WO2025125331A1

WO2025125331A1 - Process for lithium recovery

Info

Publication number: WO2025125331A1
Application number: PCT/EP2024/085689
Authority: WO
Inventors: Mohamed Takhim
Original assignee: Takhim For Technology And Business Services
Current assignee: Takhim For Technology And Business Services
Priority date: 2023-12-11
Filing date: 2024-12-11
Publication date: 2025-06-19
Anticipated expiration: 2026-06-11

Abstract

The present invention relates to a process for the production of a LiHSO4 solution comprising the following steps: (a) providing a lithium solution comprising H⁺ cations, Li⁺ cations, SO₄ ^2- anions, HSO₄ ^- anions, and water, wherein the molar ratio between the hydrogen cations and lithium cations in the lithium solution ranges from about 0.3 to 2; wherein step (a) comprises the following steps: (a1) providing a leachate solution; and (a2) adding sulphuric acid (H₂SO₄), and optionally water, to obtain the lithium solution; (b) optionally, removing insoluble impurities and/or organic impurities from the lithium solution; and (c) proceeding with nanofiltration (NF) of the lithium solution to obtain a lithium hydrogen sulphate solution. The present invention further relates to processes for the production of lithium sulphate solutions and/or lithium carbonate from the lithium sulphate solution.

Description

PROCESS FOR LITHIUM RECOVERY FIELD OF INVENTION [0001] The present invention relates to process for lithium recovery, in particular starting from a leachate solution of black mass. According to some embodiments, lithium is recovered through the production of lithium hydrogen sulphate (LiHSO₄) and lithium sulphate (Li2SO4) solutions. BACKGROUND OF INVENTION [0002] Metals such as lithium, manganese, cobalt, and nickel are essential components of lithium-ion batteries, which are used in a variety of applications including consumer products and motorised vehicles. When a battery can no longer be used, it is generally collected, dismantled, and shredded. Further processing of the shredded material produces so-called “black mass”, which typically comprises the above metals in relatively high amounts. To be re-used in the production of new batteries, it is necessary that the metals of interest can be selectively extracted from the black mass. Black mass can represent up to 50% weight by weight (w/w) of an electric vehicle battery, so that effective separation of black mass is a critical aspect of battery recycling. [0003] The use and demand for lithium increases dramatically over the years because of his criticality in many devices for energy transition, and chiefly rechargeable batterie technology; so that recovering lithium from back mass is a major challenge for metal industries. [0004] Methods using resin separation have been used for the treatment of black mass with good performance, but these systems are quite large and require a lot of chemicals for their maintenance. Simpler filtration-based systems would be desirable; however, membrane filtration, in particular nanofiltration (NF) did not provide sufficient yield and/or selectivity towards lithium and others metals present in black mass. [0005] GAO, L. et al. (“Nanofiltration Membrane Characterization and Application: Extracting Lithium in Lepidolite Leaching Solution”, Membranes, 03 August 2020, Vol.10, No. 178) have studied, in laboratory scale, whether lithium may be extracted from a lepidolite leaching solution using nanofiltration (NF). Experiments were carried out using a feed solution comprising lithium chloride (LiCl) and lithium sulphate (Li₂SO₄) under basic conditions. The authors deliberately introduced monovalent chloride ions (Cl-) in the treated solution, in particular in the form of potassium chloride and sodium chloride. They assumed that this may decrease the retention rate of the NF membrane and thus facilitate the transmission of metal cations through the membrane. However, such process cannot be conveniently used for recovering lithium present in black mass (by contrast with black mass from lepidolite), because the leaching solution from black mass treatment by the sulphuric acid process is an acidic medium, rather than basic medium as in the conditions of GAO et al. Basification - or even neutralisation - of a black mass leachate solution would require excessive amounts of strong base, whereas there is no clear evidence that the process as suggested by GAO et al. would even provide industrially relevant selectivity and/or yield. Moreover, the use of Cl- as taught by GAO et al. is strongly disadvantageous for industrial use because of the risk of corrosion, in particular in acidic medium. Furthermore, introduction of Cl- in a black mass leaching would mean in practice adding another type of impurity in the solution, which would likely require additional purification steps. [0006] Thus, there is still a need to provide improved processes that can extract value from waste residues from lithium-ion batteries, like black mass, by recovering pure lithium with high selectivity and yield, while efficiently removing the various co-products and impurities and maintaining the possibly of further extracting other metals of interest. Moreover, responsible recycling should limit as much as possible the use of reactants, energy consumption, emissions and hazardous wastes. SUMMARY [0007] The present invention relates to a process for the production of a lithium hydrogen sulphate (LiHSO4) solution comprising the following steps: (a) providing a lithium solution comprising hydrogen cations (H⁺), lithium cations (Li⁺), sulphate anions (SO₄ ^2-), hydrogen sulphate anions (HSO₄-), and water, wherein the molar ratio between the hydrogen cations and lithium cations in the lithium solution ranges from about 0.3 to 2, wherein the molar concentration of the hydrogen cations is measured by pH titration; wherein step (a) comprises the following steps: (a1) providing a leachate solution comprising hydrogen cations (H⁺), lithium cations (Li⁺), sulphate anions (SO4^2-), hydrogen sulphate anions (HSO4-), and water, wherein the molar ratio between the hydrogen cations and lithium cations in the leachate solution is lower than about 0.3, wherein the molar concentration of the hydrogen cations is measured by pH titration; and (a2) adding sulphuric acid (H₂SO₄) to the leachate solution, as needed depending on the initial content of hydrogen cations and lithium cations in the leachate solution, to obtain the lithium solution; (b) optionally, removing insoluble impurities and/or organic impurities from the lithium solution; and (c) proceeding with nanofiltration (NF) of the lithium solution to obtain a lithium hydrogen sulphate solution. [0008] Without wishing to be bound by any theory, the Applicant believes that defining the molar ratio between the hydrogen cations (H⁺) and lithium cations (Li⁺) as in the present invention is responsible for the high yield and selectivity at step (c) of the present invention, namely, nanofiltration (NF) of the leachate solution. In particular, it is the Applicant’s understanding that the H⁺/Li⁺ ratio equal to or higher than about 0.3 is sufficient to ensure that the main Li⁺ ionic species in the lithium solution involve Li⁺ and hydrogen sulphate (HSO₄-), e.g., in the form of [Li⁺, HSO₄-]^sol, rather than ionic species involving Li⁺ and sulphate (HSO₄ ^2-). The Applicant surprisingly found out that the presence of HSO4- as counter-anion for Li⁺ in sufficient amount in the lithium solution significantly favour the transfer of Li⁺ through a NF membrane and thus leads to high yield and selectivity, whereas when Li⁺ is associated with SO4^2-, the Li⁺ yield and selectivity of the NF step dramatically decreases. [0009] According to some embodiments, the molar ratio between the hydrogen cations and lithium cations in the lithium solution ranges from about 0.5 to 1.5, preferably from about 0.8 to 1.2, more preferably is about 1. [0010] According to some embodiments, the concentration of lithium cations in the lithium solution is equal to or lower than about 7500 ppm. The Applicant surprisingly found out that that the concentration of Li⁺ equal to or lower than about 7500 ppm significantly favour high filterability of the lithium solution (permeate), thus optimising the investment costs (CAPEX) and operating costs (OPEX) of the process, and is thus advantageously for industrial use of the process according to the invention. In some embodiments, the concentration of lithium cations in the lithium solution ranges from about 100 ppm to 7500 ppm, preferably from about 500 to 4000 ppm, more preferably from about 1500 to 3000 ppm, furthermore preferably from about 1200 to 2750 ppm, furthermore preferably from about 2200 to 2500 ppm. [0011] According to some embodiments, step (a2) further comprises adding water to the leachate solution; preferably water is added to the leachate solution at step (a2) in a water / leaching solution weight ratio ranging from about 1 to 10, preferably from about 2 to 6, more preferably of about 3. In some embodiments, the leachate solution is obtained from the leaching of a black mass by concentrated sulphuric acid. According to some embodiments, step (b) comprises the following step(s): (b1) removing by filtration, preferably by microfiltration (MF), insoluble impurities from the lithium solution; and/or (b2) removing by filtration, preferably by ultrafiltration (UF), organic impurities from the lithium solution. According to some embodiments, the nanofiltration (NF) at step (c) is carried out with a membrane having a molecular weight cutoff (MWCO) ranging from about 100 to 1000 Dalton, preferably ranging from about 200 to 800 Dalton, more preferably ranging from about 250 to 500 Dalton. According to some embodiments, the nanofiltration (NF) membrane is a composite membrane comprising a film and a porous support material, wherein the film comprises a polymer matrix and is layered on the porous support material, and wherein the polymer matrix is selected from polyolefins, polysulfones, polyethers, polysulfonamides, polyamines, polysulfides, and melamine polymers; preferably, the porous support material comprises polysulfone. [0012] According to some embodiments, the process further comprises the following steps: (d) adding a calcium source to the lithium hydrogen sulphate solution; and (e) proceeding with solid-liquid separation to obtain a first lithium sulphate (Li2SO4) solution. In some embodiments, the calcium source at step (d) is selected from calcium carbonate (CaCO₃), calcium hydroxide (Ca(OH)₂), calcium oxide (CaO), or mixtures thereof; preferably the calcium source is calcium hydroxide (Ca(OH)2). In some embodiments, the solid-liquid separation at step (e) is carried out by vacuum belt filter (VBF) or filter press (FP), preferably by VBF. [0013] According to some embodiments, the process further comprises the following steps: (f) adding a base to the first lithium sulphate solution; and (g) proceeding with solid-liquid separation to obtain a second lithium sulphate (Li₂SO₄) solution. In some embodiments, at step (f) the base is sodium carbonate (Na₂CO₃). [0014] According to some embodiments, the process further comprises the following step: (h) concentrating, preferably by reverse osmosis (RO), either the first lithium sulphate solution obtained by the process according to the invention or the second lithium sulphate (Li2SO4) solution obtained by the process according to the invention, to obtain a third lithium sulphate (Li2SO4) solution. [0015] According to some embodiments, the process further comprises the following steps: (i) adding a carbonatation agent, preferably sodium carbonate (Na₂CO₃), to the third lithium sulphate solution; and (j) proceeding with solid-liquid separation, preferably by vacuum belt filter (VBF), to obtain lithium carbonate (Li₂CO₃). DEFINITIONS [0016] In the present invention, the following terms have the following meanings: [0017] “About” is used herein to mean approximately, roughly, around, or in the region of. The term “about” preceding a figure means plus or less 10% of the value of said figure. When the term “about” is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the numerical values set forth by 10%. [0018] “Between [lower value] and [upper value]” and the like define a numerical range that excludes (i.e., does not encompass) both the upper value and the lower value. [0019] “Black mass” refers to a solid material obtained from retired batteries. The batteries are shredded then processed (typically by pyrometallurgy or hydrometallurgy) to yield the “black mass” as black shiny powder. Black mass comprises a mixture of metals, but the exact composition of black mass can vary considerably and depend in particular on the types of batteries, the manufacturers thereof, as well as age and condition of the batterie when collected for recycling. Graphite is present in the anodes of batteries and is thus one of the main components of black mass (typically 30-70% w/w), giving it its black coloration. Black mass made from lithium-ion batteries typically comprises lithium, copper, manganese, cobalt, and nickel in industrially significant amounts. Lithium is typically present in an amount ranging from 1 to 12%, for example, from about 2 to 8% in weight by weight of the black mass (w/w). Alternatively, black mass may be obtained from wastes from the manufacture of cathode, or a mixture of recycled batteries and cathode manufacture wastes. [0020] “Ranging from [lower value] to [upper value]” and others similar recitations define a numerical range that includes (i.e., encompasses) both the upper value and the lower value. Moreover, any range so defined in the present application should be construed as including an explicit disclosure of the corresponding narrower range “between [lower value] and [upper value]”. DETAILED DESCRIPTION [0021] Although the steps of the disclosed processes are presented throughout the specification with successive letters and/or numbers for better intelligence of the present disclosure, it should be understood that such steps are not necessarily successive nor carried out one after another. Indeed, the process according to the present invention may be a continuous process, wherein two or more steps may be carried out simultaneously rather than successively, according to industrial methods well-known in the art. For example, a step (n) of addition of a reactant and the step (n+1) of filtration of the resulting product of reaction may be carried out simultaneously if technically feasible, even if the steps are presented in the specification with successive letters and/or numbers. Process for the production of a LiHSO4 solution [0022] An object of the present invention is a process for the production of a lithium hydrogen sulphate (LiHSO4) solution comprising the following steps: (a) providing a lithium solution comprising lithium cations (Li⁺), sulphate anions (SO₄ ^2-), hydrogen sulphate anions (HSO₄-) and water, wherein the molar ratio between the hydrogen cations and lithium cations in the lithium solution is equal to or higher than about 0.3; (b) optionally, removing insoluble impurities and/or organic impurities from the lithium solution; and (c) proceeding with nanofiltration (NF) of the lithium solution to obtain a lithium hydrogen sulphate solution. [0023] The combination of steps (a) and (b) may be considered as a “Step (I)” of “pre-treatment”, insofar the content and purity of the lithium solution are adjusted so that the lithium solution is in condition for the subsequent nanofiltration (NF) step (c). Step (a) – Provision of a lithium solution [0024] In the present disclosure, the “lithium solution” or “pretreated leachate solution” are synonyms and refers to a “leachate solution” as defined herein wherein the amount of hydrogen cations (H⁺) is as set forth at step (a) as defined herein. The lithium solution may be considered “pretreated” in the sense that this parameter has been adjusted according to the present invention. The lithium solution may also be considered “pretreated” by contrast with the “leachate solution” or “primary leachate solution” as defined hereinbelow. In the present invention, the lithium solution is “pretreated” in order to be ready to be efficiently separated by nanofiltration (NF). [0025] According to some embodiments, the molar ratio between the hydrogen cations (H⁺) and lithium cations (Li⁺) in the lithium solution is equal to or higher than about 0.5, preferably equal to or higher than about 0.8, more preferably equal to or higher than about 1. According to some embodiments, the molar ratio between the hydrogen cations (H⁺) and lithium cations (Li⁺) in the lithium solution ranges from about 0.3 to 2, preferably from about 0.5 to 1.5, more preferably from about 0.8 to 1.2, furthermore preferably is about 1. [0026] In the technical context of the present invention, for a given amount of lithium cations (Li⁺) in the lithium solution, the molar ratio between the hydrogen cations (H⁺) and lithium cations (Li⁺) directly depends on the free acidity of the lithium solution. Methods for determining and controlling free acidity of a solution comprising metal cations are well-known in the art, as described for example by KERGREIS, A. (“Étude des dosages d'acidité libre en solution aqueuse”, 1966, Rapport CEA R2982), in particular Part II, Chapter II thereof (“Dosage de l’acidité libre”). A preferred method for free acidity determination is titration as described by GROS, L. et al. (“Practical Titration (Monograph): Training Manual for Titrimetric Volumetric Analysis”, Metrohm Ltd., CH- 9101 Herisau, Switzerland, 8.029.5003, May 2005). Typical titration procedure is based on the titration with a base (typically, with a strong base) of known concentration in presence of an indicator in order to observe the equivalence point reflected by a change in colour of the solution (“colorimetric titration”). Alternatively, the equivalence point may be determined by the rapid change of pH (“pH titration”). Automatic titrators that execute titration via potentiometric measurement (e.g., acid-base titration or redox titration). Automatic titration may for example be a carried out using a “Titrando” apparatus (Metrohm, Switzerland) operated by touch control or with the OMNIS Software, which is used according to the manufacturer’s instructions. [0027] Free acidity may be increased (and thus the H⁺/Li⁺ ratio increased), for example, by addition of an acid (e.g., H2SO4); and it may by decreased (and thus the H⁺/Li⁺ ratio decreased), for example, be addition of a base (e.g., Na2CO3, Ca(OH)2 or NaOH). In some preferred embodiments, the acid used to adjust free acidity comprises or is sulphuric acid (H₂SO₄). The use of sulphuric acid (H₂SO₄) is especially industrially advantageous, because the leachate solution already comprises a significant amount of sulphate anions (SO4^2-), so that the chemical content of the solution is not significantly changed by the addition of sulphuric acid (the “leachate matrix” remains the same), which simplifies the further process steps such as, for example, purification steps. The use of sulphuric acid also avoids corrosion that may be caused by the presence of anions such as, for example, chloride (Cl-), fluoride (F-) or nitrate (NO₃-) in acidic medium, especially when high pressure and temperature are used (e.g., during a NF process). The use of sulphuric acid also prevents contamination of the extraction medium (e.g., the concentrate in a NF process) by anions such as, for example, chloride (Cl-), fluoride (F-) or nitrate (NO₃-), which makes subsequent recovery of further valuable metals such as cobalt (Co) and nickel (Ni) easier to proceed (e.g., by hydrometallurgy). [0028] The molar ratio between the hydrogen cations (H⁺) and lithium cations (Li⁺) in a solution (e.g., an aqueous solution) may be noted “H⁺/Li⁺ ratio”, and may be determined by a skilled person according to methods well-known in the art such as, for example, by determination of the concentration in H⁺ by measurement of free acidity as described hereinabove (preferably, by titration as described hereinabove) and determination of the concentration in Li⁺ (preferably, by ISE as described hereinbelow); then dividing the obtained values as [H⁺]/[Li⁺] (using the same units) to calculate the H⁺/Li⁺ ratio. [0029] According to some preferred embodiments, the concentration of lithium cations (Li⁺) in the lithium solution is equal to or lower than about 7500 ppm. According to some embodiments, the concentration of lithium cations in the lithium solution is equal to or lower than about 6000 ppm, preferably equal to or lower than about 5000 ppm, more preferably equal to or lower than about 4000 ppm, furthermore preferably equal to or lower than about 3000 ppm, furthermore preferably equal to or lower than about 2750 ppm, furthermore preferably equal to or lower than about 2500 ppm. According to some embodiments, the concentration of lithium cations (Li⁺) in the lithium solution ranges from about 100 ppm to 7500 ppm, preferably from about 500 to 4000 ppm, more preferably from about 1500 to 3000 ppm, furthermore preferably from about 1200 to 2750 ppm, furthermore preferably from about 2200 to 2500 ppm. In the context of the present disclosure, “ppm” means “part per million” in weight (i.e., 1 ppm = 1 mg/kg), in weight by total weight of the solution (e.g., the leachate solution or the lithium solution). [0030] In the technical context of the present invention, for a given amount of lithium cations (Li⁺) in the lithium solution, the concentration of lithium cations (Li⁺) directly depends on the dilution of the lithium solution. Methods for controlling the dilution of a solution comprising metal cations are well-known in the art. Dilution of the solution may be decreased (and thus Li⁺ concentration decreased), for example, by addition of water; and it may be increased (and thus Li⁺ concentration increased), for example, by evaporation of water. [0031] The concentration of lithium cations (Li⁺) in a solution (in particular, an aqueous solution) may be noted “[Li⁺]”, and may be determined by a skilled person according to methods well-known in the art such as, for example, by using an ion selective electrode (ISE) specific to lithium. ISE is an analytical technique used to determine the activity of ions in aqueous solution by measuring the electrical potential of the solution, as described for example by RAJA, P. M. V. et al. (https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Physical_Methods_in_ Chemistry_and_Nano_Science_(Barron)/01%3A_Elemental_Analysis/1.07%3A_Ion_S elective_Electrode_Analysis, online; accessed 2023-12-06). An example of suitable lithium probe for ISE is DX207-Li Lithium half-cell (Mettler Toledo, Switzerland), which is used according to the manufacturer’s instructions. [0032] In some embodiments, the pH of the lithium solution ranges from about 0.2 to 1.2, preferably from about 0.5 to 0.8, more preferably about 0.7. In these embodiments, the actual acidity (or “real acidity”) of the lithium solution is “acid”. [0033] In some embodiments, the amount of sulphate and hydrogen sulphate ions (SO4^2- and HSO₄-) in the lithium solution ranges about 1.5 to 15%, preferably from about 3 to 9%, more preferably is about 6%; in weight by weight of the lithium solution. This amount depends on the nature and amounts of metals in the solid material (e.g., the black mass) and may thus dramatically change depending on the matter to be treated. [0034] In some particular embodiments, the weight ratio between water and the initial solid material (e.g., the black mass) in the lithium solution ranges from about 5 to 40. “Initial solid material” refers to the amount of solid material (e.g., the black mass) at the time of leaching by the concentrated sulphuric acid (as described in detail hereinafter). According to common practice in the field of metal recycling, the amounts of materials (e.g., reactants, solvents) used in the process may be expressed relative to the initial solid material from which the metal to recycle is to be extracted, even for subsequent steps, because this may be convenient for evaluating or comparing the efficiency of the recovery process as a whole. [0035] According to some preferred embodiments, step (a) comprises the following steps: (a1) providing a leachate solution comprising lithium cations (Li⁺), sulphate anions (SO4^2-) and water, wherein the molar ratio between the hydrogen cations and lithium cations in the lithium solution is lower than about 0.3; and (a2) adding sulphuric acid (H2SO4) and/or water to the leachate solution, as needed depending on the initial content of hydrogen cations and lithium cations in the leachate solution, to obtain the lithium solution. [0036] In some preferred embodiments, step (a2) comprises adding sulphuric acid (H₂SO₄), and optionally water, to the leachate solution. [0037] According to some preferred embodiments, the concentration of lithium cations in the leachate solution is higher than about 7500 ppm. [0038] Step (a2) as defined above basically requires adjusting the added amount of sulphuric acid so that the molar ratio between the H⁺/Li⁺ ratio in the lithium solution is equal to or higher than about 0.3 (and, optionally, adjusting the added amount of water so that the concentration of Li⁺ in the lithium solution is equal to or lower than about 7500 ppm). Therefore, the specific amount of H₂SO₄ (and, optionally, water) to be added will be easily determined by a skilled person in view of the particulars of the leachate solution, namely, the molar ratio between the H⁺/Li⁺ ratio (and, optionally, the concentration of Li⁺). Consequently, preparing the lithium solution from the leachate solution can be made without undue burden by a skilled person using their general knowledge in the art. The parameters characterising the lithium solution according to the invention, as such (per se), are well-known in the art and may be easily measured and determined by methods commonly used in the art; whereas the suitable thresholds and ranges for these parameters, as set forth in the present disclosure, were surprisingly identified by the Applicant and are not part of the general knowledge in the art. [0039] According to some embodiments, sulphuric acid (H₂SO₄) is added to the leachate solution at step (a2) in a H2SO4 / leaching solution weight ratio ranging from about 0.005 to 0.1, preferably from about 0.01 to 0.05, more preferably of about 0.02 (i.e., 2% w/w). [0040] According to some embodiments, water is added to the leachate solution at step (a2) in a water / leaching solution (water / feed) weight ratio ranging from about 1 to 10, preferably from about 2 to 6, more preferably of about 3 (i.e., 300% w/w). [0041] According to some embodiments, sulphuric acid (H₂SO₄) is added to the leachate solution at step (a2) in a H₂SO₄ / lithium cations (Li⁺) (i.e., the total amount of lithium in the leachate solution) weight ratio ranging from about 1 to 15, preferably from about 2 to 6, more preferably of about 3. [0042] According to some embodiments, water is added to the leachate solution at step (a2) in a water / lithium cations (Li⁺) (i.e., the total amount of lithium in the leachate solution) weight ratio ranging from about 100 to 1500, preferably from about 300 to 1000, more preferably of about 500. [0043] According to some embodiments, sulphuric acid (H₂SO₄) is added to the leachate solution at step (a2) in a H2SO4 / sulphate anions (SO4^2-) (i.e., the total amount of SO4^2- in the leachate solution) weight ratio ranging from about 0.01 to 0.5, preferably from about 0.05 to 0.15, more preferably of about 0.1. [0044] According to some embodiments, water is added to the leachate solution at step (a2) in a water / sulphate anions (SO4^2-) (i.e., the total amount of SO4^2- in the leachate solution) weight ratio ranging from about 4 to 40, preferably from about 12 to 18, more preferably of about 14. [0045] According to some embodiments, sulphuric acid (H2SO4) is added to the leachate solution at step (a2) in an added H2SO4 (i.e., the amount of H2SO4 added to the leachate solution) / initial H₂SO₄ (i.e., the amount of H₂SO₄ used to prepare the leachate solution, as described hereinbelow) weight ratio ranging from about 0.02 to 0.50, preferably from about 0.10 to 0.20, more preferably of about 0.12. [0046] According to some embodiments, water is added to the leachate solution at step (a2) in a water / initial H₂SO₄ (i.e., the amount of H₂SO₄ used to prepare the leachate solution, as described hereinbelow) weight ratio ranging from about 5 to 60, preferably from about 15 to 25, more preferably of about 19. [0047] According to some embodiments, sulphuric acid (H₂SO₄) is added to the leachate solution at step (a2) in a H₂SO₄ / solid material (i.e., the amount of solid material from which the leachate solution was prepared, as described hereinbelow) weight ratio ranging from about 0.04 to 0.8, preferably from about 0.12 to 0.20, more preferably of about 0.16. [0048] According to some embodiments, water is added to the leachate solution at step (a2) in a water / solid material (i.e., the amount of solid material from which the leachate solution was prepared, as described hereinbelow) weight ratio ranging from about 7 to 70, preferably from about 15 to 30, more preferably of about 24. [0049] As previously stated, the use of sulphuric acid (H₂SO₄) as the acid of step (a2) is especially industrially advantageous, because the leachate solution already comprises a significant amount of sulphate anions (SO4^2-). [0050] These embodiments wherein water is added to a leachate solution previously prepared at a separate step (a2) are especially industrially advantageous. Indeed, if the amount of water remains relatively low during the leaching of the solid material (e.g., the black mass), then the sulphuric acid is not diluted and the primary extraction yield of the leaching process as described hereinbelow is optimised. [0051] According to some alternative embodiments, the lithium solution at step (a) is directly prepared from a process for the preparation of the leachate solution as described hereinabove, except that the amount of concentrated sulphuric acid (H₂SO₄) and water is adjusted so that the leaching solution directly has the characterising features of the lithium solution. In other words, in these embodiments, the leaching conditions are adapted so that the “lithium solution” and “leachate solution” are the same solution. Although encompassed by the present invention, these embodiments are typically industrially disadvantageous, because adding a significant amount of water at the time of leaching of the solid material (e.g., the black mass) would necessarily dilute the sulphuric acid, and thus reduce the primary extraction yield of the leaching process. [0052] In the present disclosure, the “leachate solution” or “primary leachate solution” refers to a leachate solution obtained from a leaching treatment of a solid material. For the preparation the leachate solution, the process parameters are defined only in order to optimise the leaching yield, without considering any subsequent treatment step(s), such as, for example, separation by nanofiltration (NF). [0053] The leachate solution may be prepared using any suitable method known in the art such as, for example, roasting or acid leaching. In some embodiments, the leachate solution is obtained from the leaching of a solid material by concentrated sulphuric acid (H2SO4), according to conventional leaching methods used for lithium recovery from solid materials. The concentrated sulphuric acid attack is typically sufficient to extract most of the lithium from the solid material, so that no additional agent is required for lithium recycling. In some particular embodiments, a reducing agent is added during the leaching, which allows for the extraction of further metals of interest, such as, for example, cobalt and nickel. [0054] The solid material may be any artificial or natural material comprising lithium (Li). In some particular embodiments, the solid material is selected from black mass, lepidolite, spodumene and mixtures thereof. In some preferred embodiments, the solid material substantially consists of a black mass. In some preferred embodiments, the solid material is a black mass. In some preferred embodiments, the black mass is substantially as described in Example 1 herein. [0055] In some embodiments, the concentration of lithium cations in the leachate solution is higher than about 7500 ppm. [0056] In some embodiments, the pH of the leachate solution ranges from about 0.3 to 0.6. In some embodiments wherein first water and then sulphuric acid are added to the leachate solution, the pH of the leachate solution after addition of the water and before addition of the sulphuric acid ranges from about 0.8 to 1.2. In these embodiments, the actual acidity (or “real acidity”) of the leachate solution is “acid”. [0057] In some embodiments, the amount of sulphate and hydrogen sulphate ions (SO₄ ^2- and HSO4-) in the leachate solution ranges about 5 to 45%, preferably from about 10 to 30%, more preferably is about 20%; in weight by total weight of the leachate solution. This amount depends on the nature and amounts of metals in the solid material (e.g., the black mass) and may thus dramatically change depending on the matter to be treated. [0058] In some particular embodiments, the weight ratio between water and the initial solid material (e.g., the black mass) in the leachate solution ranges from about 1.25 to 10. [0059] Although the present invention is illustrated, in particular, by example embodiments wherein the lithium solution provided at step (a) is obtained from the leaching of a solid material (e.g., the black mass), the present invention is not limited thereto. Indeed, the process according to the present invention may be used to recover lithium from any aqueous solution comprising lithium cations (Li⁺) and sulphate anions (SO4^2-), regardless of the initial material from which Li⁺ was solubilised. [0060] According to some embodiments, step (a2) does not comprise adding sodium hydroxide (NaOH) to the leachate solution. In some embodiments, step (a) and/or step (b) do not comprise adding sodium hydroxide (NaOH) to the leachate solution and/or to the lithium solution. According to some embodiments, step (a2) does not comprise adding potassium hydroxide (KOH) to the leachate solution. In some embodiments, step (a) and/or step (b) do not comprise adding potassium hydroxide (KOH) to the leachate solution and/or to the lithium solution. According to some embodiments, step (a2) does not comprise adding calcium oxide (CaO) to the leachate solution. In some embodiments, step (a) and/or step (b) do not comprise adding calcium oxide (CaO) to the leachate solution and/or to the lithium solution. Step (b) – Optional removal of insoluble and/or organic impurities [0061] According to some embodiments, the process further comprises a step (b) of removing insoluble impurities and/or organic impurities from the lithium solution. The impurities removal at step (b) may be carried out using any suitable method known in the art such as, for example, filtration. [0062] In some embodiments, step (b) comprises the following step(s): (b1) removing by filtration insoluble impurities from the lithium solution; and/or (b2) removing by filtration organic impurities from the lithium solution. [0063] The removal of insoluble impurities at step (b) may be carried out using any suitable method known in the art. According to some embodiments, step (b) is carried out by solid-liquid separation such as, for example, filtration, screw separation, centrifugation, decantation, and the like. [0064] In some embodiments, step (b) comprises the following step: (b1) removing by filtration insoluble impurities from the lithium solution. In some preferred embodiments, step (b1) is carried out by microfiltration (MF). [0065] The removal of organic impurities at step (b) may be carried out using any suitable method known in the art such as, for example, filtration by means of ultrafiltration (UF), cartridge filter, sand, cellulose, diatomaceous earth, and the like. In some embodiments, step (b) comprises the following step (b2) removing by filtration organic impurities from the lithium solution. In some preferred embodiments, step (b2) is carried out by ultrafiltration (UF). [0066] Step (b) is optional where the lithium solution is substantially free of insoluble impurities and organic impurities. Step (b1) is optional where the lithium solution is substantially free of insoluble impurities. Step (b2) is optional where the lithium solution is substantially free of organic impurities. The appropriate threshold for insoluble and organic impurities content in the lithium solution depends on the particulars of the subsequent nanofiltration (NF) step (c), especially of the specifications of the NF membrane. Consequently, determining whether a purification step (b) is necessary and in which extend it should be carried out can be made without undue burden by a skilled person using their general knowledge in the art. [0067] Insoluble impurities in the lithium solution typically include metals, metallic oxides, sand, graphite, and the like. Organic impurities in the lithium solution typically include colorants, dyes, electrolyte solvents, and the like. Typically, for NF membranes commercially available, the amount of insoluble impurities in the lithium solution should be equal or lower than about 1%, preferably about 0.5%, more preferably about 0.1%, in weight by total weight of the lithium solution; and the amount of organic impurities in the lithium solution should be equal or lower than about 5%, preferably about 2.5%, more preferably about 1%, in weight by total weight of the lithium solution. Step (c) – Nanofiltration (NF) [0068] At step (c), the nanofiltration (NF) isolates the lithium hydrogen sulphate (LiHSO₄) solution. [0069] The lithium hydrogen sulphate solution is a product of interest in the lithium recovery industry, typically as intermediate product for preparing further inorganic lithium compounds. This solution is also referred to as “diluted lithium hydrogen sulphate solution” (in short, “LiHSO4d”). [0070] The nanofiltration (NF) at step (c) may be carried out by any suitable nanofiltration (NF) membrane known in the art. According to some embodiments, the nanofiltration (NF) membrane is a composite membrane comprising a film and a porous support material, wherein the film comprises a polymer matrix and is layered on the porous support material, and wherein the polymer matrix is selected from polyolefins, polysulfones, polyethers, polysulfonamides, polyamines, polysulfides, and melamine polymers. In some preferred embodiments, the porous support material has a thickness that ranges from about 0.5 to 300 pm and/or the film thickness is equal to or lower than about 1.5 pm. For example, the polymer matrix is selected from polysulfones, polysulfonamides, polyamines, and melamine polymers; preferably, the polymer matrix is or comprises polysulfonamides. For example, the porous support material is selected from polyamide, polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinylchloride, ceramics, and porous glass; preferably, the porous support material is selected from polyamide, polysulfone, polyethersulfone, polyvinylidene fluoride, and polyvinylchloride; more preferably, the porous support material is or comprises polysulfone. For example, the polymer matrix is selected from polysulfonamides and the porous support material comprises polysulfone; preferably, the porous support material has a thickness that ranges from about 0.5 to 300 pm and/or the film thickness is equal to or lower than about 1.5 pm. In some preferred embodiments, the NF membrane is polymeric membrane, preferably a polysulfone membrane. [0071] According to some embodiments, the membrane has a molecular weight cutoff (MWCO) ranging from about 100 to 1000 Dalton, preferably ranging from about 200 to 800 Dalton, more preferably ranging from about 250 to 500 Dalton. “Molecular weight cutoff” or “MWCO” of a membrane refers to the minimum molecular weight of a solute that is 90% retained by the membrane, according to the French Standard NF X 45-10 (AFNOR, December 1996). The molecular weight cutoff (MWCO) may be determined by a skilled person according to methods well-known in the art such as, for example, measure of the retention of reference compounds (e.g., polyethylene glycols (PEG), oligostyrenes, alkanes, nanoparticles (NPs), etc.) by chromatographic methods such as, for example, gel permeation chromatography (GPC). Moreover, NF membranes are common commercial devices, so that the MWCO of a given membrane will as a rule be indicated in the commercial documentation of the NF membrane, typically along with the method used for determining the MWCO. [0072] According to some embodiments, the NF at step (c) is conducted at a temperature ranging from about 10 to 55°C, preferably from about 20 to 50°C, more preferably from about 35 to 50°C. According to some embodiments, the NF at step (c) is conducted at a pressure ranging from 0.1 to 7.0 MPa, preferably from 0.1 to 6.0 MPa, more preferably from 0.1 to 5.5 MPa. Process for the production of a first Li2SO4 solution [0073] Another object of the present invention is a process for the production of a first lithium sulphate (Li₂SO₄) solution, wherein the process including steps (a) to (c), as described herein, further comprises the following steps: (d) adding a calcium source to the lithium hydrogen sulphate solution; and (e) proceeding with solid-liquid separation to obtain a first lithium sulphate solution. Step (d) – Addition of a calcium source [0074] At step (d), the addition of the calcium source converts lithium hydrogen sulphate (LiHSO₄) into lithium sulphate (Li₂SO₄) in the solution. Moreover, the calcium source is typically a base and thus neutralises, at least partially, the lithium solution, so that further purification steps may be easier to implement, in particular when using reverse osmosis (RO). [0075] “Calcium source” refers to a basic calcium inorganic compound. According to some embodiments, the calcium source at step (d) is selected from calcium carbonate (CaCO3), calcium hydroxide (Ca(OH)2), calcium oxide (CaO), and mixtures thereof. In some embodiments, the calcium source is calcium carbonate (CaCO₃). In some preferred embodiments, the calcium source is calcium hydroxide (Ca(OH)2). [0076] Step (d) of synthesis of lithium sulphate as described herein is a non-limiting example of use of the lithium hydrogen sulphate solution obtained from the process according to the present invention, which is quite relevant from an industrial perspective. However, the utility of the present invention is not limited thereto, and further uses of the lithium hydrogen sulphate solution are possible. For example, a step of electrodialysis may be carried out starting from the lithium hydrogen sulphate solution to obtain lithium hydroxide (LiOH), which is a product of interest in the lithium recovery industry, and further recycling sulphuric acid. Step (e) – Solid-liquid separation [0077] At step (e), the solid-liquid separation isolates the first lithium sulphate (Li2SO4) solution from the solid by-products of the conversion reaction of step (d), which typically include at least one insoluble calcium sulphate salt. [0078] The first lithium sulphate solution is a product of interest in the lithium recovery industry, typically as intermediate product for preparing further refined lithium sulphate solutions. This first solution is also referred to as “primary diluted lithium sulphate solution” (in short, “primary Li₂SO₄d”). [0079] The solid-liquid separation at step (e) may be carried out using any suitable method known in the art such as, for example, filtration, screw separation, centrifugation, decantation, and the like. According to some embodiments, the solid-liquid separation at step (e) is carried out by vacuum belt filter (VBF) or filter press (FP). In some preferred embodiments, the solid-liquid separation at step (e) is carried out by vacuum belt filter (VBF). [0080] The combination of steps (d) and (e) as defined herein may be considered as a step of “desulphatation” insofar the sulphate ions are at least partially removed from the solution in the form of insoluble calcium sulphate salt(s). Process for the

of a second Li2SO4 solution [0081] Another object of the present invention is a process for the production of a second lithium sulphate (Li2SO4) solution, wherein the process including steps (a) to (e), as described herein, further comprises the following steps: (f) adding a base to the first lithium sulphate solution; and (g) proceeding with solid-liquid separation to obtain a second lithium sulphate solution. Step (f) – Addition of a base [0082] At step (f), the addition of the base causes the precipitation of heavy metal(s) that may still be present in the first lithium sulphate (Li2SO4) solution, such as, for example iron (e.g., Fe²⁺or Fe³⁺), aluminium (e.g., Al³⁺), cobalt (e.g., Co²⁺), nickel (e.g., Ni²⁺), manganese (e.g., Mn²⁺), calcium (e.g., Ca²⁺), magnesium (e.g., Mg²⁺). [0083] The precipitation of heavy metal(s) at step (f) may be carried out using any suitable base known in the art. According to some embodiments, the base is selected from sodium carbonate (Na₂CO₃), calcium hydroxide (Ca(OH₂)), sodium hydroxide (NaOH) and mixtures thereof. In some preferred embodiments, the base is sodium carbonate (Na2CO3). The use of sodium carbonate as the base of step (f) is especially industrially advantageous when the process further includes a step (i) of synthesis of lithium carbonate (Li₂CO₃), as described herein, because sodium carbonate may also be used at step (i) as a carbonatation agent. Step (g) – Solid-liquid separation [0084] At step (g), the solid-liquid separation isolates the second lithium sulphate (Li₂SO₄) solution from the impurities as precipitated at step (f), which typically include at least one insoluble heavy metal salt. [0085] The second lithium sulphate solution is a product of interest in the lithium recovery industry, typically as intermediate product for preparing further refined lithium sulphate solutions. This second solution is also referred to as “pure diluted lithium sulphate solution” (in short, “pure Li2SO4d”). [0086] The solid-liquid separation at step (g) may be carried out by any suitable method known in the art, such as, for example, filtration, screw separation, centrifugation, decantation, and the like. According to some embodiments, the solid-liquid separation at step (g) is carried out by filtration. In some preferred embodiments, the solid-liquid separation at step (g) is carried out by microfiltration (MF). [0087] According to some preferred embodiments, water is recycled from the solid-liquid separation of step (g) to be re-used at step (a) as described herein, typically at step (a2) as described herein. Process for the production of a third Li2SO4 solution [0088] Another object of the present invention is a process for the production of a third lithium sulphate (Li₂SO₄) solution, wherein the process including steps (a) to (e), preferably steps (a) to (g), as described herein, further comprises the following step: (h) concentrating the first lithium sulphate solution or the second lithium sulphate solution to obtain a third lithium sulphate solution. [0089] The combination of steps (c) to (h) disclosed herein may be considered as a “Step (II)” of “lithium purification and concentration”, insofar it purifies the lithium solution prepared at the preceding steps, and also concentrate the solution in lithium compounds, so that it is suitable for subsequent industrial use, for example for lithium carbonate production as disclosed herein. Step (h) – Concentration [0090] At step (h), the concentration removes the excess of water and thereby provides a third lithium sulphate (Li₂SO₄) solution. [0091] The lithium sulphate solution that is concentrated at step (h) may be either the first lithium sulphate solution obtained at step (e) as described herein, or the second lithium sulphate solution obtained at step (g) as described herein. According to some preferred embodiments, step (h) is carried out on the second lithium sulphate solution. [0092] The third lithium sulphate solution is a product of interest in the lithium recovery industry, either as such or as intermediate product for preparing further inorganic lithium compounds. This third solution is also referred to as “pure concentrated lithium sulphate solution” (in short, “pure Li₂SO₄cc”). [0093] The concentrating at step (h) may be carried out by any suitable method known in the art such as, for example, membrane process or evaporation. According to some embodiments, the concentrating at step (h) is carried out by reverse osmosis (RO) or evaporation using a triple effect evaporator. In some preferred embodiments, the concentrating at step (h) is carried out by reverse osmosis (RO). RO may be carried out using any suitable membrane known in the art. In some preferred embodiments, the RO membrane is an organic polymeric membrane (e.g., commercial RO membranes from Dow Chemicals, Suez, or Lenntech Europe). In some preferred embodiments, the membrane is a thin-film (TFM) fiberglass membrane. Typically, the RO membrane has an average salt (NaCl) rejection rate equal to or higher than about 99%, preferably equal to or higher than about 99.5%, more preferably equal to or higher than about 99.7%. [0094] According to some preferred embodiments, water is recycled from the concentration of step (h) to be re-used at step (a) as described herein, typically at step (a2) as described herein. [0095] According to some preferred embodiments, further water and/or sulphuric acid is added to the recycled water from step (g) and/or step (h), in order to provide the lithium solution as defined at step (a). In some preferred embodiments, at least about 75% w/w, preferably at least about 80% w/w, more preferably at least about 85% w/w, furthermore preferably at least about 90% w/w, of the water added at step (a) is recycled from step (g) and/or step (h). Thus, less than about 25% w/w, preferably less than about 20% w/w, more preferably less than about 15% w/w, furthermore preferably less than about 10% w/w of the water added at step (a) is added to the recycled water from step (g) and/or step (h). In other words, advantageously, up to less than about 10% of the water injected in the process at step (a) is not recycled during the lithium recovery process. Process for the production of

[0096] Another object of the present invention is a process for the production of lithium carbonate (Li2CO3), wherein the process including steps (a) to (h) as described herein further comprises the following steps: (i) adding carbonatation agent to the third lithium sulphate solution; and (j) proceeding with solid-liquid separation to obtain lithium carbonate. [0097] The combination of steps (i) and (j) disclosed herein may be considered as a “Step (III)” of “post-treatment and valorisation”, insofar it uses the concentrated lithium solution prepared at the preceding steps for lithium carbonate production. Many other alternative post-treatment(s) and/or valorisation(s) may be considered, and any one of them is encompassed by the present invention, which shall not in any case be constructed as limited to the production of lithium carbonate. Step (i) – Addition of a carbonatation agent [0098] At step (i), the addition of the carbonatation agent converts lithium sulphate (Li₂SO₄) into lithium carbonate (Li₂CO₃) in the solution. [0099] The synthesis of lithium carbonate (Li₂CO₃) at step (i) may be carried out using any suitable carbonatation agent known in the art. According to some embodiments, the carbonatation agent is sodium carbonate (Na2CO3), potassium carbonate (K2CO3), ammonium carbonate ((NH₄)₂CO₃), or carbon dioxide (CO₂) in a basic medium. In some preferred embodiments, the carbonatation agent is sodium carbonate (Na₂CO₃). The use of sodium carbonate as the carbonatation agent of step (i) is especially advantageous industrially when the process further includes a step (f) of precipitation of heavy metal(s), as described herein, because sodium carbonate may also be used at step (f) as a base. Step (j) – Solid-liquid separation [0100] At step (j), the solid-liquid separation isolates solid lithium carbonate (Li₂CO₃) from the soluble sulphate salt(s) present in solution. The nature of the soluble sulphate salt(s) recovered in solution directly depends on the carbonatation agent used at step (i). For example, when the carbonatation agent is sodium carbonate (Na₂CO₃), then the sulphate salt is sodium sulphate (Na2SO4). [0101] Lithium carbonate is a product of interest in the lithium recovery industry, either as such or as intermediate product for preparing further inorganic lithium compounds. This obtained lithium carbonate is also referred to as “pure precipitated lithium carbonate” (in short, “pure precipitated Li2CO3”). [0102] The solid-liquid separation at step (j) may be carried out using any suitable method known in the art such as, for example, filtration, screw separation, centrifugation, decantation, and the like. According to some embodiments, the solid-liquid separation at step (j) is carried out by vacuum belt filter (VBF) or filter press (FP). In some preferred embodiments, the solid-liquid separation at step (j) is carried out by vacuum belt filter (VBF). Products obtained by the processes [0103] Another object of the present invention is a hydrogen sulphate (LiHSO₄) solution directly obtained by a process according to the invention, as described herein. According to some embodiments, the solution is “diluted”, for example the concentration of lithium cations (Li⁺) in the solution is equal to or lower than about 2000 ppm. [0104] Another object of the present invention is a lithium sulphate (Li₂SO₄) solution directly obtained by a process according to the invention, as described herein. According to some other embodiments, the solution is “diluted”, for example the concentration of lithium cations (Li⁺) in the solution is equal to or lower than about 2000 ppm. According to some embodiments, the solution is “concentrated”, for example the concentration of lithium cations (Li⁺) in the solution is equal to or higher than about 16000 ppm. According to some other embodiments, the solution is “pure”, for example the concentration of lithium cations (Li⁺) is equal to or higher than about 95%, preferably equal to or higher than about 99%, more preferably equal to or higher than about 99.7%, in weight by total weight of a lithium carbonate (Li2CO3) equivalent basis (i.e., when the solution is treated by a carbonatation agent according to step (i) herein, the resulting solid lithium carbonate has the purity as indicated). [0105] Another object of the present invention is lithium carbonate (Li2CO3) directly obtained by a process according to the invention, as described herein. According to some other embodiments, the lithium carbonate is “pure”, for example the purity of the lithium carbonate is equal to or higher than about 95%, preferably equal to or higher than about 99%, more preferably equal to or higher than about 99.7%, in weight by total weight of the lithium carbonate. BRIEF DESCRIPTION OF THE DRAWINGS [0106] Figure 1 is a flowchart showing an illustrative embodiment of the process according to the present invention comprising steps (a) to (j), from the provision of the leachate solution up to the obtention of Li₂CO₃. EXAMPLES [0107] The present invention is further illustrated by the following examples. Example 1: Preparation of lithium sulphate solution

Step (a): Preparation of lithium solutions from black masses [0108] Two different lots of black mass in solid form were commercially purchased from a European supplier in the black mass market. Their compositions are indicated in Table 1. [0109] Leachate solutions were prepared from black mass in a stirred reactor by reaction with sulphuric acid (H₂SO₄) [mass ratio H₂SO₄96% / black mass 1.8] in presence of hydrogen peroxide (H₂O₂) [mass ratio H₂O₂50% in aqueous solution / black mass 0.51] as reducing agent. The obtained leachate solution and the residue were separated using a vacuum filter and a laboratory filter press system. The residue was washed with water. The leachate solutions and residues compositions are indicated in Table 1. Table 1 Composition (mg/kg) Al As Ca Cd Cr Cu Fe K Mg Na Black mass Lot 1 3764 <20 1743 <2 27 12 156 536 13 544 Leachate solution Lot 1 173 <0,8 75,2 <0.1 1,2 <0.1 6,4 22.6 12.2 52,2 Residue Lot 1 13803 <20 973 <2 37 14 232 909 53 333 Black mass Lot 2 65201 <20 2841 268 121 18589 4123 301 1021 1423 ^{Leachate solution Lot 2} _{8485 <0,8 175 40 21 0,4 372 41 156} ⁷⁰ ^{Residue Lot 2} _{62475 <20 2639 17 71 68921 736 125 101} ⁸⁹⁹ Table 1 (continued) Composition (mg/kg) Ni P Pb Zn Li Mn Zr Co W Black mass Lot 1 401911 89 53 46 83578 116833 3972 122395 2976 Leachate solution Lot 1 44398 3.9 3.4 0.3 8674 11589 288 11589 206 Residue Lot 1 301637 169 48 14 17029 91081 7809 85663 8131 Black mass Lot 2 14854 4102 296 352 36221 31769 87 303098 162 Leachate solution Lot 2 2574 601 10 48 5563 5744 3,3 49858 4,1 Residue Lot 2 3874 522 390 375 432 272 188 1225 211 [0110] Insoluble residue represented about 3 to 5% w/w for Lot 1 and about 30% w/w for Lot 2. The yield of lithium, cobalt and manganese digestion was higher than 99% w/w. The pH of the leachate solution was 0.42 and its potential redox was from 550 to 750 mV for Lot 1 and from 0 to 200 mV for Lot 2. [0111] To about 100 kg of leaching solution from Lot 1 or Lot 2 were added 298 kg of water and 2 kg sulphuric acid (H2SO4), thereby obtaining 400 kg of the corresponding lithium solution. Thus, the water / leaching solution (water / feed) weight ratio is 3:1 and 2% w/w of H2SO4 have been added to the leaching solution. In these optimised conditions, when the concentration of Li⁺ in the lithium solution of 2500 ppm, then the H⁺/Li⁺ ratio is 1.3, which corresponds to a measured pH of 0.68 (as detailed in Example 2 below). Step (b): Microfiltration (MF) / Ultrafiltration (UF) [0112] Microfiltration (MF) and ultrafiltration (UF) were carried out on the obtained lithium solution (Lot 1) using a “Memcell, spiral-wound MF/UF” membrane. Parameters for MF were 50°C, 3 bar and the resulting permeate flow rate was 350 L/h/m². Parameters for UF were 50°C, 10 bar and the resulting permeate flow rate was 320 L/h/m². [0113] The percentage of clear filtrate recovery rate after MF was at least 99.9%, which means that the amount of solid particles was already very low in the example lithium solution. The percentage of clear filtrate recovery rate after UF was at least 99.5%, which means that the UF was relatively easy with the example lithium solution. Steps (c): Nanofiltration (NF) [0114] Nanofiltration (NF) was carried out on the obtained purified lithium solution (about 400 kg) (Lot 1) using a NF/RO Membrane Module “mini-pilot” system comprising: 1 membrane spiral-wound, 1 low pressure (LP) pump, 1 high pressure (HP) pumps, 4 tanks (feeder and receivers), 3 flow monitors and balances, piping and monitors (pH, temperature (°C) and density). The NF membrane was a polymeric membrane, specifically a polysulfone membrane with a MWCO ranging from 400 to 500 Dalton. Parameters for NF were 50°C, 45 bar and the resulting permeate flow rate was 45 L/h/m². The pH of the lithium solution before NF is about 0.68. [0115] The water / leachate solution ratio of 3:1 used for preparing the lithium solution provides a relatively high flow rate of at least 25 L/h/m² in appropriate NF working conditions (e.g., 45-55°C and 35-55 bars). When the dilution of the lithium solution increases (i.e., it is more concentrated in Li⁺), then the flow rate decreases dramatically. [0116] About 300 kg of the lithium hydrogen sulphate (LiHSO₄) solution (Lot 1) were obtained, which includes about 85% w/w of the lithium initially present in the leachate solution. The overall selectivity and recovery rate are very good as shown in Table 2. Table 2 E_lement Li Ni Mn Co K Na Recovery rate 1 stage 85% 1.14% 1.40% 1.25% 34% 55% Table 2 (continued) Element Mg Ca Fe Al Cu Zr W Recovery rate 1stage 1.25% 2.35% 0.70% 0.60% 0.50% 1.51% 9.17% Steps (d) to (f): Preparation of a diluted Li2SO4 solution [0117] To the LiHSO4 solution was added calcium hydroxide (Ca(OH)2) as calcium source, then the precipitate was removed by vacuum belt filter (VBF) and the resulting lithium sulphate (Li2SO4) solution (“first” Li2SO4 solution) was obtained. The precipitate was recovered, mainly consisting of gypsum (CaSO4.2H2O) along with small amounts of other insoluble salts such as calcium fluoride (CaF₂). Sodium carbonate (Na₂CO₃) was added to the obtained first Li₂SO₄ solution; then, microfiltration (MF) was carried out using a “Memcell, spiral-wound MF/UF” membrane. The resulting purified lithium sulphate (Li2SO4) solution (“second” Li2SO4 solution) was obtained. Step (h): Reverse osmosis (RO) [0118] Reverse osmosis (RO) was carried out on the obtained second Li2SO4 solution using a NF/RO Membrane Module “mini-pilot” system comprising: 1 membrane spiral-wound, 1 low pressure (LP) pump, 1 high pressure (HP) pumps, 4 tanks (feeder and receivers), 3 flow monitors and balances, piping and monitors (pH, temperature (°C) and density). The RO membrane was a polymeric membrane, specifically a thin-film (TFM) fiberglass membrane with an average salt (NaCl) rejection of 99.5%. Depending on the applied pressure, the resulting lithium concentrated sulphate (Li₂SO₄) solution (“third” Li2SO4 solution) were obtained with a recovery rate of 60 to 70% (55 bars), 75 to 80% (65 bars) or 90 to 95% (85 bars); which corresponds to a concentration rate of 2.5 to 3.3 (55 bars), 4 to 5 (65 bars) or 10 to 20 (85 bars). Moreover, 93% of the initial amount of water were separately recovered, which may be directly recycled for use in the preparation of a lithium solution from a leachate solution. Steps (i) and (j): Preparation of lithium carbonate (Li2CO3) [0119] Sodium carbonate (Na₂CO₃) was added to the obtained third Li₂SO₄ solution; then, the precipitate was collected by vacuum belt filter (VBF) and the resulting lithium carbonate (Li2CO3) were obtained. The purity of the obtained Li2CO3 is at least 99.7%, which is very high and make it suitable for direct use in further applications. Example 2: Effect of free acidity on lithium recovery yield Material and methods [0120] Lithium solutions comprising 2500 ppm Li⁺ were prepared from a black mass leachate solution (Lot 1) as disclosed in Example 1 above at steps (a) and (b), but using different amounts of added sulphuric acid (H2SO4) when preparing the lithium solution in order to change the free acidity thereof (“free acidity effect”). The NF was then carried out as disclosed in Example 1 above at steps (c) and the recovery rate of Li⁺ was determined. [0121] Then, the effect of temperature and pressure on the permeate flow was analysed and optimised conditions were determined. [0122] Finally, the effect of the amount of added water (i.e., different water / feed ratios) on recovery rate of Li⁺ was evaluated by preparing lithium compositions with a concentration of Li⁺ ranging from 850 to 7500 ppm. Results [0123] The results of the free acidity assay are shown on Table 3. Table 3 % H2SO4 0% 1% 2% H⁺ _/Li ⁺ _ratio ^{0.3 0.8 1.3} p_H 1.15 0.85 0.68 L_i ⁺ _{recovery yield} ^{60% 70% 85%} [0124] These results clearly evidence the criticality of the H⁺/Li⁺ ratio parameter in the lithium recovery. By providing sufficient free acidity in the lithium solution, lithium recovery as high as 85% is obtained. [0125] The results of the temperature assay are shown on Table 4. Table 4 T (°C) 45 50 55 Flow rate (L/h/m²) ^{35 45 50} [0126] The results of the pressure assay are shown on Table 5. Table 5 P_(bar) ^{35 45 55} Flow rate (L/h/m²) ^{25 45 60} [0127] From these results it may be identified that 50°C and 45 bars are optimised parameters for balancing between the efficiency and life duration of the membrane. 45 L/h/m² is already considered very good filterability as per industrial standards. [0128] The results of the Li⁺ concentration assay are shown on Table 6. Table 6 [_Li ⁺ _{] (ppm)} 850 ^{2200 3000} 7500 L_i ⁺ _{recovery yield} 85% ^{85% 85%} 85% [0129] These results clearly evidence that, as long as the H⁺/Li⁺ ratio parameter is maintained sufficiently high, the lithium recovery is not significantly affected by the concentration of the lithium solution. This means that the process of the present invention may be used to recover lithium from a diversity of lithium solutions, which may be prepared from different solid materials. [0130] The same tests carried out with another lithium solution (Lot 2) gave similar results, despite significant difference in composition between Lot 1 and Lot 2. Therefore, the high yield and selectivity of the process according to the invention do not depend on the nature of the treated black mass. The process is thus quite versatile and may be used for recovering lithium from many different types of lithium-containing solutions.

Claims

CLAIMS 1. Process for the production of a lithium hydrogen sulphate (LiHSO₄) solution comprising the following steps: (a) providing a lithium solution comprising hydrogen cations (H⁺), lithium cations (Li⁺), sulphate anions (SO₄ ^2-), hydrogen sulphate anions (HSO₄-), and water, wherein the molar ratio between the hydrogen cations and lithium cations in said lithium solution ranges from about 0.3 to 2, wherein the molar concentration of the hydrogen cations is measured by pH titration; wherein step (a) comprises the following steps: (a1) providing a leachate solution comprising hydrogen cations (H⁺), lithium cations (Li⁺), sulphate anions (SO4^2-), hydrogen sulphate anions (HSO4-), and water, wherein the molar ratio between the hydrogen cations and lithium cations in said leachate solution is lower than about 0.3, wherein the molar concentration of the hydrogen cations is measured by pH titration; and (a2) adding sulphuric acid (H₂SO₄) to said leachate solution, as needed depending on the initial content of hydrogen cations and lithium cations in said leachate solution, to obtain said lithium solution; (b) optionally, removing insoluble impurities and/or organic impurities from said lithium solution; and (c) proceeding with nanofiltration (NF) of said lithium solution to obtain a lithium hydrogen sulphate solution. 2. The process according to claim 1, wherein the molar ratio between the hydrogen cations and lithium cations in said lithium solution ranges from about 0.5 to 1.5, preferably from about 0.8 to 1.2, more preferably is about 1. 3. The process according to claim 1 or claim 2, wherein the concentration of lithium cations in said lithium solution is equal to or lower than about 7500 ppm. 4. The process according to claim 3, wherein the concentration of lithium cations in said lithium solution ranges from about 100 ppm to 7500 ppm, preferably from about 500 to 4000 ppm, more preferably from about 1500 to 3000 ppm, furthermore preferably from about 1200 to 2750 ppm, furthermore preferably from about 2200 to 2500 ppm. 5. The process according to any one of claims 1 to 4, wherein step (a2) further comprises adding water to said leachate solution; preferably water is added to said leachate solution at step (a2) in a water / leaching solution weight ratio ranging from about 1 to 10, preferably from about 2 to 6, more preferably of about 3. 6. The process according to any one of claims 1 to 5, wherein said leachate solution is obtained from the leaching of a black mass by concentrated sulphuric acid. 7. The process according to any one of claims 1 to 6, wherein step (b) comprises the following step(s): (b1) removing by filtration, preferably by microfiltration (MF), insoluble impurities from said lithium solution; and/or (b2) removing by filtration, preferably by ultrafiltration (UF), organic impurities from said lithium solution. 8. The process according to any one of claims 1 to 7, wherein the nanofiltration (NF) at step (c) is carried out with a membrane having a molecular weight cutoff (MWCO) ranging from about 100 to 1000 Dalton, preferably ranging from about 200 to 800 Dalton, more preferably ranging from about 250 to 500 Dalton and /or wherein the nanofiltration (NF) membrane is a composite membrane comprising a film and a porous support material, wherein the film comprises a polymer matrix and is layered on the porous support material, and wherein the polymer matrix is selected from polyolefins, polysulfones, polyethers, polysulfonamides, polyamines, polysulfides, and melamine polymers; preferably, the porous support material comprises polysulfone. 9. The process according to any one of claims 1 to 8, wherein said process further comprises the following steps: (d) adding a calcium source to said lithium hydrogen sulphate solution; and (e) proceeding with solid-liquid separation to obtain a first lithium sulphate (Li2SO4) solution. 10. The process according to claim 9, wherein said calcium source at step (d) is selected from calcium carbonate (CaCO₃), calcium hydroxide (Ca(OH)₂), calcium oxide (CaO), or mixtures thereof; preferably said calcium source is calcium hydroxide (Ca(OH)2). 11. The process according to claim 9 or claim 10, wherein the solid-liquid separation at step (e) is carried out by vacuum belt filter (VBF) or filter press (FP), preferably by VBF. 12. The process according to any one of claims 9 to 11, wherein said process further comprises the following steps: (f) adding a base to said first lithium sulphate solution; and (g) proceeding with solid-liquid separation to obtain a second lithium sulphate (Li₂SO₄) solution. 13. The process according to claim 12, wherein at step (f) said base is sodium carbonate (Na2CO3). 14. The process according to any one of claims 9 to 13, wherein said process further comprises the following step: (h) concentrating, preferably by reverse osmosis (RO), either said first lithium sulphate solution obtained by the process according to any one of claims 9 to 11 or said second lithium sulphate (Li₂SO₄) solution obtained by the process according to claim 12 or claim 13, to obtain a third lithium sulphate (Li2SO4) solution. 15. The process according to claim 14, wherein said process further comprises the following steps: (i) adding a carbonatation agent, preferably sodium carbonate (Na₂CO₃), to said third lithium sulphate solution; and (j) proceeding with solid-liquid separation, preferably by vacuum belt filter (VBF), to obtain lithium carbonate (Li₂CO₃).