WO2021070235A1

WO2021070235A1 - Lithium recovery method and lithium recovery device

Info

Publication number: WO2021070235A1
Application number: PCT/JP2019/039575
Authority: WO
Inventors: 泰教濃添; 賢三左右田
Original assignee: 日揮グローバル株式会社
Priority date: 2019-10-08
Filing date: 2019-10-08
Publication date: 2021-04-15

Abstract

This lithium recovery method is characterized by having: an extraction step for bringing an extraction-target liquid comprising an aqueous liquid containing at least a lithium salt and a magnesium salt or a calcium salt into contact with an extraction agent for lithium salt to cause at least a portion of the lithium salt in the extraction-target liquid to be extracted into the extraction agent; and an electrolysis step for treating an extraction residual liquid that is left in the extraction step after an extract containing the extraction agent is separated from the extraction-target liquid, to electrolysis through a membrane body that preferentially or selectively pass monovalent metal ions relative to divalent metal ions, wherein the lithium salt is recovered from the extract in the extraction step and a product passed through the membrane body in the electrolysis step.

Description

Lithium recovery method and lithium recovery device

The present invention relates to a lithium recovery method and a lithium recovery device capable of increasing and recovering the lithium concentration of an aqueous liquid containing a lithium salt and other salts.

Normally, the lithium concentration in brine (brine) collected in a salt lake is as dilute as several hundred mg / L. In the prior art, in the equipment for recovering lithium from salt lake brine, lithium is concentrated and supplied to the recovery equipment by providing an evaporation pond by natural evaporation in the front stage. If the infrastructure to operate the recovery facility is not in place near the evaporation pond, install the recovery facility in a place away from the evaporation pond and collect the concentrated brine after concentration (volume reduction) by evaporation to the recovery facility. It may be transported.

Patent Document 1 describes a method for continuously recovering lithium ions from an aqueous solution, which comprises a phosphine oxide compound and a compound capable of supplying protons (hydrogen ions) under basic conditions (alcohols, ketones, fatty acids, etc.). A step (a) of extracting lithium ions in an aqueous solution into an organic solvent using an organic solvent containing, a step (b), and a step (b) of recovering (back-extracting) lithium ions from an organic solvent containing lithium ions. A method including a step (c) of mixing the aqueous solution remaining in the a) with the organic solvent remaining in the step (b) and reusing the aqueous solution in the step (a) is described.

Patent Document 2 describes a step (a) of preparing an electrolysis cell in which a partition capable of transmitting lithium ions and protons (hydrogen ions) is arranged between an anode (anode) and a cathode (cathode), and lithium. A step (b) of obtaining an aqueous solution containing lithium by back extraction from the carried medium, a step (c) of introducing the aqueous solution obtained in the step (b) into the anode side of the electrolysis cell, and the cathode side of the electrolysis cell. The step (d) of introducing an aqueous medium into the anode, the step (e) of performing electrolysis under the condition that oxygen gas is generated at the anode, hydrogen gas is generated at the cathode, and lithium ions permeate the partition wall, and the cathode side. A method including a step (f) of recovering a product containing lithium hydroxide from the anode and a step (g) of reusing the product on the anode side for back extraction is described.

The evaporation pond, which is widely used in the conventional technology for recovering lithium from salt lake brine, requires a lot of time for natural evaporation and can be applied only to areas with low rainfall. In addition, the construction of the evaporation pond requires large-scale civil engineering work, so the initial investment cost is also high. When an artificial means such as an evaporation can is used as a method for concentrating brine by evaporation, a large running cost is required for energy such as fuel.

When the brine contains a large amount of sulfate ions, when the brine is concentrated by evaporation of water, lithium is _{precipitated as lithium sulfate (Li 2} SO ₄ ) together with sodium chloride (NaCl) and the like, and is removed from the concentrated brine. Therefore, evaporative concentration cannot be applied. Salt lake brine (chloride brine) to which the method using concentration by natural evaporation can be applied is already under development, but the amount of resources is limited. Salt lake brine (sulfate brine, etc.), which contains a large amount of impurities such as sulfate ions, is expected to be developed in the future because of its abundant resources.

As described in Patent Document 1, in the lithium recovery technique using solvent extraction, if the lithium concentration in the brine at the time of extraction is low, the lithium recovery rate decreases.
As described in Patent Document 2, in the lithium recovery technique using electrolysis, the recovery rate of lithium is determined in the pre-stage of the step (b) of obtaining an aqueous solution containing lithium by back extraction from a medium carrying lithium. Therefore, the electrolysis step described in Patent Document 2 does not solve the above-mentioned problem that the lithium recovery rate decreases when the lithium concentration in the brine is low.

International Publication No. 2013/0605050 International Publication No. 2017/137858

An object of the present invention is to provide a lithium recovery method and a lithium recovery device capable of improving the lithium recovery rate even when the lithium concentration in the raw material liquid is low because concentration by evaporation cannot be used. It is to be.

In the first aspect of the present invention, a liquid to be extracted, which comprises a lithium salt and an aqueous liquid containing at least a magnesium salt or a calcium salt, is brought into contact with a lithium salt extractant to bring at least the lithium salt in the liquid to be extracted. In the extraction step of extracting a part of the extract with the extractant and the extraction residual liquid remaining after separating the extract containing the extractant from the liquid to be extracted in the extraction step, the residual liquid remains monovalent with respect to the divalent metal ion. It has an electrolysis step of treating by electrolysis via a film body that preferentially or selectively permeates metal ions, and permeates the extract in the extraction step and the film body in the electrolysis step. It is a lithium recovery method characterized by recovering a lithium salt from a product.

A second aspect of the present invention is that the liquid to be extracted is a liquid that remains after removing the precipitate in a precipitation step of precipitating excess salt from a raw material liquid containing brine, and the film body in the electrolysis step. The lithium recovery method according to the first aspect, which comprises adding the product on the side that has permeated the mixture to the raw material liquid or the liquid to be extracted in the precipitation step.

A third aspect of the present invention is the lithium recovery method of the second aspect, characterized in that the raw material liquid in the pre-stage supplied to the precipitation step is acidic.

In a fourth aspect of the present invention, hydrochloric acid is synthesized from chlorine gas generated at the anode and hydrogen gas generated at the cathode in the electrolysis step when the extraction residual liquid contains chloride ions, and the hydrochloric acid is used to prepare the hydrochloric acid. The method for recovering lithium according to any one of the first to third aspects, which comprises recovering a lithium salt from the extract in the extraction step by back extraction.

A fifth aspect of the present invention is characterized in that, prior to the electrolysis step, a divalent metal ion removing step of removing at least a part of divalent metal ions contained in the extraction residual liquid is performed. This is the lithium recovery method according to any one of the fourth aspects.

A sixth aspect of the present invention is that the liquid to be extracted is a liquid that remains after removing the precipitate in the precipitation step of precipitating excess salt from the raw material liquid containing salt water, and the extraction residual liquid contains sodium ions. Including, carbon dioxide is reacted with the product on the side that has permeated the membrane in the electrolysis step to generate sodium carbonate, and at least a part of the sodium carbonate is supplied to the precipitation step to supply the magnesium salt. Alternatively, the method for recovering lithium according to any one of the first to fifth aspects, which comprises precipitating at least a part of a calcium salt.

In a seventh aspect of the present invention, the extraction residual liquid contains sodium ions, and in the electrolysis step, carbon dioxide is reacted with a product on the side that has permeated the film body to generate sodium carbonate, and the carbon dioxide is produced. The lithium recovery method according to any one of the first to sixth aspects, which comprises supplying at least a part of sodium to a recovery step for recovering the lithium salt and precipitating at least a part of the lithium salt. is there.

An eighth aspect of the present invention is that the liquid to be extracted is a liquid that remains after removing the precipitate in the precipitation step of precipitating excess salt from the raw material liquid containing salt water, and the film body in the electrolysis step. The lithium recovery method according to any one of the first to seventh aspects, wherein the product on the side that does not permeate the precipitate is used for washing the precipitate.

In the ninth aspect of the present invention, a precipitation portion for precipitating excess salt from a raw material liquid containing boiled water and a liquid remaining after removing the precipitate in the precipitation portion are composed of a lithium salt, a magnesium salt or a calcium salt. In the extraction unit, the extraction unit, which is brought into contact with a lithium salt extractant to extract at least a part of the lithium salt in the liquid to be extracted, and the extraction unit, as the liquid to be extracted, which comprises an aqueous liquid containing at least The extract residual liquid remaining after separating the extract containing the extractant from the liquid to be extracted is electrolyzed via a film body that preferentially or selectively permeates the monovalent metal ion with respect to the divalent metal ion. With the extract obtained from the extraction unit by adding the product on the side of the electrolysis unit that has passed through the film body to the raw material liquid or the liquid to be extracted, which has an electrolysis unit to be treated. , A lithium recovery apparatus characterized in that a lithium salt is recovered from a product that has permeated the film body in the electrolysis section.

According to the first aspect, even when the lithium recovery rate in the extraction step is lowered due to the low lithium concentration in the liquid to be extracted, the extraction residual liquid is treated by electrolysis in the electrolysis step. , A monovalent metal that permeates the membrane (or has a relatively high permeability) while removing divalent metal ions that do not permeate the membrane (or the permeability of the membrane is relatively low). The concentration of lithium ions, which are ions, can be increased preferentially or selectively. This makes it possible to improve the recovery rate of lithium. Furthermore, when sulfate ions do not permeate the membrane (or the permeability of the membrane is relatively low), the concentration of sulfate ions in the product on the side that has permeated the membrane can be reduced, so that the concentration of sulfate ions can be reduced. Even if the concentration of lithium ions is increased, precipitation of lithium sulfate is unlikely to occur.

According to the second aspect, in the electrolysis step, the product that has permeated the membrane, in which the concentration of lithium ions is preferentially or selectively increased, is returned to the precipitation step or the extraction step and brought into contact with the extractant. It is possible to increase the concentration of lithium in the liquid to be extracted and improve the recovery rate of lithium.

According to the third aspect, the present invention can be applied even if the raw material liquid in the previous stage is acidic.

According to the fourth aspect, hydrochloric acid used for back extraction can be produced by using chlorine gas and hydrogen gas obtained in the electrolysis step.

According to the fifth aspect, it is possible to prevent excess divalent metal ions from interfering with the electrolysis step.

According to the sixth aspect, sodium carbonate is produced by utilizing the product obtained by electrolysis of the extraction residual liquid containing sodium ions, and this sodium carbonate is used in the precipitation step to magnesium in the raw material liquid. The salt or calcium salt can be precipitated as magnesium carbonate or calcium carbonate.

According to a seventh aspect, the product obtained by electrolysis of the extraction residue containing sodium ions is used to produce sodium carbonate, and this sodium carbonate is used in the recovery step to lithium in an aqueous liquid. The salt can be precipitated as lithium carbonate.

According to the eighth aspect, the product on the side that does not permeate the membrane in the electrolysis step has a high concentration of magnesium salt or calcium salt and a low concentration of lithium ions, so that the precipitate is washed in the precipitation step. Can be suitably used for.
Compared with the case where water having a high lithium concentration is used for washing the precipitate, it is possible to suppress the absorption of lithium in the precipitate and the loss. Further, as compared with the case where fresh water or the like is used for washing the precipitate, the dissolution of the magnesium salt or the calcium salt contained in the precipitate can be suppressed.

According to the ninth aspect, even when the recovery rate of lithium by extraction is lowered due to the low lithium concentration in the salt water, the extraction residual liquid is treated by electrolysis and does not permeate the film body ( Alternatively, the concentration of lithium ion, which is a monovalent metal ion that permeates the membrane (or has a relatively high permeability of the membrane) while removing divalent metal ions and the like (the permeability of the membrane is relatively low). Can be preferentially or selectively increased. This makes it possible to improve the recovery rate of lithium. Furthermore, when sulfate ions do not permeate the membrane (or the permeability of the membrane is relatively low), the concentration of sulfate ions in the product on the side that has permeated the membrane can be reduced, so that the concentration of sulfate ions can be reduced. Even if the concentration of lithium ions is increased, precipitation of lithium sulfate is unlikely to occur. In addition, lithium in the liquid to be extracted, in which the concentration of lithium ions is preferentially or selectively increased by electrolysis, is returned to the precipitation part or the extraction part and brought into contact with the extractant. It is possible to increase the concentration and improve the recovery rate of lithium.

It is a flow chart which shows the outline of embodiment of the lithium recovery method. It is a flow chart which supplements the embodiment of the lithium recovery method.

FIG. 1 shows an outline of the lithium recovery method of the present embodiment. In the lithium recovery method of the present embodiment, at least the liquid to be extracted 20 composed of an aqueous liquid containing a lithium salt is brought into contact with the extractant 21, and at least a part of the lithium salt in the liquid to be extracted 20 is extracted into the extractant 21. It has an extraction step X for making the extraction step X, and an electrolysis step E for treating the extraction residual liquid 23 of the extraction step X by electrolysis. Prior to the extraction step X, a precipitation step P for precipitating excess salt from the raw material liquid 10 may be provided.

The lithium recovery device 100 shown in FIG. 1 includes a precipitation unit 13 for performing the precipitation step P, an extraction unit 24 for performing the extraction step X, and an electrolysis unit 35 for performing the electrolysis step E. ing.

In the lithium recovery method of the present embodiment, the raw material liquid 10 is not particularly limited as long as it is brine containing lithium ions, and examples thereof include salt lake brine collected in a salt lake. When salt lakes are located in arid areas, water is naturally evaporated from the lake water trapped inland and salt is concentrated. In the supply step F of the raw material liquid 10, a method of collecting brine from the salt lake using, for example, a pump, a well, or the like can be used. Examples of salts contained in brine include sodium chloride (NaCl), lithium chloride (LiCl), magnesium chloride (MgCl ₂ ), calcium chloride (CaCl ₂ ) and the like.

In the conventional lithium recovery method, the brine collected from the salt lake is transferred to an evaporation pond and dried in the sun for about one year to concentrate the brine, increasing the lithium concentration to, for example, several wt%. At this time, major salts such as sodium chloride (NaCl) and potassium chloride (KCl) are precipitated, and concentrated brine having an increased lithium concentration can be obtained as a supernatant. However, for example, influence of volcanic activity, the increase may Sulfate ion (SO 4 _^2-) concentration in the brine, the lithium ions in the brine are precipitated as lithium sulfate (Li 2 _SO _4), lithium concentration in the concentrated brine May decrease. In addition, as described above, the method of concentrating brine by evaporation has large restrictions on time and location when using natural energy such as sun and wind power, and when using artificial means such as combustion heating. The running cost will increase.

In the lithium recovery method of the present embodiment, the brine collected from the salt lake can be used as the raw material liquid 10 as it is. Brine water that has undergone a predetermined treatment or adjustment may be used as the raw material liquid 10. For example, in order to reduce or remove impurities in brine, impurities may be extracted using an impurity extractant, and the extractant containing impurities may be separated from brine. If necessary, the pH, temperature, etc. of the brine may be adjusted. When adjusting the pH, a pH adjusting agent such as an acid or an alkali can be used. When adjusting the temperature, the raw material liquid 10 may be heated or cooled to such an extent that it is not excessively concentrated. A hydrous liquid other than brine may be added to the raw material liquid 10. The raw material liquid 10 may be acidic with a pH of less than 7, neutral with a pH of about 7, or alkaline with a pH of more than 7.

When the lithium concentration of the raw material liquid 10 is low, it is preferable to perform the precipitation step P. For example, if the lithium concentration in the raw material liquid 10 is about 1700 to 1800 mg / L or more by weight, it is preferable to omit the precipitation step P. When the lithium concentration in the raw material liquid 10 is about 300 to 400 mg / L or less by weight, it is preferable to carry out the precipitation step P. When the lithium concentration in the raw material liquid 10 is between about 400 mg / L and about 1700 mg / L, it is decided whether to carry out or omit the precipitation step P in consideration of the lithium recovery rate in the extraction step X described later. You may.

In the precipitation step P, a chemical such as a precipitating agent 11 is added to precipitate an excess salt content, and the lithium concentration in the supernatant is increased. As a result, processing can be performed in a short time and at low cost as compared with the case of using an evaporation pond or an evaporation can. For example, when sodium carbonate (Na ₂ CO ₃ ) is added to the raw material liquid 10, the magnesium ions of the raw material liquid 10 can be precipitated as _{magnesium carbonate (MgCO 3).} In the settling step P, the settling section 13 used for storing the raw material liquid 10, the settling agent 11, and the like can be composed of a settling tank, a settling basin, and the like.

When the precipitation step P is carried out, the liquid remaining after removing the precipitate 12 in the precipitation step P may be the liquid to be extracted 20 in the extraction step X. When the precipitation step P is omitted, the raw material liquid 10 may be used as it is as the liquid to be extracted 20. For the separation of the precipitate 12 and the liquid to be extracted 20, a known solid-liquid separation method such as filtration or centrifugation can be used.

In the extraction step X, the lithium salt of the liquid to be extracted 20 is extracted using the extractant 21. Examples of the extractant 21 include a liquid or solid extractant 21. In the extraction step X, the extraction unit 24 used for contacting the liquid to be extracted 20 and the extraction agent 21 can be composed of an extraction tank, an extraction tower, an extraction device, and the like.

Examples of the liquid extractant 21 include an extraction compound such as a phosphoric acid ester compound, a phosphonic acid ester compound, and a phosphine oxide compound, or an organic solvent containing an extraction compound. When the extraction compound is a liquid, the extraction compound containing no other organic solvent may be used as it is as the liquid extractant 21.

The organic solvent used in the extractant 21 can be selected in consideration of dissolving the extraction compound, easy separation from water, and the like. Specific examples of the organic solvent are not particularly limited, but are compounds such as aliphatic hydrocarbons, aromatic hydrocarbons, carbon halides, halogenated hydrocarbons, ethers, ketones, phenols, esters, and amides. Examples of these are mixtures. The mixture of organic solvents may be a composition such as kerosene (kerosene).

After the liquid extractant 21 is brought into contact with the liquid to be extracted 20, the extract 22 composed of the extractant 21 containing a lithium salt and the extract residue 23 remaining after the extractant 21 is removed by a liquid separation operation are performed. And can be separated. In the liquid separation operation, it is preferable to utilize the difference in specific gravity between the extract 22 and the extraction residual liquid 23, and centrifugation may be used.

The extractant 21 used in the extraction step X may be a solid extractant. A chemical structure such as a functional group that binds to a lithium salt can be introduced into a resin such as an ion exchange resin or a carrier such as clay or ceramics. By forming the carrier into a film-like shape, a thread-like shape, a tubular shape, a granular shape, or the like, the contact area with the liquid to be extracted 20 can be increased and the extraction efficiency can be improved.

After the solid extractant 21 is brought into contact with the liquid to be extracted 20, the extract 22 composed of the extractant 21 containing a lithium salt and the extraction residual liquid remaining after the extractant 21 is removed by solid-liquid separation. 23 can be separated. For the separation of the solid extract 22 and the extraction residual liquid 23, a known solid-liquid separation method such as filtration or centrifugation can be used.

In the extraction step X, the liquid to be extracted 20 made of an aqueous liquid is brought into contact with the extractant 21, so that at least a part of the lithium salt in the liquid to be extracted 20 is extracted by the extractant 21. The proportion of impurities in the extract 22 can be reduced by the selectivity of the lithium salt with respect to the impurities such as magnesium salt, calcium salt and sodium salt contained in the liquid to be extracted 20. This simplifies the step of removing impurities when recovering the lithium salt from the extract 22. When solvent extraction is performed, the ratio (O / A ratio) of the organic phase to the aqueous phase is optimized to improve the concentration ratio of lithium ions in the lithium salt-containing extract 22. The installed capacity when recovering the lithium salt from the extract 22 can be reduced.

When the lithium concentration in the liquid to be extracted 20 is low, the amount of lithium extracted to the extract 22 side is small, and the amount of lithium discharged to the extraction residual liquid 23 side may be a considerable amount. Therefore, if lithium is recovered only from the extract 22, there is a problem that the lithium recovery rate is low. It is desirable to recover the lithium salt from the extraction residual liquid 23 as well, but the lithium concentration in the extraction residual liquid 23 is lower than the lithium concentration in the liquid to be extracted 20. Therefore, it is not easy to increase the recovery rate of the lithium salt by repeating the extraction step X.

Therefore, in the lithium recovery method of the present embodiment, the electrolysis step E is performed after the extraction step X, and the extraction residual liquid 23 of the extraction step X is treated by electrolysis. The electrolysis unit 35 used in the electrolysis step E includes an electrolysis tank in which an ion exchange membrane is installed between the anode (anode) and the cathode (cathode). The extraction residual liquid 23 is supplied to the anode chamber, which is a space on the anode side of the ion exchange membrane. By electrolysis, lithium ions can be moved toward the cathode chamber, which is a space on the cathode side of the ion exchange membrane. Desalted water 30 such as distilled water and deionized water is supplied to the cathode chamber. The volume ratio between the anode chamber and the cathode chamber can be appropriately designed.

When the raw material liquid 10 is unconcentrated brine, it is not easy to transport it by truck or the like like concentrated brine because the amount of the raw material liquid 10 required to obtain a certain amount of lithium recovery is large. Therefore, it is assumed that the lithium recovery method of the present embodiment is carried out in an area near the salt lake where the electric power infrastructure is not prepared. The electric power required for the electrolysis step E is preferably obtained from a power generation method using natural energy such as solar power generation and wind power generation.

The ion exchange membrane used in the electrolysis step E preferentially or selects monovalent metal ions such as lithium (Li) and sodium (Na) over divalent metal ions such as magnesium (Mg) and calcium (Ca). It is a film body that is transparent to calcium. Specific examples thereof include cation exchange membranes used in known chlor-alkali projects. Specific examples of the cation exchange membrane include a fluorine-containing polymer membrane having a functional group that gives an anion such as carboxylic acid and sulfonic acid.

By treating the extraction residual liquid 23 using electrolysis via the membrane body, a cathode liquid 31 in which lithium salt is concentrated is obtained in the cathode chamber as a product on the side that has passed through the membrane body. Further, in the anode chamber, an anode solution 32 having a reduced lithium salt is obtained as a product on the side that does not permeate the membrane body. In addition to recovering the lithium salt from the extract 22, the recovery rate of lithium can be improved by recovering the lithium salt from the cathode solution 31 as well.

Further, even when the raw material liquid 10 or the liquid to be extracted 20 contains sulfate ions, the sulfate ions do not permeate the membrane body used in the electrolysis step E (or the permeability of the membrane body is relatively low), so that the cathode The sulfate ion concentration in the liquid 31 becomes low. Therefore, even if the lithium concentration in the cathode liquid 31 is increased by electrolysis, the precipitation of lithium sulfate can be suppressed.

The cathode liquid 31, which is a product on the side that has passed through the membrane in the electrolysis step E, contains lithium ions, and the concentration of the lithium ions is preferentially or selectively increased in the electrolysis step E. Therefore, when the cathode liquid 31 is added to the raw material liquid 10 in the precipitation step P or the liquid to be extracted 20 in the extraction step X, the lithium salt in the cathode liquid 31 is returned to the precipitation step P or the extraction step X to return the raw material liquid 10 or the extraction step X. The lithium concentration in the liquid to be extracted 20 can be increased to improve the recovery rate of lithium.

In the anode solution 32, which is a product on the side that does not permeate the membrane in the electrolysis step E, the concentration of magnesium salt or calcium salt is high and the concentration of lithium ions is low. Therefore, the anode solution 32 can be suitably used for cleaning the precipitate 12 in the precipitation step P. Compared with the case where water having a high lithium concentration is used for washing the precipitate 12, it is possible to suppress the absorption of lithium in the precipitate 12 and the loss. Further, as compared with the case where fresh water or the like is used for washing the precipitate 12, the dissolution of the magnesium salt or the calcium salt contained in the precipitate 12 can be suppressed. The state of the precipitate 12 when washed with the anode solution 32 may be in the form of a slurry having a large amount of water or in the form of a cake having a small amount of water.

In the electrolysis step E, when a large amount of divalent metal ions such as magnesium ions and calcium ions contained in the extraction residual liquid 23 are present, at least a part of the divalent metal ions contained in the extraction residual liquid 23 is removed. It is preferable to carry out a valent metal ion removing step. In the divalent metal ion removing step, a known adsorption separation method using a chelate resin or the like can be used. By treating the extraction residual liquid 23 that has undergone the divalent metal ion removing step by electrolysis, the inhibition of the electrolysis step E can be suppressed.

Note that it does not matter if the extraction residual liquid 23 to be treated by electrolysis does not substantially contain divalent metal ions. Also in this case, in the electrolysis step E, by moving the lithium ions from the anode side to the cathode side, the concentration of lithium ions in the cathode liquid 31 is preferentially or selectively selected while suppressing the precipitation of lithium sulfate or the like. Can be enhanced.

FIG. 2 shows each step that supplements the lithium recovery method of this embodiment. These steps can be appropriately added to the steps shown in FIG. In FIG. 2, the same reference numerals are used for the configurations common to those in FIG.

When the extraction residual liquid 23 contains chloride ion (Cl ⁻ ), the chlorine gas 33 generated at the anode and the hydrogen gas 34 generated at the cathode in the electrolysis step E are supplied to the hydrochloric acid production step H to synthesize hydrochloric acid 41. be able to. It is preferable that hydrochloric acid 41 is in the state of an aqueous hydrochloric acid solution because it is easy to handle. An aqueous hydrochloric acid solution can be obtained by allowing water to absorb hydrogen chloride (HCl) gas obtained by burning hydrogen gas 34 in chlorine gas 33.

Hydrochloric acid 41 can separate the lithium-containing liquid 42 from the extractant 21 by adding it to the extract 22 in the back extraction step S in which the lithium salt is back-extracted from the extract 22. The lithium-containing liquid 42 is an aqueous liquid containing a lithium salt. The extractant 21 recovered in the back extraction step S can be reused in the extraction step X after undergoing treatments such as washing and purification as necessary.

When brine containing chloride ions is used as the raw material liquid 10, chloride ions are also present in the extraction residual liquid 23 processed in the electrolysis step E. Therefore, by using hydrochloric acid 41 synthesized from chlorine gas 33 and hydrogen gas 34 generated by electrolysis, the cost of chemicals can be reduced. However, the chemical used for the back extraction of the extract 22 is not limited to the hydrochloric acid 41 produced in the hydrochloric acid production step H.

When brine containing sodium ions is used as the raw material liquid 10, sodium ions are also present in the extraction residual liquid 23 and the cathode liquid 31 treated in the electrolysis step E. A cathode solution 31 containing sodium ions (Na ⁺ ) can be supplied to the sodium carbonate synthesis step N, and carbon dioxide 51 can be reacted to synthesize a sodium carbonate-containing solution 52.

The sodium carbonate-containing liquid 52 contains lithium hydroxide (LiOH) together with _{sodium carbonate (Na 2} CO _3). By using the sodium carbonate-containing liquid 52 containing a lithium salt in the precipitation step P or the recovery step R, the recovery rate of lithium can be improved or the loss of lithium can be reduced, as will be described later. When the sodium carbonate-containing liquid 52 is used in the recovery step R, as shown in FIG. 2, not only when lithium is recovered from the lithium-containing liquid 42 after back extraction, but also lithium from an arbitrary aqueous solution containing lithium. Can be used when collecting.

When sodium carbonate is used as the precipitating agent 11 in the precipitation step P described above, the magnesium salt or calcium salt in the raw material liquid 10 can be precipitated as magnesium carbonate or calcium carbonate. When the sodium carbonate-containing liquid 52 used as the precipitant 11 contains a lithium salt, the lithium concentration in the liquid to be extracted 20 is increased as compared with the case where an aqueous solution of the precipitant 11 not containing the lithium salt is used. Can be enhanced.

The lithium salt contained in the lithium-containing liquid 42 after the back extraction is recovered as a precipitate 62 containing _{lithium carbonate (Li 2} CO ₃ ) by adding the sodium carbonate-containing liquid 52 as a precipitant 61 in the recovery step R. can do. The lithium salt recovered as the precipitate 62 may be a lithium salt other than lithium carbonate, such as lithium sulfate. A substance other than sodium carbonate may be used as the precipitant 61. For the separation of the precipitate 62 and the aqueous liquid 63, a known solid-liquid separation method such as filtration or centrifugation can be used. When the sodium carbonate-containing liquid 52 containing a lithium salt is used as the precipitant 61, the lithium carbonate recovered as the precipitate 62 is compared with the case where the sodium carbonate-containing liquid 52 containing no lithium salt is used. The amount can be improved.

As described above, according to the lithium recovery method of the present embodiment, since the lithium concentration in the raw material liquid 10 is low, even when the ratio of lithium ions extracted in the extraction step X is relatively low. By treating the extraction residual liquid 23 in the electrolysis step E, the lithium ions remaining in the extraction residual liquid 23 can be recovered.

When the raw material liquid 10 is used without concentrating the brine, the cost of the evaporation pond, the evaporation can, etc. can be reduced, and even when the sulfate ion concentration in the brine is high, the lithium ion in the brine is lithium sulfate. The loss due to precipitation can be suppressed.

From the product obtained in the electrolysis step E, chemicals such as sodium hydroxide, sodium carbonate, and hydrochloric acid can be produced. Sodium hydroxide and sodium carbonate can be used in the precipitation step P, the recovery step R, and the like. Hydrochloric acid can be used in the back extraction step S and the like. Even when the lithium recovery method of the present embodiment is carried out in an area away from commercial and industrial areas such as a city where infrastructure is not in place, it is possible to reduce the cost of purchasing and transporting the drug.

Next, an example of recovering lithium from the brine using the extraction step X and the back extraction step S will be shown. Extraction step X and back extraction step S were carried out using brine having a lithium concentration of 295 to 335 mg / L as the raw material liquid 10. The results are shown in Table 1. In Table 1, lithium is abbreviated as "Li".

As shown in Table 1, the lithium concentration in the extraction residual liquid 23 is relatively high with respect to the lithium concentration in brine, and the lithium recovery rate is as low as 29 to 41%. The lithium concentration ratio represents the ratio at which the lithium concentration in the lithium-containing liquid 42 after back extraction is concentrated with respect to the lithium concentration in the brine used for the raw material liquid 10. The lithium recovery rate represents the ratio of lithium recovered from the brine used in the raw material liquid 10 to the lithium-containing liquid 42 after back extraction.

By adjusting or optimizing the O / A ratio in the extraction step X and the back extraction step S, the lithium concentration in the lithium-containing liquid 42 after the back extraction can be increased. As a result, the capacity of the equipment required for removing impurities or recovering lithium in the steps after the extraction step X or the back extraction step S can be reduced.

However, if the extraction step X is performed directly from the liquid to be extracted 20 having the same lithium concentration as the brine without concentrating the brine, there is a limitation in improving the lithium recovery rate. Therefore, by treating the extraction residual liquid 23 by electrolysis as in the above-described embodiment, the lithium concentration of the cathode liquid 31 is made higher than the lithium concentration of the extraction residual liquid 23, and the lithium recovery rate is improved. Is possible. Further, chlorine and hydrogen produced in the electrolysis step E can be used for producing hydrochloric acid used in the back extraction step S. The electrolysis step E and the hydrochloric acid production step H can be easily carried out by existing techniques in the same manner as the steps used in the general chlor-alkali business.

The present invention can be used for producing lithium compounds used in various applications such as lithium ion batteries, lithium-containing alloys, ceramic products, lithium soaps, and pharmaceuticals.

E ... Electrolysis process, F ... Supply process, H ... Hydrochloride production process, N ... Sodium carbonate synthesis process, P ... Precipitation process, R ... Recovery process, S ... Reverse extraction process, X ... Extraction process, 10 ... Raw material liquid, 11 ... Precipitant, 12 ... Precipitate, 13 ... Precipitate, 20 ... Liquid to be extracted, 21 ... Extractor, 22 ... Extract, 23 ... Extraction residue, 24 ... Extraction part, 30 ... Water, 31 ... Cathode liquid , 32 ... anode solution, 33 ... chlorine gas, 34 ... hydrogen gas, 35 ... electrolysis part, 41 ... hydrochloric acid, 42 ... lithium-containing solution, 51 ... carbon dioxide, 52 ... sodium carbonate-containing solution, 61 ... precipitant, 62 ... Precipitate, 63 ... Aqueous liquid, 100 ... Lithium recovery device.

Claims

A liquid to be extracted, which comprises a lithium salt and an aqueous liquid containing at least a magnesium salt or a calcium salt, is brought into contact with a lithium salt extractant, and at least a part of the lithium salt in the liquid to be extracted is extracted by the extractant. Extraction process and
In the extraction step, a film body that preferentially or selectively permeates the monovalent metal ion with respect to the divalent metal ion in the extraction residual liquid remaining after separating the extract containing the extractant from the liquid to be extracted. Has an electrolysis process, which is processed by electrolysis via
A method for recovering lithium, which comprises recovering a lithium salt from the extract in the extraction step and the product that has permeated the film body in the electrolysis step.
The liquid to be extracted is a liquid that remains after removing the precipitate in the precipitation step of precipitating excess salt from the raw material liquid containing brine.
The lithium recovery method according to claim 1, wherein the product on the side that has permeated the film body in the electrolysis step is added to the raw material liquid or the liquid to be extracted in the precipitation step.
The lithium recovery method according to claim 2, wherein the raw material liquid in the pre-stage supplied to the precipitation step is acidic.
The extraction residue contains chloride ions and contains
Hydrochloric acid is synthesized from chlorine gas generated at the anode and hydrogen gas generated at the cathode in the electrolysis step.
The lithium recovery method according to any one of claims 1 to 3, wherein the lithium salt is recovered from the extract in the extraction step by back extraction using the hydrochloric acid.
The present invention according to any one of claims 1 to 4, wherein a divalent metal ion removing step of removing at least a part of the divalent metal ions contained in the extraction residual liquid is performed prior to the electrolysis step. The lithium recovery method described.
The liquid to be extracted is a liquid that remains after removing the precipitate in the precipitation step of precipitating excess salt from the raw material liquid containing brine.
The extraction residue contains sodium ions and contains
In the electrolysis step, carbon dioxide is reacted with the product on the side that has permeated the membrane to produce sodium carbonate, and at least a part of the sodium carbonate is supplied to the precipitation step to supply the magnesium salt or calcium. The lithium recovery method according to any one of claims 1 to 5, wherein at least a part of the salt is precipitated.
The extraction residue contains sodium ions and contains
In the electrolysis step, carbon dioxide is reacted with the product on the side that has permeated the film body to generate sodium carbonate, and at least a part of the sodium carbonate is supplied to the recovery step for recovering the lithium salt. The lithium recovery method according to any one of claims 1 to 6, wherein at least a part of the lithium salt is precipitated.
The liquid to be extracted is a liquid that remains after removing the precipitate in the precipitation step of precipitating excess salt from the raw material liquid containing brine.
The lithium recovery method according to any one of claims 1 to 7, wherein the product on the side that does not permeate the membrane body is used for washing the precipitate in the electrolysis step.
A sedimentation part that precipitates excess salt from the raw material liquid containing brine,
The liquid remaining after removing the precipitate in the precipitate is brought into contact with a lithium salt extractant as a liquid to be extracted, which is an aqueous liquid containing at least a lithium salt and a magnesium salt or a calcium salt, and the liquid to be extracted. An extraction unit that allows the extractant to extract at least a part of the lithium salt in the extract.
A film body that preferentially or selectively permeates the extraction residual liquid remaining after separating the extract containing the extractant from the liquid to be extracted in the extraction unit with respect to the divalent metal ions. Has an electrolyzed part, which is processed by electrolysis via
The product on the side that has passed through the membrane in the electrolysis section is added to the raw material liquid or the liquid to be extracted.
A lithium recovery device for recovering a lithium salt from the extract obtained from the extraction unit and the product that has permeated the membrane body in the electrolysis unit.