A method for separating ions of the same charge using a non-selective ion exchange membrane

Abstract

The present invention relates to the field of ion separation, and discloses a method for separating ions of the same charge using a non-selective ion exchange membrane, the steps of which are: 1) adding a ligand to a mixed solution containing two ions of the same charge, wherein the ligand only complexes with one of the ions to form a complex that is uncharged or has an opposite charge to the ion to be separated; 2) adding the mixed solution to an electrodialysis device, and using a non-selective ion exchange membrane to separate the solution of uncomplexed ions and a complex solution; 3) adding a corresponding precipitant to the complex solution to separate the ligand from the ions to be separated. The present invention uses a ligand to complex one of the ions, so that the charge of the ions is distinguished from that of the other ion, so that the two can be separated by a non-selective ion exchange membrane, and no expensive selective ion exchange membrane is needed, which reduces the separation cost, and no pollutants or by-products are generated in the whole process, which is green, environmentally friendly and energy-saving.

Description

Technical Field

[0001] The invention relates to the technical field of ion separation, in particular to a method for separating ions of the same electrical property by using a non-selective ion exchange membrane. Background Art

[0002] Electrodialysis technology is a process that utilizes the selective permeability of ion exchange membranes to enable ions to selectively permeate the membrane and migrate in a directional manner under the action of electric field forces, thereby achieving electrolyte desalination, purification and concentration. Electrodialysis is selected as an electrically driven membrane separation process, which can be used for the screening of special ions in mixed materials. This process requires the use of selective ion exchange membranes as an important component of the device. According to the differences in physicochemical properties such as charge properties, hydration energy, and ion hydration radius between the target ions and other mixed ions, by using special functional membranes, using the specific response between the target ions and the functional membranes, there is a certain rate difference when the target ions and other mixed ions migrate in the functional membranes (usually the migration rate of the target ions is faster than that of the impurity ions). Using the electric field as the driving force and using the functional membranes in a specific arrangement, efficient separation of the target ions can be achieved. Selective ion exchange membranes are widely used in processes such as lithium extraction from salt lakes, resource utilization of concentrated brine, and green chemical production.

[0003] However, the price of selective ion exchange membranes is much higher than that of ordinary ion exchange membranes, which limits the use of this technology. At the same time, the current research on monovalent selective ion exchange membranes is still immature, and there is no large-scale production of monovalent and divalent selective ion exchange membranes. The monovalent selective ion exchange membranes used in laboratories or small devices also have some shortcomings: reduced ion flux, high membrane resistance, low stability, and they are easily affected by the environment, causing the modified layer to fall off; or when a reverse electric field is applied, the monovalent ion selective layer will fall off, thereby affecting the selectivity of the ion exchange membrane; it is easy to chemically degrade. In water treatment, feed liquid concentration and other systems, due to the influence of the feed liquid environment, the corresponding active groups are often inactivated, degraded or even fall off; the modified selective layer of the monovalent selective ion exchange membrane has poor uniformity, which affects the overall effect. Therefore, the application of selective ion exchange membranes in the separation of isoelectric ions represented by magnesium and lithium ions is limited. Summary of the invention

[0004] The present invention aims to overcome the above-mentioned problems existing in the electrodialysis technology of separating ions of the same charge by using a selective ion exchange membrane in the prior art, and provides a method for separating ions of the same charge by using a non-selective ion exchange membrane. A ligand is used to complex one of the ions so that its charge is distinguished from that of the other ion, so that the two can be separated by the non-selective ion exchange membrane, without the need for expensive selective ion exchange membranes, thereby reducing the separation cost, and no pollutants or by-products are generated in the whole process, which is green, environmentally friendly and energy-saving.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for separating ions of the same charge using a non-selective ion exchange membrane, comprising the following steps:

[0007] 1) Add a ligand to a mixture containing two ions of the same charge. The ligand only complexes with one of the ions to form a complex that is uncharged or has an opposite charge to the ion to be separated.

[0008] 2) adding the mixed solution to an electrodialysis device to separate the uncomplexed ion solution and the complex solution;

[0009] 3) Add the corresponding precipitant to the complex solution to separate the ligand from the ion to be separated;

[0010] The electrodialysis device is provided with a number of membrane units formed by alternately arranging non-selective anion exchange membranes and cation exchange membranes, and the membrane units form alternately distributed concentrated chambers and dilute chambers, the mixed liquid is added to the dilute chamber, and the desalted water is added to the concentrated chamber;

[0011] When the complex is uncharged, there is one concentrated chamber and one dilute chamber in the membrane unit;

[0012] When the complex is charged, there are two concentrated chambers and two dilute chambers in the membrane unit, and an electrolyte solution is added to the other dilute chamber.

[0013] The separation principle of the present invention is: a ligand with specific properties is added to the mixed solution of ions to be separated, so that it can complex one of the ions but not the other ion, thereby distinguishing the electrical properties of the two ions to be separated, and separating them by utilizing the repulsive effect of a non-selective ion exchange membrane on positive and negative ions.

[0014] Containing positive ions A x+ and B y+ As an example, add ligand L z- , so that B y+ With L z- Specific binding to complex [BL a ] b- (a is a positive integer, b is 0 or a positive integer). z- and B y+ Can form neutral complexes [BL a ], a two-compartment electrodialysis device containing a concentrated chamber and a diluted chamber can be used for separation. The separation principle is as follows Figure 1 As shown in z- The mixed liquid is injected into the dilute chamber, A x+ Under the action of the electric field, ions migrate through the cation exchange membrane (cation membrane) to the concentration chamber, which is Ax+ ion solution, and only [BL a ] complex, thereby achieving A x+ and B y+ Ion separation effect.

[0015] For L z- and B y+ Can form negatively charged complexes [BL a ] b- In the case of , a four-compartment electrodialysis device containing two concentrated chambers and two dilute chambers can be used for separation. The separation principle is as follows Figure 2 As shown in z- The mixed liquid is injected into the dilute chamber A, where A x+ Under the action of the electric field, ions migrate through the cation exchange membrane (cation membrane) to the concentration chamber A, and the complex [BL a ] b- Migrate to the concentrated chamber B through the anion exchange membrane (anion membrane); add the electrolyte solution (without introducing impurity ions, here taking sodium chloride solution as an example) into the diluted chamber B, Cl - and Na + Passing through the anion membrane and the cation membrane respectively, they enter the concentration chamber A and the concentration chamber B. Finally, only ACl is left in the concentration chamber A. x There are almost no ions in the dilute chamber A, the dilute chamber B is a NaCl solution, and the concentrated chamber B is NaCl and Na b [BL a ] mixed solution, so as to achieve A x+ and B y+ separation.

[0016] In both cases, the isolated a ] b- The solution can be precipitated by adding a precipitant y+ Ion precipitation separation (precipitant and B y+ The concentration product constant of the ion must be much greater than that of the ligand and B y+ The remaining ligands can be recycled by reverse osmosis or nanofiltration. For negatively charged ions, the above principles and methods can also be used for separation.

[0017] The method of the present invention does not require the use of expensive selective ion exchange membranes, thus reducing separation costs and being conducive to industrial application; and the entire process generates no pollutants or by-products, which is green, environmentally friendly and energy-saving.

[0018] Preferably, the precipitant is added to the complex solution to precipitate the resulting solution, and the ligand solution is subjected to reverse osmosis or nanofiltration to obtain the ligand solution, thereby realizing the recycling of the ligand.

[0019] Preferably, when the complex is uncharged, the conductivity of the effluent water in the dilute chamber of the membrane unit is ≥20mS / cm, and the conductivity of the effluent water in the concentrated chamber is ≥5mS / cm;

[0020] When the complex is charged, the conductivity of the effluent water in the dilute chamber of the membrane unit with the mixed solution added is ≥20mS / cm, the conductivity of the effluent water in the dilute chamber with the electrolyte added is ≥50mS / cm; the conductivity of the effluent water in the two concentrated chambers is ≥5mS / cm. If the effluent water conductivity is too low, the overall energy consumption of the membrane stack will increase.

[0021] Preferably, the pH value of the mixed solution containing two ions of the same charge is 3.0 to 6.5. Too high a pH value will lead to the precipitation of hydroxides, because the concentration product of hydroxides is generally very low, and the hydroxide will compete with the complexation reaction between the ligand and the metal, affecting the separation effect.

[0022] Preferably, in the mixed solution containing two ions of the same charge, the total mass concentration of the two ions is 0.1-50%.

[0023] Preferably, the current density of the electrodialysis device during separation in step 2) is 200-400 A / m 2 .

[0024] Preferably, the temperature of the mixed solution added to the electrodialysis device is 25-35°C.

[0025] Preferably, the two isoelectric ions in the mixed solution are magnesium ions and lithium ions; the ligand is selected from one or more of citric acid, 1,2-cyclohexanediaminetetraacetic acid, sodium catechol-3,5-disulfonate, glycine, N-(2-hydroxyethyl)ethylenediamine-triacetic acid, and 8-hydroxyquinoline-5-sulfonic acid.

[0026] Preferably, in step 3), the precipitant added to the complex solution is selected from one or more of ammonium phosphate, carbonate, fluoride, hydroxide, iodate, oxalate, phosphate and sulfite.

[0027] Preferably, when the complex is charged, the electrolyte solution added to the other dilute chamber is a sodium chloride solution.

[0028] Therefore, the present invention has the following beneficial effects:

[0029] (1) No need to use expensive selective ion exchange membranes, so the separation cost is low;

[0030] (2) No pollutants or by-products are generated during the entire process, and both salts and ligands can be recycled, which is green, environmentally friendly and energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the separation principle when forming an uncharged complex in the present invention.

[0032] Figure 2 It is a schematic diagram of the separation principle when forming a charged complex in the present invention.

[0033] Figure 3 It is a schematic diagram of the process of Examples 1 to 3 of the present invention.

[0034] Figure 4 It is a schematic diagram of the flow chart of Example 4 of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0036] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0037] Overall embodiment:

[0038] A method for separating ions of the same charge using a non-selective ion exchange membrane, comprising the following steps:

[0039] 1) Add a ligand to a mixture containing two ions of the same charge. The ligand only complexes with one of the ions to form a complex that is uncharged or has an opposite charge to the ion to be separated.

[0040] 2) adding the mixed solution to an electrodialysis device to separate the uncomplexed ion solution and the complex solution;

[0041] 3) Add the corresponding precipitant to the complex solution to separate the ligand from the ion to be separated;

[0042] The electrodialysis device is provided with a number of membrane units formed by alternately arranging non-selective anion exchange membranes and cation exchange membranes, and the membrane units form alternately distributed concentrated chambers and dilute chambers, the mixed liquid is added to the dilute chamber, and the desalted water is added to the concentrated chamber;

[0043] When the complex is uncharged, there is one concentrated chamber and one dilute chamber in the membrane unit;

[0044] When the complex is charged, there are two concentrated chambers and two dilute chambers in the membrane unit, and an electrolyte solution is added to the other dilute chamber.

[0045] As a specific implementation manner, a precipitant is added to the complex solution to precipitate, and the resulting solution is subjected to reverse osmosis or nanofiltration to obtain a ligand solution.

[0046] As a specific implementation, when the complex is uncharged, the effluent conductivity of the dilute chamber in the membrane unit is ≥20mS / cm, preferably ≥40mS / cm; the effluent conductivity of the concentrated chamber is ≥5mS / cm, preferably ≥20mS / cm.

[0047] As a specific implementation manner, when the complex is charged, the effluent conductivity of the dilute chamber in the membrane unit to which the mixed solution is added is ≥20mS / cm, and the effluent conductivity of the dilute chamber to which the electrolyte is added is ≥50mS / cm, preferably ≥100mS / cm; the effluent conductivity of the two concentrated chambers is ≥5mS / cm, preferably ≥20mS / cm.

[0048] As a specific implementation manner, the pH value of the mixed solution containing two ions of the same charge is 3.0-6.5, preferably 4-6.

[0049] As a specific implementation manner, in the mixed solution containing two ions of the same charge, the total mass concentration of the two ions is 0.1-50%, preferably 2-30%.

[0050] As a specific implementation method, in step 2), the current density of the electrodialysis device during separation is 200-400 A / m 2 , preferably 300A / m 2 .

[0051] As a specific implementation manner, the temperature of the mixed solution added to the electrodialysis device is 25-35°C, preferably 30-35°C.

[0052] As a specific embodiment, the two isoelectric ions in the mixed solution are magnesium ions and lithium ions; the ligand is selected from one or more of citric acid, 1,2-cyclohexanediaminetetraacetic acid, sodium catechol-3,5-disulfonate, glycine, N-(2-hydroxyethyl)ethylenediamine-triacetic acid, and 8-hydroxyquinoline-5-sulfonic acid; preferably selected from one or more of citric acid, 1,2-cyclohexanediaminetetraacetic acid, and glycine.

[0053] As a specific implementation, the precipitant added to the complex solution in step 3) is selected from one or more of ammonium phosphate, carbonate, fluoride, hydroxide, iodate, oxalate, phosphate, and sulfite; preferably selected from one or more of sodium phosphate, sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0054] As a specific implementation manner, when the complex is charged, the electrolyte solution added to the other dilute chamber is a sodium chloride solution.

[0055] Example 1 (negative monovalent ligand):

[0056] A method for separating magnesium and lithium ions using a non-selective ion exchange membrane, the process is as follows Figure 3 As shown in , the steps are:

[0057] 1) Add glycine ligand to a mixed solution containing magnesium chloride and lithium chloride (magnesium ion concentration 3 mol / L, lithium ion concentration 0.05 mol / L, pH 6.5, temperature 25°C), the molar ratio of glycine to magnesium ion being 2:1; glycine forms an electrically neutral complex with magnesium ions, and lithium ions do not complex with glycine;

[0058] 2) Add the mixture into Figure 1 In the dilute chamber of the two-compartment electrodialysis device shown (with a plurality of repeated membrane units formed by alternating anion exchange membranes and cation exchange membranes, a concentrated chamber and a diluted chamber are formed in the membrane unit, the anion membrane and the cation membrane are separated by a partition to provide a flow channel space, the two sides of the device are polar chambers, and the perfluorosulfonic acid membrane is used as the polar membrane), desalted water is added to the concentrated chamber and separated under the action of the electric field, and the current density is 300A / m 2 The effluent from the concentrated chamber is a lithium-rich solution (lithium chloride solution, lithium-magnesium molar ratio>1000), with a conductivity of 50 mS / cm, and the effluent from the dilute chamber is a magnesium-rich solution (a complex solution of glycine and magnesium ions, magnesium-lithium molar ratio>1000), with a conductivity of 20 mS / cm;

[0059] 3) Sodium carbonate is added to the lithium-rich solution as a precipitant and enters the sedimentation tank A to obtain lithium carbonate precipitation, and the remaining clarified liquid (sodium salt solution) is discharged;

[0060] 4) Add precipitant sodium hydroxide to the magnesium-rich solution and let it enter precipitation tank B to obtain magnesium hydroxide precipitate. The clarified liquid is a sodium glycine salt solution, which can be reused as a ligand solution after reverse osmosis concentration. The desalted water obtained by reverse osmosis can be reused in the concentration chamber.

[0061] Example 2 (negative divalent ligand):

[0062] A method for separating magnesium and lithium ions using a non-selective ion exchange membrane, the process is as follows Figure 3 As shown in , the steps are:

[0063] 1) Adding sodium catechol-3,5-disulfonate ligand to a mixed solution containing magnesium chloride and lithium chloride (magnesium ion concentration 0.1 mol / L, lithium ion concentration 0.1 mol / L, pH 6, temperature 35°C), the molar ratio of sodium catechol-3,5-disulfonate to magnesium ion is 1:1; sodium catechol-3,5-disulfonate forms an electrically neutral complex with magnesium ion, and lithium ion does not complex with sodium catechol-3,5-disulfonate;

[0064] 2) Add the mixture into Figure 1In the dilute chamber of the two-compartment electrodialysis device shown (with a plurality of repeated membrane units formed by alternating anion exchange membranes and cation exchange membranes, a concentrated chamber and a diluted chamber are formed in the membrane unit, the anion membrane and the cation membrane are separated by a partition to provide a flow channel space, the two sides of the device are polar chambers, and the perfluorosulfonic acid membrane is used as the polar membrane), desalted water is added to the concentrated chamber and separated under the action of the electric field, and the current density is 300A / m 2 ; The effluent from the concentrated chamber is a lithium-rich solution (lithium chloride solution, lithium-magnesium molar ratio>1000), with a conductivity of 50 mS / cm; the effluent from the dilute chamber is a magnesium-rich solution (complex solution of catechol-3,5-disulfonic acid and magnesium ions, magnesium-lithium molar ratio>1000), with a conductivity of 2 mS / cm;

[0065] 3) Sodium carbonate is added to the lithium-rich solution as a precipitant and enters the sedimentation tank A to obtain lithium carbonate precipitation, and the remaining clarified liquid (sodium salt solution) is discharged;

[0066] 4) Add sodium phosphate as a precipitant to the magnesium-rich solution and enter the precipitation tank B to obtain magnesium phosphate precipitate. The clarified liquid is a sodium salt solution of catechol-3,5-disulfonic acid, which can be reused as a ligand solution after reverse osmosis concentration. The desalted water obtained by reverse osmosis can be reused in the concentration chamber.

[0067] Example 3 (negative trivalent ligand):

[0068] A method for separating magnesium and lithium ions using a non-selective ion exchange membrane, the process is as follows Figure 3 As shown in , the steps are:

[0069] 1) Add citric acid ligand to a mixed solution containing magnesium chloride and lithium chloride (magnesium ion concentration 1 mol / L, lithium ion concentration 1 mol / L, pH 5.5, temperature 35°C), the molar ratio of citric acid to magnesium ion is 1:1; citric acid forms an electrically neutral complex with magnesium ions, and lithium ions do not complex with citric acid;

[0070] 2) Add the mixture into Figure 1 In the dilute chamber of the two-compartment electrodialysis device shown (with a plurality of repeated membrane units formed by alternating anion exchange membranes and cation exchange membranes, a concentrated chamber and a diluted chamber are formed in the membrane unit, the anion membrane and the cation membrane are separated by a partition to provide a flow channel space, the two sides of the device are polar chambers, and the perfluorosulfonic acid membrane is used as the polar membrane), desalted water is added to the concentrated chamber and separated under the action of the electric field, and the current density is 300A / m 2 The effluent from the concentrated chamber is a lithium-rich solution (lithium chloride solution, lithium-magnesium molar ratio>1000), with a conductivity of 40mS / cm, and the effluent from the dilute chamber is a magnesium-rich solution (a complex solution of citric acid and magnesium ions, magnesium-lithium molar ratio>1000), with a conductivity of 25mS / cm;

[0071] 3) Sodium carbonate is added to the lithium-rich solution as a precipitant and enters the sedimentation tank A to obtain lithium carbonate precipitation, and the remaining clarified liquid (sodium salt solution) is discharged;

[0072] 4) Add precipitant sodium hydroxide to the magnesium-rich solution and let it enter precipitation tank B to obtain magnesium hydroxide precipitate. The clarified liquid is sodium citrate solution, which can be reused as ligand solution after reverse osmosis concentration. The desalted water obtained by reverse osmosis can be reused in the concentration chamber.

[0073] Example 4 (negative tetravalent ligand):

[0074] A method for separating magnesium and lithium ions using a non-selective ion exchange membrane, the process is as follows Figure 4 As shown in , the steps are:

[0075] 1) Add 1,2-cyclohexanediaminetetraacetic acid ligand to a mixed solution containing magnesium chloride and lithium chloride (magnesium ion concentration 1 mol / L, lithium ion concentration 1 mol / L, pH value 5.5, temperature 35°C), the molar ratio of 1,2-cyclohexanediaminetetraacetic acid to magnesium ions being 1:1; 1,2-cyclohexanediaminetetraacetic acid forms a negatively charged complex with magnesium ions, and lithium ions do not complex with 1,2-cyclohexanediaminetetraacetic acid;

[0076] 2) Add the mixture into Figure 2 In the dilute chamber A of the four-compartment electrodialysis device shown (with a plurality of repeated membrane units formed by alternating anion exchange membranes and cation exchange membranes, two alternating concentrated chambers and two dilute chambers are formed in the membrane units, the anion membrane and the cation membrane are separated by a partition to provide a flow channel space, the two sides of the device are pole chambers, and the perfluorosulfonic acid membrane is used as the pole membrane), desalted water is added to the concentrated chamber A and the concentrated chamber B, and a sodium chloride solution with a concentration of 10wt% is added to the dilute chamber B, and separation is carried out under the action of an electric field, and the current density is 300A / m 2 ; The effluent from concentration chamber A is a lithium-rich solution (lithium chloride solution, lithium-magnesium molar ratio>1000), with a conductivity of 60mS / cm; the effluent from concentration chamber B is a magnesium-rich solution (a mixed solution of a complex of 1,2-cyclohexanediaminetetraacetic acid and magnesium ions and sodium chloride, with a magnesium-lithium molar ratio>1000), with a conductivity of 50mS / cm; the effluent from dilute chamber B is a sodium chloride dilute solution, with a conductivity of 180mS / cm;

[0077] 3) Sodium carbonate is added to the lithium-rich solution as a precipitant and enters the sedimentation tank A to obtain lithium carbonate precipitation. The clarified liquid is a sodium salt solution, which is concentrated by the reverse osmosis device B and then reused in the dilute room B;

[0078] 4) Adding sodium hydroxide as a precipitant to the magnesium-rich solution, and entering the precipitation tank B to obtain magnesium hydroxide precipitate, the clarified liquid is a mixed solution of sodium 1,2-cyclohexanediaminetetraacetate and sodium chloride, and after salt separation by a nanofiltration device, sodium chloride solution and sodium 1,2-cyclohexanediaminetetraacetate solution can be separated; the sodium chloride solution is concentrated by a reverse osmosis device B and then reused as an electrolyte solution to the dilute chamber B; the sodium 1,2-cyclohexanediaminetetraacetate solution can be reused as a ligand solution to the dilute chamber A;

[0079] 5) The effluent from the dilution chamber A is the desalinated solution of the added mixed solution. After being concentrated by the reverse osmosis device A, the concentrated water is returned to the dilution chamber A for reuse. The desalted water produced in the reverse osmosis devices A and B can be reused in the concentrate chamber A and B.

[0080] Embodiment 5:

[0081] A method for anion separation using a non-selective ion exchange membrane, comprising the steps of:

[0082] 1) Add magnesium chloride ligand to a mixed solution containing sodium chloride and sodium citrate (chloride ion concentration 0.1 mol / L, citrate concentration 0.05 mol / L, pH 6, temperature 35°C), the molar ratio of citrate to magnesium ion is 1:1; citrate forms an electrically neutral complex with magnesium ion, and chloride ion does not complex with magnesium ion;

[0083] 2) Add the mixed solution to the dilute chamber of a two-compartment electrodialysis device (with several repeated membrane units formed by alternating anion exchange membranes and cation exchange membranes, a concentrated chamber and a dilute chamber are formed in the membrane unit, the anion membrane and the cation membrane are separated by a partition to provide a flow channel space, the two sides of the device are polar chambers, and the perfluorosulfonic acid membrane is used as the polar membrane). Add desalted water to the concentrated chamber and separate under the action of the electric field. The current density is 300A / m 2 The effluent from the concentrated chamber is a chloride ion solution (sodium chloride solution) with a conductivity of 60 mS / cm, and the effluent from the dilute chamber is a complex solution of citrate and magnesium ions with a conductivity of 20 mS / cm;

[0084] 3) Adding precipitant sodium hydroxide to the complex solution of citrate and magnesium ions, and entering the precipitation tank A, after the magnesium ions are precipitated, the clarified liquid is a citrate ion solution, thereby achieving the separation of chloride ions and citrate ions.

[0085] In Examples 1 to 4, a mixed solution of magnesium chloride and lithium chloride is used as an example, and the method of the present invention is used to separate magnesium ions and lithium ions. The principle is: by utilizing the specific complexation of the ligand and the magnesium ion, almost all of the magnesium ions form a [magnesium ion-ligand] complex with the ligand, and the [magnesium ion-ligand] complex is electrically neutral or exists in a negative valence state, while the lithium element in the solution still exists almost entirely in the form of monovalent lithium ions.

[0086] The calculation formula of the complexation constant of the ligand is as follows:

[0087] .

[0088] Specifically, for the monovalent negative ligand L - (glycine in Example 1), K2(Mg) must be much greater than K1(Mg), log K2(Mg) / log K1(Mg) must be greater than 2; at the same time, Li + Almost no ligand L - Complexation. At this time, Mg 2+ Almost completely bound to ligand L - To form an electrically neutral complex of [MgL2], one can choose Figure 1 The two-compartment electrodialysis reaction device shown in FIG. - The uniform magnesium and lithium salt mixed solution is injected into the dilute chamber, and Cl - and Li + Under the action of the electric field, ions migrate through the anion membrane and the cation membrane to the concentrated chamber, which contains LiCl solution, while only [MgL2] complex remains in the dilute chamber, thus achieving the magnesium-lithium separation effect.

[0089] For the negative divalent ligand L 2- (sodium catechol-3,5-disulfonate in Example 2), Li + Ligand L 2- Complex, Mg 2+ Almost completely bound to ligand L 2- Forming an electrically neutral complex of [MgL], you can also choose Figure 1 The two-compartment electrodialysis device shown in FIG. 2- The uniform magnesium and lithium salt mixed solution is injected into the dilute chamber, and Cl - and Li + Under the action of the electric field, ions pass through the anion membrane and the cation membrane and migrate to the concentrated chamber. The concentrated chamber contains LiCl solution, while only [MgL] complex remains in the dilute chamber, thus achieving the magnesium-lithium separation effect.

[0090] For the negative trivalent ligand L 3- (citric acid in Example 3), Li + Ligand L 3- Complex, Mg 2+ Almost completely bound to ligand L 3- Forming an electrically neutral complex of [MgHL], you can also choose Figure 1 The two-compartment electrodialysis device shown in FIG. 3- The uniform magnesium and lithium salt mixed solution is injected into the dilute chamber, and Cl - and Li+ Under the action of the electric field, ions pass through the anion membrane and the cation membrane and migrate to the concentrated chamber, which contains LiCl solution, while only [MgHL] complex remains in the dilute chamber, thus achieving the magnesium-lithium separation effect.

[0091] For ligands L with negative tetravalent valence or above z - (the negative tetravalent ligand 1,2-cyclohexanediaminetetraacetic acid in Example 4), Li + Ligand L z- Complex, Mg 2+ Almost completely bound to ligand L z- Formation [MgL] (z-2)- Negatively charged complex. Figure 2 The four-compartment electrodialysis device shown in FIG. z- The uniform magnesium-lithium salt mixed solution is injected into the dilute chamber A, where Li + Under the action of the electric field, ions migrate through the cation membrane to the concentration chamber A, Cl - and [MgL] (z-2)- Migrate through the anion membrane to the concentrated chamber B; add sodium chloride solution as the electrolyte to the dilute chamber B, Cl - and Na + They pass through the anion membrane and the cation membrane respectively and enter the concentration chamber A and the concentration chamber B. Finally, there is only LiCl solution in the concentration chamber A, and almost no ions exist in the dilute chamber A. The dilute chamber B is a NaCl solution, and the concentration chamber B is NaCl and Na z-2 [MgL] mixed solution, thereby achieving the magnesium-lithium separation effect.

[0092] The magnesium-lithium molar ratio in the magnesium-rich solution obtained in Examples 1 to 4 is greater than 1000, and the lithium-magnesium molar ratio in the lithium-rich solution is greater than 1000, and magnesium and lithium can be basically completely separated. The lithium ion recovery rates in Examples 1 to 4 were calculated, and the results are shown in Table 1.

[0093] The calculation method of lithium ion recovery rate is: lithium ion recovery rate = (mass of lithium ions in the effluent of the two-compartment concentration chamber or the mass of lithium ions in the effluent of the four-compartment concentration chamber A) / (mass of lithium ions in the lithium-magnesium mixed solution input into the electrodialysis device).

[0094] Table 1: Lithium ion recovery test results

[0095]

[0096] It can be seen from the data in Table 1 that the method of the present invention can effectively extract lithium resources from a magnesium-lithium ion mixed solution, and is suitable for extracting lithium from salt lake brine with a high magnesium-lithium ratio (the molar ratio of magnesium ions to lithium ions is above 6:1). The obtained lithium carbonate is a raw material for preparing various lithium compounds. It is the product with the largest output and the widest application among lithium salt products. It can be widely used in chemical, metallurgical, ceramic, pharmaceutical, refrigeration and other industries. It can also be used to prepare catalysts for chemical reactions and is known as "industrial monosodium glutamate". Compared with the system of special ion separation using electrodialysis devices in the prior art, the present invention does not require the use of expensive selective ion exchange membranes, has a lower separation cost, and has no pollutants and by-products in the whole process. Both salts and ligands can be recycled, which is green, environmentally friendly and energy-saving.

[0097] In Example 5, the anion chloride ion and the citrate ion are separated. The chloride ion is almost not complexed with the ligand magnesium ion, and the citrate ion almost completely forms an electrically neutral complex with the ligand magnesium ion. Figure 1 The two-compartment electrodialysis device shown in the figure injects the mixed solution with magnesium ions added and mixed evenly into the dilute chamber, and Cl - and Na + Under the action of the electric field, ions pass through the anion membrane and the cation membrane and migrate to the concentrated chamber, which contains NaCl solution, while only the complex of citrate and magnesium ions remains in the dilute chamber, thus achieving the separation effect of chloride ions and citrate.

[0098] Although specific embodiments have been used to illustrate the invention, it is understood that the above embodiments are used to understand the methods and core matters of the present invention and cannot be understood as limitations on the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention shall be deemed to be within the protection scope of the present invention.

Claims

1. A method for separating ions of the same electrical property using a non-selective ion exchange membrane, characterized in that the steps for ： 1) Add a ligand to a mixture containing two ions of the same charge, and the ligand only complexes with one of the ions to form a complex that is uncharged or has an opposite charge to the ion to be separated; the pH value of the mixture containing two ions of the same charge is 3.0-6.5; 2) adding the mixed solution to an electrodialysis device to separate the uncomplexed ion solution and the complex solution; 3) Add the corresponding precipitant to the complex solution to separate the ligand from the ion to be separated; The electrodialysis device is provided with a number of membrane units formed by alternately arranging non-selective anion exchange membranes and cation exchange membranes, and the membrane units form alternately distributed concentrated chambers and dilute chambers, the mixed liquid is added to the dilute chamber, and the desalted water is added to the concentrated chamber; When the complex is uncharged, there is one concentrated chamber and one dilute chamber in the membrane unit; When the complex is charged, there are two concentrated chambers and two dilute chambers in the membrane unit, and an electrolyte solution is added to the other dilute chamber.

2. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 1, wherein: The precipitant is added to the complex solution to precipitate, and the resulting solution is subjected to reverse osmosis or nanofiltration to obtain a ligand solution.

3. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 1, wherein: When the complex is uncharged, the conductivity of the effluent water in the dilute chamber of the membrane unit is ≥20mS / cm, and the conductivity of the effluent water in the concentrated chamber is ≥5mS / cm; When the complex is charged, the effluent conductivity of the dilute chamber in the membrane unit with the mixed solution added is ≥20mS / cm, and the effluent conductivity of the dilute chamber with the electrolyte added is ≥50mS / cm; the effluent conductivity of the two concentrated chambers is ≥5mS / cm.

4. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 1, wherein: In a mixed solution containing two ions of the same charge, the total mass concentration of the two ions is 0.1~50%.

5. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 1, wherein: Step 2) The current density of the electrodialysis device during separation is 200~400A / m 2 .

6. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 1 or 5, characterized in that: The temperature of the mixed solution added to the electrodialysis device is 25~35℃.

7. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 1, wherein: The two ions of the same charge in the mixed solution are magnesium ions and lithium ions; the ligand is selected from one or more of citric acid, 1,2-cyclohexanediaminetetraacetic acid, sodium catechol-3,5-disulfonate, glycine, N-(2-hydroxyethyl)ethylenediamine-triacetic acid, and 8-hydroxyquinoline-5-sulfonic acid.

8. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 7, wherein: Step 3) The precipitant added to the complex solution is selected from one or more of ammonium phosphate, carbonate, fluoride, hydroxide, iodate, oxalate, phosphate, and sulfite.

9. The method for separating ions of the same electrical property using a non-selective ion exchange membrane according to claim 7, wherein: When the complex is charged, the electrolyte solution added to the other dilute chamber is sodium chloride solution.

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