Novel method and device for extracting scandium through electrochemical redox coupling extraction

Abstract

The invention belongs to the field of high-strength aluminum alloy, solid oxide fuel cells and semiconductor lasers, and discloses a novel method and device for extracting scandium through electrochemical oxidation-reduction coupling extraction, and the method comprises the following steps: step 1, extracting scandium in a specific reduction or oxidation state by utilizing the chemical behavior difference of phenazine extraction agent molecules in a specific reduction or oxidation state; the method comprises the following steps: step 1, extracting and enriching scandium in a complex low-concentration scandium-containing system by regulating and controlling oxidation-reduction potential and a coordination structure, and step 2, connecting an electrochemical reaction tank with a rotating disc type extraction tower, and realizing a circulation loop of an extraction agent and electrolyte by pumping, and complexing scandium ions and reduced E1-. According to the method, the complexing capacity of the extracting agent is directly changed through oxidation-reduction switching according to the complexing capacity difference of extracting agent molecules to scandium ions in a specific reduction state, the chemical environment of a solution does not need to be changed, extraction-reverse extraction can be achieved only through electric energy, a large amount of alkali consumption and energy consumption in the traditional reverse extraction process are avoided, an acid-base separating agent does not need to be additionally introduced, and the method is environmentally friendly. And no secondary pollution is caused.

Description

Technical Field

[0001] The present invention belongs to the fields of high-strength aluminum alloys, solid oxide fuel cells, and semiconductor lasers, and particularly relates to a new method and device for extracting scandium by electrochemical oxidation-reduction coupling extraction. Background Technique

[0002] Scandium (Sc), as a national strategic rare earth resource, has irreplaceable application value in the field of advanced materials. Its unique 4f electron layer structure endows scandium-based materials with excellent optical, electromagnetic, and magnetic properties, and is widely used in key fields such as high-strength aluminum alloys, solid oxide fuel cells, and semiconductor lasers.

[0003] According to the latest data of the United States Geological Survey (USGS), the proven global reserves of scandium resources are approximately 1.89 million tons (calculated as Sc2O3), of which the associated scandium resources in the vanadium-titanium magnetite in the Panxi region of China reach 386,000 tons, accounting for 58.8% of the total national reserves. However, the occurrence state of scandium resources in this region is complex, mainly dispersed in the tailings of titanium magnetite beneficiation (Sc content 15 - 40 ppm) and the acid hydrolysis tailings of titanium dioxide (Sc content 80 - 120 ppm) in the form of isomorphous substitution such as Sc-Mg-Fe. This ultra-low grade and multi-metal co-associated occurrence characteristic makes it difficult for traditional separation technologies to achieve efficient enrichment of scandium. According to literature reports, the comprehensive recovery rate of scandium in existing processes is less than 30%.

[0004] The associated scandium-rich resources in the Panxi region include smelting waste residues such as vanadium-titanium magnetite tailings, blast furnace slag, and sponge titanium soot, as well as titanium white waste acid, etc., with low content (10 - 100 ppm) and complex composition. In the scandium-containing solution after acid or alkali leaching, the contents of impurities such as Fe, Mg, Ti, Al, Mn, and Ca are all 10 2 -10 3 times or more of the scandium concentration. The traditional scandium ion extraction system is mainly acidic phosphorus-based P204, P507, etc. The oxygen atoms on its phosphoryl group and hydroxyl group jointly provide electrons to coordinate with metal ions. Its selectivity only depends on the difference in the strength of the coordination bond, and the separation factor in a complex system is very low (usually <0.1), and multiple processes need to be combined to achieve a high scandium recovery rate.

[0005] In the development process of scandium extraction technology, as an important extraction method, the process characteristics of extraction have undergone significant evolution. In the early stage, the extraction of scandium mainly relied on direct extraction of scandium, but due to the interference of impurity ions, the extraction rate increased slowly. To solve this problem, researchers gradually turned to the process route of removing impurities first and then extracting scandium. With the continuous progress of the research and development of extractants, high-selectivity and specific scandium extractants have been developed, making it possible to directly extract scandium. At present, the research and development of scandium extraction systems have advanced rapidly, mainly reflected in the optimization and improvement of process condition parameters, while the development of extraction equipment is relatively slow.

[0006] In the research of scandium extractants, it has gradually developed from single extractants to combined extractants. For example, He Yongfu et al. used a single P204-kerosene solution as the extractant to directly extract scandium from a sulfuric acid system and successfully obtained Sc with a purity greater than 99.9%. 2 O 3 . Nie Li et al. used a combined extractant of P5707 and P5709. Through a two-stage extraction process, they separated titanium and other impurities using a P5707-decanol-kerosene system and separated scandium and titanium using a P5707-TBP-kerosene system respectively. The purity of the final product was between 99.0% and 99.9%. Feng Yanlin et al. used a mixed extractant of P507-N7301-kerosene to extract scandium from titanium white waste liquid and inhibited the extraction of titanium by using H 2 O 2 under acidic conditions, achieving a scandium extraction rate of more than 95.0%. Li Yongming et al. determined the optimal content of TBP in a bis(2-ethylhexyl) phosphoric acid (P204)-tributyl phosphate (TBP)-kerosene system and found that TBP could effectively separate titanium and scandium, removing more than 95% of impurities such as titanium. These studies have gradually formed an extraction system with binary extractants for synergistic extraction and kerosene as the diluent.

[0007] In terms of the extraction process, there are relatively more research reports on the P204-TBP-kerosene extraction system. Liu Wei et al. achieved a titanium removal rate of 99.67% for the loaded organic phase through a 6-stage washing section in the sulfuric acid plus hydrogen peroxide method for titanium removal and determined the optimal titanium removal parameters. Li Yuhua adopted a cascade countercurrent extraction process and used an EL elution machine to remove titanium from the loaded organic phase. Through three-stage countercurrent elution, a titanium elution rate of 98% and a scandium loss rate of 4% were achieved. Lu Jiezheng et al. proposed a process for extracting scandium from titanium white waste liquid in sulfuric acid in one step, removing titanium by water decomposition of the alkali cake, and enriching scandium by secondary extraction. Compared with the traditional process of continuously washing titanium and iron in more than a dozen stages, this process significantly shortened the process and reduced the cost. In addition, the interference in the secondary extraction of scandium is less, and the extraction rate is as high as 99.87%. However, there are relatively few research reports on the development of scandium extraction equipment. Hongbin Qiu adopted a pre-concentration-purification-extraction process and completed the extraction by assembling a separating funnel with an oscillator, and finally obtained Sc with a purity of 99.9% 2 O 3 , and the recovery rate reached 98%.

[0008] In recent years, the research on the extraction technology of low-concentration scandium ions from associated scandium-rich resources has focused on solving two problems: developing new organic extraction systems with high distribution coefficients to meet the requirements of high extraction rates; and researching materials with targeted recognition functions (such as chelating agents) to improve the extraction selectivity of scandium ions. In response to these two major problems, units such as Pangang Group, Sichuan University, Institute of Process Engineering, Chinese Academy of Sciences, and Central South University have carried out a series of studies on extraction systems. The Institute of Process Engineering, Chinese Academy of Sciences, has developed green solvent systems such as ionic liquids and deep eutectic solvents (DES) to replace traditional organic extractants, improving the extraction rate while reducing secondary pollution. Central South University has utilized the pore size sieving and charge repulsion effects of supported liquid membranes or nanofiltration membranes, combined with the difference in the hydrated radius of scandium ions, to achieve highly selective permeation extraction. Sichuan University has designed a functionalized amidoxime-based modified resin adsorption system to enhance the chelating ability for Sc 3+ , and achieved efficient separation from Al 3+ , Fe 3+ by regulating the coordination environment; and through techniques such as redox regulation on the electrode surface (such as electrodeposition and electroadsorption), rapid enrichment of scandium in low-concentration solutions has been realized. Based on the traditional acidic phosphorus extractant system, the Research Institute of Pangang Group has achieved a scandium recovery rate > 90% and a product purity > 99% through the optimization study of extraction process conditions and the coupling and regulation of multi-step precipitation and purification processes. However, the preliminary operation results show that the alkali consumption and energy consumption are relatively high during the separation process of elements such as Fe, Mg, and Ti, and the loss rate of the extractant is relatively high, making it difficult to promote and utilize on a large scale.

[0009] Although many types of mixed extractants have been developed in the existing processes, they all basically have some common defects that are difficult to avoid.

[0010] In the traditional scandium extraction process, a large amount of alkali is consumed in the stripping step. Taking the P507-HCl system as an example, a relatively high concentration of hydrochloric acid is required in its stripping process. The preparation and use of hydrochloric acid not only increase the reagent cost but also generate a large amount of waste acid solution, which will cause environmental pollution if not properly treated. In addition, the stripping process usually needs to be carried out under specific temperature and pressure conditions, which further increases the energy consumption. For example, in some high-temperature and high-pressure stripping processes, a large amount of energy is required to maintain the reaction conditions, resulting in a significant increase in the energy consumption of the entire scandium extraction process.

[0011] Traditional solvent extraction methods are restricted by phase distribution thermodynamics during the extraction of scandium. Due to the relatively similar physicochemical properties of scandium and coexisting impurity ions (such as iron, aluminum, titanium, etc.), it is difficult to achieve efficient separation during the extraction process. This results in a low distribution coefficient of scandium during extraction, making it impossible to completely transfer from the aqueous phase to the organic phase, thus limiting the recovery rate of scandium. For example, when extracting scandium from red mud leachate, due to the complex composition of red mud containing various impurity ions with properties similar to scandium, traditional extraction methods are difficult to efficiently separate scandium, making it difficult to improve the recovery rate of scandium.

[0012] When treating feed solutions with low concentrations of scandium, due to the low initial concentration of scandium, the concentration gradient is small during extraction and stripping processes, resulting in insufficient driving force. This makes the mass transfer kinetic process slow, requiring a long time to reach extraction equilibrium, thereby reducing production efficiency. In addition, to achieve good extraction and stripping effects, independent extraction towers and stripping towers are usually set up for two-tower operation. This not only increases equipment investment and floor area but also makes the entire process flow more complex and the operation more difficult.

[0013] Most existing scandium extraction technologies are developed for specific raw materials and process conditions, with strong specificity and poor universality. For example, some processes are applicable to extracting scandium from red mud, while others are applicable to extracting scandium from titanium white waste acid. When faced with scandium-containing materials from different sources and with different compositions, these traditional methods often cannot be directly applied and require a large amount of process adjustment and optimization. In addition, even within the same type of raw materials, due to significant differences in the properties and compositions of the raw materials, traditional methods are difficult to adapt to, resulting in unstable extraction effects of scandium and difficult-to-guarantee recovery rates and product quality. Summary of the Invention

[0014] The present invention proposes a new method for extracting scandium by electrochemically coupled oxidation-reduction extraction, aiming at the problem of highly selective extraction and separation of low-concentration scandium, overcoming the key scientific and technical problems of extractant design, electrochemical reactions, and extraction phase distribution, forming a new technology for highly efficient and highly selective extraction of low-concentration scandium ions, breaking through the bottleneck of efficient extraction of scandium resources in Panxi, and promoting the technological progress of scandium resource development in China.

[0015] To achieve the above object, the present invention provides the following technical solution: An apparatus for extracting scandium by electrochemically coupled oxidation-reduction extraction includes two main units: scandium ion extraction and electrochemical reaction; the electrochemical reaction unit includes a cathode, an anode, a fibrous diaphragm, and a non-proton non-aqueous liquid electrolyte, and the extraction unit uses a redox-active phenazine molecule as an extractant to complete the extraction process in an extraction tower. The cathode of the electrochemical reaction cell is connected to the feed end of the extraction tower, the anode is connected to the discharge end, and the acidolysis solution of scandium is fed from the top of the extraction tower.

[0016] A new method for extracting scandium by electrochemical redox coupling extraction, the main process is as follows:

[0017] S1. The extractant molecule E1 is first reduced at the cathode and injects electrons to form electron-rich E1 - , which has strong cation complexation ability;

[0018] S2. Due to the different redox potentials of different elements in the scandium-containing leaching solution, the electron-rich state of E1 is precisely regulated online according to the potential to achieve selective complexation of Sc - in the extraction unit; 3+ ;

[0019] S3. Subsequently, the upper-layer extraction solution flows into the anode of the electrochemical reaction cell, and the electron-rich extractant molecule is re-oxidized to a stable E1 molecule, and Sc 3+ automatically detaches from the extractant molecule and salifies in the anode region;

[0020] S4. E1 and the electrolyte solvent on the anode side are recycled to the cathode by a pump to form a circulation loop; continuously circulating this process can form an extraction closed-loop circuit that does not consume the extractant and solvent;

[0021] Therefore, the continuous selective extraction and recovery of Sc elements can be achieved only based on the current.

[0022] Furthermore, in the above technical solution, the E1 extractant uses phenazine-based molecules, and the reduced-state phenazine-based extractant preferentially forms stable coordination bonds with specific empty orbitals of Sc 3 +, including the low-spin d0 configuration. Research shows that there are significant differences in the redox potentials of the complexation of Sc and the main impurity ion Fe with the reduced-state phenazine molecule. Through the design of the redox extraction molecule, the redox potential of the metal ion complexation is modulated, and then the online modulation of the complexation energy of scandium ions is achieved through the precise regulation of the potential, achieving extremely high selectivity for scandium ions, with a single-pass extraction rate of more than 90%, and scandium salts with a purity of 99.9% are obtained. At the same time, by controlling the length of the carbon chain attached to the phenazine molecule, an extractant recovery rate of more than 99.5% is achieved.

[0023] Furthermore, the aprotic non-aqueous electrolyte used in the electrochemical reaction cell is mainly a series of ionic liquids, including 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF 6 ), N-ethylpyridinium tetrafluoroborate (EPyBF 4 ), 1-ethyl-1-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI). Such electrolytes can be miscible with phenazine-based extractants without loss in the aqueous phase. The extractant can be closed-loop recycled in the aprotic non-aqueous liquid electrolyte, thereby realizing the redox of the extractant and the adsorption and desorption of scandium ions.

[0024] Furthermore, the liquid in the anode region of the electrolytic cell can be washed regularly to remove the precipitated scandium salts after precipitation.

[0025] Furthermore, the sources of scandium ions include vanadium-titanium magnetite tailings, blast furnace slag, smelting waste slag of sponge titanium dust, and titanium white waste acid.

[0026] Furthermore, both the extraction tower and the electro-chemical reaction cell equipment can operate stably at normal temperature and pressure. By adjusting the output voltage and current density, they can cooperate with different dosages of extractants to adapt to different inputs of scandium raw material streams.

[0027] Furthermore, the extraction tower adopts an improved rotary disk extraction tower, and a new type of rotary disk extractor is designed. Through the sedimentation - mixing - sedimentation design, rotary disk mixing is used, and through the slit design and internal circulation design, high-efficiency continuous separation of the emulsifiable system is achieved. When the rotary disk extractor operates stably in countercurrent, the extraction rate is significantly higher than that of a single equilibrium stage. The slit design strengthens the separation process, the narrow stirring space strengthens the mass transfer process, and the internal circulation channel strengthens both the mass transfer and separation processes at the same time. The flow state in the extractor can be described by the plug flow - continuous stirred tank reactor - plug flow model, in which under the optimal extraction conditions, the volume of the continuous stirred tank reactor reaches 80% of the total volume of the extractor.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. Through the difference in the complexing ability of extractant molecules for scandium ions in a specific reduced state, by changing the coordination ability of the extractant directly through redox switching, without changing the solution chemical environment, only electrical energy is required to achieve extraction - stripping. This avoids a large amount of alkali consumption and energy consumption in the traditional stripping process, without the need to introduce additional acid - base separating agents, and there is no secondary pollution;

[0030] 2. Through the precise regulation of potential and the design of extractant molecules, taking advantage of the different redox potentials of impurity elements, combined with the precise online input of electrons to adjust the distribution coefficient of low - concentration scandium ions in the extraction system, breaking the traditional phase distribution thermodynamics limit, selectively extracting scandium ions with high selectivity, and then in - situ salt precipitation of precipitates with a purity of 99.9% at the anode. The extraction process is simple and only requires one step to complete;

[0031] 3. After re - engineering the extraction - stripping process by combining electric drive, the mass transfer process is much faster than the traditional acid - base diffusion. The extraction - stripping process can be switched in seconds. The extractant can be recycled in a closed loop in a non - proton non - aqueous liquid electrolyte. In this process, the electro - chemical reaction cell is used to replace the traditional multi - stage stripping tower, realizing high - efficiency, intensive, and continuous liquid - liquid extraction for scandium extraction;

[0032] 4. The use of a new type of rotary disk extractor solves the problems of the large volume of the settling chamber in the stirring tank, the low extraction stage efficiency, the serious backmixing in the extraction tower, the complex structure and high energy consumption of the centrifugal extractor, and the small flow rate, small scale and easy blockage of the microfluidic extractor. High-efficiency mass transfer is achieved through rotary disk stirring, two-phase separation is achieved through the oilophilic channels, and the two phases flow continuously in countercurrent, adjusting the contradiction between mass transfer and separation;

[0033] 5. The sources of scandium resources, including vanadium-titanium magnetite tailings, blast furnace slag, and sponge titanium soot from smelting waste slag and titanium white waste acid, are universal. Therefore, this technology can be extended to the separation of low-concentration elements in similar complex associated solutions and has universality. Brief Description of the Drawings

[0034] Figure 1 It is the process flow diagram of the electrochemical oxidation-reduction coupled extraction and separation of scandium in the present invention;

[0035] Figure 2 It is the oxidation-reduction curve diagram of extraction and stripping of different metal ions on the phenazine-based extractant in the present invention;

[0036] Figure 3 It is the separation ratio diagram of scandium ions extracted by the graft-modified phenazine-based extractant in the present invention;

[0037] Figure 4 It is the schematic structural diagram of the rotary disk extractor applicable to the extraction of low-concentration scandium ions in the present invention. Detailed Embodiments

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] A new method for electrochemical oxidation-reduction coupled extraction and separation of scandium, the main process is as follows:

[0040] S1. The extractant molecule E1 is first reduced at the cathode and injects electrons to form electron-rich E1 - , which has strong cation complexing ability;

[0041] S2. Since the redox potentials of different elements in the scandium-containing leaching solution are different, the electron-rich state of E1 is accurately regulated online according to the potential to achieve selective complexation of Sc - in the extraction unit; 3+

[0042] S3. Subsequently, the upper-layer extraction liquid flows into the anode of the electrochemical reaction cell, and the electron-rich extractant molecules are re-oxidized into stable E1 molecules, and Sc 3+ automatically detaches from the extractant molecules and salifies in the anode region;

[0043] S4. E1 and the electrolyte solvent on the anode side are recycled to the cathode by a pump to form a circulation loop; continuously circulating this process can form an extraction closed-loop circuit that does not consume extractant and solvent;

[0044] Therefore, continuous selective extraction and recovery of Sc elements can be achieved only based on current, as Figure 1 shown.

[0045] In this embodiment, in the above technical solution, the E1 extractant uses phenazine-based molecules, and the reduced-state phenazine-based extractant preferentially forms stable coordination bonds with the specific empty orbitals of Sc 3 +, including the low-spin d0 configuration. Research shows that there are significant differences in the redox potentials of the complexation of Sc and the main impurity ion Fe with the reduced-state phenazine molecules, as Figure 2 shown. Through the design of redox extraction molecules, the redox potential of metal ion complexation is modulated, and then the online modulation of the complexation energy of scandium ions is achieved through precise potential regulation, achieving extremely high selectivity for scandium ions, with a single-pass extraction rate of over 90%, and scandium salts with a purity of 99.9% are obtained. At the same time, by controlling the length of the carbon chain attached to the phenazine molecule, an extractant recovery rate of over 99.5% is achieved, as Figure 3 shown.

[0046] In this embodiment, the aprotic non-aqueous electrolyte used in the electrochemical reaction cell is mainly a series of ionic liquids, including 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF 6 ), N-ethylpyridinium tetrafluoroborate (EPyBF 4 ), 1-ethyl-1-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI). Such electrolytes can be miscible with phenazine-based extractants without loss in the aqueous phase, and the extractant can form a closed-loop cycle in the aprotic non-aqueous liquid electrolyte, thereby realizing the redox of the extractant and the adsorption and desorption of scandium ions.

[0047] In this embodiment, the liquid in the anode region of the electrolytic cell can be washed with water regularly to remove the deposited scandium salts after precipitation.

[0048] In this embodiment, the sources of scandium ions include vanadium-titanium magnetite tailings, blast furnace slag, smelting waste slag of sponge titanium soot, and titanium white waste acid.

[0049] In this embodiment, both the extraction tower and the electrochemical reaction cell equipment can operate stably at normal temperature and pressure. By adjusting the output voltage and current density, they can cooperate with different dosages of extractants to adapt to different inputs of scandium raw material streams.

[0050] In this embodiment, an improved rotary disk extraction tower is adopted for the extraction tower. A new type of rotary disk extractor is designed. Through the sedimentation - mixing - sedimentation design, rotary disk mixing is used. High - efficiency continuous separation of the easy - emulsification system is achieved through slit design and internal circulation design, as Figure 4 shown. When the rotary disk extractor operates stably in counter - current, the extraction rate is significantly higher than that of a single equilibrium stage. The slit design strengthens the separation process, the narrow stirring space strengthens the mass transfer process, and the internal circulation channel strengthens both the mass transfer and separation processes. The flow state in the extractor can be described by the plug - flow - complete - mixing - plug - flow model, where under the optimal extraction conditions, the volume of the complete - mixing flow reaches 80% of the total volume of the extractor.

[0051] Example 1: The electrolyte 1 - butyl - 3 - methylimidazolium hexafluorophosphate (BMIMPF 6 ) is mixed with the molecular - designed phenazine - type extractant in a ratio of 3:1 - 6:1 and fully dissolved at 10 - 50 °C. The above solution is added to a 1 - 3 L electrochemical reaction cell. Platinum is used as the electrode for the reduction of the extractant, and then the mixed liquid is pumped into the extractor. At the same time, the treated leaching solution of vanadium - titanium magnetite tailings, blast furnace slag, sponge titanium fume, or titanium white waste acid containing scandium is introduced at a rate of 1 - 10 L / min. The organic phase after extraction returns to the anodic area of the electrochemical reaction cell. After the extractant is re - oxidized, scandium salt is precipitated. The extractant and the electrolyte BMIMPF 6 are pumped and circulated to the cathode to form a circulation loop again. The obtained precipitate is washed and separated multiple times and then vacuum - dried to obtain scandium salt with a purity of over 99.9%. The single - pass extraction recovery rate of scandium ions is >90%, and the loss of the extractant is <0.5%.

[0052] Example 2: The electrolyte N - ethylpyridinium tetrafluoroborate (EPyBF 4 ) is mixed with the molecular - designed phenazine - type extractant in a ratio of 4:1 - 8:1 and fully dissolved at 10 - 40 °C. The above solution is added to a 1 - 3 L electrochemical reaction cell. Platinum is used as the electrode for the reduction of the extractant, and then the mixed liquid is pumped into the extractor. At the same time, the treated leaching solution of vanadium - titanium magnetite tailings, blast furnace slag, sponge titanium fume, or titanium white waste acid containing scandium is introduced at a rate of 1 - 10 L / min. The organic phase after extraction returns to the anodic area of the electrochemical reaction cell. After the extractant is re - oxidized, scandium salt is precipitated. The extractant and the electrolyte EPyBF 4It is then circulated to the cathode by a pump to form a circulation loop. The obtained precipitate is washed and separated multiple times, and after vacuum drying, a scandium salt with a purity of over 99.9% is obtained. The single-pass extraction recovery rate of scandium ions is >90%, and the loss of the extractant is <0.5%.

[0053] Example 3: The electrolyte 1-ethyl-1-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) is mixed with the molecularly designed phenazine extractant in a ratio of 2:1 - 6:1 and fully dissolved at 15 - 60 °C. The above solution is added to a 1 - 3 L electrochemical reaction cell. Platinum is used as the electrode for the reduction of the extractant, and then the mixed liquid is pumped into the extractor. Meanwhile, the treated leaching solution of vanadium-titanium magnetite tailings, blast furnace slag, sponge titanium soot, or titanium white waste acid containing scandium is introduced at a rate of 1 - 10 L / min. The organic phase after extraction returns to the anodic region of the electrochemical reaction cell. After the extractant is re-oxidized, scandium salt precipitates out. The extractant and the electrolyte EMITFSI are then circulated to the cathode by a pump to form a circulation loop. The obtained precipitate is washed and separated multiple times, and after vacuum drying, a scandium salt with a purity of over 99.9% is obtained. The single-pass extraction recovery rate of scandium ions is >90%, and the loss of the extractant is <0.5%.

[0054] In summary, through the difference in the complexation ability of the extractant molecules for scandium ions in a specific reduced state, the coordination ability of the extractant is directly changed by redox switching. Without changing the solution chemical environment, extraction - stripping can be achieved only with electric energy, avoiding a large amount of alkali consumption and energy consumption in the traditional stripping process, without the need to additionally introduce acid-base separating agents, and there is no secondary pollution;

[0055] Through the precise regulation of the potential and the design of the extractant molecules, taking advantage of the different redox potentials of impurity elements, combined with the online input of potential and precise modulation of the distribution coefficient of low-concentration scandium ions in the extraction system by electrons, breaking the traditional phase distribution thermodynamics limit, selectively extracting scandium ions with high selectivity, and then in-situ salt precipitating a precipitate with a purity of 99.9% at the anode. The extraction process is simple and can be completed in only one step;

[0056] After reengineering the extraction - stripping process by combining electric drive, the mass transfer process is much faster than the traditional acid-base diffusion, realizing a second-level extraction - stripping process switching. The extractant can be closed-loop circulated in a non-protic non-aqueous liquid electrolyte. This process uses an electrochemical reaction cell to replace the traditional multi-stage stripping tower, achieving efficient, intensive, and continuous liquid-liquid extraction for scandium;

[0057] The use of a new type of rotary disk extractor solves the problems of the large volume of the sedimentation chamber in the stirring tank, the low extraction stage efficiency, the serious backmixing in the extraction tower, the complex structure and high energy consumption of the centrifugal extractor, and the small flow rate, small scale and easy blockage of the microfluidic extractor. High-efficiency mass transfer is achieved through rotary disk stirring, and two-phase separation is achieved through the oil-wetting channels. The two phases flow continuously in countercurrent, regulating the contradiction between mass transfer and separation;

[0058] The technology is applicable to the scandium resources from smelting waste residues including vanadium-titanium magnetite tailings, blast furnace slag and titanium sponge fume, as well as titanium white waste acid. Only by finding a suitable redox extractant can the technology achieve efficient extraction of both anions and cations. Therefore, this technology can be extended to the separation of low-concentration elements in similar complex associated solutions and has universality.

[0059] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0060] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A new method for extracting scandium by electrochemical redox coupling, characterized in that: The method comprises the following steps: Step 1: Utilizing the differences in chemical behaviors of phenazine extractant molecules in specific reduction or oxidation states, the extraction and enrichment of scandium in complex low-concentration scandium-containing systems can be achieved by regulating the redox potential and coordination structure; Step 2: The electrochemical reaction cell is connected to the rotary disc extraction tower, and the extractant and electrolyte circulation loop is realized by pumping. The scandium ions are reacted with the reduced E1 - The complex is then detached in the anode area due to the re-oxidation of the extractant, and then salted out in the anode area.

2. A rotary disc extraction tower, based on the new method for extracting scandium by electrochemical redox coupling according to claim 1, characterized in that: By adopting rotating disk mixing, high-efficiency continuous separation is achieved through the slit, that is, the narrow space of the 1mm mixing chamber and the internal circulation design. With the help of forced stirring by the disk, the macroscopic multiphase flow in the reactor is strengthened and regulated to eliminate the gradient distribution. The continuous countercurrent flow of the two phases is driven by pump pressure, and the oil phase is separated through the slit of the lipophilic material, and then stratification is achieved in the sedimentation chambers on both sides.

3. The novel method for extracting scandium by electrochemical redox coupling according to claim 1, characterized in that: A non-protonic non-aqueous electrolyte is selected as the electrochemical medium in the electrochemical reaction cell so that it is miscible with the extractant and does not cause loss when in contact with water.

4. A phenazine extractant, based on the new method for extracting scandium by electrochemical redox coupling according to claim 1, characterized in that: By predicting the electrochemical properties of molecules in non-protonic non-aqueous electrolyte systems, the implicit relationship between the extractant structure and thermodynamic properties is revealed, allowing molecular design to achieve high selectivity for scandium ions and low loss rate of the extractant.

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