BIESHEUVEL, Pieter Maarten (p/a Agora 1, Leeuwarden, NL-8934, NL)
MIEDEMA, Henk (p/a Agora 1, CJ Leeuwarden, NL-8934, NL)
SAAKES, Machiel (p/a Agora 1, CJ Leeuwarden, NL-8934, NL)
BUISMAN, Cees Jan Nico (p/a Agora 1, CJ Leeuwarden, NL-8934, NL)
BIESHEUVEL, Pieter Maarten (p/a Agora 1, Leeuwarden, NL-8934, NL)
MIEDEMA, Henk (p/a Agora 1, CJ Leeuwarden, NL-8934, NL)
SAAKES, Machiel (p/a Agora 1, CJ Leeuwarden, NL-8934, NL)
| CLAIMS Apparatus for obtaining a specific ion from a fluid, 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 at least one membrane placed between the first and second electrodes, wherein the membrane is specific ion-selective. Apparatus according to claim 1, wherein at least one of the electrodes is provided with a membrane layer comprising ion selective material. Apparatus according to claim 2, wherein the membrane layer comprises PVC and/or polyamide. Apparatus according to claim 2 or 3, wherein the membrane layer comprises a low resistance membrane support . Apparatus according to any of claims 1-4, the membrane comprising a lithium specific ionophore. Apparatus according to any of claims 1-5, wherein at least one of the electrodes comprises a porous material . Apparatus according to any of claims 1-6, the apparatus further comprising a reverse osmosis unit and/or a nanofiltration unit. 8. Artificial kidney comprising an apparatus according to any of claims 1-7. 9. Method for obtaining a specific ion from a fluid, comprising the steps of: providing an apparatus according to any of the claims 1-8; providing an opposite polarity for the first and second electrodes; and obtaining the specific ion. 10. Method according to claim 9, wherein the specific ion is an alkali metal. 11. Method according to claim 10, wherein the specific ion is Li+. 12. Method according to claim 10, wherein the specific ion is K+. 13. Method according to any of claims 9-12, wherein the fluid is sea water, a biological waste flow, and/or surface water. 14. Method according to any of claims 19-13, wherein the fluid is pre-treated in a reverse osmosis operation. |
FLUID
The present invention relates to an apparatus for 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 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 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 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;
- 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
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 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 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
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 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. Table 1
Metals in sea water
Metals Cone, (mg/ton) Total amount (xlO 8 ton)
Cobalt (Co) 0.1 1
Yttrium (Y) 0.3 3
Titanium (Ti) 1 15
Manganese (Mn) 2 30
Vanadium (V) 2 30
Uranium (U) 3 45
Molybdenum (Mo) 10 150
Lithium (Li) 170 2, 330
Boron (B) 4, 600 63, 020
Strontium (Sr) 8,000 109, 600 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 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 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.
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 NH 4 and the anions CI and NO 3 . Ionophores have a high selectivity for their respective ligand and by that can discriminate between two ion species of equal 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 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 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 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 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 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, for example. Such composite polymer-Teflon 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 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
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. 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 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 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.
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
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 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 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 .
Preferably, the reverse osmosis unit receives a fluid, for example sea water containing Na, CI, Mg, Li and
separates desalinated drinking water from this incoming flow. The remaining flow is used as an input flow for the specific ion recovery. Preferably, there is provided a membrane permeable for Na, CI 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 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 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 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.
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
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.
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 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 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 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.
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 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
- 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 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 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 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 that are separated by membrane 26. In the illustrated embodiment membrane 26 is selective for NH 4 + and K + . Sub- compartment 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 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 H + and CO 2 , 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 ¾ . ¾ exits sub- compartment 24 through exit 42. Because of the relatively high pH in the cathode sub-compartment 24, the H 4 + - H 3 equilibrium shifts to the production of gaseous N¾ that exits through output 44. OH ~ leaves sub-compartment 24 as KOH through output 46. In the illustrated embodiment apparatus 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 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 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
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 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 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 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-Teflon 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 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 a further embodiment of the present invention
(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, CI and not for magnesium and calcium. 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 the apparatuses 2,20. The input flow 48 may be sea water containing Na, CI, 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 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 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 + 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. 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 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 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
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 economic value, at least according to current market prices. The reverse osmosis (RO) unit receives a fluid, for example, sea water containing Na, CI, Mg, Li, Ca and separates desalinated drinking water from this incoming flow by using standard RO technology. The remaining concentrated solution 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, containing Na and Li, is fed into a unit to recover Li, using a membrane with high Li over Na selectivity. 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 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 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
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 excretion of K will be accompanied by the (undesired)
excretion of Na .
NH 4 + and K + recovery from wastewater.
Anammox (anaerobic ammonium-oxidizing) bacteria are widely used for the denitrification of waste water. A disadvantage of this method remains however the production of the greenhouse gas N 2 O. To address this problem, device 20 acts as a type of electrobiochemical fuel cell possessing a membrane that separates the bioanode and cathode compartment and is permeable for NH 4 and K only. Membrane 26 contains both a K selective ionophore and a NH4 selective ionophore. As a result, both NH 4 + and K+ can be recovered from waste water streams. 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 produces H+ and CO 2 . The reaction at the cathode comprises the reduction of ¾0 into OH- and ¾ . Due to the presence of the NH 4 /K selective membrane, in solution the current is carried exclusively by NH 4 and K. The fact that the NH 4 /K membrane is impermeable for OH- (liberated after the
reduction of ¾0 at the cathode) prevents dissipation of the pH gradient between the two compartments. The high pH in the cathode compartment serves shifting the NH 4 /NH 3 equilibrium to the production of (gaseous) NH 3 . Removal specific cations and anions from surface waters .
Typical ion species desirable to remove are 03 ~ , Cl ~ and heavy metals like arsene (As 3+ ) . Taking the bacteria out of the fuel cell formed by apparatus 20 leaves a set up for 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 03 ~ , from waste water .
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.