JP2010275588A - Method for recovering platinum group elements - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering platinum group elements by which the fractionating of platinum group elements by remote control corresponding to a high radiation field from a high level radioactive waste liquid is possible, while the use of a separation agent to form into secondary radioactive waste is suppressed as possible, and platinum group elements can be recovered as metals for reutilization, and further, fractionating with high selectivity and a high recovery rate can be achieved. <P>SOLUTION: A platinum group element ion-containing solution is irradiated with an ultraviolet region wavelength leaser to reduce the platinum group element ions, and the produced platinum group elements are recovered. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for recovering platinum group elements. More specifically, the present invention relates to a method for selectively separating and recovering a platinum group element from an aqueous solution in which plural kinds of element positive ions including platinum group element ions coexist in wet element separation.

  In recent years, from the viewpoint of reducing the burden on the global environment, it has been required to reduce the radioactivity of radioactive waste and to reduce the burden on processing disposal, and research on the separation and conversion of these is being promoted. Spent nuclear fuel from nuclear power generation facilities such as light water reactors and fast breeder reactors is reprocessed at the reprocessing facility. There are many long-lived radionuclides in the high-level radioactive liquid waste generated at this reprocessing facility. Fission products in high-level radioactive waste contain useful rare elements such as ruthenium, rhodium and palladium, which are platinum group elements, in addition to minor actinides and lanthanoid elements, and these rare elements are extracted from radioactive waste. By separating and collecting, it is considered not only to reduce the environmental load but also to effectively reuse it as a resource (for example, see Non-Patent Document 1).

  As a method for separating a platinum group element from a high-level radioactive liquid waste containing minor actinide and lanthanoid elements, an ion exchange separation method using a property that a platinum group element ion is strongly adsorbed on an anion exchange resin (for example, Non-Patent Document 1). And an electrochemical method using electrolytic reduction / oxidation of platinum group element ions (for example, see Non-Patent Document 1 and Patent Document 1) have been proposed. Furthermore, high-level radioactive liquid waste is usually prepared as an aqueous solution containing nitrate ions, but research is also underway on the possibility of preparing and collecting platinum group elements separately as an aqueous solution containing chlorine ions (for example, (See Patent Document 1).

  However, in the above-described method, the ion exchange resin is used in the ion exchange method and the electrode is separated in the high-level radioactive liquid waste for a long time in the electrochemical method, so that the ion exchange resin and the electrode are made of materials having high radiation resistance. is necessary. In addition, there is a problem that new radioactive waste is generated by immersing ion exchange resin or electrodes in high-level radioactive waste liquid for a long time. Furthermore, in the practical separation / conversion technology, the recovery rate of rare metals is set as a target value of 99% or more, but in the ion exchange method, platinum group elements from the adsorbed ion exchange resin are used. Elution is difficult and there is a problem in recovery. In the electrochemical method of Patent Document 1, many separation steps are required to achieve a high recovery rate with respect to palladium.

  From the above, (1) separation of platinum group elements by remote control corresponding to high radiation fields from high-level radioactive liquid waste is possible, and (2) the use of separating agents that become secondary radioactive waste is minimized. (3) The platinum group element can be recovered as a metal for reuse, and (4) a new platinum group element recovery method that can achieve high selectivity fractionation and a high recovery rate has been awaited. .

JP 2003-161798 A

JAEA-Review 2008-083. T. Suzuki et al., Progress in Nuclear Energy 50 (2008) 456-461.

  The present invention has been made in view of the circumstances as described above. (1) Separation of platinum group elements by remote operation corresponding to a high radiation field from high-level radioactive liquid waste is possible. (2) 2 Platinum that minimizes the use of separating agents that become secondary radioactive waste, (3) can recover platinum group elements as metals for reuse, and (4) can achieve high selectivity fractionation and high recovery It is an object to provide a method for recovering group elements.

As a result of earnest research, the inventors have focused on the fact that element positive ions can be reduced by photoexcitation of the charge transfer absorption band of element positive ions in a solution in the presence of negative ions. completed. That is,
In the present invention, first, the platinum group element ions are reduced by irradiating the platinum group element ion-containing solution with an ultraviolet region wavelength laser, and the generated platinum group elements are recovered.

  Secondly, in the first invention, the platinum group element ion-containing solution is a high-level radioactive waste liquid containing chlorine ions or nitrate ions, or a high-level radioactive waste liquid containing chlorine ions or nitrate ions added with alcohols. .

  Third, in the second invention, the alcohol is at least one selected from ethanol, methanol, and propanol.

  Fourth, in the second or third invention, the volume percent concentration of alcohol is 10 to 50% in the high-level radioactive liquid waste containing chlorine ion or nitrate ion to which alcohol is added.

  Fifth, in any one of the first to fourth inventions, the ultraviolet region wavelength laser is a laser having a wavelength of 193 nm to 355 nm.

  Sixth, in the fifth invention, the ultraviolet region wavelength laser is an Nd: YAG fourth harmonic laser (wavelength 266 nm).

  Seventh, in any one of the first to sixth inventions, the platinum group element is recovered by filtering the platinum group element ion-containing solution after irradiation with the ultraviolet region wavelength laser through a filter having a pore diameter of 25 nm to 800 nm. Do.

  According to the present invention, platinum group elements (palladium, rhodium, ruthenium, etc.) in a high-level radioactive liquid waste containing rare earth elements can be efficiently operated by a remote operation using a laser, particularly with respect to palladium and rhodium with an efficiency of 99% or more. It can be collected separately as metal fine particles. In addition, according to the present invention, recovery of platinum group elements by controlling the volume percent concentration of alcohols, laser light irradiation intensity, irradiation time, etc. when an aqueous solvent is used as the solvent of the platinum group element ion-containing solution. The rate can also be adjusted. Furthermore, according to the present invention, the contact time between the high-level radioactive liquid waste and the recovery device in the platinum group element recovery process is 1 minute or less, and generation of secondary waste due to radioactive contamination can be reduced.

It is a conceptual explanatory drawing of the collection | recovery method of a platinum group element. It is a figure which shows the structure of a separate collection | recovery apparatus. It is a figure which shows the wavelength dependence of the light absorbency of palladium, rhodium, ruthenium, and a neodymium mixed solution.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a conceptual explanatory diagram of a platinum group element recovery method. FIG. 1 (a) shows an embodiment of a platinum group element ion-containing solution targeted by the present invention, in which a plurality of types of element positive ions such as a platinum group element ion, a minor actinide ion, and a lanthanoid ion are present. It exists in solution with negative ions. Elemental positive ions in solution have a light absorption band called a charge transfer absorption band. By photoexciting this absorption band, it is possible to reduce the element positive ions by transferring electrons from the negative ions in the solution to the element positive ions. When elemental positive ions are neutralized by photoreduction, they may aggregate in the solution and form fine particles. Platinum group element (palladium, rhodium, ruthenium, etc.) ions have a charge transfer absorption band in the ultraviolet region wavelength (200-400 nm), so there are several types of element positive ion-containing solutions containing platinum group element ions in the ultraviolet region wavelength. By irradiating the laser, the platinum group element ions can be selectively photoreduced efficiently. When the platinum group element ions are reduced, fine particles having a particle size of about submicron (0.1 μm to 1 μm) are formed in the solution as shown in FIG. And as shown in FIG.1 (c), only the platinum group element atomized can be fractionated and collect | recovered by filtering this solution with the filter which has a suitable hole diameter.

  The solvent of the platinum group element ion-containing solution is water or a reducing solvent. Examples of the reducing solvent include alcohols that are readily soluble in water such as ethanol, methanol, and propanol, a mixed solution thereof, or an aqueous solvent obtained by mixing these with water. In the present embodiment, the platinum group element ions can be reduced even if the solvent is water alone, but the efficiency of atomizing the platinum group element is low. Since the reduction reaction is promoted by adding alcohol or the like as a reducing agent to water and fine particles can be formed in a short time, the solvent is preferably an aqueous solvent in which water and alcohol are mixed. In this case, if the volume percent concentration of alcohols is increased, the efficiency of microparticulation is reduced, and the recovery rate of platinum group elements may be reduced. Therefore, the preferred volume percent concentration of alcohols is 10 to 50%. More preferably, it is 30 to 50%.

  A preferable form of the platinum group element ion-containing solution is a solution containing chlorine ions, nitrate ions and the like as negative ions. A specific example of the platinum group element ion-containing solution targeted by the present invention is high-level radioactive liquid waste generated in the reprocessing step of spent nuclear fuel. This high-level radioactive liquid waste is a hydrochloric acid aqueous solution or a nitric acid aqueous solution, and in the aqueous solution, minor actinoids and lanthanoid elements are dissolved as ions together with platinum group elements. Some element positive ions of minor actinides and lanthanoids have a charge transfer absorption band in the ultraviolet region wavelength, but if the element is not further treated in addition to the ultraviolet region wavelength laser irradiation, efficient fine particles of this element positive ion Does not happen. Therefore, by irradiating the high-level radioactive liquid waste with an ultraviolet region wavelength laser, it is possible to separate and collect only platinum group elements as fine particles having a particle size of about submicron. And as mentioned above, considering that the preferred solvent of the platinum group element ion-containing solution is an aqueous solvent in which water and alcohol are mixed, the platinum group element is effectively separated and recovered from the high-level radioactive liquid waste. In order to do so, it is desirable to add alcohols to the high-level radioactive liquid waste. In that case, it is preferable to add the alcohols so that the volume percent concentration of the alcohols in the high-level radioactive liquid waste is 10 to 50%.

  As the ultraviolet region wavelength laser for exciting the charge transfer absorption band of the platinum group element ions in the platinum group element ion-containing solution, a laser having a wavelength of 193 nm to 355 nm can be used. For example, an Nd: YAG quadruple harmonic laser (wavelength 266 nm) can be used. Other lasers having wavelengths in the ultraviolet region include, for example, ArF (wavelength 193 nm), KrF (wavelength 248 nm), XeCl (wavelength 308 nm), XeF (wavelength 351 nm), Nd: YAG triple harmonic laser (wavelength 355 nm) However, the same effect can be obtained.

  The pore size of the filter used for the recovery of the platinum group element is only required to recover the fine particles of the platinum group element formed in the solution, and the particle size of the micronized platinum group element is about submicron (0.1 μm to 1 μm). Considering this, for example, it is considered that the thickness is 25 nm to 800 nm. When separating and recovering platinum group elements from high-level radioactive liquid waste, it is desirable to minimize the time required for filtration and to keep the recovery rate as high as possible. The preferred filter pore size in this case cannot be generally stated because the particle size distribution of the fine particles formed varies depending on the type of solvent and negative ions, laser light irradiation intensity, wavelength, etc., but for example, 50 nm to 200 nm. However, it is preferably about 100 nm.

  FIG. 2 is a schematic diagram of a platinum group element separation and recovery device. The sorting and collecting apparatus 1 includes a quartz cell 2, a stirrer 3, a magnet stirrer 4, a slit 5, an ultraviolet region wavelength laser light reflecting mirror 6, and a laser light source 7.

  The platinum group element fractionation from the platinum group element ion-containing solution is performed according to the following procedure. First, chlorides such as platinum group elements and lanthanoids are dissolved in pure water, and ethanol is added thereto to prepare a simulated waste liquid of high-level radioactive liquid waste. The produced simulated waste liquid is put into the quartz cell 2 and irradiated with an ultraviolet region wavelength nanosecond pulse laser from the laser light source 7 while being stirred by the stirrer 3, so that only the platinum group element is atomized and fractionated. Thereafter, the solution is taken out and suction filtered through a filter to recover the platinum group element as metal fine particles. Metal ion concentration in simulated waste liquid after recovery of platinum group elements is measured by inductively coupled plasma optical emission spectrometer (ICP-AES), and compared with the metal ion concentration in simulated waste liquid before ultraviolet region wavelength laser irradiation. The reduction rate (%) was calculated and used as the element recovery rate (%).

  In the present embodiment, the fractionation by the micronization of platinum group elements in the batch method in which the simulated waste liquid is sealed in the quartz cell and irradiated with the ultraviolet region wavelength laser is described, but the simulated waste liquid is continuously flowed in the quartz cell. Needless to say, if the irradiation flow method is adopted, the fractional collection of elements can be completed in a consistent process from the micronization of platinum group elements to the filtration and collection using a filter.

  While the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Examples of the present invention will be specifically described below.

  Hereinafter, using the separation and recovery apparatus 1, rhodium, ruthenium and palladium are used as platinum group elements, neodymium is used as a simulated metal for minor actinides and lanthanoids, and these chloride mixed aqueous solutions are regarded as simulated waste liquids for high-level radioactive liquid waste. An example of separation and collection of platinum group elements will be described.

In this embodiment, an Nd: YAG quadruple harmonic laser (Surelite-10 manufactured by Continuum, wavelength 266 nm) is used as the laser light source 7. The laser output is 16mJ / pulse and the repetition frequency is 10Hz. The intensity of the irradiated laser is 50 mJ / cm ² .
<Example 1>
Dissolve rhodium, ruthenium and neodymium chlorides in pure water to make a simulated waste liquid, and add equal amounts of ethanol to add 0.5 mM rhodium chloride, 0.5 mM ruthenium chloride, 0.5 mM neodymium chloride A mixed sample solution (volume percentage concentration of ethanol 50%) was prepared. Next, 3 mL of the prepared sample solution was taken out, put into a quartz cell, and irradiated with laser light for 30 minutes while stirring to make rhodium and ruthenium fine particles in the solution. And the solution after laser irradiation was suction-filtered with the membrane filter, and rhodium and ruthenium were collect | recovered as metal microparticles. The fractional collection operation was performed using three kinds of membrane filters having pore sizes of 800 nm, 100 nm, and 25 nm, and the time required for filtration and the element recovery rate were compared. The results are shown in Table 1. Here, the time required for the filtration is a time during which 3 mL of the sample solution transferred from the quartz cell to the filter does not drop.

  Table 1 shows that the recovery rate of neodymium is within the measurement error range (<3%) for all filters, and that only rhodium and ruthenium have been successfully separated and recovered. In particular, rhodium has achieved a high recovery rate of 85-97%. On the other hand, the recovery rate of ruthenium was 44-55%, indicating that about half of the ruthenium can be recovered by one fractional recovery operation.

Table 1 shows that the recovery rate of rhodium and ruthenium increases when the pore size of the filter is reduced. This is because the fine particles formed by laser irradiation have a wide particle size distribution, and smaller fine particles can be collected by reducing the pore size of the filter. When the pore size of the filter is changed from 800 nm to 100 nm, the time required for filtration remains within 1 minute, and the recovery rate increases by 10% for rhodium and 7% for ruthenium. On the other hand, when the pore size of the filter is changed from 100 nm to 25 nm, the recovery rate increases only 2% for rhodium and 4% for ruthenium, although it takes about 10 minutes of filtration time. In the platinum group separation / recovery process from high-level radioactive liquid waste, it is desired to reduce the time required for filtration as much as possible and to keep the recovery rate as high as possible. From the relationship between the required filtration time and the recovery rate when the pore size of the filter was changed in this way, it was concluded that it is preferable to perform recovery using a filter having a pore size of 100 nm in this system.
<Example 2>
Dissolve rhodium, ruthenium and neodymium chlorides in pure water to make simulated waste liquid, add ethanol in various ratios, finally 0.5 mM rhodium chloride, 0.5 mM ruthenium chloride, 0.5 A mixed sample solution of mM-neodymium chloride was prepared. Next, 3 mL of the prepared sample solution was taken out, put into a quartz cell, and irradiated with laser light for 40 minutes while stirring to atomize rhodium and ruthenium in the solution. Then, the solution after laser irradiation was suction filtered through a membrane filter having a pore diameter of 100 nm, rhodium and ruthenium were collected as metal fine particles, and the element recovery rates when the ethanol ratio was changed were compared. The results are shown in Table 2.

  The recovery rate of neodymium is within the measurement error range, and it can be seen that, as in Example 1, the selective fractionation / recovery of only the platinum group elements has been successful. The recovery rate for pure water only simulated wastewater is 20% for rhodium and 14% for ruthenium, but not so high, but the recovery rate increases to about 50% for both rhodium and ruthenium just by the ethanol ratio of 10%. Furthermore, when the ethanol ratio exceeds 33%, the recovery rate of rhodium is 95% or more, and the recovery rate hardly changes until the ethanol ratio is 50%. On the other hand, with respect to ruthenium, when the ethanol ratio increases, the recovery rate increases to 60%, though not as high as rhodium. However, when the ethanol ratio exceeds 50%, the recovery rate decreases rapidly, and both rhodium and ruthenium decrease to about 28% when the ethanol ratio is 67%. Therefore, the ethanol ratio is preferably about 50%.

In Example 1, fractional collection was performed by laser irradiation for 30 minutes, and in Example 2 by laser irradiation for 40 minutes. Both Table 1-Experiment No. 2 and Table 2—Experiment No. 4 were obtained by fractional collection using a membrane filter having a volume percent ethanol concentration of 50% and a pore diameter of 100 nm, and only the laser irradiation time was different. The recovery rate of rhodium increased from 95% to 98% and the recovery rate of ruthenium increased from 51% to 60% due to the increase of irradiation time. This comparison shows that the recovery rate of the platinum group element is improved by increasing the laser irradiation time. Therefore, the laser irradiation time is preferably 40 minutes or more.
<Example 3>
Palladium, rhodium, ruthenium and neodymium chlorides are dissolved in a water / ethanol mixed solution (ethanol ratio 50%), 0.5 mM palladium chloride, 0.5 mM rhodium chloride, 0.5 mM ruthenium chloride, 0.5 A mixed simulated waste liquid of mM-neodymium chloride was prepared. Next, 3 mL of the prepared simulated waste liquid was taken out, put into a quartz cell, and irradiated with a laser beam for 40 minutes while stirring, thereby finely dividing palladium, rhodium and ruthenium in the solution. And the solution after laser irradiation was suction-filtered with the membrane filter, and palladium, rhodium, and ruthenium were collect | recovered as metal microparticles.

  FIG. 3 is a diagram showing the wavelength dependence (absorption spectrum) of the absorbance of the mixed simulated waste liquid measured by an ultraviolet-visible spectrophotometer manufactured by JASCO (manufactured by JASCO Corporation, V-660). The solid line in FIG. 3 is the absorption spectrum of the solution before laser irradiation, and a band resulting from the charge transfer absorption band of each element ion in the mixed solution is recognized in the ultraviolet region wavelength. The dotted line in FIG. 3 is the absorption spectrum of the solution after 40 minutes of laser irradiation. It can be confirmed that the band of the ultraviolet wavelength is reduced by the reduction of the element ions. In addition, an increase in the absorption spectrum baseline is observed from visible to near-infrared wavelength. This is due to scattering and indicates the presence of fine particles generated by reduction of element ions. The broken line in FIG. 3 is the absorption spectrum of the filtrate that was suction filtered using a membrane filter with a pore size of 100 nm after 40 minutes of laser irradiation. Since the baseline is lower than the absorption spectrum observed in the spectrum after laser irradiation, it indicates that fine particles have been removed by filtration.

  Table 3 shows the recovery rates (%) of palladium, rhodium, ruthenium, and neodymium.

  From Table 3, the recovery rate of neodymium is within the measurement error range, but more than 99% of palladium and rhodium and 52% of ruthenium were recovered, and the selective separation and recovery of only platinum group elements was successful. It was shown that The inventors have separated all platinum group elements (palladium, rhodium, ruthenium) contained in the high-level radioactive liquid waste from the minor actinide and lanthanoid elements having strong radioactivity in the high-level radioactive liquid waste, and in particular, palladium. Regarding rhodium, it was proved that 99% or more of metal fine particles can be recovered by one separation and recovery operation.

1 Separation and recovery device 2 Quartz cell 3 Stirrer 4 Magnet stirrer 5 Slit 6 Ultraviolet region wavelength laser beam reflector 7 Laser light source

Claims (7)

  A method for recovering a platinum group element, wherein the platinum group element ion is reduced by irradiating a platinum group element ion-containing solution with an ultraviolet region wavelength laser to recover the generated platinum group element.   The platinum group element ion-containing solution is a high-level radioactive waste liquid containing chlorine ions or nitrate ions, or a high-level radioactive waste liquid containing chlorine ions or nitrate ions to which alcohols are added. A method for recovering platinum group elements.   The method for recovering a platinum group element according to claim 2, wherein the alcohol is at least one selected from ethanol, methanol and propanol.   The recovery of platinum group elements according to claim 2 or 3, wherein the volume percent concentration of alcohols is 10 to 50% in a high-level radioactive liquid waste containing chlorine ions or nitrate ions to which alcohols are added. Method.   The method for recovering a platinum group element according to any one of claims 1 to 4, wherein the ultraviolet region wavelength laser is a laser having a wavelength of 193 nm to 355 nm.   6. The method for recovering a platinum group element according to claim 5, wherein the ultraviolet region wavelength laser is an Nd: YAG fourth harmonic laser (wavelength 266 nm).   The platinum group element is collected by filtering the solution after irradiation with an ultraviolet region wavelength laser through a filter having a pore diameter of 25 nm to 800 nm. Collection method.