Recycling of lithium cations in molecular sieves

Abstract

The present invention relates to a process for producing a solution of lithium cations on the one hand, while producing a molecular sieve having a low lithium content on the other hand, said process comprising providing a lithium exchange molecular sieve which is a molecular sieve that is waste or not suitable for its intended application, the co-produced molecular sieve with low lithium content can be reused as a molecular sieve.

Description

[0001] This invention relates to the field of molecular sieves with partial or complete lithium exchange, and to the recovery and reuse, i.e., recycling, of lithium cations present in said molecular sieves.

[0002] Global demand for lithium is currently very high and continues to rise. Natural lithium resources are relatively scarce, so the price of this raw material has reached a level that also increases the cost of lithium-containing products. These products have a relatively long lifespan and are typically scrapped, destroyed, and / or landfilled when they reach the end of their lifespan.

[0003] To date, recycling lithium from these end-of-life products represents a path that has been largely unexplored, particularly due to the difficulty in successfully implementing recycling operations that are efficient and beneficial from both an industrial, economic, and environmental perspective.

[0004] Ion exchange technology using cation exchange materials has been known for many years. For example, patent US5451383 describes a method for removing and concentrating lithium cations derived from dilute aqueous solutions, which is carried out by injecting the solution into a column loaded with cation exchange materials. The first step of this method involves dilute lithium cations (Li... + The solution is injected into a column filled with cation exchange material immersed in a concentrated sodium chloride (NaCl) solution. At the column outlet, the concentrated NaCl solution is collected first, followed by a dilute NaCl solution. The second step involves countercurrently passing the concentrated NaCl solution through the column, collecting a dilute lithium chloride (LiCl) solution at the outlet, followed by a concentrated lithium chloride (LiCl) solution. Patent US5681477 provides an improvement by adjusting the temperature of the solutions used and describes a similar method.

[0005] Literature CN114408941 describes the preparation of X-structured lithium exchange molecular sieves by using a vacuum belt filter to continuously countercurrently exchange powdered sieves with lithium cations. This allows for multiple consecutive exchanges and the recycling of depleted effluent back to the previous exchange stage, which is another way to fully utilize lithium.

[0006] References KR101176164 and KR101319594 propose methods for recovering lithium in the form of chlorides or carbonates from liquid effluents in a process for preparing lithium zeolites via ion exchange. Lithium is thus recovered by extraction with an organic solvent.

[0007] Document CN115558798 describes a method for extracting lithium from brine from a porous solid (e.g., a molecular sieve, activated carbon, resin, or silicon carbide type) impregnated or coated with a hydrophobic organic compound capable of retaining lithium. Lithium is then extracted from the solid by acid treatment.

[0008] Document CN116179857 describes a method for extracting lithium from spent lithium molecular sieves. The molecular sieve, pre-crushed by fine grinding (<150 µm), is contacted with a sodium ion-containing solution and then aged at a pH of 5 to 6 and a temperature of 60°C to 90°C to remove silicon and aluminum. After filtration, sodium carbonate and sodium hydroxide are added to remove other impurities and recover lithium. Besides the complexity of obtaining purified lithium salts (multiple purification steps), the starting molecular sieve is completely destroyed and therefore unusable.

[0009] Following a very similar approach, document CN116440857 describes a method for reducing the concentration of sodium cations in a lithium-rich cation solution. This method involves treating a sodium-exchanged zeolite adsorbent with a sulfuric acid solution, specifically boiling it in concentrated sulfuric acid for 2 to 4 hours, repeating this treatment 3 to 6 times. The lithium cation solution to be enriched is then contacted with this acidic solution containing sodium cations to obtain an enriched lithium cation solution. In these last two documents, it is evident that the starting molecular sieve is inevitably destroyed (by grinding or acid hydrolysis), therefore, at the end of the method, the starting molecular sieve cannot be recovered and reused.

[0010] The present invention aims to meet the current growing demand for the recovery of lithium present in waste molecular sieves, while upgrading the waste molecular sieves.

[0011] Therefore, the first objective of this invention is to provide an economical method for recycling waste lithium molecular sieves and for upgrading the recycling of solids in the form of molecular sieves.

[0012] Another objective of this invention is to propose an economical method for recycling waste lithium molecular sieves, which allows for the recovery of ionic solutions with high-purity lithium loading as well as solids that are upgraded for recycling in the form of molecular sieves.

[0013] Another objective of this invention is to provide an economical method for recycling waste lithium molecular sieves and for upgrading the recycling of solids in the form of molecular sieves, such as sodium-exchange molecular sieves.

[0014] Another objective of this invention is to provide an economical method for recycling waste lithium molecular sieves and for upgrading and recycling solids in the form of molecular sieves, typically sodium exchange molecular sieves.

[0015] Other objectives will become apparent from the following description of the invention. In this description, unless otherwise stated, all numerical ranges should be understood as "inclusive of limits".

[0016] Therefore, according to the first subject matter, the present invention relates to a method for producing a solution of lithium cations on one hand, and simultaneously producing a molecular sieve having a low lithium content on the other hand, said method comprising:

[0017] a) Provide lithium-exchange molecular sieves,

[0018] b) Hydrated lithium-exchange molecular sieves,

[0019] c) Using at least one ionic solution, perform ion exchange on the hydrated molecular sieve from the preceding steps, and

[0020] d) On the one hand, the lithium cation solution is recovered, and on the other hand, the molecular sieve with low lithium content is recovered.

[0021] The method of this invention uses lithium exchange molecular sieves, and lithium exchange molecular sieves are preferably understood to mean waste lithium molecular sieves, more specifically lithium molecular sieves that have been used and have become unsuitable for their intended application. Lithium molecular sieves can also mean new (unused) lithium molecular sieves that have manufacturing defects, are "non-standard" products, and are unsuitable for their intended application.

[0022] Lithium-exchange molecular sieves particularly contain zeolite crystals, which can be of any type known to those skilled in the art, such as, but not limited to, the following zeolite crystals: FAU-type zeolite, EMT-type zeolite, LTA-type zeolite, LTL-type zeolite, MFI-type zeolite, MOR-type zeolite, BEA-type zeolite, CHA-type zeolite, HEU-type zeolite, OFF-type zeolite, or MAZ-type zeolite, preferably FAU-type zeolite, MFI-type zeolite, MOR-type zeolite, BEA-type zeolite, CHA-type zeolite, or HEU-type zeolite, very preferably FAU-type zeolite and MFI-type zeolite, particularly preferably FAU-type zeolite of FAU X-type zeolite, FAU LSX-type zeolite, FAU MSX-type zeolite, or FAU Y-type zeolite, as well as MFI-type zeolite of ZSM-5 type and MFI zeolite of pure silicate. The lithium-exchange molecular sieve comprises zeolite crystals as described above, which are typically and advantageously agglomerated with at least one agglomeration binder, which is also well known to those skilled in the art and is advantageously selected from clay.

[0023] The lithium-exchange molecular sieves that can be used in the method of the present invention may therefore comprise one or more zeolite crystals as defined above and at least one agglomerating binder, which may be partially or completely zeolized, i.e. at least partially converted into zeolite, according to techniques well known to those skilled in the art.

[0024] The lithium molecular sieve advantageously used in the method of the present invention, and more precisely in step a) of the method of the present invention, typically and advantageously has a lithium content of 0.5% to 12.0%, preferably 1.0% to 12.0%, preferably 4.0% to 12.0%, and very preferably 8.0% to 12.0%. This lithium content is measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), for example, according to the NF EN ISO 21587-3 standard applicable to lithium, on a Perkin Elmer 4300DV instrument. The lithium content is expressed as the equivalent weight of Li₂O.

[0025] The molecular sieves suitable for the methods of this invention can be of any type well known to those skilled in the art, and are generally in particulate form, such as agglomerates, beads, yarns, or more generally extrusions, simple extrudates, or polylobate extrudates, to name only the most common types. The particle size typically results in a minimum dimension (e.g., the diameter in the case of beads) of 0.10 mm to 5 mm, preferably 0.20 mm to 5 mm, more preferably 0.20 mm to 3 mm, and more particularly 0.25 mm to 1.5 mm.

[0026] The lithium-exchangeable molecular sieves used in the method of the present invention are typically fully lithium-exchangeable sieves. However, the method of the present invention is fully applicable to partially lithium-exchangeable molecular sieves, wherein the other exchangeable cations can be selected from any other cations in columns I and II of the periodic table, particularly one or more cations selected from sodium, potassium, magnesium, calcium, strontium, and barium.

[0027] However, the method of the present invention is most particularly applicable to molecular sieves with high lithium content, for example, preferably 4.0% to 12.0% and more preferably 8.0% to 12.0%, the content being expressed as Li2O, and as explained above, these values ​​are not limiting.

[0028] Therefore, the lithium-exchange molecular sieve hydration of the present invention is first performed according to any method well known to those skilled in the art, and more particularly any operation aimed at giving the lithium-exchange molecular sieve a water content of 20% to 75% as measured by loss on ignition. Loss on ignition is measured as described in standard NF EN 196-2 (April 2006), in an oxidizing atmosphere, by calcining the sample in air at a temperature of 950°C ± 25°C. The measured standard deviation is less than 0.1%.

[0029] This hydration operation is well known to those skilled in the art and can be carried out, for example, by soaking in water for the time required to achieve the desired water content, i.e., for example, soaking for several minutes to several hours. Advantageously, before or after this hydration step, preferably before this hydration step, at least one screening step is performed to specifically remove fine particles; and / or at least one sorting step is performed to remove any type of undesirable contaminants, such as metal particles from recycled waste screens or unsuitable screens.

[0030] It should be understood that the hydration step, intended to give the lithium-exchange molecular sieve provided in step a) a water content of 20% to 75% as described above, may prove unnecessary, particularly when the lithium-exchange molecular sieve provided in step a) is an already hydrated molecular sieve, such as a waste molecular sieve or a molecular sieve that has been exposed to air and is therefore capable of adsorbing a certain amount of water. Testing can be performed according to techniques well known to those skilled in the art, and the water content can then optionally be adjusted by hydration prior to the ion exchange in step c). Therefore, the molecular sieve in step a) may or may not undergo a hydration step prior to ion exchange, such that the lithium-exchange molecular sieve provided in step a) has a water content of 20% to 75% as described above.

[0031] After hydration and optionally sieving and / or sorting, the lithium exchange molecular sieve is subjected to ion exchange using at least one ionic solution in step c) according to any method well known to those skilled in the art, such as by percolation, soaking, or a combination of percolation and soaking. Preferably, the sieve is percolated to perform ion exchange. Percolation is understood to mean forcing the ionic solution through the molecular sieve. Percolation can be performed according to any method well known to those skilled in the art, and typically, percolation is performed through a fixed bed of lithium exchange molecular sieves. Percolation can be performed once or multiple times. Alternatively or additionally, the lithium molecular sieve can be ion-exchanged, for example by soaking the molecular sieve in one or more batches of ionic solution once or more.

[0032] Percolation can be carried out at ambient temperature or any other temperature, but not exceeding 150°C, preferably not exceeding 120°C, and advantageously not exceeding 110°C. Low temperatures are generally preferred, especially for obvious economic reasons.

[0033] Percolation is carried out using a solution containing sodium cations, and according to a very particularly preferred embodiment, the solution is an aqueous solution of sodium cations. Aqueous-organic solutions of sodium cations, such as water-alcohol mixtures, water-ether mixtures, or water-ketone mixtures, or mixtures thereof, may also be used. However, aqueous solutions of sodium cations are preferred.

[0034] Sodium cation solutions typically contain 0.01 mol% to 100 mol% sodium cations relative to the total number of cations present in the solution (excluding protons), more typically 0.1 mol% to 100 mol%, still more typically 1 mol% to 100 mol%, preferably 5 mol% to 100 mol%, more preferably 10 mol% to 100 mol%, advantageously 20 mol% to 100 mol%, and, for example, 50 mol% to 100 mol% or alternatively 75 mol% to 100 mol% (including endpoints) of sodium cations, measured according to methods well known to those skilled in the art, such as by ICP-AES, according to NF EN ISO 11885.

[0035] The sodium cation solution defined above may also contain one or more other cations selected from, but not limited to, calcium cations, potassium cations, barium cations, magnesium cations, and strontium cations.

[0036] Therefore, a sodium cation solution may, for example, contain a mixture of sodium cations and calcium cations, a mixture of sodium cations and potassium cations, a mixture of sodium cations and barium cations, a mixture of sodium cations, potassium cations and barium cations, a mixture of sodium cations, barium cations and strontium cations, a mixture of sodium cations, potassium cations, barium cations and strontium cations, a mixture of sodium cations, calcium cations and barium cations, etc.

[0037] However, a cationic solution containing a major portion (>50 mol%) of sodium cations, or even 80% to 100% sodium cations, more preferably 90% to 100% sodium cations, or even more preferably 95% to 100% sodium cations, is preferred relative to the total molar percentage of cations present in the solution.

[0038] The one or more anions present in the above-described cation solution are those well known to those skilled in the art, and are, for example, but not limited to, anions selected from halides, hydroxides, nitrates, sulfates, oxalates, and acetates, and preferably selected from halides, hydroxides, and nitrates, and more preferably selected from halides. Among halides, chlorides are particularly preferred.

[0039] The concentration of the sodium cation solution is such that the solution is a single-phase liquid solution without precipitation, and advantageously, the concentration is 0.05 to 1 times the solubility of one or more salts dissolved at the temperature at which the method according to the invention is carried out, preferably 0.10 to 0.80 times the solubility of said salts, more preferably 0.12 to 0.65 times the solubility of one or more salts dissolved at the temperature at which the method according to the invention is carried out, and preferably 0.15 to 0.60 times (including the endpoints).

[0040] As an illustrative example, the solubility of sodium chloride (NaCl) in water at 25°C is 36.1 g of NaCl dissolved per 100 g of water (RH Perry and CH Chilton, Chemical Engineers' Handbook, McGraw-Hill, (1973), 5th edition), which corresponds to a NaCl concentration of 5.4 M (mol per liter of solution).

[0041] The amount of ion solution used for ion exchange operations, and advantageously for percolation, is determined as a function of the cation concentration in the ion exchange solution and the amount of lithium present in the molecular sieve to be treated. The amount of cation is typically 0.9 to 2 times the amount of lithium cations to be exchanged in the molecular sieve, i.e., the molar ratio between the cations introduced into the solution and the lithium cations present in the molecular sieve is 0.9 to 2. A preferred amount is closest to 1 times, and typically closest to 0.9 to 1.1 times the amount of lithium cations to be exchanged.

[0042] In fact, this amount is equivalent to replacing one mole of lithium with one mole of cation present in the ion solution. The amount of lithium cation present in the molecular sieve is determined by ICP-AES as described above. When ion exchange step c) is percolation, the percolation rate is typically 3 cm·min in an empty column. -1 Up to 20 cm·min -1 4cm is preferred -1 Up to 18cm·min -1 And more preferably 5 cm·min -1 Up to 15cm·min -1 .

[0043] After one or more ion exchange operations via percolation and / or soaking, the molecular sieve is washed with water until the wash water concentration at the outlet has an anion (typically chloride) content of less than 25 mg / L. The recovered molecular sieve is then dried and activated before being reused as an adsorbent material.

[0044] Drying and activation are performed according to standard techniques well known to those skilled in the art. Therefore, drying is typically carried out at temperatures between 50°C and 200°C. Activation can also be performed according to any activation method known to those skilled in the art, and, for example, in a non-limiting manner, under purging with an inert gas and / or an oxidizing gas, particularly with gases such as oxygen, nitrogen, air, dry and / or decarburized air, oxygen-deficient air, optionally dry and / or decarburized, at one or more temperatures above 200°C, typically 250°C to 700°C, preferably 300°C to 650°C, for several hours, for example, 0.5 hours to 6 hours.

[0045] Therefore, the method of the present invention enables the economical recycling of molecular sieves that are primarily lithium-exchanged, particularly lithium-exchanged molecular sieves, which are waste or more generally unsuitable for their intended application, while simultaneously or concurrently producing:

[0046] - On the one hand, the solution contains lithium cations, preferably a solution mainly containing lithium cations, preferably a high-purity solution, i.e., wherein lithium cations account for 80 mol% or more of the cations present in the solution, preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, very preferably 99% or more, and

[0047] - On the other hand, molecular sieves with low lithium content, and more specifically molecular sieves containing very small amounts of lithium, for example, less than 1.8% lithium in the molecular sieve, preferably less than 1.5%, preferably less than 1%, more preferably less than 0.8%, advantageously less than 0.5%, the lithium content being expressed as the anhydrous equivalent weight of Li2O relative to the total anhydrous equivalent weight of the molecular sieve obtained by the method of the present invention.

[0048] Therefore, molecular sieves obtained with or simultaneously with lithium-ion solutions have low lithium content and typically very low residual lithium content. In this regard, molecular sieves with low lithium content are novel and constitute part of this invention.

[0049] Therefore, and according to another aspect, the present invention relates to a molecular sieve containing 0.01% to 1.8%, preferably 0.01% to 1.5%, preferably 0.01% to 1%, more preferably 0.01% to 0.8%, advantageously 0.01% to 0.5% lithium content, said lithium content being expressed as the anhydrous equivalent weight of Li2O relative to the total anhydrous equivalent weight of the molecular sieve.

[0050] In a preferred embodiment, the molecular sieve of the present invention comprises:

[0051] - A lithium content of 0.01% to 1.8%, preferably 0.01% to 1.5%, preferably 0.01% to 1%, more preferably 0.01% to 0.8%, advantageously 0.01% to 0.5%, said lithium content being expressed as the anhydrous equivalent weight of Li₂O relative to the total anhydrous equivalent weight of the molecular sieve, and

[0052] - The sodium content, as determined by ICP-AES, is 50 mol% to 99.99 mol%, preferably 80 mol% to 99.99 mol%, advantageously 90 mol% to 99.99 mol%, and more preferably 95 mol% to 99.99 mol%, relative to the total moles of cations present in the molecular sieve.

[0053] Molecular sieves with low lithium content, obtained simultaneously or concurrently with solutions containing lithium cations, can be very advantageously used as recycled zeolite adsorbent materials, and most particularly, as recycled zeolite adsorbent materials after conventional thermal activation treatment operations (removal of water present in the micropores).

[0054] Mass expressed as "anhydrous equivalent" means the product mass minus its loss on ignition (LOI). As mentioned above, the LOI is determined by calcining the sample in air at 950°C ± 25°C in an oxidizing atmosphere, as described in NF EN 196-2 (April 2006). The measured standard deviation is less than 0.1%. Lithium content is also determined by ICP-AES as described above.

[0055] Ionic solutions containing lithium cations can be readily reused, either directly or after several conventional purification processes known to those skilled in the art, and optionally after concentration or dilution as needed, for example, for the manufacture of new lithium-exchange molecular sieves. The lithium cation solution contains less than 0.05 moles of sodium per 100 g of ionic solution, preferably less than 0.03 moles, more preferably less than 0.02 moles, even more preferably less than 0.01 moles, and advantageously less than 0.005 moles of sodium.

[0056] In addition to allowing the recycling of lithium present in waste and / or unsuitable molecular sieves in the form of a solution of high-purity lithium cations, the method of the present invention also enables the production of “new” or “regenerated” molecular sieves that contain at least sodium, and optionally other cations derived from the ion solution used in the ion exchange step c) as described above.

[0057] One advantage of the method of the present invention is that it enables the production of “new” or “regenerated” molecular sieves without the need to synthesize zeolite crystals and agglomerate them with a binder. Furthermore, the production yield of the new molecular sieves produced is at least 90% or even at least 95%, more preferably at least 99% by weight, relative to the weight of the initial lithium-exchange molecular sieve; that is, there is almost no or no loss of adsorbent material throughout the entire method of the present invention.

[0058] Furthermore, the crystal integrity of the zeolite structure of the produced molecular sieve is maintained, meaning it remains unchanged relative to the lithium-exchange molecular sieve used in the method of the present invention. Therefore, and as an illustrative example, a lithium-exchange molecular sieve having a FAU LSX zeolite structure will be converted into a sodium-exchange molecular sieve having a FAU LSX zeolite structure in the method of the present invention.

[0059] As described above, the molecular sieve produced at the end of the method of the present invention contains sodium and one or more other cations optionally selected from calcium cations, potassium cations, barium cations, magnesium cations and strontium cations, but is not limited thereto, depending on the presence of these cations in one or more solutions used in the ion exchange step c) of the method of the present invention.

[0060] Therefore, the molecular sieves produced in this way can be, for example and without limitation, sodium-exchanged molecular sieves, sodium and calcium-exchanged molecular sieves, sodium and potassium-exchanged molecular sieves, sodium and barium-exchanged molecular sieves, sodium, potassium and barium-exchanged molecular sieves, sodium, barium and strontium-exchanged molecular sieves, sodium, potassium, barium and strontium-exchanged molecular sieves, or sodium, calcium and barium-exchanged molecular sieves, etc., as described above.

[0061] However, molecular sieves containing a predominantly sodium cation, or even 80% to 100% sodium cations, more preferably 90% to 100% sodium cations, or even more preferably 95% to 100% sodium cations, are preferred. The molar ratio of [sodium cations / exchangeable cations in the molecular sieve] is equal to the molar ratio of sodium cations present in the sieve after ion exchange (step c) to the molar ratio of cations present in the molecular sieve before ion exchange. The molar amount of cations in the molecular sieve is determined by ICP-AES.

[0062] Sodium molecular sieves co-produced with lithium cation solutions in the method of the present invention can find very advantageous applications, particularly in N2 / O2 separation, air pre-purification or hydrocarbon fraction purification, and more particularly in molecular sieves having FAU structures, and especially LSX type zeolites.

[0063] Therefore, the method of the present invention enables, on the one hand, the recycling of lithium present in waste and / or unsuitable molecular sieves, and on the other hand, the production of molecular sieves with complete or partial sodium exchange.

[0064] The method of the present invention can prove to be particularly effective and economically and industrially profitable, especially when implemented using lithium-exchange molecular sieves collected from several different sources and / or users. Therefore, it is conceivable to collect waste and / or unsuitable lithium-exchange sieves from several sources to implement the method of the present invention, with quantities ranging from several kilograms to several tons.

[0065] It is also conceivable to collect lithium exchange sieves with different zeolite crystal structures, such as sieves with FAU LSX crystal structures mixed with sieves with FAU MSX crystal structures and / or sieves with FAU X crystal structures, or sieves with FAU Y or LTA crystal structures, etc. In fact, the method of the present invention allows the recycling of lithium contained in any type of molecular sieve, whose zeolite crystal structures can be the same or different. However, it is preferred to operate using lithium exchange molecular sieves with a single, identical zeolite crystal structure, for example, and according to a very preferred embodiment of the invention, lithium exchange molecular sieves with FAU LSX zeolite crystal structures.

[0066] The following embodiments are provided to illustrate the present invention and are not intended to limit the invention. The scope of protection of the present invention is defined by the appended claims.

[0067] Example 1

[0068] A molecular sieve (920g, with a water content of 24% on anhydrous equivalent) from a medical oxygen concentrator that had been running continuously for 5 years was placed in a stainless steel column with a length of 2 meters and a diameter of 3 centimeters. The molecular sieve was based on lithium-exchanged FAU LSX zeolite sold by Arkema under the name NitroxySXSDM.

[0069] A 10-liter volume of 0.85M sodium chloride solution is pumped at a temperature of 30°C and a flow rate of 7 cm·min. -1 The apparent flow rate is percolated through a column containing the molecular sieve. The molar ratio between the sodium cations introduced into the solution and the lithium cations present in the molecular sieve is equal to 1.5.

[0070] After ion exchange and advantageous percolation, the column is emptied and simultaneously washed by injecting water via a pump until the chloride content in the effluent at the outlet is less than 25 mg / L.

[0071] The resulting sieve weighed 1005 g, on anhydrous equivalent, and contained 0.5% lithium, expressed as the anhydrous equivalent weight of Li₂O relative to the total anhydrous equivalent weight of the molecular sieve. X-ray diffraction confirmed no change / transformation of the crystalline phase.

[0072] The collected solution contained 4.8% by weight lithium chloride (LiCl) and 0.04% by weight NaCl.

[0073] This embodiment demonstrates that, using the method of the present invention, the following can be prepared simultaneously:

[0074] a) Sodium-exchange molecular sieves containing a very small proportion of lithium cations (0.4%, based on the anhydrous equivalent weight of Li₂O), and

[0075] b) A solution containing only a small proportion of Na (0.0007 mol% Na) and 99.5 mol% lithium cations, which constitute 99.5 mol% of the cations present in the solution.

[0076] The resulting sodium-exchange molecular sieve is fully reusable, meaning it can be used directly in applications requiring adsorbents of the sodium-exchange molecular sieve type (after routine operations of drying and calcination (also known as activation) as known to those skilled in the art), such as for nitrogen / oxygen separation or for air pre-purification.

[0077] The LiCl solution obtained at the end of the method of the present invention is pure and relatively concentrated, which allows it to be used, or used after a small concentration adjustment by evaporation or dilution, for example and advantageously for lithium exchange methods, particularly for the manufacture of lithium exchange molecular sieves.

[0078] Example 2

[0079] A 1000g (anhydrous equivalent) molecular sieve of lithium-exchange-based FAU X zeolite was placed in a 2m long, 3cm diameter stainless steel column. The molecular sieve had a Si / Al ratio of 1.25, contained 20% binder, and had a water content of 7%. Approximately 250g of water was sprayed onto the sieve spread on a plate. After this rehydration step, the water content of the molecular sieve was 31%.

[0080] A 0.85M sodium chloride solution of 9.9 liters is pumped at a temperature of 30°C and a flow rate of 7 cm·min. -1 The apparent flow rate is percolated through a column containing the molecular sieve.

[0081] Subsequently, the column is emptied and simultaneously flushed with water via a pump until the chloride content in the effluent at the outlet is less than 25 mg·L⁻¹. -1 .

[0082] The resulting sieve weighed 1087 g on anhydrous equivalent and contained 0.4% lithium, expressed as the anhydrous equivalent weight of Li₂O relative to the total anhydrous equivalent weight of the molecular sieve. X-ray diffraction confirmed no change / transformation of the crystalline phase.

[0083] The collected solution contained 4.8% by weight lithium chloride (LiCl) and 0.05% by weight NaCl.

[0084] This embodiment demonstrates that, using the method of the present invention, the following can be prepared simultaneously:

[0085] a) Sodium-exchange molecular sieves containing a very small proportion of lithium cations (0.4%, based on the anhydrous equivalent weight of Li₂O), and

[0086] b) A cation solution containing only a small proportion of sodium cations (0.0008 mol% Na) and lithium cations comprising 99.4% of the cations present in the solution.

[0087] The resulting sodium-exchange molecular sieve is fully reusable, meaning it can be used directly in applications requiring adsorbents of the sodium-exchange molecular sieve type (after routine operations of drying and calcination (also known as activation) as known to those skilled in the art), such as for nitrogen / oxygen separation or for air pre-purification.

[0088] The LiCl solution obtained at the end of the method of the present invention is pure and relatively concentrated, which allows it to be used, or used after a small concentration adjustment by evaporation or dilution, for example and advantageously for lithium exchange methods, particularly for the manufacture of lithium exchange molecular sieves.

Claims

1. A method for producing a solution of lithium cations on one hand, and simultaneously producing a molecular sieve with a low lithium content on the other hand, the method comprising: a) Provide lithium-exchange molecular sieves, b) Hydrated lithium-exchange molecular sieves, c) Using at least one ionic solution, perform ion exchange on the hydrated molecular sieve from the preceding steps, and d) On the one hand, the lithium cation solution is recovered, and on the other hand, the molecular sieve with low lithium content is recovered.

2. The method of claim 1, wherein the lithium-exchange molecular sieve is a waste molecular sieve or a molecular sieve unsuitable for its intended application.

3. The method according to claim 1 or claim 2, wherein the lithium exchange molecular sieve particularly comprises zeolite crystals selected from FAU type zeolite, EMT type zeolite, LTA type zeolite, LTL type zeolite, MFI type zeolite, MOR type zeolite, BEA type zeolite, CHA type zeolite, HEU type zeolite, OFF type zeolite or MAZ type zeolite, preferably FAU type zeolite, MFI type zeolite, MOR type zeolite, BEA type zeolite, CHA type zeolite or HEU type zeolite, very preferably FAU type zeolite and MFI type zeolite, especially FAU type zeolite, and more preferably FAU X type zeolite, FAU LSX type zeolite, FAU MSX type zeolite or FAU Y type zeolite, as well as ZSM-5 type MFI type zeolite and pure silica zeolite MFI type zeolite.

4. The method according to any one of the preceding claims, wherein the lithium molecular sieve in step a) has a lithium content of 0.5% to 12.0%, preferably 1.0% to 12.0%, preferably 4.0% to 12.0%, and very preferably 8.0% to 12.0%, said lithium content being expressed in equivalent weight of Li2O.

5. The method according to any one of the preceding claims, wherein the particle size is such that the minimum dimension is 0.10 mm to 5 mm, preferably 0.20 mm to 5 mm, more preferably 0.20 mm to 3 mm, and more particularly 0.25 mm to 1.5 mm.

6. The method according to any one of the preceding claims, wherein the hydration step b) is performed by soaking in water for several minutes to several hours.

7. The method according to any one of the preceding claims, wherein the ion exchange step c) is a percolation step using at least one ionic solution.

8. The method according to any one of the preceding claims, wherein the ion exchange step c) is a percolation step using at least one ionic solution containing sodium cations.

9. The method according to any one of the preceding claims, wherein the molecular sieve recovered in step d) is washed with water, then dried and activated.

10. The method according to any one of the preceding claims, used to prepare a sodium-exchange molecular sieve having a FAU LSX zeolite structure from a lithium-exchange molecular sieve having a FAU LSX zeolite structure, wherein the lithium-exchange molecular sieve is waste and / or unsuitable for its intended application.

11. A molecular sieve comprising a lithium content of 0.01% to 1.8%, preferably 0.01% to 1.5%, preferably 0.01% to 1%, more preferably 0.01% to 0.8%, advantageously 0.01% to 0.5%, said lithium content being expressed as the anhydrous equivalent weight of Li2O relative to the total anhydrous equivalent weight of the molecular sieve.