Method for the production of potassium chloride granules

Abstract

The present invention relates to a process for producing potassium chloride granules from a crystalline potassium chloride raw material, wherein the potassium chloride raw material is treated with at least one alkali metal carbonate and at least one metaphosphate additive in the presence of water prior to granulation. The invention also relates to the potassium chloride granules obtainable by the process.

Description

[0001] The present invention relates to a process for producing potassium chloride granules from a crystalline potassium chloride raw material, for example, from crystalline potassium chloride obtained by flotation, evaporation, crystallization, solar evaporation, or a hot dissolution process. The invention also relates to the potassium chloride granules obtainable by the process.

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

[0003] Potassium chloride is frequently marketed in granular form because of its advantageous handling properties. Compared to finely divided crystalline potassium chloride, granules are far less prone to dust formation, have a more stable storage life, are less likely to clump together, and are easier and more evenly applied by spreading when used as a fertilizer. The quality of potassium chloride granules, and therefore the price achievable on the market, depends on both their purity and the quality of the granules themselves.

[0004] The crystalline potassium chloride raw material obtained during mining typically has particle sizes significantly smaller than the desired granule size. To produce the granules, the potassium chloride raw materials are subjected to a standard granulation process in which the fine crystalline potassium chloride particles are agglomerated, resulting in an increase in particle size.

[0005] Common granulation processes for the production of potassium chloride granules are compression agglomeration and build-up agglomeration. In build-up agglomeration of potassium chloride, the finely divided starting material is intensively agitated with the addition of an aqueous liquid, resulting in numerous collisions between the primary particles. These particles then aggregate due to capillary forces mediated by the liquid. These aggregates can then combine with each other or with further primary particles. The continuous agitation leads to a continuous build-up of particle layers and compaction of the particles, ultimately yielding moist granules (green granules) of the desired size, which are then dried and hardened to produce the finished granules.In the press agglomeration of potassium chloride, the finely divided starting material is compacted by applying pressure, resulting in very high forces acting on the primary particles. This leads to deformations of the primary particles in the contact area, for example through plastic deformation, which considerably increases the adhesion between the primary particles. As a result of frictional heat, local sintering processes can also occur, leading to the formation of solid bridges between the primary particles.

[0006] The actual agglomeration is followed, if necessary after drying the moist granules, by a classification of the primary granules obtained, in which the primary granules are separated into fractions of the desired particle size.

[0007] Potassium chloride granules are generally mechanically unstable. When subjected to mechanical forces, such as those encountered during handling, storage, or especially transport, the granule particles are damaged. This leads, firstly, to a reduction in the particle diameter and a corresponding decrease in value, and secondly, to the formation of a considerable number of fine particles. These fine particles can cause problems during storage and handling of the granules, for example, by producing dust or, in humid conditions, by causing the granule particles to clump together.

[0008] To improve the mechanical stability of the granules, binders are frequently used in the aforementioned granulation processes. These binders enhance the adhesive forces between the particles and thus improve particle cohesion within the granules. Typical binders include gelatin, starch, molasses, lignosulfonates, lime, and clay minerals. The choice of binder generally has a significant impact on the properties of the granules, particularly their mechanical strength (abrasion resistance, hardness), hygroscopic properties, and dustiness. However, even with the use of such conventional binders, potassium chloride granules typically exhibit insufficient mechanical stability, leading to the problems mentioned above.

[0009] SU 990755 describes a process for the production of potassium chloride granules by a press agglomeration process in which sodium polyphosphate is added to the potassium chloride starting material in an amount of 0.2 to 1 wt.% based on potassium chloride.

[0010] RU 2083536 describes a process for the production of potassium chloride granules by press agglomeration of potassium chloride raw material, in which the potassium chloride dust produced during press agglomeration is mixed with an aqueous solution of sodium metasilicate and added to the potassium chloride raw material used for compaction.

[0011] US Patent 4,385,020 describes a process for the production of potassium chloride granules, in which potassium chloride is processed with a phosphate binder in a drum or disc granulator to form potassium chloride granules.

[0012] German patent DE 10252848 describes a process for producing potash fertilizer granules, in which a crude potash fertilizer granulate is treated with a silicate- or carbonate-containing solution. The treated granules are then subjected to kinetic energy in the form of vibrations. To improve their resistance to atmospheric moisture, the resulting granules are coated with a water-repellent substance, such as palmitic acid.

[0013] CA 2,465,461 describes a process for producing potassium chloride granules by a press agglomeration process in which hexasodium metaphosphate (SHMP), tetrasodium pyrophosphate, or trisodium phosphate is added to the potassium chloride as a binder before compaction. The SHMP is intended to bind moisture as well as the magnesium and calcium salts contained in the potassium chloride, thereby improving its mechanical strength, particularly during transport.

[0014] However, the mechanical properties of potassium chloride granules known from the prior art are unsatisfactory despite the use of these binders, particularly when the potassium chloride granules are exposed to an atmosphere with elevated humidity for an extended period. Specifically, after storage at elevated humidity, the known potassium chloride granules are characterized by insufficient fracture or burst strength and unsatisfactory abrasion resistance.

[0015] The present invention is therefore based on the objective of providing potassium chloride granules with improved mechanical strength, in particular high fracture and burst strength and satisfactory abrasion resistance. In particular, the potassium chloride granules should still exhibit satisfactory or good mechanical properties even after prolonged exposure to high humidity, for example, 70% RH (relative humidity) or higher, or other moisture exposure due to weathering; that is, the fracture and burst strengths should remain high even at high humidity, and moisture absorption should be low.

[0016] Surprisingly, it was found that these problems can be solved by treating a crystalline potassium chloride raw material with at least one alkali metal carbonate and at least one metaphosphate additive in the presence of water, for example in the form of a filter-moist fine salt, prior to granulation. The combination of at least one alkali metal carbonate and at least one metaphosphate additive significantly increases the fracture toughness at higher humidity levels of, for example, 70% RH or higher, and reduces the moisture absorption of the potassium chloride granules.

[0017] Accordingly, the present invention relates to a process for producing potassium chloride granules from a crystalline potassium chloride raw material, in which the potassium chloride raw material is treated with at least one alkali metal carbonate and at least one metaphosphate additive in the presence of water prior to granulation.

[0018] Preferred embodiments of the method according to the invention are described in the dependent claims and below.

[0019] The potassium chloride granules obtainable according to the invention are distinguished from potassium chloride granules made from untreated crystalline potassium chloride raw material, and also from potassium chloride granules made from potassium chloride raw material treated with only one additive, i.e., either with the alkali metal carbonate or with the metaphosphate additive, prior to granulation, by higher mechanical strength, in particular by higher fracture and burst strength. Furthermore, the granules are characterized by low abrasion. The advantageous mechanical strength is particularly beneficial when the potassium chloride granules are exposed to moisture as a result of weathering, e.g., an atmosphere with increased humidity, especially a relative humidity of 70% or higher.This is particularly surprising because treatment with alkali metal carbonate alone does not lead to any significant improvement in the fracture or burst strength values ​​of weathered granules.

[0020] Accordingly, the present invention also relates to the potassium chloride granules obtainable according to the inventive method.

[0021] The invention also relates to the use of a combination of at least one alkali metal carbonate, at least one metaphosphate additive and water to increase the fracture / burst strength and reduce the moisture absorption of potassium chloride granules.

[0022] The present invention further relates to the use of a combination of at least one alkali metal carbonate, at least one metaphosphate additive and water to increase the breaking strength of potassium chloride granules exposed to high humidity, in particular humidity at or above 70% RH.

[0023] In the process according to the invention, a crystalline potassium chloride raw material is used as the starting material. This crystalline potassium chloride raw material is also referred to below as fine salt. The crystalline potassium chloride raw material consists essentially, i.e., generally to at least 90 wt.%, frequently to at least 95 wt.%, in particular to at least 98 wt.%, and specifically to at least 99 wt.% or at least 99.5 wt.%, based on the solid components of the potassium chloride raw material, of potassium chloride. The potassium content of the crystalline potassium chloride raw material, calculated as K₂O, is typically at least 56.9 wt.%, frequently at least 60.0 wt.%, in particular at least 61.9 wt.%, and specifically at least 62.5 wt.%, based on the solid components of the potassium chloride raw material.

[0024] Depending on its origin, the potassium chloride raw material contains typical impurities, particularly sodium salts and alkaline earth metal salts, especially magnesium and / or calcium salts. It is assumed that these impurities, particularly the magnesium and calcium salts, contribute to the observed stability problems of the granules, especially when the granules are exposed to high humidity. Frequently, the potassium chloride raw material used contains alkaline earth metal salts, e.g., calcium and / or magnesium salts, in a total amount of 0.01 to 1.0 wt.%, particularly 0.05 to 0.7 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.

[0025] The potassium chloride raw material used to produce the granules is typically crystalline potassium chloride mined or obtained via solar evaporation or solution mining, which has been processed, for example, by flotation, evaporation, crystallization, and / or a hot dissolution process, or by a combination of these methods. In the process according to the invention, additional potassium chloride can also be added to the potassium chloride raw material. This additional potassium chloride may be, for example, a residue obtained during the classification of the potassium chloride granules according to the invention, which may have been crushed. In these mixtures of potassium chloride raw material and additional potassium chloride, the proportion of additional potassium chloride, e.g., the residue, will generally be in the range of 1 to 70 wt.%, based on the total mass of the quantity fed for granulation.

[0026] Instead of freshly processed fine salt, a pre-made fine salt can also be used for granulation, for example a pre-made fine salt with a potassium content of at least 60 wt.%, based on the dry components and calculated as K2O.

[0027] Potassium chloride raw material is typically present in the form of fine crystalline salt particles. In addition to these crystalline particles, the potassium chloride raw material may also contain coarser particles, e.g., from returned material. Typically, a potassium chloride raw material is used in which at least 90% by weight of the particles have a particle size of no more than 2 mm. In particular, 90% by weight of the particles in the potassium chloride raw material have a particle size in the range of 0.01 to 2 mm.

[0028] According to the invention, the potassium chloride raw material is treated with at least one metaphosphate additive and at least one alkali metal carbonate in the presence of water before granulation. The alkali metal carbonate and metaphosphate additive are hereinafter also referred to as additives.

[0029] The treatment of the potassium chloride raw material with alkali metal carbonate and metaphosphate additive can be carried out simultaneously or successively. If added simultaneously, the alkali metal carbonate and metaphosphate additive can be added separately or as a premix.

[0030] Examples of suitable alkali metal carbonates are sodium carbonate and potassium carbonate, which can be used in anhydrous form or in the form of their hydrates. In particular, the alkali metal carbonate is selected from anhydrous sodium carbonate (Na₂CO₃), sodium carbonate monohydrate (Na₂CO₃·H₂O), and sodium carbonate decahydrate (Na₂CO₃·10H₂O), and mixtures thereof. Anhydrous sodium carbonate is a particularly preferred alkali metal carbonate.

[0031] Suitable metaphosphate additives are primarily alkali metal metaphosphates, e.g. those of the general formula “M(PO3) n where n is a number in the range of 3 to 25, and M is an alkali metal such as Na or K. Preferred metaphosphate additives are sodium metaphosphates, i.e., those of the formula Na(PO3) n, where n has the aforementioned meanings, e.g., trisodium metaphosphate (n = 3), tetanosodium metaphosphate (n = 4), and hexasodium metaphosphate (n = 6; SHMP), as well as mixtures thereof. Hexanosodium metaphosphate is a particularly preferred metaphosphate additive.

[0032] In the process according to the invention, the alkali metal carbonate is preferably used in an amount of at least 0.05 wt.%, and in particular in an amount of at least 0.1 wt.%, based on the solid components of the potassium chloride raw material. The amount of alkali metal carbonate required to achieve the desired effect will generally not exceed 1 wt.%, and specifically 0.7 wt.%, based on the solid components of the potassium chloride raw material. In particular, the alkali metal carbonate will be used in an amount of 0.05 to 1 wt.%, and specifically in an amount of 0.1 to 0.7 wt.%, based on the solid components of the potassium chloride raw material. The amount of alkali metal carbonate used depends in particular on the alkaline earth metal salts contained in the potassium chloride raw material.Preferably, at least one alkali metal carbonate is used in an amount of 0.5 to 2 mol, in particular in an amount of 0.8 to 1.5 mol per mol of alkaline earth metal ions in the potassium chloride raw material.

[0033] In the process according to the invention, the metaphosphate additive is preferably used in an amount of at least 0.025 wt.%, in particular in an amount of at least 0.05 wt.%, based on the solid components of the potassium chloride raw material. The amount of metaphosphate additive required to achieve the desired effect will generally not exceed 2 wt.%, in particular 1.5 wt.%, and specifically 1 wt.%, based on the solid components of the potassium chloride raw material. Frequently, the metaphosphate additive will be used in an amount of 0.025 to 2 wt.%, in particular in an amount of 0.05 to 1.5 wt.%, and specifically in an amount of 0.07 to 0.4 wt.%, based on the solid components of the potassium chloride raw material. In particular, the amount of metaphosphate additive used depends on the content of alkaline earth metal salts in the potassium chloride raw material.

[0034] It is essential that the treatment of the potassium chloride raw material with the alkali metal carbonate and the metaphosphate additive takes place in the presence of water. This water may originate from the processing of the potassium chloride raw material, for example, water adhering to or trapped within the potassium chloride particles, or water of crystallization, and / or water added to the potassium chloride raw material before or during the addition of the alkali metal carbonate or metaphosphate additive. The total water content in the potassium chloride raw material during treatment with the alkali metal carbonate and the metaphosphate additive is typically at least 2% by weight, and specifically at least 3% by weight, e.g., in the range of 2 to 15% by weight, and particularly in the range of 4 to 9% by weight, in each case based on the solid components of the potassium chloride raw material.If the total water content in the potassium chloride raw material is less than 2% by weight, based on the solid components of the potassium chloride raw material, before treatment with the alkali metal carbonate and the metaphosphate additive, it will be increased, for example, before or during treatment by adding water to a value of at least 2% by weight, based on the solid components of the potassium chloride raw material.

[0035] The common approach is to use moist potassium chloride raw material that already has the desired water content. If necessary, the water content of the potassium chloride raw material is adjusted to these values ​​before or during treatment with the alkali metal carbonate and the metaphosphate additive.

[0036] When treating the potassium chloride raw material, at least one alkali metal carbonate and at least one metaphosphate additive can be added simultaneously or successively. It is generally irrelevant whether the alkali metal carbonate is added first, followed by the metaphosphate additive, or vice versa, or whether both are added simultaneously. The essential point is that the alkali metal carbonate and metaphosphate additive are added before granulation and in the presence of a sufficient amount of water. If the potassium chloride raw material is dried before granulation, the alkali metal carbonate, metaphosphate additive, and, if necessary, water are typically added before drying.

[0037] The common procedure involves adding the additives alkali metal carbonate and metaphosphate additive to the moist potassium chloride raw material. The treated moist potassium chloride raw material (i.e., treated moist fine salt) is then dried before granulation, especially if granulation is carried out by press granulation. Specifically, drying is performed to a maximum water content of 1% by weight, based on the solid components in the treated potassium chloride raw material. Granulation is then carried out. The treated and dried potassium chloride raw material can also be stored before granulation.

[0038] For the treatment of potassium chloride raw material with at least one alkali metal carbonate, the alkali metal carbonate is generally used in powder form and / or as an aqueous solution. If the alkali metal carbonate is used in powder form, the particle size will generally not exceed 1 mm and, in particular, 0.5 mm. If the total water content of the potassium chloride raw material is insufficient, the addition of alkali metal carbonate as a solution is also possible.

[0039] For the treatment of potassium chloride raw material with at least one metaphosphate additive, the metaphosphate additive is generally used in powder form and / or as an aqueous solution. If the metaphosphate additive is used in powder form, the particle size will generally not exceed 1 mm and, in particular, 0.5 mm. If the total water content of the potassium chloride raw material is insufficient, the addition of the metaphosphate additive as a solution is also possible.

[0040] To treat the potassium chloride raw material with the alkali metal carbonate and the metaphosphate additive, the alkali metal carbonate or the metaphosphate additive is usually mixed with the potassium chloride raw material in the desired quantity. As mentioned previously, this mixing must take place before granulation. The total water content in the moist potassium chloride raw material during the addition of the alkali metal carbonate and metaphosphate additive should generally be in the range of 2 to 15 wt.%, and specifically in the range of 4 to 9 wt.%, based on the solid components of the potassium chloride raw material, or adjusted to these values. In particular, the alkali metal carbonate is added to the moist potassium chloride raw material (i.e., the moist fine salt) before drying. In a specific embodiment, both the alkali metal carbonate and the metaphosphate additive are added to the moist potassium chloride raw material (i.e.,Add the desired amount to the moist fine salt before drying.

[0041] Furthermore, potassium chloride granules containing micronutrients such as B, Mn, Mo, Cu, Zn, and Fe, or mixtures thereof, can also be produced using the process according to the invention. The micronutrients can be added before, during, or after granulation. For example, a potassium chloride raw material already containing the desired amount of micronutrients can be used. However, it is more common to add the micronutrients during the process according to the invention, e.g., during the addition of the additives, or afterward, and then granulate the resulting potassium chloride raw material. The micronutrients can also be added to the finished granules, for example, by spraying an aqueous solution of the micronutrients onto the granules. The amount of micronutrients will generally not exceed 1% by weight, based on the anhydrous potassium chloride granules and calculated per element.For example, the potassium chloride granules obtainable according to the invention can contain 0.001 to 1 wt.% boron.

[0042] The actual granulation process can be carried out analogously to the agglomeration processes known from the prior art, which are described, for example, in Wolfgang Pietsch, Agglomeration Processes, Wiley – VCH, 1st edition, 2002, as well as in G. Heinze, Handbook of Agglomeration Technology, Wiley – VCH, 2000, and in Perry's Chemical Engineers' Handbook, 7th edition, McGraw-Hill, 1997.

[0043] Granulation is usually carried out by pressing or build-up agglomeration.

[0044] In granulation by build-up agglomeration, the treated potassium chloride raw material, which contains the additive alkali metal carbonate and the metaphosphate additive in the desired amounts, is set in motion by the application of mechanical forces and optionally treated with water or aqueous solutions of alkali metal carbonate and metaphosphate additive during the granulation process. The build-up agglomeration can be carried out in a manner known per se as roll, mixed, or fluidized bed agglomeration, particularly as roll agglomeration. In roll agglomeration, the potassium chloride raw material, which optionally already contains the components alkali metal carbonate and metaphosphate additive, is placed in a vessel with an inclined axis of rotation and a circular cross-section, preferably in a granulating drum or onto a granulating disc. Rotating the vessel sets the particles of the fine salt in motion. The treatment with the water or...The aqueous solutions of alkali metal carbonate and metaphosphate additive are added, for example, by spraying them onto the agitated potassium chloride raw material. This yields a relatively uniform, round granulate that can be directly subjected to classification.

[0045] Preferably, the granulation process comprises press agglomeration of the treated potassium chloride raw material and comminution of the material obtained from the press agglomeration. During press agglomeration, the treated potassium chloride raw material is compacted under pressure. In principle, all presses known for similar purposes, such as ram, extrusion, perforating, and roller presses, are suitable for compaction.

[0046] Compaction is preferably carried out using a roller press. In roller presses, compaction takes place in the gap between two counter-rotating rollers. The roller surfaces can be smooth, profiled (e.g., grooved, corrugated, or waffled), or equipped with forming troughs. 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 frequently used. In this case, the primary agglomeration product is a ribbon-like strand emerging from the roller gap, also known as a scoop.

[0047] 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, particularly in the range of 40 to 70 kN / cm, based on a diameter of 1000 mm and an average flake thickness of 10 mm. The roller press is typically operated at a roller peripheral speed of 0.2 to 1.6 m / s. Compaction usually takes place at temperatures in the range of 80 to 100°C or at the temperature resulting from the action of the mechanical forces on the treated potassium chloride raw material (i.e., the treated fine salt). If necessary, the material fed to the granulation process is preheated to the desired compaction temperature, or residual heat is available, e.g., from drying.

[0048] If necessary, the press agglomeration can be carried out in multiple stages.

[0049] Press agglomeration of the treated potassium chloride raw material using a roller press typically yields flakes, which are then subjected to comminution to adjust the particle size of the resulting granules. This comminution can be carried out in a manner known per se, for example, by grinding in suitable devices such as impact crushers, impact mills, or roller crushers.

[0050] The actual granulation process is generally followed by a classification of the granules. This involves separating the granules into those with the specified particle size, smaller granules (fine fraction), and, if necessary, coarser granules (coarse fraction). Potassium chloride granules are considered to meet specifications if at least 90% by weight of the granule particles have a particle size or diameter in the range of 0.5 to 8 mm, and particularly in the range of 2 to 4 mm. Classification can be carried out using conventional methods, especially by sieving.

[0051] The non-compliant granulate material generated during classification, the so-called return material, is usually recycled back into the process.

[0052] In a preferred embodiment of the invention, a moist potassium chloride raw material, which typically contains 2 to 15 wt.%, in particular 4 to 9 wt.%, based on the solid components of the potassium chloride raw material, is mixed with at least one alkali metal carbonate, in particular anhydrous sodium carbonate, and at least one metaphosphate additive, in particular hexasodium metaphosphate (SHMP), in the desired amount, thereby obtaining a treated (conditioned) moist potassium chloride raw material. The alkali metal carbonate and metaphosphate additive can be used in the form of solids or in the form of aqueous solutions. The conditioned potassium chloride raw material thus obtained is then dried.The dry, conditioned potassium chloride raw material is fed, if necessary with the return material, to a press agglomeration, in particular a press agglomeration using a roller press with smooth or profiled rollers. The resulting granules or flakes are then crushed and classified. The fines produced during classification are fed back into the press agglomeration along with the dried, conditioned potassium chloride raw material.

[0053] The granules obtained in this way can be processed in a manner known per se, e.g. packaged and transported.

[0054] The potassium chloride granules obtainable according to the inventive process naturally contain, in addition to potassium chloride, the additive alkali metal carbonate and metaphosphate additive (or their reaction products) in the amounts used in the inventive process. In particular, the potassium chloride granules obtainable according to the inventive process consist of at least 90 wt.%, in particular at least 95 wt.%, and specifically at least 98 wt.%, based on anhydrous granules, of: i) Potassium chloride, ii) the additive alkali metal carbonate and / or its reaction products such as MgCO3 or CaCO3, in an amount of 0.05 to 1 wt.%, in particular in an amount of 0.1 to 0.7 wt.%, based on the potassium chloride contained in the granules and calculated as alkali metal carbonate, and iii) the metaphosphate additive or its hydrolysis / conversion products, in an amount of 0.025 to 2 wt.%, in particular in an amount of 0.05 to 1.5 wt.%, based on potassium chloride and calculated as metaphosphate additive.

[0055] In addition, the potassium chloride granules obtainable according to the invention contain the impurities contained in the potassium chloride raw material / fine salt, e.g. magnesium salts and / or calcium salts in the above specified proportions.

[0056] Furthermore, the potassium chloride granules may also contain micronutrients such as boron, manganese, molybdenum, copper, zinc, and iron, or mixtures thereof. The amount of micronutrients will generally not exceed 1% by weight, based on the anhydrous potassium chloride granules and calculated as each element. For example, the potassium chloride granules obtainable according to the invention may contain 0.001 to 1% by weight of boron.

[0057] As already mentioned, the potassium chloride granules according to the invention are characterized by high mechanical stability even when stored in humid atmospheres, e.g., at relative humidity levels of 70% RH or above 70% RH. Even under these conditions, the potassium chloride granules according to the invention exhibit low dust generation, high fracture / burst strength, low moisture absorption, and low abrasion.

[0058] Fig. shows a test setup for determining the “fracture strength” of test specimens comprising a test stamp ( 1 ) with a conical test tip (R5) and a U-shaped test specimen holder ( 3 ), in which the test specimen ( 2 ) is fixed on both sides. Laboratory experiments:

[0059] The potassium chloride raw material (fine salt) used was a crystalline product obtained by hot dissolution. The potassium content of the potassium chloride was approximately 60 wt%, calculated as K₂O and based on the solids. The magnesium content, calculated as MgCl₂, and the calcium content, calculated as CaCl₂, totaled approximately 0.13 wt%, based on the solids. The particle size of the potassium chloride raw material (fine salt) was typically 0.01 to 2 mm. The water content of the moist potassium chloride raw material (moist fine salt) was 4–9 wt%, particularly 8 wt%, based on the solids before drying.

[0060] A commercially available powdered anhydrous sodium carbonate and hexasodium metaphosphate with a water content of 0.01 wt.% were used as the alkali metal carbonate and metaphosphate additives, respectively. Production of test specimens for determining fracture toughness:

[0061] For this purpose, 3 kg of potassium chloride of the above specification were mixed with 240 g of water and the respective additive (as a powder) in an intensive mixer for 1 minute. The moist potassium chloride raw material / additive mixture was dried for 24 hours in a drying oven at 105°C and then deagglomerated to a particle size of < 0.8 mm using a disc mill. For the "dry" comparison tests, the additives were mixed in after drying and after deagglomeration.

[0062] To determine the tensile strength, cuboid test specimens with dimensions of 50 × 50 × 8 mm were produced from this material. The test specimens (laboratory tests) were manufactured using a hydraulic ram press (model K50 from Komage) with a pressing force of approximately 290 kN, as described in Fig. schematically represented. Determination of the breaking strength (point load) of the test specimens:

[0063] The unweathered test specimens were measured immediately after their manufacture.

[0064] For aeration, the freshly produced test specimens were weighed and then aerated as follows: The test specimens were fixed vertically in sample holders and stored in a climate chamber for 72 hours at 20°C and 70% relative humidity.

[0065] Immediately after being removed from the climate chamber, the exposed test specimens were weighed again to determine the water / moisture absorption, and then the breaking strength was immediately determined.

[0066] The determination of the fracture strength via a point load was carried out in accordance with ASTM D5731:2008 (Point load strength index). For this purpose, the square test specimens ( 2 ) in the U-shaped sample holder ( 3 ) of the in Fig. The schematically shown test device is fixed on both sides so that the test tip (R5) is on the center of the square test body ( 2The test tip was aligned with the test specimen. Then, the test tip was pressed onto the specimen at a speed of 1 mm / min, and the force exerted on the specimen was determined using a pressure gauge. The maximum load on the specimen immediately before fracture, characterized by a drop in force towards zero, was determined. The test tip was conical with a cone angle of 60° and a radius of 5 mm (see [reference]). Fig. ).

[0067] Ten test specimens each (exposed to weathering / unexposed to weathering) were measured. The values ​​for the breaking strengths (point load) given in Table 1 are mean values ​​from 10 measurements. Table 1: Fracture strengths of test specimens made from potassium chloride raw material and the additives anhydrous sodium carbonate and SHMP, laboratory tests (square test specimens) # Additive Point loads unprotected from weather Point load ventilated** Moisture absorption at 70% RH** 1* 0.16 wt% A11 + 0.4 wt.% P931 0.38 kN 0.34 kN 0,12% 2* 0.16 wt% A11 + 0.2 wt.% P931 0.32 kN 0.28 kN 0,21% 3* 0.16 wt% A11 + 0.1 wt.% P931 0.33 kN 0.25 kN 0,30% 4* 0.16 wt% A11 + 0.05 wt.% P931 0.33 kN 0.20 kN 0,40% 5* 0.16 wt% A11 + 1.0 wt.% P931 0.39 kN 0.33 kN 0,26% V6 0.16 wt% A11 (dry) + 0.4 wt% P931 (dry) 0.35 kN 0.19 kN 0,65% V7* 0.4 wt.% P931 0.34 kN 0.23 kN 0,29% V8* 0.2 wt.% P931 0.33 kN 0.21 kN 0,50% V9* 0.1 wt.% P931 0.35 kN 0.22 kN 0,57% V10* 0.05 wt.% P931 0.33 kN 0.19 kN 0,64% V11 0.4 wt% P931 dry 0.35 kN 0.20 kN 0,71% V12* 0.13 wt.% A11 0.33 kN 0.19 kN 0,41% V13 0.16 wt% A11 dry 0.33 kN 0.15 kN 0,68% V14* Potassium chloride raw material (here: 60 MOP fine) without additive 0.34 kN 0.17 kN 0,63% *each with 8% water by weight; ** Weathered 72 h, 20°C, 70% RH; # = Attempt number; V = Comparative trial; A11 = Anhydrous sodium carbonate; P931 = hexasodium metaphosphate (SHMP); 60s MOP fine = Potassium chloride fine salt with a potassium content of at least 60.0% K2O Factory trial:

[0068] For the production of potassium chloride granules in a factory trial, moist potassium chloride raw material (i.e., moist fine salt) with a residual moisture content of 2–15 wt.% was fed to the drying process, optionally via a mixer. The additives according to the invention were added, for example, in the built-in mixer, and the mixture was homogenized. The treated fine salt was then fed to the drying process and subsequently, optionally, along with the press return material, fed to the presses in the granulation stage. After classification / compression, the usable granules, the marketable potassium chloride granules, were obtained. These granules are known, among other things, as commercially available "60% MOP granules," provided the potassium chloride content is at least 60.0% K₂O.

[0069] For press agglomeration in production, several roller presses with a return material cycle were used. The individual roller presses are constructed as follows: two counter-rotating rollers have a waffle-like profiling on their surface (typical roller diameter 1000 mm, typical working width 1000 mm, gap width typically approx. 15 mm). The press was operated with a line force of approximately 60 kN / cm and a roller speed of 18 rpm. The fine salt was generally fed via a central chain conveyor and the screw conveyors located above the presses.

[0070] The flakes produced in the roller press were crushed using an impact mill. The material was then classified using a standard screening device, the fraction with a particle size of 2–4 mm (product) was separated, the fraction with a particle size < 2 mm was returned to the feed (fine material), and the fraction with a particle size > 4 mm (coarse material) was ground and screened again.

[0071] To determine the burst strength of the granules, a test fraction (test granules) with a grain size of 2.5–3.15 mm was sieved.

[0072] The unweathered test granules were measured in parallel with the weathered granules.

[0073] For aeration, approximately 9 g of the prepared test granules were placed in a Petri dish and weighed. For conditioning, the Petri dish was stored in a climate chamber for 24 hours at 20°C and 70% or 71% relative humidity. Immediately after removal from the climate chamber, the Petri dish containing the test granules was weighed again to determine water absorption, and then the breaking strength of the granules was immediately determined using the following method.

[0074] The mean burst strengths were determined using the ERWEKA TBH 425D tablet burst strength tester based on measurements of 56 individual agglomerates of varying particle sizes (fraction 2.5–3.15 mm), and the mean value was calculated. The force required to break the granules between the plunger and plate of the tester was determined. Granule particles with a burst strength > 400 N and those with a burst strength < 4 N were excluded from the averaging process.

[0075] In the factory trial listed in Table 2, potassium chloride raw material with the following specifications was used: KCl content approximately 61% K₂O, approx. 0.2 wt% MgCl₂ / CaCl₂ content, and the residual moisture content of the (moist) potassium chloride raw material is typically 5.7–6.2 wt%. The processed quantities amount to approximately 90 t / h of potassium chloride raw material. Table 2: Factory trials of potassium chloride granules with anhydrous sodium carbonate and SHMP from filter-moist potassium chloride (KCl) raw material* (burst strengths in N and moisture absorption in %) # Additive unseasonably cool 1 day / 70% RH 1 day / 71% RH 15* 0.26 wt% A11 + 0.07 wt.% P931 80 N 47 N 0,14% 26 N 0,55% V16* 0.12 wt.% P931 70 N 18 N < 10 N V17* KCl raw material (without additive) 62 N 14 N 1,34% < 10 N 3,14% # = Attempt number; 1 d / 70% RH = 1 day of storage at 70% relative humidity 1 d / 71% RH = 1 day of storage at 71% relative humidity * each with approximately 6% water by weight; A11 = Anhydrous sodium carbonate; P931 = Hexasodium metaphosphate (SHMP)

[0076] Table 2 shows the comparative effect of combining the additives anhydrous sodium carbonate with SHMP, e.g., in comparison to SHMP alone. The potassium chloride granules from test 15 show significantly better burst strengths – even at higher relative humidity levels – than the products from comparative tests V16 and V17. Moisture absorption after one day is 0.14% (70% relative humidity) and 0.55% (71% relative humidity). Table 3: Laboratory tests with potassium chloride granules with the additives anhydrous sodium carbonate and SHMP and micronutrients** # Additive Point loads unprotected from weather Point load ventilated Moisture absorption 18* 0.16% by weight A11 + 0.4% by weight P931 + 0.5% by weight B 0.34 kN 0.39 kN 0,26% # = Attempt number; * with 8% water by weight; ** For comparative tests see No. 1 and V14 A11 = Anhydrous sodium carbonate; P931 = hexasodium metaphosphate (SHMP), B = Borax anhydrous, calculated as boron QUOTES INCLUDED IN THE DESCRIPTION

[0077] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0078] SU 990755

[0009] RU 2083536

[0010] US 4385020

[0011] DE 10252848

[0012] CA 2465461

[0013] Cited non-patent literature

[0079] Wolfgang Pietsch, Agglomeration Processes, Wiley – VCH, 1st edition, 2002

[0042] G. Heinze, Handbook of Agglomeration Technology, Wiley – VCH, 2000

[0042] Perry's Chemical Engineers' Handbook, 7th Edition, McGraw-Hill, 1997

[0042]

Claims

[1] Method for producing potassium chloride granules from a crystalline potassium chloride raw material, wherein the potassium chloride raw material is treated with at least one alkali metal carbonate and at least one metaphosphate additive in the presence of water prior to granulation. [2] Method according to claim 1, wherein the alkali metal carbonate is selected from anhydrous sodium carbonate, sodium carbonate monohydrate and sodium carbonate decahydrate, wherein it is particularly anhydrous sodium carbonate. [3] Method according to claim 1 or 2, wherein the metaphosphate additive is selected from alkali metal metaphosphates, in particular from hexasodium metaphosphate (SHMP, n = 6), tetanosodium metaphosphate (n = 4) and trisodium metaphosphate (n = 3), wherein in particular hexasodium metaphosphate (SHMP) is selected. [4] Method according to any of the preceding claims, wherein the alkali metal carbonate is used in an amount of 0.05 to 1 wt.%, in particular in an amount of 0.1 to 0.7 wt.%, based on the solid components of the potassium chloride raw material. [5] Method according to any of the preceding claims, wherein the metaphospate additive is used in an amount of 0.025 to 2 wt.%, in particular in an amount of 0.05 to 1.5 wt.%, based on the solid components of the potassium chloride raw material. [6] Method according to one of the preceding claims, wherein the water content during the treatment of the crystalline potassium chloride raw material with the alkali metal carbonate and the metaphosphate additive is in the range of 2 to 15 wt.%, in particular 4 to 9 wt.%, based on the solid components of the potassium chloride raw material. [7] Method according to any of the preceding claims, wherein the alkali metal carbonate is used in the form of a powder and / or in the form of an aqueous solution. [8] Method according to any of the preceding claims, wherein the metaphosphate additive is used in the form of a powder and / or in the form of an aqueous solution. [9] Method according to any of the preceding claims, wherein the potassium chloride crude material contains 0.01 to 1.0 wt.%, in particular 0.1 to 0.7 wt.% magnesium salts and calcium salts and mixtures thereof, in particular present as MgCl2 and CaCl2, respectively, based on KCl and calculated as MgCl2 or CaCl2. [10] Method according to one of the preceding claims, wherein a potassium chloride raw material is used for granulation, wherein at least 90 wt.% of the powdered potassium chloride raw material has a particle size in the range of less than 2 mm. [11] Method according to any of the preceding claims, wherein the granulation comprises a press agglomeration of the potassium chloride raw material. [12] Method according to any of the preceding claims, wherein the alkali metal carbonate and the metaphosphate additive are added to a moist potassium chloride raw material having a water content of at least 2 wt.%, based on the solid components of the potassium chloride raw material. [13] Method according to claim 12, wherein the moist potassium chloride raw material is dried after the addition of the alkali metal carbonate and the metaphosphate additive prior to granulation. [14] Method according to one of the preceding claims, wherein at least one micronutrient, in particular a boron-containing micronutrient, is added to the potassium chloride raw material before or during granulation. [15] Potassium chloride granules obtainable by a process according to any one of claims 1 to 14. [16] Use of a combination of at least one alkali metal carbonate, at least one metaphosphate additive and water to reduce the moisture absorption of potassium chloride granules. [17] Use of a combination of at least one alkali metal carbonate, at least one metaphosphate and water to increase the fracture / burst strength of potassium chloride granules exposed to high humidity.