Processes to produce potassium, magnesium and calcium sulphate salts from brines

Abstract

Processes for producing langbeinite (K2SO4.2MgSO4), schoenite (K2Mg(SO4)2.6H2O) and syngenite (K2SO4.CaSO4.H2O) from a bitterns brine are disclosed. The processes include the steps of: a) concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation; b) cooling the first concentrated liquor to -5 °C to 5 °C to produce solids; and c) separating the solids from step b). Langbeinite (K2SO4.2MgSO4) solids are prepared by heating a mixture of the separated solids from step c) and the first concentrated liquor from step a). Schoenite (K2Mg(SO4)2.6H2O) solids are prepared by mixing the separated solids from step c) and a first saturated potassium sulphate and magnesium sulphate solution. Syngenite (K2SO4.CaSO4.H2O) solids are prepared by mixing the separated solids from step c) with a water-gypsum (CaSO4.2H2O) slurry.

Description

"Processes to produce potassium, magnesium and calcium sulphate salts from brines"Technical Field

[0001] The present disclosure relates to processes to produce potassium, magnesium and calcium sulphate salts from brines, in particular langbeinite (K2SO4.2MgSC>4), schoenite (K2Mg(SO4)2.6H2O) and syngenite (K2SO4.CaSO4.H2O).Background

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0003] It is generally known that naturally occurring brines represent a rich resource of valuable potash minerals. In particular, brines with a significant sulphate content can provide a source of the high value fertiliser, potassium sulphate. Sea water derived bitterns and many inland salinas contain such brines.

[0004] Despite the apparent value potential and much research and development effort, only a few commercial operations based on such resources exist e.g. Great Salt Lake (USA), Bonneville (USA), Qinhai (China), SQM (Chile), and the Dead Sea (Israel / Jordan).

[0005] Because of the unlimited resource base and favourable location logistics, sea water represents the greatest development potential. While the extraction of saleable salt, NaCI, from seawater is a well developed commercial operation, utilisation of the concentrated reject brine or “bitterns” for recovery of minerals contained therein is very limited. This is particularly so for the recovery of potassium sulphate from sea water bitterns which contain substantial concentrations of potassium and sulphate ions.

[0006] Research and development activities over the years on potash recovery from sea water and high density lake brines has focussed on evaporation of such brines to deposit crystalline evaporite salts which are mechanically harvested and further processed to recover the potash values.

[0007] This approach requires skill, careful pond management and involves significant capital and operating costs.

[0008] The process as described herein seeks to alleviate some of the aforementioned problems.Summary

[0009] The processes as described herein may be used to produce potassium sulphate and mixed sulphate salts, such as langbeinite (K2SO4.2MgSO4), schoenite (K2Mg(SC>4)2.6H2O) and syngenite (K2SO4.CaSO4.H2O) from brines, in particular brines having a magnesium concentration of greater than 30 g / l.

[0010] One aspect of the disclosure provides a process for producing langbeinite (K2SO4.2MgSO4) from a bitterns brine, the process comprising the steps of:a) concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation;b) cooling the first concentrated liquor to -5 °C to 5 °C to produce solids;c) separating the solids from step b); andd) heating a mixture of the separated solids from step c) and the first concentrated liquor from step a) to produce langbeinite (K2SO4.2MgSO4) solids.

[0011] In one embodiment, step d) comprises heating the mixture of the separated solids from step c) and the first concentrated liquor from step a) to 100 °C - 110 °C. Step d) may be performed for a period of 30 to 60 minutes.

[0012] In one embodiment, the process further comprises the step of separating the langbeinite (K2SO4.2MgSO4) solids and washing the langbeinite (K2SO4.2MgSO4) solids with a saturated potassium and magnesium sulphate solution.

[0013] In one embodiment, liquids separated from the langbeinite (K2SO4.2MgSO4) solids and / or washing solution may be recycled to step a).

[0014] Another aspect of the disclosure provides a process for producing schoenite (K2Mg(SC>4)2.6H2O) from a bitterns brine, the process comprising the steps of:a) concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation;b) cooling the first concentrated liquor to -5 °C to 5 °C to produce solids;c) separating the solids from step b); andd) mixing the separated solids from step c) and a first saturated potassium sulphate and magnesium sulphate solution to produce schoenite (K2Mg(SO4)2.6H2O) solids.

[0015] In one embodiment, step d) may be performed for a period of 20 to 60 minutes.

[0016] In one embodiment, a ratio of separated solids from step c) to the first saturated potassium sulphate and magnesium sulphate solution comprises about 1 kg solids: 1 litre solution.

[0017] In one embodiment, the process further comprises the step of separating the schoenite (K2Mg(SO4)2.6H2O) solids and washing the schoenite (K2Mg(SO4)2.6H2O) solids with a second saturated potassium sulphate and magnesium sulphate solution.

[0018] In one embodiment, liquids separated from the schoenite (K2Mg(SO4)2.6H2O) solids and / or washing solution may be recycled to step a).

[0019] Another aspect the disclosure provides a process for producing syngenite (K2SO4.CaSO4.H2O) from a bitterns brine, the process comprising the steps of:a) concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation;b) cooling the first concentrated liquor to -5 °C to 5 °C to produce solids;c) separating the solids from step b); andd) mixing the separated solids from step c) with a water-gypsum (CaSC>4.2H2O) slurry to produce syngenite (K2SO4.CaSO4.H2O) solids.

[0020] In one embodiment the mixing step may be performed for period of 2-8 hours at 10-30 °C.

[0021] In one embodiment, a ratio of solids from step c) to gypsum (CaSO4.2H2O) in the resulting mixture comprises about 0.8-1.2 moles of gypsum to each mole of K2SO4 in the separated solids.

[0022] In one embodiment, the process further comprises separating the syngenite (K2SO4.CaSO4.H2O) solids and washing with water to remove Na, Mg, and Cl salts entrained in the syngenite solids.

[0023] In one embodiment, liquids separated from the syngenite (K2SO4.CaSO4.H2O) solids may be recycled to step a).

[0024] In one embodiment, the water-gypsum (CaSO4.2H2O) slurry comprises a ratio of (CaSO4.2H2O) to water of about 1:1.

[0025] The processes as defined above may be used to recover potassium sulphate from brines. For example, in some embodiments, the processes defined above may further comprise the steps of:e) leaching the separated langbeinite (K2SO4.2MgSO4), schoenite (K2Mg(SC>4)2.6H2O) solids with water to produce potassium sulphate.

[0026] Alternatively, the process defined above may further comprise the step of: e) leaching the separated syngenite (K2SO4.CaSO4.H2O) solids with water at 50 °C to 80 °C to produce a potassium sulphate solution and gypsum solids, the gypsum solids being subsequently separated and recycled to step d).

[0027] In one embodiment of the processes defined above, the bitterns brine comprises greater than 30 g / l Mg and less than 95 g / l Mg.

[0028] In another embodiment of the processes defined above, the bitterns brine has a specific gravity greater than 1.34 SG or 37°Be.

[0029] In one embodiment of the processes defined above, the solids produced in step b) comprise less than 2.5 %w / w Na.

[0030] In one embodiment of the processes defined above, the solids produced in step b) comprise one or more of schoenite (K2Mg(SC>4)2.6(H2O)), kainite (KMg(SO4)CI.3H2O), and carnallite (KCI. MgCI2.6H2O).Brief Description of Drawing

[0031] Preferred embodiments will now be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:

[0032] Figure 1 is a process flowsheet of one embodiment of a process for producing langbeinite (K2SO4.2MgSO4) from brines as disclosed herein;

[0033] Figure 2 is a process flowsheet of one embodiment of a process for producing schoenite (K2Mg(SO4)2.6H2O) from a brine as disclosed herein;

[0034] Figure 3 is a process flowsheet of one embodiment of a process for producing syngenite (K2SO4.CaSO4.H2O) and potassium sulphate from a brine as disclosed herein; and

[0035] Figure 4 is a graphical representation of K recovery in percentage terms and mass recovery per m3from cooling a series of brines evaporated towards and past a first K saturation point.Description of Embodiments

[0036] The processes as described herein may be used to produce potassium, magnesium and calcium sulphate salts, such as langbeinite (K2SO4.2MgSO4), schoenite (K2Mg(SC>4)2.6H2O), and syngenite (K2SO4.CaSO4.H2O) from brines.GENERAL TERMS

[0037] Throughout this specification, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e. one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms "a", "an" and "the" include plural aspects unless the context clearly dictates otherwise. For example, reference to "a" includes a single as well as two or more; reference to "an" includes a single as well as two or more; reference to "the" includes a single as well as two or more and so forth.

[0038] Each example of the present disclosure described herein is to be applied mutatis mutandis to each and every other example unless specifically stated otherwise. The present disclosure is not to be limited in scope by the specific examples described herein, which are intended for the purpose of exemplification only. Functionally-equivalent products, compositions and methods are clearly within the scope of the disclosure as described herein.

[0039] The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0040] When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.).

[0041] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0042] Reference to positional descriptions, such as lower and upper, are to be taken in context of the embodiments depicted in the figures, and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.

[0043] Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0044] The term "and / or", e.g., "X and / or Y" shall be understood to mean either "X and Y" or "X or Y" and shall be taken to provide explicit support for both meanings or for either meaning.

[0045] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

[0047] The term “about” as used herein means within 5%, and more preferably within 1%, of a given value or range. For example, “about 3.7%” means from 3.5 to 3.9%, preferably from 3.66 to 3.74%. When the term “about” is associated with a range of values, e.g., “about X% to Y%”, the term “about” is intended to modify both the lower (X) and upper (Y) values of the recited range. For example, “about 20% to 40%” is equivalent to “about 20% to about 40%”.

[0048] SPECIFIC TERMS

[0049] The term “bitterns” as used herein refers to a concentrated salt solution formed when halite (NaCI) crystallises from seawater brines, or brines from salt lakes. The concentrated salt solution for salt harvesting may have a specific gravity greater than 1.22, and may contain magnesium, calcium and potassium cations, as well as chloride, sulphate, iodide, bromide and other anions. It will be appreciated that bitterns are a specific type of brine as defined above.

[0050] The term “brine” as used herein refers to a concentrated salt solution having a concentration of from about 3.5 % w / v to about 26 % w / v of sodium chloride and other water-soluble alkali metal and alkaline earth metal salts such as potassium, magnesium and calcium. Brines include, but are not limited to, seawater, those formed naturally due to evaporation of saline groundwater, those generated in mine dewatering activities, or waters discarded from sea water desalination plants.

[0051] It is to be noted that leonite (K2Mg(SC>4)2.4H2O) and schoenite (K2Mg(SC>4)2.6H2O) are virtually identical and differ only by their waters of hydration. As such, throughout this application, the terms ‘leonite’ and ‘schoenite’ should be considered interchangeable.

[0052] The term ‘SOP’ refers to sulphate of potash (K2SO4).

[0053] The term “depleted” means having a lesser mole% concentration of the indicated component than the original stream from which it was formed.

[0054] The term “enriched” means having a greater mole% concentration of the indicated component than the original stream from which it was formed.PROCESSES TO RECOVER MIXED POTASSIUM AND MAGNESIUM SULPHATE SALTS FROM BRINES

[0055] Mixed potassium sulphate salts, such as langbeinite (K2SO4.2MgSO4), schoenite (K2Mg(SO4)2.6H2O), syngenite (K2SO4.CaSO4.H2O) and potassium sulphate may be recovered according to the processes disclosed herein from brines, in particular brines having a magnesium concentration (w / v) greater than 30 g / l. The brines may be from various sources including, but not limited to, evaporative sodium chloride production from seawater, evaporation of concentrate streams from desalination, salt lake brines, bitterns and so forth.

[0056] The brine may have a specific gravity above 1.25, in particular in a range of 1.25 to 1.35.

[0057] The brine may comprise less than 0.25 g / l Ca.

[0058] The brine may comprise from 5 g / l K to 45 g / l K.

[0059] The brine may comprise from 30 g / l Mg to 115 g / l Mg.

[0060] The brine may comprise from 5 g / l Na to 80 g / l Na.

[0061] The brine may comprise from 40 g / l SO4 to 125 g / l SO4.

[0062] The brine may comprise from 150 g / l Cl to 250 g / l Cl.Concentrating the brine

[0063] Various embodiments of the processes as described herein include the step of concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation. It will be appreciated by those skilled in the art that there are several factors which will determine the K concentration approaching saturation including ambient temperature, pressure and humidity and the composition of the brine, in particular the Mg, Na, Cl and SO4 concentrations. The saturation point of K for brines with varying brine compositions may be determined by reference to “Solution balances of the systems of the salts of oceanic salt deposits" by J. D’Ans, XXXI Schedules, Kali-Forschungs-Anstalt Ges.m.b.h (Berlin, 1933).

[0064] The first concentrated liquor may be obtained by evaporating the brine in one or more evaporation ponds. The number of evaporation ponds (or concentration stages) will vary according to the initial concentration of the brine, its composition, the surface area and depth of the evaporation ponds, and the ambient temperature and climatic conditions.

[0065] Alternatively, the first concentrated liquor may be obtained by other well understood conventional mechanical techniques such as pumping from lake bed trenches or sub-surface aquifers.

[0066] It will be appreciated that in some embodiments, depending on the composition of the brine, sodium chloride and magnesium sulphate salts may precipitate from the brine as the K concentration approaches saturation. Such precipitates may be separated from the first concentrated liquor by mechanical harvesting, dredging, centrifugation and other conventional separation techniques as will be well understood by those skilled in the art.Cooling the first concentrated liquor to produce solids

[0067] The first concentrated liquor may be cooled to -5 °C to 5 °C to produce solids.

[0068] The first concentrated liquor may be cooled to -5 °C to 5 °C by using established cooling methods such as evaporative cooling, compression refrigeration,adsorption refrigeration, and other suitable methods. For example, the first concentrated liquor may be passed through a heat exchanger in thermal heat exchange with a refrigerant or cooling medium.

[0069] The solids may be potassium-rich solids. The solids may comprise potassium and magnesium. The solids may be a mixture of potassium and magnesium sulphate salts such as schoenite (K2Mg(SO4)2.6H2O) and leonite (K2Mg(SC>4)2.4H2O) and potassium and magnesium chloride salts such as kainite (KMg(SC>4)CI.3H2O) and carnallite (KCLMgCh etW). It will be appreciated that the term ‘potassium-rich’ as used herein refers to a substance wherein the molar concentration of potassium is more than the molar concentration of each metal present in the substance.

[0070] Advantageously, the solids produced by cooling the first concentrated liquor have a much lower NaCI content that the solids that would be produced and harvested by evaporation of a brine of the same composition. Generally, the solids produced in the cooling step comprise less than 2.5 %w / w Na.

[0071] The solids may be separated from the cooled first concentrated liquor by decantation, centrifugation, filtration and other conventional separation techniques as will be well understood by those skilled in the art.Producing langbeinite ( SO^MgSC ) solids

[0072] The separated solids may then be mixed with a volume of the first concentrated liquor in a ratio of about 1:1 w / v. For example, 1 kilogram of separated solids may be mixed with 1 litre of the first concentrated liquor. The mixture may be heated to 100 °C - 110 °C for a period of 30 to 60 minutes to produce langbeinite (K2SO4.2MgSC>4) solids. Advantageously, up to 90 wt% of the K in the mixture (i.e. crystalline solids and concentrated brine) reports to the langbeinite (K2SO4.2MgSO4) solids.

[0073] The langbeinite (K2SO4.2MgSO4) solids may be separated from the supernatant by filtration, decantation, centrifugation and other conventional separation techniques as will be well understood by those skilled in the art.

[0074] The separated langbeinite (K2SO4.2MgSO4) solids may be washed with a saturated potassium and magnesium sulphate solution to remove entrained supernatant. In one embodiment, the saturated potassium and magnesium sulphate solution may be a solution of langbeinite (K2SO4.2MgSO4). In some embodiments, the separated langbeinite (K2SO4.2MgSO4) solids may be re-pulped with a saturated langbeinite (K2SO4.2MgSO4) solution and subsequently refiltered to produce a high purity langbeinite (K2SO4.2MgSO4) solids product.

[0075] Alternatively, the separated langbeinite (K2SO4.2MgSO4) solids may be washed with a saturated potassium sulphate solution to remove entrained impurities from the first concentrated liquor and produce langbeinite comprising <1% w / w chloride.

[0076] The supernatant from which the langbeinite (K2SO4.2MgSO4) solids have been separated may be recycled and combined with the feed brine to recover additional K, Mg and SO4 values by evaporation. The saturated langbeinite (K2SO4.2MgSC>4) solution from which the high purity langbeinite (K2SO4.2MgSO4) product is separated may similarly be recycled and combined with the feed brine to recover additional K, Mg and SO4 values by evaporation.Producing schoenite (K2Mg(SO4)2.6H2O) solids

[0077] Alternatively, the separated solids may then be mixed with a volume of a first saturated potassium sulphate and magnesium sulphate solution in a ratio of about 1:1 w / v. For example, 1 kilogram of separated solids may be mixed with 1 litre of a saturated potassium and magnesium sulphate solution. The mixture may be reacted for a period of 40 minutes to 60 minutes to produce schoenite (K2Mg(SO4)2.6H2O) solids. Advantageously, up to 100 wt% of the K in the solids reports to the schoenite (K2Mg(SO4)2.6H2O) solids.

[0078] The first saturated potassium and magnesium sulphate solution used in the above step may be prepared at about 50°C. This achieves a maximum potassium to magnesium ratio of >3:1 (mole ratio) in the first saturated potassium and magnesium solution. This ensures that the first saturated potassium and magnesium solutionremoves as little potassium as possible from the feed solids and prevents excess MgSC from reporting to the schoenite product stream.

[0079] The inventors opine that in the above mixing step, the kainite component of the separated solids is readily converted to schoenite which crystallises from solution in a substantially pure form.

[0080] Advantageously, because of the low NaCI content of the separated solids, there is no need to pretreat the separated solids to remove excess NaCI before they are converted to schoenite as would be required for conventionally harvested solids produced merely by evaporation of brines.

[0081] The schoenite (K2Mg(SO4)2.6H2O) solids may be separated from the supernatant by filtration, decantation, centrifugation and other conventional separation techniques as will be well understood by those skilled in the art. Generally, the supernatant comprises less than 30 moles of MgCl2 per 1000 moles of water.

[0082] The supernatant from which the schoenite (K2Mg(SO4)2.6H2O) solids have been separated may be recycled and combined with the feed brine to recover additional K, Mg and SO4 values by evaporation.Producing syngenite (K2SO4.CaSO4.H2O) solids

[0083] Alternatively the separated solids may be mixed with a water-gypsum (CaSC>4.2H2O) slurry whereby the mole ratio of gypsum to K2SO4 is in the separated solids is preferably in the range of 0.8-1.2 and the total water added (via the separated solids and the additional water) is approximately equal to the mass of the separated solids, minus the entrained water within the separated solids. For example, 1 kg of separated solids (7% K by weight, equivalent to 15.6% K2SO4) may be mixed with approximately 0.75 kg of water and 154 g of gypsum (1:1 mole ratio of K2SO4:CaSO4.2H2O).

[0084] The reaction between gypsum and the separated solids is preferably achieved by gradual addition of separated solids to a gypsum-water slurry to avoid forming coarse crystals of schoenite (K2Mg(SO4)2.6H2O), which may be slow to formsyngenite. The reaction is preferably performed at a temperature below 30°C, for example 20-25°C.

[0085] The mixture of syngenite (K2SO4.CaSO4.H2O) produced and supernatant liquor undergoes a solid-liquid separation in suitable separator whereby the syngenite solids can be washed with water to remove Na, Mg, and Cl salts present in the liquor entrained in the syngenite solids. The separated solids and wash liquor can be recycled to the second evaporation pond (4) via line (17) for additional recovery of potassium sulphate, while the gypsum solids are recycled to the syngenite reactor.

[0086] The washed syngenite (K2SO4.CaSO4.H2O) may be dried and sold as-is or alternatively leached with warm (70-80°C) water to extract >90% of contained K2SO4, leaving gypsum for recycle.

[0087] A method for producing langbeinite (K2SO4.2MgSO4) from brine in accordance with one embodiment will now be described with reference to the flowsheet shown in Figure 1.

[0088] Fresh brine (1) is fed to a first evaporation pond (2). Halite and magnesium sulphate salts may be deposited and the remaining brine (3) is decanted and passed to a second evaporation pond (4). The second evaporation pond (4) may also be configured to recover recycled brines and liquors from subsequent processes as will be described later. Further salts may be deposited and the remaining concentrated brine (5) decanted and passed to a third evaporation pond (6). The concentrated brine (5) is further evaporated in the third evaporation pond (6) to produce a first concentrated liquor (7) having a potassium concentration approaching saturation.

[0089] The first concentrated liquor (7) is passed through heat exchanger (8) to a crystalliser (9) where the first concentrated liquor (7) is maintained at a temperature of -5 °C to 5 °C for about 60 minutes and solids are allowed to precipitate. The resulting mixture (10) of solids and the supernatant undergo liquid-solid separation in a separator (11).

[0090] The separated solids (12) are passed to a reactor (13) where they are mixed with a volume of first concentrated liquor (7) in a 1:1 ratio (w / v). The mixture is heatedto 100 °C - 110 °C for a period of 30 to 60 minutes to produce langbeinite (K2SO4.2MgSO4).

[0091] A mixture (14) of the langbeinite (K2SO4.2MgSO4) solids and supernatant undergoes liquid-solid separation in a separator (15). The separated supernatant (16) may be recycled back to the second evaporation pond (4) via line (17) and combined with the concentrated brine or sent to waste via bleed stream (17a).

[0092] The separated langbeinite (K2SO4.2MgSO4) solids (18) are re-pulped in vessel (19) with a wash solution (20) comprising a saturated potassium and magnesium sulphate solution to remove entrained supernatant. The resulting slurry (21) of langbeinite (K2SO4.2MgSO4) solids undergoes liquid-solid separation in a separator (22). The separated langbeinite (K2SO4.2MgSO4) solids (23) may be passed to a dryer (24) and subsequent storage (25). A portion of the separated langbeinite (K2SO4.2MgSO4) solids (23a) may be diverted to prepare the wash solution (20).

[0093] A method for producing schoenite (K2Mg(SO4)2.6H2O) from brine in accordance with another embodiment will now be described with reference to the flowsheet shown in Figure 2, where like features are referred to by like references.

[0094] Fresh brine (1) is fed to a first evaporation pond (2). Halite and magnesium sulphate salts may be deposited and the remaining brine (3) is decanted and passed to a second evaporation pond (4). The second evaporation pond (4) may also be configured to recover recycled brines and liquors from subsequent processes as will be described later. Further salts may be deposited and the remaining concentrated brine (5) decanted and passed to a third evaporation pond (6). The concentrated brine (5) is further evaporated in the third evaporation pond (6) to produce a first concentrated liquor (7) having a potassium concentration approaching saturation.

[0095] The first concentrated liquor (7) is passed through heat exchanger (8) to a crystalliser (9) where the first concentrated liquor (7) is maintained at a temperature of -5 °C to 5 °C for about 60 minutes and solids are allowed to precipitate. The resulting mixture (10) of solids and the supernatant undergo liquid-solid separation in a separator (11).

[0096] The separated solids (12) are passed to a reactor (13) where they are mixed with a volume of a saturated potassium and magnesium sulphate solution (19) in a 1:1 ratio (w / v). The mixture is reacted for a period of 30 to 40 minutes to produce schoenite (K2Mg(SO4)2.6H2O). Heating is not required.

[0097] A mixture (14) of the schoenite (K2Mg(SC>4)2.6H2O) solids and supernatant undergoes liquid-solid separation in separator (15). The separated supernatant (16) may be recycled back to the second evaporation pond (4) via line (17) and combined with feed stream (3).

[0098] The separated schoenite (K2Mg(SC>4)2.6H2O) wet solids (18) may be passed to a dryer (20) and the dried solids (21) delivered to subsequent storage (22). A portion of the separated schoenite (K2Mg(SC>4)2.6H2O) solids (18a) may be diverted to prepare the saturated potassium and magnesium sulphate solution (19).

[0099] A method for producing syngenite (K2SO4.CaSO4.H2O) from brine in accordance with another embodiment will now be described with reference to the flowsheet shown in Figure 3, where like features are referred to by like references.

[0100] Fresh brine (1) is fed to a first evaporation pond (2). Halite and magnesium sulphate salts may be deposited and the remaining brine (3) is decanted and passed to a second evaporation pond (4). The second evaporation pond (4) may also be configured to recover recycled brines and liquors from subsequent processes as will be described later. Further salts may be deposited and the remaining concentrated brine (5) decanted and passed to a third evaporation pond (6). The concentrated brine (5) is further evaporated in the third evaporation pond (6) to produce a first concentrated liquor (7) having a potassium concentration approaching saturation.

[0101] The first concentrated liquor (7) is passed through heat exchanger (8) to a crystalliser (9) where the first concentrated liquor (7) is maintained at a temperature of -5 °C to 5 °C for about 60 minutes and solids are allowed to precipitate. The resulting mixture (10) of solids and the supernatant undergo liquid-solid separation in a separator (11).

[0102] The separated solids (12) are passed to a reactor (26) where they are mixed with a slurry of water (27) and gypsum (28) in an approximately 1:1 mole ratio of potassium sulphate (K2SO4) in the separated solids to gypsum (CaSO4.2H2O). The mixture is reacted for a period 2-8 hours to produce syngenite (K2SO4.CaSO4.H2O) at a temperature of 20-30°C.

[0103] A mixture (29) of syngenite (K2SO4.CaSO4.H2O) solids and supernatant undergoes liquid-solid separation in separator (15). The separated supernatant (16) may be recycled back to the second evaporation pond (4) via line (17) and combined with feed stream (3).

[0104] The separated syngenite (K2SO4.CaSO4.H2O) wet solids (30) are passed to the syngenite leach circuit (31). A small portion of syngenite solids (32) are sent to reactor (26) to seed subsequent batches. The washed syngenite (K2SO4.CaSO4.H2O) (wet) solids are then treated with warm water (70-80°C) (33) to extract the K2SO4 from the syngenite. The K2SO4 liquor (34) is then passed to a SOP evaporative crystalliser (35), producing crystalline K2SO4, which is then dried via dryer (36), before being passed to stockpile (37). The gypsum produced in syngenite leach circuit (31) is recycled to gypsum stockpile (38), where losses of gypsum in the process are made up (39), before being returned to the reactor (26) for subsequent batches.Examples

[0105] The following examples are to be understood as illustrative only. It should therefore not be construed as limiting the embodiments of the disclosure in any way.Example 1

[0106] Several feed brines with the compositions shown in Table 1 were further evaporated until saturated in potassium, depositing additional sodium chloride and magnesium sulphate salts in the process.&Table 1

[0107] Seawater 1 is seawater obtained from the open oceans; Brine 2 is ex Baseggio - density where bitterns are discarded; Brine 3 is early stage seawater bitterns ex Dampier, Western Australia; Brine 4 is an early stage bitterns ex Dampier, Western Australia evaporated to K saturation at 30 °C; Brine 5 is partially evaporated lake brine ex Beyondi, Western Australia; Brine 6 is partially evaporated lake brine ex Lake Way, Western Australia; Brine 7 is near K saturation back mix brine (i.e. Brine + evaporation end brine (EEB) ex Lake Way, Western Australia; and Brine 8 is an EEB from bitterns ex Dampier, Western Australia.

[0108] The composition of brines from different sources, for example, seawater evaporites, inland lakes (salinas) and palaeovalley systems, may differ considerably, sometimes having higher sulphate and lower MgCl2 concentrations than seawater type brines. For feed brines with significant sulphate content, but lower MgCl2 content than seawater, the K saturation point can be much higher e.g. 40-45 g / l K- see Brines 5 and 6 in Table 1.

[0109] Brines 5 and 6 in Table 1 are examples of brines where the K saturation points are 44.2 and 39.6 g / l K, respectively. These values are consistent with MgCl2 concentrations of the two brines at 36.5 and 41.5 moles of MgCl2 per 1000 moles of water respectively.Example 2

[0110] Data obtained on the cooling of seawater brines evaporated to various K concentrations approaching potassium saturation point are provided in Tables 2-4 and plotted in Figure 4.Table 2 - Feed brine assays approaching K saturation (g / l)Table 3 - Solids assays (%w / w)Table 4 - Recoveries to Solids (%) and solids yield (kg / m3) brine feed

[0111] The data summarised in Table 2 demonstrates the importance of K concentration of the feed brine approaching the K saturation point as closely as possible. In this respect, Stage 1 and Stage 2 brines in Table 2 are undersaturated inK. Stage 3 brine is very close to K saturation at 30°C, SG 1.345 and 37.2°Be. Stage 4 brine is K saturated but lower in K than brine 3 because it has been evaporated past the initial K saturation point and some K has been deposited to the evaporite solids.

[0112] Gadre, Rao, and Bhavnagary reported using sea water brine concentrated to 35.5 Be° (1.324 SG) and cooling that brine to 0°C. However, these authors reported only a 20% recovery of potassium chloride at 35.5 Be°, significantly lower than the 53.7% yield of potassium obtained in this application at Be° 37.2 (30°C). This difference is critical to the efficacy of the invention and an advantage that is not obvious from examination of the literature.

[0113] Tables 3 and 4 provide data on the analysis and K yields of the solids produced on cooling of the four sea water derived brines listed in Table 2 from 30°C to 0°C.

[0114] The data demonstrate the variation in K recovery in percentage terms and mass recovery per m3of brine cooled as the brine is evaporated to K saturation and beyond.

[0115] Data in the Tables 3-4, and Figure 4, show how the K grade and K recovery to the respective solids improves dramatically with the approach of the brine K concentration to the maximum possible then falls away as the brine K value drops upon deposition of K rich evaporite salts.

[0116] The achievable first pass K recoveries of 48-59%, and K grades of 5.0-7.5% in, the solids at the maximum brine K concentration are an excellent outcome.

[0117] The results in Tables 3 and 4 demonstrate that a reasonable range of seawater brine compositions can be processed to produce good grade solids at 50+% K first pass recovery. This has important implications in the management of evaporation ponds producing feed brine to the cooling circuit.

[0118] However, the data also demonstrates that cooling of sea water bitterns with less that 30 - 33 g / l K results in either reduced K yield or product grade (or both). Stage 1 brine (Table 2) yields 240 kg solids per m3of brine but the K grade is only3.45% w / w (Table 4). For Stage 4 brine, whilst solids grade is 4.75% K, the mass recovery is only 159 kgs solids per m3of feed brine and the K recovery reduces to 38.01%.

[0119] An important feature of the chilling process proposed is that the solids have much lower NaCI concentrations than the harvest solids that would be produced by evaporation of the same feed brines.

[0120] The Na content of the solids reported in Table 3 are all below 2.4%w / w or 6.1%w / w NaCI.

[0121] Even with lake brine 6 (Table 1) having the very high sodium content of 60+g / l, the resultant solids contain less than 12%w / w NaCI compared to a NaCI content of over 50%w / w in mixed salts that would be generated by evaporation of the same brine (to 10Og / l Mg). See Tables 5 and 6 below.

[0122] Hence, the cooling process is also of value in the treatment of the low MgCl2 lake brines in generating product with relatively low NaCI content.

[0123] This result has significant implications in the subsequent processing of the solids to value products.

[0124] Data on cooling of the low MgCl2 lake brines 6 and 7 in Table 1 are provided in Tables 5 and 6 below.Table 5 - brine assays are g / l, solids assays are %w / w, solids yield kg / m3brine feedTable 6 - brine assays are g / l, solid assays are %w / w

[0125] Cooling of lake brine 6 results in a first pass K yield to solids of 41.6% albeit at a relatively low mass pull of 115 kg per m3of brine treated. However, the product is of high K content reflecting a higher schoenite / kainite ratio compared to that produced from sea water bittern.

[0126] Importantly, the sodium chloride content of the solids is low at around 11.5% w / w relative to the mixed salt that would be generated by solar evaporation of the same brine (to 100 g / l Mg) which would contain >50%w / w NaCI.

[0127] The efficacy of the cooling technique for brines such as 6 and 7 (in Table 1) can be improved by recycle (‘back mixing’) of high MgCh brine (EEB) into the evaporation circuit feed brine early in the evaporation cycle. EEB is the brine remaining at the final stage of evaporation of brines of the type listed in Table 1.Typical EEB will contain > 105g / l Mg ,5-6g / l K and Na.

[0128] In the case of seawater brines, back mixing is not necessary because of its naturally high MgCh content.

[0129] Table 6 provides data on the K grade and recovery upon cooling of brine 7 which was generated by back mixing EEB with the evaporation cycle feed brine 6. Notwithstanding that the solids grade is significantly lower than that produced from raw brine 6 (see Table 5), the % K recovery is improved from 41.6% to 55.2% and the first pass mass recovery increased from 115 to 262 kgs solids per m3of brine. Chemical analysis of these solids suggests a much higher kainite (and carnallite) content relative to those produced via cooling of raw brine without EEB recycle.

[0130] Of particular importance from the Table 6 data is that recycle of the filtrate (obtained from separation of the solids) to the brine evaporation circuit is useful by improving K recovery per cooling cycle as the MgCl2 content of the brine increases with recycle - within certain limits. Also of significance is the result that as the MgCl2 content of the brine increases with recycle, the NaCI content of the solids decreases. The solids generated by cooling of brines 6 and 7 (see Tables 5 and 6) contain ca 11.5% and 5.18% NaCI respectively (based on Na assays).

[0131] In the case of seawater bitterns processing, it is of value, for additional K recovery, to recycle the first (or subsequent) stage cooling filtrate brine to the evaporation pond system at a point prior to bloedite (MgSO4.Na2SO4.4H2O) crystallisation to allow recovery of some of the sulphate deposited prior to K saturation. This will improve subsequent schoenite and kainite yields to solids upon cooling. In this manner, the invention provides for overall yield of K greater than 50% achieved on the first pass.Example 3

[0132] The crude mixed salts (chill solids) resulting from the cooling technique described above can be further processed to SOP by several methods. The route via langbeinite is one such method.

[0133] It has been found that combining a mass of chill solids with a volume of brine of the same or similar composition as the brine cooled to generate the chill solids followed by heating of the mixture to 100 - 110°C results in the rapid formation of langbeinite in high yield.

[0134] For example, treatment of 1 kg of chill solids obtained by cooling concentrated sea water bittern with 1 litre of the same bittern and heating to ca 105°C generated langbeinite product solids containing up to 90% of the K contained in the combined feed (chill solids + brine).

[0135] The K yield to the langbeinite product by this process considerably exceeds the K input via the solids i.e. significant extraction of K from the feed brine also occurs.

[0136] Examples of process outcomes from several chill solids + brine combinations are shown in Tables 7 and 8. Solids to brine ratio is 1 kg: 1 litre; brine assays are g / l, solid assays are %w / w; (a) K recovery to langbeinite product is based on total products; (b) K recovery to langbeinite product based on solids only; [the langeinite product is not washed] DBW refers to dry weight basis.Table 7 - brine assays are g / l, solid assays are %w / wTable 8 - brine assays are g / l, solid assays are %w / w

[0137] The results shown in Tables 7 and 8 all involve reactant inputs of 100 mass units (e.g. gms) of solids to 100 volume units (e.g. mis) of brine. However, the ratio of brine to solids may be altered to achieve a better quality langbeinite product (e.g. lower NaCI content) as this varies slightly with the composition of the feed materials being processed.

[0138] The wet langbeinite filter cake produced in the manner described in this invention has considerable sodium (ca 1%w / w) and chloride (ca 6%w / w) content due to brine entrained in the wet filter cake.

[0139] These impurities are readily removed by washing the crude product with a saturated I^SC / MgSC solution prepared from pure langbeinite product.

[0140] Tables 9 and 10 provide analytical data for the crude and refined langbeinite products, whereby for Table 9 the input ratio of solids to brine is 1 kg: 1 litre and for Table 10 the input ratio of solids to brine is 1 kg: 1.5 litre; brine assays are g / l, solid assays are %w / w; (a) K recovery to washed langbeinite product based on total products; (b) K recovery to washed langbeinite product based on unwashed langbeinite input only; DWB = Dry Weight Basis.

[0141] The K recovery to washed solids is effectively 100% provided that the wash liquor used is saturated in K.Table 9 - brine assays are g / l, solid assays are %w / wTable 10 - brine assays are g / l, solid assays are %w / wExample 4

[0142] The solids prepared via the processes described above are a preferred feedstock for producing schoenite because of their low NaCI content relative to mixed salts that would be generated by merely evaporation of a brine of the same chemical composition.

[0143] Cooling of K saturated sea water bittern produces solids in which the K mineral is primarily kainite. Cooling of brines with lower MgCl2 content than sea water brine results in solids with higher schoenite content than those produced from sea water bitterns - see Tables 5 and 6.

[0144] Processing of the solids to produce schoenite is achieved by agitating the solids with a warm saturated solution of I^SC / MgSC prepared by dissolution of schoenite in water at about 50°C.

[0145] In this manner, the kainite component of the solids is readily converted to schoenite which crystallises from solution in pure form.

[0146] Because of the low NaCI content of the solids, there is no requirement to pretreat them to remove excess NaCI as required for harvested solids produced by evaporation of brines like those listed in Table!

[0147] The quantity of (I^SC / MgSC ) conversion liquor required for complete conversion of the kainite in the solids feed is such that the filtrate from the conversion reaction contains less than 30 moles of MgCh per 1000 moles of water. The conversion liquor input required for treatment of wet chill solids filter cake is less than 1:1 w / v.

[0148] Providing that the I^SC / MgSC conversion liquor is saturated in K, the K yield to schoenite solids is close to 100%, relative to solids input - see Table 11 below.

[0149] The leach liquor is prepared by dissolution of schoenite at an elevated temperature (e.g. 50°C) to ensure that the K:Mg ratio is >3:1. It is preferable that the conversion reaction is carried out above 25 °C to achieve a high K:Mg ratio in the schoenite product. At lower temperatures, excess MgSC may accompany the schoenite product.

[0150] Typical results of treatment of solids to produce schoenite are provided in Table 11, whereby for Table 11 the input ratio of solids to brine is 1 kg: 1 litre; brine assays are g / l, solid assays are %w / w; K recovery (a) to washed schoenite product based on total inputs; K recovery (b) to washed schoenite product based on solids input only; DWB = Dry Weight Basis.Table 11 - brine assays are g / l, solid assays are %w / wExample 5

[0151] The solids produced via the cooling process described above are a preferred feedstock for the preparation of syngenite (K2SO4.CaSO4.H2O) via reaction with gypsum because of their low NaCI and MgCh content, relative to mixed salts that would be generated by merely evaporating brine of the same chemical composition.

[0152] Cooling of potassium saturated sea water bitterns produces solids in which the K mineral is predominantly kainite (KCI.MgSO4.3H2O) and NaCI below 5% water addition to the evaporated solids converts kainite to schoenite which reacts with gypsum to form syngenite at ambient temperature under the conditions described. Typical results of treatment of separated solids to produce syngenite are shown in Table 12. Processing of the separated solids to syngenite is achieved by agitating the solids with a gypsum-water slurry for 2-8 hours, preferably 4 hours at 15-30°C. To achieve the syngenite reaction, water addition is required, the amount of which varies depending on the water content of the incoming separated solids. Total water is relevant to K recovery and includes free water in the wet solid feed. By way of example, the mass of wet solids to reaction was 250 gms with a water content of approximately 90 gms to which 195 gms of water were added, leading to a total water content of approximately 285 gms. At this level of water, the resulting mixture may thicken to the extent that agitation becomes difficult. The water input must be such that the reaction end liquor contains <30 moles of MgCl2 per 1000 moles of water, or the reaction may stall or be incomplete. Under conditions similar to those shown in Table 12, the recovery to the syngenite produced is 70-75% after 3-5 hours. The syngenite product filters and washes well to provide a product low in Na, Mg, and Cl, ideal for processing to high quality potassium sulphate.Table 12 - Brine assays are g / l, solid assays are %w / w

[0153] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A process for producing langbeinite (K2SO4.2MgSO4) from a bitterns brine, the process comprising the steps of:a) concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation;b) cooling the first concentrated liquor to -5 °C to 5 °C to produce solids;c) separating the solids from step b); andd) heating a mixture of the separated solids from step c) and the first concentrated liquor from step a) to produce langbeinite (K2SO4.2MgSO4) solids.

2. The process according to claim 1, wherein step d) comprises heating the mixture of the separated solids from step c) and the first concentrated liquor from step a) to 100 °C - 110 °C.

3. The process according to claim 1 or claim 2, wherein the heating step is performed for a period of 30 to 60 minutes.

4. The process according to any one of claims 1 to 3, wherein the process further comprises the step of separating the langbeinite (K2SO4.2MgSO4) solids and washing the langbeinite (K2SO4.2MgSO4) solids with a saturated potassium sulphate and magnesium sulphate solution.

5. The process according to claim 4, wherein liquids separated from the langbeinite (K2SO4.2MgSC>4) solids and / or washing solution may be recycled to step a).

6. A process for producing schoenite (K2Mg(SO4)2.6H2O) from a bitterns brine, the process comprising the steps of:a) concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation;b) cooling the first concentrated liquor to -5 °C to 5 °C to produce solids;c) separating the solids from step b); andd) mixing the separated solids from step c) and a first saturated potassium sulphate and magnesium sulphate solution to produce schoenite (K2Mg(SO4)2.6H2O) solids.

7. The process according to claim 6, wherein step d) may be performed for a period of 30 to 60 minutes.

8. The process according to claim 6 or claim 7, wherein a ratio of separated solids from step c) to the first saturated potassium sulphate and magnesium sulphate solution comprises about 1 kg solids: 1 litre solution.

9. The process according to any one of claims 6 to 8, wherein the first saturated potassium sulphate and magnesium sulphate solution comprises a solution of K, Mg and SO4 ions.

10. The process according to any one of claims 6 to 9, wherein the process further comprises the step of separating the schoenite (K2Mg(SO4)2.6H2O) solids and washing the schoenite (K2Mg(SO4)2.6H2O) solids with a second saturated potassium sulphate and magnesium sulphate solution.

11. The process according to claim 10 or, wherein liquids separated from the schoenite (K2Mg(SO4)2.6H2O) solids and / or washing solution may be recycled to step a).

12. A process for producing syngenite (K2SO4.CaSO4.H2O) from a bitterns brine, the process comprising the steps of:a) concentrating said brine to obtain a first concentrated liquor having a K concentration approaching saturation;b) cooling the first concentrated liquor to -5 °C to 5 °C to produce solids;c) separating the solids from step b); andd) mixing the separated solids from step c) with a water-gypsum (CaSC>4.2H2O) slurry to produce syngenite (K2SO4.CaSO4.H2O) solids.

13. The process according to claim 12, wherein the mixing step is performed for a period of 2-8 hours at 10-30 °C.

14. The process according to claim 12 or claim 13, wherein a ratio of separated solids to gypsum (CaSO4.2H2O) in the resulting mixture comprises about 0.8-1.2 moles of gypsum to each mole of K2SO4 in the separated solids.

15. The process according to any one of claims 12 to 14, wherein the process further comprises separating the syngenite (K2SO4.CaSO4.H2O) solids and washing with water to remove Na, Mg, and Cl salts entrained in the syngenite solids.

16. The process according to claim 15, wherein liquids separated from the syngenite (K2SO4.CaSO4.H2O) solids are recycled to step a).

17. The process according to any one of claims 12 to 16, wherein the water-gypsum (CaSO4.2H2O) slurry comprises a ratio of (CaSO4.2H2O) to water of about 1:1.

18. The process according to any one of claims 12 to 17, wherein the process further comprises the step of:e) leaching the separated syngenite (K2SO4.CaSO4.H2O) solids with water at 50 °C to 80 °C to produce a potassium sulphate solution and gypsum solids, the gypsum solids being subsequently separated and recycled to step d).

19. The processes as defined in any one of claims 1 to 18, wherein the bitterns brine comprises greater than 30 g / l Mg and less than 95 g / l Mg.

20. The processes as defined in any one of claims 1 to 19, wherein the bitterns brine has a specific gravity greater than 1.34 SG or 37°Be.

21. The processes as defined in any one of claims 1 to 20, wherein the solids produced in step b) comprise less than 2.5 %w / w Na.

22. The processes as defined in any one of claims 1 to 21, wherein the solids produced in step b) comprise one or more of schoenite (K2Mg(SC>4)2.6H2O), kainite (KMg(SO4)CI.3H2O, and carnallite (KCI.MgCI2-6H2O.

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