METHOD FOR PRODUCING LITHIUM CARBONATE FROM LOW-LITHIUM BRINE BY SEPARATING MAGNESIUM AND ENRICHING LITHIUM

Abstract

The present invention discloses a method for producing lithium carbonate from a low-lithium brine by separating magnesium and enriching lithium. A salt-lake brine is used as a raw material and is converted into halide salts through dehydration by evaporation and separation by crystallization; the halide salts are directly extracted using trialkyl phosphate or a mixture of trialkyl phosphate and monohydric alcohol, and an organic extraction phase as well as remaining halide salts are obtained after solid-liquid separation; reverse extraction is performed on the organic extraction phase to obtain a lithium-rich solution with a low magnesium-to-lithium ratio, and lithium carbonate is obtained after concentration and removal of magnesium by alkalization. The used solid-liquid extraction method is simple with no co-extraction agent used, and a solute distribution driving force is strong, unaffected by phase equilibrium of the brine extraction agent. The mass ratio of magnesium-to-lithium significantly decreases in the extraction phase.

Claims

1. A method for producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium, comprising: a. preparation of halide salts: taking insolation-condensed salt-lake brine with a high magnesium-lithium mass ratio or taking old brine extracted by potassium salt, condensing the brine by heating and evaporation, separating out halide salts containing crystal water; and a water content of the halide salts is 30%60% in a total mass of the halide salts; b. solid-liquid extraction: extracting the halide salts by using trialkyl phosphate or a mixture of trialkyl phosphate and monohydric alcohol as an organic phase, and a mass (kg) to volume (L) ratio of a solid-liquid extraction phase is 1.0:(0.55.0); c. solid-liquid separation: filtering a mixture of the solid-liquid extraction, and obtaining an organic extracted phase as well as remaining halide salts after two-phase separation; d. reverse extraction: reverse extracting the organic extracted phase by using water as a reverse extraction agent; a volume ratio of water to liquid phase is 1.0:(0.510.0), and a stage of reverse extraction is 15; e. liquid-liquid separation: still standing a liquid-liquid reverse extracted mixture, separating a water phase after liquid layering, obtaining enriched Li.sup.+ solution with a decreased mass ratio of magnesium to lithium, and obtaining a concentrated water phase after reverse extraction by evaporation and concentration; f. removal of magnesium by alkalization: adding sodium carbonate or sodium hydroxide into the concentrated water phase after reverse extraction, precipitating magnesium carbonate or magnesium hydroxide, controlling pH of a solution to be more than 10, precipitating Mg.sup.2+ completely, separating by filtration; and g. preparation of lithium carbonate: adding sodium carbonate into the water phase after the removal of magnesium by alkalization, producing precipitation of the lithium carbonate, filtering, drying and obtaining lithium carbonate product.

2. The method for producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium according to claim 1, wherein in the step b, the solid-liquid extraction comprises: first extracting the halide salts, heating and melting the remaining halide salts, controlling the water content until the halide salts containing crystal water are separated out, adding trialkyl phosphate or a mixture of trialkyl phosphate and monohydric alcohol in a proportion of 1.0:(0.55.0) in a mass volume ratio of solid to liquid, and performing a second stage extraction, and a stage of the solid-liquid extraction is 15.

3. The method for producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium according to claim 1, wherein the solid-liquid extraction is in multi-stage cross flow or multi-stage counter flow.

4. The method for producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium according to claim 1, wherein an extraction agent trialkyl phosphate used in the solid-liquid extraction comprises one or more of compounds consisting of: tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tri-n-heptyl phosphate, trioctyl phosphate and isomerides thereof; the monohydric alcohol comprises one or more of compounds consisting of saturated monohydric alcohols with carbon numbers between C6C20; and a volume ratio of trialkyl phosphate and monohydric alcohol is 1.0: (0.24.0).

5. The method for producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium according to claim 1, wherein in the step e, when a mass ratio of magnesium to lithium is larger than 1.0 in a water phase solution of the reverse extraction, the water phase solution of the reverse extraction is taken as a raw material of the brine in next-stage solid-liquid extraction, and a new separation process for lithium and magnesium to further reduce the magnesium to lithium ratio is taken by preparation of halide salts, solid-liquid extraction, solid-liquid separation, reverse extraction and liquid-liquid separation from the step a to the step e.

6. The method for producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium according to claim 1, wherein the extraction agent trialkyl phosphate or the mixture of the trialkyl phosphate and the monohydric alcohol is reused after reverse extraction and liquid-liquid separation.

7. The method for producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium according to claim 1, characterized in that the raw material of the brine is provided from different kinds of lithium contained salt-lake brine, underground brine, oil field brine, well brine or a condensing solution of production of salt from seawater.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 shows a process flow diagram of producing lithium carbonate from low-lithium brine by separating magnesium and enriching lithium in present invention.

DETAILED DESCRIPTION

[0026] A further description of the present invention is provided with embodiments as follows.

Embodiment 1

[0027] The content of Li.sup.+, Mg.sup.2+ and SO.sub.4.sup.2+ are respectively 2.24 g/L, 118.00 g/L, 39.87 g/L and a magnesium to lithium ratio is equivalent to 52.58 in old brine in a salt lake located in Qaidam Basin of Qinghai province. 350 mL of the old brine was taken into a 1000 mL beaker and was heated for condensation above a temperature adjustable furnace. Water was evaporated, which accounted for 25% of total mass of the brine, and the solution were changed into hydrated halide salts after cooling. The salts were transferred into a mechanical mixing vessel, and 334.5 mL of trihexyl phosphate was added to achieve a mass volume ratio equivalent to 1:1 (g/mL). Solid-liquid extraction was carried out for 30 mins under room temperature. Then solid liquid mixtures were transferred in a sand core funnel and vacuum filtration was carried out, and the extracted organic-phase filtrate and remaining halide salts were obtained. The remaining halide salts were heated and melted to completion. Then the melted halide salts were cooled and completely separated out. Hydrated halide salts were obtained for the second time. Multiple stage extraction: 2.sup.nd stage, 3.sup.rd stage and 4.sup.th stage extractions were successively carried out in a cross-flow manner according to the operation requirements of the first time.

[0028] The concentrations of Li.sup.+ and Mg.sup.2+ during the extraction process were sampled and analyzed respectively by a Japanese Shimadzu atomic absorption spectrophotometer AA-7000 and an EDTA titrimetric volumetry. The results are shown in table. 1.

[0029] Table. 1 results of four stage solid liquid cross-flow extraction by trihexyl phosphate from an old brine with a magnesium to lithium mass ratio of 52.6 in a salt lake located in Qinghai province

TABLE-US-00001 E(Li.sup.+)/%.sup.a E(Mg.sup.2+)/%.sup.b m.sub.o(Mg.sup.2+)/m.sub.o(Li.sup.+).sup.c Stage of Single Single Accumulative Single Accumulative m.sub.s(Mg.sup.2+)/ extraction stage Accumulative stage stages stage stages m.sub.s(Li.sup.+).sup.d 1 21.91 21.91 4.75 4.75 11.40 11.40 64.14 2 23.45 40.22 4.77 9.30 13.05 12.15 79.79 3 25.71 55.59 4.83 13.67 14.98 12.93 102.21 4 27.03 67.59 4.86 17.87 18.36 13.90 133.28 wherein, .sup.astands for extraction rate of Li.sup.+; .sup.bstands for extraction rate of Mg.sup.2+; .sup.cstands for mass ratio of magnesium to lithium in organic phase; .sup.dstands for mass ratio of magnesium to lithium in the remaining halide salts.. The meaning of symbol is the same in following tables.

[0030] The extracted phases from four stages were merged and organic extraction phase and water were respectively added in a separating funnel with a phase ratio of organic phase to water V.sub.o/V.sub.w equivalent to 1:1 and reverse extraction was carried out. The mixtures were vibrated for 30 mins repeatedly in a temperature-constant cooling water bath SHA-2A at 20 C. and at a speed of 200 r/min. The solutions were then placed still for 30 mins and a reverse extracted water phase was finally obtained after phase separation, with a decreased magnesium to lithium ratio. Samples were analyzed and results showed that reverse extraction rate of Li.sup.+ is up to 80.3%; reverse extraction rate of Mg.sup.2+ was 56.0%; and a mass ratio magnesium to lithium declined to 9.7 in the reserve extracted water phase. In the concentrated reverse extracted solution with a low magnesium to lithium ratio, sodium carbonate solution was added to remove majority of Mg.sup.2+, then sodium hydroxide was again added into the solution after separation, to completely precipitate magnesium. Solution of sodium carbonate was added into the filtered solution to form precipitation, and separation and desiccation were carried out to obtain a lithium carbonate product.

Embodiment 2

[0031] 350 mL of the old brine in embodiment 1 was taken into a 1000 mL beaker, in which 11.49 g of LiCl.H.sub.2O with its purity analyzed as 97% was added. The mass ratio of magnesium to lithium in the mixture was equal to 20.00. The solution was heated for condensation above a temperature adjustable furnace. Water was evaporated, which accounted for 25% of total mass of the starting brine, and the solution were changed into hydrated halide salts after cooling. The salts were transferred into a mechanical mixing vessel, and 366.8 mL of trihexyl phosphate was added to achieve a mass volume ratio equivalent to 1:1 (g/mL). Solid-liquid extraction was carried out for 30 mins under room temperature. Then solid liquid mixtures were transferred in a sand core funnel and vacuum filtration was carried out, and the extracted organic-phase filtrate and remaining halide salts were obtained. The remaining halide salts were heated and melted to completion. Then the melted halide salts were cooled and separated out. Hydrated halide salts were obtained for the second time. Multiple stage extraction: 2.sup.nd stage, 3.sup.rd stage and 4.sup.th stage extractions were successively carried out in a cross flow according to the operation requirements of the first time.

[0032] The concentrations of Li.sup.+ and Mg.sup.2+ during the extraction process were sampled and analyzed. The results are shown in table.2.

[0033] Table. 2 results of four stage solid liquid cross-flow extraction by tributyl phosphate from an old brine with a magnesium to lithium mass ratio of 20.0 in a salt lake located in Qinghai province

TABLE-US-00002 E(Li.sup.+)/% E(Mg.sup.2+)/% m.sub.o(Mg.sup.2+)/m.sub.o(Li.sup.+) Stage of Single Accumulative Single Accumulative Single Accumulative m.sub.s(Mg.sup.2+)/m.sub.s extraction stage stages stage stages stage stages (Li.sup.+) 1 18.00 18.00 5.31 5.31 5.90 5.90 23.09 2 19.64 34.11 5.10 10.14 6.00 5.95 27.26 3 22.34 48.83 5.16 14.78 6.30 6.05 33.29 4 25.13 61.69 4.94 19.00 6.55 6.16 42.27

[0034] The extracted phases from four stages were merged and organic extraction phase and water were respectively added in a separating funnel with a phase ratio of organic phase to water V.sub.o/V.sub.w equivalent to 1:1 and reverse extraction was carried out. The mixtures were vibrated for 30 mins repeatedly in a temperature-constant cooling water bath SHA-2A at 20 C. and at a speed of 200 r/min. The solutions were then placed still for 30 mins and a reverse extracted water phase was finally obtained after phase separation, with a decreased magnesium to lithium ratio. Samples were analyzed and results showed that reverse extraction rate of Li.sup.+ was up to 81.5%; reverse extraction rate of Mg.sup.2+ was 55.1%; and a mass ratio magnesium to lithium declined to 4.2 in the reserve extracted water phase. In the concentrated reverse extracted solution with a low magnesium to lithium ratio, sodium carbonate solution was added to remove majority of Mg.sup.2+, then sodium hydroxide was again added into the solution after separation, to completely precipitate magnesium. Solution of sodium carbonate was added into the filtered solution to form precipitation, and separation and desiccation were carried out to obtain a lithium carbonate product.

Embodiment 3

[0035] 350 mL of the old brine in embodiment 1 was taken into a 1000 mL beaker and the mass ratio of magnesium to lithium in the mixture was equal to 52.58. The brine was heated for condensation above a temperature adjustable furnace. Water was evaporated, which accounted for 25% of total mass of the brine, and the solution were changed into hydrated halide salts after cooling. The salts were transferred into a mechanical mixing vessel, and 354.7 mL of tributyl phosphate was added to achieve a mass to volume ratio equivalent to 1:1 (g/mL). Solid-liquid extraction was carried out for 30 mins under room temperature. Then solid liquid mixtures were transferred in a sand core funnel and vacuum filtration was carried out, and the extracted organic-phase filtrate and remaining halide salts were obtained. The remaining halide salts were heated and melted to completion. Then the melted halide salts were cooled and separated out. Hydrated halide salts were obtained for the second time. Multiple stage extraction: 2.sup.nd stage, 3.sup.rd stage and 4.sup.th stage extractions were successively carried out in a cross flow according to the operation requirements of the first time.

[0036] The concentrations of Li.sup.+ and Mg.sup.2+ during the extraction process were sampled and analyzed. The results are shown in table.3.

[0037] Table. 3 results of four stage solid liquid cross-flow extraction by trihexyl phosphate from an old brine with a magnesium to lithium mass ratio of 52.6 in a salt lake located in Qinghai province

TABLE-US-00003 E(Li.sup.+)/% E(Mg.sup.2+)/% m.sub.o(Mg.sup.2+)/m.sub.o(Li.sup.+) Stage of Single Accumulative Single Accumulative Single Accumulative m.sub.s(Mg.sup.2+)/ extraction stage stages stage stages stage stages m.sub.s(Li.sup.+) 1 47.21 47.21 16.26 16.26 18.11 18.11 83.41 2 49.26 73.22 15.90 29.58 26.92 21.24 138.26 3 56.17 88.26 15.29 40.34 37.62 24.04 267.24 4 59.17 95.21 14.88 49.22 67.20 27.18 557.18

[0038] The extracted phases from four stages were merged and organic extraction phase and water were respectively added in a separating funnel with a phase ratio of organic phase to water V.sub.o/V.sub.w equivalent to 1:1 and reverse extraction was carried out. The mixtures were vibrated for 30 mins repeatedly in a temperature-constant cooling water bath SHA-2A at 20 C. and at a speed of 200 r/min. The solutions were then placed still for 30 mins and a reverse extracted water phase was finally obtained after phase separation, with a decreased magnesium to lithium ratio. Samples were analyzed and results showed that reverse extraction rate of Li.sup.+ was up to 94.1%; reverse extraction rate of Mg.sup.2+ was 93.1%; and a mass ratio magnesium to lithium declined to 26.8 in the reserve extracted water phase. Condensation was carried out in the reverse extracted water phase. A new separation process for lithium and magnesium was taken by preparation of halide salts, solid-liquid extraction, solid-liquid separation, reverse extraction and liquid-liquid separation, until the magnesium to lithium ratio declined below 10. Sodium carbonate solution was added to remove majority of Mg.sup.2+ in the concentrated reverse extracted solution with a low magnesium to lithium ratio, then sodium hydroxide was again added into the solution after separation, to completely precipitate magnesium. Solution of sodium carbonate was added into the filtered solution to form precipitation, and separation and desiccation were carried out to obtain a lithium carbonate product.

Embodiment 4

[0039] 350 mL of the old brine in embodiment 1 was taken into a 1000 mL beaker, in which 11.52 g of LiCl.H.sub.2O with its purity analyzed of 97% was added. The mass ratio of magnesium to lithium in the mixture was equal to 19.97. The solution was heated for condensation above a temperature adjustable furnace. Water was evaporated, which accounted for 25% of total mass of the starting brine, and the solution were changed into hydrated halide salts after cooling. The salts were transferred into a mechanical mixing vessel, and 366.1 mL of tributyl phosphate was added to achieve a mass to volume ratio equivalent to 1:1 (g/mL). Solid-liquid extraction was carried out for 30 mins under room temperature. Then solid liquid mixtures were transferred in a sand core funnel and vacuum filtration was carried out, and the extracted organic-phase filtrate and remaining halide salts were obtained. The remaining halide salts were heated and melted to completion. Then the melted halide salts were cooled and separated out. Hydrated halide salts were obtained for the second time. Multiple stage extraction: 2.sup.nd stage, 3.sup.rd stage and 4.sup.th stage extractions were successively carried out in a cross flow according to the operation requirements of the first time.

[0040] The concentrations of Li.sup.+ and Mg.sup.2+ during the extraction process were sampled and analyzed. The results are shown in table.4.

[0041] Table. 4 results of four stage solid liquid cross-flow extraction by tributyl phosphate from an old brine with a magnesium to lithium mass ratio of 20.0 in a salt lake located in Qinghai province

TABLE-US-00004 E(Li.sup.+)/% E(Mg.sup.2+)/% m.sub.o(Mg.sup.2+)/m.sub.o(Li.sup.+) Stage of Single Accumulative Single Single Accumulative extraction stage stages stage Accumulative stage stages m.sub.s(Mg.sup.2+)/m.sub.s(Li.sup.+) 1 40.07 40.07 16.01 16.01 7.97 7.97 27.97 2 43.14 65.92 16.02 29.47 10.39 8.92 41.31 3 44.35 81.03 15.75 40.57 14.67 9.99 62.54 4 44.99 89.57 15.83 49.98 22.00 11.14 95.69

[0042] The extracted phases from four stages were merged and organic extraction phase and water were respectively added in a separating funnel with a phase ratio of organic phase to water V.sub.o/V.sub.w equivalent to 1:1 and reverse extraction was carried out. The mixtures were vibrated for 30 mins repeatedly in a temperature-constant cooling water bath SHA-2A at 20 C. and at a speed of 200 r/min. The solutions were then placed still for 30 mins and a reverse extracted water phase was finally obtained after phase separation, with a decreased magnesium to lithium ratio. Samples were analyzed and results showed that reverse extraction rate of Li.sup.+ was up to 94.7%; reverse extraction rate of Mg.sup.2+ was 92.6%; and a mass ratio magnesium to lithium declined to 10.9 in the reserve extracted water phase. In the concentrated reverse extracted solution with a low magnesium to lithium ratio, sodium carbonate solution was added to remove majority of Mg.sup.2+, then sodium hydroxide was again added into the solution after separation, to completely precipitate magnesium. Solution of sodium carbonate was added into the filtered solution to form precipitation, and separation and desiccation were carried out to obtain a lithium carbonate product.

Embodiment 5

[0043] 20 mL of the old brine in embodiment 1 was taken into a 100 mL beaker and the mass ratio of magnesium to lithium was equal to 52.58. The brine was heated for condensation above a temperature adjustable furnace. Water was evaporated, which accounts for 25% of total mass of the brine, and the solution were changed into hydrated halide salts after cooling. The salts was transferred into a mechanical mixing vessel, and 20 mL of tributyl phosphate as well as 20 mL of 2-ethylhexanol were added to achieve a mass to volume ratio equivalent to 1:2 (g/mL). Solid-liquid extraction was carried out for 30 mins under room temperature. Then solid liquid mixtures were transferred in a sand core funnel and vacuum filtration was carried out, obtaining the extracted organic-phase filtrate and remaining halide salts. The remaining halide salts were dissolved in water and fix its volume to 1000 mL in a volumetric flask. Samples were taken to analyze the concentration of Li.sup.+ and Mg.sup.2+ thereof. The results showed that a extraction rate of Li.sup.+ is 50.2%; a extraction rate of Mg.sup.2+ is 4.1% and a mass ratio of magnesium to lithium is 4.3 in the organic extracted phase.

[0044] The extracted phases from four stages are merged and organic extraction phase and water were respectively added in a separating funnel with a phase ratio of organic phase to water V.sub.o/V.sub.w equivalent to 2:1 and reverse extraction was carried out. The mixtures were vibrated for 30 mins repeatedly in a temperature-constant cooling water bath SHA-2A at 20 C. and at a speed of 200 r/min. The solutions were then placed still for 30 mins and a reverse extracted water phase was finally obtained after phase separation, with a decreased magnesium to lithium ratio. Samples were analyzed and results showed that reverse extraction rate of Li.sup.+ is up to 96.5%; reverse extraction rate of Mg.sup.2+ is 87.2% and a mass ratio magnesium to lithium declined to 3.9 in the reserve extracted water phase. In the concentrated reverse extracted solution with a low magnesium to lithium ratio, sodium carbonate solution was added to remove majority of Mg.sup.2+, then sodium hydroxide was again added into the solution after separation, to completely precipitate magnesium. Solution of sodium carbonate was added into the filtered solution to form precipitation, and separation and desiccation were carried out to obtain a lithium carbonate product.

Embodiment 6

[0045] 20 mL of the old brine in embodiment 1 was taken into a 100 mL beaker and the mass ratio of magnesium to lithium in the mixture was equal to 52.58. The brine was heated for condensation above a temperature adjustable furnace. Water was evaporated, which accounted for 25% of total mass of the brine, and the solution were changed into hydrated halide salts after cooling. The salts were transferred into a mechanical mixing vessel, and 20 mL of tributyl phosphate as well as 20 mL of dl-2-octanol were added to achieve a mass to volume ratio equivalent to 1:2 (g/mL).

[0046] Solid-liquid extraction was carried out for 30 mins under room temperature. Then solid liquid mixtures were transferred in a sand core funnel and vacuum filtration was carried out, and the extracted organic-phase filtrate and remaining halide salts were obtained. The remaining halide salts were dissolved in water and fix its volume to 1000 mL in a volumetric flask. Samples were taken to analyze the concentration of Li.sup.+ and Mg.sup.2+ thereof. The results showed that a extraction rate of Li.sup.+ was 32.4%; a extraction rate of Mg.sup.2+ was 4.6% and a mass ratio of magnesium to lithium was 7.4 in the organic extracted phase.

[0047] The extracted phases from four stages were merged and organic extraction phase and water were respectively added in a separating funnel with a phase ratio of organic phase to water V.sub.o/V.sub.w equivalent to 2:1 and reverse extraction was carried out. The mixtures were vibrated for 30 mins repeatedly in a temperature-constant cooling water bath SHA-2A at 20 C. and at a speed of 200 r/min. The solutions w then placed still for 30 mins and a reverse extracted water phase was finally obtained after phase separation, with a decreased magnesium to lithium ratio. Samples were analyzed and results showed that reverse extraction rate of Li.sup.+ was up to 91.6%; reverse extraction rate of Mg.sup.2+ was 87.6%; and a mass ratio magnesium to lithium declined to 7.1 in the reserve extracted water phase. In the concentrated reverse extracted solution with a low magnesium to lithium ratio, sodium carbonate solution was added to remove majority of Mg.sup.2+, then sodium hydroxide was again added into the solution after separation, to completely precipitate magnesium. Solution of sodium carbonate was added into the filtered solution to form precipitation, and separation and desiccation were carried out to obtain a lithium carbonate product.

Embodiment 7

[0048] The concentration of Li.sup.+, Mg.sup.2+ and SO.sub.4.sup.2+ were respectively 0.87 g/L, 104.37 g/L, 11.13 g/L, with a magnesium to lithium ratio equivalent to 120.00 in an old brine in a salt lake located in Qaidam Basin of Qinghai province. 20 mL of the old brine in embodiment 1 was taken into a 100 mL beaker and the mass ratio of magnesium to lithium in the mixture was equal to 52.58. The brine was heated for condensation above a temperature adjustable furnace. Water was evaporated, which accounted for 30% of total mass of the brine, and the solution were changed into hydrated halide salts after cooling. The salts were transferred into a mechanical mixing vessel, and 18.33 mL of tributyl phosphate as well as 18.34 mL of 2-ethylhexanol were added to achieve a mass to volume ratio equivalent to 1:2 (g/mL). Solid-liquid extraction was carried out for 30 mins under room temperature. Then solid liquid mixtures were transferred in a sand core funnel and vacuum filtration was carried out, and the extracted organic-phase filtrate and remaining halide salts were obtained. The remaining halide salts were dissolved in water and fix its volume to 1000 mL in a volumetric flask. Samples were taken to analyze the concentration of Li.sup.+ and Mg.sup.2+ thereof. The results showed that a extraction rate of Li.sup.+ was 55.5%; a extraction rate of Mg.sup.2+ was 4.2% and a mass ratio of magnesium to lithium was 9.1 in the organic extracted phase.

[0049] The extracted phases from four stages were merged and organic extraction phase and water were respectively added in a separating funnel with a phase ratio of organic phase to water V.sub.o/V.sub.w equivalent to 2:1 and reverse extraction was carried out. The mixtures were vibrated for 30 mins repeatedly in a temperature-constant cooling water bath SHA-2A at 20 C. and at a speed of 200 r/min. The solutions were then placed still for 30 mins and a reverse extracted water phase was finally obtained after phase separation, with a decreased magnesium to lithium ratio. Samples were analyzed and results showed that reverse extraction rate of Li.sup.+ was up to 93.6%; reverse extraction rate of Mg.sup.2+ was 88.2%; and a mass ratio magnesium to lithium declined to 8.5 in the reserve extracted water phase. In the concentrated reverse extracted solution with a low magnesium to lithium ratio, sodium carbonate solution was added to remove majority of Mg.sup.2+, then sodium hydroxide was again added into the solution after separation, to completely precipitate magnesium. Solution of sodium carbonate was added into the filtered solution to form precipitation, and separation and desiccation were carried out to obtain a lithium carbonate product.

[0050] The above contents are only preferred embodiments of the present invention, and embodiments of present invention is not limited to this. The present invention have different kinds of modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement and the like made within spirits and principles of the present invention shall be included in the protection scope of the present invention.