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 5 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 0 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-con taining 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 . 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 .

[0015] 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 .

[0016] 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 .

[0017] The adsorption technique is also typically lower cost than ion exchange or solvent extraction methods .

[0018] 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.

[0019] 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] It can be appreciated that the availability of fresh water is key to the effective operation of the circuit . This is particularly crucial in arid regions . 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 .

[0021] It is desirable to provide an adsorption-desorption circuit and a method for recovering lithium from a feed brine stream that optimises use of fresh water , suitably reduces use of fresh water .

[0022] 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 .

[0023] SUMMARY OF INVENTION

[0024] The invention relates to a circuit and method for recovering 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 .

[0025] 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 .

[0026] 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 .

[0027] 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.

[0028] 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 .

[0029] The adsorption-desorption process may further include 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 advance eluate . The elution recycle step may use a lower grade portion of the eluate produced in the elution step as the first mobile phase . The portion of the eluate used in the elution recycle step may be the last portion of eluate that is discharged from the column during the elution step . This portion of eluate has a low lithium concentration , which ensures that the remainder of the eluate has as high a lithium concentration as possible . The elution recycle step avoids the need for stepwise washing using a number of washing solutions , each of which having gradually decreasing brine concentration .

[0030] The adsorption-desorption process may further include a preadsorption step to displace entrained or residual eluent in the columns (s) prior to the adsorption step . The pre-adsorption step reduces the amount of eluent required for the adsorption step and consequently becoming spent brine .

[0031] The adsorption-desorption process may include both an elution recycle step and a pre-adsorption step .

[0032] These two additional steps may optimise the adsorption and / or desorption of lithium in the columns . 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 reservoirsuch 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 .

[0033] 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 .

[0034] In this specification , the term "lithium selective adsorbent" means a solid material configured to preferentially bind lithium ions from a lithium-con taining 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 .

[0035] In this specification , the term "eluate" encompasses "advance eluate" and "intermediate eluate" , wherein "advance eluate" refers to eluate that is not returned to the feed tank and "intermediate eluate" refers to eluate formed in the elution step which may be subjected to another elution step to form "advance eluate" .

[0036] 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 , 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 .

[0037] The mobile phase for the elution recycle step may be water or eluate (i . e . first mobile phase) . Where the mobile phase for the elution recycle step is eluate , the eluate used is a lower grade portion of the eluate produced in the elution step . In some embodiments , the mobile phase for the elution recycle step is a lower grade portion of the intermediate eluate produced in the elution step . In some embodiments , the portion of the eluate used for the elution recycle step is the last portion of intermediate eluate that is discharged from the column during the elution step , prior to commencement of the pre-adsorption step . This portion of the intermediate eluate has a low lithium concentration , which ensures that the remainder of the eluate (which advances to the downstream unit operations) has a higher lithium concentration (compared to using a single type of eluate which is used for both advancing to downstream units and for feeding elution recycle) . This change also reduces the amount of lithium recycled to the feed brine for adsorption . For example , the portion of the intermediate eluate used for elution recycle may have a lithium concentration of about 400mg / L or less , whereas the advance eluate concentration could be about 400mg / L or more . For example , the portion of the intermediate eluate that is used in the elution recycle step may have a lithium concentration of 300mg / L or less , 200mg / L or less , or lOOmg / 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 .

[0038] The eluent for the elution step may be water (i . e . second mobile phase) . 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 pre-adsorption step , and the discharged eluate (which may contain low concentrations of lithium) may be recycled to the eluent tank .

[0039] The eluent may be intermediate eluate . The intermediate eluate is the result of an elution step in which a second mobile phase is directed into a column which has already undergone one elution step . The intermediate eluate may be used to elute a column that is yet to undergo elution .

[0040] The mobile phase for the pre-adsorption step may be brine (i . e . third mobile phase) . This 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 .

[0041] 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 :

[0042] (a) an adsorption step including directing lithium-containing feed brine into one of the adsorption columns , and forming lithium-loaded adsorbent and lithium-depleted brine ;

[0043] (b) an elution recycle step including directing a first mobile phase into the adsorption column from step (a) to displace at least part of the feed brine entrained in the column ;

[0044] (c) an elution step including directing a second mobile phase into a column which has already undergone one elution step to form an intermediate eluate , and returning the intermediate eluate to the same column or directing the intermediate eluate to another column which has yet to undergo elution to form advance eluate for downstream processing ; and

[0045] (d) a pre-adsorption step including directing a third mobile phase into an adsorption column from step (c) to displace at least part of the second mobile phase in the column before the column transitions to step (a) . The invention was developed to improve the efficiency of the lithium recovery process . Particularly , the invention seeks to reduce the amount of fresh water required by the circuit .

[0046] Steps (b) and (c) may be performed sequentially on the same column . In some embodiments , the adsorption-desorption circuit may coirprise 3 columns , wherein a first column performs step (a) , a second column performs steps (b) and (c) , and a third column performs step (d) . In some embodiments , the adsorption-desorption circuit may comprise 2 columns , wherein a first column performs steps (d) and (a) , and a second column performs steps (b) and (c) .

[0047] In step (c) the elution step includes directing a second mobile phase into a column which has already undergone one elution step to form an intermediate eluate , and using a portion of the intermediate eluate as the mobile phase to elute a column from step (b) to form an advance eluate for downstream processing .

[0048] The columns are configured to perform multi-pass elution .

[0049] Step (c) may involve directing a second mobile phase to a column which has already undergone one elution step (Column X) , and the product of Column X going to a preceding column (Column X-l) which has yet to undergo elution . The product of Column X-l is the "advance eluate" which proceeds to downstream processing . Alternatively , the product of Column X may be directed into a storage tank before being used as the mobile phase to form the "advance eluate" .

[0050] In some embodiments , the columns may be arranged in a grouping such that two or more columns can be used for elution . In that embodiment , a second mobile phase is directed to a column which has already undergone one elution step , and the product is directed to a preceding column yet to undergo elution to produce the "advance eluate" . In some embodiments , the intermediate eluate may pass through multiple columns to produce the advance eluate . In another embodiment , a second mobile phase is directed to a column which has already undergone one elution step , and the product (or intermediate eluate) is directed to a storage tank . When the next column is ready for elution , the intermediate eluate is directed to the column from the storage tank and is used as the mobile phase to form the "advance eluate" . This embodiment may be used when the adsorption-desorption circuit includes two columns or less .

[0051] In this manner , the lithium concentration in the advance eluate is increased compared to the traditional single pass approach .

[0052] The reasons that led the Applicant to develop a multi-pass elution step include :

[0053] • Elution is driven by the availability of water .

[0054] • There is low concentration of free water during loading because of the high concentration of sodium chloride .

[0055] • There is low concentration of sodium chloride and high concentration of free water in elution .

[0056] • It was discovered that even if the LiCl concentration was increased multi-fold (e . g . quadrupled) , the free water concentration in elution was only slightly affected.

[0057] Multi-pass elution may further reduce the amount of fresh water used for the second mobile phase .

[0058] The Applicant also sought to minimise the size of the mixing zone between the mobile phase introduced into a column and the entrained liquor in the column , for example , the first mobile phase and the entrained brine in step (b) or the third mobile phase and the entrained lithium-loaded liquor in step (d) . Without being bound by theory , it is believed that minimizing the mixing zone facilitates plug flow of the entrained liquor out of the column , for example , brine out of the column in step (b) or eluate out of the column in step (d) . This in turn is expected to reduce the amount of mobile phase , which can be water in step (b) or feed brine or depleted brine in step (d) , required to displace the entrained liquor . The Applicant discovered that one way to reduce the mixing zone is to reduce turbulence of the mobile phase in the bed of lithium selective adsorbent . Ideally , the mobile phase flowing through the bed of lithium selective adsorbent should be non-turbulent , suitably having substantially laminar flow .

[0059] At least one of the mobile phases may flow downwardly through the bed of lithium selective adsorbent having a Reynolds number less than 3 , 500 , suitably less than 2 , 000 .

[0060] The concentration of the lithium in the feed brine may range from 50-10 , OOOmg / L , suitably around 75mg / L .

[0061] The adsorption step (a) may involve directing the lithium-con taining feed brine into two or more lithium selective adsorbent-containing columns to form lithium-loaded adsorbent and lithium-depleted brine . Suitably , at least two of the columns are arranged in a lead-lag series arrangement in which brine from the feed brine tank is fed into the lead column with the lead column product stream directed into the lag column . In some embodiments , the lead column product stream may be discharged into a holding tank until the lag column is available for loading .

[0062] Step (a) may comprise a lead adsorption step including directing the feed brine into a first of the pair of columns at a flow rate ranging from 40-80 m3 / hr , suitably , 50 -70 m3 / hr , more suitably 60 m3 / hr .

[0063] Step (a) may comprise a lag adsorption step including directing the discharge from the lead adsorption step into a second of the pair of columns at a flow rate ranging from 40-80 m3 / hr , suitably , 50 -70 m3 / hr , more suitably 60 m3 / hr .

[0064] Step (a) may comprise a lead adsorption step including directing the feed brine into a first of the pair of columns at a linear velocity ranging from 0-20 m / hr , suitably 5-15 m / hr , more suitably 8-15 m / hr , even more suitably 10 -15 m / hr . In one embodiment , step (a) coirprises a lead adsorption step including directing the feed brine into a first of the pair of columns at a linear velocity of 9 . 5 m / hr .

[0065] Step (a) may comprise a lag adsorption step including directing the discharge from the lead adsorption step into a second column of the pair of columns at a linear velocity ranging from 0-20 m / hr , suitably 5-15 m / hr , more suitably 8-15 m / hr , even more suitably 10- 15 m / hr . In one embodiment , step (a) comprises a lag adsorption step including directing the discharge from the lead adsorption step into a second column of the pair of columns at a linear velocity ranging of 9 . 5 m / hr .

[0066] The method may 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 . This may maximise adsorption of lithium by the adsorbent and reduce the concentration of lithium in the spent brine .

[0067] 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 .

[0068] The method may include a drain recycle step involving removing part of the brine contained in the column after step (a) . Suitably , the drain recycle step is performed after the adsorption step , more suitably , on the adsorption lead column . The removed brine may be discharged into a brine feed tank .

[0069] 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 the adsorption step , suitably on the adsorption lead column . The backwash may be returned to the brine feed tank . The backwash step may involve directing a mobile phase upwardly into a column .

[0070] In an embodiment , the method 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 :

[0071] (a) an adsorption step including directing lithium-containing feed brine into one of the adsorption columns , and forming lithium-loaded adsorbent and lithium-depleted brine ;

[0072] (b) an elution recycle step including directing into the adsorption column from step (a) 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 ;

[0073] (c) an elution step including directing a second mobile phase into a column which has already undergone one elution step to form an intermediate eluate , and directing the intermediate eluate to another column which has yet to undergo elution to form advance eluate for downstream processing ; and

[0074] (d) a pre-adsorption step including directing a third mobile phase into an adsorption column from step (c) to displace at least part of the second mobile phase in the column before the column transitions to step (a) .

[0075] In the elution recycle step (b) the first mobile phase may be an eluent (such as water) or eluate to displace the entrained brine . When the first mobile phase is eluate , the elution recycle step may use a lower grade portion of the eluate produced in step (c) . In some embodiments , the first mobile phase for the elution recycle step is a lower grade portion of the intermediate eluate produced in the elution step . The lower grade portion of the intermediate eluate may be the last portion of eluate that is discharged from the column during the elution in step (c) . The portion of the eluate used in the elution recycle step (b) 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 elution recycle step and the elution step are performed sequentially on the same column .

[0076] In some embodiments , directing the first mobile phase into the adsorption column from step (a) is controlled to minimize turbulence and / or mixing between the brine entrained in the column and the first mobile phase . This may be achieved by directing the first mobile phase to the adsorption column at a reduced flow rate , and / or by using a flow distributor to direct the first mobile phase to the adsorption column .

[0077] Step (b) 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 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 .

[0078] 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.

[0079] The method may include mixing the displaced brine in step (b) with the lithium-containing feed brine . Suitably , the method includes directing the displaced brine in step (b) into the feed brine tank .

[0080] Step (b) may include directing the first mobile phase into the column at a flow rate ranging from 40-70 m3 / hr , suitably 50 -60 m3 / hr , and more suitably around 57 m3 / hr .

[0081] Step (b) may include directing the first mobile phase into the column at a linear velocity ranging from 2-10 m / hr , suitably 5-8 m / hr , and more suitably 4 . 2 m / hr .

[0082] In some embodiments , the first mobile phase of the elution recycle step (b) and the mobile phase of the elution step (c) are both eluent . In step (c) the second mobile phase may be water . 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 pre-adsorption step and the discharged eluate (which may contain low concentrations of lithium) may be recycled to the eluent tank . The second mobile phase is used to form the intermediate eluate .

[0083] The intermediate eluate is used to form advance eluate . The last portion of intermediate eluate that is discharged from the column during the elution in step (c) may be used in the eluent recycle step (b) while the first portion of the intermediate eluate that is discharged from the column during the elution in step (c) is used to form advance eluate . In some embodiments , the portion of the intermediate eluate used in the elution recycle step may have a lithium concentration of 400mg / L or less , 300mg / L or less , 200mg / L or less , or lOOmg / L or less , whereas the advance eluate may have a lithium concentration of 400mg / L or more , 500mg / L or more , 600mg / L or more , 700mg / L or more , or 800mg / l or more .

[0084] The method may include increasing the residence time of the second mobile phase or the intermediate eluate (i . e . eluent) in the column (s) during the elution step . This may maximise desorption of lithium from the loaded adsorbent , and reduce the total amount of mobile phase required for this step .

[0085] An increased residence time may be achieved by reducing the mobile phase flow rate , for example , the flow rate of the eluent delivered into the column (s) during step (c) .

[0086] To minimise mixing between the mobile phase and entrained liquor in a column , the method may include directing the mobile phase through a flow distributor (such as a fractal distributor) .

[0087] Step (c) may involve two or more adsorption columns , wherein the elution step includes directing a second mobile phase to a first column which has already undergone one elution step to form an intermediate eluate , and directing the intermediate eluate to a second column which has yet to undergo elution to form advance eluate for downstream processing . In some embodiments , the intermediate eluate may pass through multiple columns to produce the advance eluate . In some embodiments , the second mobile phase may pass through multiple columns that have yet to undergo elution to produce the advance eluate .

[0088] Step (c) may involve an adsorption column and a storage tank , wherein intermediate eluate from the column is directed into the storage tank before being returned to the column to form advance eluate for downstream processing .

[0089] The step of returning the intermediate eluate to the same column in step (c) may involve holding the intermediate eluate in a storage tank until the column is ready to undergo elution .

[0090] Step (c) may include directing the second mobile phase or the intermediate eluate into at least one of the columns at a flow rate ranging from 50-80 m3 / hr , suitably 60-70 m3 / hr , and more suitably 68 m3 / hr .

[0091] Step (c) may include directing the second mobile phase or the intermediate eluate into at least one of the columns at a linear velocity ranging from 1-10 m / hr , suitably 2-8 m / hr , and more suitably 5 m / hr .

[0092] Step (c) may incorporate a pause during the elution step to allow the mobile phase in the columns 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 in the eluate .

[0093] In step (d) the third mobile phase may be brine , such as depleted brine or feed brine . The third mobile phase may include eluate recycle product . In some embodiments , step (c) and (d) may be performed sequentially on the same column . 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 .

[0094] The pre-adsorption step provides a sufficient volume of the third mobile phase to displace the entrained eluate or residual eluent . For example , the volume of the third mobile phase for the preadsorption 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.

[0095] In some embodiments , directing the third mobile phase into the adsorption column from step (c) is controlled to minimize turbulence and / or mixing between the eluent entrained in the column and the third mobile phase . This may be achieved by directing the third mobile phase to the adsorption column at a reduced flow rate , and / or by using a flow distributor to direct the third mobile phase to the adsorption column .

[0096] Step (d) may include directing the third mobile phase into the column (s) at a flow rate ranging from 100-150 m3 / hr , suitably 120- 140 m3 / hr , and more suitably 129 m3 / hr .

[0097] Step (d) may include directing the third mobile phase into at least one of the columns at a linear velocity ranging from 0-20 m / hr , suitably 5-15 m / hr , more suitably 8-15 m / hr , even more suitably 10- 15 m / hr . In one embodiment , step (d) comprises directing the third mobile phase into at least one of the columns at a linear velocity of 9 . 5 m / hr .

[0098] The displaced eluate from step (d) may be directed to an eluate tank .

[0099] Step (d) may include directing the third mobile phase into the column forming the intermediate eluate .

[0100] The method may include monitoring the conductivity of the mobile phase in each column . 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 .

[0101] 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 introduces time delays . In one example , an increase in conductivity would indicate that the pre-adsorption step (d) 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 (b) has displaced the feed brine from the column and the column is ready to receive the intermediate eluate .

[0102] 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 (i . e . degree of plug flow) or flow regime of the mobile phase .

[0103] 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 .

[0104] The method may include introducing a delay when switching mobile phases to provide staggered valve timing .

[0105] 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 .

[0106] 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 .

[0107] The method may include subjecting the advance eluate from step (c) to a concentration step . Suitably , the lithium concentration step involves subjecting the advance 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 .

[0108] The method may include a step of filtering the advance eluate to remove impurities . Suitably , the filtering step may involve passing the advance eluate through a filter that is configured to separate divalent ions (such as Mg2+and Ca2+) from monovalent ions .

[0109] The concentrated advance eluate may be processed to form lithium- containing products including lithium carbonate or lithium hydroxide .

[0110] 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 .

[0111] The circuit may be configured to perform steps (a) - (d) concurrently . This means that at least once during the adsorption-desorption process , each of steps (a) - (d) being performed at the same time . The circuit may comprise 5 columns . For example , a first column performs step (a) , a second column performs steps (b) , a third and fourth column performs step (c) and a fifth column performs step (d) simultaneously .

[0112] The circuit may comprise 3 columns , wherein a first column performs step (a) , a second column performs steps (b) and (c) , and a third column performs step (d) .

[0113] The circuit may comprise 2 columns , wherein a first column performs steps (d) and (a) , and a second column performs steps (b) and (c) .

[0114] The circuit may comprise 4 columns . For example , a first and second column perform step (a) , a third column performs steps (b) and (c) , and a fourth column performs step (d) . In another example , a first column performs step (a) , a second and third column perform steps

[0115] (b) and (c) , and a fourth column performs step (d) .

[0116] The circuit may comprise at least four columns .

[0117] The circuit may comprise 6 columns . For example , two columns perform step (a) , one column performs steps (b) , two columns perform step

[0118] (c) and one column performs step (d) simultaneously . In another example , four columns perform step (d) and step (a) , and two columns perform steps (b) and step (c) .

[0119] The circuit may comprise 7 columns . For example , three columns perform step (a) , one column performs steps (b) , two columns perform step (c) and one column performs step (d) simultaneously . In another example , four columns perform step (d) and step (a) , and three columns perform steps (b) and step (c) .

[0120] The circuit may comprise 8 columns . For example , four columns perform step (a) , one column performs steps (b) , two columns perform step (c) and one column performs step (d) simultaneously . In another example , four columns perform step (d) and step (a) , and four columns perform steps (b) and step (c) . The circuit may comprise 10 columns . For example , five columns perform step (a) , one column performs steps (b) , three columns perform step (c) and one column performs step (d) simultaneously . In another example , six columns perform step (d) and step (a) , and four columns perform steps (b) and step (c) .

[0121] The circuit may comprise 12 columns . For example , five columns perform step (a) , two columns performs step (b) , four columns perform step (c) and one column performs step (d) simultaneously . In another example , six columns perform step (d) and step (a) , and six columns perform steps (b) and step (c) .

[0122] The circuit may comprise 14 columns . For example , six columns perform step (a) , two columns perform step (b) , five columns perform step (c) and one column performs step (d) simultaneously . In another example , eight columns perform step (d) and step (a) , and six columns perform steps (b) and step (c) .

[0123] 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 six to 12 columns . In another embodiment , the circuit may consists of from five to ten columns .

[0124] The circuit may include a pair or pairs of columns connected in a lead-lag series to perform adsorption step (a) . In this arrangement , brine from the feed brine tank is fed into the lead column with the product stream directed into the lag column and the depleted brine discharged into a depleted brine tank . Suitably , the columns are connected such that the mobile phase is introduced at the top of each column .

[0125] The circuit may be configured to perform a drain recycle step involving removing part of the brine contained in the column after step (a) . Suitably , the circuit is configured to perform the drain recycle step after the adsorption step , more suitably , on the adsorption lead column . The removed brine may be suitably discharged into the brine feed tank .

[0126] The circuit may be a fixed bed system.

[0127] The circuit may comprise N number of columns for step (a) and a minimum of N number of columns for step (c) . Suitably , the circuit comprises N number of columns for step (a) and a minimum of N+l number of columns for step (c) . More suitably , N number of columns for step (a) and a minimum of N+2 number of columns for step (c) .

[0128] The circuit may exclude central multiport valves or carousel systems including rotation of columns .

[0129] The circuit may include a valving system configured to deliver the mobile phases downwardly into a column .

[0130] The adsorption-desorption 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 .

[0131] The circuit may include a flow control valve to control the flow rate of a mobile phase into a column . Suitably , a flow control value is used to deliver a first mobile phase such that the mobile phase flowing through the packed bed Reynolds number less than 3 , 500 into a column performing elution recycle step (b) .

[0132] Flow control valves may also be used to deliver the second mobile phase and the third mobile phase such that the mobile phase flowing through the packed bed has a Reynolds number less than 3 , 500 , more suitably , less than 2 , 000 .

[0133] 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 step (d) . 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 (b) . 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 .

[0134] The circuit may include an eluate tank for receiving intermediate eluate from step (c) . The eluate tank may be in fluid communication with a column to deliver part of the intermediate eluate as the first mobile phase in the elution recycle step (b) . The eluate tank may be in fluid communication with a column to receive the discharge stream from pre-adsorption step (d) .

[0135] 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 .

[0136] 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 advance eluate and eluate recycle back to feed tank or to another column .

[0137] Each column may include a flow distributor to improve distribution of fluid across the cross-sectional area of a column .

[0138] 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 .

[0139] The circuit may include a filter to remove impurities from the advance eluate . Suitably , the filter is a nanofilter that separates divalent ions (such as Mg2+and Ca2+) from monovalent ions . 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 advance eluate .

[0140] BRIEF DESCRIPTION OF DRAWINGS

[0141] The present invention is described further with reference to the accompanying drawings of which :

[0142] Figure 1 is a block flow diagram of a circuit in accordance with one form of the present invention .

[0143] Figure 2 is a process flow diagram illustrating a circuit comprising four modules each comprising four columns in accordance with another form of the present invention .

[0144] Figure 3 is a process flow diagram illustrating details of one module in accordance with another form of the invention .

[0145] Figure 4 illustrates a pair of columns in a lead-lag arrangement for an adsorption step of the method in accordance with another form of the present invention .

[0146] Figure 5 illustrates a pair of columns in a multi-pass arrangement for an elution step of the method in accordance with another form of the present invention .

[0147] Figure 6 is a diagram illustrating the sequence of operation of the Figure 2 circuit .

[0148] Figures 7A-7ZZZ illustrate the sequence of operation for a 4 column embodiment of another circuit according to another form of the present invention .

[0149] Figure 8 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 .

[0150] Figure 9 illustrates the configuration of an 8 -column circuit according to another form of the present invention .

[0151] DETAILED DESCRIPTION

[0152] 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 .

[0153] The invention was developed with a desire to improve efficiency of the lithium recovery process which ideally includes reducing fresh water usage .

[0154] One key feature of the invention is multi-pass elution involving directing a second mobile phase to a column which has already undergone one step of elution , and the product of this column going to a preceding column which is undergoing its first elution . The product of the preceding column is the "advance eluate" which proceeds to downstream processing (see Figure 5) .

[0155] It is also beneficial for salinity driven adsorption-desorption systems where the "elution recycle" and the "elution" mobile phases are often the same to minimise the amount of "mixing" between the mobile phase and entrained liquor during the different steps .

[0156] Often , a mobile phase with mixed liquors needs to be retreated by returning to the feed tank . Unlike traditional ion exchange columns , a separate , recyclable wash solution cannot be used without dramatic lithium losses .

[0157] 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 connected to the feed brine tank 12 . The eluate recycle tank 22 is shown in Figure 2 which illustrates a lithium adsorption-desorption circuit 10 according to another form of the present invention .

[0158] 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 four adsorption columns each . Three of the four modules operate during the lithium recovery process with the fourth module held in reserve .

[0159] Figure 3 illustrates a module comprising four adsorption columns Cl- C4 . In this module , the eluate recycle (also known as elution recycle) is fed to the columns separately to the feed brine . This is in contrast to the circuit of Figure 2 in which the eluate recycle is returned to the feed tank . The circuit output can be increased by connecting multiple modules in a stacked arrangement .

[0160] Figure 4 illustrates column Cl of Figure 3 in the form of two columns CIA and C1B connected in series in a lead-lag arrangement to enable a two-stage adsorption step .

[0161] Figure 5 illustrates Column C3 in the form of two columns C3A and C3B connected in series . This configuration enables multi-pass elution involving directing eluent to a column which has already undergone one step of elution (Column C3B) , and directing the product of Column C3B into the previous column (Column C3A) which is undergoing its first elution . The product of Column C3A is the "advance eluate" which proceeds to downstream processing .

[0162] A key feature of a multi-pass elution is the use of the lithium- containing product stream from one column as the eluent of a second column undergoing its first elution . This reduces the amount of fresh water required for the elution step and maximises the lithium concentration of the advance eluate which is ultimately processed to recover lithium.

[0163] The lithium extraction process includes the following steps : • 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;

[0164] • 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 ;

[0165] • an optional backwash step after the adsorption lead step to reduce any pressure drop across the column ;

[0166] • a drain recycle step after the adsorption lead step or the optional backwash step to remove part of the brine entrained in the column ;

[0167] • an elution recycle step to displace at least part of the brine entrained in the column after the drain recycle step ;

[0168] • a multi-pass elution step to desorb lithium from the lithium- loaded adsorbent and form an intermediate eluate , this step involves directing eluent to a column which has already undergone one elution step , and directing the product of this column into another column which has yet to undergo elution ; and

[0169] • a pre-adsorption step to displace at least part of the second mobile phase from the elution step before the column transitions to the adsorption lag step .

[0170] The elution recycle and pre-adsorption steps improve the efficiency of elution and adsorption steps by removing brine in the column prior to the elution step (using water or eluate , such as intermediate eluate) and removing water from the column (using brine , such as feed brine) prior to the adsorption step .

[0171] In Figure 1 , the circuit 10 used to perform the lithium extraction process comprises a feed brine tank 12 for storing raw brine (RB) . The feed brine tank 12 is connected to the bank of adsorption columns 16 which received the raw brine (RB) for the adsorption step . Each column has an internal diameter of 900 mm and an external diameter of 4 , 250 mm. In some embodiments , a total of 280m3of adsorbent is distributed equally between the 12 columns . The bed height is 1 , 900 mm coirprising 1 , 700 mm of adsorbent / resin sandwiched by 200 mm of inert material at the top and bottom of the column . However , the column can be scaled up or down depending on operational requirements . Typically , the circuit can produce 3 , 500 tons of lithium carbonate .

[0172] 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 .

[0173] In the circuit illustrated in Figure 2 , the feed brine tank 12 is connected to an eluate recycle tank 22 which receives the entrained brine discharged from the elution recycle step before the discharge is returned to the feed brine tank 12 .

[0174] The bank of adsorption columns comprises two columns connected in series to provide a lead elution column C3B and a lag elution column C3A in which discharge from Column C3B is delivered to the top of Column C3A (see Figure 5 ) . This enables multi-pass elution .

[0175] The bank of adsorption columns can also comprise 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 4) .

[0176] The adsorption columns 16 are also connected to an eluent tank 14 to deliver eluent , typically in the form of water , to the column performing the elution step . The connection between the adsorption columns 16 and the eluent tank 14 also allows the eluent tank 14 to receive discharge from the pre-adsorption (PA) step .

[0177] The adsorption columns 16 are also connected to an eluate tank 18 to receive part of the eluate (ER) , such as a low grade portion of the intermediate eluate for the eluate recycle step . The connection between the adsorption columns 16 and the eluate tank 18 also allows the eluate tank 18 to receive eluate (EL) from the elution step .

[0178] The adsorption columns are further connected to a depleted brine tank which receives depleted brine (DB) from the adsorption step , particularly from the lag adsorption column C1B .

[0179] The circuit is also configured to deliver eluate (such as a low grade portion of the intermediate eluate) or water as the first mobile phase during the elution recycle (ER) step . A flow distributor may be used to improve flow of the first mobile phase across the cross-sectional area of the column . It can be appreciated that water usage will be further reduced if eluate is used instead of water for the first mobile phase .

[0180] As shown in Figure 3 , each module comprises a network of valves which connects each of the columns with each of the feed brine tank 12 , the eluent (water) tank 14 , each of the adsorption columns 16 in each module , the eluate tank 18 , the depleted brine tank 20 and the eluate recycle tank 22 . This enables each column to perform the steps of the lithium extraction process . The discontinuous line represents the connection for the optional backwash step .

[0181] In operation , raw brine from a pond or lake is optionally subjected to a pretreatment step prior to being collected and stored in the feed brine tank 12 . The concentration of the lithium in the feed brine is around 75 mg / L . In some embodiments the concentration of the lithium in the feed brine is from around 30 mg / L to around 5g / L .

[0182] The feed brine tank 12 feeds the brine into the top of a first adsorption lead column CIA at a flow rate of 120 m3 / hr and a linear velocity of 9 . 5 m / hr to initiate the adsorption step . The lead adsorption step is performed for 60 minutes . Lithium from the feed brine is adsorbed onto the lithium-loaded adsorbent .

[0183] A lag adsorption column C1B is fluidly connected to the lead adsorption column CIA to receive the discharge from the lead adsorption column CIA at a flow rate of 120 m3 / hr and a linear velocity of 9 . 5 m / hr . The lag adsorption step is performed for 50 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 second lag column is directed to a depleted brine tank .

[0184] Once the lead adsorption column CIA is saturated, a backwash step may be performed 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 .

[0185] A drain recycle (DR) step is performed on the lead adsorption column CIA either after feed brine is delivered to the column or the after the backwash step (if performed) . This step lasts for 10 minutes . This step removes part of the brine contained in the column and returns it to the feed brine tank 12 .

[0186] An elution recycle (ER) step is then performed in which a first mobile phase is fed into the top of the column , to displace at least part of the brine entrained in the column . This step lasts for 30 minutes . To minimize water usage , eluate (EL) is used as the first mobile phase , in particular , a low grade portion of the intermediate eluate . However , water is also a suitable alternative as the first mobile phase .

[0187] During the elution recycle (ER) step , the eluate (EL) flows through the column having a Reynolds number less than 3 , 500 , preferably in the laminar flow regime .

[0188] It is believed that this minimises the size of the mixing zone between the first mobile phase and the entrained brine , and enhances plug flow of the entrained brine out of the column . This consequently minimises the amount of first mobile phase required to displace the entrained brine from the column . The displaced brine (ER) is directed to eluate recycle tank 22 and ultimately returned to the feed brine tank 12 . A flow distributor (not shown) is installed in the columns to deliver one or more mobile phases more evenly over the cross- sectional area of a column .

[0189] Eluent , in the form of water , is then fed into the column in an elution step to desorb lithium from the lithium-loaded adsorbent to form an intermediate eluate (EL) .

[0190] When the column switches from the elution recycle step to elution step , eluent flows through the column , preferably in the laminar flow regime , to form eluate .

[0191] The eluate (EL) is directed into an eluate tank 18 . Part of the eluate (EL) from the eluate tank 18 is returned as the first mobile phase in the elution recycle (ER) step . The elution step lasts for 100 minutes .

[0192] The residence time of the eluent in the columns can be increased to reduce the total amount of eluent required for this step . This can be achieved by reducing the flow rate of the eluent into the column .

[0193] To further increase the residence time of the eluent in the columns , a pause may be introduced during the elution step to allow the mobile phase in the column to be held for up to 20 minutes in the column .

[0194] The eluate from the eluate tank 18 is then concentrated by either reverse osmosis , membrane separation or evaporation . The concentration step may generate water in the form of reverse osmosis permeate or evaporator condensate which can be directed to the eluent tank to be recycled as eluent .

[0195] The eluate is also passed through a filter to remove divalent impurities , particularly Mg2+and Ca2, and processed to form lithium carbonate or lithium hydroxide . The elution step is then followed by a pre-adsorption (PA) step in which a third mobile phase in the form of depleted brine or feed brine is fed into the column , typically Column C3A, to displace at least part of the eluate before the column returns to the adsorption step .

[0196] The pre-adsorption step lasts for 10 minutes . In the example wherein the adsorption step is performed by columns CIA and C1B , the column transitions into the lag adsorption step once the adsorbent in the column is depleted. The adsorption lag step lasts for 50 minutes , and completes one adsorption-desorption cycle .

[0197] During the pre-adsorption (PA) step , the third mobile phase flows through the column having a Reynolds number less than 3 , 500 , preferably in the laminar flow regime . This enhances plug flow of the entrained or residual eluate from the column . This consequently minimises the amount of third mobile phase required to displace the entrained eluate from the column .

[0198] The sequence of steps and the approximate duration of each step of the lithium extraction process for the three modules is summarized in Figure 6 and the table below provides the operating conditions for each module . The adsorption step comprising the lead and lag sub-steps total 110 minutes and the elution step total 100 minutes .

[0199] The sequence of steps and timings for the first and third modules are identical while the timings for the second module are delayed by 40 minutes .

[0200] The second column begins its lead adsorption step once the first column ends its lead adsorption step . The same applies to the third column . The C4 column of each module has a waiting period of 20 minutes before starting its lead adsorption step . This is to accommodate different adsorption and elution flowrates (see the above table) .

[0201] To optimize the transition between steps , the columns switch to the next step in the extraction process when a predetermined impurity concentration is reached . This reduces excessive elution recycle (washing) and fresh water usage .

[0202] The Applicant realised that the best way to do this is to monitor the conductivity of the mobile phase in each column (which measures the concentration of sodium chloride , the main impurity in the columns) , and activate the relevant valves to switch the columns to the next step when a predetermined conductivity level is reached. This avoids relying on analytical methods to decide when to switch column operations from one step to another which introduces time delays . When switching mobile phases , a delay may be deliberately introduced to stagger the valve timing .

[0203] When the columns shift from one step to another (e . g . when a column shifts from loading to elution recycle) , the valve which controls the mobile phase to the column usually switches to a different mobile phase at the same time that the valve which controls the destination of mobile phase leaving the column switches . Because of the residence time of the liquor in the column , the liquor at the discharge is usually the same as it was during the previous step immediately after switching the feed valve . To optimize the transition between steps , a delay based on the residence time distribution of the liquor in the column can be introduced so that the switching of the discharge valve is delayed after the feed valve is switched.

[0204] All steps except for the backwash step involve delivering the mobile phase to the top of the column to allow flow of the mobile phase down the column .

[0205] Figures 7A-7ZZZ show the sequence of operation for a 4 column embodiment of another circuit according to the present invention . The main differences between the sequence of operation of Figures 7A-7ZZZ and Figure 6 include :

[0206] (i) a 60 minute lag adsorption step ; and

[0207] (ii) a 10 minute delay after the lag adsorption step and before start of the lead adsorption step .

[0208] A description of the sequence of operation based on Figures 7A-7ZZZ will now be provided.

[0209] The mobile phases are coloured as follows to illustrate their flow through the circuit :

[0210] • Green - Raw brine

[0211] • Grey - Eluent

[0212] • Light Green - Depleted brine

[0213] • Bright Green - Discharge from Lead Adsorption Step

[0214] • Blue - Eluate

[0215] • Red - No flow

[0216] Figure 7A: Time 0

[0217] First column : Ready to receive raw brine for the start of the lead adsorption step .

[0218] Second column : Ready for the start of the lag adsorption step .

[0219] Third column : Elution step in progress .

[0220] Fourth column : Ready for the start of the eluate / elution recycle step .

[0221] Figures 7B and 7C : Time 30 minutes First column: Lead adsorption step in progress.

[0222] Second column: Lag adsorption step in progress.

[0223] Third column: Elution step in progress.

[0224] Fourth column: End of the eluate / elution recycle step, and switch to elution step.

[0225] Figures 7D and 7E : Time 60 minutes

[0226] First column: End of lead adsorption step, and switch to drain recycle step.

[0227] Second column: End of lag adsorption step, and switch to pause in operation .

[0228] Third column: End of elution step, and switch to pre-adsorption step .

[0229] Fourth column: Elution step in progress.

[0230] Figure 7F: Time 68 minutes

[0231] First column: Drain recycle step in progress.

[0232] Second column : Pause in operation .

[0233] Third column: Pre-adsorption step in progress.

[0234] Fourth column: Elution step in progress.

[0235] Figures 7G and 7H: Time 70 minutes

[0236] First column: End of drain recycle step, and switch to eluate / elution recycle step.

[0237] Second column: Pause in operation, and switch to lead adsorption step .

[0238] Third column: End of pre-adsorption step, and switch to lag adsorption step.

[0239] Fourth column: Elution step in progress.

[0240] Figures 71 and 7 J: Time 100 minutes

[0241] First column: End of eluate / elution recycle step, and switch to elution step.

[0242] Second column: Lead adsorption step in progress.

[0243] Third column: Lag adsorption step in progress.

[0244] Fourth column: Elution step in progress. Figures 7K and 7L: Time 130 minutes

[0245] First column: Elution step in progress.

[0246] Second column: End of lead adsorption step, and switch to drain recycle step.

[0247] Third column: End of lag adsorption step, and switch to pause in operation .

[0248] Fourth column: End of elution step, and switch to pre -adsorption step .

[0249] Figure 7M: Time 138 minutes

[0250] First column: Elution step in progress.

[0251] Second column: Drain recycle step in progress.

[0252] Third column : Pause in operation .

[0253] Fourth column: Pre-adsorption step in progress.

[0254] Figures 7N and 70: Time 140 minutes

[0255] First column: Elution step in progress.

[0256] Second column: End of drain recycle step, and switch to eluate / elution recycle step.

[0257] Third column: End of pause in operation, and switch to lead adsorption step.

[0258] Fourth column: End of pre-adsorption step in progress, and switch to lag adsorption step.

[0259] Figures 7P and 7Q: Time 170 minutes

[0260] First column: Elution step in progress.

[0261] Second column: End of eluate / elution recycle step, and switch to elution step.

[0262] Third column: Lead adsorption step in progress.

[0263] Fourth column: Lag adsorption step in progress.

[0264] Figures 7R and 7S: Time 200 minutes

[0265] First column: End of elution step, and switch to pre-adsorption step .

[0266] Second column: Elution step in progress.

[0267] Third column: End of lead adsorption step, and switch to drain recycle step. Fourth column: End of lag adsorption step, and switch to pause in operation .

[0268] Figure 7T: Time 208 minutes

[0269] First column: Pre -adsorption step in progress.

[0270] Second column: Elution step in progress.

[0271] Third column: Drain recycle step in progress.

[0272] Fourth column : Pause in operation .

[0273] Figures 7U and 7V: Time 210 minutes

[0274] First column: End of pre -adsorption step, and switch to lag adsorption step.

[0275] Second column: Elution step in progress.

[0276] Third column: End of drain recycle step, and switch to eluate / elution recycle step.

[0277] Fourth column: End in pause in operation, and switch to lead adsorption step.

[0278] Figures 7W and 7X: Time 240 minutes

[0279] First column: Lag adsorption step in progress.

[0280] Second column: Elution step in progress.

[0281] Third column: End of eluate / elution recycle step, and switch to elution step.

[0282] Fourth column: Lead adsorption step in progress.

[0283] Figures 7Y and 7Z: Time 270 minutes

[0284] First column: End of lag adsorption step, and switch to pause in operation .

[0285] Second column: End of elution step, and switch to pre -adsorption step .

[0286] Third column: Elution step in progress.

[0287] Fourth column: End of lead adsorption step, and switch to drain recycle step.

[0288] Figures 7ZZ: Time 278 minutes

[0289] First column: Pause in operation.

[0290] Second column: Pre-adsorption step in progress. Third column : Elution step in progress .

[0291] Fourth column : Drain recycle step in progress .

[0292] Figures 7ZZZ : Time 280 minutes

[0293] First column : End of pause in operation , and switch to lead adsorption step .

[0294] Second column : End of pre-adsorption step , and switch to lag adsorption step .

[0295] Third column : Elution step in progress .

[0296] Fourth column : End of drain recycle step , and switch to eluate / elution recycle step .

[0297] The chart shown in Figure 8 shows the change in the concentration of lithium and impurities over the duration of the elution recycle step (b) and elution step (c) . At the beginning of the elution recycle step (b) , 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 (c) is commenced and the column is eluted with intermediate eluate to form a lithium-enriched advance eluate for downstream processing . Once the lithium concentration has decreased, the eluent is changed to water (which may include low concentrations of lithium) . The first portion of the eluent that is discharged from the column is intermediate eluate and this portion is used to produce the advance eluate . The last portion of the intermediate eluate that is discharged from the column during the elution step (c) is a lower grade portion of the eluate . This last portion of eluate is used in the elution recycle step (b) 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 . In some cases , this ensures a higher recovery of lithium in the recovered advance eluate and a lower concentration of circulating lithium which can reduce the number of adsoption columns required per circuit .

[0298] In the circuit illustrated in Figure 9 , the feed brine tank 12 receives entrained brine discharged from the elution recycle step .

[0299] The bank of adsorption columns comprises 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 .

[0300] The loaded adsorption columns move in turn to an elution recycle step , where the last portion of intermediate 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 ) .

[0301] Following elution recycle , the columns move in turn to elution , where intermediate eluate is provided from the intermediate eluate tank (30 ) to produce advance eluate . The column then transitions to receive eluent (i . e . the second mobile phase) , typically in the form of water (which may contain low concentrations of lithium) . The intermediate eluate used to produce advance eluate is the first portion of intermediate eluate to be produced from the column and is stored in intermediate eluate tank (30 ) . Figure 9 shows that further eluent is then provided and the second portion of intermediate 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 .

[0302] 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) . 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 step including directing lithium-containing feed brine into one of the adsorption columns , and forming lithium-loaded adsorbent and lithium-depleted brine ;(b) an elution recycle step including directing a first mobile phase into the adsorption column from step (a) to displace at least part of the feed brine entrained in the column ;(c) an elution step including directing a second mobile phase into a column which has already undergone one elution step to form an intermediate eluate , and directing the intermediate eluate to another column which has yet to undergo elution to form advance eluate for downstream processing ; and(d) a pre-adsorption step including directing a third mobile phase into an adsorption column from step (c) to displace at least part of the second mobile phase in the column before the column transitions to step (a) .2 . The method according to claim 1 , wherein the first mobile phase of the elution recycle step (b) and the mobile phase of the elution step (c) are both eluent .3 . The method according to claim 1 , wherein the first mobile phase of the elution recycle step (b) is a portion of the intermediate eluate of step (c) .4 . The method according to claim 3 , wherein the portion of the intermediate eluate of step (c) has a lithium concentration that is lower than the lithium concentration of the advance eluate .5 . The method according to claim 3 , wherein the portion of the eluate of step (d) has a lithium concentration of 400mg / L or less .6 . The method according to any one of claims 1 to 4 , wherein the third mobile phase of the pre-adsorption step (d) is depleted brine .7 . The method according to any one of claims 1 to 5 , wherein the adsorption step includes an adsorption lead step including directing lithium-containing feed brine into one adsorption column to form lithium-loaded adsorbent and a lead column product stream, and an adsorption lag step including directing the lead column product stream into another adsorption column to form lithium-loaded adsorbent and a lithium-depleted brine stream8 . The method according to any one of claims 1 to 6 , wherein directing the first mobile phase into the adsorption column from step (a) is controlled to minimize turbulence and / or mixing between the brine entrained in the column and the first mobile phase .9 . The method according to any one of claims 1 to 7 , wherein directing the third mobile phase into the adsorption column from step (c) is controlled to minimize turbulence and / or mixing between the eluent entrained in the column and the third mobile phase .10 . The method according to claim 7 or 8 , wherein turbulence and / or mixing is minimized using a flow distributor .11 . The method according to claim 7 or 8 , wherein turbulence and / or mixing is minimized using a flow rate of ranging from 40-80 m3 / hr .12 . The method according to any one of claims 1 to 7 , wherein the flow of the mobile phase in steps (b) , (c) and (d) has a Reynolds number of less than 3 , 500 .13 . The method according to any one of claims 1 to 11 , wherein the adsorption-desorption circuit comprises from 2 to 20 columns .14 . 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 one of the adsorption columns , and forming lithium-loaded adsorbent and lithium-depleted brine ;(b) an elution recycle step including directing into the adsorption column from step (a) 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 ;(c) an elution step including directing a second mobile phase into a column which has already undergone one elution step to form an intermediate eluate , and directing the intermediate eluate to another column which has yet to undergo elution to form advance eluate for downstream processing ; and(d) a pre-adsorption step including directing a third mobile phase into an adsorption column from step (c) to displace at least part of the second mobile phase in the column before the column transitions to step (a) .15 . An adsorption-desorption circuit configured to perform the method of any one of claims 1 to 14 .

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