PROCESS FOR THE PRODUCTION OF POTASSIUM SULPHATE BASED FERTILIZERS

Abstract

The present disclosure relates to a process for the production of potassium sulphate based mineral fertilizers, by means of an exchange reaction between potassium chloride and ammonium sulphate (2KCl+(NH.sub.4).sub.2SO.sub.4<.fwdarw.K.sub.2SO.sub.4+2NH.sub.4Cl) in controlled conditions. The process, subject of the invention, makes it possible to obtain, in a single reaction stage, a crystalline product classifiable as low-chlorine-content mineral fertilizer, containing potassium sulphate, with K.sub.2O in an amount of between 40% and 50% by dry weight, ammoniacal nitrogen in an amount of less than 5% by dry weight and chlorine in an amount of less than 3% by dry weight, with a high potassium-conversion efficiency (calculated as the ratio between what the amount found in the solid main product and the amount introduced as KCl to the reaction with ammonium sulphate) and a by-product, which can be used directly as NK fertilizer (containing nitrogen (N) and potassium oxide (K.sub.2O) both in an amount comprised between 15% and 20% by dry weight) or as raw material for the production of complex fertilizers.

Claims

1. A process for the production of potassium sulphate based fertilizers having a low chlorine content, comprising the following steps in succession: (a) feeding potassium chloride and ammonium sulphate to a reactor and causing them to react in water, thus obtaining a reaction product containing solid potassium sulphate in suspension; and (b) separating the solid potassium sulphate from the mother liquors, thus obtaining a main product comprising potassium sulphate and a secondary product comprising the mother liquors; said process being characterized in that: the ratio of potassium (K.sup.+) to ammonium (NH.sub.4.sup.+) equivalents in reagents fed to the reactor is less than 1; the ratio of water moles to K+ equivalents in reagents fed to the reactor is comprised between 9 and 15; the resulting reaction temperature is comprised between 10° C. and 50° C.; the reaction time is comprised between 60 and 240 minutes; the pH of the reaction mixture is comprised between 2 and 6.

2. The process according to claim 1, wherein the ammonium sulphate is fed as an aqueous solution and the potassium chloride as a crystalline solid.

3. The process according to claim 2, wherein the concentration of ammonium sulphate in the aqueous solution is comprised between 20% and 35% by weight.

4. The process according to the claim 2, wherein the aqueous solution of ammonium sulphate is supplied by a chemical plant or by an effluent treatment plant, optionally subjected to a chemico-physical purification prior to being fed to the reactor.

5. The process according to claim 1, wherein the separation of the solid ammonium sulphate from the mother liquors takes place by means of a pusher centrifuge, or by means of a decanter centrifuge, or by means of a belt filter.

6. The process according to claim 1, furthermore comprising the subsequent step of: c) drying the main product obtained in step b), thus obtaining an end product consisting substantially of potassium sulphate.

7. The process according to claim 1, wherein the secondary product is sent as it is to an integrated cycle for the production of compound fertilizer, or is transformed into a solid fertilizer by means of evaporative crystallization, or is formulated as a liquid fertilizer.

8. The process according to claim 1, wherein, in step a) potassium chloride and ammonium sulphate are reacted in water either continuously or in batches.

9. A use of the main product obtainable with the process of claim 1 as an NK fertilizer.

10. A use of the end product obtainable with the process of claim 6 as an NK fertilizer.

11. A use of the secondary product obtainable with the process of claim 1 as an NK fertilizer.

Description

EXAMPLES

Example 1

[0054] An amount of 82.9 g of ammonium sulphate (98.9%), produced by a plant for recovery of ammonia coming from vapor stripping by abatement with sulphuric acid was weighed and dissolved in distilled water. The amount of water for dissolving the ammonium sulphate was 249.7 g.

[0055] The solution had a pH of 3.5 and a temperature of 24° C.

[0056] The solution was put in a beaker and stirred with a magnetic stirring bar and potassium chloride (with a degree of 62% as K.sub.2O) was slowly added to said solution. Introduction of potassium chloride lasted 6 min. The total amount of potassium chloride added was 80.1 g. The reaction was left to proceed under gentle stirring for 120 min. At the end of the reaction the temperature was 30° C.

[0057] The primary product of the reaction was filtered on paper and in vacuum conditions, and not washed. A moist crystalline solid was obtained on the filter paper, as well as a secondary product constituted by a limpid solution of mother liquors, which were collected in a flask (306.7 g).

[0058] The solid product on the filter was dried in a ventilated oven at 100° C. and weighed: 74.1 g.

[0059] The end product thus obtained was subjected to chemical analysis, with the following results: [0060] Potassium (K.sub.2O): 48.2% [0061] N (ammoniacal nitrogen): 2.5% [0062] Chlorine 3.2%

[0063] The secondary product thus obtained was found to have the following composition (by dry weight): [0064] Potassium (K.sub.2O): 15.5% [0065] N (ammoniacal nitrogen): 17.0% [0066] Chlorine 40.1%

[0067] It should be noted that, in this example, the operation was conducted with a defect of KCl with respect to (NH.sub.4).sub.2SO.sub.4 (approx. 0.86 equiv KCl/equiv (NH.sub.4).sub.2SO.sub.4) and a by-product was obtained in which the ratio between the amounts of (unreacted) KCl and NH.sub.4Cl (produced by the reaction) was far less than 1 (equivalent ratio of 0.41 and weight ratio of 0.57).

[0068] The potassium-conversion ratio, as already defined, was 0.72.

[0069] The amount of dry by-product obtained was 1.2 T/T of main product.

Example 2

[0070] The solution of ammonium sulphate produced by abatement of ammonia from stripping vapor of an ammoniacal effluent was used.

[0071] The solution had an ammonium-sulphate titer of 32% and a pH of 3.1, and presented a limpid appearance, with a slightly straw-colored.

[0072] Of the above solution 285 g were taken, to which 56 g of distilled water were added. The solution thus obtained was put in a beaker and stirred as in the previous example.

[0073] This was followed by gradual addition of 88 g of solid potassium chloride, and the product was left to react for 110 min.

[0074] The crystal suspension coming from the reaction was subjected to filtration in vacuum conditions on paper. The panel of crystals was washed by spraying 15 g of distilled water on the surface, and then dried in a ventilated oven at 100° C. and weighed: 84.2 g.

[0075] The dried product was subjected to chemical analysis, and the following results were obtained: [0076] Potassium (K.sub.2O): 48.1% [0077] N (ammoniacal nitrogen): 2.4% [0078] Chlorine: 2.2%

[0079] The secondary product constituted by the mother liquors after separation of the solid was found to have the following composition (by dry weight): [0080] Potassium (K.sub.2O): 15.7% [0081] N (ammoniacal nitrogen): 19.2% [0082] Chlorine 44.7%