Method

Abstract

Disclosed herein is a method of extracting lithium from a lithium-containing solid, the method comprising: (i) a dissolution step; (ii) a pH adjustment step; (iii) a first lithium precipitation step; (iv) a direct lithium extraction step; and (v) a second lithium precipitation step; thereby isolating the lithium carbonate from the lithium-containing solid.

Description

[0001] Method

[0002] Field of the Invention

[0003] The present invention relates to a method of recovering lithium carbonate from lithium-containing solutions. More specifically, the invention provides a hybrid hydrometallurgical / direct lithium extraction method.

[0004] Background

[0005] There is increasing demand in the world for batteries, in particular lithium-ion batteries, perhaps due to the increasing use of, and demand for, electric vehicles. Lithium is therefore a valuable resource, obtained from the environment either through mining lithium ore or extraction of mineral-rich salt lake brine. Both methods have environmental impact, with brine extraction thought to risk soil salinization and damage to the local eco-structure and landscape, while mining operations occupy large areas of land and often permanently scars the landscape. Lithium mining and processing also involves significant water consumption, with considerable risk of affecting local water supplies and aquaculture through leaching of by-products.

[0006] Waste materials containing lithium, such as lithium batteries, represent a valuable source of lithium. For example, materials sourced from lithium batteries. Lithium battery recycling is key to realising a circular lithium economy and assisting progress towards Net-Zero. However, current commercial applications of battery recycling technology are immature and are limited by high cost and low product recovery.

[0007] There is therefore considerable interest in improved methods for lithium extraction and in recovering and reusing lithium.

[0008] Lithium carbonate is one of two main forms of lithium used to produce lithium-ion batteries, the other being lithium hydroxide. Lithium carbonate is typically produced from other, highly soluble salts of lithium. This can be achieved through methods such as electro-chemical processes or through precipitation. However, the former processes are very energy intensive, requiring large amounts of electricity, whereas precipitation methods have limited recovery rates due to the appreciable solubility of lithium carbonate (12.9 g / L at 25 °C) and limited solubility differences between lithium hydroxide (anhydrous - 128 g / L at 25 °C) and sodium hydroxide (1000 g / L at 25 °C). In other words, a precipitative lithium carbonate production process will result in a residual solution containing 12.9 g / L of lithium carbonate. For a typical lithium- containing solution comprising 5 g / L of Li+, the residual lithium carbonate in solution limits recovery rates of carbonate-precipitation extraction to a maximum of about 75 %. Often, the rate is even lower (about 40 %) due to other loses such in the initial leeching of lithium ores, for example.

[0009] Typically sodium carbonate is used as the precipitant, therefore there will also be large quantities of sodium ions left in the residual solution. Due to the similar chemical properties of lithium and sodium, isolating the remaining lithium is difficult and is typically avoided due to high cost and complexity. This residual solution comprising 12.9 g / L of lithium carbonate (equivalent to approximately 2250 ppm of Li+), represents a highly valuable waste stream. For comparison, extraction of lithium from brines in South America having a lithium concentration of around 600 ppm is commercially viable.

[0010] Therefore, there is considerable need for improved hydrometallurgical lithium recovery methods.

[0011] The present invention has been devised in light of the above considerations.

[0012] Summary of the Invention

[0013] The present inventors sought to provide an improved and more environmentally friendly method for the extraction of lithium carbonate from lithium-containing solids, such as chopped lithium battery electrodes (so-called black mass).

[0014] In doing so, the inventors propose a hybrid method for the extraction of lithium from lithium-containing solids which combines hydrometallurgical and direct lithium extraction processes.

[0015] Direct lithium extraction and crystallization (DLECTM) represents an alternative means for extracting lithium from brines compared to current evaporation-based processes that are utilised in South America. This process selectively extracts lithium, leaving the majority of the other metal ions and impurities behind. It can be performed in various ways including membrane electrodialysis, nanofiltration and ion sorption. Of these, the latter is the most mature and is being commercially operated in some parts of the world. The advantage of DLEC™ is that it can extract lithium from solutions of low concentration and achieve high impurity removal.

[0016] The use of DLEC™ has been proposed to increase recover rates of other lithium extraction techniques, such as the precipitative method outlined above.

[0017] The process starts substantially the same as other extraction processes, that is, with the leaching / dissolution of lithium-containing solids in an acidic solution. This brings the lithium, contained within the solid, into solution, along with many other soluble elements and compounds. This step produces a dissolution step liquor.

[0018] Next, the pH of the solution is raised to precipitate insoluble metal hydroxides from the solution. At low pH, many transition metal ions and post-transition metal ions are soluble in aqueous solution, but at high pH, transition metals and post-transition metals form insoluble hydroxides and are almost entirely removed from solution.

[0019] Then, a filtration step removes any precipitates or insoluble materials from the now basic lithium- containing solution.

[0020] In a first precipitation step, a source of carbonate ions is added to the lithium-containing solution to produce a first crop of solid lithium carbonate, leaving a first precipitation step liquor that is saturated with lithium carbonate. An extraction step utilising direct lithium extraction is then performed to enrich the first precipitation step liquor in lithium ions. This increase in lithium-ion concentration thereby allows a second precipitation step to be performed, wherein a source of carbonate ions is added to the extraction step liquor to produce a second crop of solid lithium carbonate. Suitably, any direct lithium extraction process may be used (such as selective adsorption, ion exchange, membrane electrodialysis, solvent extraction or nanofiltration).

[0021] The lithium-containing solid may suitably be a natural (mined) material such as spodumene, mica or lepidolite, or a man-made material such as black mass or lithium-containing anodes.

[0022] Lithium-containing solids sourced from the recycling and reprocessing of lithium batteries and the like can often have a significantly higher concentration of lithium in comparison to natural sources such ores or salts derived from geothermal brines.

[0023] Accordingly, in a first aspect, the invention may provide a method of extracting lithium from a lithium- containing solid, the method comprising:

[0024] (i) a dissolution step comprising treating the lithium-containing solid with an acid to obtain a dissolution step liquor;

[0025] (ii) a pH adjustment step comprising adding an alkali to the dissolution step liquor to precipitate metal products as a first precipitate, then isolating the first precipitate to leave a pH adjustment step liquor;

[0026] (iii) a first lithium precipitation step comprising adding a source of carbonate ions to the pH adjustment step liquor to precipitate lithium carbonate, then isolating the lithium carbonate to leave a first precipitation step liquor;

[0027] (iv) a direct lithium extraction step comprising treating the first precipitation step liquor using direct lithium extraction to produce an extraction step liquor that has a higher concentration of lithium ions than the first precipitation step liquor; and

[0028] (v) a second lithium precipitation step comprising adding a source of carbonate ions to the extraction step liquor to precipitate lithium carbonate, then isolating the lithium carbonate.

[0029] The inventors observe that the use of a hybrid hydrometallurgical-DLEC™ process may have the following advantages:

[0030] (1 ) A higher recovery rate than typical processes. Recovery rates of the DLE process can exceed 90%, which, if combined with an approximate theoretical maximum recovery rate of 70% from a typical hydrometallurgical process, can result in an overall lithium recovery rate of greater than 97%. This would result in a highly efficient battery recycling process with minimal waste material. This could theoretically be increased to 100% if the waste stream of the process (i.e., the residual solution formed in the second precipitation step) from the invention is fed back into the process of the invention.

[0031] (2) Reduced need for expensive and toxic chemical reagents such as barium hydroxide. The process achieves high extraction rates only using readily available feedstocks such as sodium hydroxide, sodium carbonate and hydrochloric acid. Furthermore, the by-products produced may be used to regenerate the reagents.

[0032] (3) The process of the invention does not require any thermal separation or concentration steps (such as reverse osmosis), and rather relies on chemical processes to separate the lithium. This requires much less energy to perform the invention in comparison to traditional methods, thereby making the process more environmentally friendly.

[0033] In some embodiments, the supernatant liquor produced by step (v) can be added to the first precipitation step liquor before step (iv). This improves yields as there is then no lithium-containing product of the method other than the desired product (solid lithium carbonate). This would achieve up to 100% recovery of the lithium from the lithium-containing solid.

[0034] Processing of the lithium-containing solid begins with addition of an acid to dissolve the lithium-containing solid, thus creating a dissolution step liquor. This may be referred to in the art as ‘dissolving’ or ‘leaching’ the black mass, where the lithium-containing solid is black mass.

[0035] Concentrated sulfuric acid is preferably used in the dissolution step due to being strongly acidic, of a high molarity and cheap. The resultant sulfate compounds are also highly soluble in water, allowing for the dissolution step liquor to contain high concentrations of lithium.

[0036] The dissolution step can be performed at room temperature or can be performed above room temperature. This is advantageous as the elevated temperature increases the rate of dissolution and increases the solubility of the metal salts.

[0037] Optionally, an additional step of filtering the dissolution step liquor is performed after the dissolution step but before the first precipitation step. This can remove insoluble components such as carbon (in the form of graphite), plastics such as PTFE and HDPE, and metals resistant to dissolution by acids, such as gold. This allows for such metals to be recovered and improves the purity of the precipitate produced in the first precipitation step.

[0038] In embodiments where an additional filtering step is present after the dissolution step, optionally the insoluble components are washed, and the washing liquid re-added to the dissolution step liquor.

[0039] In some embodiments, before the pH adjustment step, the dissolution step liquor is diluted; however, more conveniently it is not diluted before the pH adjustment step.

[0040] Optionally, an additional step of heating the lithium-containing solid is performed before the dissolution step. The purpose of such a heating step is to remove volatile and / or organic components, which reduces impurities in the dissolution step liquor. Heating can be done, for example, until no change in mass is observed. Preferably, the lithium-containing solid contains low levels of alkaline earth metals, transition metals and post-transition elements which might also precipitate from solution upon the addition of a source of carbonate ions. In other words, the solid preferably only contains lithium, sodium, potassium, rubidium and caesium cations (the identity of the anion(s) is not particularly limited). This has the benefit that the precipitate formed in the first precipitation step is of high purity lithium carbonate.

[0041] However the lithium-containing solid typically comprises other metallic impurities such as alkali earth metals, transition metals and post transition metals. Therefore, to improve the purity of the lithium carbonate product, these are removed from the dissolution step liquor by increasing the pH of the solution to remove these insoluble metals.

[0042] The term ‘insoluble metals’ is understood in the art and refers to those metals whose relevant salt(s) (for example, hydroxides if the alkali is a source of hydroxide ions; sulfides if the alkali is a source of sulfide ions) are not soluble (<1 mg / mL, suitably <0.5 mg / mL, more suitably <0.1 mg / mL) in the liquor generated by addition of the alkali to the dissolution step liquor. The composition of the precipitate will depend on what was present in the original lithium-containing solid used and on the alkali used in the pH adjustment step. Typically, the precipitate will comprise hydroxides of the insoluble metals. The precipitate may also comprise sulfides, oxides, or carbonates of the insoluble metals. The precipitate may also comprise the alkali used in a pH adjustment step. Typically, the precipitate will comprise insoluble compounds of Nickel, Cobalt and Manganese.

[0043] Suitably, the pH of the dissolution step liquor is adjusted in a pH adjustment step before the first precipitation step. By increasing the pH of the lithium-containing solution, ions representing impurities can be precipitated from the lithium containing solution as insoluble hydroxides at certain pH. Furthermore, in acidic solutions (that is pH <7), the source of carbonate ions may be decomposed, and the precipitate of lithium carbonate may not form. By increasing the pH, the source of carbonate is not decomposed by the lithium-containing solution.

[0044] Typically, transition metal and post transition metal hydroxides are soluble at low pH (around pH 0) and at high pH (around pH 14), with low solubilities at intermediate pH. For example, the lowest solubility for aluminium is around pH 6-7; for iron, pH 7-9; for nickel, pH 10-10.5; for cobalt, pH 10-12; and for manganese, pH 11-12. However, some metals will start precipitating around pH 3, for example iron.

[0045] Therefore, the optimum pH for the lithium-containing solution provided by the adjustment step varies depending on the composition of the lithium-containing solution. In the adjustment step a quantity of the base sufficient to raise the pH of the liquor to pH 3-12 may preferably be added.

[0046] The pH can be adjusted by the used of any suitable base. However, in terms of cost, NaOH is preferred. Furthermore, when sodium carbonate is used as the source of carbonate ions in the first and second precipitation steps, NaOH is preferably used as the base in the pH adjustment step as it avoids introducing multiple types of cations that may result in impurities in the solid lithium carbonate product. The base can be provided as a solid, liquid or aqueous solution. Preferably, the base is water soluble (an alkali) as homogeneous solutions react more rapidly than heterogeneous mixtures.

[0047] The amount of the alkali required in the pH adjustment step depends on the amount of acid used and the composition of the lithium-containing solid. Preferably, at least an equimolar amount of alkali to acid is used. For diprotic acids, such as sulphuric acid, at least two moles of alkali are used per mole of acid. For triprotic acids, such as phosphoric acid, at least three moles of alkali are used per mole of acid.

[0048] In the first precipitation step, the precipitated metal products may be isolated by any suitable means to afford a first precipitate and first precipitation liquor. The insoluble metal hydroxides also represent a valuable waste stream of the inventive process. This includes, but is not limited to, gravity settling, filtration, centrifugation, and hydrocyclonic separation.

[0049] In some embodiments, for example where sulfuric acid is used in the dissolution step, there may be an optional step to remove sulphate ions from the pH adjustment step liquor.

[0050] This may be done through the addition of, for example, calcium hydroxide or barium hydroxide (Ca(OH)2 or Ba(OH)2) to precipitate calcium sulfate or barium sulfate, which have very low aqueous solubilities. The supernatant solution then contains substantially only hydroxide anions and substantially no sulfate anions.

[0051] This has the advantage that a larger amount of the source of carbonate ions can be added to the lithium- containing solution without the co-precipitation of insoluble sulfates. For example, when the lithium- containing solution comprises sulfate anions, the addition of sodium carbonate may cause a precipitate of sodium sulfate to form. The co-precipitation of insoluble sulfates is undesirable as it contaminates the lithium carbonate. Furthermore, recovered sulfate salts, such as calcium sulfate or barium sulfate, can be sold or used in other processes. This can improve the economic viability of the present process.

[0052] Before the first precipitation step, there may be a concentration step where the working liquor (for example, pH adjustment step liquor) is treated to increase the concentration of lithium within it. It may be concentrated to give a lithium concentration of 2 to 30 wt%, for example. [As an example: LiCI has a solubility limit of 850g in 1 litre; this would equate to 85 wt% lithium.]

[0053] This concentration step may be conducted in any known fashion. For example, suitable methods include membrane distillation, reverse osmosis, forward osmosis, electrodialysis, or combinations thereof (for example, membrane distillation + reverse osmosis).

[0054] In the first precipitation step, a source of carbonate ions is added to the lithium-containing solution. This causes a precipitate of lithium carbonate to form, due to the low aqueous solubility of lithium carbonate. Even if other alkali metal ions are present (for example, sodium), the addition of carbonate ions will selectively precipitate lithium carbonate (that is, the other alkali metal ions will stay in solution). This is because the solubility of lithium carbonate (12.9 g / L at 25 °C) in water is much lower than that of the other alkali metal carbonates, for example sodium carbonate (decahydrate, 210 g / L at 20 °C).

[0055] Typically, the source of carbonate ions is sodium carbonate (usually as the decahydrate but other hydrates or anhydrous sodium carbonate may be used). Sodium carbonate is preferred as it is an easily accessible and low cost chemical feedstock.

[0056] The amount of the carbonate source required to precipitate the lithium carbonate depends on the amount of lithium present in the solution. This can be calculated using titration to find the correct amount of carbonate required to maximise the lithium precipitate. Excess of the carbonate source is preferably avoided so as to reduce the number of impurities in the first precipitation step liquor.

[0057] Alternatively, the source of carbonate ions can be added in aliquots until no further precipitation is observed. Precipitation can be observed using, for example, an inline camera.

[0058] The supernatant solution formed upon the addition of the source of carbonate ions contains between 6-16 g / L of lithium carbonate (depending on temperature) as well as other soluble salts such as sodium carbonate, sodium hydroxide and the like. This supernatant solution is the so-called first precipitation step liquor.

[0059] As the amount of lithium carbonate in solution reduces with temperature, the precipitation is preferably performed at elevated temperatures.

[0060] After the precipitation is complete, the solid lithium carbonate is separated from the supernatant solution by any suitable means.

[0061] In some embodiments, an optional alkali earth metal removal step may be performed before the first precipitation step or after the extraction step and before the second precipitation step.

[0062] Alkali earth metal cations, such as magnesium and calcium cations, form insoluble carbonates.

[0063] Therefore, any alkali earth metal cations present in the solution to which the source of carbonate ions is added will cause to co-precipitation of alkali earth metal carbonates alongside the lithium carbonate. This reduces the purity of the lithium carbonate. Therefore, it is preferable to remove any alkali earth metals before the precipitation step(s) as this increases the purity of the lithium carbonate.

[0064] Such alkali earth metal cations may be introduced from the sulfate removal step or by being present in the lithium containing solid.

[0065] The alkali earth metal removal step may be done by nanofiltration, by ion-exchange, forward osmosis and electrodialysis, or by other suitable methods

[0066] The alkali earth metal removal step may be performed using ion-exchange. The removal of magnesium and calcium from aqueous solutions is well known for its use in water softening, wherein magnesium and calcium ions in solution are replaced with sodium ions. These methods are well known and will not be discussed in detail here. This has the advantage of removing the magnesium and calcium ions using a chemical process (and not a thermal one) which is not energy intensive. Furthermore, the sodium ions introduced into the solution do not negatively impact the DLEC™ process.

[0067] In the extraction step, the first precipitation step liquor is processed using DLEC™. This separates the lithium ions from the other ionic species in solution, thereby purifying the solution. Typically, this process will produce highly pure solutions of lithium chloride, however one benefit of using DLEC™ is that the anion can be selected depending on the use. In the absence of carbonate ions, this purified solution can have higher concentrations of Li+without precipitation of lithium salts occurring (for example lithium chloride has a solubility of 843 g / L at 25 °C). This allows the second precipitation step to precipitate a much larger proportion of the lithium from solution.

[0068] In comparison, merely concentrating the first precipitation step liquor will cause precipitation of lithium carbonate to occur; however, sodium carbonate can also co-precipitate, producing an impure product. Furthermore, DLEC™ is less energy intensive than concentration processes such as reverse osmosis and evaporative concentration, as DLEC™ uses chemical processes, not thermal processes.

[0069] By using DLEC™, a solution containing a single lithium compound can be produced; this can be produced at high concentration or further concentrated without the risk of co-precipitation of other metal salts.

[0070] DLE processes are known in the art and will not be discussed in great detail here.

[0071] Suitable processes include but are not limited to: selective adsorption, ion exchange, membrane electrodialysis, solvent extraction and nanofiltration.

[0072] Adsorptive DLE represents an energy-efficient process that is driven by adjustments in pH rather than applied pressure, thermal gradients or electrical current. When flowing the lithium-containing solution over a lithium-selective adsorptive media (in an adsorption step), lithium ions migrate into the selective media (that is, are adsorbed or leeched from the lithium containing solution), leaving other components in the solution. The lithium ions replace hydrogen ions (that is, protons) already present in the media. Once the lithium has been taken up by the media, the remaining solution can be removed. By then flowing a dilute acid solution (release solution) through the media (in a release step), protons from the acid exchange with the lithium ions held in the media (releasing the lithium ions into the release solution). The lithium-rich release solution that is created from this process can then be used to produce lithium carbonate in the second precipitation step.

[0073] Typically, the release acid is hydrochloric acid, although any protic acid can be used. Hydrochloric acid is used due to it being readily available and cheap. The resultant lithium chloride produced is highly soluble in water, thereby allowing for high concentrations of lithium to be reached. This maximises the recovery of lithium carbonate in the second precipitation step. Adsorptive DLE therefore has the additional benefit of producing a favourable lithium salt. That is, the anion introduced by the release acid can be varied (hydrochloric acid introduces chloride anions, acetic acid introduces acetate anions, and so on). Therefore, salts with favourable properties, such as high solubilities, can be selected easily. Without significant limitation, any acid can be used therefore allowing for a wide range of salts to be accessible through adsorptive DLE.

[0074] Other methods of DLE include ion-exchange DLE and solvent extraction DLE.

[0075] Ion-exchange DLE is similar to adsorptive DLE in that a lithium-containing solution is passed over an ionexchange medium wherein lithium ions are exchanged for other metallic ions held within the ionexchange media.

[0076] Solvent extraction DLE is performed by mixing the lithium-containing solution with a non-miscible extraction solution, which selectively uptakes lithium ions from the brine. As with adsorptive and ionexchange DLE, the lithium ions can then be ‘released’ from the enriched extraction media (in this case a solvent system) to give a purified solution enriched in lithium. A common solvent system is tributyl phosphate and ferric chloride in kerosene, or methyl isobutyl ketone. Ionic liquids are also of interest as solvents in solvent extraction DLE.

[0077] In some embodiments, an optional concentration step is performed after the extraction step. This increases the concentration of lithium ions in the extraction step liquor. This has the benefit of improving the efficiency of the second precipitation step (as the ratio of initial concentration of lithium ions to the concentration of residual lithium ions, left in solution after addition of the source of carbonate, is larger). Any suitable means known to the art can be used, for example evaporative concentration or reverse osmosis.

[0078] In the second precipitation step, largely the same procedure is used as that in the first precipitation step.

[0079] The supernatant solution formed upon the addition of the source of carbonate ions to the extraction step liquor contains between 6-16 g / L of lithium carbonate (depending on temperature) as well as other soluble salts such as sodium carbonate, and sodium chloride (if the DLE process produces lithium chloride). This supernatant solution is the so-called second precipitation step liquor.

[0080] In some embodiments, the supernatant solution produced by the second precipitation step is fed back into the process of the invention. For example, the supernatant solution can be combined with the first precipitation step liquor before the extraction step. This can be done when the process is run in batches or run continuously. This has the benefit of improving the lithium extraction efficiency to near 100% as no lithium-containing waste solutions are produced. The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0081] Summary of the Figures

[0082] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0083] Figure 1 shows a flow chart of a process according to the state of the art.

[0084] Figure 2 shows a flow chart of a process according to the invention.

[0085] Detailed Description of the Invention

[0086] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0087] Lithium-containing solid

[0088] Suitably any lithium-containing solid can be used in the invention. However, it is typically only economically viable to perform the method of the invention on materials containing more than 100 ppm lithium by mass. In some embodiments, the lithium containing solid comprises more than 500 ppm of lithium by mass.

[0089] In some embodiments, the lithium-containing solid is naturally occurring, for example spodumene, mica, lithium clays such as lepidolite (polylithionite and trilithionite), zinnwaldite, masutomilite, swinefordite, hectorite, cookeite and jadarite, and the like.

[0090] In some embodiments, the lithium-containing solid is man-made, for example black mass, lithium battery anodes, and lithium battery cathodes.

[0091] In some embodiments, the lithium-containing solid is a product or waste stream from other processes. For example, concentrated and dried brines, and waste materials from battery production.

[0092] In some embodiments, the lithium containing solid is produced from lithium-containing batteries. Preferably, the lithium-containing solid is black mass

[0093] Typically, the battery recycling process starts with the dismantling and / or shredding of the battery or battery pack itself. The output of this is a material known as black mass which is a mixture of anode and cathode components containing lithium, nickel, manganese, and cobalt as well as electrolyte materials, polymer binder and metals like aluminium and copper which originate from the current collectors. This black mass is rich in lithium and so recycling black mass is of interest both for commercial and environmental reasons. However, processing is required to separate the lithium before being reused in battery production.

[0094] Black mass is a term well-recognised in the art. It is typically formed from recycling lithium-ion batteries, although other lithium-based batteries may be used. The lithium-rich electrode material (which may be cathode, anode, or both) is chopped up, broken up and / or ground in a mechanical treatment in the first stage of battery recycling.

[0095] Black mass can have varying elemental compositions, depending on the source battery type (lithium ion, lithium polymer, lithium cobalt oxide, lithium iron phosphate, and the like). Often, black mass is largely carbon (in the form of graphite), nickel, lithium and cobalt. Black mass often contains: lithium, carbon, fluorine, sodium, magnesium, aluminium, manganese, iron, cobalt, nickel, copper, zinc, and phosphorous.

[0096] The source of the black mass is not particularly limited; any lithium-containing battery materials can be used in the process of the invention. For example, black mass may be formed of one or more battery types selected from the group of: lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminium oxide (NCA), lithium iron phosphate (LFP), lithium manganese oxide (LMO), and lithium cobalt oxide (LCO).

[0097] In some embodiments, the lithium-containing solution is derived from an NMC or LFP battery. In some embodiments, the lithium-containing solution is derived from an NMC battery.

[0098] Process according to the invention

[0099] A process according to the prior art is shown schematically in Figure 1.

[0100] Figure 1 comprises the following steps:

[0101] The first step involves the dissolution of black mass in sulfuric acid. This produces (a), which comprises:

[0102] A dissolution step liquor (strongly acidic solution of various metal sulfate compounds including Li, Cu, Co, Mn, and Fe sulfates) and a residual solid formed of materials within the black mass that are resistant to dissolution by sulfuric acid (aluminium, gold, plastics, and carbon (as graphite)).

[0103] The next step involves the precipitation of both sulfate anions and transition metal, post transition metal and alkaline earth metal cations, for example by addition of barium hydroxide Ba(OH)2. This produces (b), which comprises:

[0104] A substantially pure solution of lithium hydroxide and a mixed precipitate comprising: the insoluble materials resistant to dissolution by sulfuric acid, insoluble metal hydroxides (Cu, Co, Mn, Fe hydroxides) and barium sulfate.

[0105] After filtration, the lithium hydroxide solution (c) is then concentrated and dried to provide lithium hydroxide monohydrate.

[0106] In contrast, a process comprising a two-step precipitation according to a method of the invention is shown schematically in Figure 2.

[0107] Figure 2 comprises the following steps: The first step involves the dissolution of black mass in sulfuric acid, in substantially the same fashion as in the prior art. This produces (a), which comprises:

[0108] A dissolution step liquor (strongly acidic solution of various metal sulfate compounds including Li, Ni, Cu, Co, Mn, and Fe sulfates) and a residual solid formed of materials within the black mass that are resistant to dissolution by sulfuric acid (aluminium, gold, plastics, and carbon (as graphite)).

[0109] The next step involves a filtration to remove the solid components, leaving the dissolution step liquor (b).

[0110] The next step is the pH adjustment step, wherein sodium hydroxide is added to the dissolution step liquor. This produces (c), which comprises:

[0111] A pH adjustment step liquor (basic solution comprising NaOH, LiOH, Na2SO4, Li2SO4) and a precipitate of insoluble metal compounds (Cu, Co, Mn, Fe hydroxides).

[0112] The next step involves a filtration to remove the solid components, leaving a pH adjustment step liquor (d).

[0113] The (optional) next step involves the addition of calcium hydroxide (barium hydroxide is also suitable) to the pH adjustment step liquor. This produces (e), which comprises:

[0114] The pH adjustment step liquor, depleted of sulfate ions (basic solution comprising NaOH and LiOH), and a precipitate of CaSO4.

[0115] The (optional, carried out only if the addition of calcium or barium hydroxide is done) next step involves a filtration to remove the solid components, leaving the pH adjustment step liquor (f), now depleted of sulfate ions.

[0116] These pH adjustment liquors (d) and / or (f) may suitably be further concentrated, to a lithium concentration of for example 2 to 30 wt%, to increase the yield in the forthcoming precipitation step. Suitable methods include membrane distillation, reverse osmosis, forward osmosis, electrodialysis, or combinations thereof (for example, membrane distillation + reverse osmosis).

[0117] The next step involves addition of a concentrated solution of sodium carbonate to the pH adjustment step liquor ((d) or (f), depending on the preceding steps). This produces (g), which comprises:

[0118] A first precipitation step liquor (basic solution saturated with lithium carbonate, residual sodium hydroxide and sodium carbonate) and a first crop of solid lithium carbonate.

[0119] The next step involves a filtration to remove the solid components, in particular the lithium carbonate, leaving the first precipitation step liquor (h).

[0120] The next step is the DLEC™ step. In the process of Figure 2, hydrochloric acid is used as a source of chloride anions thereby forming a solution enriched in lithium (an essentially pure solution of lithium chloride), enriched DLE solution (i), and a waste solution that is depleted in lithium ions (containing sodium hydroxide, sodium carbonate). The next step involves the addition of a concentrated solution of sodium carbonate to the enriched DLE solution. This produces (j), which comprises:

[0121] A second precipitation step liquor (basic solution saturated with lithium carbonate, residual sodium carbonate and sodium chloride) and a second crop of solid lithium carbonate.

[0122] The next step involves a filtration to remove the solid components, in particular the lithium carbonate, leaving the second precipitation step liquor (k).

[0123] This second precipitation step liquor (k) can be combined with fresh first precipitation step liquor (h) before a repeat of the DLE step.

[0124] Dissolution step

[0125] Where the lithium-containing solid is black mass, this step may be referred to as ‘dissolving the black mass’ or ‘leaching’ and is used in the methods of the prior art as a first step in the chemical processing of lithium-ion battery waste. The acid reacts with metals, metal oxides, and other metal compounds in the black mass, converting them to salts which are soluble in the liquor. Sulfuric acid is used in the scheme of Figure 2.

[0126] The acid may be, for example, selected from sulfuric acid, phosphoric acid, hydrochloric acid, citric acid and oxalic acid. In some embodiments it is sulfuric acid.

[0127] Conventionally, concentrated (for example 98 wt%, 18 M) sulfuric acid can be used. Other acids that can be used include mineral acids such as concentrated (for example 85 wt%, 15 M) phosphoric acid, and concentrated (for example 37 wt%, 12.3 M) hydrochloric acid as well as organic acids such as citric acid, and oxalic acid. The processes of the present invention may also be conducted under milder conditions, using less concentrated acids for example between 2M and 5M solutions.

[0128] When using acids which are solid at room temperature, for instance citric acid and oxalic acid, concentrated solutions of the acids can be employed. For instance at room temperature 55-65 wt% (for example 59.2 wt%) citric acid solution or 9 wt% oxalic acid solution can be used. More concentrated acid solutions can be formed using heating, for example 76.2 wt% citric acid solution can be used at 70 °C.

[0129] The ratio of acid to lithium-containing solid being used is not particularly limited as it will depend on the lithium-containing solid and acid being used. For instance, a larger number of moles of a monoprotic acid, such as hydrochloric acid, will be required in comparison to a diprotic acid, such as sulphuric acid. The ratio of acid to lithium-containing material may be from 5-100 moles of acid to 1 kg of lithium containing material.

[0130] In one embodiment in the dissolution step, sulfuric acid is added to the lithium-containing solid, in this case black mass. In some embodiments, for each kilogram of black mass 1-50 moles of concentrated sulfuric acid is used, optionally 10-40 moles, optionally 20-30 moles, optionally 15-30 moles, optionally 20-25 moles, optionally 22-24 moles, optionally 23 moles. In some embodiments, the ratio of lithium- containing solid (such as black mass) to sulfuric acid is 100-10,000 g / L, optionally 200-5,000 g / L, optionally 400-2000 g / L, optionally 600-1200 g / L, optionally 700-900 g / L, optionally 800 g / L. The sulfuric acid may be used as a 90-100% concentrated solution (by mass, in water).

[0131] In other embodiments, phosphoric acid may be used. Phosphoric acid may be used as a 75-100% concentrated solution (by mass, in water). In other embodiments, hydrochloric acid may be used. Hydrochloric acid may be used as a 30-40% concentrated solution (by mass, in water). In other embodiments, citric acid may be used. Citric acid may be used as a 40-85% solution (by mass, in water). In other embodiments, oxalic acid may be used. Oxalic acid may be used as a 5-15% solution (by mass, in water).

[0132] Suitably, when concentrated (for example 37 wt%, 12.3 M) hydrochloric acid is used, the ratio of hydrochloric acid to lithium-containing material may be, for example, 20-80 moles of hydrochloric acid to 1 kg of lithium-containing solid, suitably 30-60 or 40-50 moles of hydrochloric acid to 1 kg of lithium- containing solid. A suitable example is about 46 moles of hydrochloric acid to 1 kg of black mass.

[0133] In some embodiments the dissolution step is performed at room temperature. In some embodiments the dissolution step is performed at above room temperature, for example 50-100°C, optionally, 40-90°C optionally 60-80°C, optionally 70-80°C, optionally 60-65°C, optionally 70 °C.

[0134] In some embodiments, an additional step of heating the lithium-containing solid is performed before the dissolution step. In some embodiments this is done at a temperature of 50-100°C, optionally 60-80°C, optionally 65-75°C and in some embodiments at about 70°C.

[0135] In some embodiments, an additional step of removing solids from the dissolution step liquor is performed after the dissolution step. For example, the mixture may be separated by gravity separation, filtration, centrifugation, hydrocyclonic separation or the like.

[0136] In embodiments where an additional filtering step is present after the dissolution step, optionally the insoluble components are washed, and the washing liquid re-added to the dissolution step liquor. pH adjustment step

[0137] The dissolution step liquor is treated with a base, suitably an alkali, to raise the pH of the solution. Sodium hydroxide is used in the scheme of Figure 2.

[0138] Suitably any base can be used. Preferably, this is sodium hydroxide due to the low cost. Other suitable bases for use in the pH adjustment step may include alkali metal hydroxides such as NaOH, KOH, RbOH, CsOH, alkaline earth metal hydroxides such as Mg(OH)2, Ca(OH)2, Sr(OH)2 or Ba(OH)2, alkaline earth metal oxides (which hydrate to provide alkaline earth metal hydroxides) such as MgO, CaO, SrO or BaO, alkali and alkaline earth metal carbonates such as Na2CO3, K2CO3, Rb2CO3, CS2CO3, MgCOs, CaCOs, SrCOs or BaCOs, alkali and alkaline earth metal sulfides such as Na2S, MgS, CaS, SrS or BaS, ammonia, ammonium hydroxide, ammonium carbonate, ammonium persulfate, alkali metal alkoxides such as sodium ethoxide and potassium ethoxide, and organic amines.

[0139] In some embodiments, in the pH adjustment step, the pH is raised to 3 or more, optionally 4 or more, optionally 5 or more, optionally 6 or more, optionally 7 or more, optionally 8 or more, optionally 9 or more, optionally 10 or more, or optionally 11 or more. Suitably the pH is raised to 12 or lower, optionally 11 or lower, optionally 10 or lower, optionally 9 or lower, optionally 8 or lower, optionally 7 or lower, optionally 6 or lower, optionally 5 or lower, or optionally 4 or lower. A suitable range for the pH after the pH adjustment step is 3-12.

[0140] By raising the pH, a precipitate comprising alkaline earth metals, transition metals and post transition metals may form. This precipitate typically contains nickel, cobalt, manganese and iron. It may also contain magnesium, aluminium, copper and zinc. It may also include metal from the first base used, for example sodium or barium. Clearly the content will depend on what was in the lithium-containing solid and the base used in the pH adjustment step.

[0141] The precipitate formed in the pH adjustment step can be separated from the supernatant pH adjustment step liquor by any suitable means. For example, the mixture may be separated by gravity separation, filtration, centrifugation, hydrocyclonic separation or the like.

[0142] This provides a mixed-metal product, also referred to as reprecipitated black mass when the lithium- containing solid was black mass. As this precipitate contains high amounts of transition metals, it represents a valuable waste stream.

[0143] Optionally the precipitate formed by the pH adjustment step is washed and the washing liquid re-added to the pH adjustment step liquor.

[0144] First precipitation step

[0145] The pH adjustment step liquor is treated with a source of carbonate ions. This precipitates lithium carbonate. Sodium carbonate is used in the scheme of Figure 2.

[0146] The supernatant solution produced in the first precipitation step is the so-called first precipitation step liquor. The first precipitation step liquor is saturated with lithium carbonate (at the given temperature the precipitation step is carried out) and will clearly also contain the source of carbonate ions used in the first precipitation step.

[0147] Suitably, any source of carbonate ions can be used, other than lithium carbonate. However, it is preferable that the source of carbonate ion is soluble in water, for example sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, rubidium carbonate, caesium carbonate, ammonium carbonate, and ammonium bicarbonate. Preferably, the source of carbonate ions is sodium carbonate, specifically sodium carbonate decahydrate.

[0148] In one embodiment, the source of carbonate ions is added as a solution. Preferably, the source of carbonate ions is a solution saturated with carbonate ions.

[0149] In other embodiments, the source of carbonate ions is added to the lithium-containing solution as a pure solid or liquid (that is, without additional water). As the precipitation step may be conducted at raised temperature, the source of carbonate ions may be a liquid (for example, sodium carbonate decahydrate is liquid at 50 °C) In one embodiment, the first precipitation step is performed at room temperature. In some embodiments, the first precipitation step is performed at above room temperature (that is, with heating), for example 30- 100 °C, optionally between 30-70 °C, which can increase the speed of the step.

[0150] In order to recover a precipitate in the first precipitation step, the concentration of lithium ions in the pH adjustment step liquor is preferably higher than the concentration of lithium ions in a saturated solution of lithium carbonate at the same temperature. For example, at 25 °C the concentration of lithium ions is preferably above 2250 ppm (about 2.4 g / L of Li+, equivalent to 0.35 M). At 100 °C, the concentration of lithium ions is preferably above 1200 ppm (about 1.3 g / L of Li+, equivalent to 0.19 M)

[0151] Preferably, the lithium containing solution contains above 1.3 g / L of Li+, more preferably above 2.4 g / L, more preferably above 5 g / L.

[0152] After the addition of the source of carbonate ions, the first precipitate is separated from the first precipitation step liquor. For example, the mixture may be separated by gravity separation, filtration, centrifugation, hydrocyclonic separation and the like.

[0153] Optionally the first precipitate formed by the first precipitation step is washed and the washing liquid readded to the first precipitation step liquor.

[0154] In some embodiments where sulfuric acid is used as the acid in the dissolution step, an optional sulfate removal step may be performed before the first precipitation step.

[0155] Alkali metal sulfate salts have very low aqueous solubilities. Therefore, the removal of sulfate anions can be performed by adding an alkali earth salt to the pH adjustment step liquor. The source of alkali earth ions is suitably an alkaline earth metal hydroxide such as Mg(OH)2, Ca(OH)2, Sr(OH)2 or Ba(OH)2, or an alkaline earth metal oxide (which hydrate to provide corresponding alkaline earth metal hydroxides) such as MgO, CaO, SrO or BaO. Preferably the second base is soluble in water therefore Ca(OH)2 or Ba(OH)2 is preferred.

[0156] For example, when calcium hydroxide is used, a precipitate of calcium sulfate is formed, which can be removed from the supernatant pH adjustment step liquor, thereby reducing impurities that may contaminate the lithium carbonate produced in the first precipitation step.

[0157] Analogously, when phosphoric acid or hydrochloric acid is used in the dissolution step, a step can be performed to remove phosphate anions or chloride anions, respectively, similarly for oxalic acid and citric acid.

[0158] In some embodiments, an optional alkali earth metal removal step may be performed before the first precipitation step or after the first precipitation step and / or before the second precipitation step.

[0159] Optionally, this can be achieved by flowing the pH adjustment step liquor or the first precipitation step liquor through a commercial water softening ion-exchange resin. Such resins include sodium salts of strongly acidic resins and sodium salts of weakly acidic resins, for example sodium polystyrene sulfonate and the like.

[0160] Optionally this can be achieved by performing nanofiltration on the pH adjustment step liquor or the first precipitation step liquor.

[0161] In some embodiments, the concentration of magnesium ions in the first precipitation step liquor (that is, the solution used in the DLE process) is less than 200 mg / L, preferably less than 100 mg / L, preferable less than 50 mg / L, preferably less than 25 mg / L, preferably less than 10 mg / L, preferably less than 5 mg / L, preferably less than 2 mg / L, preferably less than 1 mg / L.

[0162] In some embodiments, the concentration of calcium ions in the first precipitation step liquor (that is, the solution used in the DLE process) is less than 200 mg / L, preferably less than 100 mg / L, preferable less than 50 mg / L, preferably less than 25 mg / L, preferably less than 10 mg / L, preferably less than 5 mg / L, preferably less than 2 mg / L, preferably less than 1 mg / L.

[0163] In some embodiments, the concentration of sulfate ions in the first precipitation step liquor (that is, the solution used in the DLE process) is less than 200 mg / L, preferably less than 100 mg / L, preferable less than 50 mg / L, preferably less than 25 mg / L, preferably less than 10 mg / L, preferably less than 5 mg / L, preferably less than 2 mg / L, preferably less than 1 mg / L.

[0164] Extraction step

[0165] The first precipitation step liquor is then treated using a direct lithium extraction process. This selectively separates the lithium ions from the other ionic species in the first precipitation step liquor. The product of this step is a solution enriched in lithium ions, the so-called extraction step liquor.

[0166] Direct lithium extraction (DLE) is a process where lithium is selectively extracted from impure solutions containing large amounts of multiple ionic species, wherein the majority of other components are left in solution. There are a number of DLE techniques known in the art, including electrodialysis, nanofiltration, adsorption and ion-exchange. The latter two approaches hold the most promise in terms of lithium selectivity, energy consumption and cost.

[0167] DLE processes enrich a solution in lithium ions, that is, the product of the DLE process is a solution that has a higher concentration of lithium ions than the solution fed into the DLE process.

[0168] The DLE process used is not particularly limited. Any suitable DLE process can be used. General DLE methods are well known in the art and will not be discussed in great detail here.

[0169] In one embodiment, the DLE process is an adsorptive process or an ion-exchange process. These processes use materials that selectively uptake lithium from solution. The lithium can then be ‘released’ from the enriched selective material to provide substantially pure lithium containing solutions.

[0170] For example, the selective material may be provided as beads in a column, with the first precipitation step liquor poured into / through the column; or it may be provided in the form of hollow fibers, with the first precipitation step liquor fed through or over the fibers. This facilitates the uptake of the lithium and replaces protons in the material. This initial contact, removing the lithium from the first precipitation step liquor and ‘storing’ it in the selective material, can be termed an ‘adsorption step’ of the DLE process.

[0171] In order to conserve charge, clearly, in order to desorb (release) the lithium ions they must be replaced with a suitable cation; this is often a proton as suitable protic acidic solutions are readily available. Similarly, using basic solutions encourages the adsorption (take up) of lithium from solution, by removing protons from the lithium-ion sieve material. By varying pH, the selective ‘adsorption’ (take up) and ‘desorption’ (release) of lithium can be carefully controlled. A more basic lithium-containing solution provides the fastest lithium extraction rate; a more acidic release solution provides the fastest lithium release rate. However, rate must also be balanced against other factors such as acid / base safety and toxicity, additional cost and so on.

[0172] As the first precipitation step liquor comprises carbonate ions, in some embodiments no changes to the pH of the solution need to be made. In other embodiments, the pH of the solution can be raised by the addition of sodium hydroxide or the like.

[0173] Lithium selective materials

[0174] A lithium selective material (Lithium-Ion Sieve, LIS) is needed for the desired ion exchanges to occur in the extraction steps.

[0175] It may be for example a metal organic framework, a zeolite, a layered double hydroxide or a metal oxide. Lithium metal oxides and their hydrogen precursors are particularly suitable for use as a lithium selective material held in the matrix material. Lithium manganese oxide (LMO) and its corresponding hydrogen manganese oxide (HMO) derived from LMO, and lithium titanium oxide (LTO) and its corresponding hydrogen titanium oxide (HTO) derived from LTO are suitable.

[0176] [It will be recognised that, of course, during the ion exchange reaction a compound such as lithium manganese oxide (LMO) will be converted, to at least some degree, to hydrogen manganese oxide (HMO) on contact with the release solution; it will convert back when it leeches lithium ions from a suitable feedstock. Accordingly the ion selective material may be accurately described as both LMO and HMO derived from LMO depending on its state of lithium ion loading. The applies equally to LTO and HTO derived from LTO, of course.]

[0177] Typically, the lithium selective material is not used in the pure form, but it is rather contained within or embedded in a matrix.

[0178] The matrix used here is not particularly limited beyond that it has good chemical and thermal stability. Suitable matrix materials include ceramics and polymers. Suitable ceramics include oxides such as alumina, zirconia and titania. Suitable polymers include both thermoplastics and thermosetting plastics. In some preferred embodiments the matrix material comprises one or more selected from: polysulfone (PSD), polyethersulfone (PES), polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyimide. In some embodiments it consists of one of those. PES is particularly preferred. Therefore preferably the matrix material comprises or consists of PES. The matrix is suitably porous; this increases the flow of the feedstock to the selective material (which may not necessarily be present on the outer surface of the matrix material) and facilitates transfer of lithium ions. The pores effectively increase the active surface area of the material. Accordingly larger pores, for example of an average pore size 0.1-2 pm, for example 0.5-1 pm, are preferable.

[0179] For the present lithium-ion-exchange material, a porosity of > 60% may be suitable, in particular > 80%. The pores may have a size (D50) of < 2 pm, for example < 1 pm.

[0180] The selective material may suitably be provided in the form of particles.

[0181] In some embodiments, the particle size of the selective material is < 50 pm, suitably < 25 pm, or < 10 pm. Most suitable is a particle size of < 5 pm, or < 3 pm.

[0182] On the other hand, the particles may suitably have a size of > 200 nm, for example > 400 nm, > 1 pm, or > 2 pm.

[0183] Lithium ion-exchange material

[0184] As explained above, the lithium-ion-exchange material includes a selective material and a matrix material. It may be provided in various morphologies; for example, it may be formed into beads (for example, substantially spherical beads of average diameter 0.01-10 mm) or, more suitably, into a membrane form.

[0185] Such a membrane might be a simple flat (e.g., cast) membrane, or have a more complex structure such as that of a hollow fiber. Hollow fiber (HF) membranes have been found by the inventors to have several advantages in DLE processes; in particular, a high useful surface area especially where the feedstock is flown in contact with the lithium-ion-exchange material.

[0186] Such hollow fibers are known in the art of water treatment; they are elongate, generally extruded members with a bore (hollow part) inside the substantially circular cross-section fiber.

[0187] A hollow fiber morphology of the material may be preferable as a feedstock brought into contact with the fiber has surface contact with a large active area. Hollow fibers can also be packed into a housing to form a membrane module; flow of feedstock through the module again allows high surface contact and hence efficient lithium extraction and release.

[0188] Suitable hollow fiber dimensions will be apparent to those skilled in the art. For example, a hollow fiber length of 0.2-2 m, an outer diameter of 0.4-5 mm, and a wall thickness of 10-200 pm may be used.

[0189] The hollow fibers themselves may have, for example, a length of about 1 m, an outer diameter of about 1 mm, and an inner (bore) diameter of about 0.9 mm.

[0190] Methods of making suitable beads or membranes will be apparent to those of skill in the art. Hollow fiber membranes are used often in water treatment technologies; general methods for their fabrication are also well know. Adsorption

[0191] The adsorption step, as well as suitably being conducted at raised pH, may also or instead suitably be conducted at raised temperature (that is, above room temperature; for example 30°C or higher, 40°C or higher, 50°C or higher, 60°C or higher, or 70°C or higher).

[0192] A temperature of 25-70°C, and particularly 50-70°C, may be preferred,

[0193] The length of time for which there is contact between the first precipitation step liquor and the selective material depends on several factors, for example how the selective material is provided. If it is provided in fibers, or a column, through which a feedstock is flown, the rate of flow is important. If the selective material is simply placed in contact with a stationary feedstock for some length of time, the time it is left is the relevant feature.

[0194] In some embodiments, the extraction step may be conducted for 10-150 minutes.

[0195] After a given time, the de-lithiated first precipitation step liquor is suitably removed from contact with the selective material, and the selective material may be rinsed with fresh water. This can remove any impurities loosely bound to the lithium-ion-exchange material before the release step is carried out.

[0196] Desorption

[0197] In order to release the lithium from the selective material, a protic acidic solution (release solution) is introduced; this replaces the lithium ions with protons. This can be termed a ‘release step’ of the DLE process. The lithium is released from the selective material, forming a lithium-rich solution which can be removed for further processing, this lithium-rich solution is the so-called extraction step liquor.

[0198] Typically, HCI is used in the release step due to the low cost. In other embodiments, the release solution comprises one or more acids selected from the group of HCI, HBr, HI, HNO3, H2SO4, H3PO4, H3BO3, HCIO4, HBF4. In some embodiments, the release solution comprises one or more organic acids. The organic acid may be one which comprises a carboxylic acid group. Optionally, the organic acid comprises two or more carboxylic acid groups. Suitable organic acids include acetic acid, oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, citric acid, malic acid, and tartaric acid.

[0199] The pH of the release solution (which is generally aqueous) depends of course on the acid included in it and how much is included; generally, it has a pH <7, for example <6, <5, <4, or <3.

[0200] In the release step, the lithium-ion exchange material is exposed to a release solution. Suitably this can be done batch-wise or using a continual flow of organic acid solution.

[0201] The release step may suitably be conducted at raised temperature (that is, above room temperature; for example, 30°C or higher, 40°C or higher, 50°C or higher, 60°C or higher, or 70°C or higher).

[0202] The release step may suitably be conducted at up to 70°C. A temperature above room temperature, for example around 25-70°C, suitably 50-70°C, may be preferred.

[0203] Extraction step liquor The extraction step liquor produce by the DLE step substantially only contains water, lithium cations and the conjugate base anion of the acid used in the DLE step.

[0204] For example, if HCI is used in the release solution of a selective adsorption DLE process, the extraction step liquor is substantially pure LiCI in water.

[0205] As the DLE process also increases the concentration of lithium in a given solution, it is possible to produce concentrated solutions of lithium (that is, the concentration of lithium in the extraction step liquor produced by the DLE extraction is higher than the concentration of lithium in the first precipitation step liquor).

[0206] In some embodiments, an optional concentration step is performed after the extraction step, that is the extraction step liquor is concentrated. Suitable means of concentrating the extraction step liquor includes distillation processes such as solar evaporation, vacuum distillation, flash distillation and membrane distillation; reverse osmosis and electrodialysis.

[0207] Preferably, the extraction step liquor used in the second precipitation step contains more than 2500 ppm lithium by mass. Preferably 5000 ppm lithium by mass. In some embodiments, the concentration of lithium in the extraction step liquor is above 1.3 g / L of Li+, more preferably above 2.4 g / L, more preferably above 5 g / L, more preferably above 10 g / L, more preferably above 20 g / L, more preferably above 50 g / L, more preferably above 100 g / L.

[0208] In some embodiments, the concentration of lithium in the extraction step liquor is 150 g / L of Li+or lower, optionally 100 g / L or lower, optionally 50 g / L or lower, optionally 20 g / L or lower, optionally 10 g / L or lower, _optionally 5 g / L or lower.

[0209] In some embodiments, the extraction step liquor comprises one or more of lithium chloride, lithium bromide, lithium acetate, lithium hydroxide, lithium sulfate, and lithium citrate. Preferably, the extraction step liquor comprises lithium chloride, optionally the extraction step liquor is a substantially pure aqueous lithium chloride solution.

[0210] Second precipitation step

[0211] The extraction step liquor is then treated with a source of carbonate ions. This precipitates lithium carbonate. Sodium carbonate is used in the scheme of Figure 2.

[0212] The supernatant solution produced in the second precipitation step is the so-called second precipitation step liquor. The second precipitation step liquor is saturated with lithium carbonate (at the given temperature the precipitation step is carried out) and will clearly also contain the source of carbonate ions used in the second precipitation step.

[0213] Suitably, any source of carbonate ions can be used, other than lithium carbonate. However, it is preferable that the source of carbonate ion is soluble in water, for example sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, rubidium carbonate, caesium carbonate, ammonium carbonate, and ammonium bicarbonate. Preferably, the source of carbonate ions is sodium carbonate, specifically sodium carbonate decahydrate.

[0214] In one embodiment, the source of carbonate ions is added as a solution. Preferably, the source of carbonate ions is a solution saturated with carbonate ions.

[0215] In other embodiments, the source of carbonate ions is added to the extraction step liquor as a pure solid or liquid (that is, without additional water). As the precipitation step may be conducted at raised temperature, the source of carbonate ions may be a liquid (for example, sodium carbonate decahydrate is liquid at 50 °C)

[0216] In one embodiment, the second precipitation step is performed at room temperature. In some embodiments, the second precipitation step is performed at above room temperature (that is, with heating), for example 30-100 °C, optionally between 30-70 °C, which can speed up the step.

[0217] In order to recover a precipitate in the second precipitation step, the concentration of lithium ions in the extraction step liquor is preferably higher than the concentration of lithium ions in a saturated solution of lithium carbonate at the same temperature. For example, at 25 °C the concentration of lithium ions is preferably above 2250 ppm (about 2.4 g / L of Li+, equivalent to 0.35 M). At 100 °C, the concentration of lithium ions is preferably above 1200 ppm (about 1.3 g / L of Li+, equivalent to 0.19 M)

[0218] After the addition of the source of carbonate ions, the second precipitate is separated from the second precipitation step liquor. For example, the mixture may be separated by gravity separation, filtration, centrifugation, hydrocyclonic separation and the like.

[0219] In some embodiments, the second precipitate formed by the second precipitation step is washed and the washing liquid can be added to the first precipitation step liquor before the direct lithium extraction step.

[0220] In some embodiments, the second precipitation step liquor can be combined with the first precipitation step liquor before the direct lithium extraction step.

[0221] ***

[0222] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0223] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0224] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0225] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:

1. A method of extracting lithium from a lithium-containing solid, the method comprising:(i) a dissolution step comprising treating the lithium-containing solid with an acid to obtain a dissolution step liquor;(ii) a pH adjustment step comprising adding an alkali to the dissolution step liquor to precipitate metal products as a first precipitate, then isolating the first precipitate to leave a pH adjustment step liquor;(iii) a first lithium precipitation step comprising adding a source of carbonate ions to the pH adjustment step liquor to precipitate lithium carbonate, then isolating the lithium carbonate to leave a first precipitation step liquor;(iv) a direct lithium extraction step comprising treating the first precipitation step liquor using direct lithium extraction to produce an extraction step liquor; and(v) a second lithium precipitation step comprising adding a source of carbonate ions to the extraction step liquor to precipitate lithium carbonate, then isolating the lithium carbonate.

2. The method according to claim 1 wherein the lithium-containing solid is derived from lithium batteries, optionally wherein the lithium-containing solid is black mass.

3. The method according to claim 1 or claim 2 wherein the direct lithium extraction process used in step (iv) is an adsorptive direct lithium extraction process, optionally wherein the adsorptive direct lithium extraction process uses a titanate-based adsorptive material.

4. The method according to any preceding claim wherein the acid used in step (i) comprises sulfuric acid, phosphoric acid, hydrochloric acid, citric acid or oxalic acid, optionally wherein the acid used in step (i) is sulfuric acid.

5. The method according to any preceding claim wherein the alkali used in step (ii) comprises a metal hydroxide, optionally wherein the alkali used in step (ii) is sodium hydroxide.

6. The method according to any preceding claim wherein the amount of alkali used in step (ii) is sufficient to raise the pH of the liquor to pH 3-12.

7. The method according to any preceding claim wherein the source of carbonate ions used in step (iii) and / or step (iv) comprises sodium carbonate, optionally wherein the source of carbonate ions used in step (iii) and step (iv) is sodium carbonate.

8. The method according to any preceding claim wherein the amount of the source of carbonate ions used in step (iii) and step (iv) is sufficient to produce a saturated lithium carbonate solution.

9. The method according to any preceding claim wherein the supernatant solution produced in step (v) is added to the first precipitation step liquor before the step (iv).

10. The method according to any preceding claim wherein the lithium containing solid is heated to a temperature of 50-100 °C before step (i).

11. The method according to any preceding claim wherein the dissolution step liquor is filtered after step (i).

12. The method according to any preceding claim comprising a sulfate removal step after step (i), optionally wherein the sulfate removal step is after step (i) and before step (ii); or wherein the sulfate removal step is after step (ii) and before step (iii) .

13. The method according to any preceding claim comprising an alkali earth metal cation removal step after step (i), optionally wherein the alkali earth metal cation removal step is after step (i) and before step (ii).

14. The method according to any preceding claim comprising a concentration step after step (iv) and before step (v).

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