Method for efficiently separating magnesium and lithium from salt lake brine and simultaneously preparing high-purity magnesium oxide and battery-grade lithium carbonate

Abstract

This invention provides a method for efficiently separating magnesium and lithium from salt lake brine, and simultaneously preparing high-purity magnesium oxide and battery-grade lithium carbonate. The detailed processing steps are as follows: (1) adding urea into the brine to dissolve, (2) placing the solution into the reactor for hydrothermal reaction, the magnesium ion will precipitate and enter the solid phase; (3) filtering and drying the production to get the magnesium carbonate solid, while the lithium ion remains in the liquid phase; (4) after directly concentration and precipitation, the battery-grade lithium carbonate can be obtained, while the calcination of solid-phase product results in the high-purity magnesium oxide. In this method, urea is used as the precipitant to separate magnesium and lithium in salt lake without introducing any new metal ion, and the brine solution is not diluted. The solid product is white and fluffy powder, which is easy to filter and separate. The extraction rate of lithium is high than 94%, and the purity of MgO obtained by calcination is higher than 99.5%.

Claims

1. A method for the efficient separation of magnesium and lithium from salt lake brine, comprising: adding urea into the brine to dissolve to obtain a solution; placing the solution into a reactor for hydrothermal reaction to obtain a product, so that magnesium ions will precipitate and enter a solid phase; filtering and drying the product to get a magnesium carbonate solid, while lithium ions remain in a liquid phase, so that separation of magnesium and lithium is realized.

2. The method according to claim 1 wherein the step of adding urea into the brine to dissolve to obtain a solution comprises: adding urea into the brine to form a solution, the molar concentration ratio of magnesium ions to urea being, the step of placing the solution into a reactor for hydrothermal reaction comprises: transferring the solution obtained to the reactor, the reactor made of stainless steel and lined with polytetrafluoroethylene (PTFE), and conducting the hydrothermal reaction under 90-150° C. for 8-24 h, and the step of filtering and drying the product comprises: at the end of the hydrothermal reaction, cooling down a temperature of the reactor to room temperature, and then conducting decompression filtration to achieve solid-liquid separation to obtain a solid product and a filtrate, and drying the solid product at 40-60° C. for 3-8 hours without washing to obtain a white powdered magnesium carbonate solid, the lithium ions remaining in the filtrate so that separation of magnesium and lithium is achieved.

3. The method according to claim 2 wherein concentrations of cations within the brine are: [Li.sup.+]=1-20 g/L, [Mg.sup.2+]=10-100 g/L, [K.sup.+]=2-20 g/L, and [Nal.sup.+]=1−30 g/L.

4. The method according to claim 2, wherein a filling volume of the solution in the reactor does not exceed ⅔ of a total volume of the reactor.

5. The method according to claim 2, wherein the white powdered magnesium carbonate solid is Mg.sub.5(CO.sub.3).sub.4(OH).sub.2.Math.4H.sub.2O, MgCO.sub.3, or a mixture of Mg.sub.5(CO.sub.3).sub.4(OH).sub.2.Math.4H.sub.2O and MgCO.sub.3.

6. A method for efficiently separating magnesium and lithium from salt lake brine and simultaneously preparing high-purity magnesium oxide, comprising: adding urea into the brine to dissolve to obtain a solution; placing the solution into a reactor for hydrothermal reaction to obtain a product, so that magnesium ions will precipitate and enter a solid phase; filtering and drying the product to get a magnesium carbonate solid, while lithium ions remain in a liquid phase, so that separation of magnesium and lithium is realized, and calcining the magnesium carbonate solid to obtain high-purity magnesium oxide.

7. The method according to claim 6 wherein the step of calcining the magnesium carbonate solid comprises: raising a calcining temperature to 500-1000° C. for 1-8 h in air atmosphere with a rising rate of 1-10° C./min.

8. A method for efficiently separating magnesium and lithium from salt lake brine and simultaneously preparing a battery-grade lithium carbonate, comprising: adding urea into the brine to dissolve to obtain a solution; placing the solution into a reactor for hydrothermal reaction to obtain a product, so that magnesium ions will precipitate and enter a solid phase; filtering and drying the product to get a magnesium carbonate solid, while lithium ions remain in a liquid phase; and concentrating and precipitating the liquid phase to obtain the battery-grade lithium carbonate.

9. The method according to claim 8 wherein the step of concentrating and precipitating the liquid phase to obtain the battery-grade lithium carbonate comprises: heating and evaporating the liquid phase to achieve a lithium ion concentration of 20-30 g/L; adding sodium carbonate according to the Li.sup.+/CO.sub.3.sup.2− molar ratio of 0.5-1.5, and stirring continuously for 30-90 min at 50-100° C.; conducting decompression filtration to achieve solid-liquid separation and washing a solid obtained after the solid-liquid separation for 2-5 times by deionized water, and drying the solid at 90-150° C. for 1-5 h to obtain the battery-grade lithium carbonate.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is the XRD spectrum of the solid phase product in example 2.

(2) FIG. 2 is the SEM image of the solid phase product in example 2.

(3) FIG. 3 is the XRD spectrum of MgO obtained in example 2.

DETAILED DESCRIPTION OF EMBODIMENTS

Example 1

(4) A. Weighting 300 mL of salt lake brine, in which the specific concentrations of metal ions are [Li.sup.+]=2.25 g/L, [Mg.sup.2+]=28.49 g/L, [K.sup.+]=2.56 g/L, and [Na.sup.+]=3.47 g/L respectively; the mass ratio of magnesium to lithium is 12.67; adding 42.234 g of urea to prepare the solution.

(5) B. Transferring the solution obtained in step A to a stainless steel reactor lined with PTFE (500 mL), to conduct hydrothermal reaction at 120° C. for 12 h;

(6) C. At the end of the reaction, the temperature of the reactor is cooled down to room temperature, and then the solid/liquid is separated by decompression filtration to obtain the solid product and the filtrate; the solid product is dried at 60° C. for 4 hours to obtain the white powdered magnesium carbonate solids (Mg.sub.5(CO.sub.3).sub.4(OH).sub.2.4H.sub.2O and Mg CO.sub.3).

(7) Calcination of the solid product obtained in step C: raising the temperature to 600° C. for 2 h in the air atmosphere with rising rate of 10° C./min. A high purity magnesium oxide product is obtained. The molecular formula is MgO, and the purity is more than 99.5%.

(8) The filtrate obtained in step C is heated and evaporated to a lithium ion concentration of 22 g/L; adding the sodium carbonate into the filtrate according to the Li.sup.+/CO.sub.3.sup.2− mole ratio of 0.8, and stirring at 70° C. for 60 min; the solid-liquid is separated by decompression filtration, washed by deionized water for 5 times, dried at 100° C. for 2 h to obtain battery-grade lithium carbonate with the purity of 99.70%.

Example 2

(9) A. Weighting 300 mL of salt lake brine, in which the specific concentrations of metal ions are [Li.sup.+]=2.25 g/L, [Mg.sup.2+]=28.49 g/L, [K.sup.+]=2.56 g/L, and [Na.sup.+]=3.47 g/L respectively; the mass ratio of magnesium to lithium is 12.67; adding 84.468 g of urea to prepare the solution.

(10) B. Transferring the solution obtained in step A to a stainless steel reactor lined with PTFE (500 mL), to conduct hydrothermal reaction at 120° C. for 12 h;

(11) C. At the end of the reaction, the temperature of the reactor is cooled down to room temperature, and then the solid/liquid is separated by decompression filtration to obtain the solid product and the filtrate; the solid product is dried at 60° C. for 4 hours to obtain the white powdered magnesium carbonate solid. The solid-phase products obtained by the reaction are irregular lamellar structure with the size ranging from 0.1 μm to 60 μm. The XRD characterization results show that they are a mixture of Mg.sub.5(CO.sub.3).sub.4(OH).sub.2.4H.sub.2O and MgCO.sub.3. The phase and morphology characterization of the solid-phase products are shown in FIG. 1.

(12) Calcination of the solid product obtained in step C: raising the temperature to 600° C. for 2 h in the air atmosphere with rising rate of 10° C./min. A high purity magnesium oxide product is obtained. The molecular formula is MgO, and the purity is more than 99.5%. The XRD characterization of solid-phase is shown in FIG. 2.

(13) The filtrate obtained in step C is heated and evaporated to a lithium ion concentration of 24 g/L; adding the sodium carbonate into the filtrate according to the Li.sup.+/CO.sub.3.sup.2+ mole ratio of 0.8, and stirring at 80° C. for 60 min; the solid-liquid is separated by decompression filtration, washed by deionized water for 5 times, dried at 100° C. for 2 h to obtain battery-grade lithium carbonate with the purity of 99.85%.

Example 3

(14) A. Weighting 300 mL of salt lake brine, in which the specific concentrations of metal ions are [Li.sup.+]=2.25 g/L, [Mg.sup.2+]=28.49 g/L, [K.sup.+]=2.56 g/L, and [Na.sup.+]=3.47 g/L respectively; the mass ratio of magnesium to lithium is 12.67; adding 126.702 g of urea to prepare the solution.

(15) B. Transferring the solution obtained in step A to a stainless steel reactor lined with PTFE (500 mL), to conduct hydrothermal reaction at 120° C. for 12 h;

(16) C. At the end of the reaction, the temperature of the reactor is cooled down to room temperature, and then the solid/liquid is separated by decompression filtration to obtain the solid product and the filtrate; the solid product is dried at 60° C. for 4 hours to obtain the white powdered magnesium carbonate solids (Mg.sub.5(CO.sub.3).sub.4(OH).sub.2.4H.sub.2O and Mg CO.sub.3).

(17) Calcination of the solid product obtained in step C: raising the temperature to 600° C. for 2 h in the air atmosphere with rising rate of 10° C./min. A high purity magnesium oxide product is obtained. The molecular formula is MgO, and the purity is more than 99.5%.

(18) The filtrate obtained in step C is heated and evaporated to a lithium ion concentration of 26 g/L; adding the sodium carbonate into the filtrate according to the Li.sup.+/CO.sub.3.sup.2+ mole ratio of 1, and stirring at 90° C. for 60 min; the solid-liquid is separated by decompression filtration, washed by deionized water for 5 times, dried at 100° C. for 2 h to obtain battery-grade lithium carbonate with the purity of 99.65%.

Example 4

(19) A. Weighting 300 mL of salt lake brine, in which the specific concentrations of metal ions are [Li.sup.+]=2.25 g/L, [Mg.sup.2+]=28.49 g/L, [K.sup.+]=2.56 g/L, and [Na.sup.+]=3.47 g/L respectively; the mass ratio of magnesium to lithium is 12.67; adding 168.936 g of urea to prepare the solution.

(20) B. Transferring the solution obtained in step A to a stainless steel reactor lined with PTFE (500 mL), to conduct hydrothermal reaction at 120° C. for 12 h;

(21) C. At the end of the reaction, the temperature of the reactor is cooled down to room temperature, and then the solid/liquid is separated by decompression filtration to obtain the solid product and the filtrate; the solid product is dried at 60° C. for 4 hours to obtain the white powdered magnesium carbonate solids (Mg.sub.5(CO.sub.3).sub.4(OH).sub.2.4H.sub.2O and Mg CO.sub.3).

(22) Calcination of the solid product obtained in step C: raising the temperature to 600° C. for 2 h in the air atmosphere with rising rate of 10° C./min. A high purity magnesium oxide product is obtained. The molecular formula is MgO, and the purity is more than 99.5%.

(23) The filtrate obtained in step C is heated and evaporated, concentrated to a lithium ion concentration of 28 g/L; adding the sodium carbonate into the filtrate according to the Li.sup.+/CO.sub.3.sup.2+ mole ratio of 1, and stirring at 100° C. for 60 min; the solid-liquid is separated by decompression filtration, washed by deionized water for 5 times, dried at 100° C. for 2 h to obtain battery-grade lithium carbonate with the purity of 99.68%.

(24) The salt lake brine used in the above examples belongs to chloride ion type, and the composition of each ion is shown in Table 1.

(25) TABLE-US-00001 TABLE 1 the concentration values of ions in the salt lake brine Ions Mg.sup.2+ Li.sup.+ K.sup.+ Na.sup.+ Cl.sup.− SO.sub.4.sup.2− Concentration (g/L) 10~100 1~20 2~20 1~30 100~260 10~60