New process for realizing magnesium-lithium separation through coordination of complex reaction and bipolar membrane electrodialysis

Abstract

The invention relates to the technical field of membrane separation and resource recovery, and discloses a novel process for realizing magnesium-lithium separation through coordination of complex reaction and bipolar membrane electrodialysis. According to the process, magnesium-lithium separation in lithium-magnesium mixed systems such as brine, oil and gas field wastewater, seawater and the like is realized by utilizing the characteristic that ethylenediamine tetraacetic acid can be selectively complexed with magnesium ions under specific conditions to form negatively charged complexes and the anion-cation separation performance of an electrodialysis system. According to the method, the selective separation of the lithium ions in the magnesium-lithium mixed solution can be realized by utilizing the existing commercial cation exchange membrane and the feed liquid or waste liquid containing the ethylenediamine tetraacetic acid radicals, and a novel monovalent and multivalent selective ion membrane does not need to be researched and developed; the method can avoid the problems of mutual restriction of membrane selectivity and flux, poor stability of a separation layer and the like in the research and development of the current monovalent and multivalent selective cation exchange membrane, provides a new strategy for the current magnesium-lithium separation, and has the advantages of simple process, high lithium ion selectivity, short period, environmental friendliness, continuous production and the like.

Description

Technical Field

[0001] The present invention belongs to the fields of membrane separation and resource recovery, and particularly relates to a new process for realizing magnesium-lithium separation by complexation reaction synergistic bipolar membrane electrodialysis. Background Art

[0002] With the global emphasis on reducing greenhouse gas emissions, the new energy industry has developed rapidly. As a key material for manufacturing lithium-ion batteries, the extraction of lithium resources has also been increasingly emphasized. Liquid resources such as brine, oil and gas field wastewater, and seawater contain a large amount of lithium ions and have high resource utilization value. Achieving efficient separation of lithium ions and magnesium ions is a technical problem in lithium extraction from salt lakes. Currently, the feasible technologies for realizing magnesium-lithium separation from salt lake brine include chemical precipitation method, ion sieve adsorption method, ion exchange method, nanofiltration method, etc. However, most of the technologies still have application defects. For example, due to the similar properties of lithium and magnesium, the economic efficiency of extracting lithium from high magnesium-lithium ratio brine by chemical precipitation is poor; lithium ion sieves have been commercialized for lithium production, but are still limited by the problem of dissolution loss; ion exchange resins are not suitable for high magnesium-lithium ratio brine, and a large amount of elution wastewater will be generated during the desorption process; the enrichment ability of nanofiltration is limited and is restricted by membrane fouling and scaling problems.

[0003] Currently, as a green and efficient ion separation means, electrodialysis technology has received wide attention. Traditional electrodialysis technology is mainly aimed at the separation between non-isovalent ions and cannot achieve the separation between ions of the same valence state (Li + and Mg 2+ ). To solve this problem, Patent CN 103864249 A discloses a method for realizing magnesium-lithium separation by coupling precipitation method for calcium and magnesium removal, ordinary electrodialysis concentration, and precipitation method for calcium and magnesium removal again. However, this method has a complex process and requires a large amount of sodium carbonate as a precipitant, which will cause partial loss of lithium resources. Patents CN 1626443 A and CN 110065958 A disclose methods for realizing magnesium-lithium separation by using a monovalent selective electrodialysis device to treat salt lake brine, which solves the problem of magnesium-lithium separation in high magnesium-lithium ratio brine. However, the effect of this method highly depends on the performance of the monovalent selective ion membrane. Currently, the rejection rate of commercial monovalent selective ion membranes for multivalent ions is only about 90%, which affects the purity of lithium products. In addition, the currently emerging research and development of monovalent selective ion membranes face problems such as mutual restriction between membrane selectivity and flux, difficulty in scaling up, and poor stability of the separation layer, and cannot meet the demand for large-scale magnesium-lithium separation applications in a short time. Therefore, developing a new method to solve the problem of magnesium-lithium separation without developing monovalent selective ion membranes is of great significance for the extraction and utilization of lithium in liquid resources, especially brine resources.

[0004] In view of this, by utilizing the characteristic that ethylenediaminetetraacetate can easily form a negatively charged complex with magnesium ions under specific conditions without reacting with lithium ions, and combining the anion and cation separation performance of the electrodialysis system, a method for realizing the separation of magnesium and lithium by complex reaction synergistic bipolar membrane electrodialysis is developed. Without the need to develop a monovalent selective ion membrane, the efficient separation of magnesium and lithium in liquid resources such as brine, oil and gas field wastewater, and seawater is realized, which is of great significance to the recovery of lithium resources and the development of the new energy industry. Summary of the Invention

[0005] The present invention provides a new process for realizing the separation of magnesium and lithium by complex reaction synergistic bipolar membrane electrodialysis. By utilizing the characteristic that ethylenediaminetetraacetate can easily form a negatively charged complex with magnesium ions under specific conditions without reacting with lithium ions, and combining the anion and cation separation performance of the electrodialysis system, the efficient separation of magnesium and lithium in liquid resources such as brine, oil and gas field wastewater, and seawater is realized without the need to develop a monovalent selective ion membrane.

[0006] The technical solution of the present invention is as follows: A new process for realizing the separation of magnesium and lithium by complex reaction synergistic bipolar membrane electrodialysis, the method comprising: Adding ethylenediaminetetraacetate to the magnesium-lithium mixed solution, adjusting the pH with an alkali solution, and performing a pre-reaction to obtain a pre-reacted magnesium-lithium mixed solution, so that magnesium ions selectively complex with ethylenediaminetetraacetate to form a negatively charged complex; the ethylenediaminetetraacetate includes any one or more of disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, and tetra potassium ethylenediaminetetraacetate; the alkali solution is any one or more of sodium hydroxide and potassium hydroxide; Passing the pre-reacted magnesium-lithium mixed solution into the feed chamber of the bipolar membrane electrodialysis system, and applying an electric field to realize the separation of magnesium and lithium.

[0007] A new process for realizing the separation of magnesium and lithium by bipolar membrane electrodialysis synergistic complex reaction, comprising the following steps: A. Circulating the pre-reacted magnesium-lithium mixed solution into the feed chamber of the bipolar membrane electrodialysis system by a circulating pump; B. Pumping the lithium solution into the lithium chamber of the bipolar membrane electrodialysis system; C. Pumping the acid solution into the acid chamber of the bipolar membrane electrodialysis system; D. Circulating and pumping the electrolyte solutions in the electrode solution circulation device into the anode chamber and the cathode chamber of the bipolar membrane electrodialysis system respectively; E. Turning on the power supply, applying a voltage, performing bipolar membrane electrodialysis, separating magnesium and lithium from the pre-reacted magnesium-lithium solution, and obtaining a lithium solution in the lithium chamber and generating ethylenediaminetetraacetic acid and magnesium ions in the acid chamber.

[0008] Preferably: The mass ratio of magnesium to lithium in the pre-reaction magnesium-lithium mixed solution described in step A is 1 to 80.

[0009] The molar ratio of magnesium ions to ethylenediaminetetraacetate in the pre-reaction magnesium-lithium mixed solution described in step A is 1.0 to 1.2.

[0010] The lithium solution described in step B is a lithium-containing solution, and the concentration of the lithium solution is 0 to 0.1 mol / L.

[0011] The acid solution described in step C is one or more of sulfuric acid solution, hydrochloric acid solution, and nitric acid solution, and the concentration of the acid solution is 0 to 0.1 mol / L.

[0012] The electrolyte solution described in step D is one or more of sodium sulfate solution, potassium sulfate solution, sodium nitrate solution, or potassium nitrate solution, and the concentration of the electrolyte solution is 0.1 to 0.5 mol / L.

[0013] The flow rates of the simulation solution, acid solution, base solution, and electrode solution pumped into the bipolar membrane electrodialysis system are 100 to 500 mL / min.

[0014] The present invention also discloses a bipolar membrane electrodialysis device for realizing magnesium-lithium separation through complex reaction synergistic bipolar membrane electrodialysis, including: a bipolar membrane electrodialysis membrane stack, a cathode plate, an anode plate, an electrode solution storage tank, a lithium solution storage tank, an acid solution storage tank, a feed solution storage tank, an electrode solution circulation device, a lithium solution circulation device, an acid solution circulation device, a feed solution circulation device, and a DC regulated power supply; The cathode plate is connected to the negative electrode of the DC regulated power supply; The anode plate is connected to the positive electrode of the DC regulated power supply; The cathode plate and the anode plate are respectively arranged on both sides of the bipolar membrane electrodialysis membrane stack; The bipolar membrane electrodialysis membrane stack sequentially includes a bipolar membrane, a first anion exchange membrane, a cation exchange membrane, and a second anion exchange membrane from the anode plate to the cathode plate direction; The anode plate, membrane stack, and cathode plate are sequentially spaced to form an anode chamber, an acid chamber, a feed solution chamber, a lithium chamber, and a cathode chamber; The outlet of the electrode solution circulation device is connected to the inlet of the anode chamber, the outlet of the anode chamber is connected to the inlet of the cathode chamber, the outlet of the cathode chamber is connected to the electrode solution storage tank, and the electrode solution storage tank is connected to the inlet of the electrode solution circulation device; The outlet of the lithium solution circulation device is connected to the inlet of the lithium chamber, the inlet of the lithium solution circulation device is connected to the lithium solution storage tank, and the lithium solution storage tank is connected to the outlet of the lithium chamber; The outlet of the acid liquid circulation device is communicated with the inlet of the acid chamber, the inlet of the acid liquid circulation device is communicated with the acid liquid storage tank, and the acid liquid storage tank is communicated with the outlet of the acid chamber; The outlet of the feed liquid circulation device is communicated with the inlet of the feed liquid chamber, the inlet of the feed liquid circulation device is communicated with the feed liquid storage tank, and the feed liquid storage tank is communicated with the outlet of the feed liquid chamber; Beneficial effects: The present invention proposes a new process for realizing the separation of magnesium and lithium by complexation reaction synergistic bipolar membrane electrodialysis. Both magnesium ions and lithium ions in the solution carry positive charges, so ordinary bipolar membrane electrodialysis cannot achieve the separation of magnesium ions and lithium ions. The creativity of this application lies in the use of ethylenediaminetetraacetate which can selectively react with magnesium ions to form a negatively charged EDTA magnesium complex, and then combined with the electrodialysis process, so that the traditional bipolar membrane electrodialysis device can achieve the separation of magnesium and lithium. Utilizing the characteristic that ethylenediaminetetraacetate ion is easy to form a negatively charged complex with magnesium ions under specific conditions and does not react with lithium ions, combined with the anion and cation separation performance of the electrodialysis system, the efficient separation of magnesium and lithium in liquid resources such as brine, oil and gas field wastewater, and seawater is realized without the need to develop a monovalent selective ion membrane, and it has the advantages of simple process and continuous production. Brief description of the drawings

[0015] Figure 1 It is a process schematic diagram of the new process for realizing the separation of magnesium and lithium by complexation reaction synergistic bipolar membrane electrodialysis of the present invention.

[0016] Figure 2 It is a schematic diagram of the bipolar membrane electrodialysis membrane stack configuration used in the present invention.

[0017] Figure 3 It is the Li + / Mg 2+ Separation factor in the new process for realizing the separation of magnesium and lithium by complexation reaction synergistic bipolar membrane electrodialysis in Examples 1-4.

[0018] Figure 4 It is the flux of Mg[EDTA] 2- Passing through the anion exchange membrane in Examples 3-5. Detailed implementation manners Example 1

[0019] This example is used to illustrate the application of the new process for realizing the separation of magnesium and lithium by complexation reaction synergistic bipolar membrane electrodialysis in the treatment of magnesium-lithium mixed solution in a weakly alkaline environment.

[0020] The new process for realizing the separation of magnesium and lithium by complexation reaction synergistic bipolar membrane electrodialysis adopted in this example includes: adding tetrasodium ethylenediaminetetraacetate (Na 4Ethylenediaminetetraacetic acid (EDTA)), adjust the pH with 5 mol / L NaOH solution, and perform a pre-reaction to obtain a pre-reacted magnesium-lithium mixed solution, so that magnesium ions selectively complex with ethylenediaminetetraacetate to form a negatively charged complex; Feed the pre-reacted magnesium-lithium mixed solution into the feed chamber of the bipolar membrane electrodialysis system, apply an electric field, and achieve magnesium-lithium separation.

[0021] Furthermore, this embodiment includes the following steps A. Add 0.02 mol of Na 2 to a 200 mL magnesium-lithium mixed solution containing 0.1 mol / L LiCl and 0.1 mol / L MgCl 4 (the mass ratio of magnesium to lithium is 3.46) Ethylenediaminetetraacetic acid (the molar ratio of magnesium ions to ethylenediaminetetraacetate is 1), adjust its pH to 9.2 with 5 mol / L NaOH solution, and pump it into the feed chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min by a circulating pump; B. Pump 200 mL of H 2 O into the lithium chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; C. Pump 200 mL of H 2 O into the acid chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; D. Pump 200 mL of 0.5 mol / L Na 2 SO 4 into the anode chamber and cathode chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min by a circulating pump; E. Turn on the power supply, perform bipolar membrane electrodialysis under a constant current of 3 A, separate magnesium and lithium from the pre-reacted magnesium-lithium solution, generate lithium hydroxide in the alkali chamber, and obtain ethylenediaminetetraacetic acid and magnesium ions in the acid chamber. As Figure 3 shown, after continuous operation for one hour, the lithium-magnesium separation factor of the bipolar membrane electrodialysis system is 972.

[0022] The bipolar membrane electrodialysis device adopted in this embodiment includes: a bipolar membrane electrodialysis membrane stack, a cathode plate, an anode plate, an electrode liquid storage tank, a lithium liquid storage tank, an acid liquid storage tank, a feed liquid storage tank, an electrode liquid circulation device, a lithium liquid circulation device, an acid liquid circulation device, a feed liquid circulation device, and a DC regulated power supply; The effective area of the bipolar membrane electrodialysis membrane stack is 189 cm 2 ; The cathode plate is connected to the cathode of the DC regulated power supply; The anode plate is connected to the anode of the DC regulated power supply; The cathode plate and the anode plate are respectively arranged on both sides of the bipolar membrane electrodialysis membrane stack; The bipolar membrane electrodialysis membrane stack sequentially includes a bipolar membrane, a first anion exchange membrane, a cation exchange membrane, and a second anion exchange membrane from the anode plate to the cathode plate direction; The outlet of the electrode liquid circulation device is communicated with the inlet of the anode chamber, the outlet of the anode chamber is communicated with the inlet of the cathode chamber, the outlet of the cathode chamber is communicated with the electrode liquid storage tank, and the electrode liquid storage tank is communicated with the inlet of the electrode liquid circulation device; The outlet of the lithium liquid circulation device is communicated with the inlet of the lithium chamber, the inlet of the lithium liquid circulation device is communicated with the lithium liquid storage tank, and the lithium liquid storage tank is communicated with the outlet of the lithium chamber; The outlet of the acid liquid circulation device is communicated with the inlet of the acid chamber, the inlet of the acid liquid circulation device is communicated with the acid liquid storage tank, and the acid liquid storage tank is communicated with the outlet of the acid chamber; The outlet of the feed liquid circulation device is communicated with the inlet of the feed liquid chamber, the inlet of the feed liquid circulation device is communicated with the feed liquid storage tank, and the feed liquid storage tank is communicated with the outlet of the feed liquid chamber; Example 2

[0023] This example is used to illustrate the new process of complex reaction synergistic bipolar membrane electrodialysis for magnesium-lithium separation applied to the treatment of magnesium-lithium mixed solution in a strong alkaline environment.

[0024] The bipolar membrane electrodialysis system used in this example is the same as that in Example 1. Further, this example includes the following steps: A. Add 0.024 mol of Na 2 EDTA (the molar ratio of magnesium ion to ethylenediaminetetraacetate is 1) to 200 mL of a magnesium-lithium mixed solution containing 0.1 mol / L LiCl and 0.1 mol / L MgCl 4 , and adjust its pH to 12 with 5 mol / L NaOH solution, so that the magnesium ion selectively complexes with ethylenediaminetetraacetate to form a negatively charged complex, and pump it into the feed liquid chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; B. Pump 200 mL of H 2 O into the lithium chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; C. Pump 200 mL of H 2 O into the acid chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; D. Pump 200 mL of 0.5 mol / L Na 2 SO4 Circulate and pump into the anode chamber and the cathode chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; E. Turn on the power supply, conduct bipolar membrane electrodialysis under the condition of a constant current of 3 A, separate magnesium and lithium from the pre-reacted magnesium-lithium solution, generate lithium hydroxide in the alkali chamber, and obtain ethylenediaminetetraacetic acid and magnesium ions in the acid chamber. As Figure 3 shown, after continuously operating for one hour, the lithium-magnesium separation factor of the bipolar membrane electrodialysis system is 863. Example 3

[0025] This example is used to illustrate the new process of realizing magnesium-lithium separation by complexation reaction synergistic bipolar membrane electrodialysis applied to the treatment of simulated Longmu Co brine.

[0026] In this example, the mass ratio of magnesium to lithium in the simulated Longmu Co brine used is 14.2, and the main cation concentrations are shown in Table 1: Table 1 Composition of Simulated Longmu Co Brine

[0027] The bipolar membrane electrodialysis system used in this example is the same as that in Example 1. Further, this example includes the following steps: A. Add 0.094 mol of disodium ethylenediaminetetraacetate dihydrate (the molar ratio of magnesium ion to ethylenediaminetetraacetate is 1) to 200 mL of simulated Longmu Co brine and stir well. Adjust its pH to 9.2 with 5 mol / L NaOH solution so that magnesium ions selectively complex with ethylenediaminetetraacetate ions to form a negatively charged complex, and circulate and pump it into the feed liquid chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; B. Pump 200 mL of H 2 O into the lithium chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; C. Pump 200 mL of H 2 O into the acid chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; D. Circulate and pump 200 mL of 0.5 mol / L Na 2 SO 4 into the anode chamber and the cathode chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; E. Turn on the power supply, conduct bipolar membrane electrodialysis under the condition of a constant current of 3 A, separate magnesium and lithium from the simulated Longmu Co brine, generate lithium hydroxide in the alkali chamber, and obtain ethylenediaminetetraacetic acid and magnesium ions in the acid chamber. As Figure 3 shown, after continuously operating for one hour, the lithium-magnesium separation factor of the bipolar membrane electrodialysis system is 900; as Figure 4As shown, the complex of magnesium ion and ethylenediaminetetraacetate (Mg[EDTA] 2- ) has a flux of 0.0235 mol·m -2 ·h -1 . Example 4

[0028] This example is used to illustrate the application of a new process for realizing magnesium-lithium separation by complexation reaction synergistic bipolar membrane electrodialysis to the treatment of simulated Dongtai Lake brine, with a magnesium-lithium mass ratio of 35.2. To keep the total ion concentration of the simulated Longmu Co Lake brine consistent with that in Example 3, the prepared simulated Dongtai Lake brine was diluted by 2 times. The main cation concentrations in the diluted simulated Dongtai Lake brine are shown in Table 2: Table 2 Composition of Diluted Simulated Dongtai Lake Brine

[0029] The bipolar membrane electrodialysis system used in this example is the same as that in Example 1. Further, this example includes the following steps: A. Add 0.125 mol of tetrasodium ethylenediaminetetraacetate dihydrate (the molar ratio of magnesium ion to ethylenediaminetetraacetate is 1) to 200 mL of simulated Dongtai Lake brine and stir well. Use 5 mol / L NaOH solution to adjust its pH to 9.2, so that magnesium ions selectively complex with ethylenediaminetetraacetate to form a negatively charged complex, and pump it into the feed chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; B. Pump 200 mL of H 2 O into the lithium chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; C. Pump 200 mL of H 2 O into the acid chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; D. Pump 200 mL of 0.5 mol / L Na 2 SO 4 into the anode chamber and cathode chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min and circulate; E. Turn on the power supply and perform bipolar membrane electrodialysis under a constant current of 3 A to separate magnesium and lithium from the simulated Dongtai Lake brine, generate lithium hydroxide in the alkali chamber, and obtain ethylenediaminetetraacetic acid and magnesium ions in the acid chamber. As Figure 3 shown, after continuous operation for one hour, the lithium-magnesium separation factor of the bipolar membrane electrodialysis system is 1756; as Figure 4 shown, the complex of magnesium ion and ethylenediaminetetraacetate (Mg[EDTA] 2- ) has a flux of 0.001 mol·m-2 ·h -1 。 Example 5

[0030] This example is used to illustrate the application of the new process of complexation reaction combined with bipolar membrane electrodialysis to achieve magnesium-lithium separation in the treatment of real Xinjiang salt lake brine, with a magnesium-lithium mass ratio of 14.5. The main cation concentrations are shown in Table 3 as follows: Table 3 Composition of Real Xinjiang Salt Lake Brine

[0031] The bipolar membrane electrodialysis system used in this example is the same as that in Example 1. Further, this example includes the following steps: A. Add 0.005 mol of disodium ethylenediaminetetraacetate dihydrate (the molar ratio of magnesium ion to ethylenediaminetetraacetate is 1) to 200 mL of real Xinjiang salt lake brine and stir well. Adjust its pH to 9.2 with 5 mol / L NaOH solution, so that magnesium ions selectively complex with ethylenediaminetetraacetate to form a negatively charged complex, and pump it into the feed chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min by a circulating pump; B. Pump 200 mL of H 2 O into the lithium chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; C. Pump 200 mL of H 2 O into the acid chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min; D. Pump 200 mL of 0.5 mol / L Na 2 SO 4 into the anode chamber and cathode chamber of the bipolar membrane electrodialysis system at a flow rate of 100 mL / min by a circulating pump; E. Turn on the power supply and perform bipolar membrane electrodialysis under the condition of a constant current of 3 A to separate magnesium and lithium from the real Xinjiang salt lake brine, and generate lithium hydroxide in the alkali chamber and ethylenediaminetetraacetic acid and magnesium ions in the acid chamber. The flux of the complex of magnesium ions and ethylenediaminetetraacetate (Mg[EDTA] 2- ) through the anion exchange membrane into the acid chamber is 0.056 mol·m -2 ·h -1 。 Example 6

[0032] This example is used to illustrate the application of the new process of complexation reaction combined with bipolar membrane electrodialysis to achieve magnesium-lithium separation in the treatment of magnesium-lithium mixed solution under strong alkaline environment.

[0033] The bipolar membrane electrodialysis system used in this example is the same as that in Example 1. Further, this example includes the following steps: A. Add 0.002 mol of disodium ethylenediaminetetraacetate, 0.002 mol of tetrasodium ethylenediaminetetraacetate, 0.002 mol of dipotassium ethylenediaminetetraacetate, and 0.001 mol of tetra - potassium ethylenediaminetetraacetate (the molar ratio of magnesium ions to ethylenediaminetetraacetate salts is 1.2) to 200 mL of a magnesium - lithium mixed solution containing 0.1 mol / L LiCl and 0.029 mol / L MgCl 2 (the mass ratio of magnesium to lithium is 1). Use a 5 mol / L KOH solution to adjust its pH to 9.2, so that magnesium ions selectively complex with ethylenediaminetetraacetate ions to form a negatively charged complex, and pump it into the feed chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min; B. Pump 200 mL of H 2 O into the lithium chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min; C. Pump 200 mL of H 2 O into the acid chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min; D. Pump 200 mL of 0.1 mol / L Na 2 SO 4 into the anode chamber and cathode chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min in a circulating manner; E. Turn on the power supply and perform bipolar membrane electrodialysis under a constant current of 3 A to separate magnesium and lithium from the pre - reacted magnesium - lithium solution, generate lithium hydroxide in the alkali chamber, and obtain ethylenediaminetetraacetic acid and magnesium ions in the acid chamber. Example 7

[0034] This example is used to illustrate the new process of realizing magnesium - lithium separation by the combination of complexation reaction and bipolar membrane electrodialysis applied to the treatment of magnesium - lithium mixed solution in a strong alkaline environment.

[0035] The bipolar membrane electrodialysis system used in this example is the same as that in Example 1. Further, this example includes the following steps: A. Add a mixed solution containing 0.1 mol of disodium ethylenediaminetetraacetate (the molar ratio of magnesium ions to ethylenediaminetetraacetate salts is 1), with a NaOH concentration of 2.5 mol / L and a KOH concentration of 2.5 mol / L, to 200 mL of a magnesium - lithium mixed solution containing 0.02 mol / L LiCl and 0.5 mol / L MgCl 2 (the mass ratio of magnesium to lithium is 86) to adjust its pH to 9.2, so that magnesium ions selectively complex with ethylenediaminetetraacetate ions to form a negatively charged complex, and pump it into the feed chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min; B. Pump 200 mL of H 2 O into the lithium chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min; C. Pump 200 mL of H 2 O into the acid chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min; D. Circulate and pump 200 mL of 0.5 mol / L Na 2 SO 4 into the anode chamber and the cathode chamber of the bipolar membrane electrodialysis system at a flow rate of 500 mL / min; E. Turn on the power supply and perform bipolar membrane electrodialysis under the condition of a constant current of 3 A to separate magnesium and lithium from the pre-reacted magnesium-lithium solution, generate lithium hydroxide in the alkali chamber, and obtain ethylenediaminetetraacetic acid and magnesium ions in the acid chamber.

Claims

1. A new process for separation of magnesium and lithium by complex reaction and bipolar membrane electrodialysis, characterized in that: The method comprises: Adding ethylenediaminetetraacetate to a magnesium-lithium mixed solution, adjusting the pH to 9.2-12 with an alkali solution, and performing a pre-reaction to obtain a pre-reaction magnesium-lithium mixed solution, so that magnesium ions and ethylenediaminetetraacetic acid ions are selectively complexed to form a complex with a negative charge; the ethylenediaminetetraacetate includes any one or more of disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, and tetrapotassium ethylenediaminetetraacetate; the alkali solution is any one or more of sodium hydroxide and potassium hydroxide; The pre-reacted magnesium-lithium mixed solution is introduced into the feed liquid chamber of the bipolar membrane electrodialysis system, and an electric field is applied to achieve magnesium-lithium separation.

2. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 1, characterized in that: The following steps are involved: A. Circulating and pumping the pre-reacted magnesium-lithium mixed solution into the feed liquid chamber of the bipolar membrane electrodialysis system; B. pumping the lithium solution into the lithium chamber of the bipolar membrane electrodialysis system; C. pumping the acid solution into the acid chamber of the bipolar membrane electrodialysis system; D. Circulating and pumping the electrolyte solution in the electrode liquid circulation device into the anode chamber and cathode chamber of the bipolar membrane electrodialysis system respectively; E. Turn on the power supply, apply voltage, and operate the bipolar membrane electrodialysis system to separate the pre-reacted magnesium-lithium solution into magnesium and lithium, and obtain a lithium solution in the lithium chamber, and generate ethylenediaminetetraacetic acid and magnesium ions in the acid chamber.

3. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 2 is characterized in that: The mass ratio of magnesium to lithium in the pre-reaction magnesium-lithium mixed solution in step A is 1-80.

4. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 2 is characterized in that: The molar ratio of magnesium ions to ethylenediaminetetraacetate in the pre-reaction magnesium-lithium mixed solution in step A is 1.0 to 1.

2.

5. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 2, characterized in that: The lithium solution in step B is a lithium-containing solution, and the concentration of the lithium solution is 0-0.1 mol / L.

6. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 2 is characterized in that: The acid solution in step C is one or more of a sulfuric acid solution, a hydrochloric acid solution and a nitric acid solution, and the concentration of the acid solution is 0-0.1 mol / L.

7. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 2, characterized in that: The electrolyte solution in step D is one or more of sodium sulfate solution, potassium sulfate solution, sodium nitrate solution or potassium nitrate solution, and the concentration of the electrolyte solution is 0.1-0.5 mol / L.

8. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 2, characterized in that: The pre-reaction magnesium-lithium mixed solution, acid solution, lithium solution, and electrolyte solution are circulated and pumped into the bipolar membrane electrodialysis system at a flow rate of 100-500 mL / min.

9. The novel process for separation of magnesium and lithium by complex reaction in cooperation with bipolar membrane electrodialysis according to claim 2, characterized in that: The bipolar membrane electrodialysis system in step AE includes: a bipolar membrane electrodialysis membrane stack, a cathode plate, an anode plate, an electrode liquid storage tank, a lithium liquid storage tank, an acid liquid storage tank, a feed liquid storage tank, an electrode liquid circulation device, a lithium liquid circulation device, an acid liquid circulation device, a feed liquid circulation device, and a DC regulated power supply; The cathode plate is connected to the negative electrode of the DC regulated power supply; The anode plate is connected to the positive electrode of the DC regulated power supply; The cathode plate and the anode plate are respectively arranged on two sides of the bipolar membrane electrodialysis membrane stack; The membranes of the bipolar membrane electrodialysis membrane stack from the anode plate to the cathode plate include a bipolar membrane, a first anion exchange membrane, a cation exchange membrane and a second anion exchange membrane in sequence; The anode plate, the membrane stack and the cathode plate are spaced to form an anode chamber, an acid chamber, a liquid chamber, a lithium chamber and a cathode chamber in sequence; The outlet of the electrode liquid circulation device is connected to the inlet of the anode chamber, the outlet of the anode chamber is connected to the inlet of the cathode chamber, the outlet of the cathode chamber is connected to the electrode liquid storage tank, and the electrode liquid storage tank is connected to the inlet of the electrode liquid circulation device; The outlet of the lithium liquid circulation device is connected to the inlet of the lithium chamber, the inlet of the lithium liquid circulation device is connected to the lithium liquid storage tank, and the lithium liquid storage tank is connected to the outlet of the lithium chamber; The outlet of the acid liquid circulation device is connected to the inlet of the acid chamber, the inlet of the acid liquid circulation device is connected to the acid liquid storage tank, and the acid liquid storage tank is connected to the outlet of the acid chamber; The outlet of the liquid circulation device is communicated with the inlet of the liquid chamber, the inlet of the liquid circulation device is communicated with the liquid storage tank, and the liquid storage tank is communicated with the outlet of the liquid chamber.

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