and a solidified product with a compressive strength of 15 MPa was obtained after heating for 3 hours.

(Verification example 2)
Zeolite (material to be solidified), carbonate slurry, sodium aluminate powder, silica fume powder, and water were mixed at the mixing ratios shown in Table 1 to obtain three types of samples (5) to (7). The carbonate slurry was obtained by dehydrating and filtering a suspension of calcium carbonate and magnesium hydroxide in a 10 wt % sodium chloride aqueous solution so that the solid content was 10 wt %.
Then, each sample was filled in a mold and sealed, and cured and solidified at room temperature for about 2 weeks to 4 months.
Table 2 shows the results of Verification Example 2.

According to the results shown in Table 2, a solidified product having a compressive strength of 5 MPa after about 2 weeks and a compressive strength of 8 MPa to 22 MPa after about 4 months was obtained.

(Verification example 3)
Zeolite (to be solidified), carbonate slurry, sodium aluminate powder, silica fume powder, and water were mixed in the mixing ratio shown in Table 3 below, and each sample was filled in a mold, and then dried at 60 ° C. or in a dry atmosphere. It was cured in a steam atmosphere at 150°C. The carbonate slurry is the same as in Verification Example 2.

The results of Verification Example 3 are shown in FIGS. 3 to 6. FIG. FIG. 3(a) shows the relationship between the compressive strength (MPa) of the solidified body and the mass ratio W/GP(a) of water (W) and the geopolymer solidifying material (GP). Further, FIG. 3(b) shows the relationship between the compressive strength (MPa) of the solidified body and the mass ratio W/NA(a) of water (W) and sodium aluminate (NA).

FIG. 4(a) shows the relationship between the compressive strength (MPa) of the solidified body and the Si/Al molar ratio of the geopolymer solidified material (GP). Moreover, FIG. 4(b) shows the relationship between the compressive strength (MPa) and the density of the solidified body. In addition, FIG. 4(c) shows the relationship between the compressive strength (MPa) of the solidified material and the solidified material (FL)/geopolymer solidifying material (GP) mass ratio.

According to FIG. 4, compressive strengths of 2.0 MPa or more are concentrated between Si/Al molar ratios of 1.0 to 2.0. It shows that the slurry-based solidified body has the highest density and compressive strength. In addition, the solidification target (non-active filler) has a different density dependence, and the strength tends to be low even if the density is high in the steam-treated one. It shows that when the filling ratio (FL/GP) of the material to be solidified is small, the strength asymptotically approaches the strength of the solidified material of only the geopolymer solidifying material (GP).

FIG. 5(a) shows the relationship between the cation exchange capacity (CEC, meq/100 g) of the solidified material and the mass ratio of solidified material (inactive filler)/geopolymer solidifying material. Moreover, FIG. 5(b) shows the relationship between the cation exchange capacity (CEC, meq/100 g) of the solidified material and the Si/Al molar ratio of the geopolymer solidified material.

According to FIG. 5, regardless of the curing method, the CEC of solidified zeolite (GPZ) is equal to or higher than that of zeolum. In addition, in the slurry mixed system SL-GPZ, even if the mixing ratio of zeolum and carbonate slurry is 50 wt %:50 wt %, the CEC exceeds the value of zeolum by 50%. From the above results, it can be seen that in GPZ and SL-GPZ, secondary zeolitization progresses during solidification, resulting in a solidified body imparted with cation exchange properties (nuclide confinement performance).

FIG. 6 is a microphotograph of a mixture of sodium aluminate powder and silica fume only mixed with water, heated at 60° C. for 24 hours, and cured at room temperature. Among these, Fig.6 (a) is Si/Al molar ratio =0.5 (comparative example), FIG.6(b) is Si/Al molar ratio =1.25. As shown in FIG. 6A, when the Si/Al molar ratio is 0.5, the deliquescent sodium hydroxide component remains or precipitates and is not solidified. The reaction formula at a Si/Al molar ratio of 0.5 (comparative example) is as follows.
(4) Si/Al=0.5 SiO ₂ +2NaAlO ₂ +H ₂ O→2NaOH+Al ₂ SiO ₅

(Verification example 4)
As Verification Example 4, the effect of adding magnesium hydroxide was confirmed. Table 4 below shows the compounding ratio of the samples used in Verification Example 4. Magnesium hydroxide was added as a carbonate slurry as in Verification Example 2.

FIG. 7 shows the results of Verification Example 4. As shown in FIG. Among them, FIG. 7(a) is a backscattered electron image (BEI) of a mixed geopolymer of zeolite and carbonate slurry, and an elemental map of Si and Mg (enlarged). Moreover, FIG. 7(b) shows the luminance distribution along the line of FIG. 7(a), and shows that the peripheral portion of the magnesium hydroxide particles contains Si.

(Verification example 5)
As Verification Example 5, a geopolymer reactant at a Si/Al molar ratio of 1.0 in a system containing excess sodium compounds was observed. The results of Verification Example 5 are shown in FIG. FIG. 8(a) shows hydroxyl group sodalite=OH—SOD and natrolite=NAT in a system containing excess NaOH. FIG. 8(b) shows chlorine-containing sodalite=Cl—SOD and Si-rich zeolite, analcyme=ANA, in a system containing excess NaOH—NaCl. FIG. 8(c) shows a Cl—Si elemental map of the same field of view as FIGS. 8(a) and 8(b).

According to the results of Verification Example 5 shown in FIG. 8, it can be confirmed that sodalite is formed, and fixation of seawater components such as chlorine can be expected. Solidification was possible in a mixed system of zeolite and carbonate slurry, and it was confirmed that solidification is possible even in a system with a high chlorine concentration derived from carbonate slurry.

Claims (9)

A mixture of only two types of powders, consisting of alkali alumina powder and amorphous silica powder, which turns into zeolite when solidified,
A geopolymer solidifying material , wherein the mixing ratio of the amorphous silica powder to the alkali alumina powder is in the range of 1.0 or more and 2.0 or less in Si/Al molar ratio . 2. The geopolymer consolidation material of claim 1, wherein said alkali alumina powder comprises sodium aluminate powder. 3. The geopolymer solidifying material of claim 2, wherein the sodium aluminate powder is orthorhombic. The geopolymer solidifying material according to any one of claims 1 to 3, wherein the amorphous silica powder includes at least one of silica fume powder and fused silica powder. The geopolymer solidifying material according to any one of claims 1 to 4 , further comprising at least one of sodium hydroxide and sodium halide. A geopolymer solidification method using the geopolymer solidification material according to any one of claims 1 to 5 ,
A geopolymer solidification method, comprising a kneading step of forming a kneaded material by kneading the geopolymer solidification material, water, and an object to be solidified. 7. The geopolymer solidification method according to claim 6 , wherein the mixing ratio of said water to said geopolymer solidification material is in the range of 0.5 or more and 1.5 or less in mass ratio. 8. The geopolymer solidification method according to claim 6 , further comprising a heating step of heating the kneaded material to room temperature or higher. 9. The geopolymer solidification method according to any one of claims 6 to 8 , wherein the solidified material is radioactive waste.

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