JP6066267B2 - Ruthenium separation and recovery method - Google Patents

Description

  The present invention relates to a method for separating ruthenium, and in particular, volatilization contained in an off-gas generated by an evaporation concentration process of radioactive liquid waste, an electrolytic removal process of ruthenium from high-level radioactive liquid waste, or a vitrification process of high-level radioactive liquid waste. The present invention relates to a method for separating and recovering ruthenium from reactive ruthenium.

The high-level radioactive liquid waste generated in facilities related to nuclear power plants is generally subjected to a vitrification process in which it is melted and solidified together with the raw glass in a glass melting furnace in order to improve safety and handling (for example, patents). Reference 1). In the off-gas generated in such a vitrification process, volatile ruthenium composed of RuO ₄ is mixed, and the separation and recovery technology of ruthenium for efficiently removing ruthenium from the RuO ₄ is a major technical problem. It has become.

As a technique for separating and recovering volatile ruthenium mixed in off-gas in the state of RuO ₄ , for example, a technique for adsorbing RuO ₄ on a silica gel adsorbent has been studied. Patent Document 2 proposes a method for treating radioactive waste gas with an adsorbent mainly composed of silica and iron oxide in order to reduce energy loss and increase the effect of removing RuO ₄ . However, this method has a problem that the storage space and processing work increase because the adsorbent becomes a new solid radioactive waste. Further, there is a problem that the adsorption performance of RuO ₄ is likely to change during the process, and ruthenium cannot be stably separated and recovered.

In place of the treatment method using the adsorbent, Patent Documents 3 and 4 include a wet separation and recovery method in which a reduction product produced by reacting volatile ruthenium with NOx is captured or absorbed in a liquid such as water. Proposed. In Patent Document 5, as a liquid treatment method for ruthenium, there is a treatment method in which volatile ruthenium is oxidized in a solution by an electrochemical method and then reduced to be converted into an insoluble RuO ₂ (solid) form. It is disclosed. In Patent Document 6, ruthenium is volatilized by subjecting a high-level radioactive liquid waste to constant potential electrolysis, and the volatilized ruthenium is precipitated as ruthenium oxide by contacting with a reducing formic acid aqueous solution. A method for separating and recovering from an aqueous solution is disclosed.

Furthermore, instead of supplementing or absorbing volatile ruthenium mixed in the state of RuO _{4 in} the liquid, Patent Document 7 proposes a method for recovering volatile ruthenium itself. The ruthenium treatment method described in Patent Document 7 condenses volatile ruthenium and reacts with a reducing agent such as a nitrogen oxide gas or a nitrous acid solution in the condensation process, thereby making RuNO ₃ ⁺ non-volatile. The high-level waste liquid is treated as a low-level waste liquid by changing to a ruthenium compound.

On the other hand, Patent Document 8 proposes another method for vitrifying the high-level radioactive liquid waste. In this method, the radioactive waste liquid to which the carbon black reducing agent has been added is impregnated into an impregnated body made of a glass cartridge and heated, and the impregnated body is melted in a glass melting furnace and then solidified. That is, unlike the method described in Patent Document 1, the radioactive liquid waste is not directly introduced into the glass melt furnace, but in the form of stable oxide (RuO ₂ ) fine particles produced by reduction. It is a method to introduce after.

JP 2005-82417 A Japanese Patent Laid-Open No. 9-222496 Japanese Patent Laid-Open No. 2-99898 JP-A-3-209198 Japanese Patent Laid-Open No. 1-138496 JP-A-6-180392 JP-A-7-287096 JP 2010-169415 A

  As described in Patent Documents 3 to 6, as a method for separating and recovering ruthenium, a wet method in which volatile ruthenium is treated in a liquid is generally used. However, these methods only change the solution containing ruthenium after the treatment into liquid radioactive waste, and an operation for newly separating and recovering the radioactive ruthenium contained in the solution is required. The method of separating and recovering only radioactive ruthenium from a solution is a complicated process because it requires careful attention for safety. Therefore, there is a strong demand for a method that can more easily separate and recover ruthenium without performing such wet processing.

Patent Document 7 describes a method for recovering volatile ruthenium itself by changing it to a RuNO ₃ ⁺ nonvolatile ruthenium compound. It is necessary to arrange a vessel, a blowing device, etc., and the processing device itself becomes large. In addition, advanced technology for precisely controlling the reaction in the reactor is also necessary, and it has not always been a simple treatment method.

Although the vitrification method described in Patent Document 8 can be expected to reduce the amount of volatile ruthenium (RuO ₄ ) contained in the off-gas from the glass melting furnace, a reducing agent is added to the radioactive liquid waste. Later, a step of impregnating the radioactive waste liquid into the impregnated body and performing a heat treatment is required. In addition, this method is for suppressing the formation of a large particle size of platinum group elements that are likely to be deposited at the bottom of the glass melting furnace. All of ruthenium contained in the radioactive liquid waste is converted into solid RuO ₂ . The effect of reducing and completely suppressing the generation of RuO _{4 in} a glass melting furnace is not expected. Therefore, it is unclear whether this method can be applied as a ruthenium separation and recovery technique for efficiently removing ruthenium from RuO ₄ .

The present invention has been made in view of the above-described conventional problems. Separation and recovery of ruthenium from volatile ruthenium (RuO ₄ ) generated during the treatment of a ruthenium-containing radioactive waste liquid, particularly the radioactive waste liquid. Separation and recovery of ruthenium from RuO ₄ contained in the off-gas generated by the evaporative concentration process, the electrolytic removal process of ruthenium from the high-level radioactive liquid waste, or the vitrification process of the high-level radioactive liquid waste, An object of the present invention is to provide a dry method for separating and recovering ruthenium which can be carried out simply, efficiently and reliably without any treatment.

In the present invention, in the method of separating and recovering ruthenium, as a result of intensive investigations on a method of easily reducing volatile ruthenium (RuO ₄ ) to RuO ₂ and collecting RuO ₂ as solid particles, RuO ₄ is heated. The reaction to RuO ₄ → RuO ₂ is found to be accelerated, and the heating method and conditions thereof are optimized, and a simple and reliable method for recovering solid RuO ₂ produced by the reduction reaction is constructed. Thus, the inventors have found that the above-described problems can be solved, and have reached the present invention.

That is, the configuration of the present invention is as follows.
[1] In the present invention, ruthenium (Ru) contained in a liquid is volatilized and separated as tetraoxide (RuO ₄ ), and then air heated to 150 ° C. or higher in advance in an atmosphere containing the volatilized and separated RuO _4. Or, ruthenium characterized in that at least RuO ₄ is separated and recovered as a RuO ₂ solid by heating the atmosphere containing RuO ₄ at a temperature of 150 ° C. or higher while flowing air containing a reducing gas. A separation and recovery method is provided.
[2] The present invention provides the method for separating and recovering ruthenium according to [1], wherein the atmosphere containing the RuO ₄ is heated at a temperature of 200 to 250 ° C. To do.
[3] The present invention, the air containing - reducing gas which has been heated above the NOR et beforehand 0.99 ° C., characterized in that the reducing gas is air containing 30 vol% or less [ [1] A method for separating and recovering ruthenium according to [2].
[4] In the present invention, the reducing gas is a gas obtained by mixing one or more of the group consisting of carbon monoxide, NOx and hydrogen. [1] to [3] The method for separating and recovering ruthenium according to any one of the above.
[5] The present invention is characterized by advancing separation and recovery of unreacted RuO ₄ by bringing the gas after heating the atmosphere containing RuO ₄ at 150 ° C. or higher into contact with a RuO ₄ absorbent. The method for separating and recovering ruthenium according to any one of [1] to [4] is provided.
[6] In the present invention, the RuO ₄ absorbing solution is water, a sodium hydroxide aqueous solution, carbon tetrachloride, an alcohol aqueous solution, a mixed solution of alcohol and hydrochloric acid, a mixed solution of hydrochloric acid and hydrogen peroxide, and a carboxylic acid such as formic acid. The method for separating and recovering ruthenium according to [5] above, comprising one or a mixture of two or more aqueous solutions.
[7] According to the present invention, the liquid containing ruthenium is a radioactive liquid waste processed using an electrolysis process of ruthenium or a radioactive liquid waste melted in a glass melting furnace and processed as a glass solidified body. The method for separating and recovering ruthenium according to any one of [1] to [6] is provided.
[Effect of the invention]

According to the present invention, volatile ruthenium occurs when processing radioactive waste that contains ruthenium (RuO ₄₎ to 0.99 ° C. or more, preferably by heating at a temperature range of 200 to 250 ° C., from RuO ₄ RuO ₂ produced by the reduction reaction to RuO ₂ can be separated and recovered in a solid state. Thereby, it is not necessary to absorb RuO ₄ or RuO ₂ in the solution, and the wet treatment for separating and recovering radioactive ruthenium from the solution can be omitted, so that ruthenium can be easily separated and recovered. In addition, when an atmosphere containing RuO ₄ is heated, preheated air is introduced into the atmosphere, and a reducing gas is mixed into the heated air, thereby promoting a reduction reaction from RuO ₄ to RuO ₂ . Therefore, the efficiency of separation and recovery of ruthenium from RuO ₄ can be increased.

In the method of the present invention, most of the radioactive ruthenium can be separated and recovered from the volatilized and separated RuO ₄ by a heat treatment at 150 ° C. or higher, but the gas after heating the atmosphere containing RuO ₄ at 150 ° C. or higher. Is further brought into contact with the RuO ₄ absorbent, whereby separation and recovery of unreacted RuO ₄ can be promoted. The method of combining the two is employed in order to prevent radioactive ruthenium from leaking to the outside at all by reliably separating and recovering ruthenium. According to the method of the present invention, since the purpose of ruthenium separated and recovered it can be substantially achieved by heat treatment of the above 0.99 ° C., even employing the method according to the contact of said RuO ₄ absorption liquid, the use of RuO ₄ absorbing liquid It becomes possible for a long time. In that case, the effect that the frequency | count and process time of the collection | recovery process of radioactive ruthenium from a solution can be reduced significantly are acquired.

Since the method according to the present invention can separate and recover radioactive ruthenium more easily and reliably than the conventional method, volatile ruthenium (RuO ₄ ) generated from radioactive waste containing ruthenium, for example, an evaporation concentration process or high concentration process of radioactive waste liquid. RuO 4 is removed by electrolytic oxidation level radioactive liquid _waste, also be applied to any process of RuO ₄ generated by RuO _4, and the high level vitrification process radioactive liquid waste generated by incineration or melting of radioactive waste be able to. Among them, in particular, from volatile ruthenium generated by the evaporative concentration process of radioactive liquid waste and electrolytic oxidation of high-level radioactive liquid waste, or from volatile ruthenium contained in off-gas generated by vitrification process of high-level radioactive liquid waste When applied to the separation and recovery of ruthenium, a great effect can be obtained as a simpler treatment method.

Is a schematic cross-sectional view showing an embodiment of RuO ₄ dry separation and recovery device of the present invention. It is a diagram showing a collecting mechanism of RuO _4. It is a schematic sectional view showing another form of RuO ₄ dry separation and recovery device of the present invention. It is a schematic cross-sectional view of the separation and recovery apparatus according to another embodiment of the present invention of connecting the wet recovery device to RuO ₄ dry separation and recovery device. It is a schematic cross-sectional view of the separation and recovery apparatus according to another embodiment of the present invention comprising a filter RuO ₄ dry separation and recovery in the apparatus. It is a diagram showing the relationship between the anti answer temperature and ruthenium recovery in RuO ₄ dry separation and recovery device of the present invention. A Arrhenius plot of the decomposition reaction rate constant of the RuO _4. Is a diagram showing a comparison between the dry separation from the recovery device and the obtained ruthenium leak rate in the experiment was calculated from the adsorption and reaction speed RuO ₄ residual rate of the present invention.

RuO ₄ is a very unstable substance and stabilizes to RuO ₂ . As a result of actually calculating the concentration of Ru oxide after chemical equilibration using RuO ₄ as the starting material by the thermodynamic equilibrium calculation software (Factsage 6.1), the ratio existing as RuO ₄ and / or RuO _{3 at} 400 ° C. or lower. Was found to exist very little as RuO ₂ after chemical equilibrium. The reaction of RuO ₄ is located primary reaction _{O 2} desorption from RuO _4. Further, as long as it is within the range of 400 ° C. or less, the reaction rate of the decomposition into RuO ₂ and _{O 2} in RuO ₄ (reduction of Ru) is increased by raising the temperature. Accordingly, it is considered that gaseous RuO ₄ can be recovered as solid RuO ₂ by heating the RuO ₄ gas. The present invention has been made based on this finding. By heating volatile RuO ₄ gas generated when processing a radioactive liquid waste containing ruthenium, gaseous RuO ₄ is converted into solid RuO _2. It is characterized by separating and collecting. As a result, it is possible to perform separation and recovery in a dry method without using a solution, and unlike conventional off-gas treatment by a wet method, waste liquid is not generated or the amount of waste liquid can be greatly reduced, and the present invention is simple. It can be a highly efficient practical off-gas treatment method.

In the present invention, the heating for carrying out the reaction of RuO ₄ → RuO ₂ is carried out by setting the atmospheric temperature of the reaction tower to which gaseous RuO ₄ generated when treating the radioactive waste liquid containing ruthenium to 150 ° C. or higher. It needs to be heated. When the heating temperature is less than 150 ° C., the effect of rapidly recovering gaseous RuO ₄ as solid RuO ₂ cannot be obtained. Furthermore, if the heating temperature is 200 ° C. or higher, the reaction of RuO ₄ → RuO ₂ is promoted, and the ratio that can be recovered as solid RuO ₂ is greatly improved. Therefore, the present invention makes the heating temperature 200 ° C. or higher. It is more preferable. In addition, as described above, the upper limit of the heating temperature is preferably 400 ° C. or lower in order to suppress the formation of RuO ₄ and / or RuO ₃ . However, the recovery of solid RuO ₂ can be almost 100% when the heating temperature is 250 ° C. and only saturates at heating temperatures above 250 ° C. On the other hand, when the heating temperature exceeds 250 ° C., not only the energy loss increases, but also the adverse effect that the handling property and durability of the entire apparatus including the reaction furnace deteriorates, the upper limit temperature of heating is 250 ° C. The following is more preferable. Thus, in the present invention, it is necessary to set the atmospheric temperature to 150 ° C. or higher, preferably by setting it to 200 to 250 ° C., thereby recovering gaseous RuO ₄ as solid RuO ₂ for separation and recovery. The rate is greatly improved, and the separation and recovery of ruthenium can be reliably performed only by the dry method by heating.

  Hereinafter, an apparatus for carrying out a method for separating and recovering ruthenium according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of a dry recovery apparatus used in the separation and recovery method of the present invention. As shown in FIG. 1, this dry recovery apparatus is mainly composed of a gaseous RuO ₄ introduction pipe 1, a reaction tower 4 comprising a heating part 2 and a natural cooling part 3, and a gas discharge pipe 5 after heat treatment. Configured. The heating unit 2 is provided with a heating means 6 such as a heater around the periphery, for example, a heater, and the temperature can be automatically controlled. Further, separable clamps 7 are provided at locations corresponding to the inlet and the outlet of the reaction tower 4 so that the reaction tower 4 can be exchanged.

In Figure 1, RuO 4 contained in the off-gas generated from the glass melting furnace by vitrification _process, RuO 4 is generated by the electrolytic oxidation of high-level radioactive liquid _waste, or RuO ₄ generated by incineration or melting of radioactive waste Through the introduction pipe 1, the reaction tower 4 is introduced into the heating unit 2 controlled at a temperature of 150 ° C. or higher, preferably 200 to 250 ° C., heated, and then air-cooled in the natural cooling unit 3. The gas after natural cooling is discharged through the discharge pipe 5. Here, in the upper stage of the reaction tower, that is, in the heating section 2, Ru is adhered with gloss as if it was uniformly deposited inside the tower tube. In addition, the natural cooling section 3 corresponding to the lower stage has a trace that fluid (powder) has flowed through the tower tube, and relatively large particles can be confirmed, and solid RuO ₂ is observed. The

Based on the phenomenon observed on the inner wall of these reactors 4, the following two mechanisms can be considered for the collection of RuO ₄ (see FIG. 2). Although details will be described later, RuO ₄ that has flowed into the reaction tower diffuses while moving downward along the gas flow without being reacted, and is adsorbed on the wall surface of the reaction tower, or gas phase When it adheres to the minute RuO ₂ particles existing inside and moves to the lower part of the reaction tower and adheres to the inner wall surface of the reaction tower and is collected, it changes into RuO ₂ and aggregates as particles. It is a case where it adheres to the inner wall surface of the tower.

The reaction tower 4 in which the solid RuO ₂ is attached to the inner wall surface of the tower is removed and replaced from the place having the separable clamp 7 according to the processing amount and processing frequency of the radioactive waste containing the radioactive liquid waste. The separation and recovery of radioactive ruthenium is performed. The reaction tower 4 to which the solid RuO ₂ is attached is removed or stored in a predetermined isolation place. In this case, the reaction tower 4 to which RuO ₂ is attached may be stored or stored together with a solidifying agent such as concrete.

In consideration of handling properties such as strength, corrosion resistance, heat resistance, cost and ease of disposal, the reaction tower 4 used in the present invention is made of glass or stainless steel tube such as quartz tube or iron tube at least in the heating part. It is preferable to use a metal such as the above. In particular, since the glass tube is transparent, it is possible to grasp the collection state of RuO ₄ by its appearance, and it is suitable as a material for the reaction tower because it is inexpensive in terms of cost. In the present invention, the natural cooling unit 3 of the reaction tower 4 may be the same material as the heating unit 2 or a different material. Since the natural cooling part 3 has a smaller temperature rise than the heating part 2, only the natural cooling part 3 can be made of a material having low heat resistance such as a transparent or opaque plastic. At that time, as shown in FIG. 1, an additional separable clamp 8 for separating or connecting the two is provided at the boundary between the heating unit 2 and the natural cooling unit 3. By doing so, it is easy to freely adjust the length of the reaction tower, and there is an advantage that the reaction tower can be exchanged only at a portion where the RuO ₂ is significantly attached. Note that the additional separable clamp 8 is not necessarily essential in the present invention, and is shown by a dotted line in FIG.

In the reaction tower 4 described above, the lengths of the heating unit 2 and the natural cooling unit 3 are determined and optimized according to the flow rate of RuO ₄ , the diameter of the reaction tower 4, and the like. Reaction progress of RuO ₄ → RuO ₂ and adhesion and collection of RuO ₂ can be performed, and the effects of the present invention can be obtained. Furthermore, in order to advance the reaction progress of RuO ₄ → RuO ₂ and increase the recovery rate as RuO ₂ , when it is desired to lengthen the heating part and the natural cooling part of the reaction tower, or when the space for installing the reaction tower is narrow The reaction tower 4 shown in FIG. 1 can be arranged in parallel in two or more stages, and the pipes can be connected in series. For example, the heating unit is a first-stage reaction tower, and the natural cooling unit is a second-stage reaction tower, which is arranged in parallel with the first-stage heating unit. At this time, the piping for introducing and discharging RuO ₄ is connected in series. Alternatively, a reaction tower having a heating part and a natural cooling part may be arranged as the first stage, and a reaction tower having another heating part and a natural cooling part in parallel therewith may be arranged as the second stage. In that case, RuO ₄ that could not be completely separated and recovered in the first-stage reaction tower can be reprocessed in the second-stage reaction tower, and almost all of the generated RuO ₄ is solid. It is reliably separated and recovered as RuO _{2 in the} form of a solid. In the present invention, the number of reaction towers arranged in parallel is not limited to two, and may be three or more depending on the amount of radioactive waste, the length of the reaction tower, and the ruthenium recovery rate. In addition, the reaction tower 2 shown in FIG. 1 can connect not only two or more reaction towers connected in series but also connected in parallel. In that case, since the separation and recovery of ruthenium can be performed simultaneously in parallel, the effect of increasing the processing speed and the processing efficiency can be obtained.

In addition, the present invention not only heats the internal atmosphere of the reaction tower into which RuO ₄ is introduced at 150 ° C. or higher, but also provides means for introducing preheated air into the internal atmosphere of the reaction tower, thereby providing ruthenium. It is possible to increase the efficiency of separation and recovery. FIG. 3 is a schematic cross-sectional view showing an embodiment of a dry recovery apparatus used in the separation and recovery method of the present invention. As a configuration of the apparatus, means for flowing preheated air 9 together with RuO ₄ into the reaction tower is shown. Have. In FIG. 3, the inflow of the heated air 9 is directly supplied from the upper part of the reaction tower 4 by passing the inflowed air using the blower pump 10 through the heater 11.

In order to promote the reaction of RuO ₄ → RuO ₂ at 150 ° C. or higher in the heating section 2 of the reaction furnace 4, the heated air 9 is heated to a temperature of 150 ° C. or higher in the upper part of the reaction tower 4 in advance. It is preferable to adjust the temperature. The temperature adjustment of the heater 11 can be automatically performed according to the actually measured temperature, for example, by arranging a temperature sensor at the top of the reaction tower 4. In the present invention, when the temperature of the heating unit 2 of the reaction tower 4 is set to 200 to 250 ° C., the heated air 9 may be directly introduced by adjusting to a temperature range of 200 to 250 ° C., A method of raising the temperature by the heating means 6 after introducing the air 9 previously heated to 150 ° C. or more into the reaction tower 4 may be adopted.

In the present invention, there is an effect that the pressure and flow rate of the supply gas introduced into the reaction tower 4 can be adjusted by adopting a means for allowing the preheated air 9 to flow into the reaction tower together with RuO ₄ . In order for the reaction of RuO ₄ → RuO ₂ to proceed uniformly throughout the reaction tower 4, the gas flow is preferably a laminar flow. For example, a gas containing RuO ₄ supplied from the introduction pipe 1 When the pressure and flow rate of the gas are small, the laminar flow state cannot be maintained, and the reaction of RuO ₄ → RuO ₂ tends to occur unevenly inside the reaction tower 4. As a result, the adsorption of RuO ₄ and the solid RuO ₂ adhering to the inner wall of the reaction tube 4 become non-uniform, and there may be a problem that the ruthenium recovery rate is significantly reduced during the separation and recovery operation. As will be described later, when a liquid recovery device is provided after the dry separation and recovery device of the present invention, or a filter for recovering solid RuO ₂ is installed near the gas outlet of the dry separation and recovery device of the present invention. In such a case, back pressure is generated from these additional devices, and the flow of the gas containing RuO ₄ is likely to be inhibited. In the worst case, there is a possibility of backflow. Therefore, when the preheated air 9 is supplied to the inside of the reaction tower 4 together with the gas containing RuO ₄ , the occurrence of such a problem is prevented by adjusting the pressure or flow rate of the heated air 9. be able to.

In order to advance the reduction reaction of RuO ₄ → RuO _2, a reducing gas may be mixed in the heated air 9 applied in the present invention. As the reducing gas, for example, a gas composed of one or more of the group consisting of carbon monoxide, NOx and hydrogen is used. Among them, it is preferable to mix a reducing gas of NOx from the viewpoints of handleability and safety. The ratio of the reducing gas mixed in the heated air 9 can be determined according to the separation and recovery rate of ruthenium, but the reduction reaction of RuO ₄ → RuO ₂ can be almost controlled by the heating temperature. do not have to. Accordingly, the ratio of the reducing gas to the mixed gas is 30% by volume or less, preferably 10% by volume or less, and more preferably 5% by volume or less with respect to the total amount of the mixed gas.

The dry separation and recovery apparatus shown in FIG. 3 can more efficiently and stably perform the separation and recovery of radioactive ruthenium from the volatilized and separated RuO ₄ as compared with the apparatus shown in FIG. In addition, as described above, by adopting a method in which the reaction towers 4 are arranged in parallel in two or more stages, the separation and recovery of ruthenium from RuO ₄ generated during the treatment of radioactive waste is more reliably performed. Become.

In the present invention, in order to eliminate the presence of unreacted RuO ₄ and to proceed the separation and recovery of ruthenium in a nearly perfect form, the atmosphere containing RuO ₄ is set to 150 ° C. or higher, preferably 200 to 250 ° C. A wet recovery method in which the heated gas is further brought into contact with the RuO ₄ absorbent can be employed. FIG. 4 is a separation / recovery device for carrying out a method combining both of them. A separation / recovery device showing another embodiment of the present invention in which a wet recovery device is connected after the RuO ₄ dry separation / recovery device shown in FIG. FIG.

In FIG. 4, the wet recovery tank 12 is provided with a first absorption cylinder 14 and a second absorption cylinder 15 containing a RuO ₄ absorbent in a thermostatic chamber 13 for maintaining a constant temperature, and dry separation is performed. The gas that has passed through the gas discharge pipe 5 from the recovery device is guided to the first absorption cylinder 14 and the second absorption cylinder 15 via the first pipe 16 and the second pipe 17. The gas exhaust pipe 5 and the first pipe 16 may be the same pipe, or different pipes may be connected by providing a joint. The first piping 16 and the second piping 17 are made of glass or metal. In addition, as the absorption cylinders 14 and 15, commercially available glass gas cleaning bottles may be used from the viewpoint of handleability. However, in consideration of application to an actual plant, a chemical plant such as an off-gas absorption tower is used. Commonly used absorption towers are preferred. In the illustrated example, the absorption tube 2 arranged, if, when the RuO ₄ traces contained in the gas becomes absorbed in the first absorption column 14, is subsequently led to the second absorption column RuO ₄ It is designed to ensure that absorption is possible. In the present invention, the number of absorption cylinders to be arranged is not limited to two, but may be one or three or more. The ruthenium can be separated and recovered by using a wet recovery apparatus since most of the ruthenium can be separated and recovered by heat treatment at 150 ° C. or higher using the dry separation and recovery apparatus of the present invention shown in FIG. 1 or FIG. One or two absorption cylinders are sufficient. In addition, the discharge pipe 5, the first pipe 15, and the second pipes 16 and 17 included in the dry separation / recovery device are heated by winding a ribbon heater or the like so that RuO ₄ is condensed inside each pipe. You may not make it. Further, the gas can be sucked so as to guide the gas to the absorption cylinders 16 and 17 by using a pump (P) 18 so that the gas discharged from the gas discharge pipe 5 can be smoothly flowed.

Examples of the RuO ₄ absorbent include water, sodium hydroxide aqueous solution, carbon tetrachloride, alcohol aqueous solution, mixed solution of alcohol and hydrochloric acid, mixed solution of hydrochloric acid and hydrogen peroxide, and aqueous solution of carboxylic acid such as formic acid. Alternatively, a mixed solution of two or more kinds can be used. Since these RuO ₄ absorbents already have a track record of absorption capability of RuO ₄ , the amount stored in the absorption cylinder and the mixing ratio of the mixed solution can be adjusted within the technical scope of those skilled in the art. In FIG. 4, the first absorption cylinder 14 and the second absorption cylinder 15 may both store the same type of RuO ₄ absorption liquid, or store different types of RuO ₄ absorption liquid. May be.

Since the ruthenium separation and recovery method implemented using the separation and recovery apparatus shown in FIG. 4 can reliably perform the separation and recovery of ruthenium, the effect of preventing any radioactive ruthenium from leaking to the outside can be obtained. Furthermore, since the separation and recovery of ruthenium can be almost achieved by a heat treatment at 150 ° C. or higher using a dry separation and recovery apparatus, even if a wet method by the contact of the RuO ₄ absorption liquid is adopted, the RuO ₄ absorption liquid Long-term use is possible. This contributes to a significant reduction in the number and process times of separating and recovering radioactive ruthenium from the solution.

Next, an example of an apparatus will be described in which a filter for capturing solid particulates of RuO ₂ produced by heat treatment is provided below the reaction tower 4 of the RuO ₄ dry separation and recovery apparatus shown in FIG. 1, FIG. 3 or FIG. . FIG. 5 is a schematic sectional view of a separation / recovery device including a filter in the RuO ₄ dry separation / recovery device shown in FIG. In FIG. 5, the filter 19 is inserted between filter holders having metal flanges, and the filter holder is disposed at the bottom of the reaction tower 4. FIG. 5 shows an example in which a filter is provided in the apparatus shown in FIG. 4, but in the present invention, a filter can also be provided in the RuO ₄ dry separation and recovery apparatus shown in FIG. 1 or FIG. Here, the filter 19, if all of the RuO ₂ solid fine particles to be produced by heat treatment is deposited on the bottom of the not adhered to the inner wall of the reactor 4, apparatus moves downward, RuO ₂ falling downward Used to completely supplement the solid particulates. Thereby, it is possible to prevent the discharge pipe 5 from flowing out of the apparatus.

As the filter 19, a HEPA filter generally used in a plant, or more specifically, a resin such as polytetrafluoroethylene (PTFE), polyethylene or polypropylene, or a metal such as stainless steel can be used. The pore diameter of the filter is in the range of 0.1 to 3 μm. The pore size of the filter is not limited to one type, and two or more types may be laminated and used. If the filter 19 becomes clogged due to the capture of RuO ₂ solid fine particles, the filter 19 is removed from the apparatus and replaced with a new one. Since it is problematic to dispose of the used filter as it is, it is stored or stored in a place isolated from the outside.

In the present invention, RuO ₄ dry separation and recovery device comprising a filter 19, although the supplement of RuO ₂ solid particulate is effective, because of the influence of back pressure due to the provision of the filter, the gas containing RuO ₄ In special cases, such as when the pressure or flow rate is small, the ruthenium separation and recovery rate may not increase to the expected level. For this reason, it is preferable to apply a RuO ₄ dry separation and recovery device equipped with a filter according to the radioactive waste processing method and situation.

  Next, although this invention is demonstrated by specific embodiment, this invention is not limited to these embodiment.

<First Embodiment>
In order to investigate the temperature dependence of the decomposition reaction of RuO ₄ , the atmospheric temperature of the heating part of the reaction tower 4 is room temperature, 100 ° C., 150 ° C., 200 ° C., 210 ° C. using the dry separation and recovery apparatus for ruthenium shown in FIG. The recovery of ruthenium (Ru) at each temperature was determined. In the present embodiment, a wet recovery device is arranged at the subsequent stage of the ruthenium dry separation recovery device, and the respective Ru concentrations are measured in the absorption cylinders 14 and 15, whereby the initial RuO ₄ concentration and the absorption cylinders 14 and 15 are stored. From the Ru concentration in the RuO ₄ absorbent, the Ru recovery rate when using a dry separation and recovery device can be determined.

In the present embodiment, instead of treating the radioactive waste liquid to generate volatile RuO ₄ , a RuO ₄ generator was simulated to generate RuO ₄ . Ruthenium nitrate solution (0.03 mol / L) and cerium ammonium nitrate solution (0.15 mol / L) are supplied at a rate of 0.3 mL / min into the container of the RuO ₄ generator, and RuO ₄ is continuously supplied. To generate. The generated RuO ₄ is supplied to the inside of the reaction tower 4 from the introduction pipe 1 shown in FIG. At this time, the air that has flowed in using the blower pump 10 is heated via the heater 11, and this heated air is supplied directly to the upper part of the reaction tower simultaneously with the gas containing RuO ₄ . The anti-response 4 used in this embodiment is a cylindrical quartz tube having an inner diameter of 52 mm. Moreover, the length of the heating part 2 and the natural cooling part 3 of the anti-response 4 is 300 mm and 150 mm, respectively.

Gas containing RuO ₄ that caused by the above RuO ₄ generator, after the internal temperature of the heating portion 2 of the reaction column 4 is heated to a temperature setting was maintained at a constant temperature, heating by the heater 11 The air is supplied into the reaction tower 4 together with the air at a flow rate of 0.5 L / min and 1.5 L / min, respectively. A backup filter 19 (Millipore type FH (pore diameter) 0.5 μm, made of PTFE) for collecting particles was disposed at the bottom of the reaction tower. Further, in the subsequent stage, a wet recovery device 12 is arranged, and two gas absorption bottles containing 300 mL of 6M hydrochloric acid-1% ethanol solution as RuO ₄ absorption solution are connected in series to capture RuO ₄ leaking from the dry recovery device. Gathered. Here, the two gas absorption bins function as absorption towers 14 and 15, respectively.

The amount of RuO ₄ generated from the RuO ₄ generator was calculated from the difference from the input amount by measuring the concentration of Ru in the residual liquid in the generator immediately after completion of the test. The solution remaining in the RuO ₄ generator was collected in a hydrochloric acid solution having the same composition as that of the absorbing solution immediately after the test, and was fixed so that Ru was reduced and not volatilized.

As a result of actual measurement, the temperatures of the heating unit 2 of the reaction tower 4 when the experiment was performed are 22 ° C., 94 ° C., 151 ° C., 200 ° C., and 210 ° C., respectively, and after maintaining at each temperature, the RuO ₄ generator The mixed gas of RuO ₄ generated from the air was supplied at 0.5 L / min, and the air heated by the heater 11 was supplied at a rate of 1.5 L / min for about 30 minutes. The gas that passed through the reaction tower 4 was led to the absorption towers 14 and 15 comprising gas absorption bottles as described above, and Ru was collected here. By analyzing the amount of Ru, from the initial RuO ₄ concentration, by subtracting the RuO ₄ concentration of RuO ₄ absorbing liquid to be housed in the absorption tube 14, a dry separation and recovery device when changing the temperature The Ru recovery rate is obtained. Specifically, the Ru recovery rate is obtained according to the following steps.

The amount of RuO ₄ generated (C _vap ) is determined from the amount of Ru (C _in ) supplied to the RuO ₄ generator container, and the amount of Ru (C _re ) determined from the concentration of Ru in the remaining solution (both in each case) The unit is obtained by subtracting mg). In addition, the amount of RuO ₄ leaked from the dry recovery device is obtained from the amount of Ru (C _out ) collected in the subsequent Ru absorption bottle. From these values, the Ru recovery rate (RE) in the dry recovery apparatus can be obtained by the following formulas (1) and (2). In FIG. 5, it is confirmed that the Ru concentration in the second absorption cylinder 15 is not more than the detection limit value, and that the first absorption cylinder 14 can sufficiently collect Ru.

In addition, for the RuO ₂ solid particles produced by the reaction RuO ₄ → RuO _2, the change in the weight of the backup filter arranged at the rear stage of the reaction tower is about 0.1 mg, and the average generation amount of this test is 12 mg. And 1% or less. Thus, it can be confirmed that there are very few RuO ₂ solid particles captured by the backup filter, and most of them are attached to the inner wall of the reaction tower.

  The obtained recovery value is shown in FIG. FIG. 6 reveals that the higher the temperature, the higher the Ru recovery rate (RE). In addition, when the temperature is 150 ° C. or higher, the Ru recovery rate tends to be higher than when the temperature is lower than 150 ° C. The recovery rate is 89.9% at 200 ° C. and 98.6% at 210 ° C. As can be seen from FIG. 6, when the heating temperature is 210 ° C. or higher, the Ru recovery rate tends to be saturated, and a Ru recovery rate of almost 100% is obtained at a heating temperature of 250 ° C. As described above, the method for separating and recovering ruthenium according to the present invention can separate and recover ruthenium at about 90% or more by heat treatment at 200 ° C. or higher without using a wet recovery method, and further heat-treat to 250 ° C. Thus, reliable separation and recovery can be achieved. On the other hand, when the heating temperature is 150 ° C. or higher and lower than 200 ° C., the Ru recovery rate is increased, but it is difficult to recover all Ru by the dry separation and recovery method alone. However, when used in combination with the wet recovery method, the recovery rate of ruthenium can be increased, and the separation and recovery of ruthenium can proceed in a nearly perfect manner.

<Second Embodiment>
Next, in order to clarify the trapping mechanism of RuO ₄ shown in FIG. 2, in this embodiment, the influence on the reaction rate constant of RuO ₄ → RuO ₂ and the heat treatment temperature of the adsorption reaction of RuO ₄ will be examined.

FIG. 7 is a diagram in which the reaction rate constant (k) of RuO ₄ to RuO _{2 at} each temperature is obtained from the results shown in FIG. 6 and an Arrhenius plot is performed with respect to the reciprocal of the temperature. The reaction rate constant (k) is obtained as follows.

で示されるように一次反応と考えられることから、反応速度定数をｋとして、ｔ分後のＲｕＯ_４の濃度（Ｃｔ）は初期濃度（Ｃｏ）に対して、

である。ここで、反応塔内の加熱部の通過時間を反応時間として、反応速度定数ｋを求める。 The reaction of RuO ₄ to RuO ₂ is represented by the following formula (3)

Since the reaction rate constant is k and the RuO ₄ concentration (Ct) after t minutes is equal to the initial concentration (Co).

It is. Here, the reaction rate constant k is obtained using the passage time of the heating section in the reaction tower as the reaction time.

FIG. 7 also shows the document value represented by the following formula (5). The document value is substantially the same in the high temperature region, but greatly deviates in the low temperature region. I understand.

The reason why the experimental results and the literature values are greatly different in the low temperature region is considered to be caused by another reaction that raises the Ru recovery rate in addition to the reaction according to the above formula (3). As shown below, the collection mechanism of RuO ₄ in the separation and recovery of the ruthenium embodied herein, (A) collected by reaction in the RuO ₄ gas phase, and (B) of RuO ₄ to reactor It was found that it can be explained by two factors, collection by adsorption.

Based on the above two factors (A) and (B), FIG. 8 shows the result of calculating the final Ru total collection rate as the product of the collection efficiency of adsorption and reduction reaction, respectively. FIG. 8 is a diagram showing a comparison between the ruthenium leakage rate obtained by experiments from the dry separation and recovery apparatus of the present invention and the RuO ₄ residual rate calculated from the adsorption and reaction rates. The ruthenium leakage rate shown in FIG. 8 indicates the proportion of ruthenium that could not be separated and recovered from ruthenium, and is a physical quantity represented by [1- (Ru collection rate)]. That is, the smaller the leakage rate, the higher the Ru collection rate.

In FIG. 8, RuO ₄ → RuO ₂ reaction (calculation formula) is calculated from the average flow rate (m / s) and reaction time (s) of RuO ₄ at each temperature using the above formula (5). is there. This calculated value is the ratio at which unreacted RuO ₄ gas remains when it is assumed that no adsorption occurs on the inner wall surface of the reaction tower.

In FIG. 8, the adsorption (calculation formula) can be calculated as follows. Since the reaction tower used in the present embodiment has a structure in which a gas flows in a cylindrical quartz tube, the adsorption of gas to the wall in the cylindrical tube is generally performed using ammonia, dioxide, which are gaseous substances in the atmosphere. The diffusion denuder method used to recover the concentration of sulfur and nitric acid was considered to be followed. In the method, the following equations (6) and (7) are used for the concentration (C ₀ ) of the target gas at the inlet and the concentration (C) at the outlet.

Here, since Δ includes parameters (viscosity, density, kinematic viscosity, diffusion coefficient) having temperature dependency, correction for each temperature is performed. Although details are omitted, finally, viscosity (kg / m · s), density (kg / m ³ ), kinematic viscosity (m ² / s), average flow velocity (m / s), Re (Reynolds number), The adsorption rate C / C ₀ (calculated value) is calculated from the diffusion coefficient (m ² / s). The adsorption (calculation formula) shown in FIG. 8 is obtained by plotting the calculated values thus obtained against the reciprocal of the temperature.

As is apparent from FIG. 8, it was found that the total leakage rate of the comprehensive RuO ₄ calculated as the product of the collection efficiency of the adsorption and reduction reaction almost coincided with the experimental value. From this result, for the collection of RuO _4, the adsorption is mainly performed at a low temperature, but by increasing the temperature, the mechanism of the collection includes the adsorption, and the reaction from RuO ₄ to RuO ₂ . Has become the main. Therefore, it was found that the synergistic effect of both was obtained at 150 ° C. or higher, and the collection efficiency was drastically improved. In particular, the synergistic effect of both increases at 200 ° C. or higher, and as shown in FIG. 6, the Ru recovery rate can be increased to 90% or higher, and further to nearly 100%. This is because, in the dry separation and recovery apparatus shown in FIG. 5, in the upper stage of the reaction tower 4, that is, in the heating unit 2, Ru adheres with gloss as if it was uniformly deposited inside the tube of the tower. In the natural cooling section 3 corresponding to, there is a trace that fluid (powder) has flowed in the tower tube, relatively large particles can be confirmed, and solid RuO ₂ is observed. It is easily understood from the results.

<Third Embodiment>
The apparatus used in the first and second embodiments includes a wet recovery apparatus 12 and a backup filter 19 as shown in FIG. Here, the wet recovery apparatus 12 is used to conduct a rigorous experiment for the purpose of accurately obtaining the Ru recovery rate in the dry separation and recovery apparatus in order to clarify the effects of the present invention. In the present invention, by setting the heating temperature to 200 ° C. and 210 ° C. or higher, the recovery rate of ruthenium can be increased to approximately 90% and 98%% or more, respectively. The apparatus can be the basic configuration of the apparatus for carrying out the present invention. Further, as described in the first embodiment, for the RuO ₂ solid particles generated by the reaction RuO ₄ → RuO ₂ , the change in the weight of the backup filter arranged at the rear stage of the reaction tower is about 0.1 mg, Even compared with 12 mg which is the average generation amount of this test, it is 1% or less. Thus, the RuO ₂ solid particles captured by the backup filter are almost negligible. Therefore, a confirmation experiment was conducted as to whether or not the recovery rate of ruthenium can be ensured even in the case of using the dry separation and recovery apparatus that does not include the wet recovery apparatus 12 and the backup filter 19, that is, the apparatus shown in FIGS. .

As a result, setting the heating temperature of from 200 ° C. or higher to 250 ° C., by adjusting the flow rate of the heated air is supplied along with the flow rate or RuO ₄ of RuO _4, similar recoveries with the results shown in FIG. 6 It was confirmed that it was obtained. Therefore, the present invention can sufficiently achieve the effects of the present invention even in the configuration including only the dry separation and recovery apparatus shown in FIGS. 1 and 2, and is simple and efficient for separating and recovering ruthenium. It is useful for constructing a simple method.

As described above, according to the present invention, volatile ruthenium (RuO ₄ ) generated when processing radioactive waste such as radioactive liquid waste containing ruthenium is 150 ° C. or higher, preferably 200 to 250 ° C. in the heating process, the RuO ₂ produced by the reduction reaction from RuO ₄ to RuO ₂ can be separated and recovered in the solid state. Thereby, it is not necessary to absorb RuO ₄ or RuO ₂ in the solution, and the wet treatment for separating and recovering radioactive ruthenium from the solution can be omitted, so that ruthenium can be easily separated and recovered. Moreover, separation and recovery of unreacted RuO ₄ can be promoted by performing a wet recovery method in which a gas after heating an atmosphere containing RuO ₄ at 150 ° C. or higher is further brought into contact with a RuO ₄ absorbent. A great effect is obtained that no ruthenium is leaked to the outside. Furthermore, since the method according to the present invention can separate and recover radioactive ruthenium more easily and reliably than the conventional method, the process of evaporating and concentrating radioactive waste liquid, the process of electrolytic removal of ruthenium from high-level radioactive liquid waste, When applied to the vitrification process, the electrolytic removal apparatus used in the conventional electrolytic oxidation method or the like or the glass melting furnace apparatus used for vitrification and the dry separation and recovery apparatus used in the present invention are simply connected through a pipe. Since it can respond, it is convenient to construct a simpler processing method. The present invention can be applied as a method for separating and recovering ruthenium from RuO ₄ generated by incineration or melting of radioactive waste, in addition to the above-described electrolytic removal process and vitrification process, and its usefulness is extremely high.

DESCRIPTION OF SYMBOLS 1 ... Introducing pipe, 2 ... Heating part, 3 ... Natural cooling part, 4 ... Reaction tower, 5 ... Gas exhaust pipe, 6 ... Heating means, 7 ... Separable clamp, 8 ... Additional separable clamp, 9 ... Heated air, 10 ... Blow pump, 11 ... Heater, 12 ... Wet recovery tank, 13 ... Thermostatic bath, 14 ... first absorption cylinder, 15 ... second absorption cylinder, 16 ... first pipe, 17 ... second pipe, 18 ... pump, 19, ... ·filter.

Claims (7)

After ruthenium (Ru) contained in the liquid is volatilized and separated as tetraoxide (RuO ₄ ), the atmosphere containing the volatilized and separated RuO ₄ contains air or a reducing gas heated to 150 ° C. or higher in advance. A method for separating and recovering ruthenium, wherein at least RuO ₄ is separated and recovered as a RuO ₂ solid by heating the atmosphere containing RuO ₄ at a temperature of 150 ° C. or higher while flowing air . 2. The method for separating and recovering ruthenium according to claim 1, wherein heating of the atmosphere containing RuO ₄ is performed at a temperature of 200 to 250 ° C. 3. Air containing reducing gas which has been heated to above the NOR et beforehand 0.99 ° C. is ruthenium according to claim 1 or 2, characterized in that air containing a reducing gas at 30 vol% or less Separation and recovery method.   The ruthenium separation and recovery according to any one of claims 1 to 3, wherein the reducing gas is a gas obtained by mixing one or more of the group consisting of carbon monoxide, NOx and hydrogen. Method. 5. The separation and recovery of unreacted RuO ₄ is advanced by bringing the gas after heating the atmosphere containing RuO ₄ at 150 ° C. or higher into contact with a RuO ₄ absorbing solution. The method for separating and recovering ruthenium according to any one of the above. The RuO ₄ absorbing solution is one or two of water, an aqueous solution of sodium hydroxide, carbon tetrachloride, an aqueous solution of alcohol, a mixed solution of alcohol and hydrochloric acid, a mixed solution of hydrochloric acid and hydrogen peroxide, and an aqueous solution of carboxylic acid such as formic acid. The method for separating and recovering ruthenium according to claim 5, comprising the above mixed solution. The liquid containing ruthenium is a radioactive waste liquid treated using an electrolytic removal process of ruthenium, or a radioactive waste liquid melted in a glass melting furnace and treated as a vitrified body. 7. The method for separating and recovering ruthenium according to any one of 6 above.

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