WO1996011050A1

WO1996011050A1 - Water purification by extraction using mobile liquid membranes

Info

Publication number: WO1996011050A1
Application number: PCT/CH1995/000220
Authority: WO
Inventors: Patrick Raetzo
Original assignee: Patrick Raetzo
Priority date: 1994-10-08
Filing date: 1995-09-30
Publication date: 1996-04-18
Also published as: CH689822A5; AU3516295A

Abstract

Water circulating through a bath (B) is purified by a mobile liquid membrane (LM) provided by injecting a hydrophobic solvent at the bottom of a hydrophobic diaphragm (HD) so that it flows upwards in contact with the bath and the diaphragm to form a buoyant hydrophobic layer (HL). An electric field is applied in the cell (EC) to break down the water and cause ion migration and polarisation of the movable liquid membrane so that it operates as a liquid bipolar electrode. The various impurities are separated out and removed via the mobile liquid membrane (LM) and the hydrophobic layer (HL). Said hydrophobic solvent includes a chelating agent for promoting removal of the impurities. The method is particularly suitable for the fine purification of water containing a variety of known or unknown impurities.

Description

Water purification by extraction using mobile liquid membranes

Field of the invention

The present invention relates to the separation of impurities contained in aqueous liquids and relates to a method and an apparatus for purifying water by extraction using liquid membranes.

As is known, water from different sources can contain various types of organic or inorganic impurities which can be present in low concentrations and difficult to detect. The elimination of small quantities of various types of known or unknown impurities by means of a single conventional separation process is moreover particularly problematic, if not impossible in most cases.

Liquid membranes of different types have been the subject of various studies and their application is generally limited to the discontinuous extraction of given impurities. This is due in particular to the difficulty of maintaining a stable extraction for long periods using most of the liquid membranes proposed so far. Thus, the known methods using liquid membranes are generally not suitable for the continuous purification of water containing various types of impurities so as to be able to meet the most stringent requirements for domestic or industrial use.

The state of the art relating to liquid membranes and their use can be illustrated by the book by Takeo Araki and Hiroshi Tsukube entitled "Liquid Membranes: Chemical Applications" and published in 1990 by CRC Press Inc., Boca Raton.

Summary of the invention

The main object of the present invention is to obviate as much as possible the drawbacks and limitations of the separation methods by liquid membranes proposed so far and to provide a water purification process which allows the continuous separation of various impurities by means of liquid membranes in an efficient manner and by means of a relatively simple apparatus.

This object is achieved by the method according to the invention as defined in the claims which essentially provides for the following combination:

- the arrangement of one or more mobile liquid membranes in contact on the one hand with a hydrophobic, permeable, vertical diaphragm and on the other hand with a water bath to be purified;

- continuous injection of a hydrophobic solvent lighter than water at the foot of the hydrophobic diaphragm in order to form the mobile liquid membrane;

- the circulation of water in the bath in order to favor the extraction of impurities and - Separate evacuation on the one hand of the purified water from said bath and on the other hand of the solvent by means of said mobile liquid membrane and of the hydrophobic layer floating on the surface of said bath.

The floating power of the hydrophobic solvent thus ensures its continuous ascent to the top of the hydrophobic diaphragm as well as its accumulation in the form of a hydrophobic layer floating on the surface of said bath. Thus, the solvent containing the impurities extracted by the mobile liquid membranes can be recovered separately from this floating hydrophobic layer. The recovered solvent could also be regenerated and reused if necessary.

The hydrophobic solvent used to form mobile liquid membranes in accordance with the invention can advantageously be an aliphatic solvent, in particular a paraffin such as n-hexadecane, pentadecane or n-tetradecane for example.

In order to promote the extraction of various impurities by mobile liquid membranes provided for according to the invention, said hydrophobic solvent can advantageously comprise one or more liposoluble cheatating agents comprising a reversible redox group and a liposoluble group and having an oxidized form and a reduced form allowing the oxidation, reduction and chelation of various impurities which may be present in the water to be purified. The chelating agent used for this purpose can advantageously be a compound comprising a quinone function attached to an aliphatic or cyclic residue, in particular the coenzyme Q-o

Said agent is not necessarily chelating at the start, but it will always be chelating under the influence of an electric field as described below.

A mobile liquid membrane provided according to the invention can also be arranged avanta¬ advantageously between the water bath to be purified and a collecting compartment containing a renewable aqueous liquid in order to allow the evacuation of impurities accumulated in this compartment. It is advantageously possible to circulate the water to be purified in an electrolysis cell in order to apply an electric field between an anode and a cathode so as to cause the dissociation of water in said bath, the water to be purified being introduced into this cell in the vicinity of the cathode and the purified water being discharged in the vicinity of the anode.

Said anode will preferably be separated from said aqueous bath by means of a hydrophilic diaphragm which is permeable to anions and delimits an anodic compartment containing a renewable aqueous anolyte in order to ensure the migration of anions from said bath to the anodic compartment, d where these anions can be removed as needed by renewing the anolyte.

The invention also relates to an apparatus as defined in the claims for implementing the method according to the invention. The apparatus for implementing the method according to the invention essentially comprises at least one electrolysis cell comprising at least two extraction compartments separated by at least one permeable hydrophobic diaphragm and connected by a passage which is advantageously located at the bottom of this electrolysis cell. Said apparatus further comprises at least one anode, a cathode, an anode compartment delimited by a hydrophilic anion-permeable diaphragm, an upper main inlet for the water to be purified, disposed in the vicinity of said cathode and a main outlet for the water. purified, arranged in the vicinity of the anode compartment, in order to form a water bath to be purified circulating in said electrolysis cell. This apparatus further comprises means for supplying hydrophobic solvent com¬ carrying a distributor arranged so as to inject and distribute said hydrophobic solvent at the lower end of said hydrophobic diaphragm, thereby forming a mobile liquid membrane rising along said hydrophobic diaphragm and further forming a hydrophobic layer of said solvent floating on the surface of said bath. An upper outlet baffle is also arranged so as to separate said main outlet from said floating hydrophobic layer.

The whole of this device is arranged so as to circulate the water to be purified successively in said extraction compartments, to dissociate the water in said bath, to polarize said mobile liquid membrane and to discharge water separately purified and said hydrophobic solvent from said electrolysis cell.

This device can also advantageously comprise at least one collecting compartment arranged between said two extraction compartments and delimited by two permeable hydrophobic diaphragms connected to said means for supplying hydrophobic solvent in order to form two mobile liquid membranes having opposite faces intended respectively on the one hand in contact with the water circulating in said extraction compartments and on the other hand with a renewable aqueous liquid in this collecting compartment.

The method according to the invention can advantageously be used for the continuous purification of water in an apparatus comprising several juxtaposed electrolysis cells, which can moreover be combined in different ways. Thus, for example, such an apparatus comprising juxtaposed cells can advantageously be provided on the one hand with a central anode compartment, which is delimited by two permeable hydrophilic diaphragms and which contains a common anode associated with the juxtaposed cells, and provided with other part of two cathodes advantageously arranged at opposite ends of this device and associated respectively with two inlets for the water to be purified. Such an apparatus comprising juxtaposed cells can also advantageously be provided with bipolar electrodes which are indirectly polarized by the electric field applied between said common anode and said cathodes. Such an arrangement of juxtaposed cells is thus specially designed in order to reduce as much as possible the number of electrodes to be connected to the DC current source of the device. Each mobile liquid membrane polarized in accordance with the invention will furthermore always function as a bipolar liquid electrode operating as an anode on one side and as a cathode on the opposite side of the liquid membrane.

The water to be purified can also advantageously be circulated in parallel or in series in the juxtaposed cells in order to increase the total flow rate of the water purified in parallel or the number of extraction steps carried out in series in the cells. juxtaposed. The method according to the invention can also be implemented in cells of different types provided with mobile liquid membranes, as described below, these different cells can moreover be combined if necessary in any suitable manner and adapted especially for the different applications of the invention, taking into account the nature and the quantity of the impurities to be separated as well as the volume of water to be purified in each case.

The use of mobile liquid membranes in accordance with the invention more particularly makes it possible to efficiently separate different species of impurities thanks to the possibility which results from combining various physical, chemical and electrochemical separation techniques in a single process and device that can be easily controlled in order to achieve continuous purification of large quantities of water.

The invention thus offers a special combination of advantages which can be explained as follows:

The upward movement of the mobile liquid membrane ensures intimate contact of the hydrophobic solvent with all of the water circulating in the water bath to be purified and thus promotes the extraction of various liposoluble substances as well as their evacuation from the cell to the using the hydrophobic solvent originating from the liquid membrane and forming the hydrophobic layer floating on the surface of said bath.

The flow of hydrophobic solvent from the mobile liquid membrane constantly ensures its renewal and therefore maintains a stable separation action by preventing saturation of the solvent, this being particularly important in order to maintain a separation as efficient as possible at all times during the continuous purification process.

It is also possible to vary the flow rate of this hydrophobic solvent and to easily regulate it so as to ensure effective purification under varying operating conditions. Thus, for example, the flow rate of the solvent in the mobile liquid membranes can be increased in the event that the quantity of impurities present in the water to be purified in the apparatus increases for any reason. The polarization of each mobile liquid membrane forming a mobile bipolar liquid electrode enables oxidation, reduction, chelation and dissolution of various substances to be ensured, while the upward movement of the solvent in the mobile liquid membrane allows at the same time dissolving the oxidized, reduced or chelated products formed on this mobile liquid bipolar electrode and rapidly discharging them continuously thanks to the upward movement of the hydrophobic solvent.

The electrodes which cause the polarization of the mobile liquid membrane, the migration of various substances in the bath and the dissociation of water, creating fluxes of protons and hydroxyl ions, allow at the same time the separation of different substances by l 'intermediary of cathodic or anodic reactions.

The method according to the invention thus allows the effective separation of different species in a relatively simple manner, which expands its scope accordingly.

It should be noted that the continuous water purification process according to the invention can generally be used for the treatment of various aqueous liquids which lend themselves to the extraction of impurities by liquid membranes.

Therefore, the terms "water" and "aqueous liquid", "purification" and "treatment", "separation" and "extraction" are practically equivalent with respect to the present invention and could thus be used interchangeably in the context of the invention. Forms of execution of the invention

The invention will be explained using the embodiments described below by way of example and represented as follows in the figures of the appended drawing.

Fig. 1 shows a schematic section of a cell comprising a mobile liquid membrane arranged in a water bath to be purified in accordance with the invention. Fig. 2 shows a schematic section of an electrolysis cell provided with a mobile liquid membrane disposed between an anode and a cathode.

Fig. 3 shows a variant of the cell according to FIG. 2 provided with two mobile liquid membranes.

Fig. 4 shows a variant of the cell according to FIG. 3 comprising three mobile liquid membranes.

Fig. 5a shows the arrangement of a hydrophobic diaphragm in a hydrophobic solvent distributor used for the formation of a mobile liquid membrane.

Fig. 5b shows a perspective view of the hydrophobic diaphragm arranged according to FIG. 5a, without the distributor. The distributor SD shown in section fig. 5a is formed of a horizontal tubular conduit provided with a linear upper slot SD1 used for the injection of a hydrophobic solvent at the lower end of an HD diaphragm. As shown in figs. 5a and 5b, this HD diaphragm is formed of a permeable hydrophobic sheet which is folded in half and constitutes a lower loop HD12 disposed in the tubular distributor SD. This loop HD12 connects two flat diaphragm sheets HDa, HDb which pass through said slot SD1 of the distributor SD and are mounted vertically in two parallel planes using any suitable fixing means (not shown), with a small gap between them which is limited by the width of said upper slot SD1. The tubular distributor SD is intended to be supplied with hydrophobic solvent under pressure which maintains said loop HD12 of the hydrophobic sheet against the internal surface of the tubular distributor SD and is injected through the linear slot SD3 between said sheets HDa and HDb and thus performs a upward movement between these two sheets of the HD diaphragm.

As shown in fig. 1, a mobile liquid membrane LM is formed in accordance with the invention on a hydrophobic permeable diaphragm HD immersed in a bath B of water to be purified circulating in a cell C open at the top to the atmosphere. This HD diaphragm is fixed by any suitable means (not shown) to the side walls of cell C, extends from the bottom of the cell to the surface of bath B and subdivides the cell into two extraction compartments SCI, SC2 interconnected by a lower passage P12 disposed at the bottom of cell C.

The hydrophobic diaphragm HD is mounted in a vertical transverse plane in cell C between an upper main inlet 11 for the water to be purified and a main outlet 01 for the purified water. This inlet II is intended to be connected to any appropriate source of the water to be purified (not shown in the drawing). The water coming from inlet II flows downwards in the first extraction compartment SCI along the front face of the mobile liquid membrane LM, then flows through the passage P12 in the second compartment SC2 in which it flows upwards along the rear face of the mobile liquid membrane LM. The purified water is evacuated from the cell by outlet 01 and can be stored in a tank (not shown).

As further emerges from FIG. 1, the mobile liquid membrane LM is formed in accordance with the invention by injecting at the foot of the hydrophobic diaphragm HD a hydrophobic solvent HS using a tubular distributor SD mounted at the bottom of cell C and connected to any appropriate source such than a tank containing the hydrophobic solvent which is injected at the bottom of cell C.

Said hydrophobic solvent is lighter than water, does not mix with water and thus performs a long upward movement of the HD hydrophobic diaphragm so that it is brought into intimate contact with the water circulating in the bath B and that it thus forms the mobile liquid membrane ML which rises towards the upper end of the diaphragm HD and forms a hydrophobic layer HL floating on the surface of the bath B and containing the impurities separated by extraction using the LM mobile liquid membrane. A vertical outlet baffle BPo is also mounted in the vicinity of the upper main outlet 01 in the upper part of cell C so as to delimit said hydrophobic layer HL and to separate it from outlet 01 so as to avoid any mixing of purified water discharged through this outlet Ol with the solvent forming this hydrophobic layer HL.

The cell C is also provided with an upper auxiliary outlet 02 located at a higher level than the outlet Ol and above the surface of the bath and intended to be connected to evacuation means not shown allowing evacuation intermittent or continuous hydrophobic solvent constituting the HL layer floating on the surface of the bath and containing the impurities separated by extraction using the mobile liquid membrane LM.

The mobile liquid membrane, formed in accordance with the invention and described above, makes it possible to ensure the effective separation of various liposoluble impurities by liquid-liquid extraction. Impurities with preferable solubility in an organic medium, such as, for example, organochlorine compounds, oils, hydrocarbons and metallic mercury, can be easily separated from the water circulating in contact with the mobile liquid membrane, which makes it possible to dissolve such impurities in the hydrophobic solvent forming the mobile liquid membrane, to entrain them thanks to its upward movement and to evacuate them easily with the organic solvent forming the hydrophobic layer floating on the surface of the bath. The arrangement of the arrangement of the mobile liquid membrane described thus allows constant renewal of the hydrophobic solvent, thus ensuring the stability of this mobile liquid mem¬ brane and therefore an effective separation of the impurities present in the water.

Fig. 2 shows an embodiment of an electrolysis cell EC which is provided with a mobile liquid membrane LM formed on a hydrophobic diaphragm HD in the manner already described with respect to FIG. I and which also has a main inlet 11 for the water to be purified and two outlets Ol and O2 respectively serving for the evacuation of the purified water and of the organic solvent constituting the hydrophobic layer HL comprising the organic solvent coming from the liquid membrane mobile LM, floating on the surface of bath B and containing the impurities separated from the water by this LM liquid membrane.

This EC electrolysis cell is provided with a cathode E "disposed at one of its ends and with an anode E * disposed at the opposite end of the cell EC in an anode compartment AC delimited by a diaphragm hydrophilic AD permeable to anions and provided with an upper auxiliary input la and an auxiliary output Oa at the bottom of the cell allowing the renewal of the anolyte. The anode E ⁺ and the cathode E "are intended to be connected to a direct current source (not shown) allowing them to apply an adjustable voltage serving to polarize the mobile liquid membrane LM so that it constitutes a bipolar liquid electrode whose anodic and cathodic faces are indicated by δ ⁺ and δ ".

As further emerges from FIG. 2, an upper outlet baffle BPo also delimits the hydrophobic layer HL floating on the surface of the bath in order to avoid any mixing of the treated liquid discharged by the outlet Io with the solvent constituting this hydrophobic layer.

Fig. 2 shows an arrow TA which indicates the addition of a fat-soluble chelating agent which is dissolved in the hydrophobic solvent HS. This agent is composed of a reversible redox group and a liposoluble group and has an oxidized form and a reduced form allowing the oxidation, reduction and complexation of impurities present in water. The operation of the electrolysis cell described according to fig. 2 allows, in addition to the extraction of liposoluble impurities explained above, to separate ionic impurities which are brought into contact with the anode and cathode faces of the mobile liquid membrane, by the circulation of water in the bath and by ion migration. This contact makes it possible to subject the ionic species to complexation, oxidation and reduction reactions with the chelating agent, the dissolution of the complexed, reduced or oxidized reaction products in the hydrophobic solvent and consequently the extraction of these ionic impurities. and their evacuation thanks to the upward movement of the mobile liquid membrane. In addition, contact of the cathode with the water to be purified makes it possible on the one hand to reduce various impurities and the reduced products can then be eliminated by deposition on the cathode or else by means of the mobile liquid membrane by l 'through the reactions described above. On the other hand, the hydrogen released at the cathode can promote the entrainment by flotation of impurities poorly soluble in water or in the form of aggregates towards the hydrophobic layer floating on the surface of the bath, and so be removed together with the solvent constituting this layer. The hydroxyl ions formed during the evolution of hydrogen also allow the precipitation of various impurities which can settle at the bottom of the cell, from which they can then be removed by any suitable means. The anions which are in the vicinity of the diaphragm delimiting the anode compartment migrate through this diaphragm, are thus eliminated from the water and can then be evacuated from the cell by renewal of the anolyte. The embodiment shown in fig. 3 comprises an EC electrolysis cell which is similar to that described above with respect to FIG. 2. The EC cell is however provided in this case with two mobile liquid membranes LM I and LM2 which delimit a compartment RC and are formed respectively on two hydrophobic diaphragms HD1 and HD2 immersed in the bath B and associated with two distributors SD1 and SD2 supplied with hydrophobic solvent comprising a dissolved chelating agent TA as described above.

The EC electrolysis cell shown in fig. 3 is also provided with a main inlet 11 for the water to be purified, with two outlets Ol and O2 serving for the evacuation of the purified water. and of the solvent constituting the hydrophobic layer HL floating on the surface of the bath B and containing the impurities separated from the water by the mobile liquid membranes LM1 and LM2. This cell also includes a BPo outlet baffle near the Ol outlet.

The anode E ⁺ and the cathode E "are arranged in the same way as in FIG. 2 at the opposite ends of the cell EC and are intended to be connected to a source of direct current not shown allowing them to be applied an adjustable voltage serving polarizing the mobile liquid membranes LM1 and LM2 so that they constitute bipolar electrodes whose anode and cathode faces are indicated respectively by δi ⁺ , δi- and δ2 ⁺ , δ2-. The RC compartment delimited by the mobile liquid membranes LM1 and LM2 is provided with an upper auxiliary input Ir and a lower auxiliary output Or, which allow the regeneration of the aqueous liquid contained in this compartment RC. The extraction compartments SCI and SC2 are arranged on both sides other of this compartment RC and connected by the passage PI 2 which in this case extends under this compartment RC. As it further appears from Fig. 3, the outlet baffle BPo delimits the has a hydrophobic HL layer floating on the surface of the bath and separates it from the outlet Ol in order to avoid any undesirable mixing of the purified water with the solvent forming this floating hydrophobic layer.

The arrow TA further indicates the addition of a fat-soluble chelating agent which is dissolved in the hydrophobic solvent, which is capable of undergoing a reversible redox reaction and which has an oxidized form and a reduced form allowing oxidation, reduction and reversible or irreversible complexation of impurities present in the water to be purified in the EC cell.

The functioning of mobile liquid membranes in the described electrolysis cell EC shown in fig. 3 can be explained as follows: As already explained with reference to FIGS. 1 and fig. 2, the hydrophobic solvent forming the mobile liquid membranes LM1 and LM2 allows the efficient separation of various liposoluble impurities by liquid-liquid extraction and their evacuation via the hydrophobic layer HL floating on the surface of the bath B.

The TA chelating agent dissolved in this organic solvent reacts with oxidizing anions such as CrO ₄ ~~ and MnO.} "Irreversibly at the anode interface δl ⁺ of the mobile liquid membrane LMI by producing a reduced cation which is then capable of either being complexed with the TA chelating agent and entrained in the hydrophobic solvent, or of being released into water in the form of a cation which is then subjected to the electric field to migrate towards the cathode, where it can be electrolytically deposited or precipitate in the form of hydroxide The cations thus formed which reach the extraction compartment SC2 and pass through the mobile liquid membrane LM2 are collected in the compartment RC. Thus, for example, CrO ₄ "can be reduced to Cr ⁺⁺⁺ and MnO ₄ "in Mn ⁺⁺ . The chelating agent also allows the separation of various metal ions such as HQ * ^" * ^' , Cd ⁺⁺ , Tl ⁺ , Ni ⁺⁺ by a proton exchange provided by the chelating agent TA at the cathode interfaces δl ^" and δ2 ~ of mobile liquid membranes LM1 and LM2. Depending on the rate of formation and rupture of the dissolved complex, the separated impurities are evacuated via the upward movement of these mobile liquid membranes or else are collected in the RC compartment.

The anodic faces δl ⁺ and δ2 ⁺ of the mobile liquid membranes LM1 and LM2 also allow various other impurities present in the form of anions, such as acetates or phenolates, to capture a proton crossing the liquid membranes in the direction of the cathode and thus to form a liposoluble acid, which is evacuated by means of the upward movement of the mobile liquid membrane.

Thus, for example, the phenolates can be respectively transformed and disposed of in this way in the form of phenols.

The cathode also allows the separation of various metal cations such as Cu ⁺⁺ , Zn ^"""1" , Cd ⁺⁺ , Pb ^"1-1" which are dissolved in water, which undergo reduction and are deposited electrolytically in the form of metal on the cathode.

The pH gradient in the vicinity of the cathode also allows the precipitation of various cations such as Ni ⁺⁺ and Fe ⁺⁺ in the form of Ni (OH) 2 and Fe (OH) 2.

The hydrogen released at cathode E "also makes it possible to entrain various hydrophobic impurities by flotation, in particular oils, and to evacuate them on the surface of the bath above the inlet 11 for water.

The migration of various anions under the effect of the electric field, in the form of chloride, sulphate or phosphate for example, through the permeable diaphragm AD delimiting the anodic compartment AC, thus makes it possible to collect these anions in the compartment AC and to evacuate.

Fig. 4 shows a variant of a cell which differs essentially from the cell described according to FIG. 3 only by the fact that it is further provided with an additional hydrophobic permeable diaphragm HD3 which is connected to said means for supplying hydrophobic solvent in order to form an additional liquid membrane LM3, which is immersed in said bath B and extends at a level below the surface of said bath and which is arranged opposite said cathode E ", between said upper main inlet II for the water to be purified and said compartment RC, and thus delimits a compartment SC3 communicating with the first extraction compartment SCI. A second upper inlet baffle BPi is also arranged in the vicinity of the main entrance 11 between the cathode E "and the hydrophobic diaphragm HD3. This arrangement is provided in such a way that the water to be purified arriving in the cell EC through the upper main entrance II is caused to circulate first downwards the lonc of the cathode E "using the baffle of BPi input a H go up along the anode face δ3 ⁺ of said liquid membrane LM3, pass over the latter and then flow downward between the cathode face 53 "of this mobile liquid membrane LM3 and the anode face δl ⁺ of the first mobile liquid membrane LM1 delimiting the collecting compartment RC The water to be purified then flows from the extraction compartment SCI, through the passage PI 2, and then into the second extraction compartment SC2.

The use of such an additional LM3 liquid membrane as described makes it possible to effect a prior separation of impurities such as, for example, oils capable of hampering the operation of the following liquid membranes LM1 and LM2 and thus preserving these membranes delimiting the RC compartment in order to fully safeguard their effectiveness.

It is moreover obvious that it is also possible, if necessary, depending on the nature and the amount of the impurities, to use several liquid membranes such as LM3 in order to ensure optimal separation of the various impurities in the set of the cell. The comparative tests described below illustrate results obtained by means of mobile liquid membranes as provided in accordance with the present invention.

We first dissolved 3.4033 g of NiC ^ x ^ O in 4 liters of distilled water in order to prepare an aqueous test solution having a pH equal to 6, 1 and an initial concentration corresponding to 315 mg l Ni. 1) 1700 ml of the test solution comprising 315 mg / l Ni was subjected to a prior electrolytic treatment in a test cell provided with a central anode in platinum titanium placed between two cathodes in 316L stainless steel having a cathode surface 120 cm ²

This preliminary treatment consisted in applying a sufficient voltage to pass a current of 400 mA into a bath of the test solution corresponding to a cathodic current density of 3.33 mA / cm ² . The test solution was circulated at the same time in this bath by means of a pump associated with a buffer tank constituting a closed loop with the test cell. During the flow of current through the test cell, samples were taken and the dissolved nickel content of the solution flowing in a closed loop was measured periodically. After passing the current at 3.33 mA / cm ² for one hour, the test solution had lost 1 1.9 mg of nickel and a cathodic deposition was thus obtained with a faradic yield of approximately 3%. corresponding to a reduction in the concentration from 315 to 308 mg / l Ni.

2) The 308 mg / l Ni solution thus obtained was then subjected to extraction using mobile liquid membranes as provided for according to the invention. At this time, a cathode and an anode arranged on either side of an intermediate compartment delimited by two liquid membranes formed were mounted in the test cell. each on a hydrophobic diaphragm consisting in this case of two flat sheets of nonwoven polypropylene joined and mounted vertically.

By way of comparison, two immobilized liquid membranes were first formed by saturating each diaphragm with an extraction solution composed of hexadecane containing 68 × 10 −6 M of coenzyme Q _{) 0} between the two sheets of nonwoven polypropylene with 1 bottom end of each support After having formed a bath of the 308 mg / l Ni solution containing the two liquid membranes in the test cell, this solution was circulated in the intermediate compartment between these two liquid membranes and these liquid mem¬ branes were polarized by applying a voltage of 60 V and a current of 64 itiA was measured between the anode and the cathode. The active polarized surface of each liquid membrane was equal to 16 cm ² , ie a current density of 4 mA / cm ^2. Samples were taken during the passage of this current and it was possible to observe a disappearance of the dissolved nickel in a concentration range from 300 to 75 mg / l Ni with an efficiency extraction activity from 19% to 17%.

Said extraction solution was then injected continuously at the lower end of the two polypropylene sheets constituting the support, so as to form a mobile liquid membrane rising between the two sheets to the top of the diaphragm and then forming a hydrophobic layer. floating on the surface of the bath in the test cell.

Samples taken during the circulation of the test solution with an initial concentration of 75 mg / l Ni and during the passage of the current with a density of 4 mA / cm ² demonstrated a very strong increase in the extraction efficiency on mobile liquid mem¬ branes, to achieve faradic yields of 35% to 23%.

During this extraction test, the extraction liquid floated manually both on the surface of the bath and it was possible to detect the presence of nickel compounds in this liquid by their characteristic color, the final concentration in the aqueous solution then having fallen to 40 mg / l Ni. It is thus shown that the separation efficiency in this concentration range depends on the rate of introduction of the hydrophobic solvent into the cell.

The invention can be applied to the purification of water or any aqueous liquid containing various types of impurities which can be separated by extraction so as to obtain the combination of the advantages which arise from the use of mobile liquid membranes such as described above.

Claims

claims

1. Process for the purification of water by extraction using liquid membranes, characterized in that:

(a) an aqueous bath comprising the water to be purified is placed in contact with at least one mobile liquid membrane composed of a hydrophobic solvent having a density lower than water and effecting an upward movement in contact with a diaphragm hydrophobic, permeable vertically mounted in a cell,

(b) forming said mobile liquid membrane by injecting said hydrophobic solvent continuously at the lower end of said hydrophobic diaphragm, so that this hydrophobic solvent undergoes a continuous upward movement in contact with said hydrophobic diaphragm and said aqueous bath and that it forms a hydrophobic layer floating on the surface of said bath,

(c) circulating said aqueous bath in order to promote the extraction of impurities by means of said mobile liquid membrane and

(d) the purified water is removed separately from said aqueous bath and said solvent from said hydrophobic layer floating on the surface of this bath.

2. Method according to claim 1, characterized in that said hydrophobic solvent is injected between two permeable hydrophobic sheets constituting said diaphragm, so that this solvent forms a mobile liquid membrane rising between these two hydrophobic sheets.

3. Method according to claim 1 or 2, characterized in that said hydrophobic solvent comprises at least one fat-soluble chelating agent.

4. Method according to claim 3, characterized in that said chelating agent comprises a reversible redox group and a liposoluble group and that it has an oxidized form and a reduced form allowing the oxidation, reduction and chelation of impurities present in the water to be purified.

5. Method according to claim 4, characterized in that said chelating agent is a compound comprising a quinone function attached to an aliphatic or cyclic residue, in particular coenzy e Q- ₀ .

6. Method according to one of claims 3 to 5, characterized in that at least one mobile liquid membrane is arranged between said aqueous bath and a collecting compartment containing a renewable aqueous liquid.

7. Method according to one of claims 4 to 6, characterized in that the liquid is circulated in said aqueous bath in an electrolysis cell, that an electric field is applied between an anode and a cathode of so as to allow the dissociation of water in said bath, that the water to be purified is introduced in the vicinity of said cathode and that the purified water is discharged in the vicinity of said anode.

8. Method according to claim 7, characterized in that said anode is separated from said aqueous bath by means of a hydrophilic diaphragm which is permeable to anions and delimits an anodic compartment containing a renewable aqueous anolyte, so as to thus favor the migration of anions from said aqueous bath and their collection in this anode compartment.

9. Apparatus for implementing the method according to claim 1, characterized by: (a) at least one electrolysis cell (EC) comprising at least two extraction compartments (SCI, SC2) which are separated by at least a permeable hydrophobic diaphragm (HD) and communicate by a passage (PI 2), an anode (E ⁺ ), a cathode (E "), an anode compartment (AC) delimited by a hydrophilic diaphragm (AD) permeable to anions , an upper main inlet (II) for the water to be purified, arranged in the vicinity of said cathode (E ') and a main outlet (Ol) for purified water, arranged in the vicinity of said anode compartment (AC), in order to forming a bath (B) of water to be purified circulating in said electrolysis cell, (b) means for supplying hydrophobic solvent comprising a distributor (SD) arranged so as to inject and distribute said hydrophobic solvent at the end lower of said hydrophobic diaphragm (HD), thereby forming a mem liquid brane moving upward along said hydrophobic diaphragm and further forming a hydrophobic layer of said solvent floating on the surface of said bath, at least one upper outlet baffle (BPo) arranged so as to separate said main outlet (Ol) from said hydrophobic layer (HL) floating on the surface of said aqueous bath (B), the entire apparatus being arranged so as to circulate the water to be purified successively in said extraction compartments, to dissociate the water in said bath, polarizing said mobile liquid membrane and separately discharging the purified water and said solvent. 10-. Apparatus according to claim 9, characterized in that at least one collecting compartment (RC) is arranged between said two extraction compartments (SCI, SC2) and is delimited by two hydrophobic permeable diaphragms (HD1, HD2) connected to said means supplying hydrophobic solvent in order to form two mobile liquid membranes (LM I, LM2) having opposite faces intended respectively for contact with the aqueous bath circulating in said extraction compartments (SCI, SC2) and with a renewable aqueous liquid in said collecting compartment (RC).