KR20190043937A - Titanosilicate Adsorbent Having Sodium and Potassium for Simultaneously Removing Cesium and Strontium and Method of Preparing the Same - Google Patents

Abstract

A titanium silicate adsorbent containing sodium and potassium according to the present invention contains both sodium and potassium ions, thereby exhibiting a high selective removal rate even in the presence of a large amount of competitive ions, exhibiting excellent selectivity compared to existing titanium silicate adsorbents, and having an effect of economically synthesizing titanium silicate by a one-step synthesis process.

Description

TECHNICAL FIELD The present invention relates to a titanium silicate adsorbent containing sodium and potassium for simultaneous adsorption of cesium and strontium and a method for preparing the same.

The present invention relates to a titanium silicate adsorbent containing sodium and potassium for the simultaneous adsorption of cesium and strontium and a method for preparing the same. More particularly, the present invention relates to a titanium silicate adsorbent containing both sodium and potassium ions, The present invention relates to a titanium silicate adsorbent containing sodium and potassium for simultaneous adsorption of cesium and strontium, and a method for producing the same.

As energy dependence on nuclear power plants is increasing worldwide, reprocessing of normal operation or disposal of radioactive waste that can occur due to nuclear accidents is becoming a major problem (Shuvo Jit Datta et al ., Angew Chem Int Edit 2014, 53, 7203).

Of the radioactive wastes, ¹³⁷ Cs and ⁹⁰ Sr are the major sources of pollutants, each of which has a long half-life of about 30 years, releasing gamma rays and beta-particles, respectively, and classified as high risk. However, it is very difficult to selectively remove cesium and strontium because they exist in extremely low concentrations (ppm or ppb levels) in the waste together with sodium, potassium, magnesium, calcium and the like.

In order to remove such radioactive cesium and strontium, various organic or inorganic-based adsorbents have been developed to date. However, organic-based adsorbents have been limited in their practical use due to safety issues in terms of adsorption in radioactive conditions and storage after adsorption (Huajun Yang et al ., Chemistry of Materials 2016, 28, 8774). In addition, zeolite or clay based materials among existing inorganic adsorbents have difficulties in practical use because of their stability to pH and selectivity to cesium and strontium under competitive ion conditions. On the other hand, titanium silicate is not only stable under radioactive and various chemical conditions, but also has a high selectivity for trace amounts of cesium and strontium.

Typically, two types of titanium silicates are attracting much attention for the removal of radioactive materials, the chemical structures of which are shown in Formulas 1 and 2.

[Chemical Formula 1]

Na ₂ Ti ₂ O ₃ SiO ₄

(2)

M ₃ HTi ₄ O ₄ (SiO ₄ ) ₃ (M = alkali metal)

(1) is a crystalline titanosilicate (CST), and its proton (H ⁺ ) exchange form, H-CST, has a high selectivity for cesium even under a large amount of sodium, It has a disadvantage in that it does not show efficient removal performance with respect to strontium. Formula 2 is a titanium silicate having a morphology similar to the crystalline structure of a pharmacosiderite present in nature, and exhibits high removal efficiency for both cesium and strontium in the presence of competitive ion at ppm level. However, the removal efficiency of cesium and strontium is drastically decreased under a large amount of competitive ion conditions, and the production method is complicated, for example, in order to increase the removal efficiency according to each competitive ion condition, There are disadvantages.

The present inventors have made intensive efforts to solve the above problems. As a result, the inventors of the present invention have found that titanium silicates synthesized to simultaneously contain sodium and potassium ions exhibit high removal performance against both cesium and strontium, And exhibits excellent selectivity even under competitive ion conditions, thereby completing the present invention.

It is an object of the present invention to provide a titanium silicate adsorbent containing both sodium and potassium capable of specifically adsorbing cesium and strontium and a method for producing the same.

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

In order to attain the above object, the present invention provides a titanium silicate adsorbent characterized by the formula (3).

(3)

M ¹ _x M ² _3-x HTi ₄ O ₄ (SiO ₄ ) ₃

In Formula (3), M ¹ is Na, M ² is K, and x is 1 or 2.

The present invention also provides a process for preparing a titanium silicate adsorbent of Formula 3, wherein the mixture of Na precursor, K precursor, silica precursor, titanium precursor and distilled water is hydrothermally reacted.

The present invention also provides a method for adsorbing cesium or strontium using the adsorbent.

The titanium silicate adsorbent for adsorbing cesium and strontium according to the present invention is capable of simultaneous adsorption of cesium and strontium and exhibits high selectivity to cesium and strontium for a large amount of competitive ions compared with the conventional titanium silicate. And as an adsorbent material for the purification of polluted areas in the event of a nuclear accident. In addition, the process is also synthesized through the hydrothermal reaction in the first step, and is advantageous in that the production can be continued simply and economically. Therefore, due to the high efficiency from production to use of the adsorbent, It has high potential.

1 is a diagrammatic representation of a process for preparing a titanium silicate adsorbent containing both sodium and potassium ions according to an embodiment of the present invention.
2 is an XRD spectrum of a titanium silicate adsorbent containing both sodium and potassium ions according to an embodiment of the present invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly used in the art.

In the present invention, an adsorbent containing both sodium and potassium ions in the titanium silicate was synthesized through a one-step hydrothermal reaction. The prepared titanium silicate adsorbent (hereinafter referred to as DT) was added to both cesium and strontium But also high selectivity under groundwater and seawater conditions in which a large amount of competitive ions exist.

Accordingly, in one aspect, the present invention relates to a titanium silicate adsorbent characterized by the formula (3).

(3)

M ¹ _x M ² _3-x HTi ₄ O ₄ (SiO ₄ ) ₃

In Formula (3), M ¹ is Na, M ² is K, and x is 1 or 2.

In another aspect, the present invention relates to a process for preparing a titanium silicate adsorbent of formula (III), characterized in that a mixture of Na precursor, K precursor, silica precursor, titanium precursor and distilled water is hydrothermally reacted.

In the present invention, the titanium precursor may be titanium chloride, titanium isopropoxide, titanium butoxide, and titanium dioxide (TiO ₂ ) of TiCl ₃ or TiCl ₄ . One or more selected from the group consisting of titanium chloride, titanium chloride, and the like, but is not limited thereto.

In the present invention, the silica precursor may be at least one member selected from the group consisting of sodium silicate, fumed silica, tetraethyl orthosilicate, and tetrabutyl orthosilicate. And preferably, sodium silicate can be used, but is not limited thereto.

In the present invention, the Na precursor is sodium hydroxide (NaOH), sodium chloride (NaCl), sodium carbonate (Na ₂ CO _3), sodium nitrate (NaNO _3), sodium sulfate (Na ₂ SO ₄₎ and sodium And fluoride (NaF). Among them, sodium hydroxide may be used, but it is not limited thereto.

In the present invention, the K precursor is selected from the group consisting of potassium hydroxide (KOH), potassium chloride (KCl), potassium carbonate (K ₂ CO ₃ ), potassium nitrate (KNO ₃ ), potassium sulfate (K ₂ SO ₄ ) Fluoride (KF), preferably potassium hydroxide and / or potassium fluoride, more preferably potassium hydroxide and potassium fluoride mixture But is not limited thereto.

In the production process according to the present invention, the hydrothermal reaction can be carried out at a temperature of 100 to 300 ° C. for 1 to 10 days. Preferably at a temperature of 100 to 200 DEG C for 2 to 5 days, most preferably at 180 DEG C for 4 days.

The hydrothermal reaction may further comprise a washing step. After the hydrothermal reaction, it may be washed with water alone, alcohol such as ethanol or methanol, ketone such as acetone, or the like, or a solution capable of removing the residual base and unreacted materials under the condition that the titanium silicate is not decomposed. The order of washing or the number of times is also not limited.

A process for producing a titanium silicate adsorbent containing both sodium and potassium ions according to a preferred embodiment of the present invention is shown in FIG.

The mixture obtained by mixing NaOH, KOH, KF, sodium silicate, TiCl ₃ and distilled water was stirred at 30 ° C. for 2 hours. The resulting mixture was sealed in a Teflon autoclave and sealed. The reaction proceeds. The synthesized material is recovered by filtration and washed with distilled water and ethanol. The finally synthesized titanium silicate is placed in an oven at 80 캜 and dried to obtain a crystal of titanium silicate.

The titanium silicate containing sodium and potassium ions of the present invention can be removed simultaneously with cesium and strontium. In addition, even under groundwater and seawater conditions in which a large amount of competitive ions exist, the titanium silicate is superior in selectivity to cesium and strontium Respectively.

Therefore, the present invention relates to a method for adsorbing cesium or strontium using the adsorbent from a different viewpoint.

Hereinafter, the present invention will be described in more detail with reference to Examples. It will be apparent to those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not limited to these embodiments.

Example  1: sodium and potassium ions simultaneously Titanium silicate (DT) manufacture

Titanium silicates containing both sodium and potassium ions were synthesized through a one-step hydrothermal reaction (Fig. 1).

Insert the 9g of NaOH, 4.5g of KOH, 4.7g of KF, 11g sodium silicate (sodium silicate), TiCl _3, and distilled water of 54g of the 12.8g of the mixture was stirred for 2 hours at 30 ℃. The mixture was then sealed in a Teflon autoclave and hydrothermal reaction was carried out in an oven at 180 DEG C for 4 days. The synthesized material was recovered by filtration and washed with distilled water five times with ethanol once. The finally synthesized titanium silicate was placed in an oven at 80 ° C and dried. The crystal structure of the titanium silicate synthesized by the above method was confirmed by XRD (FIG. 2), and the ICP-OES component analysis is shown in Table 1.

Example  2: Simultaneous adsorption experiments of cesium and strontium over time

Experiments were conducted on the titanium silicate adsorbent (DT) containing both the sodium and potassium ions prepared in Example 1 to change the removal rate with time for cesium and strontium ions. The removal rate of CsCl and SrCl ₂ was dissolved in distilled water at the same time to prepare a solution of Cs having a concentration of Sr of about 10 ppm (initial cesium and strontium concentration C ₀ , mg / L) The adsorbent (m, g) was added to 20 mL of the solution (V, L) in an amount of 0.02 g (m, g) at 25 ° C. for 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, And stirring was carried out. Thereafter, the solution was filtered using a microfilter to prepare a filtrate (residual cesium and strontium concentration _Ct , mg / L at each time). The initial concentration C ₀ and the residual concentration C _t over time were measured by ICP-MS, and the removal rate (RE,%) was calculated by the following equation (1).

[Equation 1]

Table 2 shows the removal rates of the prepared adsorbent DT with time in the solution in which cesium and strontium are present simultaneously.

The prepared titanium silicate adsorbent (DT) shows a very high removal rate of 99.5% or more for both cesium and strontium, and it can be confirmed that most ions can be removed in about 5 minutes.

Example  3: Simultaneous removal efficiency of cesium and strontium under competitive ion conditions

The selectivity of cesium and strontium of the titanium silicate adsorbent (DT) prepared in Example 1 was performed under various conditions in which competitive ions were present.

Example  3-1

The adsorption solution was prepared by dissolving 0.05M NaCl, KCl, MgCl ₂ , and CaCl ₂ in 1 ppm cesium and strontium solution (initial cesium and strontium concentration C ₀ , mg / L) for each individual competitive ion.

The removal rate (RE,%) of about 1 ppm cesium and strontium in the Na ⁺ , K ⁺ , Mg ^{2 +} , Ca ^{2 +} solution of 0.05 M concentration of the prepared adsorbent DT is shown in Table 3.

From the results of Table 3, it can be seen that the produced adsorbent DT exhibits a very high removal rate of about 99% in all cases, except for the removal rate of cesium and strontium in solution in KCl and CaCl ₂ . The reduction in adsorption efficiency for KCl and CaCl ₂ is attributed to the hydrated ionic radius between K ⁺ and Cs ⁺ and between Ca ^{2 +} and Sr ^{2 +} , especially for Ca ^{2 +} It is because it affects.

Example  3-2

Selection of the cesium in the underground water and sea water conditions also experiments for Na ^+, the underground water and sea water solution containing a concentration of K ^+, Mg ^{2 +,} Ca ^{2 +} in the tables 4 and about 1ppm, the concentration of cesium and strontium To prepare an adsorption solution. However, in case of seawater, it actually contained about 7ppm strontium, and the initial concentration was 7ppm without additional strontium.

The compositions of Na ⁺ , K ⁺ , Mg ^{2 +} , and Ca ^{2 +} in the groundwater and seawater used in the cesium and strontium adsorption experiments of the present invention are shown in Table 4.

As a control of Experiment 2, the previously reported titanium silicates were synthesized on the basis of the literature and the same experiment was conducted (Poojary et al ., Chemistry of Materials 1994, 6, 2364, Dyer et al ., Journal of Materials Chemistry 1999 , 9, 2481). The structure of the titanium silicate of the control group was the same as that of the control groups 1, 2 and 3, and it was compared with Comparative Examples 1, 2 and 3.

[Control 1]

K ₃ HTi ₄ O ₄ (SiO ₄ ) ₃

[Control group 2]

Na ₃ HTi ₄ O ₄ (SiO ₄ ) ₃

[Control 3]

H ₂ Ti ₂ O ₃ SiO ₄ (H-CST)

To 20 mL of each of the prepared solutions, 0.02 g of adsorbent (DT and control groups 1, 2 and 3) was added, and the mixture was stirred at 25 DEG C for 24 hours. Thereafter, the solution was filtered using a microfilter to prepare a filtrate (equilibrium cesium and strontium concentration C _e , mg / L). The initial concentration C ₀ and the equilibrium concentration C _e were measured by ICP-MS and the removal efficiency (RE,%) was calculated by the following equation (1).

[Equation 1]

The removal rate (RE,%) of about 1 ppm cesium and strontium in the groundwater condition of the prepared adsorbent DT (Example 3-1) and the removal rate of about 1 ppm cesium and 7 ppm strontium in the seawater conditions of the prepared adsorbent DT ,%) (Example 3-2) are shown in Tables 5 and 6, respectively.

As shown in Table 5, it was confirmed that the prepared adsorbent DT exhibited an excellent removal rate of 95% or more for both cesium and strontium. First, K ₃ HTi ₄ O ₄ (SiO ₄ ) ₃ and Na ₃ HTi ₄ O ₄ (SiO ₄ ) ₃ Despite having built a more efficient one-stage synthesis system in comparison to the adsorbent, it is characterized by improved performance in both cesium and strontium. Compared with H ₂ Ti ₂ O ₃ SiO ₄ , which is also known as the most excellent cesium sorbent, it exhibits comparable cesium adsorption capacity and much better strontium removal.

The results of adsorption on seawater of Table 6 show that DT, K ₃ HTi ₄ O ₄ (SiO ₄ ) ₃ , Na ₃ HTi ₄ O ₄ (SiO ₄ ) ₃ All adsorbents showed a removal rate of about 36 ~ 40%. This is due to the effect of large amounts of divalent cations, Ca ^{2 +} and Mg ^{2 +} , present in seawater. H-CST still showed very low strontium removal efficiency compared to the above three adsorbents. On the other hand, for cesium, the highest removal efficiency of 97.55% for DT was obtained, which was beyond the adsorption capacity of 95.02% of H-CST. This is because the existence of both Na ⁺ and K ⁺ in the crystal structure of DT allows the Na ⁺ and K ⁺ to maintain their improved performance even under the condition that both Na ⁺ and K ⁺ act as a large amount of external competitive ions as in seawater.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereby. something to do. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (9)

A titanium silicate adsorbent characterized by the formula (3).
(3)
M ¹ _x M ² _3-x HTi ₄ O ₄ (SiO ₄ ) ₃
In Formula (3), M ¹ is Na, M ² is K, and x is 1 or 2.
Wherein the mixture is hydrothermally reacted with a mixture of Na precursor, K precursor, silica precursor, titanium precursor and distilled water.
(3)
M ¹ _x M ² _3-x HTi ₄ O ₄ (SiO ₄ ) ₃
In Formula (3), M ¹ is Na, M ² is K, and x is 1 or 2.
The method of claim 2, wherein the titanium precursor is at least one selected from the group consisting of titanium chloride, titanium isopropoxide, titanium butoxide, and titanium dioxide. Wherein the titanium silicate adsorbent is a titanium silicate adsorbent.
The method of claim 2, wherein the silica precursor is selected from the group consisting of sodium silicate, fumed silica, tetraethyl orthosilicate, and tetrabutyl orthosilicate. Or more of the titanium silicate adsorbent.
The method of claim 2, wherein the Na precursor is sodium hydroxide (NaOH), sodium chloride (NaCl), sodium carbonate (Na ₂ CO _3), sodium nitrate (NaNO _3), sodium sulfate (Na ₂ SO _4), and Wherein the titanium silicate adsorbent is at least one selected from the group consisting of sodium fluoride (NaF).
The method of claim 2, wherein the K precursor is potassium hydroxide (KOH), potassium chloride (KCl), potassium carbonate (K ₂ CO _3), potassium nitrate (KNO _3), potassium sulfate (K ₂ SO _4), and Potassium fluoride (KF). The method for producing a titania silicate adsorbent according to claim 1, wherein the titanium silicate adsorbent is selected from the group consisting of potassium fluoride (KF) and potassium fluoride (KF).
The method of claim 2, wherein the hydrothermal reaction is performed at a temperature of 100 to 300 ° C. for 1 to 10 days.
3. The method of claim 2, further comprising a cleaning step after the hydrothermal reaction.
A method of adsorbing cesium or strontium using the titanium silicate adsorbent of claim 1.

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