EP3592704A1

EP3592704A1 - Magnesium sulfate granulates based on synthetic magnesium sulphate

Info

Publication number: EP3592704A1
Application number: EP18714957.0A
Authority: EP
Inventors: Guido BAUCKE; Armin Dietrich; Scherr DADVID; Ludger Waldmann
Original assignee: K+S AG
Current assignee: K+S AG
Priority date: 2017-03-08
Filing date: 2018-03-07
Publication date: 2020-01-15
Also published as: US10723632B2; CN110650920A; US20200039832A1; DE102017104877A1; WO2018161984A1

Abstract

The invention relates to magnesium sulfate granulates consisting of at least 90 wt. % synthetic magnesium sulphate hydrate with respect to the total mass of the magnesium sulphate granulate, and having a dry loss of less than 2 wt. % determined by drying of the granulate for 2 hours at 105°c and 1 bar. The invention also relates to a method for producing said magnesium sulfate granulates and to their use in urea-containing fertilizer compositions.

Description

Magnesium sulfate granules based on synthetic magnesium sulfate

The present invention relates to magnesium sulfate granules and their use for producing solid, urea-containing fertilizer compositions. The invention also relates to a process for the production of these granules.

Although magnesium is the eighth most abundant element at about 1.94% in the Earth's crust, soils often lack magnesium. Therefore, magnesium salts are widely used as fertilizers or fertilizer additives. In particular, magnesium sulfate, often in the form of monohydrate or 5/4 hydrate, is used as fertilizer or fertilizer additive. In this case, magnesium sulfate is typically used in the form of magnesium sulfate-containing granules, which may contain macronutrients such as potassium, phosphorus or nitrogen and optionally trace elements such as manganese, zinc, copper, iron, molybdenum or boron.

Often one would like to use for fertilization magnesium sulfate together with urea. Thus, B. von Rheinbaben, Fertilizer Research 11 (1987) describes that the combined use of magnesium sulfate monohydrate and urea leads to a reduction in nitrogen loss. However, there are limits to the joint use of magnesium and nitrogen. Thus, solid mixtures of magnesium sulfate granules and urea are not storage stable. Often it comes after a short time to a reaction of the two mixing partners and the surrounding humidity, in which form pasty masses, which also easily deliquesce and therefore are difficult to handle and can no longer be deployed as fertilizer in solid form. Even when stored in the dry, clumping of the mixture, so-called nests, is observed after some time. These problems occur especially in granules with a high magnesium content.

GB 1359884 proposes to use aqueous concentrates obtained by mixing a water of hydration or water of crystallization containing magnesium sulfate, for. B. Epsom salt (magnesium sulfate heptahydrate), are obtained with solid urea. However, liquid fertilizer compositions are less suitable for some applications than solid fertilizer compositions. WO 2013/098367 proposes to solve this problem, magnesium sulfate and urea in the form of a complex compound [MgS0 ₄ · m CO (NH ₂ ) 2 · n H ₂ 0], wherein m in the range of 0.9 to 1, 1 and n are in the range of 2.9 to 3.1, wherein the compositions described therein may contain little or no free MgS0 ₄ and less than 10 wt .-%, unbound urea.

CONFIRMATION COPY A similar approach is followed by WO 2014/096372, where compositions are used there which contain a mixture of two magnesium sulfate-urea complex compounds. The disadvantage is that the complex compounds must be prepared beforehand. In addition, this only allows the use of magnesium sulfate and urea in a narrow ratio.

DE 3618058 describes a process for the preparation of granules based on kieserite by roll agglomeration of finely divided kieserite or kieserite-potassium sulfate mixtures with the addition of mono-, di- or polysaccharides as Bindebzw. Solidifying agent. The resulting mechanical properties of granules with a Kieseritanteil> 90 wt .-% are unsatisfactory.

DE 3707785 describes a process for the production of granules based on kieserite by roll agglomeration of dust kieserite in a mixture with ground recycled material with the addition of water and water-soluble phosphates as binding or solidifying agent. Without addition of phosphate, the mechanical strengths are poor and even with addition of phosphate, the abrasion is unsatisfactory. DE 4303984 describes a process for the preparation of granules based on kieserite by roll agglomeration of dust kieserite in a mixture with ground recycled material with the addition of water and a mixture of ammonium salts such as ammonium sulfate, borax and mono- or disaccharides and drying of the granules to residual moisture values of 0, 5 to 2 wt .-%. However, the granules thus obtained are characterized by a low breaking strength of a maximum of 21 N.

EP 1219571 describes the preparation of mineral fertilizer granules using organic chelating agents, namely the salts of dicarboxylic acids, polycarboxylic acids, hydroxycarboxylic acids, fruit acids, amidocarboxylic acids and polypeptides.

DE 4232567 describes the use of aqueous urea solutions to reduce the dusting tendency of sulphate granules, eg. B. of kieserite granules. The invention is therefore based on the object to provide magnesium sulfate granules which give a storage-stable fertilizer composition when mixed with solid urea. The mixtures obtained should be stable in storage under ambient conditions, ie do not melt and, if possible, do not cake or form so-called "nests". In addition, the magnesium sulfate granules should be mechanical be stable to ensure good transportability. In particular, the magnesium sulfate granules should simultaneously have a sufficient bursting strength of preferably at least 30 N, in particular at least 35 N, especially at least 40 N, and a low attrition of less than 2 wt .-%, in particular less than 1 wt .-%.

Surprisingly, it has been found that magnesium sulfate granules which have a dry loss of less than 2 wt .-%, preferably less than 1.5 wt .-%, in particular at most 1 wt .-% and especially at most 0.5 wt .-% , when mixed with solid urea, do not show the problems described at the outset, but form free-flowing, storage-stable mixtures. However, this raises the problem that conventional granules based on natural magnesium sulfate hydrate, i. H. On the basis of kieserite show only a low mechanical strength and a little satisfactory high abrasion when the dry loss is less than 2 wt .-%, in particular less than 1 wt .-%. Surprisingly, it has been found that magnesium sulfate granules which consist of at least 90% by weight, in particular at least 95% by weight and especially at least 98% by weight, of a synthetic magnesium sulfate hydrate, even at low dry losses of less than 2 wt .-%, preferably less than 1, 5 wt .-%, in particular at most 1 wt .-% and especially at most 0.5 wt .-% of the desired mechanical properties, d. H. have a high bursting strength or breaking strength of at least 30 N and a low attrition of usually less than 2 wt .-%. Surprisingly, in order to achieve the desired mechanical properties, it is not necessary to use organic binders or inorganic binder salts.

Accordingly, the present invention relates to magnesium sulfate granules which are at least 90 wt .-%, in particular at least 95 wt .-% and especially at least 98 wt .-%, based on the total mass of the magnesium sulfate granules, of synthetic magnesium sulfate hydrate and have a dry loss of less than 2 wt .-%, preferably less than 1, 5 wt .-%, in particular at most 1 wt .-%, especially at most 0.5 wt .-%, determined by drying the granules for 2 h at 105 ° C and 1 bar. Such magnesium sulfate granules generally have a bursting strength of preferably at least 30 N, in particular at least 35 N, especially at least 40 N and a low attrition of usually less than 2 wt .-% to. The fertilizer compositions obtained by mixing the granules according to the invention with solid urea, in particular with urea granules or prilled urea are storage stable and show no lingering or the formation of agglomerates even after prolonged storage of, for example, 20 days or longer, especially after 30 days or longer. Unlike the prior art, it is not necessary to first prepare complex compounds of urea and magnesium sulfate, or to dissolve the urea and to introduce the solution into the granulation process. Therefore, such magnesium granules open the production of fertilizer compositions with very different levels of solid urea.

In contrast to commercially available magnesium sulfate granules based on synthetic magnesium sulfate, the magnesium sulfate granules according to the invention have only a slight dry loss, which is preferably less than 1.5% by weight, in particular not more than 1.0% by weight and especially is at most 0.5 wt .-%, and for example in the range of 0.01 to <1, 5 wt .-%, in particular in the range of 0.05 to 1 wt .-% and especially in the range of 0.1 to 0.5 wt .-%, each determined by drying the granules for 2 h at 105 ° C and 1 bar.

Here and below the terms dry loss and drying loss are used interchangeably. This dry loss is typically determined in accordance with DIN EN 12880: 2000 by drying a sample at temperatures in the range of 105 ± 5 ° C at ambient pressure to constant weight. As a rule, the drying takes place in a drying cabinet. The time required to achieve weight constancy is typically less than 2 hours for magnesium sulfate granules. This is determined by weighing before and after drying the dry residue in%, based on the initial weight used. The dry loss in% results from the dry residue in% by subtraction of 100.

The magnesium sulfate granules according to the invention consist of at least 90% by weight, in particular at least 95% by weight and especially at least 98% by weight or exclusively of synthetic magnesium sulfate hydrate.

Synthetic magnesium sulfate hydrate, hereinafter also SMS, is understood as meaning a magnesium sulfate hydrate which is obtainable by digestion of magnesium oxide with sulfuric acid, in particular with a 50 to 90% strength by weight aqueous sulfuric acid. SMS contains in comparison to magnesium sulfate hydrate from natural sources such as kieserite, usually lower amounts of halides and a higher proportion of water-insoluble magnesium in the form of water-insoluble magnesium oxide. In particular, the proportion of water-insoluble magnesium, based on the total mass of the SMS and calculated as MgO in the range of 1, 5 to 7.0 wt .-%, especially in the range of 2.0 to 6.0 wt .-%. The proportion of salts in the SMS, the are different from magnesium sulfate and magnesium oxide, is usually less than 3 wt .-%, in particular less than 2.5 wt .-%, based on the total ^¬ mass of SMS. The total content of magnesium in the SMS is generally at least 26 wt .-%, in particular at least 27 wt .-%, calculated as MgO and is often in the range of 26 to 30 wt .-%, in particular 27 to 30 wt. %.

In the SMS, the magnesium sulfate is present mainly as magnesium sulfate monohydrate or as a mixture of magnesium sulfate monohydrate with magnesium sulfate 5/4 hydrate, although small amounts of magnesium sulfate dihydrate may be included in the SMS. Preferably, the proportion of magnesium sulfate monohydrate and magnesium sulfate 5/4 hydrate in the SMS is at least 90% by weight, based on the total mass of the SMS. Particularly preferred are magnesium sulfate granules in which the magnesium sulfate is present in the SMS to at least 90 wt .-%, based on the total amount of magnesium sulfate plus water of hydration, as magnesium sulfate monohydrate. In particular, the content of water of crystallization in the magnesium sulfate granules is 18.0 to 22% by weight, based on the total mass of the SMS, and determined by the loss on ignition at 550 ° C.

Accordingly, magnesium sulfate granules according to the invention often have at least one or all of the following characteristics in addition to the aforementioned low dry loss:

The proportion of water-soluble magnesium, based on the total mass of the magnesium sulfate granules according to the invention and calculated as MgO, is in the range from 20 to 25% by weight, in particular from 22 to 25% by weight.

The proportion of water-insoluble magnesium, based on the total mass of the magnesium sulfate granules according to the invention and calculated as MgO, is in the range from 1.5 to 7.0% by weight, in particular in the range from 2.0 to 6.0% by weight. %.

The total content of magnesium (water-soluble MgO and water-insoluble MgO), based on the total mass of the magnesium sulfate granules according to the invention and calculated as MgO, is generally at least 26% by weight, in particular at least 27% by weight, and is often Range of 26 to 30 wt .-%, in particular 27 to 30 wt .-%.

- The proportion of water of hydration, determined by loss on ignition at 550 ° C is 18.0 to 22 wt .-%, based on the total mass of the magnesium sulfate granules of the invention.

The proportion of monohydrate and / or 5/4 hydrate, based on the total mass of the magnesium sulfate + water of hydration contained in the magnesium sulfate granules, is at least 90 wt .-%. In particular, the proportion of monohydrate, based on the total mass of the magnesium sulfate and water of hydration contained in the magnesium sulfate granules, is at least 90% by weight.

The proportion of salts other than magnesium sulfate and magnesium oxide is less than 3.0% by weight, in particular not more than 2.5% by weight, based on the total mass of the magnesium sulfate granules according to the invention.

In addition to the synthetic magnesium sulfate hydrate, the magnesium sulfate granules may also contain a small amount of other inorganic compounds other than magnesium sulfate and magnesium oxide, e.g. B. Compounds from the group MgC0 ₃ , CaS0 ₄ , Na ₂ S0 ₄ , K ₂ S0 ₄ , KCl and NaCl and their hydrates. The proportion of such compounds will generally not exceed 10% by weight, in particular 5% by weight, and especially 2% by weight, based on the total mass of the constituents of the magnesium sulfate granules according to the invention.

Furthermore, the magnesium sulfate granules may also contain micronutrients. These include, in addition to the boron already mentioned, the elements manganese, zinc, copper, iron and molybdenum, which are typically used in the granules in the form of their salts or complex compounds. Manganese, copper and zinc are preferably used in the form of their sulfates. Copper and iron are preferably also in the form of chelates, z. B. with EDTA used. Boron is preferably used as calcium sodium borate, e.g. B. in the form of Ulexit, 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 its elemental form, will not exceed 1% by weight, based on the total mass of the constituents of the magnesium sulphate granules used according to the invention. The content of boron, calculated as B2O3, will generally not exceed 3% by weight and, if present, is typically in the range from 0.01 to 3% by weight, in particular 0.01 to 2% by weight. %, based on the total mass of the components of the magnesium sulfate granules used in the invention.

In contrast to conventional magnesium sulfate granules, no organic binders are required in the magnesium sulfate granules based on synthetic magnesium sulfate hydrate according to the invention, since these granules have a higher mechanical strength, which is still sufficient even with low residual moisture contents. Accordingly, the proportion of any organic binders will typically not exceed 0.1% by weight. In preferred embodiments contain the magnesium sulfate granules according to the invention no organic binders.

In a specific embodiment of the invention, the magnesium sulfate granules consist exclusively or almost exclusively, i. H. at least 99% by weight, of synthetic magnesium sulfate hydrate and optionally small amounts of water.

The magnesium sulfate granules according to the invention based on synthetic magnesium sulfate hydrate also have dry losses of less than 2% by weight, in particular not more than 1% by weight and especially not more than 0.5% by weight, for. B. 0.05 to 1 wt .-% and especially 0.1 to 0.5 wt .-%, a breaking strength or bursting strength of at least 30 N, especially at least 35 N, especially at least 40 N, z. B. 30 to 70 N, in particular 35 to 60 N and especially 40 to 45 N, on. The abrasion of such granules is also below the above-mentioned dry losses usually below 2 wt .-%, in particular below 1, 5 wt .-% and especially below 1 wt .-%.

The values of the bursting strength given here and below are average values which were determined by measuring the bursting strength of 56 granules in the particle size range from 2.5 to 3.15 mm. The terms bursting strength and breaking strength are used synonymously.

The abrasion values given here and below were determined with the Rolltrommel method according to Busch (see also Rolling drum method No. 5 in H. Rieschel, K. Zech, Comparison of different test methods for the quality testing of cal granules No. 10.3. Technik ", Hattingen, Issue 9/1981).

The magnesium sulfate granules according to the invention preferably have a small proportion of particles with a particle size or particle size of less than 1 mm. In particular, the proportion of granule particles, hereinafter granules, having a particle size of less than 1 mm is less than 10% by weight, in particular less than 5% by weight. For use in fertilizers, it is furthermore advantageous if less than 10% by weight of the granules of the magnesium sulfate granules have a particle size of less than 2 mm. Frequently, at least 60% by weight, in particular at least 80% by weight and especially at least 90% by weight, of the granules have a particle size of less than 5 mm. The granule size is preferably at least 60% by weight, in particular at least 80% by weight and especially at least 90% by weight in the range from 2 to 5 mm. The distribution of grain sizes of the granules can in a manner known per se by sieve analysis and refers to the diameter of the granules.

The magnesium sulfate granules according to the invention are generally not commercially available. However, they can be easily prepared from commercially available magnesium sulfate granules by drying. The drying is preferably carried out at temperatures in the range of 90 to 130 ° C, but can also be carried out at lower temperatures or higher temperatures. Preferably, the drying temperature will not exceed 200 ° C to avoid complete dehydration. The drying is typically carried out at ambient pressure or in the range of 900 to 1200 mbar, where higher or lower pressures can be used. The drying time depends primarily on the drying temperature and is usually carried out until the desired dry loss is achieved. The necessary duration can be determined by routine examinations. As a rule, the drying time is 0.1 to 4 h. Drying can be carried out in the apparatuses customary for drying granules, such as belt dryers, rotary kilns, drying drums, fluidized-bed dryers or plate dryers.

The magnesium sulfate granules to be dried can be prepared analogously to processes known per se for the preparation of granules from finely divided inorganic salts, as are known, for example, from the cited prior art and, for example, in Wolfgang Pietsch, Agglomeration Processes, Wiley - VCH, 1st Edition, 2002, in G. Heinze, Handbook of Agglomeration Technique, Wiley - VCH, 2000 and in Perry's Chemical Engineers' Handbook, 7th Edition, McGraw-Hill, 1997, pp. 20-56 to 20-89 are described.

In particular, the preparation of the magnesium sulfate granules to be dried is carried out by buildup agglomeration of finely divided, synthetic magnesium sulfate hydrate with the addition of small amounts of water in order to achieve wetting and agglomeration of the finely divided synthetic magnesium sulfate hydrate due to capillary forces. In general, water is used in an amount in the range of 3 to 15 wt .-%, in particular in an amount of 5 to 10 wt .-%, based on the starting material to be granulated. The use of other binders is not required and is therefore generally not more than 0.1% by weight, based on the starting material to be granulated.

The buildup agglomeration can be carried out in a manner known per se as a rolling, mixing or fluidized bed agglomeration, in particular as a roll agglomeration. In roll agglomeration, the raw material to be granulated is placed in a vessel with a tilted Rotary axis and circular cross-section, preferably in a granulating or on a granulating. By rotating the vessel, the particles of the fine salt are set in motion. The treatment with the water is carried out, for example, by spraying on the agitated magnesium sulfate. This gives a comparatively uniform round granules, which can be fed directly to a classification and / or drying.

In a specific embodiment, the granulator used for roll agglomeration is a device with a cylindrical rotating container for holding the components to be granulated, the axis of rotation of which is inclined with respect to the vertical, the container having at least one rotating eccentric to the center of rotation of the container, in particular a rotating mixing tool with a plurality of leaf-shaped vanes arranged on a rotating shaft and at least one scraper arranged eccentrically to the rotation center of the container. Such granulating devices are known and commercially available, for example as Eirich Intensive Mixer Fa. Maschinenfabrik Gustav Eirich GmbH & Co. KG, Hardheim, Germany. The synthetic magnesium sulfate hydrate required for the preparation of the magnesium sulfate granules according to the invention can be prepared in a manner known per se and is prepared in particular by digestion of magnesium oxide with aqueous sulfuric acid. The digestion of magnesium oxide with aqueous sulfuric acid is known per se and is described, for example, in CN 101486596 or CN 101624299. The aqueous sulfuric acid used for the digestion usually has a concentration in the range from 50 to 90% by weight, in particular in the range from 55 to 85% by weight. The magnesium oxide used for the digestion is typically a magnesium oxide obtained by calcination of magnesite or other magnesium carbonate minerals, which naturally may still contain small amounts of unreacted magnesium carbonate. The magnesium oxide used preferably has an MgO content of at least 80% by weight, in particular at least 85% by weight. Preferably, the sulfuric acid is used in a slightly substoichiometric amount based on the reaction shown in the following reaction equation:

MgO + H ₂ S0 ₄ -> MgSC-4 + H ₂ 0

In particular, the sulfuric acid is used in an amount of 0.8 to 0.99 mol, especially in an amount of 0.85 mol to 0.98 mol per mole of magnesium in the magnesium oxide one. Preferably, the digestion is carried out so that the reaction enthalpy liberated in the reaction to a heating of the reaction mixture to temperatures above 100 ° C, in particular above 110 ° C, for. B. leads to temperatures in the range of 120 to 160 ° C, so that excess water can escape. This can be done, for example, by adjusting the sulfuric acid by mixing concentrated sulfuric acid with water to the desired concentration and then mixing with magnesium oxide. It is also possible to proceed by suspending the magnesium oxide in water or by adding it to water and then adding concentrated sulfuric acid with thorough mixing to the aqueous suspension or to the water-containing dough.

In particular, it has proved to be advantageous if the magnesium sulfate granules according to the invention are prepared by a process comprising the following steps: i) digestion of magnesium oxide with aqueous sulfuric acid;

ii) granulating the reaction mixture obtained by digestion by means of build-up agglomeration to obtain a magnesium sulfate granule; and iii) drying the magnesium sulfate granules to a dry loss of less than 2% by weight, in particular to a dry loss of less than 1% by weight, especially to a dry loss of at most 0.5% by weight.

Accordingly, a preferred embodiment of the invention relates to magnesium sulfate granules obtainable by a process comprising steps i), ii) and iii) and such a process.

Step i) can be carried out in the manner described above, wherein it has proven to be advantageous to use the aqueous sulfuric acid in a slightly substoichiometric amount, as described above. According to the preferred embodiment, the reaction product obtained in the reaction of the magnesium oxide with the aqueous sulfuric acid is then subjected to build-up agglomeration in step ii) in order to convert the finely divided reaction product of the digestion into a coarse-particle magnesium sulfate granulate. The buildup agglomeration is carried out in the manner described above, typically with the addition of small amounts of water. The water is usually used in an amount in the range of 3 to 15% by weight, in particular in an amount in the range of 5 to 10 wt .-%, based on the reaction product to be granulated. The buildup agglomeration occurs in particular as roll agglomeration. Preferably, one then becomes the roll agglomeration using a pelletizing plate or an Eirich intensive mixer type granulator.

With regard to the mechanical properties, it has proved to be particularly advantageous if the hot reaction mixture obtained during the digestion is subjected directly to a buildup agglomeration, in particular a roll agglomeration, and after the buildup agglomeration the resulting magnesium sulfate granules are allowed to undergo a ripening phase. In this case, it will be preferable to proceed in such a way that the digestion is carried out in such a way that the reaction enthalpy released during the reaction leads to a heating of the reaction mixture to temperatures above 100.degree. C., in particular above 110.degree. B. leads to temperatures in the range of 120 to 160 ° C. The resulting still hot reaction mixture, which preferably has temperatures of at least 100 ° C, in particular at least 110 ° C, is then immediately subjected to a buildup agglomeration, preferably a roll agglomeration, in the manner described above. Preferably, the time interval from the beginning of the digestion to the beginning of the buildup agglomeration is not more than 30 minutes. In this way it is achieved that the conversion to the magnesium sulfate hydrate at the beginning of the agglomeration has not yet completed and proceeds during the granulation process. In particular, the reaction mixture at the beginning of Aufbauagglomeration a temperature of at least 100 ° C.

The actual granulation often follows a maturity phase. For this purpose, it leaves the freshly prepared granules, which is also referred to below as green granules, rest, d. H. one avoids a stronger mechanical load and there is no further particle buildup. Here, the granules reaches its actual strength. Maturation typically occurs at temperatures in the range of 50 to 130 ° C. The duration of the ripening phase or the residence time of the granules in the ripening phase is typically 0.2 to 2 h. Typically, the procedure will be such that the green granules discharged from the granulator are transported via a so-called ripening belt to a storage container or to the drying device.

In this way a granulate having the abovementioned composition is obtained, which still has a comparatively high drying loss, which is typically in the range from 5 to 10% by weight, based on the total mass of the granules.

The granules thus obtained are dried and classified. The classification can be done before, during or after the drying in step iii). Often, the classification is carried out before drying in step iii), since the granules initially obtained due to the higher dry loss have greater strength. The drying takes place in the manner described above.

It is also possible to carry out the drying of the granules before or during the ripening phase. For example, it is possible to dry the still hot granules, which are obtained in the buildup agglomeration, to the desired residual water content and then, if appropriate, to allow it to mature even further. The duration of the drying and ripening phase or the residence time of the granules in the drying and ripening phase is typically 0.2 to 2 h. With regard to the drying conditions, what has been said above applies mutatis mutandis. In general, you will then cool quickly and then classify the granules.

The magnesium sulfate granules according to the invention can be used in a manner known per se as Mg- and S-containing fertilizers. Their advantages are particularly useful when these magnesium sulfate granules are used for the production of solid, urea-containing fertilizer compositions. In these fertilizer compositions, the urea naturally exists in solid, particulate form. In particular, they are suitable for the preparation of solid fertilizer compositions in which the urea is in prilled form or in the form of granules. The prills or granules usually have a content

Urea of at least 95 wt .-%, in particular at least 98 wt .-%, on. Frequently, the nitrogen content is about 46% by weight. The grain size of the solid urea is typically in the range of 1 to 4 mm, i. H. at least 90% by weight of the prills or of the granules have a particle size in this range.

The magnesium sulfate granules of the invention are particularly suitable for the preparation of solid fertilizer compositions with a high urea content, in particular those in which the mass ratio of magnesium sulfate granules to urea in the range of 2: 1 to 1: 10 and in particular in the range of 1, 5: 1 to 1: 3 is.

The solid urea-containing fertilizer compositions typically consist of at least 60% by weight, based on the total weight of the fertilizer composition, of a mixture of magnesium sulfate granules and urea. In addition to the magnesium sulfate granules and urea, the fertilizer compositions may also contain other fertilizer ingredients. These include potassium-containing fertilizers such as potassium sulphate (SOP) and potassium chloride (MOP) as well as mixed granulates, as well as phosphorus-containing fertilizers such as superphosphate and triple superphosphate (TSP). These other fertilizers are also typically in solid form, in particular in granular form, are present in the fertilizer composition.

The fertilizer compositions may contain, in addition to the aforementioned components, urease inhibitors and / or nitrification inhibitors. Suitable urease inhibitors are known to the person skilled in the art, for example from Kiss et al. (Kiss, S., Simihäan, M. 2002, Improving Efficiency of Urban Fertilizers by Inhibition of Soil Urease Activity ISBN 1-4020-0493-1, Kluwer Academic Publishers, Dordrecht, The Netherland). Suitable urease inhibitors are, above all, N-alkylphosphoric triamides and N-alkylthiophosphoric triamides and mixtures thereof, as described, for example, in US Pat. From WO

2009/079994 and the literature cited therein are known. Preference is given to N-butylthiophosphoric triamide (NBPT), Nn-propylthiophosphoric triamide (NPPT) and mixtures thereof. Suitable nitrification inhibitors are, in addition to dicyandiamide, especially pyrazoles and their acid addition salts, in particular their phosphoric acid addition salts and thiosulfate salts, and also 1-carboxyalkylpyrazoles and mixtures thereof. Here, the pyrazoles and 1-carboxyalkylpyrazoles can be attached to the carbon atoms by one or more, e.g. B. one or two substituents from the group Ci-C ₄ - alkyl, in particular methyl, be substituted. Such compounds and their use as nitrification inhibitors are known for example from US 3635690, US 4969946, EP 0808298 and EP 1120388. Preferred nitrification inhibitors are 3-methyl-pyrazole compounds such as 3-methylpyrazole, and their acid addition salts, and 3,4-dimethyl-pyrazole (DMP) compounds such as 2- (3,4-dimethylpyrazol-1-yl) -succinic acid, N-hydroxy Methyl-3,4-dimethylpyrazole and their acid addition salts, and especially 3,4-dimethylpyrazole and the acid addition salts of 3,4-dimethylpyrazole, especially its phosphoric acid addition salts (DMPP) and thiosulfate salts.

Such fertilizer compositions contain the at least one further constituent from the group of nitrification inhibitors and urease inhibitors, generally in an amount of 0.001 to 5 wt .-%, in particular in an amount of 0.002 to 3 wt .-%, based on the total weight of the fertilizer composition. If such fertilizer compositions comprise at least one urease inhibitor, the concentration of urease inhibitor is generally 0.001 to 3% by weight, in particular 0.002 to 2% by weight, based on the urea in the fertilizer composition. If such fertilizer compositions contain at least one nitrification inhibitor, the concentration of nitrification inhibitor is generally from 0.01 to 3% by weight, in particular from 0.02 to 2% by weight, based on the total weight of the fertilizer composition, in the case of acid addition salts of pyrazole compounds , calculated as salt. If such fertilizers are used together If the composition contains at least one urease inhibitor and at least one nitrification inhibitor, the total concentration of nitrification inhibitor + urease inhibitor is generally 0.011 to 5% by weight, in particular 0.022 to 3% by weight, based on the total weight of the fertilizer composition. Typically, the weight ratio of the at least one nitrification inhibitor to the at least one urease inhibitor is then usually 1:10 to 10: 1 and preferably 1: 5 to 5: 1.

The fertilizer compositions may optionally contain micronutrients such as manganese, zinc, copper, iron, molybdenum and / or boron. Manganese, copper and zinc are preferably used in the form of their sulfates. Copper and iron are preferably also in the form of chelates, z. B. with EDTA used. Boron is preferably used as calcium sodium borate, sodium borate, potassium borate or boric acid. Molybdenum is preferably used as sodium or ammonium molybdate or as a mixture thereof. These ingredients may be included in the magnesium sulfate granules, in the further fertilizer ingredients, or added separately.

The solid, free-flowing fertilizer composition is prepared by mixing a magnesium sulphate granulate as defined herein and urea in solid form, especially in the form of granules or prills, and optionally other fertilizer components. Here you will use the ingredients so that the above proportions result. The mixing can be carried out in the manner customary for the mixing of particulate solids, in particular of granular solids such as granules and prills. Suitable devices for mixing are case mixers with and without internals such as drum mixers and ring mixers, paddle mixers such as tray mixers, plow blade mixers and twin shaft mixers, and screw mixers. The resulting fertilizer compositions are stable on storage and do not tend to caking or deliquescing even after prolonged storage.

The following examples serve to illustrate the invention. The dry loss TV was determined according to DIN EN 12880: 2000 by drying a sample of about 30 g in a drying oven at temperatures in the range of 105 ± 5 ° C at ambient pressure for 2 h and the weight of the sample before and after drying certain. 1

The burst strength or breaking strength was determined with the aid of the tablet breakage tester type TBH 425D from ERWEKA on the basis of measurements on 56 individual granules of different particle size (fraction 2.5-3.15 mm) and the mean value was calculated. Determined was the force required to break the granule between the punch and plate of the break strength tester. Granules with a burst strength> 400 N and those with a burst strength <4 N were not included in the averaging.

Abrasion values were determined by Busch roller drum method. For this purpose, 50 g of the granules with a particle size fraction of 2.5 - 3.15 mm together with 70 steel balls (diameter 10 mm, 283 g) in a roller drum of a commercially available Abriebtesters, z. B. ERWEKA, type TAR 20, and rotated for 10 min at 40 U * min. The contents of the drum were then screened on a sieve with a mesh size of 5 mm, under which a sieve with a mesh width of 0.5 mm was arranged, on a screening machine (Retsch AS 200 control type) for 1 min. The screened fine fraction corresponds to the abrasion.

In the performance test, a magnesium sulfate granule of synthetic magnesium sulfate monohydrate was used, which was prepared in the following manner:

Calcined magnesite (MgO content about 80-85%) was reacted with about 70% by weight aqueous sulfuric acid in a Mg: H ₂ SO 4 molar ratio of about 0.9. The thus obtained, about 115-120 ° C hot, solid product was immediately after the reaction on a pelletizing plate with spraying of about 5 to 10 wt .-% water processed into granules, which then on a ripening belt with a residence time of 1 h was dried. Subsequent classification yielded a magnesium sulfate granules having a total content of magnesium of 27% by weight, calculated as MgO, and a water soluble magnesium content of 22.5% by weight, calculated as MgO. About 93% by weight of the granules had a particle size in the range from 2 to 5 mm. The proportion of particles with a particle size above 5 mm was less than 1 wt .-%. The proportion of particles with a particle size below 1 mm was also less than 1 wt .-%. The dry loss of the granules used was about 7 to 9 wt .-%.

Application testing: The urea used was a commercially available urea-prill having a nitrogen content of 47% by weight and a particle size of about 0.8 to 2.5 mm. The weight-average diameter (dso value) was 1.64 mm. For the experiments, the magnesium sulfate granules were spread evenly on a plate and placed in the oven at 130 ° C for 15, 20, 25 or 30 minutes. One day later, the samples were divided into 4 fractions in the corrugated divider. With one fraction each (fractions 1 and 2), abrasion and bursting strength were measured. Fraction 3 was used to determine the drying loss (TV). Fraction 4 was used to perform the storage test. In addition, the non-dried magnesium sulfate granules were examined as a blank sample. Table 1 lists the physical properties of the dried granules so prepared:

Table 1: Physical properties of magnesium sulfate granules

Time in the drying cabinet Resistant to abrasion TV

0 min ^* 82 N 0.1% 7.3%

15 min ^* 65 N 0.6% 4.5%

20 min 60 N 1, 4% 1, 7%

25 min 62 N 1, 8% 0.8%

30 min 62 N 2.2% 0.1%

* Comparative granulate

For the determination of the storage stability, the thus dried magnesium sulfate granules were mixed with the urea prills in a weight ratio of 1: 1. The mixture was then stored for 5 minutes at 28 ° C and a relative humidity of 85% RH and transferred the so-tasted sample in an airtight sealable glass vessel. The sealed sample was then stored for a total of 44 days at 35 ° C. At regular intervals, the mixtures were visually examined and rated with the following grades: Grade 1: dry; the granules are in their initial state

Grade 2: first grains sticky; slightly gathering; some individual grains look "damp", mostly urea / magnesium sulphate aggregates Grade 3: partially moistened, nests of "sticky" urea / magnesium sulphate aggregates form, limited flowability.

Grade 4: completely moistened; the entire mixture is at least 80 wt .-% wet or wet, baked and barely pourable, there are some liquid droplets can be seen. The results are summarized in Table 2:

Table 2: Assessment of storage stability of fertilizer compositions

TV storage duration

Sample ^*

[%] 1d 2d 3d 4d 7d 9d 10d 15d 17d 23d 30d 37d 44d

0 min 7.3% 4 4 4 4 4 4 4 4 4 4 4 4 4

15 min 4.5% 1 1 1 2 2 2 2 2 2 2 3 3 3

20 min 1, 7% 1 1 1 1 1 1 1 1 1 2 2 2 2

25 min 0.8% 1 1 1 1 1 1 1 1 1 1 1 1 1

30 min 0.1% 1 1 1 1 1 1 1 1 1 1 1 1 1 * Time In the drying cabinet

In a further experiment, the magnesium sulfate was mixed before the task on a pelletizing plate with a defined amount of micronutrients and then processed under injection of 5 to 11% wt .-% water to a granulate. As micronutrients, 3.3% by weight of borax pentahydrate and 2.9% by weight of zinc sulfate monohydrate were admixed, which corresponds to a boron content, calculated as B2O3 of 1.6% by weight and a content of zinc as elemental zinc of 1, 0 wt .-% corresponds. It was found that the mixture of magnesium sulfate hydrate, borax pentahydrate and zinc sulfate monohydrate was well granulated. The dry loss of the granules was 10.6 wt .-%, the proportion of water-soluble magnesium was 22.6 wt.%, Calculated as MgO. The bursting strength based on measurements on 56 individual granules of different particle size (fraction 2.5-3.15 mm) was determined to 59 N and the abrasion to 4.4 wt .-%.

Claims

Claims:

Magnesium sulfate granules consisting of at least 90% by weight, based on the total mass of magnesium sulfate granules, of synthetic magnesium sulfate hydrate and having a dry loss of less than 2% by weight as determined by drying the granules for 2 hours 105 ° C and 1 bar.

Magnesium sulfate granules according to claim 1, having a total content of magnesium of at least 26% by weight, calculated as MgO and based on the total weight of the granules.

Magnesium sulfate granules according to claim 1 or 2, wherein the proportion of water-soluble magnesium, based on the total mass of the magnesium sulfate granules and calculated as MgO, in the range of 20 to 25% by weight.

Magnesium sulfate granules according to one of the preceding claims, wherein the proportion of water-insoluble magnesium, based on the total mass of the magnesium sulfate granules and calculated as MgO, is in the range from 1.5 to 7.0% by weight.

Magnesium sulfate granules according to any one of the preceding claims, wherein the proportion of water of hydration, determined by the loss on ignition at 550 ° C, is in the range of 18 to 22% by weight, based on the total mass of the magnesium sulfate granules.

Magnesium sulfate granules according to any one of the preceding claims, wherein the magnesium sulphate is present at least 90% by weight, based on the total mass of magnesium sulphate and water of hydration, of magnesium sulphate monohydrate.

7. Magnesium sulphate granules according to any one of the preceding claims, wherein the proportion of salts containing magnesium sulphate and magnesium oxide are less than 3 wt .-%, based on the total mass of the magnesium sulfate granules, is.

Magnesium sulfate granules according to any one of the preceding claims, having on average a bursting strength of at least 30 N, determined on granules with grain sizes in the range of 2.5-3.15 mm.

Magnesium sulfate granules according to any one of the preceding claims, wherein at least 90% by weight of the granules have a particle size in the range of 2 to 5 mm.

Magnesium sulfate granules according to any one of the preceding claims, obtainable by a process comprising

i) digestion of magnesium oxide with aqueous sulfuric acid;

ii) granulating the reaction mixture obtained by digestion by means of build-up agglomeration to obtain a magnesium sulfate granule; and

iii) drying the magnesium sulfate granules to a dry loss of less than 2% by weight.

Magnesium sulphate granules according to claim 10, wherein subjecting the obtained while digesting, still hot reaction mixture immediately to a buildup agglomeration and after the buildup agglomeration, the resulting magnesium sulfate granules can undergo a maturation phase.

A process for producing a magnesium sulfate granule according to any one of the preceding claims comprising

i) the digestion of magnesium oxide with aqueous sulfuric acid; ii) granulating the reaction mixture obtained by digestion by means of build-up agglomeration to obtain a magnesium sulfate granule; and

iii) drying the magnesium sulfate granules to a dry loss of less than 2% by weight. A process according to claim 12, wherein the still hot reaction mixture obtained during the digestion is subjected directly to a buildup agglomeration and, after the buildup agglomeration, the resulting magnesium sulfate granules are allowed to undergo a ripening phase.

Use of magnesium sulfate granules according to one of the claims

I to 11 for the preparation of solid, urea-containing fertilizer compositions.

Solid, free-flowing fertilizer compositions containing magnesium sulphate granules as defined in any one of claims 1 to 11 and urea in solid form.

Fertilizer compositions according to claim 15, consisting of at least 60% by weight, based on the total weight of the fertilizer composition, of a mixture of magnesium sulphate granules as defined in any one of claims 1 to 11 and urea.

Fertilizer compositions according to claim 15 or 16, wherein the weight ratio of magnesium sulfate granules to urea is in the range of 2: 1 to 1:10.

Fertilizer compositions according to any one of claims 15 to 17, wherein the urea is in the form of prilled or granulated urea.

A process for producing a solid, free-flowing fertilizer composition according to any one of claims 15 to 18, which comprises mixing a magnesium sulfate granule as in any one of claims 1 to

I I defined, and urea in solid form, in particular in the form of urea prills or urea granules.