Nutrient granules, their production, a device for their production and their use

Description

[0001] The invention relates to a nutrient granulate, its production, a device for its production, and its use in agriculture and / or horticulture. State of the art:

[0002] Agricultural use depletes the soil of mineral resources, such as phosphorus compounds, which must then be replenished through the application of mineral fertilizers. The material and energetic use of biomass, such as from household waste or sewage sludge, is associated with the removal of nutrients and significant amounts of organic matter from natural cycles. Maintaining soil fertility through the use of artificial mineral fertilizers derived from fossil resources is ecologically problematic, both due to the environmentally destructive extraction process and the introduction of heavy metals into the soil through these fertilizers. Phosphorus is a limited resource, and its efficient use for fertile soil is of paramount importance in light of a growing global population.From a sustainability perspective, closing natural nutrient cycles is becoming increasingly important and also offers a local source of raw materials that has so far only been used to a limited extent.

[0003] Organic residues, such as sewage sludge, digestate, or liquid manure, are in principle a cost-effective and sustainable alternative to mineral fertilizers, thus contributing to closing the nutrient cycle. These organic residues are still sometimes applied directly to fields. However, acceptance of this method has been steadily declining for some time, as direct application leads to undesirable odor nuisance, and the associated cycles are suspected of causing an undesirable concentration of certain pollutants, such as perfluorinated surfactants (PFAS) and various heavy metals. Sewage sludge that has not undergone sanitizing treatment can also contain a variety of pathogens relevant to disease and plant health, such as bacteria, viruses, parasites, and worm eggs.If organic residues are to be used in agriculture, there is always a risk that pathogens will enter humans and animals via food and feed, thus endangering them.

[0004] The thermal utilization of these organic residues is currently gaining considerable importance. Ashes from the thermal utilization or incineration of organic residues are suitable raw material sources due to their high nutrient content, such as phosphorus (P). However, because of the poor plant availability of the phosphorus (P) contained in the ash, direct use of the ash as fertilizer is hardly possible. Therefore, such ashes are currently mostly landfilled or used in landscaping and are thus, to the detriment of the nutrient cycles, no longer available as a raw material source.

[0005] Various processes for the material recovery of phosphorus-containing ash, for example from sewage sludge, are known in the prior art. These processes are mostly based on ash as a raw material, with the phosphorus content in the ash being as high as possible. The processes differ with regard to phosphorus removal (acid and precipitating agents), the recycled product, and the method of heavy metal removal. Processes for recovering phosphate from sewage sludge ash can generally be subdivided into thermochemical, thermoelectric, and wet-chemical approaches, with thermochemical approaches preferably operating below the ash melting point (<1,000°C) and thermoelectric approaches preferably operating above the ash melting point (>1,000°C).

[0006] Numerous different concepts are pursued in wet chemical processes, with a general distinction being made between processes in which the acid is only mixed with the ash and fertilizer is produced from it, and processes in which phosphorus is extracted from the ash and thus brought into the liquid phase.

[0007] From DE 10 2010 034 042 B4, a process is known in which a mixture is produced from the crushed ash from the mono-incineration of municipal sewage sludge, optionally together with other components such as alkali salts and / or other nutrients, by mixing them together. A specific amount of mineral acid, preferably orthophosphoric acid, is then added to this mixture. The treatment with mineral acid converts the phosphate present in the ash, which is only soluble in citrate, into water-soluble phosphate. The resulting fertilizer is a phosphate and multi-nutrient fertilizer, which is in granular form as a result of the production process.

[0008] A problematic aspect of this process is the coupling of the ash-acid reaction with granulation. The proportion of diluted or undiluted mineral acid serves not only to increase the solubility of the phosphate from the ash, but also simultaneously to adjust the required binding effect during granulation, since the mixture of ash, any other components, and the mineral acid is granulated directly during the ongoing reaction. Essentially, the diluted or undiluted mineral acid corresponds to the moisture content necessary for granule formation in, for example, the specified twin-shaft paddle mixer, batch mixer, continuous mixer, or granulating disc.

[0009] This relatively small liquid phase, necessary for good granulation, leads to significant process engineering problems because spontaneous and sometimes highly exothermic reactions occur when the phosphate-containing ash is mixed with the mineral acid. This considerably complicates granulation, as the vigorous exothermic reaction causes the forming granules to dry out superficially, encrustify, and burst. Furthermore, the ash-acid mixture is often particularly sticky, which significantly hinders stable process control and frequently leads to process disruptions due to adhesion and clogging of plant components. Another problem is that mineral acids are highly corrosive, and many plant components (granulation unit, drying unit, connecting lines) come into contact with them during this process and can be damaged accordingly.

[0010] EP 3 061 741 A1 describes a phosphorus recycling device for the production of a phosphate and multi-nutrient fertilizer, in which the mixing tools of the mixing device and / or the granulating surface of the granulating device are at least partially enamelled. The enamelling of the mixing tools is intended to reduce the caking of the mixture of phosphorus-containing ash and phosphoric acid. Similar to DE 10 2010 034 042 B4, this process also fails to address the very strong and violent exothermic reactions and the granulation difficulties described above.

[0011] From DE 10 2016 116 633 A1, a process is known in which a suspension is first produced from at least one phosphate-containing secondary raw material and at least one mineral acid. Then, the sparingly soluble phosphates of the phosphate-containing secondary raw material are at least partially dissolved in the produced suspension and / or converted into a water- and / or neutral ammonium citrate-soluble phosphate phase. Finally, this suspension is fed to a granulation process, whereby the fertilizer granules are formed and the P₂O₅ content in the fertilizer granules is greater than 75% neutral ammonium citrate-soluble. This publication describes the process engineering advantages as follows: by producing a raw material suspension, the reaction, which occurs partly spontaneously and violently when the phosphate-containing secondary raw materials and the mineral acid are combined directly, can be managed, controlled, and regulated by the process.The suspensions produced in this process have a significantly higher water content than those produced in processes where the phosphate-containing secondary raw materials and diluted or undiluted mineral acid are mixed directly in a near-moist, earth-moist state and, if necessary, granulated (for example, as described in DE 10 2010 034 042 B4). This higher water content is intended to act as a buffer. In this process, the suspension produced in this way is subjected to granulation, resulting in the formation of fertilizer granules. A disadvantage of this process is that the high water content in the suspension must ultimately be removed during or after granulation. In this process, this can only be achieved thermally by drying, which is particularly energy-intensive and therefore expensive. EP 3 293 165 A1, EP 3 037 396 A1, and EP 3 612 505 A1 disclose all processes for the production of fertilizer granules from inorganic secondary phosphates.

[0012] The prior art also includes newer processes for producing fertilizer granules, which aim to overcome the disadvantage of high thermal energy consumption due to the thermal drying of the high water content from the suspension. In these processes, a suspension, referred to in the prior art as a raw material dispersion, is initially produced from an inorganic secondary phosphate and at least one reactant, e.g., a mineral acid. However, a portion of the liquid phase of this suspension is mechanically separated, and granulation is carried out using the separated moist solid. The separated liquid phase is then recycled to produce a new raw material dispersion, whereby any heavy metals present in this liquid phase can be removed beforehand.The mechanically separated portion of the liquid phase therefore does not require thermal drying, resulting in significant energy savings in the process. Furthermore, granulation of moist solids can typically be carried out on granulating discs or intensive mixers, leading to considerably lower operating costs. However, a disadvantage of these processes is that the separation of the liquid phase, particularly the solid / liquid separation, and the recirculation of the liquid phase are complex, require high investment, and thus increase operating costs.

[0013] The present invention aims to provide an economical, ecological, flexible, simple, and technically feasible process for producing soil- and / or plant-specific fertilizers with a precisely adjustable nutrient composition in granular form. It is intended to be particularly suitable for solving the technological problems of the prior art. For this purpose, inorganic secondary phosphate, such as sewage sludge ash, is to be used as a nutrient source, whereby the phosphate contained therein is to be made available to plants. Furthermore, no residues are to be generated during the process.The process according to the invention is intended to enable the efficient and cost-effective processing of various inorganic secondary phosphates, whereby the typical fluctuation range of the secondary raw materials is to be compensated for by flexibly applicable further nutrient components, whereby soil- and plant-specific fertilizer compositions can also be specifically adjusted and wherein a large proportion of the phosphate in the resulting fertilizer granules is to be present in a form that is readily available to plants. Description of the invention:

[0014] The problem is solved by the features of the independent claims. Advantageous embodiments of the invention are described in the features of the dependent claims. The invention relates in particular to a method for producing a nutrient granulate. Furthermore, the invention relates to the nutrient granulate produced in this way, its use, and an apparatus for producing the nutrient granulate. One aspect of the invention solves the problem by providing a nutrient substrate in granular form (nutrient granulate) that can be produced by a manufacturing process comprising the following steps: a) Production of a first mixture with a moisture content of 10-45% comprising at least one inorganic secondary phosphate and at least one liquid reagent, wherein the incubation time between the inorganic secondary phosphate and the reagent is in the range of 10 to 500 minutes; b) Reduction of the moisture content of the first mixture by adding at least one solid component, thereby obtaining a second mixture that is a raw material mixture with a moisture content of less than 35%; c) Granulation and / or extrusion of the raw material mixture using a pelletizing or granulating disc, a granulating drum, or an intensive mixer and repeating process steps a) to c) serially or in parallel, thereby obtaining the nutrient granules.

[0015] The first mixture is preferably also referred to as an earth-moist to easily plastic mixture within the meaning of the invention. According to the invention, the first mixture has a higher moisture content than the second mixture, which is produced in process step b). It is particularly preferred within the meaning of the invention that the first mixture can be both "earth-moist" and "easily plastic." The second mixture is preferably also referred to as an earth-moist mixture within the meaning of the invention, wherein the second mixture preferably represents a raw material mixture that also has an earth-moist consistency. Preferably, the two mixtures differ with respect to their consistency, which is preferably expressed by the different designations "earth-moist to easily plastic" and "earth-moist."

[0016] It is preferred, according to the invention, that an ash always reacts with a reactant. It is particularly preferred that the ash and reactant react together as a mixture. This distinguishes the proposed invention from conventional processes known in the prior art. It is preferred, according to the invention, that further components can be added at the beginning of the manufacturing process so that they are present in the mixture during the reaction. However, it may also be preferred to add these further components at a later stage. A further distinction from the prior art is achieved by the fact that, in the context of the proposed invention, mixtures that are earth-moist or earth-moist to easily plastically moldable are used, which are not suspensions as described in the prior art.

[0017] The formulation stating that "an incubation time between the inorganic secondary phosphate and the reactant is in the range of 10 to 500 minutes" means, within the meaning of the invention, that such an incubation time is observed between the inorganic secondary phosphate and the reactant. This preferably means, within the meaning of the invention, that the inorganic secondary phosphate and the reactant are given a period of time of 10 to 500 minutes to react with each other and form the first mixture.

[0018] Granules used to improve nutrient supply in agriculture, forestry, or horticulture are difficult to characterize using chemical formulas or biophysical data. Therefore, the nutrient granules according to the invention are preferably characterized by a method for their production. This is permissible because the nutrient granules proposed here can be most easily defined by their production method. The proposed granules preferably comprise several nutrient sources. According to the invention, one of these nutrient sources is inorganic secondary phosphate, such as that found in sewage sludge ash. This secondary phosphate is made available by the action of a reagent, which is preferably in liquid form.The proposed method and apparatus enable the efficient and cost-effective processing of a wide variety of inorganic secondary phosphates, whereby the typical variations in the composition of the secondary raw materials can be compensated for by the flexible addition of further nutrient components. This also allows for the targeted adjustment of fertilizer compositions tailored to specific soil and / or plant needs, with a large proportion of the phosphate in the resulting fertilizer granules being present in a surprisingly readily available form for plant use. A further advantageous technical feature of the proposed invention is that the neutral ammonium citrate solubility of the phosphate supplied with the inorganic secondary phosphate is significantly increased by reaction with the at least one liquid reagent.Furthermore, the P₂O₅ content from the inorganic secondary phosphate in the nutrient granules is greater than 60% neutral ammonium citrate soluble, based on the total P₂O₅ content. In a preferred embodiment of the invention, the process for producing a nutrient granule comprises the following steps: a) Production of an earth-moist to easily plastically formable mixture with a moisture content of 10-45% from at least one inorganic secondary phosphate and at least one liquid reagent, with an incubation time between the inorganic secondary phosphate and the reagent of 10 to 500 minutes; b) Reduction of the moisture content of the mixture from a) and adjustment of an earth-moist raw material mixture with a moisture content of less than 35% by adding at least one solid component to the mixture from a); c) Granulation and / or extrusion of the earth-moist raw material mixture from b) using a pelletizing or granulating disc, a granulating drum or an intensive mixer, and repetition of process steps a) to c) serially or in parallel. wherein the neutral ammonium citrate solubility of the phosphate supplied with the inorganic secondary phosphate is increased by reaction with the at least one liquid reagent and the P2O5 content from the inorganic secondary phosphate in the nutrient granules is greater than 60% neutral ammonium citrate soluble.

[0019] It is preferred according to the invention that drying takes place during or after the granulation and / or extrusion of the raw material mixture. In process step b), a dry component is added, thereby reducing the moisture content of the previously earth-moist to easily plastic mixture from step a). It is particularly preferred according to the invention that the reduction of the moisture content in step b) by adding the dry components is only carried out to the extent that the resulting second mixture, which is preferably described as earth-moist, is still capable of being granulated, so that a green granulate can be produced. It is particularly preferred according to the invention that the first mixture is produced from the second mixture, wherein the second mixture has a lower moisture content than the first mixture. This reduction of the moisture content is preferably achieved by adding the at least one dry component.

[0020] According to the invention, the earth-moist to easily plastic mixture has a moisture content of 10-45%.

[0021] According to the invention, the first mixture has this moisture content. Furthermore, it is preferred that, after the incubation period, the pH value of the mixture and / or the raw material mixture is in the range of 4-8, or that the pH value of the moist to easily malleable mixture and / or the moist raw material mixture is adjusted to the range of 4-8 after the incubation period. The adjustability of the pH value advantageously makes it possible to provide particularly specific soil- and / or plant-specific fertilizer compositions, with the resulting fertilizer granules surprisingly having a large proportion of highly plant-available phosphate.

[0022] It is preferred, according to the invention, that the process comprises fractionating the produced nutrient granules, wherein a coarse fraction and / or a fine fraction, ground up, can be at least partially added to the first mixture, the second mixture, and / or process step c). In other words, it is preferred that fractionating the produced nutrient granules follows granulation, wherein the coarse fraction and / or the fine fraction can be ground up and at least partially added to step a), b), and / or c) of the proposed process. It is particularly preferred, according to the invention, that the fractionation takes place after granulation. It is also preferred, according to the invention, that the ground material is added to process step c) so that it can be incorporated or "powder" the surface of the green granules.

[0023] In accordance with the invention, it is preferred that a total of 1 to 70% of the crystallization products from the phosphorus elimination are added to step a), b) and / or c) of the proposed process, whereby drying can take place above 100°C relative to the material temperature during drying.

[0024] Also disclosed, but not according to the invention, is a device for producing a nutrient granulate, the device comprising the following components: a) at least one first mixing vessel configured to mix at least one inorganic secondary phosphate and one liquid reagent into a mixture, wherein the first mixing vessel and / or further vessels are used for an incubation period; b) optionally a second mixing vessel configured to add at least one solid component to the mixture, wherein the first mixing vessel or a separate second mixing vessel may be used for this purpose; c) at least one granulation and / or extrusion unit configured to granulate and / or extrude the mixture produced.

[0025] In other words, a device for producing nutrient granules is preferably provided, which preferably comprises the following components: a) at least one mixing vessel in which at least the inorganic secondary phosphate and the reactant are added, mixed, and an earth-moist to easily plastic mixture is produced, wherein either this mixing vessel is used for the incubation period and / or further vessels are available into which this mixture is transferred and can be mixed for the incubation period; b) at least one mixing vessel in which at least one solid component is added to the earth-moist to easily plastic mixture located therein or added therein, mixed, and an earth-moist mixture is produced, wherein this mixing vessel corresponds to the mixing vessel from a) and / or can be at least one separate mixing vessel; c) at least one granulation and / or extrusion unit in which at least the produced earth-moist mixture can be granulated and / or extruded.where mixing and feeding units for mixing and adding further components may be present in the feeding unit.

[0026] It is preferred that the mixing vessel from a), which is preferably also referred to as the "first mixing vessel," and / or the mixing vessel from b), which is preferably also referred to as the "second mixing vessel," can also function as this granulation and / or extrusion unit. Preferably, the first and / or second mixing vessel can be a separate unit into which the mixture can be transferred by means of at least one feed unit. It is further preferred that mixing and feed units for mixing and for adding further components can be provided in the feed unit. It is also preferred that a drying unit for drying the produced granules and / or extrudates is connected to the granulation and / or extrusion unit.Preferably, a separation unit for fractionating the produced granules and / or extrudates is also added, to which a grinding unit for grinding the separated coarse and / or fine fraction, as well as a return unit for this ground or unground separated coarse and / or fine fraction into at least one mixing container and / or a granulation and / or extrusion unit may be added.

[0027] According to the invention, the granulation and / or extrusion unit is a pelletizing or granulating disc, a granulating drum, an extruder or an intensive mixer.

[0028] In a further aspect, the invention relates to a nutrient granulate that can be produced by the proposed method, wherein the nutrient granulate comprises at least one inorganic secondary phosphate, wherein the neutral ammonium citrate solubility of a phosphate supplied with the inorganic secondary phosphate in the nutrient granulate is greater than 60% neutral ammonium citrate soluble and less than 40% water soluble. In other words, it is preferred that the proposed nutrient granulate can be produced by the proposed method.

[0029] According to the invention, a phosphate component of the inorganic secondary phosphate exhibits a water solubility of less than 40%. Furthermore, it is preferred that the nutrient granules comprise 0.1 to 25% humic acid, fulvic acid, their salts (humates, fulvates), and / or 0.1 to 30% organic acid and / or 0.1 to 50% structural components. The proposed nutrient granules may also contain at least one crystallization product from phosphorus removal in a concentration range between 1% and 70%.

[0030] In another aspect, the invention relates to the use of the proposed nutrient granules in agriculture, forestry and / or horticulture, wherein the nutrient granules comprise at least one inorganic secondary phosphate, as well as a P2O5 content greater than 60% soluble in neutral ammonium citrate for nutrient supply.

[0031] The process according to the invention differs from the prior art in the following points and therefore solves the problem underlying the invention: In step a), the reaction between at least one inorganic secondary phosphate and at least one liquid reaction agent is first carried out in a controlled manner and largely separated from the granulation by adhering to a specific incubation time.

[0032] Furthermore, in process step a), a mixture is initially produced that has a higher moisture content than required for granulation. Only through the subsequent addition of at least one solid component in process step b), largely separated in time from the reaction between inorganic secondary phosphate and acid, is the moisture content of the resulting mixture reduced and thus adapted to the granulation requirements. As a result, the mixture initially has a higher moisture content for the acid reaction than in conventional processes known from the prior art, in which the phosphate-containing ash is mixed together with nutrient components (e.g., alkali salts) and the acid, and in this mixture the acid reaction essentially takes place simultaneously with the granulation without observing an incubation period.

[0033] Higher humidity improves reaction control and increases the reaction rate, leading to more controllable processes and more homogeneous products. Separating the reaction from granulation solves the technical problem that the exothermic and sometimes spontaneous and very vigorous reaction between ash and reactant hinders the granulation process.

[0034] In step a), not a suspension, but rather an earth-moist to easily plastic mixture of at least ash, reagent, and optionally other liquid is produced, with a significantly lower total liquid phase than in a suspension. Due to the addition of this considerably smaller amount of liquid phase compared to a suspension, no liquid phase needs to be thermally or mechanically separated beforehand to form the green granules. Instead, a directly granulatable, earth-moist raw material mixture is produced by adding solid components with low moisture content in process step b). The average person skilled in the art knows that green granules contain at least all the components of fertilizer granules, but that they have an excessively high liquid phase content (e.g., moisture), which must be removed by final drying.

[0035] The thermal separation of the liquid phase of a raw material suspension by drying, as known from the prior art, is extremely energy-intensive and therefore expensive, and is advantageously eliminated in the context of the present invention.

[0036] By adjusting the inventive, earth-moist mixture in process step b), simple granulation technologies such as (intensive) mixers or granulating discs can be used to produce green granules. These technologies, however, cannot be used for granulating suspensions. In this case, more complex and expensive technologies such as spray granulation, agglomeration, or drying must be used.

[0037] It was completely unexpected that the nutrient granules produced by the inventive process ensured both the nutrient supply, and in particular the phosphorus supply, of plants, and also optimized the development of microorganisms, as well as bacteria and protozoa, thus enabling better plant growth. It was by no means obvious to those skilled in the art that pedosphere-improving nutrient granules, characterized by the proposed production steps, would be suitable for both optimizing the animal biomass in the soil and improving plant growth. This applies especially to the crops maize, wheat, onions, potatoes, millet, beans, apples, sugar beets, cucumbers and gherkins, grapes, tomatoes, barley, and cabbage.

[0038] It is in accordance with the invention that the percentages (%) mentioned in the context of this invention refer to weight percent (wt% i.e. % w / w) unless otherwise specified.

[0039] The total amount of phosphorus (P), as well as heavy metals such as lead, cadmium, and nickel, are determined using inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885:2009. For this purpose, the sample to be analyzed is first digested using aqua regia according to DIN EN 13346:2001-04. Various methods, particularly different extraction techniques, are known for determining the soluble phosphate content. To estimate the phosphorus availability, fertilizers are analyzed in the laboratory using different solvents and labeled accordingly. The most important solvents used are water, ammonium citrate, citric acid, formic acid, and mineral acids. The EU regulation on fertilizers also standardizes various methods for determining the phosphate solubility of fertilizers.Depending on the origin and composition of the phosphorus fertilizer being tested, different methods may be used. For characterizing the solubility of phosphate, we will focus on the following three extraction methods: Extraction of water-soluble phosphorus (P) is carried out according to DIN EN 15958:2011. Extraction of phosphorus (P) soluble in neutral ammonium citrate is carried out according to DIN EN 15957:2011. Extraction of phosphorus (P) soluble in 2% citric acid is carried out according to DIN EN 15920:2011. The phosphate content (P) is then determined by inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885:2009.

[0040] Only with high proportions of water- and ammonium citrate-soluble phosphate is it ensured that a large portion of the fertilizer phosphate is actually available to the plant in the short and medium term. The neutral ammonium citrate-soluble phosphorus content can preferably be used as an indicator of the medium-term plant availability of the fertilizer phosphorus, for example, over the period of approximately one crop rotation. The immediately available phosphorus content of a fertilizer is preferably described by its solubility in water. The higher the water-soluble phosphorus content, the faster and more readily the fertilizer phosphorus is available to the plant. Stronger solvents, such as citric or formic acid, also dissolve phosphorus components that are only available to plants in the long term or only under specific site conditions, such as low pH values.Planting and vegetation trials have shown that there is a particularly good correlation between the neutral ammonium citrate-soluble phosphate content and plant growth.

[0041] According to current scientific consensus, for reasons of resource conservation, the use of phosphorus fertilizers with a particularly high proportion of neutral ammonium citrate-soluble phosphate should be preferred. A particular advantage of the invention is that the relatively poorly soluble phosphate from the secondary phosphate is converted to a surprisingly high proportion of neutral ammonium citrate-soluble phosphate, thus enabling the production of fertilizer granules with a particularly high neutral ammonium citrate-soluble P₂O₅ content of greater than 60%, preferably greater than 70%, and optimally greater than 80% of the total P₂O₅ content in the fertilizer granules. Furthermore, the proposed process is controlled in such a way that, in addition to the described neutral ammonium citrate solubility, the lowest possible water solubility of less than 40%, preferably less than 30%, and most preferably less than 20% of the total P₂O₅ content in the fertilizer granules is achieved.

[0042] For the purposes of this invention, fertilizers or nutrient substrates are understood to be substances or mixtures of substances that supplement or adjust the nutrient supply for cultivated plants, particularly crops, in agriculture, forestry, and horticulture. They may optionally be combined with other materials and / or functionalized. The term "fertilizer" here refers to both single-nutrient fertilizers (such as phosphate fertilizers) and multi-nutrient fertilizers. Granular fertilizers, preferably also called nutrient granules, are typically a mass in an approximately spherical shape with sufficient inherent strength and an average granule size of 0.5–10 mm, preferably 1–7 mm, and most preferably 2–5 mm.

[0043] Inorganic secondary phosphate is preferably defined as substances that arise during the processing, preparation and / or manufacture of products (residue) and have a phosphorus content of greater than 5% P2O5 and a TOC content of less than 3%, wherein the abbreviation TOC preferably stands for total organic carbonExamples of inorganic secondary phosphates include ashes and / or slags from the mono- or co-incineration of sewage sludge, ashes and / or slags from the combustion or co-incineration of animal excrement, animal meal, animal remains and carcasses, or ashes and / or slags from the combustion of liquid manure and digestate as individual substances or mixtures thereof. The phosphorus compounds contained in the inorganic secondary phosphate are referred to as phosphate within the meaning of the present invention. It is preferred within the meaning of the invention that the term "phosphate" includes both the phosphorus compounds contained in the inorganic secondary phosphate and other types of phosphorus compounds.A liquid reagent is understood here to be a substance or mixture in liquid form that, in process step a), dissolves at least a portion of the phosphate supplied by the inorganic secondary phosphate and / or reacts with it. For the purposes of the invention, reagents are organic or inorganic acids or acid mixtures, or alkalis or mixtures of different alkalis, each in undiluted or diluted form. Reagents are preferably also mixtures that have a pH value less than 3 or greater than 11 and / or can dissolve and / or react with at least a portion of the phosphate supplied by the inorganic secondary phosphate, such as mixtures that contain at least a proportion of acid or alkali alongside other components, or basic or acidic process wastewater.Liquid reagents preferably also include substances that only form as a liquid phase in process step a), for example, by dissolving solids, which then dissolve at least some of the phosphate supplied by the inorganic secondary phosphate and / or react with it. Examples include acids (e.g., citric acid) or hydroxides (e.g., NaOH, KOH), which can be added as solids and are dissolved, for example, by water in process step a), and as the liquid reagent thus formed, dissolve at least some of the phosphate and / or react with it.

[0044] The term "earth-moist" is preferably defined in the context of the invention by means of a consistency. In concrete technology, concrete of a stiff consistency with a water-cement ratio ≤ 0.40 is generally referred to as earth-moist concrete. By analogy to this definition, an earth-moist raw material mixture in the context of the invention is understood to be a consistency range of the raw material mixture comparable to that of earth-moist concrete. On the one hand, the consistency range according to the invention is limited by a relatively dry mixture, but with more than 5% moisture content, based on the raw material mixture, which can just barely not be shaped in the hand, i.e., does not yet crumble like powder. On the other hand, the range is limited by the fact that the raw material mixture can be shaped in the hand, comparable to a snowball, and does not flow without the application of force, for example, by vibration.

[0045] For the purposes of the invention, a plastically malleable mixture is preferably understood to be a mixture with a clay-like consistency, wherein the plastically malleable mixture itself already exhibits dimensional stability due to effective binding forces, and wherein this dimensional stability is deformable by slight mechanical forces (such as shear, compressive, or tensile forces) and regains its dimensional stability after the force has been applied. A plastically malleable mixture preferably has a somewhat higher moisture content than mixtures that are moist at earth moisture levels.

[0046] In the context of the invention, an earth-moist mixture and a plastically malleable mixture are clearly distinct from a suspension. By definition, a suspension is a heterogeneous mixture of substances consisting of a liquid and finely dispersed solids (particles) in which the particles remain suspended in the liquid, at least partially and at least temporarily, even though settling may occur. The solids are "suspended" in the liquid phase. In contrast, the liquid referred to as moisture in the earth-moist and / or plastically malleable mixtures, as defined in the present invention, is physically bound to or adhering to the solids, or exists largely as so-called pore water. Earth-moist and / or plastically malleable mixtures have a significantly lower proportion of liquid phase than suspensions.

[0047] In the context of the present invention, the moisture content is determined gravimetrically according to DIN 52183. In this gravimetric moisture determination, also known as the drying method, the sample is first weighed and then dried at 105°C in a drying oven until a constant weight is achieved. During this process, the free water contained in the sample evaporates. The weight difference is then determined, which, by definition, corresponds to the moisture content.

[0048] In process step a) of the proposed method, a moist to easily plastic mixture of at least one inorganic secondary phosphate and at least one liquid reagent is preferably produced. It is advantageously possible to integrate further components of the nutrient granules to be produced in this process step as well. The incubation time between the inorganic secondary phosphate and the reagent is between 1 and 500 minutes.

[0049] To form the earth-moist to easily plastic mixture, at least one inorganic secondary phosphate and at least one liquid reagent are combined and sufficiently homogenized. In particular, this yields the first mixture according to the invention. To adjust the desired earth-moist to easily plastic consistency of the first mixture, one or more further liquid components, such as water, can be added in addition to the reagent.

[0050] In the process according to the invention, the inorganic secondary phosphate(s) react with at least one liquid reactant. This increases the solubility of the phosphate contained in the inorganic secondary phosphate. The phosphate content present in inorganic secondary phosphates typically exhibits relatively low solubility and plant availability. Accordingly, such substances, such as sewage sludge ash, are only conditionally suitable as fertilizers. Typically, these inorganic secondary phosphates show a water solubility of less than 30%, often even less than 10%, and a neutral ammonium citrate solubility of less than 50%, each based on the total phosphate content in the inorganic secondary phosphate. For effective use as a fertilizer, this insufficiently soluble phosphate must be converted into a more soluble and thus more plant-available phosphate.According to the invention, the conversion is achieved by at least a partial reaction of the inorganic secondary phosphate with at least one liquid reactant. The reactant is intended to dissolve at least a portion of the phosphate contained in the inorganic secondary phosphate and / or react with it, or convert the phosphate by reaction, such that a phosphate more soluble in neutral ammonium citrate is formed. The phosphate optionally dissolved by the liquid reactant, in the subsequent process, for example by precipitation, recrystallization, or drying, also forms a phosphate more soluble in neutral ammonium citrate than in the inorganic secondary phosphate. For the purposes of the invention, "more soluble in neutral ammonium citrate" preferably means that the neutral ammonium citrate solubility of the phosphate from the inorganic secondary phosphate is higher after the reaction with the reactant than before.A preferred outcome is an increase in the solubility of neutral ammonium citrate by more than 20%. This will be demonstrated in a calculation example: the neutral ammonium citrate solubility of the phosphate fraction from the untreated secondary phosphate, which is 50%, is increased to more than 60% by the reaction with the reactant; an increase of more than 50% is particularly preferred. When acids are used, the proposed process differs from the prior art in that the phosphate reacts at least partially, which advantageously increases its solubility.

[0051] The increase in solubility, however, is specified in more detail, e.g. via the neutral ammonium citrate solubility in the following description.

[0052] By selecting the reactant, for example with regard to its type and concentration, the reaction procedure, and the reaction time, the resulting neutral ammonium citrate solubility of the inorganic secondary phosphate can advantageously be influenced. Preferably, the phosphate fraction from the inorganic secondary phosphate subsequently exhibits a neutral ammonium citrate solubility of greater than 60%, more preferably greater than 70%, and particularly preferably greater than 80% in the produced fertilizer granules. This reaction, or rather the conversion of the phosphate and the resulting neutral ammonium citrate solubility from the inorganic secondary phosphate, leads to improved phosphate availability to plants and thus a very good fertilizing effect.

[0053] To ensure that the reaction between inorganic secondary phosphate and the reactant proceeds in a controlled manner in process step a), a preferably formulated, earth-moist to easily plastic mixture of one or more inorganic secondary phosphates and one or more liquid reactants, optionally with water, is produced in process step a). This mixture preferably contains no further components, consisting of inorganic secondary phosphate, reactant, and optionally water. In this preferred embodiment of the invention, any additional components that may be required, such as additional nutrients, are added only after the incubation period according to the invention.

[0054] The primary goal of the reaction between inorganic secondary phosphate and the reactant is to increase solubility. As described above, the solubility of phosphate in fertilizers is determined using various methods. It is important to note that there is no universally applicable relationship between the solubilities determined in different solvents. For example, if the solubility of neutral ammonium citrate increases by 50%, the water solubility does not necessarily increase proportionally. Phosphate solubility is ultimately dominated by the type of phosphate bond and the solvent environment. The reaction procedure in this process step (e.g., type and concentration of the reactant, reaction time, process temperature) can influence the binding of phosphate, and thus the phosphate phases that form.

[0055] According to the invention, the reaction is preferably controlled such that the phosphate component from the inorganic secondary phosphate subsequently exhibits a neutral ammonium citrate solubility of greater than 60% and a water solubility of less than 40% in the resulting fertilizer granules. By adjusting the solubilities to this degree, it is preferably ensured that the phosphate is sufficiently available to plants in the field for approximately one growing season, but is not leached out during this time. Leaching typically occurs when there is very high water solubility, i.e., significantly higher than that provided here. In a particularly preferred embodiment, the phosphate component from the inorganic secondary phosphate in the resulting fertilizer granules is adjusted to have a neutral ammonium citrate solubility of greater than 80% and a water solubility of less than 30%.Surprisingly, it has been shown that this results in a particularly favorable phosphorus supply for winter rye throughout a growing season. In another particularly preferred embodiment of the invention, the phosphate component from the inorganic secondary phosphate in the produced fertilizer granules is adjusted to have a neutral ammonium citrate solubility of greater than 90% and a water solubility of less than 15%. This ratio is particularly advantageous for wheat plants. In the prior art, high water solubility is often sought. However, investigations, for example on struvite, show that fertilizing effects comparable to triple superphosphate can be achieved even with near 0% water solubility and greater than 80% neutral ammonium citrate solubility. In this respect, the present invention departs from the prior art by achieving the aforementioned neutral ammonium citrate and water solubilities.

[0056] The phosphate contained in the inorganic secondary phosphate serves as a nutrient component in the produced fertilizer. High phosphate contents, particularly in the inorganic secondary phosphate, are therefore advantageous. In accordance with the invention, inorganic secondary phosphates with greater than 10% P₂O₅ are therefore preferred, particularly those with greater than 15% P₂O₅, and most preferably those with greater than 20% P₂O₅. The inorganic secondary phosphate may also contain other components. It is advantageous if further nutrient components are included, for example... N, K, Mg or other trace nutrients.

[0057] In a preferred embodiment of the invention, at least one liquid reagent is used which contains at least one of the elements nitrogen (N), sulfur (S), potassium (K), and / or phosphorus (P), such as phosphorous acid (H3PO3), phosphoric acid (H3PO4), nitric acid (HNO3), sulfuric acid (H2SO4), sulfurous acid (H2SO3), or potassium hydroxide (KOH). The use of such reagents introduces additional nutrient components (nitrogen, sulfur, potassium, and / or phosphorus) into the granules. Through a suitable reaction sequence, the nutrient-bound form of the nutrients contained in the reagent, e.g., nitrogen and / or sulfur, can optionally be converted into a form suitable for the fertilizer.

[0058] In a particularly preferred embodiment, the reactant is at least a dilute or undiluted phosphoric acid and / or phosphorous acid, or at least a dilute or undiluted acid mixture containing a proportion of phosphoric acid and / or phosphorous acid. The advantage of this is that the reactant increases the phosphorus content in the raw material dispersion and thus in the fertilizer ultimately produced from it. Therefore, the reactant not only provides a valuable nutrient component but also particularly facilitates the production of phosphate fertilizers. For example, nutrient granules with a total P₂O₅ content of greater than 35%, particularly preferably greater than 40%, and a neutral ammonium citrate-soluble phosphate content of greater than 80%, particularly preferably greater than 90%, can preferably be produced.

[0059] The components can be combined to form the mixture in any order and in a manner known to those skilled in the art. However, it is important in process step a) that the reactant reacts sufficiently with at least a portion of the phosphate supplied by the inorganic secondary phosphate. The term "react sufficiently" is preferably defined by the desired improvement in the solubility of neutral ammonium citrate of this phosphate. Accordingly, process step a) includes an incubation period during which the reactant is allowed to act on the inorganic secondary phosphate. The incubation according to process step a) takes place over a period of time ranging from 10 to 500 minutes.

[0060] By adjusting the incubation time, the type and intensity of solubility can be actively influenced. Surprisingly, it was found that a relatively short residence time is sufficient to increase the solubility of ammonium citrate. In a preferred embodiment of the invention, the incubation time is therefore set between 15 and 90 minutes, particularly to increase the solubility of ammonium citrate. In a particularly preferred embodiment of the invention, the incubation time is set to 15 to 45 minutes. High solubilities of ammonium citrate can also be achieved here, but the shorter incubation time allows for smaller reaction vessels, thus reducing process costs.

[0061] Surprisingly, longer reaction times are required to increase water solubility. Therefore, in another preferred embodiment of the invention, the incubation time is set between 90 and 500 minutes. In a particularly preferred embodiment of the invention, the incubation time is in the range of 90 to 200 minutes, resulting in high ammonium citrate solubility and moderate water solubility.

[0062] The necessary incubation time to achieve the desired solubilities also depends, for example, on the type of reactant used. Strong acids (such as concentrated mineral acids) or strong bases (e.g., concentrated NaOH) typically lead to an accelerated reaction, and a shorter incubation time is required. Conversely, when weaker acids, such as organic acids (such as citric or oxalic acid), are used, a longer incubation time is preferred. In a preferred embodiment of the invention, the incubation time is set in the range of 30 to 120 minutes.

[0063] By adjusting the order in which the components are combined, the timing, and the incubation time, it is advantageous to influence the reaction process and thus also the neutral ammonium citrate solubility of the phosphate in the produced fertilizer granules.

[0064] A higher process temperature advantageously increases the reaction rate between inorganic secondary phosphate and the reactant, thereby shortening the required incubation time. In a particularly preferred embodiment of the invention, the exothermic reaction energy of the reaction in the earth-moist to easily plastic mixture is used to adjust the temperature of the mixture above 30 °C, particularly preferably above 40 °C, and most preferably above 50 °C, and thus to increase the reaction rate.

[0065] The separation of the reaction for at least partial phosphate conversion from the inorganic secondary phosphate from the granulation according to the invention advantageously solves the technical problem that the exothermic, partially spontaneous and vigorous reaction strongly hinders the granulation process. The separation of the reaction from the granulation according to the invention is preferably to be understood in a technical sense. In the context of the invention, this preferably means that the vast majority of the reaction takes place in process step a), but the reaction can also continue in process steps b) and c), albeit at a significantly reduced intensity. By adhering to the incubation time according to the invention, the remaining intensity of the potential reaction progression no longer hinders the granulation process.In a preferred embodiment of the invention, process step a) is therefore controlled such that more than 80% of the increase in neutral ammonium citrate solubility of the inorganic secondary phosphate achieved over the entire process is achieved in this process step a). That is, if the reaction were stopped after process step a) by rapid drying, the phosphate from the inorganic secondary phosphate treated with the reagent of this stopped reaction product would already exhibit at least 80% of the neutral ammonium citrate solubility of a reaction product that is not stopped but continues through process steps b) and c).

[0066] Furthermore, the corrosion problems known from the prior art can be solved or at least significantly reduced by largely completing the reaction in process step a). The reaction in process step a) can take place in an acid-resistant vessel with an acid-resistant agitator or acid-resistant coatings on these vessels and agitators, whereby most of the free acid or alkali is consumed after this reaction and is therefore less harmful to the subsequent plant components. In principle, however, all or parts of the subsequent plant components can also be made of acid-resistant and / or corrosion-resistant materials and / or provided with acid and / or corrosion protection coatings. In addition, the resulting earth-moist to easily malleable mixture can be further neutralized, if necessary, by adding at least one neutralizing agent after the desired reaction has largely completed.It is therefore preferred to adjust the pH value of the earth-moist to easily plastic mixture after the incubation period to 2 to 10, particularly preferably to 3 to 9, most preferably to 4 to 8.

[0067] The proposed earth-moist to easily plastic mixture, referred to as the first mixture in the context of the invention, contains a moisture content of 10 to 45%, and is not a suspension. Mixtures with this moisture content are typically not suspensions in this system of inorganic secondary phosphate and reactant. The moisture content, or water content, in suspensions is significantly higher, which is why the present invention differs from conventional processes that use suspensions.

[0068] In a preferred embodiment of the invention, the moisture content is adjusted to a range of 15–35%. Within this range, handling is simple, homogenizable (e.g., with agitators or in an intensive mixer), and sufficient reactivity between the inorganic secondary phosphate and the reactant is ensured. In a particularly preferred embodiment of the invention, the moisture content is adjusted to a range of 15–30%. The advantage of this moisture content setting is that correspondingly less liquid needs to be removed at the end of the process by thermal drying to form the nutrient granules, which is particularly cost-effective, while the moisture content remains sufficient to allow the reaction to proceed largely without crust formation or the formation of hard agglomerates.

[0069] In process step b), preferably an earth-moist raw material mixture with a reduced moisture content of less than 35% compared to the earth-moist to easily plastic mixture from process step a) is produced by adding at least one solid component to the mixture from process step a).

[0070] Solid components are preferably all those substances that are in solid form, preferably in powder form. These solid components may also contain moisture. However, for the purposes of the invention, this moisture content is lower than the moisture content of the earth-moist to easily malleable mixture from process step a). By adding this at least one solid component, the percentage moisture content in the resulting mixture is reduced compared to the mixture from process step a). One objective of this process step is to reduce the moisture content by adding at least one solid component to the resulting earth-moist raw material mixture compared to the mixture from process step a).

[0071] The lower the moisture content of the solid component, the more the moisture content in the resulting mixture can be reduced when the same quantity is added. In a preferred embodiment of the invention, the moisture content of at least one added solid component is therefore less than 10%, particularly preferably less than 5%, and most preferably less than 3%. This allows the moisture content in the mixture from process step a) to be higher, while maintaining the same quantity of solid component, in order to achieve the target moisture content. A higher moisture content in the mixture from process step a) promotes the reaction between the inorganic secondary phosphate and the reactants, making this reaction easier and more homogeneously controllable.In accordance with the invention, it may also be preferred that this solid component with a correspondingly low moisture content serves as compensation for other supplied components (further component) whose moisture content is higher, but which can then also be used or applied in this combination.

[0072] Further components are preferably understood to be those substances that can improve the process control and / or the properties of the nutrient granules, such as nutrient-containing components, dispersing and defoaming agents, structuring agents, pH adjusters, urease inhibitors, ammonium stabilizers, humic acid, organic acids, and / or water. The difference between the solid components and the further components preferably lies in the fact that the further components have a moisture content greater than that of the earth-moist to easily malleable mixture from process step a) or may also be present as a dispersion or solution.

[0073] In process step b), it is preferred that the moisture content of the mixture is reduced by adding "solid" substances, so that the moisture content is adjusted and / or reduced such that the resulting raw material mixture can be granulated in an intensive mixer or granulating disc. It is therefore preferred that the added substances are as "dry" as possible, i.e., have a lower moisture content. Furthermore, other substances can be added that may have a higher moisture content. In accordance with the invention, it is preferred that the solid components and / or the additional components have a lower moisture content than the mixture from step a). It is further preferred that the solid components and / or the additional components therefore reduce the moisture content. Preferably, the additional components have a higher moisture content than the solid components.In accordance with the invention, it is preferred that the ratio between solid components and the other components is adjusted in such a way that the overall moisture content of the mixture is reduced.

[0074] Since, according to the invention, in process step b) an earth-moist raw material mixture with a lower moisture content than the earth-moist to easily plastic mixture from process step a) is to be produced, the average moisture content of the components added in process step b) is lower than the moisture content of the earth-moist to easily plastic mixture from process step a).

[0075] Typically, the earth-moist raw material mixture according to the invention contains a moisture content of 10 to less than 35%. Earth-moist raw material mixtures with this moisture content are suitable for granulation or extrusion. In a preferred embodiment of the invention, the moisture content is adjusted to the range of 10–25%. Such moisture contents are typically particularly well suited for granulation, for example, using pelletizing or granulating discs, granulating drums, or intensive mixers. In a particularly preferred embodiment of the invention, the moisture content is adjusted to the range of 10–20%. The advantage of this relatively low moisture content is that correspondingly less liquid needs to be removed after granulation by thermal drying, which is particularly cost-effective.

[0076] In a preferred embodiment of the invention, at least one nutrient-containing component is added as a solid and / or other components. Nutrient-containing components are substances that supply or supplement the nutrients available to the cultivated plants in order to control or support plant growth and development. These nutrient-containing components include, for example, nitrogen (N), phosphate (P), potassium (K), magnesium (Mg), sulfur (S), and essential trace elements, individually or in combination. For example, the possibility of adding nutrient-containing components allows the nutrient composition of the fertilizer granules to be precisely tailored to the specific needs of the soil and plants. Furthermore, this also compensates for the typical variations in the composition of inorganic secondary phosphate, thus ensuring consistent fertilizer quality.

[0077] In a particularly preferred embodiment of the invention, additional phosphate carriers, for example ammonium phosphate, potassium phosphate, crystallization products from phosphorus elimination (such as struvite, brushite or hydroxylapatite-like Ca-P phase), are added in the range of 1 to 70%, resulting in a nutrient granulate with a total P2O5 content of greater than 15% and a neutral ammonium citrate-soluble phosphate content of greater than 80%, in each case based on the composition of the nutrient granulate.

[0078] In a particularly preferred embodiment of the invention, crystallization products from phosphorus removal are added in the range of 10 to 30% of the composition after granulation. This results in nutrient granules with a total P₂O₅ content greater than 15%, with a neutral ammonium citrate-soluble phosphate content (i.e., based on total P₂O) greater than 80% and a water-soluble phosphate content (based on total P₂O) less than 30%, each based on the composition of the nutrient granules.

[0079] In another particularly preferred embodiment of the invention, crystallization products from phosphorus removal are added in the range of 30 to 70% of the composition after granulation. This results in nutrient granules with a total P₂O₅ content greater than 25%, with a neutral ammonium citrate-soluble phosphate content (i.e., based on total P₂O) greater than 85% and a water-soluble phosphate content (based on total P₂O) less than 20%, each based on the composition of the nutrient granules.

[0080] In a further preferred embodiment of the invention, at least one structural material is added as a solid and / or additional component, comprising a total proportion of 0.1% to 50% of the finished nutrient granules. This material can be inorganic, organic, or a mixture thereof. Examples of such structural materials include peat, humus, pyrolysis substrates from biomass, biochar from hydrothermal carbonization (HTC), preferably dried sewage sludge or digestate, animal excrement, animal and fish meal, and mineral and rock flour. Depending on the type and concentration of the at least one structural material, the fertilizing effect can be adjusted and / or a soil-improving effect can be achieved when using the nutrient granules.

[0081] Targeted soil improvement can be achieved by adding a structural element to the fertilizer granules, particularly if the structural element leads to humus formation, improved soil structure, and / or improved air and water balance in the soil when the nutrient granules are used in agriculture. This can, for example, promote root growth, activate soil life, and / or stimulate plant vitality against stress. In a particularly preferred embodiment of the invention, 5 to 50% structural element is added, as it has been surprisingly found that humus formation is particularly strongly promoted within this concentration range, resulting in especially good soil and structure improvement.However, it is particularly advantageous if the granules formed contain a carbon content of more than 5 to 25%, as it was unexpectedly found that in this range, in addition to humus formation, the air and water balance of the soil is particularly favorable for the growth of, for example, winter barley and maize.

[0082] The fertilizing effect is advantageously influenced by the addition of the structural material, which adjusts the structural properties of the resulting nutrient granules and thus their characteristics, such as porosity, pore size, strength, and solubility. This allows, for example, the nutrient release to be specifically tailored to plant growth and the plant's time-dependent nutrient requirements. Therefore, in a particularly preferred embodiment of the invention, 0.1% to less than 5% structural material is added. This relatively low concentration allows for the integration of a particularly large number of nutrient components into the fertilizer, which advantageously and surprisingly significantly enhances the fertilizing effect of the granules in this embodiment of the invention.Surprisingly, it has now been discovered that the proportion of structural material in this range leads to a pore structure that greatly improves the solubility of these nutrient components. This makes the nutrients significantly more available to plants. A structural material content of 0.1–2.5% is particularly advantageous, as this range offers good porosity for optimal solubility and, additionally, a particularly good distribution of small pores within the basic structure, resulting in exceptionally high strength.

[0083] If residual materials, such as organic flours or preferably dried sewage sludge, are used as structural components, there is a fundamental risk of contamination and the spread of pathogens. This poses a risk of pathogens being transmitted to humans and animals via food and feed, thereby endangering them. Therefore, in a preferred embodiment of the invention, when one or more residual materials are used as structural components, a sanitization step is integrated into the process to interrupt infection cycles by killing pathogens, bacteria, etc. Methods available for sanitization include, for example, the addition of chemical or bactericidal agents, sanitization by extreme pH shifts (e.g., by adding quicklime or hydrated lime), or thermal treatment.Such a process step for sanitizing the critical residue(s) can be carried out at a suitable point. For example, this sanitization can take place before the residue is added as a structural component to the raw material mixture in process step b). For instance, a residue can first be mixed separately with quicklime, and the mixture can then be added to the mixture in process step b) after a sufficiently long contact time. Alternatively, such sanitization can also be carried out, for example, after the critical residue has been added as a structural component to the raw material mixture, by means of a thermal treatment of at least 10 minutes, preferably longer than 20 minutes, and above 60 °C, particularly preferably above 75 °C. This temperature treatment largely kills the pathogens. The thermal treatment can thus take place, for example, in process step b) or during the drying of the produced green granules.

[0084] Agents for pH adjustment, such as alkalis, hydroxides, basic salts, ammonia, or quicklime, can also be added as solid and / or other components. This allows, for example, the neutralization of any remaining acid or alkali residues (from the use or formation of acids or alkalis) and / or the targeted adjustment of the pH of the fertilizer produced. The addition of these substances can also influence the viscosity and binding properties. In a preferred embodiment of the invention, the agents for pH adjustment are selected and added in such a way that the neutralization of any remaining acid residues occurs over such a period of time that the heat released by the exothermic reaction can be used to dry the resulting granules in process step c). This saves on drying energy that would otherwise be required.Such a time delay in reaction and reaction rate can be achieved, for example, by using solid agents for pH adjustment such as hydroxides (e.g. Ca(OH)2, NaOH, KOH) instead of, for example, alkalis (e.g. sodium hydroxide, potassium hydroxide).

[0085] In a preferred embodiment of the invention, humic acid and / or fulvic acid and / or their salts (humates, fulvates) are added. These substances exhibit particularly growth-promoting properties. They significantly increase the nutrient uptake capacity of the roots, thus stimulating growth. Their addition promotes plant growth and cell formation. They stimulate cell membranes and metabolic activities, thereby increasing germination rates. They also stimulate important plant enzymes. Strong root development supports nutrient uptake capacity. Plants strengthened in this way are significantly less susceptible to disease. The addition of these substances can increase phosphorus uptake by plants, as it blocks phosphorus adsorption in the soil and, through complexation with calcium, aluminum, and iron, prevents the precipitation of phosphorus into sparingly soluble compounds.Surprisingly, it was found that adding these substances in a total of 0.1–25% (based on the produced fertilizer granules) resulted in a significant increase in plant-available phosphorus in the soil and thus increased phosphorus uptake by the plants. Adding these substances in a total of 0.1–10% is particularly preferred, as even at this quantity level a considerable increase in fertilizing effect is achieved, and consequently the required amount of fertilizer can be reduced by up to 40%. Adding these substances in a total of 0.1–5% is especially preferred, as this range offers a particularly favorable economic ratio between the cost of these substances and the resulting improved properties.

[0086] In a further preferred embodiment of the invention, organic acid is particularly preferably added in solid form. Examples of organic acids include ascorbic acid, acetic acid, formic acid, gluconic acid, malic acid, succinic acid, oxalic acid, tartaric acid, and citric acid, but are not limited to these. Organic acids play a crucial role in the uptake of phosphate from the soil by plants. In particular, the presence of organic acids at the root system enables plants to absorb sufficient phosphate, with microorganisms typically producing these organic acids within the ecosystem. Surprisingly, it has now been found that plant phosphate uptake is increased when one or more organic acids are already incorporated into the supplied fertilizer granules, preferably in a total concentration ranging from 0.1% to 30%.Citric acid, oxalic acid, or tartaric acid are preferably used individually or in combination, as these organic acids are relatively inexpensive and available in sufficient quantities. The use of citric acid, oxalic acid, or tartaric acid, individually or in combination, in the quantity range of 0.1% to 10% is particularly preferred, as the absorption-enhancing effect of these acids is especially favorable in relation to the raw material costs. The listed proportions of organic acids in the fertilizer granules can either be added additionally as a further component and / or, if organic acids are used as reactants, remain after the reaction (preferably at least partially in this quantity range) and thus be transferred into the fertilizer granules.

[0087] The solid and / or other components used can be milled individually or in combination before being added. This is advantageous, for example, if the existing particle or aggregate size of one or more input materials is not fine enough to achieve sufficient homogeneity or reactivity. Reducing the particle or aggregate size can improve this. Typically, the solubility of substances or contained compounds can also be improved, or the binding effect during granulation can be increased. Depending on the type of material to be milled and the desired particle size and particle size distribution, various dry or wet milling technologies, with or without milling aids, can be used. Examples of equipment used for dry or wet milling include ball mills, pin mills, jet mills, bead mills, and stirred ball mills.

[0088] The order in which the solid and / or other components are added can be determined according to the requirements of the process and / or the desired reaction sequence. For example, all or some of the other components and / or at least some of the solid components can be added as early as process step a). The addition can be made to the already produced mixture of at least one inorganic secondary raw material and at least one reactant, and / or it can be made during the production of this mixture. It is also possible to add all or some of these components first, and then add the at least one inorganic secondary phosphate and at least one reactant, or the components required to form this mixture. Alternatively, all or some of the other components can be added and / or introduced only in process step b).

[0089] In process step b), moderate amounts of liquid components can also be added, for example, to regulate or adjust the consistency and / or the granulation or extrusion properties. According to the invention, when selecting and combining the components used, it is preferred that in process step b) an earth-moist raw material mixture with a reduced moisture content of less than 35% compared to the earth-moist to easily plastic mixture from process step a) is produced.

[0090] The solid components, and any additional components, can be added in a manner known to those skilled in the art. For example, the addition can take place in the same mixing vessel in which the earth-moist to easily plastic mixture is produced in process step a), and / or during the transfer of the earth-moist to easily plastic mixture from process step a) to process step b), and / or in a separate mixing device. The mixing device can be, for example, a mixing vessel with an agitator, a rotary mixer (also preferably referred to as a gravity, drum, or rotary mixer), a shear mixer, a forced-action mixer, a plowshare mixer, a planetary mixer kneader, a Z-kneader, a sigma kneader, a fluid mixer, or an intensive mixer. The selection of the appropriate mixer depends, among other things, on the flowability and cohesive forces of the mixture.

[0091] The combining and mixing process to produce the moist mixture can also be controlled in such a way that (pre-)granulation begins immediately. For example, it can be advantageous if so-called granule nuclei are formed, which then, for instance, promote granulation into larger granules on a granulating tray. In the context of the invention, the term "granule nucleus" preferably refers to a core that serves as the basis for further granulation into larger granules and / or promotes this process.

[0092] In process step c), the moist raw material mixture is granulated and / or extruded, and if necessary, the resulting green granules or green extrudates are dried.

[0093] The granulation and / or extrusion according to the invention can take place during the addition of the solid and / or other components and / or afterwards, either in the same mixing device or in a separate granulation or extrusion unit, according to the invention pelletizing or granulating discs, granulating drum, or intensive mixers.

[0094] Preferably, the proportion of moisture, i.e., the liquid phase, in this process step has a significant influence on the type of granulation, the product quality, and the economic efficiency of the process. The total moisture or liquid phase content can be adjusted before granulation and / or extrusion, for example, by controlling the process in process steps a) and b) and / or by adding liquid components (e.g., water, nutrient solutions) after process step b), for example, during granulation. Partial drying can also be performed before granulation, if necessary, to further adjust the total liquid phase content before granulation / extrusion. The adhesion required for granulation can also be adjusted, if desired, by adding various substances, such as binders.Optionally, a powder can be added during or after the formation of the green granules and the green granules dusted with it to reduce the tendency for them to stick together. In a preferred embodiment of the invention, this dusting is carried out with a phosphate-containing ash.

[0095] In a preferred embodiment of the invention, the earth-moist to easily plastic mixture from process step a) is placed in an intensive mixer (for example, an intensive mixer type R from Eirich), wherein the liquid phase content is adjusted and / or binders are added such that the intensive mechanical mixing yields green granules with the desired particle size, preferably in the range of 1 to 10 mm, particularly preferably 2 to 5 mm. The advantage of this preferred embodiment of the invention is that good roundness is achieved in the preferred particle size range, and the granulation technology and process costs are favorable.

[0096] In another preferred embodiment of the invention, granulation takes place on a pelletizing or granulating tray. For this purpose, the moist raw material mixture from process step b), optionally together with the other components, is fed onto the pelletizing or granulating tray. Preferably, a liquid component, optionally in combination with a binder contained therein or added separately, is sprayed onto this mixture on the granulating tray. In a preferred case, the liquid component is, for example, water. The rotational movement forms the green granules, which can be dried during and / or after granulation to produce fertilizer granules. An advantage of this embodiment of the invention is that the granulation and the necessary technology are particularly cost-effective. Furthermore, this simple granulation technology is not prone to breakdowns.

[0097] Typically, fertilizer granules require low moisture content, meaning physically bound water. A typical requirement is that the moisture content should be less than 5%, preferably less than 2%. Depending on the type of granulation and the process control, this moisture requirement can be achieved during granulation itself. If necessary, the granules produced can be dried after granulation and / or extrusion, or at least undergo additional post-drying. Various drying technologies are available for this purpose, such as contact dryers, convective dryers, and / or radiation dryers. In contact drying, the thermal energy required for drying is preferably supplied through contact with a heating surface. In convective drying, the thermal energy required for drying is preferably supplied through contact with hot gas.In radiation drying, the thermal energy required for drying is primarily supplied by radiation of a defined frequency. The drying process separates the existing liquid phase, such as water, to the required extent. The drying process may also increase the strength of the granules, for example, through the formation of binding phases or through the development of a binding agent's binding effect.

[0098] In an advantageous embodiment of the invention, drying is achieved or at least supported by the inherent heat of the produced granules. The granules acquire this inherent heat through heating. For example, heating of the granules can occur process-related through the granulation and / or extrusion process or through chemical reactions. During the granulation and / or extrusion process, for instance, mechanical energy can be introduced, whereby the mechanical energy is converted into thermal energy. For example, the reaction between CaO and acid and / or water, or the reaction between sulfuric acid and water (during dilution), provides exothermic energy that can be used to heat the raw material dispersion and / or the formed granules.

[0099] If crystallization products from phosphorus removal, such as struvite, brushite, and / or hydroxylapatite-like Ca-P phases, are added to the raw material mixture and are consequently present in the produced granules, particularly in the green granules, drying in a preferred embodiment of the invention takes place above 100°C relative to the material temperature during drying. These crystallization products contain a large proportion of chemically bound water, which preferably does not represent moisture as defined by the invention but is incorporated into the crystal structure. Above 100°C, this chemically bound water is released. By separating the water from the granules, the percentage of the remaining components increases. For example, the concentration of nutrients in the granules can be increased, as they were previously diluted by the chemically bound water.

[0100] In a particularly preferred embodiment of the invention, drying, when crystallization products from phosphorus removal are present, takes place in a preferred range of 100–140°C relative to the material temperature during drying. Above 140°C, there is a risk of increasing nitrogen release. This results in an undesirable loss of nitrogen from the granules, and the process also requires more complex purification. By limiting the temperature to a maximum of 140°C in this embodiment of the invention, this can be largely avoided. In a very specific embodiment of the invention, drying takes place in a particularly preferred range between 120°C and 140°C.

[0101] Several requirements are placed on the nutrient granules. Firstly, the granules should be producible with the highest possible degree of precision. For example, a uniform size ensures defined, consistent disintegration properties and favorable airborne characteristics when spreading them on fields using a spreader, which is necessary for targeted nutrient application. Furthermore, since the presence of oversized or undersized particles can impair the mechanical application of the fertilizer, these particles can be separated from the desired granules and, if necessary, recycled back into the production process, particularly the mixing and / or granulation process, optionally with prior processing and / or grinding. For the purposes of this invention, the term "decent granules" preferably describes granules within the desired size range. The recycling of the processed oversized and undersized particles can take place in process steps a), b), and / or c).In a preferred embodiment of the invention, at least a portion of the oversize and / or undersize material is ground up as a fine powder and applied as a separating agent to the green granules produced during or after granulation.

[0102] Furthermore, good bonding within the granules is often required to prevent dust loss during fertilizer application, even after prolonged storage. The granule strength can be adjusted through process control. For example, the drying rate and the type of granulation technology or process control influence the porosity and compactness, and thus the strength, of the granules and can be controlled accordingly. Strength can also be influenced by the type and fineness of the raw material components or increased by adding binders.

[0103] The nutrient granules produced according to the invention can be coated with one or more layers for functionalization (e.g., reducing clumping tendency, increasing strength), protection (e.g., against moisture), and / or controlled nutrient release (influencing solubility through the coating). For the purposes of the invention, all methods and technologies that produce a desired coating are preferred. In a preferred embodiment of the invention, such a single- or multi-layer coating is applied directly after granulation in the granulating device, for example, by feeding the coating component(s) to the granulating device after granulation and coating the granules through the mechanical movement of the granules within the granulating device.

[0104] To produce the nutrient granules according to the invention, process steps a) to c) of the inventive method are carried out. The individual process steps can be implemented as batch and / or continuous processes, with buffer tanks being used between the process steps. To implement the process steps, a single unit and / or, particularly for larger production quantities, several identical or similar units can be used. Several units in one or more process steps can be connected in parallel and / or alternately. In the production of the nutrient granules according to the invention, the batch and / or continuous execution of process steps a) to c) continues until the desired production quantity is reached.

[0105] Further advantages, features, and details of the invention can be found in the dependent claims and the following description. Features mentioned therein and previously mentioned can be essential to the invention, either individually or in any combination. Thus, the disclosure relating to the individual aspects of the invention can always be referenced reciprocally. In the following examples, all examples describe methods that do not conform to the invention. Example 1 (not according to the invention, to illustrate the prior art):

[0106] This embodiment according to DE 10 2010 034 042 B4 is not according to the invention, but it demonstrates the basic approach of increasing the solubility of the phosphate phase from phosphate-containing combustion ash. For this purpose, 330 kg of sewage sludge ash (P₂O₅ content 18%, of which 38% is neutral ammonium citrate soluble and <1% is water-soluble), 140 kg of phosphoric acid (72.5%), and 132 kg of ammonium sulfate are mixed in a continuously operating twin-shaft paddle mixer, whereby the ash reacts with the acid and the mixture is intended to be converted into a NP multi-nutrient fertilizer with a nutrient oxidation state of N = 5%, P₂O₅ = 23%, and S = 5%.

[0107] However, this is only achieved with considerable difficulty. The violent reaction between ash and acid is problematic, leading to encrustation, deposits, and blockages. The resulting mass of ash and acid is very viscous and sticky, making it very difficult to handle, and this severely hinders the granulation process. Furthermore, the acid mixture corrosively attacks the mixer used.

[0108] The resulting granules exhibit an inhomogeneous grain distribution in lumpy form with comparatively low strength. The total P₂O₅ content is present in a water-soluble form. Example 2 (not according to the invention, to illustrate the prior art):

[0109] This embodiment according to DE 10 2016 116 633 A1 is not according to the invention, but it shows a prior art method for separating the reaction between the phosphate carrier and the acid from the granulation process. For this purpose, a low-viscosity, readily sprayable raw material suspension is produced in a mixing vessel from 330 kg of sewage sludge ash (P2O5 content 18%, of which 38% is neutral ammonium citrate soluble and <1% is water soluble), 140 kg of phosphoric acid (72.5%), 132 kg of ammonium sulfate, and 350 kg of water.

[0110] The total amount of liquid phase added to the suspension is 490 kg (53%). During the dissolution process, a significant proportion of the added solid components (ash, ammonium sulfate) dissolves, resulting in a considerably higher proportion of liquid phase in the suspension. Only with such a high proportion of liquid phase can a sprayable suspension be achieved.

[0111] The solids content of the raw material dispersion produced in this way is approximately 59%, and consequently the moisture content is 41%. In the context of the present invention, the term "solids content" is to be understood as the amount of fertilizer produced from the raw material mixture, in this case a suspension, by drying at 105°C. The solids content is higher than the proportion of the solid phase in the suspension because, during drying, dissolved components from the liquid phase transfer into the solid phase. A significantly higher solids content is hardly achievable in industrial operation because it would significantly increase the viscosity, partly only during the course of the reaction between acid and ash. High viscosity makes stirring, conveying, and pumping difficult or impossible and poses a risk of blockages and crusting. Furthermore, it can then no longer be considered a suspension.

[0112] After the components are combined, an incubation period of 45 minutes is observed, during which time the mixture is stirred continuously. The reaction between the acid and the sewage sludge ash heats the raw material dispersion to approximately 40 °C. Due to the action of the acid on the sewage sludge ash and the resulting pH value, a portion of the phosphate and other substances are dissolved after the incubation period.

[0113] The resulting raw material dispersion is then completely granulated. Only a few granulation processes are available for the complete granulation of a raw material dispersion with a solids content of 59%. Cost-effective methods such as granulation on a granulating disc or in an intensive mixer are not feasible due to the high proportion of liquid phase. Spray granulation, for example, is possible. In this embodiment, the resulting raw material dispersion is fed into a continuous fluidized bed system for spray granulation. The spray granulation is controlled to achieve an average granule size of 3.5 mm. After spray granulation, granules smaller than 2 mm and granules larger than 5 mm are separated by sieving and fed back into the spray granulation process as core material, with the larger granules being ground beforehand.The produced granules have a round and compact granule shape in the range of 2-5 mm, a total P2O5 content of 23%, of which 92% is neutral ammonium citrate soluble and 72% is water soluble, a nitrogen content of 5% and a sulfur content of 6%.

[0114] The advantage of this embodiment compared to embodiment 1 is that the reaction between ash and acid takes place within the generated raw material dispersion and is therefore controllable. The largely reacted raw material dispersion contains hardly any free acid, so that significantly fewer corrosion problems occur during further processing. The advantage of granulation by spray granulation in this embodiment is that raw material dispersions (as in this embodiment) with a high liquid phase content can be granulated, resulting in very compact, abrasion-resistant, and spherical granules.

[0115] However, a major disadvantage is that the energy consumption is very high due to drying the high liquid phase content, generating a fluidized bed, and the necessary atomization energy. Example 3 (not according to the invention):

[0116] In this embodiment, 330 kg of sewage sludge ash as inorganic secondary phosphate (P2O5 content 18%, of which 38% is neutral ammonium citrate soluble and <1% is water soluble), 140 kg of phosphoric acid (72.5%) as a reactant and 80 kg of water are intimately mixed in a mixing device, thus producing an earth-moist to easily plastic mixture.

[0117] The total amount of liquid phase added to the earth-moist to easily plastic mixture is 220 kg, which is 40% instead of 53% in embodiment 2. The solids content of the earth-moist to easily plastic mixture thus produced is approximately 78.5% instead of approximately 59% in embodiment 2, and consequently the moisture content is only 21.5%.

[0118] After these components are combined, an incubation period of 45 minutes is observed, during which time mixing continues. Since the proportion of liquid phase in this mixture is significantly higher than in embodiment 1, the reaction between ash and acid is more controllable and proceeds more homogeneously.

[0119] Unlike in embodiment 1, here 132 kg of ammonium sulfate, a solid component according to the invention, is added to the mixture only after the incubation period, i.e., only after the reaction between ash and acid has progressed considerably. This reduces the moisture content of the mixture and results in the earth-moist raw material mixture.

[0120] By adding ammonium sulfate after the incubation period, the solids content of the resulting earth-moist raw material mixture increases from 78.5% to approximately 82.5%, and the moisture content decreases from 21.5% to 17.5%.

[0121] This moist raw material mixture is fed into a granulating disc, where granulation into green granules takes place. Preferably, the consistency and stickiness of the moist mixture can be adjusted to the process at specific points, for example, by adding water. A dry powder (e.g., sewage sludge ash) can also be used as a separating agent to prevent clumping of the green granules. In contrast to embodiment 1, the granulation process here is not hindered by the vigorous reaction between the ash and the acid, as this reaction largely occurs during the incubation period. This makes the granulation process easier to control and results in more homogeneous granules. Furthermore, the corrosion stress in the granulation unit is significantly lower, since the acid has largely reacted with the ash.

[0122] The granules are then dried, resulting in fertilizer granules with a nutrient composition of N = 5%, P₂O₅ = 23%, of which 87% is neutral ammonium citrate-soluble and 67% is water-soluble, and S = 5%. The resulting granules have a stable, round, and compact shape. In contrast to embodiment 2, the earth-moist raw material mixture has a solids content of 85%, i.e., a moisture content of 15%. Consequently, a significantly smaller proportion needs to be separated by thermal drying to form the fertilizer granules. This saves considerable energy costs. Example 4 (not according to the invention):

[0123] In a mixing device, 50 kg of sewage sludge ash (as inorganic secondary phosphate, 18% P₂O₅ content, of which 38% is neutral ammonium citrate soluble and <1% is water soluble), 25 kg of 95% sulfuric acid (as a reactant), and 28 kg of water are thoroughly mixed to create an earth-moist to easily malleable mixture. This is followed by an incubation period of 30 minutes, during which the mixture continues to be mixed.

[0124] The solids content of the resulting earth-moist to easily plastic mixture is approximately 77%, and consequently the moisture content is 23%.

[0125] After the incubation period, 25 kg of urea and 51 kg of monoammonium phosphate (59% P₂O₅, 11.5% N) are added to the mixture as solid components in the same mixing device. The addition of urea and monoammonium phosphate after the incubation period increases the solids content of the resulting earth-moist raw material mixture from 77% to approximately 85%, and reduces the moisture content from 23% to 15%.

[0126] This moist raw material mixture is fed into a granulating tray, where it is granulated into green granules. To adjust the optimal consistency and adhesion of the moist mixture, water is sprayed onto the mixture at specific points on the granulating tray.

[0127] The granules are then dried to a moisture content of 3%, resulting in fertilizer granules with a nutrient composition of N = 12% and P₂O₅ = 27%, of which 94% is soluble in neutral ammonium citrate and 78% is water-soluble. The resulting granules have a stable, round, and compact shape. Example 5 (not (according to the invention):

[0128] In a mixing device, 50 kg of sewage sludge ash (as inorganic secondary phosphate, 18% P₂O₅ content, of which 38% is neutral ammonium citrate soluble and <1% is water soluble), 25 kg of 65% nitric acid (as a reactant), and 15 kg of water are thoroughly mixed to produce an earth-moist to easily malleable mixture. The moisture content of this mixture is 26%. An incubation period of 45 minutes is then observed, during which time the mixture continues to be mixed.

[0129] The solids content of the resulting earth-moist to easily plastic mixture is approximately 73.5%, and consequently the moisture content is 26.5%.

[0130] After the incubation period, 15 kg of urea and 40 kg of monoammonium phosphate (59% P₂O₅, 11.5% N) are added to the mixture as solid components. The addition of urea and monoammonium phosphate after the incubation period increases the solids content of the resulting earth-moist raw material mixture from 73.5% to approximately 82%, and reduces the moisture content from 26.5% to 18%.

[0131] This moist raw material mixture is fed into a granulating tray, where it is granulated into green granules. To adjust the optimal consistency and adhesion of the moist mixture, water is sprayed onto the mixture at specific points on the granulating tray.

[0132] The granules are then dried to a moisture content of 3%, resulting in fertilizer granules with a nutrient composition of N = 12% and P₂O₅ = 27%, of which 91% is soluble in neutral ammonium citrate and 73% is water-soluble. The resulting granules have a stable, round, and compact shape. Exemplary embodiment 6 (not according to the invention):

[0133] A fertilizer granulate is produced analogously to embodiment 5, but using the following process variant.

[0134] The produced fertilizer granules are fractionated. The fractions smaller than 2 mm and larger than 5 mm together comprise approximately 20% and are ground to a powder fineness.

[0135] After the incubation period, this ground coarse and fine fraction is added to the earth-moist to easily plastic mixture along with urea and monoammonium phosphate.

[0136] The addition of ground coarse and fine fractions compared to embodiment 5 results in a lower moisture content in the resulting earth-moist mixture. This lower moisture content is compensated for during the granulation process by adding an appropriate amount of water by spraying it onto the earth-moist mixture on the granulation plate. Alternatively, the required amount of water can also be added in process step a) or b). This adjusts the consistency and adhesion to the modified process.

[0137] After drying and fractionation, the 2-5 mm fraction is removed as product, while the coarse and fine fractions are reground and reintroduced into the manufacturing process. This type of process results in virtually no waste streams. Exemplary embodiment 7 (not according to the invention):

[0138] In an intensive mixer (e.g., Eirich R16W), 200 kg of sewage sludge ash as inorganic secondary phosphate (P2O5 content 18%, of which 38% is neutral ammonium citrate soluble and <1% is water soluble), 60 kg of nitric acid (65%) as a reactant, and 80 kg of water are thoroughly mixed to produce an earth-moist to easily malleable mixture. This is followed by an incubation period of 45 minutes, during which mixing continues.

[0139] The solids content of the resulting earth-moist to easily plastic mixture is 70.2%, and consequently the moisture content is 29.8%.

[0140] After the incubation period, 300 kg of monoammonium phosphate (59% P₂O₅, 11.5% N) are added to the mixture as a solid component. This reduces the moisture content of the mixture from 29.8% to 18%.

[0141] As a further component, 120 kg of sewage sludge (35% dry matter with 82% organic matter and 38% carbon in the dry matter) is added to this mixture as a structural material. This increases the moisture content of the mixture from 18% to 25.5%, which is still lower than that of an earth-moist to easily malleable mixture (29.5%). All components are intensively mixed in the mixer, resulting in the formation of the green granules.

[0142] The granules are then dried on a belt dryer (convection dryer), where the material is dried for 20 minutes at a temperature above 75 °C, ensuring sufficient sanitization of the integrated sewage sludge. This results in a moisture content of 2% and the formation of fertilizer granules with a total P₂O₅ content of 38%, of which 94% is soluble in neutral ammonium citrate and 83% is water-soluble. The produced granules contain approximately 7% dried sewage sludge. This proportion contributes to the granules' structure, ensuring particularly good solubility in application. Exemplary embodiment 8 (not according to the invention):

[0143] In a mixing tank, 100 kg of sewage sludge ash (inorganic secondary phosphate, 18% P₂O₅ content, of which 38% is neutral ammonium citrate soluble and <1% is water soluble), 20 kg of phosphoric acid (72.5%) (as a reactant), and 50 kg of water are thoroughly mixed to create an earth-moist to easily malleable mixture. This mixture has a moisture content of 32.6%. An incubation period of 45 minutes is then observed, during which time the mixture continues to be mixed.

[0144] After the incubation period, 36 kg of urea and 100 kg of struvite, each in powder form, are added to the mixture as solid components. This reduces the moisture content of the mixture to 19%, resulting in the earth-moist raw material mixture.

[0145] This moist raw material mixture is fed into a granulating disc, where it is granulated into green granules. Preferably, the consistency and adhesive properties of the moist mixture can be adjusted to the specific process, for example, by adding water. A dry powder (e.g., sewage sludge ash) can also be used as a separating agent to prevent clumping of the green granules.

[0146] The granules are then dried at 130 °C, resulting in fertilizer granules with a nutrient composition of N = 12%, P₂O₅ = 27%, of which 92% is neutral ammonium citrate soluble, 12% is water soluble, and S = 5%. The resulting granules have a stable, round, and compact shape. Exemplary embodiment 9 (not according to the invention):

[0147] In a mixing vessel, 100 kg of sewage sludge ash (18% P₂O₅ content, of which 38% is neutral ammonium citrate soluble and <1% is water soluble), 50 kg of 80% sulfuric acid (as a reactant), and 30 kg of water are thoroughly mixed to create a mixture that is moist to slightly plastic. The resulting mixture has a moisture content of 22%. An incubation period of 45 minutes is then observed, during which time the mixture continues to be mixed.

[0148] After the incubation period, 50 kg of struvite powder is added to the mixture as a solid component. This reduces the moisture content of the mixture to 17%, resulting in the earth-moist raw material mixture.

[0149] This moist raw material mixture is fed into a granulating disc, where it is granulated into green granules. Preferably, the consistency and adhesive properties of the moist mixture can be adjusted to the specific process, for example, by adding water. A dry powder (e.g., sewage sludge ash) can also be used as a separating agent to prevent clumping of the green granules.

[0150] The granules are then dried, resulting in fertilizer granules with a nutrient composition of P₂O₅ = 20%, of which 94% is neutral ammonium citrate soluble and less than 5% is water-soluble, and S = 8%, corresponding to a superphosphate with a sulfur component. The resulting granules have a stable, round, and compact shape.

[0151] The invention is described in more detail with reference to the following figures; they show: Figure 1 schematic representation of part of the invention. Figure 2 schematic representation of part of the invention.

[0152] Figure 1 This describes a part of the process according to the invention. In process step a), an earth-moist to easily plastic mixture (3) is produced from at least one inorganic secondary phosphate (1) and at least one liquid reactant (2). Unlike processes known from the prior art, no suspension is produced in process step a). Although a suspension can be mixed homogeneously and the reaction between ash and acid can be buffered to a certain extent, the large quantity of liquid phase (mostly water) introduced must subsequently be separated either mechanically or energetically in a further process step, which is complex and expensive.

[0153] In this process step a), the largely insoluble phosphate components of the at least one secondary phosphate carrier (1) are converted, at least partially, into a more readily soluble phosphate form by the action of at least one reactant (2). To allow this reaction to proceed to a significant extent, an incubation period of 10 to 500 minutes is observed, during which the mixture can be further mixed. The separation of the reaction for the at least partial phosphate conversion from the inorganic secondary phosphate from the granulation according to the invention solves the technical problem that the exothermic, partially spontaneous and vigorous reaction severely hinders the granulation process. The separation of the reaction and granulation according to the invention is to be understood primarily in a technical sense.Preferably, the vast majority of the reaction takes place in process step a), but the reaction can also continue in process steps b) and c), albeit at a significantly reduced intensity. By adhering to the incubation time according to the invention of 10 to 500 min, the remaining intensity of the reaction no longer hinders the granulation process.

[0154] In process step b), at least one solid component (4) is added to the earth-moist to easily plastic mixture (3) from process step a), i.e., the first mixture according to the invention, thereby reducing the moisture content of the resulting earth-moist raw material mixture (6) compared to the mixture from process step a). In this process step, the raw material mixture (6) is conditioned and its moisture content adjusted so that it is suitable for subsequent granulation or extrusion.

[0155] In process steps a) and / or b), further components (5), for example, nutrient-containing components, dispersing and defoaming agents, structuring agents, pH adjusters, urease inhibitors, ammonium stabilizers, humic acid, organic acids, and / or water, can be added. In process step a), the reaction takes place between inorganic secondary phosphate and the reactant. In process step b), the reaction preferably proceeds such that an earth-moist raw material mixture (6) with a lower moisture content is produced compared to the earth-moist to easily plastic mixture (3) from process step a). The average moisture content of all solid components (4) and / or further components (5) added in process step b) is preferably lower than the moisture content of the earth-moist to easily plastic mixture (3) from process step a).

[0156] In process step c), the moist raw material mixture (6) is granulated / extruded and optionally dried. This results in the nutrient granules (7) according to the invention. Further components (5) can also be added before and / or during granulation. Optionally, a fine powder is added to the resulting green granules as a separating agent. This process step c) yields soil- and plant-specific nutrient granules (7) with a standardized and consistent nutrient composition, wherein at least one nutrient source is inorganic secondary phosphate (such as sewage sludge ash), and the phosphate contained therein is made more soluble and more readily available to plants by the action of the reagent.

[0157] The process steps a) to c) can be repeated any number of times, either in parallel or serially.

[0158] Figure 2Figure 1 shows part of a preferred embodiment of the invention, in particular the additional possibility of fractionating the produced nutrient granules and the possibilities for recycling the separated coarse and fine particles. For this purpose, the produced nutrient granules are fractionated after granulation and drying. The good granules (7) are removed from the process as a product.

[0159] The coarse grain fraction is milled (9). The fine grain fraction can also be milled either together with the coarse grain or separately from it, or it can be returned without milling.

[0160] This ground coarse fraction (9) can be fed together with the ground or unground fine fraction (8) to process steps a), b), and / or c), depending on the requirements of the process. The ground coarse fraction (9) and the ground or unground fine fraction (8) can also be fed separately to the same or different process steps a), b), and / or c). When the ground coarse fraction (9) and / or the ground or unground fine fraction (8) are fed to process step b), this can, for example, serve as a solid component according to the invention to reduce the moisture content in the resulting mixture. The unground fine fraction (8) and / or the ground coarse fraction (9) can also serve, for example, as a nucleating agent to support granulation in process step b) and / or c).In another embodiment, the feeding of the ground coarse and / or fine grain fraction into process step c) can, for example, act as a separating agent to separate the formed green granules from each other by reducing the tendency to stick together on the surface. Reference symbol list:

[0161] 1 Inorganic secondary phosphate or secondary phosphate carrier 2 Reactant 3 Moist to plastically malleable mixture, first mixture 4 Solid component(s) 5 Further component(s) 6 Moist raw material mixture (second mixture) 7 Fertilizer granules, good granules, nutrient granules 8 Fine fraction of fertilizer granules 9 Coarse fraction of fertilizer granules

Claims

1. A method for producing a fertilizer granulate (7) according to claim 6, comprising the following steps: a) producing a first mixture (3) with a moisture content of 10 - 45% comprising at least one inorganic secondary phosphate (1) and at least one liquid reactant (2), wherein the reactant is selected from organic or inorganic acids or acid mixtures, or alkalis, or mixtures of different alkalis, each in undiluted or diluted form, wherein the incubation time between the inorganic secondary phosphate (1) and the reactant (2) is in the range of 10 to 500 minutes, b) reducing the moisture content of the first mixture (3) by adding at least one solid component (4), resulting in a second mixture which is a raw material mixture (6) with a moisture content of less than 35%, c) granulating and / or extruding the raw material mixture (6) using a pelletizing or granulating disc, a granulating drum or an intensive mixer, resulting in the fertilizer granulate (7), and repeating process steps a) to c), wherein the steps are performed in parallel or serially.

2. The method according to claim 1 characterized in that drying takes place during or following the granulating and / or extruding of the raw material mixture (6).

3. The method according to any one of the preceding claims, characterized in that a pH value of the first mixture (3) and / or of the raw material mixture (6) after the incubation time is in a range of 4-8.

4. The method according to any one of the preceding claims, characterized in that the method comprises fractioning the produced fertilizer granulate (7), wherein a coarse fraction (9) and / or a fine fraction (8) is ground up and can be at least partially added to the first mixture (3), the raw material mixture (6) and / or the granulation step (7).

5. The method according to any one of the preceding claims, characterized in that in total, 1 to 70% of the crystallization products from the phosphorus elimination are supplied to step a), b) and / or c), wherein drying takes place above 100°C relative to the material temperature during drying.

6. A fertilizer granulate (7), which can be produced by a method according to claims 1 to 5, which comprises at least one inorganic secondary phosphate (1), wherein a neutral ammonium citrate solubility of a phosphate supplied with the inorganic secondary phosphate (1) in the fertilizer granulate is greater than 60% neutral ammonium citrate soluble, and a phosphate fraction from the inorganic secondary phosphate (1) has a water solubility of less than 40%.

7. The fertilizer granulate (7) according to claim 6, characterized in that the fertilizer granulate (7) comprises 0.1 to 25% humic acid, fulvic acid, their salts (humates, fulvates) and / or 0.1 to 30% organic acid and / or 0.1 to 50% structural materials.

8. The fertilizer granulate (7) according to one or more of claims 6 to 7, characterized in that one or more crystallization products from phosphorus elimination are contained in a concentration range between 1 and 70%.

9. Use of the fertilizer granulate (7) according to one or more of claims 6 to 8 in agriculture, forestry and / or horticulture, characterized in that the fertilizer granulate (7) comprises at least one inorganic secondary phosphate (1) and a P2O5 content soluble in neutral ammonium citrate of greater than 60% for nutrient supply.