Method for selectively separating rare earth by utilizing rigid chelating precipitant, rare earth metal organic framework and application

Abstract

The invention belongs to the technical field of rare earth, and relates to a method for selectively separating rare earth by using a rigid chelating precipitator, a rare earth metal organic framework and application. Comprising the following steps: adjusting a mixed rare earth solution to a proper pH value, and then adding a rigid chelating precipitator 1, 2, 4, 5-benzenetetraol (BTT); the precipitant has an obvious precipitation effect on part of light rare earth ions (Pr and Nd) and medium and heavy rare earth, and the rare earth is separated from a solution in a mode of forming a metal organic framework in situ; and the precipitation capacity on light rare earth La and Ce is weak, and the precipitation has obvious hysteresis, so that most La and Ce ions are still retained in the solution. In addition, according to the method, high-selectivity separation of part of rare earth elements can be achieved in complex rare earth leaching liquid containing impurity heavy metal ions. The method has the advantages of simple operation, short period and the like, has good industrial application potential, and provides a new technical path for efficient separation and utilization of rare earth resources.

Description

Technical Field

[0001] The present application belongs to the field of rare earth technology, and in particular relates to a method for selectively separating rare earths using a rigid chelating precipitant, a rare earth metal organic framework and applications. Background Art

[0002] Rare earth elements (REEs) are widely used in modern industry, medicine, military and other fields due to their unique physical and chemical properties. However, in the process of rare earth resource mining and recovery, the leaching solution is often mixed with a large amount of impurity metal ions. This poses a severe challenge to the separation and purification of rare earths. Most of the current research focuses on the separation technology of rare earth elements and heavy metal ions. These technologies can obtain mixed rare earth oxides with higher purity, but in order to meet the needs of practical applications, further separation and purification are still required to obtain single rare earth products. However, due to the high similarity between rare earth ions, such as similar ionic radius and the same oxidation state (trivalent state), the efficient separation of rare earth ions has become an extremely challenging task.

[0003] At present, the separation technology of rare earth mainly includes step-by-step precipitation method, ion exchange chromatography method and solvent extraction method. Among them, solvent extraction method is the most widely used large-scale rare earth separation technology, and about 90% of the rare earth separation processes in the world adopt this method. Its principle is to achieve separation by utilizing the small affinity difference between the N, O and P active groups in the extractant and the rare earth ions. However, due to the low separation selectivity coefficient, this method usually requires dozens or even hundreds of series treatments to collect a single rare earth. With the development of solid coordination chemistry, new technologies for selective crystallization separation of rare earths based on metal organic framework (MOF) synthesis and supramolecular compound assembly have also emerged. These technologies show greater advantages in the selectivity of separation between rare earths. However, this type of technology has the problem of harsh separation conditions, that is, the reaction process needs to be carried out in organic solvents, concentrated nitric acid or high-temperature reactors, which seriously restricts their application in actual leachates. Although oxalic acid, a commonly used precipitant in actual leachates, has the advantages of adaptability to a wide pH range, good selectivity, and strong precipitation performance, it is also difficult to achieve effective separation between rare earth elements and is easily interfered by calcium ions. Therefore, it is particularly important to develop a technology that can resist the interference of impure heavy metals in actual leaching solutions and efficiently separate light and heavy rare earths.

[0004] Oxalic acid shows a wide range of adaptability to heavy metal calcium and rare earth series. From the perspective of coordination flexibility, this is mainly attributed to the flexible characteristics of its structure. In the oxalic acid structure, the CC bond can be flexibly twisted during the crystallization process to adapt to rare earth ions and calcium ions of different sizes. From the perspective of coordination difficulty, oxalic acid is a medium-strong acid, which can easily chelate with various metal ions after deprotonation. Summary of the invention

[0005] In view of the difficulty in selectively separating rare earth ions in the background technology, the present application selects 1,2,4,5-benzenetetraphenol (BTT) with a rigid chelating cavity and a special delocalized π-electron structure as a rare earth precipitant, and provides a method for selectively separating rare earths using a rigid chelating precipitant, a rare earth metal organic framework and its application.

[0006] In a first aspect, the present application provides a method for selectively separating rare earth using a rigid chelating precipitant, the method comprising the steps of:

[0007] Step S1, adjusting the pH value of the mixed rare earth solution to 2.5-5;

[0008] Step S2, adding the rigid chelating precipitant 1,2,4,5-pyrophentetraphenol into the mixed rare earth solution and stirring, and after assembling with a part of the rare earth elements in the mixed rare earth solution, the precipitant is crystallized and precipitated in the form of a rare earth metal organic framework.

[0009] Preferably, in step S1, the adjusting pH value to 2.5-5 specifically means: the adjusting pH value to 2.5-3.

[0010] Preferably, in step S1, the mixed rare earth solution is a mixed rare earth solution containing lanthanum ions and neodymium ions, lanthanum ions and samarium ions, lanthanum ions and europium ions, lanthanum ions and gadolinium ions, lanthanum ions and terbium ions, lanthanum ions and ytterbium ions, or lanthanum ions and lutetium ions.

[0011] Preferably, in step S1, the mixed rare earth solution is a mixed rare earth solution containing lanthanum ions, cerium ions, praseodymium ions, neodymium ions, samarium ions, europium ions, gadolinium ions, terbium ions, dysprosium ions, holmium ions, erbium ions, thulium ions, ytterbium ions, lutetium ions and yttrium ions.

[0012] Preferably, in step S1, the mixed rare earth solution is a mixed rare earth solution containing lanthanum ions, cerium ions, praseodymium ions, neodymium ions, samarium ions, europium ions, gadolinium ions, terbium ions, dysprosium ions, holmium ions, erbium ions, thulium ions, ytterbium ions, lutetium ions, yttrium ions, calcium ions, magnesium ions and aluminum ions.

[0013] Preferably, in step S2, the stirring temperature is 20-30° C. and the stirring time is 2-12 h.

[0014] Preferably, in step S2, the molar ratio of the rigid chelating precipitant 1,2,4,5-pyromellitic acid to the total amount of rare earth ion substances in the mixed rare earth solution is 0.3-3:1.

[0015] The second aspect of the present application provides a rare earth metal organic framework, which is assembled from a rigid chelating precipitant 1,2,4,5-benzene tetraphenol, rare earth ions in the mixed rare earth solution of the first aspect, and water molecules; the rigid chelating precipitant 1,2,4,5-benzene tetraphenol and the rare earth ions chelate to form a two-dimensional layered coordination network, and the two-dimensional layered coordination network is connected by hydrogen bonds between interlayer water molecules to form a three-dimensional rare earth metal organic framework.

[0016] The third aspect of the present application provides a method for preparing a rare earth metal organic framework, which can be used to prepare the rare earth metal organic framework described in the second aspect. The preparation method includes the steps of: subjecting the solution from which the rare earth metal organic framework is crystallized in step S2 of the first aspect to solid-liquid separation to obtain the rare earth metal organic framework.

[0017] The fourth aspect of the present application provides the application of the rare earth metal organic framework described in the second aspect in the field of catalysis or adsorption.

[0018] Compared with the prior art, the present application provides a method for selectively separating rare earths using a rigid chelating precipitant, which has at least the following beneficial effects.

[0019] (1) The rigid chelate precipitant BTT used in this application has a unique rigid chelate cavity and a special delocalized π electron distribution, which can efficiently crystallize with most rare earth ions, but has limited crystallization ability for light rare earth La and Ce, and has a high separation coefficient between rare earths.

[0020] (2) Compared with the flexible chelating precipitant oxalic acid, the rigid chelating precipitant BTT used in this application not only has the ability to separate similar rare earth elements, but also can effectively avoid co-precipitation with calcium ions, which provides a new material design idea for the selective extraction of rare earth elements in complex leachates.

[0021] (3) The present application mentions a rare earth selective crystallization method, which can achieve the separation of rare earth elements by stirring at room temperature, with simple operation and short reaction cycle. In addition, the collected rare earth metal organic framework can also be used in the field of environmental functional materials such as catalysis and adsorption.

[0022] (4) This application does not require the use of a large amount of toxic and hazardous organic solvents, and the separation conditions are consistent with actual scenarios, and is suitable for the selective separation of rare earths from mining leaching solutions and industrial production wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0024] Figure 1 This is a graph of the rare earth precipitation rate of the rigid chelating precipitant BTT under different pH conditions in Example 1 of the present application.

[0025] Figure 2 This is a graph showing the precipitation rate of the rigid chelating precipitant BTT for all rare earth ions in Example 2 of the present application.

[0026] Figure 3 This is the morphology of the rare earth crystal product of the rigid chelating precipitant BTT in Example 2 of the present application under a 100x microscope.

[0027] Figure 4 It is the crystal structure of the Y-BTT metal organic framework in Example 2 of the present application; wherein (a) is the Y-BTT rare earth ion coordination configuration diagram; and (b) is the three-dimensional spatial network diagram of Y-BTT.

[0028] Figure 5 This is the XRD diagram of the crystal product of the rigid chelating precipitant BTT and rare earth ions in Example 2 of the present application.

[0029] Figure 6 This is the precipitation kinetics diagram of the rigid chelating precipitant BTT on light rare earth and heavy rare earth Y in Example 3 of the present application.

[0030] Figure 7 This is a crystallization selectivity diagram of the rigid chelating precipitant BTT in equimolar binary rare earth ions in Example 4 of the present application.

[0031] Figure 8 This is a graph of the metal precipitation ability of the rigid chelating precipitant BTT in the simulated rare earth leachate in Example 5 of the present application; wherein (a) is the metal ion precipitation rate at different BTT dosages; and (b) is the metal ion distribution coefficient at different BTT dosages.

[0032] Fig. 9 It is a schematic flow chart of the method for selectively separating rare earths using a rigid chelating precipitant provided in the present application. DETAILED DESCRIPTION

[0033] The present application provides a method for selectively separating rare earths using a rigid chelating precipitant, a rare earth metal organic framework and its application, which are used to solve the technical problem that rare earth ions are difficult to selectively separate in the prior art.

[0034] The technical solution of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0035] In the face of the difficulty in selectively separating rare earth ions, this application uses 1,2,4,5-benzene tetraphenol (BTT) with a rigid chelating cavity and a special delocalized π electron structure as a rare earth precipitant, and selectively separates rare earths through a rigid chelating coordination assembly method. Unlike the CC flexible skeleton in the oxalic acid chelating precipitant, the method for selectively separating rare earths with a rigid chelating precipitant provided in this application uses a strongly rigid benzene ring as a skeleton, and the ortho-phenol on the benzene ring serves as the chelating site of the rare earth ion. The rigid coordination network formed may enhance the size difference between the rare earth ions.

[0036] In addition, the π-f conjugation effect between rare earth ions and benzene rings will also affect the coordination selectivity between the host and the guest. Specifically, the delocalized π bond formed by the benzene ring and the hydroxyl oxygen will produce a unique π-f conjugation effect with the 4f orbital electrons in the rare earth ion. The number of rare earth 4f orbital electrons will change the intensity of the π-f conjugation effect, thereby affecting the stability of the formed coordination bond. In contrast, the lack of delocalized π bonds in the oxalic acid structure does not meet the conditions for the π-f conjugation effect to occur.

[0037] So far, there has been no report on the selective separation of light and heavy rare earth elements using rigid chelating precipitants. This study innovatively proposed a method for separating light and heavy rare earth elements using rigid chelating precipitants, which is expected to provide a theoretical basis and practical guidance for the efficient separation of rare earth resources.

[0038] Example 1

[0039] Example 1 of the present application studies the effect of pH on the ability of 1,2,4,5-benzene tetraphenol (BTT) to precipitate rare earths

[0040] Use rare earth chloride salts to prepare six portions of each of La, Ce, Gd, Tb, Yb, Lu and Y rare earth elements, with a volume of 100 mL and a concentration of 10 mg / L experimental sample solution. The pH values ​​of the solution were adjusted to 2, 2.5, 3, 3.5, 4 and 5 by HCl and NaOH, respectively. Weigh 79.8 mg of BTT and dissolve it in 50 mL of ultrapure water, then ultrasonically treat it for 5 minutes, then transfer 1 mL of BTT solution to the experimental sample solution and stir it for 2 hours. At this time, the starting concentration of Y is 0.1125 mM, the concentration range of other rare earth ions is 0.057-0.072 mM, and the concentration of the precipitant is 0.1125 mM.

[0041] The solution was filtered through a 0.22µm water filter membrane and the remaining REEs were detected by inductively coupled plasma mass spectrometry (ICP-MS). 3+ The concentration was calculated and the precipitation rate was calculated. Figure 1 As shown in the figure, when the pH is between 3.5 and 5, the precipitation rates of the rare earth ions are not much different; when the pH is 2, the precipitation of the seven rare earths by BTT is not obvious. However, when the pH is between 2.5 and 3, the precipitation rates of medium and heavy rare earths by BTT are all greater than 55%. The precipitation rates of light rare earths La and Ce are less than 10%, showing obvious precipitation differentiation.

[0042] Example 2

[0043] Example 2 of the present application provides the precipitation ability of 1,2,4,5-benzene tetraphenol (BTT) for all rare earth elements

[0044] Weigh 15 kinds of rare earth chloride salts (except rare earth promethium) respectively, dissolve them in ultrapure water to prepare 100mL of experimental solution with a concentration of 10mg / L, and adjust the pH to 3. Weigh 34.08mg of BTT and dissolve it in 16mL of ultrapure water, then ultrasonically treat it for 5min, transfer 1mL of BTT solution to the experimental solution and stir for 2h. After filtering the solution with a 0.22µm water filter membrane, the remaining REE was detected by ICP-MS. 3+ The concentration of Y is 0.1125 mM, the concentration of other rare earth ions is 0.057-0.072 mM, and the concentration of the precipitant is 0.15 mM. Figure 2 In the results of rare earth precipitation, the precipitation rate of BTT for rare earth elements such as Pr-Lu is close to 100%, and the rare earths are basically precipitated completely. The incomplete precipitation of Y may be due to the larger number of ions at the same mass concentration. The concentration difference between La and Ce ions and other rare earth ion substances is not large, but the precipitation ability of BTT ions is obviously weaker. The heterogeneity of this precipitation phenomenon is mainly attributed to the recognition of the rare earth size by the hydroxyl chelating site in BTT and the conjugation effect of the delocalized π bond on the benzene ring with the rare earth ions.

[0045] In this embodiment, eight groups of representative rare earth crystalline products REE-BTT (REE is La, Ce, Eu, Gd, Tb, Yb, Lu and Y) were collected and subjected to single crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD) analyses. Figure 3 The crystal morphology of various REE-BTT products is shown, all of which are dark red hexagonal flake crystals. The spatial structure of the crystal is shown in Figure 4 As shown, from Figure 4 As can be seen in a, one side of the Y ion is chelated by three BTT molecules, and the other side is three coordinated water molecules. The result after further removing the free water molecules in the pore and hiding the hydrogen atoms is as follows Figure 4 As shown in b, it can be seen that the rare earth-based metal-organic framework first uses BTT chelation coordination to form a two-dimensional structure, and then uses the hydrogen bonding between the coordinated water and the free water to connect the two-dimensional structure (the framed area is the hydrogen bonding area) to form a three-dimensional rare earth-based metal-organic framework.

[0046] Figure 5 This is the XRD pattern of the crystallization product of rigid chelating precipitant BTT and rare earth ions. The analysis results show that the main peaks of the measured PXRD and Y-BTT simulated XRD diffraction patterns of each sample are basically consistent. However, the diffraction spectrum of La-BTT has diffraction peaks different from the simulated values ​​at lower angles (7.8° and 10.0°). This difference can be attributed to the difference between BTT and La 3+ The weaker binding force causes the crystallization pattern to change.

[0047] Example 3

[0048] Example 3 of the present application provides the precipitation kinetics of 1,2,4,5-benzeneteterol (BTT) for light rare earth elements and heavy rare earth Y

[0049] Prepare 100 mL of each La, Ce, Pr, Nd and Y rare earth sample solution with a concentration of 10 mg / L, and adjust the pH to 3. Weigh 17.04 mg of BTT and dissolve it in 8 mL of ultrapure water, then ultrasonically treat it for 5 minutes, then transfer 1 mL of BTT solution into the experimental sample solution and stir for 2 hours. During this period, samples were taken every 10 minutes, and 1 mL was sampled each time. At this time, the initial concentration of Y was 0.1125 mM, the concentration range of other rare earth ions was 0.057-0.072 mM, and the concentration of the precipitant was 0.15 mM. After the sample solution was filtered with a 0.22µm water filter membrane, the remaining REEs were detected by ICP-MS. 3+ The concentration was calculated and the precipitation rate was calculated. Figure 6 As shown, the precipitation kinetics of BTT for light rare earth elements La and Ce are slow with significant hysteresis, while the precipitation rate for Y is significantly faster.

[0050] Example 4

[0051] Example 4 of the present application provides the crystallization selectivity of the rigid chelating precipitant 1,2,4,5-pyroxene tetraphenol for the binary mixed rare earth solution.

[0052] 0.05 mmol of two rare earth chloride salts were dissolved in 50 mL of ultrapure water to prepare a rare earth binary mixed solution, and the pH was adjusted to 3. 0.1 mmol of BTT was added to the binary mixed solution and stirred for 2 h. The solution was filtered with a 0.22 µm water filter membrane, and the remaining REE in the filtrate was detected by inductively coupled plasma optical emission spectrometry (ICP-OES). 3+ concentration. Figure 7is the crystallization selectivity diagram of the rigid chelating precipitant BTT in equimolar binary rare earth ions, and "In" and "Out" are the ratios of rare earth elements in the original rare earth mixed solution and the solution after the reaction. Figure 7 The precipitation ability of BTT for rare earth elements Nd, Sm, Eu, Gd, Tb, Yb and Lu is significantly better than that of La, and the selectivity coefficient (SF) in the binary mixed rare earth solution of La and Sm can reach 34.7 (Sm / La).

[0053] Example 5

[0054] Example 5 of the present application provides a treatment method for a simulated ionic rare earth ore leachate using 1,2,4,5-benzene tetraphenol (BTT)

[0055] According to the actual characteristics of the ionic rare earth ore leaching solution in the south, rare earth chloride and heavy metal sulfate were used as raw materials to prepare a simulated solution in a certain proportion, and the pH was adjusted to 4.71. Table 1 shows the metal concentration in the simulated ionic rare earth ore leaching solution. The leaching solution mainly contains heavy rare earth Y and a large number of impurity ions (such as Mg 2+ , Ca 2+ and Al 3+ ). 10, 20, 40, 60 and 80 mg of BTT were added to 100 mL of simulated rare earth leaching solution and stirred for 12 h. At this time, the total molar concentration of rare earth ions in the leaching solution was 1.93 mM, and the precipitant concentration range was 0.70-5.63 mM. After the reaction solution was filtered with a 0.22 µm water filter membrane, the remaining REE in the filtrate was detected by ICP-MS and ICP-OES. 3+ and heavy metal ion concentration, and calculate the precipitation rate. Figure 8 This is a graph showing the metal precipitation ability of the rigid chelating precipitant BTT in a simulated rare earth leaching solution. Figure 8 a, BTT has outstanding precipitation selectivity in complex leaching solutions, and it crystallizes efficiently with medium and heavy rare earths without being affected by a large amount of impurity heavy metals. Figure 8 b is the distribution coefficient of metal ions, which shows that BTT has a strong binding ability to medium rare earth ions, among which the distribution coefficient of Sm is as high as 1143. This is mainly attributed to the size matching between medium rare earth ions and BTT cavities and the strong π-f conjugation effect.

[0056] Table 1: Metal concentrations of simulated ionic rare earth ore leachate

[0057]

[0058] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for selectively separating rare earth using a rigid chelating precipitant, characterized in that: Includes steps: Step S1, adjusting the pH value of the mixed rare earth solution to 2.5-5; Step S2, adding the rigid chelating precipitant 1,2,4,5-pyrophentetraphenol into the mixed rare earth solution and stirring, and after assembling with a part of the rare earth elements in the mixed rare earth solution, the precipitant is crystallized and precipitated in the form of a rare earth metal organic framework.

2. The method for selectively separating rare earth using a rigid chelating precipitant according to claim 1, characterized in that: In step S1, the pH value is adjusted to 2.5-5, specifically: the pH value is adjusted to 2.5-3.

3. The method for selectively separating rare earth using a rigid chelating precipitant according to claim 1, characterized in that: In step S1, the mixed rare earth solution contains lanthanum ions and neodymium ions, lanthanum ions and samarium ions, lanthanum ions and europium ions, lanthanum ions and gadolinium ions, lanthanum ions and terbium ions, lanthanum ions and ytterbium ions, or lanthanum ions and lutetium ions.

4. The method for selectively separating rare earth using a rigid chelating precipitant according to claim 1, characterized in that: In step S1, the mixed rare earth solution contains lanthanum ions, cerium ions, praseodymium ions, neodymium ions, samarium ions, europium ions, gadolinium ions, terbium ions, dysprosium ions, holmium ions, erbium ions, thulium ions, ytterbium ions, lutetium ions and yttrium ions.

5. The method for selectively separating rare earth using a rigid chelating precipitant according to claim 1, characterized in that: In step S1, the mixed rare earth solution contains lanthanum ions, cerium ions, praseodymium ions, neodymium ions, samarium ions, europium ions, gadolinium ions, terbium ions, dysprosium ions, holmium ions, erbium ions, thulium ions, ytterbium ions, lutetium ions, yttrium ions, calcium ions, magnesium ions and aluminum ions.

6. The method for selectively separating rare earth using a rigid chelating precipitant according to claim 1, characterized in that: In step S2, the molar ratio of the rigid chelating precipitant 1,2,4,5-pyromellitic acid to the total amount of rare earth ion substances in the mixed rare earth solution is 0.3-3:

1.

7. A rare earth metal organic framework, characterized in that It is assembled from a rigid chelating precipitant 1,2,4,5-pyrophentetraphenol, rare earth ions in the mixed rare earth solution according to any one of claims 1 to 6, and water molecules; The rigid chelating precipitant 1,2,4,5-pyrophentetraphenol and the rare earth ions chelate to form a two-dimensional layered coordination network; The two-dimensional layered coordination network is connected by hydrogen bonds between interlayer water molecules to form a three-dimensional rare earth metal organic framework.

8. The method for preparing a rare earth metal organic framework according to claim 7, characterized in that: The method comprises the steps of: subjecting the solution in which the rare earth metal organic framework is crystallized in step S2 according to any one of claims 1 to 6 to solid-liquid separation to obtain the rare earth metal organic framework.

9. Use of the rare earth metal organic framework according to claim 7 in the field of catalysis or adsorption.

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