KR102314371B1 - Alginate beads having buckwheat hull biochar and radionuclide removal method using the same - Google Patents

Abstract

The present invention relates to alginate beads on which buckwheat hull biochar is immobilized, and more particularly, to alginate beads on which buckwheat hull biochar is immobilized, which selectively removes radioactive cobalt and is easy to recover, and a method for removing radionuclides using the same.
The biochar-alginate beads for removal of radionuclides in water of the present invention enable selective removal of radionuclides in water through ion exchange, including buckwheat hull biochar containing calcium ions, and have pores on the surface to achieve high radionuclide adsorption efficiency. have In addition, it is possible to treat waste in a large-scale process using a sieve after adsorption of radionuclides.

Description

Alginate beads having buckwheat hull biochar and radionuclide removal method using the same}

The present invention relates to alginate beads to which buckwheat hull biochar is immobilized, and more particularly, to alginate beads to which buckwheat hull biochar is immobilized, which selectively removes radioactive cobalt and is easy to recover, and a method for removing radionuclides using the same.

Various types of radioactive waste are generated during the operation and decommissioning of nuclear power plants. In particular, among these wastes, liquid radioactive waste occupies a large proportion and contains radionuclides such as cesium, strontium, and cobalt. As a corrosion product, radioactive cobalt is classified as a radionuclide harmful to the environment and human body due to its long half-life (5.27 years), high radioactivity (γ-ray and β-ray), high mobility, high water solubility, and low biodegradability. As a technology for treating radioactive cobalt, various methods such as coagulation/sedimentation, solvent extraction, evaporation, electrodialysis, and adsorption are used. While other process technologies consume a lot of energy and have poor recoverability, the adsorption process can economically treat a large amount of radioactive wastewater, and is currently being actively studied because of its high efficiency and recoverability.

Recently, biochar, which is used as a substitute for activated carbon, refers to a porous material having a rich carbon content produced by thermally decomposing biomass under an anoxic condition. In addition, the surface functional groups, cation exchange capacity, large specific surface area, and fine pore structure of biochar can adsorb and retain various cations in water, making it a promising material for efficiently removing contaminants in water. Removal of pollutants in water using various types of biochar (seaweed, sawdust, sewage sludge, fallen leaves) is being studied.

Korean Patent Registration No. 10-1506094 discloses a spherical core-shell capsule form having high adsorption capacity using chicken manure biochar. However, in the case of radioactive wastewater, selectivity for radionuclides is required, and in order to be applied to the treatment of a huge amount of liquid radioactive waste, it is required that the waste is easily separated and recovered after treatment.

Republic of Korea Patent Registration No. 10-1506094

In order to solve the above problems, an object of the present invention is to provide a biochar-alginate bead for removing radionuclides in water, which selectively adsorbs radionuclides in water and can easily remove wastes using a sieve.

Another object of the present invention is to provide a method for removing radionuclides in water using the biochar-alginate beads.

In order to achieve the above object, the present invention

As an adsorbent for adsorbing nuclides in radioactive wastewater,

alginate; and

It includes; buckwheat hull-based biochar fixed to the alginate, and provides a biochar-alginate bead for removing radionuclides in water having pores on the surface.

The present invention in order to achieve the above other object,

A first step of preparing biochar-alginate beads comprising alginate and buckwheat hull-based biochar fixed to the alginate and having pores on the surface;

a second step of adsorbing radionuclides by injecting the biochar-alginate beads into radioactive wastewater; and

A third step of recovering the biochar-alginate beads to which the radionuclide is adsorbed using a sieve (net) provides a method for removing radionuclides in the water, including a.

The biochar-alginate beads for removal of radionuclides in water of the present invention enable selective removal of radionuclides in water through ion exchange, including buckwheat hull biochar containing calcium ions, and have pores on the surface to provide high radionuclide adsorption efficiency. have an effect.

In addition, the underwater radionuclide removal method of the present invention has a high efficiency of removing radionuclides by using biochar-alginate beads having pores on the surface, and has the effect of enabling waste treatment in a large-scale process using a sieve after adsorption.

1 shows an adsorption mechanism of buckwheat hull biochar according to an embodiment of the present invention.
2 shows a method for preparing biochar-alginate beads according to an embodiment of the present invention.
3 is a graph showing the results of a radionuclide removal experiment with respect to the thermal decomposition temperature of biochar according to an embodiment of the present invention.
4 is a structural photograph of biochar-alginate beads according to an embodiment of the present invention.
5 is an FT-IR analysis graph of the surface of biochar according to an embodiment of the present invention.
6 is an XRD analysis result of biochar powder and biochar-alginate beads according to an embodiment of the present invention.
7 is a scanning electron microscope (SEM) photograph of biochar powder and beads according to an embodiment of the present invention.
8 is a graph showing a solution pH and a concentration of released calcium ions after biochar according to an embodiment of the present invention is adsorbed with cobalt.
9 is a graph showing the cobalt adsorption capacity of an adsorbent according to an embodiment or a comparative example of the present invention.
10 is a schematic diagram showing a fixed bed adsorption reactor and a recovery body (net) using biochar-alginate beads according to an embodiment of the present invention.
11 is a photograph showing the degree of dispersion in aqueous solution of biochar powder and biochar-alginate beads according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail.

According to one aspect of the present invention, as an adsorbent for adsorbing nuclides in radioactive wastewater,

alginate; and buckwheat hull-based biochar fixed to the alginate; and biochar for removing radionuclides in water having pores on the surface-alginate beads.

Biochar is biochar, which is produced by thermal decomposition of biomass when exposed to high temperatures in an oxygen-deficient state. Biomass is a renewable organic material extracted from energy-only crops and trees, agricultural and fodder crops, agricultural waste and debris, forest waste and debris, aquatic plants, animal dung, municipal waste, and other wastes. Used wood, plants, agricultural by-products, and organic components in municipal waste and industrial waste.

Among such biomass, in the present invention, biochar obtained by low-speed thermal decomposition of buckwheat hull was used. In the present specification, the buckwheat husk refers to the hull of buckwheat. Buckwheat hull biochar is a major component of this bead, and because it is a natural material, it does not cause secondary contamination, and has a large specific surface area and a porous structure, so it has excellent adsorption properties.

1 shows an adsorption mechanism of buckwheat hull biochar according to an embodiment of the present invention. Referring to FIG. 1 , radionuclides can be adsorbed through precipitation, ion exchange, and surface complexation. Particularly preferably, the removal rate for cobalt is excellent.

In relation to precipitation, beads containing buckwheat hull biochar have CO ₃ ^2- and SiO ₂ functional groups on the surface, so that radionuclides in water can be separated through co-precipitation. In particular, the binding force to cobalt ions is high, and cobalt ions can form cobalt hydroxide (Co(OH) ₂ ) based on pH 7 and form salts for surface precipitation.

In relation to ion exchange, calcium ions contained in buckwheat hull biochar can be used. Buckwheat hull biocha contains a large amount of calcium ions by electrostatic attraction, surface functional groups, and precipitation, and these calcium ions can be exchanged with cations in water. Depending on the thermal decomposition temperature of biochar, the degree of exchange of calcium ions with cations in water can be controlled.

In relation to surface complexation, beads containing buckwheat hull biochar have -OH, C-H, and C-C functional groups and bind to radionuclides to perform an adsorption function through surface complexation.

Alginate is a heteropolysaccharide in which beta-d-mannuronic acid and alpha-l-glucuronic acid are mixed. Chemically, it belongs to carbohydrates, but unlike starch fibers, it is a natural polymer having a carboxyl group. In the present invention, the alginate may be an alginic acid salt, preferably sodium alginate. Sodium alginate is prepared by saturating alginate with Na, and has a property of being solidified when added to a solution containing a divalent metal cation. Accordingly, biochar-alginate beads can be prepared by injecting and reacting a mixed solution of biochar and alginate into a metallic divalent cation solution.

The biochar-alginate beads according to the present invention have an amorphous structure and a porous structure having pores on the surface. The pores on the surface have an irregular shape, and the adsorption efficiency can be improved by increasing the specific surface area of the beads.

In addition, it has improved durability by removing moisture. Before drying, the beads (hydrogel beads) have weak durability, so there is a risk of breakage when inserted into a fixed bed adsorption reactor, and there is a problem that the components may melt or swell when exposed to an aqueous solution for a long time. On the other hand, the beads (dry beads) after drying have good durability by removing moisture, and the scope of use can be expanded in that they do not melt or swell in aqueous solution.

The radionuclide adsorbable to the biochar-alginate beads according to the present invention may be any one of cesium, strontium, and cobalt. Preferably, it may be cobalt.

The biochar-alginate beads according to the present invention may have a particle diameter of 1 to 5 mm, preferably 1 to 3 mm, and more preferably an average of 2 mm. When the particle diameter is less than 1 mm, there is a difficulty in the waste removal process after the adsorption process, and when it exceeds 5 mm, the adsorption efficiency according to the specific surface area is lowered, which is not preferable.

According to another aspect of the present invention, biochar comprising alginate and buckwheat hull biochar fixed to the alginate, and having pores on the surface - a first step of preparing alginate beads ; a second step of adsorbing radionuclides by injecting the biochar-alginate beads into radioactive wastewater; and a third step of recovering the biochar-alginate beads to which the radionuclide has been adsorbed using a sieve (net).

First, the first step of preparing the biochar-alginate beads will be described.

In the present invention, biochar obtained by low-speed pyrolysis of buckwheat hull was used as biochar. Because buckwheat hull biocha is a natural material, it does not cause secondary contamination, has a large specific surface area and a porous structure, and has excellent adsorption properties. In addition, it is possible to increase the adsorption efficiency of radionuclides according to ion exchange and surface functional groups.

The buckwheat hull biocha of the present invention may have different functional levels of surface functional groups depending on the thermal decomposition temperature. The thermal decomposition temperature may be 400 to 800 °C, preferably 450 to 750 °C, and more preferably 750 °C.

In the present invention, the alginate may be an alginic acid salt, preferably sodium alginate. Biochar-alginate beads can be prepared by injecting and reacting a mixed solution of buckwheat hull biochar and alginate into a metallic divalent cation solution. At this time, the metallic divalent cation may be CaCl ₂ , SrCl ₂ , BaCl ₂ , or AlCl ₃ , preferably calcium chloride (CaCl ₂ ).

The biochar-alginate beads of the present invention have an amorphous structure and a porous structure having pores on the surface. The pores on the surface have an irregular shape, and the adsorption efficiency can be improved by increasing the specific surface area of the beads.

It is also manufactured including a drying process to remove moisture. Before drying, the beads (hydrogel beads) have weak durability, so there is a risk of breakage when inserted into a fixed bed adsorption reactor, and there is a problem that the components may melt or swell when exposed to an aqueous solution for a long time. On the other hand, the beads (dry beads) after drying have good durability by removing moisture, and the scope of use can be expanded in that they do not melt or swell in aqueous solution.

Next, the second step of adsorbing radionuclides by injecting biochar-alginate beads into radioactive wastewater will be described.

The biochar-alginate beads of the present invention use buckwheat husks and can remove radionuclides in water through precipitation, ion exchange, and surface complexation. Particularly preferably, the removal rate for cobalt is excellent.

In relation to precipitation, beads containing buckwheat hull biochar have CO ₃ ^2- and SiO ₂ functional groups on the surface, so that radionuclides in water can be separated through co-precipitation. In particular, the binding force to cobalt ions is high, and cobalt ions can form cobalt hydroxide (Co(OH) ₂ ) based on pH 7 and form salts for surface precipitation.

In relation to ion exchange, calcium ions contained in buckwheat hull biochar can be used. Buckwheat hull biocha contains a large amount of calcium ions, which can be exchanged with cations in water. Depending on the thermal decomposition temperature of biochar, the degree of exchange of calcium ions with cations in water can be controlled.

In relation to surface complexation, beads containing buckwheat hull biochar have -OH, C-H, and C-C functional groups and bind to radionuclides to perform an adsorption function through surface complexation.

Finally, the third step of recovering the biochar-alginate beads adsorbed with radionuclides will be described.

Removal of radionuclides in water using biochar powder has difficulties in separation and recovery due to the property that biochar powder is easily dispersed in water. Accordingly, the present invention secures the ease of recovery by preparing an adsorbent in the form of a bead. The adsorbent in the form of a bead can be easily separated and removed using a sieve (net) after adsorption of radionuclides, so it can be applied to the treatment of a huge amount of liquid radioactive waste.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. On the other hand, the illustration and detailed description of the configuration and the action and effect thereof, which can be easily known from those of ordinary skill in the art, will be simplified or omitted, and the parts related to the present invention will be described in detail.

<Example>

Example 1 - Alginate beads immobilized with buckwheat hull biocha

2 shows a method for preparing biochar-alginate beads according to an embodiment of the present invention. Hereinafter, with reference to FIG. 2, a method for producing alginate beads immobilized with buckwheat hull biocha will be described.

(1) Bio tea manufacturing

To remove impurities from the buckwheat husks, it was washed several times with distilled water, dried at 60° C. for 24 hours, and then pulverized to a size of 3 to 4 mm using a grinder. 12 g of buckwheat hull powder was put into a boat-type alumina crucible and injected into a pyrolysis furnace, and the injected powder was heated at 450, 600, and 750° C. for 1 hour at a heating rate of 5° C./min under a flowing argon atmosphere, respectively. The produced biochar was pulverized to a size of 0.5 mm or less using a mortar to increase adsorption reactivity.

(2) Preparation of biochar-alginate beads

For recovery of the adsorbent after radioactive wastewater treatment, sodium alginate (C ₆ H ₉ NaO ₇ ) was used to synthesize biochar powder as a bead-type adsorbent. 1.5% w/v sodium alginate (C ₆ H ₉ NaO ₇ ) 2.5g biochar powder was added to 50 mL and stirred at 30° C. for 5 minutes. _{After stirring, the obtained mixture was slowly injected into 250 mL of 1% w/v calcium chloride (CaCl 2} ) using a syringe with a needle having a thickness of 17G, and reacted at 25° C. for 20 minutes. Finally, the beads were washed with distilled water several times to remove impurities, and dried in a vacuum oven at 25° C. for 24 hours to prepare alginate beads.

Comparative Example 1 - Powdered activated carbon (AC powder)

Conventionally commercialized powdered activated carbon (Deoksan, Activated carbon powder) was prepared.

Comparative Example 2 - Granular activated carbon (AC granule)

Conventionally commercialized granular activated carbon (Deoksan, Activated carbon granule) was prepared.

<Results and evaluation>

Removal rate and selectivity according to pyrolysis temperature conditions

In order to confirm the adsorption characteristics for radionuclides in water, the radionuclide removal rate of biochar-alginate beads prepared under different thermal decomposition temperature conditions was measured.

3 is a graph showing the results of a radionuclide removal experiment with respect to the thermal decomposition temperature of biochar according to an embodiment of the present invention. Results according to the pyrolysis temperature and the target radionuclide are shown in a graph. Referring to FIG. 3 , depending on the thermal decomposition temperature, cesium 52.28%, strontium 71.32%, cobalt 85.59%, cesium 35.30% at 600°C, strontium 58.10%, cobalt 93.29%, cesium 19.60%, strontium at 750°C, depending on the thermal decomposition temperature Removal rates of 50.25% and 99.74% of cobalt could be secured, and it was confirmed that the removal rate changed according to the pyrolysis temperature. In particular, it has a higher removal rate for cobalt than cesium and strontium, and it was confirmed that cobalt can be selectively adsorbed.

Thereafter, the experiment was conducted and the results were confirmed using buckwheat hull biochar pyrolyzed at 750° C., which has excellent cobalt removal ability.

Structure of biochar-alginate beads

(1) Average diameter

The diameter of the synthesized biochar beads was confirmed based on the average value by measuring 50 beads using a vernia caliper. 4 is a structural photograph of biochar-alginate beads according to an embodiment of the present invention. 4 (a) is a photograph of biochar-alginate beads, and (b) a photograph showing the actual size of biochar-alginate beads. Referring to FIG. 4 , it was confirmed that the diameter of the beads according to the present invention was 5 mm or less including the drying process, and the average diameter of the prepared biochar-alginate beads was about 2 mm.

(2) Surface functional group

In order to confirm the functional groups on the surface of the synthesized buckwheat hull biochar, infrared spectrophotometry (FT-IR) was performed. 5 is an FT-IR analysis graph of the surface of biochar according to an embodiment of the present invention. Fig. 5 (a) is an FT-IR analysis graph of biochar pyrolyzed at 450°C, (b) biochar pyrolyzed at 600°C, and (c) biochar pyrolyzed at 750°C. 5, 3455 cm ^-1 at -OH, 2917 and 2850 cm ^-1 at CH, 1650 cm ^-1 at CC, 1086 cm ^-1 at CO ₃ ^2- , 480 and 557 cm ^-1 between SiO ₂ was confirmed as a peak. Furthermore, it was confirmed that the peak of the surface functional group decreased as the pyrolysis temperature of the biochar increased.

(3) Surface bonding structure

X-ray diffraction analysis (XRD) was performed to confirm the binding structure of the alginate beads immobilized with buckwheat hull biocha. 6 is an XRD analysis result of biochar powder and biochar-alginate beads according to an embodiment of the present invention. Referring to FIG. 6, large and broad peaks mainly found in biochar were observed at ^{24 o} and 43 ^o , and peaks due to alginate molecular chains were observed at ^{15 o} and 22.5 ^{o as they were fixed with alginate.} It was confirmed that tea and alginate were well synthesized.

In addition, it was confirmed that the buckwheat hull biochar powder and the synthesized beads had an irregular amorphous structure. The surface structure of the beads was confirmed using a field emission scanning electron microscope. 7 is a scanning electron microscope (SEM) photograph of biochar powder and beads according to an embodiment of the present invention. Referring to FIG. 7 , it was confirmed that both the buckwheat hull biochar powder and the beads had pores of various sizes on the surface. In particular, it was confirmed that the pores of the biochar beads were relatively reduced because the surface pores were covered through the synthesis process with alginate. Through the pore structure, it was confirmed that cobalt ions in water can pass through the beads in various angles and have a large specific surface area to improve the adsorption efficiency.

Cobalt adsorption capacity

In order to confirm the cobalt adsorption capacity of the biochar-alginate beads according to the present invention, changes in surface functional groups, pH in the solution, and released calcium ions were observed after adsorption. An adsorption experiment (concentration: 1 mg/L, temperature: 25°C, adsorbent amount: 5 g/L) for radionuclides in water was performed using biochar synthesized by thermal decomposition at 750°C.

FIG. 5(d) is an FT-IR analysis graph after the biochar decomposed at 750° C. is adsorbed with cobalt. Referring to FIG. 5(d), functional groups such as -OH, CH, CC were weakened after cobalt adsorption. This was due to surface complexation in which cobalt ions were combined with surface functional groups. In addition, after adsorption, the CO ₃ ^2- functional group was strengthened, and the SiO ₂ functional group was condensed and moved to the left. This is because the above functional groups were combined with cobalt ions and co-precipitated on the surface of the biochar, confirming the excellent cobalt adsorption capacity.

8 is a graph showing a solution pH and a concentration of released calcium ions after biochar according to an embodiment of the present invention is adsorbed with cobalt. Referring to FIG. 8, it was confirmed that cobalt ions form cobalt hydroxide (Co(OH) _{2 ) from pH 7 and surface precipitation.} It was confirmed that calcium ions were discharged accordingly. Through this, it was confirmed that the cobalt ion had a high cation exchange capacity (cation exchange).

In addition, it was possible to confirm the superior cobalt adsorption capacity compared to the conventionally used powdered activated carbon and granular activated carbon. 9 is a graph showing the cobalt adsorption capacity of an adsorbent according to an embodiment or a comparative example of the present invention. Referring to FIG. 9 , the biochar-alginate beads according to the present invention fixed with buckwheat hull biochar showed a removal rate of 95.96% with respect to cobalt. On the other hand, the cobalt removal rate was 93.38% in Comparative Example 1 (powder activated carbon) and 76.37% in Comparative Example 2 (granular activated carbon). Through this, it was possible to confirm the high cobalt adsorption capacity of the biochar-alginate beads according to the present invention.

recoverability

Removal of radionuclides in water using biochar powder has difficulties in separation and recovery due to the property that biochar powder is easily dispersed in water. Accordingly, the ease of recovery of the biochar-alginate beads according to the present invention was confirmed.

10 is a schematic diagram showing a fixed bed adsorption reactor and a recovery sieve (net) using biochar-alginate beads according to an embodiment of the present invention. 11 is a photograph showing the degree of dispersion in aqueous solution of biochar powder and biochar-alginate beads according to an embodiment of the present invention.

10 and 11, the biochar-alginate beads according to the present invention have a shape by fixing the biochar powder to alginate, unlike the conventional powder form. It has the characteristic of being able to recover with high efficiency.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order to better understand the claims of the present invention. Those of ordinary skill in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the following claims rather than the above detailed description, and all changes or modifications derived from the claims and their equivalent concepts should be construed as being included in the scope of the present invention.

Claims (5)

An adsorbent bead for adsorbing nuclides in radioactive wastewater, comprising:
alginate; and
Including; buckwheat hull-based biochar fixed to the alginate;
The surface has a CO ₃ ^2- and SiO ₂ functional groups, characterized in that irregular amorphous and porous biochar for removal of radionuclides in water-alginate beads.
The method of claim 1,
The nuclide is cesium, strontium, biochar for removing radionuclides in water, characterized in that any one of cobalt-alginate beads.
The method of claim 1,
The buckwheat husk biochar biochar for removing radionuclides in water, characterized in that it contains calcium ions-alginate beads.
The method of claim 1,
The biochar-alginate beads,
Biochar for removing radionuclides in water, characterized in that the particle diameter is 1 to 5mm - alginate beads.
Contains alginate and buckwheat hull-based biochar fixed to the alginate, the surface has CO ₃ ^2- and SiO ₂ functional groups, irregular amorphous and porous biochar-alginate beads are prepared the first step;
a second step of adsorbing radionuclides by injecting the biochar-alginate beads into radioactive wastewater; and
A method of removing radionuclides from underwater, comprising a third step of recovering the biochar-alginate beads adsorbed with the radionuclide using a sieve (net).

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