Method for preparing high-purity scandium oxide from crude scandium carbonate

Abstract

The invention discloses a method for preparing high-purity scandium oxide from crude scandium carbonate, which comprises the following steps: dissolving the crude scandium carbonate with acid, adjusting the pH value to 7-9, separating out precipitate, filtering and washing; adding a formic acid solution; adding a citric acid solution, heating and stirring; heating to 80-100 DEG C, keeping the temperature for 1-2 hours, separating out a solid, and filtering while the solid is hot, so as to obtain scandium organic salt precipitate; placing the scandium organic salt precipitate in the formic acid and citric acid mixed solution, and repeating the previous step; the scandium organic salt precipitate is pulped, the pH is adjusted to 0.5-1, and solids are completely dissolved; adding an oxalic acid solution, precipitating and filtering to obtain scandium oxalate; and calcining at 850-950 DEG C for 2-4 hours to obtain the high-purity scandium oxide. According to the method, scandium salt precipitation is selectively separated out from the formic acid and citric acid mixed solution through thermal driving, ultrahigh selectivity is achieved for removal of rare earth impurities, then high-purity scandium oxide is prepared through two-step coupling with straw precipitation impurity removal in a low-impurity environment, and the absolute purity reaches 99.98%. The technological process is simple, operability is high, formic acid in the mixed solution can be recycled through evaporation, and environmental pollution is small.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrometallurgy, in particular to the technical field of crude scandium purification, and in particular to a method for preparing high-purity scandium oxide from crude scandium carbonate. Background Art

[0002] Scandium and its related materials have been widely used in defense and military industry, aerospace, new energy, new generation information technology, medical and other fields, and are an important engine for the high-quality development of new materials. At present, scandium has been extracted from minerals such as laterite nickel ore, chlorinated smoke produced during the chlorination of high-titanium slag, hydrolysis mother liquor of titanium dioxide production from ilmenite, waste acid of zirconium oxychloride, and red mud produced by alumina refining from bauxite, as well as other mineral by-products. However, the scandium oxide produced is still of low purity and high cost, which cannot meet the application needs of high-tech industries. The industrial production method of scandium ion extraction is solvent extraction. However, the selective extraction of metal ions by the extractant is limited, and it is impossible to produce high-purity scandium oxide that meets national standards through extraction alone. Therefore, further purification and preparation of high-purity scandium oxide from the scandium concentrate is an essential step.

[0003] Scandium carbonate, scandium hydroxide, scandium oxalate, and crude scandium oxide are important precursors for enriching scandium ions and preparing high-purity scandium oxide. Currently, there are many ways to remove impurities from scandium-containing precursors.

[0004] Patent CN116654970A proposes a method for purifying scandium hydroxide to produce high-purity scandium oxide. After the scandium hydroxide is re-dissolved, a certain amount of phosphate is added to precipitate iron, zirconium, and calcium ions. The resulting purified scandium solution is filtered and then extracted with an extractant, washed, stripped, precipitated, and calcined to yield 99.9% high-purity scandium oxide. However, the selective precipitation with phosphoric acid has low selectivity, and organic extraction is still required after impurity removal.

[0005] Patent CN113307298A proposes a method for producing high-purity scandium oxide from scandium oxide concentrate. The method involves dissolving the concentrate in sulfuric acid, hydrolyzing and removing impurities with sodium hydroxide to adjust the pH, adding mandelic acid, precipitating a sulfate double salt, stripping with potassium hydroxide, dissolving with hydrochloric acid, and precipitating with oxalic acid, followed by roasting to obtain 99.9% high-purity scandium oxide. However, sulfate double salt precipitation requires a high-acidity scandium solution, resulting in significant loss of inorganic acid, and wastewater treatment poses environmental pollution issues.

[0006] The article "Technology of Deep Removal of Impurities from Scandium Oxide with the Acquisition of High Purity Scandium Oxid" utilizes the different solubilities of scandium formate and other impurities to purify scandium. This involves re-dissolving scandium oxide, precipitating it with hydroxide, and calcining it with formic acid to ultimately yield 99.99% high-purity scandium oxide. Formic acid impurity removal, which uses re-dissolved scandium oxide as a precursor, involves calcining it to form scandium oxide and then purifying it through calcination. This method is energy-intensive and complex, and experiments have shown that formic acid has limited ability to remove rare earth impurities in environments with high impurity concentrations.

[0007] Patent CN118579824A proposes a method for preparing high-purity scandium oxide from crude scandium hydroxide. The method employs an organic acid (oxalic acid or a mixture of oxalic acid and tartaric acid) and an inorganic acid for synergistic impurity removal. Specifically, the crude scandium hydroxide is reacted with pure water and an organic acid to produce a solid organic acid scandium salt. The organic acid scandium salt is then reacted with hydrochloric acid and pure water to produce a purified scandium chloride solution. The purified scandium chloride solution is then neutralized with ammonia and the pH adjusted, allowing for a thorough reaction to produce purified scandium hydroxide. The purified scandium hydroxide is then reacted with hydrochloric acid and pure water to produce a refined scandium chloride solution. The refined scandium chloride solution is then reacted with an organic acid to produce a high-purity organic acid scandium salt. The high-purity organic acid scandium salt is then calcined to produce high-purity scandium oxide with a purity exceeding 99.9%. The 99.9% scandium oxide produced using tartaric acid or a mixture of oxalic acid and tartaric acid for impurity removal suffers from the relatively high cost of tartaric acid. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a method for preparing high-purity scandium oxide from crude scandium carbonate, which adopts a method of heat-driven precipitation of scandium organic salt by mixed organic acid to purify and remove impurities, and finally obtains high-purity scandium oxide with a relative rare earth purity of 99.9998% and an absolute purity of 99.98%.

[0009] To achieve this technical purpose, the present invention adopts the following scheme: The present invention provides a method for preparing high-purity scandium oxide from crude scandium carbonate, comprising the following steps: S1. Dissolving crude scandium carbonate with acid to obtain a scandium solution, adding alkali to adjust the pH to 7-9, precipitating scandium hydroxide, filtering and washing the precipitate; S2, adding the scandium hydroxide precipitate obtained in step S1 to a formic acid solution; S3, adding citric acid solution and stirring to form a mixed solution; S4, heating to 80-100°C and keeping the temperature for 1-2 hours, precipitating a solid and filtering it while hot to obtain a precipitate of an organic scandium salt; S5, placing the scandium organic salt precipitate in a mixed solution of formic acid and citric acid, and repeating step S4 to purify the scandium organic salt; S6, precipitate and slurry the organic salt of scandium in step S5, and adjust the pH to 0.5-1 to dissolve all the solids; S7, adding hot oxalic acid solution to the solution of step S6, the reaction temperature is 80-90°C, and filtering the precipitate to obtain scandium oxalate; S8. Scandium oxalate is calcined at 850-950°C for 2-4 hours to obtain high-purity scandium oxide.

[0010] Furthermore, the acid used to dissolve the crude scandium carbonate in step S1 is one of hydrochloric acid, nitric acid or sulfuric acid.

[0011] Furthermore, the base used to adjust the pH in step S1 is one of ammonia water, sodium hydroxide or potassium hydroxide.

[0012] Furthermore, the precipitate in step S1 is washed with ultrapure water at least three times.

[0013] Furthermore, the concentration of the formic acid solution in step S2 is 11.5±0.1 mol / L.

[0014] Furthermore, the concentration of the citric acid solution in step S3 is 1.05±0.05 mol / L.

[0015] Furthermore, the volume ratio of the formic acid solution in step S2 to the citric acid solution in step S3 is 2:1.

[0016] Furthermore, in the formic acid-citric acid mixed solution of step S5, the formic acid concentration is 7.67±0.03 mol / L, and the citric acid concentration is 0.35±0.02 mol / L.

[0017] Furthermore, in step S7, the amount of oxalic acid added is 1 to 5 times the mass of the scandium element.

[0018] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, a mixed solution of formic acid and citric acid is heat-driven to selectively precipitate scandium salt, which has ultra-high selectivity for the removal of rare earth impurities. Subsequently, high-purity scandium oxide is produced by coupling with grass precipitation in a low-impurity environment in two steps. In the solution formed by the combination of formic acid solution and citric acid, no precipitation of scandium ions is produced at room temperature, but scandium salt is precipitated upon heating, and the higher the temperature, the more scandium salt is precipitated. It is worth noting that the scandium salt precipitate precipitated for the first time by heating disappears when the temperature of the mixed solution drops to room temperature. During the grass precipitation process, the citrate groups present in the scandium salt can anchor and disperse metal ions, which contributes to the impurity removal effect, especially the U element.

[0019] The high-purity scandium oxide prepared by the method of this invention can remove rare earth impurities to the ultra-low ppm level, that is, a relative rare earth purity of 99.9998%, meeting the standard of scandium oxide 5N5 specified in GB / T 13219-2018. Compared with the national standard 3N level with a relative rare earth purity of ≥99.9%, prepared by re-dissolving scandium carbonate and directly calcining it with grass sediment, the trace impurity removal capability is improved by two orders of magnitude. This method is a highly efficient and highly selective separation method for scandium ions from other rare earth ions, with great application potential. It also has a high selective removal rate for non-rare earth impurities, effectively removing impurities such as iron, titanium, nickel, and uranium, and effectively purifying the difficult-to-remove impurity zirconium. The final sample has an absolute purity of 99.98%, meeting the national standard specifications for 3N scandium oxide for all elements and meeting industrial requirements for high-purity scandium oxide.

[0020] The process of the present invention is simple and highly operable. The number of purification repetitions can be determined for different crude scandium according to the impurity content, and the number of purification repetitions can be reduced by increasing the solution volume. Furthermore, the boiling point of formic acid under standard conditions is 100.6°C. The used citric formic acid solution can be recovered and recycled by evaporation, minimizing environmental pollution.

[0021] The method of the present invention is also applicable to crude scandium concentrates such as crude scandium organic salts, crude scandium hydroxide or crude scandium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0023] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0024] See also Figure 1 The present invention provides a method for preparing high-purity scandium oxide from crude scandium carbonate, comprising the following steps: S1. Dissolving crude scandium carbonate with acid to obtain a scandium solution, adding alkali to adjust the pH to 7-9, precipitating scandium hydroxide, filtering the precipitate and washing it with ultrapure water at least 3 times; wherein the acid for dissolving the crude scandium carbonate is one of hydrochloric acid, nitric acid or sulfuric acid; The base for adjusting pH is one of ammonia, sodium hydroxide or potassium hydroxide; S2, adding the scandium hydroxide precipitate obtained in step S1 to a formic acid solution, wherein the formic acid concentration is 11.5±0.1 mol / L; S3, adding citric acid solution and stirring to form a mixed solution; The concentration of the citric acid solution is 1.05±0.05 mol / L; the volume ratio of the formic acid solution in step S2 to the citric acid solution in step S3 is 2:1; S4, heating to 80-100°C and keeping the temperature for 1-2 hours, precipitating a solid and filtering it while hot to obtain a precipitate of an organic scandium salt; S5, placing the scandium organic salt precipitate in a mixed solution of formic acid and citric acid, and repeating step S4 to purify the scandium organic salt; The formic acid concentration in the formic acid-citric acid mixed solution was 7.67±0.03 mol / L, and the citric acid concentration was 0.35±0.02 mol / L; S6, precipitate and slurry the organic salt of scandium in step S5, and adjust the pH to 0.5-1 to dissolve all the solids; S7, adding oxalic acid solution to the solution of step S6, wherein the amount of oxalic acid added is 1 to 5 times the mass of the scandium element, the reaction temperature is 80 to 90° C., and the precipitation is filtered to obtain scandium oxalate; S8. Scandium oxalate is calcined at 850-950°C for 2-4 hours to obtain high-purity scandium oxide.

[0025] In the present application, crude carbonate was used for the experiment. The crude scandium carbonate used was a coarse material of scandium carbonate. The composition test results are shown in Table 1. The contents of each metal oxide in the table are in mass percentage.

[0026] Table 1 Detection results of scandium carbonate crude material composition

[0027] From the composition test results of the scandium carbonate crude material in Table 1, it can be concluded that the main impurities in the crude material are Fe, Zr, Ti, Th, Ce, Nd, Sm, Eu, U, etc., among which Fe2O3 has the highest content of 1.8%, followed by U 0.14% and TiO2 0.083%. Among the rare earth impurities, CeO2 has the highest content of 0.02%, followed by Nd2O3 0.012%. The absolute purity of the scandium carbonate is only 32.38%. Example 1

[0028] Weigh 25g of scandium carbonate crude material and beat it into pulp. Use hydrochloric acid to adjust the pH to 0.5-1 to completely dissolve the scandium carbonate to obtain a scandium chloride solution. Add ammonia water to adjust the pH to 7-9. Filter and rinse the scandium hydroxide solid with pure water to collect the scandium hydroxide. Add 100mL of formic acid (≥88 wt%) and 100 mL of ultrapure water to prepare a formic acid solution. Scandium hydroxide was placed in the formic acid solution and stirred until completely dissolved. A citric acid solution was then prepared by dissolving 20 g of citric acid in 100 mL of water. The scandium formate solution and the citric acid solution were mixed and heated to 80°C and maintained for 2 hours to precipitate an organic scandium salt. The temperature was finally raised to 100°C, and the precipitate was filtered while hot. The filtrate was reddish-brown. The organic scandium salt was then placed in a mixed solution of 100 mL of formic acid, 20 g of citric acid, and 200 mL of water. The mixture was stirred in an 80°C water bath for 2 hours, then raised to 100°C and the organic scandium salt was filtered while hot. The solution turned lemon yellow. The previous step was repeated until the filtrate was colorless and the organic scandium salt was white. The organic scandium salt was calcined at 850°C for 4 hours to obtain high-purity scandium oxide. Its components were analyzed, and the results are shown in Table 2. The relative purity in the table is the ratio of the mass of scandium oxide to the mass of all rare earth oxides, and the absolute purity is the ratio of the mass of scandium oxide to the total mass of the sample.

[0029] In this embodiment, the purification step can also be performed by increasing the volume of the formic acid lemon solution mixture to reduce the number of purification times, which is specifically determined according to the composition of the coarse material.

[0030] Table 2 Scandium oxide composition test results of Example 1

[0031] As shown in Table 2, the scandium oxide prepared by this method has a relative purity of 99.9995%, with only trace amounts of CeO2 0.0002% and Nd2O3 0.0003% of rare earth impurities remaining, and other rare earth impurities are all less than 0.0001%. Compared with Comparative Example 1, the relative purity is 99.9645%, and the trace impurity removal is increased by two orders of magnitude, reaching the national standard 5N5 level (according to GB / T13219-2018, Sc2O3-5N5, rare earth impurities ≤ 0.0005%, that is, relative rare earth purity ≥ 99.9995%). Therefore, this method is an efficient method for removing rare earth impurities from scandium oxide. For non-rare earth impurities, the absolute purity reaches 99.897%. Compared with Comparative Example 1, the Fe2O3 content is further reduced, and the absolute purity is increased by 0.064%. Therefore, this method is superior to simple formic acid precipitation purification.

[0032] Comparative Example 1 50g of crude scandium carbonate was weighed and slurried. The pH was adjusted to 0.5-1 with hydrochloric acid to completely dissolve the scandium carbonate, resulting in a scandium chloride solution. Ammonia was added to adjust the pH to 7-9. The scandium hydroxide solid was filtered and rinsed with pure water. The scandium hydroxide was collected and directly added to 500mL of formic acid (≥88 wt%) with stirring. After dissolution, scandium formate crystals precipitated. The scandium formate was filtered and rinsed three times with formic acid solution to obtain reddish scandium formate crystals. The scandium formate crystals were filtered and filtered, and the filtrate was reddish-brown. The scandium formate solid was dissolved in water and heated to 80-90°C. Oxalic acid (five times the mass of the scandium element) was weighed and dissolved in hot water. The hot oxalic acid was poured into the scandium solution and stirred until complete precipitation. The scandium oxalate was filtered and rinsed three times with hot water. The scandium oxalate solid was collected and calcined at 850°C for 4 hours to obtain scandium oxide. Its composition was analyzed (Table 3).

[0033] Table 3 Scandium oxide composition test results of Comparative Example 1

[0034] According to Table 3, the relative purity of scandium oxide prepared by this method is 99.9645%, including La2O3 (0.0004%), CeO2 (0.011%), Pr6O 11 (0.0011%), Nd2O3 (0.012%), Sm2O3 (0.0093%), Eu2O3 (0.0012%), and Gd2O3 (0.004%). Therefore, direct formic acid removal is not ideal for rare earth impurities, and a large amount of rare earth impurities still remain. Regarding non-rare earth impurities, the Fe2O3 content is still very high at 0.11%, far exceeding the national standard of 0.02% for 3N scandium oxide. The ZrO2 content is 0.0072%, reaching the national standard of 3N5, indicating that formic acid solution has a good ability to remove zirconium ions. The final scandium oxide has an absolute purity of 99.833%. Example 2

[0035] On the basis of preparing the organic salt of scandium in Example 1, a grass precipitation step was added, specifically: The purified white organic scandium salt was placed in 500 mL of ultrapure water. The pH was adjusted to 0.5–1 with hydrochloric acid to completely dissolve the precipitate, forming a scandium solution. The temperature was then raised to 80–90°C. Oxalic acid (five times the mass of the scandium element) was then dissolved in the hot water. The oxalic acid solution was poured into the scandium solution and stirred until precipitation was complete. The scandium oxalate was collected by filtration and calcined at 850°C for 4 hours to obtain high-purity scandium oxide. Its composition was analyzed, and the results are shown in Table 4.

[0036] Table 4 Scandium oxide composition test results of Example 2

[0037] According to Table 4, the scandium oxide prepared by this method has a relative rare earth purity of 99.9998%, and only 0.0002% of CeO2 is left as a rare earth impurity. All other rare earth impurities are removed, and the relative purity is further improved compared to Example 1. The absolute purity also reaches 99.98%, and the iron impurities are completely removed. The content of ZrO2 drops from 0.03% to 0.0041%, reaching the standard of full elements meeting the national standard 3N high-purity scandium oxide. It is proved that the coupling of the two steps of first forming an organic salt of citric acid and then precipitating scandium with oxalic acid is an efficient impurity removal method. It is worth noting that the content of U in scandium carbonate is 0.14%. After two-step coupling, U is also effectively removed, which may be attributed to the presence of citrate in the grass precipitation environment. Example 3

[0038] Weigh 25g of scandium carbonate crude material and beat it, use hydrochloric acid to adjust the pH to 0.5-1 to completely dissolve the scandium carbonate to obtain a scandium chloride solution, add ammonia water to adjust the pH to 7-9, filter and rinse the scandium hydroxide solid with pure water, and collect the scandium hydroxide; add the scandium hydroxide directly into 250mL of formic acid and stir, first dissolve the precipitated scandium formate crystals, filter the scandium formate, and rinse it with formic acid solution 3 times to obtain reddish scandium formate crystals, filter and obtain scandium formate, add the scandium formate into 200mL of formic acid solution (11.5 mol / L), and then add 100mL of citric acid solution (1.04 mol / L), stir in a water bath at 80℃ for 2 hours, then raise the temperature to 100℃, filter the organic scandium salt while hot, and place the purified white organic scandium salt in a 500℃ refrigeration system. In 1 mL of ultrapure water, adjust the pH to 0.5-1 with hydrochloric acid to completely dissolve the precipitate, forming a scandium solution. The temperature is then raised to 90°C. Oxalic acid (five times the mass of the scandium element) is dissolved in hot water. The oxalic acid solution is poured into the scandium solution and stirred until precipitation is complete. The scandium oxalate is collected by filtration and calcined at 850°C for 4 hours to obtain high-purity scandium oxide. Its composition is analyzed, and the results are shown in Table 5.

[0039] Table 5 Scandium oxide composition test results of Example 3

[0040] According to Table 5, the scandium oxide prepared in Example 3 has a total rare earth impurity content of 0.002%, including 0.001% CeO2 and 0.001% Nd2O3. By comparison with Comparative Examples 1 and 2, it can be seen that when the impurities are high, especially the rare earth impurity content is high, the formic acid crystal precipitation impurity removal and oxalic acid precipitation impurity removal are too poor for the rare earth impurity removal effect. For example, in Comparative Example 1, the total content of rare earth oxide impurities of Ce, Pr, Nd, Sm, Eu, and Gd is 0.0355%, and the average rare earth impurity content of the three scandium oxide samples in Table 6 is 0.0435%, including oxide impurities of Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, H, and Er. By comparison, it can be seen that the citric formic acid solution has a significant purification ability for rare earth impurities, and the rare earth impurities are greatly reduced after only one purification. After coupling the three impurity removal methods of formic acid removal, citric formic acid solution removal, and oxalic acid removal, scandium oxide with an absolute purity of 99.976% was obtained, which is very close to the 99.98% in Example 2. Therefore, a good impurity removal effect can be achieved by coupling the two impurity removal methods of citric formic acid solution removal and oxalic acid removal.

[0041] Comparative Example 2 Scandium-enriched solutions were obtained by re-dissolving crude scandium carbonate with varying impurity contents. These solutions were then directly precipitated and calcined without purification. The specific steps were as follows: 50 g of crude scandium carbonate was weighed, dissolved in hydrochloric acid, and then hot oxalic acid solution (5 times the mass of the scandium element) was added. The solution was precipitated at 90°C, filtered, and the resulting scandium oxalate solid was collected and calcined at 850°C for 4 hours to obtain scandium oxide. The composition of the scandium oxide was determined, as shown in Table 6.

[0042] Samples 1 to 3 are coarse scandium carbonate materials with different impurity contents.

[0043] According to Table 6, after removal of impurities by oxalic acid, the rare earth impurity contents were 0.0316%, 0.0547% and 0.0442%, respectively. Compared with 0.0002% in Example 2, a large amount of rare earth impurities still existed in the samples.

[0044] Table 6 Scandium oxide composition test results of Comparative Example 2

[0045] Finally, it should be noted that the above-listed embodiments are merely preferred embodiments of the present invention. Of course, those skilled in the art may make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should be considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity scandium oxide from crude scandium carbonate, characterized in that: The following steps are involved: S1. Dissolving crude scandium carbonate with acid to obtain a scandium solution, adding alkali to adjust the pH to 7-9, precipitating scandium hydroxide, filtering and washing the precipitate; S2, adding the scandium hydroxide precipitate obtained in step S1 to a formic acid solution; S3, adding citric acid solution and stirring to form a mixed solution; S4, heating to 80-100°C and keeping the temperature for 1-2 hours, precipitating a solid and filtering it while hot to obtain a precipitate of an organic scandium salt; S5, placing the scandium organic salt precipitate in a mixed solution of formic acid and citric acid, and repeating step S4 to purify the scandium organic salt; S6, precipitate and slurry the organic salt of scandium in step S5, and adjust the pH to 0.5-1 to dissolve all the solids; S7, adding hot oxalic acid solution to the solution of step S6, the reaction temperature is 80-90°C, and the precipitate is filtered to obtain scandium oxalate; S8. Scandium oxalate is calcined at 850-950°C for 2-4 hours to obtain high-purity scandium oxide.

2. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein The acid used to dissolve the crude scandium carbonate in step S1 is one of hydrochloric acid, nitric acid or sulfuric acid.

3. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein The base used to adjust the pH in step S1 is one of ammonia water, sodium hydroxide or potassium hydroxide.

4. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein The precipitate in step S1 is washed with ultrapure water at least three times.

5. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein The concentration of the formic acid solution in step S2 is 11.5±0.1 mol / L.

6. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein: The concentration of the citric acid solution in step S3 is 1.05±0.05 mol / L.

7. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein: The volume ratio of the formic acid solution in step S2 to the citric acid solution in step S3 is 2:

1.

8. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein: In the formic acid-citric acid mixed solution of step S5, the formic acid concentration is 7.67±0.03 mol / L, and the citric acid concentration is 0.35±0.02 mol / L.

9. The method for preparing high-purity scandium oxide from crude scandium carbonate according to claim 1, wherein: In step S7, the amount of oxalic acid added is 1 to 5 times the mass of the scandium element.

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