Method for clean preparation of high-purity scandium oxide from crude scandium oxalate

Abstract

The invention discloses a method for cleanly preparing high-purity scandium oxide from crude scandium oxalate, which comprises the following steps of: firstly, realizing efficient separation of scandium and most coexisting metal impurities through conversion reaction of the crude scandium oxalate and ammonium bicarbonate; then, an acidic phosphorus-containing extraction agent is adopted to selectively extract scandium in the returned solution, and thorium and rare earth impurities are deeply removed; then, solid oxalic acid is adopted for stripping scandium from the organic phase, and efficient conversion of scandium oxalate and in-situ regeneration of the organic phase are achieved while a traditional water phase is eliminated; and finally, removing an organic phase entrained in scandium oxalate through a secondary carbonate conversion step to obtain refined scandium salt, and roasting to obtain high-purity scandium oxide. The operation of all the units is linked with one another, an efficient, clean and low-consumption closed cycle is formed, and the method is used for purifying low-grade scandium oxalate raw materials with complex components.

Description

Technical Field

[0001] This invention relates to the field of crude scandium purification, and more specifically, to a method for preparing high-purity scandium oxide from crude scandium oxalate. Background Technology

[0002] Wet extraction of scandium from scandium-containing secondary resources such as nickel-cobalt hydroxide intermediates, titanium dioxide waste acid, zirconium oxychloride mother liquor, red mud, high-titanium slag chlorinated dust, and rare earth tailings is currently the main method for scandium industrial production. Among these methods, oxalic acid precipitation is widely used for the preliminary separation and enrichment of scandium due to its advantages such as high precipitation rate, large precipitate particle size, and easy solid-liquid separation. This process uses oxalic acid as a precipitant and utilizes Sc... 3+ With C2O4 2- Scandium oxalate hydrate (Sc2(C2O4)3·nH2O) precipitate, which has extremely low solubility. When the ammonium ion concentration in the leachate is high, it readily reacts with scandium to form ammonium scandium oxalate hydrate (NH4Sc(C2O4)2·nH2O) precipitate. Both of these precipitates are collectively referred to as scandium oxalates. During the oxalic acid precipitation of scandium, Fe... 3+ Ti 4+ The oxalate of impurities such as [unspecified impurities] has relatively high solubility and is unlikely to co-precipitate at low concentrations, thus enabling preliminary separation from scandium. However, this method has limitations regarding Fe [unspecified impurities]. 2+ Ca 2+ Mg 2 + Al 3+ Zr 4+ ,Th 4+ The separation effect of other rare earth elements and other impurities is limited. Impurities are easy to co-precipitate with scandium or be carried into the solid phase, resulting in low purity of scandium oxalate product, which is crude scandium oxalate. If it is directly roasted, it cannot obtain high-purity scandium oxide that meets the requirements of high-end applications. Deep purification is necessary.

[0003] To address the issue of insufficient purity in crude scandium oxalate, existing technologies mainly employ two routes. One involves directly dissolving the crude scandium oxalate in concentrated acid under heating conditions, followed by subsequent purification. However, after dissolving scandium oxalate in concentrated acid, the Sc... 3+ With C2O4 2- It still exists in the liquid phase, which brings two major problems: (1) The solution needs to be continuously heated to maintain the solubility of scandium oxalate. Once the acidity decreases or the temperature drops, scandium oxalate will re-precipitate, resulting in poor operational stability; (2) The strong complexing ability and precipitation characteristics of oxalate will seriously interfere with subsequent purification steps such as solvent extraction, ion exchange and reprecipitation.

[0004] Secondly, the crude scandium oxalate is first calcined at 700-900℃ to decompose into scandium oxide, which is then dissolved in strong acids such as hydrochloric acid and sulfuric acid for purification. However, the Sc2O3 produced by calcination is chemically very stable and difficult to dissolve at room temperature, requiring prolonged heating under high acidity to dissolve it. This process is not only energy-intensive and causes severe equipment corrosion, but also generates a large amount of waste acid that needs to be treated, resulting in a significant environmental burden.

[0005] Existing patented technologies have failed to effectively resolve the aforementioned contradictions. For example, CN103194609B uses only one oxalic acid precipitation and calcination process, yielding scandium oxide with a purity of approximately 95%, which is insufficient to meet high-purity requirements. CN102030355A dissolves the initially precipitated scandium oxalate in hydrochloric acid, followed by a second precipitation with oxalic acid. After two dissolution-precipitation cycles, calcination yields 99.5% scandium oxide. This method offers limited purity improvement and is cumbersome. CN103361486B prepares high-purity scandium oxide through the formation of scandium oxalate complex salts, sulfuric acid dissolution, potassium scandium sulfate complex salt precipitation, alkali conversion, and repeated dissolution-precipitation-conversion operations. This process is exceptionally complex, generates a large amount of waste liquid throughout, and suffers from unsatisfactory production efficiency and environmental friendliness. CN102127641B prepares high-purity scandium oxide through a process of oxalic acid precipitation, roasting, hydrochloric acid dissolution, extraction, secondary oxalic acid precipitation, and secondary roasting. While this improves purity, the process is lengthy, complex, and energy-intensive. CN111630001B attempts to reduce energy consumption by lowering the initial roasting temperature, but its technical approach remains limited to a cycle of precipitation-roasting-acid dissolution, failing to fundamentally simplify the process or reduce consumption.

[0006] As can be seen from the above methods, existing crude scandium purification technologies have achieved certain results, but also have some problems and shortcomings. There is an urgent need in this field to develop a method that can achieve efficient and complete separation of scandium and oxalate under mild conditions, thereby simplifying the process, reducing energy consumption and costs, and realizing the clean preparation of high-purity scandium oxide. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for the clean preparation of high-purity scandium oxide from crude scandium oxalate, which enables efficient and thorough separation of scandium and oxalate under mild conditions, simplifying the process and reducing energy consumption and costs.

[0008] To achieve this technical objective, the present invention adopts the following solution:

[0009] A method for cleaning and preparing high-purity scandium oxide from crude scandium oxalate includes the following steps: (1) Primary carbonate conversion: Crude scandium oxalate, ammonium bicarbonate solid and deionized water are mixed and subjected to primary carbonate conversion reaction. After the reaction is completed, solid-liquid separation is performed, the precipitate is washed and the primary scandium carbonate is obtained. (2) Dissolution and extraction: The primary scandium carbonate described in step (1) is subjected to a back dissolution treatment to obtain a scandium back solution; The scandium-containing loaded organic phase is subjected to single-stage or countercurrent extraction of the scandium back solution to obtain a scandium-containing organic phase; the scandium-containing loaded organic phase is then washed to obtain a pure loaded organic phase. (3) Oxalate conversion: The pure supported organic phase described in step (2) and solid oxalic acid dihydrate are mixed to carry out the oxalate conversion reaction. After the reaction is completed, the solid and liquid phases are separated to obtain a scandium-depleted organic phase and a scandium-containing solid phase. The unreacted oxalic acid in the scandium-containing solid phase is dissolved in deionized water, and the solid and liquid phases are separated and washed to obtain oil-containing scandium oxalate. (4) Secondary carbonate conversion: The oil-containing scandium oxalate, ammonium bicarbonate solid and deionized water are mixed to carry out a secondary carbonate conversion reaction; After the reaction is complete, the product is allowed to stand, degreased, separated into solid and liquid components, and washed with deionized water or a 0%~10% ammonium bicarbonate solution to obtain refined scandium carbonate. Alternatively, after the reaction is complete, add 6-12 mol / L hydrochloric acid to the slurry to adjust the pH to 0.1-0.5, stir at 20-95℃ for 0.5-4 h, and after standing, degreasing, filtration and washing with water, obtain refined scandium oxalate. (5) Calcination: The carbonate or oxalate of refined scandium described in step (4) is calcined at 800-900°C for 1-4 h in an air atmosphere to obtain high-purity scandium oxide, wherein the mass fraction of Sc2O3 in the high-purity scandium oxide is not less than 99.99%.

[0010] Further, in step (1), the crude scandium has an oxalate content of 10% to 32% by mass, calculated as Sc2O3, and contains one or more impurities selected from sodium, magnesium, aluminum, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, thorium, uranium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium.

[0011] Further, in step (1), the conditions for the primary carbonate conversion reaction are: reaction temperature 20~90℃, reaction time 0.5~6 h, the amount of ammonium bicarbonate used is 3.5~8.0 times the amount of scandium in the crude scandium oxalate, and the amount of deionized water used is 75~115 times the amount of scandium in the crude scandium oxalate; the washing solution used for washing the precipitate is deionized water or ammonium bicarbonate solution with a mass fraction of 0%~10%.

[0012] Further, in step (2), the reagents used in the back dissolution treatment are deionized water and 6~12 mol / L hydrochloric acid, the back dissolution temperature is 15~40℃, the solution is conditioned with 15%~31% ammonia water, the insoluble matter is removed by filtration, and the scandium concentration in the resulting scandium back solution is 10~50 g / L and the hydrogen ion concentration is 2~6 mol / L.

[0013] Further, in step (2), the organic phase comprises 10% to 40% by volume of an acidic phosphorus-containing extractant and 0% to 20% by volume of a modifier, with the remainder being sulfonated kerosene; the acidic phosphorus-containing extractant is selected from one or more of di(2-ethylhexyl) phosphate, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester or bis(2,4,4-trimethylpentyl)phosphonic acid, and the modifier is selected from tributyl phosphate and / or 2-octanol; the extraction control organic phase to aqueous phase volume ratio is 0.5:1 to 3.0:1, the extraction temperature is 15 to 45°C, the number of extraction stages is 1 to 7, and the single-stage extraction time is 1 to 8 min.

[0014] Further, in step (2), the washing treatment of the scandium-containing supported organic phase is specifically as follows: the supported organic phase is washed in single-stage or countercurrent washing with hydrochloric acid at a concentration of 2~6 mol / L, the volume ratio of the supported organic phase to the washing liquid is controlled at 2:1~5:1, the washing temperature is 15~35℃, the single-stage washing time is 1~5 min, and the number of washing stages is 1~6, so as to remove the raffinate entrained in the organic phase and obtain a pure supported organic phase.

[0015] Further, in step (3), the conditions for the oxalate conversion reaction are: reaction temperature 60~90℃, reaction time 2~5 h, the amount of oxalic acid dihydrate solid added is 4~10 times the amount of scandium in the organic phase; the particle size of the oxalic acid dihydrate solid is 0.5~1.5 mm; the specific treatment of the scandium-containing solid phase is as follows: the scandium-containing solid phase is stirred in deionized water at a stirring temperature of 20~80℃ for 1~20 min, the amount of deionized water is 5~15 times the mass of the scandium-containing solid phase, the upper floating oil is removed after the reaction, the solid and liquid are separated, the precipitate is washed with deionized water to obtain oil-containing scandium oxalate.

[0016] Further, in step (4), the secondary carbonate conversion reaction conditions are: reaction temperature of 20~90℃, reaction time of 0.5~6 h, the amount of ammonium bicarbonate used is 3.5~8.0 times the amount of scandium in the scandium oxalate, and the amount of deionized water used is 75~115 times the amount of scandium in the scandium oxalate.

[0017] Furthermore, it also includes regenerating the scandium-depleted organic phase obtained in step (3), specifically: using 3~8 mol / L hydrochloric acid to wash the scandium-depleted organic phase in a single-stage or countercurrent manner, controlling the volume ratio of organic phase to washing liquid to be 1:1~8:1, the washing temperature to be 15~45℃, the single-stage washing time to be 2~20 min, and the number of washing stages to be 1~6, in order to remove the oxalic acid mixed in, and obtain the regenerated organic phase, which is returned to step (2) for the extraction of scandium return solution.

[0018] Furthermore, it also includes: adding hydrochloric acid with a concentration of 6~12mol / L to the scandium-containing filtrate obtained from the solid-liquid separation in step (1), adjusting the pH of the filtrate to 0.3~1.0, stirring at 20~95℃ for 0.5~4 h to precipitate scandium and obtain a primary regenerated scandium salt; Add hydrochloric acid with a concentration of 6~12mol / L to the secondary scandium-containing filtrate obtained from solid-liquid separation in step (4), adjust the pH of the filtrate to 0.3~1.0, and stir at 20~95℃ for 0.5~4 h to precipitate scandium and obtain secondary regenerated scandium salt.

[0019] In this invention, the main form of scandium in the crude scandium oxalate is scandium oxalate hydrate (Sc2(C2O4)3·nH2O) and / or scandium ammonium oxalate hydrate (NH4Sc(C2O4)2·nH2O). The main form of scandium in the primary scandium carbonate and the refined scandium carbonate is scandium ammonium carbonate hydrate (NH4Sc(CO3)2·nH2O). The main form of scandium in the oil-containing scandium oxalate is scandium oxalate hydrate. The main form of scandium in the refined scandium oxalate is scandium ammonium oxalate hydrate. Di(2-ethylhexyl) phosphate is the chemical name of P204, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is the chemical name of P507, bis(2,4,4-trimethylpentyl)phosphonic acid is the chemical name of Cyanex 272, and tributyl phosphate is the chemical name of TBP. The high-purity scandium oxide refers to scandium oxide products that meet the technical requirements of grade 4N or higher in GB / T 13219-2018.

[0020] During a carbonate conversion stage, the crude scandium oxalate undergoes structural rearrangement in the ammonium bicarbonate system, with the oxalate ion entering the solution and transforming into a soluble ammonium salt form, while Sc... 3+ Priority with CO3 2- and NH4 +Hydrated scandium ammonium carbonate is formed, achieving effective separation of scandium and oxalate. Simultaneously, impurity ions such as Na, Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, and U remain stably present in the liquid phase through the synergistic complexation of oxalate, ammonium, and bicarbonate ions, inhibiting their hydrolysis and co-precipitation, thus allowing most metallic impurities to be discharged with the filtrate. However, due to the similar chemical behavior of thorium and rare earth impurities to scandium, a small amount still co-precipitates with scandium in the primary scandium carbonate precipitate.

[0021] The obtained primary scandium carbonate is dissolved in hydrochloric acid to form a NH4-containing compound. + ,Sc 3+ H + and Cl - Scandium return solution. Under the action of an acidic phosphorus-containing extractant system, Sc 3+ Scandium preferentially enters the organic phase and has a high partition ratio, while thorium and rare earth impurities have relatively low extraction rates under the same conditions and are mainly retained in the aqueous phase, thus achieving deep separation of scandium from thorium and rare earth impurities. Acid washing of the scandium-loaded organic phase can further remove entrained aqueous phase and improve the cleanliness of the organic phase.

[0022] Add solid oxalic acid to the scandium-supported organic phase, Sc 3+ Scandium oxalate precipitates with very low solubility with oxalate ions, while the extractant is regenerated and returned to the organic phase. Since the organic phase is now essentially free of thorium and rare earth impurities, the purity of the scandium oxalate precipitate is significantly improved. During the secondary carbonate conversion, its crystal structure is reconstructed, and the previously coated or entrained organic phase is released and separated into layers, forming hydrated ammonium scandium carbonate precipitate again. If trace amounts of impurity metal ions still exist in the system, they can be further purified during the secondary carbonate conversion. Finally, high-temperature calcination completely decomposes the carbonate or oxalate, generating high-purity scandium oxide.

[0023] To quantitatively evaluate the conversion effects of carbonate and oxalate, the following indicators are defined: Formula a: Percentage of unreacted scandium oxalate = (Amount of scandium in the residual scandium oxalate after carbonate conversion / Amount of scandium in the feed scandium oxalate) × 100%; Formula b: The proportion of dissolved scandium in oxalate = (Amount of scandium in the liquid phase after carbonate conversion / Amount of scandium in the oxalate of the fed scandium) × 100%; Formula c: Carbonate conversion rate = (Amount of scandium in the carbonate after carbonate conversion / Amount of scandium in the oxalate of the feed scandium) × 100%; Formula d: Oxalate conversion rate = (Amount of scandium in the scandium-containing solid phase after oxalate conversion / Amount of scandium in the original pure supported organic phase) × 100%.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The method of the present invention has good adaptability to crude scandium oxalate with different sources, grades and impurities. By adjusting parameters such as the amount of ammonium bicarbonate, the composition and number of extractants, the particle size of oxalic acid and the phase volume ratio, the process parameters can be flexibly optimized to adapt to raw materials with complex impurity systems such as high zirconium, high sodium, high iron, high aluminum, high calcium, high titanium, high thorium and high rare earth.

[0026] (2) The method of the present invention significantly shortens the traditional process of calcining and dissolving scandium oxalate or dissolving scandium in high acidity. By converting scandium oxalate, which is difficult to dissolve, into scandium carbonate, which is easily dissolved by acid, the clean, efficient and thorough separation of scandium and oxalate is achieved, reducing acid consumption and energy consumption. The reaction conditions are mild and fast. The main reagents, ammonium bicarbonate and oxalic acid, are widely available and low in cost. The extractant can be recycled by washing with hydrochloric acid. Scandium in the carbonate conversion filtrate can be recovered by acidification. The wastewater is easy to treat and the environmental pressure is low. The total recovery rate of scandium is stable at over 95%, achieving efficient utilization of resources.

[0027] (3) The method of the present invention eliminates the traditional water back-extraction process. Through the oxalate conversion reaction, scandium in the loaded organic phase is directly and efficiently precipitated as scandium oxalate solid. This step avoids the problems of introducing a large amount of acid and alkali reagents and generating a large amount of back-extraction waste liquid in the traditional water back-extraction process, and realizes the in-situ regeneration of the organic phase. Since scandium oxalate solid is easy to separate, the scandium loss rate is low, and it is closely connected with the subsequent secondary carbonate conversion step, ensuring the purity and high yield of the final scandium oxide product.

[0028] (4) The method of the present invention proposes a stepwise impurity removal strategy, which combines the carbonate transformation of crude scandium oxalate with solvent extraction. Impurities such as sodium, magnesium, aluminum, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, thorium, uranium and rare earth elements are deeply removed, and the final scandium oxide product reaches a purity of 4N or above. It is a key basic raw material for preparing high-performance Al-Sc alloys, metallic Sc, solid oxide fuel cell (SOFC) electrolytes, laser crystals, optical coating materials and AlScN thin films. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of a method for preparing high-purity scandium oxide from crude scandium oxalate according to the present invention.

[0030] Figure 2 The XRD pattern of the primary scandium carbonate described in Example 1 of this invention has diffraction peak positions that match those of NH4Sc(CO3)2·H2O.

[0031] Figure 3This is a SEM image of the primary scandium carbonate described in Example 1 of the present invention. The sample exhibits a randomly stacked nanoplate agglomerate structure.

[0032] Figure 4 The XRD pattern of scandium oxalate containing oil described in Example 1 of this invention has diffraction peak positions that match those of the Sc2(C2O4)3·6H2O phase (No. 33-1156, No. 27-0592).

[0033] Figure 5 The image shown is a SEM image of scandium oxalate containing oil as described in Example 1 of this invention. The sample exhibits a blocky structure with layered texture characteristics.

[0034] Figure 6 The XRD pattern of the refined scandium oxalate described in Example 4 of this invention has diffraction peak positions that match those of NH4Sc(C2O4)2·2H2O.

[0035] Figure 7 The image shows a SEM image of the refined scandium oxalate described in Example 4 of this invention. The sample exhibits a blocky structure with layered texture characteristics. Specific implementation methods

[0036] The present invention will be further explained below with reference to the embodiments. The following embodiments are not intended to limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation are within the protection scope of the present invention.

[0037] A method for the clean preparation of high-purity scandium oxide from crude scandium oxalate is described below. Figure 1 As shown, the process sequentially includes primary carbonate conversion, dissolution and extraction, oxalate conversion, secondary carbonate conversion, calcination to prepare scandium oxide, and scandium recovery from the filtrate. The key process parameters and control points for each step are as follows.

[0038] In this invention, the scandium content of the crude scandium oxalate, calculated as Sc2O3, is 10% to 32% by mass, and it contains one or more impurities selected from sodium, magnesium, aluminum, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, thorium, uranium, and rare earth impurities. Rare earth impurities refer to the total amount of rare earth elements excluding the main rare earth elements Sc and Pm. This invention does not impose special limitations on the source, impurity content, or degree of drying (wet or dry basis) of the crude scandium oxalate; any crude scandium oxalate well-known to those skilled in the art can be used. It should be noted that whether the crude scandium oxalate contains ammonium ions, water of crystallization, or adsorbed water does not affect its effectiveness in this invention, as long as scandium ions form a coordination structure with oxalate ions, the process requirements are met. The experimental results show that crude scandium oxalate is hygroscopic. After high-temperature drying, if it is cooled and exposed to air, it easily absorbs moisture from the air, resulting in an upper limit of its mass fraction as Sc2O3 of 32%.

[0039] First, the crude scandium oxalate is mixed with solid ammonium bicarbonate and deionized water and stirred to carry out a primary carbonate conversion reaction. The reaction temperature is 20-90℃, and the reaction time is 0.5-6 hours. The amount of ammonium bicarbonate used is 3.5-8.0 times the molar amount of scandium in the crude scandium oxalate, and the amount of deionized water used is 75-115 times the molar amount of scandium in the crude scandium oxalate. After the carbonate conversion reaction is completed, solid-liquid separation is performed. The precipitate is washed several times with deionized water or a 0%-10% ammonium bicarbonate solution to obtain primary scandium carbonate. The primary scandium-containing filtrate obtained from the solid-liquid separation enters the subsequent scandium recovery step. Care must be taken to control the amount of ammonium bicarbonate used in the carbonate conversion reaction. Insufficient ammonium bicarbonate will result in incomplete reaction, while excessive ammonium bicarbonate will reduce the carbonate conversion rate, which is not conducive to the formation of the target product. Under the ratio described in this invention, the primary carbonate conversion rate is above 70%, and there is no unreacted crude scandium oxalate. In contrast, using ammonium carbonate conversion completely dissolves scandium oxalate without any solid phase, while sodium bicarbonate has the disadvantage of low carbonate conversion rate.

[0040] During the carbonate conversion process, ammonium bicarbonate releases bicarbonate ions in water, driving the dissociation of scandium oxalate and / or scandium ammonium oxalate. The oxalate ions enter the liquid phase, and the scandium ions and ammonium ions form a carbonate double salt precipitate, while releasing water and carbon dioxide. After the reaction is completed, the original scandium oxalate disappears, and most of the scandium is converted into scandium carbonate solid. The remaining scandium remains in the liquid phase in the form of complex ions, while impurities such as zirconium, iron, aluminum, silicon, calcium, and titanium are also retained in the liquid phase due to the complexation effect of the solution. The resulting scandium carbonate has the characteristics of large particles, easy filtration, and easy acid solubility. The basic reaction relationship of the carbonate conversion process can be approximately represented by chemical reaction equations [1] and / or chemical reaction equations [2].

[0041] Chemical reaction equation [1]: Sc2(C2O4)3(s) + 8NH4HCO3(aq) → 2NH4Sc(CO3)2(s) + 3(NH4)2C2O4(aq) + 4H2O(aq) + 4CO2(g).

[0042] Chemical reaction equation [2]: NH4Sc(C2O4)2(s) + 4NH4HCO3(aq) → NH4Sc(CO3)2(s) + 2(NH4)2C2O4(aq) + 2H2O(aq) + 2CO2(g).

[0043] The primary scandium carbonate can be calcined in air at 200-500°C to remove the ammonium component; calcination at 700-900°C yields scandium oxide (Sc2O3), in which metallic impurities such as sodium, magnesium, aluminum, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, and uranium are sufficiently removed. While thorium and / or rare earth impurities are largely removed, it is still difficult to ensure that their residual amounts meet the scandium oxide purity standard of 4N or higher. In a preferred embodiment, if the thorium and rare earth impurity content in the crude scandium oxalate is extremely low, high-purity scandium oxide can be obtained by directly calcining at high temperature after the primary carbonate conversion.

[0044] To thoroughly remove thorium and rare earth impurities, the primary scandium carbonate is dissolved in deionized water and 6-12 mol / L hydrochloric acid at 15-40°C. The solution is then adjusted with 15%-31% (by mass, calculated as NH3) ammonia solution, and filtered to remove insoluble matter, yielding a scandium backflow solution with a scandium ion concentration of 10-50 g / L and a hydrogen ion concentration of 2-6 mol / L. Next, the scandium backflow solution is subjected to single-stage or countercurrent extraction, allowing scandium to selectively extract into the organic phase, while thorium and rare earth impurities remain in the aqueous phase. Phase separation yields a loaded organic phase. The organic phase used for extraction consists of an acidic phosphorus-containing extractant, a modifier, and sulfonated kerosene. The acidic phosphorus-containing extractant is selected from one or more combinations of P204, P507, or Cyanex 272, with a volume fraction of 10%–40%, preferably 15%–30%. The modifier is selected from TBP and / or sec-octanol, with a volume fraction of 0%–20%, preferably 5%–15%, and the balance is sulfonated kerosene. The volume ratio of the organic phase to the aqueous phase (O:A) is controlled at 0.5:1–3.0:1, preferably 1.0:1–2.0:1; the extraction temperature is 15–45°C, preferably 20–35°C; the single-stage extraction time is 1–8 min, preferably 3–5 min; and the number of extraction stages is 1–7, preferably 1–3. The modifier improves the phase separation effect and prevents emulsification and the formation of a third phase. Subsequently, the supported organic phase is washed with hydrochloric acid at a concentration of 2-6 mol / L in a single-stage or countercurrent manner, controlling the volume ratio of the supported organic phase to the washing liquid (O:A) to be 2:1-5:1, preferably 3:1-4:1, the washing temperature to be 15-35°C, the single-stage washing time to be 1-5 min, and the number of washing stages to be 1-6, in order to remove the raffinate entrained in the organic phase and obtain a pure supported organic phase. In conventional extraction processes, the purification ability of P204, P507, or Cyanex 272 extractants for scandium is limited; however, in this invention, since the preceding carbonate conversion has significantly reduced the content of thorium and rare earth impurities, combined with extraction and purification, it can effectively ensure that the content of thorium and rare earth impurities in the final scandium oxide product meets the purity requirement of 4N or above.

[0045] The pure supported organic phase is mixed and stirred with solid oxalic acid dihydrate (H₂C₂O₄·2H₂O) to carry out an oxalate conversion reaction, causing scandium to precipitate from the organic phase as scandium oxalate precipitate. The reaction temperature is 60-90℃, and the reaction time is 2-5 hours, preferably 3-4 hours. The amount of solid oxalic acid dihydrate used is 4-10 times, preferably 5-6 times, the amount of scandium in the pure supported organic phase. After the reaction, solid and liquid phases are separated to obtain a scandium-containing solid phase and a scandium-depleted organic phase. The oxalate conversion rate of this invention is generally above 80%, and the oxalate conversion reaction does not involve an aqueous phase. The reaction rate is too low when the reaction temperature is below 60℃. The oxalic acid dihydrate used in the oxalate conversion reaction only needs to meet the technical requirements of industrial oxalic acid, and its particle size is usually between 0.5-1.5 mm. To improve the oxalate conversion rate, the particle size can be controlled by sieving to increase the specific surface area; preferably, the oxalic acid particles are passed through a 32-200 mesh sieve. The basic reaction relationship of the oxalate conversion reaction can be approximately represented by the chemical reaction equation [3].

[0046] Chemical reaction equation [3]: 2ScA3(org) + 3H2C2O4(s) → Sc2(C2O4)3(s) + 6HA(org), where HA represents the acidic form of the extractant.

[0047] The scandium-depleted organic phase can be recycled after regeneration. Specifically, the scandium-depleted organic phase is washed with 3-8 mol / L hydrochloric acid in a single-stage or countercurrent manner, controlling the volume ratio of organic phase to washing liquid (O:A) to be 1:1-8:1, the washing temperature to be 15-45℃, the single-stage washing time to be 2-20 min, and the number of washing stages to be 1-6, in order to remove oxalic acid impurities and obtain a regenerated organic phase. It should be noted that the hydrochloric acid washing and regeneration process does not back-extract residual scandium from the scandium-depleted organic phase. Only a small portion of the extraction sites in the regenerated organic phase are occupied, resulting in a slight decrease in its effective extraction capacity, but the total number of coordination sites for scandium extraction in the organic phase does not decrease; at the same time, the regenerated organic phase does not contain thorium or rare earth metal impurities, meeting the requirements for continued use in extraction and purification.

[0048] The scandium-containing solid phase mainly consists of scandium oxalate and unreacted oxalic acid, with a small amount of organic phase. The scandium-containing solid phase is stirred in deionized water at a temperature of 20–80°C, preferably 30–60°C, for 1–20 min, preferably 5–10 min. The amount of deionized water used is 5–15 times the mass of the scandium-containing solid, dissolving the unreacted oxalic acid. Since scandium oxalate is produced in the organic phase, organic phase remains inside the particles. After the reaction, the upper floating oil is removed, and the solid and liquid are separated. The precipitate is washed with deionized water to obtain oil-containing scandium oxalate. The metallic impurities, including sodium, magnesium, aluminum, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, thorium, uranium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium, have been largely removed from the scandium oxalate containing oil. However, if scandium oxalate containing oil is directly calcined to prepare scandium oxide products, the mass fraction of Sc2O3 is usually difficult to reach 99.99%.

[0049] The scandium oxalate containing oil is mixed with solid ammonium bicarbonate and deionized water and stirred to carry out a secondary carbonate conversion reaction, which breaks down the scandium oxalate structure and releases the retained organic phase. The reaction temperature is 20-90℃, and the reaction time is 0.5-6 hours. The amount of ammonium bicarbonate used is 3.5-8.0 times the molar amount of scandium in the scandium oxalate containing oil, and the amount of deionized water used is 75-115 times the molar amount of scandium in the scandium oxalate containing oil. After the secondary carbonate conversion reaction is completed, the mixture is allowed to stand, a small amount of floating oil is removed from the upper layer, and solid-liquid separation is performed. The precipitate is washed several times with deionized water or a 0%-10% ammonium bicarbonate solution to obtain purified scandium carbonate free of organic phase. The secondary scandium-containing filtrate separated from the solid-liquid separation is then used in the subsequent scandium recovery step. Alternatively, after the secondary carbonate conversion reaction, 6-12 mol / L hydrochloric acid can be added directly to the slurry to adjust the pH to 0.1-0.5. The mixture is then stirred at 20-95°C for 0.5-4 hours, followed by settling, oil removal, filtration, and washing with water. This process yields refined scandium oxalate free of organic phase in one step, with a yield exceeding 98%. If the pH adjustment range exceeds 0.1-0.5, problems such as low yield or excessively fine precipitate particles that are difficult to filter may occur. Adjustments should be made according to actual operating conditions; a one-size-fits-all approach is not recommended. Since a large amount of ammonium ions are present during the formation of refined scandium oxalate, its main component is scandium ammonium oxalate double salt. Under the formulation described in this invention, the secondary carbonate conversion rate is above 70%, and there is no unreacted oil-containing scandium oxalate.

[0050] Finally, the refined scandium carbonate and / or refined scandium oxalate are placed in a calcination apparatus and calcined at 800~900℃ for 1~4h in an air atmosphere to obtain a high-purity scandium oxide product that meets the technical requirements of grade 4N or above in GB / T 13219-2018.

[0051] To recover scandium remaining in the liquid phase after carbonate conversion, 6-12 mol / L hydrochloric acid was added dropwise to the primary and secondary scandium-containing filtrates, respectively, to adjust the pH of the filtrates to 0.3-1.0 to break the complexation of scandium. The filtrates were stirred at 20-95℃ for 0.5-4 hours to precipitate scandium, thus obtaining the corresponding primary and secondary regenerated scandium salts. The scandium recovery rate was consistently above 98%.

[0052] Example 1

[0053] (1) The scandium content in the crude scandium oxalate, calculated as Sc2O3, was 30.35% by mass. The crude scandium oxalate was mixed with solid ammonium bicarbonate and deionized water, wherein the amount of solid ammonium bicarbonate was 5.5 times the molar amount of scandium in the crude scandium oxalate, and the amount of deionized water was 95 times the molar amount of scandium in the crude scandium oxalate. The mixture was stirred at 70°C for 2.5 h. After the reaction was completed, solid-liquid separation was performed, and the precipitate was washed with a 5% ammonium bicarbonate solution to obtain primary scandium carbonate.

[0054] (2) The primary scandium carbonate was dissolved in deionized water and 8 mol / L hydrochloric acid at 25°C, and then conditioned with 30% ammonia water. The insoluble matter was removed by filtration to obtain a scandium ion concentration of 20 g / L and a hydrogen ion concentration of 3 mol / L. An organic phase consisting of 15% P507, 10% TBP, and 75% sulfonated kerosene was prepared. The scandium ion solution was subjected to countercurrent extraction at 25°C, with an organic phase to aqueous phase volume ratio (O:A) of 3:1, a single-stage extraction time of 3 min, and two extraction stages to obtain a loaded organic phase. The loaded organic phase was then subjected to countercurrent washing at 25°C using 3 mol / L hydrochloric acid at a loaded organic phase to washing liquid volume ratio (O:A) of 3:1, with a single-stage washing time of 3 min and two washing stages to obtain a pure loaded organic phase.

[0055] (3) Transfer the pure supported organic phase to a reactor, add unsieved oxalic acid dihydrate solid (particle size between 0.5 and 1.5 mm), the amount of which is 5 times the amount of scandium in the pure supported organic phase, and stir the reaction at 75°C for 3 hours. After the reaction, perform solid-liquid separation to obtain a scandium-containing solid phase and a scandium-depleted organic phase. At 30°C, use 3 mol / L hydrochloric acid to perform countercurrent washing on the scandium-depleted organic phase, controlling the volume ratio of organic phase to washing liquid (O:A) to be 4:1, the single-stage washing time to be 10 minutes, and the number of washing stages to be 6. After phase separation, obtain the regenerated organic phase, which is returned to the scandium extraction operation for recycling.

[0056] (4) Add the scandium-containing solid phase to deionized water, the amount of deionized water being 10 times the mass of the scandium-containing solid phase. Stir at 50°C for 5 min, remove the upper layer of floating oil, filter, and wash the precipitate with deionized water to obtain scandium oxalate containing oil. Mix scandium oxalate containing oil with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid is 6.3 times the amount of scandium in the scandium-containing ...

[0057] (5) The refined scandium carbonate was calcined at 850°C for 2 hours in air atmosphere to completely decompose it and obtain high-purity scandium oxide.

[0058] (6) Adjust the pH of the primary scandium-containing filtrate obtained from solid-liquid separation in step (1) to 0.5 with 6 mol / L hydrochloric acid, stir at 20°C for 2 h, filter, and wash the precipitate with deionized water to obtain primary regenerated scandium salt; adjust the pH of the secondary scandium-containing filtrate obtained from solid-liquid separation in step (4) to 0.3 with 12 mol / L hydrochloric acid, stir at 20°C for 2 h, let stand after the reaction is completed, remove the upper floating oil, filter, and wash the precipitate with deionized water to obtain secondary regenerated scandium salt.

[0059] In Example 1, the chemical composition of crude scandium oxalate, oil-containing scandium oxalate, and high-purity scandium oxide is shown in Table 1.

[0060] The primary carbonate conversion rate was 76.6%, with 0% of the crude scandium containing oxalate being unreacted; the oxalate conversion rate was 82.1%; the secondary carbonate conversion rate was 81.6%, with 0% of the crude scandium containing oxalate being unreacted; the scandium recovery rate in the primary scandium-containing filtrate was 98.2%, and the scandium recovery rate in the secondary scandium-containing filtrate was 98.5%.

[0061] Table 1. Chemical composition of crude scandium oxalate, scandium oleate containing oxalate, and high-purity scandium oxide.

[0062]

[0063] Example 2

[0064] (1) The scandium content in the crude scandium oxalate, calculated as Sc2O3, was 32.36% by mass. The crude scandium oxalate was mixed with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid was 6.1 times the molar amount of scandium in the crude scandium oxalate, and the amount of deionized water was 75 times the molar amount of scandium in the crude scandium oxalate. The mixture was stirred at 60°C for 1 hour. After the reaction was completed, solid-liquid separation was performed, and the precipitate was washed with deionized water to obtain primary scandium carbonate.

[0065] (2) The primary scandium carbonate was dissolved in deionized water and 12 mol / L hydrochloric acid at 15 °C, and then conditioned with 15% ammonia water. The insoluble matter was removed by filtration to obtain a scandium ion concentration of 30 g / L and a hydrogen ion concentration of 6 mol / L. An organic phase was prepared consisting of 15% Cyanex 272, 3% P2O4, 10% TBP, 10% 2-octanol, and 62% sulfonated kerosene. The scandium ion solution was subjected to countercurrent extraction at 30 °C. The volume ratio of organic phase to aqueous phase (O:A) was 2:1, the single-stage extraction time was 4 min, and the number of extraction stages was 4, to obtain the loaded organic phase. At 15℃, the organic phase was countercurrently washed with 3 mol / L hydrochloric acid at a volume ratio of 2:1 (O:A) of 2:1. The single-stage washing time was 1 min and the number of washing stages was 3, resulting in a pure organic phase.

[0066] (3) Transfer the pure supported organic phase to a reactor, add unsieved oxalic acid dihydrate solid (particle size between 0.5 and 1.5 mm), the amount of which is 7 times the amount of scandium in the pure supported organic phase, and stir the reaction at 60°C for 5 h. After the reaction, perform solid-liquid separation to obtain a scandium-containing solid phase and a scandium-depleted organic phase. At 20°C, use 3 mol / L hydrochloric acid to perform a single-stage washing of the scandium-depleted organic phase, controlling the volume ratio of organic phase to washing liquid (O:A) to be 1:1, the washing time to be 2 min, and obtain a regenerated organic phase after phase separation, which is returned to the scandium extraction operation for recycling.

[0067] (4) Add the scandium-containing solid phase to deionized water, the amount of deionized water being 5 times the mass of the scandium-containing solid phase. Stir at 80°C for 1 min, remove the upper layer of floating oil, filter, and wash the precipitate with deionized water to obtain scandium oxalate containing oil. Mix scandium oxalate containing oil with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid is 5.4 times the amount of scandium in the scandium-containing scandium-containing oil, and the amount of deionized water is 115 times the amount of scandium in the scandium-containing scandium-containing oil, react at 90°C for 0.5 h, after the reaction is completed, let stand, remove the upper layer of floating oil, and then separate the solid and liquid and wash the precipitate with a 5% ammonium bicarbonate solution to obtain purified scandium carbonate.

[0068] (5) The refined scandium carbonate was calcined at 800°C for 3 hours in air atmosphere to completely decompose it and obtain high-purity scandium oxide.

[0069] (6) Adjust the pH of the primary scandium-containing filtrate obtained from solid-liquid separation in step (1) to 0.3 with 8 mol / L hydrochloric acid, stir at 95°C for 4 h, filter, and wash the precipitate with deionized water to obtain primary regenerated scandium salt; adjust the pH of the secondary scandium-containing filtrate obtained from solid-liquid separation in step (4) to 1 with 6 mol / L hydrochloric acid, stir at 95°C for 0.5 h, let stand after the reaction is complete, remove the upper floating oil, filter, and wash the precipitate with deionized water to obtain secondary regenerated scandium salt.

[0070] In Example 2, the chemical composition of crude scandium oxalate, oil-containing scandium oxalate, and high-purity scandium oxide is shown in Table 2.

[0071] The primary carbonate conversion rate was 78.6%, with 0% of the crude scandium containing oxalate being unreacted; the oxalate conversion rate was 90.6%; the secondary carbonate conversion rate was 78.4%, with 0% of the crude scandium containing oxalate being unreacted; the scandium recovery rate in the primary scandium-containing filtrate was 99.4%, and the scandium recovery rate in the secondary scandium-containing filtrate was 99.2%.

[0072] Table 2 Chemical composition of crude scandium oxalate, scandium oleate containing oxalate, and high-purity scandium oxide

[0073]

[0074] Example 3

[0075] (1) The scandium content in the crude scandium oxalate, calculated as Sc2O3, was 10.35% by mass. The crude scandium oxalate was mixed with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid was 3.5 times the molar amount of scandium in the crude scandium oxalate, and the amount of deionized water was 70 times the molar amount of scandium in the crude scandium oxalate. The mixture was stirred at 20°C for 6 hours. After the reaction was completed, solid-liquid separation was performed, and the precipitate was washed with deionized water to obtain primary scandium carbonate.

[0076] (2) The primary scandium carbonate was dissolved in deionized water and 10 mol / L hydrochloric acid at 20 °C, and then conditioned with 20% ammonia water. The insoluble matter was removed by filtration to obtain a scandium ion concentration of 10 g / L and a hydrogen ion concentration of 4 mol / L. An organic phase consisting of 10% P507% and 90% sulfonated kerosene was prepared. The scandium ion solution was subjected to single-stage extraction at 25 °C with an organic phase to aqueous phase volume ratio (O:A) of 0.5:1 to obtain a loaded organic phase. The loaded organic phase was washed at 30 °C with 6 mol / L hydrochloric acid at a loaded organic phase to washing liquid volume ratio (O:A) of 5:1 for 2 min to obtain a pure loaded organic phase.

[0077] (3) The pure supported organic phase was transferred to a reactor, and solid oxalic acid dihydrate that had passed through a 100-mesh sieve was added. The amount of oxalic acid dihydrate was 10 times the amount of scandium in the pure supported organic phase. The mixture was stirred at 80°C for 2 hours. After the reaction, solid-liquid separation was performed to obtain a scandium-containing solid phase and a scandium-depleted organic phase. The scandium-depleted organic phase was countercurrently washed at 15°C with 6 mol / L hydrochloric acid. The volume ratio of organic phase to washing liquid (O:A) was controlled at 8:1. The single-stage washing time was 20 minutes, and the number of washing stages was 2. After phase separation, a regenerated organic phase was obtained and returned to the scandium extraction operation for recycling.

[0078] (4) Add the scandium-containing solid phase to deionized water, the amount of deionized water being 15 times the mass of the scandium-containing solid phase. Stir at 20°C for 5 min, remove the upper layer of floating oil, filter, and wash the precipitate with deionized water to obtain scandium oxalate containing oil. Mix scandium oxalate containing oil with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid is 3.5 times the amount of scandium in the scandium-containing ...

[0079] (5) The refined scandium carbonate was calcined at 900°C for 1 hour in air atmosphere to completely decompose it and obtain high-purity scandium oxide.

[0080] (6) Adjust the pH of the primary scandium-containing filtrate obtained from solid-liquid separation in step (1) to 0.4 with 12 mol / L hydrochloric acid, stir at 60°C for 0.5 h, filter, and wash the precipitate with deionized water to obtain primary regenerated scandium salt; adjust the pH of the secondary scandium-containing filtrate obtained from solid-liquid separation in step (4) to 0.6 with 9 mol / L hydrochloric acid, stir at 60°C for 4 h, let stand after the reaction is completed, remove the upper floating oil, filter, and wash the precipitate with deionized water to obtain secondary regenerated scandium salt.

[0081] In Example 3, the chemical composition of crude scandium oxalate, oil-containing scandium oxalate, and high-purity scandium oxide is shown in Table 3.

[0082] The primary carbonate conversion rate was 70.3%, with 0% of the crude scandium containing oxalate being unreacted; the oxalate conversion rate was 88.5%; the secondary carbonate conversion rate was 72.9%, with 0% of the crude scandium containing oxalate being unreacted; the scandium recovery rate in the primary scandium-containing filtrate was 98.3%, and the scandium recovery rate in the secondary scandium-containing filtrate was 99.4%.

[0083] Table 3 Chemical composition of crude scandium oxalate, oil-containing scandium oxalate, and high-purity scandium oxide

[0084]

[0085] Example 4

[0086] (1) The scandium content in the crude scandium oxalate, calculated as Sc2O3, was 21.44% by mass. The crude scandium oxalate was mixed with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid was 8 times the molar amount of scandium in the crude scandium oxalate, and the amount of deionized water was 115 times the molar amount of scandium in the crude scandium oxalate. The mixture was stirred at 90°C for 0.5 h. After the reaction was completed, solid-liquid separation was performed, and the precipitate was washed with a 3% ammonium bicarbonate solution to obtain primary scandium carbonate.

[0087] (2) The primary scandium carbonate was dissolved in deionized water and 6 mol / L hydrochloric acid at 30°C, and then conditioned with 25% ammonia water. The insoluble matter was removed by filtration to obtain a scandium ion concentration of 40 g / L and a hydrogen ion concentration of 2 mol / L. An organic phase was prepared consisting of 20% P507, 20% Cyanex272, 15% TBP, and 45% sulfonated kerosene. The scandium ion solution was subjected to countercurrent extraction at 45°C, with an organic phase to aqueous phase volume ratio (O:A) of 1:1, a single-stage extraction time of 6 min, and 7 extraction stages to obtain a loaded organic phase. The loaded organic phase was then subjected to countercurrent washing at 35°C using 4 mol / L hydrochloric acid at a loaded organic phase to washing liquid volume ratio (O:A) of 3:1, with a single-stage washing time of 5 min and 3 washing stages to obtain a pure loaded organic phase.

[0088] (3) The pure supported organic phase was transferred to a reactor, and solid oxalic acid dihydrate that had passed through a 200-mesh sieve was added. The amount of oxalic acid dihydrate was four times the amount of scandium in the pure supported organic phase. The mixture was stirred at 90°C for 2 hours. After the reaction, solid-liquid separation was performed to obtain a scandium-containing solid phase and a scandium-depleted organic phase. The scandium-depleted organic phase was countercurrently washed at 45°C with 4 mol / L hydrochloric acid. The volume ratio of organic phase to washing liquid (O:A) was controlled at 5:1. The single-stage washing time was 5 minutes, and the number of washing stages was 4. After phase separation, a regenerated organic phase was obtained and returned to the scandium extraction operation for recycling.

[0089] (4) Add the scandium-containing solid phase to deionized water, the amount of deionized water being 5 times the mass of the scandium-containing solid phase. Stir at 40°C for 10 min, remove the upper layer of floating oil, filter, and wash the precipitate with deionized water to obtain scandium oxalate containing oil. Mix the scandium oxalate containing oil with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid is 8 times the amount of scandium in the scandium-containing ...

[0090] (5) The refined scandium oxalate was calcined at 800°C for 4 hours in air to completely decompose it, thus obtaining high-purity scandium oxide.

[0091] (6) Adjust the pH of the scandium-containing filtrate obtained from the solid-liquid separation in step (1) to 1 with 12 mol / L hydrochloric acid, stir at 25°C for 3 h, filter, wash the precipitate with deionized water to obtain the primary regenerated scandium salt.

[0092] In Example 4, the chemical composition of crude scandium oxalate, oil-containing scandium oxalate, and high-purity scandium oxide is shown in Table 4.

[0093] The primary carbonate conversion rate was 75.5%, and the proportion of unreacted crude scandium oxalate was 0%; the oxalate conversion rate was 93.4%; the secondary carbonate conversion rate was 75.6%, and the proportion of unreacted oil-containing scandium oxalate was 0%; the yield of refined scandium oxalate in step (4) was 98.3%; and the scandium recovery rate in the primary scandium-containing filtrate was 98.2%.

[0094] Table 4. Chemical composition of crude scandium oxalate, scandium oleate containing oxalate, and high-purity scandium oxide.

[0095]

[0096] Example 5

[0097] (1) The scandium content in the crude scandium oxalate, calculated as Sc2O3, was 16.20% by mass. The crude scandium oxalate was mixed with solid ammonium bicarbonate and deionized water, wherein the amount of solid ammonium bicarbonate was 4.5 times the molar amount of scandium in the crude scandium oxalate, and the amount of deionized water was 105 times the molar amount of scandium in the crude scandium oxalate. The mixture was stirred at 25°C for 2 hours. After the reaction was completed, solid-liquid separation was performed, and the precipitate was washed with a 10% ammonium bicarbonate solution to obtain primary scandium carbonate.

[0098] (2) The primary scandium carbonate was dissolved in deionized water and 9 mol / L hydrochloric acid at 40°C, and then conditioned with 31% ammonia water. The insoluble matter was removed by filtration to obtain a scandium back solution with a scandium ion concentration of 50 g / L and a hydrogen ion concentration of 3 mol / L. At 40°C, the regenerated organic phase from Example 1 was used for countercurrent extraction of the scandium back solution. The organic phase to aqueous phase volume ratio (O:A) was 2:1, the single-stage extraction time was 8 min, and the number of extraction stages was 6, yielding a loaded organic phase. At 20°C, the loaded organic phase was countercurrently washed with 2 mol / L hydrochloric acid at a loaded organic phase to washing liquid volume ratio (O:A) = 4:1. The single-stage washing time was 3 min, and the number of washing stages was 6, yielding a pure loaded organic phase.

[0099] (3) The pure supported organic phase was transferred to a reactor, and oxalic acid dihydrate solid that had passed through a 32-mesh sieve was added. The amount of oxalic acid dihydrate was 8 times the amount of scandium in the pure supported organic phase. The reaction was stirred at 90°C for 4 hours. After the reaction was completed, solid-liquid separation was performed to obtain a scandium-containing solid phase and a scandium-depleted organic phase. The scandium-depleted organic phase was countercurrently washed at 40°C with 8 mol / L hydrochloric acid. The volume ratio of organic phase to washing liquid (O:A) was controlled at 4:1. The single-stage washing time was 5 minutes, and the number of washing stages was 3. After phase separation, the regenerated organic phase was obtained and returned to the scandium extraction operation for recycling.

[0100] (4) Add the scandium-containing solid phase to deionized water, the amount of deionized water being 15 times the mass of the scandium-containing solid phase. Stir at 25°C for 20 min, remove the upper layer of floating oil, filter, and wash the precipitate with deionized water to obtain scandium oxalate containing oil. Mix the scandium oxalate containing oil with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid is 6 times the amount of scandium in the scandium-containing ...

[0101] (5) The refined scandium oxalate was calcined at 900°C for 2 hours in air to completely decompose it, thus obtaining high-purity scandium oxide.

[0102] (6) Adjust the pH of the scandium-containing filtrate obtained from the solid-liquid separation in step (1) to 0.6 with 12 mol / L hydrochloric acid, stir at 40°C for 1 h, filter, wash the precipitate with deionized water to obtain the primary regenerated scandium salt.

[0103] In Example 5, the chemical composition of crude scandium oxalate, oil-containing scandium oxalate, and high-purity scandium oxide is shown in Table 5.

[0104] The primary carbonate conversion rate was 73.1%, and the proportion of unreacted crude scandium oxalate was 0%; the oxalate conversion rate was 91.3%; the secondary carbonate conversion rate was 75.6%, and the proportion of unreacted oil-containing scandium oxalate was 0%; the yield of refined scandium oxalate in step (4) was 98.6%; and the scandium recovery rate in the primary scandium-containing filtrate was 98.5%.

[0105] Table 5 Chemical composition of crude scandium oxalate, oil-containing scandium oxalate, and high-purity scandium oxide

[0106]

[0107] Comparative Example 1

[0108] The carbonate conversion reagent in step (1) of Example 1 is replaced with ammonium carbonate, and the specific steps are as follows:

[0109] (1) The crude scandium oxalate from Example 1 was mixed with ammonium carbonate solid and deionized water, wherein the amount of ammonium carbonate was 5.5 times the amount of scandium in the crude scandium oxalate and the amount of deionized water was 95 times the amount of scandium in the crude scandium oxalate. The mixture was stirred at 70°C for 2.5 h.

[0110] After the reaction was completed, there were no precipitates or exudates in the system, the solution was clear and transparent, the crude scandium oxalate was completely dissolved, and no scandium carbonate or other solid products were formed.

[0111] Comparative Example 2

[0112] The amount of ammonium bicarbonate used in step (1) of Example 2 was changed to 2.6 times the amount of scandium in the crude scandium oxalate. The specific steps are as follows:

[0113] (1) The crude scandium oxalate from Example 2 was mixed with solid ammonium bicarbonate and deionized water, wherein the amount of ammonium bicarbonate was 2.6 times the amount of scandium in the crude scandium oxalate, and the amount of deionized water was 75 times the amount of scandium in the crude scandium oxalate. The mixture was stirred at 60°C for 1 hour. After the reaction was completed, solid-liquid separation was performed, and the precipitate was washed with deionized water to obtain a mixture of primary scandium carbonate and crude scandium oxalate.

[0114] In step (1) of Comparative Example 2, the proportion of unreacted crude scandium oxalate was 16.5%, the proportion of dissolved crude scandium oxalate was 33.4%, and the carbonate conversion rate was 50.1%. In step (1) of Example 2, however, the crude scandium oxalate completely participated in the reaction, and no residual unreacted material was detected. Therefore, it is evident that the amount of ammonium bicarbonate used should not be too small in order to ensure the complete conversion of crude scandium oxalate into ammonium bicarbonate.

[0115] Comparative Example 3

[0116] The carbonate conversion reagent in step (1) of Example 3 is replaced with sodium bicarbonate, and the specific steps are as follows:

[0117] (1) The crude scandium oxalate from Example 3 was mixed with sodium bicarbonate solid and deionized water, wherein the amount of sodium bicarbonate was 3.5 times the amount of scandium in the crude scandium oxalate, and the amount of deionized water was 70 times the amount of scandium in the crude scandium oxalate. The mixture was stirred at 20°C for 6 hours. After the reaction was completed, solid-liquid separation was performed, and the precipitate was washed with deionized water to obtain a scandium-containing precipitate (not scandium ammonium carbonate).

[0118] In step (1) of Comparative Example 3, the oxalate content of the unreacted crude scandium was 21.5%, the oxalate content of the dissolved crude scandium was 68.4%, and the carbonate conversion rate was 10.1%. Under the same feed ratio and conditions, when ammonium bicarbonate was used as the conversion reagent, its carbonate conversion rate was significantly higher than that of sodium bicarbonate.

[0119] Comparative Example 4

[0120] The slurry after the primary carbonate conversion reaction in Example 4 was acidified with hydrochloric acid to precipitate scandium, and then calcined to obtain secondary scandium oxide. The specific steps are as follows:

[0121] (1) The crude scandium oxalate from Example 4 was mixed with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid was 8 times the amount of scandium in the crude scandium oxalate, and the amount of deionized water was 115 times the amount of scandium in the crude scandium oxalate. The mixture was stirred at 90°C for 0.5 h. After the reaction was completed, 6 mol / L hydrochloric acid was added to the slurry to adjust the pH to 0.1, and the mixture was stirred at 20°C for 4 h. The precipitate was filtered out and washed with deionized water to obtain secondary scandium oxalate. The yield of secondary scandium oxalate was 98.2%.

[0122] (2) The oxalate of secondary scandium was calcined at 850°C for 4 hours in air atmosphere to obtain secondary scandium oxide.

[0123] The secondary scandium oxide obtained in Comparative Example 4 contained 89.95% Sc2O3, 6.81% ZrO2, 1.35% ThO2, and 0.088% ΣREO (excluding Sc and Pm). Comparative Example 4 shows that simply using the carbonate conversion-acidification scandium precipitation process cannot effectively remove zirconium, thorium, and rare earth impurities, making it difficult to obtain high-purity scandium oxide.

[0124] Comparative Example 5

[0125] The crude scandium from Example 5 was converted into crude scandium oxide by calcination of its oxalate, followed by dissolution, secondary oxalate precipitation, and secondary calcination to obtain secondary scandium oxide. The specific steps are as follows:

[0126] (1) The crude scandium oxalate from Example 5 was calcined at 900°C for 2 hours to obtain crude scandium oxide;

[0127] (2) The crude scandium oxide was dissolved in 12 mol / L hydrochloric acid and deionized water at a dissolution temperature of 95°C for 24 hours. The solution was then conditioned with 31% ammonia water and filtered to remove insoluble matter, resulting in a scandium solution with a scandium ion concentration of 50 g / L and a hydrogen ion concentration of 3 mol / L.

[0128] (3) Add oxalic acid dihydrate solid to the above scandium solution. The amount of oxalic acid dihydrate solid added is 1.5 times the physical amount of scandium in the scandium solution (theoretical amount of scandium precipitate). Stir at 95°C for 0.5 h. After the reaction is completed, filter to separate the precipitate, wash the precipitate with deionized water to obtain oxalate of secondary scandium.

[0129] (4) The oxalate of secondary scandium is calcined at 900°C for 2 hours in air atmosphere to obtain secondary scandium oxide.

[0130] The secondary scandium oxide obtained in Comparative Example 5 contained 97.16% Sc2O3, 0.091% ZrO2, 0.014% ThO2, and 0.32% ΣREO (excluding Sc and Pm). Comparative Example 5 demonstrates that the simple process of calcination-dissolution-oxalic acid precipitation cannot effectively remove zirconium, thorium, and rare earth impurities, making it difficult to obtain high-purity scandium oxide.

[0131] Comparative Example 6

[0132] The scandium solution in Comparative Example 5 was subjected to extraction, oxalate conversion, carbonate conversion, hydrochloric acid acidification, and calcination to obtain secondary scandium oxide. The specific steps are as follows:

[0133] (1) At 40°C, the scandium solution with a scandium ion concentration of 50 g / L and a hydrogen ion concentration of 3 mol / L from Comparative Example 5 was subjected to countercurrent extraction using the regenerated organic phase from Example 1. The volume ratio of organic phase to aqueous phase (O:A) was 2:1, the single-stage extraction time was 8 min, and the number of extraction stages was 6, resulting in a loaded organic phase. At 20°C, the loaded organic phase was subjected to countercurrent washing with 2 mol / L hydrochloric acid at a volume ratio of loaded organic phase to washing liquid (O:A) of 4:1. The single-stage washing time was 3 min, and the number of washing stages was 6, resulting in a pure loaded organic phase.

[0134] (2) The pure supported organic phase was transferred to a reaction vessel, and oxalic acid dihydrate solid that had passed through a 32-mesh sieve was added. The amount of solid oxalic acid dihydrate was 8 times the amount of scandium in the pure supported organic phase. The reaction was stirred at 90°C for 4 hours. After the reaction was completed, solid-liquid separation was performed to obtain a scandium-containing solid phase and a scandium-depleted organic phase.

[0135] (3) Add the scandium-containing solid phase to deionized water, the amount of deionized water being 15 times the mass of the scandium-containing solid phase. Stir at 25°C for 20 min, remove the upper layer of floating oil, filter, and wash the precipitate with deionized water to obtain scandium oxalate containing oil. Mix the scandium oxalate containing oil with ammonium bicarbonate solid and deionized water, wherein the amount of ammonium bicarbonate solid is 6 times the amount of scandium in the scandium-containing ...

[0136] (4) The oxalate of secondary scandium is calcined at 900°C for 2 hours in air atmosphere to completely decompose it and obtain secondary scandium oxide.

[0137] The secondary scandium oxide obtained in Comparative Example 6 contained 98.65% Sc2O3, 0.076% ZrO2, 0.0043% ThO2, and 0.036% ΣREO (excluding Sc and Pm). Comparative Example 6 shows that extraction separation achieved some separation of Th and rare earth impurities, but the purity level was still far lower than that of the high-purity scandium oxide in Example 5.

[0138] Comparative Example 7

[0139] The scandium carbonates from Examples 1-5 were calcined at 850°C for 4 hours to obtain their respective scandium oxides. The composition information is shown in Table 6.

[0140] Table 6. Chemical composition of scandium oxide products obtained from primary scandium carbonate roasting in Examples 1-5.

[0141]

[0142] As shown in Comparative Example 7, a single carbonate conversion reaction has a significant removal effect on sodium, magnesium, aluminum, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, thorium, uranium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still 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; if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should all be considered to be within the protection scope of the present invention.

Claims

1. A method for the clean preparation of high-purity scandium oxide from crude scandium oxalate, characterized in that, Includes the following steps: (1) Primary carbonate conversion: Crude scandium oxalate, ammonium bicarbonate solid and deionized water are mixed and subjected to primary carbonate conversion reaction. After the reaction is completed, solid-liquid separation is performed, the precipitate is washed and the primary scandium carbonate is obtained. (2) Dissolution and extraction: The primary scandium carbonate described in step (1) is subjected to a back dissolution treatment to obtain a scandium back solution; The scandium-containing loaded organic phase is subjected to single-stage or countercurrent extraction of the scandium back solution to obtain a scandium-containing organic phase; the scandium-containing loaded organic phase is then washed to obtain a pure loaded organic phase. (3) Oxalate conversion: The pure supported organic phase described in step (2) and solid oxalic acid dihydrate are mixed to carry out the oxalate conversion reaction. After the reaction is completed, the solid and liquid phases are separated to obtain a scandium-depleted organic phase and a scandium-containing solid phase. The unreacted oxalic acid in the scandium-containing solid phase is dissolved in deionized water, and the solid and liquid phases are separated and washed to obtain oil-containing scandium oxalate. (4) Secondary carbonate conversion: The oil-containing scandium oxalate, ammonium bicarbonate solid and deionized water are mixed to carry out a secondary carbonate conversion reaction; After the reaction is complete, the product is allowed to stand, degreased, separated into solid and liquid components, and washed with deionized water or a 0%~10% ammonium bicarbonate solution to obtain refined scandium carbonate. Alternatively, after the reaction is complete, add 6-12 mol / L hydrochloric acid to the slurry to adjust the pH to 0.1-0.5, stir at 20-95℃ for 0.5-4 h, and after standing, degreasing, filtration and washing with water, obtain refined scandium oxalate. (5) Calcination: The carbonate or oxalate of refined scandium described in step (4) is calcined at 800-900°C for 1-4 h in an air atmosphere to obtain high-purity scandium oxide, wherein the mass fraction of Sc2O3 in the high-purity scandium oxide is not less than 99.99%.

2. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, In step (1), the crude scandium has an oxalate content of 10% to 32% by mass, calculated as Sc2O3, and contains one or more impurities selected from sodium, magnesium, aluminum, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, thorium, uranium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium.

3. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, In step (1), the conditions for the primary carbonate conversion reaction are: reaction temperature 20~90℃, reaction time 0.5~6 h, the amount of ammonium bicarbonate used is 3.5~8.0 times the amount of scandium in the crude scandium oxalate, and the amount of deionized water used is 75~115 times the amount of scandium in the crude scandium oxalate; the washing solution used for washing the precipitate is deionized water or ammonium bicarbonate solution with a mass fraction of 0%~10%.

4. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, In step (2), the reagents used in the back dissolution treatment are deionized water and 6~12mol / L hydrochloric acid. The back dissolution temperature is 15~40℃. The solution is conditioned with 15%~31% ammonia water by mass fraction. The insoluble matter is removed by filtration. The scandium concentration in the resulting scandium back solution is 10~50g / L and the hydrogen ion concentration is 2~6mol / L.

5. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, In step (2), the organic phase comprises 10% to 40% by volume of an acidic phosphorus-containing extractant and 0% to 20% by volume of a modifier, with the remainder being sulfonated kerosene. The acidic phosphorus-containing extractant is selected from one or more of di(2-ethylhexyl) phosphate, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, or bis(2,4,4-trimethylpentyl)phosphonic acid. The modifier is selected from tributyl phosphate and / or octanol. The extraction control measures the volume ratio of the organic phase to the aqueous phase as 0.5:1 to 3.0:1, the extraction temperature as 15 to 45°C, the number of extraction stages as 1 to 7, and the single-stage extraction time as 1 to 8 min.

6. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, In step (2), the washing treatment of the scandium-containing supported organic phase is specifically as follows: the supported organic phase is washed in single-stage or countercurrent washing with hydrochloric acid at a concentration of 2~6 mol / L, the volume ratio of the supported organic phase to the washing liquid is controlled at 2:1~5:1, the washing temperature is 15~35℃, the single-stage washing time is 1~5 min, and the number of washing stages is 1~6, so as to remove the raffinate entrained in the organic phase and obtain a pure supported organic phase.

7. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, In step (3), the conditions for the oxalate conversion reaction are: reaction temperature 60~90℃, reaction time 2~5 h, the amount of oxalic acid dihydrate solid added is 4~10 times the amount of scandium in the organic phase; the particle size of the oxalic acid dihydrate solid is 0.5~1.5 mm; the specific treatment of the scandium-containing solid phase is as follows: the scandium-containing solid phase is stirred in deionized water at a stirring temperature of 20~80℃ for 1~20 min, the amount of deionized water is 5~15 times the mass of the scandium-containing solid phase, the upper floating oil is removed after the reaction, the solid and liquid are separated, the precipitate is washed with deionized water to obtain oil-containing scandium oxalate.

8. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, In step (4), the secondary carbonate conversion reaction conditions are as follows: the reaction temperature is 20~90℃, the reaction time is 0.5~6 h, the amount of ammonium bicarbonate is 3.5~8.0 times the amount of scandium in the scandium oxalate, and the amount of deionized water is 75~115 times the amount of scandium in the scandium oxalate.

9. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, It also includes regenerating the scandium-poor organic phase obtained in step (3), specifically: using 3~8 mol / L hydrochloric acid to wash the scandium-poor organic phase in a single-stage or countercurrent manner, controlling the volume ratio of organic phase to washing liquid to be 1:1~8:1, washing temperature 15~45℃, single-stage washing time 2~20 min, washing stage 1~6 stages, in order to remove the oxalic acid mixed in, and obtain the regenerated organic phase, which is returned to step (2) for the extraction of scandium return solution.

10. The method for preparing high-purity scandium oxide from crude scandium oxalate according to claim 1, characterized in that, Also includes: Add hydrochloric acid with a concentration of 6~12mol / L to the scandium-containing filtrate obtained from solid-liquid separation in step (1), adjust the pH of the filtrate to 0.3~1.0, stir at 20~95℃ for 0.5~4 h to precipitate scandium and obtain primary regenerated scandium salt; Add hydrochloric acid with a concentration of 6~12mol / L to the secondary scandium-containing filtrate obtained from solid-liquid separation in step (4), adjust the pH of the filtrate to 0.3~1.0, and stir at 20~95℃ for 0.5~4 h to precipitate scandium and obtain secondary regenerated scandium salt.

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