JP5590527B2 - Molybdenum recovery from technetium 99m generator - Google Patents

Description

The present invention relates to a method for recovering molybdenum (Mo) from a technetium 99m generator. The technetium 99m generator adsorbs molybdenum 99 ( ⁹⁹ Mo) produced by neutron irradiation of natural molybdenum in a nuclear reactor using PZC (Poly-Zirconium Compound) for imaging diagnosis such as cancer and myocardial infarction. This generator is used to produce 99m technetium for nuclear medicine diagnosis.

In imaging diagnosis of diseases such as cancer and myocardial infarction, technetium 99m ( ^99m Tc), which is a radioisotope, is used. To obtain ^99m Tc, a ⁹⁹ Mo- ^99m Tc generator (hereinafter simply referred to as a technetium 99m generator) utilizing the fact that molybdenum 99 ( ⁹⁹ Mo) with a half-life of about 66 hours decays into technetium 99m ( ⁹⁹ Tc). Is used).

The production method of ⁹⁹ Mo, ^99m Tc's parent nuclide, includes the (n, f) method for fission of enriched uranium and the (n, γ) method using ⁹⁸ Mo as the target { ⁹⁸ Mo (n, γ) ⁹⁹ Mo} There is. Compared with the (n, f) method, the specific activity of ⁹⁹ Mo produced by the (n, γ) method is low. As a result, there is a drawback that the radioactive concentration of ^99m Tc obtained is lowered. In the technetium 99m generator using ⁹⁹ Mo produced by the (n, f) method, alumina is used as an adsorbent. Alumina is not suitable as an adsorbent for ⁹⁹ Mo produced by the (n, γ) method because of its low Mo adsorption capacity. Therefore, PZC (polymeric zirconium compound) having an excellent Mo adsorption capability has been developed (see Patent Documents 1 to 3).

PZC is a zirconium-based porous adsorbent that is expected to be a generator of this type because it exhibits excellent performance in ⁹⁹ Mo adsorption performance and ^99m Tc elution rate. In that case, the technetium 99m generator using PZC is put into a special container from the manufacturing facility and transported to the hospital. In hospitals, when diagnosing a patient's disease, physiological saline is poured into it to remove ^99m Tc, and the extracted ^99m Tc is mixed with other drugs and sent into the body with a syringe. Perform diagnostic imaging. The used technetium 99m generator is discarded as radioactive waste.

JP-A-8-309182 Japanese Patent Laid-Open No. 10-30027 JP 2004-150977 A

In the (n, γ) method, a solid containing natural molybdenum (such as molybdenum trioxide pellets) is irradiated with neutrons in a nuclear reactor as a target, and ⁹⁸ Mo neutron capture reaction ( ⁹⁸ Mo (n, γ) ⁹⁹ Mo reaction) Is a method to generate ⁹⁹ Mo. In this method, ⁹⁹ Mo can be generated more efficiently as the abundance ratio of ⁹⁸ Mo in the irradiation target is higher. When natural molybdenum is used as the target material, the isotopic ratio of ⁹⁸ Mo is as small as about 24%. Therefore, ⁹⁹ Mo with high specific activity can be generated by concentrating ⁹⁸ Mo in natural molybdenum and increasing the abundance ratio of ⁹⁸ Mo in the irradiation target. Overseas, Mo enriched with ⁹⁸ Mo has already been manufactured. However, the unit price is very expensive, and it is unlikely that a large amount can be stably supplied. Furthermore, since not all ⁹⁸ Mo in the target is activated and becomes ⁹⁹ Mo, it is extremely unreasonable to treat concentrated ⁹⁸ Mo as a one-through consumable material. In order to realize industrial use, it is strongly required to establish extraction and reuse technology of ⁹⁸ Mo that has been disposed of as radioactive waste. In addition, used PZC in the following description is a general term for used PZC that has been used or not required in hospitals, or defective PZC that has occurred in the manufacturing process.

The purpose of the present invention is to note that PZC, which is an adsorbent for used technetium 99m generator, adsorbs not only ⁹⁹ Mo produced by (n, γ) reaction but also unreacted ⁹⁸ Mo and the like. The object is to provide a method for efficiently recovering Mo from used PZC from the viewpoint of effective use of Mo resources. Another aspect of the present invention is to establish a recycling system capable of reusing used PZC from the viewpoint of reducing radioactive waste.

Mo contained in PZC is eluted and recovered as molybdate anion by contacting with an alkaline solution using an elution method. It is known that the recovered molybdenum solution can be recovered in solids as molybdic acid by treating with an acid. PZC from which molybdenum has been desorbed can be used again as an adsorbent for ⁹⁹ Mo. The present invention is characterized in that these methods are efficiently improved, and further, the volume of radioactive waste can be reduced by combining with a sublimation method.

  The feature of the invention according to the first aspect of the present invention is that, in this recycling system, molybdenum remaining in the used PZC is efficiently recovered by an improved elution method and reused as a raw material for an irradiation target. is there.

  In addition, a feature of the invention according to the second aspect of the present invention is that in this system, the final PZC which has been repeatedly used and finished its role is separated into molybdenum and zirconia by the sublimation method. By combining these two features, not only can molybdenum be efficiently recovered, but also the radioactive waste that is finally generated can be reduced.

Specifically, in the Mo recovery method from the used technetium 99m generator according to the first aspect of the present invention, the Mo-containing used technetium 99m generator composed of PZC has an alkali concentration in the range of 0.1N to 10N. The alkaline solution is gradually added over a period of time and the molybdenum-containing alkaline solution is removed. While heating the solution, Mo is precipitated as molybdic acid by adding an acid and recovered.

Further, in the Mo recovery method from the used technetium 99m generator according to the second aspect of the present invention, the technetium 99m generator obtained by repeating the above-described Mo recovery method a plurality of times is heated at 700 ° C. or higher, and the contained Mo is recovered. It is sublimated and recovered as molybdenum trioxide (MoO ₃ ), and PZC is recovered as ZrO ₂ .

According to the Mo recovery method from the used technetium 99m generator according to the present invention, very expensive Mo can be recovered by a simple elution method and can be obtained in the form of molybdic acid that is easy to reuse. Further, Mo recovered by the method of the present invention has few impurities, and the recovered Mo can be used as it is. Moreover, PZC after recovering Mo can be reused by the elution method. Furthermore, non-reusable PZC can remove Mo by sublimation and recover it as ZrO ₂ , thus reducing the volume of radioactive waste.

It is a schematic explanatory drawing of the PZC recycling system which applies a sublimation method further to the elution method. It is the schematic of the molybdenum elution collection | recovery apparatus used with the elution method. It is the schematic of the molybdic acid collection | recovery apparatus used with an elution method. It is the schematic of the apparatus for implementing a sublimation method.

With reference to FIG. 1, the extraction of Mo and the volume reduction of PZC, which becomes radioactive waste, will be described using a sublimation method in addition to the elution method. FIG. 1 is a flowchart schematically showing the entire PZC recycling system. As described above, the feature of the invention according to the first aspect of the present invention is that, in this recycling system, Mo remaining in the used PZC is recovered by an improved elution method and re-used as a raw material for the irradiation target. The feature of the invention according to the second aspect of the present invention is that the final PZC that has been repeatedly used and finished its role in this system is separated into Mo and ZrO ₂ by the sublimation method. In addition, by combining these two features, not only can Mo be recovered efficiently, but also the radioactive waste that is finally generated can be reduced.

Now, refer to the processing flow of the recycling system in FIG. In step 101, molybdenum trioxide (MoO ₃ ) powder is baked and hardened into a pellet. Next, in step 102, the MoO ₃ pellet is irradiated in the reactor, and ⁹⁹ Mo is obtained from the neutron capture reaction of ⁹⁸ Mo in the pellet {(n, γ) method}. Next, the irradiated pellet is dissolved in a sodium hydroxide solution to obtain ⁹⁹ Mo / Mo (step 103). Next, PZC, which is a Mo adsorbent, is added to the ⁹⁹ Mo / Mo solution to adsorb ⁹⁹ Mo / Mo (step 104). This produces a technetium 99m generator. Now, apart from this flow, the technetium 99m generator is placed in a special container, in a hospital or the like, removed the ^99m Tc by flowing saline mixed ^99m Tc and other chemicals taken out, for example, It is sent into the patient's body with a syringe and used for diagnostic imaging of diseases such as cancer.

Returning to the flow of FIG. The used PZC in a hospital or the like is collected in a regeneration processing facility (Step 105), processed using an elution method, and Mo is extracted (Step 106). That is, in step 106, Mo contained in PZC is eluted and recovered as molybdate anions in an alkaline solution, and this solution is treated with an acid such as hydrochloric acid to recover it as molybdic acid as a solid. This molybdic acid solid is heated and oxidized to obtain MoO ₃ necessary for the pellet production in Step 101.

  The above-described reproduction is repeated several times, and the PZC that is finally determined to be unreproducible is transferred to another processing flow, and processing using the sublimation method is performed in step 107. Next, the processing in step 107 will be described.

Mo contained in PZC becomes MoO _{3 when} heated in the atmosphere. This MoO ₃ sublimates when heated to a high temperature. The sublimated Mo is collected at a low temperature part in the same system and used for pellet production in Step 101 of FIG. On the other hand, PZC heated at high temperature is reduced in volume to ZrO ₂ .

  Next, a method for recovering Mo from used PZC using the elution method in step 106 of the recycling system in FIG. 1 will be described in detail with reference to FIGS. First, the step of eluting Mo from PZC will be described. FIG. 2 shows a schematic diagram of an example of a molybdenum elution recovery apparatus used for carrying out the present invention. As a method for recovering Mo, a column 11 as shown in FIG. Next, the alkaline solution is pumped up from the alkaline solution storage tank 13 by the liquid feeding pump 14 and dropped onto the used PZC 12 from above the column 11. The material of the column 11 is preferably a material resistant to an alkaline solution, and quartz glass, polypropylene, or the like is used. Further, as this column 11, a technetium 99m generator column can be used as it is. The molybdenum eluent discharged from the lower part of the column 11 is stored in the eluent receiving tank 15.

  Next, the step of recovering molybdic acid from the above molybdenum eluent will be described. FIG. 3 shows a schematic diagram of an example of a molybdic acid recovery apparatus used for carrying out the present invention. In the apparatus of FIG. 2, acid is added to the molybdenum eluent discharged from the lower part of the column 11, and Mo is molybdic acid and the precipitate is recovered. In order to increase the generation efficiency of molybdic acid, the reaction temperature is controlled using a heating device 22 as shown in FIG. In addition, the pH meter 23 is used to precisely control the amount of acid added. The molybdate precipitate produced by the apparatus of FIG. 3 is recovered using a known solid-liquid separation apparatus.

  Next, the sublimation method in step 107 of the processing flow of the recycling system in FIG. 1 will be described in more detail with reference to FIG. FIG. 4 shows a schematic diagram of an apparatus used in the sublimation method. As shown in FIG. 4, the used PZC 33 is inserted from the left flange side of the sublimation reaction vessel 31 in a state of being stacked in a dish-shaped vessel. The material of this vessel or reaction vessel is preferably a material having a heat resistance of at least about 1000 ° C., and hastelloy, quartz glass and ceramics are used.

The molybdenum recovery container 32 is preferably in a clean state so that the sublimated molybdenum is cooled in the upper part of the container and becomes acicular crystals of molybdenum trioxide (MoO ₃ ), so that other impurities are not mixed in. It is. The material of the container is preferably a metal such as stainless steel (SUS310S) that is more resistant to heat shock than quartz glass or ceramics because of the cooling device 35.
The cooling device 35 is installed on the outer periphery of the molybdenum recovery container 32 so that the sublimated molybdenum is sufficiently cooled. The degree of cooling affects the amount of air introduced, but the temperature of the gas exiting from the air outlet 37 is preferably 500 ° C. or lower.

  In this state, while flowing a small amount of air from the air inlet 36, the heater 34 is energized to heat the contents. Since the sublimation of molybdenum starts from around 700 ° C., the cooling device 35 starts cooling as soon as the heater temperature reaches 700 ° C. If it is cooled from the beginning, the inside of the container may be contaminated by moisture contained in PZC or the like, which may adversely affect the molybdenum recovery rate.

  The heater is heated, the temperature of the contents is raised to 900 ° C. or higher, preferably 1000 ° C., and the temperature is maintained for several hours. The holding time may be about 2 to 5 hours, although it depends on the amount of contents.

Thereafter, the heater is turned off and the entire container is allowed to cool. After sufficiently cooling, the PZC container 33 is taken out from the left flange side of the reaction container 31 and transferred to a waste container or the like. Further, the right flange side of the recovery container 32 is opened, and the acicular crystals of molybdenum trioxide (MoO ₃ ) deposited on the upper part are recovered.

By this method, unreacted ⁹⁸ Mo adsorbed on the used PZC can be recovered and reused in the form of an oxide. Further, PZC heated at a high temperature is reduced in volume as zirconia (ZrO ₂ ).

Hereinafter, more specific examples of the elution method and the sublimation method performed in the present invention will be described together with numerical data. First, Examples 1 to 3 of the elution method will be described.
(Example 1)

  A glass column having an inner diameter of 10 mm was packed with 5.0 g of PZC adsorbed with 15 wt.% Of natural molybdenum. Using a peristaltic pump, 10 ml of a 2 mol / l sodium hydroxide solution prepared in advance was gradually dropped onto the top of the column over 1 hour. Thereafter, 10 ml of ion-exchanged water was fed with the same pump, and the molybdenum-containing alkaline solution remaining in the system was pushed out. Table 1 shows analytical values of molybdenum and zirconium in 20 ml of the molybdenum eluent obtained.

  Table 2 shows the relationship between the alkali concentration of sodium hydroxide (NaOH) and the recovery rate. The alkali concentration of sodium hydroxide is appropriate in the range of 0.1N to 10N, but is preferably in the range of 1N to 4N.

(実施例2)

(Example 2)

  The Mo-containing solution recovered in Example 1 was heated to 80 ° C., and hydrochloric acid was added to adjust the pH to 1.0. The mixture was stirred at 80 ° C. for 2 hours, allowed to cool, and then suction filtered using a Puchner funnel and a suction bottle. The recovered molybdic acid was 1.1 g in water. Table 3 shows the molybdenum concentration and the recovery rate in the filtrate after recovering molybdic acid.

(実施例3)

(Example 3)

  Molybdenum was re-adsorbed on the PZC from which molybdenum was eluted in Example 1. Molybdenum trioxide was dissolved in a 6 mol / l sodium hydroxide solution to prepare a sodium molybdate solution. The molybdenum molybdate solution was impregnated with 5 g of PZC recovered in Example 1, and immersed in a thermostatic bath at 50 ° C. for 3 hours to adsorb molybdenum. Table 4 shows the amount of molybdenum adsorbed on PZC.

Next, more specific examples 4 and 5 of the sublimation method used in the present invention will be described together with numerical data.
(Example 4)

  PZC (100.0 mg) adsorbed with 15 wt.% Of natural molybdenum is added to an alumina boat and inserted into a sublimation reaction vessel 31 shown in FIG. Air is sent from the air inlet 36 at a flow rate of 100 cc / min, and the temperature of the electric furnace is increased to 950 ° C. at a temperature increase rate of 10 ° C./min. And held at 950 ° C. for 100 minutes. When the furnace temperature was 950 ° C, the temperature of the contents was 900-910 ° C. Further, after the furnace temperature exceeded 700 ° C., water was passed through the cooling device 35 installed on the outer periphery of the molybdenum recovery container 32.

After the completion of the heat treatment, the whole container was allowed to cool and sufficiently cooled, and then the PZC was taken out together with the container. Further, MoO ₃ adhering to the inside of the molybdenum recovery container 32 was recovered. The weight of the recovered PZC was reduced to 60.5 mg, and the molybdenum content was reduced to 2.1 wt.%. On the other hand, 18.5 mg of MoO ₃ was obtained from the molybdenum recovery container 32. Therefore, the recovery rate of molybdenum from PZC was about 82%, and the weight loss of PZC was about 40% by performing this treatment.
(Example 5)

In the same manner as in Example 1, the temperature of the electric furnace was raised to 1050 ° C. and held for 100 minutes.
The results at this time are shown in Table 5 below together with the results of Example 1.

11: Column
12: Used PZC
13: Alkaline solution storage tank
14: Liquid feed pump
15: Eluent receiving tank
21: Reaction vessel
22: Heating device
23: pH meter
24: Acid storage tank
25: Liquid feed pump
26: Stirrer
27: Stirring blade
31: Sublimation reaction vessel
32: Molybdenum recovery container
33: Used PZC
34: Heater
35: Cooling device
36: Air inlet
37: Air outlet

Claims (6)

  To the molybdenum-containing technetium 99m generator consisting of PZC, gradually add an alkaline solution with an alkali concentration of 0.1N to 10N over a certain period of time, take out the molybdenum-containing alkaline solution, heat the solution, add acid and add strong acidity A method for recovering molybdenum from a technetium 99m generator, wherein the molybdenum is recovered as molybdic acid after being cooled to a constant temperature for a predetermined time.   The method for recovering molybdenum from a technetium 99m generator according to claim 1, wherein the acid is hydrochloric acid and the acidity to be adjusted is pH 1.0.   The method for recovering molybdenum from a technetium 99m generator according to claim 1 or 2, wherein the alkali solution is a sodium hydroxide solution, and the alkali concentration thereof is 1N to 4N.   While heating the technetium 99m generator which repeated the molybdenum collection | recovery method of any one of Claims 1 thru | or 3 times more than 700 degreeC, sublimate the contained molybdenum, and collect | recovers molybdenum as molybdenum trioxide. A method for recovering molybdenum from a technetium 99m generator, characterized in that PZC is recovered as zirconia.   To a molybdenum-containing technetium 99m generator composed of PZC, a sodium hydroxide solution having an alkali concentration of 1N to 4N is gradually added over a period of time, and the molybdenum-containing alkaline solution is taken out. Thereafter, ion-exchanged water is further fed to the generator. Technetium 99m, characterized in that the molybdenum-containing alkaline solution is taken out, all the taken-out solutions are heated, adjusted to strong acidity by adding hydrochloric acid, allowed to cool for a certain period of time, and recovering molybdenum as molybdic acid Molybdenum recovery method from generator.   A technetium 99m generator in which the molybdenum recovery method according to claim 5 is repeated a plurality of times is heated at 700 ° C. or more, the contained molybdenum is sublimated, molybdenum is recovered as molybdenum trioxide, and PZC is recovered as zirconia. A method for recovering molybdenum from a technetium 99m generator.

Images