Preparation method of noble metal catalyst, catalyst and use thereof

Abstract

The present invention relates to a preparation method, catalyst and use of a noble metal catalyst, belonging to the technical field of nuclear power waste treatment, the method comprising the following steps: S1, dispersing activated carbon in a nitric acid solution for impregnation and adsorption to obtain a first activated carbon, and then drying to obtain a first activated carbon carrier; S2, dispersing the first activated carbon carrier in a hydrochloric acid solution for impregnation and adsorption to obtain a second activated carbon, and then drying to obtain a shaped activated carbon carrier; S3, mixing the shaped activated carbon carrier with a corresponding active component solution, impregnating and adsorbing at room temperature, and then rotary evaporating to remove the solvent to obtain a dry material; S4, roasting the dry material under a reducing environment, and collecting it after cooling; S5, fully washing and filtering the collected material in deionized water, and finally drying to obtain a noble metal catalyst. The preparation method, catalyst and use provided by the present invention can remove monomethylhydrazine and dimethylhydroxylamine from radioactive waste liquid efficiently, safely, economically and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear power waste treatment and environmental protection, and specifically relates to a preparation method of a noble metal catalyst, a catalyst and a use thereof. Background Art

[0002] Nuclear power is a green, low-carbon, clean energy with mature technology. It is one of the most practical and feasible technical ways for mankind to solve the energy problem. However, nuclear power produces a large amount of highly radioactive waste - spent fuel, and its safety issue is one of the main factors restricting the large-scale promotion and application of nuclear power.

[0003] As we all know, the current utilization rate of nuclear fuel in nuclear power reactors is not high. Spent fuel contains a large amount of unconverted uranium and value-added nuclides, and is an important nuclear element resource library. Major nuclear power countries, including China, mostly adopt a closed nuclear fuel cycle route, using physical and chemical methods to separate and purify useful nuclear elements such as uranium, plutonium, and neptunium in spent fuel, and recycle them. In the Purex process, when Pu(IV) is reduced to Pu(III), monomethylhydrazine (CH3N2H3) and dimethylhydroxylamine are used as reducing agents, which will produce a large amount of nitric acid waste liquid containing reducing agents. According to the principle of minimizing radioactive waste in spent fuel reprocessing, the acidic waste liquid is evaporated, concentrated, destroyed, decomposed, and absorbed in the subsequent process to achieve the recovery and utilization of nitric acid, and the remaining slag is vitrified and solidified and then buried for deep treatment.

[0004] Dimethylhydroxylamine and monomethylhydrazine have strong reducing properties and are a type of high-energy, easily oxidized and explosive substances. In order to avoid the risk of explosion during the waste liquid concentration process, the monomethylhydrazine must be destroyed and removed in advance.

[0005] At present, the methods for removing the reducing agent that are well known to those skilled in the art mainly include adding an oxidant such as sodium nitrite or introducing nitrogen tetroxide gas, etc., which can oxidize the reducing agent into formic acid, formaldehyde, methanol, nitrous oxide, nitrogen, water, nitric oxide, etc. However, the disadvantages of this technical solution are: large consumption of oxidant and high cost; violent reaction and certain safety risks in engineering application; new solid waste sodium nitrate that is difficult to handle is generated when sodium nitrite is used as an oxidant; nitrogen dioxide makes the solution more corrosive to the equipment, the primary utilization rate is low and there is a risk of leakage.

[0006] Therefore, in view of the above-mentioned problems existing in the treatment of radioactive waste liquid, it is urgent to develop a new type of precious metal catalyst to remove monomethylhydrazine and dimethylhydroxylamine from nitric acid solution in an efficient, safe, economical and environmentally friendly manner. Summary of the invention

[0007] In order to solve the defects of the prior art, the purpose of the present invention is to provide a method for preparing a noble metal catalyst, a catalyst and use thereof, which can be used to remove monomethylhydrazine and dimethylhydroxylamine from radioactive waste liquid in an efficient, safe, economical and environmentally friendly manner.

[0008] In order to achieve the above purpose, a technical solution adopted by the present invention is:

[0009] A method for preparing a noble metal catalyst, the method comprising the following steps:

[0010] S1, dispersing activated carbon in a nitric acid solution for sufficient impregnation and adsorption to obtain a first activated carbon powder or granules, and then vacuum drying the first activated carbon powder or granules to obtain a dried first activated carbon carrier;

[0011] S2, dispersing the dried first activated carbon carrier in a hydrochloric acid solution for sufficient impregnation and adsorption to obtain a second activated carbon powder or granules, and then vacuum drying the second activated carbon powder or granules to obtain a shaped activated carbon carrier;

[0012] S3. According to the required active components, the shaped activated carbon carrier with a mass of M1 and a volume of L1 is mixed with the corresponding active component solution, fully impregnated and adsorbed at room temperature, and then the solvent is removed by rotary evaporation to obtain a dry material;

[0013] S4, roasting the dried material obtained in step S3 under a reducing environment to fully reduce it, and collecting it after cooling;

[0014] S5. The material collected in step S4 is fully washed and filtered in deionized water, and the filtered material is vacuum dried to obtain a noble metal catalyst with activated carbon as a carrier.

[0015] Furthermore, in the method for preparing the precious metal catalyst as described above, the activated carbon used in step S1 is coconut shell activated carbon or fruit shell activated carbon.

[0016] Further, in the method for preparing the precious metal catalyst as described above, step S1 is specifically: mixing activated carbon and 3-6 mol / L nitric acid solution in a volume ratio of 1:3-1:1, and heat-treating them at 50-70°C for 3-10 hours to obtain a first activated carbon powder or granules; then placing the first activated carbon powder or granules in a vacuum drying oven, and drying them at 60-80°C for 12-24 hours to obtain a dried first activated carbon carrier.

[0017] Further, in the method for preparing the precious metal catalyst as described above, step S2 is specifically: the dried first activated carbon carrier and 2-4 mol / L hydrochloric acid solution are mixed in a volume ratio of 1:2-2:1, and heat-treated at 50-70°C for 10-24 hours to obtain a second activated carbon powder or granules; then the second activated carbon powder or granules are placed in a vacuum drying oven, and dried at 60-80°C for 24-48 hours to obtain the shaped activated carbon carrier.

[0018] Furthermore, in the method for preparing the precious metal catalyst as described above, the active component selected in step S3 is one of metal ruthenium, iridium, rhodium, palladium, platinum, or a combination of two of these metals.

[0019] Furthermore, in the method for preparing the precious metal catalyst as described above, in step S3, the volume ratio of the formed activated carbon carrier to the active component solution is 1:2 to 1:1.

[0020] Further, in the method for preparing the precious metal catalyst as described above, step S4 is specifically as follows: the dried material obtained in step S3 is sintered at 400-600°C under argon for 1 hour, and after cooling to 300-500°C, hydrogen is introduced, and the flow rate of hydrogen is controlled to be 50-150 mL / min, and roasting is continued for 1-3 hours for sufficient reduction, and the dried material is taken out and collected after cooling to room temperature.

[0021] Further, in the method for preparing the precious metal catalyst as described above, step S5 is specifically: directly transferring the material collected in step S4 into deionized water without contact with air, repeatedly washing until the chloride ion concentration is no more than 100 ppm, placing the filtered catalyst in a vacuum drying oven at 80-120° C. and drying for 4-12 hours to obtain a precious metal catalyst with activated carbon as the carrier.

[0022] A precious metal catalyst prepared according to the method as described above, the components of the catalyst include a catalyst carrier and an active component, the catalyst carrier is coconut shell activated carbon or fruit shell activated carbon, the active component is one of metal ruthenium, iridium, rhodium, palladium and platinum, and the mass fraction of the active component in the catalyst is 1.5% to 10%.

[0023] A use of the noble metal catalyst as described above, for removing monomethylhydrazine and dimethylhydroxylamine from radioactive waste liquid;

[0024] When removing, a fixed bed continuous reaction method is used, and the reaction temperature is 30-90°C;

[0025] Alternatively, a suspended slurry bed intermittent reaction method is adopted, the reaction temperature is 30-90° C., the amount of catalyst used is 6.0-7.0% of the mass of the radioactive waste liquid to be treated, and the reaction time is 40-60 minutes.

[0026] The preparation method, catalyst and use of the noble metal catalyst of the present invention have the following significant technical effects:

[0027] (1) The present invention adopts a catalytic decomposition method to remove the reducing agent hazardous compounds in the nitric acid waste liquid. Compared with the traditional method of adding an oxidant, the present invention is cleaner, more environmentally friendly, has no safety hazards, and is more economical than the method of adding an oxidant;

[0028] (2) The catalyst provided by the present invention is suitable for treating waste liquid in a fixed bed continuous manner or in a reactor batch manner, is simple to operate, flexible and convenient, and can be coupled with subsequent treatment processes to improve energy efficiency;

[0029] (3) The catalyst provided by the present invention has high catalytic decomposition activity for hydrazine and hydroxylamine compounds, high catalytic decomposition efficiency, long service life, mild reaction conditions, and the catalyst can treat the feed liquid by more than 1,800 times per unit mass in a fixed bed mode and more than 800 times per unit mass in an intermittent reaction mode;

[0030] (4) The catalyst carrier provided by the present invention is activated carbon, which can be treated by incineration, making waste treatment convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention provides a flow chart of a method for preparing a precious metal catalyst. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with specific embodiments and the accompanying drawings.

[0033] In view of the problems mentioned in the background technology, the present invention provides a method for preparing a noble metal catalyst. Figure 1 A flow chart of the method is shown, comprising the following steps:

[0034] S1. Dispersing activated carbon in a nitric acid solution for sufficient immersion and adsorption to obtain a first activated carbon powder or granules, and then vacuum drying the first activated carbon powder or granules to obtain a dried first activated carbon carrier.

[0035] In a preferred embodiment of the present invention, the step is specifically as follows: activated carbon and 3-6 mol / L nitric acid solution are mixed in a volume ratio of 1:3 to 1:1, pretreated at 50-70°C for 3-10 hours, and treated with nitric acid to obtain a treated first activated carbon powder or granules; then the first activated carbon treated with nitric acid is placed in a vacuum drying oven, and dried at 60-80°C for 12-24 hours to obtain a dried first activated carbon carrier.

[0036] In a preferred embodiment of the present invention, the activated carbon used is coconut shell activated carbon or fruit shell activated carbon.

[0037] S2. Dispersing the dried first activated carbon carrier in a hydrochloric acid solution for sufficient immersion adsorption to obtain a second activated carbon powder or granules, and then vacuum drying the second activated carbon powder or granules to obtain a shaped activated carbon carrier.

[0038] In a preferred embodiment of the present invention, the step is specifically as follows: the dried first activated carbon carrier and 2-4 mol / L hydrochloric acid solution are mixed in a volume ratio of 1:2 to 2:1, pretreated at 50-70°C for 10 to 24 hours, and treated with hydrochloric acid to obtain a treated second activated carbon powder or granules; then the second activated carbon treated with hydrochloric acid is placed in a vacuum drying oven, and dried at 60-80°C for 24 to 48 hours to obtain a shaped activated carbon carrier.

[0039] S3. According to the required active components, the shaped activated carbon carrier with a mass of M1 and a volume of L1 is mixed with the corresponding active component solution, and fully impregnated and adsorbed at room temperature, and then the solvent is removed by rotary evaporation to obtain a dry material.

[0040] In the present invention, the active component selected is one of the metals ruthenium, iridium, rhodium, palladium, platinum, or a combination of two of them.

[0041] In a preferred embodiment of the present invention, the volume ratio of the shaped activated carbon carrier to the active component solution is 1:2 to 1:1.

[0042] For example, when the selected active component is ruthenium, a RuCl3·XH2O solution with a volume of 1.5L1 and a mass content of M2 is added, where M1:M2=100:3-100:10; after adding the active component solution, the mixture is immersed and adsorbed at room temperature for 12 hours and then the solvent is removed by rotary evaporation to obtain RuCl3 / C.

[0043] When the active component selected is iridium, add H2IrCl6·XH2O solution with a volume of L1 and a mass content of M3, M1:M3=100:1~100:5; after adding the solution, soak and adsorb at room temperature for 12 hours and then remove the solvent by rotary evaporation to obtain H2IrCl6 / C.

[0044] When the selected components are two metals, ruthenium and palladium, a volume of 2L1 is added, which includes a RuCl3·XH2O solution with a mass content of M2 and a PdCl2·XH2O solution with a mass content of M4, M1:(M2+M4)=100:3~100:5, wherein; M2:M4=100:1~100:20.

[0045] S4, roasting the dried material obtained in step S3 in a reducing environment to fully reduce it, and collecting it after cooling.

[0046] In a preferred embodiment of the present invention, this step is specifically as follows: the dried material obtained in step S3 is sintered at 400-600°C under argon for 1-3h, hydrogen is introduced after the temperature is reduced to 300-500°C, the flow rate of hydrogen is controlled to be 50-150mL / min, and the roasting is continued for 1-3h to fully reduce it, and it is taken out and collected after it is cooled to room temperature.

[0047] S5. The material collected in step S4 is fully washed and filtered in deionized water, and the filtered material is vacuum dried to obtain a noble metal catalyst with activated carbon as a carrier.

[0048] This step can avoid the poisoning of the catalyst by chloride ions after acidification in the nitric acid solution.

[0049] In a preferred embodiment of the present invention, this step is specifically as follows: the material collected in step S4 is directly transferred into deionized water without contact with air, and washed repeatedly until the chloride ion concentration is no more than 100 ppm, and the filtered catalyst is placed in a vacuum drying oven at 80-120° C. and dried for 4-12 hours to obtain a precious metal catalyst with activated carbon as the carrier.

[0050] The present invention also provides a noble metal catalyst with activated carbon as a carrier, which is prepared by the above-mentioned noble metal catalyst preparation method. The components of the noble metal catalyst include a catalyst carrier and an active component, the catalyst carrier is coconut shell activated carbon or fruit shell activated carbon, the active component is one of metal ruthenium, iridium, rhodium, palladium and platinum, and the mass fraction of the active component in the noble metal catalyst is 1.5% to 10%.

[0051] The present invention also provides a use of the noble metal catalyst with activated carbon as a carrier, which is used to remove monomethylhydrazine and dimethylhydroxylamine from radioactive waste liquid. The radioactive waste liquid to be treated is an aqueous solution containing 0.6-2.0 mol / L nitric acid, 0.01-0.2 mol / L monomethylhydrazine, and 0.01-0.2 mol / L dimethylhydroxylamine. When removing monomethylhydrazine and dimethylhydroxylamine from the radioactive waste liquid to be treated, a fixed bed continuous reaction method is used, and the reaction temperature is 30-90°C;

[0052] Alternatively, a suspended slurry bed intermittent reaction method is adopted, the reaction temperature is 30-90° C., the amount of catalyst used is 6.0-7.0% of the mass of the radioactive waste liquid to be treated, and the reaction time is 40-60 minutes.

[0053] Example 1

[0054] Disperse 15g of 4-8 mesh coconut shell carbon carrier in 3mol / L nitric acid solution at a volume ratio of 1:1, heat to 60℃, keep warm for 10 hours, and keep in a vacuum oven at 60℃ for 24 hours; disperse the above coconut shell carbon carrier in 4mol / L hydrochloric acid solution at a volume ratio of 1:1, heat to 50℃, keep warm for 10 hours, and keep in a vacuum oven at 60℃ for 24 hours; add 20mL of a solution containing 1.99g RuCl3·6H2O to the above activated carbon carrier. After immersion and adsorption at room temperature for 12 hours, remove the solvent by rotary evaporation. Then, the material was sintered at 400℃ in an argon atmosphere for 1 hour, then cooled to 300℃ and hydrogen (100mL / min) was introduced and continued to be roasted for 1 hour to fully reduce, and then collected after cooling to room temperature. The above materials were directly transferred to deionized water without contact with air, and washed repeatedly until the chloride ion concentration was no more than 100ppm.

[0055] Take 5g (dry weight) of 1# catalyst and load it into a glass transparent reactor with an inner diameter of 10mm. Tap the outer wall of the reactor to make the catalyst layer densely packed. The reaction temperature is 60℃. Pass the feed liquid to be treated (containing 0.9mol / L nitric acid and 0.01mol / L monomethylhydrazine). The reaction is carried out for a total of 670h, of which the feed liquid flow rate is about 0.5mL / min. A total of 20.0kg of feed is treated. During the operation of the device, samples are taken every morning and evening to detect the content of monomethylhydrazine in the effluent. The catalyst treatment waste liquid is 4kg / g.cat (4000 times). The content of monomethylhydrazine in the treated feed liquid is less than 10 -3 mol / L.

[0056] Example 2

[0057] Disperse 15g of 4-8 mesh columnar carbon carrier in 6 mol / L nitric acid solution by volume in a ratio of 1:1, heat to 60℃, keep warm for 8 hours, and treat at 60℃ in a vacuum oven for 24 hours; disperse the above coconut shell carbon carrier in 2 mol / L hydrochloric acid solution by volume in a ratio of 1:1, heat to 70℃, keep warm for 24 hours, and treat at 60℃ in a vacuum oven for 24 hours; add 30mL of a solution containing 1.99g RuCl3·6H2O to the above activated carbon carrier. After immersion and adsorption at room temperature for 12 hours, remove the solvent by rotary evaporation. Then the material is sintered at 400℃ in an argon atmosphere for 1 hour, then cooled to 300℃ and hydrogen (100mL / min) is introduced to continue roasting for 1 hour to fully reduce, and then taken out and collected after cooling to room temperature. The above materials are directly transferred to deionized water without contact with air, and washed repeatedly until the chloride ion concentration is no more than 100ppm.

[0058] Take 5g (dry weight) of 2# catalyst and load it into a glass transparent reactor with an inner diameter of 10mm. Tap the outer wall of the reactor to make the catalyst layer densely packed. The reaction temperature is 60℃. The feed liquid to be treated (containing 0.9mol / L nitric acid and 0.05mol / L monomethylhydrazine) is introduced. The reaction is carried out for a total of 330h, with a feed liquid flow rate of 0.5mL / min and a total of 10.0kg of treated material. During the operation of the device, samples are taken every morning and evening to detect the content of monomethylhydrazine in the effluent, and the catalyst treatment waste liquid is 2kg / g.cat (2000 times). The content of monomethylhydrazine in the treated feed liquid is less than 10 -3 mol / L.

[0059] Example 3

[0060] Disperse 15g of 4-8 mesh columnar carbon carrier in 6 mol / L nitric acid solution by volume in a ratio of 1:1, heat to 60℃, keep warm for 8 hours, and treat at 60℃ in a vacuum oven for 24 hours; disperse the above coconut shell carbon carrier in 3 mol / L hydrochloric acid solution by volume in a ratio of 1:1, heat to 50℃, keep warm for 20 hours, and treat at 60℃ in a vacuum oven for 24 hours; add 30mL of a solution containing 1.99gRuCl3·6H2O and 0.19gH2IrCl6·XH2O to the above activated carbon carrier. After immersion and adsorption at room temperature for 12 hours, remove the solvent by rotary evaporation. Then the material is sintered at 400℃ in an argon atmosphere for 1 hour, then cooled to 500℃ and hydrogen (150mL / min) is introduced to continue roasting for 1 hour to fully reduce, and then taken out and collected after cooling to room temperature. The above materials are directly transferred to deionized water without contact with air, and washed repeatedly until the chloride ion concentration is no more than 100ppm.

[0061] Take 5g (dry weight) of 3# catalyst and load it into a glass transparent reactor with an inner diameter of 10mm. Tap the outer wall of the reactor to make the catalyst layer densely packed. The reaction temperature is 60℃. The feed liquid to be treated (containing 0.9mol / L nitric acid, 0.05mol / L monomethylhydrazine, and 0.05mol / L dimethylhydroxylamine) is introduced. The reaction is carried out for a total of 300h, with a feed liquid flow rate of 0.5mL / min and a total of 9.0kg of treated material. During the operation of the device, samples are taken every morning and evening to detect the content of monomethylhydrazine in the effluent, and the catalyst treatment waste liquid is 1.8kg / g.cat (1800 times). The content of monomethylhydrazine and dimethylhydroxylamine in the treated feed liquid is less than 10 -3 mol / L.

[0062] Example 4

[0063] Disperse 15g of 4-8 mesh columnar carbon carrier in 4 mol / L nitric acid solution by volume in a ratio of 1:1, heat to 60℃, keep warm for 8 hours, and treat at 60℃ in a vacuum oven for 24 hours; disperse the above coconut shell carbon carrier in 4 mol / L hydrochloric acid solution by volume in a ratio of 1:1, heat to 50℃, keep warm for 10 hours, and treat at 60℃ in a vacuum oven for 24 hours; add 30mL of solution containing 3.0g H2IrCl6·6H2O to the above activated carbon carrier. After immersion and adsorption at room temperature for 12 hours, remove the solvent by rotary evaporation. Then the material is sintered at 600℃ in argon atmosphere for 1 hour, then cooled to 400℃ and hydrogen (50mL / min) is introduced to continue roasting for 1 hour to fully reduce, and then collected after cooling to room temperature. The above materials are directly transferred to deionized water without contact with air, and washed repeatedly until the chloride ion concentration is no more than 100ppm.

[0064] Take 5g (dry weight) of 4# catalyst and load it into a glass transparent reactor with an inner diameter of 10mm. Tap the outer wall of the reactor to make the catalyst layer densely packed. The reaction temperature is 60℃. Pass the feed liquid to be treated (containing 0.9mol / L nitric acid, 0.05mol / L monomethylhydrazine, and 0.05mol / L dimethylhydroxylamine). The reaction is carried out for a total of 300h, with a feed liquid flow rate of 0.5mL / min and a total of 9.0kg of treated material. During the operation of the device, samples are taken every morning and evening to detect the content of monomethylhydrazine in the effluent, and the catalyst treatment waste liquid is 1.8kg / g.cat (1800 times). The content of monomethylhydrazine and dimethylhydroxylamine in the treated feed liquid is less than 10 -3 mol / L.

[0065] Example 5

[0066] Disperse 15g of 4-8 mesh columnar carbon carrier in 6 mol / L nitric acid solution by volume in a ratio of 1:1, heat to 60℃, keep warm for 8 hours, and treat at 60℃ in a vacuum oven for 24 hours; disperse the above coconut shell carbon carrier in 3 mol / L hydrochloric acid solution by volume in a ratio of 1:1, heat to 50℃, keep warm for 10 hours, and treat at 60℃ in a vacuum oven for 24 hours; add 30mL of solution containing 3.0g H2IrCl6·6H2O to the above activated carbon carrier. After immersion and adsorption at room temperature for 12 hours, remove the solvent by rotary evaporation. Then the material is sintered at 400℃ in argon atmosphere for 1 hour, then cooled to 300℃ and hydrogen (100mL / min) is introduced to continue roasting for 1 hour to fully reduce, and then taken out and collected after cooling to room temperature. The above materials are directly transferred to deionized water without contact with air, and washed repeatedly until the chloride ion concentration is no more than 100ppm.

[0067] Take 5g (dry weight) of 5# catalyst and load it into a glass transparent reactor with an inner diameter of 10mm. Tap the outer wall of the reactor to make the catalyst layer densely packed. The reaction temperature is 60℃. The feed liquid to be treated (containing 0.9mol / L nitric acid and 0.05mol / L monomethylhydrazine) is introduced. The reaction is carried out for a total of 330h, with a feed liquid flow rate of 0.5mL / min and a total of 10.0kg of treated material. During the operation of the device, samples are taken every morning and evening to detect the content of monomethylhydrazine in the effluent, and the catalyst treatment waste liquid is 2kg / g.cat (2000 times). The content of monomethylhydrazine in the treated feed liquid is less than 10 -3 mol / L.

[0068] Example 6

[0069] Disperse 15g of 4-8 mesh columnar carbon carrier in 6 mol / L nitric acid solution by volume in a ratio of 1:1, heat to 60℃, keep warm for 8 hours, and treat at 60℃ in a vacuum oven for 24 hours; disperse the above coconut shell carbon carrier in 2 mol / L hydrochloric acid solution by volume in a ratio of 1:1, heat to 50℃, keep warm for 10 hours, and treat at 60℃ in a vacuum oven for 24 hours; add 30mL of solution containing 3.0g H2IrCl6·6H2O to the above activated carbon carrier. After immersion and adsorption at room temperature for 12 hours, remove the solvent by rotary evaporation. Then the material is sintered at 400℃ in argon atmosphere for 1 hour, then cooled to 300℃ and hydrogen (100mL / min) is introduced to continue roasting for 1 hour to fully reduce, and then collected after cooling to room temperature. The above materials are directly transferred to deionized water without contact with air, and washed repeatedly until the chloride ion concentration is no more than 100ppm.

[0070] A round-bottom flask containing 100 mL of the liquid to be treated was heated to 80°C, and 5 g (dry weight) of 5# catalyst and the liquid to be treated (containing 0.9 mol / L nitric acid and 0.05 mol / L monomethylhydrazine) were added. After the reaction was completed, samples were taken to detect the content of monomethylhydrazine in the liquid. After reaching the standard, the treated liquid was taken out and fresh liquid was added until the catalyst was deactivated. The catalyst was reused 40 times, 4 kg of liquid was treated, and the treatment capacity was 0.8 kg / g.cat (800 times). The content of monomethylhydrazine in the treated liquid was less than 10 -3 mol / L.

[0071] The preparation method, catalyst and use of the precious metal catalyst provided by the present invention adopt a catalytic decomposition method to remove reducing agent-type hazardous compounds in nitric acid waste liquid. Compared with the traditional method of adding an oxidant, the method is cleaner, more environmentally friendly, has no safety hazards, and is more economical than the method of adding an oxidant. The method is suitable for treating waste liquid in a fixed bed continuous method or a reactor intermittent method, and is simple to operate, flexible and convenient, and can be coupled with subsequent treatment processes to improve energy efficiency. The method has high catalytic decomposition activity for hydrazine and hydroxylamine compounds, high catalytic decomposition efficiency, long service life, and mild reaction conditions. The fixed bed mode can treat more than 1,800 times the feed liquid per unit mass of the catalyst, and the intermittent reaction mode can treat more than 800 times the feed liquid per unit mass of the catalyst. The catalyst carrier is activated carbon, which can be treated by incineration to facilitate waste treatment.

[0072] The above embodiments are merely illustrative of the present invention, and the present invention may also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be considered illustrative rather than restrictive in any respect. The scope of the present invention should be described by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A use of a noble metal catalyst, characterized in that: The catalyst is used to remove monomethylhydrazine and dimethylhydroxylamine in radioactive waste liquid. The components of the catalyst include a catalyst carrier and an active component. The catalyst carrier is coconut shell activated carbon or fruit shell activated carbon. The active component is one of metal ruthenium, iridium, rhodium, palladium and platinum or a combination of two of the metals. The mass fraction of the active component in the catalyst is 1.5% to 10%. The preparation method of the catalyst comprises the following steps: S1, dispersing activated carbon in a nitric acid solution for sufficient impregnation and adsorption to obtain a first activated carbon powder or granules, and then vacuum drying the first activated carbon powder or granules to obtain a dried first activated carbon carrier; S2, dispersing the dried first activated carbon carrier in a hydrochloric acid solution for sufficient impregnation and adsorption to obtain a second activated carbon powder or granules, and then vacuum drying the second activated carbon powder or granules to obtain a shaped activated carbon carrier; S3. According to the required active components, the shaped activated carbon carrier with a mass of M1 and a volume of L1 is mixed with the corresponding active component solution, fully impregnated and adsorbed at room temperature, and then the solvent is removed by rotary evaporation to obtain a dry material; S4, roasting the dried material obtained in step S3 under a reducing environment to fully reduce it, and collecting it after cooling; S5. The material collected in step S4 is fully washed and filtered in deionized water, and the filtered material is vacuum dried to obtain a noble metal catalyst with activated carbon as a carrier.

2. The use of the noble metal catalyst according to claim 1, characterized in that: Step S1 is specifically as follows: activated carbon and 3-6 mol / L nitric acid solution are mixed in a volume ratio of 1:3-1:1, and heat-treated at 50-70°C for 3-10 hours to obtain a first activated carbon powder or granules; then the first activated carbon powder or granules are placed in a vacuum drying oven and dried at 60-80°C for 12-24 hours to obtain a dried first activated carbon carrier.

3. The use of the noble metal catalyst according to claim 2, characterized in that: Step S2 is specifically as follows: the dried first activated carbon carrier and 2-4 mol / L hydrochloric acid solution are mixed in a volume ratio of 1:2-2:1, and heat-treated at 50-70°C for 10-24 hours to obtain a second activated carbon powder or granules; then the second activated carbon powder or granules are placed in a vacuum drying oven, and dried at 60-80°C for 24-48 hours to obtain the shaped activated carbon carrier.

4. The use of the noble metal catalyst according to claim 3, characterized in that: The volume ratio of the shaped activated carbon carrier to the active component solution in step S3 is 1:2 to 1:

1.

5. The use of the noble metal catalyst according to claim 4, characterized in that: Step S4 is specifically as follows: sintering the dried material obtained in step S3 at 400-600°C under argon for 1 hour, cooling to 300-500°C, introducing hydrogen, controlling the hydrogen flow rate to 50-150 mL / min, continuing roasting for 1-3 hours for full reduction, and collecting after cooling to room temperature.

6. The use of the noble metal catalyst according to claim 5, characterized in that: Step S5 is specifically as follows: directly transferring the material collected in step S4 into deionized water without contact with air, repeatedly washing until the chloride ion concentration is no more than 100 ppm, placing the filtered catalyst in a vacuum drying oven at 80-120° C. and drying for 4-12 hours to obtain a precious metal catalyst with activated carbon as a carrier.

7. The use of the noble metal catalyst according to claim 6, characterized in that: When removing, a fixed bed continuous reaction method is used, and the reaction temperature is 30-90°C; Alternatively, a suspended slurry bed intermittent reaction method is adopted, the reaction temperature is 30-90° C., the amount of catalyst used is 6.0-7.0% of the mass of the radioactive waste liquid to be treated, and the reaction time is 40-60 minutes.

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