CN114308029B - Method for preparing tetravalent uranium by hydrazine reduction of hexavalent uranium with bimetallic catalyst - Google Patents
Method for preparing tetravalent uranium by hydrazine reduction of hexavalent uranium with bimetallic catalyst Download PDFInfo
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Abstract
The invention relates to a method for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine by adopting a bimetallic catalyst. The catalyst adopted by the invention comprises the following components in parts by mass: a) The carrier is cerium oxide accounting for 70-99.89%; b) The active component is any one of metal Pt and Ir, and accounts for 0.1-20%; c) The second metal component is one or more than two of Ru, pd, rh and Au, and accounts for 0.01-10%. In an acid system, the catalyst provided by the invention can directly reduce hexavalent uranium into tetravalent uranium by taking hydrazine as a reducing agent, the conversion rate of the hexavalent uranium can reach 99%, and the utilization rate of the hydrazine is higher than 80%. The catalyst has the advantages of easily available raw materials, simple process and good application prospect.
Description
Technical Field
The invention relates to a bimetallic catalyst for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine, and a preparation method and application thereof.
Background
Nuclear fuel reprocessing is the treatment of spent nuclear fuel (spent fuel) in nuclear reactors to recover uranium and plutonium and other valuable elements and to vitrify highly radioactive wastes thereof for deep geological disposal. At present, post-processing plants at home and abroad mainly adopt a Purex (Purex) process flow. The Purex process flow mainly utilizes the difference of extraction capacity of tributyl phosphate (TBP) to uranium and plutonium with different valence states to realize the separation of the uranium, the plutonium and other fission products. First, the fission products are separated from the uranium and plutonium using TBP with less capacity to extract the fission products than uranium and plutonium. Then, the extraction capability of the TBP to the trivalent plutonium is smaller, and the uranium and the plutonium are separated. Therefore, it is necessary to add a reducing agent to reduce tetravalent plutonium to trivalent plutonium. Uranium (U (IV)) is a preferred counter-extractant for the reduction of plutonium in the presence of hydrazine as a supporting reductant. Most of the spent fuel post-treatment plants in operation and under construction use hydrazine stabilized U (IV) as a reduction stripping agent, such as UP3 and UP2-800 in France and pilot plant in China.
At present, the preparation methods of U (IV) mainly comprise an electrolysis method, a hydrogenation method and a liquid phase reduction method. The U (IV) produced by adopting the electrolysis method can not introduce impurities, and the operation process is simple. In the actual production process, however, the conversion rate of hexavalent uranium (U (VI)) is low, and is only 50% -60%, so that the recovery burden of uranium products in the post-treatment process is increased. The catalytic hydrogenation method adopts high-pressure hydrogen as a reducing agent, and can obtain higher U (VI) conversion rate. However, the use of high pressure hydrogen increases the complexity of the equipment and also creates potential safety hazards. Organic reducing agents such as hydrazine and the like are adopted, and U (VI) can be reduced into U (IV) under the action of a catalyst, as shown in formula 1. The method has the advantages of mild reaction conditions, simple operation process and good application prospect. Other side reactions also exist in a hydrazine reduction U (VI) system, such as a formula 2, which can reduce the reduction capability and the utilization rate of hydrazine. Therefore, there is a need to optimize the catalyst design to make hydrazine more prone to reaction 1, thereby improving the catalyst activity and hydrazine utilization.
N 2 H 5 + +3H + +2UO 2 2+ →2U 4+ +N 2 +4H 2 O (1)
3N 2 H 5 + +H + →N 2 +4NH 4 + (2)
Bin et al studied the reaction performance of a platinum black catalyst for preparing U (IV) by hydrazine reduction of U (VI) in a nitric acid system under different reaction conditions. At 60 ℃, the uranium concentration is 0.9mol/L, HNO 3 When the concentration is 0.8mol/L and the hydrazine concentration is 1mol/L, the conversion rate of U (VI) can reach more than 90 percent. (Nuclear and radiochemistry, 2013,35, (1): 24-28). Boltoeva et al studied Pt/SiO 2 Catalyst in H 2 SO 4 、HClO 4 、HNO 3 Hydrazine in the system reduces U (VI) to prepare the particle size effect of Pt in U (IV). It was found that the U (VI) conversion decreased with decreasing Pt particle size (Radiochemistry, 2007,49, 603-606). Anan' ev et al examined the performance of the reaction of hydrazine and formic acid to reduce U (VI) to U (IV) in a nitric acid system (Radiochemistry, 2001,43, 39-43). At present, the research on the reaction of preparing U (IV) by reducing U (VI) with hydrazine mainly focuses on the study of process conditions, and the research on the influence of a catalyst carrier on the reaction performance is less.
At present, some relevant patents are applied to the preparation of tetravalent uranium solutions. Several reported patents are listed below for details:
chinese patent CN201110097474 discloses a name: a preparation method of a tetravalent uranium solution. The patent reports the preparation of U (IV) solutions by reduction of U (VI) with organic reducing agents (hydrazine or carboxylic acids and their derivatives) over Pt, pd, rh catalysts. The patent does not relate to the support of the catalyst used.
Chinese patent CN201310743451 discloses a name: a device for preparing tetravalent uranium by electrolytic reduction. The patent reports an improved device for preparing tetravalent uranium by electrolytic reduction, and mainly solves the problem of low U (VI) conversion rate in a diaphragm-free electrolytic device. In actual production, the effectiveness of the device needs to be further checked.
Although in the above reports, U (IV) preparation by hydrazine reduction of U (VI) has been achieved. But the reactivity of the catalyst and the utilization rate of hydrazine are low. Therefore, there is a need to develop a catalyst for preparing U (IV) by reducing U (VI) with hydrazine having high activity and high hydrazine utilization rate.
The reducible carrier and the active component can form strong metal-carrier interaction, and the modulation of the structure and the property of the catalyst can be realized, so that the activity and the selectivity of the catalyst are improved. Using CeO 2 The interaction between the reducible carrier and the noble metal is combined with the modulation of the electronic property of the catalyst by the second component, so that the catalyst for preparing U (IV) by reducing U (VI) by hydrazine with high activity and high hydrazine utilization rate is expected to be developed.
Disclosure of Invention
One of the technical problems to be solved by the invention is to solve the problem of preparing U (IV) catalyst by hydrazine reduction U (VI) in an acid system, and provide a novel catalyst for preparing U (IV) by hydrazine reduction U (VI), wherein the catalyst has high U (VI) conversion rate and hydrazine utilization rate.
The second technical problem to be solved by the present invention is to adopt the method for preparing the catalyst described in the first technical problem. The catalyst has controllable content of each component, and the method has simple preparation process and good reliability.
The third technical problem to be solved by the invention is to adopt the catalyst in one of the technical problems to realize the catalytic reaction process of preparing U (IV) by reducing U (VI) with hydrazine in an acid system.
In order to solve one of the technical problems, the invention adopts the following technical scheme:
a bimetallic catalyst for preparing U (IV) by reducing U (VI) with hydrazine in an acid system comprises the following components in parts by weight: a) The carrier is cerium oxide accounting for 70-99.89%; b) The active component is any one of metal Pt and Ir, and accounts for 0.1-20%; c) The second metal component is one or more than two of Ru, pd, rh and Au, and accounts for 0.01-10%.
In the scheme, the method is characterized in that: the oxide in the component a) is cerium oxide, and the preferable content is 85 to 99.89 percent; the component b) is any one of metal Pt and Ir, and the preferable content is 0.1-10%; the component c) is preferably one or more of Ru, pd and Rh, and the content of the component c) is preferably 0.01-5%.
In order to solve the second technical problem, the invention adopts the following technical scheme:
a) Preparation of the support
1) Dissolving a certain amount of soluble cerium salt in deionized water to obtain a solution A; wherein the concentration of the metal ions is 0.001-10 mol/L;
2) Dissolving a certain amount of urea and/or ammonium carbonate in deionized water to obtain a solution B with the concentration of 0.01-10 mol/L;
3) Dropwise adding the solution B into the solution A until the pH value of the mixed solution is between 7 and 10, and stirring and aging the obtained mixture in water bath at the temperature of between 60 and 95 ℃ for 0.5 to 24 hours;
4) Filtering and washing the obtained turbid liquid to be neutral, and placing a filter cake in the air at the temperature of between 60 and 200 ℃ for drying for 12 to 48 hours;
5) And roasting the dried solid for 1-8 h at the temperature of 300-800 ℃ in the air atmosphere to obtain solid C.
b) Active ingredient loading
1) 1-5g of solid C is taken and dispersed in 100ml of deionized water, then soluble salt of any one or two of Pt and Ir is taken and dissolved in the deionized water, and the concentration of noble metal ions is 0.001-1 mol/L; slowly adding a precursor solution of the noble metal into the dispersion liquid of the solid C, and uniformly stirring;
2) Dissolving alkali in deionized water to prepare a precipitator to obtain a solution D with the concentration of 0.001-10 mol/L; adding the solution D into the dispersion liquid of the solid C until the pH value of the mixed solution is between 9 and 10, and stirring the obtained mixture in a water bath at the temperature of between 25 and 90 ℃ for 2 to 12 hours;
3) Filtering and washing the obtained turbid liquid to be neutral, and placing a filter cake in the air at the temperature of between 60 and 150 ℃ for drying for 12 to 48 hours; and roasting the dried solid in an air atmosphere at the temperature of between 200 and 600 ℃ for 1 to 8 hours to obtain a solid E.
c) Second component load
1) Dissolving any one or more soluble salts of Ru, pd, rh and Au in deionized water and/or 5-10% hydrochloric acid to prepare a solution F;
2) Taking the solid E, and dropwise adding or pouring the solution F in an amount required in the solid E according to the load amount of the second component;
3) Soaking the obtained mixture at room temperature for 0.5-48 h, and then drying at 60-120 ℃ for 4-24 h; roasting the dried mixture at 200-500 ℃ for 1-8 h to obtain solid G;
4) And (4) performing hydrogen reduction activation on the solid G. The reducing gas being H 2 (molar purity)>99 percent) and the volume space velocity of the reducing gas is 100-3600h -1 The heating rate from room temperature to the reduction temperature is 1-10 ℃/min, the reduction temperature is 200-600 ℃, the pressure is normal pressure, and the reduction time is 1-48h.
In the preparation of the carrier, the soluble cerium salt in the step 1) is one or two of cerium nitrate or ammonium cerium nitrate.
In the preparation of the carrier, the roasting temperature in the step 5) is 300-600 ℃, and the roasting time is 2-6 h;
soluble salts of Pt and Ir in the step 1) in the active component loading are one of nitrates or chlorides of corresponding noble metals;
the alkali in the step 2) in the active component loading is one or more than two of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate;
in the second component load, the soluble salts of Ru, pd, rh and Au in the step 1) are one or more than two of nitrates or chlorides of corresponding noble metals;
in order to solve the third technical problem, the invention adopts the following technical scheme: the acid system is one or more than two of nitric acid, sulfuric acid or perchloric acid system; the hexavalent uranium is uranyl ions corresponding to acid types in an acid system, and is one or more than two of uranyl nitrate solution, uranyl sulfate solution and uranyl perchlorate solution; the tetravalent uranium is the reduction product of the corresponding hexavalent uranium. The conditions of the catalyst applied to a kettle type reactor or a fixed bed reactor for preparing the uranium quadrivalent solution by hydrazine reduction of hexavalent uranium are as follows: the acid concentration (by hydrogen ion concentration) is 0.5-1.0mol/L, the uranyl ion concentration is 0.5-1.3mol/L, the hydrazine concentration is 0.5-2.0mol/L, the reaction temperature is 25-70 ℃, and the reaction pressure is normal pressure.
The invention has the advantages that:
(1) The catalyst carrier provided by the invention has the advantages of cheap and easily obtained raw materials, simple preparation method and contribution to realizing mass production.
(2) The catalyst provided by the invention has stable property and is beneficial to prolonging the service life of the catalyst.
(3) The catalyst provided by the invention can reduce U (VI) into a U (IV) solution by using hydrazine under an acidic condition. The interaction between the carrier and the active component and the modulation of the second component improve the conversion rate and the reaction rate of the U (VI). In a tank reactor, the conversion rate of U (VI) can reach 99 percent within 60 min. And the hydrazine utilization rate is higher than 80%.
Detailed Description
The technical details of the present invention are described in detail by the following examples. The embodiments are given for further illustration of the technical features of the present invention, and are not intended to limit the present invention.
Catalyst preparation and Performance evaluation
Example 1
21.7g of Ce (NO) was taken 3 ) 3 ·6H 2 O is dissolved in 100ml of deionized water to prepare a solution A, and the molar concentration of Ce ions is 0.5mol/L. 19.2g of ammonium carbonate is dissolved in 100ml of deionized water to obtain a solution B, and the molar concentration of the ammonium carbonate is 2mol/L. The solution B is added into the solution A dropwise until the pH value of the mixed solution is 10, and the mixed solution is placed in a water bath at 70 ℃ and stirred for 12 hours. Filtering and washing the obtained turbid solution to be neutral, and then drying a filter cake in air at the temperature of 80 ℃ for 12 hours; roasting the dried solid for 4 hours at 400 ℃ in an air atmosphere to obtain CeO 2 And (3) a carrier.
2.0g of prepared CeO were weighed 2 Carrier, which is dispersed in 100ml of deionized water. Weigh 0.1642g H 2 PtCl 6 ·6H 2 Dissolving it in2ml of deionized water is prepared into a mixed solution, the molar concentration of Pt is 0.16mol/L, and Pt precursor solution is added into CeO 2 Dispersing in the solution, and stirring uniformly. 4g of NaOH was weighed and dissolved in 100ml of deionized water at a molar concentration of 1mol/L, then an alkali solution was slowly added dropwise to the above solution, and the resulting mixture was stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid in an air atmosphere at 300 ℃ for 4 hours to obtain a solid E;
2.0g of the above solid E were weighed, 0.0056g of RuCl was weighed 3 ·3H 2 Dissolving the mixed solution in 2ml 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of Ru is 0.01mol/L, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Pt-Ru bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Ru is 0.1%, and the mark is 3Pt-0.1Ru/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 2
27.4g of Ce (NH) was taken 4 ) 2 (NO 3 ) 6 Dissolved in 100ml of deionized water to prepare solution A, and the molar concentration of Ce ions is 0.5mol/L. 19.2g of ammonium carbonate is dissolved in 100ml of deionized water to obtain a solution B, and the molar concentration of the ammonium carbonate is 2mol/L. The solution B is added into the solution A dropwise until the pH value of the mixed solution is 10, and the mixed solution is placed in a water bath at 60 ℃ and stirred for 24 hours. Filtering and washing the obtained turbid solution to be neutral, and then drying a filter cake in air at 60 ℃ for 48 hours; roasting the dried solid for 6 hours at 300 ℃ in an air atmosphere to obtain CeO 2 And (3) a carrier.
2.0g of prepared CeO were weighed 2 Carrier, which is dispersed in 100ml deionized water. Weigh 0.1642g H 2 PtCl 6 ·6H 2 Dissolving the precursor in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding the Pt precursor solution into CeO 2 Dispersing in the solution, and stirring uniformly. 5.6g of KOH was weighed and dissolved in 100ml of deionized water at a molar concentration of KOH of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 30 ℃ for 12 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air for drying for 48 hours at the temperature of 60 ℃; roasting the dried solid in an air atmosphere at 200 ℃ for 8 hours to obtain a solid E;
2.0g of the solid E obtained are weighed out and 0.0034g of PdCl are weighed out 2 The solution was dissolved in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, the molar concentration of Pd was 0.01mol/L, and the mixed solution was poured into E and mixed uniformly. Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 200 ℃ for 8h to obtain the Pt-Pd bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Pd is 0.1%, and the mark is 3Pt-0.1Pd/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 200h -1 The heating rate is 1 ℃/min, the reduction temperature is 200 ℃, the pressure is normal pressure, and the reduction time is 48h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 0.5mol/L, the concentration of uranyl ions is 0.5mol/L, the concentration of hydrazine is 0.5mol/L, the temperature is 30 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 3
27.4g of Ce (NH) was taken 4 ) 2 (NO 3 ) 6 Dissolved in 100ml of deionized water to prepare solution A, and the molar concentration of Ce ions is 0.5mol/L. 19.2g of ammonium carbonate is dissolved in 100ml of deionized water to obtain a solution B, and the molar concentration of the ammonium carbonate is 2mol/L. The solution B was added dropwise to the solution A until the pH of the mixed solution was 10, and the mixture was stirred in a water bath at 95 ℃ for 2 hours. Filtering and washing the obtained turbid solution to be neutral, and then carrying outDrying the filter cake in air at 200 ℃ for 48 hours; roasting the dried solid for 6 hours at 600 ℃ in the air atmosphere to obtain CeO 2 And (3) a carrier.
2.0g of prepared CeO were weighed 2 Carrier, which is dispersed in 100ml of deionized water. Weigh 0.1642g H 2 PtCl 6 ·6H 2 Dissolving the precursor in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding the Pt precursor solution into CeO 2 Dispersing in the solution, and stirring uniformly. 5.6g of KOH was weighed and dissolved in 100ml of deionized water at a molar concentration of KOH of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 90 ℃ for 2 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in the air for drying for 2 hours at the temperature of 150 ℃; roasting the dried solid in an air atmosphere at 600 ℃ for 1h to obtain a solid E;
2.0g of the solid E obtained are weighed, 0.0053g of RhCl are weighed 3 ·3H 2 Dissolving the mixed solution in 2ml 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into E, and mixing the mixed solution uniformly, wherein the molar concentration of Rh is 0.01 mol/L. Dipping for 48h at room temperature, drying for 4h at 120 ℃, and roasting for 1h at 500 ℃ to obtain the Pt-Rh bimetallic catalyst, wherein the mass content of Pt is 3 percent, the mass content of Rh is 0.1 percent, and the mark is 3Pt-0.1Rh/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 3600h -1 The heating rate is 10 ℃/min, the reduction temperature is 600 ℃, the pressure is normal pressure, and the reduction time is 6h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 4
2.0g of the form E obtained in example 1 was weighed, and 0.0042g of HAuCl was weighed 4 ·4H 2 And dissolving the Au in 2ml of deionized water solution to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of Au is 0.005mol/L, and uniformly mixing.Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 300 ℃ for 4h to obtain the Pt-Au bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Au is 0.1%, and the mark is 3Pt-0.1Au/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 5
2.0g of CeO prepared in example 1 were weighed 2 Carrier, which is dispersed in 100ml of deionized water. Weigh 0.0265g H 2 PtCl 6 ·6H 2 O is dissolved in 2ml deionized water to prepare a mixed solution, the molar concentration of Pt is 0.026mol/L, and Pt precursor solution is added into CeO 2 Dispersing in the solution, and stirring uniformly. 4g of NaOH are weighed and dissolved in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then an alkali liquor is slowly added dropwise to the solution, and the mixture obtained is stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12h; roasting the dried solid in an air atmosphere at 300 ℃ for 4 hours to obtain a solid E;
2.0g of the above solid E were weighed, 0.2432g of RhCl were weighed 3 ·3H 2 Dissolving the obtained product in 2ml 10% hydrochloric acid solution to prepare a mixed solution, wherein the molar concentration of Rh is 0.46mol/L, pouring the mixed solution into the solid E for soaking, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Pt-Rh bimetallic catalyst, wherein the mass content of Pt is 0.5 percent, the mass content of Rh is 5 percent, and the mark is 0.5Pt-5Rh/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the space velocity of 2000h -1 The temperature rise rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and during reductionThe time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 6
2.0g of CeO prepared in example 1 were weighed 2 Carrier, which is dispersed in 100ml deionized water. Weigh 0.4780g H 2 PtCl 6 ·6H 2 O is dissolved in 5ml deionized water to prepare a mixed solution, the molar concentration of Pt is 0.18mol/L, and the Pt precursor solution is added into CeO 2 Dispersing in the solution, and stirring uniformly. 5g NaOH was weighed and dissolved in 100ml deionized water at a molar concentration of 1.25mol/L, then an alkali solution was slowly added dropwise to the above solution, and the resulting mixture was stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid in an air atmosphere at 300 ℃ for 4 hours to obtain a solid E;
5.0g of the above solid E are weighed, 0.0013g of RhCl are weighed 3 ·3H 2 Dissolving the obtained product in 2ml 10% hydrochloric acid solution to prepare mixed solution, pouring the mixed solution into solid E for soaking, wherein the molar concentration of Rh is 0.0025mol/L, and mixing uniformly. Soaking at room temperature for 12h, drying at 60 deg.C for 12h, and calcining at 300 deg.C for 4h to obtain Pt-Rh bimetallic catalyst, wherein the Pt content is 10 wt%, rh content is 0.01 wt%, and the weight ratio is 10Pt-0.01Rh/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 7
2.0g of CeO prepared in example 1 were weighed 2 A carrier, which is dispersed in 100ml of deionized water. Weigh 0.1660g of H 2 IrCl 6 ·6H 2 O is dissolved in 2ml deionized water to prepare a mixed solution, the molar concentration of Ir is 0.16mol/L, and Ir precursor solution is added into CeO 2 Dispersing in the solution, and stirring uniformly. 4g of NaOH are weighed and dissolved in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then an alkali liquor is slowly added dropwise to the solution, and the mixture obtained is stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid for 4 hours at 300 ℃ in an air atmosphere to obtain a solid E;
2.0g of the above solid E were weighed, 0.0056g of RuCl was weighed 3 ·3H 2 Dissolving the mixed solution in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, wherein the molar concentration of Ru is 0.013mol/L, dropwise adding the mixed solution into the solid E, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Ir-Ru bimetallic catalyst, wherein the Ir mass content is 3%, the Ru mass content is 0.1%, and the mark is 3Ir-0.1Ru/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 8
2.0g of CeO prepared in example 1 were weighed 2 Carrier, which is dispersed in 100ml deionized water. Weigh 0.1660g of H 2 IrCl 6 ·6H 2 Dissolving the precursor solution in 2ml of deionized water to prepare a mixed solution, wherein the molar concentration of Ir is 0.16mol/L, and adding the Ir precursor solution into CeO 2 Dispersing in the solution, and stirring uniformly. 4g of NaOH was weighed and dissolved in 100ml of deionized water at a molar concentration of 1mol/L, then an alkali solution was slowly added dropwise to the above solution, and the resulting mixture was stirred in a water bath at 60 ℃ for 4 hours. For the obtained turbid liquidFiltering and washing to neutrality, and drying the filter cake in air at 80 deg.C for 12 hr; roasting the dried solid in an air atmosphere at 300 ℃ for 4 hours to obtain a solid E;
2.0g of the above solid E were weighed, 0.0053g of RhCl was weighed 3 ·3H 2 Dissolving the obtained product in 2ml 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into the solid E, wherein the molar concentration of Rh is 0.01mol/L, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Ir-Rh bimetallic catalyst, wherein the Ir mass content is 3 percent, the Rh mass content is 0.1 percent, and the mark is 3Ir-0.1Rh/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the space velocity of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 9
The 3Pt-0.1Rh/CeO which is subjected to reduction activation in the example 3 is taken 2 A catalyst. Reaction conditions in the tank reactor: the sulfuric acid concentration is 0.5mol/L (hydrogen ion concentration is 1.0 mol/L), the uranyl ion concentration is 0.9mol/L, the hydrazine concentration is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 10
The 3Pt-0.1Rh/CeO which is subjected to reduction activation in the example 3 is taken 2 A catalyst. Reaction conditions in the tank reactor: the perchloric acid concentration (calculated by hydrogen ion concentration) is 1.0mol/L, the uranyl ion concentration is 0.9mol/L, the hydrazine concentration is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 11
The 3Pt-0.1Rh/CeO which is subjected to reduction activation in the example 3 is taken 2 A catalyst. Reaction conditions in a fixed bed: uranyl with nitric acid concentration (calculated by hydrogen ion concentration) of 1.0mol/LThe ion concentration is 0.9mol/L, the hydrazine concentration is 1.0mol/L, the temperature is 60 ℃, and the liquid space velocity is 0.3h -1 The pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 12
Taking SiO 2 2.0g of support, 0.1642g of H are weighed 2 PtCl 6 ·6H 2 Dissolving O in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and dissolving SiO in the mixed solution 2 The carrier is immersed in the mixed solution and mixed uniformly. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 400 ℃ in an air atmosphere, wherein the mass content of Pt is 3%, and is recorded as 3Pt/SiO 2 A catalyst.
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (calculated by the concentration of hydrogen ions) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 13
The CeO prepared in example 1 was taken 2 2.0g of support, 0.1642g of H are weighed 2 PtCl 6 ·6H 2 Dissolving O in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding CeO 2 The carrier is immersed in the mixed solution and mixed uniformly. Dipping for 12h at room temperature, drying at 60 ℃ for 12h, and roasting at 400 ℃ for 4h in an air atmosphere, wherein the mass content of Pt is 3%, and is recorded as 3Pt/CeO 2 A catalyst.
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99.9 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the stirred tank: the concentration of nitric acid (calculated by the concentration of hydrogen ions) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 14
2.0g of the body E obtained in example 1 was weighed, and 1.02g of Ni (NO) was weighed 3 ) 2 ·6H 2 Dissolving the O in 4ml of deionized water to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of Ni is 0.88mol/L, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Pt-Ni bimetallic catalyst, wherein the mass content of Pt is 3 percent, the mass content of Ni is 0.1 percent, and the mark is 3Pt-0.1Ni/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 15
2.0g of the body E obtained in example 1 was weighed, and 1.02g of Co (NO) was weighed 3 ) 2 ·6H 2 Dissolving the mixed solution in 4ml of deionized water to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of Co is 0.88mol/L, and uniformly mixing. Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 300 ℃ for 4h to obtain the Pt-Co bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Co is 0.1%, and the mark is 3Pt-0.1Co/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 16
2.0g of the product obtained in example 1 were weighedBody E, 1.02g Fe (NO) was weighed 3 ) 3 ·9H 2 Dissolving the O in 4ml of deionized water to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of Fe is 0.88mol/L, and uniformly mixing. Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 300 ℃ for 4h to obtain the Pt-Fe bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Fe is 0.1%, and the mark is 3Pt-0.1Fe/CeO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the space velocity of 2000h -1 The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 17
The activated carbon carrier, 2.0g, was weighed and dispersed in 100ml of deionized water. Weigh 0.1642g H 2 PtCl 6 ·6H 2 Dissolving the Pt precursor solution in 2ml of deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, adding the Pt precursor solution into the active carbon dispersion solution, and uniformly stirring. 5.6g of KOH was weighed and dissolved in 100ml of deionized water at a molar concentration of KOH of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 90 ℃ for 2 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in the air for drying for 2 hours at 150 ℃; and roasting the dried solid for 1h at 600 ℃ in a nitrogen atmosphere to obtain a solid E.
2.0g of the solid E obtained are weighed, 0.0053g of RhCl are weighed 3 ·3H 2 Dissolving the obtained product in 2ml 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into E, and uniformly mixing, wherein the molar concentration of Rh is 0.01 mol/L. Dipping for 48h at room temperature, drying for 4h at 120 ℃, and roasting for 1h at 500 ℃ in a nitrogen atmosphere to obtain the Pt-Rh bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Rh is 0.1%, and the mass content is recorded as 3Pt-0.1Rh/AC.
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 3600h -1 The heating rate is 10 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 6h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 18
Weighing ZrO 2 2.0g of carrier, which was dispersed in 100ml of deionized water. Weigh 0.1642g H 2 PtCl 6 ·6H 2 Dissolving the precursor solution in 2ml of deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding the Pt precursor solution into ZrO 2 Dispersing in the solution, and stirring uniformly. 5.6g of KOH was weighed and dissolved in 100ml of deionized water at a molar concentration of KOH of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 90 ℃ for 2 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in the air for drying for 2 hours at the temperature of 150 ℃; and roasting the dried solid for 1h at 600 ℃ in an air atmosphere to obtain a solid E.
2.0g of the solid E obtained are weighed and 0.0034g of PdCl are weighed 2 The solution was dissolved in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, the molar concentration of Pd was 0.01mol/L, and the mixed solution was poured into E and mixed uniformly. Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 200 ℃ for 8h to obtain the Pt-Pd bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Pd is 0.1%, and the mark is 3Pt-0.1Pd/ZrO 2 。
Catalyst reduction activation conditions: reducing the gas to pure H 2 Molar purity of>99 percent and the airspeed of 3600h -1 The heating rate is 10 ℃/min, the reduction temperature is 600 ℃, the pressure is normal pressure, and the reduction time is 6h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. Trans formThe results are shown in Table 1.
Example analysis of results:
from the data analysis in Table 1, it is found that CeO is used 2 The conversion rate of U (VI) is higher than 90% in the reaction of preparing U (IV) by hydrazine reduction U (VI) under the acidic condition. 3Pt-0.1Rh/CeO 2 In the catalyst, the conversion rate of U (VI) reaches 99 percent, and the reaction rate reaches 116.6g U4 g -1 min -1 And the hydrazine utilization rate reaches 82 percent. The catalyst has better application prospect.
TABLE 1 reactivity of hydrazine reduction of hexavalent uranium (U (VI)) to tetravalent uranium (U (IV)) over different catalysts under acidic conditions
The reaction rate in Table 1 was calculated as the amount of U (VI) converted by the catalyst at 40 min.
Claims (8)
1. The method for preparing tetravalent uranium by hydrazine reduction of hexavalent uranium by adopting a bimetallic catalyst is characterized by comprising the following steps of: the bimetallic catalyst comprises the following components in parts by mass: a) The carrier is cerium oxide accounting for 70 to 99.89 percent; b) The active component is any one of Pt and Ir in a proportion of 0.1 to 20 percent; c) The second metal component is one or more than two of Ru, pd, rh and Au, and accounts for 0.01 to 10 percent.
2. The method of claim 1, wherein: the oxide in the component a) is cerium oxide, and the content is 85 to 99.89 percent; the component b) is any one of metal Pt and Ir, and the content is 0.1 to 10 percent; the component c) is any one or more than two of Ru, pd and Rh, and the content is 0.01 to 5 percent.
3. The method according to any one of claims 1 to 2, characterized in that: the preparation process of the bimetallic catalyst comprises the following steps:
a) Preparation of the support
1) Dissolving a certain amount of soluble cerium salt in deionized water to obtain a solution A; wherein the concentration of the metal ions is 0.001 to 10mol/L;
2) Dissolving a certain amount of urea and/or ammonium carbonate in deionized water to obtain a solution B with the concentration of 0.01 to 10mol/L;
3) Dropwise adding the solution B into the solution A until the pH value of the mixed solution is between 7 and 10, and controlling the obtained mixture to be 60 to 95 o C, stirring and aging in a water bath for 0.5 to 24 hours;
4) Filtering and washing the obtained turbid liquid to be neutral, and filtering a filter cake at 60-200 DEG C o C, drying in air for 12 to 48 hours;
5) The dried solid is dried in the temperature of 300 to 800 o C, roasting in an air atmosphere for 1 to 8 hours to obtain solid C;
b) Active ingredient loading
1) 1 to 5g of solid C is taken and dispersed in 100ml of deionized water, then soluble salt of any one of Pt and Ir is taken and dissolved in the deionized water, and the concentration of noble metal ions is 0.001 to 1mol/L; slowly adding a precursor solution of the noble metal into the dispersion liquid of the solid C, and uniformly stirring;
2) Dissolving alkali in deionized water to prepare a precipitator to obtain a solution D with the concentration of 0.001 to 10mol/L; adding the solution D into the dispersion liquid of the solid C until the pH value of the mixed solution is between 9 and 10, and keeping the obtained mixture at 25 to 90 o C, stirring in a water bath for 2 to 12 hours;
3) Filtering and washing the obtained turbid liquid to be neutral, and filtering a filter cake at 60 to 150 DEG C o C, drying in the air for 12 to 48 hours; the dried solid is maintained at 200 to 600 DEG o C, roasting for 1 to 8 hours in an air atmosphere to obtain a solid E;
c) Second component load
1) Dissolving any one or more soluble salts of Ru, pd, rh and Au in deionized water and/or 5-10% hydrochloric acid to prepare a solution F, wherein the concentration of metal ions is 0.001-10 mol/L;
2) Taking the solid E, and dropwise adding or pouring the solution F in an amount required in the solid E according to the load amount of the second component;
3)the obtained mixture is soaked for 0.5 to 48 hours at room temperature and then soaked for 60 to 120 hours o C, drying for 4 to 24 hours, and keeping the dried mixture at 200 to 500 o Roasting for 1 to 8 hours under C to obtain solid G;
4) Reducing and activating the solid G by hydrogen gas to obtain reducing gas with molar purity>99% of H 2 The volume space velocity of the reducing gas is 100-3600h -1 The temperature rising rate from room temperature to the reduction temperature is 1-10 o C/min, reduction temperature of 200-600 o And C, the pressure is normal pressure, and the reduction time is 1-48h.
4. The method of claim 3, wherein:
1) In the preparation of the carrier, the soluble cerium salt in the step 1) is one or two of cerium nitrate or ammonium cerium nitrate;
2) In the preparation of the carrier, the baking temperature in the step 5) is 300 to 600 o And C, roasting for 2 to 6 hours.
5. The method of claim 3, wherein:
1) Soluble salts of Pt and Ir in the step 1) in the active component loading are one of nitrates or chlorides of corresponding noble metals;
2) The alkali in the step 2) in the active component loading is one or more than two of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate;
3) In the second component load, the soluble salts of Ru, pd, rh and Au in the step 1) are one or more than two of nitrates or chlorides of corresponding noble metals.
6. The method of claim 3, wherein: the catalyst is used for catalyzing hydrazine to reduce hexavalent uranium in an acid system to prepare a uranic solution.
7. The method of claim 6, wherein: the acid system is one or more than two of nitric acid, sulfuric acid or perchloric acid systems; the hexavalent uranium is uranyl ions corresponding to acid types in an acid system, and is one or more than two of uranyl nitrate, uranyl sulfate and uranyl perchlorate solutions; the tetravalent uranium is the reduction product of the corresponding hexavalent uranium.
8. The method of claim 3, wherein: the conditions of preparing the uranium quadrivalent solution by hydrazine reduction of hexavalent uranium by the catalyst in a kettle type reactor or a fixed bed reactor are as follows: the acid concentration is 0.5-1.0mol/L, the uranyl ion concentration is 0.5-1.3mol/L, the hydrazine concentration is 0.5-2.0mol/L, and the reaction temperature is 25-70 o And C, the reaction pressure is normal pressure.
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| US5480854A (en) * | 1992-12-18 | 1996-01-02 | Johnson Matthey Public Limited Company | Catalyst |
| CN102249331A (en) * | 2011-04-19 | 2011-11-23 | 中国原子能科学研究院 | Preparation method of tetravalent uranium solution |
| CN105797720A (en) * | 2016-05-16 | 2016-07-27 | 北京化工大学 | Superfine supported noble metal catalyst prepared through in-situ reduction deposition method and preparing method thereof |
| WO2019237892A1 (en) * | 2018-06-11 | 2019-12-19 | 太原氦舶新材料有限责任公司 | Noble metal supported catalyst, preparation method therefor, and application thereof |
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| US5480854A (en) * | 1992-12-18 | 1996-01-02 | Johnson Matthey Public Limited Company | Catalyst |
| CN102249331A (en) * | 2011-04-19 | 2011-11-23 | 中国原子能科学研究院 | Preparation method of tetravalent uranium solution |
| CN105797720A (en) * | 2016-05-16 | 2016-07-27 | 北京化工大学 | Superfine supported noble metal catalyst prepared through in-situ reduction deposition method and preparing method thereof |
| WO2019237892A1 (en) * | 2018-06-11 | 2019-12-19 | 太原氦舶新材料有限责任公司 | Noble metal supported catalyst, preparation method therefor, and application thereof |
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