CN116426769A

CN116426769A - Method and device for extracting lithium from solution by a membraneless bipolar electrode

Info

Publication number: CN116426769A
Application number: CN202210003637.0A
Authority: CN
Inventors: 赵中伟; 刘旭恒
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2022-01-04
Filing date: 2022-01-04
Publication date: 2023-07-14
Anticipated expiration: 2042-01-04

Abstract

The invention belongs to the field of lithium extraction metallurgy, and particularly relates to a device for extracting lithium from a solution by using a membraneless bipolar electrode, which comprises an electrolytic cell, an end electrode and one or more conductive separators; the end electrodes comprise a first end electrode and a second end electrode which are respectively arranged at two ends of the electrolytic cell; the conductive separator is arranged in the electrolytic tank, and the conductive separator is connected with a power supply only through the electrodes at two ends, so that the generated induction electric field drives bipolar electrodes in the whole electrolytic tank to work in a series mode, synchronous and synchronous reaction of electroactive materials in the electrolytic tank is realized, and the stability and the circularity of the electrode materials of the electrolytic tank are improved; the current is consistent, the current is small, the control precision and manufacturing requirements on the power supply are low, the reactive power consumption is low, and the cost is low; the corrosion prevention problem of the copper bars is avoided, and the resistance heating energy consumption of the lead is low; the device has simple structure, low cost and low water quality requirement on the extracting solution without using a conductive diaphragm.

Description

Method and device for extracting lithium from solution by using membraneless bipolar electrode

Technical Field

The invention belongs to the field of lithium extraction metallurgy, and particularly relates to an electrochemical lithium extraction method and device adopting bipolar electrodes.

Background

Salt lake brine stores a large amount of lithium resources, accounting for about 78.3% of the total lithium reserves. At present, about 80% of lithium salt products are produced by taking salt lake brine as a raw material. However, the large-scale industrial production adopts the brine with low magnesium-lithium ratio at present, and most of salt lakes in China are characterized by high magnesium-lithium ratio, for example, the magnesium-lithium ratio of the salt lake brine of West Taiji-Nel is more than 40, and a small amount of Li ⁺ With a large amount of Mg ²⁺ Coexistence due to Li ⁺ And Mg (magnesium) ²⁺ Is similar in chemical nature, making extraction of lithium very difficult.

Chinese patent CN 102382984A discloses a method and device for separating magnesium from lithium and enriching lithium in salt lake brine, which adopts an anion exchange membrane to divide an electrodialysis device into a lithium salt chamber and a brine chamber, wherein the brine chamber is filled with salt lake brine, and the lithium salt chamber is filled with water containing no Mg ²⁺ Placing the conductive substrate coated with the ion sieve in a brine chamber as a cathode; placing the conductive matrix coated with the lithium-embedded ion sieve in a lithium salt chamber to serve as an anode; li in brine driven by external potential ⁺ And (3) embedding the lithium ion sieve into the ion sieve to form a lithium-embedded ion sieve, and releasing Li+ into the electrolyte by the lithium-embedded ion sieve in the lithium salt chamber to recover the lithium ion sieve. The method has the advantages of short flow, high lithium selectivity and the like.

But this method requires an anionic membrane between the cathode and anode to separate the brine from the lithium-rich liquid. However, on one hand, the ionic membrane has high cost and is easy to pollute so as to influence the service life; on the other hand, the ionic membrane is easy to physically damage in the equipment assembling and using process, so that the brine and the lithium-rich liquid solution are mixed to prevent lithium extraction, and particularly, the damage of the membrane is difficult to judge the damage position due to the damage of the membrane in the long-term continuous operation process of the device, and the ionic membrane can only be overhauled by disassembling the equipment, so that the process is complex and is not beneficial to industrial production.

In order to eliminate the influence of the diaphragm, chinese patent CN 110643831A discloses a diaphragm-free electrochemical lithium extraction system and a lithium extraction method, wherein equipment adopted by the method consists of an electrolytic tank, a washing tank, a power supply, a series of lithium absorption and desorption electrodes and an electronic balance electrode. Wherein, the electrolytic bath is divided into a raw material pool and a recovery pool which are sequentially and alternately arranged by a series of partition boards, and the different raw material pools and the recovery pools are respectively connected in series by connecting pipes. The raw material pool and the recovery pool are respectively filled with the lithium raw material to be extracted and the recovery liquid, and lithium is separated from the raw material pool and enriched in the recovery liquid through the switching of the electrodes between the raw material pool and the recovery pool.

In addition, chinese patent 201810262464.8 and 201811210840.5 disclose a continuous flow control asymmetric lithium ion capacitor lithium extraction device and method and a mobile electrochemical lithium extraction system, respectively, which do not require an ion membrane or a separator to physically isolate the cathode region from the anode region.

These methods eliminate the diaphragm and can reduce cost.

Disclosure of Invention

The inventors studied on a separator-free electrochemical lithium extraction system and a lithium extraction method, and found that although the separator is omitted, the following problems still remain:

firstly, each electrode in the method is connected with a power supply through a wire, and the use of a large number of wires also makes the equipment structure complex, increases the failure rate and increases the potential safety hazard and the production cost; the large quantity of wires occupy a large amount of space, so that the requirements on equipment layout are quite strict;

secondly, the electrode is required to be continuously moved among the raw material pool, the washing pool and the recovery pool, and the power supply is required to be repeatedly switched in the process, so that the energy consumption and the operation difficulty are certainly increased, the production is discontinuous, and the large-scale application is difficult;

third, each electrode needs to be connected with the positive electrode or the negative electrode of the electrode, and the lithium extraction device has high current and low voltage. During operation, accurate control of the voltage between adjacent electrodes is required. And in a high current mode of operation, the voltage drop across the wire is large. Also in Chinese patent 201910930569.0, fePO ₄ /KNiFe(CN) ₆ For example, the working area of the electrode plate generally required for industrial production is 1m ² Assuming that the current generated when a pair of positive and negative electrodes is operated is 10 amps, a cell with 100 pairs of electrodes will generate 1000 amps. If a cross-sectional area of 200mm is used ² (thickness. Times. Width: 5X 40 mm) ² ) Copper with a length of 1 meter was used as the conductive bar (copper resistivity of 0.072. Omega. Mm ² /m), the voltage difference across the copper bars reaches surprisingly 0.36 volts (1000 x 0.072/200 v=0.36 volts). The actual working tank voltage at the two ends of the electrode is usually 0.3-0.5V, and the current is continuously changed along with the progress of the reaction, so that the voltage drop is also continuously changed, and the accurate control of the voltage between the adjacent electrodes is further deteriorated. This results in a difference in cell voltage for each pair of electrodes during the extraction process, and a non-uniform reaction progress for each electrode. The reaction rate is slow due to too small cell voltage, so that the lithium extraction efficiency is reduced; the excessive tank voltage easily causes the overcharge of the electrode plate material, and seriously affects the cycle performance of the material.

Fourth, the large current-low voltage power supply system is complex, expensive to customize, high in reactive power consumption of equipment and unfavorable for automatic control of the process.

The invention provides the electrochemical method for extracting lithium from brine by using the electrochemical method, which aims at solving the problems that the existing electrochemical method for extracting lithium from brine is complex in connection, a large-current-low-voltage power supply system is difficult to manufacture, the electrode reaction progress is inconsistent, the automatic control is difficult, and the like.

The invention provides a device for extracting lithium from solution by using a membraneless bipolar electrode, which comprises an electrolytic cell, an end electrode and one or more conductive separators;

the end electrodes comprise a first end electrode and a second end electrode which are respectively arranged at two ends of the electrolytic cell; the conductive separator is arranged inside the electrolytic tank and is positioned between the two end electrodes; the first end electrode and the second end electrode are respectively used for connecting a positive electrode and a negative electrode of a power supply;

the surface of the conductive separator facing the first end electrode is coated with a lithium extraction layer; the lithium extraction layer is made of lithium electroactive materials which can release lithium but are in a lithium shortage state; the surface of the conductive separator facing the second end electrode is coated with an ion balance layer material, and the ion balance layer maintains ion electric neutral balance in the lithium-containing solution through chemical reaction; and the two sides of the conductive separator are respectively coated with lithium electroactive materials capable of extracting lithium but in an underlithium state and ion balance layer materials to form the bipolar electrode.

Coating materials with selective deintercalation on lithium ions and non-lithium ions on two sides of a separator material with electron conduction and ion non-conduction respectively to form bipolar electrodes; the coated bipolar electrodes are inserted into an electrolytic cell, and the two ends of the electrolytic cell are respectively provided with a specially-made first end electrode and a specially-made second end electrode, and the specially-made first end electrode and the specially-made second end electrode are respectively connected with the positive electrode and the negative electrode of a power supply, and are injected with a solution to be extracted containing lithium ions. After the power is turned on, the two end electrodes generate electric fields, and the surface of the bipolar electrode in the middle generates induced electric fields and induced charges; under the action of the electric field, lithium ions in the solution to be extracted are adsorbed on the adsorption material of the lithium extraction layer, and positive and negative ions in the solution to be extracted are balanced through the action of the ion balance layer. Because only the two ends of the electrolytic tank are connected with the positive electrode and the negative electrode of the power supply, the current passing through each electrode in the electrolytic tank is consistent, the reaction progress and the reaction degree of each electrode are synchronous, and the process is easy to control.

The essence of the technical scheme is that the electrodes at the two ends of the electrolytic cell are utilized to manufacture a uniform and stable electric field environment, and the operation environments of the surfaces of the bipolar electrodes are the same, so that the working mode of the electrolytic cell is conventional voltage-low current, the power supply system is simple, and the conductive mother discharge capacity is obviously reduced; in addition, the membrane is not arranged, so that the overall cost of the device and the requirement on the water quality of the solution to be extracted are reduced.

Further, the ion balance layer is a cation balance layer, and the cation balance layer material includes an electroactive material for adsorbing or desorbing cations other than lithium ions.

Further, the cation balance layer material adopts at least one material having a chemical formula (M) ₁ ) _x Fe _y (M ₂ ) _z (CN) ₆ Wherein 0.ltoreq.x.ltoreq.2, 0.ltoreq.y.ltoreq.2, 0.ltoreq.z.ltoreq.2, the valence state of Fe is +2 or +3, M ₁ Selected from Na, K, M ₂ Selected from Cr, ti, ni, co, mn, cu, zn.

Further, the ion balance layer is an anion balance layer, and the anion balance layer material comprises an electroactive material for adsorbing or desorbing anions.

Further, the anion balance layer material adopts at least one of polyferrocene, polypyrrole, polyaniline, polythiophene, porous carbon material, antimony, silver and bismuth.

Further, a surface of the first end electrode facing the conductive separator is coated with the ion balance layer material, and a surface of the second end electrode facing the conductive separator is coated with the lithium extraction layer material.

Preferably, the first end electrode, the second end electrode, and the conductive separator are disposed parallel to each other.

Preferably, a plurality of the bipolar electrodes are equally spaced. Further, the lithium electroactive material in the lithium extraction layer is a material capable of achieving reversible adsorption/desorption of lithium ions by valence changes.

Preferably, the lithium extraction layer may be LiFePO ₄ 、LiMn ₂ O ₄ 、LiMeO ₂ And one or more of the doped derivatives thereof (Me is one or more of Ni, co and Mn), and removing part or all of lithium after chemical oxidation or electrochemical oxidation.

To avoid a short circuit between the two electrodes, a gap must be present between the two conductive separators.

Preferably, the electrolytic cell further comprises an insulating water distribution net which is one more than the number of the conductive partition plates, wherein the water distribution net can be made of porous materials such as nylon net, PP net, PVC net and sponge, and is arranged in the electrolytic cell and distributed on two sides of the conductive partition plates. The water distribution net is arranged, so that the liquid to be extracted can be distributed more uniformly on the surface of the electrode on one hand; on the other hand, two conductive spacers may be spaced apart to prevent shorting.

Since both sides of the conductive separator respectively show different polarities during the lithium extraction process, the substrate material of the conductive separator is required to be not only electronically conductive, but also resistant to oxidation by electrooxidation and corrosion by electrochemical reduction. Further, the substrate material of the conductive separator is an inert conductive material.

Preferably, the substrate material of the conductive separator adopts dense carbon paper, dense carbon fiber sintered cloth, graphite, corrosion-resistant intermetallic compound, ruthenium-coated titanium, gold, platinum group metal and/or alloy thereof, or titanium, zirconium, hafnium, tantalum, niobium and/or alloy thereof. The shape of the material can be a plane plate shape, a corrugated plate shape and other special-shaped structures, and the surface can also be subjected to physical and chemical treatments such as smoothing, roughening and the like.

The invention also discloses a method for extracting lithium from the solution by the membraneless bipolar electrode, which comprises the following steps:

step 1, extracting lithium;

the device for extracting lithium from the solution by using the membraneless bipolar electrode is characterized in that the first end electrode is connected with the positive electrode of a power supply, the second end electrode is connected with the negative electrode of the power supply, and the solution to be extracted containing lithium elements is injected into the electrolytic tank; turning on a power supply, and allowing current to flow in from the first end electrode and flow out from the second end electrode, while changing as follows:

The lithium ions in the solution to be extracted enter the lithium extraction layer and are inserted into the lithium electroactive material in the under-lithium state to be extracted; the electroactive material in the ion balance layer maintains the balance of ionic charges in the solution to be extracted by adsorbing anions or releasing cations except lithium;

step 2, exhausting lithium liquid;

after the reaction in the step 1, the liquid to be extracted is converted into lithium-free liquid, a power supply is turned off, the lithium-free liquid is discharged, and the electrolytic tank is cleaned;

step 3, lithium enrichment;

injecting supporting electrolyte into the electrolytic tank in the step 3; changing the positive and negative poles of the power supply and turning on the power supply, the current flows in from the second end electrode and flows out from the first end electrode, and the following changes occur simultaneously:

the lithium electroactive material in the lithium extraction layer is oxidized, so that absorbed lithium ions are removed and released into the supporting electrolyte; the electroactive material in the ion balance layer maintains balance of ionic charge in the supporting electrolyte by releasing anions or adsorbing cations other than lithium;

step 4, discharging lithium-rich liquid;

after the reaction in the step 3, the supporting electrolyte is converted into lithium-rich liquid, a power supply is turned off, and the lithium-rich liquid is discharged and collected; the device for extracting lithium from the solution of the bipolar electrode is restored to the state before the start of the step 1 for reuse again.

In one embodiment, when the ion balance layer is a cation balance layer,

step 1, extracting lithium;

the lithium ions in the solution to be extracted enter the lithium extraction layer and are inserted into the lithium electroactive material in the under-lithium state to be extracted; the electroactive material in the cation balance layer is oxidized to remove other cations except lithium ions which are adsorbed, and is released into the liquid to be extracted;

step 2, exhausting lithium liquid;

step 3, lithium enrichment;

The lithium electroactive material in the lithium extraction layer is oxidized, so that absorbed lithium ions are removed and released into the supporting electrolyte; the electroactive material in the cation balancing layer is reduced and other cations in the supporting electrolyte are intercalated into the electroactive material.

Step 4, discharging lithium-rich liquid;

In another embodiment, when the ion balance layer is an anion balance layer,

step 1, extracting lithium;

the device for extracting lithium from the solution by using the membraneless bipolar electrode is characterized in that the first end electrode is connected with the positive electrode of a power supply, the second end electrode is connected with the negative electrode of the power supply, and the solution to be extracted containing lithium elements is injected into the electrolytic tank; turning on a power supply, and allowing current to flow in from the second end electrode and flow out from the first end electrode, while changing as follows:

the lithium ions in the solution to be extracted enter the lithium extraction layer and are inserted into the lithium electroactive material in the under-lithium state to be extracted; anions in the liquid to be extracted enter the anion balance layer and are solidified;

Step 2, exhausting lithium liquid;

step 3, lithium enrichment;

the lithium electroactive material in the lithium extraction layer is oxidized, so that absorbed lithium ions are removed and released into the supporting electrolyte; the anions adsorbed in the anion balance layer are desorbed and released into the supporting electrolyte.

Step 4, discharging lithium-rich liquid;

Further, the lithium-rich solution from the previous cycle can be used as a supporting electrolyte for the next cycle, and is continuously used for extracting lithium to increase the lithium concentration of the solution; the lean lithium solution from the previous cycle can be used as the lithium extraction solution for the next cycle to increase the recovery rate of lithium.

Further, the liquid to be extracted adopts any one or more mixed liquid of brine, old brine, underground brine, oil field brine, ore decomposition and lithium-containing solution and lithium precipitation mother liquor obtained by secondary resource recovery at any stage of salt lake raw brine and raw brine treatment.

Further, to balance the extraction of lithium and intercalation of other cations, the total molar amount of cations in the supporting electrolyte that are adsorbed by the cation balance layer material is greater than the delithiated molar amount of the lithium electroactive material.

The higher the lithium concentration in the solution to be extracted, the faster the electrochemical extraction of lithium can be correspondingly. Therefore, in order to maintain the extraction rate of lithium at an economically reasonable level, there is a certain requirement for the concentration of lithium in the solution.

Preferably, the lithium concentration in the solution to be extracted is preferably not less than 0.05g/L.

Due to the use, the lithium extraction layer material itself has a difference in lithium removal/intercalation potential, (wherein, liFePO ₄ Is 0.4-0.6V vs. SHE, liMn ₂ O ₄ Is 0.7 to 1.0vs. SHE, ternary material LiMeO ₂ 0.7～1.0vs.SHE、(M ₁ ) _x Fe _y (M ₂ ) _z (CN) ₆ The deintercalated sodium-potassium ions are about 0.4-0.6 v vs. she) so that the bipolar electrode has different coating materials on both sides and thus different voltages are required during the extraction of lithium. And the required voltage can be adjusted within a certain range according to the lithium concentration of the lithium-containing solution.

Preferably, the power supply voltage is (0.05-0.8) x (n+1) volts, where n is the number of conductive spacers.

The invention has the beneficial effects that:

1. the induced electric field generated by the connection of the end electrode and the power supply drives the bipolar electrode inside the whole electrolytic cell to work, so that synchronous and synchronous reaction of electroactive materials inside the electrolytic cell is realized, and the stability and the circularity of the electrode materials of the electrolytic cell are improved;

2. the current passing through each electrode is consistent, the current is small, the control precision and manufacturing requirements on the power supply are low, the reactive power consumption is low, and the cost is low;

3. the use problem of a large number of bus bars in the traditional electrochemical lithium extraction method is greatly reduced, and the problems of corrosion resistance and voltage drop of copper bars are avoided;

4. the device has simple structure, low cost and easy equipment enlargement and equipment maintenance without using the traditional anion membrane;

5. the lithium extraction process has remarkable environmental protection benefit, and can realize high-multiple enrichment of lithium.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, and it should be apparent that the drawings in the following description are only some embodiments of the present invention and should not be construed as limiting the scope. Other figures may be derived from these figures without inventive effort for a person of ordinary skill in the art.

FIG. 1 is a simplified schematic diagram of an apparatus for extracting lithium from a solution using a bipolar electrode according to the present invention;

FIG. 2 is a simplified schematic diagram of the apparatus of FIG. 1 being integrated in series;

FIG. 3 is a graph showing the change of the lithium concentration of brine and the lithium concentration of lithium-rich liquid obtained in examples 1 to 7 with time;

FIG. 4 is a graph showing the adsorption capacity of the electrode materials of examples 1 to 7 over time;

FIG. 5 is a graph showing the relationship between the lithium concentration of the lithium-rich solution and the number of cycles in the process of extracting lithium in 6 cycles in example 7;

FIG. 6 example 8 lithium concentration change of lithium rich solution during lithium extraction process of brine and lithium removal process;

FIG. 7 variation of cell voltage with time during lithium extraction in example 8;

FIG. 8 variation of adsorption capacity of materials during cyclic lithium extraction in example 8;

FIG. 9 example 9 lithium concentration change of lithium rich solution during lithium extraction process of brine and lithium removal process;

FIG. 10 adsorption capacity change during example 9 cycle.

Icon: 1-electrolytic tank, 2-first end electrode, 3-second end electrode, 4-water distribution net, 5-ion balance layer, 6-lithium extraction layer, 7-conductive separator and 8-power supply.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, based on the examples herein, which are within the scope of the invention as defined by the claims, will be within the scope of the invention as defined by the claims.

FIG. 1 is a simplified schematic diagram of an apparatus for extracting lithium from a solution using a bipolar electrode according to the present invention; fig. 2 is a simplified schematic diagram of the device of fig. 1 integrated in series. Referring to fig. 1 and 2, the apparatus comprises an electrolytic cell 1, first and

second end electrodes

2 and 3, and an electrically conductive separator 7.

The first end electrode 2 and the second end electrode 3 are respectively arranged at two ends of the electrolytic tank 1 and are positioned in the electrolytic tank 1; the conductive separator 7 is arranged inside the electrolytic cell 1 and between the first end electrode 2 and the second end electrode 3; the first end electrode 2 and the second end electrode 3 are used to connect the positive and negative poles of the power supply, respectively.

The surface of the conductive separator 7 facing the first end electrode 2 is coated with a lithium extraction layer 6; the lithium extraction layer 6 is made of lithium electroactive materials which can release lithium but are in a lithium shortage state; the surface of the conductive separator 7 facing the second end electrode 3 is coated with an ion balance layer 5, said ion balance layer 5 being used for balancing the ionic charge in the lithium-containing solution. The ion balance layer 5, the lithium extraction layer 6 and the conductive separator 7 together constitute a bipolar electrode.

The water distribution nets 4 are all arranged in the electrolytic tank 1 and distributed on two sides of the conductive partition plate 7. A water distribution net 4 is arranged between the electrodes to avoid short circuit between the electrodes and uniformly distribute the solution on the surfaces of the electrodes. As shown in fig. 1, the conductive separator 7 may or may not be made of the same material as the first end electrode 2 and the second end electrode 3, and the present application is not limited thereto; the number of bipolar electrodes in fig. 1 is also not limited to the number shown in the drawings, and may be set according to specific lithium extraction requirements. In addition, the electrodes can be vertically and parallelly arranged, can be horizontally stacked and arranged, and can be vertically and multiply or vertically/horizontally alternately arranged in the electrolytic tank 1 according to actual needs.

FIG. 2 is a simplified schematic diagram of the apparatus of FIG. 1 being integrated in series, i.e., when the number of bipolar electrodes in a single cell is too large, it can be controlled in accordance with the power output sub-module; the plurality of electrolytic cells can be externally operated in series-parallel through a power supply system. In addition, when a plurality of electrolytic tanks are in serial-parallel connection operation outside, the solution in the electrolytic tanks is conveyed, and independent waterways can be connected in series-parallel according to actual needs.

The present invention will be described in further detail with reference to examples.

Example 1

Preparation of membraneless bipolar electrode and lithium extraction device (cation balance layer adopted):

(1) 1600g of lithium iron phosphate powder, acetylene black and polyvinylidene fluoride are dry-mixed according to a ratio of 8:1:1, 2500g N-methyl pyrrolidone is added, a double-planetary stirrer is adopted for stirring, the stirring speed is 80r/min, the dispersing speed is 1000r/min, and the uniform stirring is carried out for 10 hours to obtain mixed homogenate.

(2) Will 1600g K ₂ MnFe(CN) ₆ Dry-mixing the powder, acetylene black and polyvinylidene fluoride according to a ratio of 8:1:1, then adding 2500g N-methyl pyrrolidone, stirring by a double-planetary stirrer at a stirring speed of 80r/min and a dispersing speed of 1000r/min, and uniformly stirring for 10 hours to obtain a mixed homogenate.

(3) Taking 2 pieces of 10×10cm ² The titanium sheet of (a) is respectively marked as a first end electrode and a second end electrode, one surface of the first end electrode is coated with lithium iron phosphate homogenate, and one surface of the second end electrode is coated with K ₂ MnFe(CN) ₆ Homogenizing, wherein the coating density of both homogenates is 80mg/cm ² The coated electrode was then dried in vacuo at 90℃for 12 hours.

(4) Another 4 pieces of 10×10cm ² The lithium iron phosphate homogenate was uniformly coated on one side (designated as a side) of the titanium sheet, and the coated electrode was then dried in vacuo at 90 ℃ for 12 hours.

(5) Dividing an electrolytic tank into a cathode chamber and an anode chamber by using an anion exchange membrane, taking the electrode coated with lithium iron phosphate in the step (3) as an anode, taking foam nickel as a cathode, adding 1L of 10g/L NaCl as a supporting electrolyte into the cathode and anode, and simultaneously adjusting the pH value of the cathode to be 2-3 by using sulfuric acid. Constant voltage electrolysis is carried out at the voltage of 1.0V until the current is reduced to 20 percent of the initial current, the electrode plate lithium removal pretreatment process is finished, and the electrode obtained by the lithium removal pretreatment is washed with water and dried for standby.

(6) Drying the electrode after lithium removal, and then drying K ₂ MnFe(CN) ₆ The other side (denoted as B side) of the titanium sheet was uniformly coated with the slurry having a coating density of 80mg/cm ² The coated electrode was then dried in vacuo at 90℃for 12 hours to obtain a bipolar electrode.

(7) The lithium extraction electrolytic cell is assembled by 4 bipolar electrodes, a first end electrode and a second end electrode, wherein the first end electrode and the second end electrode are end plates respectively, the A surface of the bipolar plate is opposite to the second end electrode plate, and the B surface of the bipolar plate is opposite to the first end electrode plate.

Method for extracting lithium from solution (using cation balance layer) of membraneless bipolar electrode:

(1) Injecting 1L of salt lake brine (the brine components are shown in table 1) into a cavity of an electrolytic tank, controlling the applied voltage to be 1.5V, carrying out constant-voltage electrolysis to extract lithium, connecting a first end electrode with a negative electrode of a power supply, connecting a second end electrode with a positive electrode of the power supply, ending the lithium extraction process when the current in the lithium extraction process is reduced to 10% of the initial current, discharging lithium depletion liquid, and injecting 1L of clear water into the cavity for 3 times;

(2) 1L of 10g/L KCl solution is used as supporting electrolyte to be injected into a cavity of an electrolytic tank, a first end electrode is connected with the positive electrode of a power supply, a second end electrode is connected with the negative electrode of the power supply, the external voltage is controlled to be 1.5V, constant-voltage electrolytic delithiation is carried out, the lithium extraction process is finished when the current in the delithiation process is reduced to 10% of the initial current, then the lithium-rich liquid is discharged, and 1L of clean water is injected into the cavity for cleaning.

Table 1 table of major ionic components of brine

Examples 2 to 6

Examples 2-6 are similar in operation to example 1, except that specific parameters are changed as shown in tables 2-3 below:

table 2 preparation of devices for extracting lithium of examples 1 to 6

TABLE 3 examples 1-6 main operation parameters and extraction Performance of lithium extraction procedure

To further illustrate the beneficial effects of the present invention, the lithium-rich liquid compositions obtained in examples 1-6 were tested and the data are shown in Table 4 below:

TABLE 4 Table of the components of the lithium-rich liquid obtained in examples 1 to 6

Note that: * KCl was initially added at 10g/L as a supporting electrolyte, # was initially added at 10g/L NaCl as a supporting electrolyte.

As is clear from the results shown in fig. 3, 4 and table 4, the specific adsorption capacities of the electrodes of examples 1 to 3 were slightly larger than those of examples 4 to 6. Thus, the lithium concentration in the brine can be reduced even lower during one cycle of examples 1-3. The rejection rate of the impurity ions in the lithium-rich liquid can reach more than 98 percent except that the impurity ions in the pre-added lithium-rich liquid are less.

Example 7

The operation parameters of this example are the same as those of example 1, except that in this example, for example 1, the step (5) and the step (6) of example 1 are sequentially repeated to perform a lithium extraction experiment for 6 cycles, the brine used for extracting lithium each time is fresh brine, the lithium-rich liquid used is the lithium-rich liquid obtained in the previous cycle, and at the same time, a certain amount of KCl is added to the lithium-rich liquid every cycle, so as to ensure that the KCl concentration is controlled at 10g/L.

The change in lithium concentration of the lithium-rich solution during the 6 cycles is shown in fig. 5. From the figure, it can be seen that by cyclically extracting lithium, continuous enrichment of lithium can be achieved.

Comparative example 1

This example differs from example 1 in that both sides of each titanium sheet were coated with the same material, wherein 3 titanium sheets were coated with lithium iron phosphate slurry, and the electrode coated with lithium iron phosphate was delithiated to prepare Cheng Linsuan iron by the method of example 1; coating K on 3 other electrode plates ₂ MnFe(CN) ₆ The coating density of both electrode materials was 80mg/cm ² The electrode sheets coated with the two electrode materials are alternately arranged (double sided). In the lithium extraction process, 3 phosphoric acid electrodes are used as cathodes, and each cathode electrode is connected with the cathode of a power supply; 3 pieces of K ₂ MnFe(CN) ₆ The electrodes are anodes, and each anode electrode is connected to the positive pole of the power supply. Controlling the cell voltage to be 0.3V in the lithium extraction process, controlling the current in the electrolysis ending process to be 10% of the initial reaction current, and controlling the average process current to be 1.83A; the cell voltage was controlled to 0.3V during delithiation and the average current during the process was 1.92A.

The experimental results of comparative example 1 and comparative example 1 revealed that the difference in lithium extraction effect between the two methods was not too large, but the bipolar electrode extraction method of example 1 was used to extract lithium at a current value of 1/5 of that of comparative example 1 and at a voltage of 5 times.

In the industrial production process, the electrode area of the single electrode is generally required to reach 1m ² Area of sheet Zhang Dianji according to example 1 is 0.01m ² It can be seen thatThe average current of the single Zhang Dianji in the industrial lithium extraction process can reach 36A, if the cell voltage corresponding to 100 bipolar electrodes is about 35V, the cell voltage and the cell voltage are well matched, and the power supply can be satisfied by adopting a conventional power supply. In contrast, according to the lithium extraction method of comparative example 1, the current reaches 3500A, the voltage at this time is only 0.35V, the current-voltage matching degree is poor, and the power supply system needs special custom-made processing.

Example 8

Preparation of membraneless bipolar electrode and lithium extraction device (adopting anion balance layer):

(1) Adding a lithium iron phosphate material into a sodium persulfate solution with the concentration of 0.1mol/L, controlling the molar ratio of the lithium iron phosphate to the sodium persulfate to be 2:1, reacting for 6 hours at normal temperature, and then filtering, washing and drying to obtain the pre-delithiated under-lithium ferric phosphate.

(2) Adding under-lithium ferric phosphate, acetylene black and polyvinylidene fluoride into an N-methyl pyrrolidone solvent according to a mass ratio of 8:1:1, and stirring for 10 hours by adopting a double-planetary stirrer to obtain mixed homogenate, thereby obtaining under-lithium ferric phosphate slurry; adding polypyrrole, a conductive agent acetylene black and a binder PVDF into an N-methyl pyrrolidone solvent according to a mass ratio of 7:2:1, and stirring for 10 hours by adopting a double-planetary stirrer to obtain a mixed homogenate, thus obtaining ppy slurry;

(3) Coating (2) under-lithium iron phosphate slurry and polypyrrole slurry on two sides of a 50X 50cm titanium sheet respectively, wherein the coating density is 200mg/cm ² And dried at 80 ℃ for 12 hours to obtain the bipolar electrode.

(4) Respectively coating the under-lithium ferric phosphate slurry and the polypyrrole slurry on two surfaces of two 50X 50cm titanium sheets with the coating density of 200mg/cm ² And drying at 80 ℃ for 12 hours to respectively obtain an under-lithium iron phosphate terminal electrode and a polypyrrole anion active terminal electrode.

(5) A lithium extraction lithium electrolysis tank is built by an under-lithium iron phosphate terminal electrode, a polypyrrole anion active terminal electrode, 9 bipolar electrodes and a water distribution network, and the polar distance between polar plates is 1-2mm; the iron phosphate terminal electrode is connected with the negative electrode of the power supply, and the polypyrrole terminal electrode is connected with the positive electrode of the power supply.

Method for extracting lithium from solution (using anion balance layer) of membraneless bipolar electrode:

(1) Extracting lithium: continuously and circularly injecting salt lake brine (the total volume of the brine is 250L) into the electrolytic tank, and starting a power supply. In the process of extracting lithium, constant-current electrolysis is carried out by using current of 6A to extract lithium, and when the cell voltage reaches 4.0V, constant-voltage electrolysis is carried out until the current is reduced to 0.6A. Discharging brine after electrolysis is finished, injecting 30L of clean water into the electrolytic tank for 3 times (10L each time) of cyclic cleaning, and discharging washing water after 5 minutes each time of cleaning;

(2) Removing lithium: 15L of NaCl solution with the concentration of 5g/L is injected between the electrolytic tanks as supporting electrolyte, the positive electrode and the negative electrode of the lithium extraction process are exchanged, constant voltage electrolysis is carried out at the voltage of 5.0V, the electrolysis process is finished when the current is less than 10% of the initial current, and then the lithium-rich solution obtained by the second period electrolysis is discharged.

(3) And (3) circulating the step (1) and the step (2) to realize the circulating operation of the system.

The change of the brine lithium concentration in the lithium extraction process and the change of the lithium concentration of the lithium-rich liquid in the lithium removal process are shown in tables 5 and 6, the change of the tank voltage in the lithium extraction process is shown in fig. 7, and the change of the adsorption capacity in the circulation process is shown in fig. 8.

TABLE 5 main components (g/L) of salt lake brine and lithium-rich solution during lithium extraction

Solution	Li	Na	Mg	K	B	SO ₄ ^2-
							Initial brine	0.55	59.34	86.36	5.34	1.74	18.53
Brine after lithium extraction	0.04	59.10	86.01	5.32	1.73	18.44
							Lithium-rich liquid	8.43	3.16	1.44	0.09	0.03	0.31

As can be seen from table 5 and fig. 6, the lithium extraction mode of the bipolar electrode was adopted even though the extraction of lithium could be effectively achieved. After lithium is extracted by electrolysis for 8 hours, the concentration of lithium in brine can be reduced from initial 0.55g/L to 0.04g/L, the lithium extraction rate can reach more than 90%, the rejection rate of impurity ions in the process is more than 99%, and the selectivity is good. In addition, the lithium removal can be basically completed within 4 hours, the lithium concentration in the lithium-rich liquid can reach 8.4g/L, and the impurity ions are relatively low. The Na/Li, mg/Li ratios in the lithium-rich liquor also decreased from 107:1, 157:1 in the original brine to 0.37:1 and 0.17:1. In the actual desorption process, impurities such as sodium, magnesium and the like are mainly the brine carried by the electrode plate adsorption, and if a low-concentration LiCl solution is used as a supporting electrolyte, na/Li in the lithium-rich solution can be reduced to be lower.

As can be seen from fig. 7, the whole lithium extraction process can be roughly divided into 3 sections, namely a spontaneous lithium extraction process, a constant-current lithium extraction process and a constant-voltage lithium extraction process. Lithium extraction can be realized without external power supply in the spontaneous lithium extraction process. Further, as can be seen from the cycle performance shown in fig. 8, the adsorption capacity of lithium active electrode material for lithium during lithium extraction was maintained at substantially 25mg (Li)/g (active material), and the cycle performance was excellent.

Example 9

The same electrode preparation method and procedure as in example 8 were used to change the lithium electroactive material to LiMn ₂ O ₄ The brine volume became 200L. In the lithium extraction process, constant current electrolysis is carried out by using 10A current, and when the cell voltage reaches 7.0V, constant voltage electrolysis is carried out until the current is reduced to 1A; the delithiation process was then carried out by constant voltage electrolysis at a cell voltage of 7.0V until the end of 1/10 of the initial value of the current reduction.

As can be seen from Table 6, liMn was used ₂ O ₄ The concentration of lithium in the brine can be reduced to 0.08g/L, the concentration of lithium in the lithium-rich liquid can be enriched to 6.67g/L, and the retention rate of other impurity ions is kept at about 99%. As can be seen from the lithium concentration change chart of fig. 9 and the cycle performance shown in fig. 10, the adsorption capacity of the material for lithium can be stabilized at substantially 20mg (Li)/g (active material), and the cycle performance is excellent.

TABLE 6 Main Components (g/L) of salt lake brine and lithium-rich solution during lithium extraction

Solution	Li	Na	Mg	K	B	SO ₄ ^2-	Cl ^-
								Initial brine	0.55	59.34	86.36	5.34	1.74	18.53	223.5
Brine after lithium extraction	0.08	59.16	86.10	5.32	1.73	18.46	/
								Lithium-rich liquid	6.67	3.11	1.35	0.08	0.02	0.19	/

Examples 10 to 19

Examples 10 to 19 were similar to example 8 in operation, the number of bipolar electrodes was 9, the electrode coating size was the same, constant voltage electrolysis was used for extracting lithium and removing lithium, brine and electrolyte were the same as in example, and other specific parameters were changed as shown in table 7 below.

The solution components after lithium extraction of different lithium extraction systems are shown in table 8, and the ion components of the obtained lithium-rich solution are shown in table 9.

Table 7 examples 10 to 19 lithium extraction device parameter tables

Table 8 solution Components (g/L) of brine after lithium extraction in examples 10 to 19

Table 9 examples 10 to 19 lithium-rich solution components (g/L)

It can be seen from tables 8 and 9 that the electrochemical lithium extraction system formed by matching lithium iron phosphate, lithium manganate and ternary materials with different anion electrode materials has good lithium extraction performance, and the impurity content of the obtained lithium-rich liquid is low. In addition, the current is mostly about 6 to 8A in both the lithium extraction process and the lithium release process.

Comparative example 2

(2) Iron phosphate slurry and polypyrrole slurry were prepared in the same manner as in example 1. The lithium iron phosphate slurry and the polypyrrole slurry are respectively coated on two sides of a titanium sheet (the size of the titanium sheet is 50 multiplied by 50 cm) ² The same material on both sides), the same coating density and drying conditions as in the examples were used to prepare iron phosphate electrodes and polypyrrole anion electrodes, respectively;

(3) 5 ferric phosphate electrodes and 5 polypyrrole electrodes are alternately arranged in the electrolytic tank, and water distribution is carried out between the electrodes by adopting a water distribution net; each ferric phosphate electrode is connected with the negative electrode of the power supply through a wire, and each polypyrrole electrode is connected with the positive electrode of the power supply to form the membrane stack lithium-extracted electrolytic tank in the traditional connection mode and working mode.

(4) Extracting lithium: continuously and circularly injecting salt lake brine (the total volume of the brine is 250L) into the electrolytic tank, and starting a power supply. And in the lithium extraction process, constant-voltage electrolysis is carried out to extract lithium by adopting a cell voltage of 0.4V, and the current is reduced to the initial 10 percent and is ended. Discharging brine after electrolysis is finished, injecting 30L of clean water into the electrolytic tank for 3 times (10L each time) of cyclic cleaning, and discharging washing water after 5 minutes each time of cleaning;

(5) Removing lithium: 15L of NaCl solution with the concentration of 5g/L is injected between the electrolytic tanks as supporting electrolyte, the positive electrode and the negative electrode of the lithium extraction process are exchanged, constant voltage electrolysis is carried out at the voltage of 0.4V, the electrolysis process is finished when the current is less than 10% of the initial current, and then the lithium-rich solution obtained by the second period electrolysis is discharged.

(6) And (5) circulating the steps (4) to (5) to realize the circulating operation of the system.

Comparative example 3

This comparisonThe only difference between the example and comparative example 2 is that the present comparative example changes the lithium iron phosphate in step (1) of comparative example 1 to LiMn ₂ O ₄ Polypyrrole is changed into polyaniline; in the lithium extraction process, electrolysis was performed at a voltage of 0.6V.

Comparative example 4

The present comparative example differs from comparative example 2 only in that the present comparative example changes the lithium iron phosphate in step (1) of comparative example 1 to LiNi _0.6 Co _0.2 Mn _0.2 O ₂ Polypyrrole is changed into polymeric ferrocene, and electrolysis is performed at a voltage of 0.7V in the lithium extraction process.

The lithium concentration of the brine and the main ion concentration in the lithium-rich solution before and after lithium extraction in comparative examples 2 to 4 are shown in table 10.

TABLE 10 concentration of major ions (g/L) in brine and lithium-rich liquor after lithium extraction

The lithium extraction effects of comparative examples 2 to 4 are comparable to those of the lithium extraction modes of examples 8, 15 and 18. However, it is apparent from comparison of the process currents that the voltages used in examples 8, 18 and 15 are about 10 times that of the comparative examples using the same number of electrodes; however, the current of the comparative example was about 80A, which is about 10 times that of the corresponding system examples 8, 15 and 18. It can be seen that the embodiment scheme can be adopted to convert the original low voltage mode into the conventional voltage, and simultaneously convert the high current in the comparative example into the low current.

In the actual production process, in order to ensure the lithium extraction quantity of each membrane stack electrolytic cell, the assembly quantity of the electrodes in the unit electrolytic cell is always required to reach 100-200 sheets. In this way, the current will be about 100 times that of the present patent by using the operation modes of comparative examples 2 to 4. The lithium extraction system has overlarge current, so that the manufacturing cost of a power supply is reduced, and the busbar voltage drop caused by high-current operation can greatly influence the working condition of the electrode of the electrolytic cell.

In addition, the power supply used in the comparative example is low voltage-high current, belongs to a special power supply system and has high processing cost. The bipolar electrode working mode of the patent can be converted into conventional voltage (the voltage required by 100 bipolar electrolytic cells is about 20-100V) -low current (the current when the bipolar electrodes are 1 square meter is about 20-50A), the power supply system can adopt a conventional power supply, the current passing through each bipolar electrode is consistent, and the problems of the power supply system, the electrode reaction consistency and the like in the traditional lithium lifting mode can be fundamentally solved.

The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A device for extracting lithium from a solution by a filmless bipolar electrode, characterized in that it comprises an electrolyzer, an end electrode, one or more conductive separators;

The end electrodes include a first end electrode and a second end electrode respectively arranged at both ends of the electrolytic cell; the conductive separator is arranged inside the electrolytic cell and is located between the two end electrodes Between; the first end electrode and the second end electrode are respectively used to connect the positive pole and the negative pole of the power supply;

The surface of the conductive separator facing the electrode at the first end is coated with a lithium extraction layer; the lithium extraction layer adopts a lithium electroactive material that can deintercalate lithium but is in a lithium-deficient state; the conductive separator faces the second end The surface of the electrode is coated with an ion balance layer material, and the ion balance layer maintains the ion neutrality balance in the lithium-containing solution through a chemical reaction; A bipolar electrode is formed after the lithium electroactive material and the ion balance layer material.

2. The device for extracting lithium from the solution by the filmless bipolar electrode according to claim 1, wherein the ion balance layer is a cation balance layer, and the cation balance layer material includes Electroactive materials with cations other than lithium ions;

Optionally, the cation balance layer material adopts at least one material with the chemical formula (M ₁ ) _x Fe _y (M ₂ ) _z (CN) ₆ , wherein, 0≤x≤2, 0<y≤2, 0 ≤z≤2, the valence state of Fe is +2 or +3, M ₁ is selected from Na, K, and M ₂ is selected from Cr, Ti, Ni, Co, Mn, Cu, Zn.

3. The device for extracting lithium from the solution by the membraneless bipolar electrode according to claim 1, wherein the ion balance layer is an anion balance layer, and the anion balance layer material includes an anion for adsorption or desorption. electroactive materials;

Optionally, the anion balance layer material is at least one of polyferrocene, polypyrrole, polyaniline, polythiophene, porous carbon material, antimony, silver, and bismuth.

4. The device for extracting lithium from a solution by a membraneless bipolar electrode according to any one of claims 1-3, wherein the surface of the first end electrode facing the conductive separator is coated with The ion balance layer material, the surface of the second end electrode facing the conductive separator is coated with the lithium extraction layer material.

5. The device for extracting lithium from the solution by the membraneless bipolar electrode according to any one of claims 1-3, is characterized in that, it also includes an insulating water distribution network one more than the number of the conductive separators, the The water distribution nets are all arranged in the electrolytic cell and distributed on both sides of the conductive separator;

Optionally, the conductive separator is an electrochemically inert electronic conductor, which is dense carbon paper, dense carbon fiber sintered cloth, graphite, corrosion-resistant intermetallic compound, ruthenium-coated titanium, gold, platinum group metals and/or alloys thereof, or Titanium, zirconium, hafnium, tantalum, niobium and/or their alloys.

6. The device for extracting lithium from a solution by a membraneless bipolar electrode according to any one of claims 1-3, wherein the lithium extraction layer material is LiFePO ₄ , LiMn ₂ O ₄ , LiMeO ₂ and the like A mixture of one or more of doped derivatives (Me is one or more of Ni, Co, Mn), prepared by removing part or all of lithium after chemical oxidation or electrochemical oxidation.

7. A method for extracting lithium from a solution by a membraneless bipolar electrode, comprising the steps of:

Step 1, lithium extraction;

Take the device for extracting lithium from the solution by the membraneless bipolar electrode described in any one of claims 1-6, connect the first end electrode to the positive pole of the power supply, and connect the second end electrode to the negative pole of the power supply Connected, inject lithium-containing liquid to be extracted into the electrolytic cell; turn on the power supply, the current flows in from the first end electrode, flows out from the second end electrode, and the following changes occur simultaneously:

Lithium ions in the liquid to be extracted enter the lithium extraction layer and are extracted by intercalating into the lithium-deficient lithium electroactive material; the electroactive material in the ion balance layer absorbs anions or releases cations other than lithium, Keep the ionic charge in the liquid to be extracted in balance;

Step 2, exhaust lithium solution;

After the reaction in step 1, the liquid to be extracted is transformed into a lithium-depleted liquid, the power is turned off, the lithium-deficient liquid is discharged, and the electrolytic cell is cleaned;

Step 3, lithium enrichment;

Inject the supporting electrolyte into the electrolytic cell described in step 3; switch the positive and negative poles of the power supply and turn on the power supply, the current flows in from the second end electrode and flows out from the first end electrode, and the following changes occur at the same time:

The lithium electroactive material in the lithium extraction layer is oxidized, and then the adsorbed lithium ions are released and released into the supporting electrolyte; the electroactive material in the ion balance layer makes the support The ionic charge in the electrolyte is maintained in balance;

Step 4, drain the lithium-rich solution;

After the reaction in step 3, the supporting electrolyte is converted into a lithium-rich solution, the power is turned off, and the lithium-rich solution is discharged and collected; the device for extracting lithium from the solution by the bipolar electrode returns to the state before the start of step 1 , for reuse again.

8. the filmless bipolar electrode according to claim 7 extracts the method for lithium from solution, it is characterized in that, when described ion balance layer is cationic balance layer,

In step 1, the electroactive material in the cation balance layer oxidizes and desorbs other cations except lithium ions that have been adsorbed, and is released into the solution to be extracted;

In step 3, the electroactive material in the cation balance layer is reduced, and other cations in the supporting electrolyte are embedded into the electroactive material;

Or, when the ion balance layer is an anion balance layer,

In step 1, the anions in the liquid to be extracted enter the anion balance layer and are solidified;

In step 3, the anions adsorbed in the anion balance layer are desorbed and released into the supporting electrolyte.

9. The method for extracting lithium from a solution by a membraneless bipolar electrode according to claim 7, wherein the solution to be extracted can be salt lake brine, underground brine, oil field brine, ore decomposition and secondary resource recovery Any one or several mixtures of the obtained lithium-containing solution and lithium-precipitated mother liquor;

Optionally, the concentration of lithium in the liquid to be extracted is preferably not less than 0.05 g/L.

10. the filmless bipolar electrode according to claim 8 extracts the method for lithium from solution, it is characterized in that, in the described supporting electrolyte, the molar weight of the cation that is adsorbed by the cation balance layer material is greater than lithium electroactive material and goes out lithium The molar amount is preferably 1.1 to 1.2 times the molar amount of extracted lithium;

Optionally, the power supply voltage is (0.05-0.8)×(n+1) volts, where n is the number of the conductive spacers.