METHOD AND SYSTEM FOR EXTRACTION OF MINERALS BASED ON DIVALENT CATIONS FROM BRINE

[0001] This application claims priority to U.S. Patent Application Serial No. 17/644,121, filed December 14, 2021, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The present invention relates to the design and operation of brine treatment facilities in order to separate minerals of commercial value from the desalination of saline source water, in particular for the extraction of magnesium chloride and calcium sulfate dihydrate.

BACKGROUND

[0003] Historically, many minerals and other materials of economic value have been extracted from seawater, either directly or via the bitterns remaining after production of commercial sodium chloride. These products include elemental bromine, magnesium metal and magnesium salts such as magnesium chloride and magnesium sulfate, calcium sulfate dihydrate (gypsum), potassium chloride and potassium sulfate (potash), calcium chloride, lithium chloride and lithium carbonate. Membrane-based brine concentration techniques, such as those described in U.S. Patent No. 10,947,143, filed April 1, 2019, and titled: “Desalination Brine Concentration System and Method”, which is incorporated herein by reference in its entirety, have the capacity to provide more efficient and effective methods of obtaining these materials and minerals with lower inputs of chemicals and energy than conventional thermal evaporation based brine concentrators. These more efficient and effective approaches function at least in part by separating out a stream from which divalent ions are largely excluded (e.g., an nanofiltration permeate stream) and a stream in which the divalent ions are largely contained (e.g., a nanofiltration reject stream).

[0004] Some disadvantages of some current desalination facility operations include but are not limited to, the high costs associated with facilities, labor, waste disposal, high energy consumption, relatively low purity of product streams, etc. As a result, the purified water product from such facilities has a relatively high specific cost of production per liter.

[0005] There remains a need for improved systems and methods for generating concentrated and relatively pure ion streams in a more efficient & cost effective manner. SUMMARY

[0006] For convenience of reference, at most locations herein reference is made to “seawater” as the source water. This reference is not intended to be limiting, as the source water may be any saline water recognized by those of ordinary skill in the art as possible feed water to a desalination facility, such as brackish water, high salinity wastewater and groundwater.

[0007] In a typical system comprising a nanofiltration- seawater reverse osmosis (NF- SWRO) system, approximately 25% of the initial seawater volume is rejected by the nanofiltration (NF) membrane with a significantly increased concentration of divalent anions (primarily sulfate) and divalent cations (primarily magnesium and calcium). If separated into isolated calcium and magnesium salts of acceptable purity, this nanofiltration reject stream could be a valuable source of commercial minerals.

[0008] The present invention(s) addresses the above described and other problems by a unique approach to divalent ion separation concentration arrangements and associated operating methods, in which, a divalent ion-rich NF reject stream is fed into a downstream NF unit that selectively rejects sulfate while allowing a large fraction of cations to pass through the membrane into its permeate stream. Optionally, the reduced-sulfate permeate stream may be processed through another NF unit, whose reject stream has a reduced amount of sodium relative to the amount of magnesium in the stream.

[0009] The permeate stream from the sulfate-rejecting NF unit, or if optionally present, the reject stream from the sodium-reducing NF unit, may then enter a combination of membrane crystallizer/brine concentrator(s). The crystallizer/concentrator(s) separates the incoming stream into a magnesium-rich brine stream and a low total dissolved solids (TDS) water stream, and also produces solid calcium sulfate dihydrate. The low TDS water is suitable for use as feed water to a potable water production system. The magnesium-rich stream from the crystallizer/concentrator may then be treated in a clarifier to further reduce sulfate concentration if desired, using a salt of an alkaline earth metal (e.g., a salt of beryllium, magnesium, calcium, strontium, barium, and/or radium) to precipitate out sulfate. In certain aspects, a salt of calcium is utilized to precipitate out sulfate. In certain aspects, a salt of barium is utilized to precipitate out sulfate.

[0010] In order to remove sodium chloride from the magnesium-rich stream, the stream may be concentrated to or near the sodium chloride saturation point, for example in a solar concentration pond, in a thermal process, or using a membrane process. If a membrane process is used, the low TDS water stream from the concentrator may also be suitable for use as feed water to a potable water production system. The now highly-concentrated magnesium-rich stream containing sodium chloride at or near its saturation point may then enter a crystallizer to remove solid sodium chloride from the magnesium-rich stream.

[0011] The supernatant magnesium-rich stream from the crystallizer may be fed into a further concentration unit to draw off additional low TDS water (water which may also be suitable for potable water production) and to generate a concentrated magnesium-rich bittern stream in preparation for production of a desired magnesium-rich product. For example, the magnesium-rich bitterns stream may be further concentrated to dryness in a crystallizer to generated hydrated magnesium chloride. Alternatively, some or all of the concentrated magnesium-rich bitterns stream may be prilled in a dry air process unit and then passed through a dryer in a hydrogen chloride atmosphere to produce anhydrous magnesium chloride. Prilling is a method of producing reasonably uniform spherical solid crystals from molten solids, strong solutions or slurries (e.g., pelletizing), essentially consisting of two operations, firstly producing liquid drops of brine and secondly solidifying them individually by coohng/evaporation as they fall through a rising ambient air stream.

[0012] The use of the word “a” or “an” when used in conjunction with the term “comprising” may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

[0013] The phrase “and/or” means “and” or “or”. To illustrate, A, B, and/or C includes: A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C. In other words, “and/or” operates as an inclusive or.

[0014] The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0015] The systems and methods for their use can “comprise,” “consist essentially of,” or “consist of’ any of the components, units, and/or steps disclosed throughout the specification. systems and methods “consisting essentially of’ any of the components, units, and/or steps disclosed limits the scope of the claim to the specified materials or steps which do not materially affect the basic and novel characteristic of the claimed invention.

[0016] The term “about” as used herein refers to include the usual error range for the respective value readily known. Reference to “about” a value or parameter herein includes (and describes) embodiments that are directed to that value or parameter per se. For example, description referring to “about X” includes description of “X”. In some embodiments, “about” may refer to ±15%, ±10%, ±5%, or ±1% as understood by a person of skill in the art.

[0017] It is specifically contemplated that any limitation discussed with respect to one embodiment of the invention may apply to any other embodiment of the invention. Furthermore, any system of the invention may be used in any method of the invention, and any method of the invention may be used to produce or to utilize any system of the invention. Any embodiment discussed with respect to one aspect of the disclosure applies to other aspects of the disclosure as well and vice versa. For example, any step in a method described herein can apply to any other method. Moreover, any method described herein may have an exclusion of any step or combination of steps. Aspects of an embodiment set forth in one section herein are also embodiments that may be implemented in the context of embodiments discussed elsewhere in the application, such as in the Summary, Detailed Description, Claims, Drawings, Abstract, and Brief Description of the Drawings.

[0018] Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. It should be understood, however, that the detailed description and the specific embodiments, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWING

[0019] FIG. 1 is a schematic illustration of a process for producing magnesium chloride suitable for production of magnesium (for example but not limited to, electrolytic production of magnesium) according to an embodiment of the present invention. [0020] FIG. 2 is a schematic illustration of a process for producing magnesium chloride according to an embodiment of the present invention.

[0021] FIG. 3 is a schematic illustration of a process for producing magnesium chloride according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0022] FIG. 1 shows a schematic illustration of an apparatus and process for beneficiation of a divalent-ion rich reject stream produced by an NF brine concentration system 100. A divalent ion rich brine reject stream 1, such as but not limited to a rejection stream from an NF unit in an NF-SWRO system, is first treated with a nanofiltration (NF) unit 10 containing a nanofiltration membrane which is selective for rejection of sulfate anions but has a low selectivity for rejection of cations. This NF membrane reduces the level of sulfate in the nanofiltration permeate 11 to less than or equal to the stoichiometric level of calcium in the permeate. The reject stream 12 from the NF unit 10 may be discharged from the system for separate treatment and/or environmentally-acceptable disposal.

[0023] In general, negatively charged NF membranes tend to reject sulfate, as it is strongly negatively charged and has a relatively large hydrated radius. Cations can be rejected primarily on the basis of supplying counter-ions for sulfate, for which higher charge density ions (e.g., divalent, multivalent) are more effective. For commercial NF membranes, there is in general a higher selectivity for sulfate than for divalent cations. However, as described herein, an increased sulfate rejection rate relative to divalent cations is desired. Less densely packed, more porous, looser, and/or generally more permeable NF membranes than many currently commercially employed NF membranes may be used for commercial application of increased divalent anion rejection relative to divalent cations. An exemplary NF membrane that may reduce the stoichiometric level of sulfate to magnesium and/or calcium includes Hydranautics™ ESNA1-LF2, which has been reported as rejecting about 66% of sulfate, while only rejecting about 24% of magnesium and about 18% of calcium. An alternative exemplary NF membrane that may reduce the stoichiometric level of sulfate to magnesium and/or calcium includes Dupont FilmTec™ NF270, which has been reported as rejecting about 98% sulfate, while only rejecting about 83% of magnesium and about 53% of calcium.

[0024] In some aspects, an exemplary NF membrane for reducing the stoichiometric level of sulfate to magnesium and/or calcium rejects sulfate at greater than or equal to about 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, or any range derivable therein, while rejecting magnesium and/or calcium at less than or equal to about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%,

21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%,

37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%,

53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%,

69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%, or any range derivable therein.

[0025] Referring again to FIG. 1 , optionally, the permeate 11 may be treated by an additional NF unit 20 to reduce the molar ratio of sodium to magnesium in the additional NF unit reject stream 21 to one (1) or below. As with the reject stream of the NF unit 10, the permeate stream 22 from the NF unit 20 may be discharged from the system for separate treatment and/or environmentally-acceptable disposal. In general, NF membranes permit monovalent ions to pass through the membrane while rejecting divalent ions, exemplary NF units can include Hydranautics™ PRO-XS2, Dupont FilmTec™ NF-270, and Suez Osmonics™ DL.

[0026] The NF unit magnesium rich reject stream 21, having been treated to reduce the molar ratios of sulfate-to-calcium and sodium-to-magnesium to 1 or below, may then be conveyed to a combination membrane crystallizer/brine concentrator 30 configured to produce low TDS water 31, solid calcium sulfate dihydrate 32, and concentrated magnesium-rich brine 33. The concentrated magnesium-rich brine stream 33 is further processed as follows.

[0027] Optionally, if the sulfate levels in the concentrated magnesium-rich brine stream 33 are still above desired concentrations, the concentrated magnesium-rich brine stream 33 may be treated to precipitate out residual sulfate in a clarifier 40. In certain aspects, desired concentrations and/or acceptably low levels of sulfate are less than or equal to about 800, 900, 1000, 1100, or 1200 parts per million, or any range derivable therein. In this embodiment, the treatment may include mixing the concentrated magnesium-rich brine stream 33 with a soluble salt of an alkaline earth metal 41, thereby forming a highly insoluble salt with sulfate 42. The precipitated insoluble salt stream 42 is removed from the clarifier 40, and a clarified concentrated magnesium-rich stream 43 with an acceptably low level of sulfate is output from the clarifier 40. [0028] The clarified concentrated magnesium-rich brine stream 43 is next concentrated to the saturation point of sodium chloride. The concentration process may be, for example, concentration in a solar concentration pond, in a thermal process, or a membrane process 50 which produces a low TDS water output stream 51 and a further concentrated magnesium-rich brine stream 52. The further concentrated magnesium-rich brine stream 52 is then introduced into a crystallizer 60, such as a solar concentration pond, thermal crystallizer or membrane crystallizer, in order to produce solid sodium chloride 61.

[0029] As a product of the crystallizer 60, a supernatant product stream 62 (magnesium rich bittern) may be conveyed to an additional optional bittern concentration unit 70. This additional optional bittern concentration unit may be a solar concentration pond, thermal evaporation process, or membrane separation process, which generates a low TDS water output stream 71 and a concentrated magnesium-rich bittern stream 72. The concentrated magnesium- rich bittern stream 72 may be further concentrated to solid state crystals in a thermal or membrane crystallizer 73, resulting in a product consisting primarily of hydrated magnesium chloride 74. In certain aspects, a membrane crystallizer may be a Aquastill BV Multichanneled spiral-wound membrane crystallizer.

[0030] Alternatively, the concentrated magnesium-rich bittern stream 72 may be prilled in dry air process unit 80, and the prilled magnesium chloride hydrate 81 may be dried at elevated temperature(s) in a drying oven 90 in the presence of hydrogen chloride 91 to generate a product consisting of, consisting essentially of, or comprising primarily anhydrous magnesium chloride 92.

[0031] One or more of the water streams with low total dissolved solids (TDS) 31 from the combination of membrane crystallizer/brine concentrator 30, the low TDS water output stream 51 from the concentration process 50, and/or the low TDS water output stream 71 from the concentration process 70 may be introduced as supplemental feed water into a potable water production facility 99.

[0032] FIG. 2 represents another exemplary embodiment 200 of the treatment of the NF reject stream output from a brine processing facility which produces magnesium chloride of acceptable quality for processes such as, but not limited to, electrolytic production of elemental metal magnesium. The divalent rich reject stream 201 is first treated with a nanofiltration unit 210 containing a nanofiltration membrane 210 which is selective for rejection of anions such as sulfate, but has a low selectivity for rejection of cations. This NF membrane reduces the level of sulfate in the nanofiltration permeate 211 to less than or equal to the stoichiometric level of calcium in the permeate. The reject stream 212 from the NF unit 210 may be discharged from the system for separate treatment and/or environmentally-acceptable disposal. Exemplary non-limiting NF units that may be utilized are described in the description of FIG. 1.

[0033] The NF unit magnesium rich permeate stream 211, having been treated to reduce the molar ratios of sulfate-to-calcium to 1 or below, may then be conveyed to a combination membrane crystallizer/brine concentrator 230 configured to produce low TDS water 231, solid calcium sulfate dihydrate 232, and/or concentrated magnesium-rich brine 233. The concentrated magnesium-rich brine stream 233 may be further concentrated in a second concentrator, for example, concentrated in a solar concentration pond, in a thermal process, or a membrane process 250 which can produce a low TDS water output stream 251 and a further concentrated magnesium-rich brine stream 252. The further concentrated magnesium-rich brine stream 252 can then be introduced into a crystallizer 260, such as a solar concentration pond, thermal crystallizer, or membrane crystallizer, in order to produce solid sodium chloride 261.

[0034] As a product of the crystallizer 260, a supernatant product stream 262 (magnesium rich bittern) may be conveyed to an additional bittern concentration unit 270. This additional bittern concentration unit may be a solar concentration pond, thermal evaporation process, or membrane separation process, which generates a low TDS water output stream 271 and a concentrated magnesium-rich bittern stream 272. The concentrated magnesium-rich bittern stream 272 may be further concentrated to solid state crystals in a thermal or membrane crystallizer 273, resulting in a product consisting primarily of hydrated magnesium chloride 274.

[0035] Alternatively, the concentrated magnesium-rich bittern stream 272 may be prilled in dry air process unit 280, and the prilled magnesium chloride hydrate 281 may be dried at elevated temperature(s) in a drying oven 290 in the presence of hydrogen chloride 291 to generate a product consisting of, consisting essentially of, or comprising primarily anhydrous magnesium chloride 292.

[0036] One or more of the water streams with low total dissolved solids (TDS) 231 from the combination of membrane crystallizer/brine concentrator 230, and/or the low TDS water output stream 271 from the concentration process 270 may be introduced as supplemental feed water into a potable water production facility 299.

[0037] FIG. 3 represents another exemplary embodiment 300 of treatment of an NF reject stream output from a brine processing facility which produces magnesium chloride of acceptable quality for processes such as but not limited to, electrolytic production of elemental metal magnesium. The NF reject stream 301 may be received by a NF unit 310 which provides less than 90% rejection of sulfate anions and relatively poor rejection of divalent cations, in order to reduce the molar concentration of sulfate to below the molar concentration of calcium in the permeate stream 311. The resulting reject stream 312 may be sent to waste or fed back into the main saline water intake stream. In certain aspects, relatively poor rejection of divalent cation rejection is rejection less than or equal to 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, or any range derivable therein.

[0038] The NF unit permeate stream 311 with the reduced concentration of sulfate relative to calcium is then processed through another NF stage 320 in which approximately 25% of the flow is rejected, with high selectivity for rejection of all multivalent species (e.g., sulfate, borate, magnesium, calcium, etc.), and permeability to monovalent species (e.g., sodium, etc.). In certain aspects, high selectivity for rejection of multivalent species is rejection rates greater than or equal to 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, or 75%, or any range derivable therein. In certain aspects, permeability to monovalent species is rejection rates less than or equal to 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, or any range derivable therein. This treatment reduces the total volume of the reject stream 321 to less than 5% of the incoming seawater volume, while also ensuring that the molar concentration of sodium ions in the reject stream 321 is reduced to below the concentration of the magnesium ions. In this embodiment, the permeate stream 322 may be sent to waste or fed back into a monovalent ion treatment stream. The reject stream may be further concentrated to total dissolved solids (TDS) concentration of 200,000 to 250,000 ppm, using brine concentration processes (e.g., a brine concentrator, 30, 230, 330) such as hollow fine fiber forward osmosis brine concentrators, ultra high pressure reverse osmosis brine concentrators (e.g., PRO-XP1 by Hydranautics™) and/or osmotically assisted reverse osmosis brine concentrators, with spiral wound or hollow fiber membranes, for example but not limited to, in a process as described in U.S. Patent No. 10,947,143, filed April 1, 2019, and titled: “Desalination Brine Concentration System and Method.” [0039] A membrane crystallization process 330 may be employed to also remove calcium sulfate 332 from the divalent ion stream 333, either before or after the reduction of volume of the reject stream to less than 5% of the incoming seawater volume by 320. The resulting calcium sulfate dihydrate (gypsum) precipitate 332 will be of quality acceptable for use as a commercial product, for example but not limited to, in applications such as fertilizer and construction material. This commercially-viable product has the advantage that, as sulfate concentrations will have been reduced to below the stoichiometric level of calcium, chloride will be the only anion of significant concentrations in the stream, with magnesium and sodium as the principal cations of interest and small amounts of calcium and potassium as other cations of significance. An advantage of the present invention’s approach is that, by adjustment of the number of NF stages, configuration of the NF stages, NF membrane used, and mixing of permeate back into previous NF stages, it is possible to balance the calcium and sulfate concentrations in the incoming feed streams to quantitatively remove both ions as calcium sulfate dihydrate.

[0040] Optionally, if it is desired to further reduce the residual sulfate concentrations to minimal levels, a soluble barium salt such as barium chloride or barium hydroxide 341 may be added to precipitate barium sulfate 342 in a clarifier 340, and produce a clarified concentrated magnesium-rich brine 343.

[0041] The divalent ion-rich stream may be further concentrated beyond 250,000 ppm of TDS concentration using a concentrator 350 such as solar ponds, membrane concentration systems, or thermal evaporation-based concentrators, in order to reach the saturation concentration of sodium chloride (approximately 360,000 ppm). Such concentration would leave a supernatant 352 solution containing predominantly magnesium chloride and a commercially viable sodium chloride product. The sodium chloride product 361 may then be precipitated out using a crystallizer 360. The supernatant solution 362 may then be further concentrated to near the saturation concentration of magnesium chloride (approximately 540,000 ppm) using an additional concentrator 370, such as a membrane concentration system, additional solar ponds, or thermal concentrators. This additional concentration would produce solid magnesium chloride 372 of sufficient quality to serve as a feedstock for electrolytic production of magnesium metal. For example solid magnesium chloride may be produced by prilling in dry air followed by heating under a hydrogen chloride presence at a temperature of greater than 200 °C. One or more of the water streams with low total dissolved solids (TDS) 331 from the combination of membrane crystallizer/brine concentrator 330, the low TDS water output stream 351 from the concentration process 350, and/or the low TDS water output stream 371 from the concentration process 370 may be introduced as supplemental feed water into a potable water production facility 399.

[0042] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Because such modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

[0043] Listing of reference labels:

1, 201, 301 NF-side brine concentration system product of a water purification system, such as but not limited to, an NF-SWRO system

10, 210, 310 NF system selective for rejection of sulfate

11, 211, 311 sulfate-depleted NF permeate

12, 212, 312 sulfate-enriched NF reject

20, 320 NF system for volume reduction

21, 321 magnesium rich reject of second NF system

22, 322 permeate of second NF system

30, 230, 330 membrane crystallizer/brine concentrator

31 , 231 , 331 low TDS permeate

32, 232, 332 calcium sulfate dihydrate (gypsum)

33, 233, 333 concentrated magnesium-rich brine

40, 340 clarifier

41, 341 soluble salt of an alkaline earth metal (e.g., barium salt, calcium salt, etc.)

42, 342 insoluble alkaline earth metal sulfate salt (e.g., calcium sulfate, barium sulfate, etc.)

43, 343 clarified concentrated magnesium-rich brine

50, 250, 350 brine concentration system (solar, thermal, or membrane)

51, 251, 351 low TDS water output of brine concentration system

52, 252, 352 further concentrated magnesium-rich brine

60, 260, 360 sodium chloride crystallization system (solar, thermal, or membrane)

61, 261, 361 sodium chloride

62, 262, 362 magnesium-rich bittern (supernatant product) 70, 270, 370 bittern concentration system (solar, thermal, or membrane)

71 , 271 , 371 low TDS water output of brine concentration system

72, 272, 372 concentrated magnesium-rich bittern

73, 273 crystallizer (thermal or membrane)

74, 274 hydrated magnesium chloride

80, 280 spray dryer (dry air process unit)

81, 281 prilled magnesium chloride hydrate

90, 290 drying oven

91, 291 hydrogen chloride gas

92, 292 anhydrous magnesium chloride

99, 299 potable water production facility