Method for separating rare earth and radioactive elements from monazite alkali cake

Abstract

The invention belongs to the technical field of resource recovery, and particularly discloses a method for separating rare earth and radioactive elements from a monazite alkali cake, which comprises the following steps: 1) dissolving the alkali cake to a proper pH value by using a mixed acid of hydrochloric acid and sulfuric acid; (2) adding barium chloride and an alkali cake into the acid leaching slurry until the pH is proper, precipitating radioactive elements, stirring and filtering; and 3) continuously adding the alkali cake into the filtrate until the pH value is proper, filtering to obtain a low-radioactivity rare earth chloride solution and filter residues, and returning the filter residues to the step 1) to be continuously dissolved out. According to the process method provided by the invention, efficient recovery of rare earth in the monazite alkali cake and deep separation of radioactive elements can be realized; the method has the advantages of simple operation, few added materials, high rare earth yield and good radioactive element separation effect, and develops a process route with good economic benefits and environmental protection benefits for monazite resources.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, specifically relating to a method for separating rare earth elements and radioactive elements from monazite cake. Background Technology

[0002] Monazite is rich in strategic resources such as rare earth elements, uranium, and thorium, and has the dual strategic value of rare earth and uranium resources. Its main components are phosphate minerals of Ce, La, Nd and Th, containing 50-60% REO, 0.3-0.5% U, 15-20% Th, and small amounts of impurities such as Si, Ti, Fe and Al.

[0003] The most common processing technology for monazite concentrate is the alkaline process, which mainly includes: caustic soda decomposition of the concentrate, hydrochloric acid preferential dissolution of rare earth elements to separate uranium and thorium, and barium sulfate coprecipitation for radium removal. After alkaline decomposition, monazite concentrate yields an alkaline cake (hydrochloric acid hydroxides of uranium, thorium, and rare earth elements) and a sodium phosphate solution. The alkaline cake is then dissolved in hydrochloric acid to preferentially separate uranium and thorium, bringing the pH to 1.5-3.5. At this point, some thorium and uranium also dissolve. Further alkaline cake is added for neutralization, bringing the pH to approximately 4.5, causing the dissolved thorium, uranium, iron, etc., to precipitate again. This method allows over 90% of the rare earth elements in the decomposition products to enter the solution. Filtration yields a mixed rare earth chloride solution and thorium-uranium slag. Finally, sulfuric acid and barium chloride are added to the mixed rare earth chloride solution to generate barium sulfate coprecipitate for radium removal. This process requires a relatively high pH for uranium-thorium removal. A pH of around 4.5 causes some rare earth hydrolysate to precipitate into the solvent residue, reducing the rare earth yield. If the pH is too low, uranium-thorium removal is ineffective, resulting in some uranium-thorium remaining in the rare earth chloride product. Due to the difficulty in precisely controlling the pH, the pH varies between batches, leading to inconsistent uranium-thorium content in the product, significant variations in rare earth chloride product quality, and substantial changes in yield. During radium removal, the radium removal slag also carries a large amount of rare earth. Therefore, current processes for extracting rare earth and separating radioactivity from monazite cake struggle to simultaneously achieve high rare earth recovery rates (>96%) and low radioactivity (<2000 Bq / L). Therefore, developing a more universal process to improve rare earth recovery and reduce the radioactivity of rare earth chloride products is essential. Based on this, this invention is proposed. Summary of the Invention

[0004] This invention discloses a method for separating rare earth elements and radioactive elements from monazite cake, aiming to provide a technology for efficiently extracting low-radioactive rare earth elements from monazite cake.

[0005] The monazite alkali cake is the decomposition residue obtained by alkali decomposition and washing of monazite concentrate, wherein the U content is 0.1~1%, the Th content is 5~25%, and the total rare earth content is 30~60%.

[0006] The method for separating rare earth elements and radioactive elements from monazite cake according to the present invention includes the following steps: 1) Add the mixed acid to the dissolving tank, add the monazite cake while stirring, and stir to dissolve, controlling the pH of the slurry to 0.5~1.5; 2) Add a certain amount of barium chloride to the slurry obtained in step 1), add monazite cake to adjust the pH of the slurry to 3.0~4.0 to precipitate radioactive elements, stir and filter to obtain rare earth chloride solution and high-quality slag containing radioactive elements; wash the high-quality slag, and return the washing liquid to step 1) and add it together with the mixed acid to the dissolving tank for recycling. 3) Add monazite cake to the rare earth chloride solution obtained in step 2) to adjust the pH of the slurry to 4.5~5.5, stir and filter to obtain filter residue and low radioactive rare earth chloride solution. The filter residue is returned to step 1) for further dissolution.

[0007] Preferably, the mixed acid in step 1) is a mixture of hydrochloric acid and sulfuric acid, and the molar ratio of hydrochloric acid to sulfuric acid is 50~500:1.

[0008] Preferably, the mixed acid in step 1) has [H] + The concentration is 5~12 mol / L.

[0009] Preferably, in step 1), the solution is dissolved by stirring at 5~80°C for 1~8 hours.

[0010] Preferably, the amount of barium chloride added in step 1) is 0.2 to 1.0 of the number of moles of sulfuric acid added in step 1).

[0011] Preferably, in step 2), the mixture is stirred at 5-80°C for 1-8 hours and then filtered.

[0012] Preferably, in step 3), the mixture is stirred at 5-80°C for 1-8 hours before filtration.

[0013] This invention employs a mixed acid solution containing sulfuric acid to dissolve the alkali cake, maintaining a low pH to improve the rare earth leaching rate. Then, barium chloride and alkali cake are added to control the pH of the solution to 3.0-4.0, which allows for the precipitation of radium and most of the uranium and thorium, concentrating most of the radioactive elements in the leaching residue for enrichment and separation, while rare earths show almost no precipitation. Finally, alkali cake is added to adjust the pH to 4.5-5.5, further deepening the separation of radioactive elements uranium, thorium, and radium. Higher pH results in better precipitation of uranium, thorium, and radium, and the co-precipitation of uranium and thorium also improves the radium removal efficiency. Although some rare earth elements enter the filter residue, this residue is returned to the leaching process and does not affect the rare earth yield. The process provided by this invention achieves efficient rare earth leaching, uranium-thorium-radium precipitation and separation, and deep separation of uranium-thorium-radium in stages by controlling the pH value in stages. This enables efficient recovery of rare earth elements and deep separation of radioactive elements from monazite cake, achieving a rare earth recovery rate of >96% while maintaining rare earth chloride radioactivity of <2000 Bq / L. The process requires less additives, has a high rare earth recovery rate, and provides good separation of radioactive elements, thus opening up a process route with good economic and environmental benefits for monazite resources. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0015] To further illustrate the present invention, the following detailed description, in conjunction with examples, of a method for separating rare earth elements and radioactive elements from monazite cake, should not be construed as limiting the scope of protection of the present invention.

[0016] Example 1 A certain type of monazite cake contains 0.31% U, 5.22% Th, and 30.6% total rare earth elements.

[0017] [H] + A 5 mol / L mixture of hydrochloric acid and sulfuric acid, with a molar ratio of 450:1, was added to a dissolving tank. Monazite cake was added under stirring to dissolve the slurry, adjusting the pH to 0.5. The mixture was stirred at 10°C for 8 hours. Then, 0.8 moles of barium chloride (equal to sulfuric acid) was added to the slurry, and monazite cake was added again to adjust the pH to 3.0. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a high-quality slag and a rare earth chloride solution. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Monazite cake was added to the rare earth chloride solution to adjust the slurry pH to 5.5. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a precipitate and low-radioactive rare earth chlorides. The precipitate was returned to the dissolving tank for recycling. Analysis showed a rare earth yield of 98% and a total α-radioactivity specific activity of rare earth chlorides of 1.5 × 10⁻⁶.3 Bq / L.

[0018] Example 2 A certain type of monazite cake contains 0.31% U, 5.22% Th, and 30.6% total rare earth elements.

[0019] [H] + A 10 mol / L mixture of hydrochloric acid and sulfuric acid, with a molar ratio of 50:1, was added to a dissolving tank. Monazite cake was added under stirring to dissolve the slurry, adjusting the pH to 1.5. The mixture was stirred at 80°C for 1 hour. 0.20 moles of barium chloride (equal to sulfuric acid) were added to the slurry, and monazite cake was added again to adjust the pH to 4.0. The mixture was stirred at 80°C for 1 hour. The slurry was then filtered to obtain a high-quality slag and a rare earth chloride solution. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Monazite cake was added to the rare earth chloride solution to adjust the pH to 5.0. The mixture was stirred at 80°C for 1 hour. The slurry was then filtered to obtain a precipitate and low-radioactivity rare earth chlorides. The precipitate was returned to the dissolving tank for recycling. Analysis showed a rare earth yield of 96.5% and a total α-radioactivity specific activity of rare earth chlorides of 1.9 × 10⁻⁶. 3 Bq / L.

[0020] Example 3 A certain type of monazite cake contains 0.9% U, 22.81% Th, and 59.6% total rare earth elements.

[0021] [H] + A mixture of 8 mol / L hydrochloric acid and sulfuric acid, with a molar ratio of 300:1, was added to a dissolving tank. Monazite cake was added under stirring to dissolve the slurry, adjusting the pH to 1.0. The mixture was stirred at 30°C for 4 hours. Then, 0.5 molar amounts of barium chloride (e.g., the same as sulfuric acid) were added to the slurry. Monazite cake was added again, adjusting the pH to 3.5. The mixture was stirred at 30°C for 4 hours. The slurry was filtered to obtain a high-quality slag and a rare earth chloride solution. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Monazite cake was added to the rare earth chloride solution to adjust the pH to 5.3. The mixture was stirred at 30°C for 4 hours. The slurry was filtered to obtain a precipitate and low-radioactivity rare earth chloride. The precipitate was returned to the dissolving tank for recycling. Analysis showed a rare earth yield of 97.1% and a total α-radioactivity specific activity of rare earth chloride of 1.6 × 10⁻⁶. 3 Bq / L.

[0022] Example 4 A certain type of monazite cake contains 0.9% U, 22.81% Th, and 59.6% total rare earth elements.

[0023] [H] + A 6 mol / L mixture of hydrochloric acid and sulfuric acid, with a molar ratio of 200:1, was added to a dissolving tank. Monazite cake was added under stirring to dissolve the slurry, adjusting the pH to 1.0. The mixture was stirred at 80°C for 2 hours. Then, 0.95 moles of barium chloride (equal to sulfuric acid) was added to the slurry, followed by the addition of monazite cake. The pH was adjusted to 3.2, and the mixture was stirred at 80°C for 2 hours. The slurry was filtered to obtain a high-quality slag and a rare earth chloride solution. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Monazite cake was added to the rare earth chloride solution to adjust the slurry pH to 5.3. The mixture was stirred at 80°C for 2 hours, and the slurry was filtered to obtain a precipitate and low-radioactivity rare earth chloride. The precipitate was returned to the dissolving tank for recycling. Analysis showed a rare earth yield of 97.4% and a total α-radioactivity specific activity of rare earth chloride of 1.7 × 10⁻⁶. 3 Bq / L.

[0024] Comparative Example 1 A certain type of monazite cake contains 0.31% U, 5.22% Th, and 30.6% total rare earth elements.

[0025] [H] + A 5 mol / L hydrochloric acid solution was added to a dissolving tank, and monazite cake was added under stirring to dissolve it. The pH of the slurry was adjusted to 1.5, and the mixture was stirred at 10°C for 8 hours. Monazite cake was then added to the slurry to adjust the pH to 4.5, and the mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a high-quality slag and low-radioactivity rare earth chlorides. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. 0.5 L of concentrated sulfuric acid was added to the rare earth chlorides, followed by 0.8 moles of barium chloride (e.g., the same as the concentrated sulfuric acid). The mixture was stirred at 10°C for 1 hour, and the mixture was filtered to obtain radium-removed slag and rare earth chlorides. The radium-removed slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Analysis showed that the rare earth yield was 93%, and the total α-radioactivity specific activity of the rare earth chlorides was 0.43 × 10⁻⁶. 4 Bq / L.

[0026] Comparative Example 2 A certain type of monazite cake contains 0.31% U, 5.22% Th, and 30.6% total rare earth elements.

[0027] [H] +A 5 mol / L mixture of hydrochloric acid and sulfuric acid, with a molar ratio of 450:1, was added to a dissolving tank. Monazite cake was added under stirring to dissolve the slurry, adjusting the pH to 2.0. The mixture was stirred at 10°C for 8 hours. Then, 0.8 moles of barium chloride (equal to sulfuric acid) were added to the slurry, and monazite cake was added again to adjust the pH to 3.0. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a high-quality slag and a rare earth chloride solution. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Monazite cake was added to the rare earth chloride solution to adjust the pH to 5.5. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a precipitate and low-radioactivity rare earth chlorides. The precipitate was returned to the dissolving tank for recycling. Analysis showed a rare earth yield of 94.9% and a total α-radioactivity specific activity of rare earth chlorides of 1.5 × 10⁻⁶. 3 Bq / L.

[0028] Comparative Example 3 A certain type of monazite cake contains 0.31% U, 5.22% Th, and 30.6% total rare earth elements.

[0029] [H] + A 5 mol / L mixture of hydrochloric acid and sulfuric acid, with a molar ratio of 450:1, was added to a dissolving tank. Monazite cake was added under stirring to dissolve the slurry, adjusting the pH to 0.5. The mixture was stirred at 10°C for 8 hours. Then, 0.8 moles of barium chloride (equal to sulfuric acid) was added to the slurry, and monazite cake was added again to adjust the pH to 4.5. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a high-quality slag and a rare earth chloride solution. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Monazite cake was added to the rare earth chloride solution to adjust the slurry pH to 5.5. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a precipitate and low-radioactivity rare earth chlorides. The precipitate was returned to the dissolving tank for recycling. Analysis showed a rare earth yield of 94%, and the total α-radioactivity specific activity of rare earth chlorides was 1.5 × 10⁻⁶. 3 Bq / L.

[0030] Comparative Example 4 A certain type of monazite cake contains 0.31% U, 5.22% Th, and 30.6% total rare earth elements.

[0031] [H] +A 5 mol / L mixture of hydrochloric acid and sulfuric acid, with a molar ratio of 450:1, was added to a dissolving tank. Monazite cake was added under stirring to dissolve the slurry, adjusting the pH to 0.5. The mixture was stirred at 10°C for 8 hours. Then, 0.8 moles of barium chloride (equal to sulfuric acid) was added to the slurry, and monazite cake was added again to adjust the pH to 3.0. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a high-quality slag and a rare earth chloride solution. The high-quality slag was washed, and the washing liquid was returned to the dissolving tank for recycling. Monazite cake was added to the rare earth chloride solution to adjust the slurry pH to 4.3. The mixture was stirred at 10°C for 8 hours. The slurry was filtered to obtain a precipitate and low-radioactivity rare earth chloride. The precipitate was returned to the dissolving tank for recycling. Analysis showed a rare earth yield of 98% and a total α-radioactivity specific activity of rare earth chloride of 2.25 × 10⁻⁶. 4 Bq / L.

[0032] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for separating rare earth elements and radioactive elements from monazite cake, wherein the monazite cake is a decomposition residue obtained by alkaline decomposition and washing of monazite concentrate, wherein the U content is 0.1-1%, the Th content is 5-25%, and the total rare earth content is 30-60%, characterized in that... Includes the following steps: 1) Add the mixed acid to the dissolving tank, add the monazite cake while stirring, and stir to dissolve, controlling the pH of the slurry to 0.5~1.5; 2) Add a certain amount of barium chloride to the slurry obtained in step 1), add monazite cake to adjust the pH of the slurry to 3.0~4.0 to precipitate radioactive elements, stir and filter to obtain rare earth chloride solution and high-quality slag containing radioactive elements; wash the high-quality slag, and return the washing liquid to step 1) and add it together with the mixed acid to the dissolving tank for recycling. 3) Add monazite cake to the rare earth chloride solution obtained in step 2) to adjust the pH of the slurry to 4.5~5.5, stir and filter to obtain filter residue and low radioactive rare earth chloride solution. The filter residue is returned to step 1) for further dissolution.

2. The method according to claim 1, characterized in that, The mixed acid mentioned in step 1) is a mixture of hydrochloric acid and sulfuric acid, with a molar ratio of hydrochloric acid to sulfuric acid of 50~500:

1.

3. The method according to claim 1, characterized in that, The mixed acid described in step 1) has [H] + The concentration is 5~12 mol / L.

4. The method according to claim 1, characterized in that, In step 1), the mixture is stirred at 5-80°C for 1-8 hours to dissolve it.

5. The method according to claim 1, characterized in that, The amount of barium chloride added in step 1) is 0.2 to 1.0 of the number of moles of sulfuric acid added in step 1).

6. The method according to claim 1, characterized in that, In step 2), stir at 5~80℃ for 1~8 hours and then filter.

7. The method according to claim 1, characterized in that, In step 3), the mixture is stirred at 5-80℃ for 1-8 hours and then filtered.

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