Brine valorisation method for a brine originating from a desalination plant

Abstract

The present invention relates to a method for producing salts from a brine originating from seawater desalination. The method may further be used to selectively recover NaCl, CaSO4, kainite, carnallite, magnesium sulphate, struvite, newberyite or potassium bitartrate.

Description

[0001] DESCRIPTION

[0002] TITLE: Process for recovering brine from a desalination plant.

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to a process for producing salts from brine obtained from the desalination of seawater. The process can also make it possible to selectively recover NaCI, CaSC, kainite, carnallite, magnesium sulfate, struvite, newberyite, or potassium bitartrate.

[0005] STATE OF THE ART

[0006] Seawater desalination is increasingly used worldwide to provide freshwater for agriculture and industry.

[0007] Reverse osmosis (01) is currently the desalination technology of choice. In 2020, reverse osmosis dominated the market and accounted for over 55% of the global revenue. This is attributed to its advantageous properties, such as ease of operation, low installation cost, the ability to treat different types of feedwater, and minimal chemical use.

[0008] The large quantities of brine produced by desalination plants are the major drawback of this technology. These brines typically represent 50% of the feed stream. They have a salinity twice that of seawater (approximately 70 g / L) and are generally discharged into the sea, typically after being reprocessed, for example by dilution with non-potable water before being discharged.

[0009] Brines have significant economic value due to the high amounts of salts they contain. There is therefore a strong interest in recovering the salts contained in brine from seawater desalination.

[0010] These salts can be recovered directly from brines in different forms and for several uses, for example, as simple salts such as NaCl, CaSC , KC4H5O6 and MgSC , or as mixed salts such as kainite (KCIMgSC .SFW) and carnallite (KMgCh.SFW). There are also other forms of recovery by addition of chemical reagents for the production of important products such as struvite (NhLMgPC .GFW) and newberyite (MgHPC .SFW). Various processes and technologies have been developed to reprocess and recover brines from seawater desalination.

[0011] The DOW process is one of the best-known processes for the recovery of brines and the production of metallic magnesium (Mg). In this process, calcined limestone is used to precipitate magnesium hydroxide (Mg(OH)2), which is then treated with hydrochloric acid (HCl) to form magnesium chloride (MgCh). An electrolysis step is required to produce metallic Mg[1].

[0012] In the IG Farben process, similar to the DOW process, magnesium hydroxide is calcined to oxide and chlorinated in the presence of carbon to provide a cellular feed of anhydrous magnesium chloride. The chlorine by-product of this process is recycled to an electrolyzer.[2]

[0013] Despite the interest of these two processes, they have several disadvantages, namely, the large amount of energy required, especially in the electrolysis stage and the addition of intermediate reagents (such as limestone) which do not appear in the final product which are consumed or rejected. Finally, due to the chlorine used, these processes are extremely dangerous and require extreme caution.

[0014] Another process is the SAL-PROC process used to treat reverse osmosis brine with a high bicarbonate concentration. This process is based on the sequential extraction of dissolved elements in saline water in the form of solid, suspension and liquid. The products extracted by this process are mainly: CaSC , NaCl, Mg(OH)2, CaCh, CaCOs and Na2SC>4[3].

[0015] The SAL-PROC process is limited in terms of the extracted elements to be recovered. Potassium, for example, which is a very important element, is not recovered by this process. In addition, the SAL-PROC process does not offer any mixed salts and does not provide great product flexibility, which limits its use.

[0016] Another process used by the Arab Potash Company (APC) is based on the evaporation of Dead Sea brine. Several evaporation ponds are used in series to initially produce the mixed salt Carnallite, which is then processed to produce potash.[4]

[0017] The use of this process is limited because it only allows access to two products, Carnallite and potash. However, the Dead Sea and brines in general contain other important and valuable elements. Thus, there is a need for new methods to recover brine from seawater desalination. Advantageously, the proposed process will allow the recovery of salts from brines typically produced by reverse osmosis desalination plants.

[0018] REFERENCES

[0019] [1] FJ Krenzke, JW Hays, and DL Spell, “High purity electrolytic magnesium,” JOM, vol. 10, no. 1, pp. 28-30, 1958, doi: 10.1007 / BF03397856.

[0020] [2] CJP Ball, “The history of magnesium,” J. Inst. Metals, vol. 84, 1956.

[0021] [3] J. Morillo, J. Illsero, D. Rosado, H. El Bakouri, A. Riaza, and FJ Bernaola, “Comparative study of brine management technologies for desalination plants,” Desalination, vol. 336, no. 1, pp. 32-49, Mar. 2014, doi: 10.1016 / j. desal.2013.12.038.

[0022] [4] ZSH Abu-Hamatteh and AM Al-Amr, “Carnallite froth flotation optimization and cell efficiency in the arab potash company, Dead Sea, Jordan,” Mineral Processing and Extractive Metallurgy Review, vol. 29, no. 3, pp. 232-257, Jul. 2008, doi: 10.1080 / 08827500801997894.

[0023] SUMMARY OF THE INVENTION

[0024] The present invention relates to a process for producing salts from brine obtained from the desalination of seawater, the process comprising the following steps:

[0025] (1) removal of 85% to less than 95% of the volume of water initially contained in the brine leading to the formation of a suspension comprising NaCI crystals, followed by separation of the suspension into a solution (S1) and a solid residue comprising NaCI crystals;

[0026] (2) removal of a portion of the water contained in the solution (S1) so as to reach a total volume of water removed in steps (1) and (2) corresponding to at least 95% of the volume of water initially contained in the brine leading to the formation of a suspension comprising kainite crystals, followed by the separation of the suspension into a solution (S2) and a solid residue comprising kainite crystals and optionally NaCl crystals;

[0027] (3) addition of MgO to part or all of the solution (S2) leading to the formation of a suspension (S3);

[0028] (4) adding tartaric acid to the suspension (S3) leading to the formation of a suspension (S4) containing solid potassium bitartrate (KC4H5O6); (5) separating the suspension (S4), typically by filtration, leading to the formation of solid potassium bitartrate and a solution (S5);

[0029] (6) adding a phosphate-based compound to the solution (S5) so as to obtain a mixture (S6) containing crystallized NaCl;

[0030] (7) separation of the mixture (S6) leading to the formation of crystallized NaCl and a solution (S7).

[0031] The method of the invention optionally comprises the following features, alone or in combination.

[0032] Advantageously, the method of the invention further comprises the following steps:

[0033] (8) Optional addition of N H4 salts + , to the solution (S7) resulting from step (7) leading to the formation of a solution (S8);

[0034] (9) adding NaOH to the solution (S7) and / or to the solution (S8) leading to the formation of a suspension (S11) comprising solid struvite and / or a suspension (S9) comprising solid newberyite;

[0035] (10) separation leading to the recovery of solid struvite salts and / or solid newberyite salts and a solution (S10, S12).

[0036] In some embodiments, the solution (S10, S12) from step (10) is recycled by mixing with the brine from the desalination of seawater.

[0037] Advantageously, the method of the invention further comprises the following steps:

[0038] (11) cooling a portion of the solution (S2) obtained at the end of step (2) to a temperature ranging from -30°C to 0°C, resulting in a suspension (S13) comprising crystals of hydrated magnesium sulfate; and

[0039] (12) separation of the suspension (S13) resulting from step (11) leading to a solution (S14) and a solid (M) comprising the hydrated magnesium sulfate crystals.

[0040] Advantageously, the method of the invention further comprises a step (13) of removing part of the water from the solution (S14) leading to a solid comprising carnallite salts.

[0041] Advantageously, the method of the invention further comprises the following steps: (14) rinsing the solid (M) comprising the hydrated magnesium sulfate crystals, by contacting with an organic solvent resulting in hydrated magnesium sulfate and organic rinsing solvent;

[0042] (15) optional recycling of the organic solvent to be recycled to step (14);

[0043] (16) optional drying of the solid M from step (14) and / or (15).

[0044] In some embodiments, the water removed in steps (1), (2) and / or (13) is recovered, typically as fresh water.

[0045] The brine preferably has a pH ranging from 7.5 to 8.5 and / or a salinity ranging from 4.6 to 9.0% by weight. The brine can be obtained from desalination of seawater by distillation or reverse osmosis.

[0046] Advantageously, the process of the invention comprises, prior to step (1), a step of eliminating 80% of the volume of water relative to the volume of water initially contained in the brine, leading to the formation of a suspension comprising CaSC salts followed by the separation of the suspension into a solution sent to step (1) and a solid residue comprising CaSC crystals.

[0047] In certain embodiments, the solution (S2) is cooled in step (11) to a temperature ranging from -30°C to 0°C, typically to a temperature ranging from -15°C to - 3°C, or even ranging from (-9°C) to (-4°C).

[0048] The organic solvent is typically an alcohol such as ethanol or acetone.

[0049] Other aspects of the invention are as described below.

[0050] FIGURES

[0051] Figure 1: is a general diagram of an embodiment of the process for producing salts from a solution according to the invention, typically of NaCl, kainite, potassium bitartrate, struvite and / or newberyite.

[0052] Figure 2: is a diagram of a complementary embodiment of the process of the invention for the production of carnallite and MgSC.

[0053] DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing salts from brine obtained from the desalination of seawater, the process comprising the following steps:

[0054] (1) removal of 85% to less than 95% of the volume of water initially contained in the brine leading to the formation of a suspension comprising NaCI crystals, followed by separation of the suspension into a solution (S1) and a solid residue comprising NaCI crystals;

[0055] (2) removal of a portion of the water contained in the solution (S1) so as to reach a total volume of water removed in steps (1) and (2) corresponding to at least 95% of the volume of water initially contained in the brine leading to the formation of a suspension comprising kainite crystals, followed by the separation of the suspension into a solution (S2) and a solid residue comprising kainite crystals and optionally NaCl crystals;

[0056] (3) addition of MgO to part or all of the solution (S2) leading to the formation of a suspension (S3);

[0057] (4) addition of tartaric acid to the suspension (S3) leading to the formation of a suspension (S4) containing solid potassium bitartrate (KC4H5O6);

[0058] (5) separation of the suspension (S4), typically by filtration, leading to the formation of solid potassium bitartrate and a solution (S5);

[0059] (6) adding a phosphate-based compound to the solution (S5) so as to obtain a mixture (S6) containing crystallized NaCl;

[0060] (7) separation of the mixture (S6) leading to the formation of crystallized NaCl and a solution (S7).

[0061] Advantageously, the method according to the present invention can be implemented to recover a maximum of the salts contained in the brine resulting from the desalination of seawater while limiting the environmental impact of the brines generally resulting from the desalination of seawater.

[0062] Advantageously, the method according to the present invention allows the recovery of brine into a wide range of recovered products, and this with great flexibility.

[0063] In particular, the process according to the invention can make it possible to extract, in addition to NaCl, products such as kainite, carnallite and MgSC which can be used as natural organic fertilizers with rapid release, or struvite and / or newberyite salts which can be used as slow-release fertilizers, or potassium bitartrate which can be used in the food industry such as.

[0064] An advantage of the process according to the invention is that the manufacture of all these products can be carried out without waste requiring reprocessing.

[0065] The brine:

[0066] The brine used in the process according to the invention comes from the desalination of sea water.

[0067] The term "sea water" means water from an ocean or water from an inland sea or similar.

[0068] Brine contains mainly ionic species such as chloride ions, sodium ions, sulfate ions, magnesium ions, calcium ions, potassium ions and / or carbonate ions.

[0069] The brine useful in the process of the invention is conventionally a brine resulting from the desalination of seawater by distillation or reverse osmosis.

[0070] Atlantic Ocean water has an average salinity of 35 g / L, or 3.5% by weight. Ocean water generally has a salinity ranging from 30 to 40 g / L, or 3 to 4% by weight. Inland seas and similar seas have a higher salinity because evaporation concentrates the salt there.

[0071] Brine from seawater desalination generally has a salinity ranging from 1.1 to 1.2 times, typically 1.2 to 2 times or 1.3 to 1.7 times the salinity of the seawater from which it originates.

[0072] Typically, brine from desalination, typically by reverse osmosis, has an average salinity ranging from 1 to 9.0% by weight, more particularly from 4.6 to 9.0% by weight, or from 1 to 4.5% by weight.

[0073] The brine useful in the process according to the invention can therefore have an average salinity ranging from 1 to 9.0% by weight, more particularly from 4.6 to 9.0% by weight, or even from 1 to 4.5% by weight.

[0074] Table 1 describes an example of the (majority) ion composition of a brine from desalination compared to the composition of the seawater from which it originates. [Table 1]

[0075] Table 1: Ion composition of brine compared to seawater

[0076] Seawater has a pH of 7.65; brine from desalination of seawater typically has a pH of 8.16. This basicity is associated with the salts contained in seawater.

[0077] The brine useful in the process according to the invention may have a pH ranging from 7.5 to 8.5 and typically 8.2.

[0078] The brine useful in the process according to the invention may have a density greater than 1.05 kg / L.

[0079] The brine useful in the process according to the invention may be previously filtered when solid impurities are present.

[0080] Step (1): formation of NaCI

[0081] The method according to the invention comprises a step (1) of removing 85% to less than 95% of the volume of water initially contained in the brine, leading to the formation of a suspension comprising NaCl crystals, followed by the separation of the suspension into a solution (S1) and a solid residue comprising NaCl crystals. Optionally, the method comprises, prior to step (1), a step of removing 80% of the volume of water relative to the volume of water initially contained in the brine, leading to the formation of a suspension comprising CaSO4 salts, followed by the separation of the suspension into a solution sent to step (1) and a solid residue comprising CaSO4 crystals. This step makes it possible to crystallize and selectively separate CaSO4 salts. This step is carried out when the brine to be treated contains more than 0.5% by weight of calcium sulfate (CaSO4).

[0082] Typically, water removal by evaporation is carried out at a temperature ranging from 20°C to 250°C, or even from 20 to 100°C or even from 20 to 40°C.

[0083] Generally, the crystallization of NaCl can be promoted by lowering the temperature. The removal of water from the brine to be treated is carried out in such a way as to remove at least 85% of the volume of water initially contained in the brine, and up to 95% of the volume of water, typically 85 to 90% of the volume of water, initially contained in the brine is removed. The removal of water from the brine to be treated is generally carried out in such a way as to remove 90% of the volume of water initially contained in the brine.

[0084] Advantageously, during step (1), typically during water removal, the brine has a controlled salt concentration to be in a range of 300 to 380 g / L, i.e. a salinity of 30 to 38% by weight, which makes it possible to selectively promote the crystallization of NaCl, typically over that of CaSC or the magnesium salts, MgSC and MgCh. The salt concentration is commonly determined by measuring the density.

[0085] Generally, the solid residue obtained at the end of step (1) contains at least 95% by weight of NaCl or from 95 to 99% by weight of NaCl.

[0086] Separation can be achieved by any method that allows a solid to be separated from a liquid. Typically, separation is achieved by filtration, decantation, centrifugation and / or scraping.

[0087] The solid residue containing NaCl can also be separated from the brine as the water is removed and the NaCl crystallizes. Solution (S1) therefore corresponds to the brine in which at least 90% by weight of NaCl has been removed relative to the amount of NaCl contained in the brine to be treated.

[0088] The solution (S1) typically has a density ranging from 1.1 to 1.3 kg / L, and / or a pH ranging from 8 to 9 and / or a conductivity ranging from 140 to 200 mS / cm.

[0089] The solid residue can be used in washing and / or centrifugation steps in order to recover purified NaCI salts which can then be used, for example, in human or animal food, the manufacture of soda, chlorine (Ch) and bleach (NaCIO).

[0090] The solution (S1) contains a quantity of NaCl salts less than or equal to 10% by weight, typically less than or equal to 7% by weight or even 5% by weight.

[0091] Solution (S1) is then engaged in a kainite formation step. Step (2): kainite formation

[0092] The method according to the invention comprises a step (2) of removing part of the water contained in the solution (S1) so as to reach a total volume of water removed in steps (1) and (2) corresponding to at least 95% of the volume of water initially contained in the brine leading to the formation of a suspension comprising kainite crystals, followed by the separation of the suspension into a solution (S2) and a solid residue comprising kainite crystals and optionally NaCl crystals.

[0093] Step (2) may be carried out so as to achieve a total volume of water removed in steps (1) and (2) ranging from 95% to 99% of the volume of water initially contained in the brine, typically the total volume of water removed is 95% of the volume of water initially contained in the brine.

[0094] The removal of water in step (2) can be achieved by evaporation.

[0095] Typically, water removal is carried out gradually, i.e., it is carried out slowly to promote crystallization of kainite salts. For example, slow water removal can be achieved by evaporation in the open air.

[0096] Typically, water removal by evaporation is carried out at temperatures ranging from 20°C to 250°C, or even from 20 to 100°C or even from 25 to 70°C. Evaporation can be carried out under solar radiation, typically for 8 hours.

[0097] A cooling step may also be carried out to promote the crystallization of the kainite salts, typically at a temperature ranging from 10 to 25°C, typically at a temperature < 18°C. The crystallized kainite salts may be recovered by any methods known to those skilled in the art, for example by scraping.

[0098] Separation can be achieved by any method that allows a solid to be separated from a liquid. Typically, separation is achieved by filtration, decantation, centrifugation, or scraping.

[0099] Thus, step (2) according to the invention allows the formation of kainite salts. The kainite salts are obtained by crystallization and separation of the kainite salts formed.

[0100] Kainite is a mixed salt of potassium and magnesium having the formula KCIMgSC .SfW. Typically, step (2) therefore makes it possible to obtain a solid residue containing at least 80% by weight of kainite, typically the solid residue contains at least 73% by weight of kainite or at least 50% by weight of kainite and typically 50 to 90% by weight of kainite. Optionally, the solid residue may also contain NaCl, for example less than 20% by weight of NaCl and typically 10 to 50% by weight of NaCl. Conventionally, the solution (S2) contains a quantity of kainite salts less than or equal to 5% by weight, typically less than or equal to 3% by weight or 1% by weight.

[0101] The solution (S2) typically has a density ranging from 1.3 to 1.4 kg / L, and / or a pH ranging from 8 to 9 and / or a conductivity ranging from 180 to 240 mS / cm.

[0102] The method according to the invention comprises a step (3) of adding MgO to part or all of the solution (S2) leading to the formation of a suspension (S3).

[0103] MgO, short for magnesium oxide, is added during step (3) to the solution (S2), generally with stirring, and typically for a period of 4 hours to 24 hours, leading to the formation of the suspension (S3), which is classically white, opaque and dense.

[0104] The addition of MgO commonly stabilizes the pH of the suspension. Generally, the suspension (S3) has a pH ranging from 1.0 to 1.5, and typically from 1.2 to 1.3. Advantageously, the addition of MgO stabilizes the pH of the solution (S3).

[0105] The addition of MgO can be carried out in one or more steps. Typically, MgO is added in a mass ratio MgO / solution (S2) ranging from 1 / 30 to 1 / 1.9.

[0106] The method according to the invention comprises a step (4) of adding tartaric acid to the suspension (S3) resulting from step (3) leading to the formation of a suspension (S4) containing solid potassium bitartrate (KC4H5O6, also abbreviated KHT).

[0107] Step (4) of adding tartaric acid is generally carried out with stirring, for example with mechanical stirring. Step (4) is commonly carried out without external heating, typically at a temperature ranging from 10 to 40°C, or even at a temperature ranging from 15 to 35°C or even from 20 to 25°C.

[0108] Tartaric acid can be added in solid or liquid form. Generally, tartaric acid is added in liquid form, typically in aqueous solution. The tartaric acid solution added to the suspension (S3) can have a concentration ranging from 0.1 to 2 mol / L, or from 0.1 to 1.5 mol / L, or even from 0.2 to 0.7 mol / L.

[0109] Tartaric acid can be added in a mass ratio of tartaric acid to suspension (S3) ranging from 0.5 to 1.5; for example in a mass ratio of 1.25.

[0110] Tartaric acid can be added depending on the amount of MgO added during step (3), commonly tartaric acid is added in a tartaric acid / MgO mass ratio ranging from 3 to 6, typically ranging from 4 to 5, for example 4.8. Step (4) of adding tartaric acid can be carried out by one or more additions of tartaric acid. Typically, after contacting the tartaric acid, stirring is maintained for a period ranging from 3h to 24h (hours), commonly ranging from 4h to 23h or from 15h to 23h.

[0111] The method according to the invention comprises a step (5) of separation of the suspension (S4) resulting from step (4), typically by filtration, leading to the isolation of solid potassium bitartrate (KHT) and to a solution (S5).

[0112] Typically, the solution (S5) is rich in magnesium ions.

[0113] Pure KHT has low solubility in water, typically a maximum of 5.7 g / L at 20°C, 45 g / L at 80°C, and 61 g / L at 100°C. Typically, the solubility of KHT decreases at low temperatures.

[0114] Depending on the amount of KHT in the mixture, crystallization can be spontaneous or be promoted by a lowering of the temperature or even evaporation of part of the water in the mixture.

[0115] Typically, recovered KHT is a white solid with a homogeneous, slightly sandy texture.

[0116] Recovered KHT typically contains less than 5% by weight of impurities, or even less than 1% by weight. Commonly, the amount of impurities is in the range of 1 to 5% by weight.

[0117] Impurities can be salts, commonly impurities are NaCl.

[0118] The amount of impurities can be determined by elemental analysis.

[0119] The method according to the invention comprises a step (6) of adding a phosphate-based compound to the solution (S5) leading to the formation of a mixture (S6) containing crystallized NaCl.

[0120] The phosphate-based compound may be added in a molar ratio to Mg ranging from 0.5 to 2; typically from 1 to 1.5 or even 1. Addition (6) is generally carried out with stirring, for example with mechanical stirring. Step (6) is commonly carried out without external heating, typically at a temperature ranging from 20 to 30°C, or even at a temperature ranging from 24 to 26°C.

[0121] The phosphate-based compound is a source of PC ions 2'soluble in aqueous solution. The phosphate compound may have the formula XPO4, where X may be selected from H, NH4, Na, or a combination. Typically, the phosphate compound is phosphoric acid H3PO4.

[0122] Without being bound by any theory, the addition of PC>4 ions 2 ' causes a shift in the equilibrium of the solution, which causes the precipitation of NaCl.

[0123] The method according to the invention comprises a step (7) separation of the mixture (S6) leading to the formation of crystallized NaCl and a solution (S7).

[0124] Separation can be achieved by any method that allows a solid to be separated from a liquid. Typically, separation is achieved by filtration, decantation, centrifugation, or scraping.

[0125] Typically, the solution (S7) is rich in phosphate ions. Advantageously, the solution (S7) can lead to the formation of newberyite salts (MgHPC .SFW) and / or struvite salts (NhLMgPC .SFW).

[0126] The formation of struvite requires the addition of ammonium ions followed by the addition of NaOH. Typically, struvite is obtained by performing steps (8) to (10) described below.

[0127] The formation of newberyite requires only the addition of NaOH, so step (8) is not implemented to form newberyite. Typically, newberyite is obtained from steps (9) to (10).

[0128] Advantageously, a portion of the solution (S7) is used in step (8) and the other portion is used directly in step (9) to simultaneously form newberyite and struvite salts. The solution (S7) can therefore be split into two fractions, equal or not, to be sent on the one hand to step (8) and on the other hand to step (9). The proportions of newberyite and struvite salts formed can be modulated by varying the quantity of solution (S7) used in step (8) and / or in step (9). The method of the present invention can comprise one or the other, or even all of the optional steps described below.

[0129] The method may in particular comprise the following steps (8) to (10).

[0130] The method may comprise a step (8) of optional addition of NH4 salts + to solution (S7) leading to the formation of a solution (S8). Typically, solution (S8) is rich in NH4 + .

[0131] Typically, NH4 salts + added during step (8) are chosen from (NH4)2SO4), NH4CI or NH4OH.

[0132] Adding NH4 salts + is generally carried out with stirring, typically for a period of 1 hour to 4 hours. The addition can be carried out at a temperature ranging from 20 to 30°C, typically 24 to 26°C.

[0133] Adding NH4 salts + can be done in one or more steps. Typically, NH4 salts + can be added in a molar ratio to PO4 2 ' ranging from 0.5 to 2, typically from 1 to 1.5 or even 1. Per PO4 2 ; the phosphate-based compound added in step (6) is designated.

[0134] The method may comprise a step (9) of adding NaOH to the solution (S7) and / or to the solution (S8) leading to the formation of a suspension (S11) comprising solid struvite and / or a suspension (S9) comprising solid newberyite.

[0135] Typically, the addition of NaOH is carried out so as to obtain a pH ranging from 4.5 to 7, typically 5.

[0136] Generally, NaOH is added until a white precipitate forms in the suspension (S9, S11).

[0137] The addition of NaOH is generally carried out with stirring, typically for a period of 1 hour to 2 hours. The addition of NaOH can be carried out at a temperature ranging from 20 to 30°C, typically 24 to 26°C.

[0138] The addition of NaOH can be carried out in one or more steps. The method can comprise a separation step (10) leading to the recovery of solid struvite salts and / or solid newberyite salts and a solution (S10, S12). The solutions (S10, S12) obtained at the end of the separation (10) can typically be recycled in step (1). In particular, the solution S10 or S12 resulting from step

[0139] (10) can be recycled by mixing with brine from seawater desalination.

[0140] Typically, the struvite (NhLMgPC .OW) obtained has a purity greater than 95%, generally greater than 99%.

[0141] Typically, the newberyite (NhLMgPC .OW) obtained has a purity greater than 95%, generally greater than 99%.

[0142] In certain embodiments, a portion of the solution (S2) obtained at the end of step (2) can be used to form carnallite and / or MgSC. This embodiment is shown schematically in Figure 2.

[0143] Typically, in these embodiments, the method further comprises the following steps:

[0144] (11) cooling a portion of the solution (S2) obtained at the end of step (2) to a temperature ranging from -30°C to 0°C, resulting in a suspension (S13) comprising crystals of hydrated magnesium sulfate; and

[0145] (12) separation of the suspension (S13) resulting from step (11) leading to a solution (S14) and a solid (M) comprising the hydrated magnesium sulfate crystals.

[0146] It may further comprise a step (13), as well as steps (14), (15) and (16) as described below.

[0147] The method may comprise a step (11) of cooling a portion of the solution (S2) obtained at the end of step (2) to a temperature ranging from -30°C to 0°C, resulting in a suspension (S13) comprising crystals of hydrated magnesium sulfate.

[0148] Conventionally, the part of the solution (S2) which is sent to the cooling step (11) has a water evaporation rate greater than or equal to 99% by volume compared to the volume of water initially contained in the brine.

[0149] The solution (S2) has a water evaporation rate greater than or equal to 99% by volume relative to the quantity of water initially contained in the brine. The solution (S2) may further have a density ranging from 1.1 kg / l to 1.35 kg / l, typically ranging from 1.28 kg / l to 1.32 kg / l.

[0150] The water evaporation rate refers to the volume of water that has been eliminated relative to the volume of water initially contained in the brine to be treated in the process according to the invention.

[0151] The solution (S2) can be cooled by any means, for example by a freezer, or any other suitable cooling system to promote the crystallization of the MgSC salts.

[0152] The solution (S2) is cooled to a temperature ranging from -30°C to 0°C, typically to a temperature ranging from -15°C to -3°C, or even from -9°C to -4°C. Generally, crystallization (3) is carried out for a period ranging from 1h to 10h, typically from 2h to 6h.

[0153] Typically, the formation of MgSC crystals is carried out without stirring the solution (S2) so as to promote the appearance of MgSC crystals.

[0154] The method may comprise a step (12) of separating the suspension (S13) from step (11) leading to a solution (S14) and a solid (M) comprising the hydrated magnesium sulfate crystals.

[0155] Generally, the separation step (12) of the suspension (S13) resulting from step (11) into a solution (S14) and into a solid (M) containing at least 95% by weight of MgSO4, is carried out by cold filtration.

[0156] Typically, the separation (12) is carried out at a temperature less than or equal to 0°C, typically less than or equal to -5°C, so as to promote the formation of MgSO4 crystals.

[0157] The solution (S14) can be sent to a step (13) of removing part of the water from the solution (S14) leading to the formation of a solid comprising carnallite (KMgCh.SFW).

[0158] Typically the solid comprises at least 70% by weight of carnallite relative to the total mass of the solid, typically at least 60% by weight of carnallite and for example 63% by weight of carnallite. The removal of water can be carried out as described above for steps (1) and (2). In each of steps (1), (2) and / or (13), the removed water can be used as a source of fresh water, i.e. as water having a salinity of less than 1 g / L.

[0159] The solid comprising carnallite may optionally contain NaCl, typically less than 30% by weight of NaCl relative to the total mass of the solid obtained at the end of step (13).

[0160] The water removed in steps (1), (2) and / or (13) is typically recovered as fresh water.

[0161] The solid (M) from step (12) can be purified by rinsing (14) by contacting with an organic solvent leading to the formation of MgSC crystals and the organic solvent.

[0162] Typically, the organic solvent is an alcohol such as ethanol or acetone. Any other organic solvent that can purify MgSC crystals by solubilizing impurities is suitable for use in step (14).

[0163] The organic solvent can be recycled in a recycling step (15). Optionally, the organic solvent containing impurities before being recycled is purified, for example by distillation. Conventionally, the organic solvent is recycled in step (14).

[0164] The MgSC crystals from step (14) may be dried (16), typically in an oven, for example at a temperature ranging from 30 to 80°C, so as to preserve the quality of the crystallized MgSC.

[0165] Typically, the MgSCU crystals obtained at the end of the drying step (16) have the form of a white solid, typically with a purity greater than 99%, or even greater than 95%.

[0166] Thus, the process according to the invention allows the production of a wide variety of products such as kainite, carnallite and magnesium sulfate, struvite, newberyite, or even potassium bitartrate. Advantageously, these products can be used as natural fertilizers with rapid or slow release or in the food industry.

[0167] Depending on the supply requirements for each of the products accessible by the process according to the invention, the proportions of the fractions obtained during the fractionation of the solutions (S2) and / or (S7) may be adapted. The process according to the invention therefore offers great flexibility.

[0168] Materials and methods

[0169] The purity values ​​in the description and in the examples are determined by DRX analysis and elemental analysis.

[0170] XRD analyses were performed using a Burker D8 diffractometer with Cu Ko radiation in the range of 15 to 5520, with a step size of 0.02 and a collection time of 2.5 s / step. The processing was carried out using Highscore Plus software based on COD19 data. The X-ray diffractograms of the samples obtained also allow the determination of the crystal structure of the solid phases.

[0171] Elemental analyses were performed for sodium, potassium, and calcium by flame spectrophotometry (Sherwood 410 Industrial Flame Photometer). Magnesium was determined by complexometric titration. SCU 2 ' was analyzed by gravimetric method, while Cl' was determined by potentiometric method.

[0172] The various embodiments presented throughout the description may be used alone or in combination with each other, without limitation of combination.

[0173] EXAMPLES

[0174] The following non-restrictive examples illustrate exemplary embodiments of the invention.

[0175] Example 1: Formation of KHT and newberyite

[0176] This example is an embodiment of the process according to the invention for leading to the formation of potassium bitartrate and newberyite salt, as illustrated in Figure 1. In this example, the treated brine comes from the desalination of seawater by reverse osmosis. The brine has a density of 1.045 kg / L, a concentration of 1.38 g / L of potassium chloride (KCl), 6.08 g / L of magnesium chloride (MgCh) and 48 g / L of sodium chloride (NaCl).

[0177] In step (1), 90% of the water volume of the brine was removed by evaporation so as to crystallize the NaCl. Evaporation was facilitated by external heating using a Bunsen burner.

[0178] The solid NaCl is separated and a solution (S1) is obtained.

[0179] After separation of the solid NaCl, the water contained in the solution (S1) is evaporated in the open air for 8 hours. The mixture is cooled to a temperature of 18°C ​​overnight. After cooling, the salts formed are recovered by scraping. This step is repeated 3 times until 95% of the water by volume is removed from the brine. The solution (S2) has a density greater than or equal to 1.36 kg / L, a pH of 8.6 and a conductivity of 174.6 mS / cm.

[0180] The compositions of the solids obtained after each scraping are shown in Table 2 and were determined by DRX analyses.

[0181] [Table 2]

[0182] A mass of 3.5 g of MgO is added to 100 ml of the solution (S2) with stirring for 24 hours to form a white and dense suspension (S3). Then, tartaric acid C4H6O6 (16.8 g) is added to the suspension (S3) with stirring for 24 hours until a pH of 1.3 is obtained and a white solid is formed. After separation by filtration, a solution (S5) and a solid are obtained. The solid is then dried at a temperature of 60°C for 24 hours. The solid obtained (14.8 g) is potassium bitartrate (KC4H5O6), with a purity of 99% by weight. The purity was determined by XRD analysis.

[0183] An aqueous solution of phosphoric acid at 61% by weight of P2O5 is added to the solution (S5). The mixture is stirred for 3 hours until the NaCl precipitates. After separation by filtration of the NaCl, the pH of the solution (S7) is very acidic. The pH is adjusted to a pH of 5 by adding 2M NaOH solution. Once the pH of the solution (S11) is 5, a white solid forms. This is separated by filtration. The solid obtained (14.2 g) is magnesium hydrogen phosphate (newberyite) with a purity of 99% by weight. The purity was determined by XRD analyses. Example 2: Newberyite formation

[0184] In this example, the treated brine is from seawater desalination. The brine has a density of 1.045 kg / L, a concentration of 1.38 g / L of potassium chloride (KCI), 6.08 g / L of magnesium chloride (MgCh) and 48 g / L of sodium chloride (NaCI).

[0185] In step (1), 90% of the water volume of the brine was removed by evaporation so as to crystallize the NaCl. Evaporation was facilitated by external heating using a Bunsen burner.

[0186] The solid NaCI is separated and a solution (S1) depleted in NaCI is obtained.

[0187] After separation of the solid NaCl, the water contained in the solution (S1) is evaporated in the open air for 8 hours. The mixture is cooled to a temperature of XX overnight. After cooling, the salts formed are recovered by scraping. This step is repeated 3 times until 95% of the water by volume is removed from the brine. The kainite-depleted solution (S2) has a density greater than or equal to 1.36 kg / L, a pH of 8.6 and a conductivity of 174.6 mS / cm.

[0188] The compositions of the solids obtained after each scraping are shown in Table 3 and were determined by DRX analyses.

[0189] [Table 3]

[0190] A 61% aqueous phosphoric acid solution of P2O5 (30 ml) is added to 100 ml of solution (S2) followed by the addition of NaOH until a solution pH of 5 is reached. A white precipitate appears. This is recovered by filtration. Analyses show that the white precipitate is newberyite with a purity of 99% by weight.

[0191] 3.5 g of MgO is added to 100 ml of the solution obtained from the filtration. After 24 hours of stirring, a white and dense solution is obtained. To this solution is added tartaric acid C4H6O6 with stirring for 24 hours. No trace of formation of solid potassium bitartrate appears.

[0192] Example 3: Formation of KHT and struvite This example is an embodiment of the process according to the invention to lead to the formation of potassium bitartrate and struvite salt, as illustrated in Figure 1.

[0193] In this example, the treated brine is from seawater desalination by reverse osmosis. The brine has a density of 1.045 kg / L, a concentration of 1.38 g / L of potassium chloride (KCl), 6.08 g / L of magnesium chloride (MgCh), and 48 g / L of sodium chloride (NaCl).

[0194] In step (1), 90% of the water volume of the brine was removed by evaporation so as to crystallize the NaCl. Evaporation was facilitated by external heating using a Bunsen burner.

[0195] The solid NaCl is separated and a solution (S1) is obtained.

[0196] After separation of the solid NaCl, the water contained in the solution (S1) is evaporated in the open air for 8 hours. The mixture is cooled overnight to a temperature <18°C (corresponding to a night temperature varying from 10 to 18°C). After cooling, the salts formed are recovered by scraping. This step is repeated 3 times until 95% of the water by volume is removed from the brine. The solution (S2) has a density greater than or equal to 1.36 kg / L, a pH of 8.6 and a conductivity of 174.6 mS / cm.

[0197] The compositions of the solids obtained after each scraping are shown in Table 4 and were determined by DRX analyses.

[0198] [Table 4]

[0199] A mass of 3.5 g of MgO is added to 100 ml of the solution (S2) with stirring for 24 hours to form a white and dense suspension (S3). Then, tartaric acid C4H6O6 (16.2 g) is added to the suspension (S3) with stirring for 24 hours until a pH of 1.3 is obtained and a white solid is formed. After separation by filtration, a solution (S5) and a solid are obtained.

[0200] The solid is then dried at a temperature of 60°C for 24 hours. The solid obtained (14.8 g) is potassium bitartrate (KC4H5O6), having a purity of 99% by weight. An aqueous solution of phosphoric acid at 61% by weight of P2O5 is added to the solution (S5). The mixture is stirred for 3 hours until the NaCl precipitates. After separation by filtration of the NaCl, the pH of the solution (S7) is very acidic.

[0201] To 100 ml of solution (S7) is added 2 g of NH4SO4 to form a solution (S8). Once the pH of solution (S9) is 7, a white solid is formed. The latter is separated by filtration. The solid obtained (16.8 g) is struvite (NhLMgPC .SFW) with a purity of 99% by weight.

[0202] Example 4: Struvite formation

[0203] In this example, the treated brine is from seawater desalination by reverse osmosis. The brine has a density of 1.045 kg / L, a concentration of 1.38 g / L of potassium chloride (KCl), 6.08 g / L of magnesium chloride (MgCh), and 48 g / L of sodium chloride (NaCl).

[0204] In step (1), 90% of the water volume of the brine was removed by evaporation so as to crystallize the NaCl. Evaporation was facilitated by external heating using a Bunsen burner.

[0205] The solid NaCI is separated and a solution (S1) depleted in NaCI is obtained.

[0206] After separation of the solid NaCl, the water contained in the solution (S1) is evaporated in the open air for 8 hours. The mixture is cooled to a temperature <18°C overnight. After cooling, the salts formed are recovered by scraping. This step is repeated 3 times until 95% of the water by volume is removed from the brine. The kainite-depleted solution (S2) has a density greater than or equal to 1.36 kg / L, a pH of 8.6 and a conductivity of 174.6 mS / cm.

[0207] The compositions of the solids obtained after each scraping are shown in Table 5 and were determined by DRX analyses.

[0208] [Table 5]

[0209] Table 5: Composition of the solids obtained after each scraping

[0210] An aqueous solution of phosphoric acid at 61% P2O5 (30 ml) is added to 100 ml of solution (S2) followed by the addition of 2 g of NH4SO4 then NaOH in 2M solution until a pH of 5 is reached. A white precipitate appears. This is recovered by filtration. Analyses show that the white precipitate is struvite with a purity of 99%. To 100 ml of the solution resulting from the filtration is added 3.5 g of MgO. After 24 hours of stirring, a white and dense solution is obtained. To this solution is added tartaric acid C4H6O6 with stirring for 24 hours. No trace of formation of solid potassium bitartrate appears.

[0211] To this solution, purified 61% phosphoric acid and NaOH are added with stirring until the pH of the solution reaches 5. At this pH, a white precipitate forms. XRD analysis shows that this is pure magnesium hydrogen phosphate (newberyite).

[0212] After filtration, 3.5g of MgO is added to 100ml of the said solution with stirring for 24h. This gives a white and dense solution. Then, tartaric acid C4H6O6 is added to the said solution with stirring for 24h. But no solid appears.

[0213] Example 5: Formation of MgSO4

[0214] This example illustrates an embodiment shown schematically in Figure 2.

[0215] In this example, the treated brine is from seawater desalination by reverse osmosis. The brine has a density of 1.045 kg / L, a concentration of 1.38 g / L of potassium chloride (KCl), 6.08 g / L of magnesium chloride (MgCh), and 48 g / L of sodium chloride (NaCl).

[0216] In step (1), 90% of the water volume of the brine is removed by evaporation so as to crystallize the NaCl. Evaporation was facilitated by external heating using a Bunsen burner.

[0217] The solid NaCl is separated and a solution (S1) is obtained.

[0218] In a second step (2), 95% of the volume of water relative to the quantity of water initially contained in the brine is eliminated by evaporation of the water contained in the solution (S1).

[0219] Evaporation is carried out discontinuously, after contact with solar radiation for a maximum of 12 hours, the solution is cooled to a temperature <18°C overnight for a minimum of 8 hours, then the solid is scraped off. The cycle is repeated several times until 95% of the volume of water initially contained in the brine is removed.

[0220] The compositions of the solids obtained after each scraping are shown in Table 5 and were determined by DRX analyses.

[0221] [Table 6]

[0222] The solution (S2) has a density of 1.3 kg / l, a final pH of 8.68 and a conductivity of 169.3 mS / cm.

[0223] The solution (S2) is cooled to (-5°C) for 3 hours leading to the formation of magnesium hydrate crystals. The mixture is separated, step (12), by filtration into a solution (S16) and a solid (M) in the form of magnesium hydrate crystals. The solid crystals formed are then dried at a temperature of 60°C leading to the formation of a solid in the form of fine, white crystals mainly consisting of MgSC having a purity by XRD analysis of approximately 85%. XRD analysis shows that the solid contains a mixture of several phases MgSC .ôFW, NaCI, KCI and kainite (KCI.MgSC .).

[0224] Example 6: Formation of carnallite and rinsing of crystals

[0225] This example illustrates an embodiment shown schematically in Figure 2.

[0226] In this example, a process identical to that of example 5 is implemented, except that before the drying step (16), the solid crystals are rinsed with an organic solvent, acetone.

[0227] The drying step is carried out on the rinsed solid, at 60°C.

[0228] XRD analyses confirm that the final solid is pure magnesium sulfate with the chemical formula: MgSC .ôFW. Chemical analyses show that the product obtained by the process is composed of 34.52% by weight of SO3, 17.12% by weight of MgO and 46.42% by weight of H2O. The solid (MgSC ) obtained is therefore of high purity. The solution (S13) from the separation step (12) is evaporated in the open air. XRD analyses showed that the solid obtained mainly contains mixed salt carnallite (69% by weight) and NaCl (31% by weight).

Claims

CLAIMS 1. A process for producing salts from brine obtained from the desalination of seawater, the process comprising the following steps: (1) removal of 85% to less than 95% of the volume of water initially contained in the brine leading to the formation of a suspension comprising NaCI crystals, followed by separation of the suspension into a solution (S1) and a solid residue comprising NaCI crystals; (2) removal of a portion of the water contained in the solution (S1) so as to reach a total volume of water removed in steps (1) and (2) corresponding to at least 95% of the volume of water initially contained in the brine leading to the formation of a suspension comprising kainite crystals, followed by the separation of the suspension into a solution (S2) and a solid residue comprising kainite crystals and optionally NaCl crystals; (3) addition of MgO to part or all of the solution (S2) leading to the formation of a suspension (S3); (4) addition of tartaric acid to the suspension (S3) leading to the formation of a suspension (S4) containing solid potassium bitartrate (KC4H5O6); (5) separation of the suspension (S4), typically by filtration, leading to solid potassium bitartrate and a solution (S5); (6) adding a phosphate-based compound to the solution (S5) so as to obtain a mixture (S6) containing crystallized NaCl; (7) separation of the mixture (S6) leading to crystallized NaCl and a solution (S7).

2. The method of claim 1, further comprising the following steps: (8) Optional addition of N H4 salts + , to the solution (S7) resulting from step (7) leading to the formation of a solution (S8); (9) adding NaOH to the solution (S7) and / or to the solution (S8) leading to the formation of a suspension (S11) comprising solid struvite and / or a suspension (S9) comprising solid newberyite; (10) separation leading to the recovery of solid struvite salts and / or solid newberyite salts and a solution (S10, S12).

3. Method according to claim 2, in which the solution (S10, S12) resulting from step (10) is recycled by mixing with the brine resulting from the desalination of seawater. Tl 4. A method according to any one of claims 1 to 3, further comprising the following steps: (11) cooling a portion of the solution (S2) obtained at the end of step (2) to a temperature ranging from -30°C to 0°C, resulting in a suspension (S13) comprising crystals of hydrated magnesium sulfate; and (12) separation of the suspension (S13) resulting from step (11) leading to a solution (S14) and a solid (M) comprising the hydrated magnesium sulfate crystals.

5. Method according to claim 4, further comprising a step (13) of removing part of the water from the solution (S14) leading to a solid comprising carnallite salts.

6. Method according to one of claims 4 or 5, further comprising the following steps (14) rinsing the solid (M) comprising the hydrated magnesium sulfate crystals, by contacting with an organic solvent resulting in hydrated magnesium sulfate and the organic rinsing solvent; (15) optional recycling of the organic solvent to be recycled to step (14); (16) optional drying of the solid M from step (14) and / or (15).

7. A method according to any one of claims 1 to 6, wherein the water removed in steps (1), (2) and / or (13) is typically recovered as fresh water.

8. A method according to any one of claims 1 to 7, wherein the brine has a pH ranging from 7.5 to 8.5 and / or a salinity ranging from 4.6 to 9.0% by weight.

9. Method according to any one of claims 1 to 8, in which the brine comes from desalination of seawater by distillation or reverse osmosis.

10. Method according to any one of claims 1 to 9, comprising prior to step (1) a step of eliminating 80% of the volume of water relative to the volume of water initially contained in the brine leading to the formation of a suspension comprising CaSC salts followed by separation of the suspension into a solution sent to step (1) and a solid residue comprising CaSC crystals.

11. Method according to any one of claims 4 to 10, in which the solution (S2) is cooled in step (11) to a temperature ranging from -30°C to 0°C, typically to a temperature ranging from -15°C to -3°C, or even ranging from (-9°C) to (-4°C).

12. A method according to any one of claims 6 to 11, wherein the organic solvent is an alcohol such as ethanol or acetone.

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