Method for Coextracting Scandium from Titanium White Waste Acid and Molten Salt Chlorination Waste Salt

Abstract

The present invention discloses a method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt, which comprises the following steps: leaching the molten salt chlorination waste salt with titanium white waste acid to obtain a leaching solution; adding phosphoric acid or phosphate to the leaching solution for preliminary removal of impurities such as zirconium and titanium, then adding a reducing agent, and filtering to obtain a scandium-containing solution; extracting the scandium-containing solution with a first composite extractant to obtain a first loaded organic phase; eluting the residual impurities in the first loaded organic phase with a mixed solution of hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid to obtain a second loaded organic phase; stripping the scandium in the second loaded organic phase with a first lye to obtain a stripping product; subjecting the stripping product to high-temperature conversion and fine grinding, and then leaching with a first dilute acid for impurity removal to obtain a scandium-rich solution; extracting the scandium-rich solution with a second composite extractant to obtain a second loaded organic phase, and then washing the second loaded organic phase with a second dilute acid to obtain a third loaded organic phase; stripping the third loaded organic phase with a second lye to obtain scandium hydroxide with an impurity content <1%.

Description

Technical Field

[0001] The present invention relates to the field of comprehensive utilization of industrial waste liquid and waste residue, and particularly to a method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt. Background Art

[0002] Scandium is a rare earth element and a strategic resource. However, more than 75% of scandium is associated with other minerals. The complex production process, low recovery rate, and high cost of scandium result in insufficient international supply and high prices of scandium products. It is known as one of the most expensive metals in the world. Domestic scandium ore resources are mainly distributed in bauxite, phosphorite (including weathered leached phosphorite deposits), vanadium-titanium magnetite, tungsten ore, rare earth ore and other minerals.

[0003] At present, the main raw materials for extracting scandium come from secondary resources such as waste liquid or solid waste generated in the process of comprehensive utilization of its associated minerals. Existing secondary resources that can be used as raw materials for extracting scandium include by-products of uranium ore, tungsten ore and tungsten ore slag, hydrolysis acidic waste liquid generated in the production of titanium dioxide by sulfuric acid method, chlorination fumes generated in fluidized bed chlorination for titanium extraction, titanium-containing blast furnace slag, red mud, ion-adsorbed rare earth ore, Bayan Obo tailings, etc. For different scandium-containing raw materials, their physical and chemical properties are different, especially the chemical composition and the solubility in different leaching agents vary greatly. Therefore, the scandium extraction processes involved are different.

[0004] Waste salt is generated in the process of molten salt chlorination for titanium extraction from titanium-rich materials. The molten salt chlorination waste salt contains a certain amount of valuable element scandium, and scandium basically exists in the form of soluble salts. Molten salt chlorination and fluidized bed chlorination are 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. Fluidized bed chlorination has high requirements for the quality of titanium slag raw materials (Ca + Mg < 1.0%), and less pollution, while molten salt chlorination has low requirements for raw materials but heavy pollution. There is no economically effective treatment technology for pollutants such as molten salt chlorination slag discharged during the production process at home and abroad, and they are all treated by mixing with lime and piling in the wasteland or landfilling in a professional slag yard, which wastes valuable scandium resources.

[0005] Therefore, a method for effectively using molten salt chlorination waste salt to extract scandium is needed. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt, which can solve the problems of resource waste and environmental pollution caused by direct disposal of existing molten salt chlorination waste salt.

[0007] An embodiment of the present invention discloses a method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt, including the following steps:

[0008] Leach the molten salt chlorination waste salt with titanium white waste acid at a predetermined liquid-solid ratio to obtain a leachate and a leach residue;

[0009] Phosphoric acid or phosphate is added to the leaching solution to preliminarily remove impurities such as zirconium and titanium, and then a reducing agent is added to reduce ferric iron in the leaching solution. After filtration, a scandium-containing solution is obtained;

[0010] Scandium in the scandium-containing solution is extracted by multi-stage countercurrent cyclone extraction with a first composite extractant at a first predetermined phase ratio to obtain a first loaded organic phase;

[0011] The first loaded organic phase is eluted with a mixed solution of hydrogen peroxide - sulfuric acid / hydrochloric acid - phosphoric acid at a predetermined concentration to remove residual impurities such as titanium, manganese, calcium, zirconium, iron, magnesium, and vanadium, and a second loaded organic phase is obtained;

[0012] Scandium in the second loaded organic phase is subjected to multi-stage countercurrent cyclone stripping with a first lye to obtain a scandium-enriched stripping product and a stripped organic phase;

[0013] The stripping product is subjected to high-temperature conversion and fine grinding, and then leached with a first dilute acid to remove impurities to obtain a scandium-rich solution;

[0014] Scandium in the scandium-rich solution is extracted by countercurrent cyclone extraction with a second composite extractant at a second predetermined phase ratio to obtain a second loaded organic phase, and then the second loaded organic phase is washed with a second dilute acid to obtain a third loaded organic phase;

[0015] Scandium in the third loaded organic phase is subjected to multi-stage countercurrent cyclone stripping with a second lye to obtain scandium hydroxide with an impurity content < 1%;

[0016] According to an embodiment of the present invention, one or more of the following steps are further included:

[0017] The leaching residue is washed with acidic wash water with pH < 2 until the salt content (mass percentage) < 0.05%. The washed leaching residue can be further used for titanium recovery, and the wash water is recycled until a certain extent and then collected as a raw material for scandium extraction;

[0018] The stripped organic phase is regenerated with dilute acid and reused for scandium extraction;

[0019] The scandium hydroxide is successively dissolved in hydrochloric acid with a concentration of 1 - 5 mol / L, precipitated with oxalic acid or sodium oxalate. The addition amount of oxalic acid or sodium oxalate is 1 - 1.5 times the theoretical mass required to completely precipitate scandium ions. The precipitate is centrifuged, filtered, dehydrated, and calcined at 600 - 900 °C for 3 - 6 h, and finally scandium oxide with a purity ≥ 99.9% is obtained.

[0020] According to an embodiment of the present invention, the scandium content in the molten salt chlorination waste salt is 20 - 200 g / t, the scandium concentration in the titanium white waste acid is 1 - 40 mg / L, the sulfuric acid concentration in the titanium white waste acid is 15% - 25%, the predetermined liquid-solid ratio is the volume ratio of the titanium white waste acid to the mass of the molten salt chlorination waste salt is (1 - 10):1, stirring is strengthened during the leaching process, and the leaching time is 2 - 5 h.

[0021] According to an embodiment of the present invention, the total addition amount of the phosphoric acid or phosphate is 1 - 1.2 times the theoretical amount required to completely precipitate zirconium and titanium ions; the dosage of the reducing agent is 1 - 1.2 times the theoretical demand required to completely reduce ferric ions in the leaching solution, and the temperature of the leaching solution system is controlled at 50 - 90 °C during reduction.

[0022] According to an embodiment of the present invention, the first composite extractant includes the following components by volume percentage: tributyl phosphate TBP (5% - 30%) + bis(2-ethylhexyl) phosphate P204 (5% - 30%) + cyanex272 (0% - 15%) + 260# solvent oil (50% - 90%); the first predetermined phase ratio is the volume ratio of the first composite extractant to the water-phase reduced leaching solution is 1:(1 - 30); the first composite extractant is not saponified before extraction; the extraction equipment is an acid-alkali resistant cyclone extractor, and the number of extraction stages ≥ 1.

[0023] According to an embodiment of the present invention, in the mixed solution of hydrogen peroxide - sulfuric acid / hydrochloric acid - phosphoric acid: the concentration of sulfuric acid or hydrochloric acid is 1 - 5 mol / L, the concentration of hydrogen peroxide is 1 - 2 mol / L, the addition amount of phosphoric acid is 1 - 1.3 times the theoretical amount required to completely remove titanium and zirconium in the first loaded organic phase; the elution time is 10 - 30 min, and the number of elution stages ≥ 1.

[0024] According to an embodiment of the present invention, the first lye is NaOH or ammonia water, the concentration of the first lye is 1.5 - 3 mol / L, and the volume ratio of the second loaded organic phase to the first lye is 1:(0.5 - 2); the back-extraction equipment is an acid-alkali resistant cyclone extractor, and the number of back-extraction stages ≥ 1.

[0025] According to an embodiment of the present invention, the back-extracted product includes scandium hydroxide and hydroxides of a small amount of impurity elements, wherein the scandium content is 0.1% - 30%, the back-extracted product is subjected to high-temperature conversion by roasting at 700 - 900 °C, the roasting time is 3 - 6 h, oxides are obtained after roasting, the oxides are finely ground to a particle size range of less than 250 mesh, and then leached with the first dilute acid. The first dilute acid can be sulfuric acid with a concentration of 1 - 5 mol / L or hydrochloric acid with a concentration of 1 - 5 mol / L, and the leaching time is 2 - 5 h.

[0026] According to an embodiment of the present invention, the second composite extractant comprises the following components by volume percentage: tributyl phosphate TBP (5% - 30%) + bis(2-ethylhexyl)phosphoric acid P204 (5% - 30%) + cyanex272 (0% - 15%) + solvent oil 260# (50% - 90%). The second predetermined phase ratio is the volume ratio of the second composite extractant to the reduced leaching solution of the aqueous phase, which is (1 - 30):1. Before extraction, the second composite extractant is not saponified. The second dilute acid is sulfuric acid with a concentration of 1 - 2 mol / L or hydrochloric acid with a concentration of 1 - 2 mol / L, and the number of washing stages is ≥1. The extraction equipment is an acid and alkali resistant cyclone extractor, and the number of extraction stages is ≥1.

[0027] According to an embodiment of the present invention, the second lye is NaOH or ammonia water, the concentration of the second lye is 1.5 - 3 mol / L, and the volume ratio of the third loaded organic phase to the second lye during back-extraction is 1:(0.5 - 2). The back-extraction equipment is an acid and alkali resistant cyclone extractor, and the number of back-extraction stages is ≥1.

[0028] Adopting the above technical solutions, the present invention has at least the following beneficial effects:

[0029] The method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt provided by the present invention makes full use of sulfuric acid in the titanium white waste acid to leach soluble scandium salts in the molten salt chlorination waste salt. While utilizing the waste acid in the titanium white waste acid, it realizes the comprehensive extraction of scandium in the titanium white waste acid and scandium in the molten salt chlorination waste salt, improves the content of scandium in the leaching solution, thereby improving the recovery rate of scandium. At the same time, the method provided by the present invention solves the problems of resource waste and environmental pollution caused by the direct disposal of molten salt chlorination waste salt, achieving the purpose of treating waste with waste and having good environmental protection benefits. On the other hand, due to the impurities contained in the titanium white waste acid and molten salt chlorination waste salt, the present invention effectively removes impurities from the leaching solution to maximize the effective separation of scandium and various impurities, and finally scandium oxide with a purity of ≥99.9% can be obtained. Moreover, the method provided by the present invention has the advantages of convenient operation, simple process flow and low production cost, which is conducive to realizing industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is a process flow diagram of the method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt disclosed in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further elaborates on the embodiments of the present invention in detail in conjunction with specific embodiments and with reference to the accompanying drawings.

[0033] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two entities or parameters with the same name but different identities. It can be seen that "first" and "second" are only for the convenience of expression and should not be construed as a limitation on the embodiments of the present invention. This will not be elaborated one by one in the subsequent embodiments.

[0034] As shown in the figure, an embodiment of the present invention discloses a method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt, which includes the following steps:

[0035] Leach the molten salt chlorination waste salt with titanium white waste acid at a predetermined liquid-solid ratio to obtain a leachate and a leach residue.

[0036] Add phosphoric acid or phosphate to the leachate to preliminarily remove impurities such as zirconium and titanium, and then add a reducing agent to reduce ferric iron in the leachate. After filtration, a scandium-containing solution is obtained.

[0037] Extract scandium from the scandium-containing solution by multi-stage countercurrent swirl extraction with a first composite extractant at a first predetermined phase ratio to obtain a first loaded organic phase.

[0038] Elute residual impurities such as titanium, manganese, calcium, zirconium, iron, magnesium, and vanadium in the first loaded organic phase with a mixed solution of hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid at a predetermined concentration to obtain a second loaded organic phase.

[0039] Perform multi-stage countercurrent swirl stripping on the scandium in the second loaded organic phase with a first lye to obtain a scandium-enriched stripping product and a stripped organic phase.

[0040] The stripping product is subjected to high-temperature conversion and fine grinding, and then leached with a first dilute acid to remove impurities to obtain a scandium-rich solution.

[0041] Extract scandium from the scandium-rich solution by countercurrent swirl extraction with a second composite extractant at a second predetermined phase ratio to obtain a second loaded organic phase, and then wash the second loaded organic phase with a second dilute acid to obtain a third loaded organic phase.

[0042] Perform multi-stage countercurrent swirl stripping on the scandium in the third loaded organic phase with a second lye to obtain scandium hydroxide with an impurity content <1%.

[0043] Scandium in the waste salt from molten salt chlorination is leached with waste acid from titanium dioxide production. On the one hand, both the waste acid from titanium dioxide production and the waste salt from molten salt chlorination contain scandium. The combined use of the two can increase the content of scandium in the leaching solution. For the waste salt from molten salt chlorination, compared with leaching with an acid without scandium, the content of scandium in the leaching solution is increased. On the other hand, sulfuric acid in the waste acid from titanium dioxide production can leach scandium from the scandium-containing minerals in the waste salt from molten salt chlorination, which is beneficial to cost savings.

[0044] In some embodiments, the method for co-extracting scandium from waste acid from titanium dioxide production and waste salt from molten salt chlorination further includes: washing the leaching residue with acidic wash water with pH < 2 until the salt content (mass percentage) < 0.05%. The washed leaching residue can be further used for titanium recovery. The wash water is recycled and collected as a raw material for scandium extraction after being used to a certain extent. The organic phase after back-extraction is regenerated with dilute acid and then used for scandium extraction again. Treating the wash water and the organic phase after back-extraction and using them again for scandium extraction is beneficial to greatly improve the recovery rate of scandium. Among them, washing the leaching residue with acidic wash water with pH < 2 can prevent the hydrolysis of scandium ions.

[0045] In some embodiments, the method for co-extracting scandium from waste acid from titanium dioxide production and waste salt from molten salt chlorination further includes: dissolving scandium hydroxide in hydrochloric acid with a concentration of 1 - 5 mol / L, and then precipitating with oxalic acid or sodium oxalate. The addition amount of oxalic acid or sodium oxalate is 1 - 1.5 times the theoretical mass required to completely precipitate scandium ions. The precipitate is centrifuged, filtered, dehydrated, and then calcined at 600 - 900 °C for 3 - 6 h to finally obtain scandium oxide with a purity ≥ 99.9%. In this embodiment, the hydrochloric acid dissolution process can remove silicon-containing impurities, and the scandium-containing impurity-removing solution is then used to precipitate scandium ions with oxalic acid or sodium oxalate.

[0046] In some embodiments, the scandium content in the waste salt from molten salt chlorination is 20 - 200 g / t, the scandium concentration in the waste acid from titanium dioxide production is 1 - 40 mg / L, the sulfuric acid concentration in the waste acid from titanium dioxide production is 15% - 25%, the predetermined liquid-solid ratio is the volume ratio of the waste acid from titanium dioxide production to the mass of the waste salt from molten salt chlorination, which is (1 - 10):1. Stirring is strengthened during the leaching process, and the leaching time is 2 - 5 h.

[0047] In some embodiments, the total addition amount of phosphoric acid or phosphate is 1 - 1.2 times the theoretical amount required to completely precipitate zirconium and titanium ions; the dosage of the reducing agent is 1 - 1.2 times the theoretical demand required to completely reduce ferric iron in the leaching solution. The temperature of the leaching solution system during reduction is controlled at 50 - 90 °C. In this embodiment, the reducing agent is a common reducing agent that can reduce ferric ions and does not introduce impurities that are difficult to remove.

[0048] In some embodiments, the first composite extractant comprises components with the following volume percentages: tributyl phosphate TBP (5% - 30%) + bis(2-ethylhexyl) phosphate P204 (5% - 30%) + cyanex272 (0% - 15%) + solvent oil 260# (50% - 90%); the first predetermined phase ratio is the volume ratio of the first composite extractant to the water-phase reduced leachate, which is 1:(1 - 30); the first composite extractant is not saponified before extraction, which is beneficial to simplifying the process flow and improving efficiency; the extraction equipment is an acid- and alkali-resistant cyclone extractor, and the number of extraction stages is ≥1. The acid- and alkali-resistant cyclone extractor is beneficial to the separation of stripping products. The model and operating parameters of the acid- and alkali-resistant cyclone extractor can be adjusted according to the material solution situation. In some other embodiments, increasing the acidity of the reduced leachate to be extracted during the extraction process has basically no effect on the extraction of scandium ions but is beneficial to inhibiting the extraction of other ions.

[0049] In some embodiments, in the mixed solution of hydrogen peroxide - sulfuric acid / hydrochloric acid - phosphoric acid: the concentration of sulfuric acid or hydrochloric acid is 1 - 5 mol / L, the concentration of hydrogen peroxide is 1 - 2 mol / L, and the addition amount of phosphoric acid is 1 - 1.3 times the theoretical amount required to completely remove titanium and zirconium in the first loaded organic phase; the elution time is 10 - 30 min, and the number of elution stages is ≥1.

[0050] In some embodiments, the first lye is NaOH or ammonia water, the concentration of the first lye is 1.5 - 3 mol / L, and the volume ratio of the second loaded organic phase to the first lye is 1:(0.5 - 2); the stripping equipment is an acid- and alkali-resistant cyclone extractor, and the number of stripping stages is ≥1. The acid- and alkali-resistant cyclone extractor is beneficial to the separation of stripping products. The model and operating parameters of the acid- and alkali-resistant cyclone extractor can be adjusted according to the material solution situation.

[0051] In some embodiments, the stripping product includes scandium hydroxide and hydroxides of a small amount of impurity elements, where the content of scandium is 0.1% - 30%. The stripping product is roasted at 700 - 900 °C for high-temperature conversion, and the roasting time is 3 - 6 h. After roasting, an oxide is obtained. The oxide is finely ground to a particle size range below 250 mesh, and then leached with a first dilute acid. The first dilute acid can be sulfuric acid with a concentration of 1 - 5 mol / L or hydrochloric acid with a concentration of 1 - 5 mol / L, and the leaching time is 2 - 5 h. In this embodiment, the purpose of roasting the stripping product is to convert compounds of elements such as iron, manganese, titanium, zirconium, and silicon into oxides that are insoluble or slightly soluble or dissolve slowly in dilute acid at normal temperature, so as to facilitate the separation of scandium from impurities during subsequent leaching of scandium with dilute acid at normal temperature.

[0052] In some embodiments, the second composite extractant comprises components with the following volume percentages: tributyl phosphate TBP (5% - 30%) + bis(2-ethylhexyl) phosphate P204 (5% - 30%) + cyanex272 (0% - 15%) + solvent oil 260# (50% - 90%). The second predetermined phase ratio is the volume ratio of the second composite extractant to the leaching solution after reduction in the aqueous phase, which is 1:(1 - 30). The second composite extractant is not saponified before extraction; the dilute acid is sulfuric acid at 1 - 2 mol / L or hydrochloric acid at 1 - 2 mol / L, and the number of washing stages ≥ 1; the extraction equipment is an acid and alkali resistant cyclone extractor, and the number of extraction stages ≥ 1. In this embodiment, the acid and alkali resistant cyclone extractor is conducive to the separation of the stripping product. The model and operating parameters of the acid and alkali resistant cyclone extractor can be adjusted according to the material liquid situation. Increasing the acidity of the leaching solution after reduction to be extracted has basically no effect on the extraction of scandium ions but is conducive to inhibiting the extraction of other ions.

[0053] In some embodiments, the second lye is NaOH or ammonia water, the concentration of the second lye is 1.5 - 3 mol / L, and the volume ratio of the third loaded organic phase to the second lye during stripping is 1:(0.5 - 2); the stripping equipment is an acid and alkali resistant cyclone extractor, and the number of stripping stages ≥ 1. The acid and alkali resistant cyclone extractor is conducive to the separation of the stripping product.

[0054] Taking the titanium white waste acid and molten salt chlorination waste salt obtained from a certain sampling as an example, the method for co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt disclosed in the embodiments of the present invention will be specifically described below.

[0055] Embodiment

[0056] The main components of the titanium white waste acid and molten salt chlorination waste salt obtained from sampling are shown in Table 1 and Table 2.

[0057] Table 1 Main components of the titanium white waste acid obtained from sampling

[0058]

[0059] Table 2 Main components of the molten salt chlorination waste salt obtained from sampling

[0060]

[0061] Leaching the molten salt chlorination waste salt with titanium white waste acid, the volume ratio of titanium white waste acid to the mass of molten salt chlorination waste salt is 2.5:1. Stirring is strengthened during the leaching process, the leaching time is 2 h, and the leaching rate of scandium is about 93%. The leaching solution is obtained. Sodium dihydrogen phosphate is added to the leaching solution to preliminarily remove impurities such as zirconium and titanium. The total addition amount is 1 time of the theoretical amount required to completely precipitate zirconium and titanium ions. Then, reduction iron powder with a theoretical demand of 1.1 times the amount required to completely reduce ferric iron in the leaching solution is added. The temperature is controlled at 60 °C during the reduction process. After filtration, a scandium-containing solution is obtained, and scandium is basically not lost during this process. The first composite extractant tributyl phosphate TBP (10%) + bis(2-ethylhexyl) phosphate P204 (15%) + cyanex272 (5%) + 260# solvent oil (70%) is used to directly extract scandium from the scandium-containing solution by swirling under the condition of not being saponified. The phase ratio is 1:10. The extraction rate of scandium in this process reaches 99%, and the extraction rates of the remaining impurities in the scandium-containing solution are only about 0.1% - 1.5%. The first loaded organic phase is obtained. A mixed solution of hydrogen peroxide - sulfuric acid - phosphoric acid is used to elute the residual impurities in the first loaded organic phase. The sulfuric acid concentration is 5 mol / L, the hydrogen peroxide concentration is 1.5 mol / L, and the addition amount of phosphoric acid is 1 time of the theoretical amount required to completely remove titanium and zirconium in the first loaded organic phase. The elution time is 15 min, the elution stage number is 4, and the phase ratio is 2:1. The loss rate of scandium in this process is 0.6%, and the second loaded organic phase is obtained. 2.5 mol / L NaOH solution is used to back-extract scandium in the second loaded organic phase, with a phase ratio of 1:1, and a back-extractant is obtained. The back-extraction rate of scandium in this process is 99%. The back-extractant is calcined at 800 °C for high-temperature conversion. The calcination time is 4 h. After calcination, an oxide is obtained, which is finely ground to a particle size range below 250 mesh, and then leached with 3 mol / L sulfuric acid for 2 h to obtain a scandium-rich solution. The leaching rate of scandium in this process is about 97%. The second composite extractant tributyl phosphate TBP (10%) + bis(2-ethylhexyl) phosphate P204 (15%) + cyanex272 (5%) + 260# solvent oil (70%) is used to directly extract the scandium-rich solution by swirling under the condition of not being saponified. The phase ratio is 10:1. The extraction rate of scandium in this process reaches 99%, and the extraction rates of the remaining impurities in the scandium-rich solution are only about 0.1%. The second loaded organic phase is obtained. Then, 2 mol / L sulfuric acid is used to wash the second loaded organic phase, with a phase ratio of 1:1 and a washing stage number of 2, to obtain the third loaded organic phase. The loss rate of scandium in this process is about 0.2%. 3 mol / L NaOH solution is used to swirl and back-extract the third loaded organic phase, with a phase ratio of 1:1, to obtain scandium hydroxide with an impurity content <1%. The back-extraction rate of scandium in this process is 99%. The scandium hydroxide is completely dissolved with 2.5 mol / L hydrochloric acid and then precipitated with sodium oxalate to obtain a precipitate. The addition amount of sodium oxalate is 1.05 times the theoretical mass required to completely precipitate scandium ions. The precipitate is centrifuged, filtered, dehydrated, and then calcined at 850 °C for 6 h. Finally, scandium oxide with a purity of 99.95% is obtained.

[0062] In summary, the method for synergistically extracting scandium from titanium white waste acid and molten salt chlorination waste salt provided by the embodiments of the present invention makes full use of sulfuric acid in the titanium white waste acid to leach soluble scandium salts in the molten salt chlorination waste salt. While utilizing the waste acid in the titanium white waste acid, it realizes the comprehensive extraction of scandium in the titanium white waste acid and scandium in the molten salt chlorination waste salt, increases the content of scandium in the leachate, thereby improving the recovery rate of scandium. At the same time, the method provided by the present invention solves the problems of resource waste and environmental pollution caused by the direct disposal of molten salt chlorination waste salt, achieving the purpose of treating waste with waste and having good environmental protection benefits. On the other hand, due to the impurities contained in the titanium white waste acid and the molten salt chlorination waste salt, the present invention effectively removes impurities from the leachate to maximize the effective separation of scandium and various impurities, and finally scandium oxide with a purity ≥ 99.9% can be obtained. Moreover, the method provided by the present invention has the advantages of convenient operation, simple process flow, and low production cost, which is conducive to realizing industrial production.

[0063] It should be particularly noted that each component or step in the above-mentioned various embodiments can be mutually crossed, replaced, added, or deleted. Therefore, the combinations formed by these reasonable permutations and combinations should also fall within the protection scope of the present invention, and the protection scope of the present invention should not be limited to the above-mentioned embodiments.

[0064] The above are exemplary embodiments disclosed by the present invention. The order of disclosure of the above embodiments of the present invention is only for description and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of disclosure of the embodiments of the present invention (including the claims) is limited to these examples. Without departing from the scope defined by the claims, various changes and modifications can be made. The functions, steps, and / or actions of the method claims according to the disclosed embodiments here do not need to be executed in any specific order. In addition, although the elements disclosed in the embodiments of the present invention can be described or claimed in an individual form, they can also be understood as multiple unless explicitly limited to a single number.

[0065] Those of ordinary skill 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 disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the idea of the embodiments of the present invention, the technical features between the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle 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 co-extracting scandium from titanium white waste acid and molten salt chlorination waste salt, characterized in that, It includes the following steps: Leach the molten salt chlorination waste salt with titanium white waste acid at a predetermined liquid-solid ratio to obtain a leachate and a leach residue; Add phosphoric acid or phosphate to the leachate to preliminarily remove impurities zirconium and titanium, then add a reducing agent to reduce ferric iron in the leachate, and obtain a scandium-containing solution after filtration; Extract scandium in the scandium-containing solution by multi-stage countercurrent cyclone extraction with a first composite extractant at a first predetermined phase ratio to obtain a first loaded organic phase; Elute residual impurities titanium, manganese, calcium, zirconium, iron, magnesium, and vanadium in the first loaded organic phase with a mixed solution of hydrogen peroxide-sulfuric acid / hydrochloric acid-phosphoric acid at a predetermined concentration to obtain a second loaded organic phase; Perform multi-stage countercurrent cyclone stripping on scandium in the second loaded organic phase with a first alkali solution to obtain a scandium-enriched stripping product and a stripped organic phase; The stripping product is subjected to high-temperature conversion and fine grinding, and then leached with a first dilute acid to remove impurities to obtain a scandium-rich solution; Extract scandium in the scandium-rich solution by countercurrent cyclone extraction with a second composite extractant at a second predetermined phase ratio to obtain a second loaded organic phase, and then wash the second loaded organic phase with a second dilute acid to obtain a third loaded organic phase; Perform multi-stage countercurrent cyclone stripping on scandium in the third loaded organic phase with a second alkali solution to obtain scandium hydroxide with an impurity content < 1%; 2. The method according to claim 1, wherein It further includes one or more of the following steps: Wash the leach residue with acidic wash water with pH < 2 until the salt content (mass percentage) of the leach residue < 0.05%. The washed leach residue can be further used for titanium recovery, and the wash water is recycled until a certain extent and then collected as a raw material for scandium extraction; The stripped organic phase is regenerated with dilute acid and reused for scandium extraction; The scandium hydroxide is successively dissolved in hydrochloric acid with a concentration of 1 - 5 mol / L, precipitated with oxalic acid or sodium oxalate. The addition amount of oxalic acid or sodium oxalate is 1 - 1.5 times the theoretical mass required to completely precipitate scandium ions. The precipitate is centrifuged, filtered, dehydrated, and calcined at 600 - 900 °C for 3 - 6 h, and finally scandium oxide with a purity ≥ 99.9% is obtained; 3. The method according to claim 1, wherein The scandium content in the molten salt chlorination waste salt is 20 - 200 g / t, the scandium concentration in the titanium white waste acid is 1 - 40 mg / L, the sulfuric acid concentration in the titanium white waste acid is 15% - 25%, the predetermined liquid-solid ratio is the volume ratio of the titanium white waste acid to the mass of the molten salt chlorination waste salt is (1 - 10):

1. Stirring is strengthened during the leaching process, and the leaching time is 2 - 5 h; 4. The method according to claim 1, characterized in that, The total addition amount of the phosphoric acid or phosphate is 1 - 1.2 times the theoretical amount required to completely precipitate zirconium and titanium ions; the dosage of the reducing agent is 1 - 1.2 times the theoretical demand required to completely reduce ferric iron in the leachate. The temperature of the leachate system is controlled at 50 - 90 °C during reduction.

5. The method according to claim 1, characterized in that The first composite extractant comprises the following components by volume percentage: 5% - 30% tributyl phosphate (TBP) + 5% - 30% bis(2-ethylhexyl) phosphate (P204) + 0% - 15% cyanex272 + 50% - 90% solvent oil 260#; the first predetermined phase ratio is the volume ratio of the first composite extractant to the leaching solution after reduction in the aqueous phase, which is 1:(1 - 30); before extraction, the first composite extractant is not saponified; the extraction equipment is an acid- and alkali-resistant cyclone extractor, and the number of extraction stages ≥ 1.

6. The method according to claim 1, wherein In the mixed solution of hydrogen peroxide - sulfuric acid / hydrochloric acid - phosphoric acid: the concentration of sulfuric acid or hydrochloric acid is 1 - 5 mol / L, the concentration of hydrogen peroxide is 1 - 2 mol / L, and the addition amount of phosphoric acid is 1 - 1.3 times the theoretical amount required to completely remove titanium and zirconium in the first loaded organic phase; the elution time is 10 - 30 min, and the number of elution stages ≥ 1.

7. The method according to claim 1, characterized in that The first lye is NaOH or ammonia water, the concentration of the first lye is 1.5 - 3 mol / L, and the volume ratio of the second loaded organic phase to the first lye is 1:(0.5 - 2); the back-extraction equipment is an acid- and alkali-resistant cyclone extractor, and the number of back-extraction stages ≥ 1.

8. The method according to claim 1, characterized in that The back-extraction product includes scandium hydroxide and hydroxides of a small amount of impurity elements, wherein the content of scandium is 0.1% - 30%. The back-extraction product is subjected to high-temperature conversion by roasting at 700 - 900 °C for 3 - 6 h. After roasting, an oxide is obtained. The oxide is finely ground to a particle size range of less than 250 mesh, and then leached with the first dilute acid. The first dilute acid is sulfuric acid with a concentration of 1 - 5 mol / L or hydrochloric acid with a concentration of 1 - 5 mol / L, and the leaching time is 2 - 5 h.

9. The method according to claim 1, wherein The second composite extractant comprises the following components by volume percentage: 5% - 30% tributyl phosphate (TBP) + 5% - 30% bis(2-ethylhexyl) phosphate (P204) + 0% - 15% cyanex272 + 50% - 90% solvent oil 260#. The second predetermined phase ratio is the volume ratio of the second composite extractant to the leaching solution after reduction in the aqueous phase, which is (1 - 30):

1. Before extraction, the second composite extractant is not saponified; the second dilute acid is sulfuric acid with a concentration of 1 - 2 mol / L or hydrochloric acid with a concentration of 1 - 2 mol / L, and the number of washing stages ≥ 1; the extraction equipment is an acid- and alkali-resistant cyclone extractor, and the number of extraction stages ≥ 1.

10. The method according to claim 1, characterized in that, The second lye is NaOH or ammonia water, the concentration of the second lye is 1.5 - 3 mol / L, and the volume ratio of the third loaded organic phase to the second lye during back-extraction is 1:(0.5 - 2); the back-extraction equipment is an acid- and alkali-resistant cyclone extractor, and the number of back-extraction stages ≥ 1.

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