Extraction method for strengthening low-concentration rare earth elements and equipment for implementing extraction method

Abstract

The invention relates to an extraction method for strengthening low-concentration rare earth elements and equipment for implementing the extraction method. The extraction method is a continuous extraction process based on the combination of a microfluid technology and a solvent extraction technology, and efficient enrichment and recovery of low-concentration rare earth elements are realized through combined use of a gas-liquid-liquid three-phase system and an extraction agent. The extraction method provided by the invention has the advantages of high mass transfer efficiency, simple operation, recyclable extraction agent, high extraction efficiency, good stability and the like, and is suitable for enrichment and recovery of low-concentration rare earth elements on an industrial scale under the condition of a large phase ratio (greater than 50).

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth element extraction, and relates to a method for enhancing the extraction of low-concentration rare earth elements and an apparatus for implementing the extraction method. Background Art

[0002] Due to their unique physical properties such as magnetism, optics, and electricity, as well as chemical properties such as catalysis, sensitization, and activation, rare earth elements have important application values in modern industry and are widely used in fields such as metallurgy, electronics, chemical engineering, and environmental protection. However, a large amount of rare earth ion wastewater with low concentration (<100 mg / L) is generated during the mining and processing of rare earth elements. If these wastewaters are directly discharged, it will not only cause environmental pollution but also lead to waste of rare earth resources. Therefore, how to efficiently and rapidly enrich and recover low-concentration rare earth ions has become an important problem faced by the current rare earth industry.

[0003] Traditional solvent extraction technology has many deficiencies when treating low-concentration rare earth ion wastewater, such as low mass transfer efficiency, large floor area of equipment, serious emulsification phenomenon, large loss of extractant, etc., and it is difficult to meet the requirements of industrial applications. In addition, traditional extraction equipment such as mixer-settlers and extraction towers have problems such as difficult phase separation and large mass transfer resistance when operating under conditions of a large phase ratio (aqueous phase flow rate: organic phase flow rate > 50:1), which further limits their application in the enrichment and recovery of low-concentration rare earth ions.

[0004] Citation Document 1 discloses a method for extracting and enriching rare earths from a low-concentration rare earth solution. A non-saponified organic extractant is used to perform centrifugal extraction on the low-concentration rare earth solution to obtain a rare earth-loaded organic phase and a raffinate; an inorganic acid is used to perform centrifugal stripping on the rare earth-loaded organic phase to obtain a rare earth enrichment solution. According to the actual concentration of the rare earth solution, one or two coupled centrifugal extractions are carried out, and all rare earths or light rare earths and medium-heavy rare earths can be enriched into the rare earth-loaded organic phase respectively, and then centrifugal stripping is carried out with an inorganic acid to obtain a rare earth enrichment solution containing all rare earths or mainly light rare earths or medium-heavy rare earths. However, this extraction method has complex operations and a long extraction time.

[0005] Citation Document 2 discloses a method for extracting and separating rare earth elements using an acidic-basic composite extractant. During this extraction process, the aqueous phase in the middle stage of the extraction section is led out and separated by extraction with a basic extractant, and then returned to the extraction section for continued extraction; the aqueous phase discharged from the washing section is introduced into the middle stage of the extraction section for extraction, and the washing liquid discharged from the water washing section is returned to the water washing section, the washing section, and the stripping section for use, or used to prepare an acid for dissolving rare earth ores. However, similarly, this extraction method has complex operations and a long extraction time.

[0006] Reference Document 3 discloses a method for continuously extracting and separating medium and heavy rare earth chloride solutions. In this method, the purified medium and heavy rare earth chloride solution, extractant, and diluent are mixed in a mixing chamber and then flow into a clarification chamber for clarification to separate the organic phase and the aqueous phase. Although the extraction process can proceed continuously and stably, the equipment occupies a large area and the extraction efficiency is low, making it difficult to purify, enrich, and recover low-concentration rare earth ions.

[0007] Microfluidic technology is an emerging technology for performing operations such as separation and purification of substances in microreactors and microchannel reactors. In recent years, it has developed rapidly due to the advantages of microchannel reactors, such as small equipment footprint, large overall mass transfer coefficient, short mass transfer distance, short reaction time, high mass transfer efficiency, and safety.

[0008] Currently, there have been research reports on combining microfluidic technology with solvent extraction technology for rare earth element extraction. For example, Reference Document 4 discloses a method for extracting rare earth elements in a microchannel, which includes the following steps: First, P507 or P204 is added to a 260 # solvent oil diluent according to a volume ratio of 3:10 to 10:3 to obtain an organic phase; the rare earth salt solution is used as the aqueous phase, and the organic phase and the aqueous phase are in a phase ratio of 5:1 to 1:5, and at a volume flow rate of 5.55×10 -10 ~4.17×10 -8 m 3 / s, and normal temperature extraction is carried out in the microchannel of the microreactor, and finally an extraction phase and a raffinate containing rare earth elements are obtained. Although the extraction time is significantly shortened and the extraction rate can reach more than 99%, this method has problems such as a large amount of extractant used, not being suitable for large-phase ratio operations, and being prone to generating a large amount of oily wastewater.

[0009] Reference Documents:

[0010] Reference Document 1: CN107699715B

[0011] Reference Document 2: CN109554556A

[0012] Reference Document 3: CN110331303A

[0013] Reference Document 4: CN105112658A Summary of the Invention

[0014] Problems to be solved by the invention

[0015] As described above, for a low-concentration rare earth element solution, if the solvent extraction method is directly used to extract rare earth elements, a large amount of extractant is required. To improve the enrichment rate, it is necessary to increase the extraction stage. Moreover, in traditional extraction equipment, the extractant exists in the form of small droplets, and the interfacial area between the extractant and the target component is limited, which affects the extraction efficiency. Although the combination of microfluidic technology and solvent extraction technology has many advantages in the enrichment and recovery of low-concentration rare earth elements, there is still room for research on how to ensure the rapid mixing and separation of the organic phase and the aqueous phase in a large phase ratio, as well as long-term stable operation, etc.

[0016] The main object of the present invention is to provide an extraction method for enhancing low-concentration rare earth elements. This extraction method is based on a continuous extraction process that combines microfluidic technology and solvent extraction technology, and realizes the efficient enrichment and recovery of low-concentration rare earth elements by using a gas-liquid-liquid three-phase system and a combination of extractants.

[0017] Furthermore, the present invention also provides an apparatus for implementing the extraction method for enhancing low-concentration rare earth elements. This apparatus is simple, can ensure the efficient and stable operation of the extraction method, and at the same time has a small floor area and high production efficiency.

[0018] Solutions for solving the problems

[0019] It has been found that by implementing the following technical solutions, the above technical problems can be solved:

[0020] [1]. The present invention provides an extraction method for enhancing low-concentration rare earth elements, which includes the following steps:

[0021] 1) The step of extraction and phase separation: Mix an oil solution containing an extractant and an aqueous solution containing low-concentration rare earth elements through a first micro mixer and then enter a first micro extractor for extraction. After that, it is transported to a first phase separator through a first micro reactor for phase separation treatment to obtain an oil phase containing rare earth elements; before mixing, the oil solution containing the extractant has been pre-mixed with compressed gas through a pre-micro mixer and then enters a pre-micro reactor for gas-liquid dispersion, and the pre-micro reactor is a micro packed bed reactor;

[0022] 2) The step of stripping and phase separation: Mix the oil phase containing rare earth elements and an acidic solution through a second micro mixer and then enter a second micro extractor for stripping. After that, it is transported to a second phase separator through a second micro reactor for phase separation treatment to obtain an aqueous phase containing high-concentration rare earth elements;

[0023] Among them, the structures of the first micro extractor and the second micro extractor can be the same or different, and both are micro packed bed extractors.

[0024] The extractant includes a combination of two or more of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, bis(2-ethylhexyl) phosphate, bis(2,4,4-trimethylpentyl) phosphinic acid, and bis(2,4,4-trimethylpentyl) dithiophosphinic acid.

[0025] [2]. According to the extraction method described in [1], wherein, in step 1),

[0026] The extractant includes 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, and any one of bis(2-ethylhexyl) phosphate, bis(2,4,4-trimethylpentyl) phosphinic acid, and bis(2,4,4-trimethylpentyl) dithiophosphinic acid.

[0027] [3]. According to the extraction method described in [1] or [2], wherein, in step 1),

[0028] In the aqueous solution containing low-concentration rare earth elements, the concentration of rare earth elements is less than 100 mg / L, and the concentration of hydrogen ions is 1×10 -5 ~1×10 -3 mol / L;

[0029] In the oil solution containing the extractant, the concentration of the extractant is 1 - 2 mol / L.

[0030] [4]. According to the extraction method described in any one of [1]-[3], wherein, in step 1),

[0031] The volume flow ratio of the aqueous solution containing low-concentration rare earth elements to the oil solution containing the extractant is (50 - 500):1;

[0032] The volume flow ratio of the compressed gas to the oil solution containing the extractant is (50 - 500):1.

[0033] [5]. According to the extraction method described in any one of [1]-[4], wherein, in step 1),

[0034] The temperature in the pre-microreactor is 10 - 30 °C, and the residence time in the pre-microreactor is 0.5 - 30 s.

[0035] [6]. According to the extraction method described in any one of [1]-[5], wherein, in step 1),

[0036] After pre-mixing, the pre-mixed liquid enters the pre-microreactor to form a gas-liquid mixture with an oil-in-gas structure;

[0037] After mixing, the mixed liquid enters the first microextractor to form a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0038] [7]. The extraction method according to any one of [1]-[6], wherein in step 2),

[0039] In the acidic solution, the concentration of the acidic substance is 1 to 2 mol / L.

[0040] [8]. The extraction method according to any one of [1]-[7], wherein,

[0041] The first micro mixer and the second micro mixer are each independently a microchannel mixer, a membrane dispersion mixer or a micro sieve hole mixer;

[0042] The first micro reactor and the second micro reactor are each independently a coiled tube micro reactor or a microchannel reactor.

[0043] [9]. The extraction method according to any one of [1]-[8], wherein,

[0044] The temperature in the first micro mixer is 10 to 30 °C, and the mixing time is greater than 0 and less than 5 s;

[0045] The temperature in the first micro extractor is 10 to 30 °C, and the residence time is 0.5 to 30 s;

[0046] The temperature in the first micro reactor is 10 to 30 °C, and the residence time is 0.1 to 5 min;

[0047] The temperature in the second micro mixer is 10 to 30 °C, and the mixing time is greater than 0 and less than 5 s;

[0048] The temperature in the second micro extractor is 10 to 30 °C, and the residence time is 0.5 to 120 s;

[0049] The temperature in the second micro reactor is 10 to 30 °C, and the residence time is 0.1 to 5 min.

[0050]

[10] . The present invention also provides an apparatus for implementing the extraction method according to any one of [1]-[9], wherein the apparatus comprises a pre-micro mixer, a pre-micro reactor, a first micro mixer, a first micro extractor, a first micro reactor, a first phase separator, a second micro mixer, a second micro extractor, a second micro reactor and a second phase separator which are connected in sequence.

[0051] Effects of the invention

[0052] By implementing the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] 1) The extraction method of the present invention is based on a continuous extraction process that combines microfluidic technology and solvent extraction technology, featuring high mass transfer efficiency, simple operation, low consumption of extraction solvent, high extraction efficiency, low error, and good stability. It can achieve continuous and stable operation of the extraction process, and the original extraction agent can be recycled after back-extraction of the organic phase. It is applicable to the enrichment and recovery of low-concentration rare earth elements under large phase ratios (>50) in industrial scale conditions.

[0054] 2) In the extraction equipment used in the present invention, the entire extraction process is a continuous process, which is safe, environmentally friendly, has high production efficiency, small equipment footprint, simple operation, can reduce manual operation, lower production costs, and ensure production economy.

[0055] 3) Through the extraction process of the present invention, the extraction rate of rare earth elements with low concentration (<100 mg / L) can be greater than 99%, and the enrichment rate can be as high as 800 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The equipment flow chart showing an embodiment of the method for enhancing the extraction of low-concentration rare earth elements of the present invention is shown.

[0057] DESCRIPTION OF THE REFERENCE NUMERALS

[0058] Figure 1 In the figure, 1 is an oil solution containing an extraction agent; 2 is compressed gas; 3 is pump 1; 4 is pump 2; 5 is micromixer 1; 6 is microreactor 1; 7 is an aqueous solution containing low-concentration rare earth elements; 8 is pump 3; 9 is micromixer 2; 10 is microreactor 2; 11 is microreactor 3; 12 is phase separator 1; 13 is raffinate; 14 is acidic solution; 15 is pump 4; 16 is micromixer 3; 17 is microreactor 4; 18 is microreactor 5; 19 is phase separator 2; 20 is an oil phase containing an extraction agent; 21 is an aqueous phase containing high-concentration rare earth elements. DETAILED DESCRIPTION OF THE INVENTION

[0059] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The special term "exemplary" here means "serving as an example, embodiment, or illustrative". Any embodiment described as "exemplary" here does not have to be construed as superior or better than other embodiments.

[0060] In addition, in order to better illustrate the present invention, numerous specific details are given in the following detailed description. Those skilled in the art should understand that the present invention can still be implemented without some specific details. In other instances, methods, means, equipment, and steps well-known to those skilled in the art are not described in detail to highlight the gist of the present invention.

[0061] Unless otherwise specified, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0062] In this specification, the meaning expressed by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0063] In this specification, unless otherwise specified, the "many" in "many", "multiple types", "multiple" and the like means a numerical value of 2 or more.

[0064] In this specification, "comprising", "having", "including" or "containing" may refer to inclusive or open-ended, and do not exclude additional, unrecited elements or method steps. At the same time, "comprising", "having", "including" or "containing" may also mean closed-ended, excluding additional, unrecited elements or method steps.

[0065] In this specification, the "some specific / preferred embodiments", "some other specific / preferred embodiments", "embodiments" and the like mentioned refer to the specific elements (for example, features, structures, properties and / or characteristics) related to the embodiment are included in at least one of the embodiments described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0066] In this specification, the numerical range expressed by "above" or "below" refers to the numerical range including this number.

[0067] In this specification, the numerical range expressed by "numerical value A to numerical value B" refers to the range including the endpoint numerical values A and B.

[0068] In this specification, "first", "second", "the first" or "the second" may modify various components regardless of order and / or importance, but these expressions do not limit the corresponding components. The above expressions are only configured for the purpose of distinguishing elements from other elements.

[0069] <First aspect>

[0070] The first aspect of the present invention provides an extraction method for strengthening low-concentration rare earth elements, which includes the following steps:

[0071] 1) Steps of extraction and phase separation: Mix an oil solution containing an extractant and an aqueous solution containing rare earth elements at low concentration through a first micro mixer and then feed them into a first micro extractor for extraction. After that, convey them to a first phase separator through a first micro reactor for phase separation to obtain an oil phase containing rare earth elements; before the mixing, the oil solution containing the extractant has been pre-mixed with compressed gas through a pre-micro mixer and then fed into a pre-micro reactor for gas-liquid dispersion, and the pre-micro reactor is a micro packed bed reactor;

[0072] 2) Steps of stripping and phase separation: Mix the oil phase containing rare earth elements and an acidic solution through a second micro mixer and then feed them into a second micro extractor for stripping. After that, convey them to a second phase separator through a second micro reactor for phase separation to obtain an aqueous phase containing rare earth elements at high concentration.

[0073] Each step in the extraction method of the present invention is described in detail below.

[0074] Steps of premixing

[0075] In the pre-mixing step of the present invention, an oil solution containing an extractant is mixed with compressed gas in a pre-micro mixer to obtain a pre-mixed solution. By using the pre-micro mixer for the above mixing, sufficient mixing between the gas and liquid phases can be achieved. Specifically, a pump (such as a peristaltic pump, diaphragm pump, magnetic pump, centrifugal pump, etc.) or a gas mass flow controller can be used to feed the oil solution containing the extractant and the compressed gas into the pre-micro mixer.

[0076] In some specific embodiments, the present invention does not particularly limit the compressed gas, and it can be some gases commonly used in the art. For example, it can include air, pure inert gases (such as nitrogen, argon, helium), or air diluted with inert gases such as nitrogen, argon, or helium. In some preferred embodiments, the compressed gas is nitrogen.

[0077] In some specific embodiments, the oil solution containing the extractant of the present invention preferably includes at least an extractant and an organic solvent insoluble in water.

[0078] The organic solvent can usually be appropriately selected according to the specific composition of the aqueous solution to be extracted (the specific types of rare earth elements and other substances contained in the aqueous solution to be extracted, etc.). Examples of the organic solvent include but are not limited to kerosene (such as sulfonated kerosene), light white oil, solvent oil, etc.

[0079] In some embodiments, the extractant comprises a combination of two or more of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507), bis(2-ethylhexyl) phosphate (P204), bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), and bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex 301). In some preferred embodiments, the extractant comprises 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, and any one of bis(2-ethylhexyl) phosphate, bis(2,4,4-trimethylpentyl) phosphinic acid, and bis(2,4,4-trimethylpentyl) dithiophosphinic acid. Additionally, in some preferred embodiments, in the oil solution containing the extractant, the concentration of the extractant is 1-2 mol / L, and can be, for example, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, etc.

[0080] Furthermore, for the oil solution containing the extractant of the present invention, in addition to the above-mentioned extractant and water-insoluble organic solvent, optionally, according to actual needs, other additives can also be included, such as one or more of a complexing agent, a co-extractant, an anti-extractant, a phase transfer catalyst, a stabilizer, a diluent, etc.

[0081] In some specific embodiments, the volume flow rate ratio of the compressed gas to the oil solution containing the extractant is (50-500):1, preferably (200-400):1, and can be, for example, 50:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, etc. By adjusting the volume flow rate ratio of the compressed gas to the oil solution containing the extractant to the above range, the extraction efficiency under the condition of a large phase ratio can be improved.

[0082] In some specific embodiments, the present invention has no particular limitation on the pre-micro mixer used in the pre-mixing step, and it can be any micro mixer known in the art suitable for gas-liquid mixing, such as a microchannel mixer, a membrane dispersion micro mixer, or a micro sieve hole mixer, etc. In a preferred embodiment, the pre-micro mixer is a microchannel mixer, such as a T-shaped micro three-way mixer.

[0083] In some specific embodiments, the inner diameter of the pre-micro mixer is 0.5-2 mm, preferably 0.8-1.2 mm, and can be, for example, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 2 mm, etc.

[0084] In some specific embodiments, the temperature in the pre-micro mixer is 10 to 30 °C, for example, it can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the pre-micro mixer at 10 to 30 °C, the extraction efficiency can be improved. The mixing time in the pre-micro mixer is greater than 0 and less than 5 s, for example, it can be 0.01 s, 0.02 s, 0.05 s, 0.1 s, 0.5 s, 1 s, 3 s, 4 s, etc.; by setting the mixing time to be greater than 0 and less than 5 s, it can ensure sufficient mixing while taking into account the extraction efficiency.

[0085] Steps of gas-liquid dispersion

[0086] In the gas-liquid dispersion step of the present invention, the pre-mixture is introduced into a pre-micro reactor for gas-liquid dispersion to form a gas-liquid mixture with a gas-in-oil structure. By using the pre-micro reactor for the above gas-liquid dispersion, good dispersion can be achieved between the gas and liquid phases.

[0087] In the present invention, the formation of the gas-in-oil structure significantly increases the mass transfer specific surface area. The presence of bubbles enables the oil phase to wrap the gas with a thinner film layer, which is beneficial to increasing the contact area between the oil phase and the water phase in the subsequent extraction process.

[0088] In some specific embodiments, the pre-micro reactor is a micro-packed bed reactor, wherein the inner diameter of the micro-packed bed reactor is 2 to 50 mm, for example, it can be 2 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc. The present invention does not particularly limit the packing used in the micro-packed bed reactor, and it can be some packings commonly used in the art. For example, those that can be listed include zirconia, silica, polymer microspheres such as polyethylene, activated carbon, ceramic-metal composites, etc. Additionally, in some embodiments, the size of the packing can be 50 to 500 μm, and the porosity can be 0.3 to 0.6.

[0089] In some specific embodiments, the temperature in the pre-micro reactor is 10 to 30 °C, for example, it can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the pre-micro reactor at 10 to 30 °C, good gas-liquid dispersion can be achieved. The residence time in the pre-micro reactor is 0.5 to 30 s, for example, it can be 1 s, 3 s, 5 s, 6.5 s, 8 s, 10 s, 15 s, 20 s, 25 s, 30 s, etc.; by setting the residence time to be 0.5 to 30 s, it can ensure good dispersion while taking into account the extraction efficiency.

[0090] Steps of extraction

[0091] In the extraction step of the present invention, the gas-liquid mixture and the aqueous solution containing low-concentration rare earth elements are mixed via a first micromixer and then enter a first microextractor for extraction to form a gas-liquid-liquid mixture with a water-in-oil-in-gas structure. Specifically, a pump (such as a peristaltic pump, diaphragm pump, magnetic pump, centrifugal pump, etc.) can be used to introduce the aqueous solution containing low-concentration rare earth elements into the first micromixer.

[0092] In the present invention, there is no particular limitation on the source of the aqueous solution containing low-concentration rare earth elements. For example, it can be a rare earth simulation solution or any industrial aqueous solution containing rare earth elements, such as various wastewaters, acidic leaching solutions containing rare earth elements (such as those from waste, fly ash, etc.), and various liquid intermediate products containing rare earth elements.

[0093] In the present invention, there is no particular limitation on the types of rare earth elements, and the extraction method of the present invention is applicable to the extraction of various rare earth elements. Specifically, the rare earth elements applicable to the extraction method of the present invention include the lanthanide elements in Group IIIB of the periodic table of chemical elements (lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu)), as well as scandium (Sc) and yttrium (Y).

[0094] In the present invention, there is no particular limitation on the concentration of rare earth elements in the aqueous solution containing low-concentration rare earth elements. In some preferred embodiments, the concentration of the rare earth elements is less than 100 mg / L, preferably 5 - 100 mg / L. For example, it can be 10 mg / L, 30 mg / L, 50 mg / L, 70 mg / L, 90 mg / L, etc. Additionally, in some preferred embodiments, in the aqueous solution containing low-concentration rare earth elements, the concentration of hydrogen ions is 1×10 -5 ~1×10 -3 mol / L. For example, it can be 1×10 - 5 mol / L, 5×10 -5 mol / L, 1×10 -4 mol / L, 5×10 -4 mol / L, 1×10 -3 mol / L, etc.

[0095] In some more preferred embodiments, as described above, even for an aqueous solution with a rare earth element concentration of less than 100 mg / L, the residual amount of rare earth elements in the raffinate can be less than 1.0 ppm.

[0096] In some specific embodiments, the volume flow rate ratio of the aqueous solution containing low-concentration rare earth elements to the oil solution containing the extractant is (50 - 500):1, preferably (300 - 500):1, and for example, it can be 50:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, etc. By adjusting the volume flow rate ratio of the aqueous solution containing low-concentration rare earth elements to the oil solution containing the extractant within the above range, the extraction efficiency can be improved.

[0097] In some specific embodiments, the present invention does not particularly limit the first micromixer, and it can be any micromixer known in the art suitable for gas-liquid-liquid mixing. For example, microchannel mixers, membrane dispersion micromixers, or microsieve pore mixers can be listed. In a preferred embodiment, the first micromixer is a microchannel mixer, for example, it can be a T-shaped micro three-way mixer.

[0098] In some specific embodiments, the inner diameter of the first micromixer is 0.2 - 1 mm, preferably 0.25 - 0.5 mm, and for example, it can be 0.2 mm, 0.25 mm, 0.5 mm, 0.8 mm, 1 mm, etc.

[0099] In some specific embodiments, the temperature in the first micromixer is 10 - 30 °C, and for example, it can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the first micromixer at 10 - 30 °C, the extraction efficiency can be improved. The mixing time in the first micromixer is greater than 0 and less than 5 s, and for example, it can be 0.01 s, 0.02 s, 0.1 s, 0.5 s, 1 s, 3 s, 4 s, etc.; by setting the mixing time to be greater than 0 and less than 5 s, it can ensure sufficient mixing while taking into account the extraction efficiency.

[0100] In some specific embodiments, the first microextractor is a micro-packed bed extractor, where the inner diameter of the micro-packed bed extractor is 2 - 50 mm, and for example, it can be 2 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc. The present invention does not particularly limit the packing used in the micro-packed bed extractor, and it can be some packings commonly used in the art. For example, zirconia, silica, polymer microspheres such as polyethylene, activated carbon, ceramic-metal composites, etc. can be listed. Additionally, in some embodiments, the size of the packing can be 50 - 500 μm, and the porosity can be 0.3 - 0.6.

[0101] In some specific embodiments, the temperature in the first microextractor is 10 - 30 °C, for example, it can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the first microextractor at 10 - 30 °C, good gas-liquid-liquid three-phase dispersion can be achieved. The residence time in the first microextractor is 0.5 - 30 s, for example, it can be 1 s, 3 s, 5 s, 8 s, 10 s, 15 s, 20 s, 25 s, 30 s, etc.; by setting the residence time to 0.5 - 30 s, while ensuring good dispersion, the extraction efficiency can be taken into account.

[0102] Furthermore, since the extraction rate gradually becomes slow in the later stage of extraction, to completely extract rare earth elements in the first microextractor, it is necessary to greatly increase the volume of the micro-packed bed extractor, such as the length of the micro-packed bed extractor, which is not conducive to process economy and other reasons. The present invention also transports the gas-liquid-liquid mixture with an oil-in-water-in-gas structure formed by preliminary extraction to the first microreactor for continuous extraction. Specifically, the first microreactor is a coiled tube microreactor or a microchannel reactor, among which the coiled tube microreactor is preferred. The inner diameter of the coiled tube can be 0.5 - 8 mm, preferably 2 - 6 mm, for example, it can be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, etc.

[0103] In some specific embodiments, the temperature in the first microreactor is 10 - 30 °C, for example, it can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the first microreactor at 10 - 30 °C, the extraction rate can be increased. The residence time in the first microreactor is 0.1 - 5 min, for example, it can be 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min, etc.; by setting the residence time to 0.1 - 5 min, while ensuring a high extraction rate, the extraction efficiency can be taken into account.

[0104] By transporting the gas-liquid-liquid mixture with an oil-in-water-in-gas structure formed by preliminary extraction to the first microreactor for continuous extraction. Specifically, the extractant can form a stable complex with rare earth elements that is insoluble in the aqueous phase but soluble in the organic phase, thereby enabling the rare earth elements to transfer from the aqueous phase to the organic phase through interfacial mass transfer. The presence of bubbles enhances the mass transfer efficiency. In this process, gas is introduced into the system as the third phase, which not only increases the mass transfer interface but also changes the physical properties of the system (such as density, fluidity, etc.), thus strengthening the extraction and phase separation processes.

[0105] Steps of phase separation after extraction

[0106] In the phase separation step after extraction of the present invention, the gas-liquid-liquid mixture is transported to the first phase separator through the first microreactor for phase separation treatment to obtain an oil phase containing rare earth elements and a raffinate.

[0107] In some specific embodiments, a filter cloth is provided in the first phase separator, and the material of the filter cloth includes one or more of nylon, polytetrafluoroethylene, polypropylene, and polyvinylidene fluoride. In the present invention, after the gas-liquid-liquid mixture enters from the inlet of the first phase separator, the oil phase is blocked by the filter cloth and accumulates above the filter cloth, while the water phase (i.e., the raffinate) flows through the filter cloth into the lower water phase collection chamber, realizing the efficient separation of the oil phase and the water phase. The separated oil phase can be collected from the upper part of the phase separator for subsequent back-extraction steps; the water phase is discharged from the water phase collection chamber to complete the separation process.

[0108] In some specific embodiments, the temperature of the phase separation treatment is 10 - 30 °C.

[0109] Steps of back extraction

[0110] In the back-extraction step of the present invention, the oil phase containing rare earth elements and the acidic solution are mixed via a second micro-mixer and then enter a second micro-extractor for back-extraction. Specifically, a pump (such as a peristaltic pump, diaphragm pump, magnetic pump, centrifugal pump, etc.) can be used to introduce the acidic solution into the second micro-mixer.

[0111] In some specific embodiments, in the acidic solution, the concentration of the acidic substance is 1 - 2 mol / L, for example, it can be 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, etc.

[0112] Specifically, in the present invention, the solvent for dissolving the acidic substance is not particularly limited in the present invention and can be any feasible polar solvent in the art, preferably water.

[0113] Furthermore, the acidic substance is not particularly limited in the present invention and can be a commonly used strong acidic substance in the art, such as hydrochloric acid, nitric acid, or sulfuric acid, etc., preferably hydrochloric acid.

[0114] In some specific embodiments, the volume flow rate ratio of the oil phase containing rare earth elements to the acidic solution is (1 - 5):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, etc. By adjusting the volume flow rate ratio of the oil phase containing rare earth elements to the acidic solution to the above range, the back-extraction efficiency can be improved.

[0115] In some specific embodiments, the present invention does not particularly limit the second micro-mixer, and it can be any micro-mixer known in the art suitable for liquid-liquid mixing, such as a microchannel mixer, a membrane dispersion micro-mixer, or a micro-sieve hole mixer, etc. In a preferred embodiment, the second micro-mixer is a microchannel mixer, for example, it can be a T-shaped micro-three-way mixer.

[0116] In some specific embodiments, the inner diameter of the second micro-mixer is 0.2 to 1 mm, preferably 0.25 to 0.5 mm, and can be, for example, 0.2 mm, 0.25 mm, 0.5 mm, 0.8 mm, 1 mm, etc.

[0117] In some specific embodiments, the temperature in the second micro-mixer is 10 to 30 °C, and can be, for example, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the second micro-mixer at 10 to 30 °C, the stripping efficiency can be improved. The mixing time in the second micro-mixer is greater than 0 and less than 5 s, and can be, for example, 0.1 s, 0.2 s, 0.5 s, 1 s, 3 s, 4 s, etc.; by setting the mixing time to be greater than 0 and less than 5 s, sufficient mixing can be ensured while taking into account the stripping efficiency.

[0118] In some specific embodiments, the second micro-extractor is a micro-packed bed extractor, and the inner diameter of the micro-packed bed extractor is 2 to 50 mm, and can be, for example, 2 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc. The present invention does not particularly limit the packing used in the micro-packed bed extractor, and some packings commonly used in the art can be used, such as polymer microspheres including zirconia, silica, polyethylene, etc., activated carbon, ceramic-metal composites, etc. Additionally, in some embodiments, the size of the packing can be 50 to 500 μm, and the porosity can be 0.3 to 0.6.

[0119] In some specific embodiments, the temperature in the second micro-extractor is 10 to 30 °C, and can be, for example, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the second micro-extractor at 10 to 30 °C, good oil-water two-phase dispersion can be achieved. The residence time in the second micro-extractor is 0.5 to 120 s, and can be, for example, 1 s, 3 s, 5 s, 8 s, 10 s, 15 s, 20 s, 25 s, 30 s, 60 s, 90 s, 100 s, 120 s, etc.; by setting the residence time to 0.5 to 120 s, good dispersion can be ensured while taking into account the stripping efficiency.

[0120] Further, since the rate gradually becomes slow in the later stage of stripping, to achieve complete stripping of rare earth elements in the second microextractor, it is necessary to greatly increase the volume of the micro-packed bed extractor, such as the length of the micro-packed bed extractor, which is not conducive to process economy. For these reasons, the present invention also transports the oil-water mixture formed by preliminary stripping to the second microreactor for further stripping. Specifically, the second microreactor is a coiled microreactor or a microchannel reactor, and preferably a coiled microreactor. The inner diameter of the coil can be 0.5 - 8 mm, preferably 2 - 6 mm, and can be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, etc.

[0121] In some specific embodiments, the temperature in the second microreactor is 10 - 30 °C, and can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, etc.; by controlling the temperature in the second microreactor at 10 - 30 °C, the stripping rate can be increased. The residence time in the second microreactor is 0.1 - 5 min, and can be 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min, etc.; by setting the residence time to 0.1 - 5 min, high stripping rate can be ensured while taking into account the stripping efficiency.

[0122] Steps of phase separation after back extraction

[0123] In the phase separation step after stripping of the present invention, the oil-water mixture is transported to the second phase separator through the second microreactor for phase separation treatment to obtain an aqueous phase containing high-concentration rare earth elements and an oil phase containing the extractant.

[0124] In some specific embodiments, a filter cloth is provided in the second phase separator, and the material of the filter cloth includes one or more of nylon, polytetrafluoroethylene, polypropylene, and polyvinylidene fluoride. In the present invention, after the oil-water mixture enters from the first phase separator inlet, the oil phase (containing the extractant) is blocked by the filter cloth and accumulates above the filter cloth, while the aqueous phase (containing high-concentration rare earth elements) flows through the filter cloth into the lower aqueous phase collection chamber, realizing efficient separation of the oil phase and the aqueous phase. The separated oil phase can be collected from the upper part of the phase separator and recycled; the aqueous phase can be further separated and purified by existing methods such as membrane separation and ion exchange.

[0125] In some specific embodiments, the temperature of the phase separation treatment is 10 - 30 °C.

[0126] <Second aspect>

[0127] The second aspect of the present invention provides a device for implementing the extraction method described in the first aspect, which includes a pre-micro mixer, a pre-micro reactor, a first micro mixer, a first microextractor, a first microreactor, a first phase separator, a second micro mixer, a second microextractor, a second microreactor, and a second phase separator connected in sequence.

[0128] By using the device of the present invention, it is possible to ensure the efficient and stable extraction of the low-concentration rare earth elements of the present invention, and the device has a small floor area and high production efficiency.

[0129] Example

[0130] The following will describe the implementation scheme of the present invention in detail in conjunction with the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0131] In the following embodiments, the calculation formula for the extraction rate is:

[0132] Extraction rate (%) = (1 - concentration of rare earth elements in the raffinate / concentration of rare earth elements in the rare earth ion solution before extraction) × 100%.

[0133] The parameters of the microreaction equipment used in the following Examples 1-4 are as follows:

[0134] Micro mixer 1: T-shaped micro three-way, inner diameter 0.8 mm;

[0135] Micro mixer 2: T-shaped micro three-way, inner diameter 0.25 mm;

[0136] Micro mixer 3: T-shaped micro three-way, inner diameter 0.25 mm;

[0137] Micro reactor 1: Micro packed bed, inner diameter 10 mm, length 20 cm, the packing is silica microspheres (size 200 μm, porosity about 0.45);

[0138] Micro reactor 2: Micro packed bed, inner diameter 10 mm, length 20 cm, the packing is silica microspheres (size 200 μm, porosity about 0.45);

[0139] Micro reactor 3: Micro coiled tube, inner diameter 3 mm, length 20 m;

[0140] Micro reactor 4: Micro packed bed, inner diameter 10 mm, length 20 cm, the packing is silica microspheres (size 200 μm, porosity about 0.45);

[0141] Micro reactor 5: Micro coiled tube, inner diameter 2 mm, length 4 m.

[0142] Example 1:

[0143] A method for enhancing the extraction of low-concentration neodymium elements, as Figure 1 shown, which includes the following steps:

[0144] 1. Preparation of solutions: Dissolve neodymium chloride in an aqueous hydrochloric acid solution with a pH of 4 to prepare a rare earth ion solution (where the concentration of rare earth elements is 90 mg / L); Stir and mix 17 mL of P507, 17 mL of P204, and 66 mL of sulfonated kerosene to obtain an oil solution containing an extractant, where the total concentration of the extractants (P507 and P204) is 1 mol / L.

[0145] 2. Formation of an oil-in-gas structure: The oil solution containing the extractant (flow rate of 0.2 mL / min) and nitrogen (flow rate of 60 mL / min) are respectively transported to a micromixer 1 by a peristaltic pump for mixing (mixing temperature is 20 °C, mixing time is 0.05 s), and then enter a microreactor 1 for gas-liquid dispersion (temperature is 20 °C, residence time is 8 s) to form a gas-liquid mixture with an oil-in-gas structure.

[0146] 3. Extraction: The gas-liquid mixture obtained from the outlet of the microreactor 1 and the rare earth ion solution transported by a peristaltic pump (flow rate of 80 mL / min) are transported to a micromixer 2 for mixing (mixing temperature is 20 °C, mixing time is 0.02 s), and then enter a microreactor 2 for preliminary extraction (temperature is 20 °C, residence time is 3 s), and then transported to a microreactor 3 for continued extraction (temperature is 20 °C, residence time is 1 min) to form a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0147] 4. Phase separation: The gas-liquid-liquid mixture obtained from the outlet of the microreactor 3 is introduced into a phase separator 1 for phase separation to obtain an upper oil phase (containing rare earth elements) and a lower water phase (raffinate).

[0148] 5. Back extraction: The oil phase containing rare earth elements (flow rate of 8 mL / min) and 1.0 mol / L hydrochloric acid transported by a peristaltic pump (flow rate of 4 mL / min) are transported to a micromixer 3 for mixing (mixing temperature is 20 °C, mixing time is 0.2 s), and then enter a microreactor 4 for preliminary back extraction (temperature is 20 °C, residence time is 20 s), and then transported to a microreactor 5 for continued back extraction (temperature is 20 °C, residence time is 1 min) to obtain an oil-water mixture.

[0149] 6. Phase separation: The oil-water mixture obtained from the outlet of the microreactor 5 is introduced into a phase separator 2 for phase separation to obtain an upper oil phase (containing the extractant) and a lower water phase (containing rare earth elements). The oil phase containing the extractant does not contain rare earth elements and can be recycled. Existing methods such as membrane separation and ion exchange are used to further separate and purify the water phase containing high-concentration (>1 g / L) rare earth elements.

[0150] Detected by inductively coupled plasma optical emission spectrometry (ICP-OES), the error range is within 2%, the extraction rate can reach over 99%, the concentration of rare earth elements in the raffinate is 0.10 mg / L, and the concentration of rare earth elements in the water phase enriched with rare earth elements is 72 g / L.

[0151] Stability test: Continuously operate for 10 h, take samples every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 1%.

[0152] Example 2:

[0153] An extraction method for enhancing low-concentration europium elements, as Figure 1 shown, which includes the following steps:

[0154] 1. Prepare the solution: Dissolve europium chloride with a hydrochloric acid aqueous solution of pH = 4 to prepare a rare earth ion solution (where the concentration of rare earth elements is 50 mg / L); Stir and mix 20 mL of P507, 14 mL of Cyanex 272, and 66 mL of sulfonated kerosene to obtain an oil solution containing an extractant, where the total concentration of the extractants (P507 and Cyanex 272) is 1 mol / L.

[0155] 2. Form an oil-in-gas structure: Feed the oil solution containing the extractant (flow rate of 0.2 mL / min) and nitrogen (flow rate of 60 mL / min) into the micro-mixer 1 through a peristaltic pump for mixing (mixing temperature is 20 °C, mixing time is 0.05 s), and then enter the micro-reactor 1 for gas-liquid dispersion (temperature is 20 °C, residence time is 8 s) to form a gas-liquid mixture with an oil-in-gas structure.

[0156] 3. Extraction: Feed the gas-liquid mixture obtained at the outlet of the micro-reactor 1 and the rare earth ion solution (flow rate of 80 mL / min) fed through a peristaltic pump into the micro-mixer 2 for mixing (mixing temperature is 20 °C, mixing time is 0.02 s), and then enter the micro-reactor 2 for preliminary extraction (temperature is 20 °C, residence time is 3 s), and then be fed into the micro-reactor 3 for continuous extraction (temperature is 20 °C, residence time is 1 min) to form a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0157] 4. Phase separation: Feed the gas-liquid-liquid mixture obtained at the outlet of the micro-reactor 3 into the phase separator 1 for phase separation to obtain the upper oil phase (containing rare earth elements) and the lower water phase (raffinate).

[0158] 5. Back-extraction: The oil phase containing rare earth elements (flow rate: 8 mL / min) and 1.0 mol / L hydrochloric acid transported by a peristaltic pump (flow rate: 4 mL / min) are transported to a micromixer 3 for mixing (mixing temperature: 20 °C, mixing time: 0.2 s), then enter a microreactor 4 for preliminary back-extraction (temperature: 20 °C, residence time: 20 s), and subsequently transported to a microreactor 5 for continuous back-extraction (temperature: 20 °C, residence time: 1 min) to obtain an oil-water mixture.

[0159] 6. Phase separation: The oil-water mixture obtained at the outlet of the microreactor 5 is passed into a phase separator 2 for phase separation to obtain an upper oil phase (containing the extractant) and a lower water phase (containing rare earth elements). The oil phase containing the extractant does not contain rare earth elements and can be recycled.

[0160] Detected by ICP-OES, the error range is within 2%, the extraction rate can reach over 99%, the concentration of rare earth elements in the raffinate is 0.08 mg / L, and the concentration of rare earth elements in the enriched water phase containing rare earth elements is 40 g / L.

[0161] Stability test: Continuously operate for 10 h, take samples every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 1%.

[0162] Example 3:

[0163] A method for enhancing the extraction of low-concentration dysprosium elements, as Figure 1 shown, which includes the following steps:

[0164] 1. Solution preparation: Dissolve dysprosium chloride with an aqueous hydrochloric acid solution of pH = 4 to prepare a rare earth ion solution (where the concentration of rare earth elements is 70 mg / L); stir and mix 20 mL of P507, 14 mL of Cyanex 301, and 66 mL of sulfonated kerosene to obtain an oil solution containing the extractant, where the total concentration of the extractant (P507 and Cyanex 301) is 1 mol / L.

[0165] 2. Formation of an oil-in-gas structure: The oil solution containing the extractant (flow rate: 0.2 mL / min) and nitrogen (flow rate: 60 mL / min) are respectively transported by a peristaltic pump to a micromixer 1 for mixing (mixing temperature: 20 °C, mixing time: 0.05 s), then enter a microreactor 1 for gas-liquid dispersion (temperature: 20 °C, residence time: 8 s) to form a gas-liquid mixture with an oil-in-gas structure.

[0166] 3. Extraction: The gas-liquid mixture obtained from the outlet of the microreactor 1 and the rare earth ion solution (flow rate: 80 mL / min) delivered by a peristaltic pump are transported to the micromixer 2 for mixing (mixing temperature: 20 °C, mixing time: 0.02 s), and then enter the microreactor 2 for preliminary extraction (temperature: 20 °C, residence time: 3 s). Subsequently, it is transported to the microreactor 3 for continuous extraction (temperature: 20 °C, residence time: 1 min), forming a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0167] 4. Phase separation: The gas-liquid-liquid mixture obtained from the outlet of the microreactor 3 is introduced into the phase separator 1 for phase separation to obtain the upper oil phase (containing rare earth elements) and the lower aqueous phase (raffinate).

[0168] 5. Back extraction: The oil phase containing rare earth elements (flow rate: 8 mL / min) and 1.0 mol / L hydrochloric acid (flow rate: 4 mL / min) delivered by a peristaltic pump are transported to the micromixer 3 for mixing (mixing temperature: 20 °C, mixing time: 0.2 s), and then enter the microreactor 4 for preliminary back extraction (temperature: 20 °C, residence time: 20 s). Subsequently, it is transported to the microreactor 5 for continuous back extraction (temperature: 20 °C, residence time: 1 min), obtaining an oil-water mixture.

[0169] 6. Phase separation: The oil-water mixture obtained from the outlet of the microreactor 5 is introduced into the phase separator 2 for phase separation to obtain the upper oil phase (containing extractant) and the lower aqueous phase (containing rare earth elements). The oil phase containing extractant does not contain rare earth elements and can be recycled.

[0170] Detected by ICP-OES, the error range is within 2%, the extraction rate can reach over 99%, the concentration of rare earth elements in the raffinate is 0.1 mg / L, and the concentration of rare earth elements in the enriched aqueous phase containing rare earth elements is 56 g / L.

[0171] Stability test: Continuously operate for 10 h, sample every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 1%.

[0172] Example 4:

[0173] A method for enhancing the extraction of low-concentration terbium elements, as Figure 1 shown, which includes the following steps:

[0174] 1. Solution preparation: Dissolve terbium chloride with a hydrochloric acid aqueous solution of pH = 4 to prepare a rare earth ion solution (where the concentration of rare earth elements is 30 mg / L); stir and mix 17 mL of P507, 17 mL of P204, and 66 mL of sulfonated kerosene to obtain an oil solution containing an extractant, where the total concentration of the extractant (P507 and P204) is 1 mol / L.

[0175] 2. Formation of an oil-in-gas structure: An oil solution containing an extractant (flow rate: 0.2 mL / min) and nitrogen (flow rate: 60 mL / min) are respectively delivered to a micromixer 1 by a peristaltic pump for mixing (mixing temperature: 20 °C, mixing time: 0.05 s), and then enter a microreactor 1 for gas-liquid dispersion (temperature: 20 °C, residence time: 8 s) to form a gas-liquid mixture with an oil-in-gas structure.

[0176] 3. Extraction: The gas-liquid mixture obtained from the outlet of the microreactor 1 and the rare earth ion solution (flow rate: 80 mL / min) delivered by a peristaltic pump are delivered to a micromixer 2 for mixing (mixing temperature: 20 °C, mixing time: 0.02 s), and then enter a microreactor 2 for preliminary extraction (temperature: 20 °C, residence time: 3 s), and then are delivered to a microreactor 3 for continuous extraction (temperature: 20 °C, residence time: 1 min) to form a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0177] 4. Phase separation: The gas-liquid-liquid mixture obtained from the outlet of the microreactor 3 is introduced into a phase separator 1 for phase separation to obtain an upper oil phase (containing rare earth elements) and a lower water phase (raffinate).

[0178] 5. Back extraction: The oil phase containing rare earth elements (flow rate: 8 mL / min) and 1.0 mol / L hydrochloric acid (flow rate: 4 mL / min) delivered by a peristaltic pump are delivered to a micromixer 3 for mixing (mixing temperature: 20 °C, mixing time: 0.2 s), and then enter a microreactor 4 for preliminary back extraction (temperature: 20 °C, residence time: 20 s), and then are delivered to a microreactor 5 for continuous back extraction (temperature: 20 °C, residence time: 1 min) to obtain an oil-water mixture.

[0179] 6. Phase separation: The oil-water mixture obtained from the outlet of the microreactor 5 is introduced into a phase separator 2 for phase separation to obtain an upper oil phase (containing the extractant) and a lower water phase (containing rare earth elements). The oil phase containing the extractant does not contain rare earth elements and can be recycled.

[0180] Detected by ICP-OES, the error range is within 2%, the extraction rate can reach over 99%, the concentration of rare earth elements in the raffinate is 0.06 mg / L, and the concentration of rare earth elements in the enriched water phase containing rare earth elements is 24 g / L.

[0181] Stability test: Continuously operate for 10 h, take samples every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 1%.

[0182] Example 5:

[0183] The parameters of the microreactor used in this embodiment are as follows:

[0184] Micro-mixer 1: T-shaped micro three-way, inner diameter 1.2 mm;

[0185] Micro-mixer 2: T-shaped micro three-way, inner diameter 0.5 mm;

[0186] Micro-mixer 3: T-shaped micro three-way, inner diameter 0.5 mm;

[0187] Micro-reactor 1: Micro-packed bed, inner diameter 20 mm, length 20 cm, packing is silica microspheres (size 200 μm, porosity about 0.45);

[0188] Micro-reactor 2: Micro-packed bed, inner diameter 20 mm, length 20 cm, packing is silica microspheres (size 200 μm, porosity about 0.45);

[0189] Micro-reactor 3: Micro-coiled tube, inner diameter 6 mm, length 25 m;

[0190] Micro-reactor 4: Micro-packed bed, inner diameter 10 mm, length 20 cm, packing is silica microspheres (size 200 μm, porosity about 0.45);

[0191] Micro-reactor 5: Micro-coiled tube, inner diameter 2 mm, length 4 m.

[0192] An extraction method for enhancing low-concentration neodymium element, as Figure 1 shown, includes the following steps:

[0193] 1. Prepare the solution: Dissolve neodymium chloride with hydrochloric acid aqueous solution with pH = 4 to prepare a rare earth ion solution (where the concentration of rare earth element is 90 mg / L); Stir and mix 17 mL of P507, 17 mL of P204 and 66 mL of sulfonated kerosene to obtain an oil solution containing extractant, where the total concentration of extractant (P507 and P204) is 1 mol / L.

[0194] 2. Form an oil-in-gas structure: Feed the oil solution containing extractant (flow rate 1 mL / min) and nitrogen (flow rate 300 mL / min) into Micro-mixer 1 through a peristaltic pump for mixing (mixing temperature 20 °C, mixing time 0.02 s), and then enter Micro-reactor 1 for gas-liquid dispersion (temperature 20 °C, residence time 6.5 s) to form a gas-liquid mixture with an oil-in-gas structure.

[0195] 3. Extraction: The gas-liquid mixture obtained from the outlet of the microreactor 1 and the rare earth ion solution (flow rate: 400 mL / min) delivered by a peristaltic pump are delivered to the micromixer 2 for mixing (mixing temperature: 20 °C, mixing time: 0.02 s), and then enter the microreactor 2 for preliminary extraction (temperature: 20 °C, residence time: 2.5 s), and subsequently are delivered to the microreactor 3 for continued extraction (temperature: 20 °C, residence time: 1 min), forming a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0196] 4. Phase separation: The gas-liquid-liquid mixture obtained from the outlet of the microreactor 3 is introduced into the phase separator 1 for phase separation to obtain the upper oil phase (containing rare earth elements) and the lower aqueous phase (raffinate).

[0197] 5. Back extraction: The oil phase containing rare earth elements (flow rate: 8 mL / min) and 1.0 mol / L hydrochloric acid (flow rate: 4 mL / min) delivered by a peristaltic pump are delivered to the micromixer 3 for mixing (mixing temperature: 20 °C, mixing time: 0.2 s), and then enter the microreactor 4 for preliminary back extraction (temperature: 20 °C, residence time: 20 s), and subsequently are delivered to the microreactor 5 for continued back extraction (temperature: 20 °C, residence time: 1 min), obtaining an oil-water mixture.

[0198] 6. Phase separation: The oil-water mixture obtained from the outlet of the microreactor 5 is introduced into the phase separator 2 for phase separation to obtain the upper oil phase (containing extractant) and the lower aqueous phase (containing rare earth elements), wherein the oil phase containing extractant does not contain rare earth elements and can be recycled.

[0199] Detected by ICP-OES, the error range is within 2%, the extraction rate can reach over 99%, the concentration of rare earth elements in the raffinate is 0.10 mg / L, and the concentration of rare earth elements in the enriched aqueous phase containing rare earth elements is 72 g / L.

[0200] Stability test: Continuously operate for 10 h, take samples every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 1%.

[0201] Comparative example 1:

[0202] Compared with Example 1, the difference is that no gas is introduced, and the extraction step only performs liquid-liquid extraction.

[0203] 1. Solution preparation: Dissolve neodymium chloride with a hydrochloric acid aqueous solution with pH = 4 to prepare a rare earth ion solution (wherein the concentration of rare earth elements is 90 mg / L); stir and mix 17 mL of P507, 17 mL of P204 and 66 mL of sulfonated kerosene to obtain an oil solution containing an extractant, wherein the total concentration of the extractant (P507 and P204) is 1 mol / L.

[0204] 2. Extraction: The oil solution containing the extractant (flow rate: 0.2 mL / min) and the rare earth ion solution (flow rate: 80 mL / min) are respectively transported to the micro-mixer 2 by a peristaltic pump for mixing (mixing temperature: 20 °C, mixing time: 0.02 s), and then enter the micro-reactor 2 for preliminary extraction (temperature: 20 °C, residence time: 3 s). Subsequently, it is transported to the micro-reactor 3 for continuous extraction (temperature: 20 °C, residence time: 1 min), forming a liquid-liquid mixture.

[0205] 3. Phase separation: The liquid-liquid mixture obtained from the outlet of the micro-reactor 3 is introduced into the phase separator 1 for phase separation to obtain the upper oil phase (containing rare earth elements) and the lower aqueous phase (raffinate).

[0206] 4. Stripping: The oil phase containing rare earth elements (flow rate: 8 mL / min) and 1.0 mol / L hydrochloric acid transported by a peristaltic pump (flow rate: 4 mL / min) are transported to the micro-mixer 3 for mixing (mixing temperature: 20 °C, mixing time: 0.2 s), and then enter the micro-reactor 4 for preliminary stripping (temperature: 20 °C, residence time: 20 s). Subsequently, it is transported to the micro-reactor 5 for continuous stripping (temperature: 20 °C, residence time: 1 min), obtaining an oil-water mixture.

[0207] 5. Phase separation: The oil-water mixture obtained from the outlet of the micro-reactor 5 is introduced into the phase separator 2 for phase separation to obtain the upper oil phase (containing the extractant) and the lower aqueous phase (containing rare earth elements). The oil phase containing the extractant does not contain rare earth elements and can be recycled.

[0208] Detected by ICP-OES, the error range is within 2%, the extraction rate is 40%, the concentration of rare earth elements in the raffinate is 54 mg / L, and the concentration of rare earth elements in the enriched aqueous phase containing rare earth elements is 29 g / L.

[0209] Stability test: Continuously operate for 10 h, take samples every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 20%.

[0210] Comparative Example 2:

[0211] Compared with Example 1, the difference is that the extractant is P507.

[0212] 1. Solution preparation: Dissolve neodymium chloride with a hydrochloric acid aqueous solution of pH = 4 to prepare a rare earth ion solution (the concentration of rare earth elements is 90 mg / L); stir and mix 34 mL of P507 and 66 mL of sulfonated kerosene to obtain an oil solution containing the extractant, where the concentration of the extractant (P507) is 1 mol / L.

[0213] 2. Formation of an oil-in-gas structure: An oil solution containing an extractant (flow rate: 0.2 mL / min) and nitrogen gas (flow rate: 60 mL / min) are respectively transported to a micromixer 1 by a peristaltic pump for mixing (mixing temperature: 20 °C, mixing time: 0.05 s), and then enter a microreactor 1 for gas-liquid dispersion (temperature: 20 °C, residence time: 8 s), forming a gas-liquid mixture with an oil-in-gas structure.

[0214] 3. Extraction: The gas-liquid mixture obtained from the outlet of the microreactor 1 and a rare earth ion solution transported by a peristaltic pump (flow rate: 80 mL / min) are transported to a micromixer 2 for mixing (mixing temperature: 20 °C, mixing time: 0.02 s), and then enter a microreactor 2 for preliminary extraction (temperature: 20 °C, residence time: 3 s), and then are transported to a microreactor 3 for continuous extraction (temperature: 20 °C, residence time: 1 min), forming a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0215] 4. Phase separation: The gas-liquid-liquid mixture obtained from the outlet of the microreactor 3 is introduced into a phase separator 1 for phase separation to obtain an upper oil phase (containing rare earth elements) and a lower water phase (raffinate).

[0216] 5. Back extraction: The oil phase containing rare earth elements (flow rate: 8 mL / min) and 1.0 mol / L hydrochloric acid transported by a peristaltic pump (flow rate: 4 mL / min) are transported to a micromixer 3 for mixing (mixing temperature: 20 °C, mixing time: 0.2 s), and then enter a microreactor 4 for preliminary back extraction (temperature: 20 °C, residence time: 20 s), and then are transported to a microreactor 5 for continuous back extraction (temperature: 20 °C, residence time: 1 min), obtaining an oil-water mixture.

[0217] 6. Phase separation: The oil-water mixture obtained from the outlet of the microreactor 5 is introduced into a phase separator 2 for phase separation to obtain an upper oil phase (containing the extractant) and a lower water phase (containing rare earth elements). The oil phase containing the extractant does not contain rare earth elements and can be recycled.

[0218] Detected by ICP-OES, the error range is within 2%, the extraction rate is 89%, the concentration of rare earth elements in the raffinate is 9.8 mg / L, and the concentration of rare earth elements in the enriched water phase containing rare earth elements is 64 g / L.

[0219] Stability detection: Continuously operate for 10 h, sample every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 5%.

[0220] Comparative Example 3:

[0221] Compared with Example 1, the difference lies in that a membrane disperser is used instead of a micro three-way joint and a micro packed bed.

[0222] 1. Prepare the solution: Dissolve neodymium chloride with an aqueous hydrochloric acid solution of pH = 4 to prepare a rare earth ion solution (where the concentration of the rare earth element is 90 mg / L); Stir and mix 17 mL of P507, 17 mL of P204, and 66 mL of sulfonated kerosene to obtain an oil solution containing an extractant, where the total concentration of the extractants (P507 and P204) is 1 mol / L.

[0223] 2. Form an oil-in-gas structure: Feed the oil solution containing the extractant (flow rate of 0.2 mL / min) and nitrogen (flow rate of 60 mL / min) into the membrane disperser 1 through a peristaltic pump respectively for gas-liquid dispersion (temperature is 20 °C, residence time is 8 s) to form a gas-liquid mixture with an oil-in-gas structure.

[0224] 3. Extraction: Feed the gas-liquid mixture obtained from the outlet of the microreactor 1 and the rare earth ion solution (flow rate of 80 mL / min) fed through a peristaltic pump into the membrane disperser 2 for preliminary extraction (temperature is 20 °C, residence time is 3 s), and then feed it into the microreactor 3 for continuous extraction (temperature is 20 °C, residence time is 1 min) to form a gas-liquid-liquid mixture with a water-in-oil-in-gas structure.

[0225] 4. Phase separation: Feed the gas-liquid-liquid mixture obtained from the outlet of the microreactor 3 into the phase separator 1 for phase separation to obtain the upper oil phase (containing rare earth elements) and the lower water phase (raffinate).

[0226] 5. Back-extraction: Feed the oil phase containing rare earth elements (flow rate of 8 mL / min) and 1.0 mol / L hydrochloric acid (flow rate of 4 mL / min) fed through a peristaltic pump into the membrane disperser 3 for preliminary back-extraction (temperature is 20 °C, residence time is 20 s), and then feed it into the microreactor 5 for continuous back-extraction (temperature is 20 °C, residence time is 1 min) to obtain an oil-water mixture.

[0227] 6. Phase separation: Feed the oil-water mixture obtained from the outlet of the microreactor 5 into the phase separator 2 for phase separation to obtain the upper oil phase (containing the extractant) and the lower water phase (containing rare earth elements), where the oil phase containing the extractant does not contain rare earth elements and can be recycled.

[0228] Detected by ICP-OES, the error range is within 2%, the extraction rate is 85%, the concentration of rare earth elements in the raffinate is 13.5 mg / L, and the concentration of rare earth elements in the enriched aqueous phase containing rare earth elements is 62 g / L.

[0229] Stability test: Continuously operate for 10 h, sample every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 10%.

[0230] Comparative Example 4:

[0231] Compared with Example 1, the difference is that a micro-packed bed is not used.

[0232] 1. Prepare the solution: Dissolve neodymium chloride with an aqueous hydrochloric acid solution of pH = 4 to prepare a rare earth ion solution (where the concentration of rare earth elements is 90 mg / L); stir and mix 17 mL of P507, 17 mL of P204, and 66 mL of sulfonated kerosene to obtain an oil solution containing an extractant, where the total concentration of the extractant (P507 and P204) is 1 mol / L.

[0233] 2. Form an oil-in-gas structure: Feed the oil solution containing the extractant (flow rate of 0.2 mL / min) and nitrogen (flow rate of 60 mL / min) to a micro-mixer 1 through a peristaltic pump for mixing (mixing temperature is 20 °C, mixing time is 0.05 s) to form a gas-liquid mixture.

[0234] 3. Extraction: Feed the gas-liquid mixture obtained from the outlet of the micro-mixer 1 and the rare earth ion solution (flow rate of 80 mL / min) fed through a peristaltic pump to a micro-mixer 2 for mixing (mixing temperature is 20 °C, mixing time is 0.02 s), and then feed it to a micro-reactor 3 for extraction (temperature is 20 °C, residence time is 1 min) to form a gas-liquid-liquid mixture.

[0235] 4. Phase separation: Feed the gas-liquid-liquid mixture obtained from the outlet of the micro-reactor 3 to a phase separator 1 for phase separation to obtain the upper oil phase (containing rare earth elements) and the lower water phase (raffinate).

[0236] 5. Back-extraction: Feed the oil phase containing rare earth elements (flow rate of 8 mL / min) and 1.0 mol / L hydrochloric acid (flow rate of 4 mL / min) fed through a peristaltic pump to a micro-mixer 3 for mixing (mixing temperature is 20 °C, mixing time is 0.2 s), and then feed it to a micro-reactor 5 for back-extraction (temperature is 20 °C, residence time is 1 min) to obtain an oil-water mixture.

[0237] 6. Phase separation: Feed the oil-water mixture obtained from the outlet of the micro-reactor 5 to a phase separator 2 for phase separation to obtain the upper oil phase (containing the extractant) and the lower water phase (containing rare earth elements). The oil phase containing the extractant does not contain rare earth elements and can be recycled.

[0238] Detected by ICP-OES, the error range is within 2%, the extraction rate is 32%, the concentration of rare earth elements in the raffinate is 61 mg / L, and the concentration of rare earth elements in the aqueous phase enriched with rare earth elements is 23 g / L.

[0239] Stability test: Continuously operate for 10 h, take samples every 30 min to measure the concentration of rare earth elements in the raffinate, and calculate the extraction rate. The fluctuation range of the extraction rate is within 20%.

[0240] Table 1 comprehensively shows the experimental conditions and test results of each example and comparative example.

[0241] Table 1:

[0242]

[0243] In summary, for the extraction method of strengthening low-concentration rare earth elements provided by the present invention, gas-liquid-liquid three-phase extraction system is used for extraction under a large phase ratio. Compared with the traditional liquid-liquid two-phase extraction, this three-phase microdispersion system with an oil-in-water-in-gas structure formed in the micro-packed bed greatly increases the mass transfer area and improves the mass transfer efficiency. At the same time, the introduction of gas can also reduce the density of the oil phase, promote the floating of oil droplets, accelerate the oil-water phase separation and reduce the occurrence of emulsification phenomenon. In addition, by using a combination of extractants and utilizing their synergistic effects, the extraction efficiency can be significantly improved, the dosage of extractants can be reduced, and the operation cost can be lowered.

[0244] It should be noted that although the technical solutions of the present invention are introduced by specific examples, those skilled in the art can understand that the present invention should not be limited thereto.

[0245] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other ordinary skilled persons in the technical field to understand the embodiments disclosed herein.

Claims

1. An extraction method for strengthening low-concentration rare earth elements, characterized in that, It includes the following steps: 1) The step of extraction and phase separation: The oil solution containing the extractant and the aqueous solution containing low-concentration rare earth elements are mixed through a first micromixer and then enter a first microextractor for extraction. After that, it is transported to a first phase separator through a first microreactor for phase separation treatment to obtain an oil phase containing rare earth elements; before the mixing, the oil solution containing the extractant has been pre-mixed with compressed gas through a pre-micromixer and then enters a pre-microreactor for gas-liquid dispersion. The pre-microreactor is a micro-packed bed reactor; 2) The step of stripping and phase separation: The oil phase containing rare earth elements and the acidic solution are mixed through a second micromixer and then enter a second microextractor for stripping. After that, it is transported to a second phase separator through a second microreactor for phase separation treatment to obtain an aqueous phase containing high-concentration rare earth elements; wherein, the structures of the first microextractor and the second microextractor can be the same or different, and both are micro-packed bed extractors, the extractant includes a combination of two or more of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, bis(2-ethylhexyl) phosphate, bis(2,4,4-trimethylpentyl) phosphinic acid, and bis(2,4,4-trimethylpentyl) dithiophosphinic acid.

2. The extraction method according to claim 1, wherein In step 1), the extractant includes 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester and any one of bis(2-ethylhexyl) phosphate, bis(2,4,4-trimethylpentyl) phosphinic acid, and bis(2,4,4-trimethylpentyl) dithiophosphinic acid.

3. The extraction method according to claim 1 or 2, characterized in that, In step 1), In the aqueous solution containing rare earth elements at a low concentration, the concentration of rare earth elements is less than 100 mg / L, and the concentration of hydrogen ions is 1×10 -5 ~1×10 -3 mol / L; in the oil solution containing the extractant, the concentration of the extractant is 1-2 mol / L.

4. The extraction method according to any one of claims 1 to 3, characterized in that, In step 1), the volume flow rate ratio of the aqueous solution containing low-concentration rare earth elements to the oil solution containing the extractant is (50-500):1; the volume flow rate ratio of the compressed gas to the oil solution containing the extractant is (50-500):

1.

5. The extraction method according to any one of claims 1-4, characterized in that, In step 1), the temperature in the pre-microreactor is 10-30 °C, and the residence time in the pre-microreactor is 0.5-30 s.

6. The extraction method according to any one of claims 1-5, characterized in that, In step 1), after pre-mixing, the pre-mixed liquid enters the pre-microreactor to form a gas-in-oil structured gas-liquid mixture; after mixing, the mixed liquid enters the first microextractor to form a water-in-oil-in-gas structured gas-liquid-liquid mixture.

7. The extraction method according to any one of claims 1-6, characterized in that, In step 2), in the acidic solution, the concentration of the acidic substance is 1-2 mol / L.

8. The extraction method according to any one of claims 1-7, characterized in that the first micromixer and the second micromixer are each independently a microchannel mixer, a membrane dispersion mixer, or a micro-sieve pore mixer; the first microreactor and the second microreactor are each independently a coiled tube microreactor or a microchannel reactor.

9. The extraction method according to any one of claims 1-8, characterized in that the temperature in the first micromixer is 10-30 °C, and the mixing time is greater than 0 and less than 5 s; the temperature in the first microextractor is 10-30 °C, and the residence time is 0.5-30 s; the temperature in the first microreactor is 10-30 °C, and the residence time is 0.1-5 min; The temperature in the second micro-mixer is 10 to 30 °C, and the mixing time is greater than 0 and less than 5 s; The temperature in the second micro-extractor is 10 to 30 °C, and the residence time is 0.5 to 120 s; The temperature in the second micro-reactor is 10 to 30 °C, and the residence time is 0.1 to 5 min.

10. An apparatus for implementing the extraction method according to any one of claims 1-9, characterized in that, The device includes a pre-micro-mixer, a pre-micro-reactor, a first micro-mixer, a first micro-extractor, a first micro-reactor, a first phase separator, a second micro-mixer, a second micro-extractor, a second micro-reactor, and a second phase separator connected in sequence.

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