A method for recovering scandium oxide from scandium-containing oxalic acid wastewater

Abstract

This application belongs to the field of rare earth element recovery technology and discloses a method for recovering scandium oxide from scandium-oxalic acid-containing wastewater. The method involves first mixing a phosphoric acid extractant and a solvent oil to obtain a first mixture. The scandium-oxalic acid-containing wastewater is then filtered. The first mixture is mixed with the filtered scandium-oxalic acid-containing wastewater at a volume ratio of organic phase to aqueous phase of 1:20-30. The mixture is then subjected to countercurrent extraction, stirring, and clarification to obtain a second mixture. Subsequently, the organic phase in the second mixture is back-extracted using an alkaline solution containing ethanol to obtain scandium hydroxide. Scandium hydroxide is then dissolved in hydrochloric acid solution, and finally, scandium is precipitated using oxalic acid solution to obtain scandium oxalate. The scandium oxalate is then calcined at high temperature to obtain scandium oxide. Through the above design, the scandium oxide recovery rate of this application reaches 97.9%, and the scandium oxide recovered by this method has a purity of not less than 99.5%.

Description

Technical Field

[0001] This application relates to the field of rare earth element recovery technology, and in particular to a method for recovering scandium oxide from scandium-oxalic acid-containing wastewater. Background Technology

[0002] Scandium (Sc) is widely distributed in nature, with a relatively high average abundance. Its abundance in the Earth's crust is approximately 36 × 10⁻⁶. -4 Scandium accounts for a small percentage of total selenium, but its distribution is extremely dispersed, often giving the impression of being extremely rare. Furthermore, independent scandium mineral resources are extremely scarce; the vast majority of scandium is dispersed as a mineral by-product in tungsten, aluminum, vanadium, titanium, zirconium deposits, and some rare earth minerals, making extraction and deep processing research quite difficult. Scandium and its compounds are mainly used in Al-Sc alloys, scandium-sodium halogen lamps, and solid oxide fuel cells. The extreme scarcity of independent scandium mineral resources leads to its high price, limiting its widespread application in aerospace, lasers, and electronics. Currently, although there are many companies producing scandium and related products both domestically and internationally, the total output is low. Moreover, according to data from the Adamas Intelligence Research Center, the international demand for scandium is expected to be huge in the future, resulting in a long-term supply shortage. Therefore, recovering scandium from various materials through multiple channels is of great significance in alleviating the supply-demand imbalance.

[0003] Currently, the production process of scandium oxide typically involves precipitating metallic scandium using oxalic acid solution. However, the resulting oxalic acid waste liquid is large in volume, highly acidic, and contains trace amounts of valuable scandium. Treatment of this waste liquid generally involves neutralization with alkaline substances before discharge, which results in high energy consumption and costs. Furthermore, the generated calcium oxalate is difficult to treat and poses environmental risks. Alternatively, a series of acid recovery measures, such as further separation and impurity removal, can be implemented, but this process is lengthy, requires complex equipment, and is costly. Directly reprecipitating the oxalic acid waste liquid can easily lead to the accumulation of impurities in the product, reducing its purity. Therefore, the proper disposal of oxalic acid waste liquid is of paramount importance.

[0004] Chinese patent application 200910090880.5 discloses a process for extracting and separating rare earth elements, which includes at least the following steps:

[0005] (1) The blank organic extractant is simultaneously or stepwise mixed with an aqueous solution of magnesium and / or calcium organic acid salts and a rare earth solution for pre-extraction. Rare earth ions are extracted into the organic phase. After clarification, a loaded organic phase and a raffinate aqueous phase are obtained. The rare earth content REO in the loaded organic phase is 0.05-0.23 mol / L, and the pH value of the raffinate aqueous phase is 1.5-5. The aqueous solution of magnesium and / or calcium organic acid salts is prepared by calcination-organic acid dissolution of magnesium and / or calcium minerals.

[0006] (2) The loaded organic phase containing rare earth ions is used to extract and separate rare earth feed solutions containing two or more rare earth elements. After multi-stage extraction, washing and back-extraction, raffinate, washing solution and back-extraction solution containing different rare earth elements are obtained; or the loaded organic phase containing rare earth ions is directly back-extracted with hydrochloric acid or nitric acid to obtain a mixed rare earth chloride solution or a mixed rare earth nitrate solution containing REO 0.1-2 mol / L. The solution is concentrated and crystallized to produce mixed rare earth chloride or mixed rare earth nitrate products, or further extracted and separated to produce single rare earth compound products.

[0007] This method involves mixing acidic organic extractants such as P507, P204, C272, and naphthenic acids with aqueous solutions of magnesium and / or calcium organic acid salts and rare earth solutions for extraction. Rare earth ions are extracted into the organic phase. After clarification, a rare earth ion-loaded organic phase is obtained for the extraction and separation of mixed rare earth solutions. Through multi-stage extraction and separation, single rare earth compounds or concentrates of several rare earth elements are obtained. The aqueous solutions of magnesium and / or calcium organic acid salts are prepared from minerals such as magnesite, limestone, calcite, and dolomite through roasting and organic acid dissolution. These solutions have low levels of impurities such as silicon, iron, and aluminum. The pre-extraction and extraction separation processes do not produce three-phase materials, thus not affecting product purity. Furthermore, the organic phase does not require ammonia saponification, preventing the generation of ammonia nitrogen wastewater and eliminating environmental pollution from the source. This significantly reduces the production cost of rare earth products and saves substantial waste treatment expenses.

[0008] As can be seen from the above description of the scheme, when extracting rare earth elements from rare earth solutions, an aqueous solution of organic acid salts containing magnesium and / or calcium is essential. Although the above scheme discloses that extractants such as P507, P204, and C272 can be used to extract rare earth elements, the above scheme does not use back-extraction to extract rare earth elements. It can be seen that the above scheme is significantly different from the process route of this application.

[0009] Chinese patent application 201310010538.6 discloses a method for extracting and recovering scandium from waste acid in titanium dioxide production, the method comprising the following steps:

[0010] (1) Extraction: The waste acid water from titanium dioxide production is extracted in the extraction tank using P204-TBP-kerosene extractant through 1 to 6 stages. The volume ratio of extractant to waste acid is 1:5 to 30, and the mixing time is 5 min to 20 min to obtain scandium-containing organic phase. The scandium concentration in the raffinate is <1 mg / L.

[0011] (2) Washing: The scandium-containing organic phase obtained in step (1) is washed with 2 mol / L to 4 mol / L sulfuric acid and 27% hydrogen peroxide. The volume ratio of the scandium-containing organic phase to sulfuric acid is 1:1 / 3 to 3, and the amount of hydrogen peroxide added is 1% to 10% of the volume of sulfuric acid.

[0012] (3) Circulating extraction: The scandium-containing organic phase washed in step (2) is used as the extractant to repeat steps (1) and (2), and the concentration of scandium in the raffinate is detected at regular intervals until the concentration of scandium in the raffinate is >2 mg / L.

[0013] (4) Back-extraction: The scandium-containing organic phase obtained in step (3) is back-extracted in a reaction vessel using sodium hydroxide solution;

[0014] (5) Acid dissolution and precipitation: The back-extraction solution obtained in step (4) is filtered to obtain scandium hydroxide cake. The scandium hydroxide cake is dissolved in hydrochloric acid or sulfuric acid, filtered, and then precipitated with oxalic acid to obtain scandium oxalate.

[0015] (6) Calcination: The scandium oxalate obtained in step (5) is calcined in a muffle furnace to obtain scandium oxide.

[0016] This scheme, through the above design, reduces the number of back-extraction operations, lowers labor costs, and increases scandium yield.

[0017] However, it should be noted that the alkaline solvent used in the back-extraction process in this scheme is sodium hydroxide solvent. Although this application found that sodium hydroxide solution can also be used to back-extract scandium hydroxide intermediate in actual use, after further comparison of recovery rate, purity, etc., it was found that the back-extraction time still has room for improvement when using sodium hydroxide solution alone.

[0018] Chinese patent application 201310303019.9 discloses a method for extracting high-purity scandium oxide and titanium from waste acid containing scandium and titanium. The method includes the following steps:

[0019] a. Raw material processing: Filter the waste acid containing scandium and titanium and adjust the acid concentration; when the waste acid mainly contains sulfuric acid, control the sulfuric acid concentration to 2.5-3 mol / L; when the waste acid mainly contains hydrochloric acid, control the hydrochloric acid concentration to 1.5-3.0 mol / L.

[0020] b. Extraction and back-extraction: The waste acid solution after step a is subjected to 3 to 5 stages of continuous extraction using a box-type mixing and clarification tank, and then a single-stage back-extraction is performed using a mixed alkaline solution;

[0021] c. Preparation of titanium phosphate or titanium dioxide: The solid obtained from the back-extraction in step b is dissolved in concentrated sulfuric acid or concentrated hydrochloric acid to adjust the acidity. The acidity of the sulfuric acid system is adjusted to 2.5-3 mol / L, and the acidity of the hydrochloric acid system is adjusted to 1.5-3.0 mol / L. The acid-adjusted solution is heated to boiling and boiled for 30-120 minutes. Then, 4% hydrogen peroxide and 5% phosphoric acid solution are added based on the solution volume, or only 4% hydrogen peroxide is added. After the reaction, the solution is cooled to room temperature and filtered. The filtrate is collected. The filter residue is washed with distilled water and then calcined in a calcining device at 600-980℃ for 2-8 hours to obtain titanium phosphate or titanium dioxide with a purity greater than 98%.

[0022] d. Extraction, countercurrent washing and back-extraction: The filtrate obtained in step c is subjected to 4 to 6 stages of continuous extraction in a box-type mixing and clarifying tank, then subjected to 6 to 12 stages of countercurrent washing with a solution containing sulfuric acid and hydrogen peroxide, and then subjected to two stages of back-extraction with a mixed alkaline solution.

[0023] e. Process the solid material obtained by back-extraction in step d in the same way as in step c to obtain titanium phosphate or titanium dioxide with a purity greater than 98% and filtrate.

[0024] f. Add ammonia or sodium carbonate to the filtrate obtained in step e, adjust the pH value to 0.5-2, then add EDTA, tartaric acid and oxalic acid, and filter after reaction to obtain scandium oxalate complex salt.

[0025] g. After washing the scandium oxalate complex salt with water, heat and dissolve it with 4-6 mol / L analytical grade sulfuric acid or 2-3 mol / L analytical grade hydrochloric acid, and filter to obtain a pure filtrate.

[0026] h. Add potassium sulfate to the pure filtrate obtained in step g. After reaction, filter to obtain potassium scandium sulfate complex salt precipitate. After washing, potassium scandium sulfate complex salt is converted by 18-22% liquid alkali and filtered to obtain solid scandium hydroxide.

[0027] i. After washing the scandium hydroxide solid obtained in step h, heat it to dissolve it, add potassium sulfate to precipitate it, and then convert it with alkali to obtain scandium hydroxide solid with a purity of not less than 99.9%;

[0028] j. After washing the solid scandium hydroxide obtained in step i, it is dissolved by heating with 2-3 mol / L analytical grade hydrochloric acid, filtered to obtain a pure filtrate, then ammonia or sodium carbonate is added to adjust the pH value to 0.5-2, then oxalic acid or ammonium oxalate is added, and after reaction, it is filtered to obtain scandium oxalate. After washing, scandium oxalate is calcined at 600-800℃ to obtain a high-purity scandium oxide product.

[0029] As can be seen from the above scheme, although the two possible situations of waste acid given in step a are waste acid with sulfuric acid as the main component and waste acid with hydrochloric acid as the main component, and do not include waste acid with oxalic acid as the main component, it still has certain reference value. First, the scheme uses a mixed alkaline solution to back-extract the waste acid liquid in step b. Furthermore, it can be observed that the mixed alkaline solution in the scheme contains sodium hydroxide, sodium chloride and 5-8% ethanol by weight.

[0030] The problem this solution aims to solve is: how to provide a method for recovering scandium oxide from scandium-oxalic acid-containing wastewater, while also achieving a high scandium oxide recovery rate. Summary of the Invention

[0031] The purpose of this application is to provide a method for recovering scandium oxide from scandium-oxalic acid-containing wastewater, which has a high scandium oxide recovery rate.

[0032] To achieve the above objectives, this application discloses a method for recovering scandium oxide from scandium-oxalic acid-containing wastewater, comprising the following steps:

[0033] Step 1: Mix the phosphoric acid extractant and solvent oil to obtain mixture one;

[0034] Step 2: Filter the wastewater containing scandium oxalic acid. Mix the first mixture obtained in Step 1 with the filtered wastewater containing scandium oxalic acid at a volume ratio of organic phase to aqueous phase of 1:20-30. Perform countercurrent extraction in stages 1-3, then stir and clarify to obtain the second mixture.

[0035] Step 3: Back-extract the organic phase in the mixture obtained in Step 2 using an alkaline solution to obtain scandium hydroxide. The alkaline solution is an alkaline solution doped with ethanol, and the mass fraction of ethanol in the alkaline solution is 0.1-3%.

[0036] Step 4: Dissolve the scandium hydroxide obtained in step 3 with hydrochloric acid solution, then precipitate scandium with oxalic acid solution to obtain scandium oxalate. Subsequently, calcine the scandium oxalate at a temperature of 650-850℃ for 2-4 hours to obtain scandium oxide.

[0037] It should be noted that in actual use, the role of solvent oil is only to dilute the extractant, and it does not play a decisive role in the recovery of scandium. In actual operation, we can choose any of the following substances as solvent oil: light white oil, kerosene, or sulfonated kerosene.

[0038] Preferably, in step 1, the phosphoric acid extractant is selected from at least one of P204, P507, and C272.

[0039] Preferably, in the first mixture, the mass ratio of phosphoric acid extractant to solvent oil is 10-20:80-90.

[0040] Preferably, the scandium-oxalic acid-containing wastewater refers to scandium-oxalic acid-containing wastewater containing elemental scandium or scandium ions.

[0041] Preferably, step 3 specifically involves: back-extracting the organic phase in the mixture obtained in step 2 using an alkaline solution containing ethanol, at a reaction temperature of 70–80°C, with a volume ratio of organic phase to aqueous phase of 1:1–1.2, and a reaction time of 0.5–2 h, to obtain scandium hydroxide.

[0042] Preferably, the alkaline solution in step 3 is selected from at least one of ammonia solution with a concentration of 2-3 mol / L and sodium hydroxide solution with a concentration of 2-3 mol / L.

[0043] Preferably, step 4 specifically involves: dissolving the scandium hydroxide obtained in step 3 in a 1-3 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:3-6, followed by precipitating scandium in an oxalic acid solution. The molar ratio of oxalic acid to scandium hydroxide in the oxalic acid solution is 1.8-2.1:1. The reaction time is 1-4 hours, and the reaction temperature is 60-70°C. After the reaction is complete, scandium oxalate is obtained, and then scandium oxalate is calcined at 650-850°C for 2-4 hours to obtain scandium oxide.

[0044] Preferably, the scandium oxide recovery rate is not less than 97.9%.

[0045] Preferably, the purity of the recovered scandium oxide is not less than 99.5%.

[0046] The beneficial effects of this application are: the method for recovering scandium oxide from scandium-oxalic acid-containing wastewater provided in this application improves the recovery rate of scandium oxide from oxalic acid wastewater and reduces the time required for the back-extraction process by further optimizing the compounding of alkaline solution and the amount of ethanol added during the back-extraction process. Detailed Implementation

[0047] The present application will be clearly and completely described below with reference to its embodiments. It should be noted that, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0048] Example 1

[0049] Step 1: Mix P204 and light white oil at a mass ratio of 20:80 to obtain mixture one.

[0050] Step 2: Filter the solid impurities in the scantoxalic acid-containing wastewater to obtain a clear solution. Mix the first mixture obtained in Step 1 with the filtered scantoxalic acid-containing wastewater at a volume ratio of organic phase to aqueous phase of 1:20. Perform three-stage countercurrent extraction, followed by stirring for 5 minutes and clarification for 30 minutes to obtain the second mixture.

[0051] Step 3: Separate the organic phase in the phase-separated mixture II, and then back-extract the organic phase separated from the mixture II obtained in Step 2 using a 2 mol / L sodium hydroxide solution. The sodium hydroxide solution is doped with 0.1% ethanol by mass. The reaction temperature is 70℃, the volume ratio of organic phase to aqueous phase is 1:1, and the reaction time is 2h to obtain scandium hydroxide.

[0052] Step 4: The scandium hydroxide material obtained in Step 3 was dissolved in 1 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:3, and then precipitated with oxalic acid solution. The molar ratio of oxalic acid to scandium hydroxide in the oxalic acid solution was 1.8:1. The reaction time was 1 hour and the reaction temperature was 60℃. Scandium oxalate was calcined at 650℃ for 2 hours to obtain scandium oxide with a purity of 99.7% and a recovery rate of 98.3%.

[0053] Meanwhile, it should be noted that in the actual production process, in order to reduce production costs, we can also recover the oxalic acid raffinate after extraction. First, the oxalic acid raffinate is de-oiled, and then the de-oiled oxalic acid raffinate is added to the evaporator. When the oxalic acid concentration in the solution reaches 800-900 g / L, the evaporation is stopped, the liquid is cooled to below 30°C, and filtered to obtain high-purity oxalic acid and evaporation mother liquor. At the same time, the vapor formed by the hydrochloric acid in the solution during the evaporation and concentration process can also be collected to make a dilute hydrochloric acid solution.

[0054] Example 2

[0055] Step 1: Mix P507 and kerosene at a mass ratio of 10:90 to obtain mixture one.

[0056] Step 2: Filter the solid impurities in the scantoxalic acid-containing wastewater to obtain a clear solution. Mix the first mixture obtained in Step 1 with the filtered scantoxalic acid-containing wastewater at a volume ratio of organic phase to aqueous phase of 1:30. Perform first-stage countercurrent extraction, followed by stirring for 5 minutes and clarification for 30 minutes to obtain the second mixture.

[0057] Step 3: Separate the organic phase in the phase-separated mixture II, and then back-extract the organic phase separated in the mixture II obtained in step 2 using a 3 mol / L ammonia solution. The ammonia solution is doped with 3% ethanol by mass. The reaction temperature is 80℃, the volume ratio of organic phase to aqueous phase is 1:1.2, and the reaction time is 0.5 h to obtain scandium hydroxide.

[0058] Step 4: The scandium hydroxide material obtained in Step 3 was dissolved in 3 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:6, and then precipitated with oxalic acid solution. The molar ratio of oxalic acid to scandium hydroxide in the oxalic acid solution was 2.1:1. The reaction time was 4 hours and the reaction temperature was 70℃. Scandium oxalate was calcined at 850℃ for 2 hours to obtain scandium oxide with a purity of 99.5% and a recovery rate of 97.9%.

[0059] Example 3

[0060] Step 1: Mix C272 and sulfonated kerosene at a mass ratio of 15:85 to obtain mixture one.

[0061] Step 2: Filter the solid impurities in the scantoxalic acid-containing wastewater to obtain a clear solution. Mix the first mixture obtained in Step 1 with the filtered scantoxalic acid-containing wastewater at a volume ratio of organic phase to aqueous phase of 1:25. Perform two-stage countercurrent extraction, followed by stirring for 5 minutes and clarification for 30 minutes to obtain the second mixture.

[0062] Step 3: Separate the organic phase in the phase-separated mixture II, and then back-extract the organic phase separated in the mixture II obtained in Step 2 using a 2.5 mol / L sodium hydroxide solution. The sodium hydroxide solution is doped with 1.5% ethanol by mass. The reaction temperature is 75℃, the volume ratio of organic phase to aqueous phase is 1:1.1, and the reaction time is 1 h to obtain scandium hydroxide.

[0063] Step 4: The scandium hydroxide material obtained in Step 3 was dissolved in 2 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:5, and then precipitated with oxalic acid solution. The molar ratio of oxalic acid to scandium hydroxide in the oxalic acid solution was 2:1. The reaction time was 3 hours and the reaction temperature was 65℃. Scandium oxalate was calcined at 800℃ for 4 hours to obtain scandium oxide with a purity of 99.8% and a recovery rate of 98.85%.

[0064] Example 4

[0065] The process is basically the same as in Example 1, except that the mixture in step 1 is prepared by mixing a mixed extractant of C272 and P507 with light white oil. The mass ratio of the mixed extractant to light white oil is 20:80, and the mass ratio of C272 to P507 in the mixed extractant is 1:1. Finally, scandium oxide with a purity of 99.9% and a recovery rate of 98.4% is obtained.

[0066] Example 5

[0067] The process is basically the same as in Example 1, except that in step 3, the organic phase in the mixture obtained in step 2 is back-extracted using a mixed alkaline solution. The mixed alkaline solution is a mixture of sodium hydroxide and ammonia, with a mass ratio of 1:1. The mixed alkaline solution is doped with 0.1% ethanol by mass, and finally scandium oxide with a purity of 99.95% is obtained with a recovery rate of 98.5%.

[0068] Example 6

[0069] The process is basically the same as in Example 4, except that in step 3, the organic phase in the mixture obtained in step 2 is back-extracted using a mixed alkaline solution. The mixed alkaline solution is a mixture of sodium hydroxide and ammonia, with a mass ratio of 1:1. The mixed alkaline solution is doped with 0.1% ethanol by mass, and finally scandium oxide with a purity of 99.96% is obtained, with a recovery rate of 99.3%.

[0070] Comparative Example 1

[0071] The process was essentially the same as in Example 1, except that no ethanol was added to the sodium hydroxide solution in step 3, resulting in scandium oxide with a purity of 99.3% and a recovery rate of 97.5%.

[0072] Comparative Example 2

[0073] The process is basically the same as in Example 1, except that in step 3, the amount of ethanol added is 5% of the total mass of the sodium hydroxide solution, and scandium oxide with a purity of 99.6% and a recovery rate of 98.3% is finally obtained.

[0074] Comparative Example 3

[0075] The process is basically the same as in Example 1, except that in step 2, scandium-containing sulfuric acid wastewater is used instead of scandium-containing oxalic acid wastewater, and scandium oxide with a purity of 92.4% is finally obtained with a recovery rate of 91.5%.

[0076] Results Analysis

[0077] 1. As can be seen from Examples 1-3, after making small-scale adjustments to the process parameters in the recovery of scandium oxide from oxalic acid wastewater, the purity and recovery rate of scandium oxide fluctuated to some extent, but the overall fluctuation range was not large. Nevertheless, since the purity and recovery rate of scandium oxide in Example 3 were the best results among Examples 1-3, we have reason to believe that the process parameters of Example 3 are better than those of Examples 1 and 2.

[0078] 2. As can be seen from Examples 4-6, the combination of extractant and alkaline solution has a certain promoting effect on the purity and recovery rate of recovered scandium oxide, but it is not significant. However, when the extractant and alkaline solution are combined in Example 6, the recovery rate of scandium oxide is significantly improved compared with Examples 4 and 5.

[0079] 3. As can be seen from Example 1 and Comparative Examples 1-2, when the amount of ethanol added was changed, the purity and recovery rate of scandium oxide in Comparative Examples 1 and 2 fluctuated slightly, but the fluctuation range was acceptable overall. However, the back-extraction time of Comparative Example 1 was prolonged in actual operation. Although the fluctuation range of scandium oxide purity and recovery rate was acceptable, production efficiency is also an important parameter in the production process. Meanwhile, Comparative Example 2 showed a significant improvement in the amount of ethanol added compared to Example 1, but in actual operation, Comparative Example 2 could not effectively shorten the back-extraction time. At the same time, the recovery rate and purity of scandium oxide did not show a significant difference from Example 1. We believe that production cost and production efficiency are also crucial in actual production. Therefore, the amount of ethanol added in this application is 0.1% to 3% of the mass of the alkaline solution.

[0080] 4. As can be seen from Example 1 and Comparative Example 3, although the method described in this application has achieved significant results in the recovery of scandium oxide from scandium-oxalic acid-containing wastewater, the recovery rate and purity of scandium oxide decreased significantly after the scandium-oxalic acid-containing wastewater was converted into scandium-sulfuric acid-containing wastewater. It can be seen that this method is not applicable to the extraction of scandium oxide from all scandium-containing acidic wastewater.

Claims

1. A method for recovering scandium oxide from scandium-oxalic acid-containing wastewater, characterized in that, Includes the following steps: Step 1: Mix the mixed extractant of phosphoric acid extractant C272 and P507 with light white oil to obtain the first mixture. The mass ratio of the mixed extractant to light white oil is 20:80, and the mass ratio of C272 to P507 in the mixed extractant is 1:

1. Step 2: Filter the wastewater containing scandium oxalic acid. Mix the first mixture obtained in Step 1 with the filtered wastewater containing scandium oxalic acid at a volume ratio of organic phase to aqueous phase of 1:20-30. Perform countercurrent extraction in stages 1-3, then stir and clarify to obtain the second mixture. Step 3: Back-extract the organic phase in the mixture obtained in Step 2 using an alkaline solution to obtain scandium hydroxide; Step 4: Dissolve scandium hydroxide obtained in step 3 with hydrochloric acid solution, then precipitate scandium with oxalic acid solution to obtain scandium oxalate, and then calcine scandium oxalate at 650-850℃ for 2-4 hours to obtain scandium oxide. The alkaline solution in step 3 is a mixed alkaline solution prepared by mixing sodium hydroxide and ammonia, and the mixed alkaline solution contains 0.1% to 3% ethanol by mass.

2. The method for recovering scandium oxide from scandium-oxalic acid-containing wastewater according to claim 1, characterized in that, The scandium-oxalic acid-containing wastewater refers to scandium-oxalic acid-containing wastewater containing elemental scandium or scandium ions.

3. The method for recovering scandium oxide from scandium-oxalic acid-containing wastewater according to claim 1, characterized in that, Step 3 specifically involves back-extracting the organic phase in the mixture obtained in step 2 using an alkaline solution containing ethanol. The reaction temperature is 70–80°C, the volume ratio of the organic phase to the aqueous phase is 1:1–1.2, and the reaction time is 0.5–2 h, to obtain scandium hydroxide.

4. The method for recovering scandium oxide from scandium-oxalic acid-containing wastewater according to claim 1, characterized in that, Step 4 specifically involves: dissolving the scandium hydroxide obtained in step 3 in a 1-3 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:3-6, followed by precipitating scandium in an oxalic acid solution. The molar ratio of oxalic acid to scandium hydroxide in the oxalic acid solution is 1.8-2.1:

1. The reaction time is 1-4 hours, and the reaction temperature is 60-70°C. After the reaction is complete, scandium oxalate is obtained. Subsequently, scandium oxalate is calcined at 650-850°C for 2-4 hours to obtain scandium oxide.