A method for extracting scandium from a fused salt chlorination dust residue

Abstract

The application discloses a method for extracting scandium from a molten salt chlorination dust collection residue, which comprises the following steps: water immersion is performed on the molten salt chlorination dust collection residue to obtain a leaching solution; scandium in the leaching solution is precipitated by using an alkali liquor containing a strong oxidizing substance to obtain a scandium-rich residue; scandium in the scandium-rich residue is leached by using a dilute acid to obtain a first scandium-rich liquid; scandium in the first scandium-rich liquid after reduction is extracted by using a composite extractant and a multistage countercurrent cyclone; a first loaded organic phase is obtained; the first loaded organic phase is subjected to multistage countercurrent cyclone stripping by using a strong oxidizing and strong alkaline solution; after filtration, the first loaded organic phase is subjected to acid leaching again to obtain a second scandium-rich liquid; the second scandium-rich liquid is subjected to extraction, acid washing and stripping again to obtain scandium hydroxide with an impurity content less than 1%; the scandium hydroxide is dissolved by using hydrochloric acid, precipitated by using oxalic acid and high-temperature roasted, and finally, scandium oxide with a purity greater than 99.9% is obtained. The method is convenient to operate, simple in technological process, low in production cost, good in environmental protection benefit, easy to realize industrialization, and can efficiently recover valuable scandium in the molten salt chlorination dust collection residue.

Description

Technical Field

[0001] This invention relates to the field of metal resource recycling technology, and in particular to a method for extracting scandium from molten salt chlorination dust collection residue. Background Technology

[0002] Scandium is a rare earth element and a strategic resource. Globally, scandium resources are abundant, with reserves of approximately 2 million tons. my country's scandium reserves are about 650,000 tons. However, more than 75% of scandium is associated with other minerals. The complex production process, low recovery rate, and high cost of scandium have resulted in insufficient international supply and high prices for scandium products, making it known as one of the most expensive metals in the world. Domestic scandium resources are mainly distributed in bauxite and phosphate rock (including weathered leaching phosphate deposits), vanadium-titanium magnetite, tungsten, rare earth minerals, etc. Currently, scandium extraction raw materials mainly come from secondary resources such as waste liquid or solid waste generated during the comprehensive utilization of associated minerals. Existing secondary resources that can be used as scandium extraction raw materials include by-products of uranium ore, tungsten ore and tungsten slag, hydrolyzed acidic waste liquid generated from the sulfuric acid process for titanium dioxide production, chlorinated dust generated from fluidized bed titanium extraction, titanium-containing blast furnace slag, red mud, ion adsorption type rare earth minerals, Bayan Obo tailings, etc. Different scandium-containing raw materials have different physicochemical properties, especially in terms of chemical composition and solubility in different leaching agents, so the scandium extraction processes involved are different.

[0003] Molten salt chlorination is an important production method for titanium tetrachloride. The slag from molten salt chlorination contains a certain amount of valuable scandium, which exists primarily in the form of soluble salts. However, in actual production processes, there is no economically effective treatment technology for pollutants such as molten salt chlorination slag, both domestically and internationally. The pollutants are usually treated by mixing with lime and then dumping in wasteland (overseas) or by landfilling in specialized slag yards (domestic), which wastes valuable scandium resources.

[0004] Therefore, there is a need in the prior art to improve the method for extracting scandium from molten salt chlorination dust. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for extracting scandium from molten salt chlorination dust collection residue. This method is easy to operate, has a simple process flow, low production cost, good environmental benefits, and is easy to industrialize. It can efficiently recover valuable element scandium from molten salt chlorination dust collection residue.

[0006] To achieve the above objectives, embodiments of the present invention provide a method for extracting scandium from molten salt chlorination dust collection residue, comprising the following steps:

[0007] S1. The molten salt chlorination dust collector is leached with water to obtain leachate, leaching residue and wash water. The leaching residue is washed and recycled as a titanium extraction raw material. The wash water is recycled for leaching the molten salt chlorination dust collector.

[0008] S2. Scandium in the leachate is precipitated with an alkaline solution containing strong oxidizing substances to obtain scandium-rich residue and brine. The brine is then recovered and used as raw material for the preparation of sodium, magnesium, and calcium salts.

[0009] S3. Leach scandium from the scandium-rich residue with dilute acid to obtain a first scandium-rich solution and a first residue, and use a reducing agent to reduce iron and titanium in the first scandium-rich solution;

[0010] S4. Scandium in the reduced first scandium-rich solution is extracted by multi-stage countercurrent cyclone extraction using a composite extractant to obtain a first loaded organic phase and a first raffinate.

[0011] S5. The first loaded organic phase is subjected to multi-stage countercurrent cyclone back-extraction using a strong oxidizing and strong alkaline solution to obtain a back-extracted organic phase and a solid back-extractant. The back-extracted organic phase is regenerated and recycled using dilute acid for extraction.

[0012] S6. Filter the solid back-extract and perform high-temperature roasting and fine grinding, then leach with dilute acid to obtain a second scandium-rich solution and a second residue with low impurity content;

[0013] S7. Scandium in the second scandium-rich solution is extracted countercurrently using a composite extractant to obtain a second loaded organic phase and a second raffinate.

[0014] S8. Use an acid solution containing a strong oxidizing agent to elute residual metal impurities in the second loaded organic phase;

[0015] S9. Scandium in the second loaded organic phase after elution is subjected to multi-stage countercurrent cyclone back-extraction using alkaline solution to obtain scandium hydroxide with an impurity content of <1%. The scandium hydroxide is dissolved in hydrochloric acid, precipitated with oxalic acid, and calcined at high temperature to finally obtain scandium oxide with a purity of >99.9%.

[0016] In some embodiments, in S1, the scandium content in the molten salt chlorination dust collector is 10-150 g / t, and the liquid-to-solid ratio (ml:g) during water leaching is (1-15):1. During the leaching process, the solution pH must be maintained <2 to prevent scandium ions from hydrolyzing and entering the solid leaching residue. If the pH does not meet the requirements, acid can be added appropriately to adjust the pH to <2. Stirring is strengthened during the leaching process, and the leaching time is 2-5 hours to ensure that scandium is fully leached. The water used for washing also needs to be kept at pH <2 to prevent scandium ion hydrolysis. The wash water can be returned to the water leaching process. Leaching continues until the leaching residue is washed until the salt content (mass percentage) is <0.05%.

[0017] In some embodiments, in S2, the alkaline solution and the leachate are mixed at a ratio of (1 to 1.5):1, the reaction time is 1.5 to 3 hours, and the pH at the end of the reaction needs to be controlled at 5 to 8 to ensure complete precipitation of scandium ions.

[0018] In some embodiments, in S3, the dilute acid is 1-5 mol / L sulfuric acid and / or 1-5 mol / L hydrochloric acid, and the leaching time is 2-5 h; the reducing agent includes cast iron filings, reduced iron powder, sulfite, GBS, aluminum powder or magnesium powder, and the amount of reducing agent used is 1-1.5 times the theoretical amount to completely reduce iron and titanium in the leaching solution, and the reaction temperature during reduction is controlled at 50-90°C.

[0019] In some embodiments, in S4, the composite extractant comprises, by volume percentage, TBP (5%–30%), P204 (5%–30%), P229 (0%–10%), and 260# solvent oil (50%–90%). Extraction is performed using an acid- and alkali-resistant cyclone extractor with an extraction stage ≥1. The volume ratio of the composite extractant to the first scandium-rich solution during extraction is 1:(1–30).

[0020] In some embodiments, during S5, the alkali concentration of the strongly oxidizing and strongly alkaline solution is controlled at 5% to 15%, and the volume ratio of the first loaded organic phase to the strongly oxidizing and strongly alkaline solution is 1:(1 to 10).

[0021] In some embodiments, in S6, the solid back-extractant is subjected to high-temperature calcination conversion at a temperature of 700–900°C for 3–6 hours. After high-temperature calcination conversion, an oxide is formed. The oxide is then ground to a particle size range of less than 250 mesh and then leached at room temperature with dilute acid, which is 1–5 mol / L sulfuric acid and / or 1–5 mol / L hydrochloric acid, for 2–5 hours.

[0022] In some embodiments, in S7, the composite extractant comprises, by volume percentage, TBP (5%–30%), P204 (5%–30%), P229 (0%–10%), and 260# solvent oil (50%–90%). Extraction is performed using an acid- and alkali-resistant cyclone extractor with an extraction stage ≥1. The volume ratio of the composite extractant to the second scandium-rich solution during extraction is (1–30):1.

[0023] In some embodiments, in S8, the acid solution of the strong oxidizing substance includes an acid and a strong oxidizing agent. The acid is sulfuric acid and / or hydrochloric acid with a concentration of 1 to 5 mol / L. The strong oxidizing agent is ozone or hydrogen peroxide with a concentration of 1 to 2 mol / L. The elution time is 10 to 30 min, and the elution stage number is ≥1.

[0024] In some embodiments, in S9, the alkaline solution used for back-extraction is NaOH and / or ammonia water with a concentration of 1.5–3 mol / L. The volume ratio of the second loaded organic phase to the alkaline solution during back-extraction is 1:(0.5–2). The back-extraction equipment is an acid- and alkali-resistant hydrocyclone extractor with ≥1 back-extraction stage. The back-extraction product is dissolved in hydrochloric acid with a concentration of 1–5 mol / L, and then precipitated with oxalic acid or sodium oxalate. The amount of oxalic acid or sodium oxalate added is 1–1.5 times the theoretical mass required to completely precipitate scandium ions. After centrifugation, filtration, and dehydration, the precipitate is calcined at a high temperature of 600–900°C for 3–6 hours for dehydration and transformation, finally obtaining a scandium oxide product with a purity of ≥99.9%.

[0025] The present invention has at least the following beneficial technical effects:

[0026] The method of this invention employs an adaptable extraction system, involving multiple leaching, extraction, elution, and back-extraction to efficiently recover scandium, a valuable element, from molten salt chlorination dust collector residue. This method effectively recycles and utilizes the molten salt chlorination dust collector residue, and features convenient operation, simple process flow, low production cost, good environmental benefits, and ease of industrialization. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart for extracting scandium from molten salt chlorination dust collection residue provided by the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0030] The terms "comprising" and "having," and any variations thereof, used in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0031] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] like Figure 1 The flowchart provided for the embodiment of the present invention for extracting scandium from molten salt chlorination dust collection residue illustrates the entire scandium extraction process in a simplified manner. The raw material for scandium extraction involved in this invention is the dust collection residue generated during the molten salt chlorination titanium extraction process of titanium-rich materials. The molten salt chlorination dust collection residue contains a certain amount of valuable element scandium, and scandium exists primarily in the form of a soluble salt. Therefore, the present invention provides a method for extracting scandium from molten salt chlorination dust collection residue, the specific method steps of which include:

[0033] S1. The molten salt chlorination dust collector is leached with water to obtain leachate, leaching residue and wash water. The leaching residue is washed and recycled as a titanium extraction raw material. The wash water is recycled for leaching the molten salt chlorination dust collector.

[0034] S2. Scandium in the leachate is precipitated with an alkaline solution containing strong oxidizing substances to obtain scandium-rich residue and brine. The brine is then recovered and used as raw material for the preparation of sodium, magnesium, and calcium salts.

[0035] S3. Leach scandium from the scandium-rich residue with dilute acid to obtain a first scandium-rich solution and a first residue, and use a reducing agent to reduce iron and titanium in the first scandium-rich solution;

[0036] S4. Scandium in the reduced first scandium-rich solution is extracted by multi-stage countercurrent cyclone extraction using a composite extractant to obtain a first loaded organic phase and a first raffinate.

[0037] S5. The first loaded organic phase is subjected to multi-stage countercurrent cyclone back-extraction using a strong oxidizing and strong alkaline solution to obtain a back-extracted organic phase and a solid back-extractant. The back-extracted organic phase is regenerated and recycled using dilute acid for extraction.

[0038] S6. Filter the solid back-extract and perform high-temperature roasting and fine grinding, then leach with dilute acid to obtain the second scandium-rich solution and the second residue;

[0039] S7. Scandium in the second scandium-rich solution is extracted countercurrently using a composite extractant to obtain a second loaded organic phase and a second raffinate.

[0040] S8. Use an acid solution containing a strong oxidizing agent to elute residual metal impurities in the second loaded organic phase;

[0041] S9. Scandium in the second loaded organic phase after elution is subjected to multi-stage countercurrent cyclone back-extraction using alkaline solution to obtain scandium hydroxide with an impurity content of <1%. The scandium hydroxide is dissolved in hydrochloric acid, precipitated with oxalic acid, and calcined at high temperature to finally obtain scandium oxide with a purity of >99.9%.

[0042] In some embodiments, in S1, the scandium content in the molten salt chlorination dust collector is 10-150 g / t, and the soluble components in the molten salt chlorination dust collector account for about 70%-95% of the total amount of the molten salt chlorination dust collector. The scandium in the molten salt chlorination dust collector mainly exists in the form of soluble salts. By water leaching, the scandium can be basically transferred into the solution. The liquid-to-solid ratio (ml:g) during water leaching is (1-15):1. During the leaching process, the solution pH must be kept <2 to avoid scandium ion hydrolysis into the solid phase leaching residue. If the pH does not meet the requirements, acid can be added appropriately to adjust the pH to <2. Stirring is strengthened during the leaching process, and the leaching time is 2-5 hours to ensure that the scandium is fully leached. The washing water used during washing must also be kept at pH <2 to prevent scandium ion hydrolysis. The washing water can be returned to the water leaching process. Leaching continues until the leaching residue is washed until the salt content (mass percentage) is <0.05%.

[0043] In some embodiments, in S2, the alkaline solution and the leachate are mixed at a ratio of (1 to 1.5):1, the reaction time is 1.5 to 3 hours, and the pH at the end of the reaction needs to be controlled at 5 to 8 to ensure complete precipitation of scandium ions.

[0044] In some embodiments, in S3, the dilute acid is 1-5 mol / L sulfuric acid and / or 1-5 mol / L hydrochloric acid, and the leaching time is 2-5 h; the reducing agent includes cast iron filings, reduced iron powder, sulfite, GBS, aluminum powder or magnesium powder, and the amount of reducing agent used is 1-1.5 times the theoretical amount to completely reduce iron and titanium in the leaching solution, and the reaction temperature during reduction is controlled at 50-90°C.

[0045] In some embodiments, in S4, the composite extractant includes TBP (5%–30%), P204 (5%–30%), P229 (0%–10%), and 260# solvent oil (50%–90%) by volume percentage. Extraction is performed using an acid- and alkali-resistant cyclone extractor with an extraction stage ≥1. It is not necessary to saponify the organic phase of the composite extractant before extraction. The increase in acidity during the extraction process has little effect on the extraction of scandium ions but helps to suppress the extraction of other ions. The volume ratio of the composite extractant to the first scandium-rich solution during extraction is 1:(1–30).

[0046] In some embodiments, during S5, the alkali concentration of the strongly oxidizing and strongly alkaline solution is controlled at 5% to 15%, and the volume ratio of the first loaded organic phase to the strongly oxidizing and strongly alkaline solution is 1:(1 to 10).

[0047] In some embodiments, in S6, the solid back-extractant undergoes high-temperature roasting conversion at 700–900°C for 3–6 hours. After high-temperature roasting conversion, oxides are formed. The purpose of roasting is to convert compounds of elements such as iron, manganese, titanium, and zirconium into oxides that are insoluble, slightly soluble, or slowly soluble in dilute acid at room temperature, so as to facilitate the separation of scandium from impurities during subsequent dilute acid leaching at room temperature. The oxides are ground to a particle size range of less than 250 mesh, and then leached at room temperature with dilute acid, which is 1–5 mol / L sulfuric acid and / or 1–5 mol / L hydrochloric acid, for 2–5 hours.

[0048] In some embodiments, in S7, the composite extractant includes TBP (5%–30%), P204 (5%–30%), P229 (0%–10%), and 260# solvent oil (50%–90%) by volume percentage. Extraction is performed using an acid- and alkali-resistant cyclone extractor with an extraction stage ≥1. It is not necessary to saponify the organic phase of the composite extractant before extraction. The increase in acidity during the extraction process has little effect on the extraction of scandium ions but helps to suppress the extraction of other ions. The volume ratio of the composite extractant to the second scandium-rich solution during extraction is (1–30):1.

[0049] In some embodiments, in S8, the acid solution of the strong oxidizing substance includes an acid and a strong oxidizing agent. The acid is sulfuric acid and / or hydrochloric acid with a concentration of 1 to 5 mol / L. The strong oxidizing agent is ozone or hydrogen peroxide with a concentration of 1 to 2 mol / L. The elution time is 10 to 30 min, and the elution stage number is ≥1.

[0050] In some embodiments, in S9, the alkaline solution used for back-extraction is NaOH and / or ammonia water with a concentration of 1.5–3 mol / L. The volume ratio of the second loaded organic phase to the alkaline solution during back-extraction is 1:(0.5–2). The back-extraction equipment is an acid- and alkali-resistant hydrocyclone extractor with ≥1 back-extraction stage. The back-extraction product is post-treated to obtain scandium oxide. The post-treatment includes hydrochloric acid dissolution, oxalic acid precipitation, and calcination. Specifically, the back-extraction product is dissolved in hydrochloric acid with a concentration of 1–5 mol / L. The hydrochloric acid dissolution process can remove silicon-containing impurities. The scandium-containing impurity-removing solution is then precipitated with oxalic acid or sodium oxalate. The amount of oxalic acid and sodium oxalate added is 1–1.5 times the theoretical mass required to completely precipitate scandium ions. After centrifugation, filtration, and dehydration, the precipitate is calcined at a high temperature of 600–900°C for 3–6 hours for dehydration and transformation, finally obtaining a scandium oxide product with a purity of ≥99.9%.

[0051] The present invention will be further explained below with reference to specific embodiments.

[0052] Example 1

[0053] The main components of the molten salt chlorination dust collector obtained from a certain sampling are shown in Table 1.

[0054] Table 1. Main components of molten salt chlorination dust collected from a certain sampling.

[0055]

[0056] The molten salt chlorination dust collector residue was leached with water at a liquid-to-solid ratio of 3.5:1, with enhanced stirring during the leaching process. The leaching time was 3 hours, and the scandium leaching rate was approximately 86%, yielding a leachate with a pH of approximately 0.9. The scandium in the leachate was precipitated using the highly oxidizing and alkaline waste brine generated from the molten salt chlorination tail gas purification process. The alkaline solution was mixed with the leachate at a ratio of 1.3:1, and the reaction time was 2 hours. The final pH was controlled at approximately 7 to ensure complete scandium ion precipitation, yielding scandium-rich residue. The scandium in the scandium-rich residue was then leached with 3 mol / L sulfuric acid, with enhanced stirring during the leaching process. The leaching time was 2.5 hours, resulting in near-complete scandium leaching and a leaching rate of less than 25% for other major impurities, yielding a first scandium-rich solution. Finally, a solution was used to completely reduce iron and titanium in the leachate. Iron and titanium in the leaching solution were reduced with 1.1 times the theoretical required amount of reduced iron powder. The temperature of the leaching solution system needed to be controlled at 60℃ during reduction, and scandium was not lost during the reduction process. Scandium in the first scandium-rich solution after reduction was directly extracted using a multi-stage countercurrent cyclone extraction method with a composite extractant TBP (15%), P204 (10%), P229 (5%), and 260# solvent oil (70%) without saponification. Compared to a 1:10 extraction ratio, the scandium extraction rate reached 99%, while the extraction rate of other impurities in the scandium-containing solution was only about 0.1% to 2%. The highly oxidizing and alkaline waste brine generated from the purification of molten salt chlorination tail gas with an alkali concentration adjusted to about 10% was used for multi-stage countercurrent cyclone back-extraction of the first loaded organic phase. Compared to a 1:1 extraction ratio, the scandium back-extraction rate was 99%. A scandium-enriched back-extractant was obtained; the back-extractant was calcined at 800℃ for 4 hours to obtain oxides, which were then finely ground to a particle size of less than 250 mesh. These oxides were then leached with 3 mol / L hydrochloric acid for 2 hours to obtain a scandium-rich solution with low impurity content. The scandium leaching rate in this process was approximately 97%, yielding a second scandium-rich solution. The scandium in the reduced second scandium-rich solution was then directly extracted using a multi-stage countercurrent cyclone extraction process with a composite extractant TBP (15%), P204 (10%), P229 (5%), and 260# solvent oil (70%) without saponification. Compared to a 10:1 ratio, the scandium extraction rate reached 99%, while the extraction rate of other impurities in the scandium-containing solution was only about 0.1% to 0.5%. The solution was further enriched with 1.5... Impurities remaining in the supported organic phase were eluted with a 4 mol / L hydrochloric acid solution of 1 mol / L hydrogen peroxide for 15 min, with 3 elution stages. The scandium loss rate in this process was approximately 0.2%. The supported organic phase was then subjected to multi-stage countercurrent cyclone back-extraction with a 3 mol / L NaOH solution at a 1:1 ratio to obtain scandium hydroxide with an impurity content of <1%. The scandium back-extraction rate in this process was approximately 99%. The scandium hydroxide was then completely dissolved in 2 mol / L hydrochloric acid and precipitated with sodium oxalate to obtain a precipitate. The amount of sodium oxalate added was 1.1 times the theoretical mass required for complete precipitation of scandium ions. The precipitate was centrifuged, filtered, and dehydrated, then calcined at 800℃ for 6 h to finally obtain scandium oxide with a purity of 99.9%.

[0057] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0058] It should be understood that, as used herein, the singular form “a” is intended to include the plural form as well, unless the context clearly supports an exception. It should also be understood that, as used herein, “and / or” refers to any and all possible combinations of one or more of the associated listed items.

[0059] The embodiment numbers disclosed in the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0060] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A process for the extraction of scandium from a fused salt chlorination dust residue, characterised in that, Comprise: S1. Water leaching of the molten salt chlorination dust collection residue to obtain leaching solution, leaching residue, washing water, the leaching residue is recovered as titanium extraction raw material after washing, and the washing water is recycled for leaching of the molten salt chlorination dust collection residue; S2. Precipitation of scandium in the leaching solution with alkali liquor containing strong oxidizing substances to obtain scandium-rich residue and brine, and the brine is recycled; S3. Leaching of scandium in the scandium-rich residue with dilute acid to obtain first scandium-rich liquid and first residue, and reduction of iron and titanium in the first scandium-rich liquid using a reducing agent; S4. Multi-stage countercurrent cyclone extraction of scandium in the first reduced liquid using a composite extractant to obtain first loaded organic phase and first raffinate; S5. Multi-stage countercurrent cyclone stripping of the first loaded organic phase using strong oxidizing and strong alkaline solution to obtain stripped organic phase and solid stripping product, and the stripped organic phase is recycled for extraction through regeneration of the dilute acid; S6. Filtration of the solid stripping product and high-temperature roasting conversion and fine grinding, and then dilute acid leaching to obtain second scandium-rich liquid and second residue; S7. Countercurrent cyclone extraction of scandium in the second scandium-rich liquid using the composite extractant to obtain second loaded organic phase and second raffinate; S8. Elution of residual metal impurities in the second loaded organic phase using acid solution of strong oxidizing substances; S9. Multi-stage countercurrent cyclone stripping of scandium in the second loaded organic phase after elution using alkali liquor to obtain scandium hydroxide with impurity content <1%, and the scandium hydroxide is dissolved in hydrochloric acid, precipitated with oxalic acid, and high-temperature roasted to finally obtain scandium oxide with purity ≥99.9%.

2. The method for extracting scandium from the dust residue of molten salt chlorination according to claim 1, characterized in that, In S1, the scandium content in the molten salt chlorination dust collection residue is 10-150 g / t, the liquid-solid ratio ml:g is (1-15):1 during water leaching, the solution pH should be kept <2 during leaching to avoid hydrolysis of scandium ions into the solid leaching residue, and the pH should be adjusted to <2 when it does not meet the requirements, and the leaching process should be stirred intensively, and the leaching time is 2-5 h to ensure sufficient leaching of scandium, and the water used for washing should also be kept at pH <2 to prevent hydrolysis of scandium ions, and the washing water is returned to the water leaching process, and the leaching residue is washed to <0.05% salt content.

3. The method for extracting scandium from the dust residue of molten salt chlorination according to claim 1, characterized in that, In S2, the alkali liquor is mixed with the leaching solution at a ratio of (1-1.5):1, the reaction time is 1.5-3 h, and the reaction endpoint pH should be controlled at 5-8 to ensure complete precipitation of scandium ions.

4. The method for extracting scandium from the dust residue of molten salt chlorination according to claim 1, characterized in that, In S3, the dilute acid is 1-5 mol / L sulfuric acid and / or 1-5 mol / L hydrochloric acid, and the leaching time is 2-5 h; the reducing agent includes cast iron chips, reduced iron powder, sulfite, GBS, aluminum powder or magnesium powder, and the amount of the reducing agent is 1-1.5 times the theoretical amount required for complete reduction of iron and titanium in the leaching solution, and the reaction temperature during reduction is controlled at 50-90°C.

5. The process for the recovery of scandium from the chlorination dust of molten salts according to claim 1, characterized in that, In S4, the composite extractant comprises, by volume percentage, TBP: 5%-30%, P204: 5%-30%, P229: 0%-10%, and 260# solvent oil: 50%-90%, extraction is performed using an acid-alkali resistant hydrocyclone extractor, the extraction stage number is ≥1, and the volume ratio of the composite extractant to the first liquid rich in scandium during extraction is 1:(1-30).

6. The process for the recovery of scandium from the chlorination dust of molten salts according to claim 1, characterized in that, In S5, the alkali concentration of the strong oxidizing and strong alkaline solution during stripping is controlled to be 5%-15%, and the volume ratio of the first loaded organic phase to the strong oxidizing and strong alkaline solution is 1:(1-10).

7. The process for the recovery of scandium from the chlorination dust of molten salts according to claim 1, characterized in that, In S6, the solid stripping product is subjected to high-temperature calcination conversion at a temperature of 700-900°C, the high-temperature calcination conversion time is 3-6h, the oxide is formed after the high-temperature calcination conversion, the oxide is ground to a particle size range of 250 mesh or less, and then subjected to the dilute acid normal temperature leaching, the dilute acid is 1-5mol / L sulfuric acid and / or 1-5mol / L hydrochloric acid, and the leaching time is 2-5h.

8. The process for the recovery of scandium from the chlorination dust of molten salts according to claim 1, characterized in that, In S7, the composite extractant comprises, by volume percentage, TBP: 5%-30%, P204: 5%-30%, P229: 0%-10%, and 260# solvent oil: 50%-90%, extraction is performed using an acid-alkali resistant hydrocyclone extractor, the extraction stage number is ≥1, and the volume ratio of the composite extractant to the second liquid rich in scandium during extraction is (1-30):

1.

9. The method of claim 1, wherein the method is characterized by, In S8, the acid solution of the strong oxidizing substance comprises an acid liquid and a strong oxidizing agent, the acid liquid is sulfuric acid and / or hydrochloric acid, the acid concentration is 1-5mol / L, the strong oxidizing agent is ozone or hydrogen peroxide, the addition concentration is 1-2mol / L, the elution time is 10-30min, and the elution stage number is ≥1.

10. The process for the recovery of scandium from the chlorination dust of molten salts according to claim 1, characterized in that, In S9, the alkali solution used for stripping is NaOH and / or ammonia water, the concentration is 1.5-3mol / L, the volume ratio of the second loaded organic phase to the alkali solution during stripping is 1:(0.5-2), the stripping equipment is an acid-alkali resistant hydrocyclone extractor, the stripping stage number is ≥1, the stripping product is dissolved in the hydrochloric acid with a concentration of 1-5mol / L, and then precipitated with oxalic acid or sodium oxalate, the addition amount of the oxalic acid or sodium oxalate is 1-1.5 times the theoretical mass required for complete precipitation of scandium ions, the precipitate is subjected to dehydration and transformation by calcination at a high temperature of 600-900°C for 3-6h after centrifugal filtration and dehydration, and finally a scandium oxide product with a purity of ≥99.9% is obtained.

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