Lithium extraction process and systems

Abstract

Embodiments provides a process of extracting lithium from spodumene. The process comprises providing a lithium sulfate solution (12) formed from leaching spodumene with sulfuric acid, and adding calcium chloride to the lithium sulfate solution to form a lithium chloride solution and to precipitate gypsum, for example in a conversion unit (14). The lithium chloride solution may then be subject to a sorbent process to selectively adsorb lithium ions to a sorbent, for example in a sorbent unit (16), and form a lithium-depleted solution (20). The process also includes desorbing the lithium ions from the sorbent to produce a lithium-rich solution (24).

Description

[0001] Lithium Extraction Process and Systems

[0002] Technical Field

[0003] The present disclosure relates to extraction of lithium, such as from brines and hard rock leachate solutions.

[0004] Background

[0005] The global demand for lithium has increased dramatically in recent years, driven by the rapid growth of electric vehicles and renewable energy storage systems. This surge in demand has put significant pressure on existing lithium production methods. These traditional extraction techniques not only have substantial environmental impacts but also face challenges in meeting the growing global lithium demand efficiently and sustainably.

[0006] Conventional lithium extraction methods from hard rock sources, such as spodumene, typically involve energy-intensive processes including high-temperature calcination, acid leaching, and multiple purification steps. These processes often require large quantities of water and chemicals, leading to significant waste generation and potential environmental contamination. Additionally, the recovery rates of lithium from these traditional methods can be relatively low, resulting in inefficient use of valuable lithium resources.

[0007] For brine-based lithium sources, the predominant extraction method involves pumping lithium- rich brine into large evaporation ponds, where it is left for months to selectively concentrate the lithium content. This approach is not only time-consuming and water intensive but also highly dependent on climatic conditions and requires extensive land use. Furthermore, the evaporation process can lead to the loss of water resources in often water-scarce regions, raising concerns about the long-term sustainability of such operations.

[0008] Despite ongoing research and development efforts, significant challenges remain in developing and implementing more sustainable lithium extraction technologies at a commercial scale. These include difficulties in achieving high selectivity for lithium over other ions present in the source material, maintaining process efficiency across varying feed compositions, and managing the costs associated with new extraction technologies.

[0009] Summary

[0010] In an embodiment, a process of extracting lithium from a lithium-containing brine formed from lithium extraction from spodumene is provided. The process includes providing a lithium sulfate solution formed from leaching spodumene with sulfuric acid. Calcium chloride is added to the lithium sulfate solution to form a lithium chloride solution and to precipitate gypsum. The lithium chloride solution is subjected to a sorbent process to selectively adsorb lithium ions to a sorbent and form a lithium-depleted solution. The lithium ions are desorbed from the sorbent to produce a lithium-rich solution.

[0011] The process may further comprise subjecting the lithium-depleted solution to nanofiltration to remove at least some multivalent ions to form a purified lithium-depleted solution and recycling at least a portion of the purified lithium-depleted solution back to the sorption process to increase recovery of the lithium-rich solution. The multivalent ions removed using nanofiltration may include Ca2+, Mg2+and Al3+. Nanofiltration may be performed at a pressure ranging from 5 bar to 20 bar and may have a lithium recovery rate of at least 90%.

[0012] Nanofiltration may include subjecting the lithium-depleted solution to an ion exchange resin to adsorb multivalent ions. The ion exchange resin may comprise a sulfonate, iminodiacetate, or aminomethylphosphonic acid functionalized polystyrene / divinylbenzene resin. The lithium- depleted solution may be subjected to reverse osmosis prior to recycling back to the sorption process. Reverse osmosis may be performed before at least a portion of the lithium-depleted solution is subjected to nanofiltration.

[0013] The increase in TDS using reverse osmosis may improve the lithium sorbent capacity. Reverse osmosis may be performed at a pressure ranging from 20 to 120 bar. A concentration of the purified lithium-depleted solution may be less than a concentration of the lithium sulfate solution formed from leaching spodumene with sulfuric acid.

[0014] The process may further comprise polishing the lithium sulfate solution with a calcium source before adding calcium chloride to precipitate non-lithium species. Polishing may be performed at a temperature ranging from 20°C to 80°C.

[0015] The sorbent may be an aluminium-based layered double hydroxide (LDH) sorbent. The LDH sorbent may have a lithium adsorption capacity of 1 to 10 mg Li per gram of sorbent. The LDH sorbent may be regenerated after desorption for reuse in subsequent cycles. The desorption of lithium ions from the sorbent may be performed using a dilute warm lithium chloride solution. The lithium chloride solution used for desorption may have a concentration of 100 to 350 ppm.

[0016] The sorbent may be a lithium manganese oxide (LMO) or lithium titanium oxide (LTO) sorbent. The LMO / LTO sorbent may have a lithium adsorption capacity of 1 to 20 mg Li per gram of sorbent. The LMO / LTO sorbent may be regenerated with an acidic solution. The desorption of lithium ions from the sorbent may be performed using an acidic solution.

[0017] The process may further comprise subjecting the lithium-rich solution to reverse osmosis to increase the total dissolved solids (TDS) concentration. The purified lithium solution may be converted into separate solutions of lithium hydroxide and hydrochloric acid using bipolar membrane electrodialysis. The bipolar membrane electrodialysis process may produce lithium hydroxide with a purity of at least 95%.

[0018] The lithium sulfate solution may have a lithium concentration ranging from 8,000 ppm to 20,000 ppm. The gypsum formed from the addition of calcium chloride may be removed from the lithium chloride solution before the lithium chloride solution is subjected to the sorbent process. The removal of gypsum may be performed using filtration or centrifugation.

[0019] The process may further include reductive roasting of the gypsum formed from addition of calcium chloride to form calcium oxide and sulfur dioxide. The sulfur dioxide may be converted to sulfur trioxide and then subsequently converted to sulfuric acid for reuse in leaching spodumene to form the lithium sulfate solution. The calcium oxide formed may be recycled for neutralisation of the sulfuric acid leachate. The sulfuric acid formed may be recycled for the sulfuric acid leaching of beta-spodumene.

[0020] The process may further include performing electrolysis on a solution containing the precipitated gypsum to produce calcium hydroxide and sulfuric acid. The calcium hydroxide formed may be recycled for neutralisation of the sulfuric acid leachate.

[0021] In another embodiment, a system for extracting lithium from a lithium-containing brine formed from lithium extraction from spodumene is provided. The system includes a source of lithium sulfate solution formed from leaching spodumene with sulfuric acid. A conversion unit is in fluid communication with the source of lithium sulfate solution and configured to add calcium chloride to the lithium sulfate solution to form a lithium chloride solution and precipitate gypsum. A sorbent unit is in fluid communication with the lithium chloride solution and configured to (i) subject the lithium chloride solution to a sorbent process to selectively adsorb lithium ions to a sorbent thereby forming a lithium depleted solution and (ii) to desorb the lithium ions from the sorbent to produce a lithium-rich solution.

[0022] The system may further comprise a nanofiltration unit in fluid communication with the lithium- depleted solution and the sorbent unit, the nanofiltration unit being configured to subject the lithium-depleted solution to nanofiltration to remove at least some multivalent ions to produce a purified lithium-depleted solution. The nanofiltration unit may include ion exchange resin configured to adsorb multivalent ions. The ion exchange resin may comprise a sulfonate, iminodiacetate, or aminomethylphosphonic acid functionalized polystyrene / divinylbenzene resin.

[0023] The sorbent unit and nanofiltration unit may be arranged such that at least a portion of the lithium-depleted solution can be recycled back to the sorbent unit to increase recovery of the lithium-rich solution. The system may further include a reverse osmosis unit configured to receive the lithium-depleted solution. The reverse osmosis unit may be positioned upstream of the nanofiltration unit such that the nanofiltration unit can receive lithium-depleted solution from the reverse osmosis unit prior to forming the purified lithium-depleted solution.

[0024] The system may further comprise a polishing unit positioned upstream of the conversion unit, the polishing unit having a calcium source and being configured to polish the lithium sulfate solution with the calcium source to neutralise and / or precipitate non-lithium species from the lithium sulfate solution before adding calcium chloride to further precipitate calcium sulphate.

[0025] The sorbent unit may comprise an aluminium-based layered double hydroxide (LDH) sorbent, a lithium manganese oxide (LMO) sorbent, or a lithium titanium oxide (LTO) sorbent. The sorbent unit may be configured to use a lithium chloride solution or an acidic solution for desorbing the lithium ions from the sorbent.

[0026] The system may further include an electrodialysis unit downstream of the sorbent unit, the electrodialysis unit comprising a bipolar membrane electrodialysis and configured to convert the purified lithium solution into separate solutions of lithium hydroxide and hydrochloric acid using the bipolar membrane electrodialysis.

[0027] The conversion unit may include a gypsum removal unit configured to remove the gypsum formed from the addition of calcium chloride from the lithium chloride solution before the lithium chloride solution is subjected to the sorbent process.

[0028] The system may further include a roasting unit configured to receive and perform reductive roasting of the gypsum formed from addition of calcium chloride to form lime and sulfur dioxide. The system may further include an electrolysis unit configured to receive and perform an electrolysis process on a solution containing the precipitated gypsum to produce calcium hydroxide and sulfuric acid. Brief Description of the Drawings

[0029] Embodiments will now be described, by way of example only, with reference to the accompanying non-limiting drawings, in which:

[0030] Figure 1 is a schematic diagram of a system for processing lithium-containing solutions, according to an embodiment of the present disclosure.

[0031] Figure 2 is a schematic diagram of a system for extracting lithium from a lithium-containing brine, according to embodiments of the present disclosure.

[0032] Figure 3 is a schematic diagram of a system for processing lithium-containing materials, in accordance with example embodiments.

[0033] Figure 3a is a schematic diagram showing an embodiment of an arrangement of the nanofiltration unit and reverse osmosis unit.

[0034] Figure 3B is a schematic diagram showing another embodiment of an arrangement of the nanofiltration unit and reverse osmosis unit.

[0035] Figure 4 show a plot showing the sulfate and calcium concentrations following addition of calcium chloride.

[0036] Figure 5 shows plots showing the impact of nanofiltration performance (a) individual pass Ca rejection and (b) Li recovery on overall Li recovery of process.

[0037] Figure 6 shows a plot showing the relationship between the lithium recovery and the RO TDS. Figure 7 shows a plot showing the feed lithium concentration, sorbent capacity, relative sorbent capacity (sorbent capacity I lithium concentration) and single pass lithium recovery as the TDS of the reject brine RO changes.

[0038] Figure 8 shows a plot showing lithium adsorption capacity versus magnesium chloride concentration.

[0039] Figure 9A-D shows schematics showing how different bleed ratios to the nanofiltration unit can be used to adjust TDS downwards.

[0040] Detailed Description

[0041] The present disclosure relates to a system and process for extracting and purifying lithium from a lithium-containing brine, such as a lithium sulfate solution formed from leaching - spodumene (following high temperature roasting of a-spodumene) with sulfuric acid. The system and process utilises a direct lithium extraction (DLE) sorbent technique to selectively adsorb lithium ions from the lithium-containing solution thereby forming a lithium depleted solution, and to subsequently desorb the lithium ions to produce a lithium-rich solution.

[0042] In some embodiments, the process may also subject the lithium-depleted solution following the sorbent process to nanofiltration to selectively remove at least some multivalent ions and produce a purified lithium-depleted solution. At least a portion of this purified lithium-depleted solution can be recycled back into the sorbent process to increase overall lithium recovery. This recycling approach may help to capture lithium that was not adsorbed in the initial pass through the sorbent, thereby improving the overall efficiency of the extraction process.

[0043] The system includes several components that work in sequence to process the lithium- containing solution. These components include a conversion unit for converting the lithium sulfate solution to form a lithium chloride solution, and a sorbent unit for subjecting the lithium chloride solution to a sorbent process. In some embodiments, the system may also include a nanofiltration unit to remove multivalent ions from the lithium-depleted solution, and optionally a reverse osmosis unit to increase the total dissolved solids (TDS) concentration of the solution prior to recycling.

[0044] With this approach, the sorbent can provide a lithium-rich stream, for example a high purity lithium stream, while the optional nanofiltration removes a portion of the multivalent ion impurities from the lithium-depleted solution. The removal of these multivalent ions prevents their build-up in the recycle loop and maintains stable operation, while the recycling of the purified lithium-depleted solution improves overall lithium recovery by providing additional opportunities for lithium extraction.

[0045] The system and process are designed to produce in one or more embodiments a high recovery of lithium from spodumene and a lithium-rich solution with specific properties, including a high lithium concentration and low concentration of impurities.

[0046] The term “lithium-rich solution” and variants such as lithium-rich stream may have a lithium purity of at least 90%, and in some cases at least 95%, 97%, 98%, 99%, or 99.9%. The lithium- rich solution may be characterized by significantly reduced concentrations of multivalent ions compared to the initial lithium-containing feed solution. In some embodiments, multivalent ions such as Ca2+, Mg2+, Al3+, Fe3+, and Mn2+may be reduced by at least 90%, and in some cases by at least 95% or 99%, relative to their concentrations in the lithium sulfate solution formed from leaching spodumene. The lithium-rich solution may have a lithium to calcium ratio of at least 100: 1 , and in some cases at least 300: 1 or 400: 1 . The purity of the lithium-rich stream is typically achieved through the selective adsorption properties of the sorbent, which preferentially adsorbs lithium ions while rejecting multivalent impurities during the desorption process.

[0047] In some embodiments, the system and process also provide the flexibility to use various types of sorbents, such as an aluminium-based layered double hydroxide (LDH) sorbent, a lithium manganese oxide (LMO) sorbent, or a lithium titanium oxide (LTO) sorbent.

[0048] The system may optionally include additional units for further processing and refining. These can include a reverse osmosis unit for increasing the total dissolved solids (TDS) concentration of solutions, an electrodialysis unit for converting the lithium-rich solution into separate solutions of lithium hydroxide and hydrochloric acid, and a roasting unit for performing reductive roasting of the gypsum formed from the addition of calcium chloride.

[0049] The system may optionally include an electrolysis unit to convert gypsum into calcium hydroxide and sulfuric acid. The calcium hydroxide can be recycled for the neutralisation of the spodumene acid leachate, and the sulfuric acid can be recycled for the acid leaching of p- spodumene.

[0050] One or more embodiments of the system and process described herein may provide a more efficient and sustainable approach to lithium extraction and purification, offering potential advantages in terms of reduced water and chemical usage, increased lithium recovery rates, and improved product quality.

[0051] Referring to Figure 1 , a system 10 for extracting and purifying lithium from a lithium-containing solution is shown. The system 10 includes a conversion unit 14, a sorbent unit 16, and optionally a nanofiltration unit 18. The system 10 is configured to process a lithium sulfate solution 12, which may be formed from leaching spodumene with sulfuric acid. However, in some cases, the lithium sulfate solution 12 may be formed from other sources and / or processes for example hard rock sources.

[0052] The concentration of the lithium sulfate solution 12 may vary depending on the specific source and processing conditions. In some embodiments, the lithium sulfate solution 12 may have a lithium concentration ranging from 1 ,000 ppm to 30,000 ppm. The lithium concentration may range from 5,000 ppm to 30,000 ppm. The lithium concentration may range from 5,000 ppm to 25,000 ppm. The lithium concentration may range from 5,000 ppm to 20,000 ppm. The lithium concentration may range from 10,000 ppm to 30,000 ppm. The lithium concentration may range from 10,000 ppm to 25,000 ppm. The lithium concentration may range from 8,000 ppm to 20,000 ppm.

[0053] The concentration of the lithium sulfate solution 12 may be influenced by factors such as the lithium content of the source material, the efficiency of the leaching process, and any preconcentration steps that may be employed. In some embodiments, the concentration may be adjusted prior to entering the conversion unit 14 to optimize the subsequent processing steps.

[0054] Higher concentrations of lithium in the lithium sulfate solution 12 may generally lead to improved efficiency in the downstream processes, potentially reducing energy consumption and increasing overall lithium recovery rates. For some aluminium-based layered double hydroxide sorbents, a sulfate concentration above a threshold value may hinder downstream processing due to sorbent degradation. Addition of calcium chloride will promote the precipitation of gypsum through the common ion effect thus reducing the brine sulfate concentration. In an embodiment, the threshold value is 800 ppm. For example, in an embodiment, addition of calcium chloride may reduce a concentration of sulfate to be up to 800 ppm.

[0055] The system 10 may include monitoring and control mechanisms to measure and adjust the concentration of the lithium sulfate solution 12 as needed. This may involve the use of inline sensors, sampling systems, or other analytical techniques to ensure that the concentration remains within desired ranges for optimal processing.

[0056] The conversion unit 14 is in fluid communication with the source of the lithium sulfate solution 12. The conversion unit 14 is configured to add a chloride source to the lithium sulfate solution 12 to form a lithium chloride solution and associated byproducts. The conversion unit 14 may include various components and subsystems to facilitate the conversion process, such as mixing devices, heaters, and separators.

[0057] The sorbent unit 16 is in fluid communication with the conversion unit 14 and is configured to subject the lithium chloride solution to a sorbent process. The sorbent process selectively adsorbs lithium ions to a sorbent during an adsorption phase, forming a lithium-depleted solution 20 that exits the sorbent unit 16. During a subsequent desorption phase, the lithium ions are desorbed from the sorbent to produce a lithium-rich solution which is shown as lithium chloride solution 24. The lithium-depleted solution 20 is formed when the lithium chloride solution passes through the sorbent material and the lithium ions are selectively adsorbed onto the sorbent. The lithium-depleted solution 20 contains reduced concentrations of lithium compared to the initial lithium chloride solution, along with other ions that were not adsorbed by the sorbent. The lithium-depleted solution 20 may be subjected to further processing, such as nanofiltration and reverse osmosis, before being recycled back to the sorbent unit 16 to increase overall lithium recovery. The lithium chloride solution 24 is produced during the desorption phase when a desorbing solution is used to release the adsorbed lithium ions from the sorbent. The lithium chloride solution 24 contains concentrated lithium ions with significantly reduced concentrations of impurities compared to the original input lithium chloride solution. The desorbing solution may be a dilute warm lithium chloride solution or an acidic solution, depending on the type of sorbent used.

[0058] The sorbent unit 16 may include one or more types of sorbents, such as an aluminium-based layered double hydroxide (LDH) sorbent, a lithium manganese oxide (LMO) sorbent, or a lithium titanium oxide (LTO) sorbent. Each of these sorbents may have different properties and characteristics, such as lithium adsorption capacity, selectivity, and regeneration capabilities. The sorbent unit 16 may comprise one or more columns or vessels containing a sorbent material for selectively adsorbing lithium ions from the lithium chloride solution. This may help to maximize operational efficiency.

[0059] In some embodiments, the sorbent unit 16 may utilize an aluminium-based layered double hydroxide (LDH) sorbent. The LDH sorbent may have a lithium adsorption capacity ranging from 0.5 to 15 mg Li per gram of sorbent. The LDH sorbent may have a lithium adsorption capacity ranging from 1.0 to 10 mg Li per gram of sorbent. In an embodiment, the capacity may be at least 0.5 mg Li per gram of sorbent. In other cases, the capacity may be up to 15 mg Li per gram of sorbent. The LDH sorbent may have a minimum lithium adsorption capacity of 0.5, 1 , 2, or 5 mg Li per gram of sorbent. In some implementations, the LDH sorbent may have a maximum lithium adsorption capacity of 10, 12, or 15 mg Li per gram of sorbent. The capacity may be selected from ranges such as 0.5-10 mg, 1-12 mg, or 2-15 mg Li per gram of sorbent. In certain embodiments, the lithium adsorption capacity may range from 0.5 to 12 mg, 1 to 10 mg, or 2 to 8 mg Li per gram of sorbent. The LDH sorbent may have a lithium adsorption capacity of 0.5-5 mg, 1-8 mg, 2-10 mg, 5-12 mg, or 8-15 mg Li per gram of sorbent.

[0060] This capacity may allow the LDH sorbent to selectively adsorb lithium ions from the lithium chloride solution, thereby facilitating the extraction of lithium. After the adsorption process, the LDH sorbent may be regenerated through a desorption process for reuse in subsequent cycles. This regeneration capability may contribute to the efficiency and sustainability of the lithium extraction process.

[0061] In other cases, the sorbent unit 16 may employ a lithium manganese oxide (LMO) or a lithium titanium oxide (LTO) sorbent.

[0062] The LMO or LTO sorbent may have a lithium adsorption capacity ranging from 1 to 20 mg Li per gram of sorbent. The capacity may be at least 0.5 mg Li per gram of sorbent. The capacity may be up to 25 mg Li per gram of sorbent. The LMO or LTO sorbent may have a minimum lithium adsorption capacity of 0.5 mg Li per gram of sorbent. The LMO or LTO sorbent may have a minimum lithium adsorption capacity of 1 mg Li per gram of sorbent. The LMO or LTO sorbent may have a minimum lithium adsorption capacity of 2 mg Li per gram of sorbent. The LMO or LTO sorbent may have a minimum lithium adsorption capacity of 5 mg Li per gram of sorbent. The LMO or LTO sorbent may have a maximum lithium adsorption capacity of 15 mg Li per gram of sorbent. The LMO or LTO sorbent may have a maximum lithium adsorption capacity of 20 mg Li per gram of sorbent. The LMO or LTO sorbent may have a maximum lithium adsorption capacity of 25 mg Li per gram of sorbent. The LMO or LTO sorbent may have a maximum lithium adsorption capacity of 30 mg Li per gram of sorbent. The capacity may be selected from a range of 1-10 mg Li per gram of sorbent. The capacity may be selected from a range of 5-15 mg Li per gram of sorbent. The capacity may be selected from a range of 10-20 mg Li per gram of sorbent. The capacity may be selected from a range of 1-15 mg Li per gram of sorbent. The capacity may be selected from a range of 5-20 mg Li per gram of sorbent. The capacity may be selected from a range of 2-25 mg Li per gram of sorbent. The capacity may be selected from a range of 0.5-30 mg Li per gram of sorbent.

[0063] Similar to the LDH sorbent, the LMO or LTO sorbent may selectively adsorb lithium ions from the lithium chloride solution, thereby facilitating the extraction of lithium. The LMO or LTO sorbent may also be regenerated after the desorption process for reuse in subsequent cycles. However, LMO or LTO sorbents are Li ion exchange materials which have a higher tolerance for sulfate and require acidic conditions for desorption.

[0064] The temperature for desorbing may be at least 40°C. The desorption temperature may range from 40°C to 80°C. The desorption temperature may range from 40°C to 75°C. The desorption temperature may range from 40°C to 70°C. The desorption temperature may range from 40°C to 65°C. The desorption temperature may range from 40°C to 60°C. The desorption temperature may range from 40°C to 55°C. The desorption temperature may range from 40°C to 50°C. The desorption temperature may range from 45°C to 80°C. The desorption temperature may range from 50°C to 80°C. The desorption temperature may range from 55°C to 80°C. The desorption temperature may range from 60°C to 80°C. The desorption temperature may range from 65°C to 80°C. The desorption temperature may range from 70°C to 80°C. The desorption temperature may range from 75°C to 80°C. The desorption temperature may be at least 45°C. The desorption temperature may be at least 50°C. The desorption temperature may be at least 55°C. The desorption temperature may be at least 60°C. The desorption temperature may be at least 65°C. The desorption temperature may be at least 70°C. The desorption temperature may be at least 75°C. The desorption temperature may be up to 80°C. The desorption temperature may be up to 75°C. The desorption temperature may be up to 70°C. The desorption temperature may be up to 65°C. The desorption temperature may be up to 60°C. The desorption temperature may be up to 55°C. The desorption temperature may be up to 50°C.

[0065] During the sorption process, the lithium chloride solution may flow through the sorbent unit 16 at a controlled rate to allow sufficient contact time between the solution and the sorbent material. The sorption process may be conducted at temperatures ranging from 20°C to 60°C. In some cases, the pH of the solution may be adjusted to optimize lithium adsorption, typically within a range of 6 to 8.

[0066] For desorption, the lithium-loaded sorbent may be treated with a desorbing solution to release the adsorbed lithium ions. This desorbing solution may initially contain an amount of lithium chloride to prevent sorbent degradation through extensive desorption processes. For example, when the LDH sorbent includes an aluminium hydroxide with lithium chloride intercalated, if the desorption of the sorbent is extensive, the structure collapses to gibbsite (which is a thermodynamically stable material with very little use as a sorbent). A low concentration of lithium chloride may be utilized to mitigate extensive desorption.

[0067] The desorbing solution may be a dilute warm lithium chloride solution with a concentration ranging from 100 to 350 ppm. The concentration of the lithium chloride solution may range from 100 to 300 ppm. The concentration of the lithium chloride solution may range from 100 to 250 ppm. The concentration of the lithium chloride solution may range from 100 to 200 ppm.

[0068] The concentration of the lithium chloride solution may range from 100 to 150 ppm. The concentration of the lithium chloride solution may range from 150 to 350 ppm. The concentration of the lithium chloride solution may range from 200 to 350 ppm. The concentration of the lithium chloride solution may range from 250 to 350 ppm. The concentration of the lithium chloride solution may range from 300 to 350 ppm. The concentration of the lithium chloride solution may be at least 100 ppm. The concentration of the lithium chloride solution may be at least 150 ppm. The concentration of the lithium chloride solution may be at least 200 ppm. The concentration of the lithium chloride solution may be at least 250 ppm. The concentration of the lithium chloride solution may be at least 300 ppm. The concentration of the lithium chloride solution may be up to 350 ppm. The concentration of the lithium chloride solution may be up to 300 ppm. The concentration of the lithium chloride solution may be up to 250 ppm. The concentration of the lithium chloride solution may be up to 200 ppm. The concentration of the lithium chloride solution may be up to 150 ppm. In an embodiment, the concentration of the lithium chloride solution may be 200 ppm. In an embodiment, the concentration of the lithium chloride solution may be 250 ppm. In an embodiment, the concentration of the lithium chloride solution may be 300 ppm.

[0069] Alternatively, an acidic solution may be used for desorption with the LTO / LMO ion exchange sorbents. Hydrochloric acid may be preferred for this process as the chloride ion is monovalent like the lithium ion. A concentration of hydrochloric acid may range from 0.05 to 0.5M. A concentration of hydrochloric acid may range from 0.25 M to 0.30 M.

[0070] The desorption process may be carried out at elevated temperatures to enhance the efficiency of lithium release. In an embodiment, desorption is performed by heating the sorbent to or above a desorption temperature. For example, some LDH sorbents can desorb once heated to about 95°C. The temperature for desorbing may be at least 40°C. The desorption temperature may range from 40°C to 80°C. The desorption temperature may range from 40°C to 75°C. The desorption temperature may range from 40°C to 70°C. The desorption temperature may range from 40°C to 65°C. The desorption temperature may range from 40°C to 60°C. The desorption temperature may range from 40°C to 55°C. The desorption temperature may range from 40°C to 50°C. The desorption temperature may range from 45°C to 80°C. The desorption temperature may range from 50°C to 80°C. The desorption temperature may range from 55°C to 80°C. The desorption temperature may range from 60°C to 80°C. The desorption temperature may range from 65°C to 80°C. The desorption temperature may range from 70°C to 80°C. The desorption temperature may range from 75°C to 80°C. The desorption temperature may be at least 45°C. The desorption temperature may be at least 50°C. The desorption temperature may be at least 55°C. The desorption temperature may be at least 60°C. The desorption temperature may be at least 65°C. The desorption temperature may be at least 70°C. The desorption temperature may be at least 75°C. The desorption temperature may be up to 80°C. The desorption temperature may be up to 75°C. The desorption temperature may be up to 70°C. The desorption temperature may be up to 65°C. The desorption temperature may be up to 60°C. The desorption temperature may be up to 55°C. The desorption temperature may be up to 50°C. The temperature may be adjusted based on factors such as the specific sorbent material used and the desired desorption rate.

[0071] The sorbent unit 16 may operate in a batch or continuous mode. In a continuous operation, multiple columns may be used in parallel, allowing for simultaneous sorption and desorption processes. The sorbent material may be regenerated after each desorption cycle for reuse in subsequent sorption cycles.

[0072] In some cases, the sorbent unit 16 may include additional components such as pumps, valves, and heat exchangers to control the flow rates, pressures, and temperatures of the solutions. Monitoring and control systems may be incorporated to optimize the sorption and desorption processes based on factors such as solution composition, flow rates, and sorbent capacity.

[0073] In system 10, a reverse osmosis unit may be positioned downstream of the conversion unit 14 and upstream of the sorbent unit 16 (not shown). This reverse osmosis unit may be configured to increase the total dissolved solids (TDS) concentration of the lithium chloride solution before it enters the sorbent unit 16.

[0074] The lithium chloride solution exiting the conversion unit 14 may be fed directly into the reverse osmosis unit. The reverse osmosis unit may operate at a pressure ranging from 20 bar to 300 bar. The operating pressure may be selected based on factors such as the initial TDS concentration of the lithium chloride solution and the desired final TDS concentration.

[0075] The concentrated lithium chloride solution exiting the reverse osmosis unit is then be fed into the sorbent unit 16. The increased TDS concentration of the lithium chloride solution may enhance the efficiency of the sorbent process in the sorbent unit 16. This may result in improved lithium adsorption capacity and selectivity of the sorbent material.

[0076] The reverse osmosis unit may include one or more reverse osmosis membranes arranged in various configurations. It may also incorporate feed and permeate pumps to control flow rates and pressures. The unit may feature cleaning-in-place systems to periodically clean the membranes, as well as pressure vessels, piping, valves, and instrumentation to direct and monitor fluid flows through the reverse osmosis process.

[0077] A modification to system 10 will now be described with reference to Figure 2 and system 10a. System 10a is the same as system 10 and like references are used to describe like features. In system 10a a nanofiltration unit 18 is arranged such that at least a portion of the lithium rich solution flow 20 can be recycled back to the sorbent unit 16. This recycling process can increase the lithium recovery rate by allowing the sorbent unit 16 to adsorb additional lithium ions from the recycled purified lithium-depleted solution 22. In Figure 2 the nanofiltration unit 18 may also include a reserves osmosis unit which acts in place of or in addition to the nanofiltration unit as described in system 10 (not shown).

[0078] The nanofiltration unit 18 is in fluid communication with the sorbent unit 16 and is configured to subject the lithium-rich solution flow 20 to nanofiltration. The nanofiltration process performed in nanofiltration unit 18 removes primarily multivalent ions from the lithium-rich solution flow 20 to produce a purified lithium depleted solution 22.

[0079] In some embodiments, the nanofiltration unit 18 may be configured to remove multivalent ions from the lithium-rich solution flow 20. The multivalent ions may include Ca2+, Mg2+, Fe3+, Mn2+, Mn3+, Mn4+, and AI3+. The removal of these ions may be achieved by passing the lithium-rich solution flow 20 through a nanofiltration membrane or a series of nanofiltration membranes. The nanofiltration process may be performed under various operating conditions, such as different pressures, temperatures, and flow rates, to optimize the removal of multivalent ions and the recovery of lithium ions.

[0080] In some cases, the nanofiltration unit 18 may be operated at a pressure ranging from 5 bar to 20 bar. The pressure may be selected based on factors such as the specific nanofiltration membrane used, the composition of the lithium-rich solution flow 20, and the desired lithium recovery rate. The nanofiltration process may be configured to achieve a lithium recovery rate of at least 90%, thereby maximizing the amount of lithium that can be recovered from the lithium-rich solution flow 20.

[0081] The nanofiltration unit 18 may include one or more nanofiltration membranes arranged in various configurations. In some embodiments, the nanofiltration unit 18 may comprise a single-stage nanofiltration system with one or more membrane modules connected in parallel. In other cases, the nanofiltration unit 18 may utilize a multi-stage configuration with membrane modules arranged in series to achieve higher rejection of multivalent ions. The nanofiltration unit 18 may also incorporate feed and permeate pumps to control flow rates and pressures. The unit may also feature cleaning-in-place systems to periodically clean the membranes. Pressure vessels, piping, valves, and instrumentation may be included to direct and monitor fluid flows through the nanofiltration process. In certain embodiments, the nanofiltration unit 18 may utilize spiral-wound membrane elements or hollow fibre membrane modules depending on the specific application requirements.

[0082] The nanofiltration unit 18 may operate under various conditions to optimize the removal of multivalent ions and produce a purified lithium solution.

[0083] The operating pressure of the nanofiltration unit may range from 5 bar to 20 bar. The operating pressure may range from 5 bar to 18 bar. The operating pressure may range from 5 bar to 16 bar. The operating pressure may range from 5 bar to 14 bar. The operating pressure may range from 5 bar to 12 bar. The operating pressure may range from 5 bar to 10 bar. The operating pressure may range from 5 bar to 8 bar. The operating pressure may range from 7 bar to 20 bar. The operating pressure may range from 9 bar to 20 bar. The operating pressure may range from 11 bar to 20 bar. The operating pressure may range from 13 bar to 20 bar. The operating pressure may range from 15 bar to 20 bar. The operating pressure may range from 17 bar to 20 bar. The operating pressure may be at least 5 bar. The operating pressure may be at least 7 bar. The operating pressure may be at least 9 bar. The operating pressure may be at least 11 bar. The operating pressure may be at least 13 bar. The operating pressure may be at least 15 bar. The operating pressure may be up to 20 bar. The operating pressure may be up to 18 bar. The operating pressure may be up to 16 bar. The operating pressure may be up to 14 bar. The operating pressure may be up to 12 bar. The operating pressure may be up to 10 bar. In an embodiment, the operating pressure may be 10 bar. In an embodiment, the operating pressure may be 15 bar.

[0084] The temperature of the lithium-rich solution flow 20 entering the nanofiltration unit 18 may be maintained between 20°C and 60°C. The temperature may range from 20°C to 55°C. The temperature may range from 20°C to 50°C. The temperature may range from 20°C to 45°C. The temperature may range from 20°C to 40°C. The temperature may range from 20°C to 35°C. The temperature may range from 20°C to 30°C. The temperature may range from 25°C to 60°C. The temperature may range from 30°C to 60°C. The temperature may range from 35°C to 60°C. The temperature may range from 40°C to 60°C. The temperature may range from 45°C to 60°C. The temperature may range from 50°C to 60°C. The temperature may range from 55°C to 60°C. The temperature may be at least 20°C. The temperature may be at least 25°C. The temperature may be at least 30°C. The temperature may be at least 35°C. The temperature may be at least 40°C. The temperature may be at least 45°C. The temperature may be at least 50°C. The temperature may be at least 55°C. The temperature may be up to 60°C. The temperature may be up to 55°C. The temperature may be up to 50°C. The temperature may be up to 45°C. The temperature may be up to 40°C. The temperature may be up to 35°C. The temperature may be up to 30°C. In an embodiment, the temperature may be 40°C. In an embodiment, the temperature may be 50°C.

[0085] The pH of the feed solution may be adjusted to a range of 2 to 8 to enhance the rejection of multivalent ions while allowing monovalent lithium ions to pass through the membrane. In some cases, the pH may be controlled by adding small amounts of acid or base to the feed solution.

[0086] The flow rate through the nanofiltration unit 18 may be adjusted based on the concentration of the feed solution and desired recovery rate. Typical cross-flow velocities may range from 0.1 to 2 m / s to minimize concentration polarization and fouling of the membrane surface. In some embodiments, the nanofiltration unit 18 may operate in a continuous mode, with a portion of the feed solution being recirculated to maintain a constant concentration factor.

[0087] During nanofiltration in the nanofiltration unit 18, the lithium recovery rate may range from 50% to 90%. The lithium recovery rate may range from 50% to 85%. The lithium recovery rate may range from 60% to 90%. The lithium recovery rate may range from 65% to 90%. The lithium recovery rate may range from 70% to 90%. The lithium recovery rate may range from 75% to 90%. The lithium recovery rate may range from 80% to 90%. The lithium recovery rate may range from 85% to 90%. The lithium recovery rate may be at least 50%. The lithium recovery rate may be at least 55%. The lithium recovery rate may be at least 60%. The lithium recovery rate may be at least 65%. The lithium recovery rate may be at least 70%. The lithium recovery rate may be at least 75%. The lithium recovery rate may be at least 80%. The lithium recovery rate may be at least 85%. The lithium recovery rate may be at least 90%. The lithium recovery rate may be at least 95%. The lithium recovery rate may be at least 98%. The lithium recovery rate may be at least 99%.

[0088] The nanofiltration membranes used in the nanofiltration unit 18 may have a molecular weight cut-off (MWCO) ranging from 200 to 1000 Daltons, allowing for effective separation of monovalent lithium ions from larger multivalent ions. The specific membrane characteristics may be selected based on the composition of the lithium-rich solution flow 20 and the desired purity of the final product.

[0089] In some cases, the nanofiltration unit 18 may incorporate a cleaning cycle to maintain membrane performance. This may involve periodic flushing with cleaning solutions to remove accumulated foulants and scale. The frequency and duration of cleaning cycles may be adjusted based on the feed water quality and observed membrane performance.

[0090] The nanofiltration unit 18 may include or be replaced by an ion exchange resin system to adsorb multivalent ions from the lithium-rich solution. The ion exchange resin may be a sulfonate, iminodiacetate, aminomethylphosphonic acid functionlized polystyrene / divinylbenzene resin. In an embodiment, the sulfonated resin may be a strong acid cation exchange resin.

[0091] The ion exchange resin may be packed in a column or a series of columns. The lithium-rich solution may be passed through the ion exchange resin column at a controlled flow rate. As the solution flows through the resin, multivalent ions such as Ca2+, Mg2+, and AI3+ are selectively adsorbed by the resin, while allowing monovalent lithium ions to pass through.

[0092] The ion exchange process may be operated in a continuous or batch mode. In a continuous mode, multiple columns may be used in parallel, allowing for simultaneous adsorption and regeneration processes. The flow rate through the ion exchange columns may be adjusted based on factors such as the concentration of multivalent ions in the feed solution and the desired purification level.

[0093] After a certain period of operation or when the ion exchange capacity is exhausted, the resin may need to be regenerated. The regeneration process may be performed by flushing the resin with sulfuric acid or hydrochloric acid. The concentration of the sulfuric acid or hydrochloric used for regeneration may range from 1% to 10% by weight. The regeneration process may be carried out at ambient temperature or at elevated temperatures up to 60°C.

[0094] During regeneration, the sulfuric or hydrochloric displaces the adsorbed multivalent ions from the resin, restoring its ion exchange capacity. The displaced ions and excess acid may be collected as a waste stream, which may be further treated or disposed of according to environmental regulations.

[0095] The regenerated ion exchange resin may then be rinsed with deionized water to remove any residual acid before being put back into service. This regeneration process may allow for multiple cycles of use, enhancing the efficiency and cost-effectiveness of the purification process.

[0096] In an embodiment, the ion exchange system may be used in combination with nanofiltration membranes. The ion exchange resin may serve as a pre-treatment step to remove the bulk of multivalent ions, followed by nanofiltration for final polishing of the lithium-rich solution. This combined approach may extend the life of the nanofiltration membranes and improve the overall efficiency of the multivalent ion removal process.

[0097] The system 10 produces a lithium chloride output solution 24 from the nanofiltration unit 18. The lithium chloride output solution 24 has a high lithium concentration and a low concentration of impurities, making it suitable for further processing and refining to produce high-purity lithium products.

[0098] The recycling process of sending lithium rich solution flow 20 to the nanofiltration unit 18 and back to the sorbent unit 16 may be controlled by various components and subsystems within the system 10a (not shown). For example, pumps, valves, and control systems may be used to regulate the flow rate and direction of the purified lithium depleted solution 22, ensuring that the appropriate amount of solution is recycled back to the sorbent unit 16.

[0099] In some embodiments, the recycling process may be adjusted based on the composition of the lithium-containing solution and the performance of the sorbent unit 16 and the nanofiltration unit 18. For instance, if the lithium concentration in the lithium-containing solution is high, a larger portion of the purified lithium depleted solution 22 may be recycled back to the sorbent unit 16 to maximize lithium recovery. Conversely, if the lithium concentration is low, a smaller portion of the purified lithium depleted solution 22 may be recycled to optimize the performance of the sorbent unit 16 and the nanofiltration unit 18.

[0100] The recycling process may be performed continuously or intermittently, depending on the operational requirements of the system 10a. The frequency and duration of the recycling process may be adjusted based on factors such as the lithium concentration in the lithium- containing solution, the capacity of the sorbent unit 16, and the performance of the nanofiltration unit 18.

[0101] The recycling process may be integrated with other processes within the system 10a to optimize the overall performance of the system. For example, the recycling process may be coordinated with the sorption and desorption processes in the sorbent unit, the nanofiltration process in the nanofiltration unit, and other processes within the system 10a to maximize lithium recovery and minimize energy consumption and waste production.

[0102] The recycling process may be automated using control systems and sensors to monitor and adjust the flow rate, pressure, and temperature of the purified lithium depleted solution 22. This automation can enhance the efficiency and reliability of the recycling process, reducing the need for manual intervention and ensuring consistent performance of the system 10a.

[0103] The recycling process may be designed to be flexible and adaptable, allowing for adjustments and modifications based on changes in the lithium-containing solution, the performance of the sorbent unit 16 and the nanofiltration unit 18, and other factors. This flexibility can enable the system 10a to effectively handle variations in the lithium-containing solution and maintain high lithium recovery rates under different operating conditions.

[0104] In some embodiments, the recycling process may be combined with other processes within the system 10a to create a closed-loop system that minimizes waste and maximizes resource efficiency. For example, the purified lithium depleted solution 22 may be recycled back to the sorbent unit 16, while the waste streams from the sorbent unit 16 and the nanofiltration unit 18 may be treated and reused within the system 10a. This closed-loop approach may help to enhance the sustainability of the system 10a, reducing its environmental impact and improving its overall efficiency.

[0105] Referring to Figure 3, a system 100 for extracting lithium from a lithium-containing brine formed from lithium extraction from spodumene is shown. The system 100 incorporates system 10a but includes additional components and processing steps. The system 100 begins with a lithium sulfate solution 12, which in this embodiment is formed from leaching spodumene with sulfuric acid. The lithium sulfate solution 12 is then treated in a neutralising unit 102, where a neutralising agent is added to neutralise the solution. Neutralisation may also result in precipitation of non-lithium impurities. In an embodiment, the neutralising agent is lime 104. In this way, the neutralising unit 102 may act to perform a polishing step intended to precipitate non-lithium species before conversion of the lithium sulfate solution 12 to the lithium chloride solution. Accordingly, the neutralising unit 102 may be considered as forming a polishing unit.

[0106] Polishing in the neutralising unit 102 may be performed at a temperature ranging from 20°C to 80°C. The temperature may range from 20°C to 70°C. The temperature may range from 20°C to 60°C. The temperature may range from 20°C to 50°C. The temperature may range from 20°C to 40°C. The temperature may range from 30°C to 80°C. The temperature may range from 40°C to 80°C. The temperature may range from 50°C to 80°C. The temperature may range from 60°C to 80°C. The temperature may range from 70°C to 80°C. The temperature may be at least 20°C. The temperature may be at least 30°C. The temperature may be at least 40°C. The temperature may be at least 50°C. The temperature may be at least 60°C. The temperature may be at least 70°C. The temperature may be up to 80°C. The temperature may be up to 70°C. The temperature may be up to 60°C. The temperature may be up to 50°C. The temperature may be up to 40°C. In an embodiment, the temperature may be 40°C. In an embodiment, the temperature may be 60°C.

[0107] The neutralising unit 102 may include a mixing device to ensure thorough mixing of the lime 104 with the lithium sulfate solution 12. The lime 104 may be added in a quantity sufficient to neutralise the acidity of the lithium sulfate solution 12 and precipitate non-lithium impurities, such as iron, aluminium, and manganese ions. The lime 104 may be added in the form of calcium hydroxide or calcium oxide, or a combination thereof. A target pH of the solution treated in the neutralising unit may range from about 6-8. For example, a pH closer to or 8 8 helps to precipitate Al and Fe species. The neutralised lithium sulfate solution 103 is then passed through a first filtration unit 106, which removes the precipitated non-lithium impurities, to form a polished lithium sulfate solution 105. The first filtration unit 106 may include one or more filtration devices, such as a filter press, a centrifuge, or a membrane filtration system. The filtration process may be performed at ambient temperature, or at a temperature ranging from 20°C to 80°C, depending on the specific requirements of the process.

[0108] The filtered (i.e. polished) lithium sulfate solution 105 is then fed into a conversion unit 14, where a source of calcium chloride 132 is added to convert the lithium sulfate to lithium chloride, forming gypsum as a by-product. The conversion unit 14 may include a reactor or a mixing device to facilitate the reaction between the lithium sulfate and the calcium chloride. The calcium chloride may be added in a quantity sufficient to convert all the lithium sulfate to lithium chloride, and to precipitate the remaining sulfate ions as gypsum. In an embodiment, calcium chloride is added in excess to reduce the sulfate concentration below a threshold limit above which the sorbent cannot tolerate sulfate. For example, following conversion a sulfate concentration may be at most 600ppm-800ppm. The system 100 is tolerant to elevated calcium concentrations which can assist in adding excess calcium chloride to reduce sulfate concentrations below threshold limits.

[0109] The lithium chloride solution and the precipitated gypsum are then separated in a second filtration unit 108. The second filtration unit 108 may include one or more filtration devices, similar to those used in the first filtration unit 106. The filtration process may be performed at ambient temperature, or at a temperature ranging from 20°C to 80°C, depending on the specific requirements of the process.

[0110] The separated lithium chloride solution is then ready to be subjected to the sorbent process in the sorbent unit 16, as described with reference to system 10a in Figure 2. The separated gypsum 110 is removed as a by-product and can be further processed or disposed of in an environmentally friendly manner.

[0111] The gypsum formed from the addition of calcium chloride to the lithium sulfate solution 12 in the conversion unit 14 is removed from the lithium chloride solution before the lithium chloride solution is subjected to the sorbent process in the sorbent unit 16. This removal may be performed using a gypsum removal unit (not shown) that is part of the conversion unit 14 or a separate unit. The gypsum removal unit may include one or more filtration devices, such as a filter press, a centrifuge, or a membrane filtration system. The filtration process may be performed at ambient temperature, or at a temperature ranging from 20°C to 80°C, depending on the specific requirements of the process.

[0112] The system 100 further includes a roasting unit 112 configured to receive and perform reductive roasting of the separated gypsum 110. The roasting unit 112 may include a furnace or kiln that is capable of reaching high temperatures necessary for the reductive roasting process. The reductive roasting process converts gypsum into calcium oxide, or a mixture of calcium oxide and calcium hydroxide which is depicted generally as lime 116, and sulfur dioxide.

[0113] The lime 116 is recycled for neutralisation of the lithium sulfate for example in the neutralisation unit 102. In some embodiments, the lime 116 may be reused during the impurity removal process in the neutralising unit 102. This recycling and reuse of lime 116 may help improve the efficiency of the overall lithium extraction process. Recycling the lime 116 may provide several potential advantages. It may reduce the need to purchase and transport additional lime, potentially lowering material costs. The recycling process may also minimize waste generation by reusing materials within the system 100. Overall, the recycling and reuse of lime 116 may offer opportunities to optimize resource utilization, reduce environmental impacts, and potentially improve the economics of the lithium extraction process.

[0114] The sulfur dioxide 114 generated by the roasting unit 112 is converted to sulfuric acid 130 in the acid production unit 134 for reuse in leaching spodumene to form the lithium sulfate solution 12. This recycling of sulfur dioxide may provide several advantages. In some embodiments, it may reduce the overall acid consumption of the process by allowing the regenerated sulfuric acid to be reused for leaching. Additionally, this approach may help minimize waste and improve the environmental sustainability of the lithium extraction process. The recycling of sulfur dioxide may also potentially reduce operating costs by decreasing the need for fresh acid inputs. Furthermore, converting the sulfur dioxide to sulfuric acid may help manage emissions and reduce potential environmental impacts associated with sulfur dioxide release. Overall, this integrated recycling step may contribute to a more efficient and environmentally-friendly lithium extraction process.

[0115] The system 100 further includes a recycle arrangement 140that incorporates a reverse osmosis unit 120 and / or nanofiltration unit 18 to process the lithium-depleted solution 20 before returning it to the sorbent unit 16. The recycle arrangement 140 is configured to increase the total dissolved solids (TDS) concentration and / or remove multivalent ions from the lithium-depleted solution flow 20 to form a concentrated and purified solution that is returned back to the sorbent unit 16.

[0116] The embodiment in Figure 3 shows the recycle arrangement 140 in a general form with the nanofiltration unit 18 and reverse osmosis unit 120 being used in combination. However, alternative recycle arrangements are shown in Figures 3A and 3B. In the recycle arrangement 140a shown in Figure 3A, the nanofiltration unit 18 is positioned upstream of the reverse osmosis unit 120, with a branching line 23 and bleed valve 136 allowing a portion of the purified lithium-depleted flow 22 to be directed to the reverse osmosis unit 120. In the recycle arrangement 140b shown in Figure 3B, the reverse osmosis unit 120 is positioned upstream of the nanofiltration unit 18, with a branching line 23 and bleed valve 136 allowing a portion of the concentrated lithium-depleted flow 22b to be directed to the nanofiltration unit 18.

[0117] The amount of fluid passed through the bleed valve 136 may be varied to optimize the performance of the recycle arrangement 140. The bleed ratio, which represents the proportion of the lithium-depleted solution 20 that is directed through the branching line 23, may be adjusted to control both the total dissolved solids (TDS) concentration and lithium recovery in the system. As shown in Figures 9A-9D, different bleed ratios can be used to adjust TDS downwards and optimize lithium recovery. In Figure 9A, a 20% bleed through the branching line 23 with 59% water removal in the reverse osmosis unit 120 results in a TDS of 250 g / L, while increasing the bleed to 44% while reducing water removal to 47% produces a lower TDS of 150 g / L as shown in Figure 9B. Figures 9C and 9D show that, with 100% bleed through the branching line 23, different water removal percentages in the reverse osmosis unit 120 can further adjust the TDS concentration. The bleed valve 136 may be controlled automatically or manually to maintain optimal operating conditions. In some embodiments, the bleed ratio may be adjusted based on real-time monitoring of TDS levels, lithium concentrations, and sorbent performance. This flexibility allows the system to respond to variations in feed composition and maintain stable operation while maximizing lithium recovery.

[0118] The reverse osmosis unit 120 may include one or more reverse osmosis membranes arranged in various configurations. In some embodiments, the reverse osmosis unit 120 may comprise a single-stage reverse osmosis system with one or more membrane modules connected in parallel. In other cases, the reverse osmosis unit 120 may utilize a multi-stage configuration with membrane modules arranged in series to provide the concentrated lithium-depleted flow 22b. The reverse osmosis unit 120 may also incorporate feed and permeate pumps to control flow rates and pressures. The unit may also feature cleaning-in-place systems to periodically clean the membranes. Pressure vessels, piping, valves, and instrumentation may be included to direct and monitor fluid flows through the reverse osmosis process. The reverse osmosis unit 120 may operate under various conditions to optimize the concentration of the purified lithium-depleted solution flow 22b. The operating pressure of the reverse osmosis unit 120 may range from 20 bar to 300 bar. The operating pressure may range from 20 bar to 250 bar. The operating pressure may range from 20 bar to 200 bar. The operating pressure may range from 20 bar to 150 bar. The operating pressure may range from 20 bar to 100 bar. The operating pressure may range from 40 bar to 300 bar. The operating pressure may range from 60 bar to 300 bar. The operating pressure may range from 80 bar to 300 bar. The operating pressure may range from 100 bar to 300 bar. The operating pressure may range from 200 bar to 300 bar. The operating pressure may be at least 20 bar. The operating pressure may be at least 50 bar. The operating pressure may be at least 100 bar. The operating pressure may be at least 150 bar. The operating pressure may be at least 200 bar. The operating pressure may be at least 250 bar. The operating pressure may be up to 300 bar. The operating pressure may be up to 250 bar. The operating pressure may be up to 200 bar. The operating pressure may be up to 150 bar. The operating pressure may be up to 100 bar. In an embodiment, the operating pressure may be 60 bar. In an embodiment, the operating pressure may be 80 bar.

[0119] The operating pressure may be selected based on factors such as the specific reverse osmosis membrane used, the composition of the lithium-depleted solution 20 , and the desired TDS concentration. The reverse osmosis process may be configured to increase the TDS concentration, thereby maximizing the concentration of lithium in the concentrated lithium solution flow 22b.

[0120] The reverse osmosis process may be configured to increase the TDS concentration to at least 150 g / L. The TDS concentration may range from 150 g / L to 300 g / L. The TDS concentration may range from 150 g / L to 250 g / L. The TDS concentration may range from 150 g / L to 200 g / L. The TDS concentration may range from 175 g / L to 300 g / L. The TDS concentration may range from 200 g / L to 300 g / L. The TDS concentration may range from 225 g / L to 300 g / L. The TDS concentration may range from 250 g / L to 300 g / L. The TDS concentration may be at least 175 g / L. The TDS concentration may be at least 200 g / L. The TDS concentration may be at least 225 g / L. The TDS concentration may be at least 250 g / L. The TDS concentration may be at least 275 g / L. The TDS concentration may be up to 300 g / L. The TDS concentration may be up to 275 g / L. The TDS concentration may be up to 250 g / L. The TDS concentration may be up to 225 g / L. The TDS concentration may be up to 200 g / L. In an embodiment, the TDS concentration may be 200 g / L. In an embodiment, the TDS concentration may be 250 g / L. In some embodiments, the reverse osmosis unit 120 may operate in a continuous mode, with a portion of the concentrated lithium-depleted flow 22b being recirculated to maintain a constant concentration factor. The recovery rate may range from 50% to 90% as outlined for system 10a. The recovery rate may be adjusted based on factors such as the lithium concentration in the lithium-depleted solution 20 and the capacity of the reverse osmosis unit 120, and if used upstream the performance of the nanofiltration unit 18.

[0121] The concentrated lithium solution flow 22b from the reverse osmosis unit 120 is then directly or indirection (through the nanofiltration unit 18) returned back to the sorbent unit 16. This recycling process can increase the lithium recovery rate by allowing the sorbent unit 16 to adsorb additional lithium ions from the lithium-depleted solution flow 20. The recycling process may be controlled by various components and subsystems within the system 100 (not shown). For example, pumps, valves, and control systems may be used to regulate the flow rate and direction of the purified lithium-depleted solution 22 and / or concentrated lithium solution flow 22b, as shown in Figure 3A and Figure 3B, ensuring that the appropriate amount of solution is recycled back to the sorbent unit 16.

[0122] . The recycling process may also minimize waste generation by reusing materials within the system 100. Overall, the recycling and reuse of the sorbent washing brine may offer opportunities to optimize resource utilization, reduce environmental impacts, and potentially improve the economics of the lithium extraction process.

[0123] The recycle arrangement 140 may enable the effective utilisation of sorbents that exhibit high selectivity for lithium but have relatively low adsorption capacity. In some embodiments, sorbents with high selectivity may produce very pure lithium solutions during desorption but may not be able to adsorb all available lithium in a single pass due to their limited capacity. The recycle arrangement 140 addresses this limitation by allowing multiple passes of the lithium-depleted solution through the sorbent unit 16, thereby capturing lithium that was not adsorbed in the initial pass. This approach may maximise the benefits of highly selective sorbents while compensating for their capacity limitations. In an embodiment, the nanofiltration unit 18 and reverse osmosis unit 120 work together to maintain appropriate solution conditions for repeated cycling, with the nanofiltration unit 18 removing multivalent ions that could interfere with sorbent performance and the reverse osmosis unit 120 maintaining optimal TDS levels for sorbent function. This configuration may allow the system to achieve both high purity and high recovery rates, leveraging the selectivity advantages of specialised sorbents while overcoming their capacity constraints through process intensification. The system 100 further includes an electrodialysis unit 124 downstream of the sorbent unit 16. lithium hydroxide solution 128 and a hydrochloric acid solution 126. The lithium hydroxide solution 128 has a high lithium concentration and a low concentration of impurities, making it suitable for further processing and refining to produce high-purity lithium products. The hydrochloric acid solution 126 can be reused in the system 100 or can be used in other processes.

[0124] System 100 may also include a further reverse osmosis unit upstream of the electrodialysis unit 124 to increase the lithium concentration of the solution processed in the electrodialysis unit 124 (not shown in Figure 3). The further reverse osmosis unit may be utilised to maintain performance of the electrodialysis unit 124. The further reverse osmosis unit may be a low- pressure reverse osmosis unit.

[0125] The lithium hydroxide solution 128 produced by the electrodialysis unit 124 may have a purity of at least 95%. The purity of the lithium hydroxide solution 128 may be at least 96%. The purity of the lithium hydroxide solution 128 may be at least 97%. The purity of the lithium hydroxide solution 128 may be at least 98%. The purity of the lithium hydroxide solution 128 may be at least 99%. The purity of the lithium hydroxide solution 128 may range from 95% to at least 99.9%. The purity of the lithium hydroxide solution 128 may have a maximum purity of 99.99%, 99.95%, or 99.9%.

[0126] The lithium hydroxide solution 128 may be further processed to produce lithium hydroxide monohydrate crystals. This crystallization process may involve evaporation, cooling, or a combination of both. The resulting crystals may have a purity of at least 95%.

[0127] The electrodialysis unit 124 may include one or more bipolar membrane electrodialysis cells arranged in various configurations. For example, the electrodialysis unit 124 may comprise a single-stage electrodialysis system with one or more cell modules connected in parallel. In other cases, the electrodialysis unit 124 may utilize a multi-stage configuration with cell modules arranged in series to achieve higher conversion of the purified lithium solution. The electrodialysis unit 124 may also incorporate feed and permeate pumps to control flow rates and pressures. The unit may also feature cleaning-in-place systems to periodically clean the membranes. Pressure vessels, piping, valves, and instrumentation may be included to direct and monitor fluid flows through the electrodialysis process.

[0128] The electrodialysis unit 124 may operate under various conditions to optimize the conversion of the purified lithium solution. The operating voltage of the electrodialysis unit 124 may below 0.3V. The operating voltage may be selected based on factors such as the specific bipolar membrane used, the composition of the purified lithium solution, and the desired conversion rate. The electrodialysis process may be configured to achieve a lithium hydroxide purity of at least 95%, thereby maximizing the quality of the final product.

[0129] The system and process described herein may provide several advantages over conventional lithium extraction methods. The combination of sorbent-based direct lithium extraction with nanofiltration and reverse osmosis recycling may enable higher lithium recovery rates compared to traditional evaporation pond methods, while potentially reducing processing time from months to days or weeks. The selective nature of the sorbent materials may allow for the production of high-purity lithium solutions with significantly reduced concentrations of multivalent impurities such as calcium, magnesium, and aluminium.

[0130] The integrated recycling approach may improve overall resource efficiency by allowing multiple passes of the lithium-depleted solution through the sorbent system, thereby capturing lithium that would otherwise be lost in a single-pass process. The nanofiltration step may help maintain stable operation by preventing the buildup of multivalent ions in the recycle loop, while the reverse osmosis concentration step may optimize sorbent performance by maintaining appropriate total dissolved solids levels.

[0131] From an environmental perspective, the process may offer reduced water consumption compared to evaporation-based methods and may minimize waste generation through the recycling of process streams and byproducts such as gypsum. The ability to recycle sulfuric acid and lime within the system may further reduce chemical consumption and operating costs. Additionally, the modular nature of the system may provide operational flexibility, allowing for adjustments based on feed composition variations and market demands for different lithium products such as lithium chloride, lithium carbonate, or lithium hydroxide.

[0132] In the claims that follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the disclosure.

[0133] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

[0134] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present disclosure.

[0135] Examples

[0136] Embodiments will now be described with reference to the following non-limiting examples.

[0137] Example 1

[0138] The composition of a specific spodumene concentrate (specifically, the lithium concentration and the nature of the impurities) can be have a significant effect on the sulfuric leaching of - spodumene (which results from the high temperature roasting of a-spodumene at approximately 1000-1100 °C) (see Minerals Engineering, 129, 2018, 1-8, doi:10.1016 / j.mineng.2018.09.011). This process relies on an ion-exchange reaction with an acid (i.e. , conversion of LiAISi2Oe to HAISi2Oe) to extract Li into solution. Typically, for efficient lithium recovery, an excess (typically 50 mol %) of sulfuric acid and a temperature of approximately 250 °C is necessary. It is a preferred method by industry due to its versatility, high lithium recovery and relatively high extraction selectivity for lithium. Alternative processes such as sodium hydroxide directly reacting with a-spodumene at 300 °C result in significant impurity leaching (see Minerals Engineering, 201 , 2023, 108214, doi:

[0139] 10.1016 / j.mineng.2023.108214 and ACS Sustainable Chem. Eng. 2022, 10, 13495-13504, doi:10.1021 / ascsuschemeng.2c04402). Based on these reports, a representative solution that is typical for a sulfuric acid leachate solution is provided in Table 1.

[0140] Table 1. The chemical composition of the representative sulfuric acid leach solution, Lithium-aluminium layered double hydroxide sorbents undergo massive structural degradation in the presence of sulfate ions (see AIChE Journal, 2023;69:e18176m, doi:10.1002 / aic.18176) leading to a collapse in the effective Li sorption capacity. These sorbents are typically only utilized with chloride-based brines. Lithium manganese oxide and lithium titanium oxides are ion-exchange sorbents that rely on a pH swing (neutral to slightly alkali for adsorption and acidic for desorption) for their functionality (see Mineral Processing and Extractive Metallurgy Review, 2023. 44(4): p. 261-280, doi: 10.1080 / 08827508.2022.2047041).

[0141] The acid leachate is neutralised to a pH value of 8.0 with calcium hydroxide which was chosen for its relatively low-cost and environmental footprint. This neutralisation removes virtually all of the iron, aluminium and manganese impurities (as determined by ICP analysis) from solution. Furthermore, the addition of calcium chloride (following calcium hydroxide neutralisation) reduces the amount of sulfate in solution and replaces it with a chloride anion (making the brine suitable for lithium-aluminium layered double hydroxide sorbents).

[0142] For nanofiltration (which often exhibits good monovalent ion over divalent selectivity, see Desalination, 440, 2018, 122-134, doi: 10.1016 / j. desal.2018.03.030), the replacement of sulfate ions (which are divalent) with chloride ions (which are monovalent) will ensure charge neutrality for lithium ions and thus improve lithium recovery. Figure 4 shows the sulfate and calcium concentrations following addition of calcium chloride. It is evident that increased calcium chloride decreases the sulfate concentration while increasing the calcium concentration. The optimal amount of calcium chloride addition will depend on the performance characteristics of the sorbent / nanofiltration system as well as a desire to reduce reagent use (i.e., addition of calcium chloride). The addition of calcium chloride in this second step results in precipitation of nearly pure calcium sulfate (which could be either be sold as a by-product or recycled to form calcium hydroxide / sulfuric acid which could be re-used in this process).

[0143] Example 2

[0144] With typical brine deposits of lithium (prior to solar evaporation) used in direct lithium extraction projects, the concentration is typically less than 500 ppm with concentrations as low as 100 ppm being considered viable under certain economic conditions (j.e., a high lithium commodity price). Typical granulated lithium-aluminium layered double hydroxide sorbents have an effective Li capacity of approximately 3 to 5 mg / g. For 1 L of a lithium brine of 100 to 500 ppm and assuming 100 % recovery will require between 20 to 170 grams of sorbent. With the brine resulting from the calcium hydroxide / chloride treatment of sulfuric acid-p- spodumene leachate, there is a significant amount of liquid that needs to be processed relative to the quantity of solids. The volume of solids is not sufficient to adsorb all of the lithium in the brine in a single pass. However, following high temperature conversion of a-spodumene to - spodumene and subsequent sulfuric acid leaching and pH neutralization, the lithium concentration is typically between 10000 to 20000 ppm. Under these circumstances, 1 L of leachate would require between 2 to 7 kg of sorbent; under these circumstances, this is a comparatively small amount of liquid relative to the solid. As such, it may be difficult to achieve complete recovery of lithium in a single pass through a packed sorbent column. Furthermore, the lithium salt (and its associated chloride counterion) represents a minority of the overall total dissolved salts (TDS) and as such it cannot be removed in a single step without the TDS value appreciably decreasing. However, for these sorbents to function at a high TRL, the TDS need to be quite high (typically above 150000 ppm) (see Desalination, 2024. 577: p. 117406); this criterion can be satisfied with traditional brines throughout the adsorption process as the adsorption of lithium does not appreciably decrease the TDS.

[0145] With a recycle approach as proposed, the effluent brine (combined with any washing solution needed to prevent mixing of adsorption fluid with the desorption) could be recombined with new brine (from the acid leaching of p-spodumene) to achieve a much higher lithium recovery. As such, to achieve a high extraction efficiency, the use of a recycle loop is used in an embodiment. For a recycle loop to be effective, a reverse osmosis system (or RO) can used to remove water and increase the TDS so that it can be combined with fresh brine in a recycle loop into the sorbent column. The TDS needs to be increased with RO for the lithiumaluminium layered double hydroxide sorbent to have a practical sorbent capacity. Following this nanofiltration (which is selectively permeable to lithium) is used to remove a portion of the multivalent ion impurities (e.g., Ca2+, Mg2+, Al3+). This is done to keep the multi-valent ion concentration stable so that the purity from the sorbent process remains stable as well.

[0146] In this example, a granulized lithium-aluminium absorbent was used in a chromatography column for the adsorption and desorption of lithium ions. Simulated acid leachate solution, neutralized with Ca(OH)2and converted to a chloride-based brine with CaCI2, had a high lithium ion concentration of 16,139 ppm (as shown in table 2). The volume of sorbent used was 145 mL (179 g), and the chromatography column had an internal diameter of 25 mm, an effective length of 300 mm, and a total capacity of 150 mL. A condenser column (100 mL) served as a heat exchanger, and a heat-jacketed column loaded with the sorbent was used with hot water circulation at 65°C for the absorption and desorption steps. To prevent sorbent loss, a glass filter was placed at the bottom of the column. The concept of pore volume (PV) in this embodiment refers to the amount of solution required to fill the interspaces of the granulized sorbent loaded in the column. For this sorbent, one PV was 40 mL, and 5 PVs of the lithium solution were loaded for adsorption at a flow rate of 840 mL / hour (21.75 PVs / hour).

[0147] After adsorption, the column was washed at 25°C using 5 PVs of distilled water at a flow rate of 90 mL / min to remove residual solution. Due to the high selectivity of the sorbent for lithium ions, the washing step was essential for obtaining high-purity lithium chloride. Desorption was carried out at 65°C using a lithium chloride solution with a concentration of around 1800 ppm as the stripping solution, with 16 PVs of chloride solution used to concentrate lithium chloride. The composition of the adsorption and desorption permeates is shown in Table 2. The desorption capacity was equal to 1.84 mgLi / g sorbent according to the equation below:

[0148] Desorption capacity

[0149] (Desorption outlet(Li+mg / L) — Stripping solution(Li+mg / L))

[0150] Sorbent Mass(g)

[0151] The lithium-calcium and lithium-sodium ratios for the feed (adsorption inlet) were measured by ICP to be approximately 7.6 and 68, respectively; the sorption process was highly selective for lithium resulting in ratios of 348 and 450, respectively.

[0152] Table 2. The chemical composition from ICP-OES of adsorption inlet, adsorption outlet, +washed sorbent permeate outlet, and desorption outlet.

[0153] The quantity (or pore volumes) of brine used in the sorption process can be optimized because increasing the volume will increase the sorbent capacity; however, further increases will saturate the sorbent and lead to reduce lithium recovery from a single-pass of the brine (resulting in a larger reliance on the recycle loop). Similarly, an increase in the pore volumes used for the wash step will reduce the load on the recycle loop; however, there will be a larger contamination between the absorption / desorption phases resulting in a lower purity desorption stream. Example 3

[0154] Rapid changes in salinity causing osmotic shock can be harmful to the structural integrity of various porous materials including lithium-aluminium layered double hydroxides sorbents and polymer-based ion exchange resins. While the lithium capacity of lithium-aluminium layered double hydroxides typically increases with TDS, a rapid increase in the TDS resulted in fracturing of the granulated sorbent material. In this example, increasing the TDS slowly (i.e., 2 pore volumes of 62.5 g / L LiCI / 5 g / L CaCl2 then 2 pore volumes of 125 g / L LiCI / 10 g / L CaCh followed by 250 g / L LiCI / 20 g / L CaCh) helps to maintain the structural integrity of the sorbent. Immediate exposure to the highest TDS solution in this series resulted in rapid disintegration of the sorbent material.

[0155] Following washing with 6 PV of 300 ppm Li (as LiCI) and then 6 PV of 300 ppm Li (as LiCI), a lithium capacity of 4 mg / g was obtained; however, the Li to Ca ratio only increased from 6.0 (for the inlet feed brine) to 12.1 (for the desorption brine). This smaller increase in the Ca to Li is likely due to a larger carryover of salts from the absorption phase to the desorption phase. It is also possible that the sorbents showed fundamentally lower selectivity under these higher TDS conditions.

[0156] Example 4

[0157] Nanofiltration (NF) can be used to separate monovalent ions (such as Li+) from multivalent ions (such as Ca2+and Mg2+). However, nanofiltration membranes can be ran under different pressure conditions. With a high-water recovery, the lithium recovery can be very high, but the purity will be limited. On the contrary, with a low water recovery, the lithium recovery will be much less, but the purity will be significantly higher. In this case, this strategy (like the LDH sorbent which has varying degrees of intolerance to sulphate ions) necessitates the conversion to a chloride-based brine using calcium chloride as a reagent; the initial sulfate- based brine will not work as these nanofiltration membranes are not permeable to sulfate ions. With a chloride-based brine, it is likely possible that the nanofiltration membrane could be run under conditions that would lead to high purity lithium stream on its own; however, there would be a trade-off with the lithium recovery being relatively low. Mass balance simulations highlight the performance requirements for the nanofiltration process (see Figure 5).

[0158] Using the process simulation from Example 3, Figure 5 shows the effect of Li loss during the nanofiltration process on the overall lithium recovery while also the requirements for the quantity of Ca that needs to be removed by the nanofiltration process to achieve stable operation. Table 4 highlights the requirements for the nanofiltration membrane to achieve an overall recovery of 90 % for different sorption capacity and pore volume values. Based on this analysis, it is evident that the nanofiltration membrane must be utilized in a mode where the lithium recovery is very high (e.g., with multiple nanofiltration membranes in series) and that only a relatively modest amount of Ca needs to be removed in order to have a stable process. Based on these results, the utilization of 5 pore volumes for absorption is preferred as it will put less strain on the nanofiltration performance. Furthermore, with this relatively low pore volume, the time for each cycle will be reduced thus increasing the output of the system.

[0159] Table 3. Required nano-filtration performance criteria to achieve 90 % overall Li recovery for different sorption capacity and absorption pore volume values

[0160] By using the combined approach (using both sorbents and nanofiltration / reverse osmosis), both high purity and high recovery can be attained. The dilution of the brine effluent from adsorption column (resulting from both washing liquid and the adsorbed lithium chloride onto the sorbent) will affect the behaviour of the nanofiltration membrane and will need to be considered.

[0161] Example 5

[0162] Nanofiltration (NF) is utilized in the recycle loop as a sink for multivalent ions (such as Ca2+); otherwise, there would be build-up of these ions during a continuous process. The focus of the nanofiltration implementation is to provide a high recovery of lithium (which in practice may require multiple nanofiltration membranes in series) while only a portion of the Ca2+to be removed to keeps its concentration from escalating. The sorbent material used to provide a high purity process stream while the RO / NF-based recycle loop is used to improve recovery.

[0163] A chloride-based solution of 9000 ppm Li and 1600 ppm Ca was used with a Veolia-DL membrane at a permeate pressure of 5 bar resulting in a permeate composition of 8100 ppm Li and 1020 ppm Ca and a retentate composition of 8900 ppm Li and 1600 ppm Ca. A chloridebased solution of 9000 ppm Li and 1600 ppm Ca was used with a Veolia-DL membrane at a permeate pressure of 5 bar resulting in a permeate composition of 9200 ppm Li and 640 ppm Ca and a retentate composition of 8020 ppm Li and 1770 ppm Ca. In both cases using a deadend cell, the rejection for Ca is sufficient to attain a lithium recovery greater than 90 %.

[0164] Example 6

[0165] In an iteration of the design, the nanofiltration unit was positioned directly after adsorption, prior to the RO unit. This arrangement resulted in high lithium loss; despite having a high single pass lithium recovery (98%), the overall lithium loss to the retentate was high due to the high recirculating load of lithium through the adsorption circuit. Additionally, it was resulting in a significant decrease in the TDS of the recirculating liquor and hence, the adsorption feed. This is undesirable as a higher TDS results in a higher sorbent capacity, as depicted in Figure 8. Rather than sending all adsorption permeate through the nanofiltration unit, only a portion of the recirculating liquor was sent to the nanofiltration unit to control the TDS below a level suitable for the RO unit. This leads to a reduction in the capacity of the nanofiltration unit, a higher lithium recovery and a higher TDS in the adsorption feed, leading to increased sorbent capacity. As such, in this example, the recycle loop is adjusted with the RO returning directly to the sorbent column feed inlet and a bleed immediately upstream from the RO going into the nanofiltration unit (see Figure 9A-9D) with the primary purpose of keeping the multivalent ion concentration stable; the permeate from this membrane is combined with the RO. In this simulation, the nanofiltration unit recovery for Li is assumed to be 98 % while the salt rejection for Ca is 25 %. The simulation assumes that the sorbent capacity varies with TDS as given in the literature (see Canadian Journal of Chemical Engineering, 2020, 98, 544-555).

[0166] A key driver for lithium recovery is the TDS of the adsorption feed and in turn, the concentrate TDS from the reject brine RO. In the base case design, the feed TDS of the adsorption column is controlled at 250 g / L via a bleed from the recirculating liquor to the NF unit. However, there is a risk that the TDS is too high for the RO unit. The relationship between the lithium recovery and the RO TDS is shown in Figure 6. Beyond a concentration of 110 g / L, the TDS is controlled via the bleed and the RO unit is controlled such that the lithium concentration in the RO concentrate is the same as the lithium concentration in the liquor from chlorination. The TDS in the recycled solution is more than the TDS in the fresh feed (from chlorination), leading to concentration. Below a concentration of 110 g / L, the bleed is set at 100% (all liquor runs through the NF unit) and the operation of the RO is adjusted to remove less water. The TDS in the recycled solution is less than the TDS in the fresh feed (from chlorination), leading to dilution. An increase in the sorbent capacity will only contribute to an increase in the single pass lithium recovery of the column if the sorbent capacity increases relative to the change in lithium concentration. This relationship is shown in Figure 7 which shows the feed lithium concentration, sorbent capacity, relative sorbent capacity (sorbent capacity I lithium concentration) and single pass lithium recovery as the TDS of the reject brine RO changes.

[0167] The reason why the single pass lithium recovery is lowest at 110 g / L is because the relative sorbent capacity is the lowest at this point. Below this TDS, the sorbent capacity decreases at a slower rate than the lithium recovery, therefore increasing the relative sorbent capacity. Likewise, beyond 110 g / L, the sorbent capacity increases whilst the lithium concentration decreases, therefore increasing the relative sorbent capacity again.

Claims

Claims1. A process of extracting lithium from spodumene, the process comprising: providing a lithium sulfate solution formed from leaching spodumene with sulfuric acid; adding calcium chloride to the lithium sulfate solution to form a lithium chloride solution and to precipitate gypsum; subjecting the lithium chloride solution to a sorbent process to selectively adsorb lithium ions to a sorbent and form a lithium-depleted solution; and desorbing the lithium ions from the sorbent to produce a lithium-rich solution.

2. The process of claim 1 , further comprising subjecting the lithium-depleted solution to nanofiltration to remove at least some multivalent ions to form a purified lithium- depleted solution and recycling at least a portion of the purified lithium-depleted solution back to the sorption process to increase recovery of the lithium-rich solution.

3. The process of claim 2, wherein the multivalent ions removed using nanofiltration include Ca2+, Mg2+and Al3+.

4. The process of claim 2 or 3, wherein nanofiltration is performed at a pressure ranging from 5 bar to 20 bar.

5. The process of any one of claims 2 to 4, wherein nanofiltration has a lithium recovery rate of at least 90%.

6. The process of any one of claims 2 to 5, wherein nanofiltration includes subjecting the lithium-rich solution to an ion exchange resin to adsorb multivalent ions.

7. The process of claim 6, wherein the ion exchange resin comprises a sulfonate, iminodiacetate, or aminomethylphosphonic acid functionalized polystyrene / divinylbenzene resin.

8. The process of any one of claims 2 to 7, further comprising subjecting the lithium- depleted solution to reverse osmosis prior to recycling back to the sorption process.

9. The process of claim 8, wherein reverse osmosis is performed before at least aportion of the lithium-depleted solution is subjected to nanofiltration.

10. The process of claim 8 or 9, where the increase in TDS using reverse osmosis improves the lithium sorbent capacity.

11. The process of any one of claims 8 to 10, wherein reverse osmosis is performed at a pressure ranging from 20 to 120 bar.

12. The process of any one of claims 1 to 11, wherein a concentration of the purified lithium-depleted solution is less than a concentration of the lithium sulfate solution formed from leaching spodumene with sulfuric acid.

13. The process of any one of claims 1 to 12, further comprising polishing the lithium sulfate solution with a calcium source before adding calcium chloride to precipitate non-lithium species.

14. The process of any one of claims 1 to 13, wherein polishing is performed at a temperature ranging from 20°C to 80°C.

15. The process of any one of claims 1 to 14, wherein the sorbent is an aluminium-based layered double hydroxide (LDH) sorbent.

16. The process of any one of claims 1 to 15, wherein the LDH sorbent has a lithium adsorption capacity of 1 to 10 mg Li per gram of sorbent.

17. The process of any one of claims 1 to 16, wherein the LDH sorbent is regenerated after desorption for reuse in subsequent cycles.

18. The process of any one of claims 1 to 17, wherein the desorption of lithium ions from the sorbent is performed using a dilute warm lithium chloride solution.

19. The process of any one of claims 1 to 18, wherein the lithium chloride solution used for desorption has a concentration of 100 to 350 ppm.

20. The process of any one of claims 1 to 14, wherein the sorbent is a lithium manganese oxide (LMO) or lithium titanium oxide (LTO) sorbent.

21. The process of claim 20, wherein the LMO / LTO sorbent has a lithium adsorption capacity of 1 to 20 mg Li per gram of sorbent.

22. The process of claim 20 or 21 , wherein the LMO / LTO sorbent is regenerated with an acidic solution.

23. The process of any one of claims 1 to 22, wherein the desorption of lithium ions from the sorbent is performed using an acidic solution.

24. The process of any one of claims 1 to 23, further comprising subjecting the lithium- rich solution to reverse osmosis to increase the total dissolved solids (TDS) concentration.

25. The process of any one of claims 1 to 24, further comprising converting the lithium- rich solution into separate solutions of lithium hydroxide and hydrochloric acid using bipolar membrane electrodialysis.

26. The process of any one of claim 25, wherein the bipolar membrane electrodialysis process produces lithium hydroxide with a purity of at least 95%.

27. The process of any one of claims 1 to 26, wherein the lithium sulfate solution has a lithium concentration ranging from 8,000 ppm to 20,000 ppm.

28. The process of any one of claims 1 to 27, wherein the gypsum formed from the addition of calcium chloride is removed from the lithium chloride solution before the lithium chloride solution is subjected to the sorbent process.

29. The process of claim 28, wherein the removal of gypsum is performed using filtration or centrifugation.

30. The process of any one of claims 1 to 29, further comprising reductive roasting of the gypsum formed from addition of calcium chloride to form calcium oxide and sulfur dioxide.

31. The process of claim 30, wherein sulfur dioxide is converted to sulfur trioxide and then subsequently converted to sulfuric acid for reuse in leaching spodumene to form the lithium sulfate solution.

32. The process of claim 30 or 31 , wherein the calcium oxide formed is recycled for neutralisation of the sulfuric acid leachate.

33. The process of any one of claims 30 to 32, wherein the sulfuric acid formed is recycled for the sulfuric acid leaching of beta-spodumene.

34. The process of any one of claims 1 to 33, further comprising performing electrolysis on a solution containing the precipitated gypsum to produce calcium hydroxide and sulfuric acid.

35. The process of claim 34, wherein the calcium hydroxide formed is recycled for neutralisation of the sulfuric acid leachate.

36. A system for extracting lithium from spodumene, the system comprising: a source of lithium sulfate solution formed from leaching spodumene with sulfuric acid; a conversion unit in fluid communication with the source of lithium sulfate solution and configured to add calcium chloride to the lithium sulfate solution to form a lithium chloride solution and precipitate gypsum; and a sorbent unit in fluid communication with the lithium chloride solution and configured to (i) subject the lithium chloride solution to a sorbent process to selectively adsorb lithium ions to a sorbent thereby forming a lithium depleted solution and (ii) to desorb the lithium ions from the sorbent to produce a lithium-rich solution.

37. The system of claim 36, further comprising a nanofiltration unit in fluid communication with the lithium-depleted solution and the sorbent unit, the nanofiltration unit being configured to subject the lithium-depleted solution to nanofiltration to remove at least some multivalent ions to produce a purified lithium- depleted solution.

38. The system of claim 37, wherein the nanofiltration unit includes ion exchange resin configured to adsorb multivalent ions.

39. The system of claim 38, wherein the ion exchange resin comprises a sulfonate, iminodiacetate, or aminomethylphosphonic acid functionalizedpolystyrene / divinylbenzene resin.

40. The system of any one of claims 37 to 39, wherein the sorbent unit and nanofiltration unit are arranged such that at least a portion of the lithium-depleted solution can be recycled back to the sorbent unit to increase recovery of the high purity lithium-rich solution.

41. The system of any one of claims 36 to 40, further comprising a reverse osmosis unit configured to receive the lithium-depleted solution.

42. The system of claim 41 when dependent on claim 37, wherein the reverse osmosis unit is positioned upstream of the nanofiltration unit such that the nanofiltration unit can receive lithium-depleted solution from the reverse osmosis unit prior to forming the purified lithium-depleted solution.

43. The system of any one of claims 36 to 42, further comprising a polishing unit positioned upstream of the conversion unit, , the polishing unit having a calcium source and being configured to polish the lithium sulfate solution with the calcium source to neutralise and / or precipitate non-lithium species from the lithium sulfate solution before adding calcium chloride to further precipitate calcium sulphate.

44. The system of any one of claims 36 to 43, wherein the sorbent unit comprises an aluminium-based layered double hydroxide (LDH) sorbent, a lithium manganese oxide (LMO) sorbent, or a lithium titanium oxide (LTO) sorbent.

45. The system of any one of claims 36 to 44, wherein the sorbent unit is configured to use a lithium chloride solution or an acidic solution for desorbing the lithium ions from the sorbent.

46. The system of any one of claims 36 to 45, further comprising an electrodialysis unit downstream of the sorbent unit, the electrodialysis unit comprising a bipolar membrane electrodialysis and configured to convert the purified lithium solution into separate solutions of lithium hydroxide and hydrochloric acid using the bipolar membrane electrodialysis.

47. The system of any one of claims 36 to 46, wherein the conversion unit includes a gypsum removal unit configured to remove the gypsum formed from the addition ofcalcium chloride from the lithium chloride solution before the lithium chloride solution is subjected to the sorbent process.

48. The system of any one of claims 36 to 47, further comprising a roasting unit configured to receive and perform reductive roasting of the gypsum formed from addition of calcium chloride to form lime and sulfur dioxide.

49. The system of any one of claims 36 to 48, further comprising an electrolysis unit configured to receive and perform an electrolysis process on a solution containing the precipitated gypsum to produce calcium hydroxide and sulfuric acid.

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