A method for preparing scandium oxide from scandium oxalate

Abstract

This invention provides a method for preparing scandium oxide from scandium oxalate. The method includes the following steps: slurrying scandium oxalate to obtain scandium oxalate slurry; mixing the scandium oxalate slurry with an ammonium carbonate solution, followed by solid-liquid separation after a conversion reaction to obtain a scandium-containing filtrate and a filter cake; subjecting the scandium-containing filtrate to decomplexation treatment to obtain a scandium precipitate; and calcining the scandium precipitate to obtain scandium oxide. The method of this invention utilizes the selective dissolution of ammonium carbonate, where calcium, as well as lanthanum, cerium, neodymium, and some heavy rare earth elements, form calcium carbonate and rare earth carbonate precipitates that remain in the residue, while scandium forms a soluble complex and enters the solution. This achieves the separation of scandium from other rare earth elements with similar chemical properties, efficiently removing impurities from scandium oxalate, and yielding high-purity scandium oxide through simple calcination.

Description

Technical Field

[0001] This invention belongs to the field of rare earth metallurgy technology and relates to a method for preparing scandium oxide from scandium oxalate. Background Technology

[0002] Scandium oxide, as an important rare earth oxide, has excellent properties such as high melting point, high hardness, and stable chemical properties. It is widely used in high-end fields such as aerospace, electronic devices, high-temperature materials, and catalysts. Its application value is closely related to the purity of the product. High-purity scandium oxide (purity ≥ 99.9%) is a core raw material in high-end fields. Therefore, achieving efficient purification and preparation of scandium oxide has important industrial significance and market value.

[0003] Currently, one of the commonly used raw materials for the industrial preparation of scandium oxide is scandium oxalate. Scandium oxalate is usually obtained by precipitating scandium-containing raw materials with oxalic acid. However, since scandium-containing raw materials often contain light rare earth elements such as calcium, lanthanum, cerium, and neodymium, as well as some heavy rare earth elements, these impurities are easily co-precipitated with scandium during the oxalic acid precipitation process, resulting in low purity of the obtained scandium oxalate raw materials. It is difficult to obtain high-purity scandium oxide directly through simple processing.

[0004] Since scandium has very similar chemical properties to rare earth elements such as lanthanum, cerium, and neodymium, and is a rare earth element with similar ionic radii, its chemical behavior in aqueous solution is also highly similar. Therefore, achieving efficient separation of scandium from these coexisting rare earth impurities and calcium impurities is a key challenge in improving the purity of scandium oxalate and thus preparing high-purity scandium oxide. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing scandium oxide from scandium oxalate. This method utilizes the selective dissolution of ammonium carbonate, where calcium, along with lanthanum, cerium, neodymium, and some heavy rare earth elements, form calcium carbonate and rare earth carbonate precipitates that remain in the residue. Scandium forms a soluble complex and enters the solution, thereby achieving the separation of scandium from other rare earth elements with similar chemical properties. This method can efficiently remove impurities from scandium oxalate, and high-purity scandium oxide can be obtained through simple calcination.

[0006] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for preparing scandium oxide from scandium oxalate, the method comprising the following steps: Scandium oxalate is pulped to obtain scandium oxalate slurry; Scandium oxalate slurry was mixed with ammonium carbonate solution, and after conversion reaction, solid-liquid separation was performed to obtain scandium-containing filtrate and filter cake. The scandium-containing filtrate was subjected to decomplexation treatment to obtain scandium precipitate; Scandium precipitate was calcined to obtain scandium oxide.

[0007] This invention involves mixing scandium oxalate slurry with an ammonium carbonate solution, followed by a conversion reaction that transforms scandium oxalate into a soluble scandium tricarbonate complex, which then enters the solution. Impurities (such as Ca, Fe, Al, rare earth elements, etc.) exist as precipitates in the slag phase. The scandium-containing filtrate is then subjected to a decomposition treatment to break down the scandium complex, causing it to redefine as scandium carbonate or scandium hydroxide. This redefinition, followed by calcination, yields high-purity scandium oxide.

[0008] Preferably, the solvent used for pulping includes water.

[0009] Preferably, the solid content of the scandium oxalate slurry is 15% to 25%, for example: 15%, 18%, 20%, 22% or 25%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0010] Preferably, the solute in the ammonium carbonate solution includes ammonium carbonate and / or ammonium bicarbonate.

[0011] Preferably, the mass concentration of the ammonium carbonate solution is 15% to 25%, for example: 15%, 18%, 20%, 22% or 25%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] Preferably, the molar ratio of scandium oxalate in the scandium oxalate slurry to ammonium carbonate in the ammonium carbonate solution is 1:(1.5~4), for example: 1:1.5, 1:2, 1:2.5, 1:3.5 or 1:4, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] Preferably, the temperature of the conversion reaction is 50℃~80℃, for example: 50℃, 55℃, 60℃, 70℃ or 80℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Preferably, the pH of the conversion reaction is 8 to 9.5, for example: 8, 8.2, 8.5, 9 or 9.5, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the conversion reaction time is 0.5h to 2h, for example: 0.5h, 1h or 2h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the decomposition treatment includes heating to decompose the complex and / or adding alkali to decompose the complex.

[0017] Preferably, the heating temperature for decomposing the complex is 90℃~100℃, for example: 90℃, 92℃, 95℃, 98℃ or 100℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the heating time for decomposing the complex is 1h to 2h, for example: 1h, 1.2h, 1.5h, 1.8h or 2h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the alkaline material used for the alkali addition and complex dissolution includes ammonia.

[0020] Preferably, the pH of the alkali addition for complex decomposition is 10~11.5, for example: 10, 10.2, 10.5, 11 or 11.5, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the temperature for adding alkali to dissolve the complex is 60℃~90℃, for example: 60℃, 65℃, 70℃, 80℃ or 90℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the time for adding alkali to dissolve the complex is 0.5 to 4 hours, for example: 0.5 hours, 1 hour, 2 hours, 3 hours or 4 hours, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the scandium precipitate obtained after the decomposition treatment is washed and dried.

[0024] Preferably, the calcination temperature is 800℃~1000℃, for example: 800℃, 850℃, 900℃, 950℃ or 1000℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the calcination time is 2h to 4h, for example: 2h, 2.5h, 3h, 3.5h or 4h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The method described in this invention utilizes the selective dissolution of ammonium carbonate. Calcium, as well as rare earth elements such as lanthanum, cerium, and neodymium, and some heavy rare earth elements, form calcium carbonate and rare earth carbonate precipitates that remain in the slag. Scandium forms a soluble complex and enters the solution, thereby achieving the separation of scandium from other rare earth elements with similar chemical properties. This method can efficiently remove impurities from scandium oxalate, and high-purity scandium oxide can be obtained through simple calcination. The entire process does not require the use of strong acids, strong bases, or organic solvents. Ammonium carbonate itself is easily decomposed (decomposes into ammonia and carbon dioxide upon heating), and the mother liquor is easy to treat, making it a green metallurgical process.

[0028] (2) The purity of Sc2O3 prepared by the process of the present invention is greater than 99.99%, which meets the standard of Sc2O3-4N in GB / T 13219-2018, and the yield of Sc in the process is greater than 96%. Detailed Implementation

[0029] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0030] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0031] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0032] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0033] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined according to its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order in which they are written or in any order that does not conflict with the technology.

[0034] Example 1 This embodiment provides a method for preparing scandium oxide from scandium oxalate, characterized in that the method includes the following steps: Scandium oxalate was mixed with water and slurryed to obtain a scandium oxalate slurry with a solid content of 20%. Scandium oxalate slurry was mixed with a 20% ammonium carbonate solution (the molar ratio of scandium oxalate in the scandium oxalate slurry to ammonium carbonate in the ammonium carbonate solution was 1:3). After a conversion reaction at 65°C and pH 8.8 for 2 hours, solid-liquid separation was performed to obtain scandium-containing filtrate and filter cake. The scandium-containing filtrate was mixed with ammonia water, and the pH was controlled at 10.8 and the temperature at 80℃ for 2 hours to decomplex the sample. The resulting solid was washed three times with deionized water and then dried to obtain scandium precipitate. Scandium precipitate was calcined at 900℃ for 3 hours to obtain scandium oxide.

[0035] Example 2 This embodiment provides a method for preparing scandium oxide from scandium oxalate, characterized in that the method includes the following steps: Scandium oxalate was mixed with water and pulped to obtain a scandium oxalate slurry with a solid content of 15%. Scandium oxalate slurry was mixed with a 25% ammonium carbonate solution (the molar ratio of scandium oxalate in the scandium oxalate slurry to ammonium carbonate in the ammonium carbonate solution was 1:1.5). After a conversion reaction at 55°C and pH 8 for 0.5 h, solid-liquid separation was performed to obtain scandium-containing filtrate and filter cake. The scandium-containing filtrate was heated to 95°C for 2 hours to decomplex the filtrate. The resulting solid precipitate was washed three times with deionized water and then dried to obtain the scandium precipitate. Scandium precipitate was calcined at 800℃ for 4 hours to obtain scandium oxide.

[0036] Example 3 This embodiment provides a method for preparing scandium oxide from scandium oxalate, characterized in that the method includes the following steps: Scandium oxalate was mixed with water and pulped to obtain a scandium oxalate slurry with a solid content of 25%. Scandium oxalate slurry was mixed with a 15% ammonium carbonate solution (the molar ratio of scandium oxalate in the scandium oxalate slurry to ammonium carbonate in the ammonium carbonate solution was 1:4). After a conversion reaction at 50°C and pH 9.5 for 1 hour, solid-liquid separation was performed to obtain scandium-containing filtrate and filter cake. The scandium-containing filtrate was mixed with ammonia water, and the pH was controlled at 11.5 and the temperature at 90℃ for 0.5 h to decomplex. The resulting solid precipitate was washed three times with deionized water and then dried to obtain scandium precipitate. Scandium precipitate was calcined at 1000℃ for 2 hours to obtain scandium oxide.

[0037] Example 4 This embodiment provides a method for preparing scandium oxide from scandium oxalate, characterized in that the method includes the following steps: Scandium oxalate was mixed with water and slurryed to obtain a scandium oxalate slurry with a solid content of 20%. Scandium oxalate slurry was mixed with a 20% ammonium carbonate solution (the molar ratio of scandium oxalate in the scandium oxalate slurry to ammonium carbonate in the ammonium carbonate solution was 1:4). After a conversion reaction at 65°C and pH 8.8 for 2 hours, solid-liquid separation was performed to obtain scandium-containing filtrate and filter cake. The scandium-containing filtrate was mixed with ammonia water, and the pH was controlled at 10 and the temperature at 60°C for 4 hours to decomplex the filtrate. The resulting solid was washed three times with deionized water and then dried to obtain scandium precipitate. Scandium precipitate was calcined at 900℃ for 3 hours to obtain scandium oxide.

[0038] Example 5 The only difference between this embodiment and Example 1 is that the temperature of the conversion reaction is 40°C, while the other conditions and parameters are exactly the same as in Example 1.

[0039] Example 6 The only difference between this embodiment and Example 1 is that the temperature of the conversion reaction is 90°C, while the other conditions and parameters are exactly the same as in Example 1.

[0040] Example 7 The only difference between this embodiment and Example 1 is that the pH of the conversion reaction is 7.5, while the other conditions and parameters are exactly the same as in Example 1.

[0041] Example 8 The only difference between this embodiment and Example 1 is that the pH of the conversion reaction is 10, while the other conditions and parameters are exactly the same as in Example 1.

[0042] Comparative Example 1 The only difference between this comparative example and Example 1 is that the ammonium carbonate solution is replaced with an equal amount of sodium carbonate solution; all other conditions and parameters are exactly the same as in Example 1.

[0043] Comparative Example 2 The only difference between this comparative example and Example 1 is that the ammonium carbonate solution is replaced with an equal amount of sodium hydroxide solution; all other conditions and parameters are exactly the same as in Example 1.

[0044] Performance testing: The purity and impurity content of the obtained scandium oxide were determined, and the test results are shown in Table 1: Table 1 As can be seen from Table 1, the purity of Sc2O3 prepared by the process of the present invention meets the standard of Sc2O3-4N in GB / T 13219-2018, and the yield of Sc in the process is >96%.

[0045] A comparison of Examples 1 and 5-6 shows that in the method for preparing scandium oxide from scandium oxalate according to the present invention, the temperature of the conversion reaction affects the purity and yield of the obtained scandium oxide. Controlling the conversion reaction temperature between 50℃ and 80℃ yields better purity and yield of scandium oxide. If the conversion reaction temperature is too low, the activation energy is insufficient, the complexation conversion rate of scandium oxalate and ammonium carbonate is slow, the reaction is incomplete, and a small amount of scandium oxalate remains in the filter cake without participating in the complexation reaction, resulting in scandium loss and a decrease in scandium oxide yield. Simultaneously, at low temperatures, the complexation and separation effect of impurity ions is poor, easily accompanied by co-precipitation carrying impurities, ultimately resulting in low scandium oxide purity. If the conversion reaction temperature is too high, the ammonium carbonate in the system is easily decomposed by heat, producing ammonia and carbon dioxide, disrupting the complexation reaction equilibrium, reducing the complexation solubility stability of scandium, and easily causing reverse precipitation and turbidity, thus reducing the purity and yield of scandium oxide.

[0046] A comparison of Examples 1 and 7-8 shows that in the method for preparing scandium oxide from scandium oxalate according to the present invention, the pH of the conversion reaction affects the purity and yield of the obtained scandium oxide. Controlling the pH of the conversion reaction at 8-9.5 results in better purity and yield of the obtained scandium oxide. If the pH of the conversion reaction is too low, the system is not alkaline enough, the ammonium carbonate complexation and dissociation ability is weak, and scandium oxalate is difficult to effectively convert and dissolve. The scandium complexation reaction is incomplete, and the scandium remains in the solid filter cake, resulting in scandium loss and a reduced scandium oxide yield. If the pH of the conversion reaction is too high, the system is too alkaline, the hydroxide concentration in the solution increases significantly, and scandium hydroxide is easily formed with scandium ions to precipitate prematurely, which cannot enter the filtrate, resulting in scandium loss.

[0047] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, although sodium hydroxide solution and sodium carbonate solution can dissolve scandium oxalate, they are highly corrosive to equipment and the resulting system is complex. Impurities that are also amphoteric or micro-amphetitic, as well as associated rare earth elements, are difficult to remove, and colloidal co-precipitation is easily caused during subsequent neutralization. This invention uses a carbonate solution to convert scandium oxalate into a soluble scandium tricarbonate ammonium complex, which then enters the solution. Impurities (such as Ca, Fe, Al, rare earth elements, etc.) exist as precipitates in the slag phase, thereby significantly improving the impurity removal effect.

[0048] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing scandium oxide from scandium oxalate, characterized in that, The method includes the following steps: Scandium oxalate is pulped to obtain scandium oxalate slurry; Scandium oxalate slurry was mixed with ammonium carbonate solution, and after conversion reaction, solid-liquid separation was performed to obtain scandium-containing filtrate and filter cake. The scandium-containing filtrate was subjected to decomplexation treatment to obtain scandium precipitate; Scandium precipitate was calcined to obtain scandium oxide.

2. The method as described in claim 1, characterized in that, The solvent used for pulping includes water; Preferably, the solid content of the scandium oxalate slurry is 15% to 25%.

3. The method as described in claim 1 or 2, characterized in that, The solute in the ammonium carbonate solution includes ammonium carbonate and / or ammonium bicarbonate; Preferably, the mass concentration of the ammonium carbonate solution is 15% to 25%.

4. The method according to any one of claims 1-3, characterized in that, The molar ratio of scandium oxalate in the scandium oxalate slurry to ammonium carbonate in the ammonium carbonate solution is 1:(1.5~4).

5. The method according to any one of claims 1-4, characterized in that, The temperature of the conversion reaction is 50℃~80℃; Preferably, the pH of the conversion reaction is 8-9.5; Preferably, the conversion reaction takes 0.5 h to 2 h.

6. The method according to any one of claims 1-5, characterized in that, The decomposition treatment includes decomposition by heating and / or decomposition by adding alkali.

7. The method as described in claim 6, characterized in that, The temperature for heating and decomposing the complex is 90℃~100℃; Preferably, the heating time for decomposing the complex is 1 to 2 hours.

8. The method as described in claim 6, characterized in that, The alkaline material used in the alkali-based complex-dissolving process includes ammonia water; Preferably, the pH of the alkali-addition complex-dissolving process is 10-11.5; Preferably, the temperature for adding alkali to dissolve the complex is 60℃~90℃; Preferably, the time for adding alkali to dissolve the complex is 0.5 to 4 hours.

9. The method according to any one of claims 1-8, characterized in that, The scandium precipitate obtained after the decomposition treatment is washed and dried.

10. The method according to any one of claims 1-9, characterized in that, The calcination temperature is 800℃~1000℃; Preferably, the calcination treatment time is 2h to 4h.

Images