GB2068918A - Potassium sulphate and potassium sodium sulphate production - Google Patents
Potassium sulphate and potassium sodium sulphate production Download PDFInfo
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- GB2068918A GB2068918A GB8000601A GB8000601A GB2068918A GB 2068918 A GB2068918 A GB 2068918A GB 8000601 A GB8000601 A GB 8000601A GB 8000601 A GB8000601 A GB 8000601A GB 2068918 A GB2068918 A GB 2068918A
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
- C01D5/06—Preparation of sulfates by double decomposition
- C01D5/10—Preparation of sulfates by double decomposition with sulfates of magnesium, calcium, strontium, or barium
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Abstract
Sylvinite and calcium sulphate are reacted in aqueous ammonia to produce a potassium sulphate- sodium sulphate double salt. The potassium sulphate-sodium sulphate double salt thus formed is washed with ammonia solution and then leached out from any unreacted calcium sulphate and inerts with water and the sodium sulphate converted directly with sylvite or sylvinite in aqueous ammonia solution to potassium sulphate which is simultaneously salted-out. The ammoniacal solutions from the various stages is passed to a distillation column and ammonia is recycled. <IMAGE>
Description
SPECIFICATION
A process for the manufacture of potassium sulphate-sodium sulphate double salt and potassium sulphate from calcium sulphate and sylvinite in aqueous ammonia solutions
The present invention relates to a process for the manufacture of potassium sulphate-sodium sulphate double salt and of potassium sulphate via potassium sulphate-sodium sulphate formation by the interaction of calcium sulphate with sylvinite in aqueous ammonia solution and it is based upon the equations:
No prior information on the direct or indirect conversion of calcium sulphate with sylvinite to potassium sulphate-sodium sulphate double salt is known, nor has there been any previous information published on the production of potassium sulphate from calcium sulphate with sylvinite.
Prior processes that use ammonia as an adjubant substance to drive the reaction in the desired direction use potassium chloride containing less than or about 11 per cent sodium chloride. These processes disclosed in the U.K. Patents Nos. 437,652, 717,998 and U.S. Patent No. 2,882,128 are based upon the equation:
The direct conversion of calcium sulphate and potassium chloride to potassium sulphate and calcium chloride in aqueous solutions is not possible. Processes that operate in aqueous solution form double salts such as syngenite (K2SO4 CaSO4. H2O) and/or penta-salt (K2SO4 SCaSO4 H2O), and these salts are subsequently decomposed to obtain K2SO4.
The main disadvantage of the processes disclosed in the above patents for the direct formation of potassium sulphate from calcium sulphate and potassium chloride in aqueous ammonia solutions are:
a) Require relatively high purity potassium chloride (with less than or about 11 per cent sodium chloride).
b) To operate at normal temperature (about 250C) high ammonia concentration in solution is needed (about 50% by weight or above).
c) In order to obtain such ammonia concentration in solution sufficient elevated pressure is needed (about 3kg/cm2 or more).
d) Require calcium sulphate free of inert materials to prevent contamination of the final product.
If operation of said processes at atmospheric pressure and lower ammonia concentration in solution is desired (40% by weight ammonia), then the conversion must be conducted at temperatures below 5 C.
The main disadvantage of the processes via syngenite and/or penta-salt formation in aqueous solution is owing to the fact that potassium chloride and calcium sulphate react only to a very limited extent, with the mother-liquor containing up to about 22% potassium chloride concentration, therefore, concentration of the mother-liquor by evaporation is necessary in order to avoid excessive potassium chloride losses. The presence of sodium chloride in the potassium chloride has a very negative effect on the yields of the double salts. No formation of sodium sulphate from calcium sulphate and sodium chloride has been reported before.
The main advantages of the proposed process object of this invention over the procedures disclosed in the above literature are:
a) Sylvinite containing between about 20 and about 80% sodium chloride can be used.
b) It becomes possible to greatly reduce the ammonia concentration in solution (to about 36% by weight).
c) At this low ammonia concentration the conversion process can be operated essentially at normal pressure and temperature. The term "normal pressure and temperature" is used in this
Specification to denote about or slightly above atmospheric pressure and temperature of about or slightly above 200 C.
d) The potassium sulphate produced in accordance with the present invention is of much larger grain size than it is possible to obtain by the procedures disclosed in the above patents that use sylvite instead of sylvinite.
e) The potassium sulphate-sodium sulphate double salt produced in accordance with the proposed process object of this invention can be used also as a source of sodium sulphate in addition to potassium sulphate.
The discovery that sylvinite of composition between about 2080% NaCI and 8020% KCI can be used directly for the conversion of calcium sulphate to potassium sulphate is of great industrial significance since most of the potassium chloride is present in nature as a mechanical mixture of sylvite (KCI) and halite (naCI) known as sylvinite. Common-sylvinite ores contain about 4070% halite and 6030% sylvite. Expensive potassium chloride up-grading treatments of these ores are required at present to render the potassium chloride usable for the manufacture of potassium sulphate.
In the first part of the research and development work leading to the present invention it was found that selection of the appropriate ratio of gypsum to potassium chloride in the sylvinite, ratio of potassium chloride to sodium chloride in the sylvinite, ratio of gypsum to aqueous ammonia solution, gypsum grain size, reaction time, reaction temperature, stirring speed and concentration of ammonia in solution permits a high efficiency conversion of calcium sulphate and potassium chloride to potassium sulphate. In the second part of the work it was found that selection of the appropriate leaching method, leaching temperature, leaching time and ratio of potassium sulphate-sodium sulphate double salt cake to leaching water permits the efficient extraction of the potassium sulphate-sodium sulphate product from any unreacted calcium sulphate and inerts.In the third part of the work it was found that by mixing the extract from the leaching operation with potassium chloride (in the pure state or as sylvinite) in calculated amounts to react with all the sodium sulphate and calcium sulphate present in said extract and ammonia added permits the formation of high purity potassium sulphate of a uniform large-grain size. In a fourth part of the work it was found that an "alternative" to leaching could be used, this alternative consists in mixing the washed unleached potassium sulphate-sodium sulphate double salt cake with a calculated amount of potassium chloride (in the pure state or as sylvinite), water and ammonia. This procedure gives the same potassium sulphate yields as when saturated solutions of reactants are used.In the fifth part of the work it was found that by operating the gypsum conversion step at an ammonia concentration in solution of about 40% by weight, conversions as high as 98% for potassium chloride could be obtained, provided a sufficiently high pressure is applied of about 2.5 kg/cm2 absolute. In the sixth part of the work it was found possible to reduce the minimum ammonia concentration in solution to less than 40% by weight, by operating the gypsum conversion step at temperatures below 200 C. In the seventh part of the work it was found that by appropriate selection of the process variables it was possible to produce a product in the calcium sulphate-syivinite converter with a chemical composition corresponding to glaserite.It was found advantageous with calcium sulphate of small grain size to mix it with the ammoniacal solution prior to their addition to the sylvinite in the converter. This procedure prevents pelletization of said calcium sulphate in the converter, thus increasing the rate conversion of reactants.
The possibilities of technical realisation of the process of the present invention is based among other things, upon the following discoveries:
1) Sylvinite of composition about 2080% sodium chloride and 8020% potassium chloride can be used for the conversion of calcium sulphate to potassium sulphate via potassium sulphatesodium sulphate doublt salt formation. For equation (i) to occur it is necessary to use large excess NaCI above the stoichiometric ratio. The need for so much excess NaCI is of great advantage since it permits the use of sylvinite containing low amount of KCI which is the most common ore in nature.
2) About 5% excess natural gypsum over the potassium chloride stoichiometric ratio of equation (i) is required to obtain potassium chloride conversions of about 95% or more with sylvinite containing about 2080% sodium chloride, at ammonia concentration in solution of about 36% by weight, reaction temperature of about 200 C, pressure slightly above atmospheric pressure, ratio of gypsum to aqueous ammonia solution about 1/7 or lower and reaction time about 60 minutes.
3) The potassium sulphate-sodium sulphate double salt can be efficiently separated from any unreacted gypsum and inerts by leaching it with water.
4) The sodium sulphate and any calcium sulphate in the extract can be efficiently converted to potassium sulphate by adding the required amount of potassium chloride (as sylvite or sylvinite) according with equations (ii) and (iii), and the ammonia needed to form a solution containing about 1536% by weight of ammonia.
5) It is technically possible to operate the gypsum conversion step with no excess gypsum above the stoichiometric ratio given by equation (i) and still get potassium chloride conversions above 95% provided that the ammonia concentration in solution is raised to about 40% by weight, but this condition requires operation under pressure. It is also technically possible to operate the gypsum conversion step with no excess gypsum, at ammonia concentration in solution below 40% by weight and still get potassium chloride conversion of 95% or more provided that highly reactive gypsum is used or that the conversion temperature is lowered to about 1 OOC. In the three alternatives proposed above, no leaching step is required when using reagents free of inerts, since about 98% of the gypsum is converted to K2SO4-Na2SO4 double salt.
6) It has been found also possible to operate the sodium sulphate conversion step and potassium sulphate crystallisation using slurries of reactants in saturated solutions. Any unreacted gypsum present is efficiently converted in this operation. No leaching is required if this procedure is followed.
A most important objective of this invention is to provide a method whereby calcium sulphate can be converted to potassium sulphate-sodium sulphate double salt with sylvinite of a composition of about 2080% sodium chloride and 8020% potassium chloride.
Another important objective of this invention is to provide a method whereby calcium sulphate can be converted via potassium-sodium sulphate to potassium sulphate with sylvinite of a composition of about 2080% sodium chloride and 8020% potassium chloride at about normal conditions, given potassium chloride and calcium sulphate conversion efficiencies of about 95% or higher.
Another important objective of this invention is to provide a method whereby the potassiumsodium sulphate formed is separated from any unreacted gypsum and inerts by leaching the cake with water and the extract solution treated with sylvite or sylvinite and ammonia to crystallise out high purity potassium sulphate of uniform large size crystals.
Another important objective of this invention is to provide a method for the manufacture of potassium sulphate from gypsum and sylvinite in which the reactants may contain a large amount of inert materials since they will be removed in the leaching operation.
Another important objective of this invention is to provide a method for the manufacture of a product with a chemical composition corresponding to that of Glaserite and its conversion to K2SO4.
A further important feature of this invention is that by adding a calculated amount of sylvinite to the aqueous potassium-sodium sulphate extract, any calcium sulphate dissolved in the leaching operation is converted to potassium sulphate in the crystalliser thus preventing scaling formations.
It has been established experimentally that it is possible to obtain potassium chloride conversion efficiency of about 95% or higher. It has been established also that all the potassium-sodium sulphate formed can be leached from any unreacted gypsum and inerts with water at saturation. In addition it was established that the sodium sulphate conversions to potassium sulphate with sylvite or sylvinite and potassium sulphate recovery in the salting-out operation with ammonia gas was about 99.5% efficient. The only potassium chloride losses being in the gypsum-sylvinite conversion step, all the other streams being recycled to the process.
In the process described in this invention, the sulphate carrier, calcium sulphate may be used in any desired form, such as gypsum, hemihydrate or anhydrite.
The ammonia is recovered from the mother-liquor either by distillation or by the known process of precipitation of calcium chloride ammonates and decomposition of said ammonates.
The process object of this invention produces as a by-product a highly concentrated solution of sodium and calcium chlorides which may be processes to give high purity sodium chloride crystals and concentrated calcium chloride solution which can be used as an antifreezing agent.
The following practical examples of the method of this invention are described below for the purpose of illustration but not of limitation. All parts are given by weight.
EXAMPLE 1
100 parts of gypsum containing 98.2% CaSO4. 2H2O are mixed in a vapour-tight reactor with 720 parts of aqueous ammonia solution containing 37.5% by weight of ammonia and 149.4 parts of sylvinite containing 56.8% NaCI plus 42.7% KCI are added. The resulting mixture is stirred for about one hour at 200C. The product of the reaction is passed through a filter and the cake formed is washed on the filter with water saturated with ammonia. The filtrates and washings are treated in a distillation unit for the recovery of ammonia and the ammonia recovered is recycled to the process. The cake is freed from its adhering liquor by heating it in a drier and the vapours are vented to a condenser for the recovery of ammonia.
The resulting solid product (95.8 parts), consists of:
70.2 parts of K2SO4
20.3 parts of Na2SO4
4.2 parts of CaSO4. 2H2O 1.1 parts of inerts
These data represent conversion efficiencies of 94.2% for KCI,95.7% for CaSO4. 2H2O and 19.7% for
NaCI.
In order to show the effect of varying the temperature at which the method of this invention is carried out on the conversion of gypsum with sylvinite to potassium sulphate-sodium sulphate double salt, a second test was conducted using the same procedure as above with another portion of the same mixture except that the mixture was stirred at OOC instead of 200 C.
The solid product thereby formed (95.6 parts) consists of:
71.6 parts of K2SO4
21.4 parts of Na2SO4
1.5 parts of CaSO4.2H2O 1.1 parts of inerts
These data represent conversion efficiencies of 96% for KCI,98.5% for CaSO4. 2H2O and 20.8% for
NaCI.
It is seen from these results that as the temperature at which the method of this invention of converting gypsum with sylvinite to potassium sulphate-sodium sulphate doublt salt in ammoniacal systems is lowered, the per cent conversions of the reactants are increased.
EXAMPLE 2
In order to show the effect of varying the ammonia concentration in solution at which the method of this invention is carried out, on the conversion of gypsum with sylvinite to potassium sulphatesodium sulphate double salt, a second experiment was conducted at 200 C, using the same procedure as in EXAMPLE 1 with another portion of the same mixture except that in this case the aqueous ammonia solution added contained 42% by weight of ammonia instead of 37.5% as in EXAMPLE 1.
The resulting solid product (95.9 parts) consists of:
73.1 parts of K2SO4
20.5 parts of Na2SO4
1.2 parts of CaSO4 - 2H2O 1.1 parts of inerts
These data represent conversion efficiencies of 98.1% for KCI,98.8% for CaSO4 - 2H2O and 19.9% for NaCI.
In comparing EXAMPLE 1 (reaction temperature 200C) to EXAMPLE 2, it is seen that as the percent ammonia concentration in solution is raised the per cent conversions of the reactants are increased. The same conversions can be obtained by using ratios of gypsum to aqueous ammonia solution as low as 1 to 4 or lower.
EXAMPLE 3
In order to show the effect of varying the per cent sodium chloride concentration in the sylvinite at which the method of this invention is carried out, on the conversion of gypsum with sylvinite to potassium sulphate-sodium sulphate double salt, a second experiment was conducted at 200 C, using the same procedure as in EXAMPLE 1 with another portion of the mixture except that in this case the sylvinite added (110.4 parts) contained 41.8% NaCI and 57.8% KCI instead of 56.8% NaCI and 42.7% KCI as in EXAMPLE 1.
The resulting solid product (95.9 parts) consists of:
71.1 parts of K2SO4 19.6 parts of Na2SO4
4.1 parts of CaSO4. 2H2O 1.1 parts of inerts
These data represent conversion efficiencies of 95.4% for KCI, 95.8% for CaSO4. 2H20 and 34.9% for
NaCI.
In comparing EXAMPLE 1 (reaction temperature 200C) to EXAMPLE 3, it is seen that as the per cent sodium chloride concentration in the sylvinite decreases the per cent conversions of the reactants increase. The effect is more significant for NaCI.
EXAMPLE 4
100 parts of natural gypsum containing 98.2% CaSO4 2H20 100 parts of sylvinite containing 53.5% NaCI plus 46.0% KCI
1294.0 parts of mother liquor and washings derived from the third stage of the process, consisting of:
783 parts of water
465 parts of ammonia
14.6 parts of KCI
31.6 parts of NaCI
0.1 parts of CaCI2 are reacted together at normal temperature and pressure in a vapour-tight reactor. After stirring the mixture for about one hour the reaction product is passed through a filter and the cake formed is washed on the filter with water saturated with ammonia. The filtrates and washings are treated in a distillation unit for the recovery of ammonia which is recycled to the process. Tests have revealed that the washings above can be recycled to the gypsum-sylvinite converter with no detrimental effect to the conversion process.
The resulting solid product (95.9 parts) consisting of:
67.5 parts of K2SO4
19.9 parts of Na2SO4
7.4 parts of CaSO4. 2H20
1.1 parts of inerts goes forward to the second stage of the process, together with adhering liquor. These data represent conversion efficiencies of 95.3% for KCI,92.5% for CaSO4. 2H2O and 19.3% for NaCI.
The said wet-cake is mixed in an extractor at atmospheric temperature and pressure with water in the ratio of about 1 part of wet-cake to 6 parts of water. After stirring the mixture for about 10 minutes the slurry is discharged through a filter and the spent solids (unreacted gypsum and inerts) after being washed with water on the filter are discarded and the washings go to the extractor.
The extract from the leaching operation above consisting of:
67.5 parts of K2SO4
19.9 parts of Na2SO4
0.1 parts of CaSO4 770 parts of water
13 parts of ammonia goes forward to the third stage.
The said extract is mixed in a vapour-tight reactor-crystalliser with 51 parts of sylvinite containing 29.9% NaCI and 69.7% KCI and ammonia gas added in an amount necessary to form a saturated solution, whereby potassium sulphate is precipitated. The potassium sulphate slurry is passed through a filter and the potassium sulphate crystals are washed on the filter with water saturated with ammonia.
The crystals are freed from adhering liquor by heating them in a drier and the vapours are vented to a condenser for the recovery of ammonia.
In this way 91.9 parts of solid product are recovered containing:
91.9 parts of K2SO4 and a mother liquor and washings containing:
783 parts of water
343 parts of ammonia
14.6 parts of KCI
31.6 parts of NaCI
0.1 parts of CaCI2
This mother liquor and washings are recycled to the gypsum-sylvinite converter after being enriched with ammonia.
EXAMPLE 5
100 parts of natural gypsum containing 98.2% CaSO4. 2H20
97.2 parts of sylvinite containing 5.4% NaCI and 43.2% KCI
605.7 parts of mother liquor and washings derived from the second stage of the process, consisting of:
326 parts of water
230 parts of ammonia
20.9 parts of KCI
28.0 parts of NaCI
0.8 parts of CaCI2 are reacted together at normal temperature (about 200 C) under pressure (about 2.5 kg/cm2) absolute in a vapour-tight reactor. After stirring the mixture for about 50 minutes the reaction product is passed through a filter and the cake thus formed is washed on the filter with water saturated with ammonia.
The filtrates and washings are treated in a distillation unit for the recovery of ammonia which is recycled to the process. Though the washings can be recycled to the gypsum-sylvinite converter.
The resulting solid product (95.8 parts), consisting of:
72.7 parts of K2SO4
20.8 parts of Na2SO4
1.2 partsofCaSO4.2H2O 1.1 parts of inerts goes forward to the second stage of the process, together with adhering liquor. These data represent conversion efficiencies of 97.5% for KCI,98.8% CaSO4. 2H2O and 20.9% for NaCI.
The said wet-cake is mixed with 290 parts of water and 55 parts of sylvinite containing 19.8% NaCI and 79.6% KCI and ammonia gas added in an amount necessary to form a saturated solution, whereby potassium sulphate is precipitated. The potassium sulphate slurry is passed through a filter and the potassium sulphate crystals are washed on the filter with water saturated with ammonia.
The crystals are freed from adhering liquor by heating them in a drier and the vapours are vented to a condenser for the recovery of the ammonia.
In this way 100 parts of solid product are recovered containing:
98.9 parts of K2SO4
1.1 parts of inerts and a mother liquor and washings containing:
326 parts of water
190 parts of ammonia
20.9 parts of KCI
28.0 parts of NaCI
0.8 parts of CaCI2
This mother liquor and washings are recycled to the gypsum converter after being enriched with ammonia.
The process will now be described with reference to the diagram presented in Figure 1 for the purpose of illustration but not of limitation:
Sylvinite is supplied to converter 1 via line 2 and calcium sulphate in the form of gypsum, hemihydrate or anhydrite is supplied to the said converter via line 3, both reactants are mixed in the said converter 1 with aqueous ammonia solution via line 4. After the conversion is completed in converter 1 the mixture is discharged via line 5 into filter 6. The filtrate from said filter 6 is conducted via line 7 to distilling column 8, the potassium sulphate-sodium sulphate cake is washed on said filter 6 with aqueous ammonia solution from line 10; the washings are conducted via line 10-4 to converter 1 or if free of KCI they are conducted via line 10-7 to the distillation column 8.The washed cake from filter 6 is discharged via line 11 into leaching tank 12 and water added via line 13. The mixture is stirred to dissolve all potassium and sodium sulphate and the slurry feed to filter 14. The spent unreacted calcium sulphate and inerts are washed on the filter with water from line 1 5 and then discarded via line 1 6 and the said washings are conducted via lines 1 7-1 3 to leaching take 12 while the extract containing the potassium and sodium sulphates is conducted via line 18 to the KCI conditioning tank 1 9 and potassium chloride (as sylvite or sylvinite) is added via line 20. Once the sylvinite has dissolved in tank 19 the solution is conducted via line 21 to the sodium sulphate converter-potassium sulphate crystalliser 22 and ammonia added via line 23.The potassium sulphate slurry from the crystalliser 22 is conducted via line 24 to settler 25. The clear aqueous ammonia solution overflowed from said settler 25 is conducted via line 26-4 to converter 1 and the thickened slurry from settler 25 is conducted via line 27 to filter 28. The filtrate from said filter 28 is conducted via line 29-4 to converter 1. The potassium sulphate crystals are washed on filter 29 with aqueous ammonia solution from line 30, the washings are conducted via line 31-4 to converter 1. The washed potassium sulphate cake is conducted via line 32 to drier 33 and to storage via line 34, and the vapours from said drier 33 are vented to a water cooled condenser 35 via line 36. The filtrate and washings from filter 6 are conducted via line 7 to distilling column 8 after preheating in heat exchanger 37.From the said distillation column 8 a solution rich in NaCI-CaCI2 is drained off passing the preheater 37 via line 38 and ammonia vapours are conducted via line 39 to water cooled condenser 35 and the said condensed vapours are conducted via line 40 to storage tank 41. Make-up ammonia is added to said storage tank 41 via line 42. Ammonia from storage tank 42 via line 44 is mixed in tank 43 with the aqueous ammonia solutions from settler 25 and filter 28 to give the required ammonia concentration in solution in line 4.
In the same Figure 1, is shown an "alternative", which consists in mixing the washed potassium sulphate-sodium sulphate double salt cake with water and sylvinite in a conditioning tank and then feed the said mixture to the sodium sulphate converter-potassium sulphate crystalliser and ammonia added.
The cake, water and sylvinite could also be fed directly to the sodium sulphate converter-potassium sulphate crystalliser without prior mixing and ammonia added.
When potassium sulphate-sodium sulphate double salt is intended as the final end product or part thereof, then the washed cake from filter 6 is dried in drier 33 or in a second drier 45 and the vapours from said drier are condensed in condenser 35.
The extract and sylvinite could also be fed directly to the sodium sulphate converter-potassium sulphate crystalliser without prior mixing and ammonia added.
With gypsum of very small grain size it has been found advantageous to mix it with the aqueous ammonia prior to their addition to the sylvinite in the calcium sulphate-sylvinite converter. This operation can be done in tank 43 shown in said Figure 1 or similar.
From the diagram Figure 1, and from the Examples it is clear that the present invention offers a simple, efficient, versatile, and inexpensive method for the manufacture of potassium sulphate-sodium sulphate double salt and potassium sulphate from calcium sulphate and sylvinite in aqueous ammonia solutions.
Having now particularly described and ascertained the nature of my said invention, and in what manner the same is to be performed, I declare that what I claim is:
Claims (27)
1. A process for manufacturing potassium sulphate comprising the steps of:
a) reacting calcium sulphate with practically stoichiometric amount of the potassium chloride (contained in the sylvinite) in aqueous ammonia solution containing about 36% by weight ammonia at normal temperature and pressure and stirring the said mixture for a residence time of about 60 minutes, whereby potassium sulphate-sodium sulphate double salt is formed as a solid product;
b) separating the said solids from the liquid phase by filtration and washing the solids on the filter with aqueous ammonia solution;
c) conveying the filtrates and washings from the filter to the ammonia distillation column and recycling the condensed ammonia back to the process;;
d) leaching the potassium sulphate and sodium sulphate double salt from any unreacted gypsum and inerts with water, washing said solids with water and recycling the washings to the leaching unit;
e) mixing the extract from the leaching step containing potassium sulphate, sodium sulphate and some calcium sulphate with potassium chloride (as sylvite or sylvinite) in practically stoichiometric quantity as corresponding to the amounts of sodium sulphate and calcium sulphate in the extract and ammonia added in an amount to form a saturated solution whereby the sodium sulphate and any calcium sulphate are converted to potassium sulphate, sodium chloride and calcium chloride; the potassium sulphate, thus formed crystallises out free of any impurities;
f) conveying the potassium sulphate slurry to a thickener, removing the potassium sulphate crystals from the bottom of said thickener and conveying them to a filter, removing from the top of the said thickener the clear solution and conveying it together with filtrates and washings from step (g) below, in amounts required, and after addition of the balance of ammonia to the calcium sulphate converter, and the rest, if any, conveyed to the ammonia distillation column;;
g) separating the potassium sulphate from the aqueous ammonia solution by filtration, washing and drying the said salt and conveying the filtrates and washings to the calcium sulphate converter and the vapours from the drier to the distillation unit condenser, and
h) conveying the ammonia vapours from said distillation column to a condenser and recycling the ammonia back to the process.
2. A process as claimed in claim 1 (part a), in which the calcium sulphate-sylvinite conversion to potassium sulphate-sodium sulphate is conducted in an aqueous ammonia solution containing between about 37 and 50% by weight of ammonia, the gypsum conversion operation, then, being carried out at normal temperature (about 200 C) under significant positive pressure.
3. A process as claimed in claim 1 (part a), in which the calcium sulphate-sylvinite conversion to potassium sulphate-sodium sulphate is conducted in an aqueous ammonia solution containing between about 36 and about 40% by weight of ammonia at temperatures between about 0 and 1 OOC, whereby the reaction is performed at atmospheric pressure.
4. A process as claimed in any of the preceding claims, in which the washed-wet potassium sulphate-sodium sulphate cake is mixed with water and potassium chloride (as sylvite or sylvinite) in stoichiometric quantity as corresponding to the amounts of sodium sulphate and any unreacted calcium sulphate in the cake and ammonia added in an amount to form a saturated solution at a temperature of about 200 C, whereby the sodium sulphate and any unreacted calcium sulphate are converted to potassium sulphate, sodium chloride and calcium chloride; the potassium sulphate thus formed crystallises out free of any impurities other than the inerts originally present in the reactants. The rest of the operation is then the same as described in claim 1 from step (f) down.
5. A process as claimed in claims 1, 2, 3 and 4, in which sylvinite of any composition, in terms of sodium chloride-potassium chloride, can be used.
6. A process as claimed in claim 1, 2, 3 and 4 in which calcium sulphate as gypsum, semi-hydrate or anhydrite can be used.
7. A process as claimed in claims 1,2 and 3 in which the potassium sulphate and sodium sulphate formed are extracted from any unreacted calcium sulphate and inerts with water.
8. A process as claimed in claims 1, 2, 3 and 4 in which the sodium sulphate formed is converted to potassium sulphate by reacting it with sylvite or sylvinite in aqueous ammonia solution containing about 1 5-36% by weight of ammonia.
9. A process as claimed in claims 1, 2, 3, 4 and 8 in which any unconverted calcium sulphate contained in the cake from the calcium sulphate converter is converted to potassium sulphate by reacting it with sylvite or sylvinite in the sodium sulphate conversion operation.
10. A process as claimed in claims 1,2 and 3 in which calcium sulphate is added in excess of stoichiometric ratio.
11. A process as claimed in claims 1,2 and 3 in which ratios of calcium sulphate to ammoniacal solution between about 1/3 and about 1/20 are used.
1 2. A process as claimed in claim 1, in which the calcium sulphate conversion reaction is effected at ordinary temperature and pressure.
1 3. A process as claimed in claims 1,4 and 9 in which the sodium sulphate conversion reaction is effected at ordinary temperature and pressure.
14. A process as claimed in claims 1, 4, 8, 9 and 13 whereby the ammoniacal mother-liquor, or a portion of it from the sodium sulphate conversion-potassium sulphate crystallisation step is used (with such additional ammonia as is required) as an ammoniacal aqueous medium for the conversion of further quantities of calcium sulphate and sylvinite.
1 5. A process as claimed in claims 1,2 and 3 in which sodium chloride is used in quantities between about 50 and 1000% over the stoichiometric ratio.
1 6. A process as claimed in claims 1,2 and 3 in which the solid product formed has a chemical composition corresponding to that of Glaserite or approximately so.
1 7. A process as claimed in claims 1,2 and 3 in which the calcium sulphate and aqueous ammonia solution are mixed before adding them to the sylvinite in the converter.
1 8. A process as claimed in claims 1,2 and 3 in which the calcium sulphate and the sylvinite are mixed separately with the aqueous ammonia solution and then fed to the converter as slurries.
19. A process as claimed in claims 1,2 and 3 in which the calcium sulphate, sylvinite and aqueous ammonia are fed to the converter separately.
20. A process as claimed in claims 1,2 and 3 in which the ammonia is added as ammonia gas to the reactants (calcium sulphate, sylvinite and water) in the converter.
21. A process as claimed in claims 1 (part e), 4, 8, 9 and 1 3 in which potassium chloride (as sylvite or sylvinite) is added in quantities of about 0 to 50% over the stoichiometric ratio.
22. A process as claimed in claims 1, 4, 8 and 9 in which the mother-liquor from the sodium sulphate converter-potassium sulphate crystalliser is recycled to the calcium sulphate converter.
23. A process as claimed in claim 1 in which the calcium sulphate-sylvinite conversion step is conducted between about OOC and about 200C in aqueous ammonia containing 36% by weight ammonia or about, whereby the reaction is performed essentially at atmospheric pressure.
24. A process as claimed in claims 1, 2 and 3 in which the ammonia content of the mother-liquor from the calcium sulphate conversion operation and aqueous ammonia washings are recovered and recycled back to the process.
25. A process for the manufacture of potassium sulphate-sodium sulphate double salt from calcium sulphate and sylvinite whenever produced by any of the preceding claims.
26. A process for the manufacture of potassium sulphate from calcium sulphate and sylvinite substantially as herein described with reference to examples, Figure 1 and corresponding alternatives.
27. Potassium sulphate whenever produced by any of the preceding claims.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8000601A GB2068918B (en) | 1980-01-09 | 1980-01-09 | Potassium sulphate and potassium sodium sulphate production |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8000601A GB2068918B (en) | 1980-01-09 | 1980-01-09 | Potassium sulphate and potassium sodium sulphate production |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2068918A true GB2068918A (en) | 1981-08-19 |
| GB2068918B GB2068918B (en) | 1984-06-20 |
Family
ID=10510515
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8000601A Expired GB2068918B (en) | 1980-01-09 | 1980-01-09 | Potassium sulphate and potassium sodium sulphate production |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2068918B (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4504458A (en) * | 1982-09-02 | 1985-03-12 | Superfos A/S | Gypsum conversion |
| FR2553081A1 (en) * | 1983-09-27 | 1985-04-12 | Prodeco Inc | Potassium sulphate and nitrate by syngenite decomposition |
| US4554151A (en) * | 1983-09-27 | 1985-11-19 | Prodeco, Inc. | Process for producing K3 H(SO4)2 crystals and potassium sulfate crystals |
| US4554139A (en) * | 1983-09-27 | 1985-11-19 | Prodeco, Inc. | Process for producing and decomposing syngenite |
| US4588573A (en) * | 1983-09-27 | 1986-05-13 | Prodeco, Inc. | Method for the production of potassium sulfate using sulfuric acid and potassium chloride |
| US6334990B1 (en) * | 1999-10-21 | 2002-01-01 | Airborne Industrial Minerals Inc. | Formulation of potassium sulfate, sodium carbonate and sodium bicarbonate from potash brine |
-
1980
- 1980-01-09 GB GB8000601A patent/GB2068918B/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4504458A (en) * | 1982-09-02 | 1985-03-12 | Superfos A/S | Gypsum conversion |
| FR2553081A1 (en) * | 1983-09-27 | 1985-04-12 | Prodeco Inc | Potassium sulphate and nitrate by syngenite decomposition |
| US4554151A (en) * | 1983-09-27 | 1985-11-19 | Prodeco, Inc. | Process for producing K3 H(SO4)2 crystals and potassium sulfate crystals |
| US4554139A (en) * | 1983-09-27 | 1985-11-19 | Prodeco, Inc. | Process for producing and decomposing syngenite |
| US4588573A (en) * | 1983-09-27 | 1986-05-13 | Prodeco, Inc. | Method for the production of potassium sulfate using sulfuric acid and potassium chloride |
| US6334990B1 (en) * | 1999-10-21 | 2002-01-01 | Airborne Industrial Minerals Inc. | Formulation of potassium sulfate, sodium carbonate and sodium bicarbonate from potash brine |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2068918B (en) | 1984-06-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |