Scandium oxalate precursor and its preparation method, high-purity scandium oxide and its preparation process

Abstract

This invention provides a scandium oxalate precursor and its preparation method, as well as high-purity scandium oxide and its preparation process. The preparation method of the scandium oxalate precursor includes: mixing a scandium-containing aqueous phase with an oxalic acid precipitant to obtain a scandium oxalate precipitate; and performing gradient washing of the scandium oxalate precipitate using an oil-acid mixed system to obtain the scandium oxalate precursor. The gradient washing includes a first washing stage and a second washing stage performed sequentially. In the second washing stage, the concentration of the acid solution and the volume fraction of kerosene in the oil-acid mixed system are both lower than those in the first washing stage. The preparation method of the scandium oxalate precursor provided by this invention uses an oil-acid mixed system composed of an acid solution and kerosene to perform gradient washing of the scandium oxalate precipitate. The acid removes inorganic impurities, and the kerosene removes hydrophobic organic matter. The second washing stage has a lower acid concentration and kerosene ratio, which deeply removes impurities while reducing scandium dissolution loss and kerosene residue.

Description

Technical Field

[0001] This invention belongs to the field of scandium oxide preparation technology, and relates to scandium oxalate precursors, particularly scandium oxalate precursors and their preparation methods, as well as high-purity scandium oxide and its preparation process. Background Technology

[0002] In the existing process for preparing scandium oxide by oxalic acid precipitation, metallic impurities are prone to co-precipitation and encapsulation during the precipitation process. Conventional acid washing is difficult to control the dissolution loss of scandium while deeply removing metallic impurities from the precipitate surface and grain boundaries, and cannot simultaneously achieve both deep impurity removal and scandium yield. At the same time, the organic acids in the crystals after washing are prone to generating carbon black residue during subsequent calcination, resulting in large fluctuations in product purity and making it difficult to stably obtain high-purity scandium oxide with low metallic impurities, low carbon, and low residual oil.

[0003] In summary, the existing methods for preparing scandium oxalate precursors all have certain drawbacks. Conventional acid washing is insufficient to achieve deep impurity removal while maintaining scandium yield, and the organic acids within the crystals after washing are difficult to remove, resulting in high impurity content in the prepared scandium oxide. Therefore, it is crucial to develop a novel scandium oxalate precursor and its preparation method, as well as high-purity scandium oxide and its preparation process. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a scandium oxalate precursor and its preparation method, as well as high-purity scandium oxide and its preparation process. The preparation method of the scandium oxalate precursor provided by the present invention employs an oil-acid mixed system composed of acid solution and kerosene to perform gradient washing of scandium oxalate precipitation, forming a solid-liquid-liquid three-phase washing system. The acid removes inorganic impurities, and the kerosene removes hydrophobic organic matter. Furthermore, the acid concentration and kerosene ratio are lower in the second washing stage, which reduces scandium dissolution loss and kerosene residue while deeply removing impurities.

[0005] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a scandium oxalate precursor, the method comprising: Scandium-containing aqueous phase was mixed with oxalic acid precipitant to obtain scandium oxalate precipitate; the obtained scandium oxalate precipitate was subjected to gradient washing using an oil-acid mixed system to obtain scandium oxalate precursor; The oil-acid mixture system comprises an acid solution and kerosene, and the gradient washing includes a first washing section and a second washing section performed sequentially; the first washing section and the second washing section each independently include at least one washing. The concentration of the acid solution and the volume fraction of kerosene in the oil-acid mixture used in the second washing section are both lower than those in the oil-acid mixture used in the first washing section.

[0006] The present invention provides a method for preparing scandium oxalate precursors, which employs an oil-acid mixture system composed of an acid solution and kerosene to perform gradient washing on scandium oxalate precipitate, forming a solid-liquid-liquid three-phase washing system. The acid solution promotes the desorption and dissolution of impurities adsorbed on the surface and grain boundary regions of the scandium oxalate precipitate, leading to their migration into the liquid phase. The kerosene removes hydrophobic organic residues, and the two work synergistically to enhance impurity removal. Furthermore, by using a lower concentration of acid solution and a lower volume fraction of kerosene in the second washing stage compared to the first washing stage, the present invention enhances impurity removal under the high acidity and high oil phase ratio conditions of the first washing stage. This, combined with the reduced system acidity and oil phase ratio in the second washing stage, reduces the dissolution loss of scandium oxalate in the acidic environment and the residue of kerosene and organic acids in the scandium oxalate precipitate. Thus, while achieving deep impurity removal, it also reduces scandium loss and the residue of kerosene and organic acids.

[0007] In some embodiments, the oil-acid mixture system used in the first washing section contains hydrogen chloride and oxalic acid in the acid solution, and the molar ratio of hydrogen chloride to oxalic acid is (4~8):1, for example, it can be 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1 or 8:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0008] In some embodiments, the oil-acid mixture system used in the first washing section comprises hydrochloric acid with a concentration of 0.3 mol / L to 0.8 mol / L and oxalic acid with a concentration of 0.05 mol / L to 0.15 mol / L.

[0009] In this invention, the oil-acid mixed system used in the first washing section includes hydrochloric acid with a concentration of 0.3 mol / L to 0.8 mol / L. For example, it can be 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, or 0.8 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0010] In this invention, the oil-acid mixed system used in the first washing section includes an oxalic acid solution with a concentration of 0.05 mol / L to 0.15 mol / L. For example, it can be 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.10 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, or 0.15 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0011] In some embodiments, the volume fraction of kerosene is 20% to 40%, with the volume fraction of the oil-acid mixture used in the first washing section as 100%. For example, it can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, or 40%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] In some embodiments, the volume fraction of the acid solution is 60% to 80%, with the volume fraction of the oil-acid mixture used in the first washing section as 100%. For example, it can be 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, or 80%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] In some embodiments, the first washing section includes performing a first wash and a second wash in sequence, wherein the same oil-acid mixture system is used in the first wash and the second wash, and the temperature and time of the second wash are lower than those of the first wash.

[0014] In some embodiments, the first washing method includes mixing and stirring at a temperature of 30°C to 45°C for a time of 20 to 40 minutes.

[0015] In this invention, the temperature during the first washing is 30°C to 45°C, for example, it can be 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C or 45°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] In this invention, the first washing time is 20 min to 40 min, for example, it can be 20 min, 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min, 38 min or 40 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] In some embodiments, the first washing is followed by a settling and stratification process.

[0018] In some embodiments, the second washing method includes mixing and stirring at a temperature of 25°C to 35°C for a time of 15 min to 30 min.

[0019] In this invention, the temperature of the second washing is 25°C to 35°C, for example, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C or 35°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] In this invention, the second washing time is 15 min to 30 min, for example, it can be 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In some embodiments, the second washing is followed by a settling and stratification process.

[0022] In some embodiments, the oil-acid mixture used in the second washing section contains hydrochloric acid with a concentration of 0.1 mol / L to 0.3 mol / L, for example, 0.10 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.20 mol / L, 0.22 mol / L, 0.24 mol / L, 0.26 mol / L, 0.28 mol / L, or 0.30 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0023] In some embodiments, the volume fraction of the oil-acid mixture used in the second washing section is taken as 100%, and the volume fraction of kerosene is 10% to 20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] In some embodiments, the volume fraction of the acid solution is 80% to 90%, with the volume fraction of the oil-acid mixture used in the second washing section as 100%. For example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] In some embodiments, the second washing stage includes a third washing, wherein the third washing is performed by mixing and stirring at a temperature of 20°C to 30°C for a time of 10 to 20 minutes.

[0026] In this invention, the temperature of the third washing is 20℃~30℃, for example, it can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃ or 30℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] In this invention, the third washing time is 10 min to 20 min, for example, it can be 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] In some embodiments, the third wash is followed by a settling and stratification process.

[0029] In some embodiments, the scandium-containing aqueous phase includes a scandium-containing aqueous phase purified by solvent extraction.

[0030] In some embodiments, the preparation method further includes adding citric acid to the scandium-containing aqueous phase before mixing to obtain a scandium-containing aqueous phase containing citric acid.

[0031] The method for preparing scandium oxalate precursor provided by the present invention involves adding citric acid to a scandium-containing aqueous phase to regulate the activity of metal ions through its coordination effect. Combined with low temperature and slow precipitation, this reduces local supersaturation, inhibits co-precipitation of impurities and intracrystalline inclusion, and can obtain scandium oxalate precipitate with fewer defects and lower impurity content.

[0032] In some embodiments, the preparation method further includes pH adjustment of the scandium-containing aqueous phase prior to mixing.

[0033] In some embodiments, the mixing includes sequential mixing of a precipitant and aging.

[0034] In some embodiments, the preparation method further includes solid-liquid separation between the mixing and gradient washing.

[0035] In some embodiments, the preparation method further includes supercritical CO2 treatment following the gradient washing.

[0036] The method for preparing scandium oxalate precursor provided by this invention involves supercritical CO2 treatment, during which supercritical CO2 fully penetrates into the microporous structure and grain boundary regions of the scandium oxalate precursor. By utilizing the dissolving and extracting effect of supercritical CO2 on non-polar organic matter, residual organic carbon sources such as kerosene in the micropores and grain boundaries of the scandium oxalate precipitate are deeply removed, thereby improving the purity of the obtained scandium oxalate precursor and facilitating the acquisition of higher purity scandium oxide.

[0037] In this invention, supercritical CO2 refers to a carbon dioxide fluid with both temperature and pressure higher than its critical values ​​(critical temperature 31.1℃, critical pressure 7.38MPa). It combines the high diffusion and permeability of gases with the dissolution and extraction capabilities of liquids. It has extremely low surface tension and can penetrate deep into the microporous structure of precursors to efficiently remove non-polar organic components.

[0038] In some embodiments, in the scandium-containing aqueous phase containing citric acid, the molar ratio of citrate ions to scandium ions is (0.05~0.2):1, for example, it can be 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.17:1, 0.18:1, 0.19:1 or 0.20:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0039] In some embodiments, the pH adjustment includes adjusting the pH of the scandium-containing aqueous phase to 1.0 to 1.5, for example, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0040] In some embodiments, the method of incorporating the precipitant includes adding oxalic acid precipitant to the scandium-containing aqueous phase at a dropping rate of 0.5 mL / min to 2 mL / min at a temperature of 5°C to 10°C.

[0041] In this invention, the precipitant is added at a temperature of 5°C to 10°C. For example, the temperature can be 5°C, 5.5°C, 6°C, 6.5°C, 7°C, 7.5°C, 8°C, 8.5°C, 9°C, 9.5°C, or 10°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] In this invention, the precipitant is added at a dropping rate of 0.5 mL / min to 2 mL / min. For example, the rate can be 0.5 mL / min, 0.7 mL / min, 0.8 mL / min, 0.9 mL / min, 1.0 mL / min, 1.1 mL / min, 1.4 mL / min, 1.5 mL / min, 1.6 mL / min, 1.7 mL / min, 1.9 mL / min, or 2.0 mL / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] In some embodiments, the curing method includes: holding at a temperature of 5°C to 10°C for 30 min to 120 min.

[0044] In this invention, the curing process involves maintaining a temperature of 5°C to 10°C, for example, 5°C, 5.5°C, 6°C, 6.5°C, 7°C, 7.5°C, 8°C, 8.5°C, 9°C, 9.5°C, or 10°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In this invention, the cooking process involves holding the food at a temperature of 30 min to 120 min, for example, 30 min, 35 min, 40 min, 50 min, 55 min, 60 min, 75 min, 80 min, 85 min, 90 min, 95 min, 110 min, 115 min, or 120 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In some embodiments, the supercritical CO2 treatment method includes: placing the solid obtained from the gradient washing in a supercritical CO2 treatment device, continuously feeding supercritical CO2 at a feed rate of 10 L / h to 30 L / h, and treating it for 1h to 3h under a pressure of 8 MPa to 12 MPa and a temperature of 40°C to 50°C.

[0047] In this invention, the supercritical CO2 treatment method involves continuously introducing supercritical CO2 at a feed flow rate of 10 L / h to 30 L / h, for example, 10 L / h, 12 L / h, 18 L / h, 22 L / h, 24 L / h, 28 L / h, or 30 L / h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0048] In this invention, the supercritical CO2 treatment method is carried out at a pressure of 8MPa to 12MPa, for example, 8.0MPa, 8.5MPa, 9.0MPa, 9.5MPa, 10.0MPa, 10.5MPa, 11.0MPa, 11.5MPa or 12.0MPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] In this invention, the supercritical CO2 treatment method is carried out at a temperature of 40°C to 50°C, for example, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] In this invention, the supercritical CO2 treatment method involves treating the supercritical CO2 in a supercritical CO2 treatment device for 1 to 3 hours, for example, 1.0 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2.0 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, or 3.0 h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0051] In a second aspect, the present invention provides a scandium oxalate precursor, which is obtained by the preparation method described in the first aspect.

[0052] Thirdly, the present invention provides a process for preparing high-purity scandium oxide, the process comprising: subjecting the scandium oxalate precursor described in the second aspect to a first heat treatment in a protective atmosphere, followed by a second heat treatment in a slightly positive pressure oxygen atmosphere to obtain high-purity scandium oxide.

[0053] The high-purity scandium oxide preparation process provided by this invention improves the purity of scandium oxide by controlling the temperature in stages and switching the heat treatment atmosphere. Specifically, a first heat treatment is carried out in a protective atmosphere to initially thermally decompose the scandium oxalate precursor and reduce carbon residue caused by the violent cracking of organic components. Then, a second heat treatment is carried out in a slightly positive pressure oxygen atmosphere to further decompose the pre-decomposition products and convert them into scandium oxide, while oxidizing and removing residual carbon and residual kerosene. Thus, high-purity scandium oxide with low carbon and low residual oil is obtained while maintaining low metal impurities.

[0054] In some embodiments, the first heat treatment is followed by dehydration at 120°C to 160°C for 30 to 120 minutes in a protective atmosphere.

[0055] In this invention, the protective atmosphere includes nitrogen and / or an inert gas.

[0056] In this invention, dehydration is carried out at 120℃~160℃, for example, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃ or 160℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0057] In this invention, dehydration is carried out for 30 min to 120 min, for example, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min or 120 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] In some embodiments, the temperature of the first heat treatment is 280°C to 330°C, and the time is 60 min to 180 min.

[0059] In this invention, the temperature of the first heat treatment is 280℃~330℃, for example, it can be 280℃, 285℃, 290℃, 295℃, 300℃, 305℃, 310℃, 315℃, 320℃, 325℃ or 330℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0060] In this invention, the time for the first heat treatment is 60 min to 180 min, for example, it can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min or 180 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] In some embodiments, the volume fraction of oxygen in the slightly positive pressure oxygen atmosphere is 20% to 40%, and the pressure is 0.1 kPa to 5 kPa higher than atmospheric pressure.

[0062] In this invention, the volume fraction of oxygen in the micro-positive pressure oxygen atmosphere is 20% to 40%, with the remainder being a protective gas (nitrogen and / or inert gas).

[0063] In this invention, the volume fraction of oxygen in the micro-positive pressure oxygen atmosphere is 20% to 40%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 29%, 30%, 31%, 32%, 34%, 37%, 38%, 39% or 40%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] The high-purity scandium oxide preparation process provided by this invention, wherein the pressure in the slightly positive pressure oxygen atmosphere is 0.1 kPa to 5 kPa higher than atmospheric pressure, refers to the positive pressure difference between the absolute pressure inside the furnace and the external atmospheric pressure being 0.1 kPa to 5 kPa. Under slightly positive pressure conditions, the oxidizing atmosphere inside the furnace can be continuously and slightly seeped outward, avoiding the backflow of external air and the introduction of impurities, maintaining the stability of the atmosphere composition inside the furnace, and ensuring that the decarbonization reaction proceeds fully.

[0065] In this invention, the pressure in the slightly positive pressure oxygen atmosphere is 0.1 kPa to 5 kPa higher than atmospheric pressure. For example, it can be 0.1 kPa, 0.2 kPa, 0.5 kPa, 0.6 kPa, 0.7 kPa, 0.9 kPa, 1.0 kPa, 1.2 kPa, 1.4 kPa, 2.4 kPa, 2.6 kPa, 3.0 kPa, 3.6 kPa, 3.8 kPa, 4.0 kPa, 4.6 kPa, 4.8 kPa, or 5.0 kPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0066] In some embodiments, the temperature of the second heat treatment is 850°C to 920°C, and the time is 60 min to 180 min.

[0067] In this invention, the temperature of the second heat treatment is 850℃~920℃, for example, it can be 850℃, 855℃, 860℃, 865℃, 870℃, 875℃, 880℃, 885℃, 890℃, 895℃, 900℃, 905℃, 910℃, 915℃ or 920℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0068] In this invention, the second heat treatment time is 60 min to 180 min, for example, it can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min or 180 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0069] Fourthly, the present invention provides a high-purity scandium oxide, which is obtained by the preparation process described in the third aspect.

[0070] In some embodiments, the high-purity scandium oxide has a total metal impurity content of ≤50ppb, a carbon impurity content of ≤15ppm, and a residual kerosene content of ≤1ppm.

[0071] 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.

[0072] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing scandium oxalate precursor by employing a gradient washing of scandium oxalate precipitate using an oil-acid mixture system composed of an acid solution and kerosene. This creates a solid-liquid-liquid three-phase washing system consisting of the scandium oxalate precipitate, the acid solution, and the kerosene. The acid solution promotes the desorption, dissolution, and migration of impurities adsorbed on the surface and grain boundaries of the scandium oxalate precipitate into the liquid phase, while the kerosene removes hydrophobic organic residues. These two components synergistically enhance the impurity removal effect. Furthermore, by using a lower concentration of acid solution and a lower volume fraction of kerosene in the second washing stage compared to the first washing stage, the present invention enhances impurity removal under the high acidity and high oil phase ratio conditions of the first washing stage. This, combined with the reduced system acidity and oil phase ratio in the second washing stage, reduces the dissolution loss of scandium oxalate in the acidic environment and minimizes the residue of kerosene and organic acids in the scandium oxalate precipitate. Thus, the invention achieves deep impurity removal while minimizing scandium loss and the residue of kerosene and organic acids. Detailed Implementation

[0073] 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.

[0074] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0075] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0076] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0077] 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 places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0078] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0079] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0080] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These 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" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0081] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0082] Example 1 This embodiment provides a method for preparing a scandium oxalate precursor, the method comprising: (1) Add citric acid to the scandium-containing aqueous phase (scandium-containing aqueous phase purified by solvent extraction) to obtain a scandium-containing aqueous phase containing citric acid (molar ratio of citrate to scandium ions is 0.1:1), and adjust the pH to 1.2; then add oxalic acid precipitant with a concentration of 1.0 mol / L (i.e. oxalic acid solution with a concentration of 1.0 mol / L) at a dropping rate of 1.2 mL / min at 8℃, control the dropping time to 90 min, and keep warm at 8℃ for 75 min after the dropping is completed, and then perform solid-liquid separation to obtain scandium oxalate precipitate; (2) At 38°C, the scandium oxalate precipitate obtained in step (1) was washed for 30 min by mixing and stirring using an oil-acid mixed system. After standing and separating into layers, the first washing product (solid) was obtained after solid-liquid separation. The first washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the acid solution has a volume fraction of 70% and the kerosene has a volume fraction of 30%). The molar ratio of hydrogen chloride to oxalic acid in the acid solution is 6:1. The acid solution consists of a 0.5 mol / L hydrochloric acid solution and a 0.1 mol / L oxalic acid solution. (3) At 30°C, the first washing product obtained in step (2) was washed for 22 minutes using an oil-acid mixed system (by mixing and stirring), then allowed to stand and separate into layers. After solid-liquid separation, the second washing product (solid) was obtained. The second washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the acid solution has a volume fraction of 70% and the kerosene has a volume fraction of 30%). The molar ratio of hydrogen chloride to oxalic acid in the acid solution is 6:1. The acid solution consists of a 0.5 mol / L hydrochloric acid solution and a 0.1 mol / L oxalic acid solution. (4) At 25°C, the second washing product obtained in step (3) was washed for 15 minutes using an oil-acid mixed system (by mixing and stirring), then allowed to stand and separate into layers. After solid-liquid separation, the third washing product (solid) was obtained. The third washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the acid solution has a volume fraction of 85% and the kerosene has a volume fraction of 15%), and the acid solution is hydrochloric acid with a concentration of 0.2 mol / L. The concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the second washing section (third washing) are both lower than the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the first washing section (first washing and second washing). (5) The third washing product obtained in step (4) is placed in a supercritical CO2 treatment device and supercritical CO2 is continuously introduced at a feed flow rate of 20 L / h. The product is treated for 2 h at a pressure of 10 MPa and a temperature of 45 °C to obtain scandium oxalate precursor.

[0083] This embodiment also provides a preparation process for high-purity scandium oxide, the preparation process including: The scandium oxalate precursor obtained by the preparation method provided in this embodiment was dehydrated in a nitrogen atmosphere at 140°C for 75 min; then placed in a nitrogen atmosphere and subjected to a first heat treatment at 300°C for 120 min; and then placed in a slightly positive pressure oxygen atmosphere (composed of oxygen and nitrogen) with an oxygen volume fraction of 30% and a pressure 2 kPa higher than atmospheric pressure and subjected to a second heat treatment at 880°C for 120 min to obtain high-purity scandium oxide.

[0084] Example 2 This embodiment provides a method for preparing a scandium oxalate precursor, the method comprising: (1) Add citric acid to the scandium-containing aqueous phase (scandium-containing aqueous phase purified by solvent extraction) to obtain a scandium-containing aqueous phase containing citric acid (molar ratio of citrate to scandium ion is 0.2:1), and adjust the pH to 1.5; then add oxalic acid precipitant with a concentration of 1.5 mol / L (i.e. oxalic acid solution with a concentration of 1.5 mol / L) at a dropping rate of 0.5 mL / min at 5℃, control the dropping time to 120 min, and keep warm at 5℃ for 30 min after the dropping is completed, and then perform solid-liquid separation to obtain scandium oxalate precipitate; (2) At 45°C, the scandium oxalate precipitate obtained in step (1) was washed for 20 min by mixing and stirring using an oil-acid mixture system. After standing and separating into layers, the first washing product (solid) was obtained after solid-liquid separation. The first washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the acid solution has a volume fraction of 60% and the kerosene has a volume fraction of 40%). The molar ratio of hydrogen chloride to oxalic acid in the acid solution is 4:1. The acid solution consists of hydrochloric acid with a concentration of 0.3 mol / L and oxalic acid with a concentration of 0.075 mol / L. (3) At 35°C, the first washing product obtained in step (2) was washed for 15 minutes using an oil-acid mixed system (by mixing and stirring), then allowed to stand and separate into layers. After solid-liquid separation, the second washing product (solid) was obtained. The second washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the volume fraction of the acid solution is 60% and the volume fraction of the kerosene is 40%). The molar ratio of hydrogen chloride to oxalic acid in the acid solution is 4:1. The acid solution consists of a 0.3 mol / L hydrochloric acid solution and a 0.075 mol / L oxalic acid solution. (4) At 30°C, the second washing product obtained in step (3) is washed for 10 min by mixing and stirring using an oil-acid mixture system. After standing and separating into layers, the third washing product (solid) is obtained after solid-liquid separation. The third washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the acid solution has a volume fraction of 80% and the kerosene has a volume fraction of 20%), and the acid solution is hydrochloric acid with a concentration of 0.1 mol / L. The concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the second washing section (third washing) are both lower than the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the first washing section (first washing and second washing). (5) The third washing product obtained in step (4) is placed in a supercritical CO2 treatment device and supercritical CO2 is continuously introduced at a feed flow rate of 30 L / h. The product is treated for 3 h at a pressure of 8 MPa and a temperature of 50 °C to obtain scandium oxalate precursor.

[0085] This embodiment also provides a preparation process for high-purity scandium oxide, the preparation process including: The scandium oxalate precursor obtained by the preparation method provided in this embodiment was dehydrated in an argon atmosphere at 120°C for 120 min; then placed in an argon atmosphere for a first heat treatment at 330°C for 60 min; and then placed in a slightly positive pressure oxygen atmosphere (composed of oxygen and argon) with an oxygen volume fraction of 20% and a pressure 5 kPa higher than atmospheric pressure for a second heat treatment at 920°C for 60 min to obtain high-purity scandium oxide.

[0086] Example 3 This embodiment provides a method for preparing a scandium oxalate precursor, the method comprising: (1) Add citric acid to the scandium-containing aqueous phase (scandium-containing aqueous phase purified by solvent extraction) to obtain a scandium-containing aqueous phase containing citric acid (molar ratio of citrate to scandium ion is 0.05:1), and adjust the pH to 1.0; then add oxalic acid precipitant with a concentration of 0.8 mol / L (i.e. oxalic acid solution with a concentration of 0.8 mol / L) at a dropping rate of 2 mL / min at 10℃, control the dropping time to 60 min, and keep it at 10℃ for 120 min after the dropping is completed, and then perform solid-liquid separation to obtain scandium oxalate precipitate; (2) At 30°C, the scandium oxalate precipitate obtained in step (1) was washed for 40 min by mixing and stirring using an oil-acid mixed system. After standing and separating into layers, the first washing product (solid) was obtained after solid-liquid separation. The first washing process uses an oil-acid mixture system composed of an acid solution and kerosene (the volume fraction of the acid solution is 80% and the volume fraction of the kerosene is 20%). The molar ratio of hydrogen chloride to oxalic acid in the acid solution is 8:1. The acid solution is composed of hydrochloric acid with a concentration of 0.8 mol / L and oxalic acid with a concentration of 0.1 mol / L. (3) At 25°C, the first washing product obtained in step (2) was washed for 30 minutes using an oil-acid mixed system (by mixing and stirring), then allowed to stand and separate into layers. After solid-liquid separation, the second washing product (solid) was obtained. The second washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the acid solution has a volume fraction of 80% and the kerosene has a volume fraction of 20%). The molar ratio of hydrogen chloride to oxalic acid in the acid solution is 8:1. The acid solution consists of a 0.8 mol / L hydrochloric acid solution and a 0.1 mol / L oxalic acid solution. (4) At 20°C, the second washing product obtained in step (3) was washed for 20 minutes using an oil-acid mixed system (by mixing and stirring), then allowed to stand and separate into layers. After solid-liquid separation, the third washing product (solid) was obtained. The third washing process uses an oil-acid mixture system consisting of an acid solution and kerosene (the acid solution has a volume fraction of 90% and the kerosene has a volume fraction of 10%), and the acid solution is hydrochloric acid with a concentration of 0.3 mol / L. The concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the second washing section (third washing) are both lower than the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the first washing section (first washing and second washing). (5) The third washing product obtained in step (4) is placed in a supercritical CO2 treatment device and supercritical CO2 is continuously introduced at a feed flow rate of 10 L / h. The product is treated for 1 h at a pressure of 12 MPa and a temperature of 40 °C to obtain scandium oxalate precursor.

[0087] This embodiment also provides a preparation process for high-purity scandium oxide, the preparation process including: The scandium oxalate precursor obtained by the preparation method provided in this embodiment was dehydrated in an argon atmosphere at 160°C for 30 min; then placed in an argon atmosphere for a first heat treatment at 280°C for 180 min; and then placed in a slightly positive pressure oxygen atmosphere (composed of oxygen and argon) with an oxygen volume fraction of 40% and a pressure 0.1 kPa higher than atmospheric pressure for a second heat treatment at 850°C for 180 min to obtain high-purity scandium oxide.

[0088] Example 4 This embodiment provides a method for preparing scandium oxalate precursor. Except for omitting citric acid in step (1) of the preparation method, the rest is the same as in Example 1.

[0089] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0090] Example 5 This embodiment provides a method for preparing scandium oxalate precursor. Except that in the oil-acid mixed system used for the first and second washing processes, the oxalic acid in the acid solution is replaced with an equal molar amount of hydrogen chloride, the rest is the same as in Example 1.

[0091] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0092] Example 6 This embodiment provides a method for preparing scandium oxalate precursor. Except that in the preparation method, the volume fraction of acid solution in the oil-acid mixture used for the first and second washing is 55% and the volume fraction of kerosene is 45%, the rest are the same as in Example 1.

[0093] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0094] Example 7 This embodiment provides a method for preparing scandium oxalate precursor. Except that in the preparation method, the volume fraction of acid solution in the oil-acid mixture used for the first and second washing is 84% ​​and the volume fraction of kerosene is 16%, the rest are the same as in Example 1.

[0095] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0096] Example 8 This embodiment provides a method for preparing scandium oxalate precursor. Except that in the preparation method, in the oil-acid mixed system used for the first and second washing, the molar ratio of hydrogen chloride to oxalic acid in the acid solution is kept constant, and the acid solution is adjusted to consist of a 0.25 mol / L hydrochloric acid solution and a 0.02 mol / L oxalic acid solution, the rest is the same as in Example 1.

[0097] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0098] Example 9 This embodiment provides a method for preparing scandium oxalate precursor. Except that in the preparation method, in the oil-acid mixture system used for the first and second washing processes, the molar ratio of hydrogen chloride to oxalic acid in the acid solution is kept constant, and the acid solution is adjusted to consist of a 1.0 mol / L hydrochloric acid solution and a 0.2 mol / L oxalic acid solution, the rest is the same as in Example 1.

[0099] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0100] Example 10 This embodiment provides a method for preparing scandium oxalate precursor. Except for the oil-acid mixture used in the third washing step, in which the volume fraction of acid solution is 95% and the volume fraction of kerosene is 5%, the rest are the same as in Example 1.

[0101] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0102] Example 11 This embodiment provides a method for preparing scandium oxalate precursor. Except for the oil-acid mixture used in the third washing step, in which the volume fraction of acid solution is 75% and the volume fraction of kerosene is 25%, the rest are the same as in Example 1.

[0103] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0104] Example 12 This embodiment provides a method for preparing scandium oxalate precursor. Except for the fact that in the third washing process, the acid solution in the oil-acid mixture is adjusted to hydrochloric acid with a concentration of 0.05 mol / L, the rest of the method is the same as in Example 1.

[0105] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0106] Example 13 This embodiment provides a method for preparing scandium oxalate precursor. Except for the fact that in the third washing process, the acid solution in the oil-acid mixture is adjusted to hydrochloric acid with a concentration of 0.4 mol / L, the rest of the method is the same as in Example 1.

[0107] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0108] Example 14 This embodiment provides a method for preparing scandium oxalate precursor. Except for omitting step (5) in the preparation method, the rest is the same as in Example 1.

[0109] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0110] Example 15 This embodiment provides a method for preparing scandium oxalate precursor. Except for step (5) of the preparation method, in which supercritical CO2 is introduced and supercritical CO2 treatment is carried out at a temperature of 30°C, the rest is the same as in Example 1.

[0111] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0112] Example 16 This embodiment provides a method for preparing scandium oxalate precursor. Except for step (5) of the preparation method, in which supercritical CO2 is introduced and supercritical CO2 treatment is carried out at a temperature of 60°C, the rest is the same as in Example 1.

[0113] This embodiment also provides a preparation process for high-purity scandium oxide. Except that the scandium oxalate precursor used in the preparation process is replaced with the scandium oxalate precursor obtained by the preparation method provided in this embodiment, the rest is the same as in Example 1.

[0114] Example 17 This embodiment provides a method for preparing a scandium oxalate precursor, which is the same as that in Example 1.

[0115] This embodiment also provides a preparation process for high-purity scandium oxide, which is the same as in Example 1 except that the step of "placing it in a nitrogen atmosphere and performing a first heat treatment at 300°C for 120 minutes" is omitted.

[0116] Example 18 This embodiment provides a method for preparing a scandium oxalate precursor, which is the same as that in Example 1.

[0117] This embodiment also provides a process for preparing high-purity scandium oxide, which is the same as in Example 1 except that the slightly positive pressure oxygen atmosphere during the second heat treatment is replaced with a nitrogen atmosphere at atmospheric pressure.

[0118] Example 19 This embodiment provides a method for preparing a scandium oxalate precursor, which is the same as that in Example 1.

[0119] This embodiment also provides a preparation process for high-purity scandium oxide, which is the same as in Example 1 except that the pressure in the slightly positive pressure oxygen atmosphere during the second heat treatment is 0.02 kPa higher than atmospheric pressure.

[0120] Example 20 This embodiment provides a method for preparing a scandium oxalate precursor, which is the same as that in Example 1.

[0121] This embodiment also provides a preparation process for high-purity scandium oxide, which is the same as in Example 1 except that the pressure in the slightly positive pressure oxygen atmosphere during the second heat treatment is 20 kPa higher than atmospheric pressure.

[0122] Comparative Example 1 This comparative example provides a method for preparing scandium oxalate precursor. Except for replacing the oil-acid mixture system used in the first and second washing processes with the oil-acid mixture system used in the third washing process, the rest of the method is the same as in Example 1.

[0123] This comparative example also provides a preparation process for high-purity scandium oxide. Except for replacing the scandium oxalate precursor used in the preparation process with the scandium oxalate precursor obtained by the preparation method provided in this comparative example, the rest is the same as in Example 1.

[0124] Comparative Example 2 This comparative example provides a method for preparing scandium oxalate precursor. Except for replacing the oil-acid mixture system used in the third washing step with the oil-acid mixture system used in the first and second washing steps, the method is the same as in Example 1.

[0125] This comparative example also provides a preparation process for high-purity scandium oxide. Except for replacing the scandium oxalate precursor used in the preparation process with the scandium oxalate precursor obtained by the preparation method provided in this comparative example, the rest is the same as in Example 1.

[0126] The high-purity scandium oxide obtained by the preparation processes provided in Examples 1-20 and Comparative Examples 1-2 was tested using the following methods: the total metal impurity content in the high-purity scandium oxide was determined by inductively coupled plasma mass spectrometry (ICP-MS), the carbon impurity content in the sample was determined by high-frequency infrared carbon-sulfur analyzer, and the residual kerosene content in the sample was determined by headspace gas chromatography. The total metal impurity content, carbon impurity content, and residual kerosene content in the high-purity scandium oxide were obtained as shown in Table 1.

[0127] Scandium oxide was prepared using the preparation methods and processes provided in Examples 1-20 and Comparative Examples 1-2. The scandium concentration in the initial scandium-containing aqueous phase was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The mass of the final high-purity scandium oxide was weighed and the mass fraction of scandium was determined. The scandium yield was calculated as shown in Table 1.

[0128] Table 1 From Table 1, we can obtain: (1) After obtaining the scandium oxalate precursor by the preparation method provided in Examples 1-3, the high-purity scandium oxide prepared by the method also exhibits low total metal impurity content (≤47ppb), carbon impurity content (≤13ppm) and residual kerosene content (≤0.8ppm), and the scandium yield of the preparation method is high (≥95.9%). (2) By comparing Example 1 and Example 4, it can be seen that the preparation method of scandium oxalate precursor provided by the present invention, by adding citric acid to scandium-containing aqueous phase, utilizes its coordination effect to adjust the activity of metal ions, and combined with low temperature and slow precipitation, reduces local supersaturation, inhibits impurity co-precipitation and intracrystalline inclusion, and can obtain scandium oxalate precipitate with fewer defects and lower impurity content, which is beneficial to preparing high-purity scandium oxide with lower impurity content; (3) By comparing Example 1 and Example 5, it can be seen that in the preparation method of scandium oxalate precursor provided by the present invention, when the oil-acid mixed system used in the first washing stage includes both hydrogen chloride and oxalic acid, the high-purity scandium oxide finally prepared exhibits a lower impurity content. This is because hydrogen chloride can promote the desorption and dissolution of metal impurities on the surface and at the grain boundaries of scandium oxalate precipitate, while oxalic acid is beneficial to maintaining the stability of scandium oxalate precipitate and reducing scandium dissolution loss during the washing process, thereby taking into account both deep impurity removal and scandium recovery rate. (4) By comparing Example 1 with Examples 6 and 7, it can be seen that the preparation method of scandium oxalate precursor provided by the present invention, under the condition that the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the second washing stage are both lower than the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the first washing stage, when the volume fraction of kerosene in the oil-acid mixture used in the first washing stage is taken as 100%, the volume fraction of kerosene is 20%~40%, and the high-purity scandium oxide finally prepared exhibits a lower impurity content. This is because when the volume fraction of kerosene is in this range, it can take into account both the extraction ability of oil relative to hydrophobic organic residues and the leaching ability of acid solution to metal impurities. When the proportion of kerosene is too low, the organic matter is not removed in time, and when the proportion of kerosene is too high, it will reduce the contact efficiency between acid solution and precipitate and increase kerosene residue. (5) By comparing Example 1 with Examples 8 and 9, it can be seen that the preparation method of scandium oxalate precursor provided by the present invention, under the condition that the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture system used in the second washing stage are both lower than the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture system used in the first washing stage, when the components of the acid solution in the oil-acid mixture system used in the first washing stage include hydrochloric acid with a concentration of 0.3mol / L~0.8mol / L and oxalic acid solution with a concentration of 0.05mol / L~0.15mol / L, the high-purity scandium oxide finally prepared exhibits a lower impurity content. This is because a suitable concentration of hydrochloric acid can promote the desorption and dissolution of adsorbed impurities, and a suitable concentration of oxalic acid can inhibit the dissolution of scandium oxalate through common ion interaction; when the acid concentration is too low, the impurity removal is insufficient, and when it is too high, the dissolution loss of scandium is easily increased. (6) By comparing Example 1 with Examples 10 and 11, it can be seen that the preparation method of scandium oxalate precursor provided by the present invention, under the condition that the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the second washing section are both lower than the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture used in the first washing section, when the volume fraction of kerosene in the oil-acid mixture used in the second washing section is 10%~20%, the high-purity scandium oxide finally prepared exhibits a lower impurity content. This is because when the volume fraction of kerosene is in this range, it can improve the contact degree between acid solution and precipitate while maintaining the extraction effect of oil relative to residual organic matter; when the proportion of kerosene is too low, the oil removal is insufficient, and when the proportion of kerosene is too high, the gradient washing effect will be weakened and the kerosene residue will be increased. (7) By comparing Example 1 with Examples 12 and 13, it can be seen that the method for preparing scandium oxalate precursor provided by the present invention, under the condition that the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture system used in the second washing stage are both lower than the concentration of acid solution and the volume fraction of kerosene in the oil-acid mixture system used in the first washing stage, when the concentration of hydrochloric acid in the oil-acid mixture system used in the second washing stage is 0.1mol / L~0.3mol / L, the high-purity scandium oxide finally prepared exhibits a lower impurity content. This is because when the concentration of hydrochloric acid is in this range, it can further desorb and dissolve residual metal impurities, while reducing the acid dissolution loss of scandium oxalate. When the concentration of hydrochloric acid is too low, the deep impurity removal is insufficient, and when the concentration of hydrochloric acid is too high, it will increase the dissolution of scandium and acid residue. (8) By comparing Example 1 and Example 14, it can be seen that the preparation method of scandium oxalate precursor provided by the present invention, during the supercritical CO2 treatment, allows supercritical CO2 to fully penetrate into the microporous structure and grain boundary region of scandium oxalate precursor. By utilizing the dissolution and extraction effect of supercritical CO2 on non-polar organic matter, the residual organic carbon sources such as kerosene in the micropores and grain boundaries of scandium oxalate precipitate are deeply removed, thereby improving the purity of the obtained scandium oxalate precursor, which is beneficial to obtaining scandium oxide with higher purity. (9) By comparing Example 1 with Examples 15 and 16, it can be seen that the preparation method of scandium oxalate precursor provided by the present invention, when the temperature of supercritical CO2 treatment is 40℃~50℃, the high-purity scandium oxide finally prepared exhibits a lower impurity content. This is because this temperature range can enable CO2 to maintain suitable fluid density, solubility and diffusion performance, fully penetrate the micropores of the precursor and extract residual oil. (10) By comparing Example 1 with Examples 17 and 18, it can be seen that the preparation process of high-purity scandium oxide provided by the present invention improves the purity of scandium oxide by controlling the temperature in stages and switching the heat treatment atmosphere. In this process, a first heat treatment is carried out in a protective atmosphere to initially thermally decompose the scandium oxalate precursor and reduce the carbon residue caused by the violent cracking of organic components. Then, a second heat treatment is carried out in a slightly positive pressure oxygen atmosphere to further decompose the pre-decomposition product and convert it into scandium oxide, while oxidizing and removing residual carbon and residual kerosene. Thus, while maintaining low metal impurities, high-purity scandium oxide with low carbon and low residual oil is obtained. (11) By comparing Example 1 with Examples 19 and 20, it can be seen that the high-purity scandium oxide preparation process provided by the present invention, when the pressure in the micro-positive pressure oxygen atmosphere is 0.1 kPa to 5 kPa higher than atmospheric pressure, the high-purity scandium oxide finally prepared exhibits a lower impurity content. This is because the micro-positive pressure range can stably supply oxygen and prevent backflow of external gas, so that residual carbon and organic matter can be uniformly oxidized and removed. (12) By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the method for preparing scandium oxalate precursor provided by the present invention uses an oil-acid mixed system composed of acid solution and kerosene to perform gradient washing on scandium oxalate precipitate, so that scandium oxalate precipitate, acid solution and kerosene form a solid-liquid-liquid three-phase washing system; wherein, the acid solution can promote the desorption, dissolution and migration of impurities adsorbed on the surface and grain boundary region of scandium oxalate precipitate to the liquid phase, and the kerosene can remove hydrophobic organic residues, and the two synergistically enhance the removal of impurities. Effects; In addition, by using a lower concentration of acid solution and a lower volume fraction of kerosene in the second washing stage compared to the first washing stage, this invention enhances impurity removal under the conditions of high acidity and high oil phase ratio in the first washing stage. By reducing the acidity and oil phase ratio in the second washing stage, it can reduce the dissolution loss of scandium oxalate in the acidic environment and reduce the residue of kerosene and organic acids in the scandium oxalate precipitate. Thus, while achieving deep removal of impurities, it reduces scandium loss and the residue of kerosene and organic acids.

[0129] 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 of producing a scandium oxalate precursor, characterized by, The preparation method includes: Scandium-containing aqueous phase was mixed with oxalic acid precipitant to obtain scandium oxalate precipitate; the obtained scandium oxalate precipitate was subjected to gradient washing using an oil-acid mixed system to obtain scandium oxalate precursor; The oil-acid mixture system comprises an acid solution and kerosene, and the gradient washing includes a first washing section and a second washing section performed sequentially; the first washing section and the second washing section each independently include at least one washing. The concentration of the acid solution and the volume fraction of kerosene in the oil-acid mixture used in the second washing section are both lower than those in the oil-acid mixture used in the first washing section.

2. The production method according to claim 1, characterized by, In the oil-acid mixed system used in the first washing section, the acid solution contains hydrogen chloride and oxalic acid, and the molar ratio of hydrogen chloride to oxalic acid is (4~8):

1. And / or, in the oil-acid mixed system used in the first washing section, the acid solution comprises hydrochloric acid with a concentration of 0.3 mol / L to 0.8 mol / L and oxalic acid solution with a concentration of 0.05 mol / L to 0.15 mol / L; And / or, based on the volume fraction of the oil-acid mixture used in the first washing section, the volume fraction of kerosene is 20% to 40%; And / or, based on the volume fraction of the oil-acid mixture used in the first washing section, the volume fraction of the acid solution is 60%~80%; And / or, the first washing section includes performing a first wash and a second wash in sequence, wherein the first wash and the second wash use the same oil-acid mixture system, and the temperature and time of the second wash are lower than those of the first wash.

3. The production method according to claim 2, characterized by, The first washing method includes mixing and stirring at a temperature of 30℃~45℃ for a time of 20min~40min; And / or, the second washing method includes mixing and stirring at a temperature of 25°C to 35°C for a time of 15 min to 30 min.

4. The preparation method according to claim 1, characterized in that, In the second washing section, the oil-acid mixed system contains hydrochloric acid with a concentration of 0.1 mol / L to 0.3 mol / L. And / or, based on the volume fraction of the oil-acid mixture used in the second washing section, the volume fraction of kerosene is 10% to 20%; And / or, based on the volume fraction of the oil-acid mixture used in the second washing section, the volume fraction of the acid solution is 80%~90%; And / or, the second washing section includes a third washing, wherein the third washing is performed by mixing and stirring at a temperature of 20°C to 30°C for a time of 10 to 20 minutes.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The preparation method further includes adding citric acid to the scandium-containing aqueous phase before mixing to obtain a scandium-containing aqueous phase containing citric acid; And / or, the preparation method further includes pH adjustment of the scandium-containing aqueous phase prior to mixing; And / or, the mixing includes sequential mixing of a precipitant and aging; And / or, the preparation method further includes supercritical CO2 treatment following the gradient washing.

6. The preparation method according to claim 5, characterized in that, In the scandium-containing aqueous phase containing citric acid, the molar ratio of citrate ions to scandium ions is (0.05~0.2):1; And / or, the pH adjustment includes adjusting the pH of the scandium-containing aqueous phase to 1.0~1.5; And / or, the method of incorporating the precipitant includes: adding oxalic acid precipitant to the scandium-containing aqueous phase at a dropping rate of 0.5 mL / min to 2 mL / min at a temperature of 5°C to 10°C; And / or, the curing method includes: holding at a temperature of 5°C to 10°C for 30 min to 120 min; And / or, the method of supercritical CO2 treatment includes: placing the solid obtained by gradient washing in a supercritical CO2 treatment device, continuously feeding supercritical CO2 at a feed flow rate of 10L / h to 30L / h, and treating it for 1h to 3h under a pressure of 8MPa to 12MPa and a temperature of 40℃ to 50℃.

7. A scandium oxalate precursor, characterized in that, The scandium oxalate precursor is obtained by the preparation method according to any one of claims 1 to 6.

8. A process for preparing high-purity scandium oxide, characterized in that, The preparation process includes: subjecting the scandium oxalate precursor of claim 7 to a first heat treatment in a protective atmosphere, followed by a second heat treatment in a slightly positive pressure oxygen atmosphere to obtain high-purity scandium oxide.

9. The preparation process according to claim 8, characterized in that, Prior to the first heat treatment, dehydration is carried out in a protective atmosphere at 120°C to 160°C for 30 to 120 minutes. And / or, the temperature of the first heat treatment is 280℃~330℃, and the time is 60min~180min; And / or, the volume fraction of oxygen in the micro-positive pressure oxygen atmosphere is 20%~40%, and the pressure is 0.1kPa~5kPa higher than atmospheric pressure; And / or, the temperature of the second heat treatment is 850℃~920℃, and the time is 60min~180min.

10. A high-purity scandium oxide, characterized in that, The high-purity scandium oxide is obtained by the preparation process described in claim 8 or 9.

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