FR3029191A1 - DESSALING UNIT COMPRISING AT LEAST ONE EVAPORATION BASIN, METHOD OF EXTRACTING SALTS AND METHOD OF PRODUCING A FINAL AQUEOUS SOLUTION - Google Patents

Abstract

The invention relates to a desalination unit (1) of an initial aqueous solution (SO) containing an initial salt concentration, comprising at least one desalting device (10) adapted to receive, at an inlet (101), this solution aqueous solution and to reject separately, at first and second outlets (102, 103), a first aqueous solution (S1) containing a first concentration of salts greater than said initial concentration, and a second aqueous solution (S2) containing a second concentration in salts lower than the initial concentration. According to the invention, said desalination unit further comprises at least one evaporation basin (20) and means for pouring (12) exclusively said first aqueous solution discharged by the desalination device into the evaporation basin. The invention also relates to a method for extracting salts using such a desalting unit, and a method for producing a final aqueous solution.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention relates generally to the field of desalination units. It relates more particularly to a desalination unit of an initial aqueous solution containing an initial concentration of salts, comprising at least one desalting device adapted to receive, at an inlet, this initial aqueous solution and to reject separately, at first and second outlets, a first aqueous solution containing a first concentration of salts greater than said initial concentration, and a second aqueous solution containing a second salt concentration lower than the initial concentration. The invention finds a particularly interesting application in salt marsh type installations. It also relates to a process for extracting salts from an aqueous solution and a method for producing a final aqueous solution. BACKGROUND TECHNOLOGY Various techniques are known that can be implemented in desalination units to obtain a fresh water, possibly potable, from an aqueous solution concentrated in salts such as seawater. techniques are generally based on the removal of the concentrated aqueous solution of salts, usually in the sea, then its separation into two solutions: an aqueous solution more concentrated in salts and an aqueous solution less concentrated in salts, called fresh water. The seawater withdrawn can optionally be chemically treated before this separation into two solutions. Fresh water is recovered and eventually treated to obtain drinking water. The aqueous solution, more concentrated in salts, is most often discharged into the sea or buried underground. Discharge to the sea poses environmental problems because the salt concentration of the discarded aqueous solution greatly disturbs the local salinity of the sea. Local flora and fauna can be threatened by this rejection. In addition, disposal at sea requires the use of pumping systems adapted to reject the more concentrated aqueous salt solution far from the shore, these pumping systems being very energy intensive.

Similarly, underground burial can disrupt the ecosystem. OBJECT OF THE INVENTION In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes a new optimized desalination unit allowing the valorization of at least a part of the aqueous solution more concentrated in salts resulting from the operation of the desalination unit and avoiding its discharge to the sea or its burial. More particularly, according to the invention there is provided a desalination unit as described above, said desalination unit further comprising at least one evaporation basin and means for discharging exclusively said first aqueous solution discharged by the desalination device into the evaporation basin. Other non-limiting and advantageous characteristics of the desalination unit according to the invention are as follows: the evaporation basin comprises several basin elements whose bottom and side walls are watertight; the desalination device comprises a reverse osmosis pump; the desalination device comprises a device for the distillation of the initial aqueous solution; the desalination device comprises a device for electrodialysis of the initial aqueous solution; - there is provided a pre-concentration device adapted to concentrate in salt a preliminary aqueous solution containing a preliminary concentration of salts so as to form, at least partially, the initial aqueous solution received by the desalting device at its inlet; said pre-concentration device comprises at least one other desalination device placed upstream of said desalination device, this other desalination device receiving at another inlet said preliminary aqueous solution and rejecting at another first outlet said initial aqueous solution; said pre-concentration device comprises a pipe for recirculating at least a portion of the first aqueous solution from the first outlet of said desalination device to the inlet of said desalination device, such that said initial aqueous solution supplying the desalting device is here formed by a mixture between said first aqueous solution and said preliminary aqueous solution; said evaporation pond comprises at least one water extraction device comprising at least one semipermeable membrane allowing the passage of the water contained in said first aqueous solution to a water storage element; - The storage element contains an aqueous priming solution adapted to trigger a direct osmosis phenomenon causing the passage of water from the first aqueous solution to the storage element; the evaporation basin comprises at least one internal partition comprising said semi-permeable membrane, this internal partition forming, with a portion of the evaporation basin, said water extraction device; said internal partition extends generally horizontally or vertically; the water extraction device comprises at least one open or closed container adapted to be disposed in said evaporation basin, and the storage element is constituted by said container itself which is adapted to fill with water. water; said container comprises at least one pipe or bag, at least one wall of which comprises said semi-permeable membrane; and, the water extraction device comprises a semipermeable membrane fabric or net, and the storage element is the fabric itself which is adapted to waterlogging. The invention also provides a method of extracting salts using a desalting unit as described above, wherein a) a desalination device of the desalination unit is fed with an initial aqueous solution; said first aqueous solution containing the first concentration of salts greater than said initial concentration in the evaporation basin of the desalination unit, c) evaporating the water of the first aqueous solution, d) recovering the salts of the first aqueous solution. A further feature of the extraction method described above is that in step a), the initial aqueous solution is obtained by concentrating a preliminary aqueous solution with salts using a pre-concentration device of the unit. desalination. Said pre-concentration device being as defined above, namely either one or more other desalination units placed upstream of the main desalination unit, or a recirculation line.

In addition, according to the extraction method according to the invention, in an additional step c ') carried out before step d), water is extracted from the first aqueous solution using a water extraction device. comprising at least one semipermeable membrane allowing the passage of water from said first aqueous solution to a water storage element.

The invention finally relates to a method for producing a final aqueous solution using a desalination unit as described above, according to which, e) the steps a) and b) of the extraction method described above are carried out, f ) water is extracted from the first aqueous solution contained in said evaporation basin to the storage element of the water extraction device, g) the final aqueous solution is obtained in said storage element. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description with reference to the accompanying drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: FIG. 1 is a schematic representation of a first embodiment of a desalination unit according to the invention; FIG. 2 is a schematic view of a second embodiment of a desalination unit according to the invention; FIG. 3 is a schematic view of a third embodiment of a desalination unit according to the invention; FIG. 4 is a schematic view of a fourth embodiment of a desalination unit according to the invention; FIG. 5 is a schematic view of a fifth embodiment of a desalination unit according to the invention; FIG. 6 is a schematic view from above of the evaporation basin of a sixth embodiment of a desalination unit according to the invention; and FIG. 7 is a schematic view of a seventh embodiment of a desalination unit according to the invention. In the remainder of the description, the identical or corresponding elements of the different embodiments will be identified by the same references, so that only the different elements of one embodiment to another will have different references. In the remainder of the description, the terms "upstream" and "downstream" will be used in the flow direction of the aqueous solutions to locate the elements of the desalination unit with respect to one another. Similarly, the terms "inlet" and "outlet" will be used in the flow direction of the aqueous solutions to describe the mounting direction of the elements of the desalination unit. The direction of flow of the aqueous solutions is represented by arrows in FIGS. 1 to 7. Furthermore, in the following description, the term "salts" designates, unless otherwise stated, the salts dissolved in an aqueous solution. while the terms "salt crystals" refer to salts in solid form. The term "ionic chemical compound" refers to a chemical substance composed of atoms of two or more different chemical elements interconnected by ionic chemical bonds. In the remainder of the description, the term "ionic chemical compound" will be used to designate both an ionic chemical compound in solid or dehydrated form, and in the form of a solute in aqueous solution, in which it is present in the form of of ion pairs. When the ionic chemical compound is contemplated in solid form, it is soluble in water to form an aqueous solution of the same ionic chemical compound. Salts and salt crystals are an example of an ionic chemical compound.

Finally, in the remainder of the description, the term "semipermeable membrane" means a membrane which separates a solution from another medium, allowing solvent molecules to pass freely from this solution but no or little molecule of dissolved solutes. in this solvent.

Here, the semipermeable membrane separates the first aqueous solution from another medium by letting only water pass, and none or very few dissolved ionic salts and / or chemical compounds. In common parlance, semi-permeable membranes are also sometimes called hemipermeable membranes.

Device Figures 1 to 7 show first, second, third, fourth, fifth, sixth and seventh embodiments of a desalination unit 1. Regardless of the embodiment considered, the desalination unit 1 comprises a main desalination device 10 (not shown in FIG. 6). This main desalination device 10 comprises an inlet 101 adapted to receive an initial aqueous solution SO containing an initial concentration CO salts. It is suitable for separating this initial aqueous solution SO into first and second aqueous solutions 51, S2 respectively containing a first concentration C1 in salts greater than said initial concentration CO, and a second concentration C2 in salts lower than said initial concentration CO. It is adapted to evacuate through a first outlet 102 the first aqueous solution 51, and a second outlet 103 the second aqueous solution S2. By convention, the aqueous solution entering the desalting device 10 through the inlet 101 is called the initial aqueous SO solution. Similarly, the aqueous solution exiting from the first outlet 102 of the desalter 10 and having a salt concentration greater than that of the initial solution SO is called the first aqueous solution 51 and the aqueous solution exiting through the second outlet 103 of the device. desalting 10 and having a salt concentration lower than that of the initial solution SO is called second aqueous solution S2. In the example described here, the initial aqueous solution SO is seawater which can be, according to the second and third embodiments, pre-concentrated from a preliminary aqueous solution. In general, the initial solution SO or preliminary SP is taken from a reservoir 2, here the sea. In a conventional manner, the initial CO concentration in salts of seawater varies from 5 grams per liter (g / L), for example in the Baltic Sea, at around 40g / L. On average, the initial CO concentration in salts of the initial aqueous solution SO is of the order of 35 g / l. The salts are pairs of ions conventionally contained in seawater. The seawater contains, for example, ions such as chloride ions, sulphate ions, hydrogencarbonate or carbonate ions, sodium ions, potassium ions, magnesium ions, or lithium ions. Tables 1 and 2 below show a part of the various ions conventionally contained in seawater having a salinity of 35 g / l. These Tables 1 and 2 are taken from: UNESCO, International Oceanographic Tables 15, cited by Andrew W. Dickson and Catherine Goyet (eds.), Handbooks of methods for the analysis of the various parameters of the carbon dioxide system in water, US Department of Energy, Version 2, September 1994, ORNL / CDIAC-74, Chapter 5, Part 6.1 "The Major Composition of Seawater", p. V-10. Table 1 Anions Quantity in grams per kilogram Chloride (Cr) 19.3524 Sulphate (5042-) 2.7123 Hydrogen carbonate (HCO3-) 0.1080 Bromide (Br-) 0.0673 Carbonate (C032-) 0.0156 Fluoride ( F-) 0.0013 Hydroxide (HO-) 0.0002 Table 2 Cations Quantity in grams per kilogram Sodium ion (Na) 10.7837 Magnesium ion (Mg2 +) 1.2837 Calcium ion (Ca2 +) 0.4121 Potassium ion (K +) ) 0.3991 Strontium ion (Sr2 +) 0.0079 Lithium ion (Li) 1.73.10-4 Rubidium ion (Rb) 1.20.10-4 Barium ion (Ba2 +) 2.0.10-5 Polyatomic ions (including molybdenum), c) o-5 Polyatomic Ions (including uranium) 3.3.10-6 The ion pairs of particular interest to us are lithium chloride (Li +; Cl-), potassium chloride (K +; ), sodium chloride (Na; Cl-), or lithium carbonate (2Li +; CO32-). This list of ion pairs is however not exhaustive. In the case where the initial solution SO is seawater, the first aqueous solution Si is a salt-enriched water with respect to this seawater. This first salt-enriched aqueous solution Si is more commonly called a concentrate. For a sea water whose initial concentration CO in salts is of the order of 35 grams per liter (g / L), the first concentration C1 in salts of the first aqueous solution Si is generally between 60g / L and 80g / L. The second aqueous solution S2 is a water highly salt-depleted compared to seawater. It is desalinated in this way. As shown in FIGS. 1 to 5, and 7, the desalination unit 1 comprises, upstream of the desalination device 10, a pipe 11 for conveying the seawater to the inlet 101 of the desalination device 10. The conveying duct 11 comprises a first pump 111 adapted to convey the seawater from the sea to the inlet 101 of the desalination device 10. As described later, the seawater is optionally pretreated and then directly introduced into the main desalting device 10 (first, fourth, fifth, sixth and seventh embodiments of the desalting unit), or mixed with another aqueous solution before it enters the main desalination device (second mode). of the desalination unit), is concentrated in salts before being introduced into the main desalination device 10 (third embodiment of the desalination unit). According to a first variant of the desalination device 10, it is a reverse osmosis pump. The reverse osmosis pump is a conventional means of desalting aqueous solution and will not be described in detail here. It will be recalled only that the reverse osmosis pump comprises an element in which first and second compartments are separated by a semipermeable membrane. Said element is, in general, a pipe of great length, and the semi-permeable membrane has approximately the same length as said pipe, so that the first and second compartments are formed in the direction of the length of said pipe. The inlet 101 of the reverse osmosis pump corresponds to the inlet of the first compartment. The first output 102 of the reverse osmosis pump corresponds to the output of the first compartment. The second output 103 of the reverse osmosis pump corresponds to the output of the second compartment. The reverse osmosis pump is adapted to receive at its inlet 101 the initial aqueous solution 50, and to circulate this initial aqueous solution 50 under pressure, namely under a pressure equal to 40 to 60 bar in general, in the first compartment . The first compartment is intended to evacuate at its outlet the first aqueous solution 51. The reverse osmosis pump is adapted to collect in the second compartment the second aqueous solution S2, and to evacuate at the outlet of said second compartment. The reverse osmosis pump is thus adapted to exert a pressure, greater than the osmotic pressure, on the initial aqueous solution SO contained in the first compartment, so as to force a part of the water contained in said initial aqueous solution SO towards the second compartment. The semi-permeable membrane is adapted to retain in the first compartment the vast majority of the salts, so that only the water can be transferred to the second compartment.

Thus, the reverse osmosis pump is adapted to separate the initial aqueous solution SO in the first and second aqueous solutions Si, S2, the latter being distinct. According to a second variant of the desalination device 10, it may be a distillation device.

The distillation device is a conventional means of desalting aqueous solution and will not be described in detail here. It will be recalled only that the distillation device comprises first and second circuits for circulating aqueous solutions. The inlet of the first circuit corresponds to the inlet 101 of the distillation device. The output of the first circuit corresponds to the first output 102 of the distillation device. The output of the second circuit corresponds to the second output 103 of the distillation device. The distillation device is adapted to receive at its inlet 101 the initial aqueous solution SO, and to circulate said initial aqueous solution SO in the first circuit. The first circuit is intended to heat at a selected temperature and under a selected pressure said initial aqueous solution SO. The first circuit is also intended to evacuate the first aqueous solution 51 at its output. The heating temperature and the pressure are chosen to evaporate part of the water contained in the initial aqueous solution SO. The distillation device is adapted to recover in the second circuit the water vapor originating from said initial aqueous solution SO and to condense it so as to form the second aqueous solution S2. The distillation device is also adapted to evacuate the second aqueous solution S2 at the outlet of the second circuit. Thus, advantageously, the distillation device is adapted to separate the initial aqueous solution SO in the first and second aqueous solutions Si, S2, the latter being distinct.

According to a third variant of the desalination device 10, it may be an electrodialysis device. The electrodialysis device is a conventional means of desalting aqueous solution and will not be described in detail here. The electrodialysis device comprises two electrodes separated by a plurality of compartments, each compartment being formed on one side by an ion-permeable and anion-impermeable membrane, and on the other side by an anion-permeable and cation-impermeable membrane. The input 101 of the electrodialysis device corresponds to all the inputs of the compartments. The first output 102 of the electrodialysis device 15 corresponds to the output of one compartment out of two. The second output 103 of the electrodialysis device corresponds to the output of the other compartments. The electrodialysis device is adapted to apply a voltage between the two electrodes so as to create an electric field between these two electrodes, and to circulate the initial aqueous solution SO in the compartments. One compartment out of two is intended to evacuate at its outlet the first aqueous solution 51. The other compartments are intended to evacuate at their outlet the second aqueous solution S2. Thus, advantageously, the electrodialysis device is adapted to separate the initial aqueous solution SO in the first and second aqueous solutions 51, S2, the latter being distinct. Each of the variants of the desalination device 10 can be used in all the embodiments of the desalination unit 1, or be associated in part or in whole. The desalination device may include a combination of these variants. Whatever the embodiment of the desalination unit 1 and the variant of the main desalination device 10 used, the desalination unit 1 also remarkably comprises at least one evaporation basin 20 and a means for pouring exclusively said first aqueous solution Si rejected by the main desalination device 10 into the evaporation pond 20. Thus, as shown schematically in Figures 1 to 5, and 7, the evaporation basin 20 is connected to the first Exit 102 of the main desalination device 10 through a discharge line 12. The evaporation pond 20 is adapted to collect the first aqueous Si solution which was previously discharged into the sea or buried. The marine fauna and flora are protected, as well as the subsoils. In addition, whatever the embodiment of the desalination unit 10 1, the evaporation basin 20 is adapted to evaporate all or part of the water contained in the first aqueous solution Si. is preferably arranged in the sun and / or wind, so as to facilitate the evaporation of water. The desalination unit 1 according to the invention is thus preferably installed in a region having a hot and dry climate, in a wind zone. The desalination unit 1 can in particular be installed in the Middle East, a region in which the rate of evaporation of water is of the order of 3500 millimeters per year. In addition, this region offers large free spaces for the installation of the evaporation pond 20. In general, whatever the embodiment considered here, the evaporation basin 20 comprises a bottom 212 surrounded by walls. The evaporation basin 20 is adapted to collect salt crystals contained in the first aqueous solution Si. It then acts as a settling basin for the salts. It also acts as a salt concentration pool of the first aqueous solution Si. Alternatively, it is possible to recover an aqueous solution much more concentrated in salts downstream of the evaporation basin 20 than the first aqueous solution Si, in order to post-treat this final aqueous solution to extract salt crystals. Thus, thanks to the desalination unit 1 according to the invention, the first aqueous solution Si is recovered, which limits the harmful effects of its discharge on the environment, and this first aqueous solution Si is recovered by the extraction of salt crystals that can then be exploited. Whatever the embodiment considered, the means for discharging the first aqueous solution Si into the evaporation pond 20 is here the discharge pipe 12 adapted to transport the first aqueous solution Si from the first outlet 102 of the desalination device 10 Mainly to the evaporation basin 20. Preferably, as shown in Figures 1 to 5 and 7, the gravity is sufficient to circulate the first aqueous solution Si from the first outlet 102 of the main desalination device 10 to the basin 20. Thus, advantageously, it avoids the addition of pumping systems increasing the energy consumption of the desalination unit 1. Alternatively, the discharge pipe may be provided with a second pump adapted to make circulate the first aqueous solution from the first outlet of the desalting device to the evaporation pond. In FIGS. 1 to 5, and 7, the discharge pipe 12 is provided with a pouring valve 120 adapted to regulate the flow rate of the first aqueous solution Si in said discharge pipe 12. The desalination unit 1 also comprises a 3. The recovery of this second aqueous solution being conventional, we will not expose it in more detail here. The discharge line 13 here comprises a third pump 131 adapted to circulate the second aqueous solution S2 from the second outlet 103 of the desalination device 10 to the outside of the desalting unit 1. Alternatively, as shown in FIG. 2, the gravity can suffice to circulate the second aqueous solution S2 from the second outlet 103 of the desalination device 10 towards the outside of the desalination unit 1. In addition, whatever the embodiment of the 30 desalination unit, the discharge pipe 13 is here provided with a reject valve 130 adapted to regulate the flow of second aqueous solution S2 in the discharge pipe 13. The discharge pipes and discharge 12, 13 are the same as the first and second outlets 102, 103 of the desalination device 10, so that the desalination device 10 is adapted to separate the first and second aqueous solutions separately. es Si S2. In the first, second, sixth and seventh embodiments of the desalination unit 1, shown in FIGS. 1, 2, 6 and 7, the evaporation basin 20 comprises a single basin element 21.

The evaporation basin 20 is a pool of generally rectangular or square shape. As a variant, it can obviously have any suitable form. In the third embodiment, shown in Figure 3, it can be provided that the evaporation basin 20 comprises a plurality of basin elements, here upper basin elements 21a, 21b intermediate and lower 21c. Each of these basin elements is similar to the basin of one of the first and second embodiments. These elements of upper, intermediate and lower basins 21a, 21b, 21c are placed in the direction of flow of the aqueous solution, so that the upper basin element 21a is positioned directly downstream of the discharge pipe 12 and upstream of the intermediate and lower basin elements 21b, 21c, and so that the intermediate basin element 21b is positioned directly downstream of the upper basin element 21a and upstream of the lower basin element 21c. The upper, intermediate and lower basin elements 21a, 21b, 21c are adapted to receive different by-products from the first aqueous solution Si. These by-products are, for example, aqueous solutions originating from the first aqueous solution Si or salt crystals.

As shown in FIG. 3, the upper basin elements 21a, 21b intermediate and 21c lower can be arranged in cascade with respect to each other so as to facilitate the extraction of different salt crystals. It will also be possible to envisage bearings, filters, or airlocks for passage of an upper, intermediate or lower basin element to the other. Upper and lower link valves 213a, 213b are provided here which are adapted to regulate the flow of aqueous solution transferred from an upper, intermediate or lower basin element 21a, 21b, 21c to another. As shown in FIG. 3, gravity is sufficient to transfer the concentrated aqueous solution of salts from one upper, intermediate or lower pond element to another. This limits the use of pumps that consume energy. According to a not shown variant of the third embodiment of the desalting unit, provision may be made for the upper, intermediate or lower basin elements to be arranged next to one another, or one after the other, on a same level, not cascading. Advantageously, the evaporation basin 20 comprising several upper, intermediate or lower basin elements 21a, 21b, 21c is adapted to the implementation of specific treatment steps in each upper, intermediate or lower basin element 21a, 21b, 21c. The multiple upper, intermediate or lower basin elements 21a, 21b, 21c provide some flexibility of use since the processing steps may be modulated from one upper, middle or lower basin element 21a, 21b, 21c to another, according to the wishes of an operator of the desalination unit 1. Thus, for example the upper, intermediate or lower basin elements 21a, 21b, 21c are suitable for the extraction of a single type of salt crystal, the so-called "mono-salt" extraction, or the extraction of several salt crystals of different chemical compositions, called "multi-salt" extraction.

In the first, second and third embodiments of the desalination unit 1 described above, the bottom 212 and the side walls 211 of the evaporation basin 20, the pond element 21 or the upper basin elements, intermediate or lower 21a, 21b, 21c are sealed. For example, the bottom 212 and the side walls 211 of the basin element 21, or upper, intermediate and lower basin elements 21a, 21b, 21c are made of a plastic material that is watertight and resistant to high concentrations. of salts. Thus, advantageously, the bottom 212 or the sealed side walls 211 of the evaporation basin 20 of the first, second and third embodiments are adapted to prevent the water or the salts contained in the first aqueous solution 51 from forming. from the said evaporation pond 20. Moreover, in the fourth, fifth, sixth and seventh embodiments of the desalination unit 1, shown in FIGS. 4, 5, 6 and 7, the evaporation basin 20 comprises at least one water extraction device 240; 250; 260; 270 comprising at least one semipermeable membrane 241; 251; 261; 271 allowing the passage of the water contained in said first aqueous solution Si to a storage element 242; 252; 262; 272 of this water. The water extraction device 240; 250; 260; 270 is thus adapted to extract water from the first aqueous solution Si contained in the evaporation basin 20, in parallel with the evaporation of the water occurring under the effect of the sun and / or the wind. Thus, advantageously, in the fourth, fifth, sixth and seventh embodiments of the desalination unit 1, the water extraction device 240; 250; 260; 270 of the evaporation basin 20 is adapted to accelerate the drying of the evaporation basin 20, thus the recovery of the salts contained in the first aqueous solution Si, since the extraction of the water contained in the first aqueous solution Si by the water extraction device 240; 250; 260; 270 is cumulative with the evaporation of this water.

By definition, the semipermeable membrane 241; 251; 261; 271 of the water extraction device 240; 250; 260; 270 is adapted to allow some of the water to pass, but either none or very little of the ions or impurities contained in this water. Preferably, the semipermeable membrane 241; 251; 261; 271 is adapted to retain all the ions or impurities contained in said water. For this purpose, the semi-permeable membrane 241; 251; 261; 271 comprises a relatively thick support, namely from 100 to 200 micrometers thick, and a thin layer, namely from 0.1 to 1 micrometer thick in general. The support has a high porosity and ensures the mechanical strength of the semi-permeable membrane 241; 251; 261; 271. The thin layer is an active layer responsible for the selectivity of the semi-permeable membrane in that, depending on its chemical nature, the size of its pores, a characteristic size of which generally varies from 0.4 to 1. nanometer, and its thickness, it is adapted to prevent salts and / or ionic chemical compounds from migrating through it. For example, the thin layer may have hydrophilic or hydrophobic physicochemical properties. Preferably, the semipermeable membrane 241; 251; 261; 271 is made of cellulose triacetate (CTA) or polyamide-based composite film. Preferably, the active thin layer has a thickness of about 150 nanometers. It then has a permeability of the order of 3 to 4 liters per square meter, per hour and per bar. The storage element 242; 252; 262; 272 further contains one or more ionic chemical compounds previously placed therein. Each ionic chemical compound is present in the storage element 242; 252; 262; 272 either in solid form or in the form of an aqueous solution containing the ions resulting from the dissolution of this ionic chemical compound.

The aqueous solution containing the ionic chemical compounds is called in the following description "aqueous priming solution" in that it is adapted to trigger the phenomenon of direct osmosis causing the passage of water from the first solution aqueous Si to said storage member 242; 252; 262; 272, through said semi-permeable membrane 241; 251; 261; 271. When the storage element contains the ionic chemical compound (s) in solid form, for example, in the form of a powder, this aqueous initiating solution is obtained by partial or complete dissolution of this ionic chemical compound in a little water having passed through the semi-permeable membrane because of its porosity. For example, these ionic chemical compounds are sugars, such as glucose or fructose, or salts not contained in seawater. In particular, ionic chemical compounds may constitute a powder or an ultra-concentrated solution serving as a base to the preparation of sugary drinks, vitamin supplements, or solutions for infusion. The concentration of the ionic chemical compound (s) contained in the aqueous initiating solution is adapted to trigger a phenomenon of direct osmosis through the semipermeable membrane.

In particular, the total concentration of ions of the aqueous priming solution is such that it is adapted to trigger / activate the direct osmosis phenomenon between the first aqueous solution Si and the aqueous initiating solution. Specifically, the total ion concentration of this aqueous solution is greater than the total ion concentration of the first aqueous solution Si. In other words, here, the concentration of the ionic chemical compounds in the aqueous priming solution is greater than the total ion concentration of the first aqueous solution. at the total salt concentration of the first aqueous solution Si.

Thus, said water extraction device 240; 250; 260; 270 is adapted to extract water from the first aqueous solution Si to the storage element 242; 252; 262; 272 by this phenomenon of direct osmosis. More specifically, in the fourth and fifth embodiments of the desalination unit 1, the evaporation pond 20 has at least one internal partition 243; 253 comprising said semipermeable membrane 241; 251. This internal partition 243; 253 divides the evaporation basin 20 into two compartments (fourth embodiment) or into two pelvic elements (fifth embodiment). The internal partition 243; 253 comprising said semipermeable membrane 241; 251 forms with a portion of the evaporation basin 20 said extraction device 240; 250. In the fourth embodiment, shown in FIG. 4, the evaporation basin 20 comprises a lower compartment 22 and an upper compartment 23. The lower compartment 22 is delimited by the bottom 212 sealed from the evaporation basin 20 and by a lower portion of the sealed side walls 211 of said evaporation basin 20. This lower compartment 22 is closed at the top by the semipermeable membrane 241 which forms here the internal partition 243 of the evaporation basin 20. This internal partition 243 here extends globally horizontally. The lower compartment 22 further comprises a means for evaluating the salt concentration of the aqueous solution it contains. This means of evaluation is adapted to evaluate the concentration of salts of the aqueous solution and to compare this concentration with a threshold concentration value. There is also provided in the lower compartment 22 an evacuation valve (not shown) so as to be able to pour the aqueous solution contained in the lower compartment 22 to an adjoining evaporation basin (not shown). The upper compartment 23 comprises the semi-permeable membrane 241 and is delimited by the upper part of the sealed side walls 211 of the evaporation basin 20. It is open to the external environment. Thus, in the fourth embodiment of the desalination unit 1, the water extraction device 240 comprises the upper compartment 23 of the evaporation basin 20 provided with the semi-permeable membrane 241. The storage element 242 of the water is this upper compartment 23, adapted to fill with water by the semi-permeable membrane 241. The upper compartment 23 of the evaporation basin 20 is adapted to evaporate the water contained both in the upper compartment 23 and in the lower compartment 22.

In this fourth embodiment of the desalination unit 1, as shown in Figure 4, the discharge pipe 12 is adapted to feed the lower compartment 22 of the evaporation basin 20. Here, the discharge pipe 12 also comprises a branch 122 provided with a valve 121 adapted to occasionally feed the upper compartment 23 of the evaporation basin 20. As a variant of this fourth embodiment of the desalination unit, it could be envisaged that the evaporation basin could comprise a lower compartment and an upper compartment similar to those described above, and intermediate compartments. Each intermediate compartment would then be delimited by the side walls of the evaporation basin, and by two semi-permeable membranes. In the fifth embodiment of the desalination unit 1, the evaporation pond 20 generally has a shape similar to that of the evaporation pond 20 described in the first or second embodiment.

The bottom 212 as well as the side walls 211 of this evaporation basin 20 are sealed, adapted to prevent the water, the salts or the ionic chemical compounds from escaping from the evaporation basin. The evaporation 20 comprises a main pond element 24, and a secondary pond element 25 disposed side by side and separated by the semipermeable membrane 251 which here forms the inner wall 253 of the evaporation pond 20. This internal partition 253 here extends globally vertically. Thus, the secondary basin element 25 provided with the semi-permeable membrane 251 here forms the water extraction device 250 of the fifth embodiment of the desalination unit 1.

The storage element 252 of the water is then said secondary pond element 25. Here, the water storage element 252 comprises the aqueous priming solution. In addition, the secondary pond element 25 constitutes a secondary evaporation pond 25 because it is open to the external environment. Here, the inner partition 253 comprising the semipermeable membrane 251 is fixed. Alternatively, it can be considered that it is removable. In another variant, it is conceivable to make this internal partition waterproof with a removable waterproof wall.

Advantageously, this removable waterproof wall is adapted to better control the extraction of a portion of the water from the main basin element according to the needs of the operator of the desalination unit. Advantageously again, it can be envisaged that the secondary pond element partially or completely surrounds the main basin element.

As a variant of this fifth embodiment of the desalination unit, it would be possible to envisage multiple secondary basin elements separated from each other by a semipermeable membrane as described above forming a common wall between two adjacent basin elements. The secondary pond elements can then be positioned, in a flexible manner, at the request of the operator depending on the extraction requirements of the desired salts and the progress of the specific crystallization for each type of salt allowing acceleration or a modulation of this crystallization. As an alternative to the fifth embodiment of the desalination unit, it could be envisaged that the internal septum comprising the semipermeable membrane comprises at least a portion of the bottom of the main basin element, and that the basin element secondary portion extends at least partially under the main basin element. Here, the water of the evaporation pond 20 is stagnant. As a further variant, it could be envisaged that the secondary pond element forms at least one channel in which the water extracted from the main pond element circulates. Advantageously, the water extraction device 250 of the fifth embodiment of the desalination unit 1 is adapted to accelerate the extraction of the salts of the first aqueous solution Si contained in the main basin element 24. Advantageously, if the aqueous initiating solution comprises edible ionic chemical compounds, such as sugars, the semipermeable membrane 251 being adapted to transfer water to this aqueous initiating solution, said aqueous solution can be diluted. priming to obtain, in the secondary basin element 25, a final aqueous solution for use in food and / or animal feed. Finally, as a variant of the fourth and fifth embodiments, said internal partition comprising the semipermeable membrane may extend obliquely, or have any shape. In the sixth and seventh embodiments of the desalination unit 1, the evaporation pond 20 comprises a single pond element 21, similar to that of the first and second embodiments described above. Advantageously, the bottom 212 and the side walls 211 of the evaporation basin 20 of the sixth and seventh embodiments are watertight, adapted to prevent the water or the salts contained in the first aqueous solution Si from escaping from said pond. Evaporation 20. The water extraction device 260; 270 of the evaporation basin 20 of the sixth and seventh embodiments comprises at least one open or closed container adapted to be disposed in said evaporation basin 20, and the storage element 262; 272 is constituted by said container itself which is adapted to fill with water. In the sixth embodiment of the desalination unit 1, the container of the water extraction device 260 of the evaporation basin 20 is a pipe 260 whose walls comprise the semipermeable membrane 261 and in which circulates the aqueous initiating solution. This hose 260 constitutes an open container in that its ends are open to allow the circulation of said aqueous initiating solution. Alternatively, the aqueous priming solution may stagnate in the pipe. The pipe 260 is placed in the evaporation pond 20 so that a maximum surface of the semipermeable membrane 261 is in contact with the first aqueous solution Si contained in said evaporation pond 20. For example, as this is shown in Figure 6, it is conceivable that the pipe 260 is immersed and meanders in the bottom 212 of the evaporation basin 20. Alternatively, the pipe may be positioned on the surface of the first aqueous solution. Of course, in this sixth embodiment of the desalination unit 1, the storage element 262 includes the inner portion of the pipe 260. In the seventh embodiment of the desalination unit 1, the water extraction device 270 of the evaporation basin 20 comprises at least one bag 270 whose walls comprise the semipermeable membrane 271. This bag 270 constitutes a closed container, and the interior space of the bag 270 delimited by the walls is the storage element 272 of the water. This bag 270 is adapted to be arranged by an operator in the evaporation basin 20. The bag 270 initially comprises the ionic chemical compounds in solid form, then, once placed in the evaporation basin 20, encloses the aqueous solution after dissolution of the ionic chemical compounds in water having passed through the walls of the bag 270 due to their porosity. Here, as shown in FIG. 7, the evaporation pond 20 accommodates two bags 270. An operator could obviously envisage having in the evaporation basin any number of bags, depending on the relative size of the bags. of the evaporation basin. Alternatively, it could be provided to replace the bags with buckets whose walls would include the semipermeable membrane. The interior of these buckets would constitute the storage element of the water extraction device adapted to fill with water. Advantageously, the water extraction device 270 of the seventh embodiment of the desalination unit 1 is removable in that it is adapted to be disposed in this evaporation basin 20 and then removed from the water tank. Evaporation 20.

The extraction device 270 of the seventh embodiment of the desalination unit 1 is thus particularly convenient to use. In an eighth embodiment, not shown in the drawings, the evaporation basin comprises one or more basin elements. This evaporation pond may be similar to any of the evaporation ponds described in the previous embodiments. The water extraction device comprises a semipermeable membrane fabric or mesh, and the storage element is the fabric itself which is adapted to waterlogging.

In this eighth embodiment, the fabric or net is adapted to be disposed by an operator in the evaporation basin and to be removed from said evaporation basin to be dried. The water of the first aqueous solution Si can only pass through the membrane forming the fabric or the net of the extraction device. In doing so, the salts contained in the water are deposited on the surface of this fabric and / or this net. Advantageously, the salts deposited on the surface of the fabric and / or the net can be recovered after drying. In addition, said salts deposited on the surface of the fabric and / or the net can be reintroduced into the evaporation basin 20 by soaking the fabric and / or the net to increase the salt concentration of said evaporation basin 20. This eighth embodiment can be combined with any of the embodiments described above, in the sense that one can add such a fabric or such a net in the evaporation basin of any of the modes. of the desalination unit described above.

It should be noted that whatever the embodiment of the desalination unit 1, the evaporation basin 20 and the desalination device 10 are distinct and different. They are separated by a discharge line 12. In the first, fourth, fifth, sixth, seventh and eighth embodiments of the desalination unit, the desalination device 10 is directly supplied with seawater conveyed, for example by the delivery line 11 at the inlet 101 of this desalination device 10. In the second and third embodiments of the desalination unit 1, shown in FIGS. 2 and 3, the desalination unit 1 further comprises a pre-concentration device 30, 40 of a preliminary aqueous solution SP containing a preliminary concentration of salts. This pre-concentration device 30, 40 is adapted to concentrate in salt the initial aqueous solution SO before it arrives in the inlet 101 of the main desalination device 10.

The first aqueous solution Si discharged at the outlet of the main desalination device 10 of these two embodiments of the desalting unit 1 is then also more concentrated in salts. The extraction of salts by evaporation of water from the aqueous solution is thus faster. In the second embodiment of the desalination unit 1 shown in FIG. 2, the desalination unit 1 is in all respects identical to the desalination unit 1 of the first embodiment, except that it further comprises the pre-concentration device 30. The pre-concentration device 30 is a recirculation line 30 adapted to take all or part of the first aqueous solution Si at the first outlet 102 of the desalination device 10 to reintroduce it in the delivery line 11, upstream of the inlet 101 of the main desalination device 10. The recirculation line 30 may be provided with a recirculation valve 31 adapted to regulate the flow rate of the first aqueous solution Si flowing in said recirculation line 30. Alternatively, the recirculation line may comprise a filter element adapted to allow the passing the first aqueous solution into said recirculation line when the first concentration of this first aqueous solution is below a predetermined concentration threshold value, for example 80 g / L. It can be envisaged that the filtering element comprises a sensor allowing determination of the first concentration of the first aqueous solution and control means for controlling the recirculation valve as a function of the first concentration of said first aqueous solution.

Thus, in this second embodiment, the initial aqueous solution SO introduced by the delivery line 11 to the inlet 101 of the desalination device 10 is formed of a mixture of seawater taken directly from the sea, which forms here the preliminary aqueous solution SP, and the first aqueous solution Si taken by the recirculation line 30 at the outlet of the desalination device 10. This second embodiment of the desalination unit 1 is simple to put in place and little expensive. In the third embodiment of the desalination unit 1 shown in FIG. 3, the desalination unit is similar to that described in the first embodiment, except that it further comprises, upstream of the main desalination device 10 previously described, the pre-concentration device 40. In this third embodiment, the pre-concentration device 40 is another desalination device 40, hereinafter referred to as the preliminary desalination device 40. here, the first pump 111 of the conveying conduit 11 is adapted to take the preliminary aqueous solution SP, namely seawater, and to convey it to an inlet 401 of the preliminary desalination device 40.

The preliminary desalination device 40 produces, at each of its two outlets 402, 403, as the main desalting device 10, on one side an aqueous solution more concentrated in salts than the preliminary aqueous solution SP, and on the other side an aqueous solution less concentrated in salts than the preliminary aqueous solution SP.

A connecting line 42 connects a first outlet 402 of the preliminary desalination device 40 to the inlet 101 of the main desalination device, so as to introduce the more concentrated aqueous solution of salts than the preliminary aqueous solution SP produced by the desalination device. preliminary desalination 40 at the inlet of the main desalination device 10.

Another discharge line 43 is intended to reject the less concentrated aqueous solution than the preliminary aqueous solution SP produced by the preliminary desalination device 40 from a second outlet 403 of the preliminary desalination device 40 to the outside of the desalination unit. 1.

In this third embodiment of the desalination unit 1, the main desalination device 10 and the preliminary desalination device 40 are not necessarily identical. In other words, the preliminary desalination device 40 may be a distillation device, and the main desalination device 10 may be a reverse osmosis pump for example. Alternatively, it can also be provided that the preconcentration device comprises multiple desalination devices arranged in series from each other, upstream of the main desalination device, so as to concentrate the initial aqueous solution by a succession of cooling devices. desalination. One could also consider placing upstream of the main desalting device any pre-concentration device known to those skilled in the art so as to concentrate the initial aqueous solution entering said desalination device. The use of the preliminary desalination device 40 upstream of the main desalination device 10 is particularly advantageous in the case where the main desalination device 10 is a reverse osmosis pump. Indeed, the reverse osmosis pump being relatively low energy consuming, the assembly comprising the preliminary desalination device 40 and the main desalination device 10 keeps a reasonable power consumption. Alternatively, one could consider combining the different pre-concentration devices described above. In particular, it can be provided that the recirculation line which withdraws at least a portion of the first aqueous solution at the outlet of the main desalination device returns this first aqueous solution to the inlet of the pre-concentration device formed by the preliminary desalination device. or at the inlet of the main desalination device, downstream of this preliminary desalination device.

Of course, the pre-concentration device may also be used in the fourth, fifth, sixth, seventh or eighth embodiments of the desalination unit according to the invention. In addition, regardless of the embodiment of the desalination unit 1, it is possible to place upstream of the main desalting device 10 different pretreatment elements of the initial aqueous solution SO. These pretreatment elements are suitable for removing any particles suspended in seawater, or to avoid the development of microorganisms for example. Typically, these pretreatment means of the initial aqueous solution SO are mechanical means such as sand filters or cartridge filters, for example, as well as chemical means. These pretreatment elements are preferably used in desalination units 1 whose desalination device 10 is a reverse osmosis pump. Also, whatever the embodiment of the desalination unit 1, it is possible to place downstream of the discharge line 13, post-treatment elements of the second aqueous solution S2. These post-treatment elements are intended to treat this second aqueous solution S2 in order to obtain a drinking water solution. Process The desalination unit 1 is used to carry out the salt extraction process according to the invention. According to the salt extraction method according to the invention, the operator performs the following steps: a) he controls the supply of the desalination device 10 of the desalination unit 1 with the initial aqueous solution SO, b) it controls the pouring of said first aqueous solution 51 containing the first concentration C1 salts higher than said initial concentration CO, obtained at the outlet of the desalination device 10, in the evaporation basin 20 of the desalination unit 1, c ) it allows the water of the first aqueous solution 51 to evaporate, d) it recovers the salts of the first aqueous solution 51 in the form of salt crystals. According to a first embodiment of the extraction method according to the invention, implementing the first embodiment of the desalination unit 1 according to the invention (FIG. 1), in step a), the The operator controls the first pump 111 of the conveying line 11 so as to take the initial aqueous solution SO in a tank 2, here the sea. The first pump 111 of the conveying line 11 conveys said initial aqueous solution SO to the inlet 101 of the desalination device 10. The desalting device 10 separates the initial aqueous solution SO in the first aqueous solution 51 and in the second aqueous solution S2. More specifically, when the desalination device 10 used is the reverse osmosis pump, the operator circulates the initial aqueous solution SO in the first compartment of the pump. It also imposes a pressure in the first compartment so as to force part of the water contained in the initial aqueous solution SO through the semipermeable membrane and in the second compartment. Thus, as the initial aqueous solution SO is circulated in the first compartment, the latter concentrates into salts until forming the first aqueous solution Si, conveyed to the first outlet 102 of the desalination device 10.

The forced water through the semipermeable membrane in the second compartment is mixed, in this second compartment, with an aqueous solution already present so as to form the second aqueous solution S2, conveyed to the second outlet 103 of the desalination device 10 When the desalting device 10 used is the distillation device, the operator circulates the initial aqueous solution SO in the first circuit of this distillation device. The operator imposes a pressure and a heating temperature in a portion of the first circuit so as to evaporate a portion of the water contained in the initial aqueous solution SO.

Thus, as evaporation of water of the initial aqueous solution SO, said aqueous solution is concentrated in salts so as to form the first aqueous solution Si conveyed to the first outlet 102 of the desalting device 10. L water evaporated from the first circuit is condensed in the second circuit 25 so as to form the second aqueous solution S2 conveyed to the second outlet 103 of the desalting device 10. When the desalination device 10 used is the electrodialysis device, the The operator circulates the initial aqueous solution SO in the compartments of the electrodialysis device. The operator imposes a voltage between the two electrodes so as to create an electric field in all the compartments. The electric field thus created forces the anions of one compartment out of two to migrate, in the direction of the electric field, towards the nearest neighbor compartment. At the same time, the electric field created forces the cations of the same compartment out of two to migrate in the opposite direction to the nearest neighbor compartment. One in two compartments is enriched with ions, while the other compartments are depleted in ions.

It is the position of the membranes permeable to anions or cations on one side or the other of the compartments which defines which compartments become enriched or deplete in ions. Thus, as the flow of the initial aqueous solution SO in the compartments of the electrodialysis device progresses, it becomes enriched with salts in every other compartment so as to form the first aqueous solution Si, conveyed to the first outlet 102 of the desalination device 10, and is depleted of salts in the other compartments so as to form the second aqueous solution S2, conveyed to the second outlet 103 of the desalination device 10.

Moreover, whatever the desalination device 10 used, the operator controls the third pump 131 and the reject valve 130 of the discharge line 13 so as to reject the second aqueous solution S2 from the second outlet 103 of the device. desalination 10 to the outside of the desalting unit 1.

The operator may further impose on the second aqueous solution S2 various treatments in the post-treatment elements so as to make this second aqueous solution S2 potable. The second aqueous solution S2 can be used advantageously in agriculture or as drinking water.

In step b), the operator also controls the discharge valve 120 of the discharge pipe 12 so as to discharge, under the effect of gravity, the first aqueous solution Si in the evaporation basin 20. In alternatively, in step b), the operator controls the second pump and the spill valve of the spill line so as to pump out the first aqueous solution into the evaporation basin. The water contained in the first aqueous solution Si placed in the pond element 21 evaporates with the aid of sun and wind, so that the first aqueous solution Si concentrates in salts (step c)). First salt crystals of a first chemical composition then crystallize in the bottom 212 and / or on the surface of the pond member 21. In step d), these first salt crystals are recovered from the bottom 212 and / or or on the surface of the evaporation pond 20, for example by means of a rake, a dip net, or any other means known to those skilled in the art for recovering salt crystals in an aqueous solution. Then, second salt crystals of a second chemical composition crystallize in the bottom 212 and / or on the surface of the pond member 21. These second salt crystals are also recovered from the bottom 212 and / or on the surface of the evaporation tank 20 in step d).

Indeed, in general, salt crystals crystallize in an aqueous solution concentrated in salts when the concentration of said salts in said aqueous solution is at least equal to the saturation concentration of these salts in this aqueous solution, said concentration of saturation mainly depending on the salts and the composition of the aqueous solution.

For example, the table salt crystal, namely NaCl, crystallizes in an aqueous solution from a concentration of about 260 grams per liter. Thus, the first and second salt crystals crystallize at different times in the first aqueous solution Si since they are present at different concentrations in the first aqueous solution Si. The first and second salt crystals can thus be recovered separately. The same applies to all the salt crystals obtainable from the first aqueous Si solution. The salt crystals obtained are then treated so as to obtain one or more desired end products. According to the second and third salt extraction processes, in step a), the initial aqueous solution SO is obtained by concentrating a preliminary aqueous solution SP with a pre-concentration device 30, In particular, the initial concentration CO in salts of the initial aqueous solution SO can reach 160 grams per liter (g / L) thanks to the pre-concentration device 30, 40. This concentration corresponds to at an overall concentration taking into account all the salts present in the initial aqueous solution. In practice, it may be provided additional steps so as to concentrate in salt the initial aqueous solution SO at the inlet 101 of the desalination device 10, so as to concentrate the first aqueous solution Si at the first outlet 102 of the desalination device 10. According to the second salt extraction process using the second embodiment of the desalination unit (FIG. 2), in step a), the operator controls the first pump 111 of the pipe of 11 to take the preliminary aqueous solution SP in the tank 2, here the sea. The first pump 111 of the delivery line 11 conveys said preliminary aqueous solution SP to the inlet 101 of the desalination device 10. The The operator controls the overflow valve 120 of the overflow pipe 12 and the recirculation valve 31 of the recirculation pipe 30 so as to withdraw a portion of the first aqueous solution. use 51 flowing at the first outlet 102 of the desalination device 10.

For example, the operator or the filter element controls the recirculation valve 31 so as to take at least a portion of the first aqueous solution 51 when its first salt concentration C1 is less than the predetermined concentration threshold value, at know in our example 80g / L. This portion taken from the first aqueous solution 51 is conveyed into the recirculation line 30 and reinjected into the delivery line 11 of the desalter 10, so that said first aqueous solution 51 mixes with the preliminary aqueous solution SP for These steps are repeated in a loop, as many times as desired by the operator, so as to concentrate in salt the first aqueous solution 51 discharged at the first outlet 102 of the desalination device 10. The operator controls the overflow valve 120 of the overflow pipe 12 and the recirculation valve 31 of the recirculation pipe 30 so as to discharge, under the effect of gravity, the other part of the first aqueous solution Si evacuated to the first outlet 102 of the desalination device 10 in the evaporation basin 20. Alternatively, in the case where the discharge pipe e equipped with the second pump, the operator also controls the second pump, so as to pour, by pumping, the other part of the first aqueous solution discharged to the first outlet of the desalination device in the evaporation basin. The following steps b), c) and d) of the salt extraction process are identical to those described in the first embodiment of the extraction process. Alternatively, it could be provided to recirculate, in the recirculation line, all of the first aqueous solution from the desalting device. In this case, in step a) the operator controls, for example, the overflow valve 120 of the overflow pipe 12 and the recirculation valve 31 of the recirculation pipe 30 and possibly the second pump, so as to discharge under the effect of gravity or possibly by pumping, the first aqueous solution Si evacuated at the first outlet 102 of the desalination device 10 in the evaporation basin 20 when the first concentration C1 to salts of the first aqueous solution Si is greater than or equal to the predetermined concentration threshold value. According to the third salt extraction method using the third embodiment of the desalination unit (FIG. 3), the operator controls, in step a), the first pump 111 of the delivery line 11 of The first pump 111 of the conveying line 11 conveys said preliminary aqueous solution SP to the inlet 401 of the preliminary desalination device 40. The device for removing the preliminary aqueous solution SP in the tank 2, here the sea. Preliminary desalination separates the preliminary aqueous solution SP into two parts: on one side, an aqueous solution more concentrated than the preliminary aqueous solution, and on the other side, a less concentrated aqueous solution than the preliminary aqueous solution. The more concentrated aqueous solution than the preliminary aqueous solution SP is introduced in step a) into the main desalting device at the inlet 101. In the following, this aqueous solution more concentrated than the preliminary aqueous solution SP is by convention, called initial aqueous solution SO. The operation of the preliminary desalination device 40 is similar to the operation of the main desalination device 10 already described.

The operator controls the desalination unit 1 so as to reject the aqueous solution less concentrated in salts than the preliminary solution SP from the outlet 403 of the preliminary desalination device 40 to the outside of the desalination unit 1.

The operator can also impose downstream of this outlet 403 various treatments in the aftertreatment elements of the desalination unit 1 so as to make this aqueous solution less concentrated in salts drinkable than the preliminary solution SP. As previously described, the desalting device 10 separates the initial aqueous solution SO into the first aqueous solution Si and into the second aqueous solution S2. As described in the first embodiment of the extraction method, in step b) the operator controls the third pump 131 and the reject valve 130 of the discharge line 13 so as to reject the second aqueous solution S2 since the second outlet 103 of the desalination device 10 to the outside of the desalination unit 1. Here, the evaporation basin 20 comprises several basin elements 21 (FIG. 3). In step b), the operator then controls the discharge valve 120 of the discharge pipe 12, and the upper connection valve 213a so as to discharge, under the effect of gravity, the first aqueous solution Si in the upper basin element 21a of the evaporation basin 20. In a variant, in step b), the operator also controls the second pump, the dumping valve of the discharge pipe, and the upper connecting valve, in such a way as to pump out the first aqueous solution into the upper basin element of the evaporation pond. The water contained in the first aqueous solution Si of the upper pond element 21a evaporates with the aid of the sun and the wind (step c)) so that the aqueous solution present in the upper basin element 21a is concentrated in salts.

First salt crystals of a first chemical composition then crystallize in the bottom 212 or on the surface of the upper basin element 21a. These salt crystals are recovered (step d)). The operator then controls the upper link valve 213a and the lower link valve 213b so as to transfer the aqueous solution present in the upper basin element 21a, in the intermediate basin element 21b (step b)). The operator evaporates the water contained in the aqueous solution present in the intermediate basin element 21b, here with the aid of sun and wind, so that the latter is concentrated in salts (step c)). Second salt crystals of a second chemical composition then crystallize in the bottom 212 of the intermediate basin element 21b, which are recovered (step d)). The operator then controls the lower link valve 213b so as to transfer the aqueous solution present in the intermediate basin element 21B, into the lower basin element 21c (step b)). The operator evaporates the water contained in the aqueous solution of the lower basin element 21c, here with the aid of sun and wind, so that it is concentrated in salts (step c)).

Third crystal salts of a third chemical composition then crystallize in the bottom 212 of the lower basin element 21c, which are recovered (step d)). The various salt crystals obtained are finally treated so as to obtain one or more desired end products.

As mentioned above, the steps related to the presence of several basin elements can also be performed in the first and second embodiments of the extraction process, when the first and second embodiments of the desalination unit comprise such a device. basin.

We can obviously provide two or more basin elements. The description of the third embodiment of the extraction process emphasizes that steps b), c) and d) can be carried out partly simultaneously, and not only sequentially as is the case in the first embodiment of the method. extraction for example.

According to a fourth embodiment of the extraction process according to the invention implementing the fourth, fifth, sixth, seventh and eighth embodiments of the desalination unit 1 (FIGS. 4, 5, 6 and 7), steps a), b) and c), the operator controls said desalination unit 1 in the same manner as in the first embodiment of the extraction process.

Further, in an additional step c ') performed before step d), the operator extracts water from the first aqueous solution Si using one of the water extraction devices 240; 250; 260; 270 described above. The operator preferably performs this additional step c ') in parallel with step c) of evaporation of the water contained in the first aqueous solution Si. The operator carries out step d) in the same manner as in any of the first, second and third embodiments of the extraction method according to the invention.

More specifically, in order to implement the fourth embodiment of the desalination unit 1 (FIG. 4), in step b), the operator controls the valve 121 of the branch 122 of the discharge duct 12 so as to to pour into the upper compartment 23 of the evaporation basin 20 the first aqueous solution Si. At this same step b), the operator feeds the lower compartment 22 of said evaporation basin 20. In step c), the The operator evaporates the water of the first aqueous solution Si contained in the upper compartment 23 of the evaporation basin 20, so that the aqueous solution of said upper compartment 23 concentrates into salts to form the aqueous initiating solution.

Since the aqueous initiating solution is more concentrated in salts than the first aqueous solution Si contained in the lower compartment 22, part of the water contained in the first aqueous solution Si in the lower compartment 22 passes through the semipermeable membrane 241 to the lower compartment 22. the upper compartment 23.

Thus, the aqueous solution contained in the lower compartment 22 of the evaporation basin 20 is concentrated in salts. The evaluation means of the lower compartment 22 of the evaporation basin 20 evaluates the concentration of salts of the aqueous solution contained in the lower compartment 22. When the concentration of salts of the aqueous solution contained in this lower compartment 22 reaches the value of threshold concentration, the operator controls the discharge valve to discharge the aqueous solution contained in the lower compartment 22 in the evaporating basin annex. This spill operation can be done in parallel with step d) which consists in recovering the salts of the upper compartment 23. The operator then evaporates the water from the aqueous solution contained in the annex evaporation basin, in such a way that to recover the salts it contains.

Preferably, the operator repeats all the steps b), c), c ') and d) sequentially. The evaporation of the first aqueous solution contained in the evaporation basin 20 of the fourth embodiment of the desalination unit 1 according to the invention is then faster than it would be for a basin of the same volume. having no semipermeable membrane. In addition, the aqueous solution discharged into the annex evaporation basin is more concentrated in salts than the first aqueous solution Si. As a result, the recovery of salts from this aqueous solution is faster. To implement the fifth embodiment of the desalination unit 1 (FIG. 5), in the additional step c '), the operator pours the aqueous initiating solution into the secondary pond element 25. To implement the sixth embodiment of the desalination unit 1 (FIG. 6), in the additional step c '), the operator forces the aqueous priming solution to flow in the pipe 260. implement the seventh embodiment of the desalination unit 1 (Figure 7), in the additional step c '), the operator arranges the bags 270 in the basin element 21. The solid ionic chemical compound contained Inside the bag 270 at least partially dissolves in water passing through the porous semipermeable membrane 271 to form the aqueous initiating solution. In these three cases, the aqueous initiating solution comprises said ionic chemical compounds, for example sugars, in very high concentration, and in the additional step c '), a part of the water of the first aqueous solution. If contained in the evaporation pond 20 passes through the semipermeable membrane 251; 261; 271 to the aqueous priming solution contained respectively in the secondary basin element 25, in the pipe 260 or in the bags 270 according to the embodiment considered. Thus, advantageously, the salt concentration is accelerated in the main pond element 24 (fifth embodiment) or in the pond element 21 (sixth and seventh embodiments), so that the extraction of said salts is faster. In addition, the aqueous initiating solution is advantageously diluted so as to form a final aqueous solution that can be recovered, for example for human or animal feed, or for industrial use. Indeed, thanks to the desalination unit 1 according to the invention, it is also possible to implement a method for producing a final aqueous solution.

According to the production method of the final aqueous solution according to the invention, the operator performs the following steps: e) it implements steps a) and b) of the extraction process according to the invention, f) it extracts water from the first aqueous solution 51 contained in said evaporation pond 20 to the storage element 242; 252; 262; 272 of the water extraction device 240; 250; 260; 270, g) it obtains the final aqueous solution in said storage element 242; 252; 262; In particular, during the implementation of the seventh embodiment of the desalination unit 1 (FIG. 7), the operator can remove the bags 270 from said evaporation basin 20 after a desired time, for example in order to recover said final aqueous solution contained inside the bags 270. Moreover, advantageously, thanks to the implementation of the fifth embodiment of the desalination unit 1, the operator can recover a current in a circuit adapted by forming a concentration stack between the main basin element 24 and the secondary pond element 25. Alternatively, the first, second, third and fourth embodiments of the extraction process may apply to all aqueous solutions containing salts, such as aqueous solutions from salt marshes or brines or brackish water. Thus, thanks to the desalination unit 1 according to the invention, and thanks to the salt extraction process according to the invention, it is possible to obtain fresh water, and to avoid the rejection of the solution. aqueous concentrated in salts in nature while promoting this aqueous solution concentrated in salts by extraction of salt crystals. In particular, the described invention is of interest for the extraction of lithium salts and potassium salts. Indeed, since the advent of lithium batteries involved in the industrial processes of manufacturing mobile phones, computers or even electric or hybrid cars, lithium consumption has increased sharply. Similarly, the potassium extraction is particularly interesting since potassium is involved in the manufacture of potassium hydroxide, that is to say the various solutions of potassium salts, and in particular aqueous solutions of potassium hydroxide . Potash is used in the manufacture of fertilizers, with fertilizers accounting for nearly 95% of global potash consumption. By taking the example of the first embodiment of the desalination unit 1, installed in the Middle East, in which the desalination device 10 is a reverse osmosis pump capable of taking seawater with a flow rate of 100,000 cubic meters per day, the potassium and lithium concentrations of this seawater being estimated at 400 grams per cubic meter and 0.17 grams per cubic meter respectively, the quantities of potassium and lithium that can be extracted from the Seawater by the desalination unit 1 according to the invention amounts to 40,000 tons of potassium and 20 tons of lithium per year. These amounts represent about 0.1% of the current annual world production of potassium and lithium. The dimensions of the evaporation ponds and the associated water extraction devices may alternatively be adjusted so as to optimize the yields of the desalination unit according to the invention. It is also possible to envisage that the evaporation basin comprises several water extraction devices as described above, including water extraction devices according to different embodiments.

Claims (10)

REVENDICATIONS1. Desalination unit (1) of an initial aqueous solution (50) containing an initial concentration (CO) of salts, comprising at least one desalting device (10) adapted to receive, at an inlet (101), this initial aqueous solution (50) and separately rejecting, at first and second outlets (102, 103), a first aqueous solution (51) containing a first concentration (C1) of salts greater than said initial concentration (CO), and a second aqueous solution (S2) containing a second concentration (C2) of salts lower than the initial concentration (CO), characterized in that said desalination unit (1) further comprises at least one evaporation basin (20) and means for discharging (12) exclusively said first aqueous solution (51) discharged by the desalination device (10) into the evaporation basin (20). The desalting unit (1) according to claim 1, wherein said evaporation pond (20) comprises at least one water extraction device (240; 250; 260; 270) having at least one semicircular membrane. permeable (241; 251; 261; 271) permitting passage of the water contained in said first aqueous solution (51) to a storage element (242; 252; 262; 272) thereof. The desalting unit (1) according to claim 2, wherein the storage element (242; 252; 262; 272) contains an aqueous priming solution adapted to trigger a direct osmosis phenomenon causing the passage of water. water from the first aqueous solution (51) to the storage element (242; 252; 262; 272). 4. Desalting unit (1) according to one of claims 2 and 3, wherein the evaporation basin (20) comprises at least one internal partition (243; 253) comprising said semi-permeable membrane (241; 251) said inner partition (243; 253) provided with the semipermeable membrane (241; 251) forming with said portion of the evaporation pond (20) said water extraction device (240; 250). The desalination unit (1) according to claim 4, wherein said internal partition (243; 253) extends generally horizontally or vertically. 6. desalination unit (1) according to one of claims 2 and 3, wherein the water extraction device (260; 270) comprises at least one container (260; 270) open or closed adapted to be arranged in said evaporation pond (20), and the storage member (261; 271) is constituted by said vessel (260; 270) itself which is adapted to fill with water. The desalination unit of claim 2, wherein the water extraction device comprises a semipermeable web or mesh, and the storage member is the web itself which is adapted to gorge itself. of water. 8. Process for extracting salts using a desalination unit (1) according to one of claims 1 to 7, wherein, a) a desalting device (10) is fed to the desalination unit (1) by an initial aqueous solution (SO), b) pouring said first aqueous solution (Si) containing the first concentration (C1) salts higher than said initial concentration (CO) in the evaporation basin (20) of the unit of desalination (1), c) the water is evaporated from the first aqueous solution (Si), d) the salts are recovered from the first aqueous solution (Si). 9. Extraction process according to claim 8, wherein, in an additional step c ') carried out before step d), water is extracted from the first aqueous solution (Si) using an extraction device. water (240; 250; 260; 270) having at least one semipermeable membrane (241; 251; 261; 271) allowing the passage of water from said first aqueous solution (Si) to a storage element ( 242; 252; 262; 272) of water. 10. A method of producing a final aqueous solution using a desalination unit (1) according to one of claims 2 to 7, wherein, e) it implements steps a) and b) of the extraction process. according to claim 9, f) extracting water from the first aqueous solution (Si) contained in said evaporation pond (20) to the storage element (242; 252; 262; 272) of the extraction of water (240; 250; 260; 270); g) the final aqueous solution is obtained in said storage element (242; 252; 262; 272).