Recycling lithium cations in molecular sieves

Abstract

The present invention relates to a process for the simultaneous production of a solution of lithium cations and of a molecular sieve having a low lithium content, the process comprising providing a lithium-exchanged molecular sieve which is spent or unsuitable for its intended uses, it being possible for the co-produced molecular sieve having a low lithium content to be re-used as a molecular sieve.

Description

RECYCLING OF LITHIUM CATIONS IN MOLECULAR SIEVES

[0001] The invention relates to the field of molecular sieves partially or totally exchanged with lithium, and the recovery and reuse, i.e. recycling, of the lithium cations present in said molecular sieves.

[0002] Global demand for lithium is currently very high and constantly growing. Natural lithium resources are relatively scarce, so the cost of this raw material reaches levels that increase the cost of manufactured products containing lithium. These manufactured products have a more or less long lifespan and, when used, are most often discarded, destroyed, and / or landfilled.

[0003] Recycling the lithium present in these discarded manufactured products represents an avenue that has not yet been explored, particularly due to the difficulties encountered in carrying out efficient and interesting recycling from an industrial, economic and environmental point of view.

[0004] Ion exchange techniques using cation exchange materials have been known for many years. Patent US5451383, for example, describes a process for removing and concentrating lithium cations from dilute aqueous solutions by injecting said solutions into a column loaded with a cation exchange material. The first step consists of injecting the lithium cation solution (Li +) diluted in the column filled with cation exchange material bathed in a concentrated sodium chloride (NaCl) solution. At the column outlet, a concentrated and then diluted NaCl solution is collected. The second step consists of sending a concentrated NaCl solution countercurrently into the column and collecting a diluted and then concentrated lithium chloride (LiCl) solution at the outlet. Patent US5681477 provides an improvement by describing a process of the same type, but by modulating the temperatures of the solutions used.

[0005] Document CN114408941 describes the preparation of lithium-exchanged X-structure molecular sieve by continuous countercurrent exchange of a powder sieve with lithium cations using a vacuum belt filter, allowing multiple successive exchanges with recycling of depleted effluents to the previous exchange section, which is another way to make the best use of lithium.

[0006] Documents KR101176164 and KR101319594 propose methods for recovering lithium present in liquid effluents, in chloride or carbonate form, from ion exchange preparation processes of lithium zeolites. Lithium is thus recovered by extraction with organic solvents.

[0007] Document CN 115558798 describes a method for extracting lithium from brines using porous solids, for example molecular sieves, activated carbons, resins, silicon carbides, impregnated or coated with hydrophobic organic compounds capable of retaining lithium. The lithium is then extracted from the solid by acid treatment.

[0008] Document CN116179857 presents a process for extracting lithium from a used lithium molecular sieve. The molecular sieve, previously destroyed by fine grinding (< 150 pm), is brought into contact with an ionic solution containing sodium, then left to mature by adjusting the pH to 5-6, at a temperature between 60°C and 90°C, in order to remove silicon and aluminum. After filtration, sodium carbonate and sodium hydroxide are added to remove other impurities and recover the lithium. In addition to the complexity of obtaining the purified lithium salt (several purification steps), the initial molecular sieve is completely destroyed and therefore cannot be reused.

[0009] According to a completely similar process, document CN116440857 describes a process for reducing the concentration of sodium cations in a solution rich in lithium cations. This process comprises the treatment of a sodium-exchanged zeolite adsorbent with a sulfuric acid solution, in particular the treatment under boiling in concentrated sulfuric acid for 2 to 4 hours, this treatment being able to be repeated 3 to 6 times. A solution of lithium cations to be enriched is then brought into contact with this acid solution comprising sodium cations to obtain an enriched solution of lithium cations. In these last two documents, we see that the initial molecular sieve is necessarily destroyed (grinding or acid digestion), and therefore cannot be recovered and reused at the end of the process.

[0010] The present invention proposes to meet a growing need today which is that of recovering the lithium present in used molecular sieves while recovering said used molecular sieves.

[0011] Also, a first objective of the present invention is to propose an economical process for recycling a used lithium molecular sieve and the recovery of the recycled solid in the form of a molecular sieve.

[0012] Another objective of the present invention is to propose an economical method for recycling a used lithium molecular sieve allowing the recovery of a high-purity lithium-charged ionic solution and the recovery of the recycled solid in the form of a molecular sieve.

[0013] Another objective of the present invention is to provide an economical method for recycling a used lithium molecular sieve and the recovery of the recycled solid in the form of a molecular sieve, for example exchanged with sodium.

[0014] Yet another objective of the present invention is to provide an economical method for recycling a used lithium molecular sieve and the recovery of the recycled solid in the form of a molecular sieve, typically exchanged with sodium.

[0015] Still other objects will appear in the description of the invention which follows. In this description, all ranges of values ​​are understood to be "inclusive" unless otherwise indicated.

[0016] Thus, and according to a first object, the invention relates to a method for the simultaneous production of a solution of lithium cations on the one hand and a molecular sieve with a low lithium content on the other hand, said method comprising: a) providing a lithium-exchanged molecular sieve, b) hydration of said lithium-exchanged molecular sieve, c) ion exchange, using at least one ionic solution, of the molecular sieve hydrated in the previous step, and d) recovery of a solution of lithium cations on the one hand and a molecular sieve with a low lithium content on the other hand.

[0017] The method of the invention uses a lithium-exchanged molecular sieve, and by lithium-exchanged molecular sieve is preferably meant a used lithium molecular sieve, and more specifically a lithium molecular sieve that has already been used and has become unsuitable for its intended uses. It may also be new (unused) lithium molecular sieves, but which have suffered manufacturing defects, which are "out of specification", and which are unsuitable for their intended uses.

[0018] The lithium-exchanged molecular sieves include in particular zeolite crystals which may be of any type well known to those skilled in the art and for example, and without limitation, crystals of zeolites of the FAU, EMT, LTA, LTL, MFI, MOR, BEA, CHA, HEU, OFF, MAZ type, preferably zeolites of the FAU, MFI, MOR, BEA, CHA, HEU type, most preferably zeolites of the FAU and MFI type, in particular FAU of the FAU X, FAU LSX, FAU MSX, FAU Y type and MFI of the ZSM-5 and silicalites type. The lithium-exchanged molecular sieves comprise zeolite crystals, as indicated above, said crystals being most often and advantageously agglomerated with at least one agglomeration binder which is also well known to those skilled in the art and which is advantageously chosen from clays.

[0019] The lithium-exchanged molecular sieves which are used in the process of the invention can thus comprise crystals of zeolite(s) defined above and at least one agglomeration binder, said agglomeration binder being able to be partially or totally zeolitized, that is to say converted at least partially into zeolite, according to techniques which are entirely well known to those skilled in the art.

[0020] The lithium molecular sieves which are advantageously used in the process of the invention, and more precisely in step a) of the process of the invention, most often and advantageously have a lithium content of between 0.5% and 12.0%, preferably of between 1.0% and 12.0%, preferably of between 4.0% and 12.0% and most preferably of between 8.0% and 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 adapted to lithium, on a Perkin Elmer 4300DV type device. The lithium content is expressed as equivalent weight of Ü2O.

[0021] The molecular sieves suitable for use in the process of the invention may be of any type well known to those skilled in the art, and most often in the form of particles such as agglomerates, beads, spun yarns, or more generally extruded, single extruded or polylobed, to name only the most common particles. The size of the particles is generally and most often such that the smallest dimension (for example diameter in the case of beads) is between 0.10 mm and 5 mm, preferably from 0.20 mm to 5 mm, more preferably 0.20 mm to 3 mm, and more particularly from 0.25 mm to 1.5 mm.

[0022] The lithium-exchanged molecular sieve used in the process of the present invention is typically a fully lithium-exchanged sieve. However, the process of the present invention is perfectly applicable to partially lithium-exchanged molecular sieves, the other exchangeable cations being able to be chosen from any other cation of columns I and II of the periodic table of elements, and in particular one or more cations chosen from sodium, potassium, magnesium, calcium, strontium and barium.

[0023] The process of the invention is however particularly applicable to molecular sieves having a high lithium content, for example preferably between 4.0% and 12.0% and more preferably between 8.0% and 12.0%, content expressed as Li2O, as explained above, these values ​​not being limiting.

[0024] The lithium-exchanged molecular sieve used in the process of the invention is therefore first hydrated, according to any method well known to those skilled in the art and more particularly any operation aimed at giving said lithium-exchanged molecular sieve a water content of between 20% and 75% measured by loss on ignition. The loss on ignition is determined in an oxidizing atmosphere, by calcining the sample in air at a temperature of 950°C ± 25°C, as described in standard NF EN 196-2 (April 2006). The standard deviation of measurement is less than 0.1%.

[0025] 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 necessary to achieve the desired water content, for example between a few minutes and a few hours. This hydration step can advantageously be preceded or followed, preferably preceded, by at least one sieving step in order in particular to remove fine particles, and / or by at least one sorting step aimed at eliminating any type of unwanted contaminant, for example metal particles and others originating from the recovery of used or unusable sieves.

[0026] It should be understood that this hydration step aimed at giving the lithium-exchanged molecular sieve provided in step a) a water content of between 20% and 75% as indicated above may not be necessary, in particular when said lithium-exchanged molecular sieve provided in step a) is an already hydrated molecular sieve, for example a used molecular sieve or one which has been exposed to air and has thus been able to adsorb a certain amount of water. Control according to techniques well known to those skilled in the art may be implemented before possibly adjusting, by hydration, the water content before the ion exchange of step c). Thus, the molecular sieve of step a) may or may not be subjected to a hydration step before ion exchange, so that said lithium-exchanged molecular sieve provided in step a) has the water content of between 20% and 75% indicated above.

[0027] After hydration and optional sieving and / or sorting, the lithium-exchanged molecular sieve is subjected to step c) of ion exchange, using at least one ionic solution, according to any method well known to those skilled in the art and for example by percolation, by soaking or by percolation and soaking, preferably the sieve is subjected to percolation, in order to carry out an ion exchange. By percolation is meant that an ionic solution is forced through said molecular sieve. The percolation can be carried out according to any method well known to those skilled in the art, and typically, the Percolation is carried out through a fixed bed of the lithium-exchanged molecular sieve. Percolation can be carried out in one or more stages. Alternatively or in addition, the lithium molecular sieve can be subjected to ion exchange, for example by one or more soakings of the molecular sieve in one or more batches of ionic solution(s).

[0028] Percolation may be carried out at room temperature or any other temperature, without however exceeding 150°C, preferably without exceeding 120°C, and advantageously without exceeding 110°C, low temperatures being generally preferred, in particular for obvious economic reasons.

[0029] The percolation is carried out using a solution comprising sodium cations and according to a particularly preferred embodiment, the solution is an aqueous solution of sodium cations. Hydro-organic solutions of sodium cations can also be used, for example water-alcohol, water-ether or water-ketone mixtures or mixtures thereof. However, aqueous solutions of sodium cations are preferred.

[0030] Sodium cation solutions generally comprise from 0.01% to 100% of sodium cations relative to the sum of the cations present in the solution, protons excluded, more generally from 0.1% to 100%, more generally still from 1% to 100%, preferably from 5% to 100%, more preferably still from 10% to 100%, advantageously from 20% to 100%, and for example from 50% to 100% in moles or from 75% to 100%, in moles, limits included of sodium cations, these contents being measured according to methods well known to those skilled in the art, for example by ICP-AES, according to standard NF EN ISO 11885.

[0031] The sodium cation solutions defined above may also include one or more other cations chosen from calcium cations, potassium cations, barium cations, magnesium cations and strontium cations, without this list being limiting.

[0032] Thus, sodium cation solutions may, for example, comprise mixtures of sodium and calcium cations, sodium and potassium cations, sodium and barium cations, sodium, potassium and barium cations, sodium, barium and strontium cations, sodium, potassium, barium and strontium cations, sodium, calcium and barium cations, etc.

[0033] However, cation solutions are preferred which contain a majority (> 50% in moles) of sodium cations, or even 80% to 100% of sodium cations, better still 90% to 100% of sodium cations, better still 95% to 100% of sodium cations, relative to the sum in moles of the cations present in the solution.

[0034] The anion(s) present in the cation solutions described above are those well known to those skilled in the art, and for example, in a non-limiting manner, those chosen from halides, hydroxides, nitrates, sulfates, oxalates, acetates and preferably from halides, hydroxides and nitrates, and more preferably from halides. Among the halides, chlorides are particularly preferred.

[0035] The concentration of the sodium cation solution is such that the solution is a single-phase liquid solution, without precipitate, and advantageously the concentration is between 0.05 and 1 times the solubility of the dissolved salt(s) at the temperature at which the process according to the invention is carried out, preferably between 0.10 and 0.80 times the solubility of the salt, better still between 0.12 and 0.65, preferably between 0.15 and 0.60, limits included, the solubility of the dissolved salt(s) at the temperature at which the process according to the invention is carried out.

[0036] As an illustrative example, the solubility of sodium chloride (NaCI) at 25°C in water is 36.1 g of NaCI per 100 g of water (RH Perry and CH Chilton, Chemical Engineers' Handbook, Mc Graw-Hill, (1973), 5th edition) which corresponds to a NaCI concentration of 5.4 M (moles per liter of solution).

[0037] The amount of ionic solution to be used for the ion exchange operation, and advantageously percolation, is determined as a function of the cation concentration of the ion exchange solution and the amount of lithium present in the molecular sieve to be treated. The amount of cations is typically between 0.9 and 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 between 0.9 and 2. The preferred amount is closest to 1 time, typically closest to 0.9 times to 1.1 times, the amount of lithium cations to be exchanged.

[0038] Indeed, this quantity corresponds to the replacement of one mole of lithium by one mole of cation present in the ionic solution. The quantity of lithium cations present in the molecular sieve is determined by ICP-AES, as explained previously. When step c) of ion exchange is a percolation, the percolation speed is typically between 3 cm min -1 and 20 cm min -1 , in empty barrel, preferably between 4 cm min -1 and 18 cm min -1 , and preferably still between 5 cm min -1 and 15 cm min -1 .

[0039] After the ion exchange operation(s) by percolation and / or soaking, the molecular sieve is washed with water until the concentration of the outlet wash water has an anion level (typically chloride) of less than 25 mg / L. The The recovered molecular sieve is then dried and activated before it can be reused as an adsorbent material.

[0040] Drying and activation are carried out according to the usual techniques well known to those skilled in the art. Thus, drying is typically carried out at a temperature between 50°C and 200°C. Activation can also be carried out according to any activation method known to those skilled in the art and for example, and in a non-limiting manner, under oxidizing and / or inert gas sweeping, with in particular gases such as oxygen, nitrogen, air, dry and / or decarbonated air, oxygen-depleted air, possibly dry and / or decarbonated, at one or more temperatures above 200°C, typically between 250°C and 700°C, preferably between 300°C and 650°C, for a few hours, for example between 0.5 and 6 hours.

[0041] Thus, the method of the invention makes it possible to economically recycle molecular sieves exchanged mainly with lithium, and in particular molecular sieves exchanged with lithium, used or more generally unsuitable for the applications for which they are intended, while simultaneously or concomitantly producing: - on the one hand a solution comprising lithium cations, preferably predominantly lithium cations, preferably a high purity solution, that is to say one in which the lithium cations represent more than 80% by mole of the cations present in the solution, preferably more than 90% of the cations present, more preferably more than 95%, better still more than 97%, most preferably more than 99%, and - on the other hand a molecular sieve with a low lithium content, and more specifically, containing very small quantities of lithium, for example less than 1.8%, preferably less than 1.5%, preferably less than 1%, more preferably less than 0.8%, advantageously less than 0.5% of lithium in the molecular sieve, the lithium content being expressed in anhydrous equivalent weight of Li2O, relative to the total weight in anhydrous equivalent of the molecular sieve resulting from the process of the invention.

[0042] The molecular sieve thus obtained concomitantly or simultaneously with the lithium ionic solution has a low lithium content, and most often a very low residual lithium content. As such, the low lithium molecular sieve is new and forms part of the present invention.

[0043] Thus, and according to another aspect, the present invention relates to a molecular sieve comprising a lithium content of between 0.01% and 1.8%, preferably between 0.01% and 1.5%, preferably between 0.01% and 1%, more preferably between 0.01% and 0.8%, advantageously between 0.01% and 0.5%, the lithium content being expressed in anhydrous equivalent weight of Li2O, relative to the total anhydrous equivalent weight of the molecular sieve.

[0044] In a preferred embodiment, the molecular sieve of the invention comprises: - a lithium content of between 0.01% and 1.8%, preferably between 0.01% and 1.5%, preferably between 0.01% and 1%, more preferably between 0.01% and 0.8%, advantageously between 0.01% and 0.5%, the lithium content being expressed in anhydrous equivalent weight of l_i2O, relative to the total weight in anhydrous equivalent of the molecular sieve, and - a sodium content of between 50% and 99.99%, preferably between 80% and 99.99%, advantageously between 90% and 99.99%, better still between 95% and 99.99%, in moles relative to the total number of moles of cations present in the molecular sieve, determined by ICP-AES.

[0045] The low lithium molecular sieve, obtained simultaneously or concomitantly with a solution comprising lithium cations, can be used very advantageously as a recycled zeolite adsorbent material, and particularly after the usual operations of activation heat treatments (elimination of water present in the microporosity).

[0046] A mass expressed in “anhydrous equivalent” means a mass of product reduced by its loss on ignition (LAI). The loss on ignition is determined, as previously indicated, in an oxidizing atmosphere, by calcining the sample in air at a temperature of 950°C ± 25°C, as described in standard NF EN 196-2 (April 2006). The measurement standard deviation is less than 0.1%. Lithium contents are also determined as previously indicated by ICP-AES.

[0047] The ionic solution comprising lithium cations can easily be reused, either directly or after some conventional purification treatments well known to those skilled in the art, and possibly concentration or dilution, as required, for example for the manufacture of new lithium-exchanged molecular sieves. The lithium cation solution contains less than 0.05 moles of sodium, preferably less than 0.03, more preferably less than 0.02, more preferably less than 0.01, and advantageously less than 0.005 moles of sodium per 100 grams of ionic solution.

[0048] In addition to allowing the recycling of lithium present in used and / or unusable molecular sieves, in the form of a high-purity lithium cation solution, the process of the invention also allows the production of a sieve “new” or “regenerated” molecular weight comprising at least sodium, and possibly other cations originating or not from the ionic solution used in step c) of ion exchange described above.

[0049] One of the advantages of the process of the invention is that it thus allows the production of a "new" or "regenerated" molecular sieve, without it being necessary to carry out a synthesis of zeolite crystals and an agglomeration of the crystals with a binder. Furthermore, the production yield of new molecular sieve produced is at least 90%, or even at least 95%, better still at least 99% by weight, relative to the weight of the starting lithium-exchanged molecular sieve, that is to say that there is little or no loss of adsorbent material throughout the process of the invention.

[0050] Furthermore, the crystalline integrity of the zeolite structure of the molecular sieve produced is preserved, i.e. it remains unchanged compared to the lithium-exchanged molecular sieve used in the process of the invention. Thus, and by way of illustrative example, a lithium-exchanged molecular sieve with a zeolite structure of the FAU LSX type will be converted in the process of the invention into a sodium-exchanged molecular sieve with a zeolite structure of the FAU LSX type.

[0051] As indicated above, the molecular sieve produced at the end of the process of the invention comprises sodium and optionally one or more other cations chosen from calcium cations, potassium cations, barium cations, magnesium cations and strontium cations, without this list being limiting, depending on whether these cations were present or not in the solution(s) used in step c) of ion exchange of the process.

[0052] The molecular sieve thus produced may thus be, for example and without limitation, a sodium-exchanged molecular sieve, a sodium and calcium-exchanged molecular sieve, a sodium and potassium-exchanged molecular sieve, a sodium and barium-exchanged molecular sieve, a sodium, potassium and barium-exchanged molecular sieve, a sodium, barium and strontium-exchanged molecular sieve, or a sodium, potassium, barium and strontium-exchanged molecular sieve, or a sodium, calcium and barium-exchanged molecular sieve, and others, as indicated above.

[0053] However, molecular sieves are preferred which comprise a majority of sodium cations, or even 80% to 100% sodium cations, better still 90% to 100% sodium cations, and even better still 95% to 100% sodium cations. The molar ratio [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) and of the cations present in the molecular sieve before ion exchange. The molar amounts of cations in the molecular sieve are determined by ICP-AES.

[0054] The sodium molecular sieves co-produced with a lithium cation solution in the process of the present invention can find very interesting applications, in particular in N2 / O2 separation, air pre-purification or the purification of hydrocarbon fractions, more particularly in the case of zeolite molecular sieves of FAU structure, and in particular of the LSX type.

[0055] The process of the invention thus allows on the one hand the recycling of lithium present in used and / or unusable molecular sieves, and on the other hand the production of molecular sieves exchanged totally or partially with sodium.

[0056] The method of the invention can prove to be particularly effective and profitable from an economic and industrial point of view, in particular when it is implemented using lithium-exchanged molecular sieves which are collected from several different sources and / or users. It is thus possible to envisage the collection of used and / or unusable lithium-exchanged sieves from several sources in order to implement the method of the invention with quantities of sieves which can range from a few kilograms to several tonnes.

[0057] It may also be envisaged to collect lithium-exchanged sieves with different zeolite crystal structures, for example sieves with FAU LSX crystal structure mixed with sieves with FAU MSX crystal structure and / or sieves with FAU X crystal structure, or even sieves with FAU Y crystal structure, or LTA crystal structure, and others. Indeed, the method of the invention allows the recycling of lithium contained in any type of molecular sieve whose zeolite crystal structures may be identical or different. However, it is preferred to operate with lithium-exchanged molecular sieves whose zeolite crystal structure is identical and unique, for example, and according to a very preferred embodiment of the invention, lithium-exchanged molecular sieves with FAU LSX zeolite crystal structure.

[0058] The following examples are given by way of illustration of the present invention and are not limiting in any way to the invention, the scope of protection of which is conferred by the claims annexed to the present description. Example 1

[0059] A molecular sieve from a medical oxygen concentrator that operated continuously for 5 years (920 g expressed as anhydrous equivalents, water content equal to 24%) based on lithium-exchanged FAU LSX zeolite, marketed by Arkema company under the name “Nitroxy SXSDM”, is placed in a stainless steel column of length equal to 2 meters, and diameter equal to 3 cm.

[0060] A quantity equal to 10 litres of a 0.85 M sodium chloride solution is percolated, by means of a pump, into the column containing the molecular sieve, at a temperature equal to 30°C and at a speed in an empty drum equal to 7 cm min'. 1The molar ratio between the sodium cations introduced into the solution and the lithium cations present in the molecular sieve is equal to 1.5.

[0061] After ion exchange, and advantageously percolation, the column is drained and washed simultaneously by injecting water using the pump until the chloride content in the outlet effluent is less than 25 mg / L.

[0062] The resulting sieve weighs 1005 g, expressed as anhydrous equivalent, and contains 0.5% lithium, expressed as anhydrous equivalent weight of Ü2O, relative to the total anhydrous equivalent weight of the molecular sieve. X-ray diffraction is used to verify that there is no change / transformation of the crystalline phase.

[0063] The collected solution contains 4.8% by mass of lithium chloride (LiCl) and 0.04% by mass of NaCl.

[0064] This example shows that it is possible, using the process of the invention, to simultaneously prepare: a) a sodium-exchanged molecular sieve comprising a very small proportion of lithium cations (0.4% by weight of anhydrous equivalent of LÎ2O), and b) a solution comprising only a small proportion of Na (0.0007% by mole of Na) and lithium cations representing 99.5% by mole of the cations present in the solution.

[0065] The resulting sodium-exchanged molecular sieve is fully recoverable, i.e. directly usable (after the usual operations, well known to those skilled in the art, of drying and calcination, also known as activation) in applications where sodium-exchanged molecular sieve type adsorbents are required, for example for nitrogen / oxygen separation or air pre-purification.

[0066] The LiCl solution obtained at the end of the process of the invention is pure and relatively concentrated, which allows its use, or with small concentration adjustments by evaporation or dilution, for example and advantageously in a lithium exchange process, and in particular for the manufacture of lithium-exchanged molecular sieves. Example 2

[0067] A molecular sieve (1000 g expressed in anhydrous equivalents) based on lithium-exchanged FAU X zeolite, with a Si / Al ratio of 1.25, containing 20% ​​binder and a water content of 7%, is placed in a stainless steel column 2 meters long and 3 cm in diameter. Approximately 250 g of water is sprayed onto the sieve spread on a tray. The water content after this rehydration step is 31%.

[0068] A quantity equal to 9.9 litres of a 0.85 M sodium chloride solution is percolated, by means of a pump, into the column containing the molecular sieve, at a temperature equal to 30°C and at a speed in an empty drum equal to 7 cm min'. 1 .

[0069] The column is then drained and washed simultaneously by injecting water using the pump until the chloride content in the outlet effluent is less than 25 mg L' 1 .

[0070] The resulting sieve weighs 1087 g, expressed as anhydrous equivalent, and contains 0.4% lithium, expressed as anhydrous equivalent weight of Ü2O, relative to the total anhydrous equivalent weight of the molecular sieve. X-ray diffraction is used to verify that there is no change / transformation of the crystalline phase.

[0071] The collected solution contains 4.8% by mass of lithium chloride (LiCl) and 0.05% by mass of NaCl.

[0072] This example shows that it is possible, using the process of the invention, to simultaneously prepare: a) a sodium-exchanged molecular sieve comprising a very small proportion of lithium cations (0.4% by weight of anhydrous equivalent of LÎ2O), and b) a cation solution comprising only a small proportion of sodium cations (0.0008% by mole of Na) and lithium cations representing 99.4% of the cations present in the solution.

[0073] The sodium-exchanged molecular sieve thus obtained is fully recoverable, i.e. directly usable (after the usual operations well known to those skilled in the art of drying and calcination, also called activation) in applications where sodium-exchanged molecular sieve type adsorbents are required, for example for nitrogen / oxygen separation or air pre-purification.

[0074] The LiCl solution obtained at the end of the process of the invention is pure and relatively concentrated, which allows its use, or with small concentration adjustments by evaporation or dilution, for example and advantageously in a lithium exchange process, and in particular for the manufacture of lithium-exchanged molecular sieves.

Claims

CLAIMS 1. A method for the simultaneous production of a lithium cation solution on the one hand and a low lithium molecular sieve on the other hand, said method comprising: a) providing a lithium-exchanged molecular sieve, b) hydrating said lithium-exchanged molecular sieve, c) ion exchange, using at least one ionic solution, of the molecular sieve hydrated in the previous step, and d) recovering a lithium cation solution on the one hand and a low lithium molecular sieve on the other hand.

2. The method of claim 1, wherein the lithium-exchanged molecular sieve is a used molecular sieve or one unsuitable for the applications for which it is intended.

3. Method according to claim 1 or claim 2, in which the lithium-exchanged molecular sieve comprises in particular zeolite crystals chosen from those of the FAU, EMT, LTA, LTL, MFI, MOR, BEA, CHA, HEU, OFF, MAZ type, preferably of the FAU, MFI, MOR, BEA, CHA, HEU type, most preferably of the FAU and MFI type, in particular of the FAU type and more preferably of the FAU X, FAU LSX, FAU MSX, FAU Y type and the MFIs of the ZSM-5 and silicalites type.

4. Process according to any one of the preceding claims, wherein the lithium molecular sieve of step a) has a lithium content of between 0.5% and 12.0%, preferably between 1.0% and 12.0%, more preferably between 4.0% and 12.0% and most preferably between 8.0% and 12.0%, expressed as equivalent weight of IJ2O.

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

6. Method according to any one of the preceding claims, in which step b) of hydration is carried out by soaking in water for a period of between a few minutes and a few hours.

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

8. Method according to any one of the preceding claims, in which step c) of ion exchange is a percolation step using at least one ionic solution comprising sodium cations.

9. A 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. Process according to any one of the preceding claims, for the preparation of a sodium-exchanged molecular sieve with a zeolitic structure of the FAll LSX type from a molecular sieve, used and / or unsuitable for the uses for which it is intended, exchanged with lithium with a zeolitic structure of the FAll LSX type.

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