Method for deeply removing calcium impurities in scandium oxide

Abstract

This application provides a method for deep removal of calcium impurities from scandium oxide, belonging to the field of rare earth metal oxide purification. The method includes: dissolving scandium oxide raw material containing calcium impurities to obtain a calcium-containing scandium solution; adding a pH adjuster to the calcium-containing scandium solution to obtain a first scandium solution; reacting the first scandium solution with phosphoric acid and / or phosphate to obtain a second scandium solution and solid calcium phosphate; reacting the second scandium solution with a complexing agent to obtain a third scandium solution; reacting the third scandium solution with oxalic acid and / or sodium oxalate to obtain scandium oxalate crystals and a calcium complex solution; adding a strong acid solution to the calcium complex solution; and calcining the scandium oxalate crystals to obtain scandium oxide. Through calcium phosphate precipitation-complexation-crystallization, not only can calcium impurities be deeply removed from scandium oxide products, but impurities such as iron, titanium, and zirconium can also be removed, resulting in scandium oxide products with a purity of over 99.99%.

Description

Technical Field

[0001] This application relates to the field of rare earth metal oxide purification technology, and in particular to a method for deep removal of calcium impurities from scandium oxide. Background Technology

[0002] Scandium is a rare earth element, hailed as an important strategic metal for the new century. Scandium and its compounds are widely used in defense, aerospace, lasers, electronics, optics, metallurgy, chemicals, glass, batteries, superconductivity, and medicine. However, due to its extremely dispersed distribution and low content in the Earth's crust, industrially, scandium is mainly recovered as a byproduct from solid waste or wastewater, making the purification process for scandium products quite complex.

[0003] Conventional methods for purifying crude scandium products mainly include extraction, chemical precipitation, and ion exchange. Extraction is primarily for the initial recovery and purification of scandium. Ion exchange can remove trace impurities from the solution, but its cost is generally high due to limitations in resin adsorption performance and lifespan. Precipitation is effective for removing impurities from scandium products, but there is currently no method for the deep removal of calcium impurities. Because calcium and scandium have similar chemical properties under acidic conditions, especially in scandium-rich raw materials such as red mud with high calcium content, calcium impurities are always present alongside scandium during the extraction and purification process. Conventional methods struggle to selectively separate them, resulting in calcium impurities ultimately entering the final product. Therefore, efficiently removing calcium from scandium oxide products is a key technical challenge in purification. Summary of the Invention

[0004] This application provides a method for deep removal of calcium impurities from scandium oxide to solve the following technical problem: how to deeply remove calcium impurities from scandium oxide.

[0005] This application provides a method for deep removal of calcium impurities from scandium oxide, the method comprising: Scandium oxide raw material containing calcium impurities is dissolved in a strong acid solution to obtain a calcium-containing scandium solution. A pH adjuster is added to the calcium-containing scandium solution to adjust the pH value to 0.5-2.0, thereby obtaining a first scandium solution; The first scandium solution is subjected to a first stirring reaction with phosphoric acid and / or phosphate to react with phosphate ions to form calcium phosphate precipitate, thereby obtaining a second scandium solution and calcium phosphate solid. The second scandium solution is subjected to a second stirring reaction with a complexing agent to allow the complexing agent to complex with the residual calcium ions in the second scandium solution, thereby obtaining a third scandium solution; The third scandium solution is subjected to a third stirring reaction with oxalic acid and / or sodium oxalate to generate scandium oxalate crystal precipitate by reacting scandium ions with oxalate ions in the third scandium solution, thereby obtaining scandium oxalate crystals and calcium complex solution. Add the strong acid solution to the calcium complex solution to obtain a regenerated strong acid solution for redissolving scandium oxide raw materials; The scandium oxalate crystals were calcined to obtain scandium oxide.

[0006] Optionally, the strong acid solution includes at least one of hydrochloric acid solution or nitric acid solution.

[0007] Optionally, the pH adjuster includes at least one of ammonia, sodium hydroxide solution, or sodium carbonate solution.

[0008] Optionally, the temperature of the first stirring reaction is 10℃~40℃, and the reaction time is 15min~40min.

[0009] Optionally, the PO4 in the phosphoric acid and / or phosphate 3- With Ca in the first scandium solution 2+ The molar ratio is (1.0~2.0):1.

[0010] Optionally, the complexing agent includes at least one of ethylenediaminetetraacetic acid, sodium citrate, or sodium gluconate.

[0011] Optionally, the molar amount of the complexing agent is 1.0 to 2.0 times the molar amount of calcium ions in the second scandium solution.

[0012] Optionally, the temperature of the second stirring reaction is 10℃~60℃, and the reaction time is 15min~40min.

[0013] Optionally, the molar amount of oxalic acid and / or sodium oxalate is 1.5 to 3.0 times the molar amount of scandium ions in the third scandium solution.

[0014] Optionally, the temperature of the third stirring reaction is 60℃~90℃, and the reaction time is 1h~2h.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for deep removal of calcium impurities from scandium oxide, which removes calcium impurities from scandium oxide through precipitation-complexation-crystallization.

[0016] First, the scandium oxide raw material containing calcium impurities is dissolved in a strong acid solution, allowing all scandium and calcium impurities to enter the solution phase, resulting in a calcium-containing scandium solution. A pH adjuster is added to this calcium-containing scandium solution to adjust the pH to 0.5 to 2.0, obtaining a first scandium solution. Under these weakly acidic conditions, phosphoric acid or phosphate is added to the first scandium solution and a first stirring reaction is performed, causing calcium ions in the solution to react with phosphate ions to form calcium phosphate precipitate. After filtration, the calcium phosphate solid is separated, yielding a second scandium solution. This step utilizes the poor solubility of calcium phosphate within a specified pH range to remove most of the calcium in the calcium-containing scandium solution as a precipitate. Trace amounts of calcium ions remain in the second scandium solution. A complexing agent is added to the second scandium solution and a second stirring reaction is performed, causing the complexing agent to form a soluble calcium complex with the residual calcium ions, yielding a third scandium solution. This complexation step locks the residual calcium ions in the solution, preventing them from combining with oxalate ions to form calcium oxalate precipitate during the subsequent oxalate precipitation process.

[0017] Subsequently, oxalic acid or sodium oxalate is added to the third scandium solution, and a third stirring reaction is carried out, causing scandium ions to react with oxalate ions to form scandium oxalate crystals. After filtration, high-purity scandium oxalate crystals and a calcium complex solution are obtained. Since the calcium ions have been removed by the phosphoric acid precipitate and the residual calcium is stably complexed in the solution by the complexing agent, no calcium oxalate impurities will precipitate during the scandium oxalate crystallization process, thus ensuring the high purity of the scandium oxalate crystals.

[0018] Finally, the high-purity scandium oxalate crystals are roasted and decomposed to obtain high-purity scandium oxide product. At the same time, a strong acid solution is added to the separated calcium complex solution to obtain a regenerated strong acid solution, which is used to redissolve the next batch of scandium oxide raw material, realizing the recycling of the acid solution.

[0019] In summary, this application employs a two-stage calcium removal strategy: phosphoric acid precipitation to remove the main calcium and a complexing agent to lock in the residual calcium. Combined with the selective precipitation of scandium with oxalic acid, this approach achieves deep removal of calcium impurities from scandium oxide. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic flowchart illustrating a method for deep removal of calcium impurities from scandium oxide, provided in an embodiment of this application; Figure 2 This is a simplified flowchart illustrating a method for deep removal of calcium impurities from scandium oxide, as provided in an embodiment of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0025] Figure 1 A schematic flowchart illustrating a method for deep removal of calcium impurities from scandium oxide, provided in an embodiment of this application; Figure 2 This is a simplified flowchart illustrating a method for deep removal of calcium impurities from scandium oxide, as provided in an embodiment of this application.

[0026] like Figure 1 and Figure 2 As shown in the embodiments of this application, a method for deep removal of calcium impurities from scandium oxide is provided, the method comprising: S1. Dissolve scandium oxide raw material containing calcium impurities in a strong acid solution to obtain a scandium solution containing calcium. S2. Add a pH adjuster to the calcium-containing scandium solution to adjust the pH value to 0.5~2.0 to obtain the first scandium solution; S3. The first scandium solution is stirred with phosphoric acid and / or phosphate to react with phosphate ions to form calcium phosphate precipitate, thereby obtaining a second scandium solution and calcium phosphate solid. S4. The second scandium solution is subjected to a second stirring reaction with the complexing agent to complex the complexing agent with the residual calcium ions in the second scandium solution, thereby obtaining the third scandium solution; S5. The third scandium solution is reacted with oxalic acid and / or sodium oxalate in a third stirring reaction to generate scandium oxalate crystals precipitate by reacting scandium ions with oxalate ions in the third scandium solution, thus obtaining scandium oxalate crystals and calcium complex solution. S6. Add a strong acid solution to the calcium complex solution to obtain a regenerated strong acid solution for redissolving scandium oxide raw materials; S7. The scandium oxalate crystals are calcined to obtain scandium oxide product.

[0027] It should be noted that steps S1 to S7 form a complete technical chain of acid dissolution → selective precipitation to remove major calcium → complexation to lock residual calcium → oxalic acid precipitation of high-purity scandium → mother liquor regeneration and recycling. Each step is designed to address specific difficulties in removing calcium impurities, and together they achieve deep removal of calcium from scandium oxide.

[0028] S1 (acid dissolution) is the starting point of the entire purification process. Its function is to convert all scandium and associated impurities such as calcium, iron, and titanium in the solid scandium oxide feedstock into soluble chlorides or nitrates, forming a homogeneous calcium-scandium-containing solution, providing the necessary reaction medium for subsequent wet separation. The choice of strong acid (hydrochloric acid or nitric acid) ensures efficient scandium leaching without introducing difficult-to-remove sulfate or fluoride ions, which could interfere with subsequent precipitation reactions.

[0029] The key role of S2 (pH adjustment) is to create a suitable acidic environment for the subsequent selective precipitation of calcium by phosphate. By precisely controlling the solution pH within the weakly acidic range of 0.5 to 2.0, it is possible to avoid the formation of soluble monocalcium phosphate (causing calcium removal failure) by phosphate ions with calcium ions under strongly acidic conditions, while also preventing premature hydrolysis and precipitation of scandium ions due to excessively high pH. Furthermore, this pH range is also conducive to the co-precipitation removal of iron ions (forming ferric phosphate). Therefore, this step is a prerequisite for achieving the selective separation of calcium and scandium.

[0030] S3 (phosphate precipitation for calcium removal) is the first core impurity removal step in this method. It utilizes the reaction of phosphate ions with calcium ions under weakly acidic conditions to form a sparingly soluble calcium phosphate precipitate, thus removing most of the calcium (and some iron) from the solution in solid form through filtration. This step can reduce the calcium content from a few percent or thousandths to a few ten-thousandths with minimal chemical reagent consumption, significantly reducing the burden on subsequent deep calcium removal processes. Simultaneously, the recovered calcium phosphate solid can be used as a byproduct or directly processed, demonstrating the process's economic efficiency.

[0031] S4 (deep complexation of residual calcium with complexing agents) is a crucial step to ensure that calcium impurities do not ultimately enter the scandium oxalate product. After S3 precipitation, trace amounts of calcium ions (approximately 0.02~0.04 g / L) still remain in the solution. If oxalate is added directly to precipitate scandium, these trace amounts of calcium will combine with oxalate ions to form calcium oxalate precipitate, thus mixing into the scandium oxalate crystals and causing the product to exceed the calcium limit. Adding complexing agents such as EDTA or sodium citrate to the solution can form highly stable soluble complexes with the residual calcium ions (such as Ca-EDTA). 2- This allows calcium ions to remain in the solution in a "encapsulated" form, preventing the precipitation of calcium oxalate when oxalic acid is added subsequently. Simultaneously, these complexing agents can also complex impurity ions in the solution, such as iron, titanium, and zirconium, which easily form oxalate precipitates, further improving product purity.

[0032] S5 (scandium oxalate precipitation) is the core crystallization step that ultimately separates scandium from all soluble impurities (including complexed calcium, iron, titanium, etc.). At suitable temperature and oxalate concentration, scandium ions selectively react with oxalate ions to form insoluble scandium oxalate crystals, while the oxalates of impurity ions such as calcium, magnesium, aluminum, and iron in the solution either have high solubility (e.g., magnesium oxalate) or are pre-complexed by the complexing agent and cannot form precipitates. High-purity scandium oxalate crystals are obtained through filtration and washing, while the calcium complex solution serves as the mother liquor in the next cycle.

[0033] S6 (acid regeneration and mother liquor recycling) is a crucial step in achieving process closed-loop operation, reducing costs, and minimizing wastewater discharge. It involves regenerating the acid to contain calcium complexes (such as Ca-EDTA). 2- Add a strong acid to the mother liquor of ) and use H + The strong binding force with the complexing agent anion disrupts the Ca-EDTA equilibrium, causing the complexing agent to be protonated and calcium ions to be released again. Simultaneously, the acid is regenerated (the regenerated acid contains both the newly added acid and the acid anions displaced from the complex). This regenerated acid can be directly used to dissolve the next batch of scandium oxide raw material, achieving a dual recycling of acid and complexing agent resources and significantly reducing reagent consumption.

[0034] S7 (calcination) is the conversion step to obtain the final high-purity scandium oxide product. Scandium oxalate crystals are placed in a muffle furnace and calcined at high temperature. The scandium oxalate decomposes upon heating, successively losing its water of crystallization and decomposing the oxalate ion, ultimately transforming into scandium oxide. This process requires control of the heating rate and holding temperature to ensure complete decomposition and avoid excessively coarse crystals. The scandium oxide product obtained after calcination can achieve a purity of over 99.99%, with calcium impurities reduced to below 0.001%, fully meeting the quality requirements for high-purity scandium oxide.

[0035] In some embodiments, the strong acid solution includes at least one of hydrochloric acid solution or nitric acid solution.

[0036] Hydrochloric acid and nitric acid are both non-oxidizing (or weakly oxidizing) strong acids, capable of efficiently dissolving scandium oxide and its associated impurities such as calcium, iron, and titanium oxides, forming soluble chlorides or nitrates. These two acids do not introduce sulfate ions (which readily react with calcium to form slightly soluble calcium sulfate) or fluoride ions (which readily form stable complexes with scandium, affecting subsequent precipitation) that could interfere with subsequent impurity removal processes, thus ensuring the cleanliness and reaction selectivity of the entire purification system.

[0037] In some embodiments, the pH adjuster includes at least one of ammonia, sodium hydroxide solution, or sodium carbonate solution.

[0038] Ammonia, sodium hydroxide, or sodium carbonate solutions can all gently raise the pH of a solution without introducing high-valence metal cations or difficult-to-remove organic impurities. Ammonia acts as a buffer while adjusting pH, preventing localized over-alkalinity; sodium hydroxide solution offers high adjustment efficiency, suitable for rapid industrial-scale pH control; and sodium carbonate solution can slightly complex or adsorb some impurities during pH adjustment. All three solutions can meet the requirement of precisely controlling the pH within the weakly acidic range of 0.5–2.0, creating optimal conditions for subsequent selective precipitation of calcium phosphate.

[0039] In some embodiments, the temperature of the first stirring reaction is 10°C to 40°C, and the reaction time is 15 min to 40 min.

[0040] By limiting the temperature of the first stirring reaction to 10℃~40℃ and the reaction time to 15min~40min, the calcium phosphate precipitation reaction proceeds smoothly, crystal nuclei grow in an orderly manner, and the generated calcium phosphate particles are large and easy to filter. This reaction time ensures sufficient contact and complete reaction between calcium ions and phosphate ions, without increasing energy consumption or introducing unnecessary side reactions due to excessive time. For example, the temperature of the first stirring reaction can be 10℃, 15℃, 20℃, 25℃, 30℃, 33℃, 37℃, 40℃, etc.; the reaction time of the first stirring reaction can be 15min, 20min, 23min, 28min, 32min, 35min, 38min, 40min, etc.

[0041] In some embodiments, PO4 in phosphoric acid and / or phosphate 3- With Ca in the first scandium solution 2+ The molar ratio is (1.0~2.0):1.

[0042] Limiting the molar ratio of phosphate to calcium ions (1.0~2.0:1) ensures a slight excess of phosphate relative to calcium ions, promoting the near-complete conversion of calcium ions in the solution into calcium phosphate precipitate, thus improving calcium removal efficiency. A moderate excess of phosphate can also form co-precipitates with impurity ions such as iron and zirconium, synergistically enhancing solution purity. For example, PO4 in phosphoric acid and / or phosphates... 3-With Ca in the first scandium solution 2+ The molar ratio can be 1.0:1, 1.15:1, 1.3:1, 1.45:1, 1.6:1, 1.75:1, 1.9:1, 2.0:1, etc.

[0043] In some embodiments, the complexing agent includes at least one of ethylenediaminetetraacetic acid, sodium citrate, or sodium gluconate.

[0044] Ethylenediaminetetraacetic acid (EDTA), sodium citrate, and sodium gluconate all contain multiple coordinating atoms (O, N), enabling them to form soluble complexes with calcium ions that have moderate stability constants. EDTA exhibits the strongest complexing ability, making it suitable for treating trace amounts of residual calcium. Sodium citrate and sodium gluconate demonstrate good biocompatibility and lower cost. Their function is to lock in residual calcium ions before the addition of oxalic acid, preventing the subsequent formation of calcium oxalate precipitate.

[0045] In some embodiments, the molar amount of the complexing agent is 1.0 to 2.0 times the molar amount of calcium ions in the second scandium solution.

[0046] By limiting the amount of complexing agent to 1.0 to 2.0 times the molar amount of calcium ions in the second scandium solution, a moderate excess of complexing agent relative to calcium ions can be achieved. This ensures that each calcium ion is surrounded by sufficient complexing molecules to coordinate with it, forming a stable complex with a 1:1 or higher ratio. This reduces the concentration of free calcium ions in the solution to an extremely low level, completely blocking their binding to oxalate. For example, the molar amount of complexing agent relative to the molar amount of calcium ions in the second scandium solution can be 1.0, 1.15, 1.3, 1.45, 1.6, 1.75, 1.9, or 2.0 times, etc.

[0047] In some embodiments, the temperature of the second stirring reaction is 10°C to 60°C, and the reaction time is 15 min to 40 min.

[0048] Limiting the temperature of the second stirring reaction to 10℃~60℃ and the reaction time to 15min~40min is beneficial for improving the complexation reaction rate and the stability of the complex, allowing calcium ions to quickly reach coordination equilibrium with the complexing agent. This reaction time is sufficient to ensure the complexation reaction proceeds completely, guaranteeing that all residual calcium ions are converted into soluble calcium complexes. For example, the temperature of the second stirring reaction can be 10℃, 18℃, 25℃, 32℃, 40℃, 48℃, 55℃, 60℃, etc.; the reaction time can be 15min, 20min, 23min, 28min, 32min, 35min, 38min, 40min, etc.

[0049] In some embodiments, the molar amount of oxalic acid and / or sodium oxalate is 1.5 to 3.0 times the molar amount of scandium ions in the third scandium solution.

[0050] The amount of oxalic acid or sodium oxalate is limited to 1.5 to 3.0 times the molar amount of scandium ions in the third scandium solution. This ensures a significant excess of oxalate relative to scandium ions, utilizing the common ion effect to maximize the precipitation of scandium ions as scandium oxalate, thereby improving scandium recovery. Simultaneously, a moderate excess of oxalic acid can also inhibit the co-precipitation of certain impurity ions, improving the purity of scandium oxalate crystals. For example, the molar amount of oxalic acid and / or sodium oxalate can be 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.8, or 3.0 times the molar amount of scandium ions in the third scandium solution.

[0051] In some embodiments, the temperature of the third stirring reaction is 60°C to 90°C, and the reaction time is 1 hour to 2 hours.

[0052] Limiting the temperature of the third stirring reaction to 60℃~90℃ and the reaction time to 1h~2h accelerates the formation and growth of scandium oxalate crystal nuclei, enabling the crystallization process to complete rapidly. The high temperature also promotes the formation of larger scandium oxalate crystals that are easier to filter and wash. Sufficient holding time ensures the integrity of the crystallization process, allowing most of the scandium ions in the solution to precipitate, guaranteeing a high yield. For example, the temperature of the third stirring reaction can be 60℃, 65℃, 70℃, 75℃, 80℃, 83℃, 87℃, 90℃, etc.; and the reaction time can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.6h, 1.8h, 2h, etc.

[0053] This application provides a method for deep removal of calcium impurities from scandium oxide, which is applicable to the deep removal of calcium from scandium products extracted from raw materials with high calcium content. This method can also remove iron, titanium, and zirconium impurity ions from scandium oxide products, and the final scandium oxide product purity reaches more than 99.99%.

[0054] In summary, the precipitation-complexation-crystallization method for removing calcium impurities from scandium oxide products provided in this application demonstrates significant advantages in improving the purity of scandium oxide products, as detailed below: (1) First, calcium ions in the scandium-containing solution are removed by selective precipitation of calcium ions under acidic conditions. The pH value and reaction temperature of the first reaction are controlled, while iron ions in the scandium-containing solution are precipitated as iron phosphate crystals.

[0055] (2) By adding a complexing agent, the residual trace calcium ions can form a soluble and stable calcium salt with the complexing agent, thus avoiding the formation of calcium oxalate by combining with oxalic acid when oxalic acid is added, which is accompanied by the precipitation of scandium oxalate crystals. At the same time, the addition of the complexing agent can also form soluble complexes with the residual iron ions, titanium ions, zirconium ions, etc. in the solution, thus avoiding the precipitation of scandium oxalate crystals.

[0056] (3) Using phosphate to first combine with calcium in calcium-containing scandium solutions to precipitate and separate greatly reduces the amount of complexing agent to be added, thus saving costs.

[0057] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0058] Example 1 In this embodiment, the component content in the scandium oxide raw material was detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and the purity and calcium impurity content of the high-purity scandium oxide product were also detected by ICP-OES.

[0059] The main components of the scandium oxide raw material used are shown in Table 1.

[0060] Table 1. Composition and content of scandium oxide raw materials

[0061] 100 g of scandium oxide raw material containing calcium impurities was dissolved in 1000 mL of 6 mol / L hydrochloric acid to obtain a scandium solution containing calcium. The concentrations of scandium and impurity ions in the scandium solution containing calcium are shown in Table 2.

[0062] Table 2 Ion concentrations in scandium solutions containing calcium

[0063] Slowly add a 5% sodium hydroxide solution to the above-mentioned calcium-containing scandium solution while stirring, and adjust the pH value to 0.5 to obtain the first scandium solution.

[0064] Add sodium phosphate (analytical grade) to the first scandium solution, according to PO4. 3- : Ca 2+ The molar ratio was 1.0:1, and the amount added was calculated to be 1.26 g. The reaction temperature was controlled at 30℃, the stirring rate at 200 r / min, and the reaction time at 20 minutes. During the reaction, a white calcium phosphate precipitate was observed to form. After the reaction, the sample was filtered under vacuum, and the precipitate was washed three times with deionized water (100 mL of water each time). The filtrate was collected to obtain the second scandium solution. The residual Ca was detected. 2+ The content is 0.032 g / L.

[0065] Sodium citrate (a complexing agent) was added to the second scandium solution, at an amount 1.5 times the molar amount of calcium ions in the second scandium solution. The reaction temperature was controlled at 30°C, and a second stirring reaction was carried out at a stirring rate of 200 r / min for 25 minutes to obtain the third scandium solution. Upon testing, residual Ca... 2+ The content is 0.005g / L.

[0066] Oxalic acid (analytical grade) was added to the third scandium solution, the amount of which was 2.5 times the molar amount of scandium ions in the third scandium solution. The reaction temperature was controlled at 70℃, and a third stirring reaction was carried out at a stirring rate of 200 r / min for 1.5 hours. During the reaction, white scandium oxalate crystals were formed. After the reaction was completed, the solution was vacuum filtered, and the crystals were washed twice with dilute oxalic acid solution (0.2 mol / L) to obtain high-purity scandium oxalate crystals and calcium complex solution.

[0067] Hydrochloric acid with a concentration of 6 mol / L was slowly added to the above calcium complex solution to obtain a regenerated hydrochloric acid solution, which was used to dissolve scandium oxide raw materials in subsequent batches.

[0068] High-purity scandium oxalate crystals were placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then to 900°C at a rate of 8°C / min. The temperature was maintained for 1 hour, and the scandium oxalate was calcined and decomposed to obtain high-purity scandium oxide product.

[0069] The high-purity scandium oxide product obtained in this embodiment, as detected by ICP-OES, has a scandium oxide purity of 99.992%, a calcium impurity content reduced to 0.003%, a calcium removal rate of 99.16%, and significantly reduced contents of impurities such as titanium, iron, and zirconium.

[0070] Example 2 Comparing Example 2 with Example 1, the difference between Example 2 and Example 1 is as follows: A 15% sodium carbonate solution was slowly added dropwise to a scandium solution containing calcium while stirring. The pH was adjusted to 1.5 to obtain the first scandium solution.

[0071] Add disodium hydrogen phosphate (analytical grade) to the first scandium solution, according to PO4 3- : Ca 2+ The molar ratio was 2.0:1, and the amount added was calculated to be 1.09 g. The reaction temperature was controlled at 40℃, the stirring rate at 200 r / min, and the reaction time at 15 minutes. During the reaction, a white calcium phosphate precipitate was observed to form. After the reaction, the sample was filtered under vacuum, and the precipitate was washed three times with deionized water (100 mL of water each time). The filtrate was collected to obtain the second scandium solution. The residual Ca was detected. 2+ The content is 0.036 g / L.

[0072] Sodium gluconate (a complexing agent) was added to the second scandium solution, at an amount 2.0 times the molar amount of calcium ions in the second scandium solution. The reaction temperature was controlled at 60℃, and a second stirring reaction was carried out at a stirring rate of 200 r / min for 40 minutes to obtain the third scandium solution. Upon testing, residual Ca2+ was found to be present. 2+ The content is 0.008g / L.

[0073] Sodium oxalate (analytical grade) was added to the third scandium solution, the amount of which was 1.5 times the molar amount of scandium ions in the third scandium solution. The reaction temperature was controlled at 80℃, and a third stirring reaction was carried out at a stirring rate of 200 r / min for 1 hour. During the reaction, white scandium oxalate crystals were formed. After the reaction was completed, the solution was filtered under vacuum and washed twice with dilute oxalic acid solution (0.2 mol / L) to obtain high-purity scandium oxalate crystals and calcium complex solution.

[0074] Hydrochloric acid with a concentration of 6 mol / L was slowly added to the above calcium complex solution to obtain a regenerated hydrochloric acid solution, which was used to dissolve scandium oxide raw materials in subsequent batches.

[0075] High-purity scandium oxalate crystals were placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then to 900°C at a rate of 8°C / min. The temperature was maintained for 1 hour, and the scandium oxalate was calcined and decomposed to obtain high-purity scandium oxide product.

[0076] The high-purity scandium oxide product obtained in this embodiment, as detected by ICP-OES, has a scandium oxide purity of 99.99%, a calcium impurity content reduced to 0.0032%, a calcium removal rate of 99.11%, and significantly reduced contents of impurities such as titanium, iron, and zirconium.

[0077] Example 3 Comparing Example 3 with Example 1, the difference between Example 3 and Example 1 is as follows: 100 g of scandium oxide raw material containing calcium impurities was dissolved in 1000 mL of 6 mol / L nitric acid to obtain a scandium solution containing calcium. The concentrations of scandium and impurity ions in the scandium solution containing calcium were the same as in Example 1.

[0078] Slowly add 20% ammonia solution to the above-mentioned calcium-containing scandium solution while stirring, and adjust the pH value to 2.0 to obtain the first scandium solution.

[0079] Add phosphoric acid (analytical grade, 85% concentration) to the first scandium solution, according to PO4 3- : Ca 2+The molar ratio was 1.5:1, and the amount added was calculated to be 0.48 mL. The reaction temperature was controlled at 25℃, the stirring rate at 200 r / min, and the reaction time at 30 minutes. During the reaction, a white calcium phosphate precipitate was observed to form. After the reaction, the solution was vacuum filtered, and the precipitate was washed three times with deionized water (100 mL of water each time). The filtrate was collected to obtain the second scandium solution. The residual Ca was detected. 2+ The content is 0.018g / L.

[0080] EDTA (a complexing agent) was added to the second scandium solution in an amount 1.2 times the molar amount of calcium ions in the second scandium solution. The reaction temperature was controlled at 50°C, and a second stirring reaction was carried out at a stirring rate of 200 r / min for 25 minutes to obtain the third scandium solution. The residual Ca2+ was then detected. 2+ The content is 0.004 g / L.

[0081] Oxalic acid (analytical grade) was added to the third scandium solution, the amount of which was 2.0 times the molar amount of scandium ions in the third scandium solution. The reaction temperature was controlled at 80℃, and a third stirring reaction was carried out at a stirring rate of 200 r / min for 1 hour. During the reaction, white scandium oxalate crystals were formed. After the reaction was completed, the solution was vacuum filtered, and the crystals were washed twice with dilute oxalic acid solution (0.2 mol / L) to obtain high-purity scandium oxalate crystals and calcium complex solution.

[0082] Slowly add 6 mol / L nitric acid to the above calcium complex solution to obtain a regenerated nitric acid solution, which is used for dissolving subsequent batches of scandium oxide feedstock.

[0083] High-purity scandium oxalate crystals were placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then to 850°C at a rate of 8°C / min. The temperature was maintained for 1 hour, and the scandium oxalate was calcined and decomposed to obtain high-purity scandium oxide product.

[0084] The high-purity scandium oxide product obtained in this embodiment, as detected by ICP-OES, has a scandium oxide purity of 99.998%, a calcium impurity content reduced to 0.0005%, a calcium removal rate of 99.86%, and significantly reduced contents of impurities such as titanium, iron, and zirconium.

[0085] Example 4 Comparing Example 4 with Example 3, the difference between Example 4 and Example 1 is as follows: Ammonia solution with a mass fraction of 20% was slowly added dropwise to a scandium solution containing calcium while stirring. The pH value was adjusted to 1.0 to obtain the first scandium solution.

[0086] Add phosphoric acid (analytical grade, 85% concentration) to the first scandium solution, according to PO4 3- : Ca 2+The molar ratio was 1.5:1, and the amount added was calculated to be 0.48 mL. The reaction temperature was controlled at 20℃, the stirring rate at 200 r / min, and the reaction time at 35 minutes. During the reaction, a white calcium phosphate precipitate was observed to form. After the reaction, the mixture was vacuum filtered, and the precipitate was washed three times with deionized water (100 mL of water each time). The filtrate was collected to obtain the second scandium solution. The residual Ca was detected. 2+ The content is 0.020 g / L.

[0087] EDTA (a complexing agent) was added to the second scandium solution, the amount being 1.0 times the molar amount of calcium ions in the second scandium solution. The reaction temperature was controlled at 60℃, and a second stirring reaction was carried out at a stirring rate of 200 r / min for 35 minutes to obtain the third scandium solution. Upon testing, residual Ca... 2+ The content is 0.0038 g / L.

[0088] Sodium oxalate (analytical grade) was added to the third scandium solution, the amount of which was 3.0 times the molar amount of scandium ions in the third scandium solution. The reaction temperature was controlled at 85℃, and a third stirring reaction was carried out at a stirring rate of 200 r / min for 1.5 hours. During the reaction, white scandium oxalate crystals were formed. After the reaction was completed, the solution was vacuum filtered, and the crystals were washed twice with dilute oxalic acid solution (0.2 mol / L) to obtain high-purity scandium oxalate crystals and calcium complex solution.

[0089] Slowly add 6 mol / L nitric acid to the above calcium complex solution to obtain a regenerated nitric acid solution, which is used for dissolving subsequent batches of scandium oxide feedstock.

[0090] High-purity scandium oxalate crystals were placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then to 875°C at a rate of 8°C / min. The temperature was maintained for 1 hour, and the scandium oxalate was calcined and decomposed to obtain high-purity scandium oxide product.

[0091] The high-purity scandium oxide product obtained in this embodiment, as detected by ICP-OES, has a scandium oxide purity of 99.995%, a calcium impurity content reduced to 0.00054%, a calcium removal rate of 99.85%, and significantly reduced contents of impurities such as titanium, iron, and zirconium.

[0092] Example 5 Comparing Example 5 with Example 1, the difference between Example 5 and Example 1 is as follows: A 5% sodium hydroxide solution was slowly added dropwise to a scandium solution containing calcium while stirring. The pH was adjusted to 1.6 to obtain the first scandium solution.

[0093] Add phosphoric acid (analytical grade, 85% concentration) to the first scandium solution, according to PO4 3- : Ca2+ The molar ratio was 1.0:1, and the amount added was calculated to be 0.32 mL. The reaction temperature was controlled at 10℃, the stirring rate at 200 r / min, and the reaction time at 40 minutes. During the reaction, a white calcium phosphate precipitate was observed to form. After the reaction, the sample was filtered under vacuum, and the precipitate was washed three times with deionized water (100 mL of water each time). The filtrate was collected to obtain the second scandium solution. The residual Ca was detected. 2+ The content is 0.034 g / L.

[0094] EDTA (a complexing agent) was added to the second scandium solution in an amount 1.2 times the molar amount of calcium ions in the second scandium solution. The reaction temperature was controlled at 50°C, and a second stirring reaction was carried out at a stirring rate of 200 r / min for 25 minutes to obtain the third scandium solution. The residual Ca2+ was then detected. 2+ The content is 0.0028 g / L.

[0095] Sodium oxalate (analytical grade) was added to the third scandium solution, the amount of which was 1.5 times the molar amount of scandium ions in the third scandium solution. The reaction temperature was controlled at 60℃, and a third stirring reaction was carried out at a stirring rate of 200 r / min for 2 hours. During the reaction, white scandium oxalate crystals were formed. After the reaction was completed, the solution was vacuum filtered, and the crystals were washed twice with dilute oxalic acid solution (0.2 mol / L) to obtain high-purity scandium oxalate crystals and calcium complex solution.

[0096] Slowly add 6 mol / L nitric acid to the above calcium complex solution to obtain a regenerated nitric acid solution, which is used for dissolving subsequent batches of scandium oxide feedstock.

[0097] High-purity scandium oxalate crystals were placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then to 850°C at a rate of 8°C / min. The temperature was maintained for 1 hour, and the scandium oxalate was calcined and decomposed to obtain high-purity scandium oxide product.

[0098] The high-purity scandium oxide product obtained in this embodiment, as detected by ICP-OES, has a scandium oxide purity of 99.994%, a calcium impurity content reduced to 0.0005%, a calcium removal rate of 99.86%, and significantly reduced contents of impurities such as titanium, iron, and zirconium.

[0099] Comparative Example 1 (insufficient phosphoric acid) In this comparative example, the molar ratio of phosphate to calcium ions is lower than the range specified in this application. The remaining steps and parameters are the same as in Example 1. This is used to compare the effect of phosphate addition on calcium removal efficiency. The specific steps are as follows: Slowly add a 5% sodium hydroxide solution to the above-mentioned calcium-containing scandium solution while stirring, and adjust the pH value to 0.5 to obtain the first scandium solution.

[0100] Add sodium phosphate (analytical grade) to the first scandium solution, according to PO4. 3- : Ca 2+ The molar ratio was 0.5:1, and the amount added was calculated to be 0.63 g. The reaction temperature was controlled at 30℃, the stirring rate at 200 r / min, and the reaction time at 20 minutes. During the reaction, a white calcium phosphate precipitate was observed to form. After the reaction, the sample was filtered under vacuum, and the precipitate was washed three times with deionized water (100 mL of water each time). The filtrate was collected to obtain the second scandium solution. The residual Ca was detected. 2+ The content is 0.15g / L.

[0101] Sodium citrate (a complexing agent) was added to the second scandium solution, at an amount 1.5 times the molar amount of calcium ions in the second scandium solution. The reaction temperature was controlled at 30°C, and a second stirring reaction was carried out at a stirring rate of 200 r / min for 25 minutes to obtain the third scandium solution. Upon testing, residual Ca... 2+ The content is 0.08g / L.

[0102] Oxalic acid (analytical grade) was added to the third scandium solution, the amount of which was 2.5 times the molar amount of scandium ions in the third scandium solution. The reaction temperature was controlled at 70℃, and a third stirring reaction was carried out at a stirring rate of 200 r / min for 1.5 hours. During the reaction, white scandium oxalate crystals were formed. After the reaction was completed, the solution was vacuum filtered, and the crystals were washed twice with dilute oxalic acid solution (0.2 mol / L) to obtain high-purity scandium oxalate crystals and calcium complex solution.

[0103] Hydrochloric acid with a concentration of 6 mol / L was slowly added to the above calcium complex solution to obtain a regenerated hydrochloric acid solution, which was used to dissolve scandium oxide raw materials in subsequent batches.

[0104] High-purity scandium oxalate crystals were placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then to 900°C at a rate of 8°C / min. The temperature was maintained for 1 hour, and the scandium oxalate was calcined and decomposed to obtain high-purity scandium oxide product.

[0105] The high-purity scandium oxide product obtained in this comparative example, as tested by ICP-OES, showed a scandium oxide purity of 99.68%, a calcium impurity content of 0.15%, a calcium removal rate of 58.33%, and relatively high contents of impurities such as titanium, iron, and zirconium.

[0106] Comparative Example 2 (without deep complexation calcium removal) This comparative example does not use a complexing agent for deep calcium removal; the remaining steps and parameters are the same as in Example 3. It is used to compare the effect of the complexation step on calcium removal efficiency. The specific steps are as follows: 100 g of scandium oxide raw material containing calcium impurities was dissolved in 1000 mL of 6 mol / L nitric acid to obtain a scandium solution containing calcium. The concentrations of scandium and impurity ions in the scandium solution containing calcium were the same as in Example 1.

[0107] Slowly add 20% ammonia solution to the above-mentioned calcium-containing scandium solution while stirring, and adjust the pH value to 2.0 to obtain the first scandium solution.

[0108] Add phosphoric acid (analytical grade, 85% concentration) to the first scandium solution, according to PO4 3- : Ca 2+ The molar ratio was 1.5:1, and the amount added was calculated to be 0.48 mL. The reaction temperature was controlled at 25℃, the stirring rate at 200 r / min, and the reaction time at 30 minutes. During the reaction, a white calcium phosphate precipitate was observed to form. After the reaction, the solution was vacuum filtered, and the precipitate was washed three times with deionized water (100 mL of water each time). The filtrate was collected to obtain the second scandium solution. The residual Ca was detected. 2+ The content is 0.018g / L.

[0109] Oxalic acid (analytical grade) was added to the second scandium solution in an amount 2.0 times the molar amount of scandium ions in the third scandium solution. The reaction temperature was controlled at 80°C, and a third stirring reaction was carried out at a stirring rate of 200 r / min for 1 hour. During the reaction, white scandium oxalate crystals were formed. After the reaction was completed, the solution was vacuum filtered and washed twice with dilute oxalic acid solution (0.2 mol / L) to obtain high-purity scandium oxalate crystals and calcium complex solution.

[0110] Slowly add 6 mol / L nitric acid to the above calcium complex solution to obtain a regenerated nitric acid solution, which is used for dissolving subsequent batches of scandium oxide feedstock.

[0111] High-purity scandium oxalate crystals were placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then to 850°C at a rate of 8°C / min. The temperature was maintained for 1 hour, and the scandium oxalate was calcined and decomposed to obtain high-purity scandium oxide product.

[0112] The high-purity scandium oxide product obtained in this comparative example, as tested by ICP-OES, showed a scandium oxide purity of 99.71%, a calcium impurity content reduced to 0.12%, a calcium removal rate of 66.66%, and relatively high contents of impurities such as titanium, iron, and zirconium.

[0113] The results of scandium oxide purity, calcium impurity content, and calcium removal rate of Examples 1-5, Comparative Examples 1 and 2 are summarized in Table 3.

[0114] Table 3 Product performance data for examples and comparative examples

[0115] As shown in Table 3, the high-purity scandium oxide products obtained in Examples 1 to 5 have a purity of 99.99% to 99.998%, a calcium impurity content of 0.0005% to 0.0032%, and a calcium removal rate of 99.11% to 99.86%, indicating that the method of this application can stably achieve deep removal of calcium impurities from scandium oxide.

[0116] In Comparative Example 1, due to insufficient phosphate addition, the concentration of residual calcium ions in the solution increased significantly after the first stirring reaction. Even with the subsequent addition of a complexing agent, the excess calcium ions could not be completely locked, resulting in a large amount of calcium precipitating along with scandium oxalate during the oxalic acid precipitation process. The final product had a calcium impurity content as high as 0.15%, and the calcium removal rate was only 58.33%.

[0117] Comparative Example 2 completely omitted the complexing agent addition step. Although phosphoric acid precipitation removed most of the calcium, the residual trace calcium ions directly combined with oxalate ions during the oxalic acid precipitation stage to form calcium oxalate precipitate, which was mixed into the scandium oxalate crystals, resulting in a calcium impurity content of 0.12% in the product and a calcium removal rate of only 66.66%.

[0118] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: (1) Selective precipitation to remove calcium, significantly reducing calcium content: By reacting calcium ions with phosphate ions under weakly acidic conditions (pH 0.5~2.0) to form calcium phosphate precipitate, most of the calcium ions in the scandium-containing solution can be removed in one go, significantly reducing the burden of subsequent deep calcium removal.

[0119] (2) Complexing and locking residual calcium to prevent co-precipitation of calcium oxalate: EDTA, sodium citrate and other complexing agents are used to form stable and soluble complexes with residual trace calcium, avoiding the generation of calcium oxalate mixed into the product when oxalate precipitates scandium, thereby achieving deep removal of calcium and ensuring that the calcium impurity content in the final scandium oxide is less than 0.001%.

[0120] (3) Synergistic removal of multiple impurities such as iron, titanium, and zirconium: The phosphate precipitation step can simultaneously remove iron ions (generating ferric phosphate); the complexing agent can form soluble complexes with titanium, zirconium, etc., preventing them from precipitating during oxalic acid precipitation. This method has the effect of multi-element purification, and the product purity can reach over 99.99%.

[0121] (4) The process is simple and the cost is controllable: It only requires unit operations such as acid dissolution, precipitation, complexation, oxalic acid precipitation, and calcination, without the need for complex extraction or ion exchange equipment, making it suitable for industrial-scale production. Phosphoric acid precipitation removes the main amount of calcium, which greatly reduces the amount of expensive complexing agents used and lowers reagent costs.

[0122] (5) Recycling of acid and complexing agent, green economy: Adding hydrochloric acid or nitric acid to the calcium complexing mother liquor after oxalic acid precipitation can regenerate a strong acid solution for dissolving a new batch of scandium oxide raw materials. At the same time, the complexing agent can be recycled in the system, which significantly reduces waste liquid discharge and chemical reagent consumption, which is in line with the concept of green chemical industry.

[0123] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for deep removal of calcium impurities from scandium oxide, characterized in that, The method includes: Scandium oxide raw material containing calcium impurities is dissolved in a strong acid solution to obtain a calcium-containing scandium solution. A pH adjuster is added to the calcium-containing scandium solution to adjust the pH value to 0.5-2.0, thereby obtaining a first scandium solution; The first scandium solution is subjected to a first stirring reaction with phosphoric acid and / or phosphate to react with phosphate ions to form calcium phosphate precipitate, thereby obtaining a second scandium solution and calcium phosphate solid. The second scandium solution is subjected to a second stirring reaction with a complexing agent to allow the complexing agent to complex with the residual calcium ions in the second scandium solution, thereby obtaining a third scandium solution; The third scandium solution is subjected to a third stirring reaction with oxalic acid and / or sodium oxalate to generate scandium oxalate crystal precipitate by reacting scandium ions with oxalate ions in the third scandium solution, thereby obtaining scandium oxalate crystals and calcium complex solution. Add the strong acid solution to the calcium complex solution to obtain a regenerated strong acid solution for redissolving scandium oxide raw materials; The scandium oxalate crystals were calcined to obtain scandium oxide.

2. The method according to claim 1, characterized in that, The strong acid solution includes at least one of hydrochloric acid solution or nitric acid solution.

3. The method according to claim 1, characterized in that, The pH adjuster includes at least one of ammonia, sodium hydroxide solution, or sodium carbonate solution.

4. The method according to claim 1, characterized in that, The temperature of the first stirring reaction is 10℃~40℃, and the reaction time is 15min~40min.

5. The method according to claim 1, characterized in that, The PO4 in the phosphoric acid and / or phosphate 3- With Ca in the first scandium solution 2+ The molar ratio is (1.0~2.0):

1.

6. The method according to claim 1, characterized in that, The complexing agent includes at least one of ethylenediaminetetraacetic acid, sodium citrate, or sodium gluconate.

7. The method according to claim 1, characterized in that, The molar amount of the complexing agent is 1.0 to 2.0 times the molar amount of calcium ions in the second scandium solution.

8. The method according to claim 1, characterized in that, The temperature of the second stirring reaction is 10℃~60℃, and the reaction time is 15min~40min.

9. The method according to claim 1, characterized in that, The molar amount of oxalic acid and / or sodium oxalate is 1.5 to 3.0 times the molar amount of scandium ions in the third scandium solution.

10. The method according to claim 1, characterized in that, The temperature of the third stirring reaction is 60℃~90℃, and the reaction time is 1h~2h.

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