FR2553081A1 - Potassium sulphate and nitrate by syngenite decomposition - Google Patents

Abstract

Decomposition of syngenite, CaSO4.K2SO4.H2O, comprise reaction with an acid having a dissociation constant of at least 1.2 x 10-2, at a sufficient temp. and for sufficient time to decompose the syngenite into CaSO4 or penta salt/ 5CaSO4.K2SO4.H2O) and KHSO4. The acid is pref. a mineral acid esp. H2SO4 or nitric acid, in which case KNO3 is formed during the decomposition. The reaction is generally effected at 60-100 deg.C when H2SO4 is used may be represented by the following equations. CaSO4.K2SO4.H2O + H2SO4=CaSO4 + 2KHSO4 + H2O or 5(CaSO4.K2SO4.H2O) + 4H2SO4 5CaSO4.K2SO4.H2O (penta salt) + 8 KHSO4 + H2O. The process may be developed to produce potassium sulphate, K2SO4, and potassium nitrate and the starting syngenite may be obtd. from potassium chloride.

Description

 Potassium chloride, the main form of use of potassium in fertilizers, has been known for many years to have agronomic disadvantages compared to some other potassium salts. Thus, sulphate and nitrate are generally widely used for crop plants such as tobacco, tomato and potato, especially that to be used in the production of "chips".

 The chloride ion, if allowed to accumulate at sufficiently high levels, is toxic to most plant species and its removal is a desirable objective for the fertilizer industry. In arid regions, depending entirely on irrigation for water supply, for example, the accumulation of chloride ions in the soil can become a major factor in the decrease of crop yield. Large amounts of water are needed in this case to remove the chloride.

This disposal not only wastes large amounts of usable water but at the same time removes the necessary components of the fertilizer from the soil.

 The main, if not the only, factor behind the continued use of potassium chloride in these circumstances is the easy availability and hence the low price of chloride compared to other potassium salts.

 The most common potassium chloride substitution product is potassium sulphate. This salt exists in various mineral forms in a number of places, but its separation, generally by crystallization techniques, is more complex and more expensive than that of chloride. It is produced directly in the form of a double sulphate together with magnesium sulphate in western U.S. but this material, although inexpensive in itself, has a low concentration of potassium and is thus more expensive to transport and store.

For many years, potassium chloride has been converted into sulphate by a high temperature reaction with sulfuric acid, and considerable quantities have been produced in this way, particularly in Belgium. US Patent No. 4,342,737 describes such a method. The main factors still limiting production by this process are threefold
1. The big energy needs.

 2. The highly corrosive nature of the reactants and by-product hydrogen chloride.

 3. The need for a local market for hydrogen chloride produces - otherwise it must be neutralized at great expense before it can be discarded.

 For many years, various means have been described for converting chloride using calcium sulphate or sodium sulphate, but none has been commercially exploited so far.

 Several of the proposed methods converge on the production of glaserite, a salt of potassium and sodium sulphate, Na2SO4.3K2SO41, which is then reacted with an excess of potassium chloride to convert sodium sulphate into potassium sulphate.

The product can be recovered, for example, by evaporation and recrystallization. The U.S. Patent No. 4,215,100 relates to such a process. Other means involve the production of calcium double salt, syngenite, CaSO 4 K 2 SO 4 -H 2 O, as an intermediate. This can be decomposed by water at high temperature and pressure, as described in British Patent No. 435,772, or by low temperature concentrated ammonia, as described in French Pat. No. 787,713. British Patent No. 2,068,918, sylvinite, which is a double salt of potassium and sodium chloride of variable composition, and calcium sulfate are reacted with aqueous ammonia to produce the double salt, sodium sulfate. potassium and sodium sulphate, the double salt is reacted with sylvinite or a supplement of sylvinite in aqueous ammonia to obtain crystals of potassium sulphate.

 All these procedures are complex, expensive, expend a lot of energy and may require undesirable operating conditions. Thus, there is still a need for a process for producing K 2 SO 4 using readily available raw materials of low price, said process being relatively uncomplicated, having a high energy efficiency, and not requiring large investments in equipment.

Potassium nitrate is essentially produced by one of two processes. In the first method, which is the only one to be common practice in the USA, potassium chloride is reacted with nitric acid at a high temperature to form potassium nitrate and chlorine, by virtue of the following reactions

 The corrosive nature of the various reagents with consequent design and maintenance issues as well as the need to dispose of the byproduct chlorine prevented further application of the process.

 In recent years, an increasing amount of potassium nitrate has been imported to the US. An important source is Israel, where a process is used by which nitric acid and potassium chloride react in solution and the hydrogen chloride co-produced is separated from the solution by extraction with the aid of a solution. solvent. The viability of this process depends on the ability to economically sell hydrogen chloride that is not needed in many parts of the world.

 Thus, there is still a need for a method of producing KNO3 according to another process which does not present problems of maintenance and design or disposal of by-products.

 An object of the present invention is to produce an agronomically acceptable form of potassium.

 Another object of the present invention is to produce potassium in the form of potassium sulphate or potassium nitrate.

 Another object of the present invention is to provide potassium sulphate or potassium nitrate by a relatively uncomplicated and energy efficient process in its implementation.

 Yet another object of the present invention is to produce potassium sulphate or potassium nitrate from syngenite.

 Still another object of the present invention is to produce potassium sulphate using a process in which the various by-products obtained in carrying out the process are brought back into the production cycle.

 These and other objects of the invention, as will be seen more clearly below, have been achieved by a simple process which produces and then decomposes syngenite to give potassium sulfate or potassium nitrate.

5(CaSO4.K2S04.H2O) + 8NaCl
Après séparation, la syngénite est introduite à l'étape 2 de la réaction où elle réagit avec une solution contenant un acide approprié, par exemple une solution contenant de l'acide sulfurique chaude, et est ainsi décomposée en sulfate de calcium ou penta-sel et sulfate de potassium, selon les conditions réactionnelles.La stoechiométrie est comme :

In step 1 of the reaction, potassium chloride and a sulfate are stirred with a suspension of calcium sulfate or penta-salt which can be recycled from a subsequent decomposition, step 2, to produce sodium chloride and syngenite in suspension according to the equation:

5 (CaSO 4 K 2 SO 4 .H 2 O) + 8NaCl
After separation, the syngenite is introduced in step 2 of the reaction, where it reacts with a solution containing a suitable acid, for example a solution containing hot sulfuric acid, and is thus decomposed into calcium sulphate or penta-salt. and potassium sulphate, depending on the reaction conditions. Stoichiometry is like:

5CaSO4.K2804.H20 + 8KHS04 + 4H2O
The slurry so produced is separated at the reaction temperature, and the removed calcium sulfate or pentasalt can be recycled in step 1 from another synthesis of syngenite. The resulting hot solution containing potassium sulphate and bisulphate ions, at the appropriate concentrations, is cooled to crystallize K3H (SO4) 2, a double salt of sulphate and potassium bisulfate. This salt is separated by filtration or other suitable means and the mother liquor can be recovered and recycled in Step 2 to further break down syngenite.

 Crystallization of an aqueous solution of the double salt X3H (SO4) 2 gives crystals of potassium sulfate, constituting the desired product, and a mother liquor containing potassium bisulfate and free sulfuric acid which can be separated and recycled. to step 2 to further decompose syngenite.

In the case of decomposition of syngenite with nitric acid instead of sulfuric acid, the potassium, hydrogen, bisulphate and nitrate ions remain in solution after removal of calcium sulphate.

 In order to optimize the decomposition using nitric acid, the nitric acid content in solution must therefore be sufficient to convert all of the potassium sulfate to potassium bisulfate.

The addition of lime or calcium carbonate, in appropriate amounts, to such a solution causes the precipitation of an additional amount of calcium sulphate leaving a solution effectively containing the potassium and nitrate ions, from which the potassium nitrate can to be crystallized.

The presence of an excess of nitric acid can be advantageous because it reduces the solubility of potassium nitrate and ensures a lower potassium recycling. Alternatively, calcium nitrate may be added to the solution to precipitate calcium sulfate and, after crystallization and removal of potassium nitrate, the remaining nitric acid solution, containing a little potassium nitrate, may be recycled in the decomposition step of syngenite.

CaSO4 + ZK + + ON03 + 2Hf 2K + + 4NO, - + 2H + Crystallization

 Although the above processes are carried out using nitric acid it is obvious that any process which reduces the sulfate content in the reaction-body solutions to a degree lower than the equilibrium with the lasyngenite, results in the release of potassium ions from syngenite even in the absence of hydrogen ions.

Thus, the addition of calcium ions to such a solution effectively causes the precipitation of calcium sulphate and release of potassium ions.

The addition of calcium ions in the form of calcium nitrate, which can be produced in situ from nitric acid and carbonate or calcium hydroxide, results in the production of a solution of potassium nitrate wherein solid KN03 can crystallize, i.e.

What can be interpreted as follows

In the accompanying drawings
Fig. 1 is a block diagram of the process of the present invention wherein the sylvinite is converted to potassium sulfate;
Fig. 2 is a block diagram showing an embodiment in which syngenite is decomposed with HNO3 and a further amount of sulfate ion is precipitated by addition of calcium in the form of calcium carbonate, calcium hydroxide or nitrate of calcium. calcium, which is followed by the recovery of KNO3 in the crystalline state; and
Fig. 3 is a block diagram showing another embodiment in which the syngene is decomposed by the addition of calcium ion in the form of calcium nitrate, followed by the recovery of KNO3 in the crystalline state. .

 A large proportion of the potassium chloride used in the world is in the form of sylvinite, a double salt of the sodium and potassium chloride type of variable composition. The process used to prepare syngenite from potassium chloride can be easily modified to use sylvinite as a starting material. In fact, it is advantageous to use sylvinite in that the sodium chloride generated by synthesis of syngenite can be discarded with the sodium chloride of sylvinite without additional separation and evaporation.

 The results presented by A. E. Hill, J. Am. Chem.

Soc. 56, 1071-8 (1934), ibid. 59, 2242-4 (1937) and N.V. Bodaleva and I.N. Lepeshkov, Zh. Neorgan. Khim 1, 995-1007 (1956), show that the stability of syngenite decreases as the temperature increases from 40 C to 100 ° C.

This shows that synthesis of syngenite is best performed at lower temperatures and that syngenite decomposes to calcium sulfate and potassium at higher temperatures.

 These same results further indicate that, in order to produce stable syngenite, the potassium sulfate concentration in the solution should exceed about 4% by weight at 40 C, increasing to about 11% by weight at 100 ° C.

 Any process that synthesizes syngenite from potassium sulphate solutions must then operate within these parameters. The Applicant has shown that it is possible, with solid calcium sulphate, to produce syngenite from solutions containing potassium ions, added in the form of potassium chloride, and sulphate ions, added in the form of sulphate of calcium. sodium, ammonium sulphate or other soluble sulphates, at concentrations satisfying the solubility of the product for syngenite at the reaction temperature.

 The Applicant has again shown, on the basis of the data of E. Cornec and H. Krombach, Compt. Makes. 194, 714-6 (1932), that satisfactory concentrations of potassium chloride can be obtained directly from sylvinite by taking advantage of the mutual solubilities of sodium and potassium chlorides.

 The compositions of equilibrium solutions with both sodium and potassium chlorides at various temperatures can be graphically established from Cornec et al. Thus, a solution at equilibrium at 20 ° C, when heated to 80 ° C and used to leach the sylvinite, will dissolve the potassium chloride and reject the solid sodium chloride until it reaches equilibrium with both sodium and potassium chlorides.

 If such a solution is now brought into contact with the appropriate amount of calcium sulphate and a quantity of sodium sulphate equivalent to calcium sulphate is added to the solution, which is allowed to cool to 20 ° C., form of syngenite.

est en excès de la solution au pointd'invarianceà2O0C, en sorte que l'excès précipitera avec la syngénite alors que le reste restera en solution au pointd1invarianceou d'équilibre à 20 C. Après séparation des matières solides précipitées, la solution peut être chauffée à 80 C et recyclée pour lixivier de la sylvinite et dissoudre du chlorure de potassium frais tout en reJetant- le chlorure de sodium engendré par l'étape de synthèse de la syngénite.Ce chlorure de sodium et ensuite jeté avec celui restant après dissolution du chlorure de potassium à partir de la sylvinite.The concentration of potassium chloride can be reduced to that of the equilibrium point of equilibrium at 200 ° C by selecting the appropriate amounts of calcium and sodium sulphates. Sodium chloride produced by the reaction

is in excess of the solution at the point of invariance at 20 ° C, so that the excess will precipitate with syngenite while the remainder will remain in solution at the point of equilibrium or equilibrium at 20 ° C. After separation of the precipitated solids, the solution may be heated to 80 C and recycled to leach the sylvinite and dissolve fresh potassium chloride while rejecting the sodium chloride generated by the synthesis step syngenite.Sodium chloride and then discarded with that remaining after dissolution of the chloride of potassium from sylvinite.

Alternatively, potassium chloride alone can be added to the solution at 80 ° C where it will dissolve until equilibrium is reached and the sodium chloride will precipitate and can be removed.

 Phase considerations also limit the conditions of syngenite decomposition and separation of potassium sulfate thus produced. The phase diagram of K2SO4-H2SO4 in water can be plotted from the data of J.Z. Ans, Anorg. Chem. 63, 225-9 (1909), W. Stortenbecker, Rec. Trav. Chem. 21, 407 (1909) and A.W. Babaewa, Trans. Inst. Pure Chem. Reagents (Moscow), 111 114 (1931).

 Studies carried out by the Applicant have shown that in the presence of hydrogen ion at high temperature (> 60 ° C.), the syngenite decomposes into calcium sulphate or penta-salt (5CaSO 4 K 2 SO 4 · H 2 O) depending on the conditions.

The mechanism seems to depend on the conversion of the sulphate ion solution to bisulphate ion with consequent dissolution of K2SO4 from syngenite to tend to restore the sulphate concentration of the solution.

 If a sufficient amount of hydrogen ion is present in the sulfuric acid or other acid form with a dissociation constant greater than the second dissociation constant of sulfuric acid, 1.2 x the syngeneite is completely decomposed into solid CaSO 4 and the potassium and bisulfate ions in solution.

 In order to optimize the decomposition using sulfuric acid, the sulfuric acid content must therefore be sufficient to convert all the potassium sulphate, that initially in solution as well as that released by syngenite, into potassium bisulfate.

Solutions, after decomposition of syngenite, having compositions with a molar ratio of sulfates
K: SO4 greater than 1: 1 compared with a solution of potassium bisulfate, will be technically usable but economically unsatisfactory, since the amount of potassium sulphate released by syngenite is directly equivalent to the amount of free sulfuric acid available in the decomposition solution, because it is the hydrogen ions that transform the sulphate ions into bisulphate ions.

 Data from Ans, Stortenbecker and Babaewa show that even solutions containing free sulfuric acid in excess of that necessary to form bisulphate by cooling, give, under appropriate conditions, crystals, not of potassium bisulfate, but of salt. double K3-H (SO4) 2. However, at low starting temperatures (> 30 ° C), the solutions having a bisulfate composition will actually give potassium sulfate by cooling. The mother liquor will contain free acid and may be recycled to decompose the fresh syngenite.

 The Ans, Stortenbecker and Babaewa data also show that at any given temperature, with sulfuric acid concentrations lower than that at the point of invariance (i.e., to which the K3H solid double salt (SO4) 2 at the same time as solid potassium sulphate are in equilibrium with the solution), the equilibrium solid phase is potassium sulphate. Thus, for example, at 30 ° C., the addition of double salt to solutions containing less than 20 g of H 2 SO 4 per 100 g of water results in the crystallization of potassium sulphate until these additions bring the concentration of sulfuric acid in the mother liquor at 20 g per 100 g of water.After separation of solid potassium sulphate, this mother liquor can be recycled to the decomposition of syngenite after a suitable concentration by evaporation. up to the boiling point of the solution, a similar result is obtained, but higher concentration solutions are recycled, which reduces the degree of evaporation required.

 Although this isothermal crystallization of potassium sulfate is preferred, the double salt, K3H (SO4) 2, can be dissolved in hot water. This solution, after cooling, will give potassium sulphate as a solid phase, and the mother liquor rich in acid can be recycled to the decomposition of syngenite.

 The preferred temperature for this dissolution step is equal to or close to the boiling point.

For example, a solution containing 46.5% K3H (SO4) 2 on a weight basis (87.5 g K3H (SO4) 2/100 g water) at 95 ° C when cooled to 0 ° C , will precipitate K2SO4 crystals (68.5 g of K2SO4 - 187.5 g of initial solution).

 To implement the process in the most economical manner, it is desirable to minimize the size of the plant, which means operating under conditions giving maximum efficiency for a given unit size.

For this reason, it is of course ideal to leach the sylvinite at the highest possible temperature, about 100 C, so as to extract the maximum amount of potassium chloride and obtain the maximum concentration solution at the point ofvariance. Assuming that it is desired to maintain the potassium chloride concentration, after synthesis, greater than 3.5%, this defines the amount of KC1 that can react and hence the amount of
NaCl product. It is evident that at this portion of the solubility curve the temperature is unimportant.

The lowest potassium concentration determined above is based on the data presented by Hill and Bodaleva et al. mentioned above, which define the lowest concentration of K 2 SO 4 in equilibrium with syngenite at 40 ° C. as being about 4 grams per 100 grams of solution, which is equivalent for the potassium concentration to 3.5 grams of KCl for 100 grams of solution. In practice, the Applicant has shown that at 20 C KCl concentrations as low as 2.9 grams per 100 grams are satisfactory.
Hill and Bodaleva et al. also show that the stability range of syngene is greater at lower temperatures, which defines the temperature range of the most useful synthesis as being less than 600C, probably less than 40C, which, in fact, is confirmed by experience.

 As already indicated, D'Ans, Stortenbecker and Babaewa data show that the most effective syngeneic decomposition conditions are those according to which the composition of the solution, after decomposition, corresponds to a K: SO 4 molar ratio of 1: 1 . These compositions should also give the double salt, K 3 H (SO 4) 2, after cooling, and the solution at the highest concentration satisfying these conditions is that which is at about 31.6 grams of K 2 SO 4 and 17.8 grams of H 2 SO 4 for 100 grams of solution which, after cooling to 0 C, gives a solution at a concentration of about 12 grams of K2SO4 and 18.5 grams of H2SO4 per 100 grams of solution.

The cooling therefore causes the crystallization of the double salt containing the equivalent of 22.86 grams of K 2 SO 4 w together with 4.3 grams of H 2 SO 4 per 100 grams of initial solution. No other solution composition exhibits a favorable K 2 SO 4 yield with a good K 2 SO 4 / H 2 SO 4 ratio.

 The invention may be described in greater detail with reference to FIG. 1. A salt of the potassium chloride type, such as sylvinite or XCI, and a recycling solution A, which will be described hereinafter, are brought into contact with each other. leaching system 1 where the potassium chloride is dissolved and the sodium chloride precipitates Sodium chloride is rejected The preferred temperatures for this step are between about room temperature and the boiling point of the solution. . The most preferred time zone is between 80 ° C and the boiling point.

 The leaching solution B is now introduced into the syngenite preparation unit 2 where it is allowed to cool while reacting with a calcium sulfate and other sulfate salt. Suitable sources for the other sulfate include, but are not limited to, INS4) 2SO and alkali metal sulfates. Suitable calcium sulfates include, but are not limited to, CaSO4 and penta-salt, 5CaSO4 # K2SO4 # H2O. At least part of this addition can come from the recovery of byproducts from the subsequent decomposition of syngenite.

The syngenite slurry, D, thus produced, is separated, for example by filtration, and washed to remove sodium chloride in unit 3. The mother liquor and the wash liquors, E, can be concentrated to remove the salt. washing water in the concentrator 4 and be recycled to 1 t leaching stage in the form of the concentrate A.

 The solid syngenite, F, is introduced into the container 5 for the decomposition of syngenite, maintained at elevated temperature, together with a mineral acid. The mineral acid can be supplied in the recycled liquor, G and H, from the last stages according to the process. The "gypsum" slurry, J, is separated by filtration in the separation unit 6, and the solid "gypsum", 1, is washed at 7 with water. This "gypsum" can be recycled to the syngenite preparation, 2, as designated C.

 Suitable temperatures for the acidic decomposition of syngenite are between room temperature and boiling point, with temperatures above about 70 ° C being preferred. Still preferred are temperatures of 80 C or more. The reaction is continued at atmospheric pressure, generally requiring a period of about 30 minutes to 2 hours. Appropriate concentrations for the next step are 31.6% by weight of K 2 SO 4 and 17.8% by weight of H 2 SO 4.

 The mother liquor, K, from 6, containing KHSO4, is cooled to 0 ° C. in a crystallizer 8 to precipitate a crystalline suspension, L, of K3H (SO4) 2 which is separated, for example by filtration, into 9. It is preferable that the suspension containing KHSO4 is cooled to a raster time of between about 0 ° C and 45 ° C, preferably between about 0 ° C and 30 ° C. The most preferable range is about 0 ° C to 20 ° C. mother liquor G can be recycled to the decomposition of syngenite in 5.

 The double salt K3H (SO4) 2 obtained in the cooling step above is suspended at 100 ° C. in the washing liquors N and O in the crystallizer 10.

The wash liquor N is recycled from the gypsum wash unit 7, while the wash liquor O is recycled from the subsequent potassium sulfate wash.

 The potassium sulphate crystals thus produced, P, are separated at 11 and the mother liquor, Q, after concentration in the evaporator 12, is recycled to the syngenite decomposition at 5. The crude crystals of potassium sulphate R are washed at 13 with saturated potassium sulfate solution S before being conveyed in the form of wet potassium sulfate T to the dryer 14 from which the product K 2 SO 4 is obtained.

 Referring now to Figure 2, syngenite 136, recycle solution 148, and the appropriate amount of fresh nitric acid 137 are reacted in a syngeneite decomposition vessel 138. Suitable temperatures for the acidic decomposition of syngenite are between room temperature and boiling point, with temperatures above 70 ° C being preferred, and temperatures of 80 ° C or higher are still preferred. The reaction is carried out at atmospheric pressure, generally requiring a duration of about 5 minutes to 2 hours.

 The slurry of calcium sulfate 140 thus produced is separated, for example by filtration, in the separator 142 of the first stage. The solids 144 holding calcium sulphate are washed in 132 with water 134 and the washing liquors 139 are recycled by an evaporator 146 as part of a solution 148 to the container 138. The washed calcium sulfate 130 is rejected or recycled in the synthesis of syngenite, as appropriate.

Solution 143 separated at 142 is reacted in the second stage calcium sulfate precipitator 152 with the appropriate amounts of calcium carbonate, calcium hydroxide or calcium nitrate 150. The suspension of calcium sulfate 154 thus produced is separated, for example by filtration, in the separator 156 of the second stage. The calcium sulfate 158 is washed in 160 with
Water 162 and discarded, or recycled to the syngene preparation, as appropriate, at 164. Washing liquor 161 is recycled via evaporator 146 as part of solution 148 to the decomposition vessel. of syngenite 138.

 The separated solution 180 is cooled in a crystallizer 182 to crystallize the solid potassium nitrate which is separated from the mother liquor of the suspension 184 in a separator 186. The solution 180 is for example cooled in the crystallizer 182 to a temperature between about 00C and 45C, more usually about 00C to 30C. The preferred range is about 0C to 20C. The filtrate 198 is recycled via the evaporator 146 as part of the solution. 148 to the decomposition of syngenite.

 In Fig. 3, syngenite 236 and a recycle solution 248 are reacted at the same temperatures as mentioned in connection with Fig. 1 with the equivalent amount of calcium nitrate 237 in a syngeneite decomposition apparatus 238. The suspension of calcium sulphate 240 thus obtained is introduced into a separator 242 from which the calcium sulphate 244 is removed and washed with water 234 at 232 before being discharged or recycled, for example, in the preparation of syngenite.

 The wash liquor 239 is introduced into an evaporator 246 and hence recycled to 238 as part of the recycle solution 248.

 Solution 254 separated from calcium sulfate is now cooled in crystallizer 282 to crystallize potassium nitrate. The crystallizer 282 operates at the same temperatures as the crystallizer 182 of FIG.

The suspension of potassium nitrate 284 thus obtained is separated in the separator 286. The mother liquor 298 is introduced into the evaporator 246 before being recycled as part of the solution to the decomposition of the syngenite at 23B. The produced potassium nitrate is washed and dried as needed to give 296 KNO3 crystals.

 The invention will now be described in more detail with reference to certain specific preclinical examples which are intended to illustrate the invention without limiting it unless otherwise specified.

Example 1
This example shows that potassium chloride and sodium sulfate can be used to prepare syngenite.

 A saturated solution of potassium chloride is prepared by dissolving 858 g of potassium chloride in 2500 g of water at 23 ° C. 115 g of potassium chloride, 216.5 g of sodium sulphate and 186 g of anhydrous calcium sulphate This mixture is reacted at 23 ° C. for two hours. The suspension is filtered, the product is washed and dried. The product contains 22.3% potassium and 60.43% sulphate. The 414.2 g of the dried product represents a yield of 92.3% based on calcium sulfate.

Example 2
This example demonstrates that ammonium sulfate can be used for the preparation of syngenite by reaction with potassium chloride and calcium sulfate.

 A suspension of calcium sulfate is prepared by adding 77 g of calcium hydroxide to 730 g of water and reacting this mixture with 101.6 g of concentrated sulfuric acid (97%) and cooling to 10 ° C.

 The syngenite is prepared from the above mixture by adding 149.1 g of potassium chloride, 132 g of ammonium sulfate and 520 g of additional water. This mixture is stirred for one hour at 10 ° C., filtered and the product washed with approximately 600 g of water.

 The washed product, after drying, weighs 266.9 g (yield 81%) and has potassium, sulfate, calcium, ammonium (as nitrogen) and chloride contents of 18.46%, 62.65%. %, 14.17%, 0.0% and 0.07%, respectively. This represents a 100% conversion on the basis of potassium, taking into account the potassium sulphate remaining in the solution and the washing liquors in equilibrium with syngenite.

Example 3
This example shows that the syngenite can be prepared from sylvinite leach liquor mutually saturated with potassium and sodium chloride, having contents of potassium chloride, sodium chloride and water of 20%, 17.5% and 62.5%, respectively.

 1 kg of the clear solution above is placed at 80 ° C. in a reactor and 71 g of sodium sulphate and 68 g of calcium sulphate are added in this order. The mixture is reacted at 80 ° C for 30 minutes and then cooled to 23 ° C. The total reaction time is about two hours.

The reaction suspension is washed, washed and dried.

The dried product, which weighs 140.7 g, contains 22.3% potassium ion, 59.1% ion sulfate and 0% chloride ion. The 40.7 g of product represents a 96% yield based on calcium sulphate.

Example 4
This example shows that syngenite can be efficiently broken down by sulfuric acid.

 A 476 g filtration solution from an earlier decomposition containing 29.2% potassium sulfate and 14.7% sulfuric acid was reacted with 47.9 g of sulfuric acid (97%). and 140 g of syngenite for 2 hours at 100 ° C., and the resulting suspension is filtered while hot (90 ° C.) The residue is washed and dried to obtain 43.2 g of calcium sulphate solids containing 2 g. , 6% of potassium ion, -64.2% of sulfate ion and 0% of chloride ion The decomposition yield, when applied to 5.9 g of potassium sulphate contained in the remaining solution in the wet gypsum residue before drying, is about 100%.

Example 5
This example shows that nitric acid also breaks down syngenite. 241 g of syngenite are reacted with 500 g of a 1.51 molar HNO3 acid solution containing 48.3 g of HNO3 for 2 hours at 60 ° C.

 The resulting suspension is filtered, the 166 g of wet solids washed and dried. The 116.8 g of dry solids contain 9.5% potassium ion and 63.9% sulfate ion. The decomposition yield applied to calcium sulphate under these conditions is 81% based on the potassium remaining in the decomposition residues and, applied to the pentasalt, 95%.

Example 6
This example demonstrates the crystallization of the double salt, K3H (SO4) 2, in solutions having a molar ratio of sulfuric acid to potassium sulfate of 1: 1, equivalent to potassium bisulfate. 300 g of potassium sulphate and 180.9 g of sulfuric acid (94%) are dissolved in 519.1 g of water at 50 ° C. The solution is cooled to 0 ° C. and the crystallized solids are filtered off to obtain 283 ° C. , 6 g of wet solids which, after drying, give 283.6 g of dry crystals of the double salt having the analysis: 40.1% K and 61.8% 504.

 (K3H (SO4) 2 requires 37.7% K and 61.9% SO4). The yield on the basis of potassium sulfate is 77.8%.

Example 7
This example illustrates the isothermal crystallization of K2SO4 from a solution of K3H (SO4) 2 at 30 C.

250 g of K3H (SO4) 2 are added to 200 g of water at 30 ° C. and the solution thus obtained is stirred for 2 hours. At the end of this time, the solids were filtered off and dried to obtain, after washing with water, 148.9 g of solids with analysis: 44.4% K and 54.7%. of SO4. (K2SO4 requires 44.8% K and 55.2% SO4). The mother liquor contains 8.4% K and 19.9% SO4, which corresponds to 26.2 g of K2SO4 per 100 g of H2O and 13.7 g of
H2S04 for 100 g of H2O.

Example 8
This example demonstrates the separation of potassium sulfate crystals from solutions of the double salt,
K3H (SO4) 2.

 225 g of the double salt produced in Example 6 are dissolved in 250 g of water at about 100 ° C., while cooling to 0 ° C., the solution gives 152.4 g of wet potassium sulphate crystals which give a dry weight of 144.3 g of material having the analysis: 44.9% of K and 54.9% of 504.

 (K2SO4 requires 44.8% K and 55.2% SO4). The yield, based on potassium sulfate, is 72.0%.

Example 9
This example shows that a solution from an earlier syngenite preparation can be regenerated by leaching a sylvinite-type composite ore before reuse.

845.6 g of a solution containing 6% of potassium, 0.91% of sulfate and 17.2% of chloride, or about 11.5% of XCl are mixed. and 20% NaCl, with 175 g of potassium chloride and 132 g of sodium chloride at 80 ° C. for 1 hour. The suspension is filtered to obtain 253.3 g of wet solid and 831.9 g of solution. The wet solid is dried to 244 g and contains 21.8% potassium, 2.11% sulfate and 55.0% chloride. The resulting leach solution contains 10.2% potassium, 19.5 g. X chloride and 0.8% sulfate or 19.4% KCl and 16.9% NaCl
This solution composition, as indicated in Example 3, is satisfactory for the preparation of syn-gunite
Example 10
This example shows the use of nitric acid and calcium carbonate
256 g of syngenite containing 67 g of K are stirred at 100 ° C. for 2 hours in a nitric acid solution containing 155 g of nitric acid at 69% of HNO 3 and 345 g of water. The calcium sulfate produced is separated by filtration which, after washing with water and drying, weighs 113 g (the washing liquors are discarded). The liquor is neutralized, weighing 355 g, stirring to pH 7 by the addition of calcium carbonate at 50 ° C. Filtration of the suspension thus obtained gives 89 g of dry washed calcium sulfate and 306 g of filtrate ( the washing liquors are discarded) which, after cooling to 0 ° C., gives 67 g of potassium nitrate crystals, which, after drying of the product up to 61.5 g, measure 3 S, 23% of K (KNO 3 requires 38 , 67% of K).

Example 11
This example illustrates the use of nitric acid and calcium nitrate. 149 g of syngenite are stirred at 100 ° C. for two hours with a solution of 137.g of 69% nitric acid in 458 g of water The calcium sulphate thus obtained is separated by filtration and, after washing and drying it weighs 52 g (wash liquors are discarded).

The mother liquor, weighing 593 g, is stirred for 30 minutes with 147.5 g of Ca (NO 3) 2-4H 2 O (calcium nitrate tetrahydrate) at 50 ° C. Filtration of the resulting suspension gives 54 g of sulphate. of washed, dry calcium and 574 g of filtrate (washing liquors are discarded). By cooling to 0 ° C., the solution gives 70 g of wet potassium nitrate crystals which, after drying, give 38.5 g of product with analysis: 38.5% of K (gNO 3 requires 38.67% of K).

Example 12
This example illustrates the direct decomposition of syngenite using calcium nitrate.

 149 g of syngenite at 100 OC are stirred for two hours with a solution of 147.5 g of calcium nitrate tetrahydrate in 500 g of water.

 The calcium sulfate produced is separated by filtration and, after washing with water and drying, weighs 122 g.

The washing liquors are thrown away. After cooling to OOC, the filtrate weighing 426 g gives 33.7 g of wet crystals which, after drying, give 25.2 g of potassium nitrate titrating 38.1% of K.

 It goes without saying that the invention is not limited to the embodiments described and is capable of various variants without departing from its scope as defined in the appended claims.

Claims (22)

 A process for the decomposition of syngenite, characterized in that it comprises reacting said syngenite with an acid, said acid being selected from the group consisting of acids having a dissociation constant of at least 1.2. x 10 2, its temperature and for a time sufficient for the syngenite to break down into CaSO4, or penta-salt, and KHS04.  2. Method according to claim 1, characterized in that the acid is a mineral acid.  3. Method according to claim 2, characterized in that the mineral acid is H2SO4.  4. Method according to claim 2, characterized in that the mineral acid is nitric acid and KNO3 is formed during the decomposition of syngenite.  5. Method according to claim 1, characterized in that the temperature is between 60 = C and 100 C.  6. Method according to claim 1, characterized in that it is represented by the equation

 7. Method according to claim 1, characterized in that it is represented by the equation

 5CaSO4 # K2SO4 # H2O + 8KHSO4 + 4H2O  8. The method of claim 1, characterized in that it further comprises the step of separating KHSO4 from CaSO4 or 5CaSO4 # K2SO4 # H2O and recycle the recovered CaSO4 or 5CaS04.K2SO4.H2O.  9. A process for producing K2SO4 characterized in that it consists of: (a) forming syngenite; (b) decomposing the syngenite from (a) with sulfuric acid to obtain a KHSO4 solution; (c) crystallizing the KHSO4 solution from (b) to form K3B double crystalline salt (SO4) ) 2; (d) crystallizing K3H (SO4) 2 from (c) to form crystalline K2SO4; and (e) recovering K2SO4 crystals.  A process for producing K2SO4 according to claim 9, characterized in that the syngenite in (a) is formed by reacting a calcium sulfate salt with a water-soluble sulfate and a solution-based potassium chloride salt. aqueous.  11. Process for producing K2SO4 according to claim 10, characterized in that the salt based on potassium chloride is potassium chloride.  12. Process for producing K2SO4 according to claim 10, characterized in that the salt based on potassium chloride is sylvinite.  13. A process for producing K2SO4 according to claim 10, characterized in that the potassium chloride in aqueous solution is prepared by lixiviation of sylvinite at a relatively high temperature with a solution saturated with NaCl and KCl at a relatively low temperature.  14. Process for the production of potassium nitrate, characterized in that it consists in: (a) decomposing syngenite (CaSO4 # K2SO4 # H2O) in the presence of the nitrate ion to form a solution of KN03 and a precipitate of CaSO4 (b) separating said KNO3 in solution from said precipitate of CaSO4; and (c) recovering solid KN03 from said KN03 in solution.  15. The method of claim 14, characterized in that the decomposition of the syngenite in (a) comprises (a) reacting said syngenite with HNO3 to form a solution of ions K +, HSO4 and NO3 and a precipitate of CaSO4; (b) separating said CaSO4 precipitate from said solution; and (c) further precipitating CaSO4 to obtain KN03 in solution.  16. The method of claim 14, characterized in that the additional precipitation of CaSO4 in (c) is carried out by the addition of lime or CaCO 3.  17. The method of claim 14, characterized in that the additional precipitation of CaSO4 in (c) is carried out by the addition of Ca (N03) 2.  18. The method of claim 14, characterized in that the decomposition of the syngenite in (a) comprises: (a) reacting said syngenite with Ca ++ ions and N03 to form a precipitate of CaSO4 and K + ions and N03 in solution; (b) separating said precipitate from CaSO4 and said K + and NO3 ions in solution; and (c) recovering said K + and NO3 ions as solid KNO3.  19. The method of claim 18, characterized in that said Ca ++ ions in (a) are added as Ca (N03) 2.  20. The method of claim 19, characterized in that said Ca (NO) 2 is produced by the in situ reaction of HNO3 and CaCO3 or Ca (OH) 2.  21. The method of claim 14, characterized in that step (c) comprises crystallization of said KNO3 in solution.  22. The method of claim 21, characterized in that said crystallization is carried out at a temperature between 00C and 45 C.