METHOD OF FORMULATING ALKALI METAL SALTS

Abstract: Methodology for formulating sodium bicarbonate and potassium sulfate. In one embodiment, sodium sulfate and ammonium bicarbonate are reacted to form sodium bicarbonate with the remaining liquor or brine treated with sulfuric acid to remove carbonates with subsequent precipitation of potassium sulfate. A further embodiment employs ammonium bicarbonate, ammonia gas or carbon dioxide to precipitate sodium bicarbonate. The result of the methods is the production of high quality fertilizer and food grade sodium bicarbonate.

Description: METHOD OF FORMULATING ALKALI METAL SALTS TECHNICAL FIELD The present invention relates to a method of formulating alkali earth salts and more particularly, the present invention relates to a method of generating food grade sodium bicarbonate and fertilizer grade potassium sulfate. BACKGROUND ART A significant amount of prior art has been promulgated with respect to the formulation of alkali earth salts. Sodium bicarbonate, as an example, has been prepared in as many different ways as it has been known. Despite this fact, previous unit operations for bicarbonate synthesis have been hampered by inefficient energy use which results directly in increased synthesis costs. As a further limitation, known processes do not make efficient use of the unit operations involved in the preparation of salts. Typically, a single high quality product is formulated with concomitant byproduct formation of a quality inadequate for commercial purposes or that would require too substantial an investment to render them commercially viable. Representative of the prior art is United States Patent No. 3,429,657, issued February 25, 1969, to D'Arcy. The reference discusses a method for recovering and producing potassium salts. In the reference, a potassium bearing brine is reacted with sodium perchlorate to precipitate potassium perchlorate. The potassium is removed by ion exchange with sodium and the free potassium is then combined with chloride, sulfate, nitrate inter alia. INDUSTRIAL APPLICABILITY The present invention has applicability in the fertilizer art. DISCLOSURE OF THE INVENTION One object of one embodiment of the present invention is to provide a method of formulating food grade sodium bicarbonate and potassium sulfate, characterized in that the method comprises the steps of: a) providing a source of liquid sodium sulfate; b) providing a source of ammonium bicarbonate; c) contacting the sodium sulfate and the ammonium bicarbonate; d) precipitating sodium bicarbonate and forming a liquor; e) precipitating sodium bicarbonate and forming a liquor by contacting the liquor from step d) with sodium sulfate; f) saturating the liquor from step e) with sodium sulfate; g) filtering solids from the liquor of step f); h) contacting the liquor from step g) with sulfuric acid to precipitate carbonates; i) cooling the liquor from step h) to 0°C to form Glauber's salt precipitate; j) heating the liquor from step i) to between 30° to 40°C; and k) precipitating potassium sulfate by contacting the liquor from step j) with potassium chloride. A further object of one embodiment of the present invention is to provide a method of formulating food grade sodium bicarbonate and potassium sulfate, characterized in that the method comprises the steps of: a) providing a source of liquid sodium sulfate; b) providing a source of ammonium bicarbonate; c) contacting the sodium sulfate and the ammonium bicarbonate; d) precipitating sodium bicarbonate and forming a liquor; e) precipitating sodium bicarbonate and forming a liquor by contacting the liquor from step e) with sodium sulfate; f) saturating the liquor from step e) with anhydrous sodium sulfate; g) filtering solids from the liquor of step f); h) contacting the liquor from step g) with at least one of ammonium bicarbonate, ammonia gas or carbon dioxide to precipitate sodium bicarbonate; i) cooling the liquor from step h) to 0°C to a precipitate of sodium bicarbonate and sodium sulfate; and j) precipitating potassium sulfate by contacting the liquor from step i) with potassium chloride. It has been found that following the sodium bicarbonate formulation, significant success in cooling the liquor to 0°C is realized for removing sodium sulfate as Glauber's salt and sodium bicarbonate. Glauber's salt solubility in the system is contemplated by the ammonium sulfate-sodium sulfate phase diagram. By increasing the sodium sulfate in the bicarbonate circuit with increased Glauber's salt recycle, there is a tendency to decrease the bicarbonate solubility and increase the process efficiency. Regarding the conversion of the starting reagents to potassium sulfate, particular success has been encountered by maintaining a mole ratio of five (5) or greater for the potassium and ammonium ions. This ratio ensures high conversion efficiency in the second stage of the process. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a process flow diagram illustrating a first part of one process according to the present invention; Figure 1a illustrates a second part of the process illustrated in Figure 1; Figure 1 b illustrates a third part of the process illustrated in Figure 1 ; Figure 2 is a is a process flow diagram illustrating a first part of a variation of the process according to the present invention; Figure 2a illustrates a second part of the process illustrated in Figure 2; and Figure 2b illustrates a third part of the process illustrated in Figure 2. Similar numerals in the figures denote similar elements. MODES FOR CARRYING OUT THE INVENTION Referring now to the drawings, Figures 1 through 1b illustrate the process according to a first embodiment. A source of liquid sodium sulfate 10 dissolved in fresh water and centrate water 12 discussed herein after. The solution is mixed in vessel 14 at 40°C to a specific gravity of 1.30. The solution is filtered in filter 16 which, as an example, may comprise a 5 micron filter. The solids 18 are disposed of while the filtrate 20 is passed into a first sodium bicarbonate crystallization vessel 27. Feeds of water, ammonia and carbon dioxide all denoted by numeral 24 are reacted in vessel 22 in order to synthesize ammonium bicarbonate. Formulated ammonium bicarbonate is centrifuged in centrifuge 26, with the solid product being passed into crystallization vessel 27. A recycle loop 28 recirculates ammonium bicarbonate solids and liquor into reaction vessel 29. The result of the combination in vessel 29 is the formulation of sodium bicarbonate. The mixture is filtered by filter 30 and centrifuged. The sodium bicarbonate is washed with water in vessel 32, centrifuged in centrifuge 34 and the solid retained as food grade sodium bicarbonate. The wash water is returned to vessel 14. The liquor from filter 30 has a specific gravity of 1.25 with the contents including approximately 10.4% sodium sulfate, 17.1% ammonium sulfate, 8% sodium bicarbonate and excess ammonium bicarbonate for reaction with the Glauber's salt (discussed herein after ). The liquor is reacted in a vessel 36 at 40°C with Glauber's salt formulated in the cooling phase of the process, which will be discussed later, to produce sodium bicarbonate from the excess of ammonium bicarbonate from crystallization vessel 29. Alternatively, the ammonium bicarbonate may be added to the second stage (vessel 36) as solid, slurry or solution. To the liquor from vessel 36 is added to solid sodium sulfate from source 41 in vessel 40 to formulate a saturated liquor of sodium sulfate/ammonium sulfate. Sufficient ammonium bicarbonate may be present to complete the reaction is solution or some may be added to result in the liquor having a specific gravity of 1.285. The slurry from vessel 40 is filtered with filter 42. The sodium bicarbonate solids 48 are passed to vessel 32 and the liquor 44 is further processed with additional separation of sodium bicarbonate, which is returned to vessel 32. The liquor 44, is then passed to vessel 46 (Figure 1 A). Circuit volume from the sodium bicarbonate circuit can be controlled by evaporating the purified sodium sulfate in the feed to produce solid sodium sulfate to ensure circuit saturation. Returning to Figure 1A, vessel 46 contains sulfuric acid to precipitate carbonate compounds. The so treated liquor is cooled to 0°C in chiller 48 to recover Glauber's salt and filtered in filter 50. The recovered Glauber's salt is returned to the sodium bicarbonate crystallization vessel 36. The filtrate contains 25.25% by weight ammonium sulfate and up to 11 % by weight sodium sulfate and is passed into a vessel 52 heated to between 30°C and 40°C and combined with solids 65 from filter 66. This solution is passed into vessel 54 where solid potassium chloride is reacted therewith to formulate a 20% by weight solution of ammonium chloride also containing, by weight approximately, 20.2% ammonium chloride, 6.7% potassium chloride, 4.9% sodium chloride, 2.3% as (x) 2 SO 4 , where x = Na, K, and solid mixed crystals of potassium sulfate with 10% - 20% ammonium sulfate. The solution is filtered in filter 56, with the solid fraction containing approximately by weight, 5% potassium chloride, 80% - 85% potassium sulfate, 10% - 15% ammonium sulfate. The solid fraction is combined in vessel 58 with water and potassium chloride brine from vessel 60. The potassium sulfate solid is centrifuged and filtered in filter 62 and recrystallized with a solution of potassium chloride at 25°C. The remaining ammonium sulfate is converted to potassium sulfate. Grades of greater than 98% potassium sulfate are achievable. In further unit operations, the liquor or filtrate from the potassium sulfate operations and specifically from filter 56 is processed in accordance with the unit operations set forth in Figure 1 c. The liquor is evaporated in evaporator in order to concentrate the ammonium chloride liquor such that upon cooling the potassium chloride and residual sulphates are minimized in solution. The solution is filtered with filter 66 with the solid material 67 recycled to vessel 54. The filtrate containing approximately 22% to 30% ammonium chloride is reacted with lime in reactor 68 with liberated ammonia recycled. The calcium chloride formed may be passed to a settler 70 or scrubber 72 depending on intended subsequent uses. Having set forth the process according to this first embodiment, reference will now be made to an example of the process. EXAMPLE 1 BICARBONATE KILL PRIOR TO POTASSIUM SULFATE PROCESS Feed - 1 litre ® 1.3 S.G. 360 g/l Na 2 SO 4 1st STAGE Production of NaHCO 3 Brine Exit at reaction termination: 130g Na 2 SO 4 10.4% Na 2 SO 4 40°C 213.8g (NH 4 ) 2 SO 4 17.1% (NH 4 ) 2 SO 4 1.250 S.G. @ 0.95 I 100g NaHCO 3 8.0% NaHCO, solution This makes 172g NaHCO 3 solids SECOND STAGE ESTIMATE consumes 55g NH 3 A) 25.07g NH 3 + 64.9g CO 2 142.5g CO 2 B) 51.2g NH 3 + 132.6g CO 2 2nd STAGE 0.95 I of brine will dissolve the following: 2nd STAGE Final Solution Composition BICARB KILL 412g (NH 4 ) 2 SO 4 200g NaSO 4 160 X 98 =93.3g H 2 SO 4 160g NaHCO 3 84(2) 1267α H,O 2039g (1.6 1) 1.285 S.G. This becomes: 412g (NH 4 ) 2 SO 4 335g Na 2 SO 4 1267α H,O 2014g @ 1.265 = (1.61) must add Na 2 SO 4 to Saturation of 1.30 S.G. 1.61 x 1.30 = 2080 Therefore: 412g (NH 4 ) 2 SO 4 2079g total (1.61) Cooling 412g (NH 4 ) 2 SO 4 28.7% 116g Na 2 SO 4 8.0% 907 H,O 63% 1435g Solution Feed to Evaporator NH4C1 330.8 g 21.9 KC1 130 g 8.6% NaC1 94.7 g 6.3% X-SO4 50 3.3% H ? O 907α 60.0 1512g @ 33% NH 4 CI then: - 2.8% KCI then: - 2.0% K 2 SO 4 Therefore: 330.8 = 1002 g .33 Evaporation Load = 907 - 623 = 284q 0.79t/t Na 2 SO 4 add 0.5 1 for washing 1.29 t H 2 O / t Na 2 SO 4 KoSO, Reaction a) K 2 SO 4 from (NH 4 ) 2 SO 4 = 412 x 174 = 543g 132 b) K 2 SO 4 from Na 2 SO 4 = 116 x 174 = 142g 142 c) Losses of K 2 SO 4 = -43g TOTAL K 2 SO 4 642g KCI Recovery a) KCI intermig reaction = 685 x 2 x 74 = 582g 174 b) KCI lost to tails = 50g c) Therefore: KCI need = 632g K 2 SO, yield = 642 x 100 = 93.7% 685 KCI Conversion Efficiencv = 582 x 100 = 92.1% 632 BASIS: One Tonne of Na 2 SO 4 feed Turning to Figures 2 through 2b, an alternative processing scheme is schematically depicted. In this reaction scheme, prior to the production of sodium bicarbonate, the liquors are saturated with anhydrite. In this embodiment, sodium bicarbonate is produced in crystallization unit 22 and undergoes generally similar steps as set forth for Figures 1 through 1 B. The brine or filtrate is saturated with anhydrous sodium sulfate in vessel 36 and filtered with filter 38 to remove insolubles which are discarded. The filtrate from this operation is reacted with ammonium bicarbonate in vessel 80. As an alternative, the filtrate could be reacted with ammonia or carbon dioxide to precipitate the sodium bicarbonate. The solution is filtered with filter 82 and the sodium bicarbonate remains. The latter is combined with the sodium bicarbonate from filter 30 and then washed, centrifuged and dried. These steps are not shown. The filtrate remaining has a composition of approximately, on a by weight basis, 10% sodium sulfate, 24% ammonium sulfate and 8% sodium bicarbonate. The solution has a specific gravity of 1.285 at 40°C. From this stage, the filtrate solution is cooled in a chiller 84 to approximately 0°C in order to produce a filtrate containing approximately, on a by weight basis 5% sodium sulfate, 28% ammonium sulfate and 6% sodium bicarbonate. The solution is filtered with filter 86 and precipitated sodium bicarbonate and sodium sulfate are recycled back to the bicarbonate crystallization vessel 32, while the filtrate is reacted with potassium chloride in vessel 88 to synthesize first stage potassium sulfate in a purity range of about 75% to 90%. The solid potassium sulfate is repulped with potassium chloride brine from vessel 92 in vessel 94. This results in high quality, high grade potassium sulfate. The product is washed with water in a conventional washing stage 96 with recycle to vessel 94. The solution from filter 90 is evaporated in evaporator 98 (Figure 2A) to concentrate ammonium chloride liquor whereby upon cooling the potassium chloride and sulfates are minimized. The solution is filtered using filter 100 with the precipitated potassium chloride and (x)SO 4 , where x = K, Na, recycled to vessel 88. The filtrate from filter 100 containing ammonium chloride, potassium chloride and potassium sulfate is passed into evaporator 102. The sodium bicarbonate backs the reaction and as a result, ammonia and carbon dioxide are released. These gases are then scrubbed/handled using suitable techniques. The calcium chloride generated is then discarded or sold. EXAMPLE 2 NO BICARBONATE KILL Feed - 1 litre ® 1.3 S.G. 360 g/l Na 2 SO 4 1st STAGE Production of NaHCO 3 Brine Exit at reaction termination: 130g Na 2 SO 4 10.4% Na 2 SO 4 40°C 213.8g (NH 4 ) 2 SO 4 17.1% (NH 4 ) 2 SO 4 1.250 S.G. @ 0.95 100 g NaHCO 3 8.0%NaHCO 3 solution 907g H,O 1350.8 This makes 172g NaHCO 3 solids consumes 55g NH 3 142.5g CO 2 Resaturation with Na 2 SO 4 : brine will hold 150g Na 2 SO 4 . This brine is then filtered and fed to the second stage NaHCO 3 crystallizer. The exit brine is then cooled to 0°C. Brine composition is : 5.0% Na 2 SO 4 which mean 60g Na 2 SO 4 precipitates as 136g of Na2SO410H 2 O precipitate and remove 76g of H 2 O. Therefore: 907 - 76 = 831 g H 2 O. Brine composition @ 0°C and 1.26 S.G. 70g Na 2 SO 4 353g (NH 4 ) 2 SO 4 100g NaHCO 3 831 α H,O 1354α TOTAL About 1 litre brine K,SO, a) 70α Na SO, x 174 = 85.8 142 b) 353α (NH^.SO, x 174 = 465.3α 132 EXIT BRINE: Boil up to 33.0% NH 4 CI. Release of NH 3 and CO 2 from evaporator but NH 4 CI salts out KCI and not the NaCI. KCI is recovered same as in Example 1. BASIS: One Tonne NaoSO, feed EXAMPLE 3 - BICARBONATE KILL - NO EVAPORATION OF AMMONIUM CHLORIDE Feed Solution: from#1 412 g (NH 4 ) 2 SO 4 335 g Na 2 SO 4 1267 gH ? O 2014 g@ 1.265 = 1.60 I Cooling to 0°C yields a filtered solution of: 412g(NH 4 ) 2 SO 4 28.7% 116gNa 2 SO 4 8.0% 907 α H,O 1435 g solution This brine is then heated to 25 C C where KCI solid is added to produce K 2 SO 4 . The exit brine from the K 2 SO 4 circuit has the following composition: NH4CI 330.8 g 21.9% KCI 130g 8.6% NaCI 94.7 6.3 % x-SO 4 50 g 3.3% x = Na/K 1512g This brine is than heated and reacted with lime to recover the ammonia and bypass the evaporator. The KCI reports to the CaCI 2 brine rather than being recovered in the evaporator. This represents a 15 to 20 % loss of K to the CaCI 2 brine. The KCI in the CaCI 2 brine can be reduced to as low as 1.0% by adding solid Na 2 SO 4 to CaCI 2 /KCI brine. The potassium is effectively collected as apprecipitated of syngenite (CaSO 4 • K 2 SO 4 • xH 2 O) at 0 to 100°C with preferred temperatures of 20 to 30°C so that SO 4 solubility is kept to minimum and the reaction occurs at a reasonable rate. CaCI 2 Brine composition 343.3 g CaCI2 22.5 % 130 g KCI 8.5 % 94.7 g NaCI 6.3 % 50 g x SO 4 32.% (Na/K) 907 α H,O 59.5% 1525 g 100 % 140 g Na 2 SO 4 addition: Exit Brine Exit Cake 234. 8 g CaCI 2 17.8% 15.25 g KCI 1.1 % 310 g CaSO 4 * K 2 SO 4 209 g NaCI 15.9 % + 100 g H2O 50 g x SO 4 3.8 % 807 61.3 % The exit brine can be deep well disposed of and cake can be blended into the K 2 SO 4 product as binder or further processed to remove the CaSO 4 . The cake can be reacted with (NH 4 ) 2 HCO 3 from the NaHCO 3 process feed and the CaSO 4 reacts quickly to produce a brine of (NH 4 ) 2 SO 4 and K 2 SO 4 and a filter CaCI 3 precipitate which is disposed of. The (NHa) 2 SO 4 /K 2 SO 4 brine is recycled to K 2 SO 4 first stage crystallizer.

Claims: CLAIMS 1. A method of formulating food grade sodium bicarbonate and potassium sulfate, characterized in that the method comprises the steps of: a) providing a source of liquid sodium sulfate; b) providing a source of ammonium bicarbonate to precipitate sodium bicarbonate; c) contacting said sodium sulfate and said ammonium bicarbonate; d) precipitating sodium bicarbonate and forming a liquor; e) filtering said sodium bicarbonate; f) saturating liquor from step e) with sodium sulfate; g) contacting said liquor with ammomium carbonate ammonia gas or carbon dioxide to precipitate further sodium bicarbonate; h) filtering precipitated sodium bicarbonate from step g); i) combining sodium bicarbonate precipitate from step e) and h) and washing to form food grade sodium bicarbonate; j) cooling liquor from step i) to 0°C to at least form Glauber's salt precipitate; k) treating liquor from step j) with sulfuric acid to convert carbonate minerals to sulfate minerals and release carbon dioxide gas; I) heating liquor from step k) to between 30°C and 40°C; and m) precipitating potassium sulfate by contacting said liquor from step I) with potassium chloride. 2. The method as set forth in claim 1 , characterized in that the method further includes the step of separating precipitated potassium sulfate and washing with potassium chloride. 3. The method as set forth in claim 2, characterized in that the method further includes the step of treating liquor from said step of separating precipitated potassium sulfate with lime to liberate ammonia gas. 4. The method as set forth in claim 3, characterized in that the method further includes the step of recycling said ammonia gas to step g. 5. The method as set forth in claim 4, characterized in that the method further includes the step of evaporating filtrate from claim 4. 6. The method as set forth in claim 1 , characterized in that said sodium sulfate has a specific gravity of between 1.30 and 1.34 at 40°C. 7. The method as set forth in claim 1 , characterized in that said liquor from step d) has a specific gravity of 1.25 and contains, by weight, 10.4% sodium sulfate, 17.1% ammonium sulfate, between 8% to 12% sodium bicarbonate and an excess of ammonium bicarbonate. 8. The method as set forth in claim 1 , characterized in that said sodium sulfate from step e) comprises Na 2 SO 4 • 10 H 2 O. 9. The method as set forth in claim 1 , characterized in that said liquor from step f) has a specific gravity of 1.285 at 40°C. 10. The method as set forth in claim 1 , characterized in that said liquor from step k) is a saturated liquor of sodium sulfate, ammonium sulfate and sodium bicarbonate. 11. The method as set forth in claim 1 , characterized in that said potassium sulfate is generated in a yield of at least 80% with a purity of at least 98%. 12. The method as set forth in claim 1 , characterized in that said potassium sulfate is generated in a yield of at least 80% with a purity of at least 98%. 13. A method of formulating food grade sodium bicarbonate and potassium sulfate, characterized in that the method comprises the steps of: a) providing a source of liquid sodium sulfate; b) providing a source of ammonium bicarbonate; c) contacting said sodium sulfate and said ammonium bicarbonate; d) precipitating sodium bicarbonate and forming a liquor; e) precipitating sodium bicarbonate and forming a liquor by contacting said liquor from step d) with sodium sulfate; f) saturating said liquor from step d) with sodium sulfate; g) filtering solids from said liquor of step e); h) contacting said liquor from step f) with sulfonic acid to precipitate carbonates; i) cooling said liquor from step h) to 0°C to form Glauber's salt precipitate; j) heating said liquor from step I) to between 30°C to 40°C; and k) treating said liquor from step j) with potassium chloride to precipitate potassium sulfate; I) evaporating liquor from step k) to recover potassium values for recycling to step k); and m) drying said potassium sulfate. 14. The method as set forth in claim 13, characterized in that the method further includes the step of treating liquor remaining from step I) with lime and ammonium chloride. 15. The method as set forth in claim 14, characterized in that ammonia gas is liberated and recycled. 16. The method as set forth in claim 13, characterized in that used potassium chloride solution is recycled to step k).

Inventors: PHINNEY ROBIN, PHINNEY, ROBIN
Applicants: AIRBORNE IND MINERALS INC, PHINNEY ROBIN, AIRBORNE INDUSTRIAL MINERALS INC., PHINNEY, ROBIN
Application year: 1999
Main classification: C01D7
IPC codes: C01D5, C01D7, C05D1, C05D7