A method for recovering scandium oxide from scandium slag, scandium oxide and its applications

Abstract

This invention relates to the field of hydrometallurgical technology, specifically to a method for recovering scandium oxide from scandium slag, scandium oxide, and its applications. The invention involves acid leaching of scandium slag obtained from MHP (methods for hydrometallurgical processes), followed by an N1923 extraction stage, then a P350 extraction stage, followed by an N235 extraction stage. Finally, a scandium chloride solution is precipitated and calcined to obtain high-purity scandium oxide. This method avoids the alkaline reaction process required for scandium-loaded organic phases. The entire extraction process can be carried out in the extraction tank without filtration, resulting in high automation, excellent continuity, a short process, and significantly reduced acid consumption. Furthermore, this invention uses the amine extractant N1923, which has strong selectivity for scandium. When used as the first extraction stage to separate most impurities, the extraction and back-extraction temperatures are lower than those required by acidic phosphine extractants, preventing aging and deterioration of the organic phase. This significantly reduces the number of back-extraction stages and substantially lowers production costs.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, and more specifically, to a method for recovering scandium oxide from scandium slag, scandium oxide and its applications. Background Technology

[0002] Scandium metal, scandium oxide, and scandium alloys are widely used in aerospace, metallurgy, chemical engineering, and clean energy. In the pressurized acid leaching (HPAL) process of laterite nickel ore, scandium is mainly distributed in the production of nickel-cobalt hydroxide intermediate (MHP). Due to the large volume of MHP processing in recent years, the output of scandium as a byproduct has also increased. Current technology processes MHP by acid leaching, adjusting the pH of the leaching solution, adding a reducing agent to precipitate scandium, and then filtering to obtain scandium-rich slag. This slag is then acid-dissolved to obtain scandium solution. Compared to using tungsten, titanium, or rare earth metal deposits or metallurgical waste as scandium-containing raw materials, the scandium solution obtained from MHP is essentially free of rare earth elements, thus the scandium purification process is relatively simple.

[0003] Currently, most industrial processes in China for purifying scandium from MHP use acidic phosphine extractants, such as P204 and P507 extractants. These extractants are widely used because they exhibit high selectivity for scandium at specific pH values ​​and can effectively separate scandium from impurity elements.

[0004] However, the scandium-loaded organic phase obtained by extraction with acidic phosphine extractants requires back-extraction with liquid alkali, followed by dissolution and acidity adjustment with hydrochloric acid, consuming a very large amount of acid. Furthermore, the scandium-rich solution obtained after back-extraction is a suspension, requiring filtration, resulting in poor continuity. Liquid alkali requires a series of post-treatment processes, leading to a long process and high costs. Additionally, using acidic phosphine extractants first separates most impurities, and the organic phase is prone to aging or deterioration due to high-temperature back-extraction, requiring a relatively large number of back-extraction stages.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a method for recovering scandium oxide from scandium residue. This method avoids the use of acidic phosphine extractants, thus eliminating the need for alkaline reaction processes required for scandium-loaded organic phases. The entire extraction process can be carried out in the extraction tank without filtration, resulting in high automation, excellent continuity, a short process, and low cost. Furthermore, this invention fully considers the characteristics of the extractant; apart from the back-extraction operation, no additional acid is needed to adjust the acidity of the extraction feed, significantly reducing acid consumption. In addition, this invention first uses the amine extractant N1923, which has strong selectivity for scandium. When used as the first extraction stage to separate most impurities, the extraction and back-extraction temperatures required are lower than those required by acidic phosphine extractants, virtually eliminating the aging or deterioration of the organic phase due to high temperatures. Moreover, the number of stages in the back-extraction stage is significantly reduced, further contributing to cost savings.

[0007] A second objective of this invention is to provide a scandium oxide with high purity.

[0008] A third objective of this invention is to provide applications of scandium oxide in the fields of aerospace, information technology, metallurgy and chemical engineering, and clean energy.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] This invention first provides a method for recovering scandium oxide from scandium residue, comprising the following steps:

[0011] (a) The scandium residue obtained from MHP is mixed with sulfuric acid and leached, followed by solid-liquid separation to obtain a leachate; the leachate is subjected to a first extraction using N1923 extractant to obtain an N1923 organic phase and an N1923 aqueous phase; wherein, the N1923 extractant is mainly composed of secondary carbon amine, isooctanol and sulfonated kerosene; the N1923 organic phase is washed and then subjected to a first back-extraction using hydrochloric acid to obtain an N1923 back-extraction solution;

[0012] (b) The N1923 back-extraction solution is subjected to a second extraction using P350 extractant to obtain a P350 organic phase and a P350 aqueous phase; wherein, the P350 extractant is mainly composed of dimethylheptyl methylphosphonate and sulfonated kerosene; the P350 organic phase is subjected to a second back-extraction using hydrochloric acid to obtain a P350 back-extraction solution.

[0013] (c) The P350 back-extraction solution is subjected to a third extraction using N235 extractant to obtain N235 organic phase and N235 aqueous phase; wherein, the N235 extractant is mainly composed of trioctyldecyl tertiary amine, sec-octanol and sulfonated kerosene.

[0014] (d) Adjust the pH of the N235 aqueous phase and add a precipitant to perform scandium precipitation treatment. After solid-liquid separation, a scandium-containing precipitate is obtained. The scandium-containing precipitate is then calcined to obtain scandium oxide.

[0015] Further, in step (a), the volume ratio of the secondary carbon amine, the isooctyl alcohol, and the sulfonated kerosene in the N1923 extractant is 15-25:5-15:60-80.

[0016] Further, in step (a), the volume ratio of the N1923 extractant to the leachate is 2 to 5:1.

[0017] Further, in step (a), the first extraction is a 2-5 stage extraction.

[0018] Furthermore, in step (a), the temperature of the first extraction is 40–55°C.

[0019] Further, in step (a), the N1923 organic phase is washed with a sulfuric acid solution with a molar concentration of 0.5 to 2 mol / L; preferably, the volume ratio of the sulfuric acid solution used for washing to the N1923 organic phase is 2 to 4:1; preferably, the washing is a 5 to 12-stage washing process.

[0020] Further, in step (a), a hydrochloric acid solution with a molar concentration of 3 to 5 mol / L is used for the first back-extraction.

[0021] Further, in step (a), during the first back-extraction process, the volume ratio of the hydrochloric acid to the washed N1923 organic phase is 3 to 5:1.

[0022] Furthermore, in step (a), the first back-extraction is a 3-5 stage back-extraction.

[0023] Furthermore, in step (a), the temperature of the first back-extraction is 40–55°C.

[0024] Further, in step (a), the sulfuric acid used for leaching comprises 0.5 to 3 mol / L dilute sulfuric acid.

[0025] Further, in step (a), the final acidity of the leaching is 0.2 to 1.0 mol / L.

[0026] Further, in step (b), the volume ratio of the dimethylheptyl methylphosphonate and the sulfonated kerosene in the P350 extractant is 30-50:50-70.

[0027] Further, in step (b), the volume ratio of the P350 extractant to the N1923 back-extraction solution is 2 to 4:1.

[0028] Further, in step (b), the second extraction is a 5-12 stage extraction.

[0029] Furthermore, in step (b), the temperature of the second extraction is 40–55°C.

[0030] Further, in step (b), hydrochloric acid with a molar concentration of 1 to 2 mol / L is used for the second back-extraction.

[0031] Further, in step (b), during the second back-extraction process, the volume ratio of the hydrochloric acid to the P350 organic phase is 1 to 2:1.

[0032] Furthermore, in step (b), the second back-extraction is a 2-4 stage back-extraction.

[0033] Furthermore, in step (b), the temperature of the second back-extraction is 40–55°C.

[0034] Further, in step (c), the volume ratio of the trioctyldecyl tertiary amine, the sec-octanol, and the sulfonated kerosene in the N235 extractant is 5-25: 5-15: 60-90.

[0035] Further, in step (c), the volume ratio of the N235 extractant to the P350 back-extraction solution is 1 to 4:1.

[0036] Furthermore, in step (c), the third extraction is a 1-3 stage extraction.

[0037] Further, in step (d), the pH of the N235 aqueous phase is adjusted to 1.0–2.0.

[0038] Further, in step (d), the pH of the N235 aqueous phase is adjusted using a neutralizing agent, the neutralizing agent comprising at least one of an ammonia solution, an ammonium carbonate solution, and an ammonium bicarbonate solution.

[0039] Further, in step (d), the precipitant comprises an oxalic acid solution with a mass fraction of 5% to 10%.

[0040] Furthermore, in step (d), the temperature of the scandium precipitation treatment is 45–90°C.

[0041] Furthermore, in step (d), the scandium precipitation treatment time is 0.5 to 1 hour.

[0042] Further, in step (d), the reaction pH of the scandium precipitation treatment is 1.0 to 2.0.

[0043] Furthermore, in step (d), the calcination temperature is 1000–1100°C.

[0044] Furthermore, in step (d), the calcination holding time is 4 to 6 hours.

[0045] The present invention further provides scandium oxide prepared by the method for recovering scandium oxide from scandium slag, wherein the scandium oxide has a purity >99.9%.

[0046] The present invention also provides applications of the scandium oxide in the fields of aerospace, information technology, metallurgy and chemical industry and clean energy.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0048] (1) The method for recovering scandium oxide from scandium residue provided by this invention does not use acidic phosphine extractants, thus avoiding the alkaline reaction process required for scandium-loaded organic phases. The entire extraction process can be carried out in the extraction tank without filtration, resulting in high automation, excellent continuity, short process, and low cost. At the same time, this invention fully considers the characteristics of the extractant, and except for the back-extraction operation, no additional acid is needed to adjust the acidity of the extraction solution, thus significantly reducing acid consumption. In addition, this invention first uses the amine extractant N1923, which has strong selectivity for scandium. When used as the first extraction stage to separate most impurities, the temperature required for extraction and back-extraction is lower than that required by acidic phosphine extractants, and there is basically no problem of aging or deterioration of the organic phase due to high temperature. Furthermore, the number of stages in the back-extraction stage is also greatly reduced, which is more conducive to saving production costs.

[0049] (2) The method for recovering scandium oxide from scandium residue provided by the present invention, compared with the conventional P204 extraction process, fully considers the characteristics of raw materials and the properties of extractant. By optimizing the combination of extractant and metal extraction performance, the present invention avoids the disadvantages of high-temperature back-extraction with liquid alkali loaded with organic matter, and greatly improves production processing efficiency and safety.

[0050] (3) The method for recovering scandium oxide from scandium residue provided by the present invention fully considers the specific acidity values ​​required for extraction and back-extraction using N1923, P350, and N235 extractants. Before entering the next extraction stage, the acidity does not need to be readjusted with acid or alkali. This method requires fewer extraction stages, has a shorter process flow, excellent extractant recyclability, and low production costs.

[0051] (4) The method for recovering scandium oxide from scandium slag provided by the present invention has a high scandium recovery rate and the obtained scandium oxide has a purity of over 99.9%. Attached Figure Description

[0052] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0053] Figure 1 This is a schematic flowchart of the method for recovering scandium oxide from scandium slag provided by the present invention. Detailed Implementation

[0054] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0055] In a first aspect, the present invention provides a method for recovering scandium oxide from scandium slag, and also a method for extracting and purifying scandium from scandium slag, comprising the following steps:

[0056] (a) The scandium residue obtained from MHP is mixed with sulfuric acid and leached, followed by solid-liquid separation to obtain the leachate, which is the N1923 extraction solution.

[0057] It is understandable that the leachate obtained after acid leaching of MHP raw material is reduced, precipitated, and filtered to obtain the scandium residue obtained from MHP as described above.

[0058] The leachate was subjected to a first extraction using N1923 extractant to obtain an N1923 organic phase and an N1923 aqueous phase. The N1923 extractant mainly consisted of secondary carbon amine, isooctanol, and sulfonated kerosene. After washing, the N1923 organic phase was subjected to a first back-extraction using hydrochloric acid to obtain the N1923 back-extraction solution, which is the P350 extraction feed solution and also a scandium chloride solution.

[0059] (b) The N1923 back-extraction solution is subjected to a second extraction using P350 extractant to obtain a P350 organic phase and a P350 aqueous phase; wherein, the P350 extractant is mainly composed of dimethylheptyl methylphosphonate and sulfonated kerosene; the P350 organic phase is subjected to a second back-extraction using hydrochloric acid to obtain a P350 back-extraction solution, which is the N235 extraction solution and also a scandium chloride solution.

[0060] (c) The P350 back-extraction solution is subjected to a third extraction using N235 extractant to obtain an N235 organic phase and an N235 aqueous phase, which is a scandium-rich solution. The N235 extractant mainly consists of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene.

[0061] (d) Adjust the pH of the N235 aqueous phase and add a precipitant to perform scandium precipitation treatment. After solid-liquid separation, a scandium-containing precipitate is obtained. The scandium-containing precipitate is then calcined to obtain scandium oxide.

[0062] This invention uses an extraction process to recover scandium oxide from scandium residue obtained from MHP, wherein the sample first passes through an N1923 extraction section, then through a P350 extraction section, and finally through an N235 extraction section.

[0063] Specifically, in this invention, scandium residue obtained from MHP is leached with sulfuric acid, and the leachate is input into the N1923 extraction section. At this point, the pH of the system is suitable, and scandium, iron, calcium, sodium, silicon, etc., in the leachate enter the N1923 organic phase, while most impurity elements remain in the solution, forming the N1923 aqueous phase. Subsequently, the N1923 organic phase is washed to separate sodium and silicon from the organic phase. Then, the N1923 organic phase is back-extracted with hydrochloric acid to separate scandium from the organic phase, obtaining a crude scandium chloride solution containing small amounts of iron and calcium (i.e., the N1923 back-extract). The remaining organic phase after back-extraction can be recovered and used as the extractant for N1923 extraction.

[0064] Further, the obtained crude scandium chloride solution (i.e., N1923 back-extraction solution) is fed into the P350 extraction section. At this point, the system pH is suitable, and scandium and iron enter the P350 organic phase, while most of the calcium remains in the solution, forming the P350 aqueous phase. The P350 organic phase is then back-extracted using hydrochloric acid to obtain a further purified scandium chloride solution (i.e., P350 back-extraction solution). The back-extracted P350 organic phase is further washed, and the remaining organic phase can be recovered as the P350 extractant.

[0065] Further, the scandium chloride solution, after further purification (i.e., the P350 back-extraction solution), is fed into the N235 extraction section. At this point, the system pH is suitable, iron enters the N235 organic phase, and most of the scandium remains in the solution to form the N235 aqueous phase, thus obtaining a purified scandium chloride solution. Then, the organic phase is back-extracted with pure water, and the remaining organic phase can be recovered and used as the extractant for N235 extraction.

[0066] Furthermore, the obtained refined scandium chloride solution is subjected to scandium precipitation treatment, which can leave trace impurity elements in the aqueous phase. After high-temperature calcination, the scandium-containing precipitate yields high-purity scandium oxide.

[0067] The method for recovering scandium oxide from scandium residue provided by this invention does not use acidic phosphine extractants, thus avoiding the alkaline reaction process required for scandium-loaded organic phases. The entire extraction process can be carried out in the extraction tank without the need for filtration, resulting in high automation, excellent continuity, short process, and low cost. At the same time, this invention fully considers the characteristics of the extractant, and apart from the back-extraction operation, there is no need to add additional acid to adjust the acidity of the extraction solution, thereby significantly reducing acid consumption.

[0068] In addition, the present invention first uses amine extractant N1923, which has strong selectivity for scandium. When used as the first extraction stage to separate most impurities, the temperature required for extraction and back-extraction is lower than that required for acidic phosphine extractants. There is basically no problem of aging or deterioration of the organic phase due to high temperature. Furthermore, the number of stages in the back-extraction stage is also greatly reduced, which is more conducive to saving production costs.

[0069] The process flow of this invention fully considers the extraction principles of N1923, P350, and N235 extractants. N1923 extractant requires a sulfuric acid system for reaction, while P350 and N235 extractants require a hydrochloric acid system. The loaded organic matter after N1923 extraction of scandium needs to be stripped off with hydrochloric acid, thus completing the system conversion from sulfuric acid to hydrochloric acid. However, the extraction and back-extraction processes of P350 and N235 cannot achieve this conversion. If the P350 or N235 extraction process is performed first, the resulting hydrochloric acid back-extraction solution cannot be used for scandium extraction after entering N1923. The extraction and back-extraction process of N1923 is the only system conversion method in this process; therefore, the first extraction step using N1923 extractant cannot be replaced by P350 or N235. On the other hand, in addition to its ability to extract iron ions, N235 extractant also has the ability to extract hydrochloric acid. If the back-extraction solution obtained after N1923 back-extraction is first extracted with N235, it will cause a decrease in the acidity of the extract, affecting the subsequent extraction ability of P350 extractant for scandium. Therefore, the extraction sequence of N1923-P350-N235 in the process flow of this invention cannot be adjusted.

[0070] like Figure 1 The diagram shows a flow chart of the method for recovering scandium oxide from scandium slag provided by the present invention.

[0071] In some specific embodiments, in step (a), the volume ratio of the secondary primary amine, the isooctanol, and the sulfonated kerosene in the N1923 extractant is 15-25 (including but not limited to point values ​​of any one of 15, 16, 18, 20, 22, 23, 25 or any range between any two): 5-15 (including but not limited to point values ​​of any one of 5, 6, 7, 8, 9, 10, 12, 13, 15 or any range between any two): 60-80 (including but not limited to point values ​​of any one of 60, 63, 65, 68, 70, 72, 75, 77, 80 or any range between any two). By controlling the proportion of the secondary primary amine, the extraction rate of scandium can be improved; by controlling the proportion of isooctanol, the phase separation time of the extraction process can be significantly reduced.

[0072] In some specific embodiments, in step (a), the volume ratio of the N1923 extractant to the leachate is 2 to 5:1, including but not limited to the point value of any one of 2:1, 3:1, 4:1, and 5:1, or the range between any two. When the volume ratio of the N1923 extractant to the leachate is 2 to 5:1, the extraction rate of scandium is high, and the extractant utilization efficiency is high.

[0073] In some specific implementations, in step (a), the first extraction is a 2- to 5-stage extraction, such as a 2-stage extraction, a 3-stage extraction, a 4-stage extraction, or a 5-stage extraction.

[0074] In some specific embodiments, in step (a), the temperature of the first extraction is 40 to 55°C, including but not limited to any one of 40°C, 42°C, 43°C, 44°C, 45°C, 46°C, 48°C, 50°C, 53°C, and 55°C, or any range between two of them.

[0075] In some specific embodiments, in step (a), the N1923 organic phase is washed with a sulfuric acid solution with a molar concentration of 0.5 to 2 mol / L. The molar concentration of the sulfuric acid solution includes, but is not limited to, any one of 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L, and 2 mol / L, or a range between any two.

[0076] In some specific embodiments, the volume ratio of the sulfuric acid solution used for washing to the N1923 organic phase is 2 to 4:1, including but not limited to the point value of any one of 2:1, 3:1, and 4:1 or the range between any two.

[0077] In some specific implementations, the washing is a level 5 to 12 washing; for example, level 5 washing, level 6 washing, level 7 washing, level 8 washing, level 9 washing, level 10 washing, level 11 washing, level 13 washing or level 15 washing.

[0078] In some specific embodiments, in step (a), a hydrochloric acid solution with a molar concentration of 3 to 5 mol / L is used for the first back-extraction; wherein, the molar concentration of the hydrochloric acid solution includes, but is not limited to, any one of 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, or any range between two of them.

[0079] In some specific embodiments, in step (a), during the first back-extraction process, the volume ratio of the hydrochloric acid to the washed N1923 organic phase is 3 to 5:1, including but not limited to the point value of any one of 3:1, 4:1, and 5:1 or the range value between any two.

[0080] In some specific implementations, in step (a), the first back-extraction is a 3- to 5-stage back-extraction, such as a 3-stage back-extraction, a 4-stage back-extraction, or a 5-stage back-extraction.

[0081] Traditional extraction methods using acidic phosphine-based extractants involve multiple back-extraction stages, typically more than 10. In contrast, this invention employs fewer first-stage back-extraction, which helps reduce production costs.

[0082] The present invention has fewer back-extraction stages, which helps to shorten the process time and reduce costs.

[0083] In some specific embodiments, in step (a), the temperature of the first back-extraction is 40 to 55°C, including but not limited to any one of 40°C, 42°C, 43°C, 44°C, 45°C, 46°C, 48°C, 50°C, 53°C, and 55°C, or any range between two of them.

[0084] Traditional processes using acidic phosphine extractants require a back-extraction temperature of 70–80°C to obtain the scandium-loaded organic phase. This high temperature easily leads to aging or deterioration of the extractant. The present invention, however, uses a lower first back-extraction temperature, thus avoiding the problems of extractant aging or deterioration.

[0085] In some specific embodiments, in step (a), the sulfuric acid used for leaching includes 0.5 to 3 mol / L dilute sulfuric acid.

[0086] In some specific embodiments, in step (a), the acidity at the leaching endpoint is 0.2–1.0 mol / L, including but not limited to any one of 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, and 1 mol / L, or a range between any two. Here, acidity refers to hydrogen ion concentration. The endpoint acidity of leaching is the molar concentration of hydrogen ions in the reaction system at the leaching endpoint. As the endpoint acidity increases, scandium can be better leached from the raw material; however, excessively high endpoint acidity increases the cost of wastewater treatment. Therefore, this invention selects 0.2–1.0 mol / L as the endpoint acidity for leaching, balancing leaching effectiveness and cost.

[0087] In some specific implementations, in step (a), if the acidity at the leaching endpoint is too high, water can be added to the leachate for dilution.

[0088] In some specific embodiments, in step (b), the volume ratio of dimethylheptyl methylphosphonate to sulfonated kerosene in the P350 extractant is 30–50 (including but not limited to point values ​​of any one of 30, 32, 35, 38, 40, 42, 45, 47, 50 or any range between the two): 50–70 (including but not limited to point values ​​of any one of 50, 53, 55, 58, 60, 63, 65, 68, 70 or any range between the two). Using the above ratio of dimethylheptyl methylphosphonate to sulfonated kerosene can reduce the phase separation time during back-extraction.

[0089] In some specific embodiments, in step (b), the volume ratio of the P350 extractant to the N1923 back-extraction solution is 2 to 4:1, including but not limited to the point value of any one of 2:1, 3:1, and 4:1 or the range value between any two.

[0090] In some specific implementations, in step (b), the second extraction is a 5- to 12-stage extraction; for example, a 5-stage extraction, a 6-stage extraction, a 7-stage extraction, an 8-stage extraction, a 10-stage extraction, or a 12-stage extraction.

[0091] In some specific embodiments, in step (b), the temperature of the second extraction is 40 to 55°C, including but not limited to any one of 40°C, 42°C, 43°C, 44°C, 45°C, 46°C, 48°C, 50°C, 53°C, and 55°C, or any range between two of them.

[0092] In some specific embodiments, in step (b), hydrochloric acid with a molar concentration of 1 to 2 mol / L is used for the second back-extraction. The molar concentration of the hydrochloric acid includes, but is not limited to, any one of 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, and 2 mol / L, or a range between any two.

[0093] In some specific embodiments, in step (b), during the second back-extraction process, the volume ratio of the hydrochloric acid to the P350 organic phase is 1 to 2:1.

[0094] In some specific implementations, in step (b), the second back-extraction is a 2- to 4-stage back-extraction, such as a 2-stage back-extraction, a 3-stage back-extraction, or a 4-stage back-extraction.

[0095] In some specific embodiments, in step (b), the temperature of the second back-extraction is 40 to 55°C, including but not limited to any one of 40°C, 42°C, 43°C, 44°C, 45°C, 46°C, 48°C, 50°C, 53°C, and 55°C, or any range between two of them.

[0096] In some specific embodiments, in step (c), the volume ratio of the trioctyldecyl tertiary amine, the sec-octanol, and the sulfonated kerosene in the N235 extractant is 5–25 (including but not limited to any one of 5, 7, 8, 9, 10, 12, 13, 15, 18, 20, 23, 25 or any range between any two): 5–15 (including but not limited to any one of 5, 7, 8, 9, 10, 12, 13, 15 or any range between any two): 60–90 (including but not limited to any one of 60, 63, 65, 68, 70, 72, 75, 77, 80, 82, 85, 87, 90 or any range between any two). This invention achieves excellent extraction effect for iron ions and high extractant utilization efficiency by controlling the proportion of trioctyldecyl tertiary amine; by controlling the proportion of sec-octanol, the phenomenon of a third phase appearing during the extraction process can be effectively avoided.

[0097] In some specific embodiments, in step (c), the volume ratio of the N235 extractant to the P350 back-extraction solution is 1 to 4:1, including but not limited to the point value of any one of 1:1, 2:1, 3:1, and 4:1 or the range value between any two.

[0098] In some specific implementations, in step (c), the third extraction is a 1-3 stage extraction, such as a 1-stage, 2-stage, or 3-stage extraction.

[0099] In some specific implementations, in step (c), the temperature of the third extraction is an indoor temperature, such as 10 to 30°C, including but not limited to a point value of any one of 10°C, 15°C, 20°C, 25°C, and 30°C, or a range between any two.

[0100] In some specific embodiments, in step (d), the pH of the N235 aqueous phase is adjusted to 1.0–2.0; including but not limited to any one of 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 2.0, or a range between any two. In this invention, a pH of 1.0–2.0 for the N235 aqueous phase results in a higher extraction rate for iron ions.

[0101] In some specific embodiments, in step (d), the pH of the N235 aqueous phase is adjusted using a neutralizing agent, wherein the neutralizing agent includes at least one of an ammonia solution, an ammonium carbonate solution, and an ammonium bicarbonate solution.

[0102] In some specific embodiments, in step (d), the precipitant comprises an oxalic acid solution with a mass fraction of 5% to 10%. The mass fraction of the oxalic acid solution includes, but is not limited to, a value from any one of 5%, 6%, 7%, 8%, 9%, and 10%, or a range between any two.

[0103] In some specific implementations, in step (d), the temperature of the scandium precipitation treatment is 45 to 90°C; including but not limited to any one of 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, or any range between two of them.

[0104] In some specific implementations, in step (d), the scandium precipitation treatment time is 0.5 to 1 hour, for example, 0.6 hours or 0.8 hours.

[0105] In some specific embodiments, in step (d), the reaction pH of the scandium precipitation treatment is 1.0 to 2.0, that is, the pH of the reaction system during the scandium precipitation treatment is 1.0 to 2.0, including but not limited to any one of 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 2.0 or any range between two of them.

[0106] In some specific embodiments, in step (d), the calcination temperature is 1000 to 1100°C; including but not limited to any one of 1000°C, 1010°C, 1020°C, 1030°C, 1050°C, 1060°C, 1080°C, and 1100°C, or any range between two of them.

[0107] In some specific implementations, in step (d), the calcination holding time is 4 to 6 hours, for example, 5 hours.

[0108] Secondly, the present invention provides a scandium oxide prepared by the above-described method for recovering scandium oxide from scandium slag, wherein the purity of the scandium oxide is >99.9%.

[0109] The method for recovering scandium oxide from scandium slag provided by this invention can obtain high-purity scandium oxide, which is beneficial for the widespread application of scandium metal, scandium alloys, etc.

[0110] Thirdly, the present invention provides applications of the aforementioned scandium oxide in the fields of aerospace, information technology, metallurgy and chemical engineering, and clean energy.

[0111] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0112] The scandium residue obtained from MHP in the following embodiments and comparative examples is obtained by reducing precipitation and filtering the leachate obtained after acid leaching of MHP raw material.

[0113] Example 1

[0114] The method for recovering scandium oxide from scandium residue provided in this embodiment includes the following steps:

[0115] (1) 1000g of scandium residue obtained from MHP was leached with 1mol / L dilute sulfuric acid and filtered to obtain leachate with an acidity (i.e. hydrogen ion concentration) of 0.91mol / L. The acidity of the leachate was then adjusted to 0.5mol / L with water as the extraction solution for N1923.

[0116] (2) The N1923 extractant was prepared by mixing secondary carbon amine, isooctyl alcohol and sulfonated kerosene in a volume ratio of 20:15:65.

[0117] (3) The N1923 extractant and the N1923 extractant solution obtained in step (1) are subjected to three-stage extraction (i.e., the first extraction) at a volume ratio of 4:1 to obtain the N1923 organic phase and the N1923 aqueous phase.

[0118] Seven stages of washing were performed using 2 mol / L sulfuric acid and the N1923 organic phase at a volume ratio of 3.6:1 to remove impurities other than scandium, iron, and calcium.

[0119] The washed N1923 organic phase was subjected to three-stage back-extraction (i.e., the first back-extraction) using 3 mol / L hydrochloric acid at a volume ratio of 4:1 to obtain a crude scandium chloride solution as the P350 extraction feed (i.e., the N1923 back-extraction solution).

[0120] (4) P350 extractant was prepared by mixing dimethylheptyl methylphosphonate and sulfonated kerosene in a volume ratio of 40:60.

[0121] (5) The P350 extractant and the P350 extractant solution obtained in step (3) are subjected to five-stage extraction (i.e., the second extraction) at a volume ratio of 2:1 to obtain the P350 organic phase and the P350 aqueous phase.

[0122] The P350 organic phase was subjected to three-stage back-extraction (i.e., the second back-extraction) using 1 mol / L hydrochloric acid at a volume ratio of 2:1. The phase separation time during back-extraction was within 5 minutes, resulting in a scandium chloride solution for further impurity removal, i.e., N235 extraction feed (i.e., P350 back-extraction solution).

[0123] (6) Prepare N235 extractant by mixing trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene in a volume ratio of 5:10:85;

[0124] (7) The N235 extractant and the N235 extractant solution obtained in step (5) are subjected to a two-stage extraction (i.e., the third extraction) at a volume ratio of 2:1 to obtain the N235 organic phase and the N235 aqueous phase. The N235 aqueous phase is the scandium chloride solution.

[0125] (8) The pH of the scandium chloride solution in step (7) was adjusted to 1.5 using ammonia as a neutralizing agent. Then, 10% oxalic acid solution was added to the scandium chloride solution as a precipitant. During this process, ammonia was continuously added to control the pH at 1.5. The reaction was carried out at 80°C for 1 hour. After the scandium precipitation treatment, the solution was filtered to obtain a scandium-containing precipitate.

[0126] The scandium-containing precipitate in step (8) was calcined at 1000℃ for 4 hours to obtain scandium oxide.

[0127] Example 2

[0128] The method for recovering scandium oxide from scandium residue provided in this embodiment includes the following steps:

[0129] (1) 1000g of scandium residue obtained from MHP was leached with 1mol / L dilute sulfuric acid and filtered to obtain leachate with an acidity of 0.91mol / L. The acidity of the leachate was then adjusted to 0.5mol / L with water as the extraction solution for N1923.

[0130] (2) The N1923 extractant was prepared by mixing secondary carbon amine, isooctyl alcohol and sulfonated kerosene in a volume ratio of 25:15:60.

[0131] (3) The N1923 extractant and the N1923 extractant solution obtained in step (1) are subjected to five-stage extraction at a volume ratio of 4:1 to obtain the N1923 organic phase and the N1923 aqueous phase.

[0132] Seven stages of washing were performed using 2 mol / L sulfuric acid and the N1923 organic phase at a volume ratio of 3.6:1 to remove impurities other than scandium, iron, and calcium.

[0133] The washed N1923 organic phase was back-extracted in three stages using 3 mol / L hydrochloric acid at a volume ratio of 4:1 to obtain a crude scandium chloride solution, which was then used as the P350 extraction feed.

[0134] (4) P350 extractant was prepared by mixing dimethylheptyl methylphosphonate and sulfonated kerosene in a volume ratio of 40:60.

[0135] (5) The P350 extractant and the P350 extractant solution obtained in step (3) are subjected to 10 stages of extraction at a volume ratio of 2:1 to obtain the P350 organic phase and the P350 aqueous phase.

[0136] The P350 organic phase was subjected to three-stage back-extraction using 1 mol / L hydrochloric acid at a volume ratio of 2:1. The phase separation time during back-extraction was within 5 minutes, resulting in a scandium chloride solution, i.e., N235 extraction feed, which was further purified.

[0137] (6) Prepare N235 extractant by mixing trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene in a volume ratio of 10:10:80;

[0138] (7) The N235 extractant and the N235 extractant solution obtained in step (5) are subjected to two-stage extraction at a volume ratio of 3:1 to obtain the N235 organic phase and the N235 aqueous phase. The N235 aqueous phase is the scandium chloride solution.

[0139] (8) The pH of the scandium chloride solution in step (7) was adjusted to 1.5 using ammonia solution as a neutralizing agent. Then, 10% oxalic acid solution was added to the scandium chloride solution as a precipitant. During this process, ammonia solution was continuously added to control the pH at 1.8. The reaction was carried out at 80°C for 1 hour. After the scandium precipitation treatment, the solution was filtered to obtain a scandium-containing precipitate.

[0140] The scandium-containing precipitate in step (8) was calcined at 1000℃ for 4 hours to obtain scandium oxide.

[0141] Example 3

[0142] The method for recovering scandium oxide from scandium residue provided in this embodiment includes the following steps:

[0143] (1) 1000g of scandium residue obtained from MHP was leached with 1mol / L dilute sulfuric acid and filtered to obtain leachate with an acidity of 0.91mol / L. The acidity of the leachate was then adjusted to 0.5mol / L with water as the extraction solution for N1923.

[0144] (2) The N1923 extractant was prepared by mixing secondary carbon amine, isooctyl alcohol and sulfonated kerosene in a volume ratio of 20:15:65.

[0145] (3) The N1923 extractant and the N1923 extractant solution obtained in step (1) are subjected to five-stage extraction at a volume ratio of 4:1 to obtain the N1923 organic phase and the N1923 aqueous phase.

[0146] The N1923 organic phase was washed in 12 stages with 2 mol / L sulfuric acid at a volume ratio of 3.6:1 to remove impurities other than scandium, iron, and calcium.

[0147] The washed N1923 organic phase was back-extracted in three stages using 3 mol / L hydrochloric acid at a volume ratio of 4:1 to obtain a crude scandium chloride solution, which was then used as the P350 extraction feed.

[0148] (4) P350 extractant was prepared by mixing dimethylheptyl methylphosphonate and sulfonated kerosene in a volume ratio of 30:70.

[0149] (5) The P350 extractant and the P350 extractant solution obtained in step (3) are subjected to 12 stages of extraction at a volume ratio of 2:1 to obtain the P350 organic phase and the P350 aqueous phase.

[0150] The P350 organic phase was subjected to three-stage back-extraction using 1 mol / L hydrochloric acid at a volume ratio of 2:1. The phase separation time during back-extraction was within 5 minutes, resulting in a scandium chloride solution, i.e., N235 extraction feed, which was further purified.

[0151] (6) Prepare N235 extractant by mixing trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene in a volume ratio of 5:10:85;

[0152] (7) The N235 extractant and the N235 extractant solution obtained in step (5) are subjected to two-stage extraction at a volume ratio of 4:1 to obtain the N235 organic phase and the N235 aqueous phase. The N235 aqueous phase is the scandium chloride solution.

[0153] (8) The pH of the scandium chloride solution in step (7) was adjusted to 1.5 using ammonia as a neutralizing agent. Then, 5% oxalic acid solution was added to the scandium chloride solution as a precipitant. During this process, ammonia was continuously added to control the pH at 1.3. The reaction was carried out at 80°C for 1 hour. After the scandium precipitation treatment, the solution was filtered to obtain a scandium-containing precipitate.

[0154] The scandium-containing precipitate in step (8) was calcined at 1000℃ for 4 hours to obtain scandium oxide.

[0155] Example 4

[0156] The method for recovering scandium oxide from scandium residue provided in this embodiment is basically the same as that in embodiment 1. The difference is that in step (2), the volume ratio of secondary carbon amine, isooctyl alcohol and sulfonated kerosene is replaced with 15:5:80.

[0157] Example 5

[0158] The method for recovering scandium oxide from scandium residue provided in this embodiment is basically the same as that in embodiment 1. The difference is that in step (3), the volume ratio of N1923 extractant to N1923 extractant liquid is replaced with 2:1; and the volume ratio of hydrochloric acid to washed N1923 organic phase is replaced with 5:1.

[0159] Example 6

[0160] The method for recovering scandium oxide from scandium residue provided in this embodiment is basically the same as that in Example 1, except that in step (4), the volume ratio of dimethylheptyl phosphonate to sulfonated kerosene is replaced with 50:50.

[0161] Example 7

[0162] The method for recovering scandium oxide from scandium residue provided in this embodiment is basically the same as that in embodiment 1. The difference is that in step (5), the volume ratio of P350 extractant to P350 extractant is replaced with 4:1; and the volume ratio of hydrochloric acid to P350 organic phase is replaced with 1:1.

[0163] Example 8

[0164] The method for recovering scandium oxide from scandium residue provided in this embodiment is basically the same as that in Example 1. The difference is that in step (6), the volume ratio of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene is replaced with 25:5:60.

[0165] Comparative Example 1

[0166] The method for recovering scandium oxide from scandium residue provided in this comparative example is basically the same as that in Example 1, except that in step (2), the volume ratio of secondary carbon amine, isooctyl alcohol and sulfonated kerosene is replaced with 30:20:50.

[0167] Comparative Example 2

[0168] The method for recovering scandium oxide from scandium residue provided in this comparative example is basically the same as that in Example 1, except that in step (4), the volume ratio of dimethylheptyl phosphonate to sulfonated kerosene is replaced with 60:40. The phase separation time during back-extraction in step (5) of this comparative example is more than 1 hour.

[0169] Comparative Example 3

[0170] The method for recovering scandium oxide from scandium residue provided in this comparative example is basically the same as that in Example 1, except that in step (6), the volume ratio of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene is replaced with 30:20:50.

[0171] The chemical composition of the leachate obtained by leaching scandium residue with dilute sulfuric acid in each embodiment and comparative example is shown in Table 1.

[0172] Table 1 Chemical composition of leachate

[0173] element Sc Ni Cu Fe Ca Mg Na Al Si Content (g / L) 22.42 5.84 11.12 1.42 0.045 0.033 2.69 1.68 0.039

[0174] In each embodiment and comparative example, step (3) was performed using N1923 extractant for the first extraction, and the extraction rates of each element are shown in Table 2.

[0175] Table 2 shows the extraction rates (%) of each element during the first extraction using N1923 extractant.

[0176] element Sc Ni Cu Fe Ca Mg Na Al Si Example 1 99.36 0.21 0.0032 5.42 1.56 0.043 0.087 0.35 0.059 Example 2 99.64 0.25 0.0054 5.68 1.55 0.036 0.098 0.42 0.057 Example 3 99.07 0.2 0.0028 5.33 1.47 0.028 0.047 0.28 0.018 Example 4 98.28 0.17 0.0034 5.28 1.36 0.041 0.080 0.31 0.055 Example 5 93.87 0.18 0.0030 5.34 1.38 0.039 0.074 0.33 0.054 Example 6 99.28 0.20 0.0031 5.44 1.59 0.041 0.090 0.34 0.058 Example 7 99.34 0.21 0.0038 5.38 1.59 0.043 0.081 0.34 0.049 Example 8 99.28 0.19 0.0041 5.48 1.58 0.041 0.079 0.35 0.051 Comparative Example 1 99.68 0.27 0.0055 5.89 1.58 0.036 0.092 0.47 0.042 Comparative Example 2 99.32 0.21 0.0031 5.48 1.57 0.041 0.084 0.27 0.053 Comparative Example 3 99.48 0.21 0.0048 5.34 1.51 0.044 0.075 0.34 0.048

[0177] In each embodiment and comparative example, step (5) was performed using P350 extractant for a second extraction, and the extraction rates of each element are shown in Table 3.

[0178] Table 3. Extraction rates (%) of each element using P350 extractant in the second extraction.

[0179]

[0180]

[0181] In each embodiment and comparative example, step (7) was performed using N235 extractant for the third extraction, and the extraction rates of each element are shown in Table 4.

[0182] Table 4. Extraction rates (%) of each element using N235 extractant in the third extraction.

[0183] element Sc Ni Cu Fe Ca Mg Na Al Si Example 1 1.59 0.0084 0.0005 >99.9 0.0079 0.0078 0.0005 30.78 1.32 Example 2 2.04 0.012 0.0008 >99.9 0.010 0.0087 0.0008 45.89 2.48 Example 3 1.89 0.0079 0.0006 >99.9 0.0082 0.0063 0.0005 37.84 1.08 Example 4 1.48 0.0087 0.0005 >99.9 0.0075 0.0077 0.0005 33.78 1.34 Example 5 1.53 0.0079 0.0005 >99.9 0.0077 0.0080 0.0005 32.45 1.29 Example 6 1.57 0.0087 0.0005 >99.9 0.0097 0.0084 0.0006 47.66 2.37 Example 7 1.48 0.0078 0.0008 >99.9 0.0099 0.0087 0.0009 46.36 2.84 Example 8 2.31 0.0110 0.0008 >99.9 0.0120 0.0077 0.0008 49.33 2.43 Comparative Example 1 1.59 0.0074 0.0006 >99.9 0.0074 0.0082 0.0006 30.24 1.39 Comparative Example 2 1.42 0.0092 0.0004 >99.9 0.0076 0.0084 0.0005 33.47 1.29 Comparative Example 3 2.98 0.0190 0.0008 >99.9 0.0130 0.0083 0.0008 44.57 2.38

[0184] The scandium yield and the purity of the obtained scandium oxide in step (8) of each embodiment and comparative example are shown in Table 5.

[0185] Table 5. Scandium yield and purity of scandium oxide obtained after scandium precipitation treatment.

[0186]

[0187]

[0188] As shown in Tables 1 to 5, the total scandium yield (total scandium yield = extraction rate of the first scandium extract × extraction rate of the second scandium extract × (1 - extraction rate of the third scandium extract) × scandium yield of the precipitation treatment) in each embodiment is >90%, indicating excellent separation of impurity elements. The final scandium oxide purity is >99.9%. Therefore, the technical solution of this invention can efficiently separate scandium from impurity elements while maintaining a high scandium recovery rate, resulting in high-purity scandium oxide.

[0189] In Comparative Example 1, the volume ratio of secondary carbon amine, isooctanol, and sulfonated kerosene was unsuitable. Although the scandium extraction rate in the first extraction was not significantly different from that in Example 1, the amount of extractant used was increased by 50%, resulting in low extractant utilization and increased production costs.

[0190] In Comparative Example 2, the volume ratio of dimethylheptyl phosphonate to sulfonated kerosene was not suitable. Although the scandium extraction rate in the second extraction was not much different from that in Example 1, the phase separation time during back-extraction in Comparative Example 2 reached more than 1 hour, which was significantly longer than the phase separation time during back-extraction in Example 1, which was not conducive to actual production operation.

[0191] In Comparative Example 3, the volume ratio of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene was unsuitable. Although the iron extraction rate in the third extraction was essentially the same as in Example 1, the scandium extraction rate increased by 1.39%, resulting in scandium loss. Furthermore, the extractant dosage increased sixfold, leading to extremely low extractant utilization and a significant increase in production costs.

[0192] In summary, this invention addresses several problems: the scandium-loaded organic phase obtained by extraction with acidic phosphine extractants requires back-extraction with liquid alkali followed by dissolution and acidity adjustment with hydrochloric acid, resulting in a large acid consumption; the scandium-rich solution obtained after back-extraction is a suspension requiring filtration, leading to poor continuity; the liquid alkali requires a series of post-treatments, resulting in a long process and high cost; and the use of acidic phosphine extractants to first separate most impurities, the organic phase being prone to aging or deterioration due to high-temperature back-extraction, and the relatively large number of back-extraction stages. In contrast, this invention achieves high scandium recovery rate, obtains high-purity scandium oxide, saves on production processes, and significantly reduces costs.

[0193] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for recovering scandium oxide from scandium residue, characterized in that, Includes the following steps: (a) The scandium residue obtained from MHP is mixed with sulfuric acid and leached, followed by solid-liquid separation to obtain a leachate; the leachate is subjected to a first extraction using N1923 extractant to obtain an N1923 organic phase and an N1923 aqueous phase; wherein, the N1923 extractant is mainly composed of secondary carbon amine, isooctanol and sulfonated kerosene; the N1923 organic phase is washed and then subjected to a first back-extraction using hydrochloric acid to obtain an N1923 back-extraction solution; (b) The N1923 back-extraction solution is subjected to a second extraction using P350 extractant to obtain a P350 organic phase and a P350 aqueous phase; wherein, the P350 extractant is mainly composed of dimethylheptyl methylphosphonate and sulfonated kerosene; the P350 organic phase is subjected to a second back-extraction using hydrochloric acid to obtain a P350 back-extraction solution. (c) The P350 back-extraction solution is subjected to a third extraction using N235 extractant to obtain N235 organic phase and N235 aqueous phase; wherein, the N235 extractant is mainly composed of trioctyldecyl tertiary amine, sec-octanol and sulfonated kerosene. (d) Adjust the pH of the N235 aqueous phase and add a precipitant to perform scandium precipitation treatment. After solid-liquid separation, a scandium-containing precipitate is obtained. The scandium-containing precipitate is then calcined to obtain scandium oxide.

2. The method for recovering scandium oxide from scandium residue according to claim 1, characterized in that, In step (a), at least one of the following conditions must be met: (1) The volume ratio of the secondary carbon primary amine, the isooctyl alcohol and the sulfonated kerosene in the N1923 extractant is 15~25:5~15:60~80; (2) The volume ratio of the N1923 extractant to the leachate is 2~5:1; (3) The first extraction is a 2-5 stage extraction; (4) The temperature of the first extraction is 40~55℃.

3. The method for recovering scandium oxide from scandium residue according to claim 1, characterized in that, In step (a), at least one of the following conditions must be met: (1) The N1923 organic phase is washed with a sulfuric acid solution with a molar concentration of 0.5~2 mol / L; the volume ratio of the sulfuric acid solution used for washing to the N1923 organic phase is 2~4:1; the washing is a 5~12 stage washing; (2) The first back-extraction was performed using a hydrochloric acid solution with a molar concentration of 3~5 mol / L; (3) During the first back-extraction process, the volume ratio of the hydrochloric acid to the washed N1923 organic phase is 3~5:1; (4) The first back-extraction is a 3-5 stage back-extraction; (5) The temperature of the first back-extraction is 40~55℃.

4. The method for recovering scandium oxide from scandium residue according to claim 1, characterized in that, In step (a), at least one of the following conditions must be met: (1) The sulfuric acid used for leaching includes 0.5~3 mol / L dilute sulfuric acid; (2) The final acidity of the leaching is 0.2~1.0 mol / L.

5. The method for recovering scandium oxide from scandium residue according to claim 1, characterized in that, In step (b), at least one of the following conditions must be met: (1) The volume ratio of the dimethylheptyl methylphosphonate and the sulfonated kerosene in the P350 extractant is 30~50:50~70; (2) The volume ratio of the P350 extractant to the N1923 back-extraction solution is 2~4:1; (3) The second extraction is a 5-12 stage extraction; (4) The temperature of the second extraction is 40~55℃; (5) The second back-extraction is performed using hydrochloric acid with a molar concentration of 1~2 mol / L; (6) During the second back-extraction process, the volume ratio of the hydrochloric acid to the P350 organic phase is 1~2:1; (7) The second back-extraction is a 2-4 stage back-extraction; (8) The temperature of the second back-extraction is 40~55℃.

6. The method for recovering scandium oxide from scandium residue according to claim 1, characterized in that, In step (c), at least one of the following conditions must be met: (1) The volume ratio of the trioctyldecyl tertiary amine, the sec-octanol and the sulfonated kerosene in the N235 extractant is 5~25:5~15:60~90; (2) The volume ratio of the N235 extractant to the P350 back-extraction solution is 1~4:1; (3) The third extraction is a 1-3 stage extraction.

7. The method for recovering scandium oxide from scandium residue according to claim 1, characterized in that, In step (d), at least one of the following conditions must be met: (1) The pH of the N235 aqueous phase is adjusted to 1.0~2.0; (2) Adjust the pH of the N235 aqueous phase using a neutralizing agent, wherein the neutralizing agent includes at least one of ammonia solution, ammonium carbonate solution and ammonium bicarbonate solution; (3) The precipitant includes an oxalic acid solution with a mass fraction of 5% to 10%.

8. The method for recovering scandium oxide from scandium residue according to claim 1, characterized in that, In step (d), at least one of the following conditions must be met: (1) The temperature of the scandium precipitation treatment is 45~90℃; (2) The scandium precipitation treatment time is 0.5~1h; (3) The reaction pH of the scandium precipitation treatment is 1.0~2.0; (4) The roasting temperature is 1000~1100℃; (5) The roasting time is 4 to 6 hours.

9. Scandium oxide prepared by the method for recovering scandium oxide from scandium slag as described in any one of claims 1 to 8, characterized in that, The scandium oxide has a purity >99.9%.

10. The application of scandium oxide as described in claim 9 in the fields of aerospace, information technology, metallurgy, chemical industry and clean energy.

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