Method for recycling lanthanum and cerium rare earth metals in water by using metal organic framework

Abstract

The application discloses a method for recycling lanthanum and cerium rare earth metals in water by using a metal organic framework. The method utilizes the strong coordination affinity between the rich imidazole nitrogen active sites in the ZIF-67 material framework and rare earth ions, and a coupling mechanism of adsorption-framework dissociation-phase transformation of ZIF-67 induced by rare earth ions, to realize one-step efficient and selective recovery of La 3+ and Ce 3+ in water and in-situ crystal phase conversion. The recycling method of the application realizes efficient recovery of La 3+ and Ce 3+ , and is more comprehensive in rare earth recycling types and better in pH adaptability, and is especially suitable for acid wastewater treatment, breaks the bottleneck that products are difficult to collect under acidic conditions in the prior art, and can directly treat typical acid smelting wastewater without pre-neutralization treatment.

Description

Technical Field

[0001] This invention relates to the fields of water treatment and rare earth resource recovery, and in particular to a method for recovering lanthanum and cerium rare earth metals from water using a metal-organic framework. Background Technology

[0002] Rare earth elements hold significant value in high-tech fields such as permanent magnets, optoelectronics, and catalysis. Traditional rare earth mining and smelting processes generate large quantities of acidic wastewater with high concentrations of rare earth elements, leading to resource depletion and harming the ecosystem and human health. Excessive rare earth ions in water can inhibit algal photosynthesis, damage aquatic ecosystems, and accumulate in the human body through the soil-plant-food chain, posing long-term health risks. Therefore, the efficient recovery of rare earth elements from industrial wastewater is crucial for sustainable resource utilization and ecological protection.

[0003] Currently, the mainstream processes for rare earth recovery from wastewater are chemical precipitation, ion exchange, and traditional adsorption. Chemical precipitation is simple to operate, solidifying rare earth ions by adding a precipitant, but it suffers from poor selectivity, low product purity, and generates large amounts of waste residue. Ion exchange offers better separation selectivity, but the resin is expensive, regeneration is difficult, and the processing cycle is long. Traditional adsorption commonly uses materials such as activated carbon and zeolite, which, while possessing considerable specific surface area, have insufficient adsorption capacity and selectivity, and require multiple steps including strong acid desorption, precipitation, and calcination to prepare rare earth products. These processes generally suffer from cumbersome procedures, low efficiency, high costs, and a high risk of secondary pollution. Therefore, novel rare earth recovery technologies with simplified procedures and high selectivity have become a research hotspot in the field. Summary of the Invention

[0004] Metal-organic frameworks (MOFs) have shown significant potential in rare earth adsorption and recovery due to their high specific surface area, tunable pore structure, and abundant active sites. However, most existing rare earth recovery technologies still follow the traditional "adsorption-desorption-precipitation-calcination" route, which is lengthy and energy-intensive. Specifically, after the adsorbent material enriches rare earths, it requires multiple steps such as strong acid desorption, precipitation separation, and high-temperature calcination to obtain rare earth oxide products. The overall process is complex, energy-intensive, and costly. Furthermore, existing methods generally have poor selectivity and poor extraction performance in complex aquatic environments. Actual industrial wastewater often contains a large number of coexisting interfering ions (such as Ca2+). 2+ Mg 2+ Na + K + Existing adsorption materials have insufficient selectivity for rare earth ions, which significantly affects extraction efficiency and product purity.

[0005] To address the shortcomings of existing technologies, this invention proposes a method for recovering rare earth metals using metal-organic frameworks.

[0006] This invention provides a method for recovering lanthanum and cerium rare earth metals from water using a metal-organic framework, comprising the following steps:

[0007] S1: Synthesize zeolite imidazolium ester framework material-67; the zeolite imidazolium ester framework material-67 is ZIF-67; S2: First, the rare earth solution is filtered to remove suspended impurities and the pH value is adjusted. Then, the ZIF-67 obtained in step S1 is added to the rare earth solution and reacted at room temperature, generating a solid precipitate. The precipitate is then filtered and dried to obtain the rare earth recovery product. The rare earth solution contains La. 3+ and / or Ce 3+ .

[0008] ZIF-67, a typical zeolite imidazole ester metal-organic framework material, possesses a well-organized three-dimensional porous cage-like framework structure with a large specific surface area, well-developed pore channels, and excellent structural stability in aqueous phase. Its framework is constructed by the coordination of cobalt ions with 2-methylimidazolium ligands, and its surface is enriched with numerous nitrogen-containing active functional groups and polar sites. Simultaneously, the framework surface readily forms negative charges, exhibiting excellent enrichment capabilities for heavy metals and rare earth ions. The nitrogen atom in the 2-methylimidazolium ligand contains a lone pair of electrons, which can form stable coordination bonds with lanthanum and cerium trivalent rare earth cations, achieving selective targeted binding and enabling the enrichment of La in solution. 3+ and / or Ce 3+ Recycling.

[0009] When ZIF-67 and La 3+ During the reaction, depending on the initial rare earth element concentration, it can be converted to La(OH)3 at high concentrations and to La2(CO3)3 at low concentrations; while for Ce... 3+ The recovered materials are converted into cubic fluorite CeO2 crystals through an oxidation-precipitation pathway.

[0010] Y was recovered using the same method 3+ 、Nd 3+ 、Sm 3+ Eu 3+ and Gd 3+ The XRD diffraction pattern of the obtained solid sample only showed an amorphous state, unlike the recovery of La. 3+ Ce 3+ La(OH)3, La2(CO3)3, and CeO2 crystals were obtained directly.

[0011] Furthermore, the concentration of ZIF-67 in the reaction system is 200-400 ppm.

[0012] Furthermore, the pH of the rare earth solution reaction is 3-7.

[0013] Furthermore, La is recovered from the solution. 3+ The reaction pH is 5-7.

[0014] ZIF-67 against Ce 3+ The extraction exhibits excellent pH adaptability, with an extraction efficiency consistently above 95% within a pH range of 3-7, and directly generates high-purity CeO2 crystals.

[0015] In the rare earth solution, La2(CO3)3 is mainly generated. 3+ At concentrations of 10-60 ppm, La mainly forms La(OH)3. 3+ The concentration is 61-200 ppm.

[0016] Furthermore, the reaction time of ZIF-67 with the rare earth solution is 2-12 hours.

[0017] Furthermore, the synthesis method of ZIF-67 includes any one of the following: room temperature liquid phase precipitation, hydrothermal method, and mechanical grinding method.

[0018] Furthermore, the room temperature liquid phase precipitation method includes the following steps: cobalt nitrate hexahydrate and 2-methylimidazole are dissolved in deionized water, mixed rapidly and stirred at room temperature to carry out a crystallization reaction, the precipitate is collected by centrifugation after the reaction is completed, the precipitate is washed with deionized water and methanol in sequence, and ZIF-67 crystals are obtained after vacuum drying.

[0019] Furthermore, the Co 2+ The molar ratio of 2-methylimidazole to H2O is 1:(55-60):(1000-1200).

[0020] Furthermore, the stirring time is 4-6 hours.

[0021] Furthermore, the vacuum drying time is 6-12 hours, and the temperature is 50-80℃.

[0022] In some implementations, ZIF-67 can still effectively extract Ce even under acidic conditions at pH=3. 3+ It generates CeO2 crystals, breaking through the bottleneck of existing technology where products are difficult to collect under acidic conditions. It can directly treat typical acidic smelting wastewater without the need for pre-neutralization treatment.

[0023] In summary, compared with the prior art, the present invention achieves the following technical effects: (1) This invention uses ZIF-67 material, which is not only effective against Ce 3+ It exhibits superior extraction performance (maximum capacity 728.2 mg / g) and also achieves La 3+Highly efficient recovery (maximum capacity 495.8 mg / g), and for the first time revealed La 3+ It can be converted into crystalline La(OH)3 or La2(CO3)3, rather than remaining in the amorphous adsorbed state.

[0024] (2) In this invention, ZIF-67 is effective against Ce 3+ The extraction efficiency remains above 95% within the pH range of 3-7, and the extraction capacity is basically unchanged with pH. This breaks through the bottleneck of existing technologies where the product is difficult to collect under acidic conditions. It can directly treat typical acidic smelting wastewater without the need for pre-neutralization treatment.

[0025] (3) The recycling method of the present invention has a simple process flow and few operation steps. Rare earth recovery can be completed in one step without the need for multiple complicated processes such as desorption, precipitation, and roasting. The reaction conditions are mild and do not require the addition of a large amount of chemical reagents. Rare earth oxides, hydroxides or carbonate crystals can be generated in situ. Rare earth precursors with application value can be obtained without secondary treatment. Almost no waste residue or waste liquid is generated throughout the process, which effectively avoids secondary pollution. It is green and environmentally friendly with low operating costs and is suitable for the treatment of industrial acidic rare earth wastewater. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The image shows the X-ray diffraction pattern of ZIF-67 synthesized in Example 1 of this invention.

[0028] Figure 2 This is a scanning electron microscope image of ZIF-67 synthesized in Example 1 of the present invention.

[0029] Figure 3 The XRD patterns of La(OH)3, La2(CO3)3 and CeO2 generated after reaction using ZIF-67 in Example 2 of this invention are shown.

[0030] Figure 4 The graph shows the recovery efficiency and recovery amount of La and Ce by ZIF-67 at different pH values ​​in Example 2 of this invention.

[0031] Figure 5 The graph shows the recovery efficiency and recovery amount of La and Ce by ZIF-67 at different concentrations in Example 2 of the present invention.

[0032] Figure 6Example 3 of this invention utilizes ZIF-67 to recover La from simulated wastewater. 3+ Ce 3+ Result image. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] Example 1: Preparation of ZIF-67 material Weigh out 2.704 g of cobalt nitrate hexahydrate and dissolve it in 24 g of deionized water; dissolve 44.24 g of 2-methylimidazole in 160 g of deionized water. Mix the two solutions rapidly at room temperature to allow the Co... 2+ The molar ratio of 2-methylimidazolium to H2O was 1:58:1100. Crystallization was carried out by magnetic stirring at room temperature for 6 hours. After the reaction, the precipitate was separated by centrifugation at 2655 RCF for 30 minutes, washed three times each with deionized water and methanol, and dried under vacuum at 70°C for 12 hours to obtain high-purity ZIF-67 (Zeolitic imidazolateframework-67) crystals. The prepared material was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

[0035] like Figure 1 As shown, the XRD pattern of the prepared sample is highly consistent with the characteristic diffraction peaks of standard ZIF-67, and the peaks are sharp and intense, indicating that the product has high crystallinity, complete crystal form, and no obvious amorphous phase or impurity phase. High-purity ZIF-67 crystals were successfully synthesized. Figure 2 The SEM results showed that the sample exhibited the typical rhombic dodecahedral morphology of ZIF-67, with clear particle outlines, smooth surfaces, and distinct edges, further verifying that the highly crystalline and structurally complete ZIF-67 crystal material has been successfully prepared.

[0036] Example 2: Selective recovery of lanthanum and cerium from water using a one-step ZIF-67 method I. Sample Preparation Prepare 10-200 ppm Ce using cerium nitrate hexahydrate and lanthanum nitrate hexahydrate reagents. 3+ La 3+The pH of the solution was adjusted to the target value (pH 2-7) by adding trace amounts of HNO3 and NaOH solution; three parallel samples were set for each group to ensure data reliability. At preset time points, the reaction solution was filtered using a polyethersulfone membrane filter with a pore size of 0.22 μm, and the filtrate was collected for subsequent analysis.

[0037] II. ZIF-67 One-Step High-Efficiency Recovery of La 3+ Ce 3+ The prepared ZIF-67 material was added to a prepared rare earth solution at a solid-liquid ratio of 0.2 g / L and reacted at room temperature (298 K) for 2 hours to form a precipitate. The precipitate was filtered, dried, and analyzed by XRD and XPS. Figure 3 As shown, for La 3+ Under low concentration conditions (10 ppm), significant La2(CO3)3·8H2O diffraction peaks began to appear in the spectrum, indicating that low concentrations of La2(CO3)3·8H2O... 3+ It is mainly recovered by combining with carbonate ions to form carbonate precipitates. With the development of La... 3+ When the concentration was increased to 60 ppm and 150 ppm, the characteristic peak of La2(CO3)3·8H2O disappeared, replaced by a strong and sharp La(OH)3 diffraction peak. Simultaneously, the intensity of the characteristic peak of ZIF-67 decreased significantly or even disappeared. This change indicates that as the concentration of La2(CO3)3 increases, the characteristic peak of La2(CO3)3·8H2O decreases. 3+ With increased loading, the recovered product shifts from carbonate to thermodynamically more stable hydroxide. For Ce... 3+ Within a concentration range of 10-150 ppm, the characteristic diffraction peaks of the recovered product were dominated by CeO2, with no other salt intermediate phases appearing. With the increase in Ce... 3+ With increasing initial concentration, the characteristic peak intensity of CeO2 continuously increased, while the peak intensity of ZIF-67 correspondingly decreased, indicating that CeO2... 3+ During the recovery process by ZIF-67, it is more easily oxidized and directly converted into a stable CeO2 precipitate, and this process is also accompanied by the consumption of the ZIF-67 framework. In summary, XRD results confirm that ZIF-67 has a significant effect on La. 3+ and Ce 3+ All have excellent recycling capabilities and are effective against Ce. 3+ The extraction of [elements] is an irreversible framework dissociation process, but their mechanisms of action differ significantly: La 3+ The recovery exhibits a concentration-dependent precipitate phase transition process, while Ce... 3+ It is mainly fixed by directly generating CeO2.

[0038] III. Evaluation of Recycling Effectiveness The concentration of rare earth elements in the filtrate was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). The extraction capacity and extraction efficiency were calculated. All data are the average of three independent measurements.

[0039] Figure 4 The results show that ZIF-67 has an effect on Ce 3+ The extraction process maintained a high removal rate of over 95% across a wide pH range of 3-7, with extraction capacity largely unaffected by pH. Even under strongly acidic conditions at pH 3, ZIF-67 effectively captured Ce. 3+ And it generates stable CeO2 crystals. Figure 5 Statistical results show that ZIF-67 in Ce 3+ and La 3+ ZIF-67 achieves efficient recovery of rare earth metals over a wide concentration range of 10-200 ppm. Recovery results show that ZIF-67 effectively recovers Ce... 3+ Its extraction performance is superior, with a maximum extraction capacity of 728.2 mg / g; at the same time, it has better extraction performance for La. 3+ It also achieves efficient recovery, with a maximum capacity of 495.8 mg / g.

[0040] Example 3: Recovery of La from Wastewater Using ZIF-67 3+ Ce 3+ Introducing a competitive cation commonly found in mining wastewater, Mn, into a rare earth solution. 2+ Mg 2+ Ca 2+ K + and Na + Simulating real wastewater, evaluating the effect of ZIF-67 on La 3+ and Ce 3+ The selective extraction performance of [the method] is described in Example 2 for the recovery of La from wastewater. 3+ Ce 3+ .

[0041] Figure 6 Experimental results show that when interfering ions and rare earth elements coexist, ZIF-67 has an effect on La 3+ and Ce 3+ The extraction efficiency remains above 95%, demonstrating superior selective extraction capability.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering lanthanum and cerium rare earth metals from water using a metal-organic framework, characterized in that, It consists of the following steps: S1: Synthetic zeolite imidazole ester framework material-67, abbreviated as ZIF-67; the synthesis method of ZIF-67 is room temperature liquid-phase precipitation. The room temperature liquid phase precipitation method consists of the following steps: cobalt nitrate hexahydrate and 2-methylimidazole are dissolved in deionized water, mixed rapidly and stirred at room temperature to carry out crystallization reaction, and after the reaction is completed, the precipitate is collected by centrifugation, and the precipitate is washed with deionized water and methanol in sequence, and ZIF-67 crystals are obtained after vacuum drying. S2: First, the rare earth solution is filtered to remove suspended impurities and the pH value is adjusted. Then, the ZIF-67 obtained in step S1 is added to the rare earth solution and reacted at room temperature, generating a solid precipitate. The precipitate is then filtered and dried to obtain the rare earth recovery product. The rare earth solution contains La. 3+ and / or Ce 3+ The pH of the rare earth solution reaction is 3-7; the concentration of ZIF-67 in the reaction system is 200-400 ppm; and La is recovered from the solution. 3+ The reaction pH is 5-7; the reaction time of ZIF-67 with rare earth solution is 2-12 h.

2. The method for recovering lanthanum and cerium rare earth metals from water using a metal-organic framework according to claim 1, characterized in that, The stirring time is 4-6 hours.

3. The method for recovering lanthanum and cerium rare earth metals from water using a metal-organic framework according to claim 1, characterized in that, The vacuum drying time is 6-12 hours, and the temperature is 50-80℃.

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