WO2025257582A1

WO2025257582A1 - Offshore lithium extraction

Info

Publication number: WO2025257582A1
Application number: PCT/IB2024/000287
Authority: WO
Inventors: Frank DESPINOIS; Stephane Jouenne; Jérôme BOTEREL; Pierre Pedenaud
Original assignee: TotalEnergies Onetech SAS
Current assignee: TotalEnergies Onetech SAS
Priority date: 2024-06-12
Filing date: 2024-06-12
Publication date: 2025-12-18
Anticipated expiration: 2026-12-12

Abstract

The invention relates to a method for offshore lithium extraction, the method comprising steps of withdrawing an aqueous stream from an offshore aquifer; providing the withdrawn stream to an offshore unit for lithium extraction; and treating the withdrawn stream in the offshore unit to recover lithium from the withdrawn stream and obtain a lithium-depleted stream.

Description

OFFSHORE LITHIUM EXTRACTION

Technical field

The present invention relates to a method of offshore lithium extraction.

Technical background

Lithium is a valuable metal that is used in a wide range of applications, including batteries and lubricants. The demand for lithium extraction from its sources has increased significantly in recent years due to the growing popularity of electric vehicles and renewable energy storage systems. For example, lithium recovered from water produced when extracting oil and gas may be used in different fields such as ceramics, greases, aerospace, polymers, metal additives and particularly in the manufacture of lithium-ion batteries.

Document WO 2019/000095 A1 relates to a method for recovering lithium from energy process water, using a reactor column containing a titanium oxide molecular sieve that adsorbs lithium ions.

Document EP 3382043 A1 relates to an onshore lithium-recovering device for a lithium ion adsorption and desorption process including a supply unit for supplying lithium-containing water in which lithium is dissolved, a composite unit, a washing unit, a desorbing liquid unit, an extract liquid unit, a pressure adjusting unit, a discharge unit, and a control unit.

Document WO2022/129973A1 relates to a modular installation for the treatment of an aqueous stream of produced water from an oil or gas field, comprising: one or more movable precipitation tanks; a filtration container; and a separation container.

Document CN103045879A discloses a method and a device for extracting trace lithium irons in seawater, characterized in that large-scale seawater is guided through a flow channel which is narrow in front and wide in back, magnetic nano-lithium ion sieve suspension is injected to extract lithium, and the magnetic nano-lithium ion sieve suspension is concentrated into a high-concentration concentration flow.

However, these extraction methods result in a low concentration of recovered lithium, high operational costs, or environmental impact. Within this context, there is a need for improved solutions for producing lithium.

Summary of the invention

It is a first object of the invention to provide a method for offshore lithium extraction, the method comprising steps of:

- withdrawing an aqueous stream from an offshore aquifer,

- providing the withdrawn stream to an offshore unit for lithium extraction, and

- treating the withdrawn stream in the offshore unit to recover lithium from the withdrawn stream and obtain a lithium-depleted stream.

In some embodiments, the aqueous stream has a lithium concentration equal to or higher than 50 mg/L.

In some embodiments, the step of withdrawing the aqueous stream comprises pumping the aqueous stream from at least one production well to the surface of the sea, the production well being located within the seabed.

In some embodiments, the method further comprises a post-treatment of the lithium-depleted stream by neutralization and/or deoxygenation.

In some embodiments, the method further comprises injecting a part or all of the lithium-depleted stream or the treated lithium-depleted stream into the offshore aquifer, into an oil and gas reservoir, and/or into the sea.

In some embodiments, the step of injecting a part or all of the lithium- depleted stream or the treated lithium-depleted stream into the oil and gas reservoir is performed via a floating unit, preferably a floating production storage and offloading (FPSO) unit.

In some embodiments, the step of treating the withdrawn stream comprises a step of lithium extraction, preferably by ion exchange adsorption in a column or in a stratified bed; electrochemical recovery; liquid-liquid extraction; membrane extraction; or a combination thereof.

In some embodiments, the ion exchange adsorption comprises passing the withdrawn stream through an ion exchange adsorbent in a column, the ion exchange adsorbent preferably comprising a metal oxide.

In some embodiments, the ion exchange adsorption comprises passing the withdrawn stream through a stratified bed comprising a stack of membranes, each of the membranes comprising lithium adsorbent material fixed thereon.

In some embodiments, the step of treating the withdrawn stream further comprises, before the step of lithium extraction, a pre-treatment of the withdrawn stream by removing at least a part of suspended solids, hydrocarbons or contaminant ions from the withdrawn stream, the contaminant ions preferably being chosen from magnesium, iron, calcium, sodium, potassium, and combinations thereof.

In some embodiments, the step of pre-treatment comprises precipitating at least a part of contaminant ions in the withdrawn stream by the addition of a base, preferably of a sodium hydroxide solution, in the withdrawn stream and/or by bubbling an oxygen-containing gas in the withdrawn stream.

In some embodiments, the step of pre-treatment comprises coagulating and/or flocculating at least a part of the suspended solids, hydrocarbons or contaminant ions.

In some embodiments, the step of pre-treatment comprises filtering the withdrawn stream.

In some embodiments, the step of treating the withdrawn stream further comprises purifying recovered lithium, preferably by electrodialysis, filtration, ion exchange, or a combination thereof.

In some embodiments, the offshore unit for lithium extraction is a fixed unit, preferably a jacket, or a floating unit, comprising a lithium extraction unit, preferably further comprising a pre-treatment unit, a purification unit, and/or a post-treatment unit.

In some embodiments, the floating unit is a moored floating structure, preferably a tension-leg platform (TLP) or a flat-bottomed structure, preferably a barge, a semi-submersible, a ship, a boat, or a vessel.

In some embodiments, the offshore unit comprises a diesel engine, a gasoline engine, a solar power system, and/or a wind turbine system and is preferably energetically autonomous.

In some embodiments, the offshore unit is powered by an external source.

In some embodiments, the external source is an onshore power generation facility or a floating production storage and offloading (FPSO) unit.

In some embodiments, the method further comprises preparing an acid and a base from seawater, and using a part or all of the acid and a part or all of the base in the step of treating the withdrawn stream and/or in the step of posttreatment of the lithium-depleted stream, if present.

In some embodiments, the method further comprises using the part or all of the acid in at least one of the step of the above-mentioned lithium extraction; the step of purifying recovered lithium, preferably by above-mentioned electrodialysis; and the step of post-treatment of the lithium-depleted stream, preferably above-mentioned neutralization. In some embodiments, the method comprises using the part or all of the base in at least one of the step of pre-treatment of the withdrawn stream, preferably above-mentioned precipitation; the step of above-mentioned lithium extraction; and the step of post-treatment of the lithium-depleted stream, preferably above-mentioned neutralization.

In some embodiments, the step of preparing an acid and a base from seawater is carried out by bipolar membrane electrodialysis.

The invention further relates to an installation for offshore lithium extraction, comprising:

- at least one production well located within the seabed,

- an offshore unit for lithium extraction comprising a lithium extraction unit, and

- at least one conduit that flu idically connects the production well and the offshore unit.

In some embodiments, the installation further comprises at least one pump associated with each production well.

In some embodiments, the offshore unit for lithium extraction comprises an ion exchange unit, preferably an ion exchange column and/or stratified bed, an electrochemical unit, a liquid-liquid extraction unit, a membrane extraction unit, or a combination thereof.

In some embodiments, the offshore unit further comprises a pre-treatment unit, preferably a precipitation unit, coagulation and flocculation unit, dissolved air flotation unit, and/or a filtration unit; a purification unit, preferably an electrodialysis unit, a filtration unit, and/or an ion exchange unit; and/or a post-treatment unit, preferably a neutralization unit and/or a deoxygenation unit.

In some embodiments, the offshore unit for lithium extraction is a fixed unit or a floating unit, preferably a flat-bottomed structure floating offshore, more preferably a barge, a semi-submersible, a ship, a boat, or a vessel.

In some embodiments, the offshore unit is powered by an external source.

In some embodiments, the installation further comprises a bipolar membrane electrodialysis unit.

In some embodiments, the method as described above is implemented in the above installation. The present invention makes it possible to address the need expressed above. In particular, the invention provides a method for more efficient lithium extraction. This is achieved by performing the extraction method at sea, specifically by withdrawing an aqueous stream from an offshore aquifer to an offshore unit for lithium extraction, and treating the withdrawn stream in the offshore unit to recover lithium.

The lithium extraction at sea offers flexibility and mobility, compared to fixed onshore extraction, allowing the lithium extraction method to be performed in various offshore locations. This advantage is even more prominent when the offshore unit for lithium extraction is a floating unit since such a floating unit (and possible other additional floating units, if present) can be easily relocated when necessary.

In addition, it has been surprisingly discovered that offshore aquifers tend to be rich in lithium. Thus, lithium extraction from an offshore aquifer allows for an improved lithium recovery, especially in comparison with lithium extraction from seawater in which lithium is naturally present at a low concentration.

Furthermore, the lithium extraction of the invention is compatible with other conventional methods such as FPSO (Floating, Production, Storage and Offloading) processes, bipolar membrane electrodialysis of seawater, and electricity generation by osmotic power. For example, the combination of the lithium extraction method of the invention with FPSO processes allows for disposal of the lithium-depleted water and the maintenance of the pressure within an oil and gas reservoir, providing synergetic effect between the lithium extraction and the oil and gas production. The combination of the lithium extraction method of the invention with bipolar membrane electrodialysis of seawater and/or electricity generation by osmotic power allows for further optimization of the extraction method while significantly reducing the environmental impact.

Brief description of the drawings

Figure 1 schematically illustrates an installation according to an embodiment of the invention.

Detailed description

The invention will now be described in more detail without limitation in the following description.

Method for offshore lithium extraction The present invention relates to a method for offshore lithium extraction. By “offshore" is meant that the method is implemented at sea. In other terms, the method is implemented away from the coast, typically on the continental shelf or open ocean. For example, the offshore lithium extraction may be carried out at a distance of from 1 to 250 km, preferably from 100 to 200 km, away from the coast.

The method comprises a step of withdrawing an aqueous stream from an offshore aquifer.

By “aquifer” is meant an underground layer of water-bearing material, consisting of permeable rocks or of unconsolidated materials, that are saturated with water, usually saline water called brine.

The offshore aquifer may be located at a depth of at least 3000 m deep from the ground surface, for example, as deep as 1500 m from the ground surface, and within 100 km, more preferably within 200 km of the coast.

Such offshore aquifer may comprise lithium at a sufficiently high concentration. In some embodiments, the aqueous stream from the offshore aquifer has a lithium concentration equal to or higher than 50 mg/L, for example, from 50 to 600 mg/L, preferably 200 to 600 mg/L. For example, the aqueous stream from the offshore aquifer may have a lithium concentration of 50 to 100 mg/L, 100 to 150 mg/L, 150 to 200 mg/L, 200 to 250 mg/L, 250 to 300 mg/L, 300 to 350 mg/L, 350 to 400 mg/L, 400 to 450 mg/L, 450 to 500 mg/L, 500 to 550 mg/L, 550 to 600 mg/L. This content may be measured by inductively coupled plasma (ICP) methods.

The aqueous stream from the offshore aquifer may contain contaminant ions, such as magnesium, iron, calcium, sodium, potassium ions, and combinations thereof. For example, the aqueous stream may contain such contaminant ions at a content from 0 to 6000 mg/L, preferably from 1000 mg/L to 4000 mg/L, for example, 0 to 1000 mg/L, 1000 to 2000 mg/L, 2000 to 3000 mg/L, 3000 to 4000 mg/L, 4000 to 5000 mg/L, 5000 to 6000 mg/L.

The aqueous stream from the offshore aquifer may also contain dissolved solids (total dissolved solids (TDS)) of from 0 to 250,000 mg/L, preferably from 180,000 mg/L to 200,000 mg/L, for example 0 to 50,000 mg/L, 50,000 to 100,000 mg/L, 100,000 to 150,000 mg/L, 150,000 to 200,000 mg/L, 200,000 to 250,000 mg/L.

The aqueous stream from the offshore aquifer may have a content in suspended solids of lower than 5 g/L, for example from 0 to 70 mg/L, or preferably from 50 to 70 mg/L. This content may be measured by filtration or turbidity methods. In some embodiments, the step of withdrawing the aqueous stream may comprise pumping the aqueous stream from at least one production well to the surface of the sea, for example, via a conduit connecting the production well(s) with the offshore unit of the invention.

The production well(s) may be located within the seabed.

The step of withdrawing the aqueous stream may comprise pumping the aqueous stream via at least one pump.

The flow rate of the withdrawn stream may be altered and controlled due to the presence of the at least one pump, and possibly at least one valve.

For example, the withdrawn stream may be provided with a flow rate of 300 to 1300 m³/h, and preferably from 300 to 1300 m³/h.

The method also comprises providing the withdrawn stream to an offshore unit for lithium extraction.

Unless otherwise stated, the withdrawn stream has the same composition as that of the aqueous stream (e.g., in terms of the lithium concentration, contaminant ion concentration, and/or TDS concentration).

The offshore unit for lithium extraction may comprise a lithium extraction unit (which will be described in detail later).

In some embodiments, the offshore unit for lithium extraction may further comprise a pre-treatment unit, a purification unit, and/or a post-treatment unit (which will be described in detail later).

The method then comprises treating the withdrawn stream in the offshore unit to recover lithium from the withdrawn stream and obtain a lithium-depleted stream.

In some embodiments, the step of treating the withdrawn stream comprises a step of lithium extraction.

The step of lithium extraction may be performed in the lithium extraction unit.

The step of lithium extraction may preferably comprise lithium extraction by ion exchange adsorption, preferably ion exchange adsorption in a column or in a stratified bed, electrochemical recovery, liquid-liquid extraction, membrane extraction, or a combination thereof, more preferably by ion exchange adsorption in a column or in a stratified bed.

These lithium extraction processes are referred to as direct lithium extraction (DLE) processes and allows for more efficient extraction of lithium from a stream obtained from the offshore aquifer, compared to conventional lithium extraction by evaporation processes. According to some embodiments, lithium may be recovered as a solution, such as lithium chloride solution.

The ion exchange adsorption may comprise passing the withdrawn stream through an ion exchange adsorbent in a column.

For example, such ion exchange adsorption may be carried out by chromatographic purification, for example by passing the withdrawn stream through one or more chromatographic columns that adsorb lithium to be recovered and separate it from the withdrawn stream. The lithium may then be collected by elution of the chromatographic columns with an elution solution (such as water or a hydrochloric solution). Before passing the withdrawn stream, the ion exchange adsorbent may be pre-conditioned to an optimal pH for better lithium adsorption, for example, by adding a basic solution such as a sodium hydroxide solution.

The ion exchange adsorbent may comprise a resin or polymer that has a high affinity for lithium, or a metal oxide, preferably a metal oxide.

In some embodiments, the metal oxide may be selected from titanium oxide, manganese oxide, and aluminum oxide hydroxide.

In some embodiments, the metal oxide may be in the form of particles fixed on a matrix with a ligand.

The ion exchange adsorption in a column filled with metal oxide in the form of particles allows for a higher lithium selectivity and extraction efficiency.

In some embodiments, the ion exchange adsorption may comprise passing the withdrawn stream through a stratified bed. The stratified bed extraction may comprise a stack of membranes, each of the membranes comprising lithium adsorbent material fixed thereon. The lithium adsorbed on the lithium adsorbent material may be then collected by elution of the stratified bed with an elution solution (such as water or a hydrochloric solution).

The lithium adsorbent material may be preferably the metal oxide as described above.

The ion exchange adsorption in a stratified bed extraction may provide reduced media loss and a larger contact surface area (surface area for the contact between the withdrawn stream and the adsorbent material), while mitigating concerns about fluidization of a media (e.g., problems such as controlling the fluidlike behavior of the media).

The electrochemical recovery may comprise passing the withdrawn stream through an electrochemical cell, and applying an electrical potential to the electrodes in the cell, which results in lithium recovery through a lithium-capturing electrode. The liquid-liquid extraction may comprise extracting lithium ions into an organic phase, by mixing the withdrawn stream with a solvent, and then recovering lithium back into an aqueous solution. Any conventional solvent used for lithium extraction may be used.

The membrane extraction may be an electro-membrane extraction or nanofiltration.

The electro-membrane extraction may comprise placing the withdrawn stream on one side of a lithium-selective membrane or a permselective membrane, placing an aqueous solution on the other side, and applying an electrical potential across the membrane, thereby recovering the permeate (lithium-rich solution).

The nanofiltration may comprise pumping the withdrawn stream through a semi-permeable membrane, optionally under pressure, and collecting the permeate (lithium-rich solution).

In some embodiments, the recovered lithium (or optionally purified lithium, which will be explained later), for example in a form of a solution, may be transported via a pipeline, i.e., through a network of pipes, from the offshore unit to a location where it will be used. Alternatively, the recovered lithium (or optionally purified lithium) may be stored on the offshore unit and periodically transferred to another location (for example by a ship).

At the end of this step, a withdrawn stream enriched in lithium (recovered lithium) is obtained on the one hand and a withdrawn stream depleted in lithium (lithium-depleted stream) is obtained on the other hand.

The withdrawn stream enriched in lithium may have a concentration equal to or higher than 1500 mg/L in lithium, for example, a concentration of from 1500 to 4000 mg/L, preferably of from 1500 to 2000 mg/L, as measured by inductively coupled plasma (ICP) methods.

By “lithium-depleted stream" is meant that the stream has a lower concentration of lithium compared to the withdrawn stream from which lithium is recovered. In other words, the term “lithium-depleted’ does not mean that the stream is completely free of lithium, and thus the lithium-depleted stream may contain residual lithium.

In some embodiments, the method may further comprise injecting a part or all of the lithium-depleted stream (or optionally post-treated lithium-depleted stream, which will be described later) into the offshore aquifer, into an oil and gas reservoir, and/or into the sea. In some embodiments, the step of injecting a part or all of the lithium- depleted stream or the treated lithium-depleted stream into the oil and gas reservoir is performed via a floating unit.

The floating unit may be a FPSO unit. By “FPSO unit’ is meant a floating vessel used by the offshore oil and gas industry for the production and processing of hydrocarbons, and for the storage of oil.

The injection of the lithium-depleted stream into an oil and gas reservoir (possibly via the FPSO unit) can help maintain the pressure within the oil and gas reservoir and improve the oil sweeping in the reservoir, providing enhanced oil and/or gas recovery.

In some embodiments, the method may comprise injecting a part of the lithium-depleted stream (or post-treated lithium-depleted stream) into the offshore aquifer; injecting a part of the lithium-depleted stream (or post-treated lithium- depleted stream) into an oil and gas reservoir, for example via a floating unit such as FPSO; and/or injecting a part of the lithium-depleted stream (or post-treated lithium-depleted stream) into the sea.

In other embodiments, the method may comprise injecting all of the lithium- depleted stream (or post-treated lithium-depleted stream) into the offshore aquifer; into an oil and gas reservoir; or into the sea.

In some embodiments, the step of treating the withdrawn stream may further comprise, before the step of lithium extraction, a pre-treatment of the withdrawn stream, by removing at least a part of suspended solids, hydrocarbons or contaminant ions from the withdrawn stream.

The contaminant ions may be as described above.

In some embodiments, the step of pre-treatment may comprise precipitating at least a part of contaminant ions in the withdrawn stream by the addition of a base, for example a sodium hydroxide solution to precipitate magnesium and/or calcium, in the withdrawn stream (also referred to as chemical precipitation). Additionally or alternatively, the step of pre-treatment may comprise bubbling an oxygen-containing gas in the withdrawn stream to precipitate, for example, iron (also referred to as oxidation precipitation).

Such pre-treatment may be carried out in at least one precipitation unit (which will be explained layer).

After such chemical and/or oxidation precipitation, at least 80%, preferably at least 90%, more preferably 95%, and even more preferably at least 99% of contaminant ions present in the withdrawn stream prior to the precipitation may be removed. For example, at least 80%, preferably at least 90%, more preferably 95%, and even more preferably at least 99% of the magnesium present in the withdrawn stream prior to the precipitation may be removed, and/or at least 80%, preferably at least 90%, more preferably 95%, and even more preferably at least 98% of the iron present in the withdrawn stream prior to the precipitation may be removed.

More particularly, the withdrawn stream after the pre-treatment may have a content in magnesium of from 0 to 1000 mg/L, for example 500 to 1000 mg/L, and/or a content in iron of from 0 to 1000 mg/L, for example 500 to 1000 mg/L. This content may be measured by inductively coupled plasma (ICP) methods.

The precipitates formed as above may exit the precipitation unit(s) in the withdrawn stream in the form of (additional) suspended solids, and/or may sediment at the bottom of the precipitation unit(s). In the latter case, the precipitation unit(s) may be treated (in other words rinsed) periodically in order to remove such precipitates.

Alternatively or additionally, the step of pre-treatment may comprise coagulating and/or flocculating at least a part of the suspended solids, hydrocarbons or contaminant ions.

The coagulation and flocculation of at least a part of the suspended solids, hydrocarbons or contaminant ions may be performed, for example, by adding a coagulant in order to destabilize particles through chemical reaction between the coagulant and the particles, respectively by adding a flocculant to transport the destabilized particles that will form flocs or flakes.

The coagulation and flocculation may be performed in a coagulation and flocculation unit (which will be described in detail later).

The coagulant used may be an emulsion comprising one or more anionic polyacrylamide such as FLOPAMTM EM 430 commercialized by SNF Floerger.

The flocculant used may be an aqueous solution of aluminum chloride such as FLOQUATTM PAC 18 commercialized by SNF Floerger.

Injection and dosing of the coagulant and the flocculant may be fully automated. The flocculant may be previously diluted at the right concentration by a full automatic dosing system.

Alternatively or additionally, the step of pre-treatment may further comprise passing the withdrawn stream though a dissolved air flotation unit (which will be described in detail later). The hydrocarbons and the suspended solids may form a sludge in the dissolved air flotation unit. The sludge may be removed from the dissolved air flotation unit, for example via a pump.

Alternatively or additionally, the step of pre-treatment may comprise filtering the withdrawn stream. More specifically, the withdrawn stream may be filtered, using a filter or a membrane.

For example, the step of filtering the withdrawn stream may be performed in a filtration unit (which will be described later).

The withdrawn stream leaving the filtration unit may have a content in suspended solids equal to or lower thanl O mg/L, and preferably equal to or lower than 5 mg/L, as measured by filtration or turbidity methods.

The above pre-treatment (especially the chemical precipitation by addition of a base) may increase the pH of the withdrawn stream up to, for example, a value of from 9 to 11. In this case, in some embodiments, the pH may then be adjusted, by decreasing the pH, to a pH within the operation range of the lithium extraction. Thus, the pre-treatment may further comprise adjusting the pH of the withdrawn stream, before it is subjected to the lithium extraction, to a pH suitable for the operation range of the lithium extraction, by the addition of an acidic solution (such as hydrochloride) in the withdrawn stream. According to some embodiments, during this step, the pH of the withdrawn stream may be adjusted at a value from 3 to 8, and preferably from 5 to 7.

The steps of precipitation, coagulation and flocculation, flotation, and/or filtration of the withdrawn stream, as explained above, may be performed in any order. Preferably, the method comprises precipitation (most preferably with a pH increase as described above), coagulation and flocculation, flotation, and then filtration of the withdrawn stream in this order.

The pre-treated withdrawn stream may be stored, prior to the step of lithium extraction, in an auxiliary tank, thereby allowing for the continuous operation of the lithium extraction, for a duration from 1 to 4 hours and preferably from 1 to 2 hours.

In some embodiments, the step of treating the withdrawn stream may further comprise purifying recovered lithium, preferably by electrodialysis, filtration, ion exchange, or a combination thereof.

For example, the recovered lithium (e.g., lithium chloride solution) may be passed through an electrodialysis cell comprising a plurality of membranes, a plurality of anodes, a plurality of cathodes, and a voltage may be applied across the electrodes. This allows lithium ions to migrate towards the negative electrode through the membranes while other ions are blocked by the membranes.

The filtration may comprise passing the recovered lithium (e.g., lithium chloride solution) through a fine membrane filter, thereby separating lithium ions from larger impurities based on size exclusion or adsorption properties. The ion exchange may comprise passing the recovered lithium (e.g., lithium chloride solution) through an ion exchange column filled with an ion exchange resin that selectively binds to impurities such as barium or strontium, and feeding a regeneration solution to displace the bound impurities.

The purified lithium (e.g., concentrated lithium chloride solution) may be converted to the form of lithium hydroxide or lithium carbonate, for example, by adding a reagent such as sodium phosphate, sodium carbonate or sodium hydroxide with CO2 insufflation. The recovery in the form of lithium hydroxide or lithium carbonate may be advantageous for battery production or lubricant production, for example. Lithium hydroxide or lithium carbonate may be also referred to as purified lithium.

In some embodiments, the method of the invention may further comprise a post-treatment of the lithium-depleted stream by neutralization and/or deoxygenation.

The neutralization of the lithium-depleted stream may comprise adjusting the pH of the stream by, for example, adding an acidic solution (for example a hydrochloride solution) and/or a basic solution (for example a sodium hydroxide solution).

Advantageously, the method may comprise increasing the pH during the pre-treatment (for the precipitation step) and then decreasing the pH of the lithium- depleted stream during the post-treatment neutralization step.

The suitable pH may vary depending on the application of the lithium- depleted stream. For example, in the case of injecting a part or all of the lithium- depleted stream into the offshore aquifer, the pH may be adjusted to a value of from 5 to 6, for example. In the case of injecting a part or all of the lithium-depleted stream into the sea, the pH may be adjusted to a value of from 7 to 8, for example. In the case of injecting a part or all of the lithium-depleted stream into the oil and gas reservoir, the pH may be adjusted to a value of from 5 to 6, for example.

The deoxygenation of the lithium-depleted stream may comprise adjusting the oxygen concentration, for example, by adding a bisulfite solution.

The deoxygenation may be especially required when the lithium-depleted stream is re-injected, for example, into the offshore aquifer or into an oil and gas reservoir, via a conduit(s) (e.g., pipes or tubes) and/or a well(s), which may be susceptible to corrosion by oxygen.

When the conduits and/or wells are not made from oxygen-corrodible materials, or when the lithium-depleted stream is re-injected into the sea, the deoxygenation may be omitted. In some embodiments, the method of the invention may further comprise preparing an acid and a base from seawater, and using a part or all of the acid and a part or all of the base in the step of treating the withdrawn stream and/or in the step of post-treatment of the lithium-depleted stream, if present.

The step of preparing an acid and a base from seawater may be carried out by bipolar membrane electrodialysis.

Bipolar membrane electrodialysis is a well known technique in the domain. Specifically, the bipolar membrane allows, in an electrodialysis setup, to convert water molecules into hydrogen ions and hydroxide ions. The hydrogen ions and hydroxide ions may then generate an acidic solution (for example with chloride counterions) and a basic solution (for example with sodium counterions), respectively.

In some embodiments, the method may comprise using the part or all of the acid in at least one of the step of lithium extraction; the step of purifying recovered lithium, preferably by electrodialysis; and the step of post-treatment of the lithium-depleted stream, preferably neutralization, as described above.

In some embodiments, the method may comprise using the part or all of the base in at least one of the step of pre-treatment of the withdrawn stream, preferably precipitation; the step of lithium extraction; and the step of posttreatment of the lithium-depleted stream, preferably neutralization, as described above.

Such preparation of acid and base can optimize the offshore method of the invention. By generating the necessary acids and bases directly from the seawater at sea, where the method of the invention is carried out, the method can be optimized and its environmental impact can be significantly reduced.

In some embodiments, the method of the invention may use more acid than base during operation. In such cases, as a result of the acid/base preparation as above, an excess of base may be produced. This excess base may be utilized, for example, in precipitating calcium carbonate in seawater. Thus, the method may further comprise providing seawater into a tank, and precipitating calcium carbonate in the seawater using the part of the base prepared as above in the tank. Synthetic calcium carbonate has a wide range of applications across various industries due to its versatile properties.

In some embodiments, the method of the invention may further comprise generating electricity by osmotic power.

The step of generating electricity by osmotic power is a well-known renewable energy technology, and uses salinity gradient power between two water bodies, for example seawater and water having a lower salinity, e.g., freshwater or a water having a higher salinity, e.g., an aquifer brine, separated by a semi-permeable membrane. More specifically, the osmotic pressure difference allows the water having a lower salinity to flow into the seawater through a turbine (or seawater into the water having a higher salinity), thereby driving the turbine and generating electricity.

In some embodiments, the water having a higher salinity may be the lithium-depleted stream.

The generated electricity may be used to power the offshore unit used in the method of the invention.

Such electricity generation can also optimize the offshore method of the invention, and is renewable without producing any greenhouse gas emissions or other pollutants during operation.

Installation for the offshore lithium extraction

The present invention also relates to an installation for offshore lithium extraction. The installation according to the present invention will be described by making reference to Figure 1.

The method as described above may be implemented in the installation as described below.

The installation comprises at least one production well 1 located within the seabed; a offshore unit 2 for lithium extraction comprising a lithium extraction unit 20; and at least one conduit 3 that flu id ically connects the production well and the offshore unit.

The production well(s) 1 may be located within the offshore seabed, where the offshore aquifer 4 is located. The term “offshore" is as defined above.

The production well(s) may each comprise a borehole that is drilled into the seabed, more particularly the offshore seabed.

The production well(s) may further comprise a pipe for withdrawing an aqueous stream from the offshore aquifer.

Figure 1 illustrates that the installation comprises 4 production wells 1 , but the number of the production wells is not limited thereto; the installation may comprise, for example, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, up to 15 production wells, preferably 1 to up to 4 productions wells.

The offshore unit for lithium extraction may be a fixed unit or a floating unit, preferably a floating unit. As an example, Figure 1 illustrates a floating unit 2.

In some embodiments, the fixed unit may be a jacket. By “jacket" is meant a structure consisting of vertical or battered legs supported by a lateral bracing system. In some embodiments, the floating unit may be a moored floating structure, or a flat-bottomed structure floating offshore.

The moored floating structure may be a tension-leg platform (TLP). By “TLP’ is meant a structure anchored to the seafloor by tensioned vertical tendons, designed to provide stability for drilling and production operations in deepwater environments.

The flat-bottomed structure may be a barge, a semi-submersible, a ship, a boat, or a vessel. The flat-bottomed structure may be suitably chosen, depending on several factors, such as water depth, environmental conditions, and operational requirements. For example, barges may be suitable for relatively calm, shallow waters due to their flat-bottom design, and semi-submersibles may be used for operations in rough sea conditions due to their stability.

The at least one conduit 3 may be a pipe or a tube.

Figure 1 illustrates a conduit 3 which is connected to the floating unit 2 and branches into four sub-conduits, each connected to the production well 1 . In other variants, the installation may have a conduit which branches into the same number of sub-conduits as the number of production wells, or may have the same number of conduits as the number of production wells.

In some embodiments, the offshore unit may comprise a diesel engine, a gasoline engine, a solar power system, and/or a wind turbine system. The offshore unit may be preferably energetically autonomous.

Alternatively or additionally, the offshore unit may be powered by an external source.

The external source may be an onshore power generation facility or a floating production storage and offloading (FPSO) unit.

Figure 1 shows that the floating unit 2 is connected to a FPSO unit 5.

In this case, such external source may be connected to the floating unit via an electric cable 6.

In some embodiments, the lithium extraction unit 20 of the installation may comprise an ion exchange unit, an electrochemical unit, a liquid-liquid extraction unit, a membrane extraction unit, or a combination thereof.

The ion exchange unit may preferably comprise an ion exchange column or stratified bed.

The ion exchange column may comprise an ion exchange adsorbent filled in a column.

The ion exchange adsorbent is as described above in relation to the method for offshore lithium extraction. The stratified bed may comprise a stack of membranes, each of the membranes comprising lithium adsorbent material fixed thereon. The lithium adsorbent material is as described above in relation to the method for offshore lithium extraction.

In some embodiments, the lithium adsorbent material may be fixed on the membrane with a binder.

Each membrane may comprise at least one of carbon fibers, glass fibers, metal, and a polymer.

The stack of membranes may further comprise a plurality of separators for maintaining the space of a channel created between two adjacent membranes of the stack, thereby increasing the rigidity and the stability of the stack.

The separators may be fixed to one surface (e.g., one side) of each membrane or two surfaces (i.e., two surfaces of each membrane).

The electrochemical unit may comprise an electrochemical cell, a cathode, an anode, an electrolyte solution, and a power source.

The liquid-liquid extraction unit may comprise a solvent tank, and a vessel for mixing a solvent and the withdrawn stream.

The membrane extraction unit may comprise an electro-membrane, a power source, electrodes for connecting the power source and the electromembrane, a feeding unit for feeding the withdrawn stream, and a permeate tank for collecting the permeate. The electro-membrane may be a lithium-selective membrane or a permselective membrane which is selective to anions or cations.

Alternatively, the membrane extraction unit may comprise a nanofiltration membrane, a feeding unit, a pump, and a permeate tank. The nanofiltration membrane may be a semi-permeable membrane having pores that selectively allow, based on their size and charge, lithium ions to pass while retaining other larger ions.

In some embodiments, the offshore unit may further comprises a storage tank for storing the recovered lithium (or optionally purified lithium as described above) and/or a conduit (a pipe or a tube for example) for transporting recovered lithium (or purified lithium). Thus, the lithium extraction unit may be fluidically connected to the storage tank via a tube or a pipe and/or connected to the conduit for the transportation of recovered lithium.

The storage tank may be present on the offshore unit.

In some embodiments, the installation may further comprise at least one pump associated with each production well. In some embodiments, the installation may further comprise at least one valve. The pump and/or valve may be configured for controlling the flow rate of the withdrawn stream.

In some embodiments, the offshore unit may further comprise a pretreatment unit 10.

The pre-treatment unit 10 may be present between the production well 1 (via the conduit 3) and the lithium extraction unit 20 in fluid communication (via a pipe or a tube for example).

The pre-treatment unit 10 may preferably comprise a precipitation unit, a coagulation unit and flocculation unit, dissolved air flotation unit, and/or a filtration unit.

In some embodiments, the precipitation unit may be configured to precipitate the contaminant ions from the withdrawn stream.

The contaminant ions are as described above.

According to some embodiments, the precipitation unit may comprise a chemical precipitation unit and/or an oxidation precipitation unit.

By “chemical precipitation unit’ is meant a unit wherein a separable solid substance from a solution is formed, by converting the substance into an insoluble form. The process of the chemical precipitation may be as described above.

The chemical precipitation unit may comprise a chemical precipitation tank, a feeding unit for feeding the withdrawn stream to the tank, a discharge unit for discharging the pre-treated withdrawn stream from the tank, and a supplying unit for supplying a basic solution such as sodium hydroxide or sodium carbonate to the tank.

The term “feeding/discharge/supplying unit’ as used in the present application means a device or mechanism that pumps or transfers a fluid to/from one unit to another unit. For example, the feeding/discharge/supplying unit may comprise a pipe, or a hose. The feeding/discharge/supplying unit may further comprise a valve, or a pump to move the fluid. The presence of such valve and pump make it possible to control the flow rate of the withdrawn stream entering the unit.

By “oxidation precipitation unit’ is meant a unit wherein the oxidation of a substance makes it possible to separate such substance from a solution. In the context of the present invention, the oxidation of the contaminant ions makes it possible to precipitate such contaminant ions and separate it from the withdrawn stream. The process of the oxidation may be as described above.

The oxidation precipitation unit may comprise an oxidation tank, a feeding unit for feeding the withdrawn stream to the oxidation tank, a discharge unit for discharging the pre-treated withdrawn stream from the oxidation tank, and one or more oxygen-containing gas bubbling devices. The oxygen-containing gas may be oxygen or, preferably, air.

In case the installation comprises two precipitation units (e.g., the chemical precipitation unit and the oxidation precipitation unit), the second precipitation unit is fluid ically connected to the first precipitation unit. This fluidic connection may be in series (in other words the second precipitation unit is fluidically connected to the first precipitation unit, and the withdrawn stream is first treated in the first precipitation unit and then in the second precipitation unit). Alternatively, this fluidic connection may be in parallel (in other words the withdrawn stream is treated at the same time in either the first or second precipitation unit).

Alternatively or additionally, the pre-treatment unit may comprise a coagulation and flocculation unit.

The process of the coagulation and flocculation may be as defined above.

The coagulation and flocculation unit may comprise a coagulation/flocculation tank, a feeding unit for feeding the withdrawn stream to the tank, a discharge unit for discharging the pre-treated withdrawn stream from the tank, and a supplying unit for supplying a coagulant and a flocculant. The coagulant and the flocculant may be as described above.

The coagulation and flocculation unit may further comprise a sludge handling system (e.g., hopper or pump) and/or a sludge tank for storing a sludge.

Alternatively or additionally, the pre-treatment unit may comprise a dissolved air flotation unit.

The dissolved air flotation unit may be configured to remove at least part of the suspended solids and residual hydrocarbons from the withdrawn stream.

The dissolved air flotation device may comprise a flotation tank, a feeding unit for feeding the withdrawn stream to the tank, a discharge unit for discharging the pre-treated withdrawn stream from the tank, and a supplying unit for supplying pressurized water saturated with air.

The dissolved air flotation unit may further comprise a sludge handling system (e.g., hopper or pump) and/or a sludge tank for storing a sludge.

Alternatively or additionally, the pre-treatment unit may further comprise a filtration unit.

The process of the filtration may be as defined above.

The filtration unit may comprise a filtration tank and a filter, a feeding unit for feeding the withdrawn stream to the tank, and a discharge unit for discharging the pre-treated withdrawn stream from the tank. The pre-treatment unit may further comprise an auxiliary tank of the same capacity as the tank as described above, thereby ensuing the continuity of the lithium extraction process in case of maintenance and/or cleaning of the said tank.

When more than one of the precipitation unit, the coagulation and flocculation unit, the dissolved air flotation unit, and the filtration unit are present, the position of the units may be suitably determined, and the units may be fluidically connected to each other via respective tubes or pipes. For example, when all of the these units are present, the precipitation unit may be positioned downstream of the production well(s); the dissolved air flotation unit may be positioned downstream of the precipitation unit, the coagulation and flocculation unit may be positioned downstream of the dissolved air flotation unit; and the filtration unit may be positioned downstream of the coagulation and flocculation unit and upstream of the lithium extraction unit.

The terms “upstream" and “downstream" as used herein refer to the location relative to the flow direction of a fluid. For example, “A is positioned upstream of B” means that A is located before B in the flow direction (the withdrawn stream flows from A to B). Likewise, “A is present downstream of B” means that A is located after B in the flow direction (the withdrawn stream flows from B to A).

In some embodiments, the offshore unit may further comprise a purification unit 30, preferably an electrodialysis unit, a filtration unit, and/or an ion exchange unit, for purifying the recovered lithium.

The purification unit 30 may be fluidically connected to the lithium extraction unit, via a tube or a pipe, for example.

A conventional electrodialysis unit may be used. For example, the electrodialysis unit may comprise a plurality of membranes, a plurality of anodes, a plurality of cathodes, and a power source.

A conventional filtration unit may be used. For example, the filtration unit may comprise a filtration tank and a filter, a feeding unit for feeding the withdrawn stream to the tank, and a discharge unit for discharging the pre-treated withdrawn stream from the tank.

A conventional ion exchange unit may be used. For example, the ion exchange unit may comprise an ion exchange column filled with an ion exchange resin that selectively binds to impurities such as barium or strontium, and a feeding unit for feeding a regeneration solution to displace the bound impurities.

In some embodiments, the offshore unit may further comprise a posttreatment unit 40, preferably a neutralization unit and/or a deoxygenation unit, for treating the lithium-depleted stream. The post-treatment unit 40 may be fluidically connected to the lithium extraction unit, via a tube or a pipe, for example.

The neutralization unit may be configured to adjust the pH of the lithium- depleted stream, especially when a part of the lithium-depleted stream may be injected into the aquifer or into the sea.

The neutralization unit may comprise a neutralization tank, a feeding unit for feeding the lithium-depleted stream to the tank, a discharge unit for discharging the neutralized lithium-depleted stream from the tank, and a supplying unit for supplying an acidic solution such as hydrochloric acidic solution.

The deoxygenation unit may comprise a deoxygenation tank, a feeding unit for feeding the lithium-depleted stream to the tank, a discharge unit for discharging the deoxygenated lithium-depleted stream from the tank, and a supplying unit for supplying an oxygen scavenger such as a bisulfite solution.

Alternatively or additionally, the deoxygenation unit may comprise at least one of a vacuum deoxygenation column, a gas stripping column, or a deoxygenation membrane.

In some embodiments, the offshore unit may further comprise a bipolar membrane electrodialysis unit. The process of the electrodialysis with a bipolar membrane is as described above.

The bipolar membrane electrodialysis unit may comprise, for example, a bipolar membrane, a cation exchange membrane, an anion exchange membranes, an anode, a cathode, and a tank a power supply, and a feeding unit for feeding seawater, a discharge unit for discharging the acidic solution and basic solution.

In some embodiments, the offshore unit may further comprise an osmotic electricity generation unit. The process of the electricity generation by osmotic power is as described above.

The osmotic electricity generation unit may comprise, for example, a feeding unit for feeding seawater, a feeding unit for feeding freshwater, a semipermeable membrane, a turbine connected to a generator, and a discharge unit for discharging the seawater and freshwater.

In some embodiments, at least one of the pre-treatment unit, lithium extraction unit, purification unit, and the post-treatment unit may further comprise one or more sensors present in one or more unit. Such sensors may be chosen from oxygen sensors, pH sensors, temperature sensors, pressure sensors, gas detectors, and online metals monitoring sensors.

In some embodiments, at least one of the pre-treatment unit, lithium extraction unit, purification unit, and the post-treatment unit may further comprise at least one pH adjustment unit. The pH adjustment unit may comprise a tank for storing an acidic solution or a basic solution, and a feeding unit for feeding the acidic solution or the basic solution to at least one of the above units. Thus, the pH adjustment unit which may be fluidically connected to at least one of the pre- treatment unit, the lithium extraction unit, the purification unit, and the posttreatment unit.

Claims

1. A method for offshore lithium extraction, the method comprising steps of:

- withdrawing an aqueous stream from an offshore aquifer,

- treating the withdrawn stream in the offshore unit to recover lithium from the withdrawn stream and obtain a lithium- depleted stream.

2. The method according to claim 1 , wherein the aqueous stream has a lithium concentration equal to or higher than 50 mg/L.

3. The method according to claim 1 or 2, wherein the step of withdrawing the aqueous stream comprises pumping the aqueous stream from at least one production well to the surface of the sea, the production well being located within the seabed.

4. The method according to any one of claims 1 to 3, further comprising a post-treatment of the lithium-depleted stream by neutralization and/or deoxygenation.

5. The method according to any one of claims 1 to 4, further comprising injecting a part or all of the lithium-depleted stream or the treated lithium-depleted stream into the offshore aquifer, into an oil and gas reservoir, and/or into the sea.

6. The method according to claim 5, wherein the step of injecting a part or all of the lithium-depleted stream or the treated lithium-depleted stream into the oil and gas reservoir is performed via a floating unit, preferably a floating production storage and offloading (FPSO) unit.

7. The method according to any one of claims 1 to 6, wherein the step of treating the withdrawn stream comprises a step of lithium extraction, preferably by ion exchange adsorption in a column or in a stratified bed; electrochemical recovery; liquid-liquid extraction; membrane extraction; or a combination thereof.

8. The method according to claim 7, wherein the ion exchange adsorption comprises passing the withdrawn stream through an ion exchange adsorbent in a column, the ion exchange adsorbent preferably comprising a metal oxide.

9. The method according to claim 7, wherein the ion exchange adsorption comprises passing the withdrawn stream through a stratified bed comprising a stack of membranes, each of the membranes comprising lithium adsorbent material fixed thereon.

10. The method according to any one of claims 1 to 9, wherein the step of treating the withdrawn stream further comprises, before the step of lithium extraction, a pre-treatment of the withdrawn stream by removing at least a part of suspended solids, hydrocarbons or contaminant ions from the withdrawn stream, the contaminant ions preferably being chosen from magnesium, iron, calcium, sodium, potassium, and combinations thereof.

11. The method according to claim 10, wherein the step of pre-treatment comprises precipitating at least a part of contaminant ions in the withdrawn stream by the addition of a base, preferably of a sodium hydroxide solution, in the withdrawn stream and/or by bubbling an oxygen-containing gas in the withdrawn stream.

12. The method according to claim 10 or 11 , wherein the step of pretreatment comprises coagulating and/or flocculating at least a part of the suspended solids, hydrocarbons or contaminant ions.

13. The method according to any one of claims 10 to 12, wherein the step of pre-treatment comprises filtering the withdrawn stream.

14. The method according to any one of claims 1 to 13, wherein the step of treating the withdrawn stream further comprises purifying recovered lithium, preferably by electrodialysis, filtration, ion exchange, or a combination thereof.

15. The method according to any one of claims 1 to 14, wherein the offshore unit for lithium extraction is a fixed unit, preferably a jacket, or a floating unit, comprising a lithium extraction unit, preferably further comprising a pre-treatment unit, a purification unit, and/or a post-treatment unit.

16. The method according to claim 15, wherein the floating unit is a moored floating structure, preferably a tension-leg platform (TLP) or a flat-bottomed structure, preferably a barge, a semi-submersible, a ship, a boat, or a vessel.

17. The method according to any one of claims 1 to 16, wherein the offshore unit comprises a diesel engine, a gasoline engine, a solar power system, and/or a wind turbine system and is preferably energetically autonomous.

18. The method according to any one of claims 1 to 17, wherein the offshore unit is powered by an external source.

19. The method according to claim 18, wherein the external source is an onshore power generation facility or a floating production storage and offloading (FPSO) unit.

20. The method according to any one of claims 1 to 19, further comprising preparing an acid and a base from seawater, and using a part or all of the acid and a part or all of the base in the step of treating the withdrawn stream and/or in the step of post-treatment of the lithium-depleted stream, if present.

21. The method according to claim 20, comprising using the part or all of the acid in at least one of the step of lithium extraction of claim 7; the step of purifying recovered lithium, preferably by electrodialysis of claim 14; and the step of post-treatment of the lithium-depleted stream, preferably neutralization of claim 4.

22. The method according to claim 20 or 21 , comprising using the part or all of the base in at least one of the step of pre-treatment of the withdrawn stream, preferably precipitation of claim 10; the step of lithium extraction of claim 7; and the step of post-treatment of the lithium-depleted stream, preferably neutralization of claim 4.

23. The method according to any one of claims 20 to 22, wherein the step of preparing an acid and a base from seawater is carried out by bipolar membrane electrodialysis.

24. An installation for offshore lithium extraction, comprising:

- at least one production well located within the seabed,

- at least one conduit that fluidically connects the production well and the offshore unit.

25. The installation according to claim 24, which further comprises at least one pump associated with each production well.

26. The installation according to claim 24 or 25, wherein the offshore unit for lithium extraction comprises an ion exchange unit, preferably an ion exchange column and/or stratified bed, an electrochemical unit, a liquid-liquid extraction unit, a membrane extraction unit, or a combination thereof.

27. The installation according to any one of claims to 24 to 26, wherein the offshore unit further comprises a pre-treatment unit, preferably a precipitation unit, coagulation and flocculation unit, dissolved air flotation unit, and/or a filtration unit; a purification unit, preferably an electrodialysis unit, a filtration unit, and/or an ion exchange unit; and/or a post-treatment unit, preferably a neutralization unit and/or a deoxygenation unit.

28. The installation according to any one of claims to 24 to 27, wherein the offshore unit for lithium extraction is a fixed unit or a floating unit, preferably a flat-bottomed structure floating offshore, more preferably a barge, a semi-submersible, a ship, a boat, or a vessel.

29. The installation according to any one of claims 24 to 28, wherein the offshore unit comprises a diesel engine, a gasoline engine, a solar power system, and/or a wind turbine system and is preferably energetically autonomous.

30. The installation according to any one of claims 24 to 29, wherein the offshore unit is powered by an external source.

31. The installation according to claim 30, wherein the external source is an onshore power generation facility or a floating production storage and offloading (FPSO) unit.

32. The installation according to any one of claims 24 to 31 , further comprising a bipolar membrane electrodialysis unit.

33. The method according to any one of claims 1 to 23, implemented in the installation according to any one of claims 24 to 32.