Fertilizer granules containing sodium sulfate and potassium chloride

Abstract

The present invention relates to fertilizer granules containing sodium sulfate and potassium chloride, and to a process for their production. The production of the fertilizer granules comprises the agglomeration of salt mixtures of potassium chloride with sodium sulfate, in which the mass ratio of potassium chloride to sodium sulfate is in the range from 1:9 to 95:5, in particular in the range from 1:4 to 9:1, preferably in the range from 1:2 to 5:1 and especially in the range from 1:1 to 4:1, and the sodium sulfate is present in the form of the anhydrate to an extent of at least 70 wt.%, in particular at least 75 wt.% and especially at least 80 wt.%, based on the total amount of Na2SO4 in the salt mixture.

Description

[0001] The present invention relates to fertilizer granules containing sodium sulfate and potassium chloride and a process for their preparation.

[0002] Potassium chloride is an important component of agricultural fertilizers. Potassium chloride is typically extracted from underground mines through conventional mining, solution mining, or solar evaporation of saline water. The resulting potassium chloride is then further processed into the desired application forms.

[0003] Potassium chloride is often marketed in granular form due to its advantageous handling properties. Compared to fine-particle crystalline potassium chloride, granules are much less prone to dust formation, are more stable in storage, are less prone to caking, and, when used as fertilizer, are easier and more evenly spread by spreading. The quality of potassium chloride granules is not always satisfactory. In particular, moisture generally leads to a decrease in the breaking strength of the potassium chloride granules, resulting in increased abrasion under mechanical stress, such as during conveying, loading, or transport of the granules.

[0004] To improve the mechanical stability of potassium chloride granules, various proposals have been made for the addition of binders such as molasses, as well as the use of phosphate additives or a combination of phosphate additives with alkali metal carbonates (see, for example, CA 2,465,461, WO 2018 / 041285, WO 2018 / 041286, and WO 2018 / 041287). However, these phosphate additives are comparatively expensive and increase the manufacturing costs of potassium chloride granules.

[0005] Sodium sulfate typically comes from the mining of the natural mineral mirabilite. For a long time, sodium sulfate was an important material in the production of various detergents and paper. However, constant progress in these two sectors and the application of new standards have greatly reduced the role of sodium sulfate in these industries. However, sodium sulfate is increasingly being generated as a by-product or waste product of various chemical processes such as paper production, battery manufacturing, the recycling of battery acid, or the refining of silica pigments in the form of aqueous sodium sulfate solutions. Therefore, increasing quantities of sodium sulfate, particularly waste sodium sulfate, are being generated for which there is currently no practical use and which therefore must be disposed of in landfills.Possible uses for waste sodium sulfate are suggested in the literature, such as the conversion to potassium sulfate by reacting the sodium sulfate with potassium chloride (see, for example, DE 4340839 and the literature cited therein), the electrodialysis of aqueous sodium sulfate solutions to produce sodium hydroxide and sulfuric acid (see, for example, DE 3529649 and EP 449071 and the literature cited therein), the reduction to sodium sulfide with coal (see Römpp Chemielexikon, 10th edition, p. 2840, Georg Thieme Verlag, Stuttgart New York, 1998) and the production of sodium carbonate using the Leblanc process.

[0006] However, the aforementioned processes have some disadvantages, such as the generation of large amounts of waste sodium chloride in the case of potassium sulfate production, and are only partially competitive with other processes in terms of price or have not yet been implemented on a large scale. Therefore, there is still a high demand for further uses for sodium sulfate.

[0007] It has surprisingly been found that salt mixtures of sodium sulfate in the form of its anhydrate, or in the form of mixtures of the anhydrate with hydrates of sodium sulfate, which predominantly contain the anhydrate, and potassium chloride can be processed into granules with good mechanical properties if the mass ratio of potassium chloride to sodium sulfate in the salt mixture is in the range from 1:9 to 95:5, in particular in the range from 1:4 to 6:1.

[0008] Granules made from such salt mixtures exhibit high breaking strength and, compared to potassium chloride granules, reduced abrasion, particularly in moist conditions, which can occur during weathering or storage at high humidity, even after prolonged exposure to high humidity, for example, at 70% RH (relative humidity) or higher. Since granules made from such salt mixtures contain the plant macronutrients potassium and sulfate, these granules are also suitable as fertilizers or as components in fertilizer mixtures.

[0009] Accordingly, the present invention relates to the use of salt mixtures of potassium chloride with sodium sulfate, in which the mass ratio of potassium chloride to sodium sulfate is in the range from 1:9 to 95:5, in particular in the range from 1:4 to 9:1, preferably in the range from 1:2 to 5:1 and especially in the range from 1:1 to 4:1 and the sodium sulfate is present in the form of the anhydrate to at least 70% by weight, in particular to at least 75% by weight and especially to at least 80% by weight, based on the total amount of Na2SO4 in the salt mixture, for the production of fertilizer granules.

[0010] The invention also relates to a process for producing fertilizer granules, comprising agglomerating a salt mixture of potassium chloride with sodium sulfate, in which the mass ratio of potassium chloride to sodium sulfate is in the range from 1:9 to 95:5, in particular in the range from 1:4 to 9:1, preferably in the range from 1:2 to 5:1 and especially in the range from 1:1 to 4:1 and the sodium sulfate is present in the form of the anhydrate to at least 70% by weight, in particular to at least 75% by weight and especially to at least 80% by weight, based on the total amount of Na2SO4 in the salt mixture.

[0011] The invention also relates to the fertilizer granules obtainable by the process according to the invention disclosed here.

[0012] Here and below, the quantities for sodium sulfate refer to the anhydrate of sodium sulfate, i.e., the anhydrous form of the formula Na2SO4. Likewise, the quantities for potassium chloride refer to pure potassium chloride of the formula KCl. The mass ratio of potassium chloride to sodium sulfate according to the invention refers to the mass ratio of KCl to Na2SO4 in the salt mixture and can be determined, for example, by elemental analysis.

[0013] Here and below, the terms sodium sulfate anhydrate and sodium sulfate anhydrate are used synonymously and refer to the crystalline, anhydrous form of sodium sulfate [CAS 7757-82-6]. Sodium sulfate anhydrate can be identified by its characteristic X-ray data. These are known from the literature and compiled in publicly accessible databases, for example, The International Centre for Diffraction Data (ICDD).

[0014] The terms "hydrates of sodium sulfate" and "sodium sulfate hydrate" are used synonymously and refer to the crystalline forms of sodium sulfate that contain bound water (water of crystallization). These terms refer in particular to sodium sulfate decahydrate (Na2SO4 10 H2O - [CAS 7727-73-3]), also known as Glauber's salt or sodium sulfate 10-hydrate. Sodium sulfate 10-hydrate can be identified by its characteristic X-ray data. These are known from the literature and compiled in publicly accessible databases, such as those of the International Centre for Diffraction Data (ICDD).

[0015] Unbound or free water is water that is not bound in the crystal structure of the salts used, e.g., adhering water.

[0016] According to the invention, in principle, all grades of sodium sulfate are suitable. In addition to sodium sulfate, these may also contain minor amounts of other mineral components, which can typically be found in mined sodium sulfate (mirabilite) or in waste sodium sulfate. The amount of these components will generally not exceed 10 wt.%, in particular 5 wt.%, based on the total mass of all non-water components of the sodium sulfate. These include sulfate minerals, in particular sulfates of magnesium, calcium, and potassium, as well as mixed salts with different cations. These include, for example, kieserite (MgSO4 · H2O), anhydrite (CaSO4), arcanite (K2SO4), langbeinite (K2Mg2(SO4)3), kainite (KMgClSO4 · 3 H2O), polyhalite (K2MgCa2((SO4)4 · 2 H2O) and glaserite K3Na(SO4)2 as well as mixtures of the above-mentioned minerals.

[0017] The sodium sulfate can be mined or solution-mined, or it can be waste sodium sulfate from a chemical process such as battery manufacturing or the paper industry. These waste sodium sulfate grades often occur as aqueous solutions, from which the sodium sulfate decahydrate is usually extracted by concentrating these solutions. This is then melted, causing the sodium sulfate anhydrate to precipitate and be separated.

[0018] The sodium sulfate contained in the salt mixture can be present essentially exclusively in the form of its anhydrate. However, it is also possible for the salt mixtures used to produce the granules to be a mixture of sodium sulfate in the form of its anhydrate with a hydrate of sodium sulfate, namely the decahydrate or another hydrate of sodium sulfate. In this case, the sodium sulfate is present in the form of the anhydrate to an extent of at least 70 wt.%, in particular at least 75 wt.%, and especially at least 80 wt.%, based on the total amount of Na2SO4 in the salt mixture. The proportion of sodium sulfate present in the form of a hydrate makes up no more than 30 wt.%, in particular no more than 25 wt.%, and particularly preferably no more than 20 wt.% of the salt mixture. The proportion of hydrate, in particular, can be controlled via the feedstocks and, if necessary, determined via the content of water of hydration in the sodium sulfate used.The proportion of water of hydration in the sodium sulfate used is preferably no more than 27.5 wt.%, in particular no more than 24.1 wt.%, and particularly preferably no more than 20.2 wt.%, based on the total mass of sodium sulfate anhydrate and sodium sulfate hydrate. In particular, the sodium sulfate used in the salt mixture is selected such that the salt mixture contains no more than 10 wt.%, in particular no more than 7.5 wt.%, and especially no more than 5 wt.% sodium sulfate in the form of a hydrate, based on the weight of the solid constituents of the salt mixture, including any water of crystallization.

[0019] Specifically, a sodium sulfate is used in which the sodium sulfate is present to an extent of at least 90 wt.%, in particular at least 95 wt.%, based on the total amount of Na2SO4 in the salt mixture, or exclusively, i.e., to an extent of 100 wt.%, in the form of the anhydrate. The crystal water content is then particularly preferably at most 11 wt.%, in particular at most 6 wt.%, based on the total mass of sodium sulfate anhydrate and sodium sulfate hydrate.

[0020] The sodium sulfate anhydrate used in the salt mixtures generally has a grain size range customary for the production of granules, with typically at least 80% by weight, in particular at least 90% by weight of the sodium sulfate anhydrate grains having a grain size of at most 2 mm, in particular at most 1.5 mm and especially at most 1.2 mm and preferably at least 80% by weight, in particular at least 90% by weight of the sodium sulfate anhydrate grains having grain sizes in the range from 0.01 to 2.0 mm, in particular in the range from 0.02 to 1.5 mm, and especially in the range from 0.05 to 1.2 mm, determined by means of sieve analysis according to DIN 66165:2016-08. The average grain size (weight average) of the sodium sulfate anhydrate grains is typically in the range of 20 µm to 1000 µm, especially in the range of 50 µm to 800 µm. The d 90-value of the sodium sulfate anhydrate grains is generally a maximum of 2 mm, in particular a maximum of 1.5 mm and especially a maximum of 1.2 mm. The salt grains of the hydrates of sodium sulfate, in particular its decahydrate, have a comparable grain size range to sodium sulfate anhydrate, although larger grain sizes are also available and suitable depending on the crystallization conditions. Typically, at least 80 wt.%, in particular at least 90 wt.% of the sodium sulfate hydrate grains have a grain size of a maximum of 3.0 mm, in particular a maximum of 2.5 mm and especially a maximum of 2.0 mm, and preferably at least 80 wt.%. In particular, at least 90 wt.% of the sodium sulfate hydrate grains have grain sizes in the range of 0.01 to 3 mm, in particular in the range of 0.02 to 2.5 mm, and especially in the range of 0.05 to 2.0 mm, determined by sieve analysis according to DIN 66165:2016-08.The average grain size (weight average) of the sodium sulfate hydrate grains is typically in the range of 20 µm to 2500 µm, particularly in the range of 50 µm to 2000 µm. 90 -value of the sodium sulfate hydrate grains is usually a maximum of 3.0 mm, in particular a maximum of 2.5 mm and especially a maximum of 2.0 mm.

[0021] The particle sizes stated here and below are generally the values determined by sieve analysis according to DIN 66165:2016-08. The determination of the mass fractions of the respective particle sizes or particle size ranges is carried out in accordance with DIN 66165:2016-08 by fractionating the dispersed material using several sieves by means of mechanical sieving in pre-calibrated systems. Unless otherwise stated, percentages in connection with particle or particle sizes are to be understood as values in wt.%. In this context, the d 90-value is the grain size below which 90 wt.% of the salt grains fall. The d 10 -value refers to the grain size below which 10 wt.% of the salt grains are smaller. The d 50 The value refers to the weight-average grain size. The grain size distribution can also be determined by laser light scattering (laser light diffraction), for example, according to the method specified in ISO 13320:2009, especially in the case of very small particles with particle sizes < 200 µm.

[0022] According to the invention, in principle all potassium chloride qualities are suitable. Typically, a potassium chloride with a potassium content of at least 40 wt. %, calculated as K2O, corresponding to a potassium chloride content of at least 63 wt. %, is used. In particular, such a potassium chloride has a KCl content of at least 79.1 wt. %, e.g., in the range from 79.1 to 99.9 wt. %, in particular at least 90 wt. %, e.g., in the range from 90 to 99.9 wt. %, in each case based on the constituents of the potassium chloride other than water. In addition to KCl, the potassium chloride may also contain other constituents other than potassium chloride and water.These components include in particular sodium chloride (halite, NaCl), bromides of sodium or potassium or alkaline earth metal halides and sulfates such as magnesium chloride (MgCl2), calcium chloride (CaCl2), kieserite (MgSO4 · H2O) and anhydrite (CaSO4) and their oxides, as well as arcanite (K2SO4), as well as mixed salts of alkali and alkaline earth metal halides, e.g. B. Carnallite (KMgCl3 6 H2O), Langbeinite (K2Mg2(SO4)3), Kainite (KMgClSO4 3 H2O), Polyhalite (K2MgCa2((SO4)4 2 H2O) and Glaserite K3Na(SO4)2 as well as mixtures of the above-mentioned minerals. The total amount of such components will generally not exceed 20 wt.%, in particular 15 wt.% and especially 10 wt.% and is typically in the range of 0.1 to 20 wt.%, in particular in the range of 0.1 to 15 wt.% and especially in the range of 0.1 to 10 wt.%. The potassium chloride often contains alkaline earth metal salts, e.g. calcium and / or magnesium salts, in a total amount of 0.01 to 1.0 wt.-% each calculated as alkaline earth metal chloride, e.g. as MgCl2 or CaCl2, and based on the potassium chloride (KCl) contained in the raw material.

[0023] The potassium chloride contained in the salt mixture is often crystalline potassium chloride mined via solar evaporation or solution mining, which has been processed, for example, by flotation, by dry electrostatic separation processes as described, for example, by Fricke, Kali und Steinsalz, Issue 9 / 1986, pages 287 to 295, EP 0231441, EP 1884287, DE 3921073 and WO 2019 / 072331 (ESTA®), by evaporation, crystallization and / or by a hot dissolution process, or by a combination of these measures. Other potassium chloride qualities can also be used together with or instead of the crystalline potassium chloride mined via solar evaporation or solution mining. This could be, for example, a waste product resulting from the classification of the granules according to the invention, which may be comminuted.In these mixtures of mined potassium chloride raw material obtained via solar evaporation or solution mining and other potassium chloride, the proportion of additional potassium chloride, e.g., the waste, will generally be in the range of 1 to 70 wt.%, based on the total mass of the quantity added for granulation. Instead of freshly processed potassium chloride, a pre-processed fine salt can also be used for granulation, for example, a pre-processed fine salt with a potassium content of at least 60 wt.%, based on the dry matter and calculated as K2O.

[0024] The potassium chloride used in the salt mixtures generally has a grain size range customary for the production of granules, with typically at least 80 wt.%, in particular at least 90 wt.% of the potassium chloride grains having a grain size of maximum 2 mm, in particular maximum 1.5 mm and especially maximum 1.2 mm, and preferably at least 80 wt.%, in particular at least 90 wt.% of the potassium chloride grains having grain sizes in the range from 0.01 to 2 mm, in particular in the range from 0.02 to 1.5 mm, and especially in the range from 0.05 to 1.2 mm, determined by sieve analysis according to DIN 66165:2016-08. The average grain size (weight average) of the potassium chloride is typically in the range from 20 µm to 1000 µm, in particular in the range from 50 µm to 800 µm. 90 -value of the potassium chloride used in the process according to the invention is generally a maximum of 2 mm, in particular a maximum of 1.5 mm and especially a maximum of 1.2 mm.

[0025] The mass ratio of potassium chloride to sodium sulfate in the salt mixture used for granulation is preferably in the range from 1:4 to 9:1, in particular in the range from 1:2 to 5:1 and especially in the range from 1:1 to 4:1. The mass fraction of potassium chloride will preferably not exceed 90 wt.%, in particular 85 wt.% and especially 80 wt.%, based on the total mass of the solid components contained in the salt mixture, in order to ensure sufficiently high sulfate contents in the fertilizer granules. The proportion of sodium sulfate will preferably not fall below 10 wt.%, in particular 15 wt.% and especially 20 wt.% of the total mass of the solid components contained in the salt mixture in order to achieve sufficient strength of the granules.

[0026] In addition to the aforementioned components, the salt mixture may contain other salts. Their mass fraction will generally not exceed 30 wt.%, in particular not exceed 20 wt.%, and particularly preferably not exceed 10 wt.%, based on the total weight of the salt mixture, less the water contained therein. Accordingly, the total mass of potassium chloride and sodium sulfate generally amounts to at least 70 wt.%, in particular at least 80 wt.%, and especially at least 90 wt.%, based on the total weight of the salt mixture, less the water contained therein. The water contained in the salt mixture can be either water of crystallization or unbound or free water.

[0027] In addition to the aforementioned impurities contained in the sodium sulfate and potassium chloride used, other salts include salt-like macronutrients and salt-like micronutrients, such as those frequently used in fertilizers. Salt-like macronutrients include salt-like sodium and potassium compounds other than sodium sulfate and potassium chloride, magnesium and calcium compounds, particularly chlorides and sulfates, and salt-like phosphorus compounds such as alkali metal phosphates, alkali metal metaphosphates, and alkali metal hydrogen phosphates, particularly sodium and potassium. Salt-like micronutrients include salt-like boron compounds as well as salts and complexes of the elements manganese, zinc, copper, iron, cobalt, selenium, and molybdenum. Manganese, copper, and zinc are preferably used in the form of their sulfates. Copper and iron are also preferably used in the form of chelates, e.g., with EDTA.Boron is preferably used as calcium sodium borate, e.g., in the form of ulexite, colemanite, sodium borate, potassium borate, or boric acid. Molybdenum is preferably used as sodium or ammonium molybdate or as a mixture thereof. Typically, the proportion of micronutrients other than boron, calculated in their elemental form, will not exceed 3 wt.%, based on the total mass of the salt mixture. The boron content, calculated as B2O3, will generally not exceed 3 wt.% and, if present, is typically in the range of 0.01 to 3 wt.%, in particular 0.01 to 2 wt.%, based on the total mass of the components of the salt mixture used according to the invention.

[0028] Furthermore, the salt mixtures used for granulation can also contain one or more binders. These include organic binders, for example, tylose, molasses, gelatin, starch, ligninsulfonates, salts of polycarboxylic acids such as sodium citrate or potassium citrate, or fatty acid salts such as calcium stearate. These also include inorganic binders, for example, silica, sodium carbonate, sodium diphosphate, sodium metaphosphates such as sodium trimetaphosphate and sodium hexametaphosphate, sodium hydrogen phosphate, and combinations thereof. The proportion of binders will typically not exceed 2% by weight and is preferably less than 1% by weight, each based on the total mass of the components of the salt mixture other than unbound water.

[0029] In a preferred embodiment of the invention, a salt mixture containing a small amount of water is used in the press agglomeration. This can be water of crystallization or free, i.e., unbound water. The total amount of unbound or free water and water of crystallization in the salt mixture is preferably a maximum of 8 wt.%, in particular a maximum of 5 wt.%, and especially a maximum of 4 wt.%, based on the total mass of the salt mixture, and is generally in the range from 0.1 to 8.0 wt.%, in particular 0.2 to 5.0 wt.%, and especially 0.3 to 4 wt.%. This can increase the strength of the granules and reduce abrasion.

[0030] The salt mixture is produced in a manner known per se by mixing the constituents of the salt mixture in the desired proportions in suitable equipment. Suitable equipment for mixing the components of the salt mixture are tumble mixers with and without internals such as drum mixers and ring mixers, paddle mixers such as trough mixers, plow blade mixers and twin-shaft mixers as well as screw mixers. The mixing of the constituents can be followed by drying of the salt mixture, in particular if the total amount of unbound or free water and water of crystallization in the salt mixture is more than 8 wt.%, in particular more than 5 wt.% and especially more than 4 wt.%, based on the total mass of the salt mixture. This is particularly advantageous if the granulation of the salt mixture comprises press agglomeration. The drying of the salt mixture can be carried out in a manner known per se, for example byA heated gas stream, e.g., fresh air, is passed through the salt granules, or by applying heat, or by a combination of these measures. Drying preferably takes place at temperatures in the range of 80 to 250 °C.

[0031] According to the invention, the salt mixture is used to produce fertilizer granules. For this purpose, the salt mixture is subjected to granulation.

[0032] The granulation of the salt mixture can be carried out analogously to the agglomeration processes for salts and salt mixtures known from the state of the art, which are described, for example, in Wolfgang Pietsch, Agglomeration Processes, Wiley - VCH, 1st edition, 2002, in G. Heinze, Handbook of Agglomerations Technology, Wiley - VCH, 2000, in Perry's Chemical Engineers' Handbook, 7th edition, McGraw-Hill, 1997, as well as in the state of the art cited at the beginning.

[0033] The salt mixture is preferably granulated by press agglomeration. In principle, granulation can also be carried out by build-up granulation.

[0034] In granulation by means of built-up granulation or built-up agglomeration, the salt mixture is set in motion by the action of mechanical forces and optionally treated with water or aqueous solutions of other additives during the granulation process. The built-up agglomeration can be carried out in a conventional manner as roller, mixed, or fluidized bed agglomeration, in particular as roller agglomeration. In roller agglomeration, the salt mixture, which may contain other additives, is placed in a vessel with an inclined axis of rotation and a circular cross-section, preferably in a granulation drum or on a granulation plate. By rotating the vessel, the particles of the salt mixture are set in motion. Treatment with the water or the aqueous solutions of additives takes place, for example, by spraying onto the moved salt mixture.This produces a comparatively uniformly round granulate that can be directly fed into a classification system.

[0035] The salt mixture is preferably granulated by means of press agglomeration. This typically involves compacting the salt mixture and comminuting the material obtained during compaction. During compaction, the salt mixture is compacted using pressure. In principle, all presses known for similar purposes are suitable for compaction, such as ram presses, extruders, perforators, and especially roller presses.

[0036] In a preferred embodiment of the invention, a moist salt mixture is used in the press agglomeration which, in addition to the water of crystallization possibly contained in the salt mixture, contains free water, preferably 0.1 to 3.0% by weight, in particular 0.2 to 2.0% by weight, and especially 0.3 to 1.5% by weight of free water, based on the solid constituents of the salt mixture.

[0037] As a rule, the procedure here is to add 0.1 to 3.0 wt.%, in particular 0.2 to 2.0 wt.%, and especially 0.3 to 1.5 wt.%, based on the weight of the salt mixture, of water to the salt mixture before press agglomeration. If necessary, any residual moisture in the salt mixture, also referred to as loss on drying, will be taken into account when adding the water, so that the water quantities stated here are based on the total mass of the salt mixture. As a rule, the total amount of water added will be selected such that the total amount of unbound or free water and water of crystallization in the salt mixture does not exceed 8 wt.%, in particular 5 wt.% and especially 4 wt.%, based on the total mass of the salt mixture, and is in particular in the range from 0.1 to 8.0 wt.%, in particular 0.2 to 5.0 wt.%, and especially 0.3 to 4 wt.%.

[0038] The water can be added to the salt mixture immediately before press agglomeration, e.g., immediately before the salt mixture is fed to the press. Often, however, the water is mixed with the salt mixture and the moist salt mixture is then fed to the press agglomeration. The water can be added to the salt mixture, which already contains all the components required for press agglomeration. Alternatively, the addition of water and the mixing of the solid components of the salt mixture can be combined, for example, by adding the water during mixing of the solid components or by adding the water in the form of a solution of one of the solid components, e.g., a micronutrient or a binder. The water can be added in a conventional manner, e.g., by spraying it onto the solid components of the salt mixture in suitable devices, e.g., one of the mixing devices mentioned above.

[0039] The actual press agglomeration can be carried out analogously to the agglomeration processes known from the state of the art, which are described, for example, in Wolfgang Pietsch, Agglomeration Processes, Wiley - VCH, 1st edition, 2002; in G. Heinze, Handbuch der Agglomerationstechnik, Wiley - VCH, 2000; in Perry's Chemical Engineers' Handbook, 7th edition, McGraw-Hill, 1997; and in WO 2018 / 041285, WO 2018 / 041286, and WO 2018 / 041287. Here and in the following, the terms press agglomeration and press granulation are used synonymously.

[0040] In press agglomeration, the dry or moist salt mixture of sodium sulfate and potassium chloride, and optionally other components, is compacted or pressed under pressure. Depending on the type of compaction / compression, the finely divided components of the salt mixture are agglomerated into coarse agglomerates or ribbon-like strands. The coarse material obtained during compaction is then usually crushed. In principle, all presses known for similar purposes are suitable for compaction, such as ram presses, extruders, perforators, and roller presses.

[0041] Compaction is preferably carried out using a roller press. In roller presses, compaction occurs in the gap between two counter-rotating rollers. The roller surfaces can be smooth, profiled (e.g., grooved, corrugated, or waffled), or equipped with molded recesses. Any profiling of the roller surface primarily serves to improve the feed ratio into the roller gap. Roller presses with smooth or profiled roller surfaces are often used. In this case, the primary agglomeration product is a ribbon-like or plate-like strand emerging from the roller gap, also known as a slug.

[0042] The pressing forces required for compaction, which are usually related to the roller width and specified as line forces, are generally in the range of 1 to 75 kN / cm, in particular in the range of 20 to 70 kN / cm and related to a 1000 mm diameter and an average flake thickness of 10 mm. The roller press is generally operated at a roller circumferential speed in the range of 0.2 to 1.6 m / s. Compaction usually takes place at temperatures in the range of 20 to 140 °C or at the temperature that is established due to the effect of the mechanical forces on the salt mixture. If necessary, the salt mixture fed to the granulation is preheated to the temperature desired for compaction or there is still residual heat, e.g. from drying. If necessary, compaction can be carried out in several stages.

[0043] The material obtained during compaction is generally subjected to comminution to adjust the particle size of the granulate to be produced. Comminution can be carried out in a conventional manner, for example, by grinding in suitable devices, such as impact crushers, impact mills, or roller crushers.

[0044] Typically, the actual granulation process—i.e., in the case of press agglomeration, after compaction and comminution—is followed by classification of the granules. This involves separating the granules into granules with the specified grain size, smaller granules (fine fraction or undersize), and, if appropriate, coarser granules (coarse fraction or oversize). Granules that meet the specifications are those in which at least 90% by weight of the granule particles have a particle size or diameter in the range of 1 to 8 mm, frequently 2 to 6 mm, and especially in the range of 2 to 5 mm. Classification can be carried out using conventional methods, in particular by sieving.

[0045] The off-spec granulate material generated during classification, known as return material, is generally returned to the process. The undersize can be returned directly to the process. The oversize is usually ground to a particle size suitable for press agglomeration or used for another application before being returned.

[0046] The resulting granulate, which conforms to specifications, can be processed in a conventional manner, e.g., packaged and transported.

[0047] In a preferred embodiment of the invention, the granules resulting from press agglomeration are subjected to a post-treatment with water prior to processing. The water can also be added in the form of an aqueous solution, e.g., in the form of an aqueous solution of one or more micronutrients and / or one or more macronutrients. If the granules are classified, the post-treatment can be carried out both before and after classification. If the press agglomeration includes a comminution stage, the post-treatment generally takes place after comminution and before or after any classification.

[0048] For the post-treatment, the granules are moistened with a small amount of water. The amount of water is generally chosen so that it is completely adsorbed by the granules. The water used for the post-treatment is preferably in an amount of 0.1 to 3.0 wt.%, in particular 0.2 to 2.5 wt.%, and especially 0.5 to 2.0 wt.%, based on the mass of the finished, untreated granules. If a moist salt mixture was used to produce the granules, the amount of water for the post-treatment is preferably chosen so that the total amount of free water in the treated granules, i.e. water that is not bound as water of crystallization, is in the range of 0.1 to 5 wt.%, in particular 0.2 to 4 wt.% and especially 0.5 to 3.5 wt.%, based on the total mass of the freshly produced granules.

[0049] For post-treatment, the water is generally applied as evenly as possible to the finished granules, particularly in a finely distributed form, e.g. by spraying or atomizing. For this purpose, the water is usually sprayed or atomized using one or more suitable atomizers, e.g. fixed or rotating nozzles. It has proven advantageous if the granules are moved while the water, particularly the atomized water, is applied in order to achieve a more even application of the water to the surface of the granule particles. In particular, the granules are guided in a relative movement through a spray cone or a spray curtain made up of several overlapping spray cones. For example, the water can be applied by using a conveyor belt to guide the granules through an area in which water is sprayed or atomized.is atomized, for example by creating one or more spray cones or one or more spray curtains on the moving conveyor belt. It is also possible to create an area in which water is sprayed or atomized, for example at the transfer point between two conveyor belts. This achieves a particularly even application of the water to the surface of the granulate particles. In principle, it is also possible to apply the water to the surface of the granulate particles in mixing devices, for example gravity mixers with and without internals such as drum mixers and ring mixers, paddle mixers such as trough mixers, plow blade mixers and twin-shaft mixers. When applying the water, the mechanical stress on the granulate should preferably be kept as low as possible.

[0050] The water used for granulation and / or post-treatment of the granules can generally be pure water, e.g. deionized water, but also tap water or process water, as well as aqueous solutions, e.g. of micro- or macronutrients.

[0051] If necessary, the post-treatment may be followed by a drying step, for example by passing a gas stream, e.g. fresh air, through the granulate or by applying heat or by a combination of these measures.

[0052] The fertilizer granules obtainable by the process according to the invention contain sodium, potassium, and sulfate. The sodium content of the fertilizer granules obtainable according to the invention, calculated as Na2O, is generally in the range from 4 to 35 wt.%, in particular in the range from 8 to 29 wt.%, and especially in the range from 9 to 22 wt.%, based on the total mass of the granules. The potassium content of the fertilizer granules obtainable according to the invention, calculated as K2O, is generally in the range from 12 to 58 wt.%, in particular in the range from 20 to 53 wt.%, and especially in the range from 30 to 50 wt.%, based on the total mass of the granules. The sulfate content of the fertilizer granules obtainable according to the invention, calculated as SO3, is generally in the range of 5 to 45 wt.%, in particular in the range of 8 to 29 wt.% and especially in the range of 9 to 23 wt.%, based on the total mass of the granules.

[0053] In addition to the aforementioned components, the fertilizer granules obtainable according to the invention can contain one or more of the aforementioned salt-like micronutrients, e.g., salt-like boron compounds as well as salts and complex compounds of the elements manganese, zinc, copper, iron, cobalt, selenium, and molybdenum. These include, in particular, the sulfates of manganese, copper, and zinc; chelates of copper and iron, e.g., with EDTA; borates such as calcium sodium borate, e.g., in the form of ulexite, colemanite, sodium borate, potassium borate, or boric acid; and also sodium or ammonium molybdate or mixtures thereof. Typically, the proportion of micronutrients other than boron, calculated in their elemental form, will not exceed 3% by weight, based on the total mass of the granules. The boron content, calculated as B2O3, will generally not exceed 3 wt.% and, if present, is typically in the range of 0.01 to 3 wt.%, in particular 0.01 to 2 wt.-%, based on the total mass of the granules.

[0054] In addition to the aforementioned components, the fertilizer granules obtainable according to the invention contain the accompanying salts of sodium sulfate or potassium chloride, if present in the salt mixture used, in the proportions specified for the salt mixture, as well as, if present, binding agents in the amounts specified for the salt mixture.

[0055] The fertilizer granules obtainable according to the invention generally have a size that complies with the specifications as described above. Generally, at least 90% by weight of the granule particles have a particle size or diameter in the range of 1 to 8 mm, frequently 2 to 6 mm, and in particular in the range of 2 to 5 mm. The particle size is determined by sieve analysis, as previously stated for the salts.

[0056] The fertilizer granules obtainable by the process according to the invention are distinguished by a strength sufficient for fertilizer granules and thus by a lower sensitivity to mechanical stress, such as occurs, for example, during storage or withdrawal from storage, or during handling or transport of the granules. This is reflected in less grain destruction and less dust formation due to abrasion, i.e. of particles with grain sizes below 1 mm. Granules obtained according to the invention therefore have a lower tendency to cake during storage, particularly under pressure, as occurs in heaps or during storage in silos. Surprisingly, the improved mechanical strength of the granules is retained even during storage over longer periods, so that the stresses and strains encountered during withdrawal from storage orThe mechanical stresses occurring during handling lead to less grain destruction in the granules obtained according to the invention, even after prolonged storage.

[0057] The granules obtainable according to the invention are therefore suitable as fertilizers not only due to their components, in particular due to the simultaneous presence of potassium and sulfur, but also due to their mechanical strength. In particular, the granules obtainable according to the invention exhibit low abrasion in the moist state (at 0.5 wt.% water absorption) at 20°C, determined by the Busch roller drum method, of generally less than 15 wt.%, in particular less than 12 wt.%, and especially less than 10 wt.% (see Table 2). This reduces the risk of damage to the granules, particularly if the granules absorb moisture during transport to the intermediate storage facility, through bulk handling, and storage at the customer's site. Accordingly, the granules obtainable according to the invention can be used in particular in the fertilizer applications typical for potassium-containing fertilizers.

[0058] The following examples serve to illustrate the invention.

[0059] Abbreviations: Example: Example

[0060] The particle size distribution was determined on an analytical vibrating sieve machine (type Retsch AS 200 control).

[0061] The composition of the feedstocks was determined by ICP-OES (optical emission spectrometry) according to DIN EN ISO 11885:2009-09.

[0062] The grain hardness (bursting strength or breaking strength) was determined using the ERWEKA TBH 425D tablet breaking strength tester based on measurements of 56 individual granules of varying particle sizes (fraction 2.5–3.15 mm), and the mean value was calculated. The force required to break the granule between the punch and the plate of the breaking strength tester was determined. Granules with a bursting strength of > 400 N and those with a bursting strength of < 4 N were not considered when calculating the mean value.

[0063] The values for dry abrasion (dry abrasion) were determined using the Busch rolling drum method. For this purpose, 50 g of the granulate with a particle size fraction of 2.5–3.15 mm were placed together with 70 steel balls (10 mm diameter, 283 g) in a rolling drum of a commercially available abrasion tester, e.g., ERWEKA, type TAR 20, and tested for 10 minutes at 40 rpm. -1The contents of the drum were then sieved for 1 minute on a sieve machine (Retsch AS 200 control) onto a 5 mm mesh sieve, with a 0.5 mm mesh sieve underneath. The sieved fines correspond to the abrasion.

[0064] The values for abrasion in the moist state (wet abrasion) were determined using the Busch rolling drum method. For this purpose, 50 g of the granulate with a grain size fraction of 2.5 - 3.15 mm were mixed with 0.5 wt.% water and stored in a closed container for 48 h. The prepared material was then placed with 70 steel balls (10 mm diameter, 283 g) in a rolling drum of a commercially available abrasion tester, e.g., ERWEKA, type TAR 20, and rotated for 10 minutes at 40 rpm. The contents of the drum were then sieved for 1 minute on a sieve machine (type Retsch AS 200 control) onto a sieve with a mesh size of 5 mm, below which a sieve with a mesh size of 0.5 mm was arranged. The sieved fine fraction corresponds to the abrasion.

[0065] The following materials were used: Potassium chloride 1 (KCl-1): Potassium chloride (untreated) with the following specifications: KCI content of 95.9 wt% (= 60.6% K2O). Total Ca + Mg content: 0.37% by weight Na content: 0.69 wt% Loss on drying at 105 °C: 0.3 wt%.

[0066] The potassium chloride had the following particle size distribution: d 10 : 39.0 µm, d 50 : 267.7 µm, d 90 : 612.6 µm. Sodium sulfate anhydrate (Na2SO4) Na content: 32.1 wt% SO4 content: 67.3 wt.% Loss on drying at 105 °C: <0.1 wt%.

[0067] The sodium sulfate anhydrate had the following grain size distribution: d 10 : 60.9 µm, d 50 : 169.9 µm, d 90 : 263.4 µm Sodium sulfate decahydrate (Na2SO4 10 H2O) Na content: 13.9 wt% SO4 content: 29.2 wt.% Loss on drying at 105 °C: 56.4 wt%.

[0068] The sodium sulfate decahydrate had the following particle size distribution: d5: 0.77 mm, d 50 : 1.51 mm µm, d90 : 2.44 mm Sodium chloride (NaCl) Na content: 38.8 wt% CI content: 60.2 wt% Loss on drying at 105 °C: <0.1 wt%.

[0069] The sodium chloride had the following particle size distribution: d 10 : 297.7 µm, d 50 : 525.8 µm, d 90 : 885.5 µm Production of the granules:

[0070] For the press agglomeration, a Bepex laboratory press, type L200 / 50, was used. It featured two counter-rotating rollers with rod-shaped depressions on the roller surface (roller diameter 200 mm, working width 50 mm). The laboratory press operated at a specific pressing force of 28 kN / cm and a roller speed of 6.2 rpm. The salt mixture was fed via a screw conveyor arranged above the press rollers. The feed rate of the salt mixture was approximately 0.5 to 2 kg / min.

[0071] The shreds resulting from compaction using the laboratory press were crushed using a Hazemag impact mill. The impact mill had two impact plates and a rotor diameter of 300 mm. The gap width for the front impact plate was set to 10 mm and for the rear impact plate to 5 mm. The impact mill operated at a rotor peripheral speed of 15 m / s. Shredding took place immediately after the shreds had been produced. The shred throughput was approximately 0.5 to 2 kg / s.

[0072] The material was then classified using a commercially available screening device, separating the fraction with a grain size of 2-5 mm (product). The fraction with a grain size of < 2 mm can be returned to the feed (fines). The fraction with a grain size of > 5 mm (coarse material) can be ground and also returned. To determine the breaking strength or bursting strength of the granules, a test fraction (test granules) with a grain size of 2.5-3.15 mm was screened. Examples 1 to 12 and comparative examples V1 and V2:

[0073] Potassium chloride 1 and sodium sulfate anhydrate or mixtures of sodium sulfate anhydrate and sodium sulfate decahydrate were added to an intensive mixer in the mass ratio specified in Table 1 and mixed for 1 minute. If necessary, 0.5 wt% water, based on the total mass of the salts, was added during mixing. The mixture was then fed to the laboratory press at a feed rate of 0.5 to 2 kg / min and immediately crushed and classified.

[0074] The resulting granules were then stored under ambient conditions, and after 7 days, their fracture strength and abrasion were determined. The relative amounts of the feedstocks (in wt. %) and the composition of the granules are listed in Table 1, and the mechanical properties of the granules are summarized in Table 2. The composition of the granules listed in Table 1 was calculated based on the analytically determined composition of the feedstocks. Table 1: Composition of salt mixture / granules (in wt.%) Example . 1 2 3 4 5 6 7 salt mixture KCl-1 (%) 67,0 67,0 67,0 67,0 50,0 60,0 70,0 Na2SO4 (%) 33,0 33,0 25,5 28,0 50,0 40,0 30,0 Na2SO4 · 10 H2O (%) 0,0 0,0 7,5 5,0 0,0 0,0 0,0 NaCl (%) 0,0 0,0 0,0 0,0 0,0 0,0 0,0 Water addition (%) 0,5 0 0 0 0,5 0,5 0,5 granules K2O (%) 40,6 40,6 40,6 40,6 30,3 36,6 42,4 SO3 (%) 18,5 18,5 16,2 17,0 28,1 22,5 16,9 Na2O (%) 14,9 14,9 13,1 13,7 22,1 17,9 13,7 Continuation of Table 1: Example . 8 9 10 11 12 V1 V2 salt mixture KCl-1 (%) 80,0 85,0 90,0 56,0 45,0 100,0 0,0 Na2SO4 (%) 20,0 15,0 10,0 33,0 33,0 0,0 100,0 Na2SO4 · 10 H2O (%) 0,0 0,0 0,0 0,0 0,0 0,0 0,0 NaCl (%) 0,0 0,0 0,0 11,0 22,0 0,0 0,0 Water addition (%) 0,5 0,5 0,5 0,5 0,5 0,0 0,5 granules K2O (%) 48,5 51,5 54,5 33,9 27,3 60,6 0,0 SO3 (%) 11,2 8,4 5,6 18,5 18,5 0,0 56,2 Na2O (%) 9,4 7,3 5,2 20,6 26,2 0,16 43,3 Table 2: Mechanical properties of granules Example . 1 2 3 4 5 6 7 Abrasion dry (%) 7,0 7,3 8 7,8 4,1 6,0 7,0 Abrasion wet (%) 5,2 3,6 10,4 9,3 4,0 5,3 5,1 Grain hardness (N) 60 43 19 39 63 53 57 Continuation of Table 2: Example . 8 9 10 11 12 V1 V2 Abrasion dry (%) 10,0 14,0 10,0 9,4 8,0 14,0 24,0 Abrasion wet (%) 7,2 10,8 13,8 4,6 4,2 15,9 8,2 Grain hardness (N) 50 46 44,0 55 58 37 31 QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] CA 2,465,461

[0004] WO 2018 / 041285 [0004, 0039] WO 2018 / 041286 [0004, 0039] WO 2018 / 041287 [0004, 0039] DE 4340839

[0005] DE 3529649

[0005] EP 449071

[0005] EP 0231441

[0023] EP 1884287

[0023] DE 3921073

[0023] WO 2019 / 072331

[0023] Cited non-patent literature

[0000] Römpp Chemistry Encyclopedia, 10th edition, p. 2840, Georg Thieme Verlag, Stuttgart New York, 1998

[0005] DIN 66165:2016-08 [0020, 0021, 0024] ISO 13320:2009

[0021] Fricke, Potash and Rock Salt, Issue 9 / 1986, pages 287 to 295

[0023] Wolfgang Pietsch, Agglomeration Processes, Wiley - VCH, 1st edition, 2002, in G. Heinze, Handbook of Agglomeration Technology, Wiley - VCH, 2000 in Perry's Chemical Engineers' Handbook, 7th edition, McGraw-Hill, 1997 [0032, 0039] DIN EN ISO 11885:2009-09

[0061]

Claims

[1] Use of salt mixtures of potassium chloride with sodium sulfate, in which the mass ratio of potassium chloride to sodium sulfate is in the range from 1:9 to 95:5 and the sodium sulfate is present in the form of the anhydrate to at least 70% by weight, based on the total amount of Na2SO4 in the salt mixture, for the production of fertilizer granules. [2] Process for the production of fertilizer granules, comprising an agglomeration of a salt mixture of potassium chloride with sodium sulfate, in which the mass ratio of potassium chloride to sodium sulfate is in the range from 1:9 to 95:5 and the sodium sulfate is present in the form of the anhydrate to at least 70% by weight, based on the total amount of Na2SO4 in the salt mixture. [3] Use according to claim 1 or process according to claim 2, wherein the agglomeration of the salt mixture is carried out as press agglomeration. [4] Use or method according to claim 3, wherein the salt mixture is dried before press agglomeration so that the total amount of free water and water of crystallization is not more than 8.0% by weight, based on the weight of the salt mixture. [5] Use or process according to claim 3 or 4, wherein up to 3.0 wt.%, based on the weight of the salt mixture, of water is added to the salt mixture before press agglomeration. [6] Use or method according to claim 5, wherein the water is mixed with the salt mixture and the moist salt mixture is fed to the press agglomeration. [7] Use or method according to any one of claims 3 to 6, wherein the preparation of the granules comprises (i) pressing the salt mixture by means of a roller press, (ii) followed by comminution of the resulting flakes and (iii) classification of the granules resulting from the comminution. [8] Use or method according to claim 7, wherein the undersize resulting from the classification is returned to the press agglomeration. [9] Use or method according to one of claims 3 to 8, wherein the press agglomeration is followed by a treatment of the freshly produced granules with water. [10] Use or method according to claim 9, wherein the amount of water used for the treatment is in the range of 0.1 to 3.0 wt.%, based on the total mass of the freshly prepared granules. [11] Use or method according to one of claims 9 or 10, wherein the amount of water used for the treatment is selected such that the total amount of unbound water in the treated granules is in the range of 0.1 to 5% by weight, based on the total mass of the freshly produced granules. [12] Use or method according to any one of the preceding claims, wherein the total amount of potassium chloride and sodium sulfate amounts to at least 90% by weight, in particular at least 95% by weight, based on the total weight of the salt mixture, less the water contained therein. [13] Use or method according to one of the preceding claims, wherein the potassium chloride used in the salt mixture has a potassium content, calculated as K2O and determined by elemental analysis, of at least 40 wt.% K2O, in particular at least 50 wt.% K2O and especially at least 55 wt.% K2O. [14] Use or method according to any one of the preceding claims, wherein the sodium sulfate used in the salt mixture contains not more than 10% by weight of sodium sulfate in the form of a hydrate, based on the weight of the salt mixture. [15] Use or method according to any one of the preceding claims, wherein at least 80% by weight of the salt particles in the salt mixture have a particle size in the range of 0.01 to 2 mm. [16] Use or method according to any one of the preceding claims, wherein micronutrients such as boron, manganese, zinc, copper, iron, cobalt, selenium and / or molybdenum are added to the salt mixture before granulation. [17] Fertilizer granules obtainable by a process according to any one of claims 2 to 15, in particular by press agglomeration of the salt mixture of potassium chloride with sodium sulfate. [18] Fertiliser granules according to claim 16 having a sodium content, calculated as Na2O, in the range from 4 to 35% by weight and a potassium content, calculated as K2O, in the range from 12 to 58% by weight. [19] Fertiliser granules according to claim 17 or 18, which, after moisture absorption of 0.5% by weight, have an abrasion of less than 15%, determined by the Busch rolling drum method.