Composite extracting agent for separating rubidium and cesium

Abstract

The invention belongs to the technical field of resource recycling, and particularly relates to a composite extraction agent for separating rubidium and cesium from a recovery liquid for extracting lithium, the composite extraction agent comprises a synergistic extraction agent, a diluent and a phase regulator; the synergistic extraction agent comprises a main extraction agent and a synergistic extraction agent; the main extraction agent is a substituted phenol extraction agent, and the synergistic extraction agent is an organic phosphorus extraction agent. On one hand, the composite extraction agent improves the rubidium and cesium extraction effect, and the cost is reduced; and on the other hand, the requirement of the extraction agent for alkalinity is reduced, efficient extraction of rubidium and cesium can be achieved under the low-alkalinity condition, and a series of problems that a traditional substituted phenol extraction system is serious in emulsification phenomenon, large in extraction agent dissolution loss and the like are solved. The organic phase of the extraction system can be recycled, the defects of easy emulsification, equipment corrosion and the like of the traditional extraction method can be effectively avoided, and industrial production is easy.

Description

Technical Field

[0001] The invention relates to the technical field of resource recycling, in particular to the technical field of separating and extracting rubidium and cesium from a recovery liquid of lithium extraction, in particular to a composite extractant for separating rubidium and cesium. Background Art

[0002] In the process of lithium extraction industry, whether it is lithium battery leaching liquid or lithium precipitation mother liquor, it actually contains valuable metals such as rubidium and cesium. If these liquids are directly circulated and harmlessly treated, it will cause waste of valuable metals such as rubidium and cesium. Therefore, it is necessary to find a suitable process method to extract rubidium and cesium.

[0003] Solvent extraction is widely used to separate and extract rubidium and cesium resources due to its high efficiency, low cost, and large processing capacity. The commonly used extraction systems for this method are mainly substituted phenols, crown ethers, and dibitramines. Among them, crown ether extractants have only been studied in the laboratory and have no basis for industrial application; while dibitramine and nitro compounds have rarely been used in recent years. The most commonly used are substituted phenol extractants of phenol alcohols, such as 4-sec-butyl-2 (α-methylbenzyl) phenol (s-BAMBP) and 4-tert-butyl-2 (α-methylbenzyl) phenol (t-BAMBP). This type of extractant is a weak acid extractant with excellent properties such as low volatility, low water solubility, and rapid extraction. For example, many existing rubidium and cesium manufacturers mainly use the t-BAMBP extraction system.

[0004] The Chinese invention patent announcement text CN107254589B proposes a method for separating and extracting rubidium and cesium from salt lake brine by t-BAMBP extraction. The technical solution uses t-BAMBP as an extractant and adopts a box-countercurrent method to extract and separate rubidium and cesium from salt lake brine, and the yield and purity of the rubidium and cesium solution are high. However, when t-BAMBP separates rubidium and cesium, it must be carried out in a strong alkaline environment, resulting in a large amount of alkali consumption, high cost, and the generation of alkaline wastewater to cause environmental pollution. At the same time, in a strong alkaline environment, the ester bond in the t-BAMBP molecule is easily broken, resulting in the destruction of the molecular structure, and reactions such as hydroxylation may occur, thereby reducing the effective ingredients of t-BAMBP. At the same time, due to the serious emulsification of t-BAMBP in the strong alkaline extraction environment, the extraction agent dissolution loss is large, especially when the pH exceeds 12, the extraction agent dissolution loss increases sharply, and a large amount of acid needs to be consumed during the stripping process. Therefore, the stability of the high alkaline environment limits the application of the t-BAMBP system for separating and extracting cesium.

[0005] In view of the above technical problems, the prior art is improved by adding alkali to saponify treatment in advance. The Chinese invention patent publication CN117187560A proposes a method for extracting and separating potassium, rubidium and cesium from a potassium, rubidium and cesium mixed solution, and discloses the use of NaOH solution to saponify t-BAMBP, and the separation and recovery of rubidium and cesium by multi-stage continuous extraction. Although such an improved method avoids the consumption of a large amount of alkali by saponifying the organic phase in advance, and also avoids the problem of alkali recovery treatment in the extraction tail liquid, the hydrogen ions on the phenolic hydroxyl groups of the substituted phenols are difficult to dissociate, and the saponification process requires the use of a high-concentration NaOH solution. The chemical stability of the substituted phenols under high alkalinity will face great challenges, and the cyclic stability of the extraction process needs to be further considered.

[0006] Therefore, how to overcome the defects of existing extractants and develop an extraction system with low alkalinity drive, low dissolution loss and wide application, and solve the problems of extractant dissolution loss and alkali consumption pollution in strong alkaline environment, has important practical value for rubidium and cesium extraction. Summary of the invention

[0007] In view of this, in order to solve the above technical problems, the present invention provides a composite extractant for separating rubidium and cesium, which can improve the extraction effect of rubidium and cesium, further reduce costs, and solve a series of problems such as alkaline tail liquid discharge, organic phase circulation performance and environmental protection caused by alkali consumption in traditional substituted phenol extraction systems.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] A composite extractant for separating rubidium and cesium, the composite extractant comprising a synergistic extractant, a diluent and a phase regulator; the synergistic extractant comprising a substituted phenol extractant and an organic phosphorus extractant; wherein the molar ratio of the substituted phenol extractant to the organic phosphorus extractant is (0.1-9.5):(0.5-1.5), the volume ratio of the diluent to the synergistic extractant is (0.1-98):(0.8-1.3), and the volume of the phase regulator is 0-60 vol.% of the volume of the synergistic extractant.

[0010] The organophosphorus extractant is any one of a neutral organophosphorus extractant and an acidic organophosphorus extractant, or a combination of at least two of them.

[0011] Preferably, the neutral organophosphorus extractant comprises any one of tributyl phosphate, triisoamyl phosphate, dialkyl alkyl phosphonates, trialkyl phosphine oxides, diisoamyl methyl phosphonate, dibutyl butyl phosphonate, diisoamyl methyl phosphonate or dimethylheptyl methyl phosphonate, or a combination of at least two thereof.

[0012] Preferably, the acidic organophosphorus extractant comprises any one or a combination of at least two of dibutylphosphoric acid, dipentylphosphoric acid, dihexylphosphoric acid, diheptylphosphoric acid and di(2-ethylhexyl)phosphoric acid, dibutylphosphonic acid, dipentylphosphonic acid, dihexylphosphonic acid or diheptylphosphonic acid and di(2,4,4,trimethylpentyl)phosphonic acid.

[0013] Preferably, the substituted phenol extractant includes any one or a combination of at least two of 4-sec-butyl-2(α-methylbenzyl)phenol (s-BAMBP), 4-tert-butyl-2(α-methylbenzyl)phenol (t-BAMBP), 4-ethyl-2-(α-methylbenzyl)phenol, 4-isopropyl-2-(α-methylbenzyl)phenol, 4-tert-amyl-2-(α-methylbenzyl)phenol, 4-fluoro-2-(α-methylbenzyl)phenol or 2,4-dimethyl-6-(α-methylbenzyl)phenol.

[0014] Preferably, the diluent includes any one of kerosene, D series dearomatized solvent oil, A series aromatic solvent oil, diethylbenzene isomer mixture, butylbenzene isomer mixture, 200# solvent oil, n-12-alkane or 260# solvent oil, or a combination of at least two thereof.

[0015] Preferably, the phase regulator comprises one or both of C6-C14 alcohol compounds or ester compounds.

[0016] Preferably, the C6-C14 alcohol compound includes any one of heptanol, n-octanol, sec-octanol, isooctyl alcohol, nonanol, decanol, undecanol, dodecanol, isotridecanol or tetradecanol, or a combination of at least two thereof.

[0017] The ester compound includes any one of dioctyl phthalate, dioctyl isophthalate, dioctyl terephthalate, diisooctyl phthalate, dibutyl phthalate, diisobutyl phthalate, dibutyl isophthalate, dibutyl terephthalate, dimethyl phthalate, amyl nonanoate or isoamyl nonanoate, or a combination of at least two thereof.

[0018] Preferably, the molar ratio of the substituted phenol extractant to the organophosphorus extractant is (3-9):(0.9-1.2), the volume ratio of the diluent to the co-extractant is (5-10):(0.9-1.1), and the volume of the phase regulator is 20-40 vol.% of the volume of the co-extractant.

[0019] Preferably, the molar ratio of the substituted phenol extractant to the organophosphorus extractant is (0.2-10): 1. The volume ratio of the diluent to the co-extractant is (1-15):1.

[0020] More preferably, the molar ratio of the substituted phenol extractant to the organophosphorus extractant is (3-10):1.

[0021] More preferably, the volume ratio of the diluent to the synergistic extractant is (5-10):1.

[0022] A method for preparing a composite extractant for separating rubidium and cesium, wherein the composite extractant is the composite extractant described above, comprising the following steps:

[0023] (1) A substituted phenol extractant and an organophosphorus extractant are mixed in a molar ratio of (0.1-9.5):(0.5-1.5) to obtain a synergistic extractant.

[0024] (2) Adding a phase regulator in an amount of 0 to 60 vol. % based on the volume of the synergistic extractant to the synergistic extractant obtained in step (1).

[0025] (3) The mixed solution obtained in step (2) is mixed with a diluent in a volume ratio of (0.1-98) to (0.8-1.3) to obtain a rubidium-cesium composite extractant product.

[0026] Preferably, in step (3), after the mixed solution is mixed with the diluent, it is stirred for 1-30 min and at a stirring intensity of 10-500 r / min until the mixed solution is uniform, thereby obtaining a separated rubidium-cesium composite extractant product.

[0027] The technical effects of the present invention are:

[0028] (1) The present invention creatively combines an organic phosphorus extractant with a substituted phenol extractant as a synergistic extractant in the process of separating and extracting rubidium and cesium. Since the above-mentioned phenol extractants can synergize with neutral phosphorus extractants and / or acidic extractants, especially methylphosphonic acid diisoamyl ester, butylphosphonic acid diisoamyl ester, methylphosphonic acid diisoamyl ester, methylphosphonic acid dimethylheptyl ester, tributyl phosphate and other synergistic extractants, whose functional groups are P=O, the extraction is achieved by the formation of coordination bonds between the lone pair of electrons of the oxygen atom of the extractant and the alkali metal. That is, the present invention does not simply add an organic phosphorus extractant to the composite extractant, but forms an intermolecular interaction force between the phosphonyl group of the organic phosphorus extractant and the substituted phenol extractant, so that the electron cloud density of the phenolic hydroxyl group is reduced, and H + It is easier to dissociate, so that under relatively low alkalinity conditions, the anions of the dissociated substituted phenol extractants and Cs + Combined, undissociated organophosphorus extractants and substituted phenolic extractants with Cs + Through weak interactions, hydrophobic extractants are generated and enter the organic phase, achieving efficient extraction in a low-alkaline environment, thereby greatly improving the extraction effect of rubidium and cesium.

[0029] (2) The synergistic extractant proposed in the present invention screens different types of organophosphorus synergistic extractants due to the influence of alkoxy groups on phosphonyl groups and alkyl carbon chains on steric hindrance. By reducing the number of alkoxy groups and different carbon chain lengths, the electron cloud density of the phosphonyl group increases, and the phenolic hydroxyl groups of substituted phenols are attracted through weak interactions, making the oxygen-hydrogen bond more easily dissociated and reacting with Cs + The coordinated hydrophobic phenolate enters the organic phase. The addition of the co-extractant makes it easier for the phenolic hydroxyl group of the substituted phenol to dissociate. Therefore, it is not necessary to make it have a large alkalinity (for example, a pH value greater than 14) to achieve effective extraction of rubidium and cesium, thereby solving a series of problems in the traditional substituted phenol extraction system such as alkaline tail liquid discharge caused by alkali consumption, organic phase circulation performance and environmental protection.

[0030] 3) The present invention coordinates with each component by setting the ratio of each component in detail, and cooperates with the specific settings in the preparation method, so that the obtained composite extractant can be realized only through existing operations in the extraction process, and due to the operation of low alkalinity, the organic phase dissolution loss is reduced, the reuse rate of the organic phase can be increased, and the organic phase can be circulated and continuously produced, thereby effectively avoiding the shortcomings of the traditional extraction method such as easy emulsification and equipment corrosion, and is easy to industrialize. DETAILED DESCRIPTION

[0031] Example 1

[0032] This embodiment shows a composite extractant for separating rubidium and cesium, and the composite extractant includes a synergistic extractant, a diluent and a phase regulator; the synergistic extractant includes a substituted phenol extractant and an organophosphorus extractant; the substituted phenol extractant of this embodiment is t-BAMBP, and the organophosphorus extractant is diisopentyl methylphosphonate which is a neutral organophosphorus extractant, wherein the molar ratio of t-BAMBP and diisopentyl methylphosphonate in this embodiment is 3:1, the diluent of this embodiment is kerosene, and the phase regulator is n-octanol, wherein the volume of n-octanol is 30% of the volume of diisopentyl methylphosphonate, and the volume ratio of kerosene to diisopentyl methylphosphonate is 6:1.

[0033] In other embodiments, the organophosphorus extractant may be a plurality of neutral organophosphorus extractants and / or acidic organophosphorus extractants as defined in the present invention, thereby enhancing the compounding effect of the organophosphorus extractant.

[0034] In other embodiments, the molar ratio of the substituted phenol extractant to the organophosphorus extractant can be specifically set in the range of (0.1-9.5):(0.5-1.5) (for example, it can be: 0.1:1.2, 0.5:1, 1:1.2, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 9:0.9, 9.5:0.8, etc.), and the volume ratio of the diluent to the synergistic extractant can be (0.1-98):(0.8-1.5). 3) can be specifically set in the range of (for example, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 10:0.9, etc.), and the volume of the phase regulator can be specifically set in the range of 00 to 60 vol.% of the volume of the synergistic extractant (for example, 0.1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, etc.).

[0035] Example 2

[0036] This example shows the preparation method of the composite extractant for separating rubidium and cesium described in Example 1, comprising the following steps:

[0037] (1) t-BAMBP and diisoamyl methylphosphonate are mixed in a molar ratio of 3:1 to obtain a synergistic extractant.

[0038] (2) adding n-octanol in an amount of 30% by volume of the synergistic extractant to the synergistic extractant obtained in step (1).

[0039] (3) The mixed solution obtained in step (2) is mixed with kerosene at a ratio of 6:1, and then stirred until the mixed solution is uniform to obtain a separated rubidium-cesium composite extractant product.

[0040] This embodiment is a preferred embodiment. In other embodiments, the components can be mixed in other orders.

[0041] Application Example 1

[0042] This application example is used to illustrate the application of the composite extractant product of Example 1 prepared by the method of Example 2 to extract cesium from lithium precipitation mother liquor. Specifically, it includes the following steps:

[0043] The cesium content in the raw material lithium precipitation mother liquor was tested for concentration, and the initial concentration of cesium was 5.3 g / L, and the initial concentration of rubidium was 10.6 g / L. The pH value of the lithium precipitation mother liquor was adjusted to 10 to obtain an alkaline raw material liquid. The raw material liquid was subjected to 8-stage countercurrent extraction with the composite extractant of Example 1, the two-phase contact time was 8.5 min, the extraction temperature was 26 ° C, and the ratio of the raw material liquid to the composite extractant of Example 1 was 1:2 to obtain a cesium-rich organic phase. After the extraction was completed, the obtained cesium-rich organic phase was subjected to 6-stage countercurrent washing with a NaOH aqueous solution with a pH of 9, the two-phase contact time was 8 min, the washing temperature was 30 ° C, and the ratio of the two was 1:3 to obtain a clean cesium-rich organic phase and a rubidium-rich washing solution. Then, the clean cesium-rich organic phase was subjected to 5-stage countercurrent stripping with 0.5 mol / L hydrochloric acid, the two-phase contact time was 6 minutes, the washing temperature was 23°C, and the ratio of the two was 1:3, to obtain a cesium-rich solution, which was then evaporated and concentrated to prepare a cesium product. The cesium concentration in the raffinate was measured, and the cesium content in the raffinate was 0.987 g / L, and the cesium extraction rate was 81.38%. After the extraction was completed, the organic phase content in the raffinate was measured, and the extraction agent loss was 0.033 g / L.

[0044] Application Example 2

[0045] This application example is an application of extracting rubidium using the composite extractant of Example 1 and the rubidium-rich washing solution obtained in Application Example 1. Specifically, it includes the following steps:

[0046] The rubidium-rich washing liquid obtained after washing the cesium-rich organic phase in Application Example 1 was subjected to 7-stage multi-stage countercurrent extraction with the composite extractant of Example 1, the two-phase contact time was 9 minutes, the extraction temperature was 25°C, and the ratio between the two was 1:3. After the extraction was completed, the rubidium-rich organic phase was subjected to 4-stage countercurrent washing with a NaOH aqueous solution with a pH of 9, the two-phase contact time was 6 minutes, the washing temperature was 25°C, and the ratio was 1:4. A clean rubidium-rich organic phase was obtained, and the rubidium-rich organic phase was subjected to 5-stage countercurrent stripping with 0.5 mol / L hydrochloric acid, the two-phase contact time was 6 minutes, the washing temperature was 25°C, and the two were 1:3. A rubidium-rich solution was obtained, and rubidium products were prepared by evaporation and concentration. The concentration of rubidium in the raffinate was measured, and the rubidium content in the raffinate was 5.432 g / L, and the rubidium extraction rate was 49.14%. After the extraction was completed, the organic phase content in the raffinate was measured, and the extraction agent loss was found to be 0.037 g / L.

[0047] Comparative Example 1

[0048] The other configurations of this comparative example are the same as those of Application Example 1 and Application Example 2, except that the extractant does not use the composite extractant of Example 1, but directly uses the extractant obtained by mixing t-BAMBP and kerosene in a volume ratio of 1:4, and the other configurations are the same as those of Application Example 1 and Application Example 2. And the cesium concentration in the raffinate in the cesium extraction step is measured to be 3.690 g / L, that is, the cesium extraction rate is 30.38%, and the rubidium concentration in the raffinate in the rubidium extraction step is measured to be 9.462 g / L, and the rubidium extraction rate is 10.74%. After the extraction is completed, the organic phase content in the raffinate is measured, and the extraction agent dissolution loss is 0.124 g / L.

[0049] Comparative Example 2

[0050] The other configurations of this comparative example are the same as those of Application Example 1 and Application Example 2, except that the pH value of the lithium precipitation mother liquor is adjusted to 13, and the extractant does not use the composite extractant of Example 1, but directly uses t-BAMBP and kerosene in a volume ratio of 1:4. The extractant obtained by mixing, and the other configurations are the same as those of Application Example 1 and Application Example 2. And the cesium concentration in the raffinate in the cesium extraction step is measured to be 0.976g / L, that is, the cesium extraction rate is 81.58%, and the rubidium concentration in the raffinate in the rubidium extraction step is measured to obtain a rubidium content of 5.897g / L in the raffinate, and the rubidium extraction rate is 44.37%. After the extraction is completed, the organic phase content in the raffinate is measured, and the extraction agent dissolution loss is 3.5g / L.

[0051] It can be concluded that without adding an organic phosphorus extractant, at pH = 10 and other conditions being the same as those of the present invention, the extraction rate of cesium is 51 percentage points lower and the extraction rate of rubidium is 38 percentage points lower, that is, without adding an organic phosphorus extractant in a proportion set in detail by the present invention, the extraction rates of cesium and rubidium both decrease to a certain extent. When t-BAMBP is used alone as an extractant, its extraction rate at pH = 13 is equivalent to the extraction rate under the condition of pH = 10 using the synergistic extraction system of the present invention, but under high alkaline conditions, the t-BAMBP anion has a greater polarity, and the electrostatic attraction between it and the water molecule is enhanced, making it easier to dissolve in water, and the dissolution loss of the organic phase of the t-BAMBP extraction system is as high as 3.5 g / L.

[0052] Comparative Example 3

[0053] The other configurations of this comparative example are the same as those of Application Example 1 and Application Example 2, except that the extractant does not use the composite extractant of Example 1, but directly uses diisoamyl methylphosphonate as an extractant mixed with kerosene at a volume ratio of 1:4, and the other configurations are the same as those of Application Example 1 and Application Example 2. In addition, the cesium concentration in the raffinate in the cesium extraction step is measured to be 5.134 g / L, that is, the cesium extraction rate is 3.13%, and the rubidium concentration in the raffinate in the rubidium extraction step is measured to be 10.245 g / L, and the rubidium extraction rate is 3.35%.

[0054] Even when other conditions are the same as those of the present invention, the extraction rate of cesium and rubidium is only about 3% when only the organophosphorus extractant with the detailed ratio set in the present invention is used. The single organophosphorus extractant has almost no extraction effect on rubidium and cesium. That is, the synergistic extractant composed of the substituted phenol extractant and the organophosphorus extractant specifically set in the present invention is not a simple mixture of the two types of substances, but a composite extractant that can achieve efficient extraction and separation of rubidium and cesium without the need for particularly high alkalinity is obtained by specifically setting the synergistic effect between the two. The two have a very strong close coordination and cooperation, rather than a conventional simple combination.

[0055] The technical principle of the present invention is described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the scope of protection of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without paying creative labor, and these methods will fall within the scope of protection of the present invention.

Claims

1. A composite extractant for separating rubidium and cesium, characterized in that: The composite extractant comprises a synergistic extractant, a diluent and a phase regulator; the synergistic extractant comprises a substituted phenol extractant and an organic phosphorus extractant; wherein the molar ratio of the substituted phenol extractant to the organic phosphorus extractant is (0.1-9.5):(0.5-1.5), the volume ratio of the diluent to the synergistic extractant is (0.1-98):(0.8-1.3), and the volume of the phase regulator is 0-60 vol.% of the volume of the synergistic extractant; The organophosphorus extractant is any one of a neutral organophosphorus extractant and an acidic organophosphorus extractant, or a combination of at least two of them.

2. The composite extractant for separating rubidium and cesium according to claim 1, characterized in that: The neutral organic phosphorus extractant includes any one of tributyl phosphate, triisoamyl phosphate, dialkyl alkylphosphonates, trialkylphosphine oxides, diisoamyl methylphosphonate, dibutyl butylphosphonate, diisoamyl methylphosphonate or dimethylheptyl methylphosphonate, or a combination of at least two thereof.

3. The composite extractant for separating rubidium and cesium according to claim 1, characterized in that: The acidic organic phosphorus extractant includes any one or a combination of at least two of dibutylphosphonic acid, dipentylphosphonic acid, dihexylphosphonic acid, diheptylphosphonic acid and di(2-ethylhexyl)phosphonic acid, dibutylphosphonic acid, dipentylphosphonic acid, dihexylphosphonic acid or diheptylphosphonic acid and di(2,4,4,trimethylpentyl)phosphonic acid.

4. The composite extractant for separating rubidium and cesium according to claim 2 or 3, characterized in that: The substituted phenol extractant includes any one of 4-sec-butyl-2(α-methylbenzyl)phenol (s-BAMBP), 4-tert-butyl-2(α-methylbenzyl)phenol (t-BAMBP), 4-ethyl-2-(α-methylbenzyl)phenol, 4-isopropyl-2-(α-methylbenzyl)phenol, 4-tert-amyl-2-(α-methylbenzyl)phenol, 4-fluoro-2-(α-methylbenzyl)phenol or 2,4-dimethyl-6-(α-methylbenzyl)phenol or a combination of at least two thereof.

5. The composite extractant for separating rubidium and cesium according to claim 2 or 3, characterized in that: The diluent includes any one of kerosene, D series dearomatized solvent oil, A series aromatic solvent oil, diethylbenzene isomer mixture, butylbenzene isomer mixture, 200# solvent oil, n-12 alkane or 260# solvent oil, or a combination of at least two thereof.

6. The composite extractant for separating rubidium and cesium according to claim 2 or 3, characterized in that: The phase regulator includes one or both of C6-C14 alcohol compounds or ester compounds.

7. The composite extractant for separating rubidium and cesium according to claim 6, characterized in that: The C6-C14 alcohol compound includes any one of heptanol, n-octanol, sec-octanol, isooctyl alcohol, nonanol, decanol, undecanol, dodecanol, isotridecanol or tetradecanol, or a combination of at least two thereof; The ester compound includes any one of dioctyl phthalate, dioctyl isophthalate, dioctyl terephthalate, diisooctyl phthalate, dibutyl phthalate, diisobutyl phthalate, dibutyl isophthalate, dibutyl terephthalate, dimethyl phthalate, amyl nonanoate or isoamyl nonanoate, or a combination of at least two thereof.

8. The composite extractant for separating rubidium and cesium according to claim 2 or 3, characterized in that: The molar ratio of the substituted phenol extractant to the organophosphorus extractant is (3-9):(0.9-1.2), the volume ratio of the diluent to the co-extractant is (5-10):(0.9-1.1), and the volume of the phase regulator is 20-40 vol.% of the volume of the co-extractant.

9. A method for preparing a composite extractant for separating rubidium and cesium, characterized in that: The composite extractant is the composite extractant according to any one of claims 1 to 8, comprising the following steps: (1) mixing a substituted phenol extractant and an organophosphorus extractant in a molar ratio of (0.1-9.5):(0.5-1.5) to obtain a synergistic extractant; (2) adding a phase regulator in an amount of 0 to 60 vol.% based on the volume of the synergistic extractant to the synergistic extractant obtained in step (1); (3) The mixed solution obtained in step (2) is mixed with a diluent in a volume ratio of (0.1-98) to (0.8-1.3) to obtain a rubidium-cesium composite extractant product.

10. The method for preparing the composite extractant for separating rubidium and cesium according to claim 9, characterized in that: In step (3), after the mixed solution is mixed with the diluent, it is stirred for 1-30 minutes and at a stirring intensity of 10-500 r / min until the mixed solution is uniform, thereby obtaining a separated rubidium-cesium composite extractant product.