KR102095858B1 - Clay Mineral Having Layered Structure-Based Adsorbent for Simultaneously Removing Cesium and Strontium and Method of Preparing the Same - Google Patents

Abstract

The present invention relates to a layered clay mineral-based adsorbent and a method for manufacturing the same, and more specifically, by controlling the thermal reaction in the solid state of the layered clay mineral and the alkali material, thereby increasing the surface area, fine pores, and cation exchange capacity of the layered clay mineral. Manufactured by a simple method using a solid state reaction without using a solvent, and has the advantage of being able to continue production economically, and the adsorption capacity for cesium and strontium is greatly increased, and cesium and strontium are stably stabilized even after irradiation. Since it can be removed, it has utility as an adsorbent to be applied to the actual radionuclide removal process.

Description

Layer Mineral Having Layered Structure-Based Adsorbent for Simultaneously Removing Cesium and Strontium and Method of Preparing the Same}

The present invention relates to a layered clay mineral-based adsorbent that simultaneously removes cesium and strontium, and a method for manufacturing the same, more specifically, by controlling the thermal reaction of the layered clay mineral and the alkali material in a solid state, the surface area and fine pores of the layered clay mineral And a layered clay mineral-based adsorbent that can be used as an adsorption material for simultaneously removing strontium and cesium by increasing a cation exchange capacity, and a method for manufacturing the same.

Nuclear power plants, which have been in the spotlight due to the carbon emission reduction effect and high power generation efficiency, are currently in a decommissioning and dismantling trend due to the danger of nuclear accidents and the difficulty in managing radioactive waste generated in large quantities. For this reason, studies on effective waste treatment methods have been actively conducted in recent years. The most problematic elements in radioactive waste are cesium ( ¹³⁷ Cs) and strontium ( ⁹⁰ Sr), which emit strong gamma rays and have a long half-life of 30 years, damaging the ecosystem for a long time. In addition, they have a high solubility in water, so they can easily enter the ecosystem and the human body.

In order to effectively remove these radionuclides, inorganic-based adsorbents such as zeolite, hexacyanoferrate, and titanosilicate have been used. They have been studied with advantages in terms of manufacturing convenience and selective removal performance for cesium or strontium, respectively. On the other hand, although the clay having a cation exchange ability is abundant in nature and has excellent economic feasibility, it has a difficulty in practical application due to its lack of adsorption capacity and selectivity for cesium and strontium.

Among clay-based adsorbents, montmorillonite having a high cation exchange capacity has a layered structure in which cations such as magnesium, sodium, and potassium are present between unit layers in the form surrounding the alumina layer with a silica layer. The cations present between the unit layers are exchanged with the cations present in the aqueous solution and purification of the waste liquid is achieved. Introduce magnetic nanoparticles to increase process availability of montmorillonite (S. Yang et al., Journal of Hazardous Materials, 2016, 301, 8-16), or introduce hexacyanoferrite to increase adsorption capacity (H Zhang et al., Journal of Materials Chemistry A, 2017, 5, 15130), etc., have been continuously researching performance improvement, but still have difficulties because they do not significantly improve performance while maintaining the economic advantages of montmorillonite.

Thus, the present inventors tried to solve the above problems, as a result, while maintaining physical stability through a simple base treatment of montmorillonite solids, while increasing the surface area compared to montmorillonite before reaction, the adsorption capacity for cesium and strontium is greatly increased. By confirming, the present invention was completed.

An object of the present invention is to provide a layered clay mineral-based adsorbent capable of specifically adsorbing cesium and strontium in a large amount and a method for manufacturing the same.

Another object of the present invention is to provide a method for individually and simultaneously adsorbing cesium and strontium using the adsorbent.

In order to achieve the above object, the present invention provides a layered clay mineral based adsorbent characterized in that an alkali substance is attached to an oxygen-containing functional group present on the surface of the layered clay mineral.

The present invention further comprises: (a) mixing a layered clay mineral with an alkali material; And (b) provides a method for producing a layered clay mineral based adsorbent comprising the step of heating the mixture to react to produce a layered clay mineral based adsorbent.

The present invention also provides a method for adsorbing cesium or strontium using the layered clay mineral-based adsorbent.

The layered clay mineral-based adsorbent base-treated with a solid phase according to the present invention is produced through a simple reaction of a solid phase that does not require a solvent, so the manufacturing method is simple, and low-cost montmorillonite and alkali hydroxide are used as raw materials, so economical mass production is possible. It has the advantage of being able to.

In addition, the active montmorillonite base-treated as a solid phase according to the present invention has a large amount of fine pores, so it can remove cesium and strontium in a short time, and has a high adsorption capacity due to the mass-produced surface functional group, which is applied to actual processes It has utility as an adsorbent that can be used.

FIG. 1 is a diagram schematically showing a process for preparing an active montmorillonite treated with sodium hydroxide according to an embodiment of the present invention.
FIG. 2 (a) shows the cesium adsorption equilibrium data of montmorillonite (MT) and sodium hydroxide-treated active montmorillonite (NaMT1) and the corresponding Langmuir adsorption isotherm, and FIG. 2 (b) shows strontium adsorption of the adsorbents. Equilibrium data and Langmuir adsorption isotherms are shown.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

In the present invention, it was confirmed that through a simple base reaction of montmorillonite and alkali hydroxide in a solid phase, the surface area increased compared to montmorillonite before the reaction, and the adsorption capacity for cesium and strontium was significantly increased, thereby improving the removal efficiency of cesium and strontium. Did.

Therefore, in one aspect, the present invention relates to a layered clay mineral based adsorbent characterized in that an alkali substance is attached to an oxygen-containing functional group present on the surface of the layered clay mineral.

In another aspect, the present invention, (a) mixing a layered clay mineral and an alkali material; And (b) reacting the mixture by heating to prepare a layered clay mineral-based adsorbent.

In the present invention, the layered clay mineral is one or more from the group consisting of montmorillonite, smectite, kaolinite, bentonite, hectorite, hectorite fluorite, videlite, saponite, nontronite, vermiculite, macadamite and mica. It may be selected, preferably montmorillonite may be used, but is not limited thereto.

In the present invention, the alkali material may be an alkali hydroxide, and the alkali hydroxide may be selected from one or more selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca (OH) ₂ ). Sodium hydroxide may be used, but is not limited thereto.

In the present invention, the alkali material may be 50 to 200 parts by weight based on 100 parts by weight of the layered clay mineral. When the alkali material is less than 50 parts by weight based on 100 parts by weight of the layered clay mineral, there is a problem of insufficient pore generation and surface activation effect, and when it exceeds 200 parts by weight, the surface activation effect does not increase.

In the present invention, the layered clay mineral may have a surface area of 15 to 150 m2 / g, a micropore volume of 0.05 to 0.5 cm3 / g, and a micropore size of 1 to 12 nm, preferably 120 to 150 m2 / g. It may have a surface area, a micropore volume of 0.3 to 0.5 cm3 / g, and a micropore size of 1 to 2 nm.

In the manufacturing method of the present invention, the layered clay mineral and the alkali material are mixed in an aqueous solution and then dried or mixed in a solid state to obtain a mixture of the layered clay mineral and the alkali material.

The step (b) may be performed for 1 to 2 hours at a temperature of 200 to 400 ° C at a heating rate of 5 to 10 ° C / min.

The step (b) can be performed while maintaining 0.05 to 50 atmospheres while flowing nitrogen or argon as an inert gas.

In the production method of the present invention, (c) after the step (b) may further include the step of terminating the reaction by cooling with water of 15 ~ 30 ℃ at a temperature of 110 ~ 150 ℃.

In the manufacturing method of the present invention, it may further remove the impurity salts that may be included in the synthesis process, further comprising washing with hot or cold water until the pH is 8 or less after step (c).

In the production method of the present invention, (e) after the step (d) may further include a step of drying at an absolute pressure of 0 to 1 atmosphere and 50 to 90 ° C.

1 shows a process for preparing active montmorillonite base-treated with a solid phase produced through a reaction between montmorillonite and a solid alkali hydroxide according to a preferred embodiment of the present invention.

In the embodiment of the present invention, the active montmorillonite base-treated with the solid phase prepared by the above method has adsorption capacity for cesium and strontium that is more than twice that of montmorillonite before treatment, and selects cesium even in groundwater conditions where a large amount of competitive ions are present. It was confirmed that it shows excellent performance to remove.

Therefore, in another aspect, the present invention relates to a method for adsorbing cesium and strontium using the adsorbent.

Hereinafter, the present invention will be described in more detail by examples. These examples are only for explaining the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited to these examples.

Example  1: Solid phase using sodium hydroxide Base-treated  Preparation of active montmorillonite

A method of preparing active montmorillonite base-treated in a solid phase by controlling the degree of reaction using sodium hydroxide (NaOH) and montmorillonite is described in detail as follows.

1.5 g of montmorillonite was physically mixed with a certain amount of sodium hydroxide for 20 minutes. At this time, sodium hydroxide had a mass of 50 to 200% compared to the mass of montmorillonite as shown in Table 1. Thereafter, the mixture was placed in an alumina crucible, placed in a reactor, and nitrogen (N ₂ ,> 99%) was flowed at 50 mL / min for 30 minutes to adjust the gas composition. After that, the temperature of the reactor was raised from 25 ° C to 300 ° C at 5 ° C / min and maintained at 300 ° C for 1 hour. After the reaction was completed, the temperature of the reactor was allowed to cool naturally, and to maintain the functional group, the mixture was rapidly cooled using 25 ° C of cold water when the reactor temperature became 135 ° C. Active montmorillonite base-treated with the prepared solid phase was washed with cold water to remove residual sodium hydroxide and impurity salts. After a series of cold water washing and centrifugation, when the pH of the centrifuged supernatant became 8 or less, the active montmorillonite base-treated with the prepared solid phase was dried in an oven at 80 ° C.

Through the above process, active montmorillonite base-treated with a solid phase having a different reaction degree was prepared, and the manufacturing process is schematically illustrated in FIG. 1.

Mass ratio of sodium hydroxide to montmorillonite Experimental group One 2 3 Sodium hydroxide / montmorillonite 0.5 One 2

Example  2: Separate adsorption equilibrium experiment of cesium and strontium

Adsorption equilibrium experiments for cesium and strontium ions were performed on an adsorbent having a sodium hydroxide / montmorillonite mass ratio of 1 (NaMT1) and montmorillonite (MT) without sodium hydroxide treatment among active montmorillonite prepared using Example 1. Did. In the adsorption equilibrium experiment, cesium chloride (CsCl) and strontium chloride (SrCl ₂ ) were dissolved in distilled water to prepare cesium and strontium solutions (5 to 1000 mg / L) with different concentrations, and 0.02 g of adsorbent was added to 0.02 L of the solution. It was performed by stirring at 200 rpm for 24 hours at ℃. Thereafter, the solution was filtered using a micro filter having a pore size of 0.45 μm, and the initial concentration C ₀ and the final equilibrium concentration C _e were measured by ICP-MS, and the adsorption capacity (Q _e , mg / g) was calculated.

[Equation 1]

In this case, V is the volume of the cesium or strontium solution (L), and m is the mass of the adsorbent (g).

The adsorption capacity Q _e obtained through the experiment is shown in FIG. 2 according to the final equilibrium concentration C _e . Tables 2 and 2a relate to cesium adsorption equilibrium experiments, and Tables 3 and 2b relate to strontium adsorption equilibrium experiments. Each data was approximated using a Langmuir adsorption isotherm and the maximum adsorption capacity parameter obtained through this was included in FIG. 2 through a table. As a result of the analysis, NaMT1 significantly increased the adsorption capacity for cesium and strontium compared to the MT used as a control group, and showed the maximum adsorption capacity for cesium and the maximum adsorption capacity for strontium. Through this, it can be seen that the adsorption performance of montmorillonite is greatly increased through reaction with alkali hydroxide.

Example 3: Efficiency of simultaneous removal of cesium and strontium

Adsorption experiments were performed on a solution containing a mixture of cesium and strontium ions. The experimental group used in this experiment was 1) prepared by the same method as in Example 1 using an adsorbent having a sodium hydroxide / montmorillonite mass ratio of 1 in active montmorillonite using sodium hydroxide prepared in Example 1 (NaMT1), 2) potassium hydroxide. One active montmorillonite (KMT), 3) Active montmorillonite (KNaMT) prepared in the same manner as in Example 1 using a mixture of potassium hydroxide and sodium hydroxide.

First, cesium chloride (CsCl) and strontium chloride (SrCl ₂ ) are dissolved in distilled water to prepare cesium and strontium solutions of different concentrations (0.7 to 15 mg / L). It was carried out by stirring at 200 rpm for an hour. Thereafter, the solution was filtered using a micro filter having a pore size of 0.45 μm, and the initial concentration C ₀ and the final equilibrium concentration C _e were measured by ICP-MS to remove the removal efficiency (RE) through Equations 2 and 3 below. ,%) And partition coefficient (K _d , mL / g).

[Equation 2]

[Equation 3]

Table 4 shows the removal efficiency and distribution coefficient obtained through the experiment.

As shown in Table 4, the cesium and strontium removal efficiencies were higher than 85% for each experimental group, and the strontium removal efficiency was somewhat higher than the cesium removal efficiency. In addition, the experimental group in which sodium hydroxide was included in the manufacturing method was effective in removing cesium.

Example 4: Cesium and strontium removal efficiency in the presence of competitive ions

Selective adsorption experiments for cesium and strontium in a groundwater condition in which competitive ions are present, an adsorbent (NaMT1) having a sodium hydroxide / montmorillonite mass ratio of 1 in active montmorillonite base-treated with solid phase using sodium hydroxide prepared in Example 1 It was performed on montmorillonite (MT) without sodium hydroxide treatment. For the for the experiment for the competitive ion for Na ⁺ in the solution is about cesium and strontium present in from about 1 ppm about 145 ppm, K ⁺ from about 230ppm, Ca ^{2 +} at a concentration of about 25 ppm NaCl, KCl, CaCl ₂ Each was dissolved to prepare a solution for groundwater conditions. 0.02 g of NaMT1 and MT were added to 0.02 L of the prepared solution, respectively, and the adsorption experiment was performed by stirring at 200 rpm at 25 ° C. for 24 hours. Thereafter, the solution was filtered using a micro filter having a pore size of 0.45 μm, and the initial concentration C ₀ and the final equilibrium concentration C _e were measured by ICP-MS to remove the removal efficiency (Equation 2 and 3). ,%) And partition coefficient (K _d , mL / g).

[Equation 2]

[Equation 3]

Table 5 shows the distribution coefficient and removal efficiency obtained through the experiment.

As shown in Table 5, MT before base treatment was only used to remove less than 20% of cesium and strontium in groundwater conditions where a large amount of cations were present, whereas NaMT1 after base treatment was selectively 60% of cesium and strontium. It was removed abnormally. The distribution coefficient also showed that NaMT1 was about 10 times higher than MT.

Example 5: cesium and strontium removal efficiency after irradiation

Adsorption experiments in a mixed solution containing cesium and strontium were performed using an adsorbent irradiated with gamma rays. The adsorbent used at this time is an adsorbent (NaMT1) having a sodium hydroxide / montmorillonite mass ratio of 1 among the active montmorillonite base-treated in a solid phase using sodium hydroxide prepared in Example 1 and montmorillonite (MT) without sodium hydroxide treatment. For the experiment, a cesium isotope having a mass number of 137 was used as the gamma ray source irradiated to NaMT1 and MT, and irradiated at 6 Gy / h for 30 minutes. The adsorption experiment was performed by adding 0.02 g of NaMT1 and MT irradiated with gamma rays to 0.02 L of a mixed solution containing cesium and strontium at about 15 ppm and stirring at 200 ° C at 25 ° C for 24 hours. Then, the solution was filtered using a micro filter having a pore size of 0.45 μm, and the initial concentration C ₀ and the final equilibrium concentration C _e were measured through ICP-MS to calculate removal efficiency through Equation 3.

Table 6 shows the removal efficiency obtained through the experiment.

As shown in Table 6, after irradiation, NaMT1 removed cesium and strontium 86% and 92%, respectively, and showed excellent adsorption performance. In addition, both NaMT1 and MT showed no significant difference in adsorption performance compared to before irradiation. This showed that the base reaction did not inhibit the adsorption performance and structural stability of montmorillonite.

Therefore, it can be seen that in the removal of trace amounts of cesium and strontium present in the actual nuclear power plant waste, the active montmorillonite base-treated as a solid phase according to the embodiment can effectively remove cesium and strontium even under conditions of radiation and competition ions.

Since the specific parts of the present invention have been described in detail above, for those skilled in the art, it is obvious that this specific technique is only a preferred embodiment, and the scope of the present invention is not limited thereby. something to do. Therefore, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (14)

Method for producing a layered clay mineral based adsorbent comprising the following steps:
(a) mixing 50 to 200 parts by weight of a solid alkali material with respect to 100 parts by weight of the layered clay mineral and the layered clay mineral; And
(b) preparing a layered clay mineral-based adsorbent by heating and reacting the mixture for 1 to 2 hours at a temperature of 200 to 400 ° C at a heating rate of 5 to 10 ° C / min;
(c) after the step (b), cooling with water of 15 to 30 ° C at a temperature of 110 to 150 ° C to terminate the reaction;
(d) washing with hot or cold water until pH 8 or less after step (c); And
(e) drying after the step (d) at an absolute pressure of 0 to 1 atmosphere, 50 to 90 ° C,
The layered clay mineral-based adsorbent has an alkali substance attached to an oxygen-containing functional group present on the surface of the layered clay mineral, a surface area of 15 to 150 m ² / g, a micropore volume of 0.05 to 0.5 cm ³ / g, and 1 to 12 nm. Characterized by having a micropore size of.
The layered clay mineral is 1 selected from the group consisting of montmorillonite, smectite, kaolinite, bentonite, hectorite, hectorite fluoride, videlite, saponite, nontronite, vermiculite, macadamite and mica. Method of manufacturing a layered clay mineral based adsorbent, characterized in that more than species.
The method of claim 1, wherein the alkali material is an alkali hydroxide.
The method according to claim 3, wherein the alkali hydroxide is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide.
delete delete delete delete delete The method of claim 1, wherein the step (b) is carried out while maintaining 0.05 to 50 atmospheres while flowing an inert gas.
delete delete delete The method of claim 1, wherein the layered clay mineral based adsorbent is used for adsorption of cesium or strontium.

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