JPH0310577B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for desorbing uranium from an amidoxime-type chelate resin that has adsorbed uranium from seawater. [Conventional technology] The concentration of uranium in seawater is approximately 3μg/
Although this is extremely low, the total amount is approximately 40
It is said to be worth 100 million tons of uranium, making it a resource that cannot be ignored, and research into extracting uranium from seawater has been progressing in various places in recent years. Co-precipitation, flotation, solvent extraction, bioconcentration, adsorption, and other methods are being studied as methods for extracting uranium from seawater, but adsorption is seen as the most promising method. The process of extracting uranium from seawater using the adsorption method consists of three steps: adsorption, desorption, and separation and concentration. Examples of adsorbents include inorganic adsorbents such as hydrous titanium oxide, and various chelate resins such as amidoxime type resins, phosphonic acid type resins, dithiocarbamate type resins, macrocyclic hexacarboxylic acid immobilized resins, and hydroxamic acid type resins. is being studied. The purpose of the desorption process is to obtain a desorption solution with a high concentration of uranium to facilitate the subsequent secondary concentration process and to facilitate the separation of co-adsorbed alkaline earth metals, etc. and to sufficiently recover the adsorption properties of the adsorbent after desorption and regeneration. [Problems to be solved by the present invention] A method for adsorbing uranium using an amidoxime-type chelate resin as an adsorbent has been proposed, but an efficient method that can easily achieve the purpose of the desorption process described above has been proposed. A method for desorbing uranium from resin is not yet known. Therefore, an object of the present invention is to provide an excellent method for desorbing uranium from an amidoxime-type chelate resin adsorbing uranium from seawater, which can easily achieve the purpose of the desorption step. [Means for Solving the Problem] In order to achieve the above objective, the present inventors have developed various conditions for desorbing uranium from an amidoxime-type chelate resin that has adsorbed uranium in seawater through contact with seawater. As a result of various studies, we found that co-adsorbed alkaline earth metal ions such as calcium and magnesium can be desorbed without desorbing uranium by contacting the adsorbent with an acid aqueous solution at a pH of 2 or above. was packed in a column to a bed height of 2 m or more, and the superficial linear velocity was 9.
By flowing the acid aqueous solution at an extremely low flow rate of less than m/hr, the uranium concentration in the desorption solution can be reduced to 1500 m/hr or less.
It was discovered that it can be obtained at a high concentration of 2000 ppm or more, and the present invention was achieved. That is, the gist of the present invention is to provide a method for desorbing uranium from an amidoxime-type chelate resin that has adsorbed uranium from seawater by contacting it with the seawater.
After contacting the adsorbent with the acid aqueous solution as described above, the adsorbent is packed into a column with a bed height of 2 m or more, and the acid aqueous solution is passed through the column at a flow rate of 9 m/hr or less in superficial linear velocity. It depends on the method of attachment and detachment. The present invention will be explained in more detail below. The amidoxime type chelate resin used in the present invention is a chelate resin having an amidoxime group as a functional group, and is produced by various known methods. That is, it is produced by reacting a polymer having a nitrile group with hydroxylamine. As the polymer having a nitrile group, for example, a copolymer of monomers having a nitrile group or a copolymer of a monomer having a nitrile group and another comonomer is used. In addition to acrylonitrile, preferred monomers having a nitrile group include α-substituted acrylonitriles such as methacrylonitrile, chloracrylonitrile, vinylidene cyanide, and the like, as well as crotonitrile, 2-cyanoethyl acrylate, 2-cyanoethyl methacrylate, etc. may be used alone or in combination of two or more. As the comonomer, all aliphatic and aromatic compounds that can be copolymerized with the above-mentioned nitrile group-containing monomers can be used, and for example, the following are preferred. Monovinyl compounds such as ethylene,
propylene, butylene, acrylic acid, methacrylic acid, esters of acrylic acid and methacrylic acid, vinyl halides such as vinyl chloride or vinyl fluoride, vinyl alcohols, vinyl esters such as vinyl acetate, vinyl ethers such as vinyl ethyl ether, vinylidene halides, For example vinylidene chloride or vinylidene fluoride, aromatic monovinyl compounds such as styrene, α-methylstyrene or vinyltoluene, also vinylcarbazole or vinylpyrrolidone, polyvinyl compounds such as divinylbenzene, divinyltoluene, maleic anhydride, ethylene glycol dimethacrylate. acid esters, polyalkylene polyol dimethacrylate esters, and mixtures thereof. In addition to the above-mentioned polymers having nitrile groups, examples include cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, and halomethylated copolymers of aromatic monovinyl compounds and polyvinyl compounds or haloacetalized polyvinyl alcohols. Products treated with iminodiacetonitrile to introduce a nitrile group, as well as aromatic or aliphatic compounds having a nitrile group, such as condensation resins containing dicyandiamide, oxybenzonitrile, dioxybenzonitrile, etc. as one component, are also used. . Amidoxime type chelate resin has granular, spherical, etc.
A shape convenient for column packing is preferred. The particle size is
The thickness is preferably about 100 μm or 1 mm. The method of bringing the amidoxime type chelate resin into contact with seawater to adsorb uranium is not particularly limited. Various methods can be used, such as a method of contacting seawater using natural energy such as ocean currents and wave power, and a method of contacting seawater using a pump. According to the present invention, in order to obtain a desorption solution with a high uranium concentration, it is necessary to increase the amount of uranium adsorbed on the amidoxime type chelate resin. The uranium concentration in the adsorbent is 0.6 mg/g or more,
Preferably it is 1 mg/g or more. By bringing the adsorbent into contact with seawater for a sufficiently long period of time, the uranium concentration in the adsorbent can be increased. In the present invention, before desorbing uranium, the adsorbent is treated with acid to elute alkaline earth metals adsorbed on the adsorbent. The pH of the treatment liquid at this time is preferably 2 to 3. If the pH is higher than 3, the elution of alkaline earth metals will be insufficient. on the other hand
If the pH is less than 2, desorption of uranium will occur. The acid used is not particularly limited, and hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. are preferably used. Pretreatment can be carried out by adding acid to the adsorbent slurry in a stirring tank to achieve the specified pH, or by filling a column with the adsorbent and passing an acid aqueous solution with the specified pH in a downward or upward flow. , the pH of the liquid flowing out from the column is at a specified level.
This is done as appropriate by passing fluid until the pH is reached. In the present invention, following pretreatment, an adsorbent is packed into a long column, and an acid aqueous solution is passed through the column at a low flow rate to desorb uranium. In order to increase the uranium concentration in the desorption solution, it is necessary to increase the height of the column layer and to decrease the flow rate of the acid aqueous solution for desorption. Column bed height is 2m or more,
Preferably it is 3 m or more. The flow rate is 9 m/hr or less, preferably 3 m/hr or less in terms of superficial linear velocity.
The higher the concentration of the acid aqueous solution, the better, but if the concentration is too high, there is a concern that the chelate resin will deteriorate.
0.3N to 5N, preferably 0.5N to 3N. The temperature is not particularly limited, and may be close to room temperature. Next, the present invention will be specifically explained using Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. [Example] Examples 1 to 4, Comparative Examples 1 to 2 An amidoxime type chelate resin obtained by reacting crosslinked polyacrylonitrile and hydroxylamine was brought into contact with seawater for a long period of time to adsorb uranium into an adsorbent. The adsorption amounts of the main metals adsorbed were as shown in Table-1.

[Table] Measure the dry weight of this adsorbent in the amount shown in Table 2 in a beaker, add 1 part of water, and stir with a stirrer, being careful not to let the pH drop below 2.
12N~HCl was added dropwise and the pH was finally adjusted to 2.5. The amount of metal eluted at each PH value obtained by this treatment was measured by atomic absorption spectrometry. The results were as shown in Figure 1. In Figure 1, Wo is the initial adsorption amount of each metal. Furthermore, the broken line indicates the PH value in the aqueous solution. Next, column desorption was performed with 1N HCl under the conditions shown in Table 2, and 5 ml of the eluate was fractionated, and the uranium concentration in each fraction was analyzed. Uranium analysis was performed using solid-state fluorescence method. The results are shown in Figure-2, Figure-3, and Figure-4.
and shown in Figure-5.

〔effect〕

According to the method of the present invention, a highly concentrated uranium desorption solution containing few foreign ions can be easily obtained.
When a highly concentrated uranium desorption solution is obtained in this way,
It also becomes possible to omit the separation and concentration step, which has a great effect. Furthermore, the amidoxime type chelate resin desorbed by the method of the present invention does not impair its adsorption properties and can be repeatedly used as a uranium adsorbent in seawater after regeneration.

[Brief explanation of the drawing]

Figure 1 is a graph showing the amount of each metal ion eluted by acid treatment of an amidoxime-type chelate resin adsorbing uranium, etc. in seawater in an example of the present invention. In the figure, the left vertical axis is Elution amount (W/Wo) relative to initial adsorption amount of each metal ion, right vertical axis
PH, the horizontal axis is the amount of acid added per gram of dry resin (meq/
gdry resin). In addition, Figure-2 and Figure-3 are
This is a graph showing a uranium desorption curve when a uranium-adsorbing amidoxime-type chelate resin pretreated with an acid aqueous solution is desorbed by an acid column. Figure 2 shows the results of a comparative example, and Figure 3 shows the results of an example. . Figure-4
and FIG. 5 show the results of Examples 3 and 4, respectively.

Claims (1)

[Claims] 1. In a method of desorbing uranium from an adsorbent made of an amidoxime-type chelate resin that has adsorbed uranium from seawater by contacting it with seawater, the adsorbent is contacted with an acid aqueous solution at a pH of 2 or higher, and then the adsorbent is The column is packed at bed height, and the superficial linear velocity is 9
A uranium desorption method characterized by flowing an acid aqueous solution at a flow rate of m/hr or less.