A method for treating acid leach residue and recovering rare earths

Abstract

The application provides a method for extracting and separating thorium from rare earth ore radioactive acid leaching residue, comprising the following steps: mixing and extracting the rare earth ore radioactive acid leaching residue with an organic extractant, extracting the thorium in the rare earth ore radioactive acid leaching residue leaching solution into an organic phase, so as to separate the rare earth and the thorium; wherein the organic extractant is composed of an ionic liquid and an extraction solvent; the ionic liquid is selected from at least one of [N 1888 ][DOO], [N 1888 ][DEAO] and [N 1888 ][DDO]; and the extraction solvent is selected from at least one of 260# kerosene, n-heptane, toluene and n-hexane. The method of the application does not depend on acid in the extraction process, reduces the use of alkali, and only uses a washing liquid for washing. The ionic liquid concentration of the extractant used in the extraction process is low, which is beneficial to improve the separation effect of the extractant on the rare earth and the thorium, and no salting agent is additionally added in the extraction process, which helps to reduce the use of salt and the generation of salt-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the field of rare earth separation technology, specifically relating to a method for treating acid-soluble residue and recovering rare earths using ionic liquids. Background Technology

[0002] Thorium is a typical metallic element in common industrial systems that is easy to extract but difficult to back-extract. As a tetravalent element, it is relatively easier to extract than trivalent elements, but it tends to remain in the organic phase, significantly impacting the purity of easily extractable rare earth components exiting the organic phase using cascade extraction processes. In common rare earth industries, the P507 process for thorium separation requires a lengthy and complex back-extraction process to remove it. Besides the aforementioned separation difficulties, common acidic extractants often require alkali for back-extraction, making it difficult to achieve ideal results. For example, alkaline back-extraction agents can react with acidic extractants, affecting the recycling of the acidic extractants and ultimately significantly reducing the back-extraction effect. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for extracting and separating thorium from radioactive acid-dissolved slag of rare earth minerals, comprising the following steps:

[0004] The radioactive acid-soluble residue of rare earth ore is mixed with an organic extractant for extraction, and thorium in the leachate of the radioactive acid-soluble residue of rare earth ore is extracted into the organic phase, thereby separating rare earth and thorium.

[0005] The organic extractant consists of an ionic liquid and an extraction solvent; the ionic liquid is selected from [N...]. 1888 [DOO], [N] 1888 ][DEAO] and [N 1888 At least one of [DDO]; the extraction solvent is selected from at least one of 260# kerosene, n-heptane, toluene, and n-hexane;

[0006] The structures of the three ionic liquids are shown below:

[0007]

[0008] According to an embodiment of the present invention, the leachate of the radioactive acid-soluble residue of the rare earth ore is prepared by leaching the radioactive acid-soluble residue of the rare earth ore six times consecutively using 6 mol / L hydrochloric acid.

[0009] According to an embodiment of the present invention, the concentration of thorium in the leachate of the radioactive acid leaching residue of the rare earth ore before extraction is 7-10 mg / L; after extraction, the concentration of thorium is less than 0.8 mg / L, preferably less than 0.6 mg / L, for example 0.5 mg / L.

[0010] According to an embodiment of the present invention, the concentration of the ionic liquid in the organic extractant is 0.02-0.08 mol / L, preferably 0.02-0.04 mol / L.

[0011] According to an embodiment of the present invention, the volume ratio of the organic extractant to the leachate is (1-2):1, preferably (1.2-1.5):1.

[0012] According to an embodiment of the present invention, the method further includes a step of washing the obtained organic phase with a washing solution, wherein the washing solution is selected from NH4HCO3, Na2CO3 or NaHCO3, preferably NH4HCO3; the concentration of the washing solution is 0.01 to 0.05 mol / L.

[0013] According to an embodiment of the present invention, the volume ratio of the organic extractant to the washing liquid is (1-2):1, preferably (1.2-1.5):1.

[0014] According to an embodiment of the present invention, the method further includes back-extracting the thorium-containing organic phase obtained after extraction using a back-extracting agent. The back-extracting agent used is a combination of sodium hydroxide, sodium oxalate, hydrochloric acid, oxalic acid, NH4HCO3, NH4HCO3, and sodium hydroxide, or a combination of sodium oxalate and sodium hydroxide. The sodium oxalate is a saturated aqueous solution, and the concentration of the other back-extracting agents is 0.5–3 mol / L, for example, 1.5 mol / L. The volume ratio of the back-extracting agent to the thorium-containing organic phase is 1–5:1, for example, 1–3:1.

[0015] According to an embodiment of the present invention, the extraction is performed in stages 1 to 10, such as stages 2 to 8, or stages 4 to 6.

[0016] According to an embodiment of the present invention, the washing is of grade 1 to 10, for example, grade 3 to 7.

[0017] As an example, the extraction is a cascade process of four-stage extraction and three-stage washing.

[0018] According to an embodiment of the present invention, the method further includes the step of recycling the back-extracted organic phase as an organic extractant.

[0019] Beneficial effects

[0020] This invention addresses the resource and environmental challenges posed by radioactive acid-leached slag from ionic rare earth mines in southern China. It utilizes an organic extractant containing ionic liquids to extract and separate thorium, meeting the thorium removal requirements of the leaching solution for these ionic rare earth ore acid-leached slags. The extraction process involves cascade extraction, yielding a rare earth solution with a thorium content of less than 0.6 mg / L. This cascade extraction process is acid-free, reducing the use of alkalis; only a washing solution is used for washing. The low concentration of ionic liquids in the extractant improves the separation efficiency of rare earths and thorium (facilitating thorium cleaning and recovery). Furthermore, no additional salting-out agent is added during the extraction process, reducing salt usage and the generation of saline wastewater. After extraction, a back-extraction agent is used to enrich and separate thorium. After five cycles of back-extraction, the extraction rate remains above 70%, demonstrating good back-extraction efficiency. The alkaline liquids generated during extraction (including wastewater and washing solution) can be recycled and added to the leaching solution for pH adjustment, ensuring that no excess wastewater or waste salt is generated during the extraction process. This reduces the environmental and storage pressures on rare earth industrial waste to some extent. It enables the effective utilization of rare earth elements in acid-soluble slag and facilitates the collection of the radioactive element thorium.

[0021] Finally, the saturated loading capacity of the ionic liquid for thorium (IV) in the organic extractant of this invention is 1.02 g / L, and slope analysis shows that the ratio of the ionic liquid to thorium (IV) in the extractant is close to 4. However, the thorium content in southern ionic rare earth ores is low, and the thorium content increases after being enriched in the acid-soluble slag. But according to reports, the highest thorium concentration in the leachate of acid-soluble ion-adsorption rare earth ores can reach 25 mg / L, which is far lower than the loading capacity of the ionic liquid for thorium (IV) in the organic extractant of this invention. Therefore, the method of this invention can meet the needs of treating thorium in actual leachates. Attached Figure Description

[0022] Figure 1 This is a flowchart of the extraction process in the extraction unit of the extraction section.

[0023] Figure 2 The extraction effects of several back-extraction agents are shown.

[0024] Figure 3 This is a cycle experiment for the back-extraction process.

[0025] Figure 4 The extraction effects of three different ionic liquids are shown. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0027] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0028] In the examples below, the concentrations / contents of rare earth elements and thorium were obtained by ICP-OES measurement.

[0029] Preparation Example 1: Three Ionic Liquid Extractants [N] 1888 [DOO], [N] 1888 ][DEAO] and [N 1888 Preparation process of [DDO]

[0030] 1) Add appropriate amounts of dichloromethane and triethylamine to three round-bottom flasks, then add 0.1 mol of diisooctylamine, di-n-octylamine, and didecylamine respectively, and cool by standing in ice water for 10 minutes. Weigh 0.11 mol of oxaloyl chloride monoethyl ester into each flask, dilute each with 30 mL of dichloromethane, and add the solution dropwise to the cooled mixture. After reacting for 30 minutes, wash the product twice with deionized water, and then concentrate under reduced pressure. Add 80 mL of ethanol and 20 mL of water to each of the three concentrated solutions, add 8 g of sodium hydroxide, and reflux at 80 °C for 4 hours. Add an appropriate amount of acid to the cooled mixture to adjust the pH of the solution to about 1. Add an appropriate amount of dichloromethane to extract the product, remove the aqueous phase, and wash the organic phase twice with deionized water.

[0031] 2) Prepare ionic liquids from the three carboxylic acids obtained in step 1): Dissolve approximately 0.01 mol of each of the three acids prepared in step 1) in an appropriate amount of methanol, and add 0.01 mol of methyltrioctylammonium chloride, an appropriate amount of 5 mol / L sodium hydroxide solution, and a small amount of water. Adjust the pH of the solution to approximately 8, react for 4 hours, and after the reaction is complete, distill under reduced pressure to obtain a viscous liquid. Add an appropriate amount of n-heptane to dissolve the ionic liquid, and wash with water. Finally, remove n-heptane by reduced pressure distillation, and dry in a vacuum oven for 12 hours to obtain the final product. The structures of the three ionic liquids are shown below.

[0032]

[0033] Preparation Example 2: Preparation of Leachate from Radioactive Acid-Soluble Residue of Southern Ionic Rare Earth Ore

[0034] The specific composition of the leaching solution of radioactive acid-soluble residue from southern ionic rare earth ore obtained by multiple leaching with 6 mol / L hydrochloric acid is shown in Table 1 below:

[0035] Table 1

[0036]

[0037] The thorium content was 7.06 mg / L.

[0038] Example 1

[0039] Use [N] 1888 [DEAO] was used to extract the leaching solution of the radioactive acid-soluble residue from the above-mentioned southern ionic rare earth ore. [N] 1888 [DEAO] was dissolved in 5 mL of 260# kerosene to form an organic extractant, and an equal volume of leachate (i.e., the feed solution, which is the aqueous phase) was added. The mixture was shaken at 25°C for 30 minutes to ensure extraction equilibrium. The washing agent used during the extraction process was NH4HCO3 (0.03 mol / L), and the back-extraction agent was a combination of saturated NaC2O4 solution and NaOH solution (where the concentration of NaOH solution was 1.5 mol / L, and the volume ratio of NaC2O4 solution to NaOH solution was 1:1).

[0040] The extraction process employs four-stage extraction and three-stage washing. After a total of 12 equilibration stages, thorium can be extracted into the organic phase, while the thorium content at the rare earth aqueous phase outlet can be controlled below 0.6 mg / L (the amounts of organic phase, feed solution, and detergent used in the extraction process are shown in Table 2 below). Figure 1 This is the extraction unit in the extraction section. Through these two stages of extraction, the extractant extracts relatively little rare earth, thus resulting in minimal rare earth loss. After the above cascade extraction, the rare earth recovery rate at the aqueous phase outlet is greater than 95%, while the thorium content is controlled below 0.6 mg / L (obtained by ICP-OES testing). This effectively achieves the recovery of rare earth from the waste leachate and the removal of the radioactive element thorium.

[0041] Table 2

[0042]

[0043] Note: The above ionic liquid concentration refers to the concentration of the ionic liquid in the organic phase.

[0044] The flow ratio is the volume ratio.

[0045] The thorium-containing organic phase was back-extracted using a combination of NaC₂O₄ and NaOH solutions (the volume ratio of the back-extraction solution to the organic phase was 1:1). After back-extraction, the thorium content in the aqueous phase was 5 mg / L. Since NaC₂O₄ forms a precipitate with thorium, thorium can be effectively precipitated and enriched.

[0046] This embodiment employs a four-stage extraction and three-stage washing process within a cascade cycle. Through repeated equilibration between the organic and aqueous phases, the ratio of metal ions in the organic and aqueous phases continuously changes during extraction. The easily extractable component, thorium, is transferred from the aqueous phase to the organic phase, while the difficult-to-extract components in the organic phase are continuously transferred to the aqueous phase with the addition of washing solution, resulting in effective separation. Finally, under the action of the newly added organic phase and washing solution, the difficult-to-extract and easily extractable components in both the aqueous and organic phases are purified and discharged to their corresponding outlets, completing the cascade separation.

[0047] Example 2

[0048] Following the same procedure as in Example 1, several other back-extraction agents (sodium hydroxide, sodium oxalate, hydrochloric acid, oxalic acid, NH4HCO3, a combination of NH4HCO3 and sodium hydroxide, and a combination of sodium oxalate and sodium hydroxide) were also used for thorium back-extraction, and the results were as follows: Figure 2 As shown. Except for saturated Na₂C₂O₄, the concentration of all other back-extraction agents was 1.5 mol / L, and the volume ratio of the two in the composition was 1:1. [N] 1888 [DEAO] = 0.015 mol / L, and the volume ratio of the back-extraction solution to the organic phase is 1:1. From Figure 2 It can be seen that the back-extraction agents used can achieve the back-extraction enrichment of thorium, and most of the back-extraction agents used are alkaline, which will not affect the structure of the extractant and can be reused.

[0049] Example 3

[0050] Following the same procedure as in Example 1, the supported organic phase was back-extracted and cycled using a combination of saturated NaC₂O₄ solution and NaOH solution (2.5 mL saturated NaC₂O₄ solution + 2.5 mL 5 mol / L NaOH solution, rare earth concentration [RE] = [Th] = 0.002 mol / L, [N] = 0.002 mol / L). 1888 [DEAO] = 0.015 mol / L). After four back-extractions and five extractions, the results are as follows: Figure 3 As shown in the figure, the extraction efficiency of thorium ions can be consistently maintained above 70%. This indicates that the ionic liquid extractant [N 1888 [DEAO] remains stable during back-extraction and extraction processes, enabling multiple cycles. This good cycle stability ensures [N] 1888 [DEAO] maintained good separation performance in subsequent cascade extraction studies, laying the foundation for the design and successful implementation of cascade extraction.

[0051] Example 4

[0052] Extraction was performed using three ionic liquids in the same manner as in Example 1 (where rare earth concentration [RE] = [Th] = 0.002 mol / L, pH = 2.4, and extractant concentration = 0.02 mol / L). The extraction results are as follows: Figure 4 As shown, by Figure 4 It can be seen that the three ionic liquids have comparable extraction effects on thorium (Th) in the leaching solution of radioactive acid slag from rare earth minerals (extraction rate close to 99%), while the extraction rate on other rare earth elements is only below 10%. Therefore, they can all achieve effective separation of thorium and rare earth elements.

[0053] Example 5 Extraction Capacity Experiment

[0054] The specific testing method is as follows: using a thorium-containing solution ([ThCl4] = 0.01 mol / L) and [N 1888 [DEAO] was extracted at pH = 2.4, wherein the organic phase contained [N] 1888 [DEAO] = 0.04 mol / L. Five aliquots of fresh feed solution were used sequentially for organic phase extraction. ICP-OES analysis was performed to obtain [N] 1888 The extraction capacity of ][DEAO] for thorium is 1.02 g / L.

[0055] The test results above show that the saturated loading capacity of the ionic liquid for thorium (IV) in the organic extractant of this invention is 1.02 g / L. Slope analysis indicates that the ratio of the ionic liquid to thorium (IV) in the extractant is close to 4. However, the thorium content in southern ionic rare earth ores is low, and the content increases after thorium is enriched in the acid-soluble slag. According to reports, the highest thorium concentration in the leachate of acid-soluble ion-adsorption rare earth ores can reach 25 mg / L, which is far lower than the loading capacity of the ionic liquid for thorium (IV) in the organic extractant of this invention. Therefore, the method of this invention can meet the needs of treating thorium in actual leachates.

[0056] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for extracting and separating thorium from radioactive acid-dissolved residue of rare earth minerals, characterized in that, Includes the following steps: The leaching solution of radioactive acid slag from rare earth mines is mixed with an organic extractant for extraction, thereby extracting thorium from the leaching solution into the organic phase, thus separating rare earth and thorium. The organic extractant consists of an ionic liquid and an extraction solvent; the ionic liquid is selected from [N...]. 1888 [DOO], [N] 1888 ][DEAO] and [N 1888 At least one of [DDO]; the extraction solvent is selected from at least one of 260# kerosene, n-heptane, toluene, and n-hexane; The structures of the three ionic liquids are shown below: ； The concentration of the ionic liquid in the organic extractant is 0.02-0.08 mol / L.

2. The method according to claim 1, characterized in that, The rare earth ore radioactive acid leaching solution was prepared by leaching the rare earth ore radioactive acid leaching residue six times consecutively using 6 mol / L hydrochloric acid.

3. The method according to claim 1, characterized in that, Before extraction, the concentration of thorium in the leaching solution of the radioactive acid residue of the rare earth ore was 7-10 mg / L; after extraction, the concentration of thorium was below 0.8 mg / L.

4. The method according to claim 1, characterized in that, The concentration of the ionic liquid in the organic extractant is 0.02-0.04 mol / L.

5. The method according to claim 1, characterized in that, The volume ratio of the organic extractant to the leachate is (1~2):

1.

6. The method according to any one of claims 1-5, characterized in that, The method further includes a step of washing the obtained organic phase with a washing solution selected from NH4HCO3, Na2CO3 or NaHCO3; the concentration of the washing solution is 0.01~0.05 mol / L.

7. The method according to claim 6, characterized in that, The volume ratio of the organic extractant to the washing liquid is (1~2):

1.

8. The method according to any one of claims 1-5, characterized in that, The method further includes back-extracting the thorium-containing organic phase obtained after extraction using a back-extracting agent. The back-extracting agent used is a combination of sodium hydroxide, sodium oxalate, hydrochloric acid, oxalic acid, NH4HCO3, NH4HCO3 and sodium hydroxide, or a combination of sodium oxalate and sodium hydroxide. The sodium oxalate is a saturated aqueous solution, and the concentration of the other back-extracting agents is 0.5~3 mol / L. The volume ratio of the back-extractant to the thorium-containing organic phase is 1 to 5:

1.

9. The method according to claim 8, characterized in that, The volume ratio of the back-extractant to the thorium-containing organic phase is 1~3:

1.

10. The method according to claim 6, characterized in that, The extraction process is grade 1 to 10; the washing process is grade 1 to 10.

11. The method according to claim 8, characterized in that, The method also includes the step of recycling the back-extracted organic phase as an organic extractant.

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