CN115874070A - Method for extracting scandium from molten salt chlorination waste salt - Google Patents
Method for extracting scandium from molten salt chlorination waste salt Download PDFInfo
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- CN115874070A CN115874070A CN202211702172.4A CN202211702172A CN115874070A CN 115874070 A CN115874070 A CN 115874070A CN 202211702172 A CN202211702172 A CN 202211702172A CN 115874070 A CN115874070 A CN 115874070A
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Abstract
The invention discloses a method for extracting scandium from molten salt chlorination waste salt, which comprises the following steps: the method comprises the steps of carrying out water leaching on waste salt of molten salt chlorination to obtain leachate, reducing iron and titanium in the leachate by using a reducing agent, carrying out multistage countercurrent rotational flow extraction by using a composite extracting agent, carrying out back extraction by using a strong oxidizing property and strong alkaline solution to obtain a solid back extract, roasting, carrying out high-temperature conversion and fine grinding on the solid back extract, then carrying out leaching by using dilute acid to obtain a scandium-rich liquid, carrying out countercurrent rotational flow extraction, acid liquor elution and back extraction on the scandium-rich liquid to obtain scandium hydroxide with the impurity content of less than 1%, dissolving the scandium hydroxide by using hydrochloric acid, carrying out oxalic acid precipitation and carrying out high-temperature roasting, and finally obtaining scandium oxide with the purity of more than or equal to 99.9%. The method provided by the invention is convenient to operate, simple in process flow, low in production cost, good in environmental protection benefit, easy to realize industrialization, and capable of efficiently recovering valuable element scandium in the waste salt of molten salt chlorination.
Description
Technical Field
The invention relates to the technical field of resource recovery, in particular to a method for extracting scandium from waste salt in molten salt chlorination.
Background
Scandium oxide (Sc) 2 O 3 ) Is the most important product in scandium products. Scandium is very rare in the crust and is often associated with other metals, so that scandium oxide or compounds thereof cannot be directly extracted from scandium-containing minerals at present; on the other hand, the physicochemical properties of the scandium oxide are very close to those of other transition elements, especially rare earth elements, which makes the extraction of the scandium oxide very difficult.
China has abundant titanium resources, but high-quality titanium ores are few. The scandium oxide and oxides of niobium, uranium, vanadium and the like have high heat of formation and are very stable, and during molten salt chlorination, the scandium oxide and the oxides of niobium, uranium, vanadium and the like are remained in the waste molten salt slag, wherein the content of the scandium can reach 200-350 g/t and is about 10 times higher than that in raw ore, so the waste salt of the molten salt chlorination is a good raw material for extracting the scandium oxide. However, in the prior art, no economical and effective treatment technology for pollutants such as fused salt chloride slag discharged in the production process is available at home and abroad, and the pollutants are treated in a barren stacking (at home) mode or a professional slag yard landfill (at home) mode after lime mixing, so that valuable scandium resources are wasted.
Therefore, there is a need in the art for improved methods of extracting scandium from molten salt chlorination waste salts.
Disclosure of Invention
In view of this, an object of the embodiment of the present invention is to provide a method for extracting scandium from waste molten salt chlorination salt, which is convenient to operate, simple in process flow, low in production cost, good in environmental protection benefit, easy to implement industrialization, and capable of efficiently recovering valuable element scandium from waste molten salt chlorination salt.
Based on the above purpose, the embodiment of the invention provides a method for extracting scandium from molten salt chlorination waste salt, which comprises the following steps:
s1, leaching the waste salt of the molten salt chlorination to obtain a leaching solution, leaching residues and washing water, wherein the leaching residues are recycled as a titanium extraction raw material after being washed, and the washing water is recycled for leaching;
s2, reducing iron and titanium in the leachate by using a reducing agent;
s3, carrying out multistage countercurrent rotational flow extraction on scandium in the reduced leachate by using a composite extractant to obtain a first loaded organic phase and a first raffinate;
s4, carrying out multi-stage counter-current rotational flow back extraction on the first loaded organic phase by using a strong oxidizing property and strong alkaline solution to obtain a back extraction organic phase and a solid back extract, and regenerating the back extracted organic phase by using dilute acid for recycling and reusing for scandium extraction;
s5, roasting the solid back extract, converting at high temperature, finely grinding, and leaching with dilute acid to obtain scandium-rich liquid and residue;
s6, extracting scandium in the scandium-rich liquid by using a compound extractant in a countercurrent rotational flow manner to obtain a second loaded organic phase and a second raffinate;
s7, eluting residual metal impurities in the second loaded organic phase by using a composite acid solution;
s8, carrying out multi-stage counter-current rotational flow back extraction on the eluted second loaded organic phase by using alkali liquor to obtain scandium hydroxide with the impurity content of less than 1%, and dissolving the scandium hydroxide by hydrochloric acid, precipitating by oxalic acid, and roasting at high temperature to finally obtain scandium oxide with the purity of more than or equal to 99.9%.
In some embodiments, in S1, the scandium content in the molten salt chlorination waste salt is 20 to 200g/t, and the liquid-solid ratio in water immersion is volume: mass = (1 to 10): 1, in the leaching process, the pH value of a solution needs to be kept less than 2 to avoid scandium ions from being hydrolyzed to enter solid-phase leaching residues, when the pH value does not meet the requirement, acid is added to adjust the pH value to be less than 2, the leaching process is stirred intensively, the leaching time is 2-5 hours to ensure that scandium is leached sufficiently, the pH value of washing water is kept less than 2 to prevent scandium ions from being hydrolyzed in the washing process, the washing water can return to the water leaching process, and the leaching residues are washed until the mass percentage of salt is less than 0.05%.
In some embodiments, in S2, the reducing agent comprises iron filings, reduced iron powder, sulfite, GBS, aluminum powder or magnesium powder, the amount of the reducing agent is 1 to 1.5 times of the theoretical requirement for complete reduction of iron and titanium in the leachate, and the temperature of the leachate system is controlled to be 50 to 90 ℃ during reduction.
In some embodiments, in S3, the composite extractant includes the following components in percentage by volume: 5-30% of TBP, 5-30% of P204, 0-10% of P229 and 50-90% of No. 260 solvent oil, wherein the volume ratio of the composite extractant of the organic phase and the leachate after aqueous phase reduction during extraction is 1: (1-30), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction stage number is more than or equal to 1.
In some embodiments, in S4, the strongly oxidizing, strongly basic solution includes a strongly oxidizing, alkaline waste brine and/or a chlor-alkali chemical tail gas absorption waste liquid generated by purification of a molten salt chlorination tail gas, and the volume ratio of the first loaded organic phase to the strongly oxidizing, strongly basic solution in stripping is 1: (1-10), the back extraction equipment is an acid and alkali resistant cyclone extractor, and the back extraction stage number is more than or equal to 1.
In some embodiments, in S5, the solid back-extract includes hydroxides or oxides of elements such as iron, manganese, titanium, magnesium, zirconium, calcium, aluminum, and scandium, wherein the content of scandium is 0.1% to 5%, the solid back-extract is subjected to calcination high-temperature conversion at a temperature of 700 to 900 ℃ for 3 to 6 hours, the solid back-extract is converted into oxides after calcination, the calcined product is finely ground to a particle size range below 250 meshes, and then leached at normal temperature with dilute acid, the dilute acid is 0.5 to 5mol/L sulfuric acid or 0.5 to 5mol/L hydrochloric acid, and the leaching time is 2 to 5 hours.
In some embodiments, in S6, the composite extractant includes the following components in percentage by volume: 5-30% of TBP, 5-20% of P204, 0-10% of P229 and 50-90% of No. 260 solvent oil, wherein the volume ratio of the composite extractant of the organic phase and the leachate after aqueous phase reduction during extraction is 1: (1-10), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction stage number is more than or equal to 1.
In some embodiments, in S7, the complex acid solution includes an acid solution and a strong oxidant, the acid solution includes sulfuric acid or hydrochloric acid with a concentration of 1 to 5mol/L, the strong oxidant includes ozone and hydrogen peroxide, the concentration of the strong oxidant is 1 to 2mol/L, the elution time is 10 to 30min, and the number of elution stages is greater than or equal to 1.
In some embodiments, in S8, the lye is NaOH or ammonia, the concentration is about 1.5 to 3mol/L, and the volume ratio of the second loaded organic phase to the lye during stripping is 1: (0.5-2), the back extraction equipment is an acid and alkali resistant cyclone extractor, and the back extraction stage number is more than or equal to 1.
In some embodiments, in S8, scandium hydroxide is dissolved by hydrochloric acid, the hydrochloric acid concentration is 1 to 5mol/L, then oxalic acid or sodium oxalate is used for precipitation, the addition amount of oxalic acid or sodium oxalate is 1 to 1.5 times of the theoretical mass required for completely precipitating scandium ions, and the precipitate is subjected to centrifugal filtration dehydration and then calcined at 600 to 900 ℃ for 3 to 6 hours for dehydration and transformation, so as to obtain a scandium oxide product with the purity of not less than 99.9%.
The invention has at least the following beneficial technical effects:
according to the method, leachate is separated by leaching with the waste salt water of the molten salt chlorination, the leachate is subjected to reduction, multistage countercurrent rotational flow extraction and back extraction, the solid back extract enriched with scandium is subjected to high-temperature conversion to be basically converted into oxide, the scandium hydroxide is obtained by performing multistage countercurrent rotational flow extraction and back extraction again through acid liquor leaching, and the scandium oxide product with the purity of not less than 99.9% is finally obtained after treatment.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other embodiments can be obtained by using the drawings without creative efforts.
FIG. 1 is a schematic diagram of an embodiment of scandium extraction from molten salt chlorination waste salt provided by the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following embodiments of the present invention are described in further detail with reference to the accompanying drawings.
The terms "including" and "having," and any variations thereof, in the description and claims of this invention and the description of the above figures are intended to cover non-exclusive inclusions; the terms "first," "second," and the like in the description and in the claims, or in the drawings, are used for distinguishing between different objects and not necessarily for describing a particular sequential order. The meaning of "plurality" is two or more unless explicitly defined otherwise.
Furthermore, reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein may be combined with other embodiments.
Fig. 1 shows a method for extracting scandium from molten salt chlorination waste salt, which comprises the following steps:
s1, leaching the waste salt of the molten salt chlorination to obtain a leaching solution, leaching residues and washing water, wherein the leaching residues are recycled as a titanium extraction raw material after being washed, and the washing water is recycled for leaching;
s2, reducing iron and titanium in the leachate by using a reducing agent;
s3, carrying out multistage countercurrent rotational flow extraction on the scandium in the reduced leaching solution by using a composite extractant to obtain a first loaded organic phase and a first raffinate;
s4, carrying out multi-stage counter-current rotational flow back extraction on the first loaded organic phase by using a strong oxidizing and strong alkaline solution to obtain a back extraction organic phase and a solid back extract, and regenerating the back extracted organic phase by using dilute acid for recycling and reusing the back extracted organic phase for scandium extraction;
s5, roasting the solid back extract, converting at high temperature, finely grinding, and leaching with dilute acid to obtain scandium-rich liquid and residue;
s6, extracting scandium in the scandium-rich liquid by using a composite extractant through countercurrent and rotational flow to obtain a second loaded organic phase and a second raffinate;
s7, eluting residual metal impurities in the second loaded organic phase by using a composite acid solution;
s8, carrying out multi-stage counter-current rotational flow back extraction on the eluted second loaded organic phase by using alkali liquor to obtain scandium hydroxide with the impurity content of less than 1%, and dissolving the scandium hydroxide by hydrochloric acid, precipitating by oxalic acid, and roasting at high temperature to finally obtain scandium oxide with the purity of more than or equal to 99.9%.
Further, in S1, the content of scandium in the molten salt chlorination waste salt is 20-200 g/t, because the soluble components in the molten salt chlorination waste salt account for about 75% -90% of the total amount of the molten salt chlorination waste salt, scandium in the molten salt chlorination waste salt mainly exists in the form of soluble salt, scandium can be basically transferred into the solution through water leaching, and the liquid-solid ratio during the water leaching is volume: the mass is (1-10): 1, in the leaching process, the pH value of the solution needs to be kept less than 2 to avoid scandium ions from hydrolyzing and entering solid-phase leaching residues, when the pH value does not meet the requirement, acid can be properly added to adjust the pH value to be less than 2, the leaching process is stirred intensively, the leaching time is 2-5 h to ensure that scandium is leached sufficiently, the pH value of water used for washing needs to be kept less than 2 to prevent scandium ions from hydrolyzing during washing, the washing water can return to the water leaching process, and the leaching residues are washed until the mass percentage of salt is less than 0.05%.
Further, in S2, the reducing agent comprises scrap iron, reduced iron powder, sulfite, GBS, aluminum powder or magnesium powder, the dosage of the reducing agent is 1-1.5 times of the theoretical requirement for completely reducing iron and titanium in the leachate, and the temperature of the leachate system needs to be controlled at 50-90 ℃ during reduction.
Further, in S3, the composite extracting agent includes the following components by volume percent: 5-30% of TBP, 5-30% of P204, 0-10% of P229 and 50-90% of No. 260 solvent oil, wherein a composite extractant of an organic phase is not required to be saponified before extraction, the acidity increase in the extraction process basically has no influence on the extraction of scandium ions but is beneficial to inhibiting the extraction of other ions, and the volume ratio of the composite extractant of the organic phase to a leachate after aqueous phase reduction is 1: (1-30), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction stage number is more than or equal to 1.
Further, in S4, the strong oxidizing property and strong alkaline solution includes strong oxidizing property, alkaline waste brine and/or chlor-alkali chemical industry tail gas absorption waste liquid generated by purification of the molten salt chlorination tail gas, caustic soda may be properly added to ensure that the alkali concentration in the strong oxidizing property and strong alkaline solution is 5% to 15%, and the volume ratio of the first loaded organic phase to the strong oxidizing property and strong alkaline solution is 1: (1-10), the back extraction equipment is an acid and alkali resistant cyclone extractor, and the back extraction stage number is more than or equal to 1.
Further, in S5, the solid back extract comprises hydroxides or oxides of elements such as iron, manganese, titanium, magnesium, zirconium, calcium, aluminum, scandium and the like, wherein the content of scandium is 0.1-5%, the solid back extract is subjected to roasting high-temperature conversion at the temperature of 700-900 ℃, the roasting time is 3-6 h, the solid back extract is converted into oxides after roasting, the roasting aims to convert compounds of elements such as iron, manganese, titanium, zirconium and the like into oxides which are insoluble or slightly soluble or slowly soluble in normal-temperature dilute acid so as to facilitate the separation of scandium and impurities during subsequent dilute acid normal-temperature leaching, the roasted products are finely ground to the particle size range below 250 meshes, and then are leached at the dilute acid normal temperature, the dilute acid is 0.5-5 mol/L sulfuric acid or 0.5-5 mol/L hydrochloric acid, and the leaching time is 2-5 h.
Further, in S6, the composite extracting agent includes the following components by volume percent: 5-30% of TBP, 5-30% of P204, 0-10% of P229 and 50-90% of No. 260 solvent oil, wherein a composite extractant of an organic phase is not required to be saponified before extraction, the acidity increase in the extraction process basically has no influence on the extraction of scandium ions but is beneficial to inhibiting the extraction of other ions, and the volume ratio of the composite extractant of the organic phase to a leachate after aqueous phase reduction is 1: (1-10), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction stage number is more than or equal to 1.
Further, in S7, the composite acid solution comprises an acid solution and a strong oxidant, the acid solution comprises sulfuric acid or hydrochloric acid with the concentration of 1-5 mol/L, the strong oxidant comprises ozone and hydrogen peroxide, the addition concentration is 1-2 mol/L, the elution time is 10-30 min, and the elution stage number is more than or equal to 1.
Further, in S8, the alkali liquor is NaOH or ammonia water, the concentration is about 1.5-3 mol/L, and the volume ratio of the second loaded organic phase to the alkali liquor in back extraction is 1: (0.5-2), the back extraction equipment is an acid and alkali resistant cyclone extractor, and the back extraction stage number is more than or equal to 1.
Further, in S8, scandium hydroxide is dissolved by hydrochloric acid, the concentration of the hydrochloric acid is 1-5 mol/L, silicon-containing impurities can be removed in the hydrochloric acid dissolving process, scandium ions are precipitated by oxalic acid or sodium oxalate from scandium-containing impurity removing liquid, the adding amount of the oxalic acid and the sodium oxalate is 1-1.5 times of the theoretical mass required for completely precipitating the scandium ions, and precipitates are roasted at 600-900 ℃ for 3-6 hours for dehydration and transformation after being subjected to centrifugal filtration and dehydration, so that scandium oxide products with the purity of more than or equal to 99.9% are finally obtained.
The invention is further explained below with reference to specific embodiments.
Example 1
The main components of the molten salt chlorination waste salt obtained by a certain sampling are shown in the table 1.
TABLE 1 molten salt chlorination waste salt main component obtained from a certain sampling
And (2) according to the liquid-solid ratio of 2.5:1, carrying out water leaching on the waste salt of the molten salt chlorination, wherein the leaching process is carried out under the condition of strengthened stirring, the leaching time is 3 hours, and the leaching rate of scandium is about 88 percent, so as to obtain a leaching solution, and the pH value of the leaching solution is 0.8; reducing the iron and the titanium in the leachate by using a GBS reducing agent which is 1.1 times of the theoretical requirement for completely reducing the iron and the titanium in the leachate, wherein the temperature of a leachate system needs to be controlled at 55 ℃ during reduction, and scandium is not lost in the reduction process; the method is characterized in that a composite extracting agent of 10 percent of TBP, 15 percent of P204, 5 percent of P229 and 70 percent of No. 260 solvent oil is used for directly carrying out multistage countercurrent rotational flow extraction on scandium in a reduced solution under unsaponifiable conditions, and compared with the method that 1:10, the extraction rate of scandium reaches 99%, and the extraction rate of the rest impurities in the scandium-containing solution is only about 0.1-6%; and (2) performing back extraction on the loaded organic phase by using strong oxidizing property and alkaline waste brine generated by purifying the molten salt chlorination tail gas with the alkali concentration adjusted to about 10%, wherein the ratio of the strong oxidizing property to the alkaline waste brine is 1:1, scandium back extraction rate is 99%, and a back extract enriched with scandium is obtained; roasting the back extract at 800 ℃ for high-temperature conversion for 4h to obtain an oxide, finely grinding the oxide to a particle size range below 250 meshes, and leaching for 2h by using 3mol/L sulfuric acid to obtain a scandium-rich solution with low impurity content, wherein the leaching rate of scandium in the process is about 96%; compared with the prior art that 10 percent of TBP, 15 percent of P204, 5 percent of P229 and 70 percent of No. 260 solvent oil are used as the composite extracting agent to directly perform multistage countercurrent rotational flow extraction on scandium in the reduced solution under unsaponifiable conditions, the method is characterized in that: 1, the extraction rate of scandium reaches 99%, and the extraction rate of the rest impurities in the scandium-containing solution is only about 0.1-1%; eluting impurities remained in the loaded organic phase by using a 5mol/L sulfuric acid solution added with 1.5mol/L hydrogen peroxide, wherein the elution time is 15min, the elution stage number is 3, and the scandium loss rate in the process is about 0.25%; and (3) carrying out multistage countercurrent rotational flow back extraction on the loaded organic phase by using 2.5mol/L NaOH solution, wherein compared with 1:1, obtaining scandium hydroxide with impurity content less than 1%, wherein the scandium back extraction rate in the process is about 99%; and (2) completely dissolving scandium hydroxide by hydrochloric acid with the concentration of 3mol/L, and precipitating by sodium oxalate to obtain a precipitate, wherein the addition amount of the sodium oxalate is 1.1 times of the theoretical mass required for completely precipitating scandium ions, and the precipitate is subjected to centrifugal filtration and dehydration and then is roasted at 800 ℃ for 6 hours to finally obtain scandium oxide with the purity of 99.95%.
The foregoing is an exemplary embodiment of the present disclosure, but it should be noted that various changes and modifications could be made herein without departing from the scope of the present disclosure as defined by the appended claims. The functions, steps and/or actions of the method claims in accordance with the disclosed embodiments described herein need not be performed in any particular order. Furthermore, although elements of the disclosed embodiments of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.
It should be understood that, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly supports the exception. It should also be understood that "and/or" as used herein is meant to include any and all possible combinations of one or more of the associated listed items.
The numbers of the embodiments disclosed in the embodiments of the present invention are merely for description, and do not represent the merits of the embodiments.
Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, of embodiments of the invention is limited to these examples; within the idea of an embodiment of the invention, also technical features in the above embodiment or in different embodiments may be combined and there are many other variations of the different aspects of the embodiments of the invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, substitutions, improvements, and the like that may be made without departing from the spirit and principles of the embodiments of the present invention are intended to be included within the scope of the embodiments of the present invention.
Claims (10)
1. A method for extracting scandium from molten salt chlorination waste salt is characterized by comprising the following steps:
s1, leaching the waste salt of the molten salt chlorination to obtain a leaching solution, leaching residues and washing water, wherein the leaching residues are recycled as a titanium extraction raw material after being washed, and the washing water is recycled for leaching;
s2, reducing iron and titanium in the leachate by using a reducing agent;
s3, carrying out multistage countercurrent rotational flow extraction on the scandium in the reduced leaching solution by using a composite extractant to obtain a first loaded organic phase and a first raffinate;
s4, carrying out multi-stage counter-current rotational flow back extraction on the first loaded organic phase by using a strong oxidizing property and strong alkaline solution to obtain a back extraction organic phase and a solid back extract, and regenerating the back extracted organic phase by using dilute acid for recycling and reusing for scandium extraction;
s5, roasting the solid back extract, converting at high temperature, finely grinding, and leaching with dilute acid to obtain scandium-rich liquid and residue;
s6, performing countercurrent rotational flow extraction on scandium in the scandium-rich liquid by using a composite extractant to obtain a second loaded organic phase and a second raffinate;
s7, eluting residual metal impurities in the second loaded organic phase by using a composite acid solution;
s8, carrying out multi-stage counter-current rotational flow back extraction on the eluted second loaded organic phase by using alkali liquor to obtain scandium hydroxide with the impurity content of less than 1%, and finally obtaining scandium oxide with the purity of more than or equal to 99.9% through hydrochloric acid dissolution, oxalic acid precipitation and high-temperature roasting of the scandium hydroxide.
2. The method for extracting scandium from molten salt chlorination waste salt according to claim 1, wherein in S1, the content of scandium in the molten salt chlorination waste salt is 20-200 g/t, and the liquid-solid ratio in water leaching is volume: mass = (1 to 10): 1, in the leaching process, the pH value of the solution needs to be kept less than 2 to avoid scandium ions from hydrolyzing and entering solid-phase leaching residues, acid is added to adjust the pH value to be less than 2 when the pH value does not meet the requirement, the leaching process is stirred intensively, the leaching time is 2-5 h to ensure that scandium is leached sufficiently, the pH value of washing water is kept less than 2 to prevent scandium ions from hydrolyzing during washing, the washing water can return to the water leaching process, and the leaching residues are washed until the mass percent of salt is less than 0.05%.
3. The method for extracting scandium from molten salt chlorination waste salt according to claim 1, wherein in S2, the reducing agent includes iron scrap, reduced iron powder, sulfite, GBS, aluminum powder or magnesium powder, the amount of the reducing agent is 1 to 1.5 times of the theoretical requirement for completely reducing iron and titanium in the leachate, and the temperature of the leachate system during reduction is controlled to be 50 to 90 ℃.
4. The method of extracting scandium from molten salt chlorination waste salt according to claim 1, wherein in S3 the composite extractant includes the following components by volume percent: 5-30% of TBP, 5-30% of P204, 0-10% of P229 and 50-90% of No. 260 solvent oil, wherein the volume ratio of the composite extracting agent of an organic phase to the leachate after aqueous phase reduction during extraction is 1: (1-30), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction stage number is more than or equal to 1.
5. The method of claim 1, wherein in S4, the strong oxidizing and strong alkaline solution comprises strong oxidizing and alkaline brine waste and/or chlor-alkali chemical tail gas absorption waste liquor generated by tail gas purification of molten salt chlorination, and the volume ratio of the first loaded organic phase to the strong oxidizing and strong alkaline solution in stripping is 1: (1-10), the back extraction equipment is an acid and alkali resistant cyclone extractor, and the back extraction stage number is more than or equal to 1.
6. The method for extracting scandium from molten salt chlorination waste salt according to claim 1, wherein in S5, the solid strip includes hydroxides or oxides of elements such as iron, manganese, titanium, magnesium, zirconium, calcium, aluminum, scandium, etc., wherein the content of scandium is 0.1% -5%, the solid strip is subjected to the roasting high-temperature conversion at a temperature of 700-900 ℃, the roasting time is 3-6 h, the roasted product is converted into an oxide, the roasted product is finely ground to a particle size range below 250 meshes, and then the roasting product is subjected to normal temperature leaching with dilute acid, the dilute acid is 0.5-5 mol/L sulfuric acid or 0.5-5 mol/L hydrochloric acid, and the leaching time is 2-5 h.
7. The method for extracting scandium from molten salt chlorination waste salt according to claim 1, wherein in S6, the composite extracting agent includes the following components by volume percent: 5-30% of TBP, 5-20% of P204, 0-10% of P229 and 50-90% of No. 260 solvent oil, wherein the volume ratio of the composite extracting agent of an organic phase to the leachate after reduction of a water phase during extraction is 1: (1-10), the extraction equipment is an acid and alkali resistant cyclone extractor, and the extraction stage number is more than or equal to 1.
8. The method for extracting scandium from molten salt chlorination waste salt according to claim 1, wherein in S7, the complex acid solution includes an acid solution and a strong oxidant, the acid solution includes sulfuric acid or hydrochloric acid with a concentration of 1-5 mol/L, the strong oxidant includes ozone and hydrogen peroxide, the addition concentration is 1-2 mol/L, the elution time is 10-30 min, and the elution number is greater than or equal to 1.
9. The method for extracting scandium from waste salt of molten salt chlorination according to claim 1, wherein in S8, the alkali solution is NaOH or ammonia water, the concentration is about 1.5-3 mol/L, and the volume ratio of the second loaded organic phase and the alkali solution in the back extraction is 1: (0.5-2), the back extraction equipment is an acid and alkali resistant cyclone extractor, and the back extraction stage number is more than or equal to 1.
10. The method for extracting scandium from molten salt chlorination waste salt according to claim 1, wherein in S8, the scandium hydroxide is dissolved by hydrochloric acid, the concentration of the hydrochloric acid is 1-5 mol/L, then the scandium hydroxide is precipitated by oxalic acid or sodium oxalate, the addition amount of the oxalic acid or the sodium oxalate is 1-1.5 times of the theoretical mass required for complete precipitation of scandium ions, and the precipitate is subjected to centrifugal filtration dehydration and then is roasted at 600-900 ℃ for 3-6 h for dehydration and transformation, and finally scandium oxide products with the purity of not less than 99.9% are obtained.
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