Production of nesquehonite-containing slurry
By adding sodium carbonate to bitterns at a specific stoichiometric ratio to produce nesquehonite, the method addresses the inefficiencies in existing bittern processing, enabling high-purity magnesium oxide and potassium sulphate recovery with reduced moisture and contamination.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ECOMAG LTD
- Filing Date
- 2025-12-22
- Publication Date
- 2026-07-23
AI Technical Summary
Existing technologies for processing bitterns derived from seawater do not effectively recover magnesium oxide, salt, or other derivative products, and often result in the formation of double salts that are difficult to filter and process.
A method involving the addition of sodium carbonate to bitterns containing magnesium chloride at a stoichiometric molar ratio of 0.9 to 1.0 to produce a nesquehonite-containing slurry, followed by filtration, washing, and combined drying/roasting to convert nesquehonite to magnesium oxide, while controlling sulphate concentrations to avoid double salt formation.
This method enhances the recovery of nesquehonite, allowing for high purity magnesium oxide production and efficient separation of potassium sulphate, salt, and other derivatives with minimal contamination and moisture content.
Smart Images
Figure AU2025051478_23072026_PF_FP_ABST
Abstract
Description
PRODUCTION OF NESQUEHONITE-CONTAINING SLURRY Technical Field
[0001] The present invention in one aspect is broadly directed to a method of producing a nesquehonite-containing slurry from bitterns containing magnesium chloride. In another aspect the invention is generally directed to a method of treating bitterns such as that resulting from precipitation of seawater in salt production or brines in desalination.Background
[0002] Existing technologies disclose processing of bitterns or other high-sulphate brine solutions derived from seawater. For example, Reward Minerals Ltd have developed a process flowsheet for recovering potassium sulphate (potash) from high-sulphate brines. This involves concentration of the brine prior to its reaction with gypsum to form syngenite from which the required high grade potash is separated. This technology is the subject of their International patent publication no.W02024 / 031139. Reward Minerals recover potash without any disclosures or teachings directed to other resulting products including but not limited to magnesium oxide, salt, or other derivative products typically of a relatively high purity.Summary of Invention
[0003] According to a first aspect of the present invention there is provided a method of producing a nesquehonite-containing slurry, said method involving addition of sodium carbonate (Na2CO3) to bitterns containing magnesium chloride (MgCl2) in a precipitation reaction at a stoichiometric molar ratio of carbonate to magnesium of between 0.9 to 1.0.
[0004] According to a second aspect of the invention there is provided a method of treating bitterns, said method comprising:adding sodium carbonate (Na2CO3) to the bitterns containing magnesium chloride (MgCl2) in a precipitation reaction at a stoichiometric molar ratio of carbonate to magnesium of between 0.9 to 1.0 to produce nesquehonite-containing slurry;filtering the nesquehonite-containing slurry to separate materially all nesquehonite in trapped liquor.
[0005] Importantly the production of nesquehonite in the precipitation reaction at the defined stoichiometric ratio is in preference to the formation of double salts (such as hydromagnesite and dypingite) which are otherwise produced at stoichiometry exceeding the defined range. Advantageously the nesquehonite-containing slurry produced provides increased recovery of nesquehonite in the trapped liquor.
[0006] Preferably the method of treating bitterns also comprises washing the trapped liquor containing nesquehonite to obtain wet cake of a relatively low moisture content at between 15 to 25% free adsorbed water.
[0007] Preferably the method of treating bitterns further comprises combined drying and roasting of the wet cake to produce magnesium oxide at substantially 100% conversion of nesquehonite to magnesium oxide. More preferably said combined drying and roasting is performed at 500 to 800 °C within 1 to 3 hours.
[0008] Importantly the combined drying and roasting of the wet cake is permitted at the relatively low moisture content achieved with filtration and washing of the nesquehonite-containing liquor. On the other hand, in operating the precipitation reaction above the defined stoichiometry, production of double salts means higher moisture content in any nesquehonite which requires drying prior to roasting in separate steps.
[0009] Preferably the method of treating bitterns also comprises desulphation of spent liquor separated from the nesquehonite-containing slurry. More preferably desulphation of the spent liquor involves addition of calcium chloride to the spent liquor to produce hydrated calcium sulphate as a precipitate and a desulphated liquor at or below threshold sulphate concentrations.
[0010] Preferably the method of treating bitterns further comprises evaporation of the desulphated liquor to obtain concentrated brine containing potassium sulphate (K2SO4). More preferably said evaporation of the desulphated liquor crystallises high purity salt (NaCl) in trapped liquor separate from the K2SO4-containing concentrated brine.
[0011] Preferably the method of treating bitterns also comprises addition of calcium sulphate (CaSO4) to the K2SO4-containing brine to produce a syngenite-containing concentrate in a precipitation reaction.
[0012] Preferably the method of treating bitterns further comprises filtering the syngenite-containing concentrate to separate syngenite (CaSO4. K2(SC>4).2H2O) from said concentrate. More preferably said filtering of the syngenite-containing concentrate is effective in separating residual salt (NaCI) brine from the sygenite-containing concentrate. Still more preferably the method also comprises processing of the syngenite-containing concentrate to obtain potassium sulphate (K2SO4) or a derivative thereof.
[0013] Preferably the method of treating bitterns also comprises evaporation of the residual NaCI brine to obtain a high purity NaCI.
[0014] According to a third aspect of the invention there is provided a method of producing a syngenite-containing concentrate, said method comprising:adding sodium carbonate (Na2CO3) to bitterns containing magnesium chloride (MgCl2) in a precipitation reaction at a stoichiometric molar ratio of carbonate to magnesium between 0.9 to 1.0 to produce a nesquehonite-containing slurry;filtering the nesquehonite-containing slurry to separate materially all nesquehonite in trapped liquor;desulphation of spent liquor separated from the nesquehonite-containing slurry to produce a desulphated liquor at or below threshold sulphate concentrations;evaporation of the desulphated liquor to obtain a concentrated brine containing potassium sulphate (K2SO4);adding calcium sulphate (CaSO4) to the K2SO4-containing brine to produce the syngenite-containing concentrate in a precipitation reaction.
[0015] Importantly the desulphation of spent liquor reducing the sulphate concentrations at or below the defined threshold concentrations promotes high purity salt recovery from both crystallisation of NaCI from the trapped liquor, and evaporation of the residual NaCI brine.
[0016] It is to be understood that Na2CO3 may be in the form of synthetic soda ash or natural trona ore, K2SO4 may be in the form of potash, and CaSO4 may be in the form of gypsum.Brief Description of Drawings
[0017] In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a method of producing a nesquehonite-containing slurry from bitterns together with other aspects of the technology will now be described, by way of example only, with reference to the accompanying drawings in which:Figure 1 is a schematic and summary flowsheet depicting application of the various aspects of the invention in the context of solar salt production and resulting streams; Figure 2 is a flowsheet of an embodiment of first and second aspects of the invention together with exemplary mass balances;Figure 3 is a flowsheet of an embodiment of a third aspect of the invention when considered together with the flowsheet of figure 2, both incorporating exemplary mass balances.Detailed Description
[0018] As seen in figure 1, there is a summary flowsheet for application of the present technology to bitterns (typically 4 to 5% Mg) from solar salt production 2. The invention in this context and embodiment produces salt (NaCI) 10 together with key magnesium products 12 and potassium and syngenite by-products 14. In this example the magnesium products include or are derived from hydrated magnesium carbonate (HMC), and syngenite or a derivative thereof such as potassium sulphate or potash,and calcium sulphate or gypsum. It can be seen that the technology boosts regular solar salt production in providing a return stream of NaCI-rich brine for evaporation and production of high purity salt. It can also be seen that the technology recycles spent liquor being rich in potassium for subsequent production of syngenite or derivatives thereof.
[0019] It is thus to be understood that the summary flowsheet of figure 1 is effectively a zero discharge process for treating solar salt bitterns wherein any waste stream may include impurities comparable to or at lower levels as those in seawater. It will be understood that the technology of the present invention in at least its preferred embodiment is likewise applicable to waste brine in desalination of seawater.
[0020] Figure 2 illustrates production of a nesquehonite-containing slurry 20 from which HMC 22 and MgO 24 are derived. In an embodiment of the first aspect of the invention the nesquehonite-containing slurry 20 is produced by addition of sodium carbonate (Na2CO3) or soda ash 26 to bitterns 28 containing magnesium chloride (MgCl2). This precipitation reaction at 27 occurs at a stoichiometric molar ratio of carbonate to magnesium of between around 0.9 to 1.0. This means the precipitation reaction proceeds at a steady state pH wherein the nesquehonite-containing slurry 20 is absent any double salts such as hydromagnesite and dypingite.
[0021] In an embodiment of the second aspect of the flowsheet of figure 2 there is a method of treating the bitterns 28 comprising the steps of:1. adding the soda ash 26 to the bitterns 28 in the precipitation reaction at 27 of the first aspect of the technology to produce nesquehonite-containing slurry 20; 2. filtering at 29 the nesquehonite-containing slurry 20 to separate materially all wet nesquehonite with trapped liquor 30.
[0022] In this embodiment the method for treating bitterns also comprises washing at 31 to remove the trapped liquor 30 contained in the nesquehonite to obtain wet cake 32 of a relatively low moisture content at between 15 to 25% free water. For ease of reference the flowsheet of figure 2 depicts drying at 33 of the wet cake 32 to produce the HMC product 22 which is roasted at 35 to produce the MgO product 24. However,it is to be understood that in the preferred embodiment the drying and roasting steps are combined to produce MgO at substantially 100 percent conversion of nesquehonite to MgO. The combined drying and roasting is performed at around 500°C to 800°C for around 1 to 3 hours.
[0023] Significantly the combined drying and roasting of the wet cake 32 is permitted at the relatively low moisture content of around 20 percent achieved with filtration 29 and washing 31 of the nesquehonite. On the other hand, should the precipitation reaction occur outside the defined stoichiometry, production of double salts means higher moisture content (of 50% or higher) in the resulting liquor which requires drying prior to roasting in separate steps.
[0024] In an embodiment of the third aspect of the invention as illustrated in the flowsheets of figures 2 and 3 there is a method of producing a syngenite-containing concentrate 36. In this embodiment the production method broadly comprises:1. adding soda ash 26 to bitterns 28 in a precipitation reaction at 27 to produce a nesquehonite-containing slurry 20 according to the first and second aspects of the invention;2. filtering the nesquehonite-containing slurry 20 to separate materially all nesquehonite in trapped liquor 30 according to the second aspect of the invention;3. desulphation at 37 of spent liquor 38 separated from the nesquehonitecontaining trapped slurry 20 to produce a desulphated liquor 40 at or below threshold sulphate concentrations;4. evaporation at 41 of the desulphated liquor 40 to obtain a concentrated brine 42 containing potassium sulphate (K2SO4) or potash;5. adding calcium sulphate (CaSO4.H2O) or gypsum 44 to the K2SO4-containing brine 42 to produce the syngenite-containing concentrate 36 in a precipitation reaction at 45.
[0025] In this embodiment of the third aspect the syngenite-containing slurry 36 is filtered at 47 to separate syngenite (CaSC>4. K2 (SC>4).2H2O) 48 from said slurry 36. This filtration at 47 of the syngenite-containing concentrate 36 is effective in separatingresidual salt (NaCI) brine at 50 from the syngenite-containing concentrate product at 48. In this embodiment the residual NaCI brine 50 undergoes evaporation at 53 to obtain high purity salt at 54. It is to be understood that evaporation at 41 of the desulphated liquor 40 is effective in crystallising high purity NaCI 56 in trapped liquor 58 separated from the K2SO4-containing concentrated brine 42. The method may also comprise processing of the syngenite-containing concentrate to obtain potassium sulphate (K2SO4) or potash 52.
[0026] It is to be understood that desulphation at 37 of the spent liquor 38 is effective in reducing the sulphate concentrations of the desulphated liquor 40 to at or below the required level for forming potassium sulphate with the available potassium in the concentrated brine 42. For high sulphate spent liquors it is also if needed better to add Ca chloride at 43 to precipitate Ca sulphate (gypsum) to reduce sulphate concentrations to this level and at the same time produce gypsum for syngenite formation later. If there is a shortage of sulphate for potassium sulphate formation it is required to add sulphate as sodium sulphate at 46. This promotes recovery of high purity salt 56 and 54 by crystallisation of the side stream 58, and evaporation at 53 of the residual brine 50. It is to be understood that without reducing or controlling the sulphate concentrations the resulting NaCI is potentially contaminated with impurities.
[0027] The applicant conducted experiments to explore magnesium recovery in the precipitation reaction for production of the nesquehonite-containing slurry. The stoichiometric ratio of carbonate to magnesium was varied within the preferred range of molar ratios and the Mg recovery and concentration determined as shown below.
[0028] The experiments confirmed formation of a Mg carbonate species which was easy to filter having a relatively low moisture content. A steady state pH was observed during the precipitation reaction which resulted in formation of a more stable precipitate identified on the below XRD analysis as nesquehonite.
[0029] In the examples shown, by aging the slurry after about 120 minutes, it can be seen that nesquehonite is the predominant precipitate. It should be noted that the presence of the double salts like dypingite is more predominant at up to about 120 minutes. This and other double salts such as hydromagnesite disappear on longer aging beyond about 180 minutes. The advantage of producing predominantly nesquehonite is that the free moisture content of this precipitate is around 15 to 25% whereas for the double salt the free moisture content is generally greater than 50%.1: Barringtonite - MgCO3.2H2OPoint 1 180minPoint 1_240min5 10 15 20 25 30 35 40 45 50 55 60 65 702-Theta
[0030] In these experiments the nesquehonite precipitate remained stable at around 150°C. This can be seen in the SEM image below.
[0031] The SEM photo shows the predominant precipitate of nesquehonite (rod-like structure) with traces of double salts (hexagonal plate-like structure). This structure allows opening of the agglomerates, allowing less water retention, leading to lower free moisture in the precipitate. The applicant conducted further experiments involving calcining of the nesquehonite precipitate to produce Mg oxide (MgO) in the temperature range of around 500 to 800°C.
[0032] In at least an embodiment of the first and second aspects, the precipitation of Mg from the rejected bitterns from solar salt fields or concentrated desalination wastes by adding sodium carbonate needs to be at conditions to produce nesquehonite (MgCO3.3H2O). At conditions outside the defined carbonate / Mg molar ratio higher than 1:1 double salts of dypingite (4MgCOs. Mg(OH)2. 5 or 8 H2O) and hydromagnesite (4MgCOs. Mg(OH)2. 4 H2O) are formed. Nesquehonite has a rod-like crystal structure hence does not trap much liquor or washwater compared to dypingite or hydromagnesite with their plate structure. As a result, it is much easier to filter nesquehonite compared to hydromagnesite and dypingite. Hence the nesquehonite product only has 15 - 25% free moisture compared to >50% with the other two double salts above. The conversion of nesquehonite to MgO is in a preferred embodiment carried out in one step roasting (combined drying / roasting) due to its lower free moisture content, compared to double salt materials with >50% moisture which require pre-drying prior to roasting.
[0033] In at least an embodiment of the third aspect, after Mg is removed double salts of Mg / K / Na sulphate or chloride (eg. shoenite, kainite, leonite, carnallite,, etc) willnot form leading to simpler evaporation process to recover potassium sulphate.However, the level of sulphate and potassium needs to be balanced for the formation of the syngenite required for separation from the NaCI brine wherein:1. If there is not enough sulphate to form potassium sulphate, sodium sulphate needs to be added;2. To form syngenite (CaSO4. K2SO4.2H2O) to selectively precipitate potassium sulphate from the brine, gypsum / CaSO4needs to be present.3. If there is a surplus of sulphate to form both potassium sulphate and the double salt syngenite (CaSO4. K2SO4.2H2O) to selectively remove K2SO4, Ca chloride needs to be added to remove surplus sulphate;4. As gypsum is reproduced when syngenite is further processed to recover potassium sulphate the level of sulphate has to be properly balanced so not to have excess sulphate in the final NaCI brine which would contaminate the final salt product.
[0034] In these embodiments proper mass balance needs to be conducted for different brines containing various levels of potassium, sulphate and chloride to allow the correct addition of required amounts of sodium sulphate, calcium chloride and extra gypsum to effectively recover potash as syngenite. The remaining brine contains mostly NaCI salt which can be further evaporated to produce high purity salt products.
[0035] It is to be understood that to completely recover substantially all mineral products from the bitterns discharged from a typical solar salt operation both magnesium and sulphate have to be removed to avoid the precipitation of double salts (Mg, K, Cl and S04) such as leonite: K2SO4. MgSO4.4H2O, kainite:4KCI.4MgSO4.11H2O, schoenite: K2SO4. MgSO4.6H2O, etc. Due to low Ca in the bitterns (generally <200 - 300 mg / L) double salts of Ca with Mg and Na are avoided. The crystallisation of K, Mg double salts is seen on the evaporation curves of Na, K, Mg and sulphate as shown below.
[0036] In one example a dilute bittern (at SG 1.075) was evaporated slowly to SG 1.3 and cooled down to observe the variation of Na, K, Mg and sulphate. It can be seen that only Na as NaCI does not crystallise in the range SG 1.075 - 1.25 as the concentration of Na varies in the same ratio compared to evaporation ratio. However, the concentration of Mg, K and SO4 increases at a lower rate compared to evaporation, indicating they have precipitated as evaporation takes place. In the context of the present invention it is to be understood that sulphate can be removed from either (1) the original bitterns before Mg is recovered, or (2) the high sulphate spent liquor after Mg is precipitated as HMC.
[0037] Option 1 in removing sulphate from the original bitters may be achieved as set out below in either of examples 1 or 2.Example 1
[0038] To remove sulphate as CaSO4, Ca chloride (either as anhydrous CaCI2 or di-hydrate CaCI2.2H2O) is added to the bitterns at different Ca: S molar ratios as shown below. Sulphate concentrations in these tests were measured as S by Inductively Coupled Plasma (ICP) equipment. The conversion of S to sulphate is: SO4 (ppm or mg / L) = S (mg / L) x 2.996).
[0039] Residual sulphate measured as S in the liquors after treatment varied from 1.48 g / L at Ca: S molar ratio of 1:1 to 0.501 g / L at 1.3:1 Ca: S molar ratio. As the precipitation of SO4 by Ca is selective, high purity CaSO4 > 99% was produced after filtration and washing.Example 2
[0040] As shown below after the SO4 is removed from the spent liquor the addition of by Ca chloride at a Ca: S molar ratio of 1:1, the addition of Ba chloride (anhydrous or di-hydrate) substantially removed SO4 to < 50 ppm. This is understood to be because the solubility of BaSO4 is much lower than for CaSO4.. &.> £[ ¥
[0041] This sequential precipitation allows high purity CaSO4 and BaSO4 to be recovered separately as precipitation-by-products. This can be seen from the sulphur removal results in the table below.
[0042] Option 2 in removing sulphate from the high sulphate spent liquor may be achieved as set out below in example 3.Example 3
[0043] In this example CaCl2 is added to the spent liquor after Mg is recovered from a spent bittern according to the earlier embodiments e.g. by adding soda ash (Na2CO3) at CO3: Mg molar ratio of 0.95 - 1.2:1. By way of example, the spent bittern may be of the following composition:Na K Ca Mg S SO4 mg / kg mg / kg mg / kg mg / kg mg / kg mg / kg50,768 9,802 117 550 8,896 26,654
[0044] In this example, the conditions for removal of sulphate based on a Ca: SO4 molar ratio of 0.9:1 are set out below:Sulphate removal from bitternsCaClj + SO / ■■■> CaSO4+ 2CI-:qiBittern1.248|kgSO4in bittern 0.28|molCa added 0.25|molCaCl2.2H2O* 37.08|gWater for dissolving 126.13|mL_ _*99% grade
[0045] In this case an amount of 37.08 g of CaCI2.2H2O was dissolved in 126 mL of water (0.25 mol) to react with the above spent bittern containing 0.28 mol of SO4. CaSO4 was precipitated and reached steady state within 20 min, as shown in the table below listing the decrease in sulphate concentration with time.Time, min SO4 remained, mg / kg % SO4 removal0 26,654 0.05 5,538 79.710 5,185 81.020 5,426 80.130 5,184 81.040 4,704 82.850 4,917 82.060 5,060 81.5
[0046] Similar to Example 2, BaCI2 can thereafter be added to remove the residual sulphate to <50 ppm SO4 as the solubility of BaSO4 is much lower than for CaSO4. The resultant liquor is a pure mixture of NaCI and KCI.
[0047] In a variation on this technology a mechanical vapour recompression (MVR) crystalliser could instead of syngenite precipitation be used to separate and recover NaCI alone. This is due to the fact the solubility of NaCI (in mol / L) is much higher than KCI at temperatures <60 deg C.
[0048] Depending on the type of bitterns chosen for processing (TDS 250 - 310 g / kg, with Mg in the range 40 - 80 g / kg) it is possible to evaporate the solution to recover NaCI selectively. At higher TDS >280 g / kg and Mg >40 g / L the Na / K weight ratio is in the range 8- 10:1. This is ideal for evaporation of the mixture of NaCI and KCI to selectively crystallise NaCI leaving a spent liquor saturated with NaCI and residual KCI. By evaporating the NaCI-KCI brine to 95%, 89.9% of NaCI could be crystallised, while KCI still remains in solution, not yet reaching saturation at 20-30 deg C. The following mass balance shows the amounts of fresh water recovered (95%) and NaCI recovered (89.9%), leaving a residual NaCI-KCI mixture as water treatment or salt-lick products.EVAPORATION TO RECOVER WATER USING A MVR CIRCUIT37.35RecoverySTART, g / kg water89,9%0.0%95%Residual concentration KC: not reaching saturationLiquor from MgO plant7,500 Residual brinet / yearNaCl recovered Residual NaClKCl recovered Residual KClWater regenrated Water left inresidual brine
[0049] It is to be understood that in removing sulphate from the high sulphate spent liquor, the removal of sulphate is first based on the use of CaCI2 to precipitate CaSO4. Polishing of the spent liquor is also possible to remove Ca and Mg to < 20 ppm to facilitate the production of high purity NaCI subsequently, using combined NaOH and Na2CO3. The applicant has conducted testwork where SO4 level is reduced to <500 ppm using CaCI2. The second stage of sulphate removal is based on BaSO4 precipitation using BaCI2 to reduce the sulphate level to <50 ppm.
[0050] It is to be understood that this embodiment of the process employing MVR does not discharge any waste, yet recovers substantially all mineral products from the bitterns as HMC, high purity NaCI and NaCI-KCI mixed salt. The mixed salt of NaCI- KCI has application as a water treatment chemical or as an animal feed (salt licks). It will be understood that water is also regenerated from the MVR circuit to be re-used in the process.
[0051] Now that an embodiment of the various aspects of the technology have been described it will be apparent to those skilled in the art that the production ofnesquehonite-containing slurry and other aspects of the invention possess the following advantages:1. the overall flowsheet is effectively a zero-discharge method or process recovering substantially all magnesium and potassium values together with salt (NaCI) from bitterns;2. the production of nesquehonite in the precipitation reaction involving sodium carbonate at the defined stoichiometric ratio avoids formation of double salts which are difficult to filter or otherwise remove;3. the relatively dry nesquehonite wet cake derived from the nesquehonitecontaining slurry lends itself to combined drying / roasting which is not otherwise possible in the presence of double salts leading to higher moisture content of the precipitate;4. the desulphation of spent liquor derived from the nesquehonite-containing slurry ensures high purity salt recovery with limited contamination from impurities.
[0051] Those skilled in the art will appreciate that the invention as described herein is susceptible to variations and modifications other than those specifically described. For example, the invention may extend to derivatives of compounds involved in precipitation reactions of the technology, or extend to natural or synthetic compounds including the defined reactants. For example, the defined Na2COs of the precipitation reaction to produce nesquehonite-containing slurry may be delivered in the form of synthetic soda ash or natural trona minerals. Similarly, the defined CaSCU in the precipitation reaction to produce syngenite-containing concentrate may be delivered in the form of gypsum.
[0052] All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.
Claims
Claims1. A method of producing a nesquehonite-containing slurry, said method involving addition of sodium carbonate (Na2CO3) to bitterns containing magnesium chloride (MgCl2) in a precipitation reaction at a stoichiometric molar ratio of carbonate to magnesium of between 0.9 to 1.0.
2. A method of treating bitterns, said method comprising:adding sodium carbonate (Na2CO3) to the bitterns containing magnesium chloride (MgCl2) in a precipitation reaction at a stoichiometric molar ratio of carbonate to magnesium of between 0.9 to 1.0 to produce nesquehonite-containing slurry;filtering the nesquehonite-containing slurry to separate materially all nesquehonite in trapped liquor.
3. The method of claim 2 also comprising washing the trapped liquor containing nesquehonite to obtain wet cake of a relatively low moisture content at between 15 to 25% free adsorbed water.
4. The method of claim 3 further comprising combined drying and roasting of the wet cake to produce magnesium oxide at substantially 100% conversion of nesquehonite to magnesium oxide.
5. The method of claim 4 wherein said combined drying and roasting is performed at 500 to 800 °C within 1 to 3 hours.
6. The method of any one of claims 2 to 5 also comprising desulphation of spent liquor separated from the nesquehonite-containing slurry.
7. The method of claim 6 wherein desulphation of the spent liquor involves addition of calcium chloride to the spent liquor to produce hydrated calcium sulphate as a precipitate and a desulphated liquor at or below threshold sulphate concentrations.
8. The method of claim 7 further comprising evaporation of the desulphated liquor to obtain concentrated brine containing potassium sulphate (K2SO4).
9. The method of claim 8 wherein said evaporation of the desulphated liquor crystallises high purity salt (NaCI) in trapped liquor separate from the K2SO4-containing concentrated brine.
10. The method of claim 9 also comprising addition of calcium sulphate (CaSO4) to the K2SO4-containing brine to produce a syngenite-containing concentrate in a precipitation reaction.
11. The method of claim 10 further comprising filtering the syngenite-containing concentrate to separate syngenite (CaSO4. K2(SC>4).2H2O) from said concentrate.
12. The method of claim 11 wherein said filtering of the syngenite-containing concentrate is effective in separating residual salt (NaCI) brine from the sygenite-containing concentrate.
13. The method of claim 12 also comprising processing of the syngenite-containing concentrate to obtain potassium sulphate (K2SO4) or a derivative thereof.
14. The method of either of claims 12 or 13 also comprising evaporation of the residual NaCI brine to obtain a high purity NaCI.
15. A method of producing a syngenite-containing concentrate, said method comprising:adding sodium carbonate (Na2CO3) to bitterns containing magnesium chloride (MgCl2) in a precipitation reaction at a stoichiometric molar ratio of carbonate to magnesium between 0.9 to 1.0 to produce a nesquehonite-containing slurry;filtering the nesquehonite-containing slurry to separate materially all nesquehonite in trapped liquor;desulphation of spent liquor separated from the nesquehonite-containing slurry to produce a desulphated liquor at or below threshold sulphate concentrations;evaporation of the desulphated liquor to obtain a concentrated brine containing potassium sulphate (K2SO4);adding calcium sulphate (CaSO4) to the K2SO4-containing brine to produce the syngenite-containing concentrate in a precipitation reaction.