NL2004860C2

NL2004860C2 - Apparatus and method for obtaining a specific ion from a fluid.

Info

Publication number: NL2004860C2
Application number: NL2004860A
Authority: NL
Inventors: Cees Jan Nico Buisman; Machiel Saakes; Pieter Maarten Biesheuvel; Henk Miedema
Original assignee: Stichting Wetsus Ct Excellence Sustainable Water Technology
Priority date: 2010-06-09
Filing date: 2010-06-09
Publication date: 2011-12-12
Also published as: WO2011155839A1

Description

APPARATUS AND METHOD FOR OBTAINING A SPECIFIC ION FROM A

FLUID

The present invention relates to an apparatus for 5 obtaining a specific ion from a fluid. More specifically, such fluid relates to sea water. An example of specific ions is an alkali metal like lithium.

Obtaining specific ions, such as alkali metals, requires providing sufficient sources to explore and obtain 10 these specific ions as known reservoirs of most alkali metals are limited. In addition, known reservoirs of these metals are located in geographical areas that often are difficult to access. These reservoirs involve mines and brines on land. Considering the increasing demand for these 15 specific ions, for example by the increasing production of electric cars requiring lithium batteries, a sufficient supply of these specific ions is needed.

The object of the present invention is to provide an apparatus for obtaining a specific ion as an alternative to 20 the existing operations for obtaining such specific ion.

This object is achieved with the apparatus for obtaining a specific ion from a fluid according to the present invention, the apparatus comprising: a compartment for containing the fluid; 25 - a first and a second electrode placed in the compartment, wherein in use the first and second electrodes are of an opposite polarity; and at least one membrane placed between the first and second electrodes, wherein the membrane is 30 specific ion-selective.

By providing a compartment with at least a first and a second electrode that in use are of an opposite polarity the ions in the fluid tend to move towards their preferred 2 electrode. By placing at least one membrane between the first and second electrodes, with the membrane being from a specific ion selective material, a specific type of ion is separated from the fluid. Other ions can not however pass 5 through the selective membrane, at least not in substantial amounts. This enables obtaining such specific ion from a fluid.

For example, alkali metals can be obtained with the apparatus according to the present invention. More 10 specifically, lithium can be obtained by providing a membrane between the first and second electrodes in the compartment of the apparatus with the membrane being lithium selective. This provides an apparatus for obtaining lithium that is obtained form a fluid, such as sea water. Sea water 15 comprises lithium. It will be understood that besides lithium also other ions can be obtained from sea water for example. As an example some ions that can be obtained from sea water are mentioned below in table 1.

2 0 Table 1

Metals in sea water

Metals Cone, (mg/ton) Total amount (xlO8 ton)

Cobalt (Co) Ö7Ï Ï

Yttrium (Y) 0.3 3 25 Titanium (Ti) 1 15

Manganese (Mn) 2 30

Vanadium (V) 2 30

Uranium (U) 3 45

Molybdenum (Mo) 10 150 30 Lithium (Li) 170 2,330

Boron (B) 4,600 63,020

Strontium (Sr) 8,000 109,600 3

In the particular case of lithium removal, instead of the ionophore, the membrane may contain spinel-type manganese-oxide with high lithium-intercalating capacity.

In a preferred embodiment according to the present 5 invention at least one of the electrodes is provided with a membrane layer comprising ion selective material.

By providing the electrodes with a membrane layer comprising ion selective material, the electrode is effectively separated from the fluid in the rest of the 10 compartment by the membrane. Preferably, the membrane layer comprises PVC and/or polyamide. The (impermeable) polymer matrix material is impregnated with an ion selective ionophore that possesses the desired selectivity for the specific ion.

15 Ionophores are either produced by bacteria or chemically synthesized. The ionophores act as an ion selective material for the membrane for, for instance, the cations K, Li and NH4 and the anions Cl and NO3. Ionophores have a high selectivity for their respective ligand and by 20 that can discriminate between two ion species of egual valence and very similar (dehydrated) ionic radius.

The mechanical strength of a coated electrode arises from the electrode itself. This has the advantage that the thickness of the membrane can be as thin as possible. This 25 ensures a minimal resistance of the membrane, thereby improving the overall efficiency of the apparatus according to the present invention.

Furthermore, to obtain a good recovery rate of the specific ion from the fluid, large ion fluxes should be 30 enabled, implying the ionophore content of the polymer matrix should be as high as possible. One way to achieve high ionophore concentrations is to attach the ionophores covalently to the polymer following a two-step chemical 4 procedure. Employing controlled radical polymerization or living anionic/cationic polymerization, macromolecules will be functionalized by attaching, for instance, a hydroxy or amine group. The advantage of such living polymerization 5 reactions is that polymer growth cannot end because of chain termination (as in classical polymerization reactions) . This, in turn, implies a monomer functionalization success rate of virtually 100%. During the second step, functional groups on the ionophore couple to those attached to the 10 polymer.

The ionophore-containing polymer membranes can be coated directly on porous carbon electrodes, for example. Alternatively, a polymer layer is coated on a (low resistance) support first. Such support can be of Teflon, 15 for example. Such composite polymer-TefIon membrane can be attached to, or positioned in front of, an electrode. The advantage of using the electrode (and Teflon) as support is that the support provides the desired mechanical strength whereas the polymer coating solely serves to render the ion 20 selectivity. By implication, the ionophore-containing polymer coating can be as thin as possible, which, in turn, promotes a low resistance and thus high fluxes.

In case the selective ion is lithium and the fluid relates to sea water the lithium selective ionophore 25 requires a high lithium over sodium selectivity to guarantee the obtaining of lithium form the fluid. Such lithium selected ionophore in the membrane material assures that lithium and not sodium reaches the electrode. For example, an appropriate lithium-selected ionophore is the 12-crown-4. 30 In a presently preferred embodiment the membrane layer involves a coating that is applied to the electrodes. As mentioned above the mechanical strength of the coated electrode may arise from the electrode itself. This has as 5 an advantage that the thickness of the membrane can be limited or as thin as possible, for example a few micrometers. This achieves a minimal resistance of the membrane, thereby improving the overall efficiency of the 5 apparatus according to the present invention. Preferably, to obtain large ion fluxes the membrane should contain an ionophore density as high as possible. Optionally, a spinal-type manganese-oxide is used that possesses a relative high lithium-intercalating capacity.

10 In a preferred embodiment according to the present invention, the electrode comprises a porous material.

By providing the electrodes from a porous material, the specific ions that have passed through the membrane can be absorbed by the electrode. This enables an efficient 15 recovery of the specific ion by either switching off the potential and flushing out the absorbed ions from the electrode, or reversing the polarity of the electrodes, such that specific ions are released by electrostatic repulsive forces. Preferably, the porous material comprises activated 20 carbon.

In a further preferred embodiment according to the present invention the apparatus further comprises a reverse osmosis unit and/or a nanofiltration unit.

By adding a reverse osmosis unit to the specific ion 25 recovery as described above drinking water and/or a recovery of a second species like magnesium (Mg) may be achieved.

This renders the overall process is made more cost-effective. In addition, the overall process is more sustainable .

30 Preferably, the reverse osmosis unit receives a fluid, for example sea water containing Na, Cl, Mg, Li and separates desalinated drinking water from this incoming flow. The remaining flow is used as an input flow for the 6 specific ion recovery. Preferably, there is provided a membrane permeable for Na, Cl and water and not for Mg and Ca. The concentrated brine of magnesium and calcium is subjected to further treatments. The remaining flow is used 5 to recover a specific ion such as lithium, using a membrane with a high lithium over sodium selectivity.

The present invention also relates to an artificial kidney comprising an apparatus as described above.

Such kidney provides the same effects and advantages as 10 described above. Preferably, the membrane has a high K over Na selectivity. More specifically, such kidney enables a type of continuous dialysis that would improve lives of people suffering from kidney failure significantly. Preferably, the kidney or apparatus enabling blood dialysis 15 is a wearable device to improve its applicability. As a kidney regulates the potassium level in the blood plasma the ion selective membrane material possesses a high selectivity of potassium over sodium. For example, blood plasma contains about 135 mM sodium and 4 mM potassium.

20 The present invention also relates to a method for obtaining a specific ion from a fluid, comprising the steps of : - providing the apparatus as described above; - providing an opposite polarity for the first and 25 second electrodes; and - obtaining the specific ion.

Such method provides the same effects and advantages as those related to the apparatus. The method according to the present invention enables obtaining a specific ion.

30 Preferably, this specific ion is an alkali metal like lithium and/or K. In a presently preferred embodiment the fluid that is provided to the operation for obtaining a specific ion is sea water, biological waste flow and/or 7 surface water, for example. The type of input flow depends amongst other things on the desired specific ion that needs to be obtained.

In a preferred embodiment according to the present 5 invention the fluid is pretreated involving a reverse osmosis operation. The combination of the recovery and the reverse osmosis enables an increased efficiency and cost effectiveness of the overall operation. Preferably, a membrane is incorporated in between the different processing 10 steps to separate the concentrated brine of magnesium and calcium. Especially, the separation of magnesium is commercially interesting, as it is at present one of the valuable components of sea water, at least according to the current market prices.

15 Further advantages, features and details of the invention are elucidated on basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, wherein: - figure 1 shows an apparatus according to the present 20 invention; - figure 2 shows alternative embodiment of the apparatus according to the present invention; - figures 3-5 show kinetics of a capacitive deionization process; and 25 - figure 6 shows a schematic overview of a combination of reverse osmosis and specific ion recovery.

An apparatus 2 (figure 1) comprises a process compartment 4. Compartment 4 comprises a fluid compartment 6 and a porous carbon electrode 8 that is separated from fluid 30 compartment 6 by anion exchange membrane 10. Electrode 8 is provided with the current collector 12. Furthermore, compartment 4 comprises a second porous carbon electrode 14 acting as cathode that is separated from the fluid 8 compartment 6 by cation exchange membrane 16. Electrode 14 is provided with a current collector 18. Current collectors 12, 18 enable connection to external circuitry enabling the provision of charged electrodes thereby driving the specific 5 ion recovery from the fluid. In the illustrated embodiment membrane layers 10,16 involve coated membrane layers selective for one ion species only.

In another embodiment apparatus 20 (figure 2) comprises a first sub-compartment 22 and a second sub-compartment 24 10 that are separated by membrane 26. In the illustrated embodiment membrane 2 6 is selective for NH4+ and K+. Subcompartment 22 is provided with a first electrode 28 and second sub-compartment 24 is provided with a second electrode 30. Source 32 provides a potential difference over 15 electrodes 28,30. Sub-compartment 22 is provided with an input 34 for the input of a flow or organic compounds (COD). Electrochemically active bacteria oxidize these organic compounds and are able to funnel produced electrons directly to anode 28. The oxidation of the organic compounds produces 20 H+ and CO2, the latter leaving sub-compartment 22 through output 36. Remaining components in sub-compartment 22 exit through output 38. Sub-compartment 24 is provided with input 40 through which water enters sub-compartment 24. At the cathode water is reduced into OH” en H2. H2 exits sub-25 compartment 24 through exit 42. Because of the relatively high pH in the cathode sub-compartment 24, the NH4+-NH3 equilibrium shifts to the production of gaseous NH3 that exits through output 44. OH” leaves sub-compartment 24 as KOH through output 46. In the illustrated embodiment apparatus 30 20 serves to selectively remove K+ and NH+ for, for instance, waste waters. It will be understood however that the precise system functioning, i.e. the components and reactions 9 mentioned above, depend on the incoming flows and used membrane characteristics.

Experiments with the apparatus 2 (Figure 1) are performed by measuring the conductivity of the solution as a 5 measure for the salt concentration (figures 3-5, in figure 3 current in mA, in figure 4 concentration in mM, in figure 5 pH, as function of time in seconds). In the first stage the concentration decreases as the electrodes adsorb the ions.

In the second stage the concentration equals the 10 concentration of the incoming fluids as the electrodes are saturated with the ions. In the third step the potential over the electrodes is reversed such that the absorbed ions are released. These results illustrate the possibility for adsorbing the salts and releasing them afterwards, thereby 15 obtaining the possibility for recovery of a specific ion.

Membranes 10,16,26 used in the apparatuses 2,20 according to the present invention discriminate between types of ion species, including discriminating between ion species with the same valence and similar size. The basic 20 material for the polymer membrane can be PVC that is plasticized with NPOE or DOS, for example. Alternatively, a metacrylic can be used as basic material in which case plasticizer can be omitted. The desired selective permeability is realized by impregnating the matrix with 25 specific ion selective ionophores. The ionophore-containing polymer membranes 10,16 can be coated directly on porous carbon electrodes 8,14. Alternatively, the polymer layer is coated on a (low resistance) support (e.g., Teflon) first. This composite polymer-TefIon membrane can be attached to or 30 positioned in front of an electrode. The advantage of using the electrode (and Teflon) as support is that the support provides the desired mechanical strength whereas the polymer coating solely serves to render the ion selectivity. By 10 implication, the ionophore-containing polymer coating can be as thin as possible, which, in turn, promotes a low resistance and thus high fluxes.

In a further embodiment of the present invention 5 (figure 6) a fluid 48 is fed to a reverse osmosis membrane 50 that is permeable for water but not for salt. The flow of desalinated drinking water 52 is separated from the retentate 54, which in turn is forwarded to membrane 56 that is permeable for Na, Cl and not for magnesium and calcium.

10 The flow 58 of concentrated brine of magnesium and calcium is separated from the rest flow 60. Flow 60 is fed to the separation or recovery unit 62 for separation of lithium from sodium such that the flow of lithium 64 is separated from the Na 66. The separation of lithium is possible using 15 the apparatuses 2,20. The input flow 48 may be sea water containing Na, Cl, Mg and Li, for example. It will be understood that other combinations may be possible in accordance with the present invention.

Below a few applications in accordance with the present 20 invention will be described in more detail.

The mining of Li* from seawater.

Given the world is running out of oil, electric cars are predicted a bright future. Of all existing battery 25 technologies, the one based on Li+ is by far the most promising. The known reservoirs of Li+ on land are limited and often located in difficult accessible areas. Even though seawater only contains a small amount of Li (0.17 ppm), the total volume of ocean water makes the total amount of Li+ 30 present far exceeding the amount currently known to be present in mines and brines on land. Apparatus 2 enables the recovery or mining of lithium from seawater.

11

Sea water contains high levels of Na (11.000 ppm=ll gr/1). Therefore, in case the selective ion is Li and the fluid relates to sea water, Li selective ionophore requires a high Li over Na selectivity to guarantee obtaining of Li from the 5 fluid. Such Li selective ionophore in the membrane material assures that Li and not Na reaches the electrode. An appropriate Li selective ionophore is, for example, the commercially available 12-crown-4. The cathode will be coated with a Li selective membrane consisting of PVC 10 impregnated with ionophore. This membrane will prevent (useless) Na reaching the cathode and by that ensure that the electrode selectively adsorbs Li.

To make the overall process of Li recovery from sea water more cost-effective and, in addition, more 15 environmentally sustainable, the production of drinking water and the recovery of a second ion species can be included (Figure 6). Especially, the separation of magnesium (Mg) is commercially interesting, as it is present at high concentrations in seawater and (therefore) represents high 20 economic value, at least according to current market prices. The reverse osmosis (RO) unit receives a fluid, for example, sea water containing Na, Cl, Mg, Li, Ca and separates desalinated drinking water from this incoming flow by using standard RO technology. The remaining concentrated solution 25 is used as an input flow for specific ion recovery.

Preferably, there is provided a (nanofiltration) membrane permeable for Na and Li but not for Mg and Ca. Magnesium is recovered from the retentate, i.e., the (impermeable) concentrated brine containing Mg and Ca. The permeate, 30 containing Na and Li, is fed into a unit to recover Li, using a membrane with high Li over Na selectivity.

12 K+ regulation by an artificial kidney device.

Due to life style, the number of people that suffer from kidney failure rises exponentially. Kidney dialysis with the patient linked up to an apparatus in a hospital 5 environment is far from ideal, both from the physiological as social point of view. A device or apparatus 2,20 enables a wearable blood cleansing device that enables continuous dialysis and by that improves the lives of people suffering from kidney failure significantly. Preferably, the apparatus 10 enabling blood dialysis is a wearable device to improve its applicability.

Among many other functions, the kidney plays a key role in K homeostasis and the blood K level is tightly regulated in between 2 and 4 mM. The Na concentration in blood 15 typically is around 120-130 mM. The K level in the blood is regulated independently from the Na level. To regulate K independently from Na, the artificial kidney device 2,20 possesses a membrane 10,16,26 with a high K over Na selectivity. The K selective membrane will prevent that the 20 excretion of K will be accompanied by the (undesired) excretion of Na.

NH4+ and K+ recovery from wastewater.

Anammox (anaerobic ammonium-oxidizing) bacteria are 25 widely used for the denitrification of waste water. A disadvantage of this method remains however the production of the greenhouse gas N2O. To address this problem, device 20 acts as a type of electrobiochemical fuel cell possessing a membrane that separates the bioanode and cathode compartment 30 and is permeable for NH4 and K only. Membrane 26 contains both a K selective ionophore and a NH4 selective ionophore. As a result, both NH4+ and K+ can be recovered from waste water streams.

13

Anode 28 is covered by a layer of electrochemically active bacteria. While oxidizing organic compounds (COD), these bacteria funnel the liberated electrons directly to the anode. Apart from electrons, the oxidation of COD 5 produces H+ and CO2. The reaction at the cathode comprises the reduction of H2O into OH- and H2. Due to the presence of the NH4/K selective membrane, in solution the current is carried exclusively by NH4 and K. The fact that the NH4/K membrane is impermeable for OH- (liberated after the 10 reduction of H20 at the cathode) prevents dissipation of the pH gradient between the two compartments. The high pH in the cathode compartment serves shifting the NH4/NH3 equilibrium to the production of (gaseous) NH3.

15 Removal specific cations and anions from surface waters.

Typical ion species desirable to remove are N03”, Cl” and heavy metals like arsene (As3+) . Taking the bacteria out of the fuel cell formed by apparatus 20 leaves a set up for 20 electrodialysis. This is another technology that in combination with an ion-selective membrane separating both electrode compartments can be used to selectivity isolate one specific ion species, e.g., Cl” or N03”, from waste water.

25 The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.

14

CLAUSES

1. Apparatus for obtaining a specific ion from a fluid, 5 the apparatus comprising: a compartment for containing the fluid; a first and a second electrode placed in the compartment, wherein in use the first and second electrodes are of an opposite polarity; and 10 - at least one membrane placed between the first and second electrodes, wherein the membrane is specific ion-selective.

2. Apparatus according to clause 1, wherein at least one 15 of the electrodes is provided with a membrane layer comprising ion selective material.

3. Apparatus according to clause 2, wherein the membrane layer comprises PVC and/or polyamide.

20 4. Apparatus according to clause 2 or 3, wherein the membrane layer comprises a low resistance membrane support.

25 5. Apparatus according to any of clauses 1-4, the membrane comprising a lithium specific ionophore.

6. Apparatus according to any of clauses 1-5, wherein at least one of the electrodes comprises a porous 30 material.

7. Apparatus according to any of clauses 1-6, the apparatus further comprising a reverse osmosis unit and/or a nanofiltration unit.

35 15 8. Artificial kidney comprising an apparatus according to any of clauses 1-7.

9. Method for obtaining a specific ion from a fluid, 5 comprising the steps of: providing an apparatus according to any of the clauses 1-8; - providing an opposite polarity for the first and second electrodes; and 10 - obtaining the specific ion.

10. Method according to clause 9, wherein the specific ion is an alkali metal.

15 11. Method according to clause 10, wherein the specific ion is Li+.

12. Method according to clause 10, wherein the specific ion is K+ .

20 13. Method according to any of clauses 9-12, wherein the fluid is sea water, a biological waste flow, and/or surface water.

25 14. Method according to any of clauses 19-13, wherein the fluid is pre-treated in a reverse osmosis operation.

Claims

A device for acquiring a specific ion from a fluid, the device comprising: a compartment for containing the fluid; a first and a second electrode provided in the compartment, wherein in use the first and second electrodes are of opposite polarity; and at least one membrane disposed between the first and second electrodes, wherein the membrane is specifically ion-selective. 15

Device as claimed in claim 1, wherein at least one of the electrodes is provided with a membrane layer comprising ion-selective material.

Device as claimed in claim 2, wherein the membrane layer comprising PVC and / or polyamide.

4. Device as claimed in claim 2 or 3, wherein the membrane layer comprising a low resistance membrane support.

5. Device as claimed in one or more of the claims 1-4, the membrane comprising a lithium specific ionophore.

The device according to one or more of claims 1-5, wherein at least one of the electrodes comprises a porous material. 35

Device according to one or more of claims 1-6, the device further comprising a reverse osmosis unit and / or a nanofiltration unit.

An artificial kidney comprising a device comprising one or more of claims 1-7.

A method for acquiring a specific ion from a fluid, comprising the steps of: 10. providing a device according to one or more of claims 1-7; providing an opposite polarity for the first and second electrodes; and acquiring the specific ion. 15

The method of claim 9, wherein the specific ion is an alkali metal.

11. A method according to claim 10, wherein the specific ion is Li +.

The method of claim 10, wherein the specific ion is K +.

Method according to one or more of claims 9-12, wherein the fluid is sea water, a biological waste stream and / or waste water.

A method according to any one of claims 9-13, wherein the fluid is pretreated in a reverse osmosis operation.