JP7833720B2 - Cesium and strontium adsorption filter and cesium and strontium removal system using the same - Google Patents

Description

This invention relates to a cesium and strontium adsorption filter (hereinafter referred to as "adsorption filter") and a spring-type filter system for removing cesium and strontium using the same (hereinafter referred to as "this system").

Numerous metals exist in the environment as ions in liquids, and if these metals are ingested by the human body, they can cause health problems. For example, some metals, such as heavy metals, are highly lethal, while others, like radioactive metals, accumulate in the body and cause health problems through internal exposure.

Radioactive cesium and radioactive strontium (hereinafter referred to as "radioactive materials") accumulate in the human body when ingested, causing internal exposure and health problems due to simple heavy metal intake. Therefore, pre-treatment of radioactive materials and heavy metals using adsorbents, etc., before discharge into the environment is extremely important to prevent the spread of contamination.

Various technologies are being considered for the removal of radioactive materials. For example, Non-Patent Document 1 below describes the adsorption of radioactive cesium by ammonium phosphomolybdate.

https://unit.aist.go.jp/georesenv/information/20150917/TechRep_Cs_Monitoring_Water.pdf

However, while the inventors were diligently studying the technology described in the above non-patent literature, they discovered that ammonium phosphomolybdate (hereinafter referred to as "AMP") has a problem in its use: significant component elution. Significant component elution means that the radioactive material that has been adsorbed is released back into the environment. Furthermore, from the viewpoint of achieving higher removal efficiency, it is preferable to have an adsorption filter that does not elute components even under strongly acidic or salt-containing conditions, and that also possesses a higher adsorption rate.

Therefore, in view of the above problems, the present invention aims to provide an adsorption filter agent with low elution properties and higher adsorption efficiency, and a system using the same.

An adsorption filter according to one aspect of the present invention, which solves the above problems, contains ammonium phosphotungstate (hereinafter referred to as "AWP").

Furthermore, while not limited to this perspective, it is preferable that the above-mentioned adsorbent filter material has an average particle size in the range of 1 μm to 2000 μm.

Furthermore, while not limited to this perspective, the above-mentioned adsorbent filter is preferably for use with acidic solutions containing radioactive materials.

Furthermore, while not limited to this perspective, the above-mentioned adsorbent filter is preferably for use in saline solutions such as freshwater and seawater containing radioactive materials, as well as for oils and organic solvents.

Furthermore, while not limited to this viewpoint, it is preferable that the adsorption filter aid is for spring-shaped filters.

Furthermore, while not limited to this perspective, it is preferable that the material be an adsorption filtration aid for container filling.

Furthermore, a system according to another aspect of the present invention is a radioactive material removal system comprising a spring-shaped filter, a housing for holding the spring-shaped filter, and an adsorption filter agent placed on the outer surface of the spring-shaped filter during use, wherein the adsorption filter agent contains AWP.

In summary, the present invention provides an adsorption filter with a higher adsorption rate and a radioactive material removal system using the same.

This is a schematic diagram of the spring-shaped filter device within the system according to this embodiment. This is a partial cross-sectional view showing the outer surface of a spring-shaped filter in the system according to this embodiment, with a filter aid pre-coated. This figure shows a schematic diagram of a spring-shaped filter system for processing insoluble and dissolved substances according to an embodiment. This is a schematic diagram of a spring-shaped filter according to an embodiment. This is a partial cross-sectional view of a spring-shaped filter according to an embodiment. This figure shows a magnified image (1500x) of the AWP in the example taken with an electron microscope. This figure shows a magnified image (10,000x) of the AWP in the example taken with an electron microscope. This figure shows photographs of the appearance of the filtrate after treatment in the examples and comparative examples. This graph shows the adsorption rates in the examples.

The embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention can be implemented in many different forms, and the specific examples described in the embodiments and examples below can be modified and adjusted as appropriate, and are not limited thereto. Hereinafter, the term "adsorbent" may be used, but such adsorbent can be used as a filter material.

(Radioactive material removal system)
Figure 1 is a schematic diagram of the spring-shaped filter device in the system according to this embodiment. As shown in this figure, the system consists of a spring-shaped filter 11, a support member 12 that supports the spring-shaped filter 11, and a housing 13 that holds the spring-shaped filter 11 and the support member 12, with the internal space of the housing divided vertically by the support member 12. As will be clear from the description below, an adsorbent filter material that has taken in radioactive material (radioactive cesium and radioactive strontium) remains on the outer surface of the spring-shaped filter 11, and the liquid from which the radioactive material has been removed passes through to the inside. In other words, the space outside the spring-shaped filter and the space inside are separated into a raw liquid side and a filtrate side.

Figure 2 is a partial cross-sectional view of the spring-shaped filter 11 with a pre-coated filter aid or adsorbent filter 15 on its outer surface. This system utilizes a spring-shaped filter 11, which is equipped with a filter aid or adsorbent filter 15 on its outer surface. While the details of removal by this spring-shaped filter will be described later, in this system, the adsorbent filter 15 placed on the outer surface of the spring-shaped filter 11 is an AWP (Autonomous Water Packet). By pumping it into the spring-shaped filter 11, a flow is formed from the outside to the inside of the spring-shaped filter 11. The adsorbent filter 15 in the path of this flow can adsorb radioactive substances present in the solution being treated, and by discharging this adsorbent filter, the radioactive substances can be removed. Further details will be described after the mention of the adsorbent filter.

(Adsorbent filter)
As described above, the adsorbent filter in this system is a powder containing AWP. While it is most preferable to use this AWP powder in this system, the method of using it as an adsorbent is not particularly limited. For example, it can be used as a general container-filled ion exchange system to remove radioactive materials by forming it into granules, like a normal ion exchange resin, and densely packing it into a container, and passing the liquid containing the radioactive material to be treated through this container. In this specification, as described above, we will first explain AWP, and then provide a detailed explanation of this system.

AWP is a hydrate of the ammonium salt of phosphotungstic acid, and is represented by the following molecular formula.

AWP is a solid at room temperature, and when used as an adsorbent, its average particle size is preferably in the range of 1 μm to 2000 μm. For use in spring-type filters, it is more preferably in the range of 5 μm to 200 μm. A particle size of 1 μm or larger enables filtration by the spring-type filter in this system. For container filling, it is more preferably in the range of 300 μm to 1000 μm. When using a spring-type filter, it is possible to perform both physical filtration and chemical filtration by adsorption of radioactive materials without including other components.

Furthermore, AWP is preferably an adsorbent filter for acidic solutions containing radioactive materials. Radioactive materials have a tendency to dissolve in acidic solutions, and when removing radioactive materials contained in soil, etc., they are first dissolved in an acidic solution and then separated and recovered using an adsorbent, etc., so it is important that the adsorbent filter is applicable under acidic conditions. The pH is not limited, but it is preferably able to handle pH 6 or lower, more preferably pH 5 or lower, even more preferably pH 3 or lower, and particularly preferably pH 2 or lower.

Furthermore, AWP can be used for neutral or basic solutions, and also for freshwater or seawater (pH 8-9) containing radioactive materials. AWP can selectively and efficiently remove radioactive cesium even when it is dissolved in seawater.

On the other hand, AWP not only efficiently adsorbs cesium but also exhibits high adsorption performance for strontium. In particular, AWP has a higher adsorption rate than known AMPs, and the elution of the adsorbent itself is extremely low. As a result, the adsorption efficiency is synergistically extremely high. Furthermore, since AWP achieves the maximum adsorption rate in this system using a spring-type filter, the processing speed can be significantly increased compared to general container-filled ion exchange systems.

(System and Method)
Here, we will explain in detail the details of this system and the radioactive material removal method achieved by this system (hereinafter referred to as "this method").

First, this method comprises the steps of (1) performing primary filtration on the raw liquid to be treated, (2) mixing the primary filtrate obtained by primary filtration with an adsorbent filter capable of adsorbing radioactive materials dissolved in the primary filtrate, and (3) performing secondary filtration on the primary filtrate mixed with the adsorbent filter.

Figure 3 is a schematic diagram of the system S, which specifically comprises a primary spring-type filter device 1, a primary filtrate tank 2 connected to the primary spring-type filter device 1 and containing the primary filtrate, a secondary spring-type filter device 3 for filtering the primary filtrate contained in the primary filtrate tank 2, and a secondary filtrate tank 4 connected to the secondary spring-type filter device 3 and containing the secondary filtrate. The system and method will be described in detail below.

First, this method includes (1) a step of performing primary filtration on the raw liquid to be treated.

In this method, the "stock solution" to be treated is, quite literally, the liquid to be treated, and this liquid contains the radioactive material to be removed. The liquid is not limited to examples of liquids applicable to this method; generally, it mainly contains water, but it may also contain oil, organic solvents, etc., as long as it is applicable. Furthermore, the radioactive material to be removed may not only be dissolved in the liquid, but also present or suspended as particulate matter or other quantifiable substances, or insoluble materials such as sand or microorganisms to which radioactive material has been adsorbed.

In this method, "primary filtration" refers to the removal of insoluble substances that do not dissolve in water and are present or suspended as fine particles in the raw liquid to be treated, and is also called physical filtration. While the primary filtration in this method is not limited to any method that can perform the above-described treatment, it is preferable to use a filtration device with a spring-type filter. Therefore, this embodiment shows an example using a primary spring-type filter device 1.

The internal structure of the primary spring-type filter device 1 in this embodiment is the same as that shown in Figure 2 above, and this figure shows a schematic cross-sectional view thereof. As shown in this figure, the primary spring-type filter device 1 is composed of at least a spring-type filter 11 and a support member 12 that supports it. As will be clear from the description below, insoluble substances remain on the outside of the spring-type filter 11, while the liquid from which the insoluble substances have been removed passes through the inside. In other words, the outer space and the inner space are separated into a raw liquid side and a filtrate side.

Furthermore, the primary spring-type filter device 1 of this embodiment has a housing 13 that houses the spring-type filter 11 and the support member 12, in addition to the support member 12. The support member 12 divides the space 14 inside the housing 13 into two spaces: an upper space and a lower space, and the support member 12 functions as a partition plate. More specifically, the support member 12 has multiple holes formed in it, and by inserting and installing the spring-type filter 11 into these holes, the space 14 inside the housing 13 can be divided into a lower space 141 (hereinafter simply referred to as the "lower space") and an upper space 142 (hereinafter simply referred to as the "upper space") of the spring-type filter. In addition, as will be described later, in the primary spring-type filter device 1, a filtration aid 15 is applied to the outside of the spring-type filter 11 during primary filtration. Figure 4 shows a schematic of the spring-type filter 11 according to this embodiment. A partial cross-section is shown in Figure 5, and when the filtration aid is applied, it is as shown in Figure 2 above. During primary filtration, the filter aid 15 is placed on the outer surface of the spring-shaped filter 11, forming a cake that functions as a filter layer. Specifically, the support member 12 separates the lower space 141 and upper space 142 of the filter. As the raw liquid to be processed moves from the lower space 141 through the filter layer to the upper space 142, insoluble substances cannot pass through the filter layer and remain in the filter layer, thus being removed from the raw liquid.

To reiterate, the spring-shaped filter 11 of the primary spring-shaped filter device 1 is, as the name suggests, a spring-shaped filter. As shown in the figure above, the spring-shaped filter 11 is a filter in which wires 111 are wound in a ring shape and overlap with predetermined gaps. Furthermore, although not limited to this, the wires 111 of the spring-shaped filter 11 in the primary spring-shaped filter device 1 are provided with protrusions 112 to ensure the predetermined distance between adjacent wire portions. This allows for the stable maintenance of the average gap width of the spring-shaped filter, more specifically, the gap between the wires.

Furthermore, the average gap width (average gap between wires) of the spring-type filter in the primary spring-type filter device 1 can be set appropriately and is not limited, but it is preferably in the range of 5 μm to 200 μm, and more preferably in the range of 10 μm to 120 μm. By setting it within this range, insoluble impurities that are to be removed from the liquid during primary filtration can be efficiently removed.

Furthermore, the material of the spring-shaped filter 11 in the primary spring-shaped filter device 1 is not limited as long as it maintains its shape and allows the primary spring-shaped filter device 1 to achieve the desired effect. Examples include metallic materials such as single metals like copper, iron, titanium, and nickel, or alloys like stainless steel; resin materials such as polystyrene, polypropylene, polyvinyl chloride, and PPS; and ceramic materials.

Furthermore, while the spring-shaped filter 11 in the primary spring-shaped filter device 1 can be easily realized by winding a single wire 111 in a spiral pattern, a similar structure can also be achieved by, for example, using an annular laminate made of multiple annular wires with protrusions or resin materials stacked together. Even in this case, the spring-shaped filter is still considered part of the primary spring-shaped filter device 1. That is, in the primary spring-shaped filter device 1, the spring-shaped filter 11 encompasses either a coiled spring shape or an annular laminate structure.

Furthermore, in this embodiment, the spring-shaped filter 11 may be configured as shown in the figure above, with a core material 113 at the center of the wire 111, and a pair of retaining fittings provided near both ends of this core material 113. This configuration allows for more stable holding of the wire. In particular, it is preferable that one of the fittings connects to the support member 12, and that a screw groove is formed to reduce the gap between the support member 12 and the filter. This configuration allows for the support member 12 to also have a screw groove that fits into it, enabling stable fixation of the support member 12 and the spring-shaped filter 11 by fitting them together.

Furthermore, as is clear from the above description, in the primary spring-type filter device 1, while there may be only one spring-type filter 11, it is preferable to have multiple filters. Specifically, it is preferable that numerous holes are formed in the support member 12, and that the spring-type filters 11 are inserted and fixed into each of these holes. This makes it possible to improve the filtration efficiency.

Furthermore, in this embodiment, the lower space 141 and upper space 142 of the spring-type filter 11 within the housing 13 are connected to the stock tank 5, the primary precoat tank 6, and the primary waste liquid tank 7, respectively, via circulating piping. The piping T is also equipped with valves V for opening and closing each path. Specifically, there is a valve V51 for controlling the opening and closing of piping T51 from the stock tank 5 to the primary spring-type filter device 1, a valve V61 for controlling the opening and closing of piping T61 from the primary precoat tank 6 to the primary spring-type filter device 1, and a valve V71 for controlling the opening and closing of piping T71 from the primary spring-type filter device 1 to the primary waste liquid tank 7. Additionally, the piping T51 from the stock tank 5 to the primary spring-type filter device 1, and the piping T61 from the primary precoat tank 6 to the primary spring-type filter device 1, are equipped with pumps P51 and P61, respectively, for sending the liquid contained in them to the lower space 141 of the primary spring-type filter device 1. Furthermore, these pipes, valves, and pumps can be shared, and their positions and numbers can be adjusted as needed.

Furthermore, in this embodiment, the upper space 142 of the spring-type filter 11 within the space 14 of the housing 13 is connected to the primary filtrate tank 2 via piping T1. This allows for the storage of the primary filtrate. Specifically, piping T1 connects the primary spring-type filter device 1 and the primary filtrate tank 2. Piping T1 is also equipped with a valve V1 for controlling the opening and closing of the path formed by this piping.

Furthermore, in this embodiment, the upper space 142 within the housing 13 may be connected to the stock solution tank 5 or the primary precoat tank 6 via piping T. Specifically, the liquid is returned to the stock solution tank 5 via piping T52, and the liquid is returned to the primary precoat tank 6 via piping T62. Piping T52 and T62 are also equipped with valves V52 and V62, respectively, to control the opening and closing of their respective paths. This allows for the formation of loops between the stock solution tank 5 and the primary spring-type filter device 1, and between the primary precoat tank 6 and the primary spring-type filter device 1. This is necessary for preparatory processing and precoating (the process of placing the filter aid 15 on the outer surface of the spring-type filter 11) before primary filtration is performed and the process stabilizes.

Furthermore, as described above, a filter aid 15 for the spring-shaped filter is arranged around the spring-shaped filter 11 in the primary spring-shaped filter device 1 during primary filtration (removal of insoluble impurities). More specifically, the filter aid 15 is layered on the outer surface of the spring-shaped filter 11 by the force with which the spring-shaped filter 11 pumps liquid from the lower space 141 to the upper space 142 during filtration. This allows the filter aid 15 to function as a filter layer for removing insoluble matter.

Furthermore, in this method, the form of the filter aid is not limited, but it is preferably in powder form. Using a powdered filter aid makes it easier to disperse in the liquid and allows for stable placement due to the so-called pre-coat effect of layering it on the outer surface of the spring-shaped filter 11. The size of the filter aid powder is not particularly limited, but it is preferably in the range of an average particle size of 5 μm to 200 μm, and more preferably in the range of an average particle size of 10 μm to 100 μm.

Furthermore, the composition of the filter aid 15 is not limited as long as it can perform the above-mentioned functions. For example, it may be inorganic particles such as diatomaceous earth, activated carbon, or zeolite, or it may be organic particles such as polyolefins containing polyethylene, polypropylene, etc. and their derivatives, polyvinyl chloride, polyvinyl acetate, polyethylene tetrafluoroethylene, etc. and their derivatives, halogenated polyolefins containing ethylene vinyl alcohol, etc. and their derivatives, halogenated olefin copolymers containing cellulose, etc. and their derivatives, cellulose, etc. and cellulose derivatives having a cellulose backbone. Of course, ammonium phosphotungstate, which is the adsorbent that can perform chemical adsorption, can also be used.

As described above, the primary filtration method, through the combination of the spring-shaped filter 11 and the filter aid 15 arranged around it, makes it possible to remove insoluble matter larger than a predetermined size. The resulting filtered primary filtrate is stored in the primary filtrate tank 2.

Here, we will explain the details of the primary filtration method step by step. First, as preparation for primary filtration, the raw liquid to be treated is placed in the raw liquid tank 5.

Meanwhile, the primary precoat tank 6 contains a filtration aid 15 and a liquid such as water. This liquid is supplied to the lower space 141 of the housing 13 via piping T61, and then collected back into the precoat tank 6 via the spring-shaped filter 11 and piping T62. At this time, valves V61 and V62 attached to these components are opened, and pump P61 is driven to create a liquid flow within the loop formed by this pathway member, the precoat tank 6, and the housing 13. As a result, the filtration aid gradually adheres to the outer surface of the spring-shaped filter.

Then, after sufficient filtration aid has adhered to the outer surface of the spring-shaped filter, valve V1 is switched, supplying the raw liquid from the raw liquid tank 5 to the lower space 141 of the housing 13. This liquid is then discharged through the spring-shaped filter 11 to the primary filtration liquid tank 2 from the upper space 142. This removes insoluble substances. These insoluble substances are then discharged to the primary waste liquid tank 7 via piping T71 after the primary filtration is complete.

Next, this method includes the step of (2) mixing the primary filtrate obtained by primary filtration with an adsorbent filter capable of adsorbing radioactive materials dissolved in the primary filtrate. This step is a preliminary step to remove dissolved radioactive materials after primary filtration.

Furthermore, while this method uses a primary spring-type filter device 1 in the primary filtration described above, the primary filtration can be omitted if sufficient physical filtration of insoluble substances has been performed beforehand, or if these can be sufficiently removed by secondary filtration. In this case, it is sufficient to use only the configuration from the primary filtrate tank 2 onward.

The adsorption filter used here is AWP, which, as described above, can remove radioactive materials dissolved in the liquid. Details are provided above. This system effectively removes dissolved radioactive materials by using such an adsorption filter. In particular, by separating the primary and secondary filtration processes and treating each separately, dissolved materials removed after primary filtration can be efficiently recovered. AWP is especially effective when used because it has low self-dissolution.

Furthermore, in this step, it is preferable to stir the primary filtrate to which the adsorbent filter agent has been added. Stirring allows for more efficient removal of dissolved radioactive materials. Specifically, a preferred example is, but is not limited to, a primary filtrate tank 2 equipped with a stirring member and a drive device K for driving this stirring member.

Furthermore, this method includes (3) a step of performing secondary filtration on the primary filtrate mixed with the adsorbent filter agent. This step involves adsorbing and removing radioactive materials dissolved in the liquid using the adsorbent filter agent introduced in the above step, and is called secondary filtration.

In this step, the secondary filtration uses the secondary spring-type filter device 3 as described above. This spring-type filter device 3 can be the same as the primary spring-type filter device 1 used in step (1) above, and the explanation of the overlapping parts will be omitted. However, this step differs in that the primary filtrate and the adsorbent filter agent are pre-mixed, and the process is specifically designed to separate them. That is, in this method, first, insoluble substances mixed in the liquid are removed by primary filtration to obtain the primary filtrate. Next, AWP, an adsorbent filter agent for adsorbing dissolved radioactive substances, is added to the primary filtrate containing dissolved radioactive substances. Furthermore, by recovering the adsorbent filter agent on which the radioactive substances have been adsorbed in this step, both insoluble substances and dissolved radioactive substances in the target liquid can be reliably removed in a series of processes.

To explain this method in more detail, in step (1) above, before primary filtration of the raw liquid to be treated, a filter aid 15 is placed on the outer surface of the spring-shaped filter 11 by a pre-coating treatment. After confirming that the filter aid 15 is sufficiently placed on the outer surface of the spring-shaped filter, the raw liquid to be treated is introduced into the housing 13 of the primary spring-shaped filter device 1 for treatment. On the other hand, in step (3), this is an important process in which dissolved radioactive substances are adsorbed onto the adsorbent filter while stirring the primary filtrate, and also a process for separating the adsorbent filter that has adsorbed the radioactive substances from the liquid. For example, the primary filtrate is supplied from the primary filtrate tank to the lower space of the housing, passed through the spring-shaped filter, and then returned to the primary filtrate tank. At the stage when it is determined that a certain amount of dissolved radioactive substances have been removed, the valve in the piping is switched, and the secondary filtrate from which the radioactive substances have been removed is discharged into the secondary filtrate tank. In some cases, it may be possible to discharge directly into the secondary filtrate tank without forming this loop.

Incidentally, since the secondary filtrate has been able to remove insoluble substances and dissolved radioactive materials, if it meets the standards, it can be discharged directly without being stored in the secondary filtrate tank 4. On the other hand, radioactive materials adhere to the adsorbent filter of the secondary filtration device, and since these dissolved materials adhere at a higher concentration than in the original stock solution, it is possible to significantly reduce the amount of waste.

In summary, this method provides a spring-type filter system capable of more efficiently removing dissolved radioactive materials.

In this embodiment, a spring-type filter system is presented for the purpose of optimal removal of radioactive materials. However, other filter systems can also be used, as long as this method is applicable.

The adsorbent containing AWP proposed in this invention and the system using it are not limited to the removal of cesium and strontium. For example, they can also be used for the purpose of adsorbing lead, thorium, and uranium. Furthermore, these adsorbed substances are not limited to radioactive isotopes, and the adsorbent containing AWP proposed in this invention can also be used for the adsorption of stable isotopes.
Furthermore, the method for removing metal ions (e.g., lead, thorium, uranium, etc.) from a solution using adsorbents containing these AWPs can be carried out in the same manner as described above for the removal of cesium and strontium.

A preferred example of an adsorbent containing AWP in the present invention is characterized in that the AWP, which functions as an adsorbent group, is not fixed to the substrate (base material). In other words, an adsorbent consisting substantially of AWP is preferred, and an adsorbent consisting solely of AWP is more preferred.

Conventional adsorbents consist of adsorbent groups fixed to a substrate (e.g., an organic polymer). While such adsorbents, with adsorbent groups fixed to a substrate (e.g., an organic polymer), can be given features such as high mechanical strength depending on the properties of the substrate, they tend to be bulky because the substrate does not have the adsorption function to adsorb the target ions.
On the other hand, adsorbents in which AWPs functioning as adsorbent groups are not fixed to a substrate (preferably adsorbents substantially composed of AWPs) do not contain a substrate within the adsorbent, thus allowing for a higher density of adsorbent groups per unit volume. In other words, the adsorption capacity per unit can be increased. This reduces the bulk (volume) of adsorbent required to adsorb the same amount of metal ions, thereby reducing the volume of waste after metal ion adsorption. This reduces the environmental burden, particularly the volume of radioactive contaminated waste containing adsorbed radioactive metal ions.
This is useful because it can solve the problem of reduced adsorption capacity in adsorbents where adsorption groups are fixed to a general substrate, due to the volume of the base material that does not contribute to the adsorption of the target object, and the problem of reducing the amount of waste after adsorption.

Furthermore, an adsorbent in which the AWP (Autonomous Web Pack) functioning as an adsorbent group is not fixed to the substrate (preferably an adsorbent substantially composed of AWP) can increase the amount of adsorbent that can be filled into the housing (typically the amount of adsorbent groups per unit volume) in the system and removal method described above. This makes it possible to shorten the processing time for the adsorption treatment and/or reduce the volume of the housing.

Furthermore, in adsorbents where the AWP (Autonomous Glue Plant) functioning as adsorbent groups is not fixed to the substrate (preferably an adsorbent substantially composed of AWP), there is no concern about the adsorbent groups detaching from the substrate. When the object to be adsorbed by the adsorbent groups is a radioactive substance, it is crucial to prevent secondary contamination caused by the detachment of the object from the adsorbent. Since adsorbents where the AWP functioning as adsorbent groups is not fixed to the substrate (preferably an adsorbent substantially composed of AWP) do not allow the adsorbent groups to detach from the substrate, secondary contamination caused by the detachment of the radioactive substance from the adsorbent can be prevented.

As an example of an adsorbent whose adsorbent groups are not fixed to the substrate (preferably an adsorbent consisting substantially of adsorbent groups), the case where the adsorbent groups are AWP was described as an example, but it is not limited to this as long as the adsorbent groups alone have sufficient mechanical strength to withstand metal adsorption treatment from a liquid. It is preferable that it has sufficient mechanical strength to withstand the spring-based system and removal method described above.

Examples of such adsorbent groups include zirconium, aluminum sulfate, polyaluminum chloride, zeolite, and activated carbon.
The above-mentioned zirconium is suitably used for the adsorption of arsenic and fluorine. The above-mentioned aluminum sulfate is suitably used for the adsorption of iron, arsenic, chlorine, etc. The above-mentioned polyaluminum chloride is suitably used for the adsorption of iron, boron, arsenic, etc. Zeolite is suitably used for the adsorption of arsenic, fluorine, boron, and cesium. Activated carbon is suitably used for the adsorption of any of these elements.

The ability to adsorb anions (such as arsenic, boron, and fluorine) and monovalent cations (such as cesium, potassium, and sodium) with high selectivity, which are known as difficult-to-remove substances from solutions, is extremely valuable for industrial applications.

Furthermore, AWP, zirconium, aluminum sulfate, polyaluminum chloride, zeolite, and activated carbon have higher mechanical strength compared to organic polymers. In the spring-based systems and removal methods described above, physical damage to the filter aids or pressure loss due to the liquid flow pressure that can occur when the liquid being treated is passed through at high speed is less likely to occur.

(Example 1)
Here, we have actually confirmed the removal performance of the radioactive material adsorption filter according to the above embodiment, and will explain it below.

A cesium adsorption test was conducted using AWP.

The AWP used as an adsorbent consisted of almost all particles approximately 1–10 μm in size, confirming a small particle size distribution. The results of this electron microscope (SEM) observation are shown in Figures 6 and 7.

On the other hand, as a treatment solution containing cesium, 30 ml of an eluent with a pH of 0.9 and containing 10.3 ppm of cesium ions was prepared.

0.3 g of the above adsorbent was added to the above eluent and stirred. Adsorption was allowed at 25°C for 71 hours, and the solution was filtered through a 0.2 μm filter before analysis. The resulting solution was confirmed to be clear.

As a result, it was confirmed that the cesium adsorption rate was 91%, and the amount of tungsten leached was suppressed to approximately 1514 mg/kg.

(Example 2)
In Example 1 described above, the test was conducted under the same conditions except that the filter filtration was performed using a 0.45 μm filter.

As a result, it was confirmed that the cesium adsorption rate was 91%, and the amount of tungsten leached was suppressed to 1782 mg/kg.

(Example 3)
In Example 1 described above, the test was conducted under the same conditions as in Example 1, except that 30 ml of a simulated solution containing 9.3 ppm of cesium ions and with a pH of 5.3 was used as the treatment solution containing cesium.

As a result, it was confirmed that the cesium adsorption rate was almost 100%, and the amount of tungsten leached was kept to 127 mg/kg.

(Example 4)
In Example 2 described above, the test was conducted under the same conditions as in Example 2, except that 30 ml of a simulated solution containing 9.3 ppm of cesium ions and with a pH of 5.3 was used as the treatment solution containing cesium.

As a result, it was confirmed that the cesium adsorption rate was almost 100%, and the amount of tungsten leached was kept to 128 mg/kg.

(Comparative Example 1)
In comparison with the above embodiment, the test was conducted under the same conditions as in Embodiment 1, except that AWP was replaced with AMP.

As a result, the cesium adsorption rate was 87%, and the molybdenum elution amount was 4810 mg/kg. This confirmed that the adsorption amount was lower and the elution amount was significantly higher compared to the tungsten AWP case.

(Comparative Example 2)
In Example 2 described above, the test was conducted under the same conditions except that AWP was replaced with ammonium phosphomolybdate AMP.

As a result, the cesium adsorption rate was 88%, and the molybdenum elution amount was 402,646 mg/kg. This confirmed that the adsorption amount was lower and the elution amount was significantly higher compared to the AWP (Autonomous Weapon Processing) method.

The results for Examples 1-4, Comparative Example 1, and Comparative Example 2 are shown in the table below. From these results, it was confirmed that AWP has higher adsorption capacity and lower elution volume compared to AMP.

Furthermore, Figure 8 shows photographic images of the residual solutions from Example 1 and Comparative Example 1. In this figure, the left side shows the residual solution from Example 1, which was removed using AWP, and the right side shows the residual solution from Comparative Example 1, which was removed using AMP. As is clear from this figure, the comparative example shows significant discoloration and severe molybdenum elution.

Based on these results, it was confirmed that AWP has a higher cesium adsorption rate and, furthermore, is extremely resistant to elution.

(Example 5)
On the other hand, a cesium adsorption test was conducted using ammonium phosphotungstate as an adsorbent. 300 mg, 30 mg, and 3 mg of the above adsorbent were added to 30 ml of cesium solution, respectively, and adsorption was carried out in a shaker at 25°C and 150 rpm/min for 71 hours. The cesium solution used was a cesium standard solution (Cs 1000) (Kanto Chemical Co., Ltd.) adjusted to 9.6 ppm and pH 5.4.

After 71 hours, the solution was filtered using syringe filters with pore sizes of 0.45 μm and 0.2 μm. The filtrate was diluted 1,000-fold, and cesium and tungsten were quantified using ICP-MS (Agilent 7700x).

These results are shown below and in Figure 9. Although the adsorption rate was high at all solid-liquid ratios, it was found that the optimal solid-liquid ratio was between 3 and 30.

(Example 6)
A metal adsorption test was conducted using ammonium phosphotungstate as the adsorbent. The adsorption solution was prepared by adding lithium, sodium, and calcium—all substances with properties similar to cesium—to a cesium solution adjusted to 50 ppb and pH 2.4, resulting in a solution with the same concentration and pH. 30 mg of the adsorbent was added to 50 ml of the above adsorption solution and adsorbed in a shaker at 25°C and 150 rpm/min for 1 hour. After adsorption, the solution was filtered using a 0.2 μm syringe filter.

After filtration, cesium was quantified using ICP-MS (Agilent 7700x) along with lithium, sodium, and calcium, which are elements with properties similar to cesium, among the elements contained in XSTC-13. The results are shown below.

(Example 7)
Similar to the above example, metal adsorption tests were conducted using two types of ammonium phosphotungstate adsorbents. The adsorption solution was prepared by adding lithium and sodium, which have properties similar to cesium, to a cesium solution adjusted to 50 ppb and pH 2.4, to achieve the same concentration and pH. Strontium, uranium, and thorium, which are expected to be mixed as other radioactive elements besides cesium, were also added in the same manner. Lead, a reactor component, was also added and evaluated in the same way. 30 mg of the above adsorbent was added to 50 ml of the adsorption solution, and adsorption was carried out in a shaker at 25°C and 150 rpm/min for 1 hour.

After adsorption, the sample was filtered using a 0.45 μm syringe filter. Following filtration, each element was quantified using ICP-MS (Agilent 7700x). The results are shown below.

As a result of the above analysis, all elements other than Cs, including strontium, lead, thorium, and uranium—the elements that needed to be removed—were recovered with high yield. Furthermore, this selectivity remained unchanged even 18 hours after adsorption, indicating that it was maintained.

(Example 8)
The sample was immersed and stirred at room temperature for 18 hours in a solution of artificial seawater with a solid-liquid ratio of 1:100, resulting in a cesium concentration of 10 mg/L. As a result, it exhibited an adsorption capacity of 1.2 × 10², which is twice that of general zeolites.

(Example 9)
18.7 mg of ammonium phosphotungstate was added to 50 ml of a 1 μg/L cesium solution and immersed and stirred for 24 hours. As a result, the cesium adsorption rate was 96.8%. Similarly, a high adsorption rate of 94.8% was also observed when evaluated in a 50 μg/L cesium solution.

The effects of the present invention were confirmed by this embodiment.

This invention has potential applications in the nuclear field and other areas as a radioactive material adsorption filter and radioactive material removal system.

Claims (2)

A cesium and strontium adsorption filter for spring-type filters, comprising ammonium phosphotungstate with an average particle size in the range of 1 μm to 2000 μm (excluding those containing at least one of water-insoluble carboxylated cellulose and anhydrous titanium oxide spheres ). A mixing tank for adding a cesium and strontium adsorption filter containing ammonium phosphotungstate (excluding those containing at least one of water-insoluble carboxylated cellulose and anhydrous titanium oxide spheres ) to the stock solution to be treated and stirring,
A spring-shaped filter,
A housing that holds the spring-shaped filter,
A cesium and strontium removal system comprising an adsorbent filter placed around the spring-shaped filter during use,
The cesium and strontium removal system is a cesium and strontium adsorption filter containing ammonium phosphotungstate (excluding those containing at least one of water-insoluble carboxylated cellulose and anhydrous titanium oxide spheres).