Backflow cascade novel process for producing lithium-7 isotope

Abstract

Provided is a backflow cascade novel process for producing a lithium-7 isotope. The process comprises an upper backflow section, an extraction section, an enrichment section, a lower backflow section, and a product acquiring section. Upper backflow phase-conversion liquid and lower backflow phase-conversion liquid are respectively added to the upper backflow section and the lower backflow section, and upper backflow phase-conversion liquid and lower backflow phase-conversion liquid of the lithium material are controlled; the product is precisely acquired in the product acquiring section; an organic phase is added to the upper backflow section, and is recycled in the lower backflow section. By means of cascade connection with a high-performance liquid separator, environmental protection, high efficiency, and multi-level enrichment of the lithium-7 isotope are achieved, and a high-abundance lithium-7 isotope product is obtained.

Claims

1. A method for producing lithium-7 isotope which comprises the following steps: (1) continuously and countercurrently running an aqueous phase and an organic phase; wherein the organic phase sequentially passes through an upper backflow section, an extraction section, an enrichment section, and a lower backflow section circularly, and wherein the aqueous phase sequentially flows through the lower backflow section, the enrichment section, the extraction section and the upper backflow section, and then flows out; (2) adding a lower backflow phase-conversion liquid into the lower backflow section; adding an upper backflow phase-conversion liquid into the upper backflow section; and adding a reverse extraction liquid into the product acquiring section; (3) adding a feed liquid comprising lithium-7 into the enrichment section, said feed liquid being extracted by the extraction section and the upper backflow section, and enriched in the enrichment section, wherein the organic phase from the enrichment section is separated into two parts: (a) one part flowing into the product acquiring section for reverse extraction, thus obtaining an enriched product comprising the lithium-7 isotope; and (b) the other part flowing into the lower backflow section.

2. The method of claim 1, wherein the method further comprises a step of discharging waste from the extraction section.

3. The method of claim 1, wherein in step (3): the organic phase extracts the feed liquid comprising lithium-7 in the enrichment section, the extraction section, the upper backflow section; and/or lower backflow phase-conversion liquid extracts the organic phase in the lower backflow section; and/or the reverse extraction liquid extracts the organic phase in the product acquiring section so as to obtain the product.

4. The method of claim 1, wherein the method further comprises the following step: after extracting the organic phase in the lower backflow section with lower backflow phase-conversion liquid, the aqueous phase from the lower backflow section backflows into the enrichment section for circular extraction.

5. The method of claim 4, wherein the method comprises the following step: the organic phase from the lower backflow section flows through the product acquiring section into the upper backflow section.

6. The method of claim 1, wherein the organic phase comprises an extractively effective amount of a compound of formula (I): ##STR00003## wherein in the formula (I), Z is oxygen atom, sulfur atom, or nitrogen atom substituted by R.sub.9, wherein R.sub.9 is hydrogen, C.sub.1-6 alkyl-sulfonyl, C.sub.1-6 haloalkyl-sulfonyl, benzenesulfonyl or C.sub.1-6 alkyl-benzenesulfonyl; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are independently hydrogen, C.sub.1-6 alkyl, C.sub.1-6 haloalkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl, C.sub.1-6 alkoxy, C.sub.3-6 cycloalkyl, halogen or phenyl.

7. The method of claim 1, wherein the method further comprises one or more of the following features: the upper backflow phase-conversion liquid being an aqueous solution containing a solute selected from the group consisting of: sodium hydroxide, potassium hydroxide, cesium hydroxide, ammonium hydroxide, and combinations thereof; the lower backflow phase-conversion liquid being an aqueous solution containing a solute selected from the group consisting of: HCl, H.sub.2SO.sub.4, HBr, NaCl, NH.sub.4Cl, NaBr, (NH.sub.4).sub.2SO.sub.4, Na.sub.2SO.sub.4, NaNO.sub.3, NH.sub.4NO.sub.3, KCl, K.sub.2SO.sub.4, and combinations thereof; and the reverse extraction liquid being an aqueous solution containing a solute selected from the group consisting of: HCl, H.sub.2SO.sub.4, HBr, NaCl, NH.sub.4Cl, (NH.sub.4).sub.2SO.sub.4, Na.sub.2SO.sub.4, and combinations thereof.

8. The method of claim 1, wherein each of the upper backflow section, the extraction section, the enrichment section, the lower backflow section and the product acquiring section comprises a cascade connected liquid-liquid separation equipment.

9. The method of claim 1, wherein the concentration of Li-7 in the aqueous phase at the exit of the upper backflow section and the concentration of Li-7 in the organic phase at the exit of the lower backflow section are less than 10.sup.2 mol/L; and/or the ratio between Li-7 molar flow N1 at the exit of the product acquiring section and Li-7 molar flow N2 at the exit of the enrichment section is N1:N2=0.001 to 0.025; and/or the method further comprises: controlling a fluctuation of a flow rate for the aqueous phase and the organic phase, wherein the fluctuation of flow rate is within 0.5%.

10. The method of claim 6, wherein the organic phase further comprises a synergic extractant.

11. The method of claim 8, wherein the upper backflow section is constituted by X cascade connected centrifugal extractors, wherein 2X20.

12. The method of claim 8, wherein the extraction section is constituted by N cascade connected centrifugal extractors, wherein 10N500.

13. The method of claim 8, wherein the enrichment section is constituted by M cascade connected centrifugal extractors, wherein 10M500.

14. The method of claim 8, wherein the lower backflow section is constituted by Y cascade connected centrifugal extractors, wherein 2Y20.

15. The method of claim 8, wherein the upper product acquiring section is constituted by Z cascade connected centrifugal extractors, wherein 2Z20.

16. The method of claim 8, wherein the liquid-liquid separation equipment is a centrifugal extractor.

17. The method of claim 9, wherein N1:N2=0.001 to 0.02.

18. The method of claim 9, wherein the concentration of Li-7 in the aqueous phase at the exit of the upper backflow section and the concentration of Li-7 in the organic phase at the exit of the lower backflow section are less than 510.sup.3 mol/L.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a design diagram of the backflow cascade process of the present invention;

(2) FIG. 2 shows the relationship between refluxing time and abundance of Li-7 in Example 1 of the invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

(3) Through long-term and intensive research aiming to overcome deficiencies of the amalgam method in the field, the inventors have developed a method to easily produce Li-7 products in high abundance. The method is environmental friendly and free of pollution; the organic phase can easily enrich Li-7 isotope and can be recycled for further use. The upper and lower backflows and phase inversions are easy and efficient; the product acquiring section can achieve precise acquisitions, and the multiple stage cascade can obtain Li-7 isotope product in high abundance.

Terms

(4) As used herein, the term C.sub.1-6 alkyl refers to a linear or branched alkyl having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, or the like

(5) The term C.sub.3-6 cycle alkyl refers to a cyclic alkyl having 3 to 6 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cycloheptyl, or the like.

(6) The term C.sub.2-6 alkenyl refers to alkenyls having 2 to 6 carbon atoms, such as vinyl, propenyl, isopropenyl, butenyl, isobutenyl, sec-butenyl, tertiary butenyl, or the like

(7) The term C.sub.2-6 alkynyl refers to alkynyls having 2 to 6 carbon atoms, such as ethynyl, propynyl, iso-alkynyl group, butynyl, iso-alkynyl group, sec-butynyl, tert-butynyl, or the like.

(8) The term C.sub.1-6 alkoxy refers to a linear or branched alkoxy having 1 to 6 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, or the like.

(9) The term halogenated means that one or more hydrogen atom (s) of the group is substituted by a halogen atom.

(10) The term halogen refers to F, Cl, Br and I.

(11) Single Stage Separation Factor

(12) As used herein, the terms single stage separation factor and separation factor can be used interchangeably, and both refer to the rate between the relative content before and after separation of two substances in a single unit (single-stage separation operation).

(13) Lithium isotopes are separated by chemical exchange. The isotopes exchange reaction is expressed as follows:
.sup.7LiA+.sup.6LiB.sup.7LiB+.sup.6LiA

(14) wherein A and B represent different coordination environment of lithium ion in two phases, such as organic phase and aqueous phase.

(15) The separation coefficient of isotopes ( value) represents the single stage separation effect of lithium isotopes, that is to say, the quotient of the specific value of lithium isotopes in B phase divided by the specific value of lithium isotopes in A phase:

(16) $=\frac{\left[{}^7\mathrm{LiB}\right]/\left[{}^6\mathrm{LiB}\right]}{\left[{}^7\mathrm{LiA}\right]/\left[{}^6\mathrm{LiA}\right]}$

(17) The separation coefficient represents the separation degree of two substances after-a certain unit separation operation or a certain separation process, and the value of which reflects how difficult it is to separate two substances. When the separation coefficient is 1, the separation cannot be achieved; the more the separation coefficient deviates from 1, the easier the separation.

(18) A preferred lithium isotope separation system should have a high separation coefficient of isotopes value in the process of chemical exchange; meanwhile, the isotope exchange reaction is quick when two phases contact. Reverse extraction can easily be achieved, thus achieving a multi-stage enriching extraction and the chemical structure of the extractant is stable and economically practical.

(19) Organic Phase (O)

(20) In the backflow cascade process of the present invention for enriching Lithium isotopic, the preferred organic phase comprises a compound of formula (I):

(21) ##STR00002##

(22) wherein, Z is oxygen atom, sulfur atom, or nitrogen atom substituted by R.sub.9, wherein R.sub.9 is selected form the following group: hydrogen, C.sub.1-6 alkyl-sulfonyl, C.sub.1-6 haloalkyl-sulfonyl, benzenesulfonyl or C.sub.1-6 alkyl-benzenesulfonyl; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are independently selected from the group consisting of: hydrogen, C.sub.1-6 alkyl, C.sub.1-6 haloalkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl, C.sub.1-6 alkoxy, C.sub.3-6 cycloalkyl, halogen and phenyl.

(23) In another preferred embodiment, R.sub.9 is hydrogen, trifluoromethanesulfonyl, methylsulfonyl or p-toluenesulfonyl.

(24) In another preferred embodiment, R.sub.1 is hydrogen, C.sub.1-6 alkyl, C.sub.1-6 haloalkyl or phenyl.

(25) In another preferred embodiment, the organic phase further comprises a synergic extractant.

(26) In another preferred embodiment, the synergic extractant is a phosphorus-containing compound, nitrogen-containing compound, alkyl quaternary sulfonium salt compound or sulfoxide compound.

(27) In another preferred embodiment, the synergic extractant is a neutral phosphorus-containing compound, quaternary ammonium salt compound, long-chain alkyl quaternary sulfonium salt compound or neutral sulfoxide compound.

(28) In another preferred embodiment, the synergic extractant comprises: tributyl phosphate (TBP), trioctyl-phosphine oxide (TOPO), dibutyl butanephosphonate (DBBP), butyl dibutylphosphate (BDBP), methylene tetrabutyldiphosphate, trioctyl ammonium oxide, 1,10-phenanthroline, quaternary ammonium salt N263, dimethyl bis (N-octadecyl) ammonium chloride, methyldioctylsulfoniumate chloride, dioctyl sulfoxide, or combinations thereof.

(29) In another preferred embodiment, the diluent comprises: kerosene, octanone, chloroform, carbon tetrachloride, toluene, dimethylbenzene, diethylbenzene, bromobenzene, anisole, nitromethane, 2-methyl cyclohexanone, methyl isobutyl ketone, chlorobenzene, dichlorobenzene, trichlorobenzene, diphenyl ether, or combinations thereof.

(30) In another preferred embodiment, the extraction organic phase further comprises lithium ion.

(31) In another preferred embodiment, the concentration of lithium ion in the extraction organic phase is 0-2.0 mol/L, and preferably 0.01-0.5 mol/L.

(32) The extraction agent in the organic phase plays a role in the extraction of a lithium ion. Further, the organic complex forms a chemical environment different from that of lithium-ion in the aqueous phase, resulting in a relatively large single stage separation factor. The single-stage separation factor of the organic phase extraction agents used in the present invention is generally 1.012 to 1.028. Different from amalgam method, the organic phase extraction agent of the present invention can easily enrich for lithium-7 isotope. During the multi-stage tandem (or cascade) process, the organic phase extraction agent has good chemical stability, and does not decompose over a long period. Therefore, the novel process of the present invention is more advantageous than the amalgam method in the production of a lithium-7 product having an abundance of 99.99% or more.

(33) Reverse Extraction Liquid (C)

(34) In the present invention, the organic phase is reversely extracted by reverse extraction liquid to obtain the product.

(35) During the separation of isotopes, the product taking amount (P) has a great influence on the entire enrichment process. The product taking amount (P) must be smaller than the maximum quantity taken in the entire process, and should be stable and of small fluctuation to ensure stable multi-level isotope enrichment (Chen Guanghua, precious metals, 1982, 1,9).

(36) In the present process, by precisely controlling the lithium-7 molar flow rate in the organic phase at the exit of the product acquiring section and the amount of reverse extraction liquid used, it is ensured that the Li-7 molar flow rate of the lithium enriched product (P) is 0.1 to 2.5% of that of the organic phase at the exit of the enrichment section. Ultimately, a lithium-7 product of high abundance is obtained.

(37) The reverse extraction liquid suitable for use comprises an aqueous solution that has a solute selected from the following group: HCl, H.sub.2SO.sub.4, HBr, NaCl, NH.sub.4Cl, (NH.sub.4).sub.2SO.sub.4, Na.sub.2SO.sub.4, or combinations thereof.

(38) Backflow Phase-Conversion Liquid (S)

(39) In the present invention, preferably, the backflow phase-conversion liquid is added into the system to utilize the extract organic phase in cycle.

(40) The backflow phase-conversion liquid used in the present invention preferably includes upper backflow phase-conversion liquid (S1) and lower backflow phase-conversion liquid (S2), wherein the upper backflow phase-conversion liquid is added in the upper backflow section to efficiently and thoroughly extract and phase-convert the lithium materials in the aqueous phase at the exit of the product acquiring section. The lithium materials are transferred from the aqueous phase into the organic phase by the contacting organic phase and the upper backflow phase-conversion liquid, while the lithium material is discharged from system at the first level of the upper backflow section. Preferably, the lithium concentration in the aqueous phase discharged from the the upper backflow section is <0.01 mol/L, and preferably <510.sup.3 mol/L.

(41) The lower backflow phase-conversion liquid is added into the lower backflow section to reversely extract the organic phase in the enrichment section to efficiently and thoroughly recycle the lithium materials in the organic phase at the exit of the enrichment section. The reversely extracted organic phase backflows into the upper backflow section for circular extraction, an aqueous phase containing Li-7 material forms after the reverse extraction of the lower backflow phase-conversion liquid, and re-enters into the enrichment section for circular extraction. Preferably, the lithium concentration in the organic phase which has been reversely extracted and backflowed in the lower backflow section is <0.01 mol/L, and preferably <5mol/L.

(42) In the present invention, preferably, the upper backflow phase-conversion liquid (S1) comprises an alkaline solute. The alkaline solute is an alkali hydroxide, preferably sodium hydroxide, potassium hydroxide, cesium hydroxide, ammonium hydroxide, and combinations thereof.

(43) In the preferred embodiments of the present invention, the concentration range of the alkaline solute is 1-15 mol/L.

(44) In the present invention, preferably, the lower backflow phase-conversion liquid is an aqueous solution containing a solute selected from the following group: HCl, H.sub.2SO.sub.4, HBr, NaCl, NH.sub.4Cl, NaBr, (NH.sub.4).sub.2SO.sub.4, Na.sub.2SO.sub.4, NaNO.sub.3, NH.sub.4NO.sub.3, KCl, K.sub.2SO.sub.4, or combinations thereof.

(45) High-Purity Lithium-7 Production Technology

(46) The backflow cascade process mainly comprises the following sections: an upper backflow section, an extraction section, an enrichment section, a lower backflow section, and a product acquiring section.

(47) Since the single-stage separation factor of chemical systems is small during the isotopic enrichment process, multistage cumulative enrichment of lithium isotopes can be achieved based on the single stage separation factor of the system and by connecting and controlling the multi-stage extraction equipment using the backflow cascade process of the present invention. Since the separation equipment needs multiple stages and high reliability, the selection of separation equipment is quite important. For incompatible organic phase and aqueous phase, the use of liquid-liquid separation equipment of high efficiency can greatly shorten the equilibrium time, reduce the amount of extractant used and reduce the volume of the extraction equipment. The highly efficient liquid-liquid separation equipment used in the present invention is preferably a centrifugal extractor.

(48) In another preferred embodiment in the present invention, the upper backflow section, the extraction section, the enrichment section, the lower backflow section and the product acquiring section are constituted by a couple of cascade connected liquid-liquid separation equipments, wherein, the upper backflow section can be constituted by X cascade connected centrifugal extractors, wherein 2X20;

(49) the extraction section can be constituted by N cascade connected centrifugal extractors, wherein 10N500;

(50) the enrichment section can be constituted by M cascade connected centrifugal extractors, wherein 10M500;

(51) the lower backflow section can be constituted by Y cascade connected centrifugal extractors, wherein 2Y20;

(52) the product acquiring section can be constituted by Z cascade connected centrifugal extractors, wherein 2Z20.

(53) In order to obtain an isotope product of high abundance, the separation system must be multi-stage and cascaded. Such a separation system requires realization of a strict method of controlling upper and lower back flow backflow, and the backflow should be thorough, easy to use, and of low energy consumption.

(54) As shown in FIG. 1, in the present invention, the upper backflow section is used for upper backflow phase-conversion of lithium materials. The organic extractant (O) is added into the front of the upper backflow section and preferably into the first stage of the upper backflow section, and the upper backflow phase-conversion liquid (S1) is added into the back of upper backflow section, and preferably into the Xth stage of the upper backflow section to achieve highly efficient and thorough extraction and phase inversion of the lithium material in the aqueous phase at the exit of the extracting section. The lithium enters into the extracting section after it is transferred from the aqueous phase into the organic phase. Preferably, after the extraction and phase inversion of upper back flow section, the phase inversion is deemed complete when the lithium concentration of the upper backflow aqueous phase (A) at the exit is within less than 510.sup.3 mol/L.

(55) The extraction section and the enrichment section are mainly used for extraction and enrichment of lithium isotopes. The feed liquid (F) is added at the front of the enrichment section, and preferably at the first stage of the enrichment section, and then it enters into the aqueous phase of the extraction section. The Li-7 depleted waste (W) is obtained after being extracted for several times, in which the Li-7 isotope abundance is less than that in the feed liquid. The organic phase is divided into two parts at the exit of the enrichment section and preferably at the rear-end of the Mth stage of the enrichment section. One part enters into the product acquiring section, and the other part enters into the lower backflow section. A concentrator is installed in front of the aqueous phase in the lower backflow section to conduct necessary concentration of the aqueous phase discharged from the lower backflow section, and then the aqueous phase enters into the enrichment section.

(56) The lower backflow section is used for lower backflow phase-conversion of lithium materials. Adding the lower backflow phase-conversion liquid (S2) into the rear part of the lower backflow section, and preferably into the Yth stage of the lower backflow section conducts reverse extraction and phase inversion of the organic phase in the enrichment section. High efficiency and thorough phase inversion and backflow of lithium materials in the organic phase at the exit of enrichment section are achieved. The lithium materials enter into the enrichment section after being transferred into the aqueous phase from the organic phase.

(57) Preferably, the phase inversion is completed when the lithium concentration of the lower backflow organic phase (O) at the exit is controlled to less than 510.sup.3 mol/L after the extraction and phase inversion in the lower backflow section.

(58) Another important problem during enrichment of isotopes with multi-stage extraction equipment is that the fluctuation of flow rate for two phases should be small. Otherwise, the stage efficiency of the enrichment section and the depletion section is greatly decreased, and the product may not be obtained after multi-stage enrichment. In the present method, the multi-stage enrichment of isotopes is ensured by using the product acquiring section, feeding system and flow stabilization system to control the fluctuation range of the liquid flow rate within 0.5%. The stage efficiency of the enrichment section is high and is more than 90%.

(59) Through several times of repeated experimental verification and continuous optimization, the backflow cascade process of the present invention controls the lithium material concentration at exit of the upper and lower backflow section. Meanwhile, by using an effective product acquiring section, feeding system and flow stabilization system, the flow fluctuations during the cascade process are accurately measured and controlled. Ultimately, a multi-stage enrichment of lithium isotopes is achieved. For example, in an embodiment of the present invention, 98.55% of Li-7 isotope-enriched product is obtained.

(60) The Main Advantages of the Present Invention are:

(61) (1) By using the upper and lower backflow sections, highly efficient and thorough phase inversion of lithium materials in organic and aqueous phase at the exit is achieved. The run off of the lithium materials is controlled, thus ensuring multi-stage accumulation and enrichment of isotopes and obtaining a Li-7 isotope product of high abundance.

(62) (2) The process of the present invention is well-designed and easy to operate. By using an effective product acquiring section and flow stability system, the quantity of materials and fluctuation of flow rate of the entire backflow technology are controlled, and the isotope enrichment process has high efficiency.

(63) (3) When compared to the amalgam method, the method of the present invention has reduced the risks of mercury and is environmental friendly. The method of the present invention is also superior in producing products in which the Li-7 abundance is more than 99.99%.

(64) (4) The organic phase can be recycled, and the aqueous phase of the upper backflow section can be re-concentrated to recycle the alkaline liquid, thus significantly reducing the cost of lithium isotope enrichment and having considerable economic benefits.

(65) (5) By using the highly efficient centrifugal extractors and flow stabilization system, the balancing time, the extraction solvent quantity used and the equipment size are greatly reduced, thus saving manpower and costs.

(66) The present invention will be further illustrated below with reference to specific examples. It should be understood that these examples are only to illustrate the invention but are not to limit the scope of the invention. The experimental methods with no specific conditions described in the following examples are generally performed under the conventional conditions, or according to the manufacture's instructions. Unless indicated otherwise, parts and percentage are calculated by weight.

Example 1

(67) The lines were connected according to the design diagram of the backflow cascade process figure, wherein the stage number of every section was as follows: 10 stages in the upper backflow section, 37 stages in the extraction section, 63 stages in the enrichment section, 10 stages in the lower backflow section and 5 stages in the product acquiring section.

(68) The organic phase comprised 7-trifluoromethyl-10-hydroxy benzoquinoline (the concentration was 0.38 mol/L), synergistic extractant and diluents. The nuclear magnetism of 7-trifluoromethyl-10-hydroxy benzoquinoline: 1H NMR: 8.91 (d, J=4.2 Hz, 1H), 8.37 (d, J=8.7 Hz, 1H), 8.21 (d, J=9.3 Hz, 1H), 8.00 (d, J=8.7 Hz, 1H), 7.83 (d, J=9.3 Hz, 1H), 7.68 (dd, J=8.4 Hz, J=4.8 Hz, 1H), 7.24 (d, J=8.7 Hz, 1H). .sup.19F NMR: .sup.58.0 (s, 3F).

(69) Upper backflow phase-conversion liquid (S1): sodium hydroxide aqueous solution having a concentration of 4 mol/L.

(70) Lower backflow phase-conversion liquid (S2): NaCl aqueous solution having a concentration of 3 mol/L.

(71) The liquid-liquid separation equipment-high-speed centrifugal extractor.

(72) The aqueous phase and the organic phase were continuously run, and the lithium concentration in the aqueous phase at the exit of the upper backflow section was measured to be 4*10.sup.4 mol/L, while the lithium concentration in the organic phase at exit of the lower backflow section was measured to be 2*10.sup.4 mol/L.

(73) The backflow cascade process was taken. At different times during the process, the change in isotope Li-7 abundance of the product (P) was determined, as shown in FIG. 2.

(74) The backflow process steadily ran for 230 hours to achieve balance. The Li-7 molar flow in the product (P) of the product acquiring section was controlled at 0.9% of that in the organic phase at the exit of the enrichment section. It was determined that the abundance of isotope Li-7 in the feed liquid (F) at entrance was 95.81%, while that of the enriched product (P) was 98.55%.

(75) The stage efficiency of the enrichment section was 90%.

Example 2

(76) The lines were connected according to the design diagram of backflow cascade process, wherein the stage number of every section was as follows: 10 stages in the upper backflow section, 14 stages in the extraction section, 26 stages in the enrichment section, 10 stages in the lower backflow section and 5 stages in the product acquiring section.

(77) The organic phase comprised 9-trifluoromethyl-10-hydroxy benzoquinoline (concentration was 0.65 mol/L), synergistic extractant and diluents. The nuclear magnetism of 9-trifluoromethyl-10-hydroxy benzoquinoline: 1H NMR: 8.85 (d, J=4.8 Hz, 1H), 8.33 (d, J=8.4 Hz, 1H), 7.85 (d, J=8.7 Hz, 1H), 7.83 (d, J=8.7 Hz, 1H), 7.75 (d, J=9.3 Hz, 1H), 7.64 (dd, J=8.4 Hz, J=4.8 Hz, 1H), 7.43 (d, J=8.4 Hz, 1H). .sup.19F NMR: .sup.62.1 (s, 3F).

(78) Upper backflow phase-conversion liquid (S1): potassium hydroxide aqueous solution having a concentration of 6 mol/L.

(79) Lower backflow phase-conversion liquid (S2): KCl aqueous solution having a concentration of 0.8 mol/L.

(80) The liquid-liquid separation equipment: high-speed centrifugal extractor.

(81) The aqueous phase and the organic phase were continuously run, and the lithium concentration in the aqueous phase at exit of the upper backflow section was measured to be 3*10.sup.4 mol/L, while the lithium concentration in the organic phase at exit of the lower backflow section was measured to be 2*10.sup.4 mol/L.

(82) The backflow process steadily ran for 45 hours to achieve balance. The Li-7 molar flow in the product (P) of the product acquiring section was controlled at 1% of that in the organic phase at the exit of the enrichment section. It was determined that the abundance of isotope Li-7 in the feed liquid (F) at entrance was 92.50%, while that of the enriched product (P) was: 94.21%.

(83) The stage efficiency of the enrichment section was 91%.

(84) It can be seen that by using the backflow cascade process of the present invention, the lithium-7 isotopes was efficient, fast, multi-stage enriched, and a high abundance lithium-7 product was obtained. The process is simple and reasonable, enrichment section is highly efficient. The organic phase has good chemical stability and can be recycled, so it is environmental friendly as well as economical.

(85) All literature mentioned in the present application are incorporated herein by reference, as though each one is individually incorporated by reference. Additionally, it should be understood that after reading the above teachings, those skilled in the art can make various changes and modifications to the present invention. These equivalents also fall within the scope defined by the appended claims.