Method for separation and enrichment of lithium

Abstract

A method for separation and enrichment of lithium includes the following steps: pretreatment: carrying out at least two dilutions and at least two filtrations on salina aged brine to obtain pretreated brine; separation: separating the pretreated brine via a nanofiltration separation system to obtain nanofiltration permeate and nanofiltration concentrate; first concentration: carrying out first concentration on the nanofiltration permeate via a reverse osmosis system to obtain reverse osmosis concentrate and reverse osmosis permeate; second concentration: carrying out second concentration on the reverse osmosis concentrate via an electrodialysis system to obtain electrodialysis concentrate and electrodialysis permeate, and the electrodialysis concentrate is solution enriching lithium ions. The present application couples several different membrane separation technologies and dilutes the salina aged brine for many times, thereby realizing the purposes of improving separation efficiency of magnesium and lithium and improving the enrichment efficiency of lithium.

Claims

1. A method for a separation and enrichment of lithium, comprising: a pretreatment step: performing at least two dilutions and at least two filtrations on a salina aged brine to obtain a pretreated brine; a separation step: separating the pretreated brine via a nanofiltration separation system to obtain a nanofiltration permeate and a nanofiltration concentrate; a first concentration step: performing a first concentration on the nanofiltration permeate via a reverse osmosis system to obtain a reverse osmosis concentrate and a reverse osmosis permeate; and a second concentration step: performing a second concentration on the reverse osmosis concentrate via an electrodialysis system to obtain an electrodialysis concentrate and an electrodialysis permeate, wherein the electrodialysis concentrate is a solution enriching lithium ions; wherein the reverse osmosis system is formed by connecting a plurality of sections of reverse osmosis units in series, the nanofiltration permeate is subjected to the first concentration via the plurality of sections of the reverse osmosis units in sequence to obtain the reverse osmosis concentrate and the reverse osmosis permeate, and the reverse osmosis permeate is circulated back to the pretreatment step for diluting the salina aged brine; wherein the reverse osmosis system is formed by connecting three sections of reverse osmosis units in series, and a quantity ratio of reverse osmosis membranes of the three sections of the reverse osmosis units is (22-62):(15-45):(5-43); an operation pressure in the first concentration step is 2.0 MPa-10.0 MPa, a concentration of lithium ions in the reverse osmosis concentrate is 2.0 g/L-10 g/L, and a mass ratio of magnesium to lithium in the reverse osmosis concentrate is (0.05-3.0):1.

2. The method according to claim 1, wherein the pretreatment step comprises: after the salina aged brine is subjected to a first dilution of the at least two dilutions, filtering the salina aged brine successively in a multi-media filter and an ultrafiltration system, and performing a second dilution of the at least two dilutions on the salina aged brine to obtain the pretreated brine.

3. The method according to claim 2, wherein in a salina aged brine before the pretreatment step, a concentration of lithium ions in the salina aged brine is 0.2 g/L-5.0 g/L, the mass ratio of magnesium to lithium is (6-180):1; and in the pretreatment step, a dilution multiple of the first dilution of the salina aged brine is 0.5-4.5 times, and a dilution multiple of the second dilution of the salina aged brine is 3.5-20 times after the salina aged brine is filtered via the ultrafiltration system.

4. The method according to claim 3, wherein in the salina aged brine before the pretreatment step, the concentration of the lithium ions in the salina aged brine is 2.5 g/L-4.0 g/L, and the mass ratio of magnesium to lithium is (6-55):1; and in the pretreatment step, the dilution multiple of the salina aged brine after being subjected to the first dilution and the second dilution is 5-20 times.

5. The method according to claim 1, wherein in the separation step, the nanofiltration separation system adopts a monovalent ion selective nanofiltration membrane, the nanofiltration separation system comprises at least two stages of nanofiltration separation devices, and each stage of the at least two stages of the nanofiltration separation devices is formed by connecting a plurality of sections of nanofiltration separation units in series; the pretreated brine is subjected to a first separation of magnesium and lithium via the plurality of sections of the nanofiltration separation units of a first-stage nanofiltration separation device of the at least two stages of the nanofiltration separation devices and subjected to a second separation of magnesium and lithium via the plurality of sections of the nanofiltration separation units of a second-stage nanofiltration separation device of the at least two stages of the nanofiltration separation devices to obtain the nanofiltration permeate and the nanofiltration concentrate, wherein the nanofiltration concentrate is recycled by an energy recovery device.

6. The method according to claim 5, wherein the nanofiltration separation system comprises two stages of nanofiltration separation devices, and each stage of the two stages of the nanofiltration separation devices is formed by connecting three sections of nanofiltration separation units in series; a quantity ratio of nanofiltration membranes of the three sections of the nanofiltration separation units in each stage of the two stages of the nanofiltration separation devices is (35-85):(43-70):(25-55); an operation pressure of the nanofiltration separation system is 1.0 MPa-5.0 MPa, a concentration of lithium ions in the nanofiltration permeate is 0.2 g/L-2.0 g/L, and a mass ratio of magnesium to lithium in the nanofiltration permeate is (0.02-0.5):1.

7. The method according to claim 1, wherein in the electrodialysis step, an ion exchange membrane used in the electrodialysis system is one selected from the group consisting of a homogeneous membrane, a semi-homogeneous membrane and a non-homogeneous membrane; the electrodialysis permeate is circulated back to the first concentration step for concentrating lithium ions, and a mass ratio of magnesium to lithium in the electrodialysis concentrate is (0.05-1.0):1.

8. The method according to claim 7, wherein in the electrodialysis step, the ion exchange membrane used in the electrodialysis system is the homogeneous membrane, and a cation exchange membrane is a CMX homogeneous membrane, and an anion exchange membrane is an AMX homogeneous membrane; a concentration of the lithium ions in the electrodialysis concentrate is 14 g/L-21 g/L, and the mass ratio of magnesium to lithium in the electrodialysis concentrate is (0.07-0.2):1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIGURE is a flow chart of a method for separation and enrichment according to example 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) The salina aged brine in embodiments of the present application is from sulfate type lakes in Qinghai Area. In the salina aged brine, the concentration of lithium ions is 2.5 g/L, and the mass ratio of magnesium to lithium is 50:1.

Example 1

(3) This example provides a method for separation and enrichment of lithium. In combination with the procedure of this example shown in FIGURE, the method of this example comprises the following steps:

(4) Pretreatment: the above salina aged brine was diluted for the first time, the salina aged brine after first dilution was filtered in the multi-media filter to remove mechanical impurities such as partial sediment, subsequently filtered in an organic ultrafiltration system to completely remove impurities, and then diluted for the second time, so as to obtain pretreated brine, wherein the dilution multiple after two dilutions was 15 times.

(5) Separation: the pretreated brine was separated by the nanofiltration separation system to obtain nanofiltration permeate and nanofiltration concentrate, wherein the concentration of lithium ions in the nanofiltration permeate is 1.2 g/L, the concentration of magnesium ions was reduced to 0.06 g/L, and the mass ratio of magnesium to lithium was 0.05:1. Specifically, the nanofiltration separation system adopts the monovalent ion selective nanofiltration membrane. The nanofiltration separation system included two stages of nanofiltration separation devices, and each stage of the nanofiltration separation device was formed by connecting three sections of nanofiltration separation units in series. The pretreated brine was subjected to separation of magnesium and lithium via three sections of nanofiltration separation units of the first-stage nanofiltration separation device and then subjected to further separation of magnesium and lithium via three sections of nanofiltration separation units of the second-stage nanofiltration separation device, so as to obtain nanofiltration permeate and nanofiltration concentrate after two stages of nanofiltration separation, wherein the nanofiltration concentrate was recycled through the energy recovery device to reduce the discharge of waste water. In the nanofiltration separation device of this example, the quantity ratio of nanofiltration membranes of three sections of nanofiltration separation units was (55˜65):(52˜68):(35˜45) in sequence, and the operation pressure of the nanofiltration separation system was 3.6 MPa˜4.5 MPa. Separation of magnesium and lithium can be more effectively realized by using the quantity ratio of various nanofiltration membranes. Meanwhile, since the nanofiltration separation in this example was carried out under the condition of ultrahigh pressure of greater than 3.6 MPa, it is beneficial to further improving the separation effect of magnesium and lithium and improving the content of lithium ions in the nanofiltration permeate.

(6) First concentration: the nano filtration permeate was subjected to first concentration via the reverse osmosis system to obtain reverse osmosis concentrate and reverse osmosis permeate, wherein the concentration of lithium ions in the reverse osmosis concentrate was 5 g/L, and the mass ratio of magnesium to lithium was 0.07:1. Specifically, the reverse osmosis system was formed by connecting three reverse osmosis units in series, each section of reverse osmosis unit respectively contained different quantities of reverse osmosis membranes, the nanofiltration permeate was subjected to first concentration via various reverse osmosis units in turn to obtain reverse osmosis concentrate and reverse osmosis permeate, the reverse osmosis permeate was circulated back to the pretreatment step for diluting salina aged brine so as to improve the utilization rate of the reverse osmosis permeate. In the reverse osmosis system of this example, the quantity ratio of reverse osmosis membranes of various sections of the reverse osmosis units was (38˜46):(25˜35):(20˜28), and the operation pressure of the first concentration was 7.0 MPa. Through a manner of adopting the quantity ratio of multi-section different reverse osmosis membranes, the permeability of lithium in the reverse osmosis permeate can be sufficiently reduced, which is conductive to enrichment of lithium in the reverse osmosis concentrate.

(7) Second concentration: a homogeneous membrane was used as an ion exchange membrane of an electrodialysis system, the reverse osmosis concentrate was subjected to second concentration via the electrodialysis system to obtain electrodialysis concentrate and electrodialysis permeate, wherein the concentration of lithium ions in the electrodialysis concentrate was 18 g/L, and the mass ratio of magnesium to lithium was 0.07:1. Accordingly, after two concentrations, the concentration of enriched lithium ions in this example had reached the concentration of lithium ions required for preparing high-purity lithium salts. In addition, the electrodialysis permeate was circulated back to the first concentration step for concentrating lithium ions. Specifically, the electrodialysis permeate was blended with the nanofiltration permeate obtained from the separation step, recovery of residual lithium and reuse of electrodialysis permeate were realized through the reverse osmosis system for first concentration.

(8) Compositions of salina aged brine adopted in this example and solution in various separation and concentration stages are as shown in Table 1

(9) TABLE-US-00001 TABLE 1 Compositions of salina aged brine and solution in various separation and concentration stages in example 1 Ion concentration (g/L) Mass ratio of magnesium Stage Mg.sup.2+ Li.sup.+ to lithium Salina aged brine 125 2.5 50 Nanofiltration 0.06 1.2 0.05 permeate Reverse osmosis 0.35 5.0 0.07 concentrate Electrodialysis 1.42 20 0.07 concentrate

(10) The method in this example realizes the separation of magnesium and lithium and efficient enrichment of lithium in sulfate salt lake brine. The finally obtained electrodialysis concentrate (i.e., second concentrate) can be directly used for preparing high-purity lithium salts due to its high lithium ion concentration. The yield of lithium ions is more than 87% in the whole separation process of magnesium and lithium, and the yield of lithium ions is more than 95% in the whole process of concentrating lithium ions. It can be seen that, the method in this example can effectively improve the utilization rate of lithium ions in the whole process.

Example 2

(11) This example provides a method for separation and enrichment of lithium, comprising the following steps:

(12) Pretreatment: the above salina aged brine was diluted for the first time, the salina aged brine after first dilution was filtered in the multi-media filter to remove mechanical impurities such as partial sediment, subsequently filtered in an organic ultrafiltration system to completely remove impurities, and then diluted for the second time, so as to obtain pretreated brine, wherein the dilution multiple after two dilutions was 5 times.

(13) Separation: the pretreated brine was separated by the nanofiltration separation system to obtain nanofiltration permeate and nanofiltration concentrate, wherein the concentration of lithium ions in the nanofiltration permeate wash is 0.2 g/L, the concentration of magnesium ions was reduced to 0.10 g/L, and the mass ratio of magnesium to lithium was 0.5:1. Specifically, the nanofiltration separation system adopts a monovalent ion selective nanofiltration membrane, the nanofiltration separation system included two stages of nanofiltration separation devices, and each stage of the nanofiltration separation device was formed by connecting three sections of nanofiltration separation units in series; the pretreated brine was subjected to separation of magnesium and lithium via three sections of nanofiltration separation units of the first-stage nanofiltration separation device and then subjected to further separation of magnesium and lithium via three sections of nanofiltration separation units of the second-stage nanofiltration separation device, so as to obtain nanofiltration permeate and nanofiltration concentrate after two stages of nanofiltration separation, wherein the nanofiltration concentrate was recycled by an energy recovery device to reduce the discharge of waste water. In the nanofiltration separation device of this example, the quantity ratio of nanofiltration membranes of three sections of nanofiltration separation units was (55˜65):(52˜68):(35˜45), and the operation pressure of the nanofiltration separation system was 4.5 MPa. Separation of magnesium and lithium was more effectively realized by using the quantity ratio of various nanofiltration membranes. Meanwhile, since the nanofiltration separation in this example was carried out at the ultrahigh pressure of 4.5 MPa, it was beneficial to further improving the separation effect of magnesium and lithium and improving the content of lithium ions in the naofiltration permeate.

(14) First concentration: the nanofiltration permeate was subjected to first concentration via the reverse osmosis system to obtain reverse osmosis concentrate and reverse osmosis permeate, wherein the concentration of lithium ions in the reverse osmosis concentrate was 2.0 g/L, the mass ratio of magnesium to lithium was 0.5:1. Specifically, the reverse osmosis system was formed by connecting three reverse osmosis units in series, each section of reverse osmosis unit respectively contained different quantities of reverse osmosis membranes, the nanofiltration permeate was subjected to first concentration via various sections of reverse osmosis units in turn to obtain reverse osmosis concentrate and reverse osmosis permeate, the reverse osmosis permeate was circulated back to the pretreatment step for diluting salina aged brine so as to improve the utilization rate of the reverse osmosis permeate. In the reverse osmosis system of this example, the quantity ratio of reverse osmosis membranes of various sections of the reverse osmosis units was (22˜34):(15˜22):(32˜43), and the operation pressure of the first concentration was 7.0 MPa. Through a manner of adopting the quantity ratio of multi-section different reverse osmosis membranes, the permeability of lithium in reverse osmosis permeate was sufficiently reduced, which was conductive to enrichment of lithium in the reverse osmosis concentrate.

(15) Second concentration: a homogeneous membrane was used as an ion exchange membrane of an electrodialysis system, the reverse osmosis concentrate was subjected to second concentration via the electrodialysis system to obtain electrodialysis concentrate and electrodialysis permeate, wherein the concentration of lithium ions in the electrodialysis concentrate was 10.0 g/L, and the mass ratio of magnesium to lithium was 0.52:1. Accordingly, after two concentrations, the concentration of enriched lithium ions in this example had reached the concentration of lithium ions required for preparing high-purity lithium salts. In addition, the electrodialysis permeate was circulated back to the first concentration step for concentrating lithium ions. Specifically, the electrodialysis permeate was blended with the nanofiltration permeate obtained from the separation step, recovery of residual lithium and reuse of electrodialysis permeate were realized through the reverse osmosis system for first concentration.

(16) Compositions of salina aged brine adopted in this example and solution in various separation and concentration stages are as shown in Table 2

(17) TABLE-US-00002 TABLE 2 Compositions of salina aged brine and solution in various separation and concentration stages in example 2 Ion concentration (g/L) Mass ratio of magnesium Stage Mg.sup.2+ Li.sup.+ to lithium Salina aged brine 125 2.5 50 Nanofiltration 0.10 0.20 0.5 permeate Reverse osmosis 1.0 2.0 0.5 concentrate Electrodialysis 5.2 10.0 0.52 concentrate

(18) The method in this example realizes the separation of magnesium and lithium and efficient enrichment of lithium in sulfate salt lake brine. The finally obtained electrodialysis concentrate (i.e., second concentrate) can be directly used for preparing high-purity lithium salts due to its high lithium ion concentration. The yield of lithium ions is more than 65% in the whole separation process of magnesium and lithium, and the yield of lithium ions is more than 65% in the whole process of concentrating lithium ions. It can be seen that, the method in this example can effectively improve the utilization rate of lithium ions in the whole process.

Example 3

(19) This example provides a method for separation and enrichment of lithium, comprising the following steps:

(20) Pretreatment: the above salina aged brine was diluted for the first time, the salina aged brine after first dilution was filtered in the multi-media filter to remove mechanical impurities such as partial sediment, subsequently filtered in an organic ultrafiltration system to completely remove impurities, and then diluted for the second time, so as to obtain pretreated brine, wherein the dilution multiple after two dilutions was 10 times.

(21) Separation: the pretreated brine was separated by the nanofiltration separation system to obtain nanofiltration permeate and nanofiltration concentrate, wherein the concentration of lithium ions in the nanofiltration permeate was 0.36 g/L, the concentration of magnesium ions was reduced to 0.14 g/L, and the mass ratio of magnesium to lithium was 0.38:1. Specifically, the nanofiltration separation system adopts a monovalent ion selective nanofiltration membrane, the nanofiltration separation system included two stages of nanofiltration separation devices, and each stage of the nanofiltration separation device was formed by connecting three sections of nanofiltration separation units in series; the pretreated brine was subjected to separation of magnesium and lithium via three sections of nanofiltration separation units of the first-stage nanofiltration separation device and then subjected to further separation of magnesium and lithium via three sections of nanofiltration separation units of the second-stage nanofiltration separation device, so as to obtain the nanofiltration permeate and the nanofiltration concentrate after two stages of nanofiltration separation, wherein the nanofiltration concentrate was recycled by an energy recovery device to reduce the discharge of waste water. In the nanofiltration separation device of this example, the quantity ratio of nanofiltration membranes of three sections of nanofiltration separation units was (55˜65):(52˜68):(35˜45), and the operation pressure of the nanofiltration separation system was 4.5 MPa. Separation of magnesium and lithium can be more effectively realized by using the quantity ratio of various nanofiltration membranes. Meanwhile, since the nanofiltration separation in this example was carried out at the ultrahigh pressure of 4.5 MPa, it was beneficial to further improving the separation effect of magnesium and lithium and improving the content of lithium ions in the nanofiltration permeate.

(22) First concentration: the nanofiltration permeate was subjected to first concentration via the reverse osmosis system to obtain reverse osmosis concentrate and reverse osmosis permeate, wherein the concentration of lithium ions in the reverse osmosis concentrate was 2.5 g/L, and the mass ratio of magnesium to lithium was 0.39:1. Specifically, the reverse osmosis system was formed by connecting three sections of reverse osmosis units in series, each section of reverse osmosis unit respectively contained different quantities of reverse osmosis membranes, the nanofiltration permeate was subjected to first concentration via various sections of reverse osmosis units in turn to obtain reverse osmosis concentrate and reverse osmosis permeate, the reverse osmosis permeate was circulated back to the pretreatment step for diluting the salina aged brine so as to improve the utilization rate of the reverse osmosis permeate. In the reverse osmosis system of this example, the quantity ratio of reverse osmosis membranes of various sections of reverse osmosis units was (22˜34):(15˜22):(32˜43), and the operation pressure of the first concentration was 7.0 MPa. Through a manner of adopting the quantity ratio of multi-section different reverse osmosis membranes, the permeability of lithium in reverse osmosis permeate can be sufficiently reduced, which was conductive to enrichment of lithium in the reverse osmosis concentrate.

(23) Second concentration: a homogeneous membrane was used as an ion exchange membrane of an electrodialysis system, the reverse osmosis concentrate was subjected to second concentration via the electrodialysis system to obtain electrodialysis concentrate and electrodialysis permeate, wherein the concentration of lithium ions in the electrodialysis concentrate was 9.5 g/L, and the mass ratio of magnesium to lithium was 0.43:1. Accordingly, after two concentrations, the concentration of enriched lithium ions in this example had reached the concentration of lithium ions required for preparing high-purity lithium salts. In addition, the electrodialysis permeate was circulated back to the first concentration step for concentrating lithium ions. Specifically, the electrodialysis permeate was blended with the nanofiltration permeate obtained from the separation step, recovery of residual lithium and reuse of electrodialysis permeate were realized through the reverse osmosis system for first concentration.

(24) Compositions of salina aged brine adopted in this example and solution in various separation and concentration stages are as shown in Table 3

(25) TABLE-US-00003 TABLE 3 Compositions of salina aged brine and solution in various separation and concentration stages in example 3 Ion concentration (g/L) Mass ratio of magnesium Stage Mg.sup.2+ Li.sup.+ to lithium Salina aged brine 125 2.5 50 Nanofiltration 0.14 0.36 0.38 permeate Reverse osmosis 0.97 2.5 0.39 concentrate Electrodialysis 4.58 12 0.38 concentrate

(26) The method in this example realizes the separation of magnesium and lithium and efficient enrichment of lithium in sulfate salt lake brine. The finally obtained electrodialysis concentrate (i.e., second concentrate) can be directly used for preparing high-purity lithium salts due to its high lithium ion concentration. The yield of lithium ions was greater than 73% in the whole separation process of magnesium and lithium, the yield of lithium ions was greater than 79% in the whole separation process of magnesium and lithium. It can been seen that the method of the present application can effectively improve the utilization rate of lithium ions in the whole process.

Example 4

(27) This example provides a method for separation and enrichment of lithium, comprising the following steps:

(28) Pretreatment: the above salina aged brine was diluted for the first time, the salina aged brine after first dilution was filtered in the multi-media filter to remove mechanical impurities such as partial sediment, subsequently filtered in an organic ultrafiltration system to completely remove impurities, and then diluted for the second time, so as to obtain pretreated brine, wherein the dilution multiple after two dilutions was 20 times.

(29) Separation: the pretreated brine was separated by the nanofiltration separation system to obtain nanofiltration permeate and nanofiltration concentrate, wherein the concentration of lithium ions in the nanofiltration permeate was 1.1 g/L, the concentration of magnesium ions was reduced to 0.06 g/L, and the mass ratio of magnesium to lithium was 0.05:1. Specifically, the nanofiltration separation system adopts a monovalent ion selective nanofiltration membrane, the nanofiltration separation system included two stages of nanofiltration separation devices, and each stage of the nanofiltration separation device was formed by connecting three sections of nanofiltration separation units in series; the pretreated brine was subjected to separation of magnesium and lithium via three sections of nanofiltration separation units of the first-stage nanofiltration separation device and then subjected to separation of magnesium and lithium via three sections of nanofiltration separation units of the second-stage nanofiltration separation device, so as to obtain nanofiltration permeate and nanofiltration concentrate after two stages of nanofiltration separation, wherein the nanofiltration concentrate was recycled by an energy recovery device to reduce the discharge of waste water. In the nanofiltration separation device of this example, the quantity ratio of nanofiltration membranes of three sections of nanofiltration separation units was (55˜65):(52˜68):(35˜45), and the operation pressure of the nanofiltration separation system was 4.5 MPa. Separation of magnesium and lithium can be more effectively realized by using the quantity ratio of various nanofiltration membranes. Meanwhile, since the nanofiltration separation in this example was carried out at the ultrahigh pressure of 4.5 MPa, it was beneficial to further improving the separation effect of magnesium and lithium and improving the content of lithium ions in the nanofiltration permeate.

(30) First concentration: the nanofiltration permeate was subjected to first concentration via the reverse osmosis system to obtain reverse osmosis concentrate and reverse osmosis permeate, wherein the concentration of lithium ions in the reverse osmosis concentrate was 4.7 g/L, and the mass ratio of magnesium to lithium was 0.08:1. Specifically, the reverse osmosis system was formed by connecting three sections of reverse osmosis units in series, each section of reverse osmosis unit respectively contained different quantities of reverse osmosis membranes, the nanofiltration permeate was subjected to first concentration via various sections of reverse osmosis units in turn to obtain reverse osmosis concentrate and reverse osmosis permeate, the reverse osmosis permeate was circulated back to the pretreatment step for diluting the salina aged brine so as to improve the utilization rate of the reverse osmosis permeate. In the reverse osmosis system of this example, the quantity ratio of reverse osmosis membranes of various sections of reverse osmosis units was (22˜34):(15˜22):(32˜43), and the operation pressure of the first concentration was 7.0 MPa. Through a manner of adopting the quantity ratio of multi-section different reverse osmosis membranes, the permeability of lithium in the reverse osmosis permeate can be sufficiently reduced, which was conductive to enrichment of lithium in the reverse osmosis concentrate.

(31) Second concentration: a homogeneous membrane was used as an ion exchange membrane of an electrodialysis system, and the reverse osmosis concentrate was subjected to second concentration via the electrodialysis system to obtain electrodialysis concentrate and electrodialysis permeate, wherein the concentration of lithium ions in the electrodialysis concentrate was 17 g/L, and the mass ratio of magnesium to lithium was 0.06:1. Accordingly, after two concentrations, the concentration of enriched lithium ions in this example had reached the concentration of lithium ions required for preparing high-purity lithium salts. In addition, the electrodialysis permeate was circulated back to the step of first concentration for concentration of lithium ions. Specifically, the electrodialysis permeate was blended with the nanofiltration permeate obtained from the separation step, recovery of residual lithium and reuse of electrodialysis permeate were realized through the reverse osmosis system for first concentration.

(32) Compositions of salina aged brine adopted in this example and solution in various separation and concentration stages are as shown in Table 4

(33) TABLE-US-00004 TABLE 4 Compositions of salina aged brine and solution in various separation and concentration stages in example 3 Ion concentration (g/L) Mass ratio of magnesium Stage Mg.sup.2+ Li.sup.+ to lithium Salina aged brine 125 2.5 50 Nanofiltration 0.06 1.1 0.05 permeate Reverse osmosis 0.38 4.7 0.08 concentrate Electrodialysis 1.02 17 0.06 concentrate

(34) The method in this example realizes the separation of magnesium and lithium and efficient enrichment of lithium in sulfate salt lake brine. The finally obtained electrodialysis concentrate (i.e., second concentrate) can be directly used for preparing high-purity lithium salts due to its high lithium ion concentration. The yield of lithium ions was greater than 88% in the whole separation process of magnesium and lithium, the yield of lithium ions was greater than 95.6% in the whole separation process of magnesium and lithium. It can been seen that the method of The present application can effectively improve the utilization rate of lithium ions in the whole process.

(35) It should be understood that the above embodiments are only for illustrating the present application but not intended to limit the scope of protection of the present application. At the same time, it should be understood that after reading the technical content of the present application, those skilled in the art can make appropriate changes to the conditions and steps in the technical solution of the disclosure without departing from the principle of the present application, so as to realize the final technical solution. All these equivalents fall within the scope of protection defined in the appended claims of the present application.