Method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid

Abstract

This invention discloses a method for co-extracting scandium from byproducts of molten salt chlorination using waste acid from titanium dioxide production. The method includes: leaching iron-manganese slag, a byproduct of the titanium dioxide process, with sulfuric acid to obtain a leachate; using a composite extractant for multi-stage countercurrent cyclone extraction of scandium from the leachate to obtain a first loaded organic phase; performing multi-stage countercurrent cyclone back-extraction on the first loaded organic phase using a strong oxidizing and strong alkaline solution; after high-temperature conversion and fine grinding, leaching with dilute acid to obtain a scandium-rich solution; using a composite extractant for countercurrent cyclone extraction of scandium from the reduced scandium-rich solution to obtain a second loaded organic phase; eluting residual metal impurities in the second loaded organic phase with a hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid / phosphate mixed solution; eluting with an alkaline solution; and post-treatment to obtain scandium oxide. This method rationally utilizes the large amount of waste acid from the titanium dioxide process, co-extracting scandium with iron-manganese slag, resulting in good environmental benefits and ease of industrialization.

Description

Technical Field

[0001] The invention relates to the technical field of resource recovery, and in particular to a method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization by utilizing titanium dioxide waste acid. Background Art

[0002] At present, the production of titanium dioxide in the titanium dioxide industry is still mainly based on the sulfuric acid method. According to the average calculation that 5 to 8 tons of waste sulfuric acid with a by-product of 20% to 25% w(H2SO4) per ton of titanium dioxide is produced, the amount of waste sulfuric acid in 2020 has reached 25 million tons. Since the waste acid contains about 5% w(Fe), about 0.7% w(Ti) and a small amount of metal ions such as calcium, magnesium, manganese, and scandium, it is difficult to treat. Currently, most of it is mainly neutralized with lime, which not only produces a large amount of titanium gypsum but also has high treatment costs, which seriously restricts the green development of the sulfuric acid method of titanium dioxide.

[0003] Molten salt chlorination waste salt is the waste salt produced by the molten salt chlorination process of titanium-rich materials, which contains a certain amount of valuable element scandium, and scandium basically exists in the form of soluble salt. Molten salt chlorination and boiling chlorination are the two major production methods of titanium tetrachloride. The titanium tetrachloride produced by molten salt chlorination accounts for 40% of the global annual output of titanium tetrachloride. Boiling chlorination has high requirements for the quality of titanium slag raw materials (Ca+Mg<1.0%) and little pollution, while molten salt chlorination has low requirements for raw materials (also suitable for titanium slag raw materials with high calcium and magnesium), but heavy pollution. There is no economical and effective treatment technology for pollutants such as molten salt chlorination slag discharged during the production process at home and abroad, which wastes valuable scandium resources. The Chinese patent application with publication number CN105883911A discloses a comprehensive utilization method of molten salt chlorination waste salt. According to investigations, the scandium in the molten salt chlorination waste salt is basically enriched in the iron-manganese slag mentioned in the invention. The iron-manganese slag is simple in composition and high in scandium content relative to the molten salt chlorination waste salt, and is a high-quality raw material for extracting scandium. However, the prior art does not make efficient use of the ferromanganese slag, resulting in a waste of resources.

[0004] Therefore, there is a need in the prior art for improving the method of using titanium dioxide waste acid to synergistically extract scandium from the by-products of molten salt chlorination comprehensive utilization. Summary of the invention

[0005] In view of this, the purpose of an embodiment of the present invention is to propose a method for synergistically extracting scandium from the by-products of molten salt chlorination comprehensive utilization using titanium dioxide waste acid. The 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 scandium from the by-product iron-manganese slag produced in the comprehensive utilization process of titanium dioxide waste acid and molten salt chlorination waste salt.

[0006] Based on the above purpose, the embodiment of the present invention provides a method for synergistically extracting scandium from the byproducts of molten salt chlorination comprehensive utilization by using titanium dioxide waste acid, comprising the following steps:

[0007] a. Use sulfuric acid titanium dioxide waste acid to leach the by-product iron-manganese slag produced in the comprehensive utilization process of molten salt and chlorinated waste salt to obtain leaching solution and leaching residue, and the leaching residue is washed with titanium dioxide waste acid and recycled for gypsum raw material, and the titanium dioxide waste acid washing water is recycled for leaching;

[0008] b. extracting scandium from the leachate using a composite extractant in a multi-stage countercurrent cyclone to obtain a first loaded organic phase and a first raffinate;

[0009] c. using a strong oxidizing, strong alkaline solution to perform multi-stage countercurrent cyclone stripping on the first loaded organic phase to obtain a stripped organic phase and a solid stripping product, and the stripped organic phase is regenerated and recycled for extraction by dilute acid;

[0010] d. The solid stripping product is subjected to high temperature conversion and fine grinding and then leached by dilute acid to obtain a scandium-rich solution and a second leaching residue, and the iron in the scandium-rich solution is reduced using a reducing agent;

[0011] e. using a composite extractant to extract the scandium-rich solution after reduction by countercurrent cyclone to obtain a second loaded organic phase and a second raffinate;

[0012] f. using a hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid / phosphate mixed solution to elute the metal impurities remaining in the second loaded organic phase;

[0013] g. Use alkaline solution to perform multi-stage countercurrent cyclone stripping on the scandium in the second loaded organic phase after elution to obtain scandium hydroxide with an impurity content of less than 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 more than 99.9%.

[0014] In some embodiments, in step a, the scandium content in the ferromanganese slag is 50-600 g / t, the scandium concentration in the titanium dioxide waste acid is 1-40 mg / L, the sulfuric acid concentration is 15%-25%, the liquid-solid ratio (volume: mass) of the titanium dioxide waste acid and the ferromanganese slag is (1-10):1, the leaching time is 2-5 hours, the stirring is strengthened during the leaching process, and the leaching time is 2-5 hours to ensure that the scandium is fully leached. During washing, the pH of the washing water is less than 2 to prevent the hydrolysis of the scandium ions, and the leached residue is washed until the salt content (mass percentage) is less than 0.05%.

[0015] In some embodiments, in step b, the composite extractant includes, by volume percentage: TBP (5% to 30%), P204 (5% to 30%), cyanex925 (0% to 10%) and 260# solvent oil (50% to 90%), the volume ratio of the composite extractant of the organic phase to the leachate of the aqueous phase during extraction is 1:(1 to 30), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction level is ≥1.

[0016] In some embodiments, in step c, the strongly oxidizing and alkaline solution is a strongly oxidizing and alkaline waste brine produced by molten salt chlorination tail gas purification or a chlor-alkali chemical tail gas absorption waste liquid, the alkali concentration in the strongly oxidizing and alkaline solution is 5% to 15%, and the volume ratio of the first loaded organic phase to the strongly oxidizing and alkaline solution during stripping is 1: (1 to 10), the stripping equipment is an acid and alkali resistant cyclone extractor, and the stripping stage is ≥1.

[0017] In some embodiments, in step d, the scandium content in the solid stripping product is 0.1% to 10%, the solid stripping product is subjected to high-temperature conversion by roasting at 700 to 900°C for 3 to 6 hours, and is converted into oxides after roasting. The roasting product is ground to a particle size range of less than 250 mesh, and then leached with dilute acid, the dilute acid is 1 to 5 mol / L sulfuric acid or 1 to 5 mol / L hydrochloric acid, and the leaching time is 2 to 5 hours.

[0018] In some embodiments, in step e, the composite extractant includes, by volume percentage: TBP (5% to 30%), P204 (5% to 30%), cyanex925 (0% to 10%) and 260# solvent oil (50% to 90%), the volume ratio of the composite extractant of the organic phase to the leachate of the aqueous phase during extraction is 1:(1 to 30), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction level is ≥1.

[0019] In some embodiments, in step f, the metal impurities include titanium, manganese, calcium, zirconium, iron, magnesium, and vanadium. The concentration of sulfuric acid or hydrochloric acid in the hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid / phosphate mixed solution is 1 to 5 mol / L, the concentration of hydrogen peroxide is 1 to 2 mol / L, the amount of phosphoric acid or phosphate added is 1 to 1.5 times the theoretical amount of titanium and zirconium in the organic phase for complete removal, the elution time is 10 to 30 min, and the elution order is ≥1.

[0020] In some embodiments, in step g, the alkali solution is NaOH solution or ammonia water, and the concentration is about 1.5-3 mol / L. The volume ratio of the loaded organic phase and the alkali solution during stripping is 1:(0.5-2). The stripping equipment is an acid-base resistant cyclone extractor, and the stripping stage is ≥1. The stripping product is dissolved in hydrochloric acid to remove silicon-containing impurities, and the hydrochloric acid concentration is 1-5 mol / L. The scandium-containing impurity-removing liquid is then precipitated with oxalic acid or sodium oxalate to precipitate the scandium ions. The amount of oxalic acid or sodium oxalate added is 1-1.5 times the theoretical mass required to completely precipitate the scandium ions. The precipitate is centrifuged and filtered for dehydration and then roasted at 600-900°C for 3-6 hours for dehydration and transformation, and finally a scandium oxide product with a purity of ≥99.9% is obtained.

[0021] The present invention has at least the following beneficial technical effects:

[0022] The invention provides a method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization by utilizing titanium dioxide waste acid, wherein the byproduct is ferromanganese slag, the scandium content in the ferromanganese slag is 50-600 g / t, and the scandium concentration in the titanium dioxide waste acid is 1-40 mg / L. The method of the invention rationally utilizes a large amount of waste acid in the titanium dioxide process and synergistically extracts scandium with the ferromanganese slag. The method is easy to operate, has a simple process flow, low production cost, good environmental benefits, is easy to realize industrialization, and can efficiently recover scandium from the byproduct ferromanganese slag generated in the comprehensive utilization process of titanium dioxide waste acid by sulfuric acid method and molten salt chlorination waste salt. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of an embodiment of a method for synergistically extracting scandium from by-products of molten salt chlorination comprehensive utilization using waste titanium dioxide acid provided by the present invention. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0026] The terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions; the terms "first", "second", etc. in the specification and claims of the present invention or the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0027] In addition, reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0028] like Figure 1 The schematic diagram of an embodiment of a method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid provided by the present invention is shown. The method of the present invention comprises the following steps:

[0029] a. Use sulfuric acid titanium dioxide waste acid to leach the by-product iron-manganese slag produced in the comprehensive utilization process of molten salt and chlorinated waste salt to obtain leaching solution and leaching residue, and the leaching residue is washed with titanium dioxide waste acid and recycled for gypsum raw material, and the titanium dioxide waste acid washing water is recycled for leaching;

[0030] b. extracting scandium from the leachate using a composite extractant in a multi-stage countercurrent cyclone to obtain a first loaded organic phase and a first raffinate;

[0031] c. using a strong oxidizing, strong alkaline solution to perform multi-stage countercurrent cyclone stripping on the first loaded organic phase to obtain a stripped organic phase and a solid stripping product, and the stripped organic phase is regenerated and recycled for extraction by dilute acid;

[0032] d. The solid stripping product is subjected to high temperature conversion and fine grinding and then leached by dilute acid to obtain a scandium-rich solution and a second leaching residue, and the iron in the scandium-rich solution is reduced using a reducing agent;

[0033] e. using a composite extractant to extract the scandium-rich solution after reduction by countercurrent cyclone to obtain a second loaded organic phase and a second raffinate;

[0034] f. using a hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid / phosphate mixed solution to elute the metal impurities remaining in the second loaded organic phase;

[0035] g. Use alkaline solution to perform multi-stage countercurrent cyclone stripping on the scandium in the second loaded organic phase after elution to obtain scandium hydroxide with an impurity content of less than 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 more than 99.9%.

[0036] Furthermore, in step a, the scandium content in the by-product of molten salt chlorination comprehensive utilization is 50-600 g / t, mainly in the form of hydroxide, the scandium concentration in titanium dioxide waste acid is 1-40 mg / L, the sulfuric acid concentration is 15%-25%, the liquid-solid ratio (volume: mass) is (1-10): 1, the leaching time is 2-5 hours, the stirring is strengthened during the leaching process, and the leaching time is 2-5 hours to ensure that the scandium is fully leached. The water used for washing also needs to maintain a pH value of less than 2 to prevent the hydrolysis of the scandium ions. The washing water can be returned to the water leaching process, and the leaching residue is washed until the salt content (mass percentage) is less than 0.05%. The leaching residue after washing can be recovered as gypsum slag, and the acidic washing water can be used as a raw material for configuring a leaching agent for the iron-manganese slag, a by-product generated in the next leaching of the molten salt chlorination waste salt comprehensive utilization process.

[0037] Furthermore, in step b, the composite extractant includes the following components in volume percentage: TBP (5% to 30%) + P204 (5% to 30%) + P229 (0% to 10%) + 260# solvent oil (50% to 90%). The composite extractant of the organic phase does not need to be saponified before extraction. The increase in acidity during the extraction process has little effect on the extraction of scandium ions but is beneficial to inhibiting the extraction of other ions. During extraction, the volume ratio of the organic phase composite extractant and the leaching solution after the aqueous phase reduction is 1: (1 to 30). The extraction equipment is an acid-base resistant cyclone extractor. The model and operating parameters of the cyclone extractor can be adjusted according to the feed liquid conditions, and the extraction level is ≥1.

[0038] Furthermore, in step c, the solution with strong oxidizing and strong alkalinity can be the strong oxidizing and alkaline waste brine produced by molten salt chlorination tail gas purification or the chlor-alkali chemical tail gas absorption waste liquid. In order to ensure that the alkali concentration in the strong oxidizing and strong alkaline solution is 5% to 15%, caustic soda can be appropriately added thereto. During stripping, the volume ratio of the loaded organic phase to the strong oxidizing and strong alkaline solution is 1: (1 to 10). The stripping equipment is an acid and alkali resistant cyclone extractor. The model and operating parameters of the cyclone extractor can be adjusted according to the feed liquid conditions, and the stripping stage is ≥1.

[0039] Further, in step d, the solid stripping product enriched with scandium is mainly hydroxides or oxides of elements such as iron, manganese, titanium, magnesium, zirconium, calcium, aluminum, and scandium, and the scandium content thereof is 0.1% to 5%. The acid used to leach scandium can be sulfuric acid (concentration 1 to 10 mol / L) or hydrochloric acid (concentration 1 to 6 mol / L), the liquid-solid ratio (volume: mass) is (1 to 5): 1, the leaching time is 0.5 to 2 hours, and a scandium-rich solution and a leaching residue are obtained. The iron in the leaching solution is reduced by a reducing agent, the reducing agent includes iron filings, reduced iron powder, sulfite, GBS, aluminum powder or magnesium powder, and the amount of the reducing agent is 1 to 1.2 times the theoretical requirement for completely reducing the iron in the leaching solution. During the reduction, the temperature of the leaching solution system needs to be controlled at 50 to 90°C.

[0040] Furthermore, in step e, the composite extractant includes the following components in volume percentage: TBP (5% to 30%) + P204 (5% to 30%) + cyanex923 (0% to 10%) + 260# solvent oil (50% to 90%). The composite extractant of the organic phase does not need to be saponified before extraction. The increase in acidity during the extraction process has little effect on the extraction of scandium ions but is beneficial to inhibiting the extraction of other ions. During extraction, the volume ratio of the organic phase composite extractant and the leaching solution after the aqueous phase reduction is 1: (1 to 30). The extraction equipment is an acid-base resistant cyclone extractor. The model and operating parameters of the cyclone extractor can be adjusted according to the feed liquid conditions, and the extraction level is ≥1.

[0041] Furthermore, in step f, a hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid / phosphate mixed solution is used to elute impurities such as titanium, manganese, calcium, zirconium, iron, magnesium, and vanadium in the loaded organic phase, the concentration of sulfuric acid or hydrochloric acid is 1 to 5 mol / L, the concentration of hydrogen peroxide is 1 to 2 mol / L, the amount of phosphoric acid or phosphate added is 1 to 1.5 times the theoretical amount required to completely remove titanium and zirconium in the organic phase, the elution time is 10 to 30 min, and the elution order is ≥1.

[0042] Furthermore, in step g, the alkali solution used for stripping can be NaOH or ammonia water with a concentration of about 1.5 to 3 mol / L. The volume ratio of the loaded organic phase and the alkali solution during stripping is 1:(0.5 to 2). The stripping equipment is an acid-base resistant cyclone extractor (which is beneficial to the separation of the stripping product). The model and operating parameters of the cyclone extractor can be adjusted according to the feed liquid conditions, and the stripping stage is ≥1. The stripping product is post-treated to obtain a scandium oxide product, and the post-treatment includes hydrochloric acid dissolution, oxalic acid precipitation, and high-temperature roasting. Specifically, the stripping product is dissolved in hydrochloric acid with a hydrochloric acid concentration of 1 to 5 mol / L. The hydrochloric acid dissolution process can remove silicon-containing impurities, and the scandium-containing impurity removal liquid is then used to precipitate scandium ions with oxalic acid or sodium oxalate. The amount of oxalic acid and sodium oxalate added is 1 to 1.5 times the theoretical mass required for complete precipitation of scandium ions. The precipitate is centrifugally filtered and dehydrated, and then roasted at 600 to 900° C. for 3 to 6 hours for dehydration and transformation, and finally a scandium oxide product with a purity of ≥99.9% is obtained.

[0043] The following uses the titanium dioxide waste acid and molten salt chlorination comprehensive utilization by-products obtained from a certain sampling as an example to specifically illustrate the method for synergistically extracting scandium from the molten salt chlorination comprehensive utilization by-products using titanium dioxide waste acid disclosed in an embodiment of the present invention.

[0044] Example 1

[0045] The main components of the by-products of the comprehensive utilization of titanium dioxide waste acid and molten salt chlorination obtained by sampling are shown in Tables 1 and 2.

[0046] Table 1 Main components of titanium dioxide waste acid obtained by sampling

[0047]

[0048] Table 2 Main components of by-products obtained by sampling molten salt chlorination comprehensive utilization

[0049]

[0050] The by-product iron-manganese slag was leached with sulfuric acid titanium dioxide waste acid at a liquid-solid ratio of 3:1 to obtain a leachate. The stirring was strengthened during the leaching process. The leaching time was 3 hours. The leaching rate of scandium was about 90%, and the leaching rate of other major impurity elements was less than 25%. The composite extractant TBP (5%), P204 (20%), cyanex925 (5%) and 260# solvent oil (70%) were used to directly extract the scandium in the leachate under non-saponification conditions by multi-stage countercurrent cyclone to obtain the first loaded organic phase. Compared with 1:10, the extraction rate of scandium reached 99.5%, and the extraction rates of other impurities in the scandium-containing solution were about 0.1% to 4%; the strong oxidizing agent produced by the molten salt chlorination tail gas purification with an alkali concentration of 8% , the first loaded organic phase is subjected to multi-stage countercurrent cyclone stripping with alkaline waste brine, with a ratio of 1:1 and a scandium stripping rate of 99%, thereby obtaining a stripping product enriched in scandium; the stripping product is subjected to high-temperature conversion by roasting at 850°C for 3 hours, and an oxide is obtained after roasting, which is finely ground to a particle size range below 300 mesh, and then leached with 3 mol / L sulfuric acid for 3 hours to obtain a scandium-rich solution, in which the scandium leaching rate is about 96%, and the leaching rates of the main impurity elements titanium, manganese, zirconium, and iron are less than 1%, 1%, 0.5%, and 3%, respectively; 1.1 times the theoretical amount of reduced iron powder required to completely reduce the trivalent iron therein is added to the scandium-rich solution, the temperature of the reduction process is controlled at 60°C, the trivalent iron is completely reduced, and after filtration A scandium-containing solution was obtained, and scandium was basically not lost in the process; the composite extractant TBP (15%), P204 (10%), cyanex925 (5%) and 260# solvent oil (70%) were used to directly countercurrent cyclone extract the scandium in the reduced scandium-rich solution under unsaponified conditions to obtain a second loaded organic phase, and the extraction rate of the scandium was 99% compared with 10:1, and the extraction rate of the remaining impurities in the scandium-containing solution was only about 0.1% to 1%; a hydrogen peroxide-hydrochloric acid-phosphoric acid mixed solution was used to elute the metal impurities remaining in the second loaded organic phase, and the hydrochloric acid concentration was 4 mol / L, the hydrogen peroxide concentration was 1.3 mol / L, and the amount of phosphoric acid added was to completely remove the titanium and The method is as follows: the elution time is 15 minutes, the elution stage is 3, the ratio is 2:1, and the loss rate of scandium in this process is about 0.3%; the loaded organic phase after elution is subjected to multi-stage countercurrent cyclone stripping with a 3 mol / L ammonia aqueous solution, the ratio is 1:1, and a scandium hydroxide with an impurity content of less than 0.3% is obtained, and the stripping rate of scandium in this process is about 99%; the scandium hydroxide is completely dissolved in 1 mol / L hydrochloric acid and precipitated with oxalic acid to obtain a precipitate, the amount of oxalic acid added is 1.05 times the theoretical mass required for completely precipitating the scandium ions, the precipitate is centrifuged and dehydrated, and then calcined at 850°C for 5 hours, and finally scandium oxide with a purity of 99.95% is obtained.

[0051] The above are exemplary embodiments disclosed in the present invention, but it should be noted that various changes and modifications may be made without departing from the scope disclosed in the embodiments of the present invention as defined in the claims. The functions, steps and / or actions of the method claims according to the disclosed embodiments described herein do not need to be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless explicitly limited to the singular.

[0052] It should be understood that, as used herein, the singular forms "a", "an" are intended to include the plural forms 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 including one or more of the associated listed items.

[0053] The serial numbers of the embodiments disclosed in the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0054] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid, characterized in that: The following steps are involved: a. using sulfuric acid titanium dioxide waste acid to leach the by-product iron-manganese slag produced in the comprehensive utilization process of molten salt chlorination waste salt to obtain a leachate and a leaching residue, wherein the leaching residue is washed with the titanium dioxide waste acid and then recycled for gypsum raw material, and the titanium dioxide waste acid washing water is recycled for leaching, and the scandium content in the iron-manganese slag is 50-600 g / t; b. extracting the scandium in the leachate using a composite extractant in a multi-stage countercurrent cyclone to obtain a first loaded organic phase and a first raffinate; c. using a strong oxidizing, alkaline solution to carry out multi-stage countercurrent cyclone stripping of the first loaded organic phase to obtain a stripping organic phase and a solid stripping product, wherein the stripping organic phase is regenerated by dilute acid and recycled for extraction; d. converting the solid stripping product at high temperature and grinding it to obtain a scandium-rich solution and a second leaching residue by dilute acid, and reducing the iron in the scandium-rich solution using a reducing agent; e. using a composite extractant to extract the scandium-rich solution after reduction by countercurrent cyclone to obtain a second organic phase and a second raffinate; f. using hydrogen peroxide + sulfuric acid or hydrochloric acid + phosphoric acid / phosphate mixed solution to elute the metal impurities remaining in the second loaded organic phase; g. The scandium in the second loaded organic phase after elution is subjected to multi-stage countercurrent cyclone stripping 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%.

2. The method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid according to claim 1, characterized in that: In step a, the scandium concentration in the titanium dioxide waste acid is 1-40 mg / L, the sulfuric acid concentration is 15%-25%, the liquid-solid ratio of the titanium dioxide waste acid to the ferromanganese slag is (1-10):1, the leaching time is 2-5 hours, the stirring is strengthened during the leaching process, and the leaching time is 2-5 hours to ensure that the scandium is fully leached. During washing, the pH of the washing water is less than 2 to prevent the hydrolysis of the scandium ions, and the leached residue is washed until the salt content (mass percentage) is less than 0.05%.

3. The method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid according to claim 1, characterized in that: In step b, the composite extractant includes, by volume percentage: TBP: 5%~30%, P204: 5%~30%, cyanex925: 0%~10% and 260# solvent oil: 50%~90%. During extraction, the volume ratio of the composite extractant of the organic phase to the leaching liquid of the aqueous phase is 1:(1~30), the extraction equipment is an acid-base resistant cyclone extractor, and the extraction level is ≥1.

4. The method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid according to claim 1, characterized in that: In step c, the highly oxidizing and alkaline solution is the highly oxidizing and alkaline waste brine produced by molten salt chlorination tail gas purification or the chlor-alkali chemical tail gas absorption waste liquid, the alkali concentration in the highly oxidizing and alkaline solution is 5%~15%, and the volume ratio of the first loaded organic phase to the highly oxidizing and alkaline solution during stripping is 1: (1~10), the stripping equipment is an acid and alkali resistant cyclone extractor, and the stripping stage is ≥1.

5. The method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid according to claim 1, characterized in that: In step d, the scandium content in the solid stripping product is 0.1% to 10%, and the solid stripping product is calcined at 700 to 900° C. for high-temperature conversion, and the calcination time is 3 to 6 hours. After calcination, it is converted into oxides, and the calcined product is ground to a particle size range of less than 250 mesh, and then leached with dilute acid, and the dilute acid is 1 to 5 mol / L sulfuric acid or 1 to 5 mol / L hydrochloric acid, and the leaching time is 2 to 5 hours.

6. The method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid according to claim 1, characterized in that: In step e, the composite extractant includes, by volume percentage: TBP: 5%~30%, P204: 5%~30%, cyanex925: 0%~10% and 260# solvent oil: 50%~90%. During extraction, the volume ratio of the composite extractant of the organic phase to the leaching solution of the aqueous phase is 1:(1~30), the extraction equipment is an acid-base resistant cyclone extractor, and the extraction level is ≥1.

7. The method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid according to claim 1, characterized in that: In step f, the metal impurities include titanium, manganese, calcium, zirconium, iron, magnesium, and vanadium. The concentration of sulfuric acid or hydrochloric acid in the hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid / phosphate mixed solution is 1-5 mol / L, the concentration of hydrogen peroxide is 1-2 mol / L, the amount of phosphoric acid or phosphate added is 1-1.5 times the theoretical amount of titanium and zirconium in the organic phase for complete removal, the elution time is 10-30 min, and the elution order is ≥1.

8. The method for synergistically extracting scandium from byproducts of molten salt chlorination comprehensive utilization using titanium dioxide waste acid according to claim 1, characterized in that: In step g, the alkali solution is a NaOH solution or an ammonia solution with a concentration of 1.5-3 mol / L. During stripping, the volume ratio of the loaded organic phase to the alkali solution is 1:(0.5-2). The stripping equipment is an acid-base resistant cyclone extractor with a stripping stage of ≥1. The stripping product is dissolved in hydrochloric acid to remove silicon-containing impurities with a hydrochloric acid concentration of 1-5 mol / L. The scandium-containing impurity-removing liquid is then precipitated with oxalic acid or sodium oxalate to precipitate scandium ions. The amount of oxalic acid or sodium oxalate added is 1-1.5 times the theoretical mass required for complete precipitation of scandium ions. The precipitate is centrifugally filtered and dehydrated, and then roasted at 600-900°C for 3-6 hours for dehydration and transformation, and finally a scandium oxide product with a purity of ≥99.9% is obtained.

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