A method for separating scandium from other rare earth elements

Abstract

The present application relates to the field of hydrometallurgy, and discloses a method for separating scandium from other rare earth elements. An acidic aqueous phase containing scandium and other rare earth elements is mixed with an organic phase containing an extractant to obtain an organic phase containing scandium and an aqueous phase containing other rare earth elements by extraction separation; the extractant is any one of the structures shown below; the present application uses a nitrogen-containing heterocyclic extractant, and most of the scandium elements can be extracted by solvent extraction, while the remaining rare earth elements are almost not extracted and remain in the aqueous phase, so that the separation effect is excellent. High-purity scandium products are obtained after back extraction and crystallization of scandium in water, the extraction rate of scandium is high, the obtained scandium products have high added value, and the economic benefits of production are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrometallurgy, in particular to a method for separating scandium from other rare earth elements. BACKGROUND

[0002] Scandium is widely used in chemical industry, mineral metallurgy, aerospace, military and nuclear technology due to its excellent doping performance, electrical performance and luminescent performance. Among them, scandium-containing materials are important components of high-efficiency laser devices, superconducting materials, solid fuel cell electrolytes, chip doping metals and new ceramic materials. Therefore, the separation and extraction of scandium have important industrial significance and economic value.

[0003] Scandium has different physical and chemical properties from other rare earth elements due to its small ionic radius and large mass-to-charge ratio. Although the abundance of scandium in the earth's crust is not low, it is difficult to be collected alone into a mine, but tends to be associated with compatible elements (Al, Fe, Ni, Ti, REs) and has a very low grade. Currently, the main source of scandium is the tailings of processed minerals, such as titanium white waste acid, red mud tailings, tungsten uranium tailings and laterite nickel ore residues. The scandium in these tailings is preliminarily enriched, and the grade is improved, but the concentration of various elements increases to varying degrees during the enrichment process. Compared with transition metals, associated rare earth elements are more difficult to separate due to their closer extraction properties with scandium, especially heavy rare earth elements such as ytterbium and lutetium.

[0004] CN115418485A discloses a method for recovering scandium oxide from a scandium-containing loaded organic phase. The commonly used extractants in industry include P204, P350 and other phosphorus-containing extractants with strong affinity, which are difficult to be back-extracted from the scandium-containing loaded phase, resulting in low recovery rate and easy poisoning of the extractant. The method mixes and disperses the scandium-containing loaded phase with solvent oil, adds alkali to precipitate and back-extract, separates the solid, then adds acid for acid leaching, and finally obtains scandium oxide product through oxalic acid precipitation and calcination. The patent focuses on solving the problem of difficult back-extraction of extractants in industry, but the extractants that are easy to back-extract can avoid these problems.

[0005] CN116027712A discloses a method for extracting rare earth elements from rare earth-rich materials and zirconium smelting waste acid and its application. The acid solution contains uranium oxycerium zirconium, scandium and other rare earth elements. The method adjusts the pH value of the solution to 4-4.8 and 9-11 respectively in two steps, and then separates the solid and liquid twice to obtain rare earth-rich materials. The product obtained in the invention is rich in scandium and other rare earth elements, with high rare earth content and low impurity content, but the patent does not further separate and apply scandium and rare earth elements.

[0006] CN114959264A discloses an environmentally friendly extraction system and a method for extracting scandium based thereon. The invention uses quaternary phosphonium salt ionic liquid as an extractant, hydrophobic ionic liquid as a co-extraction agent, and organic solvent as a diluent to prepare an environmentally friendly extraction system for the recovery of scandium from scandium-containing solution. The system can obtain scandium products with purity of more than 90% through extraction, stripping and evaporation crystallization. However, the ionic liquid is still far from large-scale industrial application, and the purity of the product is still lower than that of the general market crude scandium (95%-97%). SUMMARY

[0007] The present application aims to solve the problems in the prior art, such as the difficulty in separating scandium from other rare earth elements, the low extraction rate of the existing extraction method, and the complexity of stripping, and provides a method for separating scandium from other rare earth elements. The method selectively extracts scandium from the solution by solution extraction, while almost no other rare earth elements are extracted, effectively separating them. Moreover, the method is simple to strip and the product has high purity.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0009] A method for separating scandium from other rare earth elements, comprising the steps of: mixing an acidic aqueous phase containing scandium and other rare earth elements with an organic phase containing an extractant to obtain an aqueous phase containing scandium and an organic phase containing other rare earth elements by extraction separation; the extractant has any one of the following A-C structures:

[0010]

[0011] wherein R and R' are independently selected from any one of C2-20 straight chain or branched alkyl, phenyl, tolyl.

[0012] In the present application, nitrogen-containing heterocyclic extractants are used to extract and separate scandium and other rare earth elements. It is found that the extractant has a high extraction rate for scandium, while almost no other rare earth elements are extracted. This is because scandium has a smaller ionic radius than other rare earth elements due to its smaller atomic number, but its nuclear charge number is also trivalent, which is common for rare earth elements. The larger charge-to-mass ratio makes it have different separation characteristics from other rare earth elements, and it is easier to form bonds with N and O atoms in the ligand and be extracted. Moreover, the hard O atoms and soft N atoms in the ligand used in the present application make the combination not too tight, and the loaded scandium ions can be completely stripped using a lower concentration of dilute acid.

[0013] Preferably, the extractant structure is as shown in C, and the extractant with a phenanthroline skeleton has more excellent extraction kinetics, can reach extraction equilibrium faster, and greatly improves the efficiency of extraction.

[0014] Further preferably, R and R' are independently selected from any one of C6-10 straight chain or branched alkyl, phenyl, tolyl.

[0015] Further, R and R' are independently selected from any one of n-octyl, n-hexyl, n-heptyl, n-octyl, phenyl, tolyl, ethylphenyl, cyclohexyl. The active site of the nitrogen-containing heterocyclic amide extractant involved in coordination is mainly N, O atom, and the polarity of the above side chain substituent may affect the extraction effect and the solubility in different organic phase solvents, but does not change the extraction rule, and the extraction effect is better.

[0016] The preparation method of the extractant A comprises the steps of: adding di-n-octylamine dropwise into a solution of 2,6-pyridine dicarboxylic chloride under ice bath, and refluxing the reaction after the dropwise addition is completed to obtain the extractant.

[0017] Preferably, the preparation of the extractant is carried out under inert gas protection, the molar ratio of di-n-octylamine to 2,6-pyridine dicarboxylic chloride is 1.8-2.2:1, and an acid binding agent is further included, and the amount of the acid binding agent is a conventional amount.

[0018] The solvent used in the reaction includes dichloromethane, tetrahydrofuran, etc. The reaction is carried out at the reflux temperature of the solvent for 3-6h. After the product is washed and dried, the product is purified to obtain the product.

[0019] Preferably, the other rare earth elements include any one or more of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu).

[0020] Further preferably, the other rare earth elements include any one or more of lanthanum, cerium, praseodymium, neodymium, europium, and ytterbium.

[0021] Preferably, the acidic aqueous phase is an aqueous nitric acid solution or an aqueous perchloric acid solution; preferably, the acidic aqueous phase is an aqueous nitric acid solution.

[0022] Preferably, the acidity of the acidic aqueous phase is 1.0-6M. Further preferably, the acidity of the acidic aqueous phase is 3-6M.

[0023] Preferably, the organic phase is an organic solution containing the extractant, and the organic solvent used includes one or more of F-3, n-octanol, sulfonated kerosene, and n-dodecane.

[0024] Preferably, the sum of the molar concentrations of other rare earth elements in the acidic aqueous phase is 20 times or less than the molar concentration of scandium. More preferably, the molar ratio of the sum of the molar concentrations of other rare earth elements to scandium is 1-10:1. Only scandium can be extracted in large amounts in this system, and the rest of the elements are extracted in small amounts. When the total concentration of the rest of the rare earth elements is too high, it will affect the purity of the product scandium. In theory, even if the total molar ratio is larger, scandium will still be extracted preferentially, but it is not appropriate to be too large, which may reduce the purity of the scandium product.

[0025] Preferably, the molar ratio of the extractant to scandium in the acidic aqueous phase is 1:1-3;

[0026] Preferably, the volume ratio of the organic phase to the acidic aqueous phase is 1-5:1;

[0027] Preferably, the extraction mixing time is more than 5 minutes, preferably 5-60 minutes, and further preferably 10-30 minutes. The extraction is carried out at room temperature.

[0028] Preferably, the method for separating scandium from other rare earth elements further comprises the step of: mixing the organic phase containing other rare earth elements with the aqueous phase containing the extractant again for extraction, and repeating 1-5 times.

[0029] Further comprising the step of: adding the scandium-containing aqueous phase to a stripping solution for stripping; and evaporating and crystallizing the obtained aqueous phase to obtain a scandium product, the purity of the scandium product being 95% or more, preferably 95-98%.

[0030] The stripping solution is dilute hydrochloric acid or dilute sulfuric acid with an acidity of 0.01-0.5M.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] The present application uses a nitrogen-containing heterocyclic extractant, and separates scandium from the rest of the rare earth elements through solvent extraction, stripping, evaporation and crystallization. The extraction rate of scandium is high, and the rest of the rare earth elements are hardly extracted. High-purity scandium products can be obtained through simple stripping. Compared with the existing process, the present application can separate scandium from one or more rare earth elements at the same time, and the stripping and transformation are integrated in one step, which shortens the process flow and obtains a scandium product with high purity and high economic value. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The effect of the acidity of the extractant on the extraction rate of scandium and other rare earth elements in Example 5. 1 H nuclear magnetic resonance spectrum.

[0034] Figure 2 The effect of the acidity of the extractant on the extraction rate of scandium and other rare earth elements in Example 5. DETAILED DESCRIPTION

[0035] In order to make the purposes, technical solutions and advantages of the present application more clear and understandable, the present application is further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. Those skilled in the art can make modifications or equivalent replacements without departing from the spirit and scope of the present application based on the technical solutions of the present application, which should be covered within the protection scope of the present application.

[0036] The raw materials used in the following specific embodiments are all purchased from the market, and the purity of the product in the embodiments is tested and calculated by using the iCAP PRO inductively coupled plasma emission spectrometer of Thermo Fisher Scientific Company.

[0037] Example 1

[0038] (1) A small amount of 1 equivalent of 2,6-pyridinecarbonyl chloride was dissolved in super-dry dichloromethane (DCM) and stirred to dissolve under a helium atmosphere and ice water bath;

[0039] (2) 4 equivalents of triethylamine and 2 equivalents or more of di-n-octylamine were added dropwise into the mixed solution, and stirring was continued during the process;

[0040] (3) After the dropwise addition was completed, the system was warmed to 45°C, refluxed, and stirred for 4h;

[0041] (4) After the reaction was completed, 100ml of dilute hydrochloric acid was used for washing twice, and the obtained aqueous phase was extracted with 50ml of dichloromethane twice and then combined with the organic phase, and anhydrous sodium sulfate was added for drying for 24h or more;

[0042] (5) The liquid phase was obtained by filtration, and after rotary evaporation, the residue was purified by a silica gel chromatographic column to obtain a pyridine amide extractant product with the following structure, and the yield was 83.5%.

[0043]

[0044] The product was characterized by nuclear magnetic resonance, and the structure of the product was obtained. 1 H NMR as Figure 1 shown, and the target structure product was obtained.

[0045] The composition of the feed liquid was scandium, lanthanum, cerium, praseodymium and neodymium, and the molar ratio was 1:2:2:2:2. The perchloric acid concentration was 4M. The extractant was dissolved in F-3 to form an organic phase, and the molar ratio of the extractant concentration to the scandium element in the aqueous phase was 1:1. 60mL of the organic phase and 20mL of the aqueous phase were taken into a centrifuge tube, and in this case, the volume ratio of the organic phase to the aqueous phase was 3:1.

[0046] Put the centrifuge tube into the shaker, the shaking speed is 3000 rpm, and the shaking time is 15 min. After the shaking is finished, transfer the water phase to a new centrifuge tube, and add the same organic phase again, repeat the shaking extraction operation according to the above parameters. Repeat the above shaking four times, take out the organic phase respectively and combine, add the same volume of 0.01M dilute hydrochloric acid, shake back extraction. After taking out the water phase, evaporate and crystallize to obtain the product, the purity is 96.7%. Among them, the total extraction rate of scandium element is 99.77%, and the single-stage extraction rate is 81.30%.

[0047] Example 2:

[0048] The structure of the extractant used in this example is:

[0049]

[0050] Its source is synthesized according to the preparation method in the literature "Towards understanding the correlation between UO2+2 extraction and substitute groups in 2,9-diamide-1,10-phenanthroline".

[0051] Its preparation process is:

[0052] (1) Under the protection of helium atmosphere, a small amount of 1 equivalent of 2,9-phenanthroline dicarboxylic acid is dissolved in an appropriate amount of dichlorosulfide, and the whole process is continuously stirred;

[0053] (2) After the dissolution is completed, the temperature is raised to 85°C, continuously stirred, refluxed, and reacted for 3h;

[0054] (3) After the reaction is completed, the excess dichlorosulfide is removed by rotary evaporation under reduced pressure;

[0055] (4) In the helium atmosphere and ice water bath, the residue is dissolved in an appropriate amount of ultradry dichloromethane, and 4 equivalents of triethylamine and 2 equivalents of di-n-octylamine are added dropwise;

[0056] (5) After the dropwise addition is completed, the system is heated to 45°C, refluxed, and stirred for 4h;

[0057] (6) After the reaction is completed, wash with 100ml dilute hydrochloric acid twice, and then extract the obtained water phase with 50ml dichloromethane twice, combine with the organic phase, and add anhydrous sodium sulfate to dry for more than 24h;

[0058] (7) Filter to obtain the liquid phase, and after rotary evaporation, purify the residue with a silica gel chromatographic column to obtain the product, the yield is 81.2%.

[0059] The composition of the feed solution is scandium, cerium, neodymium, europium, holmium, and the molar ratio is 1:1:2:3:2, and the concentration of nitric acid is 4M. The phenanthroline amide extractant is dissolved in F-3 to form an organic phase, and the molar ratio of the concentration of the extractant to scandium in the aqueous phase is 2:1. 60mL of the organic phase and 30mL of the aqueous phase are taken into a centrifuge tube, and in this case, the volume ratio of the organic phase to the aqueous phase is 2:1.

[0060] The centrifuge tube is placed in a shaker, the shaking speed is 2500rpm, and the shaking time is 10min. After shaking, the aqueous phase is transferred to a new centrifuge tube, and the same organic phase is added again, and the shaking extraction operation is repeated according to the above parameters. The above shaking is repeated four times, the organic phase is taken out and combined, and an equal volume of 0.05M dilute hydrochloric acid is added for back extraction. After the aqueous phase is taken out, evaporation and crystallization are carried out to obtain the product, and the purity is 97.2%. Among them, the total extraction rate of scandium is 98.39%, and the single-stage extraction rate is 78.96%.

[0061] Example 3:

[0062] The extractant used in this example is the same as that of Example 2, and the composition of the feed solution is scandium, europium, erbium, ytterbium, and lutetium, and the molar ratio is 1:4:2:3:5, and the concentration of nitric acid is 5M.

[0063] The phenanthroline amide extractant is dissolved in sulfonated kerosene to form an organic phase, and the molar ratio of the concentration of the extractant to scandium in the aqueous phase is 3:1. 60mL of the organic phase and 40mL of the aqueous phase are taken into a centrifuge tube, and in this case, the volume ratio of the organic phase to the aqueous phase is 3:2.

[0064] The centrifuge tube is placed in a shaker, the shaking speed is 3000rpm, and the shaking time is 20min. After shaking, the aqueous phase is transferred to a new centrifuge tube, and the same organic phase is added again, and the shaking extraction operation is repeated according to the above parameters. The above shaking is repeated four times, the organic phase is taken out and combined, and an equal volume of 0.1M dilute hydrochloric acid is added for back extraction. After the aqueous phase is taken out, evaporation and crystallization are carried out to obtain the product, and the purity is 97.5%. Among them, the total extraction rate of scandium is 99.42%, and the single-stage extraction rate is 88.25%.

[0065] Example 4:

[0066] The structure of the extractant used in this example is:

[0067]

[0068] The source is according to the literature "Novel diamides of 2,2'-dipyridyl-6,6'-dicarboxylic acid:

[0069] synthesis, coordination properties, and possibilities of use in electrochemical

[0070] synthesis, coordination properties, and possibilities of use in electrochemical

[0071] The preparation process is as follows:

[0072] (1) A small amount of 1 equivalent of 2,9-dipyridine dicarboxylic acid is dissolved in an appropriate amount of dichlorosulfide under a helium protective atmosphere, and the whole process is continuously stirred;

[0073] (2) After dissolution, the temperature is raised to 85°C, continuously stirred, refluxed, and reacted for 3h;

[0074] (3) After the reaction is completed, the excess dichlorosulfide is removed by rotary evaporation under reduced pressure;

[0075] (4) In a helium atmosphere and ice water bath, the residue is dissolved in an appropriate amount of super-dry dichloromethane, and 4 equivalents of triethylamine and 2 equivalents or more of di-n-octylamine are added dropwise;

[0076] (5) After the dropwise addition is completed, the system is heated to 45°C, refluxed, and stirred for 4h;

[0077] (6) After the reaction is completed, wash with 100ml dilute hydrochloric acid twice, extract the obtained aqueous phase with 50ml dichloromethane twice, and then combine with the organic phase, add anhydrous sodium sulfate and dry for 24h or more;

[0078] (7) Filter to obtain the liquid phase, rotary evaporate, and then purify the residue with a silica gel chromatography column to obtain the product, with a yield of 82.7%.

[0079] The aqueous phase has a composition of scandium, europium, erbium, ytterbium, and lutetium, with a molar ratio of 1:3:2:3:4, and a perchloric acid concentration of 4M.

[0080] Dissolve the phenanthroline amide extractant in n-octanol to form an organic phase, with a concentration of 2:1 molar ratio of scandium element in the aqueous phase. Take 60mL of organic phase and 15mL of aqueous phase and add them to a centrifuge tube. In this case, the volume ratio of organic phase to aqueous phase is 4:1.

[0081] Centrifuge tubes were placed in a shaker at 4000 rpm for 15 minutes. After shaking, the aqueous phase was transferred to a new centrifuge tube, and the same organic phase was added again. The shaking extraction operation was repeated with the same parameters. This shaking process was repeated four times. The organic phases were then collected and combined, and an equal volume of 0.01 M dilute sulfuric acid was added for back-extraction. The aqueous phase was then removed and evaporated to obtain the product with a purity of 98.4%. The total extraction rate of scandium was 99.94%, and the single-stage extraction rate was 99.74%.

[0082] Example 5

[0083] Following the steps of Example 2, to explore the conditions for scandium separation, the concentrations of nitric acid in the aqueous phase were adjusted to 0.5M, 1.0M, 1.5M, 2.0M, and 2.5M, respectively. The concentrations of all rare earth elements were the same as the scandium concentration, while other conditions remained unchanged. After extraction, the extraction rates of each rare earth element were calculated. The extraction rate was calculated as follows: (C i -C a ) / C i *100%.

[0084] Among them, C i : Concentration of metal ions in the aqueous phase before extraction; C a The concentrations of metal ions in the aqueous phase after extraction were measured by ICP-OES.

[0085] Extraction rates of each element, such as Figure 2 As shown, from Figure 2 It is evident that, except for scandium, the other rare earth elements are hardly extracted in this system and do not change with acidity. The extraction rate of scandium gradually increases with increasing nitric acid concentration. This is because, during the extraction process, nitrate ions participate as coordinating anions in the formation of the extracted compound; the increase in nitrate concentration promotes a positive shift in chemical equilibrium, thus leading to an increase in the scandium extraction rate.

Claims

1. A method for separating scandium from other rare earth elements, characterized by, The method comprises the steps of mixing an acidic aqueous phase containing scandium and other rare earth elements with an organic phase containing an extractant to obtain an aqueous phase containing scandium and an organic phase containing other rare earth elements by extraction separation; the extractant has any one of the structures shown in A or B: wherein R and R' are independently selected from any one of C2-20 linear or branched alkyl, phenyl, tolyl.

2. The method of separating scandium from other rare earth elements according to claim 1, characterized by, R and R' are independently selected from any one of C6-10 linear or branched alkyl, phenyl, tolyl.

3. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The other rare earth elements include any one or more of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

4. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The acidic aqueous phase is an aqueous nitric acid solution or an aqueous perchloric acid solution.

5. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The acidity of the acidic aqueous phase is 1-6M.

6. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The organic phase is an organic solution containing an extractant, and the organic solvents used include one or more of F-3, n-octanol, sulfonated kerosene, and n-dodecane.

7. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The total molar concentration of other rare earth elements in the acidic aqueous phase is 20 times or less than the molar concentration of scandium. And / or, the molar ratio of the extractant to scandium in the acidic aqueous phase is 1:1-3.

8. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The volume ratio of the organic phase to the acidic aqueous phase is 1-5:

1. And / or, the extraction mixing time is more than 5 minutes.

9. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The method further comprises the step of mixing the organic phase containing other rare earth elements with an aqueous phase containing an extractant again for extraction, which is repeated 1-5 times.

10. The method of separating scandium from other rare earth elements according to claim 1, characterized by, The method further comprises the step of adding the aqueous phase containing scandium to a stripping solution for stripping. The stripping solution is dilute hydrochloric acid or dilute sulfuric acid with an acidity of 0.01-0.5M.

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