CN114308029B - Method for preparing tetravalent uranium by hydrazine reduction of hexavalent uranium with bimetallic catalyst - Google Patents

Abstract

The invention relates to a method for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine using a bimetallic catalyst. The catalyst used in the present invention includes the following components in parts by mass: a) the carrier is an oxide of cerium, and the share is 70% to 99.89%; b) the active component is any metal selected from Pt and Ir. One, accounting for 0.1-20%; c) the second metal component is one or more selected from Ru, Pd, Rh, Au, accounting for 0.01-10%. The catalyst provided by the invention can directly reduce hexavalent uranium to tetravalent uranium by using hydrazine as a reducing agent in an acidic system, and the conversion rate of hexavalent uranium can reach 99%, and the utilization rate of hydrazine is higher than 80%, providing a A method for preparing tetravalent uranium solution under mild conditions. The catalyst raw material of the invention is easy to obtain, the process is simple, and the invention has good application prospects.

Description

Method for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine using bimetallic catalyst

technical field

The invention relates to a bimetallic catalyst for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine, a preparation method and application thereof.

Background technique

Nuclear fuel reprocessing refers to the treatment of nuclear fuel (spent fuel) used in nuclear reactors, recovery of uranium, plutonium and other valuable elements, and vitrification of high-level radioactive waste in it and sending it to deep geological disposal. At present, the reprocessing plants at home and abroad mainly adopt the Purex process. The Purex process mainly uses tributyl phosphate (TBP) to separate uranium, plutonium and other fission products due to the different extraction capabilities of uranium and plutonium in different valence states. First, the fission products are separated from TBP, which has a smaller extraction capacity than uranium and plutonium. Then, the extraction capacity of trivalent plutonium is smaller by using TBP to realize the separation of uranium and plutonium. Therefore, it is necessary to add a reducing agent to reduce tetravalent plutonium to trivalent plutonium. Under the condition of hydrazine as the supporting reducing agent, tetravalent uranium (U(IV)) is a better reducing and stripping agent for tetravalent plutonium. Most of the spent fuel reprocessing plants in operation and under construction use hydrazine-stabilized U(IV) as the reductive stripping agent, such as UP3 and UP2-800 in France and pilot plants in my country.

At present, the preparation methods of U(IV) mainly include electrolysis, hydrogenation and liquid phase reduction. The production of U(IV) by electrolysis can not introduce impurities, and the operation process is simple. However, in the actual production process, the conversion rate of hexavalent uranium (U(VI)) is low, only 50%-60%, which increases the recovery burden of uranium products in the reprocessing process. The catalytic hydrogenation method uses high-pressure hydrogen as a reducing agent, which can obtain a higher conversion rate of U(VI). However, the use of high-pressure hydrogen increases the complexity of the equipment and also poses safety hazards. Using an organic reducing agent such as hydrazine, U(VI) can be reduced to U(IV) under the action of a catalyst, as shown in Formula 1. The reaction condition is mild, the operation process is simple, and the application prospect is good. There are other side reactions in the hydrazine reduction U(VI) system, such as formula 2, which will reduce the reducing ability of hydrazine and the utilization rate of hydrazine. Therefore, it is necessary to optimize the design of the catalyst to make hydrazine more inclined to carry out reaction 1, so as to improve the activity of the catalyst and the utilization of hydrazine.

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)

Li Bin et al. studied the reaction performance of platinum black catalysts under different reaction conditions in nitric acid system for the reduction of U(VI) to U(IV) by hydrazine. At 60°C, when the concentration of uranium is 0.9mol/L, the concentration of _HNO3 is 0.8mol/L, and the concentration of hydrazine is 1mol/L, the conversion rate of U(VI) can reach more than 90%. (Nuclear Chemistry and Radiation Chemistry, 2013, 35, (1): 24–28). Boltoeva et al. studied the particle size effect of Pt/SiO ₂ catalyst in H ₂ SO ₄ , HClO ₄ , HNO ₃ system by hydrazine reduction of U(VI) to Pt in U(IV). It was found that the conversion of U(VI) decreased with the decrease of Pt particle size (Radiochemistry, 2007, 49, 603-606). Anan'ev et al. investigated the reaction performance of hydrazine and formic acid to reduce U(VI) to U(IV) in nitric acid system (Radiochemistry, 2001, 43, 39–43). At present, the research on the reaction of U(VI) to U(IV) by hydrazine reduction mainly focuses on the investigation of process conditions, while the influence of catalyst support on the reaction performance is less studied.

At present, some related patents have been applied for the preparation of tetravalent uranium solutions. A few reported patents are listed below for detailed description:

The public name of Chinese patent CN201110097474 is: a preparation method of tetravalent uranium solution. This patent reports that U(VI) is reduced to prepare U(IV) solution by using an organic reducing agent (hydrazine or carboxylic acid and its derivatives) under the action of Pt, Pd and Rh catalysts. This patent is silent on the supports of the catalysts used.

The public name of Chinese patent CN201310743451 is: a device for preparing tetravalent uranium by electrolytic reduction. This patent reports an improved electrolytic reduction device for preparing tetravalent uranium, which mainly solves the problem of low conversion rate of U(VI) in the diaphragmless electrolysis device. In actual production, the effectiveness of the device needs to be further tested.

Although in the above reports, the reduction of U(VI) by hydrazine to prepare U(IV) has been achieved. But the reactivity of the catalyst and the utilization rate of hydrazine are low. Therefore, it is necessary to develop a catalyst for the reduction of U(VI) to U(IV) by hydrazine with high activity and high hydrazine utilization.

A strong metal-support interaction can be formed between the reducible support and the active component, which can realize the modulation of the structure and properties of the catalyst, thereby improving the activity and selectivity of the catalyst. Utilizing the interaction between reducible supports such as CeO2 and noble metals, combined with the modulation of the electronic properties of the catalyst by the _second component, it is expected to develop a highly active and high hydrazine utilization rate for the preparation of U(VI) by hydrazine reduction. Catalyst for U(IV).

Contents of the invention

One of the technical problems to be solved by the present invention is to solve the problem of hydrazine reduction U(VI) system U(IV) catalyst in the acidic system, provide a kind of catalyst of novel hydrazine reduction U(VI) system U(IV), this catalyst has High U(VI) conversion and hydrazine utilization.

The second technical problem to be solved by the present invention is to adopt the preparation method of the catalyst described in one of the above technical problems. The content of each component of the catalyst is controllable, and the method has simple preparation process and good reliability.

The third technical problem to be solved by the present invention is to use the catalyst described in one of the above technical problems to realize the catalytic reaction process of reducing U(VI) to U(IV) by hydrazine in an acidic system.

In order to solve one of the above technical problems, the present invention adopts the following technical solutions:

The bimetallic catalyst for preparing U(IV) by reducing U(VI) with hydrazine in an acidic system comprises the following components in parts by mass: a) the carrier is cerium oxide, and the proportion is 70-99.89%; b) The active component is any one selected from metal Pt and Ir, and the share is 0.1-20%; c) the second metal component is one or two selected from Ru, Pd, Rh, Au Above, the share is 0.01 to 10%.

In the above scheme, it is characterized in that: the oxide in component a) is an oxide of cerium, with a preferred content of 85% to 99.89%; component b) is any one of metal Pt and Ir, with a preferred content of 0.1% ~10%; component c) is preferably any one or two or more of Ru, Pd, Rh, and the preferred content is 0.01-5%.

In order to solve the above technical problem two, the present invention adopts the following technical solutions:

a) Preparation of carrier

1) Dissolving a certain amount of soluble cerium salt in deionized water to obtain solution A; wherein the concentration of metal ions is 0.001-10mol/L;

2) Dissolve a certain amount of urea and/or ammonium carbonate in deionized water to obtain solution B with a concentration of 0.01-10mol/L;

3) adding solution B to solution A dropwise until the pH value of the mixed solution is between 7-10, and aging the obtained mixture in a water bath at 60-95°C for 0.5-24 hours;

4) Filter and wash the obtained turbid liquid to neutrality, and dry the filter cake in air at 60-200°C for 12-48 hours;

5) Calcining the dried solid in an air atmosphere at 300-800° C. for 1-8 hours to obtain solid C.

b) active ingredient loading

1) Take 1-5g of solid C, disperse it in 100ml of deionized water, then take any one or two soluble salts of Pt and Ir and dissolve them in deionized water, the concentration of noble metal ions is 0.001～1mol/L; Slowly add the precursor solution of the noble metal to the dispersion of solid C, and stir evenly;

2) Take alkali and dissolve it in deionized water to prepare a precipitant to obtain solution D with a concentration of 0.001-10mol/L; add solution D to the dispersion of solid C until the pH value of the mixed solution is between 9-10, Stir the resulting mixture in a water bath at 25-90°C for 2-12 hours;

3) Filtrate and wash the obtained turbid liquid to neutrality, dry the filter cake in the air at 60-150°C for 12-48h; roast the dried solid in the air atmosphere at 200-600°C for 1-8h, E was obtained as a solid.

c) Second component loading

1) dissolving any one or two or more soluble salts of Ru, Pd, Rh, Au in deionized water and/or 5%-10% hydrochloric acid to prepare solution F;

2) Take solid E, and drop or pour the required amount of F solution into solid E according to the load of the second component;

3) impregnating the obtained mixture at room temperature for 0.5-48 hours, and then drying at 60-120° C. for 4-24 hours; roasting the dried mixture at 200-500° C. for 1-8 hours to obtain solid G;

4) The solid G is activated by hydrogen reduction. The reducing gas is H ₂ (molar purity>99%), the volumetric space velocity of the reducing gas is 100-3600h ^-1 , the heating rate from room temperature to the reducing temperature is 1-10°C/min, and the reducing temperature is 200-600°C, The pressure is normal pressure, and the reduction time is 1-48h.

The soluble cerium salt described in step 1) in the preparation of the support is one or both of cerium nitrate or ammonium cerium nitrate.

The calcination temperature in step 5) in the preparation of the carrier is 300-600° C., and the calcination time is 2-6 hours;

The soluble salt of Pt and Ir in step 1) in the active component loading is one of the nitrates or chlorides of the corresponding precious metals;

The alkali described in step 2) in the loading of active components is one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate;

The soluble salts of Ru, Pd, Rh, and Au described in step 1) in the second component loading are one or more of the nitrates or chlorides of the corresponding precious metals;

In order to solve the third technical problem above, the present invention adopts the following technical scheme: the acidic system is one or more of nitric acid, sulfuric acid or perchloric acid system; the hexavalent uranium is the corresponding acid type in the acidic system Uranyl ions are one or more of uranyl nitrate, uranyl sulfate, and uranyl perchlorate solutions; tetravalent uranium is the reduction product of corresponding hexavalent uranium. The conditions for the catalyst to be used in tank reactors or fixed-bed reactors for the reduction of hexavalent uranium by hydrazine to prepare tetravalent uranium solutions are as follows: the acid concentration (in terms of hydrogen ion concentration) is 0.5-1.0 mol/L, and 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°C, and the reaction pressure is normal pressure.

The advantages of the present invention are:

(1) The raw materials of the catalyst carrier provided by the present invention are cheap and easy to obtain, and the preparation method is simple, which is beneficial to realize mass production.

(2) The catalyst provided by the present invention is stable in nature, which is beneficial to improve the service life of the catalyst.

(3) The catalyst provided by the present invention can utilize hydrazine to reduce U(VI) to a U(IV) solution under acidic conditions. The interaction between the carrier and the active component and the modulation of the second component improve the conversion rate and reaction rate of U(VI). In the tank reactor, the conversion rate of U(VI) can reach 99% within 60 min. And the utilization rate of hydrazine is higher than 80%.

detailed description

The technical details of the present invention are described in detail by the following examples. It should be noted that the examples cited are only used to further illustrate the technical features of the present invention, rather than to limit the present invention.

Catalyst preparation and performance evaluation

Example 1

Solution A was prepared by dissolving 21.7g Ce(NO ₃ ) ₃ ·6H ₂ O in 100ml of deionized water, and the molar concentration of Ce ions was 0.5mol/L. Get 19.2g ammonium carbonate and dissolve in 100ml deionized water to obtain solution B, the molar concentration of ammonium carbonate is 2mol/L. Solution B was added dropwise to solution A until the pH value of the mixed solution was 10, and the mixed solution was placed in a 70° C. water bath and stirred for 12 h. The obtained turbid liquid was filtered and washed until neutral, and then the filter cake was dried in air at 80°C for 12h; the dried solid was calcined in air atmosphere at 400°C for 4h to obtain a CeO ₂ support.

Weigh 2.0 _g of the prepared CeO2 support and disperse it in 100 ml of deionized water. Weigh 0.1642g H ₂ PtCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Pt is 0.16mol/L. Add the Pt precursor solution to the CeO ₂ dispersion and stir uniform. Weigh 4g of NaOH and dissolve it in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then slowly add lye to the above solution dropwise, and stir the resulting mixture in a 60°C water bath for 4h. The obtained turbid liquid was filtered and washed to neutrality, and the filter cake was dried in air at 80°C for 12 hours; the dried solid was roasted in an air atmosphere at 300°C for 4 hours to obtain solid E;

Weigh 2.0g of the above solid E, weigh 0.0056g RuCl ₃ 3H ₂ O, dissolve it in 2ml of 10% hydrochloric acid solution to form a mixed solution, the molar concentration of Ru is 0.01mol/L, pour it on the solid E Dip and mix well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain a Pt-Ru bimetallic catalyst, in which the mass content of Pt was 3%, and the mass content of Ru was 0.1%, which was recorded as 3Pt-0.1Ru/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 2

Solution A was prepared by dissolving 27.4g Ce(NH ₄ ) ₂ (NO ₃ ) ₆ in 100 ml of deionized water, and the molar concentration of Ce ions was 0.5 mol/L. Get 19.2g ammonium carbonate and dissolve in 100ml deionized water to obtain solution B, the molar concentration of ammonium carbonate is 2mol/L. Solution B was added dropwise to solution A until the pH value of the mixed solution was 10, and the mixed solution was placed in a 60° C. water bath and stirred for 24 h. The obtained turbid liquid was filtered and washed until neutral, and then the filter cake was dried in air at 60°C for 48h; the dried solid was calcined in air atmosphere at 300°C for 6h to obtain a CeO ₂ support.

Weigh 2.0 _g of the prepared CeO2 support and disperse it in 100 ml of deionized water. Weigh 0.1642g H ₂ PtCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Pt is 0.16mol/L. Add the Pt precursor solution to the CeO ₂ dispersion and stir uniform. Weigh 5.6g KOH and dissolve it in 100ml deionized water, the molar concentration of KOH is 1mol/L, then slowly add lye to the above solution until the pH value of the mixed solution is 10, and the obtained mixture is dissolved at 30 ° C in a water bath and stirred for 12h. The obtained turbid liquid was filtered and washed until neutral, and the filter cake was dried in air at 60°C for 48 hours; the dried solid was roasted in air atmosphere at 200°C for 8 hours to obtain solid E;

The solid E that weighs 2.0g obtains, weighs _0.0034g PdCl It is dissolved in the hydrochloric acid solution of 2ml 10% and is made into mixed solution, and the molar concentration of Pd is 0.01mol/L, it is poured in E, and It mixes well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 200°C for 8 hours to obtain a Pt-Pd bimetallic catalyst, in which the mass content of Pt is 3%, and the mass content of Pd is 0.1%, which is recorded as 3Pt-0.1Pd/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 200h ^-1 , the heating rate is 1°C/min, the reduction temperature is 200°C, the pressure is normal pressure, and the reduction time is 48h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 0.5mol/L, the concentration of uranyl ion is 0.5mol/L, the concentration of hydrazine is 0.5mol/L, the temperature is 30°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 3

Solution A was prepared by dissolving 27.4g Ce(NH ₄ ) ₂ (NO ₃ ) ₆ in 100 ml of deionized water, and the molar concentration of Ce ions was 0.5 mol/L. Get 19.2g ammonium carbonate and dissolve in 100ml deionized water to obtain solution B, the molar concentration of ammonium carbonate is 2mol/L. Solution B was added dropwise to solution A until the pH value of the mixed solution was 10, and the mixed solution was placed in a water bath at 95° C. and stirred for 2 h. The obtained turbid liquid was filtered and washed until neutral, and then the filter cake was dried in the air at 200°C for 48h; the dried solid was calcined in the air atmosphere at 600°C for 6h to obtain the CeO ₂ support.

Weigh 2.0 _g of the prepared CeO2 support and disperse it in 100 ml of deionized water. Weigh 0.1642g H ₂ PtCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Pt is 0.16mol/L. Add the Pt precursor solution to the CeO ₂ dispersion and stir uniform. Weigh 5.6g KOH and dissolve it in 100ml deionized water, the molar concentration of KOH is 1mol/L, then slowly add lye to the above solution until the pH value of the mixed solution is 10, and the obtained mixture is dissolved at 90 ℃ water bath and stirred for 2h. The obtained turbid liquid was filtered and washed until neutral, and the filter cake was dried in air at 150°C for 2 hours; the dried solid was roasted in air atmosphere at 600°C for 1 hour to obtain solid E;

Weigh 2.0g of the obtained solid E, weigh 0.0053g RhCl ₃ 3H ₂ O, dissolve it in 2ml of 10% hydrochloric acid solution to form a mixed solution, the molar concentration of Rh is 0.01mol/L, pour it into E in, and mix it well. Immersed at room temperature for 48 hours, dried at 120°C for 4 hours, and calcined at 500°C for 1 hour to obtain a Pt-Rh bimetallic catalyst, in which the mass content of Pt is 3%, and the mass content of Rh is 0.1%, which is recorded as 3Pt-0.1Rh/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 3600h ^-1 , the heating rate is 10°C/min, the reduction temperature is 600°C, the pressure is normal pressure, and the reduction time is 6h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 4

Weigh 2.0g of the body E obtained in Example 1, weigh 0.0042g HAuCl ₄ ·4H ₂ O, dissolve it in 2ml of deionized aqueous solution to form a mixed solution, the molar concentration of Au is 0.005mol/L, pour it Dip in Solid E and mix well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain a Pt-Au bimetallic catalyst, in which the mass content of Pt was 3%, and the mass content of Au was 0.1%, which was recorded as 3Pt-0.1Au/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 5

Weigh 2.0 g of the CeO2 support prepared in Example ₁ and disperse it in 100 ml of deionized water. Weigh 0.0265gH ₂ PtCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Pt is 0.026mol/L. Add the Pt precursor solution to the CeO ₂ dispersion and stir evenly . Weigh 4g of NaOH and dissolve it in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then slowly add lye to the above solution dropwise, and stir the resulting mixture in a 60°C water bath for 4h. The obtained turbid liquid was filtered and washed to neutrality, and the filter cake was dried in air at 80°C for 12 hours; the dried solid was roasted in an air atmosphere at 300°C for 4 hours to obtain solid E;

Weigh 2.0g of the above solid E, weigh 0.2432g RhCl ₃ 3H ₂ O, dissolve it in 2ml of 10% hydrochloric acid solution to form a mixed solution, the molar concentration of Rh is 0.46mol/L, pour it on the solid E Dip and mix well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain a Pt-Rh bimetallic catalyst, in which the mass content of Pt is 0.5%, and the mass content of Rh is 5%, which is recorded as 0.5Pt-5Rh/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 6

Weigh 2.0 g of the CeO2 support prepared in Example ₁ and disperse it in 100 ml of deionized water. Weigh 0.4780gH ₂ PtCl ₆ 6H ₂ O and dissolve it in 5ml deionized water to form a mixed solution. The molar concentration of Pt is 0.18mol/L. Add the Pt precursor solution to the CeO ₂ dispersion and stir evenly . Weigh 5g of NaOH and dissolve it in 100ml of deionized water, the molar concentration of NaOH is 1.25mol/L, then slowly add lye to the above solution dropwise, and stir the resulting mixture in a 60°C water bath for 4h. The obtained turbid liquid was filtered and washed to neutrality, and the filter cake was dried in air at 80°C for 12 hours; the dried solid was roasted in an air atmosphere at 300°C for 4 hours to obtain solid E;

Weigh 5.0g of the above solid E, weigh 0.0013g RhCl ₃ 3H ₂ O, dissolve it in 2ml of 10% hydrochloric acid solution to form a mixed solution, the molar concentration of Rh is 0.0025mol/L, pour it on the solid E Dip and mix well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain a Pt-Rh bimetallic catalyst, in which the mass content of Pt is 10%, and the mass content of Rh is 0.01%, which is recorded as 10Pt-0.01Rh/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 7

Weigh 2.0 g of the CeO2 support prepared in Example ₁ and disperse it in 100 ml of deionized water. Weigh 0.1660gH ₂ IrCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Ir is 0.16mol/L. Add the Ir precursor solution to the CeO ₂ dispersion and stir evenly . Weigh 4g of NaOH and dissolve it in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then slowly add lye to the above solution dropwise, and stir the resulting mixture in a 60°C water bath for 4h. The obtained turbid liquid was filtered and washed to neutrality, and the filter cake was dried in air at 80°C for 12 hours; the dried solid was roasted in an air atmosphere at 300°C for 4 hours to obtain solid E;

Weigh 2.0g of the above solid E, weigh 0.0056g RuCl ₃ 3H ₂ O, dissolve it in 2ml of 10% hydrochloric acid solution to form a mixed solution, the molar concentration of Ru is 0.013mol/L, add it dropwise to the solid E, and mix it well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain an Ir-Ru bimetallic catalyst with a mass content of Ir of 3% and a mass content of Ru of 0.1%, denoted as 3Ir-0.1Ru/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 8

Weigh 2.0 g of the CeO2 support prepared in Example ₁ and disperse it in 100 ml of deionized water. Weigh 0.1660gH ₂ IrCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Ir is 0.16mol/L. Add the Ir precursor solution to the CeO ₂ dispersion and stir evenly . Weigh 4g of NaOH and dissolve it in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then slowly add lye to the above solution dropwise, and stir the resulting mixture in a 60°C water bath for 4h. The obtained turbid liquid was filtered and washed to neutrality, and the filter cake was dried in air at 80°C for 12 hours; the dried solid was roasted in an air atmosphere at 300°C for 4 hours to obtain solid E;

Weigh 2.0g of the above solid E, weigh 0.0053g RhCl ₃ 3H ₂ O, dissolve it in 2ml of 10% hydrochloric acid solution to form a mixed solution, the molar concentration of Rh is 0.01mol/L, pour it on the solid E in, and mix it well. Immerse at room temperature for 12 hours, dry at 60°C for 12 hours, and bake at 300°C for 4 hours to obtain an Ir-Rh bimetallic catalyst, in which the mass content of Ir is 3%, and the mass content of Rh is 0.1%, which is recorded as 3Ir-0.1Rh/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Example 9

Take the reduction-activated 3Pt-0.1Rh/CeO catalyst in Example ₃ . Reaction conditions in the tank reactor: the concentration of sulfuric acid is 0.5mol/L (1.0mol/L in terms of hydrogen ion concentration), the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, and the temperature is 60°C , the stirring rate is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.

Example 10

Take the reduction-activated 3Pt-0.1Rh/CeO catalyst in Example ₃ . Reaction conditions in the tank reactor: perchloric acid concentration (calculated as hydrogen ion concentration) is 1.0mol/L, uranyl ion concentration is 0.9mol/L, hydrazine concentration is 1.0mol/L, temperature is 60°C, stirring The speed was 800 rpm and the pressure was normal pressure. The reaction results are shown in Table 1.

Example 11

Take the reduction-activated 3Pt-0.1Rh/CeO catalyst in Example ₃ . Reaction conditions in fixed bed: nitric acid concentration (calculated as hydrogen ion concentration) is 1.0mol/L, uranyl ion concentration is 0.9mol/L, hydrazine concentration is 1.0mol/L, temperature is 60°C, liquid space velocity is 0.3 h ^-1 , the pressure is normal pressure. The reaction results are shown in Table 1.

Comparative Example 12

Take 2.0g of SiO ₂ carrier, weigh 0.1642g H ₂ PtCl ₆ 6H ₂ O, dissolve it in 2ml deionized water to make a mixed solution, the molar concentration of Pt is 0.16mol/L, impregnate the SiO ₂ carrier in the above mixed solution solution and mix it well. Immerse at room temperature for 12 hours, dry at 60°C for 12 hours, and bake at 400°C for 4 hours in an air atmosphere. The mass content of Pt is 3%, which is recorded as 3Pt/SiO ₂ catalyst.

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (calculated as hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm, the pressure is normal pressure. The reaction results are shown in Table 1.

Comparative Example 13

Get the CeO prepared in Example ₁ Carrier 2.0g, weigh 0.1642g H ₂ PtCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to make a mixed solution, the molar concentration of Pt is 0.16mol/L, the CeO ₂ The carrier is immersed in the above mixed solution and mixed evenly. Immerse at room temperature for 12h, dry at 60°C for 12h, and bake at 400°C for 4h in an air atmosphere. The mass content of Pt is 3%, which is recorded as 3Pt/CeO ₂ catalyst.

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99.9%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the stirred tank: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm. The pressure is normal pressure. The reaction results are shown in Table 1.

Comparative Example 14

Weigh 2.0g of the body E obtained in Example 1, weigh 1.02g Ni(NO ₃ ) ₂ 6H ₂ O and dissolve it in 4ml deionized water to form a mixed solution, the molar concentration of Ni is 0.88mol/L, Pour it into the solid E dip and mix it well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain a Pt-Ni bimetallic catalyst with a mass content of 3% Pt and 0.1% Ni, denoted as 3Pt-0.1Ni/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Comparative Example 15

Weigh 2.0g of the body E obtained in Example 1, weigh 1.02g Co(NO ₃ ) ₂ 6H ₂ O and dissolve it in 4ml deionized water to form a mixed solution, the molar concentration of Co is 0.88mol/L, Pour it into the solid E dip and mix it well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain a Pt-Co bimetallic catalyst with a mass content of Pt of 3% and a mass content of Co of 0.1%, denoted as 3Pt-0.1Co/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Comparative Example 16

Weigh 2.0g of the body E obtained in Example 1, weigh 1.02g Fe(NO ₃ ) ₃ 9H ₂ O and dissolve it in 4ml deionized water to form a mixed solution, the molar concentration of Fe is 0.88mol/L, Pour it into the solid E dip and mix it well. Immersed at room temperature for 12 hours, dried at 60°C for 12 hours, and calcined at 300°C for 4 hours to obtain a Pt-Fe bimetallic catalyst with a mass content of Pt of 3% and a mass content of Fe of 0.1%, denoted as 3Pt-0.1Fe/CeO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 2000h ^-1 , the heating rate is 5°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 4h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Comparative Example 17

Weigh 2.0 g of activated carbon carrier and disperse it in 100 ml of deionized water. Weigh 0.1642g H ₂ PtCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Pt is 0.16mol/L. Add the Pt precursor solution to the activated carbon dispersion and stir evenly . Weigh 5.6g KOH and dissolve it in 100ml deionized water, the molar concentration of KOH is 1mol/L, then slowly add lye to the above solution until the pH value of the mixed solution is 10, and the obtained mixture is dissolved at 90 ℃ water bath and stirred for 2h. The obtained turbid liquid was filtered and washed until neutral, and the filter cake was dried in air at 150° C. for 2 h; the dried solid was roasted at 600° C. in a nitrogen atmosphere for 1 h to obtain solid E.

Weigh 2.0g of the obtained solid E, weigh 0.0053g RhCl ₃ 3H ₂ O, dissolve it in 2ml of 10% hydrochloric acid solution to form a mixed solution, the molar concentration of Rh is 0.01mol/L, pour it into E in, and mix it well. Immerse at room temperature for 48 hours, dry at 120°C for 4 hours, and roast at 500°C for 1 hour in a nitrogen atmosphere to obtain a Pt-Rh bimetallic catalyst, in which the mass content of Pt is 3%, and the mass content of Rh is 0.1%, which is recorded as 3Pt-0.1Rh/AC .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 3600h ^-1 , the heating rate is 10°C/min, the reduction temperature is 300°C, the pressure is normal pressure, and the reduction time is 6h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Comparative Example 18

Weigh _2.0 g of the ZrO2 carrier and disperse it in 100 ml of deionized water. Weigh 0.1642g H ₂ PtCl ₆ 6H ₂ O and dissolve it in 2ml deionized water to form a mixed solution. The molar concentration of Pt is 0.16mol/L. Add the Pt precursor solution to the ZrO ₂ dispersion and stir uniform. Weigh 5.6g KOH and dissolve it in 100ml deionized water, the molar concentration of KOH is 1mol/L, then slowly add lye to the above solution until the pH value of the mixed solution is 10, and the obtained mixture is dissolved at 90 ℃ water bath and stirred for 2h. The obtained turbid liquid was filtered and washed until neutral, and the filter cake was dried in air at 150°C for 2h; the dried solid was calcined at 600°C in air atmosphere for 1h to obtain solid E.

The solid E that weighs 2.0g obtains, weighs _0.0034g PdCl It is dissolved in the hydrochloric acid solution of 2ml 10% and is made into mixed solution, and the molar concentration of Pd is 0.01mol/L, it is poured in E, and It mixes well. Immerse at room temperature for 12 hours, dry at 60°C for 12 hours, and bake at 200°C for 8 hours to obtain a Pt-Pd bimetallic catalyst, in which the mass content of Pt is 3%, and the mass content of Pd is 0.1%, which is recorded as 3Pt-0.1Pd/ZrO ₂ .

Catalyst reduction and activation conditions: the reduction gas is pure H ₂ , the molar purity is >99%, the space velocity is 3600h ^-1 , the heating rate is 10°C/min, the reduction temperature is 600°C, the pressure is normal pressure, and the reduction time is 6h. Reaction conditions in the tank reactor: the concentration of nitric acid (in terms of hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ion is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70°C, and the stirring rate is 800rpm , the pressure is normal pressure. The reaction results are shown in Table 1.

Embodiment result analysis:

From the data analysis in Table ₁ , it can be seen that the bimetallic catalyst prepared with CeO2 as the carrier, in the reaction of U(IV) to U(IV) by hydrazine reduction under acidic conditions, the conversion rate of U(VI) is higher than 90%. In the 3Pt-0.1Rh/CeO ₂ catalyst, the conversion rate of U(VI) reached 99%, the reaction rate reached 116.6g _U4 g ^-1 min ^-1 , and the utilization rate of hydrazine reached 82%. The catalyst has a good application prospect.

Table 1 Reaction performance of hydrazine reduction of hexavalent uranium (U(VI)) to tetravalent uranium (U(IV)) under acidic conditions on different catalysts

The reaction rate in Table 1 is calculated by the amount of U(VI) converted by the catalyst at 40 min.

Claims (8)

1. A method for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine using a bimetallic catalyst, characterized in that: the bimetallic catalyst comprises the following components in parts by mass: a) the carrier is an oxide of cerium, the proportion of The number is 70~99.89%; b) The active component is any one selected from metal Pt and Ir, and the share is 0.1~20%; c) The second metal component is selected from Ru, Pd, Rh , Au in one or more than two kinds, the number of shares is 0.01~10%. 2. method according to claim 1, it is characterized in that: oxide is the oxide of cerium in component a), and content is 85～99.89%; Component b) is any one in metal Pt, Ir, The content is 0.1~10%; component c) is any one or more of Ru, Pd, Rh, and the content is 0.01~5%. 3. according to the arbitrary described method of claim 1～2, it is characterized in that: the preparation process of bimetallic catalyst comprises the following steps: a) Preparation of vectors 1) A certain amount of soluble cerium salt is dissolved in deionized water to obtain solution A; wherein the concentration of metal ions is 0.001~10 mol/L; 2) Dissolve a certain amount of urea and/or ammonium carbonate in deionized water to obtain a solution B with a concentration of 0.01-10 mol/L; 3) adding solution B to solution A dropwise until the pH value of the mixed solution is between 7-10, and aging the obtained mixture in a water bath at 60-95 ^o C for 0.5-24 h; 4) Filter and wash the obtained turbid solution to neutrality, and place the filter cake in air at ^{60-200 o} C for 12-48 h; 5) calcining the dried solid in an air atmosphere at 300-800 ^o C for 1-8 h to obtain solid C; b) Active ingredient loading 1) Take 1~5 g of solid C, disperse it in 100 ml of deionized water, then take any soluble salt of Pt and Ir and dissolve it in deionized water, the concentration of noble metal ions is 0.001~1 mol/L; Slowly add the precursor solution of the noble metal to the dispersion of solid C, and stir evenly; 2) Dissolve alkali in deionized water to prepare a precipitant to obtain solution D with a concentration of 0.001~10 mol/L; add solution D to the dispersion of solid C until the pH of the mixed solution is between 9-10 , the resulting mixture was stirred in a 25~90 ^o C water bath for 2~12 h; 3) Filter and wash the obtained turbid liquid to neutrality, dry the filter cake in the air at 60-150 ^o C for 12-48 h; roast the dried solid in the air atmosphere at 200-600 ^o C for 1 ~8 h, solid E was obtained; c) Second component loading 1) Take any one or more soluble salts of Ru, Pd, Rh, Au and dissolve them in deionized water and/or 5%-10% hydrochloric acid to make solution F, wherein the concentration of metal ions is 0.001~10mol/L; 2) Take solid E, and drop or pour the required amount of F solution into solid E according to the load of the second component; 3) Immerse the obtained mixture at room temperature for 0.5-48 h, then dry at 60-120 ^o C for 4-24 h, and roast the dried mixture at 200-500 ^o C for 1-8 h to obtain solid G ; 4) Reductively activate the solid G with hydrogen, the reducing gas is H ₂ with a molar purity >99%, the volumetric space velocity of the reducing gas is 100-3600 h ^-1 , and the heating rate from room temperature to the reduction temperature is 1-10 ^o C /min, the reduction temperature is 200-600 ^o C, the pressure is normal pressure, and the reduction time is 1-48 h. 4. The method according to claim 3, characterized in that: 1) The soluble cerium salt described in step 1) in the preparation of the carrier is one or both of cerium nitrate or ammonium cerium nitrate; 2) In the preparation of the carrier, the calcination temperature in step 5) is 300-600 ^o C, and the calcination time is 2-6 h. 5. The method according to claim 3, characterized in that: 1) The soluble salts of Pt and Ir in step 1) in the loading of active components are one of the nitrates or chlorides of the corresponding noble metals; 2) The alkali described in step 2) in the loading of active components is one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate; 3) The soluble salts of Ru, Pd, Rh, and Au described in step 1) in the loading of the second component are one or more of the nitrates or chlorides of the corresponding noble metals. 6. The method according to claim 3, characterized in that: the catalyst is used in an acidic system to catalyze the reduction of hexavalent uranium with hydrazine to prepare a tetravalent uranium solution. 7. The method according to claim 6, characterized in that: the acidic system is one or more of nitric acid, sulfuric acid or perchloric acid system; the hexavalent uranium is the acid type in the corresponding acidic system Uranyl ions are one or more of uranyl nitrate, uranyl sulfate, and uranyl perchlorate solutions; tetravalent uranium is the reduction product of corresponding hexavalent uranium. 8. The method according to claim 3, characterized in that: the condition that the catalyst carries out hydrazine reduction of hexavalent uranium in a tank reactor or a fixed bed reactor to prepare a tetravalent uranium solution is: the acid concentration is 0.5 in terms of hydrogen ion concentration -1.0 mol/L, the uranyl ion concentration is 0.5-1.3 mol/L, the hydrazine concentration is 0.5-2.0 mol/L, the reaction temperature is 25-70 ^o C, and the reaction pressure is normal pressure.