Process for the separation and recovery of scandium from a high concentration iron impurity containing scandium leach

Abstract

This invention discloses a method for separating and recovering scandium from scandium leachate containing high concentrations of iron impurities, comprising: adding an alkaline reagent to the scandium leachate containing ferric ions to adjust the pH to 6.0-9.0, causing scandium and iron to co-precipitate, and washing to obtain a mixed precipitate containing scandium and iron; adding deionized water and formic acid to the mixed precipitate, and reacting at 10-80°C for 0.5-3 hours to obtain a transparent solution or a slurry containing scandium and ferric formate; and further processing the dissolved precipitate with... An ammonium source is added to the material to make the amount of ammonium ions in the system 6 to 14 times the amount of scandium ions. The pH of the system is adjusted to 1.5 to 1.8 with formic acid, and the reaction is carried out at 10 to 80°C for 0.5 to 3 hours. The above material is then evaporated and concentrated at 50 to 90°C and a vacuum of -0.09 to -0.05 MPa to saturate and precipitate iron formate, while scandium remains in the liquid phase. Solid-liquid separation yields an iron-containing solid phase and a scandium-rich liquid phase. Compared with the prior art, this invention introduces an ammonium source to effectively separate iron and scandium. The resulting scandium-rich liquid phase has a scandium concentration as high as 120 to 180 g / L and an extremely low iron impurity content, which can be used for subsequent scandium purification processes after dilution.

Description

Technical Field

[0001] This invention relates to the field of crude scandium purification technology, and more particularly to a method for separating and recovering scandium from scandium leachate with high concentrations of iron impurities. Background Technology

[0002] Scandium is a typical rare earth metal with excellent physicochemical properties, making it highly valuable in high-end fields such as aerospace, new energy materials, electronic components, and alloy additives. Scandium has low abundance in the Earth's crust, mostly occurring as a by-product in industrial solid wastes such as waste acid from titanium dioxide production, nickel-cobalt hydroxide, tungsten slag, red mud, and waste acid from zirconium salt production. After pretreatment such as acid leaching and roasting leaching, the resulting scandium-containing leachate generally contains a large amount of ferric ions (Fe3+) impurities. The chemical properties of ferric ions and scandium ions are similar, and their separation coefficient is relatively small, which is one of the core technological bottlenecks restricting the large-scale production of high-purity scandium products.

[0003] At present, a large amount of research and development and application exploration has been carried out on scandium-iron separation technology, mainly focusing on technical routes such as precipitation method, solvent extraction method, ion exchange resin method, and calcination pretreatment method.

[0004] Precipitation is a conventional technique for removing iron from scandium-containing solutions. Patent CN106636684B uses metatitanic acid seeds to induce the precipitation of titanium water, simultaneously removing iron impurities from the solution. Patent CN115094229B uses the goethite method to control the crystal form of iron precipitation, allowing scandium to enter the iron slag in the form of doping or adsorption to achieve nickel-cobalt separation; however, the subsequent scandium recovery process from the precipitated slag is cumbersome. Oxalic acid precipitation is suitable for selectively precipitating iron in scandium-rich solutions with extremely low iron content, but if the iron content is too high, it is easily reduced to ferrous iron by oxalate ions, leading to co-precipitation and failing to achieve efficient iron removal and purification at the front end.

[0005] Solvent extraction is currently the mainstream technology for scandium enrichment and purification. Patent CN103695671B discloses a tandem extraction process involving N235 extraction for iron removal, P507 enrichment for scandium, and P350 deep purification for scandium. Patents CN103468948B, CN103468949B, and CN103468980B disclose a process for selective iron removal via washing after scandium-iron extraction. Patent CN105907964B uses sodium sulfite / sodium thiosulfate to reduce ferric ions to ferrous ions before selectively extracting scandium. However, these methods generally suffer from high extractant costs, severe co-extraction of iron ions in high-acid systems, and trace iron impurities remaining in the back-extraction solution, making it difficult to achieve deep iron removal and high-purity scandium enrichment in one step.

[0006] Ion exchange and resin adsorption is another selective separation technique. Patent CN106244831B separates iron and scandium by adjusting the solution acidity, adding chloride ions to form complex anions with iron ions, and then using anion exchange resin to adsorb iron. However, this method has strict requirements for controlling solution acidity and chloride ion concentration, has limited resin adsorption capacity, and high regeneration costs, making it only suitable for processing low-concentration, small-volume scandium-containing solutions.

[0007] Roasting pretreatment-assisted separation technologies include concentrated sulfuric acid roasting, ammonium sulfate roasting, and reduction roasting. By controlling the roasting temperature and reaction atmosphere, the phase morphology of iron and scandium compounds is changed, reducing the leaching rate of iron or increasing the selective leaching efficiency of scandium, thereby alleviating the pressure on subsequent solution iron removal. Patent CN114480887B uses laterite nickel ore sulfation roasting-water leaching for iron removal, patent CN110331289B uses red mud ammonium sulfate roasting-water leaching for iron removal, and patent CN103898330B uses red mud reduction roasting to convert iron oxide into magnetic magnetite (Fe3O4). Magnetic separation is then used to initially separate iron and scandium. However, these roasting processes suffer from drawbacks such as high energy consumption, severe equipment corrosion, and incomplete iron separation, and still require a supplementary solution iron removal process.

[0008] In summary, existing scandium-iron separation technologies generally suffer from drawbacks such as lengthy process flows, low scandium recovery rates, incomplete removal of iron impurities, high production costs, and significant environmental impact assessment challenges, making it difficult to meet the technical requirements for the industrial production of high-purity scandium oxide. Therefore, developing a simple, highly selective, low-scandium-loss, and environmentally friendly method for the efficient separation of scandium-iron from solution is a key technical challenge that urgently needs to be addressed in the field of scandium metallurgy. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a method for separating and recovering scandium from scandium leachate containing high concentrations of iron impurities, thereby obtaining a scandium-rich liquid phase with high concentrations and low iron impurities.

[0010] To achieve this technical objective, the present invention adopts the following solution:

[0011] This invention provides a method for separating and recovering scandium from scandium leachate with high concentrations of iron impurities, comprising the following steps: (1) Add an alkaline reagent to the scandium leaching solution containing ferric ions and adjust the pH to 6.0~9.0 so that scandium and iron precipitate together. After washing with deionized water, a mixed precipitate containing scandium and iron is obtained. (2) Add deionized water and formic acid to the mixed precipitate to dissolve it, and react at 10~80℃ for 0.5~3h to obtain the dissolved solution; (3) Add an ammonium source to the dissolved solution to form a complex, so that the amount of ammonium ions in the system is 6 to 14 times the amount of scandium ions. Adjust the pH of the system to 1.5 to 1.8 with formic acid and react at 10 to 80°C for 0.5 to 3 hours to obtain the complexed solution. (4) The complexed liquid is evaporated and concentrated at 50~90℃ and vacuum degree -0.09~-0.05MPa to precipitate iron in the form of formate and scandium is retained in the liquid phase to obtain crystal slurry; (5) Separate the solid and liquid phases of the crystal slurry to obtain an iron-containing solid phase and a scandium-rich liquid phase.

[0012] Furthermore, the Scandium leachate contains Sc 3+ with Fe 3+ The mass concentration ratio is 1:0.2~15, and the hydrogen ion concentration is 0.05~6 mol / L; the anion of the scandium leachate is at least one of sulfate, chloride, formate, nitrate, acetate, citrate, and perchlorate.

[0013] The scandium leaching solution containing ferric ions of this invention refers to the selective leaching of scandium from scandium raw materials containing iron impurities (such as red mud, titanium dioxide waste acid, laterite nickel ore, iron-aluminum slag, crude scandium oxide, crude scandium carbonate, crude scandium hydroxide, etc.) into a solution through acid leaching and / or other leaching processes, accompanied by a large amount of Fe. 3+ Impurities enter the solution together, forming a liquid mixture with scandium ions as the target component and iron ions as the main impurity component.

[0014] The high concentration of iron impurities in this invention refers to those that meet one of the following conditions: a. The absolute concentration of iron is relatively high, i.e., Fe... 3+ a. The mass concentration of Fe is ≥10 g / L; b. The relative concentrations of Fe and Scandium are relatively high, i.e., Fe 3+ Concentration and Sc 3+ The mass concentration ratio is ≥1. This invention specifies high concentrations of iron impurities to highlight its technical advantages and application value, but it is equally applicable to cases with low iron impurities.

[0015] When the scandium leachate contains Sc 3+ with Fe 3+ When the total concentration is >20g / L, dilute with deionized water to a total concentration ≤20g / L before adding the alkaline reagent, or slowly add a 5%~20% dilute alkaline solution to avoid local over-alkalinity leading to gelation.

[0016] Further, the alkaline reagent mentioned in step (1) is at least one of ammonia water, sodium hydroxide solution, sodium carbonate solid, ammonium bicarbonate solid, sodium bicarbonate solid, and ammonium carbonate solid.

[0017] Furthermore, in step (1), the precipitation reaction temperature is 10~80℃ and the reaction time is 0.5~4h.

[0018] Furthermore, in step (2), the amount of deionized water used is 1 to 8 times the mass of the mixed precipitate; the mass fraction of formic acid is 85% to 99%, and the amount of formic acid added is such that the pH of the system after the dissolution reaction is controlled at 1.5 to 1.8.

[0019] Further, the ammonium source mentioned in step (3) is one or more of the following: ammonium formate solid, ammonia water, ammonium bicarbonate solid, and ammonium carbonate solid.

[0020] Furthermore, in step (4), the evaporation and concentration temperature is 50~90℃, the vacuum degree is -0.09~-0.05MPa, and the evaporation time is 2~5h.

[0021] The iron-containing solid phase mainly consists of two parts: iron formate solid and scandium-containing liquid entrained on its surface and in its pores. Furthermore, the iron formate solid may also contain a small amount of scandium, so it is necessary to recover the scandium in the iron-containing solid phase.

[0022] Further, after solid-liquid separation in step (5), the iron-containing solid phase is washed with ammonium formate solution to recover the entrained scandium. The mass fraction of the ammonium formate solution is 20%~40%, the amount of ammonium formate solution is 2~5 times the mass of the iron-containing solid phase, the washing temperature is 40~80℃, and the washing time is 0.2~1h.

[0023] Furthermore, in step (5), the scandium concentration in the scandium-rich liquid phase is 120~180 g / L, and the iron concentration is no more than 2 g / L.

[0024] Under normal ammonium-free conditions, the system's water and formic acid decrease during heating and evaporation, while the ion concentration continues to rise. Iron formate and scandium formate will precipitate simultaneously, making it impossible to effectively separate scandium and iron.

[0025] This invention introduces a sufficient ammonium source into the formic acid-scandium-iron system, resulting in a significant increase in the concentration of ammonium ions in the system. 3+ HCOO - and NH4 + The complex is stable in the liquid phase, and the precipitated scandium formate can be redissolved. Scandium does not crystallize out during evaporation, and the mother liquor (i.e., the scandium-rich liquid phase) remains liquid from the evaporation temperature to room temperature. Therefore, scandium remains in the liquid phase throughout the process. Iron formate does not have this stable solubility. During concentration, it gradually crystallizes out due to supersaturation and eventually accumulates in the solid phase. Thus, by evaporation concentration and solid-liquid separation, scandium and iron can be effectively separated.

[0026] To clearly demonstrate the beneficial effects of the present invention, the following indicators are defined: The liquid phase enrichment rate of scandium refers to the percentage of scandium mass in the scandium-rich liquid phase obtained from solid-liquid separation relative to the total scandium mass in the crystal slurry before separation (i.e., the sum of scandium mass in the scandium-rich liquid phase and the scandium mass in the iron-containing solid phase), calculated according to formula [1]: Formula [1]: Scandium enrichment rate in liquid phase (%) = mass of Sc in scandium-rich liquid phase / (mass of Sc in scandium-rich liquid phase + mass of Sc in iron-containing solid phase) × 100%.

[0027] Scandium elution rate is the percentage of scandium mass in the washing solution after washing to the mass of scandium in the iron-containing solid phase before washing, and is calculated according to formula [2]: Formula [2]: Scandium elution rate (%) = mass of Sc in washing liquid / mass of Sc in iron-containing solid phase × 100%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The method of the present invention uses formic acid as a dissolving agent. The distilled formic acid can be condensed, recovered and recycled. There are no toxic extractants or precipitants left, reducing wastewater discharge. The process steps are simple and do not require complex procedures such as high-temperature roasting and multi-stage extraction.

[0030] 2. The scandium-rich liquid phase obtained by the method of the present invention has a high scandium concentration of 120~180g / L and extremely low iron impurity content. It can be directly diluted and used in subsequent scandium purification processes such as solvent extraction, carbonate precipitation, and oxalic acid precipitation without additional pretreatment.

[0031] 3. The method of the present invention can treat scandium-containing leachates with iron concentrations much higher than scandium concentrations, covering a variety of industrial scandium-containing by-product systems such as titanium dioxide waste acid, nickel-cobalt hydroxide, and red mud, and has broad application prospects.

[0032] 4. The method of the present invention has good scandium-iron separation effect and low scandium loss rate. Compared with the existing ammonium-free source process, the liquid phase enrichment rate of scandium is increased from less than 20% to more than 90%, and the scandium loss rate is significantly reduced. Attached Figure Description

[0033] Figure 1 This is a flowchart of the method for separating and recovering scandium from scandium leachate with high concentrations of iron impurities according to the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0035] Unless otherwise specified, the experimental methods used in the embodiments and comparative examples of this invention are conventional methods. Unless otherwise specified, the materials and reagents used are commercially available.

[0036] Please see Figure 1 This invention provides a method for separating and recovering scandium from scandium leachate with high concentrations of iron impurities, the specific steps of which are as follows:

[0037] First, a precipitation reaction is carried out, involving a large amount of Fe. 3+ An alkaline reagent is added to the scandium leaching solution to adjust the pH to 6.0-9.0, causing scandium and iron to precipitate. The solution is then washed with deionized water to remove residual reaction liquid, yielding a mixed precipitate containing scandium and iron. This step aims to achieve phase transformation of scandium; it does not separate scandium and iron, but it can facilitate the precipitation of Na. + Cl - SO4 2- Soluble impurities remain in the liquid phase, creating conditions for subsequent scandium-iron separation.

[0038] The scandium leachate contains Sc 3+ with Fe 3+ The mass concentration ratio is 1:0.2~15, the hydrogen ion concentration is 0.05~6 mol / L, and the anions in the scandium leachate are at least one of sulfate, chloride, formate, nitrate, acetate, citrate, and perchlorate ions. It should be noted that the concentrations of other metal impurity ions in the scandium leachate are much lower than those in the Sc leachate. 3+ and Fe 3+ It is negligible, therefore it was not separately detected or described in subsequent embodiments and comparative examples.

[0039] The alkaline reagent is selected from one or a combination of ammonia water, sodium hydroxide solution, solid sodium carbonate, solid ammonium bicarbonate, solid sodium bicarbonate, and solid ammonium carbonate; the precipitation reaction temperature is 10~80℃, and the reaction time is 0.5~4h. If the scandium leaching solution contains Sc... 3+ with Fe 3+ When the total concentration is >20 g / L, adding a high concentration of alkaline reagent can easily cause the reaction solution to form a large amount of gel-like slurry, making the system difficult to stir. To address this, water can be added to the reaction system before adding the alkaline reagent to reduce the Sc... 3+ Fe 3+ Dilute the total concentration to ≤20g / L; or replace the high-concentration alkaline reagent with a dilute alkaline aqueous solution to ensure the reaction proceeds fully.

[0040] Next, a dissolution reaction is carried out by adding deionized water and formic acid to the above mixed precipitate and reacting at 10-80°C for 0.5-3 hours to obtain a dissolved solution. The amount of deionized water used is 1-8 times the mass of the mixed precipitate, and the mass fraction of formic acid is 85%-99%. The amount of formic acid added should ensure that the pH of the liquid phase after the reaction is between 1.5 and 1.8 to ensure that the mixed precipitate containing scandium and iron is completely dissolved and fully converted. The dissolved solution is either a transparent solution or a solid-liquid mixture containing scandium and iron formate. When the scandium and iron content in the system is high, the scandium and iron formate will precipitate out due to the saturation of the concentration, thus forming a solid-liquid mixture.

[0041] Next, a complexation reaction is carried out. An ammonium source is added to the dissolved solution to make the amount of ammonium ions in the system 6 to 14 times the amount of total scandium ions. The pH of the system is adjusted to 1.5 to 1.8 with formic acid (85% to 99% by mass) to inhibit the hydrolysis and precipitation of scandium and iron. The reaction is carried out at 10 to 80°C for 0.5 to 3 hours. After the reaction is completed, a complexed solution is obtained. The complexed solution is either a transparent solution or a solid-liquid mixture containing ferric formate solids. The total amount of scandium ions is the sum of the amounts of scandium ions in the solid and liquid phases of the dissolved solution.

[0042] The ammonium source is selected from one or more of solid ammonium formate, ammonia, solid ammonium bicarbonate, or solid ammonium carbonate. When the amount of ammonium ions is less than 6 times the amount of formate, the formate-ammonium system cannot effectively complex scandium, leading to scandium crystallization and loss during the evaporation stage. When the amount of ammonium ions is greater than 14 times the amount of formate, it increases raw material costs without providing additional stabilizing effects. If ammonium bicarbonate is used as the alkaline reagent in the precipitation reaction, iron will form an amorphous hydroxide precipitate without ammonium, and scandium will form a scandium ammonium carbonate double salt. The molar ratio of scandium to ammonium in this double salt is 1:1. Although a small amount of ammonium ions can be introduced during formic acid dissolution, the ammonium concentration in the system is low. Without sufficient external ammonium source, the formate of iron and scandium formate will co-precipitate during evaporation and concentration, and the liquid phase enrichment rate of scandium is less than 20%, making effective separation of scandium and iron impossible.

[0043] Next, the complexed liquid was evaporated and concentrated, with the evaporation temperature controlled at 50~90℃ and the vacuum degree at -0.09~-0.05MPa. The endpoint was reached when no obvious liquid evaporated from the system, or the scandium concentration in the mother liquor was measured, and the endpoint scandium ion concentration in the mother liquor was controlled at 120~180g / L to obtain a crystal slurry. During the evaporation process, the water and formic acid in the system continuously decreased, and there was no volatilization loss of scandium and iron; Fe in the liquid phase 3+ The formic acid gradually precipitates as formate crystals, while scandium remains stably in the liquid phase. The distilled formic acid and water vapor can be condensed and recovered, achieving formic acid recycling. The evaporation time can be adjusted according to the actual evaporation volume, typically controlled between 2 and 5 hours to achieve the desired technical effect. If evaporation is carried out at atmospheric pressure, the evaporation time needs to be extended.

[0044] Finally, the crystal slurry is subjected to solid-liquid separation to obtain an iron-containing solid phase and a scandium-rich liquid phase. Solid-liquid separation can be performed by centrifugation or filtration. The iron-containing solid phase is washed with a 20%–40% (w / w) ammonium formate solution. The scandium in the iron-containing solid phase is recovered by utilizing the physical displacement effect of the ammonium formate solution and its selective complexation and stabilization effect on scandium. The amount of ammonium formate solution used is 2–5 times the mass of the iron-containing solid phase, the washing temperature is 40–80℃, the washing time is 0.2–1 h, and the scandium elution rate is not less than 95%.

[0045] The resulting scandium-rich liquid phase has a scandium ion concentration of 120-180 g / L, an iron ion concentration of no more than 2 g / L, and a scandium enrichment rate of no less than 90%, which meets the requirements for subsequent purification.

[0046] Scandium-rich liquid phase can be diluted with water and then directly used in subsequent scandium purification or precipitation processes, such as solvent extraction, carbonate precipitation or oxalic acid precipitation, to further prepare high-purity scandium products.

[0047] The following describes in detail, with reference to embodiments, a method for separating and recovering scandium from scandium leachate with high concentration of iron impurities provided by the present invention. Example 1

[0048] (1) Sc in the original scandium leachate 3+ Concentration 0.1 g / L, Fe 3+ The concentration was 1.5 g / L, the hydrogen ion concentration was 0.05 mol / L, and the anion was sulfate. A 30% sodium hydroxide solution was added to adjust the pH to 9.0, and the mixture was stirred at 80℃ for 4 hours. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 99% and an iron precipitation rate of 99%.

[0049] (2) Add deionized water and 99% formic acid to the above mixed precipitate for dissolution. The amount of deionized water is 4 times the mass of the mixed precipitate. Stir at 80℃ for 0.5h. The pH of the liquid phase after the reaction is 1.5, and the dissolved liquid is obtained.

[0050] (3) Add 25% ammonia water as an ammonium source to the dissolved solution to complex the ammonium ion content in the system to 14 times the total amount of scandium ion content. Adjust the pH of the system to 1.5 with 99% formic acid to inhibit the hydrolysis and precipitation of scandium and iron. Stir at 10°C for 3 hours to obtain the complexed solution.

[0051] (4) The complexed liquid was placed in an evaporation apparatus, the evaporation temperature was set to 50℃, the vacuum degree to -0.09MPa, and the mixture was evaporated and concentrated for 5 hours until no liquid was distilled off, thus obtaining a crystalline slurry; during the process, water and formic acid continued to evaporate, and Fe...3+ It precipitates as a formate, while scandium remains stably in the liquid phase. The evaporated water and formic acid are then condensed and recovered.

[0052] (5) The solid-liquid separation of the evaporated and concentrated slurry was carried out by vacuum filtration to obtain an iron-containing solid phase and a scandium-rich liquid phase. The iron-containing solid phase was washed with a 20% ammonium formate solution to recover the entrained scandium. The amount of ammonium formate solution used was twice the mass of the iron-containing solid phase. The washing temperature was 40℃ and the washing time was 1h.

[0053] Testing revealed that the scandium-rich liquid phase remained liquid at room temperature, and the Sc in the scandium-rich liquid phase... 3+ The concentration is 121 g / L, Fe 3+ The concentration was 1.4 g / L; the liquid phase enrichment rate of scandium was 95%; and the scandium elution rate was 98%. Example 2

[0054] (1) Sc in the original scandium leachate 3+ Concentration 12 g / L, Fe 3+ The concentration was 60 g / L, the hydrogen ion concentration was 6 mol / L, and the anion was chloride ion. The mixture was diluted 4 times with deionized water, and ammonium bicarbonate was added to adjust the pH to 6.0. The mixture was stirred at 60 °C for 0.5 h. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 98% and an iron precipitation rate of 99%.

[0055] (2) Add deionized water and formic acid with a mass fraction of 85% to the above mixed precipitate for dissolution. The amount of deionized water is 8 times the mass of the mixed precipitate. Stir at 60°C for 1 hour. The pH of the liquid phase after the reaction is 1.7, and the dissolved liquid is obtained.

[0056] (3) Add solid ammonium formate to the dissolved solution as an ammonium source for complexation, so that the amount of ammonium ions in the system is 8 times the amount of scandium ions. Adjust the pH of the system to 1.7 with 85% formic acid to inhibit the hydrolysis and precipitation of scandium and iron. Stir at 80°C for 1 hour to obtain the complexed solution.

[0057] (4) The complexed liquid was placed in an evaporation apparatus, the evaporation temperature was set to 70℃, the vacuum degree to -0.07MPa, and the mixture was evaporated and concentrated for 2 hours until no liquid was distilled off, thus obtaining a crystalline slurry; during the process, water and formic acid continued to evaporate, and Fe... 3+ It precipitates as a formate, while scandium remains stably in the liquid phase. The evaporated water and formic acid are then condensed and recovered.

[0058] (5) The evaporated and concentrated slurry was separated into solid and liquid phases by centrifugation to obtain an iron-containing solid phase and a scandium-rich liquid phase. The iron-containing solid phase was washed with a 40% ammonium formate solution to recover the entrained scandium. The amount of ammonium formate solution used was 5 times the mass of the iron-containing solid phase. The washing temperature was 80℃ and the washing time was 0.2h.

[0059] Testing revealed that the molar ratio of scandium ions to ammonium ions in the mixed precipitate was 1:1, and the molar ratio of ammonium ions to total scandium ions in the dissolved liquid system was also 1:1. The scandium-rich liquid phase remained liquid at room temperature, and the Sc in the scandium-rich liquid phase... 3+ The concentration is 145 g / L, Fe 3+ The concentration was 1.1 g / L; the liquid phase enrichment rate of scandium was 94%; and the scandium elution rate was 96%. Example 3

[0060] (1) Sc in the original scandium leachate 3+ Concentration 45 g / L, Fe 3+ The concentration was 27 g / L, the anion was nitrate ion, and the hydrogen ion concentration was 1 mol / L. Ammonia solution with a mass fraction of 10% was added to adjust the pH of the system to 8.5, and the mixture was stirred at 10℃ for 2 h. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 99% and an iron precipitation rate of 99%.

[0061] (2) Add deionized water and 90% formic acid to the above mixed precipitate for dissolution. The amount of deionized water is 1 times the mass of the mixed precipitate. Stir at 10°C for 3 hours. The pH of the liquid phase after the reaction is 1.8, and the dissolved liquid is obtained.

[0062] (3) Add solid ammonium bicarbonate to the dissolved solution as an ammonium source for complexation, so that the amount of ammonium ions in the system is 10 times the amount of scandium ions. Adjust the pH of the system to 1.8 with 94% formic acid to inhibit the hydrolysis and precipitation of scandium and iron. Stir at 50°C for 0.5 h to obtain the complexed solution.

[0063] (4) The complexed liquid was placed in an evaporation apparatus, the evaporation temperature was set to 90℃, the vacuum degree to -0.05MPa, and the mixture was evaporated and concentrated for 3 hours until no liquid was distilled off, thus obtaining a crystal slurry; during the process, water and formic acid continued to evaporate, and Fe... 3+ It precipitates as a formate, while scandium remains stably in the liquid phase. The evaporated water and formic acid are then condensed and recovered.

[0064] (5) The evaporated and concentrated slurry was separated into solid and liquid phases by vacuum filtration to obtain an iron-containing solid phase and a scandium-rich liquid phase. The iron-containing solid phase was washed with a 30% ammonium formate solution to recover the entrained scandium. The amount of ammonium formate solution used was 3 times the mass of the iron-containing solid phase. The washing temperature was 60℃ and the washing time was 0.6h.

[0065] Testing revealed that the scandium-rich liquid phase remained liquid at room temperature, and the Sc in the scandium-rich liquid phase... 3+ The concentration is 180 g / L, Fe 3+ The concentration was 1.5 g / L; the liquid phase enrichment rate of scandium was 90%; and the scandium elution rate was 98%. Example 4

[0066] (1) Sc in the original scandium leachate 3+ Concentration 15g / L, Fe 3+ The concentration was 3 g / L, the anion was chloride ion and the hydrogen ion concentration was 3 mol / L. Sodium carbonate solid was added to adjust the pH of the system to 2.0, followed by the addition of 20% ammonia solution to adjust the pH to 8.8. The mixture was stirred at 25°C for 1 hour. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 99% and an iron precipitation rate of 99%.

[0067] (2) Add deionized water and formic acid with a mass fraction of 85% to the above mixed precipitate for dissolution. The amount of deionized water is twice the mass of the mixed precipitate. Stir at 25°C for 0.5 h. After the reaction, the pH of the liquid phase is 1.7, and the dissolved liquid is obtained.

[0068] (3) Add solid ammonium carbonate to the dissolved solution as an ammonium source for complexation, so that the amount of ammonium ions in the system is 6 times the amount of scandium ions. Adjust the pH of the system to 1.7 with 85% formic acid to inhibit the hydrolysis and precipitation of scandium and iron. Stir at 25°C for 2 hours to obtain the complexed solution.

[0069] (4) The complexed liquid was placed in an evaporation apparatus, the evaporation temperature was set to 60℃, the vacuum degree to -0.09MPa, and the mixture was evaporated and concentrated for 3 hours until no liquid was distilled off, thus obtaining a crystalline slurry; during the process, water and formic acid continued to evaporate, and Fe... 3+ It precipitates as a formate, while scandium remains stably in the liquid phase. The evaporated water and formic acid are then condensed and recovered.

[0070] (5) The evaporated and concentrated slurry was separated into solid and liquid phases by vacuum filtration to obtain an iron-containing solid phase and a scandium-rich liquid phase. The iron-containing solid phase was washed with a 40% ammonium formate solution to recover the entrained scandium. The amount of ammonium formate solution used was twice the mass of the iron-containing solid phase. The washing temperature was 40℃ and the washing time was 1h.

[0071] Testing revealed that the scandium-rich liquid phase remained liquid at room temperature, and the Sc in the scandium-rich liquid phase... 3+ The concentration is 128 g / L, Fe 3+ The concentration was 1.6 g / L; the liquid phase enrichment rate of scandium was 94%; and the scandium elution rate was 98%. Comparative Example 1

[0072] The ammonium source addition step in Example 1 is omitted, and evaporation and concentration are carried out directly, with the remaining process parameters unchanged. The specific steps are as follows:

[0073] (1) Sc in the original scandium leachate 3+ Concentration 0.1 g / L, Fe 3+ The concentration was 1.5 g / L, the hydrogen ion concentration was 0.05 mol / L, and the anion was sulfate. A 30% sodium hydroxide solution was added to adjust the pH to 9.0, and the mixture was stirred at 80℃ for 4 hours. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 99% and an iron precipitation rate of 99%.

[0074] (2) Add deionized water and 99% formic acid to the above mixed precipitate for dissolution. The amount of deionized water is 4 times the mass of the mixed precipitate. Stir at 80℃ for 0.5h. The pH of the liquid phase after the reaction is 1.5, and the dissolved liquid is obtained.

[0075] (3) The above dissolved liquid was placed directly into the evaporation device, the evaporation temperature was set to 50°C, the vacuum degree was -0.09MPa, and the system was evaporated and concentrated for 5 hours until no liquid was evaporated out. During the evaporation process, scandium and iron formate precipitated simultaneously. Finally, the system was completely dried out and no liquid residue was left. Scandium and iron were not effectively separated. Comparative Example 2

[0076] The ammonium source addition step in Example 2 is omitted, and evaporation and concentration are carried out directly, with the remaining process parameters unchanged. The specific steps are as follows:

[0077] (1) Sc in the original scandium leachate 3+ Concentration 12 g / L, Fe 3+ The concentration was 60 g / L, the hydrogen ion concentration was 6 mol / L, and the anion was chloride ion. The mixture was diluted 4 times with deionized water, and ammonium bicarbonate was added to adjust the pH to 6.0. The mixture was stirred at 60 °C for 0.5 h. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 98% and an iron precipitation rate of 99%.

[0078] (2) Add deionized water and formic acid with a mass fraction of 85% to the above mixed precipitate for dissolution. The amount of deionized water is 8 times the mass of the mixed precipitate. Stir at 60°C for 1 hour. The pH of the liquid phase after the reaction is 1.7, and the dissolved liquid is obtained.

[0079] (3) The above dissolved liquid was placed directly into the evaporation device, the evaporation temperature was set to 70℃, the vacuum degree was -0.07MPa, and the evaporation and concentration were carried out for 2 hours until no liquid was distilled out of the system to obtain crystal slurry; during the evaporation process, scandium and iron formates precipitated simultaneously and severely.

[0080] (4) The crystal slurry was separated into solid and liquid phases by centrifugation to obtain an iron-containing solid phase and a scandium-rich liquid phase.

[0081] Testing revealed that the molar ratio of scandium ions to ammonium ions in the mixed precipitate was 1:1, and the molar ratio of ammonium ions to total scandium ions in the dissolved liquid system was also 1:1. The scandium-rich liquid phase remained liquid at room temperature, and the Sc in the scandium-rich liquid phase... 3+ The concentration was 132 g / L, Fe 3+ The concentration was 1.6 g / L; the liquid phase enrichment rate of scandium was 18%, which is relatively poor. Comparative Example 3

[0082] The precipitation rates of scandium and iron after the dissolution reaction in Example 3 were tested, with other process parameters remaining unchanged. The specific steps are as follows:

[0083] (1) Sc in the original scandium leachate 3+ Concentration 45 g / L, Fe 3+ The concentration was 27 g / L, the anion was nitrate ion, and the hydrogen ion concentration was 1 mol / L. Ammonia solution with a mass fraction of 10% was added to adjust the pH of the system to 8.5, and the mixture was stirred at 10℃ for 2 h. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 99% and an iron precipitation rate of 99%.

[0084] (2) Add deionized water and 90% formic acid to the above mixed precipitate for dissolution. The amount of deionized water is 1 times the mass of the mixed precipitate. Stir at 10°C for 3 hours. The pH of the liquid phase after the reaction is 1.8, and the dissolved liquid is obtained.

[0085] Analysis revealed the presence of scandium and iron formate solids in the dissolved solution. Specifically, 54.2% of the scandium in the original mixed precipitate precipitated as scandium formate, with the remainder entering the liquid phase. Similarly, 83.9% of the iron in the original mixed precipitate precipitated as iron formate, with the remainder entering the liquid phase. The dissolved solution contained Fe... 3+ The concentration is 4.5 g / L, Sc 3+ The concentration is 21.5 g / L. Comparative Example 4

[0086] In Example 3, the ammonium source was replaced with solid sodium bicarbonate, while the other process parameters remained unchanged. The specific steps are as follows:

[0087] (1) Sc in the original scandium leachate 3+ Concentration 45 g / L, Fe 3+The concentration was 27 g / L, the anion was nitrate ion, and the hydrogen ion concentration was 1 mol / L. Ammonia solution with a mass fraction of 10% was added to adjust the pH of the system to 8.5, and the mixture was stirred at 10℃ for 2 h. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 99% and an iron precipitation rate of 99%.

[0088] (2) Add deionized water and 90% formic acid to the above mixed precipitate for dissolution. The amount of deionized water is 1 times the mass of the mixed precipitate. Stir at 10°C for 3 hours. The pH of the liquid phase after the reaction is 1.8, and the dissolved liquid is obtained.

[0089] (3) Add sodium bicarbonate solid to the dissolved solution as a sodium source so that the amount of sodium ions in the system is 10 times the amount of scandium ions. Adjust the pH of the system to 1.8 with 94% formic acid to inhibit the hydrolysis and precipitation of scandium and iron. Stir at 50°C for 0.5 h to obtain sodium-containing solution.

[0090] (4) The sodium-containing liquid was placed in an evaporation device, the evaporation temperature was set to 90℃, the vacuum degree was -0.05MPa, and the evaporation concentration was carried out for 3 hours. During the evaporation concentration process, scandium and iron formates precipitated simultaneously and severely. In the end, the system was completely dried and there was no liquid residue. Scandium and iron were not effectively separated. Comparative Example 5

[0091] The ammonium source in Example 4 was changed to solid ammonium chloride, while the other process parameters remained unchanged. The specific steps are as follows:

[0092] (1) Sc in the original scandium leachate 3+ Concentration 15g / L, Fe 3+ The concentration was 3 g / L, the anion was chloride ion and the hydrogen ion concentration was 3 mol / L. Sodium carbonate solid was added to adjust the pH of the system to 2.0, followed by the addition of 20% ammonia solution to adjust the pH to 8.8. The mixture was stirred at 25°C for 1 hour. After the reaction was complete, the precipitate was washed with deionized water to remove residual reaction solution, yielding a mixed precipitate containing scandium and iron, with a scandium precipitation rate of 99% and an iron precipitation rate of 99%.

[0093] (2) Add deionized water and formic acid with a mass fraction of 85% to the above mixed precipitate for dissolution. The amount of deionized water is twice the mass of the mixed precipitate. Stir at 25°C for 0.5 h. After the reaction, the pH of the liquid phase is 1.7, and the dissolved liquid is obtained.

[0094] (3) Add solid ammonium chloride to the dissolved solution as an ammonium source for complexation, so that the amount of ammonium ions in the system is 6 times the amount of scandium ions. Adjust the pH of the system to 1.7 with 85% formic acid to inhibit the hydrolysis and precipitation of scandium and iron. Stir at 25°C for 2 hours to obtain the complexed solution.

[0095] (4) The complexed liquid was placed in an evaporation device, the evaporation temperature was set to 60°C and the vacuum degree to -0.09MPa, and the evaporation and concentration were carried out for 3 hours until no liquid was distilled out of the system. The slurry after evaporation and concentration was viscous, and the slurry solidified completely before it cooled to room temperature, leaving no liquid residue. Subsequent solid-liquid separation operations could not be carried out, and scandium and iron were not effectively separated. Application Example 1

[0096] The scandium-rich liquid phase in Example 1 was diluted 10 times with deionized water, and ammonium bicarbonate solid was slowly added until no more bubbles emerged from the system. The reaction was carried out at 40°C for 1 hour, and the solid and liquid phases were separated. The precipitate was washed with deionized water. The precipitation rate of scandium was 99.5%, and the precipitation rate of iron was 99.9%, thus obtaining scandium carbonate precipitate.

[0097] Tests showed that the precipitation rate of scandium was 99.5%, and the precipitation rate of iron was 99.9%; the mass fraction of Sc2O3 in the scandium carbonate precipitate (dry basis) was 30.2%.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 be considered to be within the protection scope of the present invention.

Claims

1. A method for separating and recovering scandium from scandium leachate with high concentrations of iron impurities, characterized in that, Includes the following steps: (1) Add an alkaline reagent to the scandium leaching solution containing ferric ions and adjust the pH to 6.0~9.0 so that scandium and iron precipitate together. After washing with deionized water, a mixed precipitate containing scandium and iron is obtained. (2) Add deionized water and formic acid to the mixed precipitate to dissolve it, and react at 10~80℃ for 0.5~3h to obtain the dissolved solution; (3) Add an ammonium source to the dissolved solution to form a complex, so that the amount of ammonium ions in the system is 6 to 14 times the amount of scandium ions. Adjust the pH of the system to 1.5 to 1.8 with formic acid and react at 10 to 80°C for 0.5 to 3 hours to obtain the complexed solution. (4) The complexed liquid is evaporated and concentrated at 50~90℃ and vacuum degree -0.09~-0.05MPa to precipitate iron in the form of formate and scandium is retained in the liquid phase to obtain crystal slurry; (5) Separate the solid and liquid phases of the crystal slurry to obtain an iron-containing solid phase and a scandium-rich liquid phase.

2. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, The scandium leachate contains Sc 3+ with Fe 3+ The mass concentration ratio is 1:0.2~15, and the hydrogen ion concentration is 0.05~6 mol / L; the scandium leaching solution anion is at least one of sulfate, chloride, formate, nitrate, acetate, citrate, and perchlorate. When the scandium leachate contains Sc 3+ with Fe 3+ When the total concentration is >20g / L, dilute with deionized water to a total concentration ≤20g / L before adding the alkaline reagent, or slowly add a 5%~20% dilute alkaline solution to avoid local over-alkalinity leading to gelation.

3. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, The alkaline reagent mentioned in step (1) is at least one of ammonia water, sodium hydroxide solution, sodium carbonate solid, ammonium bicarbonate solid, sodium bicarbonate solid, and ammonium carbonate solid.

4. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, In step (1), the precipitation reaction temperature is 10~80℃ and the reaction time is 0.5~4h.

5. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, The amount of deionized water used in step (2) is 1 to 8 times the mass of the mixed precipitate; the mass fraction of formic acid is 85% to 99%, and the amount of formic acid added is such that the pH of the system after the dissolution reaction is controlled at 1.5 to 1.

8.

6. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, The ammonium source mentioned in step (3) is one or more of the following: solid ammonium formate, ammonia, solid ammonium bicarbonate, and solid ammonium carbonate.

7. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, In step (4), the evaporation and concentration temperature is 50~90℃, the vacuum degree is -0.09~-0.05MPa, and the evaporation time is 2~5h.

8. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, After solid-liquid separation in step (5), the iron-containing solid phase is washed with ammonium formate solution to recover the entrained scandium. The mass fraction of the ammonium formate solution is 20%~40%, the amount of ammonium formate solution is 2~5 times the mass of the iron-containing solid phase, the washing temperature is 40~80℃, and the washing time is 0.2~1h.

9. The method for separating and recovering scandium from a scandium leachate containing high concentrations of iron impurities according to claim 1, characterized in that, In step (5), the scandium concentration in the scandium-rich liquid phase is 120~180 g / L, and the iron concentration is no more than 2 g / L.

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