Method for recovering rare earth in neodymium iron boron waste based on ternary eutectic solvent

Abstract

The invention discloses a method for recovering rare earth in neodymium iron boron waste based on a ternary eutectic solvent, 13 HDESs composed of trioctylphosphine oxide (TOPO) as HBA and an alcohol compound as HBD are totally prepared and characterized, through optimization, batch counter-current extraction experiments are carried out by taking actual leachate as mother liquor under the optimal condition, and the recovery rate of rare earth in neodymium iron boron waste is greatly improved. HDES is used for three-stage counter-current extraction, the total rare earth concentration in mother liquor is reduced from 4389.3 mg / L to 33.5 mg / L, complete recovery of rare earth is achieved, a loaded organic phase can be stripped through 0.2 mol / L sodium oxalate, HDES after reverse extraction can enter circulation after being washed with deionized water, and the HDES still keeps good stability after five times of circulation. And roasting the back-extracted rare earth to finally form a rare earth oxide product. The process is green and clean, does not need to use toxic volatile solvents, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrometallurgy, and in particular relates to a method for recovering rare earths in NdFeB waste based on a ternary low eutectic solvent. Background Art

[0002] The importance of rare earth elements is self-evident. Rare earth elements have excellent magnetic, optical, electrical and chemical properties, making them indispensable key raw materials for high-tech industries such as advanced equipment manufacturing, new energy, and new materials. At present, rare earth elements mainly come from mineral mining, but excessive mining will cause serious environmental pollution. Therefore, it is urgent to develop new ways to recycle rare earths.

[0003] In recent years, NdFeB magnets have been welcomed by the market due to their high energy density and low price. According to statistics, the total global demand for rare earth permanent magnets has been on the rise from 2000 to 2017, of which NdFeB permanent magnets accounted for more than 90%. NdFeB permanent magnets are widely used in wind turbines, new energy vehicles and other fields. It is understood that NdFeB permanent magnets are mainly composed of neodymium, iron and boron, of which iron accounts for 60-70%. In addition, by adding other chemical elements (such as Dy, Tb, Gd, Nb, Co, Cu, Ga), some of its physical and magnetic properties can be changed to meet the needs of a wide range of applications. During the production process, due to the hardness and brittleness of NdFeB magnets, a large amount of raw material waste, scraps and defective products will be generated. The service life of NdFeB permanent magnets also depends on their application areas. For example, the service life of general electronic products is 2-3 years, and the service life of wind turbines is 20-30 years. Therefore, waste NdFeB permanent magnets have become an important secondary resource of rare earths. However, there is currently no relatively mature and economically feasible method for recycling waste NdFeB permanent magnets. Therefore, how to recover rare earths from waste NdFeB permanent magnets has attracted the attention of more and more scholars. The currently disclosed methods for recycling waste NdFeB permanent magnets include direct reuse, alloy reprocessing after hydrogen explosion, hydrometallurgy and pyrometallurgy. Among them, hydrometallurgy seems to be the best choice for recycling waste NdFeB magnets because it can process all types of permanent magnets. The hydrometallurgical treatment of waste NdFeB permanent magnets mainly includes two links: leaching and rare earth separation. The leaching process is mainly divided into complete leaching and selective leaching. However, even with selective leaching, it is still difficult to limit the entry of impurity elements into the solution due to insufficient separation effect, thereby affecting the subsequent recovery of rare earths. The rare earth separation technologies for NdFeB permanent magnet waste mainly include precipitation, solvent extraction and ionic liquid extraction. Rabatho et al. recovered rare earths from NdFeB magnetic waste mud by selective precipitation. They first adjusted the pH value to precipitate and remove iron, then used oxalic acid precipitation to recover rare earths, and then calcined them at high temperature to make rare earth oxide products. The problem with this process is that iron precipitation will lead to a large loss rate of rare earths. Solvent extraction is also used for the recovery of waste NdFeB permanent magnets due to its strong continuity, high selectivity, and greater convenience for industrial operation. However, its disadvantages such as easy emulsification, easy volatility of solvents, large amounts of acid and alkali, and large amounts of wastewater discharge limit its further application. Considering the environmental pollution caused by solvent extraction, in recent years, scholars have shifted their research focus to hydrophobic ionic liquids because of their advantages such as low vapor pressure, high stability, wide liquid phase range, and environmental friendliness. For example, Xue et al. designed and synthesized two carboxylic acid-based ionic liquids ([A336][BTA] and [A336][OTA]) to effectively extract Nd(III); KoenBinnemans et al. also proposed the use of undiluted fluoride-free ionic liquid trihexyl(tetradecyl)phosphine chloride to extract Fe(III) and Nd(III) from hydrochloric acid solution.Although ionic liquids are more environmentally friendly than solvent extraction, their viscosity is much higher than that of solvent extraction, and the extraction process also needs to be carried out under high salting agent concentration conditions to improve their extraction and separation performance. At the same time, the synthesis process of ionic liquids is complicated and purification is difficult, which limits their further application. The emergence of hydrophobic low eutectic solvents (HDES) successfully solved the problems of ionic liquids. Generally speaking, HDES is a low eutectic mixture composed of two or more compounds, hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD). Due to its simple preparation, non-toxicity, environmental friendliness and relatively low cost, it has attracted more and more scholars in the field of liquid-liquid extraction. For example, Van Osch et al. first discovered the hydrophobic type of HDES and studied the extraction of volatile fatty acids from aqueous phases by HDESs based on quaternary ammonium salts. Fan et al. used natural products such as DL-menthol and anise alcohol to prepare HDES to extract betaine from aqueous phases. Tereshatove et al. also expanded the application of HDES in metal ion extraction, and for the first time used ibuprofen, menthol, quaternary ammonium salts and fatty acids to form HDES to extract and separate indium (In) from aqueous phases. Summary of the invention

[0004] In order to improve the above technical problems, the present invention provides a HDES extractant, which includes trioctylphosphine oxide (TOPO), decanol (DA) and tetradecanol (MA).

[0005] According to an embodiment of the present invention, in the HDES extractant, the molar ratio of DA, MA and TOPO is (9:1:5) to (1:9:5), (5:5:3) to (5:5:7), exemplified by 9:1:5, 7:3:5, 5:5:3, 5:5:4, 5:5:5, 3:7:5, 1:9:5, and preferably 5:5:4.

[0006] According to an embodiment of the present invention, the water content of the HDES extractant is lower than 3%, preferably 2.95% to 2.0%.

[0007] According to an embodiment of the present invention, the organic carbon content in the aqueous phase of the HDES extractant is less than 100 mg / L, preferably 10 to 95 mg / L.

[0008] According to an embodiment of the present invention, the viscosity of the HDES extractant is less than 40 mPa·s, preferably 30 to 39.9 mPa·s.

[0009] According to an embodiment of the present invention, the density of the HDES extractant is 0.85 g / cm -3 About 0.84 to 0.86 g / cm -3 .

[0010] The present invention provides a method for preparing the HDES extractant, comprising mixing trioctylphosphine oxide (TOPO), decanol (DA) and tetradecanol (MA) to prepare the HDES extractant.

[0011] Preferably, the components are mixed in the above molar ratio. According to an embodiment of the present invention, the preparation method further comprises heating the mixed reaction solution. Preferably, the heating temperature is 40 to 80°C, exemplified by 40°C, 60°C, and 80°C.

[0012] The present invention also provides the above HDES extractant for recovering rare earth elements from NdFeB waste materials, preferably for recovering rare earth elements from waste NdFeB permanent magnet leaching solution.

[0013] The present invention also provides a method for recovering rare earths from NdFeB waste using the above-mentioned HDES extractant, comprising mixing the HDES extractant with NdFeB waste, separating HDES loaded with rare earth ions through countercurrent extraction, stripping through a stripping agent to obtain a rare earth precipitate, and finally high-temperature roasting to obtain rare earth oxides.

[0014] According to an embodiment of the present invention, the stripping agent is selected from at least one of HNO3, HCl or Na2C2O4, preferably selected from Na2C2O4.

[0015] According to an embodiment of the present invention, the initial acidity of the NdFeB waste liquid is 0.5-2.5 mol / L, exemplified by 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, and 2.5 mol / L.

[0016] According to an embodiment of the present invention, the equilibrium time of the countercurrent extraction is 0-30 min, exemplified by 5 min, 10 min, 15 min, 20 min, 25 min, and 30 min.

[0017] According to an embodiment of the present invention, the phase ratio O / A during the countercurrent extraction is 1 / 2-4 / 1, exemplified by 1 / 2, 1 / 3, 1 / 4.

[0018] According to an embodiment of the present invention, the countercurrent extraction is a multi-stage countercurrent extraction, such as two-stage, three-stage, four-stage, preferably three-stage.

[0019] According to an embodiment of the present invention, the high temperature calcination temperature is 800-1000°C, exemplified by 800°C, 900°C, 1000°C; the calcination time is 2-4h, exemplified by 2h, 3h, 4h.

[0020] The present invention also provides rare earth oxides separated and prepared by the above method.

[0021] The present invention also provides rare earth oxides separated and prepared by the above method, which can be applied to the fields of fluorescence, magnetism, optics and catalysis.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention proposes to use HDESs based on trioctylphosphine oxide (TOPO) as a hydrogen bond acceptor (HBA) and decanol (DA), dodecanol (LA), and tetradecanol (MA) as hydrogen bond donors (HBD) for the first time to separate and recover REEs from waste NdFeB permanent magnet leachate. The HDESs of the present invention can recover 99% of the rare earths in the waste NdFeB permanent magnet leachate in the presence of high concentrations of iron ions, and the purity of the recovered rare earth oxide mixture is greater than 99%, thereby achieving complete separation of rare earths and iron. Compared with traditional solvent extraction, the present invention does not require the use of volatile solvents (kerosene), which is green and clean. In addition, the traditional process requires iron removal before using traditional solvent extraction to recover rare earths.

[0024] (2) The present invention comprehensively evaluates the physicochemical properties of all HDESs based on TOPO as HBA, decanol (DA), dodecanol (LA), and tetradecanol (MA) as HBD. The best HDES (DA: MA: TOPO = 5: 5: 4) was screened by comparing the extraction and separation performance of different HDESs under the same conditions. The present invention studies the factors affecting the extraction and separation performance of the HDES under the nitric acid system (such as nitric acid concentration, iron ion concentration, reaction time, relative ratio, etc.). The stripping and regeneration performance of HDES was evaluated. Under the optimal conditions, a new process for recycling waste NdFeB permanent magnets was designed and batch countercurrent extraction experiments were carried out. Except for a small amount of nitric acid used in leaching and sodium oxalate used in stripping, the process of the present invention does not require additional consumption of chemicals such as acids, alkalis or salts.

[0025] (3) This paper proposes a new process for recovering rare earths from nitric acid leaching solution of waste NdFeB permanent magnets based on HDES. Thirteen kinds of HDESs were prepared and characterized, which have low viscosity (<50 mPa·s), low water solubility (<100 mg / L), low water content (<3%), and a large density difference with water (about 0.15 g / cm -3) make it an extremely potential extractant. Through a series of screening work, it was found that the new ternary HDES (for example, DA:MA:TOPO=5:5:4) has the best extraction and separation performance in the waste NdFeB nitric acid system leachate. By optimizing the extraction conditions (nitric acid concentration, iron ion concentration, reaction time), combined with infrared spectroscopy analysis, the ion association mechanism was proposed. Ternary HDES (for example, DA:MA:TOPO=5:5:4) still has good stability after five cycles. By comparing solvent extraction with HDES extraction, it was found that HDES has better extraction and separation performance, and the loading amount is also much greater than solvent extraction. Under the optimal conditions, HDES was used for three-stage countercurrent extraction with the actual leachate at a phase ratio (O / A) of 2. There was almost no rare earth residue (0.1%) in the raffinate, and the loaded organic phase could be stripped and separated from the rare earth and a small amount of iron in the loaded organic phase by 0.2 mol / L sodium oxalate. After five cycles, the ternary HDES (for example, DA:MA:TOPO=5:5:4) still has good stability. In addition, the process of the present invention does not require a salting-out agent and a toxic volatile solvent, which is conducive to safe and clean production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the structural formula of hydrogen bond acceptor (TOPO) and hydrogen bond donor (DA, LA, MA).

[0027] Figure 2 (a), (b), and (c) are the hydrogen spectrum of DA:TOPO(2:1)HDES, the comparison of the infrared spectra of DA:TOPO(2:1)HDES and its precursor, and the electrostatic potential diagrams of hydrogen bond acceptors (TOPO) and hydrogen bond donors (DA, LA, MA) on the van der Waals surface.

[0028] Figure 3 (a) and (b) are the comparison results of the effects of five different combinations of hydrogen bond donors on the extraction rate of HDES and the comparison chart of the separation coefficients of three HDES for iron and rare earth.

[0029] Figure 4 The effect of different molar ratios of DA:MA:TOPO in ternary HDES on the extraction rate.

[0030] Figure 5 (a) and (b) are the results of the effect of the concentration of the salting-out agent (NaNO3) on the extraction rate and the infrared spectra comparison results of HDES loaded with rare earth (Dy, Nd, Pr) and without rare earth (Dy, Nd, Pr).

[0031] Figure 6(a), (b), and (c) are the results of the effects of nitric acid concentration, trivalent iron ion concentration, and reaction time on the extraction rate.

[0032] Figure 7 (a), (b), and (c) are respectively the effect of the concentrations of three stripping agents (HNO3, HCl, and Na2C2O4) on the stripping rate, the effect of the regeneration performance of DA:MA:TOPO (5:5:4) HDES after five cycles on the extraction rate, and the comparison of the infrared spectra of DA:MA:TOPO (5:5:4) HDES before and after five cycles.

[0033] Figure 8 (a) and (b) are the comparison charts of TOPO's ability to load Pr on HDES and kerosene, and the comparison of the extraction rate of a single load based on actual leachate.

[0034] Fig. 9 (a) and (b) are the results of the effect of the ratio on the extraction rate and the McBee diagram of rare earth countercurrent extraction, respectively.

[0035] Fig.10 This is a process flow chart for recovering rare earth from NdFeB magnet leachate. DETAILED DESCRIPTION

[0036] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0037] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0038] Example 1

[0039] 1 Experimental part

[0040] 1.1 Reagents and Materials

[0041] In the following examples of the present invention, Dy(NO3)3·6H2O (99.99%, ),Nd(NO3)3·6H2O(99.99%, ),Pr(NO3)3·6H2O(99.99%, ),Fe(NO3)3·9H2O(99.99%, ),Co(NO3)2·6H2O(99.99%, ) was dissolved in deionized water to prepare a simulated feed solution for pre-screening HDES and optimizing the extraction process conditions. HNO3 can be used to adjust the acidity of the solution. NaNO3 can be used to adjust the concentration of the salting-out agent. In addition to HNO3, the stripping agent also includes HCl (36-38%, Xiya reagent) and Na2C2O4 (99%). The precursor materials used to prepare HDES include trioctylphosphine oxide (TOPO) (98%, Macklin), decanol (DA) (97%, )、Lauryl alcohol (LA) (99%, Adamas-beta) ), myristyl alcohol (MA) (98%, ). In order to compare the solvent extraction, the traditional solvent sulfonated kerosene (Shanghai Rare Earth Chemical Co., Ltd.) was also selected.

[0042] 1.2 Instruments and analytical methods

[0043] The metal ion concentrations in the water samples were determined by inductively coupled plasma atomic emission spectrometry (ICP-OES, Jy-Horiba ICP-OES Ultima 2). The density, viscosity, water content and solubility of HDES in the aqueous phase were measured by Biolin automatic surface tension meter Sigma 701 (density accuracy ±0.001 g*cm -3 ), viscosity was determined by a rotational viscometer (NDJ-5, Shanghai, China, accuracy ±2%), Metrohm 831kf coulometer (accuracy ±0.01wt%), total organic carbon analysis (TOC, Shimadzu TOC-L CPH analyzer), and the element concentration loaded in the HDES organic phase can be calculated by the law of conservation of mass. The acidity of the sample can be measured by a digital pH meter pHS-3C (accuracy ±0.01) manufactured by Shanghai Rex Instrument Factory after dilution by weighing and then calculated. The purity of the final rare earth product was determined by EDS. HDES 1 The HNMR spectrum was measured by AV III-500 Bruker spectrometer with CDCl3 as solvent. The Fourier transform infrared spectrum (FT-IR) of HDES before and after extraction was measured by Thermo Nicolet IS50 instrument, with the wave number range of 400-4000cm -1 .

[0044] 1.3 Calculation method

[0045] The initial structures of HBDs and HBAs were constructed by GaussView 5.0 program. Quantum chemical calculations were performed by Gaussian 09 program. Density functional theory calculations (DFT) at the B3LYP / 6-311G (d, p) level coupled with van der Waals semiempirical contributions of Grimme's DFT-D3 (BJ) method were used to optimize stable configurations. Frequency calculations were then performed on the optimized structures on the same method and basis set to confirm the absence of imaginary frequencies. The Multiwfn3.8 program was used in conjunction with the VMD1.9.3 program to perform electrostatic potential (ESP) analysis and plotting.

[0046] 1.4 Preparation of HDES

[0047] The physicochemical properties of the hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) components selected in the present invention are shown in Table 2. All HDES are prepared by mixing HBA and HBD in a predetermined molar ratio in a glass bottle and heating at 60°C for 15 minutes. The physical properties of the prepared HDES are shown in Table 2. All HDESs remain colorless, transparent, and liquid with good fluidity after being placed at room temperature (25°C ± 2) for 48 hours.

[0048] 1.5 Extraction and stripping experiments

[0049] All extraction experiments of the present invention were carried out at room temperature, the initial acidity of the feed simulation solution was 1 mol / L, the elements contained in the simulated feed solution were Nd, Dy, Pr, Fe, Co, and the initial concentrations were all 0.01 mol / L, the ratio of HDES to the aqueous phase was 1:1, and in order to ensure sufficient reaction, the extraction process was carried out at a shaking speed of 300 rpm for 30 minutes. After extraction, the element concentration in the raffinate was determined by ICP-OES.

[0050] The effects of initial acidity of the feed solution (0.5-2.5 mol / L), equilibrium time (0-30 min), iron ion concentration (0.01-0.21 mol / L), and O / A (1 / 2-4 / 1) on the rare earth extraction performance and rare earth and iron separation performance of HDES were investigated.

[0051] Three different stripping agents (HNO3, HCl, Na2C2O4) were used to strip the loaded HDES (the loading conditions were: the nitric acid concentration in the solution was 1 mol / L, Dy 3+ , Nd 3+ , Pr 3+ , Fe 3+ ,Co 2+The stripping experiment was carried out with the ion concentration of 0.01 mol / L, the phase ratio of 1:1, and the reaction time of 15 min. The rare earth elements not stripped in the organic phase were stripped completely with a strong acid at a phase ratio of 1:1, and the residual ion concentration of the stripping solution was determined by ICP-OES. The same HDES was contacted and reacted 5 times with 5 fresh feed solutions, and the raffinate obtained each time was measured. The maximum loading capacity of the HDES was calculated by the law of conservation of matter. The mechanism of the HDES in extracting rare earths in a nitric acid system was inferred by infrared and salting-out agent experiments.

[0052] 1.6 Leaching and recovery of NdFeB waste

[0053] The NdFeB waste selected by the present invention was purchased from Alibaba Hebei Chaoyue Metal Products Co., Ltd. Using 3 mol / L nitric acid at S / L=0.02 g / L, 80°C oil bath constant temperature heating conditions, it was fully leached for 2 hours. No solid residue remained at the end of the reaction, indicating that complete leaching was achieved. The main components and concentrations of the actual slurry after complete leaching are shown in Table 1 below. Under the optimal experimental conditions (nitric acid concentration of 2.21 mol / L, phase ratio of 2:1, reaction time of 15 min, temperature of room temperature (25°C), three-stage countercurrent extraction.), a predetermined HDES was selected for batch countercurrent extraction experiments. The HDES loaded with rare earth elements was stripped with sodium oxalate, and the oxalic acid rare earth precipitate was washed and dried and then placed in a muffle furnace for calcination at 800°C for 3 hours to produce rare earth oxides.

[0054] Table 1 Main components and concentrations of the actual solution after complete leaching of NdFeB

[0055]

[0056] 2. Results and Discussion

[0057] 2.1 Characterization of HDESs

[0058] Since phenol is highly toxic and water-soluble, the main trend is to find a low-toxic, low-water-soluble hydrogen bond donor (HBD) and trioctylphosphine oxide (TOPO) to prepare a low eutectic solvent. The present invention uses decanol (DA), dodecanol (LA), and tetradecanol (MA) as hydrogen bond donors (HBD) and hydrogen bond acceptors (TOPO) to prepare low eutectic solvents (DESs) for selective recovery of rare earth elements in a nitric acid system. The present invention prepares a total of 13 DESs, and the chemical structures of the selected materials (hydrogen bond acceptors (TOPO) and hydrogen bond donors (DA, LA, MA)) are as follows: Figure 1 The physicochemical properties of these materials are summarized in Appendix 2. The advantages of the selected materials mainly include almost negligible water solubility, non-volatility, relatively low-cost pure components, stable physicochemical properties, and environmental friendliness.

[0059] The prepared HDESs can remain in a uniform and transparent liquid state after being stored at room temperature for 48 hours. Taking HDES with a composition of DA:TOPO (molar ratio of 2:1) as an example, it can be seen that the HDES 1 H NMR ( Figure 2 (a)) and FT-IR ( Figure 2 The analysis of (b) shows no new peaks compared with the two original components, indicating that no chemical reaction occurred between decanol (DA) and TOPO. However, through FT-IR analysis, we can see that the P=O stretching vibration peak in HDES is at 1139.72 cm -1 Compared with the P=O stretching vibration peak (1144.06cm-1) of pure TOPO, it shifts significantly to a low frequency. This change indicates the existence of a hydrogen bond between the two.

[0060] Electrostatic potential (ESP) is an important tool for identifying interaction sites and hydrogen bonding interactions. Figure 2 It can be clearly seen in (c) that the oxygen (O) atom at the P=O double bond position of TOPO exhibits the most negative potential (shown as the red area). In contrast, the hydrogen (H) atom in the -OH group of the linear alcohols DA, LA, and MA exhibits the most positive potential (shown as the blue area). Therefore, it is expected that TOPO and the linear alcohols form intermolecular hydrogen bonds in the maximum / minimum potential region driven by electrostatic attraction. As described above, these findings further support the results obtained from infrared spectroscopy, thereby confirming the existence of hydrogen bonding interactions between TOPO and the linear alcohols.

[0061] Good physicochemical properties are necessary conditions for excellent extractants. For this reason, we measured the main physicochemical properties of the prepared HDESs (including water content, organic carbon content in the water phase, viscosity, density, etc.). From Table 2, we can see that even after the HDESs prepared under the condition of 1:1 were fully in contact with deionized water for 24 hours. The water content of HDESs is still less than 3%; the organic carbon content in the water phase is less than 100 mg / L. It can be seen that the HDESs prepared by the present invention have good hydrophobicity and environmental friendliness.

[0062] Considering that the leaching of waste NdFeB magnets requires the use of strong acid, it is necessary to evaluate the stability of HDES under acidic conditions. Taking LA:TOPO (molar ratio of 2:1) as an example, the prepared HDES is balanced with 3 mol / L nitric acid. 1No new peaks appeared in the HNMR spectrum, indicating that the HDES has good stability under strong acid conditions. In addition, it can be found from the FT-IR spectrum that the P=O stretching vibration peak shifts to a low frequency, which may be caused by the protonation of the HDES. In the liquid-liquid extraction process, the low viscosity of the organic phase is beneficial to improving the mass transfer rate and extraction efficiency, and avoiding problems such as phase separation difficulties. The viscosity of the HDESs prepared by the present invention is less than 40 mPa·s at room temperature, which is much lower than most reported highly hydrophobic ionic liquids. Therefore, during the extraction process, there is no need to add toxic volatile organic solvents. In addition, the density of the HDESs prepared by the present invention is about 0.85, which is quite different from the density of the water phase, and is therefore conducive to better separation of HDESs from water after liquid-liquid extraction.

[0063] Table 2 Physicochemical properties of all HDESs at 25±2℃

[0064]

[0065] 2.2 Screening of HDESs

[0066] The present invention first evaluated the extraction and separation performance of rare earth elements and impurity elements (iron and cobalt) in a simulated liquid of waste neodymium ferromagnets by HDESs prepared from five different combinations of HBD and HBA (TOPO) at a molar ratio of 1:1. Figure 3 As can be seen in (a), in terms of rare earth extraction performance, the rare earth extraction rates of HDES prepared by three different HBDs, DA, LA, and DA:MA, and HBA (TOPO) are almost the same, while the rare earth extraction rate of HDES prepared by LA:MA (molar ratio of 1:1) and HBA (TOPO) is greatly reduced, and the HDES prepared by MA and HBA (TOPO) has almost no extraction performance in this system, so the HDESs prepared by LA:MA and MA and HBA (TOPO) are first excluded. In terms of iron extraction performance, DA:MA<LA<DA, so the separation performance of HDES prepared by DA:MA and HBA (TOPO) is much greater than that of the other two. This may be because the hydrogen bond effect of TOPO, as a hydrogen bond acceptor, is gradually enhanced, resulting in the inhibition of the iron extraction performance of HDESs, thereby improving the separation coefficient of rare earth and iron. Therefore, DA and MA were finally selected as HBDs and TOPO as HBA to prepare HDES for subsequent experiments.

[0067] We prepared different HDES by changing the molar ratio of DA, MA and TOPO, and studied the influence of each component on its performance by comparing the extraction and separation performance of different HDES under the same conditions. Figure 4 As shown. Figure 4It can be seen that under the condition of fixed TOPO molar dosage, when the molar ratio of DA to MA is less than or equal to 1, the rare earth extraction rate does not change significantly, while the iron extraction rate gradually decreases to 0, and when the DA:MA:TOPO molar ratio is 3:7:5, the rare earth extraction rate drops sharply. This may be because the hydrogen bonding force of MA on TOPO in HDES is much greater than the hydrogen bonding force of DA on TOPO. In addition, under the condition of fixed DA to MA molar ratio, with the increase of TOPO molar fraction, the extraction rate of rare earth and iron shows an overall upward trend, which may be because the component TOPO in HDES plays a major role in the extraction process. Finally, after comprehensive consideration of rare earth extraction performance and impurity separation performance, HDES prepared by DA:MA:TOPO at a molar ratio of 5:5:4 is preferred as the extractant.

[0068] 2.3 Study on extraction mechanism

[0069] In order to explore the extraction mechanism of HDES in the extraction system, so as to better regulate the extraction process to achieve the best extraction effect. In order to avoid the mutual influence between elements, we used a single element solution (the solution composition was: a single element (rare earth element Dy, Nd or Pr), the concentration of the rare earth element was 0.1 mol / L, and the hydrogen ion concentration (acidity) was 1 mol / L.) to observe the effect of the salting-out agent (by adding sodium nitrate to change the concentration of nitrate anions, the ratio was 1:1, and the reaction time was 20 minutes.) on the extraction process. Figure 5 In (a), it can be found that as the concentration of NaNO3 in the solution increases from 0 to 0.7 mol / L, the extraction rate of all rare earth elements increases from about 30% to about 75%, and the reaction proceeds in a positive direction, which indicates that NO3 - Anions participate in the reaction. Figure 5 (b) is the infrared spectrum characterization diagram of HDES before and after loading rare earth (Dy, Nd, Pr), where: 2918-2924cm -1 、2847-2858cm -1 、1460-1466cm -1 They are the asymmetric stretching vibration, symmetric stretching vibration and shear vibration peaks of the TOPO alkyl chain, 1144-1150cm -1 Nearby is the stretching vibration peak of P=O of TOPO. At the same time, we can see that after HDES is loaded with rare earth ions, the stretching vibration peak of P=O changes from 1140cm -1 Move to 1122cm -1This indicates that TOPO in HDES plays a dominant role in the extraction process and interacts with rare earth ions. At the same time, since the electronegativity of O atoms is greater than that of P atoms, the electron cloud of the double bond of P=O is biased towards O atoms, but the lone pair of electrons in O atoms can form complexes with rare earth ions, resulting in changes in the electron cloud, which in turn causes the stretching vibration peak of P=O to red shift. In summary, it is speculated that the extraction mechanism of HDES in the system of the present invention is an ion association mechanism, and the equation is:

[0070]

[0071] 2.4 Optimization of extraction conditions

[0072] In order to further improve the extraction and separation performance of HDES, the present invention investigates the effects of nitric acid concentration, reaction time, iron ion concentration and other parameters on the extraction rate (the elements contained in the simulated feed solution are Dy 3+ , Nd 3+ , Pr 3+ , Fe 3+ ,Co 2+ , the initial ion concentration was 0.01mol / L, the ratio was 1:1, and the reaction time was 15min. In the experiment of the effect of nitric acid concentration on the extraction rate, by keeping other conditions unchanged, the nitric acid concentration changed from 0.5mol / L to 2.5mol / L. Similarly, in the experiment of the effect of reaction time on the extraction rate, by keeping other conditions unchanged, the reaction time changed from 1min to 25min; in the experiment of the effect of iron ion concentration on the extraction rate, by keeping other conditions unchanged, the iron ion concentration changed from 0.01mol / L to 0.21mol / L. ). The experimental results are as follows Figure 6 As shown in (a), (b) and (c).

[0073] Figure 6 (a) shows that when the concentration of nitric acid increases from 0.5 mol / L to 2.5 mol / L, the extraction rate of rare earth and iron decreases. This may be because under high acidity, hydrogen ions compete with rare earth ions. As the concentration of nitric acid increases, the competitive ability of hydrogen ions increases, resulting in a decrease in the extraction rate of rare earth and iron.

[0074] also, Figure 6 (c) shows that after the reaction time reaches 10 minutes, the extraction rate of rare earth does not change significantly, indicating that the extraction of rare earth has reached kinetic equilibrium. However, when the reaction time is further extended to 25 minutes, the extraction rate of iron still shows an upward trend, which indicates that the extraction kinetics of rare earth is faster than that of iron. Therefore, the separation performance of rare earth and iron can be further improved by properly adjusting the reaction time.

[0075] Considering that the concentration of iron ions in the actual feed solution is relatively high, the present invention studies the effect of increasing the iron ion concentration on the extraction and separation performance. Figure 6 In (b), it can be found that as the iron ion concentration increases from 0.01mol / L to 0.21mol / L, the rare earth extraction rate shows an overall upward trend. This may be due to the participation of nitrate in coordination. As the concentration of nitrate in the feed solution increases, the reaction proceeds in the forward direction and the extraction rate increases. The iron extraction rate also increases from 0.09% to 3.11%, and the iron loading in the organic phase also increases from 0.0005g / L to 0.3647g / L. This is mainly due to the common ion effect.

[0076] 2.5 Stripping and regeneration of HDES

[0077] Simple, green and clean stripping and recycling are important criteria for HDES as an extractant. The present invention selects three stripping agents (HCl, HNO3 and Na2C2O4) for stripping and regeneration experiments. Figure 7 In (a), it can be found that: under the same conditions, the stripping effect of hydrochloric acid is better than that of nitric acid. This may be because the chloride ions of hydrochloric acid do not participate in the extraction reaction and do not affect the reaction process, while the nitrate ions of nitric acid participate in the coordination, resulting in poor stripping effect. Although 5 mol / L hydrochloric acid can achieve complete stripping of rare earths, considering factors such as the high acidity of the stripping and the inability to strip off the small amount of iron loaded in HDES in the subsequent actual feed liquid, we chose to use sodium oxalate (Na2C2O4) for the stripping experiment. This is because sodium oxalate can separate the rare earths in the form of a precipitate, while iron oxalate exists in the form of a solution, which is conducive to further separation of rare earths and iron elements and improving the purity of the final product. From Figure 7 As can be seen in (a), 0.2 mol / L sodium oxalate can achieve complete stripping of HDES.

[0078] After complete stripping, the HDES washed with deionized water several times can enter the next round of utilization. In order to better reflect the recycling performance of HDES, we used the actual leachate as the circulating feed liquid. As can be seen from Figure 7 (b), the extraction rate of the HDES of the present invention remains basically unchanged in five cycles, showing high stability. Through infrared spectroscopy analysis, we can also see that the structure of the HDES before and after the cycle has basically not changed. This shows that the HDES of the present invention has good stripping regeneration and reuse performance.

[0079] 2.6 Comparison between HDES and solvent extraction

[0080] It is reported that the highest concentration of TOPO in kerosene is 0.5 mol / L. However, due to the existence of hydrogen bond interaction forces in HDES, the concentration of TOPO in HDES can be as high as about 1 mol / L, which is much higher than the concentration in kerosene. Taking Pr, the most difficult rare earth element to extract in NdFeB permanent magnets, as an example, the present invention compares the loading capacity of HDES and solvent extraction. Although the concentration of TOPO in HDES is much higher than that in kerosene, the loading amounts of the rare earth element Pr by the two are almost the same. We speculate that this may be because HBD (mixed alcohol DA:MA, molar ratio of 5:5) has a relatively strong effect on TOPO, resulting in part of TOPO being unable to participate in the reaction. In order to better reflect the difference between TOPO in HDES and in kerosene solvent, we used the actual leachate as the mother liquor for comparison. Figure 8 As can be seen in (b), the extraction ability of HDES for rare earths is better than that of TOPO in kerosene. At the same time, compared with TOPO, which will extract a small amount of impurity elements in kerosene (the extraction rate of Fe is 4.38%, and the extraction rate of Co is 0.61%), HDES can achieve the complete separation of rare earths and impurity elements without extracting other impurity elements such as Fe and Co under this condition. At the same time, HDES does not need to use volatile toxic solvents, providing a new idea for green and clean production.

[0081] 2.7 New technology for rare earth recovery in actual liquid feed

[0082] In order to explore the effect of the comparison on the separation and extraction performance of HDES, we conducted a series of experiments (the simulated liquid contained elements such as Dy 3+ , Nd 3+ , Pr 3+ , Fe 3+ ,Co 2+ , the initial ion concentration was 0.01mol / L, the phase ratio was 1:1, and the reaction time was 15min. By keeping other conditions unchanged, the phase ratio (O / A) changed from 1:2 to 4:1. ), and the relationship between the phase ratio and rare earth extraction rate was plotted. Fig. 9It can be seen in (a) that when the phase ratio increases from 1:2 to 4:1, the extraction efficiency of the HDES system for rare earths is significantly improved; the reason may be that with the increase in the phase ratio, the probability of the active TOPO molecules in the HDES and the rare earth ions in the solution contacting and colliding with each other increases. At the same time, with the increase in the phase ratio, the extraction rate of the impurity element iron also increases, but after the phase ratio reaches 4:1, the extraction rate of iron tends to stabilize, which indicates that the HDES may have been saturated with iron. In order to achieve complete recovery of rare earths in the leachate of waste NdFeB magnets, we need to perform multi-stage countercurrent extraction and use the MaCabe-Thiele diagram to optimize the parameters. We choose a phase ratio of 2:1 and draw an operating line with a slope of 1 / 2 in the figure to estimate the number of stages required to extract rare earths. According to Fig. 9 The results in (b) show that three extraction stages are required to completely extract and separate the rare earth elements. Therefore, under the optimal experimental conditions, a new process for recovering rare earths from NdFeB waste leachate was developed, and batch countercurrent extraction experiments were carried out.

[0083] First, HDES was used with a phase ratio (O / A) of 2:1 through three-stage countercurrent extraction to selectively extract rare earth elements from the feed solution, and the HDES organic phase loaded with rare earths was stripped and regenerated using 0.2 mol / L sodium oxalate. The organic phase was washed and then entered the cycle, and the oxalate rare earth product was washed, dried, and then roasted to obtain a rare earth product. The detailed parameters of the countercurrent extraction experiment are shown in Table 3. After three-stage countercurrent extraction, the total rare earth ion concentration in the mother liquor was reduced from 4325.7 mg / L to 32.32 mg / L, and the rare earth recovery rate reached more than 99%, while the iron loaded in the organic phase was about 266 mg / L, but the small amount of iron loaded in the organic phase could be further separated from the rare earth by sodium oxalate stripping.

[0084] Table 3 Results of countercurrent extraction experiments

[0085]

[0086] In summary, this paper proposes a new process for recovering rare earths from nitric acid leaching solution of waste NdFeB permanent magnets based on HDES. A total of 13 kinds of HDESs were prepared and characterized. Based on their low viscosity (<50mPa·s), low water solubility (<100mg / L), low water content (<3%) and large density difference with water (about 0.15g / cm -3) make it an extremely potential extractant. Through a series of screening work, it was unexpectedly discovered that the new ternary HDES (DA:MA:TOPO=5:5:4) has the best extraction and separation performance in the waste NdFeB nitric acid system leachate. Through the study and optimization of the extraction conditions (nitric acid concentration, iron ion concentration, reaction time), the ion association mechanism was proposed in combination with infrared spectroscopy analysis. Ternary HDES (DA:MA:TOPO=5:5:4) still has good stability after five cycles. At the same time, the present invention compares solvent extraction with HDES extraction and finds that HDES has better extraction and separation performance, and the loading amount is also much greater than solvent extraction. Under the optimal conditions, HDES is used with a phase ratio (O / A) of 2 for three-stage countercurrent extraction with the actual leachate. There is almost no rare earth residue in the raffinate (the rare earth residue is as low as 0.1%), and the loaded organic phase can be stripped and separated from the rare earth and a small amount of iron in the loaded organic phase by 0.2 mol / L sodium oxalate. After five cycles, the ternary HDES (DA:MA:TOPO=5:5:4) still has good stability. In addition, the process does not require salting-out agents and toxic volatile solvents, which is conducive to safe and clean production.

[0087] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A HDES extractant, characterized in that These include trioctylphosphine oxide (TOPO), decanol (DA) and tetradecanol (MA).

2. The extractant according to claim 1, characterized in that In the HDES extractant, the molar ratio of DA, MA and TOPO is (9:1:5) to (1:9:5), (5:5:3) to (5:5:7).

3. The extractant according to claim 1, characterized in that The water content of the HDES extractant is less than 3%, preferably 2.95% to 2.0%. Preferably, the organic carbon content in the aqueous phase of the HDES extractant is less than 100 mg / L, preferably 10 to 95 mg / L. Preferably, the viscosity of the HDES extractant is less than 40 mPa·s, preferably 30 to 39.9 mPa·s. Preferably, the density of the HDES extractant is 0.85 g / cm -3 About 0.84 to 0.86 g / cm -3 .

4. The method for preparing the HDES extractant according to any one of claims 1 to 3, characterized in that: The preparation method comprises mixing trioctylphosphine oxide (TOPO), decanol (DA) and tetradecanol (MA) to prepare the HDES extractant.

5. The preparation method according to claim 4, characterized in that: The components are mixed in the above molar ratio. According to an embodiment of the present invention, the preparation method further comprises heating the mixed reaction solution. Preferably, the heating temperature is 40 to 80°C.

6. The HDES extractant according to any one of claims 1 to 3 and / or the HDES extractant prepared by the preparation method according to any one of claims 4 to 5 is used to recover rare earth elements from NdFeB waste materials, preferably used to recover rare earth elements from waste NdFeB permanent magnet leachate.

7. A method for recovering rare earths from NdFeB waste using the HDES extractant according to any one of claims 1 to 3 and / or the HDES extractant prepared by the preparation method according to any one of claims 4 to 5, characterized in that: The method comprises mixing the HDES extractant with NdFeB waste, separating the HDES loaded with rare earth ions by countercurrent extraction, stripping the HDES by stripping agent to obtain rare earth precipitates, and finally calcining at high temperature to obtain rare earth oxides.

8. The method according to claim 7, characterized in that The stripping agent is selected from at least one of HNO3, HCl or Na2C2O4. Preferably, the initial acidity of the NdFeB waste liquid is 0.5-2.5 mol / L. Preferably, the equilibrium time of the countercurrent extraction is 0-30 min. Preferably, the phase ratio O / A during the countercurrent extraction is 1 / 2-4 / 1. Preferably, the countercurrent extraction is a multi-stage countercurrent extraction. Preferably, the high temperature calcination temperature is 800-1000° C., and the calcination time is 2-4 hours.

9. The rare earth oxide prepared by separation according to claim 7 or 8.

10. The rare earth oxides separated and prepared by the method according to claim 7 or 8 are applied in the fields of fluorescence, magnetism, optics and catalysis.

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