JPH0328130A - Recoverer of uranium in marine - Google Patents

Abstract

PURPOSE:To recover uranium from marine water with adsorption beds reduced in costs, increased efficiency in contact with marine water, and facilitated transportation of the adsorbent, by bundling filament fibers and fibrous adsorbent, arranging them in a screen or network to form the adsorption bed. CONSTITUTION:Aramid resin fibers or the like are used as a material bearing the strength to bundle a fibrous adsorbent such as amidoximized acrylonitrile fibers 1 and they are arranged in network or screen in marine water. In this case, the upper part of the fibrous adsorbent is connected to the upper holder 2, while the lower part to the lower holder 4. The upper holder 2 is further bound to the buoys 3 and the buoys are connected through the cable 5 to the anchor 6 whereby the adsorption bed is set in the marine stream.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention is directed to an apparatus for recovering trace elements in seawater for efficiently recovering valuable tIR sources such as uranium contained in trace amounts in seawater. (Prior art) Various methods are currently being proposed for recovering valuable vR sources such as uranium dissolved in seawater. Broadly speaking, recovery equipment is installed on land, and seawater is pumped up and used as an adsorbent. There are two methods: a method in which the adsorbent is brought into contact with the seawater, and a method in which the adsorbent is placed in seawater and the adsorbent is brought into contact with the seawater using energy such as ocean currents and wave force. Let's talk about technology.

When installing an adsorbent in seawater, a typical method is to fill the adsorbent into a support to form an adsorption bed. Fixed bed as the form of adsorption bed
etc.), diaphragm beds (Japanese Unexamined Patent Publication No. 58-69726, etc.), sedimentation beds (Tokuma 1970-8 1707, etc.), etc. have been devised.Also, adsorbents are laminated onto reinforcing materials to form belts or strips. Attempts have also been made to improve the contact efficiency between seawater and adsorbent by forming an adsorption bed (such as Tokuma 1983-91839). (Problems to be solved by the invention) Trace amounts of uranium etc. dissolved in seawater In order to recover jRR, it is necessary to bring the adsorbent into efficient contact with a large amount of seawater.In addition, it is necessary to be technically easy to install the adsorbent in seawater and recover it at sea. Generally speaking, a method is considered in which an adsorbent is placed in a support to form an adsorption bed, and this is placed in a stream.Inorganic adsorption and organic adsorption can be used as uranium adsorbents in seawater. Adsorbents, and granular and fibrous adsorbents are intermittent.Whether inorganic or organic, granular adsorbents are placed in a support and brought into contact with seawater in a fixed bed. In order to prevent the adsorbent from being lost in the ocean current, it is necessary to provide seawater passage holes with at least the particle size of the adsorbent on the upstream and downstream sides of the tm flow.The particle size of the adsorbent is Since the diameter is around 1 mm, the water holes are minute.
Such micropores not only increase water flow resistance, but also require the use of expensive materials such as titanium alloys to prevent corrosion from seawater. Additionally, a separate structure is required as a strength IIIS material to hold the adsorbent support. Methods such as slurry transport have been devised for transporting granular adsorbents. In the method of forming a fixed bed by placing fibrous adsorbent in a support, it is not necessary to provide micropores to prevent the adsorbent from flowing out, but a panel structure is required to hold the adsorbent. In addition, in order to install the adsorption bed stably against ocean currents, an external structure is required to hold the adsorption bed.
It is difficult to automate the replacement of adsorbents, and unit adsorption beds with a panel structure must be handled from time to time, which poses a major problem when implemented in actual seawater. Furthermore, fixed beds have a large seawater flow resistance, which not only reduces seawater utilization efficiency, but also increases the possibility of clogging due to adhesion of organisms and suspended matter. In a method in which granular adsorbent is placed in a support and brought into contact with seawater in a fluidized bed, the area of the seawater intake must be made smaller than the area of the adsorption bed support in order to obtain the height of the fluidized bed, making it difficult to utilize seawater. Efficiency deteriorates. The volume of the support becomes large relative to the amount of adsorbent, which increases the cost of manufacturing the support and increases the fluid resistance applied to the support.
This also increases the cost of mooring the adsorption bed.
Furthermore, there is a strong possibility that adsorbent loss will increase due to changes in sea conditions in the ocean area. When forming an adsorption bed, as long as the adsorbent is placed in a support and brought into contact with seawater, there will be an increase in the cost of manufacturing the support that holds the adsorbent and of the structure for fixing the support. Problems include increased maintenance costs for the structure, decreased seawater utilization efficiency, and difficulty in transporting the adsorbent. The method of attaching adsorbent to reinforcing material to form an adsorption bed simplifies the support for the adsorbent and is expected to improve the efficiency of contact with seawater, but the biggest problem is the loss of adsorbent. In other words, the interface between the reinforcing material and the adsorbent is bonded by the adhesive, but the bond between the adsorbents is weak, and loss due to separation between the adsorbents is expected if they are immersed in ocean currents for a long time. Ru.

In order to prevent adsorbent loss, it is difficult to layer adsorbents, resulting in an extremely inefficient adsorption bed. In addition, in order to prevent loss of adsorbent, if strong adhesion is established between adsorbents, the permeability of seawater will be lost. <Means for Solving the Problems> The present invention forms the adsorption bed itself using an adsorbent, thereby reducing the cost of the adsorption bed, increasing the efficiency of contact with seawater, and facilitating the transportation of the adsorbent. It provides a method for doing so.

In the present invention, the only thing that forms the adsorption bed is the adsorbent structure in which bundled fibers and lI fibrous adsorbents are arranged in a blind or mesh pattern, and the upper and lower supports that support this. This means that it is extremely simplified. Due to the presence of the upper and lower supports, the adsorption bed maintains a constant shape in +Itffi. Also, +11
By adjusting the weight of the lower support according to the flow velocity, it is possible to install the adsorption bed at an angle of inclination appropriate for the Ig% relative to the ocean current. The fiber, which is an adsorbent, not only retains its own weight and the weight of the lower support in seawater, but also has the strength to retain the weight of seawater retained within the fiber bundle when the adsorbent bed is lifted out to sea. , the adsorption bed can be easily transported by simple crane operations. (Effects of the Invention) The most important feature of the present invention is that the support for the adsorbent is simplified as much as possible, reducing the manufacturing cost of the adsorption bed structure, and the structure is such that the adsorbent and seawater can come into direct contact with each other. In other words, according to the cost estimation results for a seawater uranium recovery system that consists of an adsorption process, a desorption process, an enrichment/separation process, etc., the cost ratio of the adsorption process to the total process reaches approximately 80%, and the adsorption process The cost of the adsorption bed and structure excluding the adsorbent is estimated to account for 38-47% of the adsorption process (Journal of the Seawater Society of Japan, 40
(5), 205 (+987), same, 4 1 (5
), 257(+988)). That is, the cost of the adsorption bed and structure accounts for 30 to 35% of the total recovery cost, and it goes without saying that this reduction is important for reducing the recovery cost.

In the present invention, the structure forming the adsorption bed is only the upper and lower supports, and since the supports only need to have strength against bending moments, a simple beam structure is sufficient, and processing costs are not required. For the above reasons, the costs associated with adsorption beds and structures are almost nil, and the economic effects of building a recovery system are enormous. Furthermore, the adsorbent can take full advantage of the properties of fiber and wA fibrous adsorbents. That is, the raw material fibers can be used as long fibers of several tens of meters without being cut into short lengths, and are also effective in automating chemical processing during adsorbent production. This also leads to a reduction in adsorbent production costs.

Furthermore, since the adsorption bed can be installed and lifted by a crane, there is no need for a complicated transportation system, such as transporting slurry of granular adsorbent, and there is no risk of wear and tear on the adsorbent.

Furthermore, a! The U-shaped adsorbent is connected to the upper and lower supports and held in +tl ti, and since there is nothing covering it, the ocean current acts on the entire surface of the adsorption bed, maximizing the seawater flow. It can be used.

(Examples) Examples of the present invention will be described below with reference to the drawings, but the present invention is not limited to these examples in any way. Figure 1 shows an example of the unit components of a uranium recovery device installed in an ill stream. An example in which MG* adsorbent 1 is arranged in a mesh pattern at equal intervals is shown. The upper part of the fiber adsorbent 1 is connected to the upper support 2, and the lower part is connected to the lower support 3 to form an adsorption bed, and the upper support 2 is further connected to the floating body 4.
The adsorption bed is installed in the ocean current by connecting the floating body 4 to the anchor 6 via the mooring line 5. By using seawater-resistant and chemical-resistant materials such as FRP, these supports can be used repeatedly, including adsorption and desorption processes, along with the adsorbent. The lower support 3 has a structure in which metal pieces and the like can be attached and removed, and by adjusting the weight, the installation angle of the adsorption bed relative to the ocean current can be adjusted. When the ocean current speed is relatively low and the adjustment weight is large, the adsorption bed will be }11 as shown in Figure 1.
Place it almost perpendicular to the flow. Although the above arrangement can make the most effective use of ocean currents, excessive loads will increase the fiber east density, increase seawater flow resistance, and if the fiber bundle becomes large, uniform uranium adsorption to the inside of the fiber east will not be achieved. Tend. On the other hand, if the flow velocity is relatively high and the adjustment weight is light or absent, a windsock state will occur as shown in Figure 2. In this case, the adsorption rate tends to be slow because the pressure gradient in the diametrical direction of the fiber bundle is small. Additionally, the above arrangement results in extremely low ocean current utilization efficiency. However, depending on sea conditions, it may be effective to utilize ocean currents effectively by connecting multiple adsorption beds and adopting the arrangement shown in Figure 3. In any case, the most suitable installation method may be adopted depending on the sea area where the adsorption bed is to be installed.

Since the adsorption bed of this method is basically classified as a fixed bed,
There is a possibility of clogging due to adhesion of living organisms or suspended matter. The adsorption bed is installed at a water depth that has a low amount of microorganisms! By installing it at a depth of 10 m or more, the cleaning effect is achieved by the expansion and contraction movement of the m fibers due to the up-and-down movement of the floating body, and the vibrations caused by the generation of Karman vortices. did not occur. Although an example in which the fiber bundles of the adsorbent are arranged in a mesh pattern has been shown above, it is also effective to tie the fiber bundles at appropriate intervals and arrange them in a blind pattern. Figure 4 shows a partially enlarged view of the adsorption bed. By bundling at intervals of about 5 to 10 times the east diameter of the fibers, they form a circular &1 fiber bundle as a whole,
The bundled intermediate fiber bundles allow free movement between the fibers,
When installed in ocean currents, it deforms into a shape that allows the ocean currents to pass through it most easily. That is, the fiber bundle is deformed into a concave shape as shown in FIG. 6 with respect to the upstream side of the ocean current, and a state in which seawater flows evenly between each fiber of the fiber bundle is realized. Therefore, even if the fiber east diameter is relatively large, uniform uranium adsorption performance can be obtained throughout the interior. As the horizontal binding material 7, as in Fig. 1, an absorbent material is used! al
Navy blue may be used, or a material with excellent seawater and chemical resistance may be selected. Fiber adsorbent 1 was produced by reacting acrylonitrile fibers in a methanol solution containing hydroxylamine for a predetermined period of time to form an amidoxime, and then subjecting the fibers to an alkali treatment for a predetermined period of time. It is well known that the amidoxime type 1111 adsorbent obtained through such a process has excellent uranium adsorption properties. Furthermore, it is known that the adsorption rate and adsorption capacity are greatly affected by the amidoxime formation time and the alkali treatment time. However, regardless of the treatment process, as shown in Figure 6, the uranium adsorption performance and fiber strength are in a contradictory relationship, and over 1.5 mg of uranium is adsorbed per 1 g of adsorbent in 7 days of adsorption. Adsorbents that do this have almost no strength. Since the adsorbent wA fiber in the present invention needs to act as a strength member,
Adsorption performance must be sacrificed to some extent. We will discuss the strength required for adsorbent fibers. In Figure 1, the apparent density of the fiber bundle is 0.15g/cm3,
The calculations were made for the case where the diameter D of the fiber bundle is 3 cm, the width W of the adsorption bed is 30 m, the length of the adsorption bed is 40 m, and a mesh adsorption bed is formed with an interval of 3 cm. Assuming the Kuroshio current, the ocean current V is 2 knots, and the drag coefficient of the adsorption bed is 0.88, the maximum stress acting on the upper part of the fiber bundle is approximately 2 knots.
．． It is 7MPa. On the other hand, when the adsorption bed is pulled up onto the ship with seawater retained in the fiber bundles, the pressure is 5.5 MPa, which means that a larger force is applied when the adsorption bed is pulled up. Considering the variation in fiber strength, the strength of the adsorbent fiber is required to be at least 1OMPa or more.
By the way, the fiber strength shown in FIG. 6 indicates the short fiber strength per denier, and the single A fiber strength of 1 g per denier corresponds to about 110 MPa. In other words, if the strength is 0.1 g or more per denier, the above-mentioned adsorption bed can be formed. The adsorption experiment focused on fiber strength, and the amidoxime formation time was 4 hours and the alkali treatment time was 4 hours (Figure 6).
The conditions indicated by A in the figure) were selected, and it was planned that 1 mg of uranium would be adsorbed on 1 g of fiber with a fiber strength of 55 MPa and contact with seawater for 7 days. m Usui bundle diameter 3 cm m. Binding length 1
5cm, of the lower support! II! ! The weight is 4. 9M
It was set as Pa. The seawater current speed was 0.5 knots. The amount of uranium adsorbed under the above experimental conditions was approximately 0.
It was 7mg/g. Although the lack of adsorption amount is thought to be due to insufficient flow rate or inappropriate adjustment weight, almost the expected amount of adsorption was obtained. In addition, as shown in Fig. 7, seawater-resistant and chemical-resistant fibers such as aramid resin fibers and untreated acrylic fibers are placed in the east center of the fibers as the strength member 8, and an adsorbent l is placed around the reinforcement. Of course, it is also possible to use a fiber east adsorbent.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the mesh adsorption bed of the present invention. FIG. 2 shows II? of the embodiments. A diagram of the windsock situation when R speed is fast or when there is no lower adjustment weight. FIG. 3 is a schematic diagram of an embodiment in which the adsorption beds shown in FIG. 2 are connected and arranged. FIG. 4 shows an example of an adsorption bed in which adsorbent A fibers are tied together at regular intervals and arranged in a screen-like manner. Figure 5 shows an adsorbent that can be placed in ocean currents! 6l
i Deformation status of the fibrous bundle. Figure 6 shows the relationship between uranium adsorption performance and single fiber strength. Figure 7 is an example of a reinforced fiber bundle. 1. Fiber adsorbent, 2. Upper support, 3.4 bodies, 4. Lower support,...

Claims (1)

[Scope of Claims] 1. An apparatus for recovering uranium in seawater, characterized in that fibers and fibrous adsorbents are bundled and arranged in seawater in the form of a screen or mesh to form an adsorption bed. 2. A patent claim characterized in that the screen-like and mesh-like adsorption beds are held in seawater by connecting the upper end of the adsorbent to a support, connecting the upper support to a floating body, and mooring the floating body. A device for recovering uranium from seawater as described in Scope 1. 3. Connect the lower end of the adsorbent to a support to maintain the shape of the adsorption bed in ocean currents, and at the same time adjust the weight of the lower support to adjust the placement of the adsorption bed in relation to the ocean currents, thereby improving the relationship between the adsorption bed and seawater. The apparatus for recovering uranium in seawater according to claim 1, which maintains contact efficiency.