Recovery of lithium from an aqueous solution

Abstract

The present invention relates to a method for recovering lithium products from an aqueous solution, the method comprising the following steps: (i.) contacting the solution with an alkaline substance to precipitate a target amount of magnesium in a brine solution and separating the precipitated solid from the intermediate solution; (ii.) contacting the intermediate solution with a controlled amount of a hydroxide salt to precipitate magnesium in the intermediate solution; (iii.) contacting the intermediate solution with a controlled amount of sodium carbonate to precipitate impurities and separating the precipitated solid from the purified solution; and (iv.) recovering the lithium product from the purified solution.

Description

Technical Field

[0001] The present invention relates to a method for recovering lithium products from an aqueous solution. More specifically, the method of the present invention allows for the recovery of high-purity lithium products. The method of the present invention is particularly applicable to the recovery of lithium products from brine solutions. Background Art

[0002] The following discussion of the background art is intended only to facilitate an understanding of the present invention. The discussion is not an admission or acknowledgment that any of the materials cited is part of the common general knowledge as of the priority date of the present application.

[0003] Lithium can occur naturally in brine solutions derived from salt lakes or underground water sources. These solutions typically contain relatively small amounts of dissolved lithium cations compared to sodium chloride. These solutions also contain other dissolved impurities such as potassium, magnesium, calcium, chlorides, sulfates, and borates. The lithium concentration in these solutions is typically increased by storing the solution in evaporation ponds for a long period of time, thereby increasing the lithium concentration. The evaporation process will cause some impurities to precipitate in the form of salts, allowing for separation. The concentrated brine solution is then treated to remove the remaining impurities and recover the lithium. The treatment of the concentrated brine solution varies depending on the impurities present in the concentrated brine solution.

[0004] Lithium is then recovered from the solution by adding sodium carbonate (soda ash) to precipitate lithium carbonate. Although this process is relatively simple, the purity of the precipitated lithium carbonate product is not high unless the impurities are removed prior to adding sodium carbonate. The most problematic impurity is magnesium, which has very similar chemical properties to lithium. If magnesium is present in the solution during lithium carbonate precipitation, it will typically co-precipitate as MgCO3. The recovered product must then be subjected to further purification processes to remove the impurities.

[0005] The most common method for removing magnesium from brine solutions is by adding lime Ca(OH)2 to increase the solution pH and precipitate magnesium hydroxide, allowing for subsequent separation by filtration. The main drawback of this process is the large amount of lime required to increase the pH of a solution with a large water component. In addition, the use of lime introduces calcium into the solution, and the calcium must be removed prior to lithium recovery.

[0006] Many other techniques have been proposed for recovering lithium from brines. These techniques generally focus on the selective absorption of lithium from the salt source. Lithium-selective ion exchange resins based on alumina compounds exhibit high lithium absorption but require subsequent acid treatment to strip the lithium and then treatment to regenerate the resin. Electrochemical methods for separating lithium from brine solutions have also been proposed, but these methods require a large energy input. Nanofiltration membranes have also been shown to selectively recover lithium, but there are challenges associated with operating these membranes on an industrial scale.

[0007] The main problem faced in the treatment of brine solutions is the low concentration of lithium. This requires the treatment of large volumes of brine, which makes it difficult to scale up the processes used.

[0008] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations thereof will be understood to imply the inclusion of the stated integer or group of integers but not the exclusion of any other integer or group of integers. Summary of the Invention

[0009] According to the present invention, there is provided a method for recovering lithium products from an aqueous solution, the method comprising the following steps:

[0010] i. contacting the aqueous solution with an alkaline substance to precipitate a target amount of magnesium in the aqueous solution and separating the precipitated solid from the intermediate solution;

[0011] ii. contacting the intermediate solution with a controlled amount of a hydroxide salt to precipitate magnesium in the intermediate solution;

[0012] iii. contacting the intermediate solution with a controlled amount of sodium carbonate to precipitate impurities and separating the precipitated solid from the purified solution; and

[0013] iv. recovering the lithium product from the purified solution.

[0014] The inventors of the present invention have found that using separate stages to precipitate out impurities allows better control of the additional cations introduced into the solution to remove the impurities. It has been found that this limits the amount of downstream processing that must be carried out to subsequently remove these cations from the solution. In particular, the inventors have found that controlling the amount of alkaline substance introduced in step (i) will limit the alkaline cations that subsequently need to be removed from the system. It has been found that this is particularly useful when calcium hydroxide is used as the alkaline solution, since the addition of calcium cations to the system is controlled. While limiting the amount of calcium hydroxide used in step (i) reduces the amount of impurities precipitated in that step, the inventors have found that this reduces the amount of sodium carbonate required in step (iii). It has been found that this reduces the proportion of lithium that is precipitated as lithium carbonate in that step, thereby increasing the amount of lithium recovered.

[0015] It has been found that the method of the present invention is particularly useful for recovering lithium products from brine solutions. Throughout the specification, the term "brine solution" will be understood to refer to an aqueous solution containing alkali metal and / or alkaline earth metal salts, where the concentration of the salts can vary from trace amounts to the saturation point. It should be understood that brine solutions can be obtained from natural sources or can be produced by industrial processing. As will be understood by those skilled in the art, such solutions typically contain a range of impurities. The method of the present invention seeks to economically remove many of these impurities in order to allow the direct recovery of high-purity lithium products from the solution.

[0016] The method of the present invention is particularly suitable for recovering lithium from brine solutions containing less than 6% lithium.

[0017] In one form of the present invention, the aqueous solution is subjected to a concentration step before step (i). Preferably, the concentration step is an evaporation step.

[0018] In one form of the present invention, the concentration step increases the concentration of lithium in the aqueous solution to 0.1 - 1.2%. Preferably, the maximum concentration of lithium is 0.7%.

[0019] In one form of the present invention, the aqueous solution is treated to reduce the concentration of sulfate.

[0020] In one form of the present invention, the concentration of sulfate in the aqueous solution is maintained below 4%. In one form of the present invention, the concentration of sulfate in the aqueous solution is maintained by adding a precipitant. Preferably, the precipitant is CaCl2. More preferably, the CaCl2 is recycled from other parts of the process.

[0021] In one form of the present invention, the alkaline substance includes calcium. Preferably, the alkaline substance includes calcium hydroxide.

[0022] In one form of the present invention, the alkaline substance is lime. Preferably, the alkaline substance is slaked lime.

[0023] In one form of the present invention, step (i) precipitates a target amount of magnesium in the aqueous solution. Preferably, 50 - 80% of the magnesium in the aqueous solution is precipitated.

[0024] In one form of the present invention, step (i) precipitates a target amount of boron in the aqueous solution. Preferably, 63 - 83% of the boron in the aqueous solution is precipitated.

[0025] In one form of the present invention, the pH of the aqueous solution is maintained at 9 or lower during step (i).

[0026] In one form of the present invention, the intermediate solution is directed to a secondary concentration step before step (ii). Preferably, the secondary concentration is an evaporation step.

[0027] In one form of the present invention, the secondary concentration step increases the concentration of lithium in the aqueous solution to at least 1.2%. Preferably, the concentration of lithium is 1.2% - 2.2%. More preferably, the concentration of lithium is 1.2% - 1.6%.

[0028] In an alternative form of the present invention, the secondary concentration step increases the concentration of lithium in the aqueous solution to at least 1.6%. Preferably, the concentration of lithium is 1.6% - 6.0%. More preferably, the concentration of lithium is 1.6% - 4.5%.

[0029] In one form of the invention, the hydroxide salt is sodium hydroxide.

[0030] In one form of the invention, the amount of hydroxide salt added in step (ii) is related to the Mg 2+ concentration of the intermediate solution. Preferably, the target stoichiometric concentration of Mg 2+ :OH - is 1.25:1–1:1.25. Preferably, in the case of using sodium hydroxide, the target stoichiometric concentration of Mg 2+ :NaOH is 1.25:1–1:1.25.

[0031] In one form of the invention, during the step of contacting the intermediate solution with a controlled amount of hydroxide salt to precipitate magnesium in the intermediate solution, the solution pH is maintained below 10.

[0032] In one form of the invention, the amount of sodium carbonate added in step (iii) is related to the Ca 2+ concentration of the intermediate solution. Preferably, the target stoichiometric concentration of Ca 2+ :Na2CO3 is 1.25:1-1:1.25.

[0033] In an embodiment of the invention, where the target of the secondary concentration step is to have a lithium concentration in the aqueous solution of at least 1.6%, the method preferably further comprises subjecting the purified solution to a dilution step before the step of recovering the lithium product from the purified solution. Preferably, the dilution step comprises adding water to the purified solution to reduce the lithium concentration in the purified solution.

[0034] In one form of the invention, lithium carbonate is recovered from the purified solution. Preferably, a controlled amount of sodium carbonate is added to the purified solution to precipitate lithium carbonate. In one form of the invention, the amount of sodium carbonate added to the purified solution is related to the Li 2+ concentration of the intermediate solution. Preferably, the target stoichiometric concentration of Li 2+ :Na2CO3 is 1.25:1-1:1.25.

[0035] In one form of the invention, lithium carbonate is converted to lithium hydroxide.

[0036] In one form of the invention, lithium hydroxide is recovered from the purified solution.

[0037] In one form of the invention, the recovered lithium product is subjected to a purification step. Preferably, the purification step comprises a hot repulp washing stage. Additionally or alternatively, the purification step comprises a lithium carbonate dissolution step followed by a lithium carbonate recrystallization step. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further features of the present invention are more fully described in the following description of several non - limiting embodiments of the present invention. This description is included for purposes of illustration of the present invention only. It should not be construed as a limitation of the broad overview, disclosure, or description of the present invention above. The description will be made with reference to the accompanying drawings, in which:

[0039] Figure 1 A flowchart depicting a method for recovering lithium products from an aqueous solution according to a first embodiment of the present invention;

[0040] Figure 2 A flowchart depicting a method for recovering lithium products from an aqueous solution according to a second embodiment of the present invention;

[0041] Figure 3 Is a concentration path diagram of lithium in the test conducted in Example 1;

[0042] Figure 4 Is a concentration path diagram of sulfate in the test conducted in Example 1;

[0043] Figure 5 Is a concentration path diagram of lithium in the second test conducted in Example 1;

[0044] Figure 6 Is a concentration path diagram of sulfate in the second test conducted in Example 1;

[0045] Figure 7 Is a concentration path diagram of lithium in the test conducted in Example 2;

[0046] Figure 8 Is a concentration path diagram of sulfate in the test conducted in Example 2;

[0047] Figure 9 Is a graph of the impurity removal test conducted in Example 3;

[0048] Figure 10 Is a graph of the impurity removal test regarding pH in Example 3;

[0049] Figure 11 Is a graph showing the total divalent impurities removed during the test in Example 3; and

[0050] Figure 12 Is a graph of the relationship between the removal of magnesium and boron and pH when lime is added in the test conducted in Example 4. Detailed Description

[0051] The present invention broadly relates to a method for recovering lithium products from an aqueous solution. While the method of the present invention can be used to recover lithium from a range of aqueous solutions, the method of the present invention is particularly suitable for recovering lithium from brine solutions. InFigure 1 In [description], a method 10 for recovering lithium products from a brine solution 12 according to an embodiment of the present invention is shown.

[0052] In one embodiment, the brine solution contains less than 6% lithium. In one embodiment, the brine solution contains less than 5% lithium. In one embodiment, the brine solution contains less than 4% lithium. In one embodiment, the brine solution contains less than 3% lithium. In one embodiment, the brine solution contains less than 2% lithium. In one embodiment, the brine solution contains less than 1% lithium. In one embodiment, the brine solution contains less than 0.9% lithium. In one embodiment, the brine solution contains less than 0.8% lithium. In one embodiment, the brine solution contains less than 0.7% lithium. In one embodiment, the brine solution contains less than 0.6% lithium. In one embodiment, the brine solution contains less than 0.5% lithium. In one embodiment, the brine solution contains less than 0.4% lithium. In one embodiment, the brine solution contains less than 0.3% lithium. In one embodiment, the brine solution contains less than 0.2% lithium. In one embodiment, the brine solution contains less than 0.1% lithium.

[0053] The brine solution 12 enters a concentration step 14 to increase the lithium concentration. In Figure 1 The illustrated embodiment, the concentration step 14 includes a solar evaporation process in which the brine solution 12 is directed to an evaporation pond or pan to reduce the water content. It is contemplated that other means known to those skilled in the art for concentrating brine solutions may also be used. As the brine solution is concentrated, some solids will precipitate out. The main precipitate is rock salt (NaCl). It is contemplated that if there is sufficient lithium in the brine solution, a precipitation step may not be required.

[0054] The concentration step continues until the desired lithium concentration is reached. In one embodiment, the concentration step increases the concentration of lithium in the aqueous solution to 0.1 - 1.2%. In one embodiment, the concentration step increases the concentration of lithium in the aqueous solution to 0.2 - 1.2%. In one embodiment, the concentration step increases the concentration of lithium in the aqueous solution to 0.3 - 1.2%. In one embodiment, the concentration step increases the concentration of lithium in the aqueous solution to 0.4 - 1.2%. In one embodiment, the concentration step increases the concentration of lithium in the aqueous solution to 0.5 - 1.2%. In one embodiment, the concentration step increases the concentration of lithium in the aqueous solution to 0.6 - 1.2%.

[0055] In one embodiment, the maximum concentration of Li in the brine solution is 1.0%. In one embodiment, the maximum concentration of lithium in the brine solution is 0.9%. In one embodiment, the maximum concentration of lithium in the brine solution is 0.8%. In one embodiment, the maximum concentration of Li in the brine solution is 0.7%.

[0056] In one embodiment, the concentration step is carried out until the maximum sulfate concentration is reached. In one embodiment, the maximum sulfate concentration is 4%. It is contemplated that known techniques in the art, such as by inductively coupled plasma mass spectrometry (ICP-MS) techniques, can be used to monitor the concentration of lithium and / or sulfate in the aqueous solution.

[0057] The inventors have determined that when the brine solution is concentrated, an increase in the lithium concentration will result in the precipitation of KLiSO4. The lithium concentration at which KLiSO4 begins to precipitate depends on the temperature and the concentrations of Ca 2+ and SO4 2- in the brine solution. The inventors have found that by restricting the concentrations of lithium and sulfate in the brine solution, the precipitation of KLiSO4 is significantly reduced. This prevents the loss of lithium in the concentration step 14. It is contemplated that in cases where the ratio of SO4 2- :Li 2+ in the system is relatively high, a Ca 2+ source, such as a recycled CaCl2 solution, can be introduced to advantageously precipitate CaSO4 over KLiSO4.

[0058] The concentrated solution is recovered and filtered to remove any entrained solids 15.

[0059] The filtered brine solution 16 is directed to a preliminary impurity removal step 18 to precipitate a target amount of magnesium in the brine solution. To precipitate magnesium, an alkaline substance 20 is added to the brine solution. In Figure 1 the preliminary impurity removal step 18 shown, the brine solution is contacted with slaked lime Ca(OH)2 to precipitate a target amount of magnesium in the brine solution. Adding slaked lime causes magnesium hydroxide to precipitate along with some gypsum CaSO4·2H2O. If boron is present in the brine solution, adding lime will also cause boron to precipitate as borate.

[0060] Slaked lime is added to precipitate the target amount of magnesium contained in the brine solution. The inventors have found that by restricting the amount of magnesium precipitated, the amount of Ca 2+ ions introduced into the brine solution is also restricted. This will in turn reduce the amount of calcium that must be removed from the solution prior to lithium recovery. Without wishing to be bound by theory, the inventors have found that lithium will be lost during the calcium removal process. By restricting the amount of calcium removed, the loss of lithium is also restricted.

[0061] In one embodiment, 50 - 80% of the magnesium in the aqueous solution is precipitated. In one embodiment, 55 - 75% of the magnesium in the aqueous solution is precipitated. In one embodiment, 70% of the magnesium in the aqueous solution is precipitated.

[0062] In one embodiment, 63 - 83% of the boron in the aqueous solution is precipitated. In one embodiment, 68 - 78% of the boron in the aqueous solution is precipitated. In one embodiment, 73% of the boron in the aqueous solution is precipitated.

[0063] To control the amount of precipitated magnesium, the addition of calcium hydroxide is based on the concentration of total magnesium in the brine solution. It is contemplated that titrimetric analysis can be used to monitor the magnesium in the brine solution. In a preferred embodiment, an on - line titrator unit is used to monitor and control the magnesium concentration after the addition of calcium hydroxide. To ensure that an excessive amount of calcium hydroxide is not added, temperature and mass flow control are preferably implemented.

[0064] In one embodiment, the pH of the solution is maintained below 9.0. Without wishing to be bound by theory, the inventors have found that the precipitated borate reacts with lime above pH 9.0, resulting in increased lime consumption, redissolution of boron, and introduction of calcium into the brine solution. The inventors have found that at lower temperatures, the pH of the solution may increase above 9.

[0065] After adding slaked lime, the resulting slurry is sent to a solid / liquid separation step to remove solid 22 and produce an intermediate solution 24. In a preferred embodiment, the solid / liquid separation step includes a thickening step (not shown). The thickener underflow is directed to a filtration step (not shown). The filtrate is mixed with the overflow, and the recovered solids are disposed of.

[0066] The intermediate solution 24 is directed to a secondary concentration step 26 to increase the lithium concentration. In Figure 1 the illustrated embodiment, the concentration step includes a solar evaporation process, where the intermediate solution 24 is directed to an evaporation pond or evaporation pan to reduce the water content. It is contemplated that other means known to those skilled in the art for concentrating brine solutions can also be used. As the brine solution is concentrated, many solids will precipitate out. The main precipitants are rock salt (NaCl) and potassium chloride (KCl).

[0067] The concentration step continues to the target lithium concentration. In a preferred embodiment, the target concentration of Li is at least 1.2%.

[0068] In one embodiment, the secondary concentration step 26 increases the concentration of lithium in the aqueous solution to at least 1.3%. In one embodiment, the secondary concentration step increases the concentration of lithium in the aqueous solution to at least 1.4%. In one embodiment, the secondary concentration step increases the concentration of lithium in the aqueous solution to at least 1.5%.

[0069] In one embodiment, the secondary concentration step increases the concentration of lithium in the aqueous solution to 1.2% - 2.2%. In one embodiment, the secondary concentration step increases the concentration of lithium in the aqueous solution to 1.2% - 1.6%.

[0070] The concentrated solution is recovered and filtered to remove any entrained solids 28 from the filtered solution 30.

[0071] The filtered solution is directed to a primary precipitation step 32 where it is contacted with a hydroxide salt (such as sodium hydroxide 34) to precipitate the remaining magnesium in the solution as Mg(OH)2. The addition of sodium hydroxide 34 is based on the concentration of magnesium in the solution. The amount of sodium hydroxide 34 added should target a stoichiometric relationship between Mg 2+ and NaOH of 1.25:1 - 1:1.25. It is contemplated that titrimetric analysis can be used to monitor the magnesium in the intermediate solution 24. In a preferred embodiment, an on-line titrator unit is used to monitor and control the magnesium concentration after the addition of sodium hydroxide 34. It is also contemplated that other hydroxide salts can equally be used to precipitate Mg(OH)2, and the inventors have found that using NaOH is preferred because sodium cations are already present in the system.

[0072] As will be understood by those skilled in the art, the addition of sodium hydroxide 34 will cause the pH of the solution to increase. The inventors have found that the increased pH will result in lithium loss. By restricting the addition of sodium hydroxide 34, the pH is also restricted. In one embodiment, the solution pH in the primary precipitation step 32 is maintained below 10. In one embodiment, the solution pH in the primary precipitation step 32 is maintained below 9.5. In one embodiment, the solution pH in the primary precipitation step 32 is maintained below 9.

[0073] Once the pH has stabilized, a secondary precipitation step 36 is carried out. Although not necessary, it is contemplated that the precipitated material can be removed between the primary precipitation step 32 and the secondary precipitation step 36. In the secondary precipitation step 36, the solution is contacted with sodium carbonate 38 to precipitate calcium carbonate. Sodium carbonate 38 is incorporated based on the concentration of Ca 2+ in the solution. The amount of sodium carbonate 38 added should target a stoichiometric relationship between Ca 2+ and NaCO3 of 1.25:1–1:1.25. It is contemplated that titrimetric analysis can be used to monitor the calcium in the intermediate solution 24. In a preferred embodiment, an on-line titrator unit is used to monitor and control the calcium concentration after the addition of sodium hydroxide 34.

[0074] In one embodiment, the solution pH is maintained below 10. In one embodiment, the solution pH is maintained below 9.5. The inventors have found that lithium carbonate precipitation is related to the solution pH. It can be understood that by maintaining the pH of the solution below 10, the precipitation of lithium carbonate can be restricted.

[0075] Using sodium carbonate 38 to precipitate calcium carbonate has been shown to also co-precipitate lithium carbonate, which ultimately limits lithium recovery. The inventors of the present invention have found that by managing the concentration of divalent cations present in the intermediate solution 24, the amount of sodium carbonate 38 required in the secondary precipitation step 36 can be reduced. The two main sources of divalent cations are Mg 2+ and Ca 2+ . Although using Ca(OH)2 in the preliminary impurity removal step 18 will precipitate and remove Mg 2+ from the brine solution, it will also introduce Ca 2+ into the brine solution. The inventors have found that by controlling the amount of Mg 2+ precipitated in the preliminary precipitation step, the total divalent cation load in the intermediate solution 24 can be managed. This is achieved by incorporating Ca(OH)2 according to the Mg 2+ concentration in the brine solution. Although prior art processes have used Ca(OH)2 to precipitate magnesium from brine solutions, the Ca(OH)2 dosage is typically based on achieving a target solution pH to precipitate the maximum possible amount of Mg 2+ . This introduces a large amount of Ca 2+ cations, which then have to be removed with sodium carbonate 38.

[0076] To address the remaining Mg 2+ and Ca 2+ in the intermediate solution 24, a two-stage precipitation process is used to first remove Mg 2+ and then remove Ca 2+ . By managing the Ca 2+ introduced in the preliminary impurity removal step 18, the inventors have found that less sodium carbonate 38 is required in the secondary precipitation step 36. This limits the amount of lithium carbonate co-precipitated in this secondary precipitation step 36. Another advantage is that the pH of the solution is kept below 10, thereby further limiting the precipitation of lithium carbonate.

[0077] The addition of both sodium hydroxide 34 and sodium carbonate 38 dilutes the lithium content in the brine solution. As will be understood by those skilled in the art, minimizing dilution is key to obtaining a high-purity lithium product from the solution. The inventors have found that after the impurity removal step, the lithium in the solution should be maintained above 1.1 wt%. Without wishing to be bound by theory, the inventors understand that if there is not enough lithium in the solution to precipitate as a carbonate, other impurities will precipitate. This will result in impurities in the lithium product.

[0078] After the secondary precipitation step 36, the resulting slurry is transferred to a solid / liquid separation step to remove the resulting solid stream 40, obtaining a purified solution 42. In a preferred embodiment, the solid / liquid separation step includes a thickening step. The thickener underflow is directed to a filtration step. The filtrate is mixed with the overflow, and the recovered solid 40 is disposed of.

[0079] The purified solution 42 is transferred to a lithium recovery step 44. In Figure 1 the illustrated embodiment, the lithium recovery step 44 includes the crystallization of lithium carbonate. To crystallize lithium carbonate, the purified solution 42 is heated to between 80 - 85 °C. Then the purified solution 42 is contacted with sodium carbonate 46 to precipitate lithium carbonate.

[0080] In a preferred embodiment of the present invention, the dosage of sodium carbonate 46 is based on the concentration of Li+ in the purified solution 42. In one embodiment, sodium carbonate 46 is added to the solution to achieve a target stoichiometric relationship between Li + and Na2CO3 of 1.25:1 - 1:1.25.

[0081] Then the resulting slurry is sent to a solid / liquid separation step to recover lithium carbonate 48. The recovered product is washed to reduce the entrapment of impurities (such as NaCl and KCl).

[0082] Then the washed product is sent to a purification step (not shown) to further reduce the entrapped impurities. In Figure 1 the illustrated embodiment, the washed product is redissolved. Then the lithium carbonate is recrystallized and the recovered solid is washed to produce high-purity lithium carbonate. It is contemplated that alternative purification means may also be used. In one embodiment, the lithium product can be subjected to a hot repulping wash step. The inventors understand that at temperatures above about 80 °C, the solid impurities will dissolve, leaving the solid lithium product.

[0083] Although Figure 1 the embodiment shown in

[0084] In Figure 2 involves the recovery of lithium carbonate as the lithium product, it is contemplated that other lithium products may also be recovered. In one embodiment, lithium carbonate is further processed to produce lithium hydroxide. In an alternative embodiment, lithium hydroxide is directly recovered from the purified solution 42. Figure 2 The embodiment shown in Figure 1 has many similarities with the embodiment shown in

[0085] The brine solution 12 is transferred to a concentration step 14 to increase the lithium concentration. In Figure 2In the illustrated embodiment, concentration step 14 includes a solar evaporation process in which the brine solution is directed to an evaporation pond or pan to reduce the water content. It is contemplated that other means known to those skilled in the art for concentrating brine solutions may also be used. As the brine solution is concentrated, many solids will precipitate out. The main precipitate is rock salt (NaCl).

[0086] Concentration step 14 continues until the desired lithium concentration is reached. The preferred lithium concentration and the method for measuring the lithium concentration are similar to those discussed above with respect to Figure 1 those discussed above.

[0087] The concentrated solution is recovered and filtered to remove any entrained solids 15.

[0088] The filtered brine solution 16 is directed to a preliminary impurity removal step 18 to precipitate a certain amount of magnesium in the brine solution. To precipitate magnesium, an alkaline substance 20 is added to the brine solution. In Figure 2 the illustrated preliminary impurity removal step 18, the brine solution is contacted with slaked lime Ca(OH)2 to precipitate a target amount of magnesium in the brine solution. Adding slaked lime causes magnesium hydroxide to precipitate along with some gypsum CaSO4·2H2O. If boron is present in the brine solution, adding lime will also cause boron to precipitate in the form of borate.

[0089] In one embodiment, 50 - 80% of the magnesium in the aqueous solution is precipitated. In one embodiment, 55 - 75% of the magnesium in the aqueous solution is precipitated. In one embodiment, 70% of the magnesium in the aqueous solution is precipitated.

[0090] In one embodiment, 63 - 83% of the boron in the aqueous solution is precipitated. In one embodiment, 68 - 78% of the boron in the aqueous solution is precipitated. In one embodiment, 73% of the boron in the aqueous solution is precipitated.

[0091] As discussed above with respect to Figure 1 the similar method of controlling magnesium also applies to Figure 2 18.

[0092] After adding slaked lime, the resulting slurry is transferred to a solid / liquid separation step to remove the solids and produce an intermediate solution 24. In a preferred embodiment, the solid / liquid separation step includes a thickening step. The thickener underflow is directed to a filtration step. The filtrate is mixed with the overflow, and the recovered solids are disposed of.

[0093] The intermediate stream is directed to a secondary concentration step 26 to increase the lithium concentration. In Figure 2In the illustrated embodiment, the secondary concentration step 26 includes a solar evaporation process in which the intermediate solution 24 is directed to an evaporation pond or pan to reduce the water content. It is contemplated that other means known to those skilled in the art for concentrating brine solutions may also be used. As the brine solution is concentrated, many solids will precipitate out. The main precipitants are rock salt (NaCl) and potassium chloride (KCl).

[0094] The concentration step continues to the target lithium concentration. In Figure 2 the illustrated embodiment, the target concentration of Li is increased to the range of 1.6% - 6%.

[0095] In Figure 2 the illustrated embodiment, the concentration step will increase the lithium concentration in the intermediate solution 24 to be higher than that of the embodiment discussed above with respect to Figure 1 The inventors have found that by increasing the lithium concentration in the intermediate stage, a higher purity lithium product can subsequently be recovered. The inventors have found that the increased concentration of the intermediate solution 24 will increase the ratio of lithium to other impurities in the intermediate solution 24. Without wishing to be bound by theory, it should be understood that impurities such as potassium and sodium have lower solubility limits than lithium, so they will reach saturation before lithium. Once the impurities reach saturation, further concentration of the intermediate solution 24 will only result in the precipitation of impurity solids. This will limit the concentration of such substances in the intermediate solution 24 while allowing the lithium concentration to increase further. Thus, the ratio of lithium to impurities in the solution is increased. The inventors have found that this increase in the lithium-to-impurity ratio can be utilized to reduce the impurities in the final lithium product recovered.

[0096] The concentrated solution is recovered and filtered to remove any entrained solids.

[0097] The filtered solution is directed to a primary precipitation step 32 where it is contacted with sodium hydroxide 34 to precipitate the remaining magnesium in the solution as Mg(OH)2. The addition of sodium hydroxide 34 is based on the concentration of magnesium in the solution. The amount of sodium hydroxide 34 added should target a stoichiometric relationship between Mg 2+ and NaOH of 1.25:1 - 1:1.25. It is contemplated that titration analysis can be used to monitor the magnesium in the intermediate solution 24. In a preferred embodiment, an on-line titrator unit is used to monitor and control the magnesium concentration after the addition of sodium hydroxide 34.

[0098] As those skilled in the art will understand, adding NaOH will cause the pH of the solution to increase. The inventors have found that the increased pH will result in lithium loss. By restricting the addition of NaOH, the pH is also restricted. In one embodiment, the pH of the solution in the primary precipitation step 32 is maintained below 10. In one embodiment, the pH of the solution in the primary precipitation step 32 is maintained below 9.5. In one embodiment, the pH of the solution in the primary precipitation step 32 is maintained below 9.

[0099] Once the pH has stabilized, the secondary precipitation step 36 is carried out. In the secondary precipitation step 36, the solution is contacted with sodium carbonate 38 to precipitate calcium carbonate. The sodium carbonate 38 is incorporated based on the concentration of Ca 2+ in the solution. The amount of sodium carbonate 38 added is targeted at a 1:1 stoichiometric relationship between Ca 2+ and NaCO3. It is contemplated that titrimetric analysis is used to monitor the calcium in the intermediate solution 24. In a preferred embodiment, an on-line titrator unit is used to monitor and control the calcium concentration after adding sodium hydroxide 34.

[0100] In one embodiment, the pH of the solution is maintained below 10. In one embodiment, the pH of the solution is maintained below 9.5. The inventors have found that lithium carbonate precipitation is related to the pH of the solution. It can be understood that by maintaining the pH of the solution below 10, the precipitation of lithium carbonate can be restricted.

[0101] After the secondary precipitation step 36, the resulting slurry is transferred to a solid / liquid separation step to remove the resulting solid stream 40 and obtain a purified solution 42. In a preferred embodiment, the solid / liquid separation step includes a thickening step. The thickener underflow is directed to a filtration step. The filtrate is mixed with the overflow and the recovered solids are disposed of.

[0102] The purified solution 42 is sent to a dilution step, in which it is contacted with purified water to reduce the lithium concentration. As previously mentioned, the inventors have found that the lithium concentration in the purified solution should be maintained above 1.1 wt% in order to recover high-purity lithium products from the solution. In Figure 2 the illustrated embodiment, the intermediate solution 24 is concentrated to increase the lithium concentration. This results in a purified solution 42 having a lithium concentration far above the required minimum value. The dilution step will reduce the lithium concentration as well as the concentration of any residual impurities in the solution. By controlling the amount of water added in the dilution step, the concentration of these impurities can be reduced as much as possible while ensuring that the lithium concentration is above 1.1 wt%. The low impurity concentration will improve the purity of the subsequently recovered lithium product.

[0103] After the dilution step, the purified solution 42 is transferred to a lithium recovery step 44. In Figure 2In the illustrated embodiment, the lithium recovery step 44 includes the crystallization of lithium carbonate. To crystallize lithium carbonate, the purified solution 42 is heated to between 80 - 85 °C. Then the purified solution 42 is contacted with sodium carbonate 46 to precipitate lithium carbonate.

[0104] In a preferred embodiment of the present invention, the dosage of sodium carbonate 46 is based on the concentration of Li+ in the purified solution 42. In one embodiment, sodium carbonate 38 is added to the solution to achieve the goal of an approximate 1:1 stoichiometric relationship between Li+ and Na2CO3.

[0105] The resulting slurry is then sent to a solid / liquid separation step to recover lithium carbonate 48. The recovered product is washed to reduce the occlusion of impurities (such as NaCl and KCl).

[0106] Example 1

[0107] A series of tests were conducted to determine the effect of sulfate concentration on lithium recovery by evaporation ponds. To better understand the precipitation of KLiSO4 during evaporation, it is first necessary to understand the (apparent) relationship between sulfate concentration and the onset of KLiSO4 precipitation.

[0108] This was done by conducting two (2) evaporation curve tests using real brine that had been evaporated to a concentration of 0.8 wt% Li. The tests were conducted in parallel on a small scale (∼100 mL). In one test, the feed was slightly diluted (<15%, "untreated"), while in the other test, a small aliquot of concentrated CaCl2 solution (78 g / L Ca) was added to reduce the sulfate by approximately 60% ("sulfate reduction"). Then the two brines were evaporated at approximately 20 °C under atmospheric conditions for over 8 days. The concentration profiles of lithium and sulfate are shown respectively in Figure 3 and Figure 4 as shown.

[0109] Figure 3 The data in shows a significant difference in the lithium concentration profiles of the two evaporation tests. For the sulfate-reduced brine, no significant change in the Li:Mg ratio was observed, and it was determined by elemental analysis of the precipitated solids that the brine could be evaporated to the target of 1.2 wt% Li without KLiSO4 precipitation. For the untreated brine, KLiSO4 precipitation occurred from the very beginning of the evaporation process, as indicated by the early difference in the lithium concentration profile. In this test, a final lithium concentration of only 1.0 wt% was achieved, indicating that approximately 20% of the lithium had precipitated during evaporation.

[0110] Figure 4The data in [[ ]] show that the precipitation of lithium from untreated brine is accompanied by the precipitation of sulfate. Throughout the evaporation curve, the molar ratio of precipitated Li:SO4 is approximately 1:1, which is consistent with the precipitation of KLiSO4. In contrast, no sulfate precipitates from sulfate-reduced brines, as shown by the constant SO4:Mg ratio maintained during evaporation.

[0111] Additional evaporation tests were conducted with generic brines to better determine the effect of sulfate concentration. These evaporation tests were carried out under reduced pressure in a rotary evaporator at 25 °C (the temperature used during the BV evaporation tests) for several hours. The evaporation of untreated brine was compared with the evaporation of brines from which 30, 40, and 50% of their sulfate had been removed by adding concentrated CaCl2 solution. The concentration paths of Li and SO4 are shown respectively in Figure 5 and Figure 6 .

[0112] Figure 5 The data in [[ ]] show that each sulfate-reduced generic brine was able to evaporate to the target of ~1.2 wt% Li without lithium precipitation. In contrast, it was observed that untreated brine lost approximately 28% of its lithium when evaporated to 1.1 wt% Li.

[0113] For generic brines, only the brine from which approximately 30% of the sulfate had been removed before evaporation showed any further reduction in sulfate during evaporation ( Figure 6 ). Since this was not due to KLiSO4, it was suggested that this was due to the precipitation of K2SO4. The (relatively) accelerated evaporation rate used in these tests may have an impact on the competitive precipitation of KLiSO4 and K2SO4.

[0114] Example 2

[0115] To determine what effect temperature has on the precipitation of KLiSO4, a generic brine representative of a brine that had been evaporated to ~0.6 wt% Li before the precipitation of KLiSO4 was evaporated to a target value of ~1.1 wt% Li at 15, 25, and 35 °C.

[0116] These evaporation tests were carried out using a water bath controlled by a thermostat and a rotary evaporator under reduced pressure to strictly control the brine temperature. Evaporation was typically carried out for more than 20 hours or as required.

[0117] The concentration paths of Li and SO4 are presented respectively in Figure 7 and Figure 8 .

[0118] Figure 7The data in [[]] only shows a slight difference in the lithium concentration path between the three evaporation temperatures. However, the data does show that for a given Mg wt% (evaporation level), a higher concentration of lithium can be maintained at a lower temperature. Figure 8 The sulfate concentration paths shown also reflect a similar trend.

[0119] For each temperature at which lithium precipitation was determined, the molar ratio of precipitated lithium to sulfate was 1:1 Li:SO4, consistent with the precipitation of KLiSO4. These results suggest that KLiSO4 has a lower solubility at higher temperatures and thus is more likely to precipitate as the evaporation temperature increases.

[0120] Example 3

[0121] A series of tests were conducted to characterize the performance of magnesium, calcium, boron, and sulfate during the addition of 0.7 wt% Li with lime.

[0122] Figure 9 The data in [[]] shows the percentage removal of magnesium, boron, and sulfate versus the stoichiometry of lime addition calculated relative to Mg and B. In this case, the lime stoichiometry was calculated based on the titration alkalinity of the lime (which was only 22 mmol / g, i.e., 83% of the expected alkalinity of pure Ca(OH)2).

[0123] The first feature to note about this data is that in order to achieve nearly complete removal of magnesium (>99%), this requires an excess of lime (130 - 150%). This suggests that the utility of the added lime is relatively low, likely due to the passivation of the lime particle surface by gypsum. It is reasonable to expect improved utility in continuous operation.

[0124] The second feature to note about this data is that the removal of boron is maximized at approximately 85% stoichiometric addition of lime (which translates to approximately 70 - 80% removal of magnesium). As the lime addition increases, at the maximum lime addition studied, the removal of boron actually decreases from 85% to approximately 65%, and even 40%.

[0125] To further understand the changes in brine chemistry during lime addition, a graph was plotted for the test with 151% lime stoichiometry (relative to Mg&B), plotting the concentrations of the major elements against pH in [[]] Figure 10 for [[]].

[0126] For boron, the concentration profile is unusual, showing a "U-shaped" curve centered at pH 8.5. Boron initially decreases between pH 7.0 - 8.5 and then increases above pH 8.5. This behavior indicates that as more lime is added, the initially precipitated boron species react with the lime. This behavior also explains the data at pH 9.5, which is the result of returning the solids removed using the withdrawn sub-sample to the reaction tank. This causes a sharp drop in pH, resulting in a sharp drop in boron concentration. To restore the pH of the reaction to pH 9.5, additional lime is required, thus increasing the calcium concentration in the solution.

[0127] Thus, the result of pursuing very high (>99%) magnesium removal using lime is threefold. First, boron removal decreases as the continuous reaction of the precipitated borate solids and lime dissolves boron at pH > 8.5. Second, this reaction consumes lime without promoting impurity removal, thus effectively reducing the utility of lime. Third, this reaction releases calcium into the brine in excess of the amount required to remove only magnesium, which effectively increases the divalent ion concentration (i.e., Ca and Mg) of the brine, as shown in ( Figure 11 ). This increased divalent loading will result in higher reagent consumption and higher solid production in softening, which has an adverse effect on process efficiency.

[0128] Example 4

[0129] The effect of pH on magnesium removal was studied. Figure 12 The data in show the relationship between the removal of magnesium and boron and the pH observed when adding lime, but only for the pH range of 7.5 - 10. The data show that to achieve almost complete magnesium rejection (>99%), a pH of approximately 10 is required. However, boron removal drops to only ~40%. The lack of data distribution in this high pH region indicates a strong relationship.

[0130] Conversely, in the lower pH range of 8.0 - 8.5, the correlation between magnesium and boron removal (at a given pH) is particularly poor. For example, at pH 8.5, boron removal is approximately 80%, and magnesium removal varies between 20 - 80%. Although the reproducibility of the degree of magnesium removal was observed to be relatively consistent for a single brine feed, these data indicate that changes in brine composition have a profound effect. In addition, this indicates that caution must be exercised when relying on pH to control the performance of the lime application stage.

[0131] Lime stoichiometry (mass / volume flow ratio) was shown to be a more reliable control strategy for this step. However, as a practical guide, a general operating range between pH 8.2 - 8.8 is recommended to achieve optimal boron removal levels (~75 - 85%) and minimize the divalent ion concentration reported to Softening.

[0132] Example 5

[0133] A total of eight (8) softening tests were conducted using a combination of sodium hydroxide and sodium carbonate to remove calcium and magnesium prior to lithium carbonate precipitation. Particular attention was paid to determining what level of magnesium removal in lime application would result in optimal performance in softening, especially in terms of lithium loss.

[0134] In each test, sodium hydroxide was first added to remove magnesium at approximately pH 10, and then sodium carbonate was added to the resulting slurry relative to the concentration of (soluble) calcium. The results of these tests are summarized in Table 1.

[0135] Table 1: Summary of Softening Test Work - Sodium Hydroxide and Sodium Carbonate

[0136]

[0137] a Run 10: Li removal from the feed was underestimated by the K link; calculated from the mass balance of the wash liquor and filter cake

[0138] For Runs 8, 9, and 10, lime application was carried out at 0.7 wt% Li, targeting high (∼26 g / L), medium (∼17 g / L), and low (∼0.7 g / L) residual calcium concentrations, respectively. For Runs 11 and 12, brine lime application was carried out at 1.0 wt% Li, targeting high (∼13 g / L) and low (∼4 g / L) residual calcium concentrations, respectively. Finally, Runs 13A - C were carried out based on the results of Runs 8 - 12 to attempt to optimize the softening conditions using the preferred lime application conditions.

[0139] In each of the tests for Runs 8, 9, 10, and 12, a significant amount of lithium precipitation (8 - 14%) was observed, but the loss of lithium after washing was typically ∼3%. Surprisingly, the degree of lithium precipitation during softening does not seem to be related to the expected calcium concentration in the feed liquor. No obvious problems with the experimental execution were noted in these tests.

[0140] What was unusual about Run 11 was that it did not result in lithium precipitation from the solution. Run 11 had two unique features that may have contributed to the unusually low lithium precipitation. First, the lithium concentration in the softened feed was significantly lower than that of every other run (∼6 g / L Li), and second, the pH of the final reaction was slightly lower than that of the other runs (at least ∼0.3 pH units). The low reaction pH was due to the low NaOH stoichiometry required to achieve the pH 10 target for magnesium precipitation.

[0141] The exact reason for no lithium loss during Run 11 remains unclear. However, it is suspected that the reduced lithium concentration is the most likely cause. Since the precipitation of LC is actually a reactive crystallization process, it is suspected that the reduced concentration results in a slower crystallization rate of LC than higher concentrations (i.e., > 10 g / L Li) in other runs.

[0142] The importance of crystallization conditions has been noted during previous LC precipitation test work, and it seems reasonable to expect that a similar effect might be at play here, although the step was for calcium precipitation.

[0143] The lime application conditions selected for Run 13A - C were essentially the same as those used for Run 9; i.e., lime was applied at 0.7 wt% Li, targeting about 65% magnesium removal. Lime was applied at 0.7 wt% Li because better lime reactivity was obtained with lower concentration brines, and both the post - evaporation lime application and softening result in a certain degree of dilution, which in turn reduces the stage efficiency and reliance on LC barren, thus limiting lithium loss.

[0144] The lime application was set to target about 65% magnesium removal to achieve the best lime utility regarding magnesium and boron removal. Targeting more or less magnesium removal increases the divalent load in the softening stage and reduces boron removal.

[0145] After lime application, the brine was evaporated to ∼1.1 wt% Li. During softening, the amount of caustic soda added was slightly reduced compared to previous tests, and the stoichiometric amount (105%) relative to the magnesium present was added, rather than adding to achieve a target pH of 10. A similar sodium carbonate addition was used compared to previous tests.

[0146] In Run 13A, the reaction was carried out at 40 °C, while in Run 13B, the reaction was carried out at 20 °C. No difference in reaction performance was observed with temperature, and both tests effectively resulted in no lithium precipitation. The final reaction pH for these tests was also relatively low; pH 9.4 (Run 13A) and pH 9.9 (Run 13B). Despite the low pH, very high magnesium removal (<23 mg / L) was still achieved in these tests. In Run 13C, the reaction temperature was also 20 °C, but the reagent addition was changed, so that sodium carbonate was added first, then NaOH. This resulted in 5% lithium precipitation and a higher reaction pH of 10.7.

[0147] Example 6

[0148] The precipitation of lithium carbonate (LC) was carried out using the resulting liquid from the combined caustic soda / sodium carbonate divalent removal test, in which high levels of magnesium and calcium were obtained. These are the liquids from Runs 8 - 12 and 13B described in Example 5. A summary of the composition of the resulting LC is given in Table 2.

[0149] Table 2: Summary of LC precipitation test work

[0150]

[0151] For Runs 8 - 12 and 13B, the LC purity for all tests reached >99%. Run 11 obtained the best result with a purity of 99.5% and extremely low levels of potassium, sodium, and chloride impurities. Run 11 had 1.0 wt% Li plus lime, with dilution introduced by lime application and then more dilution introduced by softening, resulting in a very low lithium concentration (∼6 g / L) in the LC precipitation feed. This may have led to slower and more uniform crystal growth, thereby reducing the entrapment of NaCl and KCl by the LC. This result highlights the high degree of NaCl and KCl rejection that can be achieved in LC precipitation under favorable crystallization conditions.

[0152] Due to the very low lithium concentration (∼6 g / L) in the feed to the LC precipitation, Run 11 also resulted in the lowest lithium recovery (61%) for the LC. In contrast, if lime application was carried out at 0.7 wt% Li and then evaporated to >1.1 wt% Li, a higher lithium concentration (∼9 - 14 g / L) was present in the feed to the LC precipitation, and a higher lithium recovery (72–86%) was obtained. This result highlights another drawback of lime application at the end of evaporation, namely that the additional dilution introduced by lime application significantly reduces the recovery of LC.

[0153] The worst LC purities of 99.0% and 99.1% were produced by Runs 8 and 9, mainly due to higher NaCl contents. Compared to the other runs (pH 9.9–10.6), the feed solutions for these tests had a higher pH (11.3), which may have led to more rapid LC crystallization, irregular crystal growth, and more NaCl entrapment.

[0154] Sodium, potassium, and chloride are the major impurities in each LC sample, as expected from the precipitation of LC from the mixed Na / K chloride brine feed. Generally, there is a good correlation between the amount of chloride impurity present in the LC and the amount of sodium and potassium impurities present, indicating that these impurities do indeed arise from the occlusion of NaCl and KCl in the LC crystals. Importantly, the occluded salts are not easily "washed out" of the LC. Note that LC crystallization is known to be improved under continuous process operation, which has conditions not easily replicated in laboratory-scale, batch test work, such as seed cycling, extended operation times, optimized reactor design, etc.

[0155] Although each feed contains relatively low concentrations of calcium and magnesium, calcium and magnesium appear as major impurities in each LC produced because the associated carbonates are highly insoluble and they report to the resulting LC. Based on the results of impurity removal and softening test work, improving the rejection of calcium and magnesium from the resulting LC requires treatment by ion exchange (IX) prior to LC precipitation.

[0156] The behavior of boron in the resulting LC is somewhat variable and does not appear to be related to the composition of the various feeds. Nevertheless, most of the boron does not report to the resulting LC as observed in previous process development procedures.

[0157] The presence of sulfate impurity in the LC has not previously been a concern in the process development work carried out to date. Lime addition is usually sufficient to produce very low sulfate concentrations in the brine. However, in Run 10, low lime addition was used for impurity removal and the increased sulfate concentration was carried through to the LC precipitation, which resulted in elevated sulfate impurity in the LC, i.e., 118 ppm S compared to <25 ppm S, where much higher sulfate removal was achieved with lime application (e.g., Runs 8 and 13B).

[0158] Example 7

[0159] Softening tests were repeated on solutions with lithium concentrations increased to 1.7 wt% Li and 2.1 wt% Li after the lime application stage. Similar to Example 5, these tests were carried out using a combination of caustic soda and sodium carbonate to remove calcium and magnesium prior to lithium carbonate precipitation.

[0160] In each test, caustic soda was first added to effect magnesium removal at approximately pH 10, and then sodium carbonate was added to the resulting slurry relative to the concentration of (soluble) calcium. The results of these tests are summarized in Tables 3 and 4 for 1.7 wt% and 2.1%, respectively:

[0161] Table 3: Softening Tests for 1.7 wt% Li Solution

[0162]

[0163] Table 4: Softening test for 2.1 wt% Li solution

[0164]

[0165] For the 1.7 wt% solution, the Li:K ratio increased from 0.99 to 1.63. For the 2.1 wt% solution, the Li:K ratio increased from 1.41 to 2.13. This indicates that increasing the lithium concentration in the secondary concentration step can be used to increase the lithium-to-potassium ratio in the purified solution.

[0166] Those skilled in the art will understand that changes and improvements to the invention described herein will be apparent without departing from its spirit and scope. Changes and improvements that are apparent to those skilled in the art are considered to fall within the broad scope and ambit of the invention as described herein.

Claims

1. A method for recovering lithium products from an aqueous solution, the method comprising the following steps: i. contacting the solution with an alkaline substance comprising calcium hydroxide to precipitate 50 - 80% of magnesium in the brine solution and separating the precipitated solid from the intermediate solution; wherein the pH of the aqueous solution is maintained at 9 or lower during step (i); ii. Contact the intermediate solution with a controlled amount of sodium hydroxide to precipitate magnesium in the intermediate solution, wherein the amount of sodium hydroxide added is targeted at a stoichiometric concentration of 1.25:1 - 1:1.25 of Mg 2+ :OH - and the solution pH is maintained below 10 during step (ii); iii. contacting the intermediate solution with a controlled amount of sodium carbonate to precipitate divalent cations and separating the precipitated solid from the purified solution; and iv. recovering the lithium products from the purified solution.

2. The method according to claim 1, wherein the aqueous solution is subjected to a concentration step before step (i).

3. The method according to claim 2, wherein the concentration step increases the concentration of lithium in the aqueous solution to 0.1 - 1.2%.

4. The method according to any one of the preceding claims, wherein step (i) precipitates 63 - 83% of boron in the aqueous solution.

5. The method according to claim 1, wherein the intermediate solution is directed to a secondary concentration step before step (ii).

6. The method according to claim 5, wherein the secondary concentration step increases the concentration of lithium in the aqueous solution to at least 1.2%.

7. The method according to claim 6, wherein the secondary concentration step increases the lithium concentration in the aqueous solution to between 1.2% - 2.2%.

8. The method according to claim 5, wherein the secondary concentration step increases the concentration of lithium in the aqueous solution to at least 1.6%.

9. The method according to claim 1, wherein the amount of sodium carbonate added in step (iii) is targeted at a stoichiometric concentration of Ca 2+ :Na2CO3 of 1.25:1 - 1:1.

25.

10. The method according to claim 8, wherein the method further comprises a dilution step of the purified solution before the step of recovering the lithium products from the purified solution.

11. The method according to claim 1, wherein lithium carbonate is recovered from the purified solution.

12. The method according to claim 11, wherein sodium carbonate is added to the purified solution to precipitate lithium carbonate.

13. The method according to claim 12, wherein the amount of sodium carbonate added to the purification solution is targeted at a stoichiometric concentration of Li 2+ :Na2CO3 of 1.25:1 - 1:1.

25.

14. The method according to claim 1, wherein lithium hydroxide is recovered from the purified solution.

15. The method according to claim 1, wherein the recovered lithium products are subjected to a purification step.

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