CN118221519A - Ionic liquid and preparation method and application thereof - Google Patents

Abstract

The invention discloses an ionic liquid and a preparation method and application thereof. Based on the cationic functionalized ionic liquid, the method is used for efficiently separating and recovering Th and REs in the waste residue leaching solution, almost all Th are separated from REs by the preferable ionic liquid, and rare earth is hardly extracted to an organic phase. The separation strategy of the recyclable ionic liquid provided by the invention greatly simplifies the separation process of Th and rare earth elements, reduces the consumption of chemicals, and provides a new idea for the treatment of radioactive waste residues of ionic rare earth ores.

Description

Ionic liquid and preparation method and application thereof

Technical Field

The invention belongs to the field of extraction of thorium and rare earth metals, and particularly relates to an ionic liquid and a preparation method and application thereof.

Background

With the advancement of technology, rare earth is increasingly used in communication, display, medical equipment, and some renewable green energy sources such as solar cells, electric car nickel-metal hydride batteries, wind turbines, etc. Rare earth resources need to be separated from other impurities in the minerals, such as Fe, al, ca, mg, cu, etc., before use. Ionic rare earth ores containing over 80% of the medium and heavy rare earths worldwide are a valuable strategic resource, and unfortunately, some of the natural radioactive elements (mainly Th) are often associated therewith and transferred and enriched with the progress of the rare earth metallurgical process. In order to reduce the harm of the diffusion of the radioactive elements to the subsequent rare earth separation process, the radioactive elements are usually transferred to corresponding impurity removing residues, dissolving residues and acid-base neutralization residues in advance in the impurity removing and acid dissolving stages, and most of ThO ₂ is concentrated in the dissolving residues after the optimal dissolution of hydrochloric acid, so that the total mass of the residues is 1.25%. Even so, due to the relatively low radionuclide content in the ionic rare earth ores, hardly any measures are taken to control the radiation pollution of the production plant. This results in some of the residues in the ionic rare earth mining areas having a total specific activity of alpha and beta significantly higher than the level of 1Bq/g specified by the state of the art radioactive environment standard, belonging to the accompanying radioactive solid waste that needs to be treated or well stored.

Acidic/neutral organic phosphines, primary amines and naphthenic acids, etc. are common industrial extractants for the separation of thorium and rare earths, which all have drawbacks that are difficult to compensate in certain respects, such as difficult back extraction, aberration of extraction, complex operation, extraction only under severe and specific conditions, etc. Ionic liquids are room temperature molten salts composed entirely of ions and are commonly used as solvents in organic synthesis, inorganic synthesis, catalysis, analytical systems and biological systems. In addition, the ionic liquid is considered as a green extractant with very good application prospect because of the characteristics of high separation efficiency, easy back extraction, mild extraction conditions, easy recycling and the like during extraction and separation. Interestingly, both its anions and cations support self-design, suggesting that it can meet the extraction and separation requirements by changing and optimizing the structure. Ionic liquids are used as solvent extractants and the balance between hydrophobicity and hydrophilicity is usually considered in the structural design. Based on the basic principle of liquid-liquid extraction, the hydrophilic part can extract the extract from water, and the hydrophobic part is responsible for preventing the extract from dissolving in water. They are capable of extracting metal ions efficiently and in large amounts under mild extraction conditions, without the need for high acidity, high temperature, specific mineral acid radical systems (e.g., NO ₃ ^- systems), and without exchanging organic or inorganic cations to the aqueous phase.

Disclosure of Invention

In order to solve the technical problems, the invention provides an ionic liquid, wherein the cationic structure is selected from any one of formulas I, II, III, IV, and the anion is sec-octyl phenoxy substituted acetic acid [ CA12] ^-;

the structural formulas of formula I, II, III, IV are respectively:

Wherein R ₁ is C1-C6 alkyl, R ₂ is C6-C12 alkyl, R ₃ is C1-C6 alkyl, R ₄ is C2-C10 alkyl; preferably, R ₂ is a C6-C10 straight chain alkyl group; more preferably, R ₂ is C8 straight chain alkyl;

The structural formula of the anionic sec-octyl phenoxy substituted acetic acid [ CA12] ^- is as follows:

In some embodiments, R ₁ may be tert-butyl;

In some embodiments, R ₂ can be octyl;

in some embodiments, R ₃ can be ethyl;

in some embodiments, R ₄ can be hexyl.

In some embodiments, the cation is selected from any of [ bis (3, 3-dimethyl-2-oxybutylene butyl) ] dioctyl ammonium chloride [ OB2DTA ] ⁺, [ bis (1-ethoxy-1-oxybutylene oct-2-yl) ] dioctyl ammonium bromide [ EO2DTA ] ⁺, (1-ethoxy-1-oxybutylene oct-2-yl) trioctyl ammonium chloride [ OBTA ] ⁺, (3, 3-dimethyl-2-oxybutylene butyl) trioctyl ammonium bromide [ EOTA ] ⁺;

Wherein the structural formula of [ OB2DTA ] ⁺、[EO2DTA]⁺、[OBTA]⁺、[EOTA]⁺ is respectively as follows:

In some embodiments, the ionic liquid is [OB2DTA]⁺[CA12]^-、[EO2DTA]⁺[CA12]^-、[OBTA]⁺[CA12]^-、[EOTA]⁺[CA12]^-;, preferably [ OB2DTA ] ⁺[CA12]^-.

The invention provides a preparation method of the ionic liquid, which comprises the following steps: the halide of the cation reacts with the anion of the completely sodium soap to obtain the ionic liquid;

For example, the reaction is carried out in a solvent selected from any one of ethanol, methanol, acetonitrile;

For example, the reaction conditions are 50 to 80℃and 6 to 12 hours.

According to an embodiment of the invention, the cationic halide is prepared by the following method: heating and reacting octylamine with a compound A under the assistance of microwaves to obtain the product;

The octylamine may be selected from n-trioctylamine or di-n-octylamine;

the compound A can be selected from 1-chloropinacolone or ethyl 2-bromooctoate;

for example, the microwave reaction conditions are heated to 60-80℃and reacted for 2-4 hours.

In one embodiment, n-trioctylamine and 1-chloropinacolone under the assistance of microwave heating reaction, to obtain (1-ethoxy-1-oxyoctylen-2-yl) trioctylammonium chloride;

for example, the molar ratio of n-trioctylamine to 1-chloropinacolone is 1:1-1.5, preferably 1:1.2.

In one embodiment, n-trioctylamine is reacted with ethyl 2-bromooctoate under microwave-assisted heating to give (3, 3-dimethyl-2-oxybutylene butyl) trioctylammonium bromide;

for example, the molar ratio of n-trioctylamine to ethyl 2-bromooctanoate is 1:1 to 1.5, preferably 1:1.1.

In one embodiment, di-n-octylamine and 1-chloropinacolone under the assistance of microwave heating reaction, to obtain [ bis (3, 3-dimethyl-2-oxybutylene butyl) ] dioctyl ammonium chloride;

For example, di-n-octylamine and 1-chloropinacolone molar ratio is 1:1-1:1.5, preferably 1:1.2.

In one embodiment, di-n-octylamine is reacted with ethyl 2-bromooctoate under microwave-assisted heating to give [ bis (1-ethoxy-1-oxyoctylen-2-yl) ] dioctyl ammonium bromide;

For example, the molar ratio of di-n-octylamine to ethyl 2-bromooctanoate is 1:1 to 1:1.5, preferably 1:1.

According to an embodiment of the invention, a method for preparing an ionic liquid [ OBTA ] ⁺[CA12]^- or [ EOTA ] ⁺[CA12]^- comprises the steps of:

Heating n-trioctylamine and 1-chloropinacolone or 2-bromooctanoic acid ethyl ester under the assistance of microwaves to react to obtain (1-ethoxy-1-oxyoctylene-2-yl) trioctylammonium chloride) or (3, 3-dimethyl-2-oxybutylene) trioctylammonium bromide; and then reacting with sec-octyl phenoxy substituted acetic acid of the completely sodium soap to obtain the ionic liquid.

According to an embodiment of the present invention, there is provided a method for producing the above-mentioned ionic liquid [ OB2DTA ] ⁺[CA12]^- or [ EO2DTA ] ⁺[CA12]^-, comprising the steps of:

Heating di-n-octylamine and 1-chloropinacolone or ethyl 2-bromooctoate with the aid of microwaves to react to obtain [ bis (3, 3-dimethyl-2-oxybutylene butyl) ] dioctyl ammonium chloride or [ bis (1-ethoxy-1-oxybutylene-2-yl) ] dioctyl ammonium bromide; and then reacting with sec-octyl phenoxy substituted acetic acid of the completely sodium soap to obtain the ionic liquid.

The invention also provides application of the ionic liquid as an extractant, preferably application of the ionic liquid as a thorium and/or rare earth ion extractant.

The invention also provides an extractant, which comprises the ionic liquid.

In some embodiments, the extractant further comprises a phase modifier; preferably, the phase modifier is isooctyl alcohol or TBP tributyl phosphate.

In some embodiments, the phase modifier is used in an amount of 5 to 20% by volume of the organic phase, preferably 10% by volume of the organic phase.

In some embodiments, the extractant is renewable and reusable.

The invention also provides a method for recycling thorium and rare earth, which comprises the following steps:

1) Calcining the waste residue of the rare earth ore, and leaching the waste residue by hydrochloric acid in a multi-stage way to obtain a waste residue leaching solution;

2) Regulating the pH value of the waste residue leaching solution, and filtering to obtain a supernatant;

3) Adding the extractant into the supernatant in the step 2) for extraction to obtain an organic phase loaded with Th and raffinate;

4) The organic phase loaded with Th in the step 3) is back extracted by acid solution to obtain back extraction liquid rich in Th, and the pH is regulated to obtain precipitate Th (OH) ₄ and precipitate supernatant;

5) Removing impurities from the raffinate obtained in the step 3) to obtain a precipitation supernatant, and enriching the precipitation supernatant with H ₂C₂O₄ to obtain RE ₂(C₂O₄)₃.

In some embodiments, the above-described process for recovering thorium and rare earth comprises the steps of:

1) Calcining ion adsorption type rare earth ore waste residues at 600 ℃ to form mixed oxides, and then leaching the mixed oxides by using hydrochloric acid in multiple stages to obtain waste residue leaching liquid;

2) Adjusting the pH value of the waste residue leaching solution by using ammonia water, and filtering to obtain a supernatant;

3) Adding the extractant into the supernatant in the step 2) for extraction to obtain an organic phase loaded with Th and raffinate;

4) The organic phase loaded with Th in the step 3) is back extracted by acid solution to obtain back extraction liquid rich in Th, and the pH is regulated to obtain precipitate Th (OH) ₄ and precipitate supernatant;

5) Removing impurities from the raffinate obtained in the step 3) to obtain a precipitation supernatant, and enriching the precipitation supernatant with H ₂C₂O₄ to obtain RE ₂(C₂O₄)₃.

In some embodiments, the slag leachate of step 1) contains Mg ²⁺、Ca²⁺、Cl^-、Al³⁺、Fe³⁺、RE³⁺、Th⁴⁺ plasma.

In some embodiments, in step 2), ammonia is used to adjust the pH of the slag leachate to 1.0-3.0, preferably 3.0.

In some embodiments, in step 3), the operation of the extraction is: the two-phase mixture was placed in a constant temperature gas bath shaking box and shaken at 500rpm for 30-60 minutes to reach equilibrium, and finally centrifuged at 2000rpm for 3 minutes to accelerate phase separation.

In some embodiments, in step 3), the number of extractions is 1-3, preferably 2.

In some embodiments, in step 3), the concentration of extractant is from 0.006 to 0.012mol/L.

In some embodiments, in step 3), the extractant further comprises a phase modifier, preferably TBP, isooctyl alcohol, at a concentration of preferably 10%.

In some embodiments, in step 3), the concentration of NaCl in the extractant is from 0 to 1.0mol/L, preferably from 0.5 to 1.0mol/L.

In some embodiments, the extractant in step 3) is an ionic liquid of [OB2DTA]⁺[CA12]^-、[EO2DTA]⁺[CA12]^-、[OBTA]⁺[CA12]^-、[EOTA]⁺[CA12]^-,, preferably [ OB2DTA ] ⁺[CA12]^-.

In some embodiments, the precipitate supernatant in step 4) is combined and mixed with the precipitate supernatant in step 5) and then enriched with H ₂C₂O₄ to yield RE ₂(C₂O₄)₃.

In some embodiments, in step 4), the acid solution is 0.05 to 0.5mol/L aqueous HCl, preferably 0.1 to 0.2mol/L aqueous HCl.

In some embodiments, the organic phase after back extraction with the acid solution in step 4) is recycled to step 3) for use as an extractant after regeneration treatment with an alkaline solution and water washing;

Preferably, the alkali solution is 0.01 to 0.05mol/L NaOH aqueous solution or 0.01 to 0.05mol/L KOH aqueous solution.

In some embodiments, the above-described process does not involve an acid wash stage.

Advantageous effects

The invention provides an ionic liquid containing functionalized cations and a preparation method thereof, and the ionic liquid is used for realizing the purposes of separating and recycling thorium and rare earth. In addition, the ionic liquid can be recycled, and the extraction and separation effects are kept stable, so that the separation process of Th and rare earth elements is greatly simplified, the consumption of chemicals is reduced, and a new idea is provided for the treatment of radioactive waste residues of ionic rare earth ores.

Drawings

FIG. 1 shows the effect of initial pH (a) of the solution and the concentration of extractant (b) on the extraction behavior.

Fig. 2: (a) interfacial phenomena of two phases under different phase modifiers; (b) effect of different phase modifiers on extraction efficiency.

FIG. 3 shows the effect of NaCl concentration on the extraction.

Fig. 4: (a) stripping efficiency at different hydrochloric acid concentrations; (b) the effect of different phase modifiers on stripping; (c) Circulating extraction of [ OB2DTA ] ⁺[CA12]^- extractant; (d) [ OB2DTA ] ⁺[CA12]^- and infrared spectra before and after cation circulation.

Fig. 5: (a) The extraction efficiency of the metal elements in the two-stage extraction process for separation; (b) The distribution of main metal elements in an organic phase and an aqueous phase in the two-stage extraction process; (c) a scheme for separating and recovering REs and Th in the slag leaching solution.

Detailed Description

The technical scheme of the invention will be further described in detail below with reference to specific embodiments. It is to be understood that the following examples are illustrative only and are not to be construed as limiting the scope of the invention. All techniques implemented based on the above description of the invention are intended to be included within the scope of the invention.

Unless otherwise indicated, the starting materials and reagents used in the following examples were either commercially available or may be prepared by known methods.

Example 1 extractant and its synthesis

The cationic halides are prepared mainly by quaternization, and then combined with the deprotonated CA12 into an ionic liquid by means of ion exchange and neutralization.

Preparation of cationic monofunctional Quaternary ammonium salt: to 50mmol of tri-n-octyl amine ethanol containing 60mmol 1-chloro pinacolone/55 mmol ethyl 2-bromo octoate ethanol mixture, under the assistance of microwave heating to 80 ℃ for 2h, evaporation of ethanol and with a small amount of petroleum ether multiple washing, water washing in dichloromethane multiple times, anhydrous Na2SO4 water removal, vacuum drying to obtain orange liquid ((1-ethoxy-1-oxy-2-octyl-2-radical) trioctylammonium chloride)/light yellow liquid ((3, 3-dimethyl-2-oxy-butyl) trioctylammonium bromide), yield of 70% and 74%.

Preparation of cationic difunctional quaternary ammonium salts: 50mmol of di-n-octylamine is dissolved in ethanol containing 55mmol of NaOH, a mixture of 60mmol of 1-chloropinacolone/50 mmol of ethyl 2-bromooctoate is dropwise added, the mixture is heated to 80 ℃ with the aid of microwaves for reaction for 2 hours, and 60mmol of 1-chloropinacolone/55 mmol of ethyl 2-bromooctoate are respectively dropwise added into the mixture again for continuous reaction for 2 hours. After the completion of the reaction, the solvent was distilled off, and the crystals were washed with petroleum ether several times, followed by vacuum evaporation of petroleum ether and dissolution of the remaining product in chloroform, followed by washing with deionized water several times. Anhydrous Na ₂SO₄ was used to remove residual water and after removal of chloroform vacuum drying gave a yellow solid ([ bis (3, 3-dimethyl-2-oxybutylidene) ] dioctyl ammonium chloride) and a white solid ([ bis (1-ethoxy-1-oxybutylidene-2-yl) ] dioctyl ammonium bromide) in 82% and 85% yields, respectively.

Respectively dissolving the four quaternary ammonium salts and an industrial extractant sec-octyl phenoxy substituted acetic acid (purity 90%) of the sodium soap into ethanol, reacting for 6 hours at 50 ℃, washing and drying to finally obtain four ionic liquids:

(1) [ [ bis (3, 3-dimethyl-2-oxybutylene) dioctyl ammonium ] [ sec-octylphenoxy ] substituted acetate ] (yield 91%, english abbreviation) [OB2DTA]⁺[CA12]^-).IR:1632.5,1599.6(C＝O);1219.1,1057.5(＝C-O-C).¹H NMR(500MHz,Chloroform-d,ppm):δ7.05(dd,J＝8.8,6.7Hz,1H),7.03–6.99(m,1H),6.90(t,J＝7.4Hz,1H),6.82(dd,J＝8.6,2.2Hz,1H),4.45–4.39(m,2H),3.70(s,4H),3.25(dt,J＝44.5,7.3Hz,1H),2.65–2.60(m,4H),1.60(tt,J＝11.0,6.7Hz,6H),1.25(s,49H),0.90(t,J＝7.0Hz,6H),0.88–0.83(m,3H).

(2) [ [ Bis (1-ethoxy-1-oxyoctylen-2-yl) ] dioctyl ammonium ] [ sec-octylphenoxy-substituted acetate ] (yield 95%, english abbreviation) [EO2DTA]⁺[CA12]^-).IR:1739.2,1600.0(C＝O);1218.8,1058.3(＝C-O-C).¹H NMR(500MHz,Chloroform-d,ppm):δ7.08–7.03(m,1H),7.01(d,J＝8.6Hz,1H),6.90(t,J＝7.4Hz,1H),6.81(dd,J＝8.7,2.2Hz,1H),4.45–4.39(m,2H),4.29–4.22(m,2H),4.24–4.13(m,4H),3.44–3.22(m,1H),2.67–2.63(m,4H),1.65(s,6H),1.39–1.15(m,53H),0.90(t,J＝7.0Hz,12H),0.87–0.83(m,3H).

(3) [ (1-Ethoxy-1-oxooct-2-yl) trioctylammonium ] [ sec-octylphenoxy ] substituted acetate ] (yield 70%, english abbreviation [OBTA]⁺[CA12]^-).IR:1686.3,1600.6(C＝O);1219.7,1058.7(＝C-O-C).¹H NMR(500MHz,Chloroform-d,ppm):δ7.19–7.08(m,1H),7.09–6.98(m,1H),6.92–6.85(m,1H),6.87–6.79(m,1H),4.47–4.41(m,2H),4.07(t,J＝6.7Hz,2H),3.35–3.17(m,1H),2.62(dt,J＝18.7,6.8Hz,4H),1.60(s,2H),1.51(s,6H),1.28(t,J＝6.5Hz,47H),1.23–1.17(m,3H),0.90(t,J＝6.9Hz,9H),0.88–0.81(m,3H).

(4) [ (3, 3-Dimethyl-2-oxybutylene butyl) trioctylammonium ] [ sec-octylphenoxy ] substituted acetate ] (yield 61%, english abbreviation [EOTA]⁺[CA12]^-).IR:1742.7,1586.5(C＝O);1175.5,1094.7(＝C-O-C).¹H NMR(500MHz,Chloroform-d,ppm):δ7.19–7.08(m,1H),7.05(d,J＝8.7Hz,1H),6.97(t,J＝7.5Hz,1H),6.86(dd,J＝8.6,3.0Hz,1H),4.73(d,J＝11.7Hz,2H),4.29–4.21(m,2H),4.21(d,J＝7.5Hz,1H),3.34–2.99(m,1H),2.57(t,J＝7.9Hz,6H),2.12–1.93(m,2H),1.82(dtd,J＝35.2,10.3,9.3,4.5Hz,2H),1.54(s,4H),1.36–1.21(m,54H),0.89(t,J＝6.9Hz,15H).

The structures of anions and cations in the four ionic liquids [OB2DTA]⁺[CA12]^-、[EO2DTA]⁺[CA12]^-、[OBTA]⁺[CA12]^-、[EOTA]⁺[CA12]^- are respectively:

example 2 optimization of extraction and stripping Experimental conditions

Extraction experiment: the organic phase containing extractant and feed solution were mixed in a volume ratio of 1:1 and placed in a constant temperature gas bath shaking box and shaken at 500rpm for 30-60 minutes to reach equilibrium, removed and centrifuged at 2000rpm for 3 minutes to accelerate phase separation.

Back extraction experiment: the loaded organic phase and stripping solution were mixed in a volume ratio of 1:1 and placed in a constant temperature gas bath shaker box and shaken at 500rpm for 10-20 minutes to equilibrate, removed and centrifuged at 2000rpm for 3 minutes to accelerate phase separation.

And (3) cycle experiment: the circulation experiment is carried out by adopting the sequence of the extraction experiment, the back extraction experiment and the regeneration experiment, wherein the regeneration experiment is carried out by using NaOH/KOH solution with the concentration of 0.05-0.2 mol/L, and then washing the organic phase with deionized water with the concentration of 30-100% of the organic phase volume for one to two times until the organic phase is neutral after being tested by pH test paper. The metal element content in the organic phase is calculated by mass conservation between the two phases.

Preparing a solution: the ThCl ₄ and RECl ₃ solutions were diluted to prepare a simulated mixed solution with a total element content ratio of 1:1, wherein the rare earth element contained 15 total elements of lanthanoid except Pm and Y.

The extraction efficiency of the rare earth in the leaching liquid of the actual waste residue is that the total amount of the extracted rare earth accounts for the percentage of the content of the original feed liquid. All experiments were performed simultaneously in three parallel groups, the measured data being their average amount, and the error level was below 5% unless the data were close to the span limit. The total rare earth extraction efficiency is an average extraction level of 15 rare earths, extraction efficiency (E%), stripping efficiency (S%), partition ratio (D) can be expressed by the following equation:

Where Mi and Me represent the mass concentration of metal in the aqueous solution at the initial and equilibrium, respectively. Ms represents the mass concentration of metal in the stripped stripping solution.

2.1 Effect of aqueous acidity

Effect of aqueous phase acidity experiments: several parts of feed liquid water phases containing the same components are adjusted to pH values within the range of 1-3 in advance, extraction experiments are carried out by using the organic phases under the same conditions, the metal content in the water phases is measured, and the extraction efficiency at different feed liquid pH values is calculated.

As a result, it was found that extraction efficiency of Th by these four ionic liquids was reduced with an increase in pH, and pH was controlled to be within 3 to prevent precipitation of Th (fig. 1 a). Similar to the extraction of other metal ions using ionic liquids, the process of extracting Th is also relatively sensitive to the concentration of H ⁺ in the aqueous phase, and to some extent H ⁺ competes with other metal ions for extraction, similar to the trend of neutral organophosphine extractants. In addition, the metal ions to be extracted are most easily extracted when approaching to the hydrolysis pH, and the hydrolysis pH of REs ions is relatively high, so that the pH is raised as much as possible on the premise that Th is not precipitated, thereby being beneficial to separation.

2.2 Effect of extractant concentration

Influence of extractant concentration experiments: several parts of feed liquid water phases containing the same components are subjected to extraction experiments by using an organic phase containing 0.006-0.012 mol/L extractant, the metal content of the water phases is measured, and the extraction efficiency at different feed liquid pH values is calculated.

As can be seen from fig. 1b, the difunctional quaternary ammonium ionic liquid at the same concentration has a higher extraction capacity for Th than the full alkyl chain (a 336) quaternary ammonium ionic liquid, but the monofunctional species has significantly lower extraction performance than the precursor. At these concentrations, all extractants have negligible extraction of rare earths. Unlike [ A336] ⁺[CA-12]^-, they have an oxygen-containing functional group inserted into their cations, which is expected to have an effect on extraction and separation. Similar to the effect of the anionic structure on selective extraction and separation, the carbon chain composition, mono-and di-functionalization of the cation will also have different extraction behaviour, affected by several possible factors, respectively: (1) acidity of quaternary ammonium ions; (2) an oxy subunit substitution of the N center; (3) Alkyl chain structure (length and branching) attached to the N center; (4) steric hindrance effect of all substituents. Substitution of the functional groups may alter the way the extractant acts on Th, as will be mentioned in subsequent experiments.

In FIG. 1 b, the meanings of O2, E2, O1, E1, A336 respectively represent [OB2DTA]⁺[CA12]^-、[EO2DTA]⁺[CA12]^-、[OBTA]⁺[CA12]^-、[EOTA]⁺[CA12]^-、[A336]⁺[CA-12]^- ionic liquid extractants.

2.3 Effect of phase modifier

Impact experiments of phase modifier: several parts of feed water phases containing the same components are subjected to extraction experiments in advance by using an organic phase containing the extractant with the same concentration but containing 10% of different phase modifiers, the metal content of the water phases is measured, and the extraction efficiency at different feed liquid pH values is calculated.

As shown in fig. 2a, when no phase modifier is added, the difunctional cationic ionic liquid is obviously emulsified, and after isooctyl alcohol is added, [ OB2DTA ] ⁺[CA12]^- does not generate a third phase any more, and the influence of emulsification can be effectively relieved by TBP. In contrast, for monofunctional cations and alkyl chain quaternary amines, the addition of the phase modifier may lead to slight emulsions, while CA12 produces a more pronounced third phase. The addition of phase modifier affects the extraction behaviour (b in fig. 2). The addition of isooctanol slightly reduces the extraction efficiency of the difunctional cationic ionic liquid, whereas the amount of extracted Th can be increased for TBP.

It is worth noting that the addition of isooctanol can improve the Th extraction capacity of monofunctional cationic liquids, probably because the added isooctanol can form intermolecular hydrogen bonds with oxygen on the extractant on the one hand, so that they can be well dispersed in the organic phase, but this can weaken symmetry and stability of the extract to a certain extent, affect the extraction performance and reduce the difficulty of back extraction at the same time, which is often mentioned in the P507-isooctanol extraction system; on the other hand, the hydroxyl group in isooctanol (including phosphoryl group in TBP) may also participate in Th coordination with extractant molecule, forming more stable complexes. [ OB2DTA ] ⁺[CA12]^- clearly shows the highest extraction capacity of the better performing extractant due to its presence of isooctanol and no emulsification occurs. More, although having a weak effect on extraction, th is able to be fully stripped at lower acidity in the presence of isooctanol.

2.4 Influence of NaCl

Influence experiment of NaCl: the aqueous phases of feed liquid containing the same components but different amounts of NaCl are subjected to extraction experiments in advance using organic phases containing the same conditions, the metal content of the aqueous phases is measured and the extraction efficiency at different feed liquid pH values is calculated.

As shown in FIG. 3, the extraction amount of Th of the four synthesized ionic liquids increases with the increase of NaCl concentration in the feed liquid, and the extraction efficiency is almost stable after higher than 0.5mol/L, which indicates that the Cl ^- driving and salting-out effects are saturated. The trend towards increased extraction efficiency also suggests their more strongly NaCl-dependent effect on the extraction of Th with a ：[OB2DTA]⁺[CA12]^-＞[EO2DTA]⁺[CA12]^-＞[OBTA]⁺[CA12]^-＞[EOTA]⁺[CA12]^-. di-functional cationic ionic liquid with a lazy array of NaCl concentrations.

2.5 Stripping and circulation of extractant

Five ionic liquids and their precursor CA12 were studied and compared for their counter-extraction with hydrochloric acid (a in fig. 4). The results show that the stripping is easy under the condition that the extraction mechanisms of the first three are the same: [ OB2DTA ] ⁺[CA12]^-＞[A336]⁺[CA12]^-＞[EO2DTA]⁺[CA12]^-, which may be due to the effect of cationic functionality on stripping, for [ OB2DTA ] ⁺[CA12]^- 0.2mol/L HCl is able to strip the loaded Th almost completely. It is also notable that the other three extractants were diametrically opposed in terms of stripping difficulty and extraction capacity, although as stripping acidity increased to 2, no more Th was replaced by H ⁺. In our previous studies, 0.5mol/L HCl was required to achieve complete stripping without the addition of phase modifier, indicating that the added isooctanol has a very negative effect on stripping of CA 12. In contrast, the phase modifier can act as a stripping aid to greatly enhance the stripping effect of [ OB2DTA ] ⁺[CA12]^-、[EO2DTA]⁺[CA12]^- (FIG. 4 b).

In combination with various factors, among these extractants, [ OB2DTA ] ⁺[CA12]^- has the strongest extraction capacity, the stripping with the lowest acid consumption, no third phase and good Th and REs separation effect.

In order to ensure the possibility of being able to be reused, a plurality of extraction-stripping-regeneration processes were carried out using 0.3mol/L HCl solution and 0.01mol/L NaOH solution as stripping agent and regeneration agent, respectively. Wherein the regenerant was used to neutralize the H ⁺ contained in the organic phase, and a small amount of deionized water was used to wash the organic phase after each regeneration. After 5 cycles, the extraction separation capacity of the extractant for Th and REs remained stable (c in FIG. 4). Also, the initial infrared spectrum of the organic phase was consistent with the spectrum after five cycles, and the c=o infrared characteristic peak shift and peak shape at 1606.8 were unchanged (d in fig. 4). All of these results described above are sufficient to demonstrate good renewable and recyclable performance.

Example 3 separation of Th and REs from slag leachate

The experiment of separating Th and REs from slag leaching solution includes calcining ion adsorption RE slag at 600 deg.c to form mixed oxide, multistage leaching with hydrochloric acid, regulating pH to 3.0 with ammonia water to separate out most Fe from the liquid, twice extraction with fresh organic matter containing OB2DTA ⁺[CA12]^-, stripping loaded Th and Fe with 0.1-0.2 mol/L HCl water solution to water phase, and water washing to reuse the organic phase. The back raffinate can be precipitated into Th (OH) ₄ by adjusting the pH, and the precipitate supernatant can be added into the non-radioactive leaching solution after Th and Fe removal for the next stage of REs impurity removal, enrichment and recovery (c in figure 5).

The results in FIG. 5a show that after two-stage extraction under the optimal extraction conditions, the residual Th in the aqueous phase is below 0.1mg/L, all Fe is extracted into the organic phase, and the separation rates of Th/RE and Fe/RE reach 99.5% and 100%, respectively. Further, the total amount of REs lost in the two extraction stages is below 15mg/L, the loss rate is only 0.3%, so that washing with acid is no longer necessary (b in FIG. 5).

The above circularly regenerated bifunctional ionic liquid is used for efficiently removing thorium as a main radioactive pollution source from waste residues. Preferred [ OB2DTA ] ⁺[CA12]^- ionic liquids are capable of highly selective extraction of thorium in aqueous solutions under a chlorination system. It is notable that the supported Th can be stripped out of the organic phase most easily while possessing the strongest extraction capacity so that a large amount of acid can be saved, which can be attributed to the ion-associated extraction mode and the change in extraction environment due to the addition of isooctanol. The regeneration of the extractant can be well achieved with a relatively low concentration of alkali, which can then be fed to the extraction stage a number of times in succession. In addition, functionalization of the cations can provide more coordination sites for extraction of Th, and optimized slope analysis shows that 3 [ OB2DTA ] ⁺[CA12]^- molecules coordinate with 2 ThCl ₄ to form an ion pair. At the laboratory scale, the two-stage extraction of [ OB2DTA ] ⁺[CA12]^- can simultaneously remove the radioactive Th and impurity Fe in the waste residue leaching solution. Th contained in the raffinate is lower than 0.1mg/L, and the separation rate of REs reaches 99.5%, and the rare earth loss amount is not more than 15mg/L.

In conclusion, the invention provides a high-efficiency recyclable method for treating the radioactive waste residues of the ionic rare earth ores, can reduce the consumption of chemicals, simplify the separation process and realize recovery of valuable metals.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. An ionic liquid is characterized in that the cationic structure in the ionic liquid is selected from any one of formulas I, II, III, IV, and the anion in the ionic liquid is sec-octyl phenoxy substituted acetic acid [ CA12] ^-;

the structural formulas of formula I, II, III, IV are respectively:

Wherein R ₁ is C1-C6 alkyl, R ₂ is C6-C12 alkyl, R ₃ is C1-C6 alkyl, R ₄ is C2-C10 alkyl; preferably, R ₂ is a C6-C10 straight chain alkyl group; more preferably, R ₂ is C8 straight chain alkyl;

The structural formula of the acetic acid [ CA12] ^- with the anion being sec-octyl phenoxy is as follows:

2. The ionic liquid of claim 1, wherein R ₁ is tert-butyl,

And/or R ₂ is octyl,

And/or R ₃ is ethyl,

And/or R ₄ is hexyl.

3. An ionic liquid according to claim 1 or 2, wherein the cation is selected from any one of [ bis (3, 3-dimethyl-2-oxybutylene) ] dioctyl ammonium chloride [ OB2DTA ] ⁺, [ bis (1-ethoxy-1-oxybutylene-2-yl) ] dioctyl ammonium bromide [ EO2DTA ] ⁺, (1-ethoxy-1-oxybutylene-2-yl) trioctyl ammonium chloride [ OBTA ] ⁺, (3, 3-dimethyl-2-oxybutylene) trioctyl ammonium bromide [ EOTA ] ⁺;

Wherein the structural formula of [ OB2DTA ] ⁺、[EO2DTA]⁺、[OBTA]⁺、[EOTA]⁺ is respectively as follows:

4. An ionic liquid as claimed in claim 3 wherein the ionic liquid is [OB2DTA]⁺[CA12]^-、[EO2DTA]⁺[CA12]^-、[OBTA]⁺[CA12]^-、[EOTA]⁺[CA12]^-;, preferably [ OB2DTA ] ⁺[CA12]^-.

5. A method of preparing an ionic liquid as claimed in any one of claims 1 to 4, comprising the steps of: the halide of the cation reacts with the anion of the completely sodium soap to obtain the ionic liquid;

For example, the reaction is carried out in a solvent selected from any one of ethanol, methanol, acetonitrile;

For example, the reaction conditions are 50 to 80℃and 6 to 12 hours.

6. The method of claim 5, wherein the cationic halide is prepared by: heating and reacting octylamine with a compound A under the assistance of microwaves to obtain the product;

The octylamine is selected from n-trioctylamine or di-n-octylamine, and the compound A is selected from 1-chloropinacolone or ethyl 2-bromooctoate;

preferably, the molar ratio of the octylamine to the compound A is 1:1-1.5.

7. The preparation method according to claim 5 or 6, wherein the preparation method of the ionic liquid [ OBTA ] ⁺[CA12]^- or [ EOTA ] ⁺[CA12]^- comprises the following steps:

Heating n-trioctylamine and 1-chloropinacolone or 2-bromooctanoic acid ethyl ester under the assistance of microwaves to react to obtain (1-ethoxy-1-oxyoctylene-2-yl) trioctylammonium chloride) or (3, 3-dimethyl-2-oxybutylene) trioctylammonium bromide; then reacting with sec-octyl phenoxy substituted acetic acid of the complete sodium soap to obtain an ionic liquid;

The preparation method of the ionic liquid [ OB2DTA ] ⁺[CA12]^- or [ EO2DTA ] ⁺[CA12]^- comprises the following steps:

Heating di-n-octylamine and 1-chloropinacolone or ethyl 2-bromooctoate with the aid of microwaves to react to obtain [ bis (3, 3-dimethyl-2-oxybutylene butyl) ] dioctyl ammonium chloride or [ bis (1-ethoxy-1-oxybutylene-2-yl) ] dioctyl ammonium bromide; and then reacting with sec-octyl phenoxy substituted acetic acid of the completely sodium soap to obtain the ionic liquid.

8. Use of an ionic liquid as claimed in any one of claims 1 to 4 as an extractant, preferably as an extractant for thorium and/or rare earth ions.

9. An extractant comprising an ionic liquid as claimed in any one of claims 1 to 4.

Preferably, the extractant further comprises a phase modifier,

Wherein, the phase modifier is preferably isooctyl alcohol or TBP tributyl phosphate;

and/or the phase modifier is used in an amount of 5-20% by volume of the organic phase.

10. A process for the recovery of thorium and rare earth comprising the steps of:

1) Calcining the waste residue of the rare earth ore, and leaching the waste residue by hydrochloric acid in a multi-stage way to obtain a waste residue leaching solution;

2) Regulating the pH value of the waste residue leaching solution, and filtering to obtain a supernatant;

3) Adding an extractant into the supernatant in the step 2) for extraction to obtain an organic phase loaded with Th and raffinate; wherein the extractant is the extractant of claim 9;

4) The organic phase loaded with Th in the step 3) is back extracted by acid solution to obtain back extraction liquid rich in Th, and the pH is regulated to obtain precipitate Th (OH) ₄ and precipitate supernatant;

5) Removing impurities from the raffinate obtained in the step 3) to obtain a precipitation supernatant, and enriching the precipitation supernatant with H ₂C₂O₄ to obtain RE ₂(C₂O₄)₃.