A circuit and process for extracting lithium from brine

Abstract

The present invention relates to a circuit and method for extracting lithium from lithium-containing brine, from a lithium bearing brine reservoir such as a salt flat or salar. The invention may recover the lithium using a direct lithium extraction method which involves subjecting a lithium-containing feed brine stream to a lithium adsorption-desorption process. The adsorption-desorption process can be separated into a number of steps including a step wherein lithium from the feed brine is adsorbed onto a bed of lithium selective adsorbent and an elution step wherein the lithium is displaced from the adsorbent using an eluent and exits the column in an eluate stream.

Description

[0001] A CIRCUIT AND PROCESS FOR EXTRACTING LITHIUM FROM BRINE

[0002] FIELD OF INVENTION

[0003] The present invention relates to a circuit and method for extracting lithium from lithium-containing brine , from a lithium bearing brine reservoir such as a salt flat or salar .

[0004] The present invention relates particularly, although by no means exclusively, to a circuit and method for extracting lithium from brine using a direct lithium extraction method.

[0005] The present invention relates particularly, although by no means exclusively, to a circuit and method for extracting lithium from brine using a direct lithium extraction method involving adsorption and desorption of lithium from a plurality of columns each comprising a bed of lithium selective adsorbent.

[0006] BACKGROUND OF INVENTION

[0007] Traditionally, recovery of lithium from brine can be achieved using brine ponds in which lithium-containing brine is pumped into ponds where water from the brine is removed by evaporation. Once the brine in the pond reaches a target lithium concentration, the brine is delivered to a carbonation plant to recover lithium in the form of lithium carbonate .

[0008] Disadvantages of this process include :

[0009] (i) slow evaporation of water from the brine ;

[0010] (ii) large site footprint to accommodate the evaporation ponds ;

[0011] (iii) accumulation of environmentally hazardous impurities in the brine ponds ;

[0012] (iv) recoveries (from brine to product) of typically less than 70% due to co-precipitation of lithium with other salts and entrainment of lithium bearing brine in precipitated salts in the ponds ;

[0013] (v) evaporation of the majority of the brine , which lowers the water level of the brine in the salar, which can influence the surrounding fresh water tables ; and

[0014] (vi) requires magnesium to be removed via lime addition . In this specification, the term "fresh water" refers to water introduced externally into the circuit and excludes water recovered from lithium recovery processes such as recycled from the downstream reverse osmosis and evaporator units that are used to concentrate the lithium chloride solution after adsorption .

[0015] Direct lithium extraction is an alternative method of recovering lithium from brine . This process avoids the need for evaporation ponds and typically involves separating lithium from brine using adsorption , ion exchange or solvent extraction techniques .

[0016] A key difference between adsorption and ion exchange is that during the adsorption step, lithium, typically in the form of lithium chloride , from brine is physically adsorbed onto a lithium selective adsorbent and removed using a stripping solution . In contrast, during ion exchange, a lithium ion is chemically absorbed into an ion exchange material and exchanged for another positive ion .

[0017] An advantage of the adsorption technique is that an environmentally benign stripping solution such as water can be used to recover the lithium instead of ion exchange or solvent extraction reagents such as acids which are typically environmentally hazardous .

[0018] The adsorption technique is also typically lower cost than ion exchange or solvent extraction methods .

[0019] An adsorption-desorption circuit comprises a plurality of columns , each containing a bed of lithium selective adsorbent. The circuit is used to perform an adsorption (also known as loading) step wherein lithium from the feed brine stream is adsorbed (loaded) onto the adsorbent, a washing step wherein the spent brine is washed from the column using a solution of gradually decreasing brine concentration to avoid displacing adsorbed lithium from the adsorbent, and an elution step wherein the adsorbed lithium is displaced (eluted) from the adsorbent into an eluate stream. The eluate is then typically concentrated using reverse osmosis , evaporation or similar processes , and further processed to form lithium carbonate as the final product.

[0020] Capital cost for installing a lithium adsorption-desorption circuit at a lithium processing plant is often substantial . As a consequence , it would be highly desirable to provide an adsorptiondesorption circuit for recovering lithium that can be installed cost effectively without significantly impacting product output.

[0021] 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.

[0022] SUMMARY OF INVENTION

[0023] The invention relates to a circuit and method for recovery of lithium from lithium-containing brine , typically sourced from a lithium chloride containing salt flat or salar . The invention is also applicable to underground lithium-bearing brines .

[0024] The Applicant has developed another circuit and method for recovery of lithium from brine which is the subject of an Australian provisional patent application also titled "A CIRCUIT AND PROCESS FOR EXTRACTING LITHIUM FROM BRINE" filed on the same day. The disclosures in this patent specification are incorporated herein by cross-reference .

[0025] The invention may recover the lithium using a direct lithium extraction method. The method may involve subjecting a lithium- containing feed brine stream to a lithium adsorption-desorption process .

[0026] The adsorption-desorption process can be separated into a number of steps including at least an adsorption (also known as loading) step wherein lithium from the feed brine is adsorbed onto a bed of lithium selective adsorbent (also known as resin or sorbent) and an elution step wherein the lithium is displaced from the adsorbent using an eluent and exits the column in an eluate stream.

[0027] The adsorption-desorption process may be performed by one or more adsorption columns containing a bed of lithium selective adsorbent. Each step of the adsorption-desorption process is performed by each of the one or more adsorption columns . The columns may be connected in series , in parallel or a combination. Having the columns connected may permit certain steps of the adsorption-desorption process to be performed sequentially and / or permit certain steps of the adsorption-desorption process to be performed simultaneously.

[0028] In this specification, the term "raw brine" refers to a saline solution containing dissolved lithium salts obtained directly from a subsurface or surface lithium-bearing brine reservoir such as a salt flat, salar, brine aquifer, geothermal brine , oilfield brine , or other lithium-bearing aqueous source and present in an unprocessed state prior to undergoing any concentration, purification, or chemical treatment. Such raw brine typically comprises lithium chloride and / or lithium sulfate together with other dissolved salts and minerals , which may include sodium, potassium, magnesium, calcium, boron, and associated anions .

[0029] In this specification, the term "feed brine" refers to a raw brine that that has optionally undergone one or more pretreatment operations prior to subsequent processing. Such pretreatment may include , for example , the removal of deleterious constitutents (such as silica, carbonates , bicarbonates , borates , arsenic, ferrous or ferric, zinc, cadmium or other impurities) , adjustment of pH, removal of suspended or precipitated solids , and / or modification of the brine temperature .

[0030] In this specification, the term "lithium selective adsorbent" means a solid material configured to preferentially bind lithium ions from a lithium-containing feed brine, thereby facilitating the capture and separation of lithium relative to other dissolved species . The lithium selective adsorbent may comprise , for example, an aluminum- containing layered double hydroxide material . In this specification, the term "eluate" encompasses "advance eluate" , wherein "advance eluate" refers to eluate that is not returned to the feed tank . The term eluate also encompasses a lower grade portion of the eluate that is produced in step (d) and is used for the elution recycle step .

[0031] The invention provides a method of recovering lithium from feed brine using an adsorption-desorption circuit comprising a plurality of adsorption columns , each containing a bed of lithium selective adsorbent, the method including:

[0032] (a) an adsorption lead step including directing lithium-containing feed brine into one of the adsorption columns to form lithium-loaded adsorbent and a lead column product stream ;

[0033] (b) an adsorption lag step including directing the lead column product stream from step (a) into another adsorption column to form lithium-loaded adsorbent and a lithium-depleted brine stream;

[0034] (c) an elution recycle step including directing a first mobile phase into one of the columns from step (a) ; and

[0035] (d) an elution step including directing a second mobile phase into the column from step (c) to form a lithium-enriched eluate for downstream processing, wherein up to three of steps (a) - (d) are performed simultaneously.

[0036] In sea® embodiments , step (c) and step (d) are psrformsd or step (d} is performed simultaneously with, stops (a) and (b) .

[0037] Suring adsorption, the adsorbent first receives the discharge from the lead step (lead product stream} so that any lithium that was not adsorbed can be loaded onto th® adsorbent leaving a lithium-depleted brine stream. The adsorbent then receives feed brine to form lithium- loaded adsorbent and a lead column product stream which is the mobile phase for the adsorption lag step (b) .

[0038] In this specification, the term "mobile phase" refers to the fluid stream that passes through a column and can comprise one or more liquors including feed brine , the lead column product stream from step (a) , eluent and eluate depending on the step of the adsorption- desorption process . This is in contrast to the "stationary phase" comprising the bed of lithium selective adsorbent.

[0039] The first mobile phase for the elution recycle step may be water or eluate . Where the mobile phase for the elution recycle step is eluate , the eluate used is a lower grade portion of the eluate produced in step (d) . The eluate used for the elution recycle may be from the last portion of eluate that is discharged from the column during the elution in step (d) . The portion of the eluate used in the elution recycle step (c) has a low lithium concentration, which ensures that the remainder of the eluate has as high a lithium concentration as possible . In some embodiments , the portion of the eluate of step (d) that is used in the elution recycle step (c) may have a lithium concentration of 400mg / L or less , whereas the advance eluate may have a lithium concentration of 400mg / L or more . For example , the portion of the eluate of step (d) that is used in the elution recycle step (c) may have a lithium concentration of 300mg / L or less , 200mg / L or less , or 100mg / L or less whereas the advance eluate concentration may have a lithium concentration of 500mg / L or more , 600mg / L or more, 700mg / L or more , or 800mg / l or more . The mobile phase for the elution recycle step displaces the depleted brine entrained in the column. The mobile phase for the elution recycle step does not use a number of washing solutions , each of which having a gradually decreasing brine concentration .

[0040] The second mobile phase (i .e . eluent) may be water . Suitably, the water may be sourced from one or more of fresh water, evaporator condensate and reverse osmosis permeate (e .g. from concentrating the eluate exiting the elution step) . The water may be pure water, may contain low concentrations of lithium or may contain impurities . In some embodiments , entrained eluate is displaced during a preadsorption step, and the discharged eluate (which may contain low concentrations of lithium) may be recycled to the eluent tank .

[0041] The present invention was developed to reduce capital costs of a lithium recovery plant by reducing the number of columns required for the process . Traditionally, an adsorption-desorption circuit includes at least one adsorption column per step so that the discharge from one column is delivered to a different column to perform the next step, and the loaded column can be washed while a washed column is eluted ready for re-loading. This means that a bank of at least four adsorption columns is required to perform a method that involves a first adsorption step, a second adsorption step, a washing step and a desorption step.

[0042] It is expected that maximizing desorption of lithium from the loaded adsorbent during the elution stage optimizes the economic output of the lithium recovery process . This is typically done by increasing the duration of the washing and / or elution stages .

[0043] However, the Applicant observed a rate of diminishing returns as lithium depletes from the adsorbent (i .e . a longer elution time or more eluant is required to desorb lithium as the adsorbent approaches 100% desorption) .

[0044] The Applicant has discovered that a similar amount of lithium could be recovered by taking a directly opposite approach, specifically by reducing the washing step and / or reducing the elution step, or performing either or both these stages faster . As one example , eluent flow rate can be increased during the elution stage in favour of completing more operational cycles , where each operational cycle comprises steps (a) - (d) .

[0045] This also led to the realization that an efficient adsorptiondesorption circuit could potentially be developed with a reduced number of columns , and in some cases , having one less column than the number of steps required for the lithium recovery process .

[0046] Reducing the number of columns also reduces the footprint of the circuit and may potentially lead to savings on land cost.

[0047] In an embodiment, the invention provides a method of recovering lithium from feed brine using an adsorption-desorption circuit comprising a plurality of adsorption columns , each containing a bed of lithium selective adsorbent, the method including:

[0048] (a) an adsorption step including directing lithium-containing feed brine into at least one of the adsorption columns to form lithium- loaded adsorbent and a lithium-depleted brine stream;

[0049] (b) an elution recycle step including directing, into a column containing lithium-loaded adsorbent, a first mobile phase comprising a lower grade portion of eluate obtained from a prior elution step, said lower grade portion having a lower lithium concentration than an advance eluate portion; and

[0050] (c) an elution step including directing a second mobile phase comprising water into the column from step (b) to displace lithium from the adsorbent and form a lithium-enriched eluate stream for downstream processing.

[0051] The adsorption-desorption process includes an elution recycle step to displace entrained or residual brine in the column (s) prior to the elution step. Particularly, the elution recycle step reduces the concentration of unwanted ions (e . g. sodium) in the brine from reaching the eluate . The elution recycle step may use a lower grade portion of the eluate produced in step (d) as the first mobile phase , which may be the last portion of eluate that is discharged from the column during the elution in step (d) . The portion of the eluate used in the elution recycle step (c) has a low lithium concentration, which ensures that the remainder of the eluate has as high a lithium concentration as possible .

[0052] The elution recycle step avoids the need for stepwise washing using a number of washing solutions , each of which having gradually decreasing brine concentration .

[0053] In some embodiments , the elution recycle step and the elution step are performed sequentially on the same column .

[0054] The direction of flow of the elution recycle step may be downwards so that the first mobile phase (which has a lower density) efficiently displaces the entrained feed brine or depleted brine (which has a higher density) and reduces mixing. The elution recycle step provides a sufficient volume of the first mobile phase to displace the entrained or residual brine . For example , the volume of the first mobile phase for the elution recycle step is about equal to the void volume of the column plus the associated piping. In some embodiments , the volume of the first mobile phase for the elution recycle step is from about 0 . 5 BV to about 1.5 BV.

[0055] The method may include a pre-adsorption step to displace entrained or residual eluent in the columns (s) prior to lag adsorption step (b) . The pre-adsorption step reduces the amount of feed brine required for the adsorption step and consequently becoming spent brine . In some embodiments , the pre-adsorption step and lagadsorption step are performed sequentially on the same column .

[0056] The pre-adsorption step (e) may include directing a third mobile phase into the adsorption column from step (d) to displace at least part of the eluent in the column. In some embodiments , step (e) and (b) may be performed sequentially on the same column. In some embodiments , step (d) and (e) may be performed sequentially on the same column.

[0057] The third mobile phase for the pre-adsorption step may be brine . The third mobile phase may include depleted brine or feed brine . Suitably, the third mobile phase includes feed brine . The third mobile phase may include eluate recycle product. The direction of flow of the pre-adsorption step may be upwards so that the third mobile phase (which has a higher density) efficiently displaces the entrained eluent or eluate (which has a lower density) and reduces mixing .

[0058] The pre-adsorption step provides a sufficient volume of the third mobile phase to displace the entrained eluate or residual eluent. For exanrple , the volume of the third mobile phase for the pre- adsorption step is about equal to the void volume of the column plus the associated piping. In some embodiments , the volume of the third mobile phase for the pre-adsorption step is from about 0 . 5 BV to about 1.5 BV.

[0059] Step (e) may include directing the third mobile phase into the adsorption column from step (d) at a linear velocity ranging from fl- 20 m / hr, suitably 5-15 m / hr, more suitably 8-15 m / hr, and even more suitably 10-15 m / hr. In one embodiment, step (e) includes directing the third mobile phase into the adsorption column from step (d) at a linear velocity of 9.5 m / hr .

[0060] Step (e) may include directing the third mobile phase into the adsorption column from step (d) at a flow rate ranging from 40-80 m3 / hr, suitably, 50-70 m3 / hr, more suitably 60 m3 / hr .

[0061] In this specification, the linear velocity is calculated based on an em ty column. Volumetric flow rate may be calculated by multiplying the linear velocity with the cross-sectional area of the column .

[0062] An additional column may be required to accommodate the preadsorption step. Alternatively, some steps may be carried out sequentially on the same column. For example , the pre-adsorption step may precede the lag adsorption step and be performed on the same column, or may follow the elution step and be performed on the same column prior to commencing the adsorption step .

[0063] The timing for each step may be adjusted to reduce wait times or inactivity of at least one column during the process . The duration of each step may be adjusted by adjusting the flow rate of the mobile phase for that step, or by adjusting the volume of mobile phase to be used for that step .

[0064] Whilst developing this methodology, the Applicant discovered that reducing the elution recycle or elution time or performing either or both these stages faster may result in one or more columns not being fully utilized due to an imbalance of the mass flow rates of the incoming and outgoing mobile phases . This inefficiency was mitigated by adjusting the duration or flow rate of one or more steps of the method. The concentration of the lithium in the feed brine may range from 50-10 , OOOmg / L, suitably around 75mg / L .

[0065] Step (a) may include directing the feed brine into the column at a linear velocity ranging from 0-20 m / hr, suitably 5-15 m / hr, more suitably 8-15 m / hr, and even more suitably 10-15 m / hr . In one embodiment, step (a) includes directing the feed brine into the column at a linear velocity of 9.5 m / hr.

[0066] Step (a) may include directing the feed brine into the column at a flow rate ranging from 40-80 m3 / hr, suitably, 50-70 m3 / hr, more suitably 60 m3 / hr.

[0067] Step (b) may include directing the discharge from step (a) into another adsorption column at a linear velocity ranging from 0-20 m / hr, suitably 5-15 m / hr, more suitably 8-15 m / hr, and even more suitably 10-15 m / hr. In one embodiment, step (b) includes directing the discharge from step (a) into another adsorption column at a linear velocity of 9.5 m / hr .

[0068] Step (b) may include directing the discharge from step (a) into another adsorption column at a flow rate ranging from 40-80 m3 / hr, suitably, 50-70 m3 / hr, more suitably 60 m3 / hr .

[0069] The use of an adsorption lead step (a) and an adsorption lag step (b) in the method assists in maximizing the adsorption of lithium from the feed brine . The method may also include increasing the residence time of the feed brine and / or the discharge from the lead adsorption step in the column (s) during the adsorption step. Suitably, the pause may be up to 30 minutes , more suitably, up to 20 minutes , even more suitably, up to 10 minutes . This may maximise adsorption of lithium by the adsorbent and reduce the concentration of lithium in the spent brine .

[0070] An increased residence time may be achieved by reducing the flow rate of the feed brine and / or the discharge from the lead adsorption step . The method may include a drain recycle step involving removing part of the brine entrained in the column after step (a) or (b) . Suitably, the drain recycle step is performed after step (a) . The removed brine may be discharged into a brine feed tank .

[0071] The method may include a backwash step . This step is suitably performed when pressure drop across a column increases . Suitably, the backwash step is performed after step (a) or (b) , suitably after step (a) . The backwash may be returned to the brine feed tank . The backwash step may involve directing a mobile phase upwardly into a column .

[0072] Step (c) may displace at least part of the feed brine in the column. Suitably, step (c) may involve using eluate to displace the entrained brine . One benefit of using eluate instead of water is that the higher concentration of lithium in the eluate reduces the amount of lithium that may be displaced from the adsorbent during this step. The elution recycle step may use a lower grade portion of the eluate produced in step (d) as the first mobile phase, which may be the last portion of eluate that is discharged from the column during the elution in step (d) . The portion of the eluate used in the elution recycle step (c) has a low lithium concentration, which ensures that the remainder of the eluate has as high a lithium concentration as possible .

[0073] Step (c) may include directing a first mobile phase into the column from step (a) .

[0074] The method may include mixing the displaced brine in step (c) with the lithium-containing feed brine . Suitably, the method includes directing the displaced brine in step (c) into the feed brine tank.

[0075] Step (c) may include directing the first mobile phase into the column at a linear velocity ranging from 0-20 m / hr, suitably 5-15 m / hr, more suitably 8-15 m / hr, and even more suitably 10-15 m / hr . In one embodiment, step (c) includes directing the first mobile phase into the column at a linear velocity of 9.5 m / hr . Step (c) may include directing the first mobile phase into the column at a flow rate ranging from 40-80 m3 / hr, suitably, 50-70 m3 / hr, more suitably 60 m3 / hr. In some embodiments , the elution recycle step may be performed at a higher flow rate, such as greater than 60 m3 / hr, such as a flow rate ranging from 60-80 m3 / hr .

[0076] Step (d) may include directing a second mobile phase (eluent) into the column from step (c) .

[0077] Step (d) may include directing the second mobile phase into the column from step (c) at a linear velocity ranging from 0-20 m / hr, suitably 5-15 m / hr, more suitably 8-15 m / hr, and even more suitably 10-15 m / hr. In one embodiment, step (d) includes directing the second mobile phase into the column from step (c) at a linear velocity of 9.5 m / hr .

[0078] Step (d) may include directing the second mobile phase into the column from step (c) at a flow rate ranging from 40-80 m3 / hr, suitably, 50-70 m3 / hr, more suitably 60 m3 / hr . In some embodiments , the elution step may be performed at a higher flow rate , such as greater than 60 m3 / hr, such as a flow rate ranging from 60-80 m3 / hr. Step (d) may incorporate a pause during the elution step to allow the mobile phase in the column to be held for a short period in the column. Suitably, the pause may be up to 30 minutes , more suitably, up to 20 minutes , even more suitably, up to 10 minutes . This provides more time for lithium to desorb from the adsorbent. This can increase the concentration of lithium on the eluate .

[0079] The displaced eluate from step (d) may be directed to an eluate tank .

[0080] The method may include monitoring the conductivity of the mobile phase in each column .

[0081] Ideally, columns switched from one step to the next at a precise point based primarily on impurity content. This is particularly important in the elution recycle step, so as to balance fresh water use and the recycling of eluted lithium back to the feed, against insufficient displacement of the feed brine which increases impurity loads in the eluate .

[0082] The step of monitoring conductivity of the mobile phase resulted from the Applicant' s realization that the main impurities (e . g. sodium chloride) of the process contribute significantly to conductivity. This provided a way of deciding when to switch column operations from one step to another without having to use analytical methods which inevitably introduce time delays . In one example, an increase in conductivity would indicate that the pre-adsorption step (e) is complete, and the second mobile phase has been displaced from the column and replaced by the third mobile phase . In another example , a decrease in conductivity would indicate that the elution recycle step (c) has displaced the feed brine from the column and the column is ready to receive the second mobile phase .

[0083] Monitoring conductivity of the mobile phase may also allow the distribution of the impurities , suitably sodium, in the column to be tracked. This may provide a means of monitoring the mixing of the mobile phase and entrained liquor or flow regime of the mobile phase .

[0084] The method may include monitoring the flow velocity of the mobile phase . This may allow the flow regime of the mobile phase to be determined .

[0085] The method may include introducing a delay when switching mobile phases to provide staggered valve timing.

[0086] Default operation when the columns shift from one step to another (e . g . when a column shifts from loading to elution recycle) , typically involving central multiport valves or carousel systems , is that the valve which controls the mobile phase to the column switches to a different mobile phase at the same time that the valve which controls the destination of mobile phase leaving the column switches . But because columns have a residence time, the liquor at the discharge is still the same as it was during the previous step immediately after changing the feed valve . The Applicant realised that if the residence time distribution of liquor in the column is measured or estimated, then a delay can be incorporated so that the discharge valve position is switched some time after the feed source valve .

[0087] The method may include subjecting the lithium-enriched eluate from step (d) to a concentration step. Suitably, the lithium concentration step involves subjecting the lithium-enriched eluate to reverse osmosis , membrane separation or similar process . The concentration step may generate water in the form of reverse osmosis permeate or evaporator condensate . The water generated in this step may be recycled, for example , for use as the first or second mobile phase or as the eluent.

[0088] The method may include a step of filtering the eluate to remove impurities from the eluate . Suitably, the filtering step may involve passing the eluate through a filter that is configured to separate divalent ions (such as Mg2+and Ca2+) from monovalent ions .

[0089] The concentrated lithium-enriched eluate may be processed to form lithium-containing products including lithium carbonate or lithium hydroxide .

[0090] Th® method may include controlling th® flow rate of the second mobile phase in elution step (d) to and / or providing sufficient eluent to elute up to 80% of the adsorbed lithium, Thia approach avoids over-eluting the adsorbed lithium which may dilute the final advance eluate .

[0091] Terminating step (d) around the time when the rate of lithium desorption is maximum may reduce elution tim® while mawimiring lithium concentration in the eluate .

[0092] The method may include terminating step (d) before a maximum of 8Qwt% , suitably a maximum of 70wt% , more suitably a maximum of 60wt% , or even more suitably 40wt% of lithium is desorbed from th® lithium loaded adsorbent into th® lithium enriched, eluate stream. Th® Applicant deliberately avoids complete (100%) desorption of lithium from th® adsorbent to minimise irrsvereibl® elution which may reduce th® maximum loading capacity of th© adsorbent.

[0093] The method may include a step of controlling the loading time to elution time rati© during each operational cycle . Suitably, a 3- column circuit has a 1 : 2 elution to loading ratio . Suitably, a 4~ column circuit has a 2 : 2 elution to loading ratio , Suitably, a 5~ column circuit has a 2 : 3 or 3 : 2 elution to loading ratio . Suitably, a 6 -column circuit has a 3 : 3 elution to loading ratio . Suitably, a 7-©olumn circuit has a 3 : 41 elution to loading ratio . Suitably, an 8- column circuit has a 4 : 4 elution to loading ratio . Suitably, a 9- column circuit has a 4 : 5 elution to loading ratio , Suitably, a 10~ column circuit has a 5 : S elution to loading ratio .

[0094] In this specification, ''‘unloading"' encompasses elution recycle (i .® , washing) and ®lution steps and "loading” encompasses pra-adsorption and adsorption steps .

[0095] The invention also provides a lithium adsorption-desorption circuit configured to perform the previously described method.

[0096] The circuit may comprise at least three columns . In one embodiment, the circuit consists of three columns . In another embodiment, the circuit consists of five columns . In another embodiment, the circuit may consists of from five to ten columns .

[0097] The circuit may be configured to perform a pre-adsorption step . This step displaces entrained or residual eluate in the column (s) prior to the adsorption step to reduce the amount of eluent required for the adsorption phase and then becoming spent brine . In one embodiment, the pre-adsorption step (step (e) ) precedes step (b) . In other words , steps (e) and (b) are performed sequentially on the same column of the circuit.

[0098] The circuit may be configured to perform a drain recycle step involving removing part of the brine contained in the column after step (a) or (b) . Suitably, the circuit is configured to perform the drain recycle step after step (a) . The removed brine may be suitably discharged into a brine feed tank .

[0099] The circuit may be a fixed bed system.

[0100] The circuit may exclude central multiport valves or carousel systems including rotation of columns .

[0101] The circuit may include a valving system configured to deliver the mobile phases downwardly into a column .

[0102] The circuit may be configured to perform a backwash step . Suitably, the valving system is configured to deliver a mobile phase upwardly into a column during a backwashing step.

[0103] The circuit may include a flow control valve to control the flow rate of a mobile phase into a column.

[0104] The circuit may include a depleted brine tank for receiving the depleted brine . The tank may be in fluid communication with a column to deliver the depleted brine as the third mobile phase for a preadsorption step.

[0105] The circuit may include a feed brine tank for storing feed brine . The feed brine tank may be in fluid communication with a column to receive displaced brine from elution recycle step (c) . The feed brine tank may be in fluid communication with a column to receive brine from a drain recycle step. The feed brine tank may be in fluid communication with a column to receive backwash from a backwash step .

[0106] The circuit may include a low grade eluate tank for receiving the low grade eluate . The tank may be in fluid communication with a column to deliver the low grade eluate to be used as the first mobile phase for an elution recycle step.

[0107] The circuit may include at least one conductivity meter to measure the concentration of impurities in the mobile phases . This allows conductivity values to be used as triggers to switch columns from one step to another. Suitably, the conductivity meter (s) may be connected to a valve that switches flow between eluate advance and eluate recycle back to feed tank or to another column .

[0108] Each column may include a flow distributor to reduce turbulence of the mobile phase being introduced into a column . Suitably, the flow distributor evenly distributes fluid across the cross-sectional area of a column. The flow distributor may be a fractal distributor .

[0109] The circuit may be connected to a concentrator . Suitably, the concentrator may be a reverse osmosis or membrane separation unit. The concentrator may be connected to an eluent tank to direct water removed from the eluate to the tank .

[0110] The circuit may include a filter to remove impurities from the eluate . Suitably, the filter is a nanofilter that separates divalent ions (such as Mg2+and Ca2+) from monovalent ions .

[0111] Incorporating a filter into the circuit may reduce the amount of NaOH and Na2CO3addition required to remove Mg (OH)2and CaCO3when forming the final lithium chloride product from the eluate .

[0112] The invention also provides an adsorption-desorption circuit configured to perform the previously described method. The process may include multiple circuits or modules that are operated together to process the feed brine .

[0113] The circuit may comprise from two to 30 columns . The circuit may comprise from two to 28 columns . The circuit may comprise from two to 25 columns . The circuit may comprise from two to 20 columns . The circuit may comprise from four to 20 columns . The circuit may comprise from four to 18 columns . The circuit may comprise from four to 16 columns . The circuit may comprise from four to 12 columns . The circuit may comprise from five to 10 columns . The circuit may comprise from six to 12 columns . BRIEF DESCRIPTION OF DRAWINGS

[0114] The present Invention is described further with reference to the accompanying drawings of which:

[0115] Figure 1 is a block flow diagram of a circuit in accordance with one form of the present invention.

[0116] Figure 2 is a process flow diagram illustrating a circuit comprising four modules each comprising three columns in accordance with another form of the present invention .

[0117] Figure 3 illustrates a pair of columns in a lead-lag arrangement for the adsorption step in accordance with another form of the present invention .

[0118] Figure 4 is a diagram illustrating the sequence of operation of a 3- column circuit according to another form of the present invention.

[0119] Figures 5A-5I illustrate the sequence of operation for a 3 -column circuit according to another form of the present invention.

[0120] Figure 6 illustrates the concentration of lithium and impurities over the duration of the elution recycle step (c) and elution step (d) showing the lower grade portion of the eluate produced in step (d) which may be used as the first mobile phase in the elution recycle step (c) in accordance with another form of the present invention .

[0121] Figure 7 illustrates the configuration of a 7 -column circuit according to another form of the present invention . DETAILED DESCRIPTION The following description of the invention is in the context of recovering lithium from a lithium chloride-containing brine pond or lake . However, it can be appreciated that the invention is equally applicable to recovery of lithium from other lithium-containing sources . The invention was developed with a desire to reduce the footprint of a lithium recovery plant, suitably by reducing the number of columns required to perform the lithium recovery process of the invention.

[0122] A key feature of the invention is the use of a reduced number of columns for the lithium recovery process . Specifically, the present invention utilizes one less column than the steps required to perform the lithium recovery process . This would result in a maximum of three of the four steps being able to be performed simultaneously during the process .

[0123] In order to mitigate the loss of one column in the process , the duration or flow rate of each step may need to be adjusted to generate a similar eluate output to a circuit including the full complement of columns .

[0124] Figure 1 provides a general block diagram of a lithium adsorptiondesorption circuit 10 according to the present invention . In this figure , the circuit comprises a feed brine tank 12 , an eluent (water) tank 14 , a bank of adsorption columns 16 , an eluate tank 18 and a depleted brine tank 20 . In another form of the circuit illustrated in Figure 1 , there is an eluate recycle tank 22 connected to the feed brine tank 12 . The eluate recycle tank 22 is shown in Figure 2 which illustrates another lithium adsorptiondesorption circuit 10 according to the present invention .

[0125] The adsorption columns may be arranged in modules , with each module comprising a pre-determined number of columns . Figure 2 illustrates a circuit comprising four modules comprising three adsorption columns each. Three of the four modules operate during the lithium recovery process with the fourth module held in reserve .

[0126] In this example, the circuit can produce 3 , 500 tons of lithium carbonate . A total of 210m3of adsorbent is distributed equally between the 9 columns .

[0127] Each column has an internal diameter of 900 mm and an external diameter of 4 ,250 mm. The bed height is 1 , 900 mm comprising 1 ,700 mm of adsorbent / resin sandwiched by 200 nun of inert material at the top and bottom of the column. However, the column can be scaled up or down depending on operational requirements .

[0128] The lithium extraction process includes the following steps :

[0129] • an adsorption lag step in which discharge from an adsorption lead column is fed into an adsorption lag column to adsorb lithium from the discharge onto the bed of lithium selective adsorbent in the adsorption lag column to form lithium- loaded adsorbent and a lithium-depleted brine stream;

[0130] • an adsorption lead step in which brine from a feed brine tank is fed into an adsorption lead column to adsorb lithium from the feed brine onto the bed of lithium selective adsorbent in the adsorption lead column;

[0131] • an elution recycle step in which a first mobile phase is used to displace at least part of the brine entrained in the adsorption lag column; and

[0132] • an elution step in which a second mobile phase is used to desorb lithium from the lithium-loaded adsorbent, and form a lithium-enriched eluate .

[0133] A key feature of the invention is the use of a reduced number of columns for the lithium recovery process . In some of the examples , the present invention utilizes a circuit comprising three columns to perform the four steps of the lithium extraction process . This would result in a maximum of three of the mentioned four steps being able to be performed simultaneously during the process .

[0134] In order to mitigate the loss of one column in the process , the duration or flow rate of each step may be adjusted to generate a similar eluate output to a circuit including the full complement of four columns and / or to balance the loading and unloading phases .

[0135] The lithium extraction process may include the following optional steps :

[0136] • a backwash step after the adsorption lead step to reduce any pressure drop across the column; • a drain recycle step after the adsorption lead step to remove part of the brine entrained in the column; and

[0137] • a pre-adsorption step to displace at least part of the eluate in the column after the elution step and before the column transitions to the adsorption lag step .

[0138] The pre-adsorption step improves the efficiency of the adsorption step by removing water from the column (using brine) prior to the adsorption step.

[0139] In Figure 1 , the circuit 10 used to perform the lithium extraction process comprises a feed brine tank 12 for storing feed brine (FB) . The feed brine tank 12 is connected to the bank of adsorption columns 16 which received the raw brine (RB) for the adsorption step .

[0140] The feed brine tank 12 is also in fluid communication with the adsorption columns to receive the discharge from the elution recycle (ER) , backwash (BK) and drain recycle (DR) steps from the columns .

[0141] In the circuit illustrated in Figure 2 , the feed brine tank 12 is connected to an eluate recycle tank 22 . Tank 22 receives entrained brine discharged from the elution recycle step before the discharge is returned to the feed brine tank 12 .

[0142] The bank of adsorption columns comprises two columns connected in series to provide a lead adsorption column CIA and a lag adsorption column C1B in which discharge from the lead adsorption column is delivered to the top of the lag adsorption column (see Figure 3) .

[0143] The adsorption columns 16 are also connected to an eluent tank (or water tank) 14 to deliver eluent (i . e . the second mobile phase) , typically in the form of water, to the column performing the elution step (see Figure 1) .

[0144] The adsorption columns 16 are also connected to an eluate tank 18 to receive part of the eluate (ER) as the first mobile phase for the eluate recycle step (see Figure 1) . The connection between the adsorption columns 16 and the eluate tank 18 also allows the eluate tank 18 to receive discharge from the pre-adsorption (PA) step and eluate (EL) from the elution step (see Figure 1) .

[0145] The adsorption columns are further connected to a depleted brine tank (2) which receives depleted brine (DB) from the adsorption step (see Figure 1) , particularly from the lag adsorption column C1B (see Figure 3) .

[0146] The sequence of steps and the duration of each step of the lithium extraction process for the three modules is illustrated in Figure 4 . Each column is represented by a pair of coloured lines . The top line represents the feed (mobile phase) introduced into the column and the bottom line represents the destination of the mobile phase .

[0147] A description of the steps performed by each column during the process is set out below.

[0148] In Figure 4 , Column 1 begins with a lead adsorption step (in orange) in which feed brine is introduced into the column. During this step, lithium from feed brine is adsorbed onto the bed of adsorbent in the column. This step is performed for 1 hour . Advance eluate is then delivered into Column 1 to displace entrained or residual brine , which can be returned to the feed tank, in an elution recycle step (in blue) . This step is performed for 12 minutes . Column 1 then transitions into an elution step (in green) in which an eluent in the form of water is introduced into the column to displace the adsorbed lithium from the adsorbent into an eluate stream. This step lasts for 48 minutes . Column 1 then performs a pre-adsorption step involving the use of brine to displace entrained or residual eluate in the column prior to Column 1 transitioning into a lag adsorption step (in red) . The lag adsorption step involves the feeding of brine from the previous column (the product of lead column loading) into Column 1 and lasts for 1 hour. Thereafter, Column 1 receives fresh feed brine and performs a new lead adsorption step to complete one cycle of the process . In Figure 4 , Column 2 undergoes the same sequence of steps as Column

[0149] 1 but is offset from Column 1 by 1 hour. In this respect, the Column

[0150] 2 process cycle begins with the pre-adsorption step and transitions into a 1 hour long lag adsorption step .

[0151] In Figure , Column 3 undergoes the same sequence of steps as Columns 1 and 2 but is offset from Column 2 by 1 hour . In this respect, the Column 3 process cycle begins with a 12 minute elution recycle step before transitioning into a 48 minute elution step .

[0152] Figures 5A-5I illustrate the sequence of fluid flow during operation of another circuit according to the invention comprising three adsorption Columns 1-3. The circuit output can be increased by connecting multiple modules in a stacked arrangement.

[0153] In operation, feed brine from a pond or lake is collected and is optionally subjected to pre-treatment operations prior to being stored in the feed brine tank 12 . The concentration of the lithium in the feed brine typically ranges from is around 75mg / L .

[0154] Figure 5A shows the feed brine tank 12 feeding the brine into adsorption column 2 to initiate the lead adsorption step . The lead adsorption step is performed for 60 minutes during which lithium from the feed brine is adsorbed onto the lithium-loaded adsorbent.

[0155] Column 1 is fluidly connected to Column 2 to receive the discharge from the lead adsorption step. The lag adsorption step is performed for 60 minutes . This lead-lag arrangement increases the residence time of the feed brine in the adsorption step to maximise adsorption of lithium from the feed brine . The DB stream exiting the lag column is directed to a depleted brine tank.

[0156] Figure 5A also shows Column 3 receiving eluent from eluent tank 14 to perform an elution recycle step in which discharge from the Column 3 is directed into eluate recycle tank 22 which is itself connected to feed brine tank 12 . This step displaces at least part of the brine entrained in the column. To minimize water usage , advance eluate can be used as the first mobile phase . However, water is also a suitable alternative as the first mobile phase .

[0157] A description of the next steps performed by each column during the lithium recovery process is summarized below. The change in fluid flows is illustrated by the coloured lines in which red denotes no flow and green denotes fluid flow.

[0158] Figure 5B

[0159] • Column 1 continues the adsorption lag step.

[0160] • Column 2 continues the adsorption lead step.

[0161] • Column 3 transitions into the elution step in which discharge from Column 3 is directed to an eluate tank 18 . The transition of the elution recycle step to the elution step in Column 3 occurs while the steps being performed in the other columns remain unchanged.

[0162] A backwash step may be performed on the lead adsorption column if a pressure drop increase is detected. To perform this step, part of the feed brine is directed upwards into the lead adsorption column with the backwash discharge returning to the feed brine tank 12 . This step terminates when the pressure drop returns to an acceptable predetermined value .

[0163] Figure 5C

[0164] • Column 1 transitions from the adsorption lag step into a stand-by mode in which no fluid flows through the column.

[0165] • Column 2 transitions from an adsorption lead step into a drain recycle step. The drain recycle step returns part of the brine contained in Column 2 to the feed brine tank 12 .

[0166] • Column 3 continues the elution step .

[0167] Figure 5D

[0168] • Column 1 transitions from standby mode into the adsorption lead step in which Column 1 receives brine from feed brine tank 12 .

[0169] • Column 2 transitions from the drain recycle step into the elution recycle step in which displaced brine from the column is discharged into the eluate recycle tank 22 and ultimately returned to feed brine tank 12 .

[0170] • Column 3 transitions from the elution step into the adsorption lag step to receive discharge from Column 1 .

[0171] Figure 5E

[0172] • Column 1 continues the adsorption lead step.

[0173] • Column 2 transitions from elution recycle step into the elution step in which discharge from Column 2 is directed to an eluate tank 18 . The transition of the elution recycle step to the elution step in Column 3 occurs while the steps being performed in the other columns remain unchanged.

[0174] • Column 3 continues the adsorption lag step. jure 5F

[0175] • Column 1 transitions from the adsorption lead step into a drain recycle step . The drain recycle step returns part of the brine contained in Column 1 to the feed brine tank 12 .

[0176] • Column 2 continues the elution step .

[0177] • Column 3 transitions from the adsorption lag step into the standby mode in which no fluid flows through the column. jure 5G

[0178] • Column 1 transitions from the drain recycle step into the elution recycle step in which displaced brine from the column is discharged into the eluate recycle tank 22 and ultimately returned to feed brine tank 12 .

[0179] • Column 2 transitions from elution step into the adsorption lag step which receives discharge for Column 3 and discharges effluent into the depleted brine tank .

[0180] • Column 3 transitions from standby mode into the adsorption lead step which receives brine from feed brine tank 12 and discharges into Column 2 .

[0181] • Column 1 transitions from the elution recycle step into the elution step which receives eluent from eluent tank 14 and discharges eluate into eluate tank 18 . The transition of the elution recycle step to the elution step occurs while the steps being performed in the other columns remain unchanged.

[0182] • Column 2 continues the adsorption lag step.

[0183] • Column 3 continues the adsorption lead step.

[0184] Figure 51

[0185] • Columns 1 continues the elution step.

[0186] • Column 2 transitions from the adsorption lag step into standby mode in which fluid flow through the column stops .

[0187] • Column 3 transitions from the adsorption lead step into the drain recycle step . The drain recycle step returns part of the brine contained in the column to the feed brine tank 12 .

[0188] The chart shown in Figure 6 shows the change in the concentration of lithium and impurities over the duration of the elution recycle step (c) and elution step (d) . At the beginning of the elution recycle step (c) , the column contains lithium-loaded adsorbent and lithium depleted brine . During the elution recycle step, the lithium depleted brine is displaced from the column . The discharge from the column during the elution recycle step contains both lithium and impurities so this discharge is returned to the feed tank to recover the lithium in subsequent adsorption steps . Once the depleted brine has been displaced, elution step (d) is commenced and the column is eluted with eluent to form a lithium-enriched eluate for downstream processing. The last portion of the eluate that is discharged from the column during the elution step (d) is a lower grade portion of the eluate . This last portion of eluate is used in the elution recycle step (c) as it has a low lithium concentration, which ensures that the remainder of the eluate has as high a lithium concentration as possible . By using a lower grade portion of eluate to displace the depleted brine, a lower concentration of lithium is re-circulated to the feed tank which may ensure a higher concentration of lithium in the recovered eluate and a lower concentration of re-circulating lithium which can reduce the number of adsorption columns required per circuit.

[0189] In the circuit illustrated in Figure 7 , the feed brine tank 12 receives entrained brine discharged from the elution recycle step. The bank of adsorption columns coirprises three columns connected in series to provide a lead adsorption column and two lag adsorption columns in which discharge from the lead adsorption column is delivered to the top of the lag adsorption column. The adsorption columns are also connected to a depleted brine tank 20 which receives the lithium depleted discharge from the third column .

[0190] The loaded adsorption columns move in turn to an elution recycle step, where the last portion of eluate from the elution step is used to displace the entrained brine from the adsorption step . The displaced brine is then returned to the feed brine tank (12) .

[0191] Following elution recycle , the columns move in turn to elution, where eluent (i . e . the second mobile phase) , typically in the form of water (which may contain low concentrations of lithium) , is provided to elute the column . The first portion of eluate to be produced from the column is advance eluate . Figure 7 shows that further eluent is then provided and the second portion of eluate to be produced from the column is provided as the mobile phase to the elution recycle step . While not shown in this figure, this lower grade eluant could also be stored in a tank .

[0192] Before the columns are returned to again commence adsorption, the columns move from the elution step to pre-adsorption, where the entrained eluate is displaced by depleted brine from the depleted brine tank (20) . The displaced eluate can be recycled to the water tank (14) .

[0193] In the claims which follow and in the preceding description of the invention, 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 invention.

Claims

CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS :1 . A method of recovering lithium from feed brine using an adsorption-desorption circuit comprising a plurality of adsorption columns , each containing a bed of lithium selective adsorbent , the method including :(a) an adsorption lead step including directing lithium-containing feed brine into one of the adsorption columns to form lithium-loaded adsorbent and a lead column product stream;(b) an adsorption lag step including directing the lead column product stream from step (a) into another adsorption column to form lithium-loaded adsorbent and a lithium-depleted brine stream;(c) an elution recycle step including directing a first mobile phase into one of the columns from step (a) or step (b) ; and(d) an elution step including directing a second mobile phase into the column from step (c) to form a lithium-enriched eluate for downstream processing , wherein up to three of steps (a) - (d) are performed simultaneously .2 . The method of claim 1 , wherein either step (c) or step (d) is performed simultaneously with steps (a) and (b) .3 . The method according to claim 1 or 2 , wherein the first mobile phase of the elution recycle step (c) is a portion of the eluate of step (d) .4 . The method according to claim 3 , wherein the portion of the eluate of step (d) has a lithium concentration of 400mg / L or less .The method of any one of claims 1 to 4 , wherein in step (d) eluent is provided to elute up to 80% of the adsorbed lithium.The method according to any one of claims 1 to 5 , wherein turbulence and / or mixing is minimized using a flow distributor .7 . The method according to any one of claims 1 to 6 , wherein the flow rate of steps (a) and (d) are controlled so that step (c ) and (d) can be performed on the same column , while steps (a) and (b) are performed simultaneously .8 , The method according to any one of claims 1 to 7 , wherein the flow rate of step (c) ranges from 40-80 m3 / hr .9 , The method according to any one of claims 1 to 8 , wherein the flow rate of step (d) ranges from 40-80 m3 / hr .10 , The method according to any one of claims 1 to 9 , wherein the adsorption-desorption circuit comprises from 2 to 20 columns .11 . A method of recovering lithium from feed brine using an adsorption-desorption circuit comprising a plurality of adsorption columns , each containing a bed of lithium selective adsorbent , the method including :(a) an adsorption step including directing lithium-containing feed brine into at least one of the adsorption columns to form lithium- loaded adsorbent and a lithium-depleted brine stream;(b) an elution recycle step including directing , into a column containing lithium-loaded adsorbent , a first mobile phase comprising a lower grade portion of eluate obtained from a prior elution step , said lower grade portion having a lower lithium concentration than an advance eluate portion ; and(c) an elution step including directing a second mobile phase comprising water into the column from step (b) to displace lithium from the adsorbent and form a lithium-enriched eluate stream for downstream processing .12 . An adsorption-desorption circuit configured to perform the method of any one of claims 1 to 11 .13 . An adsorption-desorption circuit according to claim 11 consisting of three to 12 adsorption columns .14 . An adsorption-desorption circuit according to claim 11 consisting of five to 10 adsorption columns .

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