Method for Recovering Metallic Uranium from Fluorination Residue

Abstract

Method for recovering metallic uranium from fluorination slag, wherein the fluorination slag is the slag generated during the preparation of UF6 in a fluorination furnace, and its components include uranium fluoride and impurity metal fluorides; the steps are as follows: 1. Pretreatment; 2. Dissolving uranium fluoride: Place the fluorination slag in a reaction kettle, first add hydrogen peroxide to the reaction kettle, and then add an excessive amount of potassium carbonate solution to the reaction kettle to fully react and dissolve the uranium fluoride in the fluorination slag; 3. Filtering out impurities; 4. Acidification treatment; 5. Recovering metallic uranium: Add solid potassium hydroxide to the acidified solution to promote the reaction of uranium oxyfluoride to form potassium diuranate slag and obtain an alkaline solution; after the reaction is complete, filter out the potassium diuranate slag in the alkaline solution. The advantages of the present invention are that it realizes the transformation of complex fluorination slag into potassium diuranate slag with a single component, and the potassium diuranate slag can be collected together with the potassium diuranate slag recovered in the uranium conversion wastewater recovery system, which is convenient for further research and recovery in the later stage.

Description

Technical Field

[0001] The present invention relates to the technical field of uranium conversion, and particularly to a method for recovering metallic uranium from fluorination slag. Background Art

[0002] The fluorination furnace is a key equipment for preparing uranium hexafluoride from natural uranium conversion. During the reaction to prepare uranium hexafluoride (UF6), a certain amount of fluorination slag (0.3%-0.8%) will be generated. The main chemical components of the fluorination slag are uranium fluorides (UF4, UF5, U2F9, U4F 17 ), and its uranium content can reach up to 40%-60%, which has high recycling value. In addition to metallic uranium elements, the fluorination slag also contains other metal impurity elements and fluorine elements. The content of metal impurity elements can reach 30 mg / L, and the fluoride ion concentration is 160 g / L. How to remove the metal impurity elements and fluorine elements in the fluorination slag has become the key to recovering metallic uranium from the fluorination slag.

[0003] At present, the domestic production capacity of uranium hexafluoride is small, and the output of fluorination slag is also small. There is not much research in this regard. Each uranium hexafluoride production unit stores the fluorination slag in a sealed container. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for recovering metallic uranium from fluorination slag, which realizes the recycling of metallic uranium in the fluorination slag, is easy to industrialize, and has significant economic and environmental benefits.

[0005] The technical solution of the present invention is: a method for recovering metallic uranium from fluorination slag, wherein the fluorination slag is the slag generated during the preparation of UF6 by a fluorination furnace, and its components include uranium fluoride and impurity metal fluoride;

[0006] The method steps are as follows:

[0007] S01, pretreatment: Place the fluorination slag in a special workshop with a lead shielding layer and let it stand naturally for 3-5 months to reduce its radioactivity intensity to the natural uranium level;

[0008] S02, dissolve uranium fluoride: Place the standing fluorination slag in a reaction kettle, first add hydrogen peroxide with a mass concentration of 30% to the reaction kettle, and then add an excessive amount of potassium carbonate solution with a mass concentration of 50% to the reaction kettle. Control the dissolution temperature at 85-95°C and stir evenly to make the uranium fluoride in the fluorination slag fully react and dissolve to obtain a uranyl solution;

[0009] The following chemical reactions occur in the above process:

[0010] 2UF5 + 2H2O = UO2F2 + UF4 + 4HF;

[0011] 2U2F9 + 2H2O = UO2F2 + 3UF4 + 4HF;

[0012] 2U4F 17 + 2H2O = UO2F2 + 7UF4 + 4HF;

[0013] UO2F2 + 3K2CO3 = K4[UO2(CO3)3] + 2KF;

[0014] UF4 + 4K2CO3 + H2O2 = K4[UO2(CO3)3] + 4KF + H2O + CO2↑;

[0015] S03, Filter out impurities: Filter out the precipitate in the uranyl solution to obtain a clear uranyl solution. The precipitate is an impurity metal fluoride;

[0016] S04, Acidification treatment: Add hydrofluoric acid with a mass concentration of 40% to the clear uranyl solution, stir evenly, adjust the pH value to 3, and control the temperature at 70 - 90°C to remove the carbonate in the clear uranyl solution, thereby obtaining an acidified solution;

[0017] The following chemical reactions occur during the above process:

[0018] 6HF + K4[UO2(CO3)3] = 4KF + UO2F2 + 3CO2↑ + 3H2O;

[0019] S05, Recover metallic uranium:

[0020] Add solid potassium hydroxide to the acidified solution, stir evenly, adjust the pH value to 13, and control the temperature at 70 - 90°C to promote the reaction of uranyl fluoride to form potassium diuranate slag and obtain an alkaline solution; After the reaction is complete, filter out the potassium diuranate slag in the alkaline solution, which achieves the purpose of recovering metallic uranium and obtains a clear alkaline solution;

[0021] The following chemical reactions occur during the above process:

[0022] KOH + UO2F2 = KU2O7↓ + KF.

[0023] A further technical solution of the present invention is: The fluorination slag is divided into multiple grades according to the mass concentration of the impurity metal fluoride from low to high, namely the primary slag, the secondary slag, the tertiary slag... the Nth slag;

[0024] The method for obtaining the primary slag is as follows: Collect the slag generated by preparing UF6 from the UF4 raw material through a fluorination furnace, and the primary slag is obtained;

[0025] The method for obtaining the secondary fluorination slag is as follows: 1. Place the primary fluorination slag in a special workshop with a lead shielding layer, and let it stand for 3 - 5 months to reduce its radioactivity intensity to the natural uranium level; 2. Crush the standing primary fluorination slag and screen out the materials with a particle size below 20 μm; 3. Uniformly mix the screened primary fluorination slag and UF4 raw material in a ratio of 1:10, and collect the slag generated by preparing UF6 from this mixture through a fluorination furnace, then the secondary fluorination slag is obtained;

[0026] The method for obtaining the tertiary fluorination slag is as follows: 1. Place the secondary fluorination slag in a special workshop with a lead shielding layer, and let it stand for 3 - 5 months to reduce its radioactivity intensity to the natural uranium level; 2. Crush the standing secondary fluorination slag and screen out the materials with a particle size below 20 μm; 3. Uniformly mix the screened secondary fluorination slag and UF4 raw material in a ratio of 1:10, and collect the slag generated by preparing UF6 from this mixture through a fluorination furnace, then the tertiary fluorination slag is obtained;

[0027] The method for obtaining the fluorination slag of subsequent grades can be deduced by analogy and will not be elaborated here;

[0028] Start monitoring the mass concentration of impurity metal fluorides from the secondary fluorination slag. When the mass concentration of impurity metal fluorides > 1.5%, stop obtaining the fluorination slag of subsequent grades, and use the fluorination slag of the current grade for the recovery of metallic uranium.

[0029] A further technical solution of the present invention is: it further includes step S06 following step S05; S06, post - treatment: Excessively add light calcium carbonate powder to the alkaline clear liquid, stir evenly until the pH value drops below 10, and filter the reacted solution; collect and temporarily store the obtained calcium fluoride slag, and return the obtained potassium carbonate solution to step S02 for use;

[0030] The following chemical reactions occur in the above process:

[0031] 2KF + CaCO3 = CaF2↓ + K2CO3.

[0032] A further technical solution of the present invention is: In step S02, the weight ratio of the fluorination slag to hydrogen peroxide is 5:2; control the dissolution temperature at 90°C.

[0033] A further technical solution of the present invention is: In steps S04 and S05, add hydrofluoric acid and solid potassium hydroxide respectively according to the molar amounts required for the reaction.

[0034] The present invention has the following advantages compared with the prior art:

[0035] 1. On the one hand, the recycling of fluorinated slag is realized, improving the utilization efficiency of metallic uranium. On the other hand, the transformation of complex fluorinated slag into single-component potassium diuranate slag is achieved. The potassium diuranate slag can be collected together with the potassium diuranate slag recovered in the uranium conversion wastewater recovery system, facilitating further research on recovery in the later stage.

[0036] 2. By using the selective dissolution of potassium carbonate and hydrogen peroxide in uranium fluoride, the key problem of removing other metal fluoride impurities from fluorinated slag is solved.

[0037] 3. The process route basically does not generate wastewater, realizes the recycling of potassium carbonate solution, and is easy to industrialize, with significant economic and environmental benefits. Specific implementation mode

[0038] Example 1:

[0039] A method for recovering metallic uranium from fluorinated slag. The fluorinated slag is the slag generated in the process of preparing UF6 in a fluorination furnace, and its components include uranium fluoride and impurity metal fluorides. The fluorinated slag is divided into multiple grades according to the mass concentration of impurity metal fluorides from low to high, namely primary slag, secondary slag, tertiary slag... Nth slag.

[0040] The method for obtaining primary slag is as follows: Collect the slag generated by preparing UF6 from UF4 raw materials through a fluorination furnace, and the primary slag is obtained.

[0041] The method for obtaining secondary slag is as follows: 1. Place the primary slag in a special workshop with a lead shielding layer and let it stand for 3 - 5 months to reduce its radioactivity intensity to the natural uranium level; 2. Crush the standing primary slag and screen out the materials below 20um; 3. Uniformly mix the screened primary slag and UF4 raw materials in a ratio of 1:10, and collect the slag generated by preparing UF6 from this mixture through a fluorination furnace, and the secondary slag is obtained.

[0042] The method for obtaining tertiary slag is as follows: 1. Place the secondary slag in a special workshop with a lead shielding layer and let it stand for 3 - 5 months to reduce its radioactivity intensity to the natural uranium level; 2. Crush the standing secondary slag and screen out the materials below 20um; 3. Uniformly mix the screened secondary slag and UF4 raw materials in a ratio of 1:10, and collect the slag generated by preparing UF6 from this mixture through a fluorination furnace, and the tertiary slag is obtained.

[0043] The methods for obtaining subsequent grades of fluorinated slag can be deduced by analogy and will not be elaborated here.

[0044] Start monitoring the mass concentration of impurity metal fluorides from the second-grade fluorinated slag. When the mass concentration of impurity metal fluorides > 1.5%, stop obtaining fluorinated slag of subsequent grades, and use the fluorinated slag of the current grade for the recovery of metallic uranium.

[0045] The method steps are as follows:

[0046] S01, Pretreatment: Place the fluorinated slag in a dedicated workshop with a lead shielding layer, and let it stand naturally for 3 - 5 months to reduce its radioactivity intensity to the level of natural uranium.

[0047] S02, Dissolve uranium fluoride: Place the standing fluorinated slag in a reaction kettle. First, add hydrogen peroxide with a mass concentration of 30% to the reaction kettle, and then add an excessive amount of potassium carbonate solution with a mass concentration of 50% to the reaction kettle. Control the dissolution temperature at 90°C and stir evenly to fully react and dissolve the uranium fluoride in the fluorinated slag to obtain a uranyl solution;

[0048] The following chemical reactions occur in the above process:

[0049] 2UF5 + 2H2O = UO2F2 + UF4 + 4HF;

[0050] 2U2F9 + 2H2O = UO2F2 + 3UF4 + 4HF;

[0051] 2U4F 17 + 2H2O = UO2F2 + 7UF4 + 4HF;

[0052] UO2F2 + 3K2CO3 = K4[UO2(CO3)3] + 2KF;

[0053] UF4 + 4K2CO3 + H2O2 = K4[UO2(CO3)3] + 4KF + H2O + CO2↑;

[0054] In this step, the weight ratio of the fluorinated slag to hydrogen peroxide is 5:2.

[0055] S03, Filter out impurities: Filter out the precipitate in the uranyl solution to obtain a clear uranyl solution. The precipitate is impurity metal fluoride.

[0056] S04, Acidification treatment: Add hydrofluoric acid with a mass concentration of 40% to the clear uranyl solution, stir evenly, adjust the pH value to 3, and control the temperature at 70 - 90°C to remove the carbonate in the clear uranyl solution, thereby obtaining an acidified solution;

[0057] The following chemical reactions occur in the above process:

[0058] 6HF + K4[UO2(CO3)3] = 4KF + UO2F2 + 3CO2↑ + 3H2O;

[0059] In this step, hydrofluoric acid is added according to the molar amount required for the reaction.

[0060] S05, recovering uranium metal:

[0061] Solid potassium hydroxide is added to the acidified solution, and it is stirred evenly to adjust the pH value to 13, and the temperature is controlled at 70-90 °C to promote the reaction of uranium oxyfluoride to form potassium diuranate slag and obtain an alkaline solution; after the reaction is complete, the potassium diuranate slag in the alkaline solution is filtered out, thus achieving the purpose of recovering uranium metal and obtaining an alkaline clear liquid;

[0062] The following chemical reactions occur in the above process:

[0063] KOH + UO2F2 = KU2O7↓ + KF;

[0064] In this step, solid potassium hydroxide is added according to the molar amount required for the reaction.

[0065] S06, post-treatment: An excessive amount of light calcium carbonate powder is added to the alkaline clear liquid, and it is stirred evenly until the pH value drops below 10, and the reaction solution is filtered; the obtained calcium fluoride slag is collected and temporarily stored, and the obtained potassium carbonate solution is returned to the S02 step for use;

[0066] The following chemical reactions occur in the above process:

[0067] 2KF + CaCO3 = CaF2↓ + K2CO3.

[0068] In this example, the fluorinated slag is measured to contain 68.2% uranium and 30.8% fluorine. In the recovered potassium diuranate slag, the dissolution rate of uranium is 89.7% (uranium content in potassium diuranate slag / uranium content in fluorinated slag). The uranium content in the final recovered liquid (potassium carbonate solution filtered in the S06 step) is lower than 1 mg / L, and the fluorine content is lower than 2 g / L, meeting the wastewater recycling standard.

[0069] Example 2:

[0070] This example is different from Example 1 only in the substance content in the fluorinated slag.

[0071] In this example, the fluorinated slag is measured to contain 71.3% uranium and 27.6% fluorine. In the recovered potassium diuranate slag, the dissolution rate of uranium is 91.5% (uranium content in potassium diuranate slag / uranium content in fluorinated slag). The uranium content in the final recovered liquid (potassium carbonate solution filtered in the S06 step) is lower than 0.7 mg / L, and the fluorine content is lower than 2 g / L, meeting the wastewater recycling standard.

Claims

1. A method for recovering metallic uranium from fluorination slag, wherein the fluorination slag is the slag generated during the preparation of UF6 in a fluorination furnace, and its composition includes uranium fluoride and impurity metal fluoride; It is characterized in that, The method steps are as follows: S01, Pretreatment: Place the fluorinated slag in a dedicated workshop with a lead shielding layer and let it stand naturally for 3 to 5 months to reduce its radioactive intensity to the natural uranium level; S02, Dissolve uranium fluoride: Place the standing fluorinated slag in a reaction kettle. First, add hydrogen peroxide with a mass concentration of 30% to the reaction kettle, and then add an excessive amount of potassium carbonate solution with a mass concentration of 50% to the reaction kettle. Control the dissolution temperature at 85 - 95 °C and stir evenly to fully react and dissolve the uranium fluoride in the fluorinated slag to obtain a uranyl solution; The following chemical reactions occur in the above process: 2UF5 + 2H2O = UO2F2 + UF4 + 4HF; 2U2F9 + 2H2O = UO2F2 + 3UF4 + 4HF; 2U4F 17 + 2H2O = UO2F2 + 7UF4 + 4HF; UO2F2 + 3K2CO3 = K4[UO2(CO3)3] + 2KF; UF4 + 4K2CO3 + H2O2 = K4[UO2(CO3)3] + 4KF + H2O + CO2↑; S03, Filter out impurities: Filter out the precipitate in the uranyl solution to obtain a clear uranyl solution. The precipitate is impurity metal fluoride; S04, Acidification treatment: Add hydrofluoric acid with a mass concentration of 40% to the clear uranyl solution, stir evenly, adjust the pH value to 3, and control the temperature at 70 - 90 °C to remove the carbonate in the clear uranyl solution, thereby obtaining an acidified solution; The following chemical reactions occur in the above process: 6HF + K4[UO2(CO3)3] = 4KF + UO2F2 + 3CO2↑ + 3H2O; S05, Recover metallic uranium: Add solid potassium hydroxide to the acidified solution, stir evenly, adjust the pH value to 13, and control the temperature at 70 - 90 °C to promote the reaction of uranium oxyfluoride to form potassium diuranate slag and obtain an alkaline solution; After the reaction is complete, filter out the potassium diuranate slag in the alkaline solution, which achieves the purpose of recovering metallic uranium and obtains an alkaline clear solution; The following chemical reactions occur in the above process: KOH + UO2F2 = KU2O7↓ + KF; S06, Post-treatment: Add an excessive amount of light calcium carbonate powder to the alkaline clear solution, stir evenly until the pH value drops below 10, and filter the reacted solution; Collect and temporarily store the calcium fluoride slag, and return the obtained potassium carbonate solution to step S02 for use; The following chemical reactions occur in the above process: 2KF + CaCO3 = CaF2↓ + K2CO3.

2. The method for recovering metallic uranium from fluorination slag according to claim 1, characterized in that: The fluorinated slag is divided into multiple grades according to the mass concentration of impurity metal fluoride from low to high, namely primary slag, secondary slag, tertiary slag... Nth slag; The method for obtaining the primary slag is as follows: Collect the slag generated by preparing UF6 from UF4 raw materials through a fluorination furnace, and the primary slag is obtained; The method for obtaining the secondary slag is as follows:

1. Place the primary slag in a dedicated workshop with a lead shielding layer and let it stand for 3 to 5 months to reduce its radioactive intensity to the natural uranium level; 2. Crush the standing primary slag and screen out the materials with a particle size below 20um; 3. Uniformly mix the screened primary slag and UF4 raw materials in a ratio of 1:10, and collect the slag generated by preparing UF6 from this mixture through a fluorination furnace to obtain the secondary slag; The method for obtaining the third-grade fluorination slag is as follows:

1. Place the second-grade fluorination slag in a special workshop with a lead shielding layer and let it stand for 3 to 5 months to reduce its radioactive intensity to the natural uranium level; 2. Crush the second-grade fluorination slag after standing and screen out the materials with a particle size below 20 μm; 3. Uniformly mix the screened second-grade fluorination slag with UF4 raw material in a ratio of 1:10, and collect the slag generated by preparing UF6 from this mixture through a fluorination furnace, then the third-grade fluorination slag is obtained; The method for obtaining the subsequent-grade fluorination slag can be deduced by analogy and will not be elaborated here; Start monitoring the mass concentration of impurity metal fluorides from the second-grade fluorination slag. When the mass concentration of impurity metal fluorides > 1.5%, stop obtaining the subsequent-grade fluorination slag, and use the current-grade fluorination slag for the recovery of metallic uranium.

3. The method for recovering metallic uranium from fluorination slag according to claim 2, characterized in that: In step S02, the weight ratio of the fluorination slag to hydrogen peroxide is 5:2; control the dissolution temperature at 90°C.

4. The method for recovering metallic uranium from fluorination slag according to claim 3, characterized in that: In steps S04 and S05, add hydrofluoric acid and solid potassium hydroxide respectively according to the molar amounts required for the reaction.