Phosphate-enriched, heavy-metal depleted granular fertilizer, method of production, device and use

Abstract

The invention relates to a phosphate-enriched, heavy-metal depleted granular fertilizer from at least one inorganic secondary phosphate that is produced in a double-strand method. According to the method, a raw material dispersion is supplied to process strand A and to process strand B by either producing the raw material dispersion in process step a) from at least one inorganic secondary phosphate and at least one reagent and supplying the raw material dispersion so produced to process strand A and B separately, or first separating the inorganic secondary phosphate in process step a, a'), producing two raw material dispersions (comprising each a partial amount of the at least one inorganic secondary phosphate and at least one reagent) separately from each other and supplying these separately produced raw material dispersions to process strand A and B, wherein the liquid phase content of the raw material dispersion is greater 30% and the incubation time between the inorganic secondary phosphate and the reagent is between 1 to 100 minutes, wherein process strand A comprises the following process steps, i) adding a heavy-metal precipitating agent during the production of the raw material dispersion and / or during the incubation time and / or after the incubation time, j) separating part of the phosphate-containing liquid phase of the raw material dispersion that is low in heavy metal and removing the remaining heavy-metal containing filter cake from the process, k) precipitating phosphate from the phosphate-containing liquid phase, l) separating the precipitated phosphate and returning the separated liquid phase to process step a) to produce a raw material dispersion, wherein process step B comprises the following process steps m) separating part of the liquid phase of the raw material dispersion, n) producing a mixture from at least part of the precipitated phosphate produced in process strand A and at least part of the remaining raw material dispersion with reduced liquid phase from process step f) and granulating and / or extruding the mixture so produced, wherein the produced granular and / or extruded material can be dried or coated, and removing the produced heavy-metal depleted granular fertilizer from the process, o) returning the liquid phase separated in process step f) in order to produce a raw material dispersion in analogy to process step a) and / or supplying it to process step g), wherein heavy metals can be at least partially removed from the liquid phase separated in process step f) and these heavy metals can be removed from the process previously, and repeating process steps a) to h).

Description

[0001] Phosphate-enriched, heavy metal-depleted fertilizer granules, manufacturing process, device and use

[0002] The invention relates to a phosphate-enriched, heavy metal-depleted fertilizer granulate which can be used for nutrient supply in agriculture, forestry and / or horticulture, as well as a production method therefor and a device for its production.

[0003] State of the art:

[0004] The thermal utilization of these organic residues is currently gaining increasing importance. Ashes from the thermal utilization and / or incineration of organic residues are often suitable raw material sources due to their high nutrient content, such as phosphorus (P). Due to the high combustion temperatures, nutrient components such as phosphorus are usually in a form that is poorly available to plants. In addition, combustion also concentrates heavy metals. Due to the poor plant availability of the phosphorus (P) contained in the ashes and the pollutant content, direct use of the ashes as fertilizer is hardly possible. Therefore, such ashes are currently mostly landfilled or used in landscaping and are thus no longer available as a raw material source for the material cycles.

[0005] Various processes for the material recycling of phosphorus-containing combustion residues, such as sewage sludge, are known in the state of the art. These processes are based on ash as a raw material, with the phosphate (P) content in the ash being as high as possible. The processes for extracting phosphate from sewage sludge ash can generally be divided into thermochemical, thermoelectric, and wet-chemical approaches.

[0006] Numerous different concepts are pursued in wet chemical processes, whereby a distinction is generally made between processes in which phosphorus is extracted from the ash and thus brought into the liquid phase (leaching process) and processes in which the acid is mixed with the ash, thereby making the insoluble phosphate available to plants and producing a fertilizer from this total mixture (phosphate conversion process).

[0007] Leaching processes, such as BioCon, SEPHOS, SESALPhos, Tetraphos, PASCH, or Leachphos, are based on the use of a solvent to selectively dissolve the phosphorus from the combustion residue and separate this phosphorus-containing solution from the insoluble residue. The resulting phosphorus-containing solution is then purified of accompanying components and converted into a secondary phosphate product (e.g., calcium phosphate, phosphoric acid). The processes differ from one another with regard to the solvents and precipitants used for phosphate separation, the recycling product, and the type of heavy metal separation. The advantage of these processes is that only a portion of the heavy metals in the combustion residue are dissolved by the solvent. The dissolved heavy metals and their accompanying components are then largely selectively separated from the phosphate-containing solution over several purification stages.The result is a phosphate-containing product with a low heavy metal concentration that is as free as possible from accompanying components. The goal is to achieve particularly high product and varietal purity because it is intended for use as a chemical product or further processed. The products produced from these processes generally have a variety of applications. However, in practice, these products often only offer the option of being used as intermediates for the fertilizer industry. Compared to conventionally produced fertilizers, these products are generally too expensive for use in the fertilizer industry. This is due, on the one hand, to the fact that a very high proportion of residue from the dissolution process (insoluble residue) remains as waste, which must be disposed of at great expense.In addition, the desired separation of accompanying components as completely as possible is usually a multi-stage and therefore very complex and expensive process, since, as a phosphate-rich product, a high product purity for the intended fields of application is usually required. These processes attempt to dissolve the phosphate as selectively as possible from the phosphate-containing combustion residue, since dissolved accompanying components must then be laboriously separated in order to obtain a product with the purest possible phase. Thus, the undissolved fraction remaining as waste from the processes is very high, typically equal to or more than 50% of the phosphate-containing combustion ash used. This high proportion of waste in these processes is not only disadvantageous for sustainability reasons, but also contains nutrients and trace elements (e.g.Mg, K, S), which are useful for plant nutrition and growth or for soil quality (e.g., air permeability, water retention capacity) as a basis for good yields (e.g., aluminates, silicates). Due to these processes, these remain unused as waste in the undissolved residue.

[0008] Another approach is pursued by processes that specifically make the phosphate phase available to plants and convert almost the entire phosphate-containing combustion residue into a fertilizer (phosphate conversion process). A solvent (usually a mineral acid) reacts with a phosphate-containing combustion residue, dissolving the poorly plant-available phosphate phase from the combustion residue. Unlike leaching processes, however, the phosphate-containing solution is not subsequently separated from the undissolved residue; instead, the entire mixture is converted into a fertilizer. The advantage of these processes is that no insoluble residue is produced, which usually requires expensive disposal. These processes are also technically simpler and less complex. This makes them generally significantly more cost-effective and sustainable than leaching processes. An example of such a process is DE 10 2010 034 042 B4.

[0009] ■ In some embodiments of this type of phosphate conversion process, a portion of the heavy metals can be separated, for example, in WO 2019 / 149405 A1. The fundamental disadvantage is that only those heavy metals that were previously dissolved from the phosphate-containing combustion residue into the liquid phase by the reactant can be separated. This is problematic because the heavy metals are bound to different phases in the phosphate-containing combustion residue, and these phases are dissolved to varying degrees by the reactant. Accordingly, heavy metals bound to the insoluble residue (typically, in particular, Pb, Zn, Ni) cannot be separated or can only be separated to a very limited extent.This means that phosphate-containing combustion residues with this type of bound heavy metals cannot be converted into fertilizers using these processes in accordance with the Fertilizer Ordinance and are therefore not usable.

[0010] ■ Another disadvantage of these processes (phosphate conversion processes) is that the phosphate content of the produced fertilizers, which originates from the phosphate-containing combustion residue, is relatively low. This results from the fact that the phosphate-containing combustion residues are treated with the solvent, and both are transferred into the fertilizer product, resulting in a reduction (dilution) of the percentage phosphate content from the phosphate-containing combustion residue. For example, if sewage sludge ash, as a phosphate-containing combustion residue, contains 15% P2O5, this proportion is reduced by the addition of the reactant, and a fertilizer with significantly less than 15% P2O5 is formed. However, potential users or processors of such manufactured fertilizers, such as farmers or fertilizer manufacturers, often require highly phosphate-rich phosphate fertilizers such as at least "superphosphate" (approx. 18% P2O5), double superphosphate (approx.35% P2O5) or, better yet, triple superphosphate (46% P2O5), as its use in agriculture or as a base component for the production of complex fertilizers is more efficient and easier. These high-phosphate fertilizers cannot be produced using these processes, as is the case with sewage sludge ash.

[0011] ■ While these processes offer the possibility of using either a phosphate-containing solvent (e.g., phosphoric acid) or adding phosphate-containing nutrient components (e.g., monoammonium phosphate (MAP)), thereby increasing the phosphate content in the fertilizer, these phosphate-containing solvents or nutrient components are expensive and highly dependent on a highly volatile global market.

[0012] Furthermore, these additional phosphate-containing solvents or nutrient components then come from conventional production. In other words, their production is based on rock phosphate, which has been mined from deposits and processed using established extraction methods in the fertilizer industry. By adding such conventional phosphate-containing solvents or nutrient components, the resulting fertilizers lose their status as pure phosphate recyclate, since the phosphate no longer comes solely from recycling, but has been partially extracted conventionally from mined rock phosphate.However, since the mining and processing of rock phosphate has harmful and invasive consequences for the environment, is energy-intensive, and incurs high transport costs, users with high sustainability requirements, such as organic farming, want to avoid the use of conventional phosphate fertilizers, which is therefore prohibited in these areas. Phosphate conversion processes, as described in WO 2019 / 149405 A1, therefore do not offer the possibility of producing pure phosphate-recycled fertilizers with a phosphate content greater than the used combustion residue without the addition of conventional phosphate-containing solvents or phosphate-containing nutrient components. Accordingly, this agricultural segment cannot be served with high-percentage phosphate fertilizers.

[0013] In EP 3 037 396 Al, ash or carbonization residue is also mixed with a mineral acid. This involves various processing steps, ultimately resulting in a moist filter cake that can be further processed and, according to the description, used as fertilizer in agriculture.

[0014] ■ This process consequently produces a filter cake whose phosphate concentration, due to the digestion and mixing with the acid, is lower than the phosphate-containing ash or carbonization residue used. EP 3 037 396 A1 does not disclose how a phosphate-concentrated filter cake with a higher phosphate content than the phosphate-containing combustion residue used can be produced, in particular no concentrated pure phosphate recyclate without the addition of conventional phosphate components such as phosphoric acid or phosphate salts.

[0015] ■ In addition, the process can be used to separate heavy metals from the solution separated from vessel 2. This means that at most the heavy metals that are dissolved in this solution can be separated. Heavy metals that are not dissolved by the reactant (solvent) cannot be separated. In order for them to be separated in the separated solution, the heavy metals must first be dissolved, which can be done by the mineral acid used. However, it remains unclear whether this should actually happen, since a special feature of the process is that the mineral acid in the first vessel absorbs heavy metal ions and phosphate at the beginning of the process, but becomes increasingly saturated with phosphate and heavy metal ions over the course of the process. As a result, no further phosphate and no further heavy metal ions from the ash or the carbonization residue dissolve in the acid.

[0016] ■ This described peculiarity of the process also appears unsuitable for converting poorly soluble phosphate in combustion residues into more soluble phosphate, i.e., making it plant-available. This requires acid digestion similar to that used for rock phosphate. However, if no further phosphate is dissolved in the acid in the first vessel and no further acid is added as a reactant in the subsequent batch, no conversion can take place. The phosphate remains unchanged, and so does its poor solubility.

[0017] Object of the invention:

[0018] In view of the state of the art, the invention is based on the object of offering improved phosphate-enriched and heavy metal-reduced fertilizer granules that optimize the pedosphere with regard to soil flora and fauna. This phosphate enrichment results from a concentration of the phosphate content from the inorganic secondary phosphate (e.g., phosphate-containing ash), only small amounts of waste are generated, and heavy metals in general, and in particular those that are poorly soluble in the solvent, are better separated. The soil flora predominantly includes plant or non-animal organisms, such as bacteria, ray fungi, fungi, algae, and lichens. The soil fauna is composed of single-celled animals and multicellular organisms, which are differentiated according to their size into microfauna (< 0.2 mm; e.g., ciliates, flagellates, amoebas, small nematodes), mesofauna (< 2 mm; e.g.,Springtails, rotifers, mites), macrofauna (> 2 mm; e.g., bristle worms, woodlice, insects), and megafauna (> 20 mm; e.g., vertebrates such as voles, shrews, and moles). Optimization (improvement) primarily concerns improved plant growth, as well as the growth of bacteria, flagellate animals, nematodes, annelids, insects, and others.

[0019] In particular, phosphate enrichment by concentrating the phosphate content of the inorganic secondary phosphate should make it possible to produce a highly phosphate-rich, purely recycled phosphate fertilizer without the addition of conventional (conventionally obtained) phosphate components such as phosphoric acid or phosphate salts, i.e. a pure phosphate recyclate.

[0020] The present invention is also based on the object of providing an economical, ecological, flexible, simple and technically feasible process for the production of soil and / or plant-specific fertilizers with a precisely adjustable nutrient composition in granular form.

[0021] The process according to the invention is intended to enable the efficient and cost-effective processing of a wide variety of inorganic secondary phosphates, while also providing targeted soil- and plant-specific fertilizer compositions. The resulting fertilizer granules should contain a large portion of the concentrated phosphate in a readily plant-available form, and at least some of the heavy metals should be removed. Furthermore, a fertilizer is intended to be used and / or applied as a soil conditioner in agriculture, forestry, or horticulture.

[0022] Description of the invention:

[0023] The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0024] According to the invention, a phosphate-enriched, heavy metal-depleted fertilizer granulate is provided which can be produced from at least one inorganic secondary phosphate, which is produced using a two-strand process, wherein a raw material dispersion is fed to process strand A and process strand B, in which this raw material dispersion

[0025] ■ either in process step a) from at least one inorganic secondary phosphate and at least one reactant is produced and this produced raw material dispersion is fed to the process line A and B separately

[0026] ■ or in process step a, a') the inorganic secondary phosphate is first divided, two raw material dispersions (each comprising a portion of the at least one inorganic secondary phosphate and at least one reactant) are produced separately from one another and these separately produced raw material dispersions are fed to process strands A and B, wherein the proportion of a liquid phase in the raw material dispersion is greater than 30% and the incubation time between inorganic secondary phosphate and reactant is between 1 and 100 minutes, wherein process strand A comprises the following process steps, b) addition of a heavy metal precipitant during the production of the raw material dispersion and / or during the incubation period and / or after the incubation period, c) separation of a portion of the phosphate-containing, low-heavy-metal liquid phase of the raw material dispersion and discharge of the remaining heavy-metal-containing filter cake from the process,d) precipitation of phosphate from the phosphate-containing liquid phase, e) separation of the precipitated phosphate and recycling of the separated liquid phase to process step a) for producing a raw material dispersion, wherein process line B comprises the following process steps: f) separation of a portion of the liquid phase of the raw material dispersion, g) production of a mixture of at least a portion of the precipitated phosphate produced in process line A and at least a portion of the remaining raw material dispersion with reduced liquid phase from process step f) and granulation and / or extrusion of this produced mixture,wherein drying or coating of the produced granules and / or extrudates can take place and discharge of the produced heavy metal-depleted fertilizer granules from the process h) recycling of the liquid phase separated in process step f) for the production of a raw material dispersion analogous to process step a) and / or feeding into process step g), wherein at least a partial separation of heavy metals from the liquid phase separated in process step f) and discharge of these heavy metals from the previous process can take place, and repeating process steps a) to h).

[0027] In one embodiment, the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention can be produced from at least one inorganic secondary phosphate (1) using a two-strand process, wherein the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) has a higher phosphate concentration resulting (solely) from the concentration of the added phosphate portion from the at least one inorganic secondary phosphate (1) than in comparison to / compared to the mixture of the added at least one inorganic secondary phosphate (1).

[0028] In other words, in embodiments of the fertilizer granulate according to the invention, this has a higher phosphate concentration than in comparison to / compared to the at least one inorganic secondary phosphate (1) added due to enrichment / concentration of the added phosphate portion(s) from the at least one inorganic secondary phosphate.

[0029] Consequently, in the phosphate-enriched, heavy metal-depleted fertilizer granules (10) obtained according to the invention - in comparison to the at least one added inorganic secondary phosphate (1) and / or a mixture thereof - a higher phosphate concentration results according to the invention due to the concentration / enrichment of the added phosphate portion from the at least one inorganic secondary phosphate (1) and preferably a lower heavy metal concentration, preferably due to a heavy metal depletion according to the invention.

[0030] In embodiments, the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) has a phosphate concentration that is at least 30% higher than that of the inorganic secondary phosphate(s) (1) added to the mixture.

[0031] All percentages (%) in the context of the invention refer to weight percent (wt% ie % VJ / VJ), unless otherwise stated.

[0032] Quite surprisingly, the inventive combination of the precipitated phosphate (produced via strand A) with the remaining raw material dispersion with a reduced liquid phase from process step f) (obtained from strand B) results in a phosphate-enriched phosphate-recyclate mixture that exhibits a significantly higher fertilizing effect. This higher fertilizing effect results, on the one hand, in improved plant growth compared to the individual products from the respective strands A and B.

[0033] This completely unexpected, enhancing synergistic effect (“booster” effect) compared to the individual phosphate components from strand A or strand B results from the inventive combination of different phosphate phases, which are obtained from the two different processes in strand A and B. This synergistic effect of combining both processes in a single, inventive process could not be derived from the prior art. Phosphates in general are a mineral group that includes numerous different phosphate phases, such as Ca, Al, Fe, Mg phosphates and their largely seamless mixed oxide combinations. Due to the extensive replaceability of the cations, mixed oxide variations arise, such as in whitlockite, which is characterized by its molecular formula Ca(Mg,Fe) 2+)[PO3(OH) | (PO4)6 can be described. In addition, there is the range of variation in incorporated crystal and / or hydroxide in precipitation products depending on the type of precipitation process. Although all of these variations are generally assigned to the phosphate group, they sometimes differ fundamentally in their crystal structure and the resulting bond forms. Due to their different crystal structures, the various phosphate phases each exhibit very different chemical and physical properties. The chemical composition and solubility behavior are particularly important for the fertilizing effect. The phosphate must not only be generally soluble in the root system, but also soluble over time so that the plant can absorb sufficient phosphate through the roots throughout the entire growth period. In addition, the soil flora should also be adjusted or promoted to create a growth-promoting environment around the root system.In addition to physical solubility in the root zone, the chemical composition of the added phosphate phase of the fertilizer plays an important role. Depending on the element, uptake by the roots can be promoted or hindered (e.g., through inappropriate complex formation, absorption), and the soil flora can be optimized for plant growth.

[0034] Through planting experiments, the inventors have now surprisingly discovered that the inventive mixture of precipitated phosphate, produced via strand A, with the remaining raw material dispersion with a reduced liquid phase from process step f) in strand B, can be further processed according to the invention, thus resulting in a phosphate mixture with a significantly higher fertilizing effect than that of the individual components. The phosphate mixture according to the invention was found to exhibit a significantly improved development rating (development quality) in flower formation, higher fresh masses during the growth period, and a higher phosphate content in the plant sap analysis compared to the individual components from strands A and B.

[0035] In strands A and B, the phosphate contained in the starting material (inorganic secondary phosphate) is converted in completely different ways. While in both strands the phosphate is first dissolved by a reactant, in strand A the dissolved phosphate is specifically precipitated by adding a precipitant in step d). In strand B, however, no precipitant is preferably added, which is why the dissolved phosphate only crystallizes during the drying process, for example, when the solubility limit is exceeded. This results in completely different phosphate phases as well as different morphological properties of the product, such as particle size or surface area.

[0036] It was completely surprising that the phosphate-enriched, heavy metal-depleted fertilizer granules produced according to the invention, which represent a specific mixture of the different phosphates produced from strand A and strand B, both ensures the phosphorus supply of plants and optimizes the development of microorganisms as well as bacteria and protozoa in such a way that the plants grow significantly better.

[0037] The soluble phosphate content is an important property in fertilizers and is usually determined using various extraction methods, for example, using solvents such as water, ammonium citrate, citric acid, formic acid, and mineral acids. The neutral ammonium citrate-soluble portion of the phosphate may be of particular interest. The advantageous, synergistic effect of the fertilizer according to the invention was also surprising because these analytical methods, frequently used for characterization of the soluble phosphate content, yield comparable / similar results for the two individual different phosphates from strand A and strand B. Thus, a person skilled in the art would expect a comparable fertilizing effect, and not synergy, even with a combination of both phosphates (with similar solubility).

[0038] It was by no means obvious to the expert that a mixture of the different phosphates obtained from strand A and strand B would be suitable for both optimizing soil animal biomass and improving plant growth. This applies in particular to corn, wheat, onions, potatoes, millet, beans, apples, sugar beets, cucumbers and gherkins, grapes, tomatoes, barley, and cabbage plants.

[0039] Accordingly, in a further aspect, the invention relates to a process for producing a phosphate-enriched, heavy metal-depleted fertilizer granulate (10) producible from at least one inorganic secondary phosphate (1) by a two-strand process, wherein a raw material dispersion (3, 3') is fed to process strand A and process strand B, in which this raw material dispersion

[0040] ■ either in process step a) from at least one inorganic secondary phosphate (1) and at least one reactant (2) is produced and this produced raw material dispersion (3) is fed to the process line A and B in parts

[0041] ■ or in process step a), a') the inorganic secondary phosphate (1) is first divided, two raw material dispersions (3, 3') each comprising a portion of the at least one inorganic secondary phosphate (1) and at least one reactant (2, 2') are produced separately from one another and these separately produced raw material dispersions (3, 3') are fed to process lines A and B, wherein the proportion of a liquid phase in the raw material dispersion (3, 3') is greater than 30% and the incubation time between inorganic secondary phosphate (1) and reactant (2, 2') is between 1 and 100 minutes, wherein process line A comprises the following process steps, b) addition of at least one heavy metal precipitant (4) during and / or after the incubation time, c) separation of a portion of the phosphate-containing, low-heavy-metal liquid phase (5) of the raw material dispersion and discharge of the remaining heavy-metal-containing filter cake (6) from the process,d) precipitation of phosphate (7) from the phosphate-containing liquid (5) phase, e) separation of the precipitated phosphate (7) and at least partial recirculation of the separated liquid phase (8) into process step a) for producing a raw material dispersion, wherein process line B comprises the following process steps: f) separation of a portion of the liquid phase of the raw material dispersion (3), g) production of a mixture of at least a portion of the precipitated phosphate (7) produced in process line A and at least a portion of the remaining raw material dispersion with reduced liquid phase (9) from process step f) and granulation and / or extrusion of this produced mixture, wherein drying or coating of the produced granules and / or extrudates can take place and discharge of the produced phosphate-enriched, heavy metal-depleted fertilizer granulate (10) from the process,h) At least partial recycling of the liquid phase 11, 11') separated in process step f) for producing a raw material dispersion analogous to process step a) and / or feeding it into process step g), whereby at least partial separation of heavy metals (12) from the liquid phase separated in process step f) and discharge of these heavy metals (12) from the process beforehand can take place, and repeating process steps a) to h).

[0042] In one embodiment of the method for producing a phosphate-enriched, heavy metal-depleted fertilizer granulate (10) from at least one inorganic secondary phosphate (1) by a two-strand process, the concentration of the added phosphate portion from the at least one inorganic secondary phosphate results (solely) in a higher phosphate concentration in the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) compared to / in comparison to the mixture of the added at least one inorganic secondary phosphate.

[0043] In other words, in embodiments of the method according to the invention, a higher phosphate concentration in the phosphate-enriched, heavy metal-poor fertilizer granulate (10) results from the enrichment of the supplied phosphate portion / phosphates from the at least one inorganic secondary phosphate compared to the at least one inorganic secondary phosphate supplied thereto and preferably a lower heavy metal concentration preferably through a heavy metal depletion according to the invention.

[0044] In the context of the invention, all percentages (%) refer to weight percent (wt% ie % VJ / VJ), unless otherwise stated.

[0045] The essence of the process according to the invention is that the phosphate-containing secondary phosphate(s) used is / are divided into two different process lines A and B, i.e. two process lines are used in parallel.

[0046] ■ In process line A, the phosphate is separated from the heavy metals in the portion of at least one phosphate-containing secondary phosphate and precipitated. The result is a highly concentrated, precipitated phosphate, which is significantly more plant-available than the inorganic secondary phosphate used. A special feature is that in this process line A, the heavy metals not dissolved by the reactant (sparingly soluble heavy metals) are also separated, along with the readily soluble heavy metals (dissolved by the reactant).

[0047] ■ In process line B, the (complete) portion of the at least one phosphate-containing secondary phosphate is converted into a fertilizer, whereby the phosphate is made available to plants and the heavy metals dissolved by the reactant can be at least partially separated. According to the invention, the precipitated, largely heavy metal-free phosphate produced in process line A is added to increase the phosphate content (phosphate-enriched) in the fertilizer produced. The precipitated phosphate produced in process line A from the partial stream of phosphate-containing secondary phosphate used there o increases the phosphate content of the fertilizer produced without the need to add a phosphate-containing nutrient component (phosphate-enriched) and o leads to a reduced heavy metal content, particularly for the poorly soluble heavy metals.

[0048] "Phosphate-enriched" fertilizer within the meaning of the invention is defined by the fact that the phosphate concentration of the fertilizer produced in the process according to the invention, based solely on the total amount of phosphate added with the inorganic secondary phosphate, is higher than the phosphate concentration in the inorganic secondary phosphate used. Thus, for example, if an inorganic secondary phosphate used contains 7% P2O5 as phosphate, the process according to the invention results in a fertilizer with more than 7% P2O5 as phosphate, whereby this more than 7% P2O5 results solely from the inorganic secondary phosphate (e.g., phosphate-containing ash). If, in embodiments, additional phosphate-containing components (e.g., phosphoric acid or phosphate salts) are added to the process, this additional phosphate is not contained in this more than 7% P2O5, but rather increases this proportion even further.

[0049] Since at least one inorganic secondary phosphate is used in the process according to the invention, several inorganic secondary phosphates can consequently also be used. The meaningful analogy between the used and the inorganic secondary phosphate(s) used in the description and definition applies here. The process according to the invention thus comprises the use of at least one (or one or more) inorganic secondary phosphate(s). The definition of "phosphate-enriched" fertilizer therefore applies, by way of example, to the use of several inorganic secondary phosphates: The phosphate concentration of the fertilizer produced in the process according to the invention, based solely on the total amount of phosphate added with the inorganic secondary phosphates (in total), is higher according to the invention than the phosphate concentration in a mixture of the inorganic secondary phosphates used.If, for example, 50% inorganic secondary phosphate with 7% P2O5 and 50% inorganic secondary phosphate with 8% P2O5 are used, the mixture of the inorganic secondary phosphates used results in a P2O5 concentration of 7.5% and the "phosphate-enriched" fertilizer according to the invention results in a P2O5 concentration of more than 7.5%.

[0050] According to the invention, the partial flow quantities of phosphate-containing secondary phosphate for process streams A and B are controlled in such a way that a desired phosphate content in the fertilizer product and the amount of separated heavy metals are specifically adjusted. The advantage of the two-stream process according to the invention (comprising stream A and stream B) is thus that an adjustable phosphate-enriched, heavy metal-depleted fertilizer granulate is produced from at least one inorganic secondary phosphate. Possible configurations of the process according to the invention are presented in the following description.

[0051] The method according to the invention surprisingly offers various advantages over known methods from the prior art, such as:

[0052] ■ In the above-described prior art phosphate conversion processes, such as those known from DE 10 2010 034 042 B4 or WO 2019 / 149405 A1, a phosphate-containing combustion residue (inorganic secondary phosphate) is treated with the solvent (reactant), and both are converted into the fertilizer product, resulting in a reduction (dilution) of the percentage phosphate content of the phosphate-containing combustion residue. In contrast, the process according to the invention produces a phosphate-enriched fertilizer granulate with a higher phosphate concentration than the inorganic secondary phosphate used.

[0053] This increase in phosphate concentration is advantageous, for example, because potential users or processors often desire highly phosphate-rich phosphate fertilizers such as at least "superphosphate" (comprising approximately 18% P2O5), double superphosphate (comprising approximately 35% P2O5), or preferably triple superphosphate (comprising approximately 46% P2O5). The use of these superphosphates is thus more efficient and simpler in agriculture or when used as a basic component for the production of complex fertilizers. These highly phosphate-rich fertilizers can be produced, for example, from sewage sludge ash using the inventive two-stream process, which typically has significantly lower P2O5 concentrations than, for example, these 18%, 35%, or even 46%. In process stream A of the inventive process, the inorganic secondary phosphate is converted into a highly concentrated precipitated phosphate (7).By converting this highly concentrated, precipitated phosphate (7) into the fertilizer to be produced (process step g) according to the invention, the phosphate content in the fertilizer produced is increased accordingly to the desired target value, for example to 18%, 35% or even 46%.

[0054] Although these prior art processes, such as those disclosed in DE 10 2010 034 042 B4 or WO 2019 / 149405 A1, offer the possibility of either using a phosphate-containing solvent (e.g., phosphoric acid) or adding phosphate-containing nutrient components (e.g., monoammonium phosphate (MAP)), thereby correspondingly increasing the phosphate content in the fertilizer and resulting in a highly phosphate-rich fertilizer, these phosphate-containing solvents or nutrient components are more expensive than the fertilizer obtained according to the invention and are heavily dependent on a volatile global market. In the process according to the invention, no additional phosphate-containing solvents need to be used or phosphate-containing nutrient components added to produce such highly phosphate-rich fertilizers. This can be achieved solely by the inventive method of concentrating the phosphate content from the added inorganic secondary phosphate.

[0055] If phosphate-containing solvents or nutrient components from conventional production from rock phosphate are used, the resulting fertilizers lose their status as pure phosphate recyclate, since the phosphate then no longer originates solely from recycling. This means that these fertilizers can no longer be used in the market segment for applications with high sustainability requirements, such as organic farming. Due to the possible concentration of the phosphate content in the process according to the invention, highly phosphate-rich fertilizers can be produced solely from the inorganic secondary phosphate used, which are therefore considered pure phosphate recyclate.

[0056] ■ While prior art P conversion processes such as WO 2019 / 149405 A1 can remove some of the heavy metals, they can only remove those heavy metals that were previously dissolved by the solvent (reactant). Undissolved heavy metals cannot be removed in these processes. In contrast, the process according to the invention also partially removes the heavy metals undissolved by the solvent (reactant). Preferably, more than 30%, particularly preferably more than 50%, of the heavy metals contained in the inorganic secondary phosphate, fed to process lines A and B with the inorganic secondary phosphate, and not dissolved by the reactant are removed in the process according to the invention.

[0057] ■ State-of-the-art leaching processes result in a very large amount of undissolved residue because the leaching process is controlled so that as much phosphate and as few accompanying components as possible are dissolved. In these processes, the accompanying components that are nevertheless dissolved are then separated out in a complex process, often in several stages. The separated undissolved residue and the separated accompanying components with dissolved components could (basically only theoretically) be used for other purposes, but are typically waste for disposal. In the process according to the invention, however, an insoluble residue only arises in process stream A. The accompanying components that are dissolved there are, unlike in the prior art, transferred into the fertilizer together with the precipitated phosphate and are therefore not waste. In process line B, all of the supplied inorganic secondary phosphate is transferred into the fertilizer and is thus recycled.Thus, the process according to the invention produces significantly less undissolved residue (i.e. waste) than known leaching processes.

[0058] Since a high product purity of the phosphate-rich products should be achieved for most of the intended fields of application, the desired complete separation of accompanying components in a conventional leaching process results in the loss of valuable nutrients and trace elements (e.g. Mg, K, S) that are useful for plant nutrition and growth or for soil quality as a basis for good yields. In a conventional leaching process, these nutrients remain unused as waste in the undissolved residue. In the process according to the invention, however, these nutrients and trace elements are transferred into the fertilizer and are thus used instead of being discarded. According to the invention, the transfer of these nutrients and trace elements takes place on the one hand by the fact that no insoluble residue is separated and discharged in line B, but rather the entire material can be transferred into the fertilizer.On the other hand, in strand A these dissolved nutrients and trace elements are not separated from the phosphate-rich solution (5), but are transferred into the precipitated phosphate (7) during precipitation, and thus ultimately into the fertilizer.

[0059] 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 determined is first digested with aqua regia digestion according to DIN EN 13346:2001-04. Various methods, particularly extraction methods, are known for determining the soluble phosphate content. To estimate P availability, the fertilizers are analyzed in the laboratory using various solvents and labeled accordingly. The most important solvents used are water, ammonium citrate, citric acid, formic acid, and mineral acids. The EU Fertilizer Regulation also standardizes various methods for determining the phosphate solubility of fertilizers.Depending on the origin and nature of the P fertilizer to be tested, a different method can be used. To characterize the solubility of phosphate, the following three extraction methods are used in the context of the present invention: The extraction of water-soluble phosphorus (P) is carried out according to DIN EN 15958:2011. The extraction of neutral ammonium citrate-soluble phosphorus (P) is carried out according to DIN EN 15957:2011. The extraction of 2% citric acid-soluble phosphorus (P) is carried out according to DIN EN 15920:2011. The phosphate content (P) is then determined using inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885:2009. Especially with high proportions of water- and ammonium citrate-soluble phosphate, it is ensured that a large part of the fertilizer phosphate is actually available to the plant in the short and medium term.The neutral ammonium citrate-soluble phosphorus content can be used as an indicator of the medium-term plant availability of the fertilizer phosphorus, i.e., over a period of approximately one crop rotation. The immediately available P content of a fertilizer is described by its solubility in water. The higher the water-soluble P content, the faster and easier the availability of the fertilizer phosphorus to the plant. Stronger solvents, such as citric or formic acid, also dissolve P components that are only available to plants in the long term or only under certain 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.High water solubility makes phosphate available very quickly in large quantities, which the plant may not be able to fully absorb in a consistent time sequence during growth, thus remaining unused and possibly being washed out. According to currently agreed scientific opinion, for reasons of resource conservation, the use of P fertilizers with a particularly high neutral ammonium citrate-soluble phosphate content should be preferred. In this respect, the present invention meets the requirement for high neutral ammonium citrate-soluble phosphate contents by providing fertilizer granules with a particularly high neutral ammonium citrate-soluble PjOs content of greater than 60%, preferably greater than 70%, particularly preferably greater than 80% of the total PjOs content in the fertilizer granules using the proposed process.

[0060] For the purposes of the invention, fertilizers are substances or mixtures of substances that supplement or adjust the nutrient supply for cultivated plants, particularly crops, in agriculture, forestry, and horticulture. They can optionally be combined and / or functionalized with other materials. Fertilizers are understood here to include both single-nutrient fertilizers, such as phosphate fertilizers, and complex fertilizers. Fertilizers in granular form, i.e., fertilizer granules, are a typically approximately spherical aggregate with sufficient inherent strength, with an average granule size of 0.5-10 mm, preferably 1-7 mm, and most preferably 2-5 mm.

[0061] For the purposes of the invention, inorganic secondary phosphate is defined as substances which arise during the processing, preparation or manufacture of something (residue) and which have a phosphorus content of greater than 5% P2O5 and a TOC content (TOC = total organic carbon) of less than 3%. Examples of inorganic secondary phosphates are ashes and / or slags from the mono- or co-incineration of sewage sludge, ashes and / or slags from the incineration or co-incineration of animal excrement, animal meal, animal remains and animal carcasses or ashes / slags from the incineration of liquid manure and digestate as individual substances or mixtures thereof. The phosphorus compounds contained in the inorganic secondary phosphate, the intermediate products and the fertilizers produced in the process according to the invention are referred to here as phosphate and the phosphorus orPhosphate concentration is uniformly indicated as P2O5, even if in individual cases this may not or not completely correspond to the binding type of the phosphorus.

[0062] Organic sludges, such as sewage sludge, are expressly not considered inorganic secondary phosphates according to the invention, as their TOC content is significantly above the defined limit of 3%. However, the chemical and physical constitution of sewage sludge also differs fundamentally from the inorganic secondary phosphates according to the invention, for example, in the type, concentration, and plant availability of the phosphate it contains. Sewage sludge is directly suitable as fertilizer and has been used for this purpose for decades, as the phosphates already present in it are sufficiently plant-available. Sewage sludge ash according to the invention (as a possible inorganic secondary phosphate) is produced by the thermal combustion of sewage sludge. However, the phosphates in the sewage sludge are converted into poorly soluble Ca(Mg) phosphates during the combustion process.Thus, while phosphates are present in both sewage sludge and sewage sludge ash, the binding form of the phosphates is fundamentally different. This results in fundamentally different requirements for the reaction process aimed at improving solubility and plant availability. Sewage sludge has been used for fertilization for decades because the phosphates there are sufficiently available to plants. However, sewage sludge ash, due to the different phosphate form—the poorly soluble phosphates present here—is unsuitable as fertilizer without prior digestion, as plants cannot absorb the poorly soluble phosphates to a sufficient extent.

[0063] In the context of the present invention, a reactant is understood to mean a substance or mixture which, on the one hand, dissolves at least a portion of the phosphate supplied by the inorganic secondary phosphate and / or reacts with it, and, on the other hand, dissolves at least a portion of the heavy metals from the inorganic secondary phosphate. The reactant is preferably designed to dissolve at least a portion of the phosphate contained in the inorganic secondary phosphate and / or to react with it or to convert the phosphate by reaction to form a phosphate that is more soluble in neutral ammonium citrate. In the subsequent process, for example by precipitation, recrystallization, or drying, the phosphate preferably dissolved by the reactant advantageously forms a phosphate that is more soluble in neutral ammonium citrate than the phosphate contained in the inorganic secondary phosphate.The phosphate solubility in the produced phosphate-enriched, heavy metal-depleted fertilizer granules (10) is preferably determined by the type of phosphate bond and the solution environment (e.g., chemical composition and / or pH). This can be influenced, for example, by the type and concentration of the reactant. In addition to other parameters such as the reaction regime and reaction time, the type and concentration of the reactant can also influence the type and proportion of dissolved heavy metals. Reactants include, for example, organic or inorganic acids or acid mixtures or alkalis or mixtures of different alkalis, each in undiluted or diluted form.

[0064] In the context of the present invention, the liquid phase is defined as the sum of the liquid substances in a coherent system. Thus, the raw material dispersion consists of a solid and a liquid phase. In the context of the present invention, the solid phase is the sum of the undissolved substances. The liquid phase in a system, for example, in a raw material dispersion, can be formed from various liquid components. For example, liquid components can be supplied at least partially in the form of moisture, partially in a suspension or as a liquid via various substances or, for example, as water, or at least partially contained in the reactant, for example, liquid acids, especially diluted acids. The term "moisture" in the sense of the invention corresponds to the physically bound water (water content) that adheres to the substance or mixture of substances.The term "humidity" is also used synonymously with the term "moisture content".

[0065] In the context of the present invention, the moisture content is determined gravimetrically according to DIN 52183. In the gravimetric moisture determination, also known as the Darr method, the sample is first weighed and then dried to constant weight at 105°C in a drying oven. This evaporates the free water contained in the sample. The weight difference is determined, which in the context of the present invention corresponds to the moisture content. Since the liquid phase can also contain dissolved components that remain as solids during drying, the percentage of the liquid phase is usually significantly higher than the moisture content. The percentage of the liquid phase corresponds to the mass fraction of the liquid components (including dissolved constituents therein) in a system.

[0066] In process step a), a raw material dispersion is provided for process line A and process line B, whereby the proportion of liquid phase in the raw material dispersion is greater than 30%.

[0067] In a preferred embodiment, a raw material dispersion is produced from at least one inorganic secondary phosphate and at least one reactant, and this produced raw material dispersion is fed separately to process lines A and B. The advantage of this embodiment is, for example, that the production of only one raw material dispersion for process lines A and B together is easier to handle, less complex to control, and only one suitable reaction vessel is required to produce the raw material dispersion.

[0068] In another preferred embodiment, the inorganic secondary phosphate is first divided into two separate substreams for subsequent further processing into process streams A and B.

[0069] One embodiment comprises the variant that at least one inorganic secondary phosphate is initially divided into two separate sub-streams for subsequent processing into process streams A and B. One embodiment further comprises the variant that, when using a plurality of inorganic secondary phosphates, these are mixed beforehand and the inorganic secondary phosphate thus mixed is then divided into two separate sub-streams for subsequent processing into process streams A and B. In embodiments, the separate sub-streams for process streams A and B can also comprise different inorganic secondary phosphates or different amounts of different inorganic secondary phosphates. From the divided sub-streams, a raw material dispersion is then produced from the respective sub-stream of the at least one inorganic secondary phosphate orA mixture of inorganic secondary phosphates and at least one reactant is produced separately and fed to process line A or B. The advantage of this embodiment is that the two separate raw material dispersions produced in this way can be conditioned differently, adapted to the respective process line. For example, different reactants or different proportions of liquid phase can be used, or different reaction parameters such as pH or incubation time can be selected in order to specifically adjust the dissolution and conversion reaction between inorganic secondary phosphate and reactant, also with regard to the requirements for different further processing in process line A or B.For example, in a preferred embodiment, the proportion of dissolved phosphate from the inorganic secondary phosphate in the raw material dispersion for process line A can be set to greater than 90%, resulting in particularly economical recovery of the phosphate as a phosphate-containing filter cake from this partial stream. In the raw material dispersion for process line B, however, the phosphate can initially be dissolved, but then at least partially precipitated, resulting in easier separation in the subsequent process step.

[0070] The raw material dispersion used in the context of the proposed process has a significantly higher proportion of liquid phase than conventional processes known from the prior art, for example from DE 10 2010 034 042 B4. It is known in the prior art that the phosphate ash is mixed directly with mineral acid at a relatively low moisture content and simultaneously granulated. The production of a raw material dispersion envisaged in the context of the proposed invention therefore has significant technical advantages. For example, the reactions that often occur spontaneously and are sometimes highly exothermic when mixing the phosphate-containing secondary raw materials with the mineral acid can be monitored and controlled. The higher proportion of liquid phase according to the invention advantageously acts as a reaction buffer. A raw material dispersion with a significantly higher proportion of liquid phase is also considerably less sticky.This significantly facilitates stable process control and effectively reduces adhesion and blockage of plant components. For this reason, the raw material dispersion(s) produced contain(s) a liquid phase content of preferably greater than 50%, particularly preferably greater than 70%.

[0071] In a preferred embodiment of the invention, the raw material dispersion(s) preferably contain(s) an undissolved solid phase of less than 40% after the incubation time provided according to the invention. In this range, particularly good and simple homogenization of the raw material dispersion produced is possible. In a particularly preferred embodiment of the invention, one or both raw material dispersions contain(s) an undissolved solid phase of less than 30% after the incubation time provided according to the invention. Under such conditions, the dissolution rate is relatively high, whereby the necessary reaction time can advantageously be shortened. In another, likewise preferred embodiment of the invention, the raw material dispersion fed to process line B contains a solid phase content of less than 15% after the incubation time provided according to the invention.With this low undissolved fraction and the correspondingly high liquid phase fraction, relatively low concentrations of dissolved heavy metals are established in the liquid phase because the dissolved heavy metal fraction is diluted by the high liquid phase fraction. The partial separation of the liquid phase in process step f) then results in a lower heavy metal content in the remaining, unseparated liquid phase. This results in the desired higher heavy metal removal in step f) with the same separation intensity.

[0072] To adjust the preferred proportion of liquid phase, one or more liquid components can be added to the raw material dispersion(s). In a preferred embodiment of the invention, the liquid phase from process step h) is at least partially recycled to process step a). This liquid phase from process step h) may still contain a portion of the dissolved nutrient components, for example, phosphate. Alternatively or additionally, water and / or liquid nutrient-containing solutions can also be added. Nutrient-containing solutions preferably contain nutrients and / or trace elements present in the proposed fertilizer granules.

[0073] The phosphate contained in the inorganic secondary phosphate advantageously serves as a nutrient component in the resulting fertilizer. High phosphate contents, especially in the inorganic secondary phosphate, are therefore desirable. Therefore, inorganic secondary phosphates with greater than 5% P2O5 are preferred, particularly with greater than 7% P2O5, and most preferably with greater than 10% P2O5. The inorganic secondary phosphate may also contain other components. It is advantageous if it contains additional nutrient components, such as N, K, Mg, or other trace nutrients.

[0074] The phosphate content of inorganic secondary phosphate typically has a relatively low solubility. Accordingly, such substances, such as sewage sludge ash, are only suitable as fertilizers to a limited extent. These inorganic secondary phosphates typically have a water solubility of less than 20% and a

[0075] Neutral ammonium citrate solubility of less than 50%, preferably based on the total phosphate content in the inorganic secondary phosphate. For meaningful use as a fertilizer, it is preferred according to the invention that this insufficiently soluble phosphate is converted into a more soluble and thus more plant-available phosphate. According to the invention, the conversion takes place by at least partially reacting the inorganic secondary phosphate with at least one reactant. The reactant is preferably designed to dissolve at least a portion of the phosphate contained in the inorganic secondary phosphate and / or to react with it or to convert the phosphate by reaction to produce a phosphate that is more soluble in neutral ammonium citrate.The phosphate, preferably dissolved by the reactant, advantageously forms a phosphate with better neutral ammonium citrate solubility than in the inorganic secondary phosphate in the subsequent process, for example, by precipitation, recrystallization, or drying. The term "better neutral ammonium citrate solubility" in the context of the invention preferably means that the neutral ammonium citrate solubility of the phosphate in the inorganic secondary phosphate is higher after the reaction with the reactant. An increase in neutral ammonium citrate solubility of greater than 20% is preferred, with an increase of greater than 50% being particularly preferred. A corresponding calculation example could be as follows: the neutral ammonium citrate solubility of the phosphate portion from the untreated secondary phosphate of 50% is increased by 20% to 60% by the reaction with the reactant.The reactant is selected in particular so that it preferably meets the aforementioned requirements during application. When using acids, the proposed process differs from the prior art in particular in that the phosphate reacts at least partially, increasing its solubility.

[0076] According to the invention, it is preferred that the reaction between inorganic secondary phosphate and reactant increases the solubility of the phosphate from the inorganic secondary phosphate. The P solubility is preferably determined by the type of P bond and the solution environment. The type of reaction in process step a) can influence the binding of the P, i.e. the phosphate phases that form. This can be done, for example, by the type and concentration of the reactant, the reaction time and / or the process temperature. The phosphate portion from the inorganic secondary phosphate preferably has a neutral ammonium citrate solubility of greater than 60%, preferably greater than 70%, particularly preferably greater than 80% in the fertilizer granules produced.Conversion of the phosphate and the preferred resulting neutral ammonium citrate solubility from the inorganic secondary phosphate advantageously results in better phosphate plant availability and thus an improved fertilizing effect. In a preferred embodiment of the invention, the reaction is preferably controlled such that the phosphate portion from the inorganic secondary phosphate subsequently has a neutral ammonium citrate solubility of greater than 60% and a water solubility of less than 40% in the fertilizer granules produced. By adjusting the solubilities in this way, the phosphate is actually sufficiently available to the plants in the field for approximately one growing season, but is not leached out during this time. Leaching can typically occur when very good water solubility is present, i.e., significantly higher than the level envisaged here.In a particularly preferred embodiment of the invention, a neutral ammonium citrate solubility of greater than 80% and a water solubility of less than 30% is set for the phosphate portion from the inorganic secondary phosphate in the produced fertilizer granules. Surprisingly, it has been shown that this provides winter rye, in particular, with a particularly favorable P supply over a growing period. In another particularly preferred embodiment of the invention, a neutral ammonium citrate solubility of greater than 90% and a water solubility of less than 15% is set for the phosphate portion from the inorganic secondary phosphate in the produced fertilizer granules. This ratio is particularly favorable for wheat plants. The type and concentration of the reactant, the reaction procedure, and the reaction time can also influence the type and proportion of dissolved heavy metals.For example, a higher acid strength preferentially results in a higher proportion of dissolved heavy metals. A higher proportion of dissolved heavy metals is preferred in this process step, as this allows more heavy metals to be separated in process step f) with the partial separation of the liquid phase and fed into the at least partial separation of the heavy metals in process step h).

[0077] In a preferred embodiment of the invention, at least one reactant is used which comprises at least one of the elements nitrogen (N), sulfur (S), potassium (K) and / or phosphorus (P), for example phosphorous acid (H3PO3), phosphoric acid (H3PO4), nitric acid (HNO3), sulfuric acid (H2SO4), sulfurous acid (H2SO3) and / or potassium hydroxide solution (KOH). By using such reactants, additional nutrient components such as nitrogen, sulfur, potassium and / or phosphorus are introduced into the granules. By means of a suitable reaction sequence, the nutrient-binding form of the nutrients contained in the reactant, e.g. nitrogen and / or sulfur, can preferably be converted into a form suitable for the fertilizer.

[0078] The components of the raw material dispersion can be combined in any order. For the purposes of the invention, it is necessary that the reactant in process step a) reacts sufficiently with at least a portion of the phosphate supplied by the inorganic secondary phosphate. The term "react sufficiently" for the purposes of the invention means that the desired improvement in the neutral ammonium citrate solubility of the phosphate is achieved. Accordingly, an incubation period is provided in process step a), in the sense of allowing the reactant to act on the inorganic secondary phosphate. The incubation according to process step a) takes place over a period of time in the range of 1 to 100 minutes, preferably in the range of 5 to 60 minutes, and particularly preferably in the range of 10 to 30 minutes.The order in which the components are combined, the timing and the incubation time can, for example, influence the reaction taking place and thus also the proportion of dissolved heavy metals and the neutral ammonium citrate solubility of the phosphate in the produced fertilizer granules.

[0079] The intended separation of the reaction for at least partial phosphate conversion from the inorganic secondary phosphate from the subsequent process steps preferably solves the technical problem that the exothermic, sometimes spontaneous and violent reaction severely hinders further process control. The separation of the reaction from the subsequent process steps provided for according to the invention is preferably to be understood in the technical sense such that by far the largest proportion of the reaction takes place in process step a). However, it may also be preferred for the reaction to continue in the subsequent process steps, but then at a significantly reduced intensity. By adhering to the incubation time provided for according to the invention, the remaining intensity of the possible continuation of the reaction no longer hinders process control.In a preferred embodiment of the invention, process step a) is preferably 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 process step a). This means that if the reaction were to be stopped after process step a) by rapid drying, the phosphate from the inorganic secondary phosphate treated with the reactant would already exhibit at least 80% of the neutral ammonium citrate solubility of a reaction product that was not stopped but still undergoes process steps b) and c). Additional components can be added to the raw material dispersion in process step a).Other components here are generally substances that can improve the process control and / or the properties of the fertilizer granules, such as nutrient-containing components, dispersing and defoaming agents, structural agents, pH adjusting agents, urease inhibitors, ammonium stabilizers, humic acid, organic acids and / or water.

[0080] The pH of the raw material dispersion produced can be adjusted as needed during or after the incubation period. In a preferred embodiment, the pH is set between 1-2, since in this range the dissolved phosphate remains largely dissolved. In another preferred embodiment, the pH of the raw material dispersion for process strand B is adjusted above a pH of 2, whereby the dissolved phosphate is at least precipitated. Particularly preferably, the pH of the raw material dispersion for process strand B is adjusted to a value above 3, since this ensures particularly good precipitation of the dissolved phosphate. In a very special embodiment, the pH is adjusted such that more than 90% of the dissolved phosphate precipitates. This simplifies the partial separation of the liquid phase in process step f) due to the lower dissolved fractions.

[0081] Thus, in embodiments of the invention, the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention and / or the method according to the invention are characterized in that in process step b) the addition of the at least one heavy metal precipitant (4) and the heavy metal precipitation are carried out at a pH value of less than 2 and the separation of a part of the phosphate-containing, heavy metal-poor liquid phase (5) of the raw material dispersion and discharge of the remaining heavy metal-containing filter cake (6) from the process also take place at a pH value of less than 2.

[0082] The amount of raw material dispersion, and thus of inorganic secondary phosphate (substream), provided for each process line A and process line B is adjusted, for example, according to the product quality requirements of the produced fertilizer and / or for economic reasons. Unlike prior art processes, the flexibly adjustable amount of the substreams according to the invention allows the process to be controlled in such a way that it is particularly economical, even with different or fluctuating chemical constitutions of the inorganic secondary phosphates, while still meeting quality requirements, for example, regarding heavy metal limit values.

[0083] ■ According to the invention, in process line A the heavy metals not dissolved during the reaction between inorganic secondary phosphate and reactant can also be largely separated, while in process line B (only) the dissolved heavy metals can be separated in process step h). Thus, by adjusting the amount of inorganic secondary phosphate added to process line A and process line B, not only an overall depletion rate of heavy metals can be set, but also a targeted depletion rate of particularly problematic heavy metals which, for example, exceed the limit values. Thus, for example, the partial flow amount of inorganic secondary phosphate added to process line A can be used to influence the depletion rate of heavy metals which are not dissolved by the reactant.

[0084] ■ In process line A (as is typical for leaching processes) an insoluble residue is created which is generally disposed of as waste. In process line B, however, no such process residue is produced. The type of distribution of the amount of inorganic secondary phosphate between process line A and B influences the amount of this residue. Unlike with known leaching processes from the prior art, however, the invention always supplies process line B with a partial stream of the inorganic secondary phosphate. This reduces the amount of process residue from the overall process, which is not only more cost-effective, but also means that the accompanying components from the inorganic secondary phosphate which are transferred into the fertilizer in process line B contain some additional nutrients and trace elements which the plant requires.This eliminates the need to add such components from conventional production and makes the process not only more economical but also more sustainable.

[0085] ■ In process line A, the inorganic secondary phosphate is converted into a highly concentrated phosphate. The inventive conversion of this highly concentrated phosphate into the fertilizer to be produced (process step g) increases the phosphate content in the fertilizer produced. Depending on the distribution of the inorganic secondary phosphate between process lines A and B, an adjustable, in any case higher, P concentration than in the inorganic secondary phosphate in the fertilizer can be achieved without the addition of additional phosphate as a nutrient component, compared to what would result from process line B alone. This is economically advantageous because phosphate nutrient components are expensive and increasingly difficult to obtain.

[0086] This resulting phosphate concentration in the fertilizer produced can surprisingly be achieved in the process according to the invention by adjusting the partial flow quantities for process lines A and B. According to the invention, a phosphate-enriched fertilizer is produced, wherein the phosphate concentration of the fertilizer produced, based solely on the phosphate supplied with the inorganic secondary phosphate, is higher than the phosphate concentration in the supplied inorganic secondary phosphate itself. In a particularly preferred embodiment, the at least one inorganic secondary phosphate is distributed among the partial flow quantities in such a way that the phosphate concentration in the fertilizer granules produced is at least 30% higher, based solely on the phosphate supplied with the inorganic secondary phosphate or the mixture of several supplied inorganic secondary phosphates, than in the supplied inorganic secondary phosphate.This results in a particularly phosphate-rich fertilizer granulate, which is suitable, for example, for further processing with other nutrients. For example, if in this embodiment the inorganic secondary phosphate used contains 7% P2O5 as phosphate, this inorganic secondary phosphate is distributed between process lines A and B to produce a fertilizer granulate with more than 9.1% P2O5 as phosphate (based on phosphate from the inorganic secondary phosphate alone). If several inorganic secondary phosphates are used simultaneously, an average phosphate concentration for the inorganic secondary phosphate results, and the calculation method is analogous.

[0087] Thus, embodiments of the phosphate-enriched, heavy-metal-depleted fertilizer granules (10) according to the invention and / or of the method according to the invention are characterized in that the phosphate-enriched, heavy-metal-depleted fertilizer granules (10) have a phosphate concentration that is at least 30% higher than that of the inorganic secondary phosphate(s) added. In other words, in embodiments, the fertilizer granules (10) obtained according to the invention and / or the method according to the invention are characterized in that the phosphate-enriched, heavy-metal-depleted fertilizer granules (10) have a phosphate concentration that is at least 30% higher than that supplied by and / or contained in the inorganic secondary phosphate(s) (1) used (starting materials).

[0088] According to the invention, heavy metal depletion occurs in the process. Surprisingly, a depletion of at least 20% of the total amount of heavy metals added by the inorganic secondary phosphate(s) (sum of all heavy metals) can be achieved, particularly preferably a depletion of more than 30% of the total amount of heavy metals added by the inorganic secondary phosphate, whereby fewer heavy metals are released into the environment by the produced fertilizer during fertilization.

[0089] Therefore, embodiments of the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention and / or of the method according to the invention are characterized in that the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) has a total heavy metal concentration that is at least 20% lower than that of the added inorganic secondary phosphate(s). In other words, in embodiments of the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention and / or of the method according to the invention, the latter is characterized in that the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) has a total amount of heavy metals that is at least 20% lower than that supplied by the at least one inorganic secondary phosphate used.

[0090] The problem with state-of-the-art processes such as WO 2019 / 149405 Al is that only those heavy metals can be separated that have previously been dissolved by the reactant.

[0091] In the process according to the invention, surprisingly, these heavy metals not dissolved by the reactant can also be separated in process line A. In a preferred embodiment, the at least one inorganic secondary phosphate is distributed among the partial stream quantities in such a way that the fertilizer granules produced are depleted by at least 30% of the heavy metals supplied by the inorganic secondary phosphate and not dissolved by the reactant. The depletion of these heavy metals essentially takes place in process line A according to the invention. If, for example, 100 mg / kg of a heavy metal type (e.g. Pb) supplied to the process by the inorganic secondary phosphate is not dissolved by the reactant, at least 30 mg / kg of this is separated from the process and thus not transferred into the fertilizer granules.For many inorganic secondary phosphates, the removal of such a quantity of heavy metals is sufficient to fall below the limits for a legally compliant fertilizer. In another preferred embodiment, at least 50% of these undissolved heavy metals are similarly removed from the process. This embodiment is necessary, for example, if the inorganic secondary phosphate has a particularly high concentration of this type of heavy metal, and this embodiment is particularly sustainable because it reduces the amount of heavy metals introduced into the fertilizer by agriculture.

[0092] In process step b), a heavy metal precipitant is added to the raw material dispersion produced and fed to process step b) in process line A during the incubation period and / or after the incubation period.

[0093] Therefore, embodiments of the phosphate-enriched, heavy metal-depleted fertilizer granules (10) according to the invention and / or of the method according to the invention are characterized in that in process step b) at least one heavy metal precipitant is added during the incubation period.

[0094] In embodiments, in process step b), more than 80% of the total dissolved heavy metals are precipitated from the raw material dispersion (3, 3') by the added at least one heavy metal precipitant (4), wherein after the heavy metal precipitation, at least 80% of the previously dissolved P2O5 remains dissolved in the raw material dispersion (3, 3'). According to the invention, heavy metal precipitants are understood to mean substances that can precipitate or crystallize dissolved heavy metals in the raw material dispersion, i.e., can convert them from the dissolved phase to the solid phase. Such heavy metal precipitants can, for example, be substances that raise the pH of the raw material dispersion, whereby the dissolved heavy metals at least partially precipitate. Examples of such substances are alkalis such as NaOH, KOH or basic substances such as CaO, MgO, Mg(OH)2 or Ca(OH)2.Heavy metal precipitants can also be substances that react with the dissolved heavy metal and precipitate at least partially as a compound. Examples of this type of substance are sulfides such as H2S, CH4N2S, Na2S, which react with the heavy metals to form heavy metal sulfides. A heavy metal precipitant within the meaning of the invention can also be a so-called sacrificial metal. Within the meaning of the invention, a sacrificial metal is preferably referred to as a less noble metal than the heavy metals to be separated, for example selected from the group of aluminum, iron and zinc or mixtures thereof. If the sacrificial metal comes into contact with the dissolved heavy metals, a reduction of the more noble metals present in dissolved form advantageously takes place on the surface of the less noble sacrificial metal, which is oxidized in the process and thus at least partially transforms into the solid state.The reductive conditions can be triggered or enhanced by the addition of a suitable reducing agent.

[0095] Therefore, embodiments of the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention and / or of the method according to the invention are characterized in that at least one heavy metal precipitant (4) added, preferably in process step b), is a sulfide.

[0096] According to the invention, the addition of the heavy metal precipitant converts at least a portion of the dissolved heavy metals present in the raw material dispersion added in process step b) into the solid phase. This enables the separation of these undissolved heavy metals by a simple solid-liquid separation in process step c).

[0097] Preferably, more than 50%, particularly preferably more than 70%, of the heavy metals dissolved in the added raw material dispersion are converted into the solid phase by the heavy metal precipitant. Since the necessary reaction between inorganic secondary phosphate and the reactant dissolves relevant portions of heavy metals, typically Cd or As in sewage sludge ash, for example, such separation rates are necessary to comply with the required limit values ​​in the fertilizer produced. In a particularly preferred embodiment, more than 80% of the heavy metals dissolved in the added raw material dispersion are converted into the solid phase by the heavy metal precipitant, resulting in fertilizer granules with a particularly low heavy metal concentration.

[0098] To increase the effectiveness of the heavy metal precipitant, the raw material dispersion can be conditioned in process step a) and / or process step b). Conditioning means that the properties of the raw material dispersion or the reaction environment are improved with respect to an increased precipitating effect of the heavy metals. Such conditioning can, for example, involve adjusting the pH value, temperature, redox potential, or the concentration of the dissolved substances.

[0099] In a preferred embodiment, more than 80% of the P2O5 from the inorganic secondary phosphate added in process step b) is dissolved, and the addition of the heavy metal precipitant and the transfer of the heavy metals into the solid phase occur at pH values ​​below 2. In this range, the dissolved phosphate is largely dissolved even without prior complexation. One or more sulfides, such as H2S, CH4N2S, or Na2S, are preferably used as the heavy metal precipitant. The added sulfides precipitate at least a portion of the dissolved heavy metals as heavy metal sulfides.Surprisingly, it was found that, in a particularly preferred embodiment, more than 80% of the total dissolved heavy metals can be precipitated by sulfide(s) as heavy metal precipitant even in this low pH range of less than 2, whereby the phosphate, which is also present in dissolved form in the raw material dispersion, subsequently continues to be dissolved at more than 80% (relative to the previously dissolved portion). Thus, for example, if a total of 100 mg of heavy metals (e.g., the sum of Cd, As, Cu) and 5 g of P2O5 are dissolved in the raw material dispersion, after the addition of sulfide(s) as heavy metal precipitant and the precipitation reaction, less than 20 mg of heavy metal and more than 4 g of P2O5 are dissolved.

[0100] Therefore, embodiments of the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention and / or of the method according to the invention are characterized in that in process step b) more than 80% of the total dissolved heavy metals are precipitated from the raw material dispersion by the added at least one heavy metal precipitant (4), wherein after the heavy metal precipitation at least 80% of the previously dissolved P2O5 continues to be dissolved in the raw material dispersion.

[0101] In a preferred embodiment, the sulfide(s) is added in a pH range below 1. Surprisingly, it has been found that the desired precipitation of the heavy metals by sulfides in the reaction medium of the raw material dispersion occurs sufficiently quantitatively even at these very low pH values. The advantage here is that the sulfide can be added during the incubation period or while the reaction between inorganic secondary phosphate and reactant is still ongoing. As a result, the reaction between inorganic secondary phosphate and reactant, as well as between heavy metal precipitant and dissolved heavy metals, takes place at least temporarily simultaneously, which shortens the overall process time or allows for a longer reaction time with the same overall process time. In another preferred embodiment, the sulfide(s) is added in a pH range between 1 and 2.The advantage of this design is that precipitation by sulfide is more efficient in this pH range than in the pH range below 1, thus precipitating a higher amount of heavy metals. At the same time, the dissolved phosphate remains largely in dissolved form.

[0102] In process step c) of the proposed process, a portion of the phosphate-containing, heavy metal-poor liquid phase is separated from the raw material dispersion produced in process step a) and fed to process line A, and the resulting heavy metal-containing filter cake is discharged from the process.

[0103] The heavy metals contained in the filter cake are preferably removed from the process along with the heavy metals. This includes, on the one hand, the portion of heavy metals that are preferably not dissolved in process steps a) and / or b), particularly by the reactant used. These heavy metals cannot be separated by the process in line B.

[0104] By controlling the amount of inorganic secondary phosphate added for strands A and B as well as the process execution in strand A (such as type of reactant, incubation time, reaction conditions), the desired amount of these heavy metals that are not dissolved by the reactant can be discharged in process step c) of strand A. Typically, this is at least a proportion of Pb, Zn, Ni, for example. On the other hand, it includes the proportion of heavy metals that precipitate again until the heavy metal-containing filter cake is separated in this process step, for example by the precipitant in process step b).

[0105] It is preferable to separate off sufficient phosphate-containing, heavy-metal-poor liquid phase in this process step so that the moisture content in the heavy-metal-containing filter cake is less than 50%. By separating off such a proportion of the liquid phase in which the phosphate is dissolved, a significant proportion of phosphate can be obtained for the further process and thus an economically attractive phosphate yield. In a particularly preferred embodiment, sufficient phosphate-containing, heavy-metal-poor liquid phase is separated off so that the moisture content in the heavy-metal-containing filter cake is less than 40%. This advantageously means that less water needs to be removed from the heavy-metal-containing filter cake by drying prior to landfilling, which is more cost-effective.

[0106] The partial separation of the liquid phase within the meaning of the present invention can be carried out continuously and / or discontinuously in one or more steps, for example by filtration or centrifugation. Filtration can be carried out discontinuously, for example by means of autopress, pressure filters, stirred pressure filters, suction filters, disc filters, (pressure) leaf filters, bag filters, candle filters, hose filters, sheet filters, filter presses such as frame filter presses, chamber filter presses, membrane filter presses; plate filters and / or bed filters, or continuously, for example by means of crossflow filtration, shear gap filters, tubular rotor filters, belt filters, rotary pressure filters, drum filters, rotary vacuum filters, disc pressure filters and / or sliding belt presses, without being limited thereto.Centrifugation can be carried out continuously, for example, using sieve centrifuges, sieve screw centrifuges, impact ring centrifuges, sliding centrifuges, pusher centrifuges, oscillating centrifuges, tumbling centrifuges, and / or solid bowl centrifuges, or discontinuously, for example, using suspended pendulum centrifuges, horizontal peeler centrifuges, inverting filter centrifuges, pusher bag centrifuges, and / or vertical centrifuges. According to the invention, it is preferred that the solid-liquid separation be carried out using filter presses or vacuum belt filters.

[0107] During the partial separation of the liquid phase, it is preferably not absolutely necessary that all solid components be completely separated from the separated liquid phase. In particular, very fine solid particles, which are preferably referred to as suspended particles within the meaning of the invention, can preferably remain in the separated phase. This simplifies the separation process, for example during filtration or centrifugation, since the complete separation of fine particles in particular is very complex in a solid-liquid separation with a high solids load. It is therefore preferred that a solids content of less than 10%, particularly preferably less than 5%, and most preferably less than 2% be set in the separated liquid phase.

[0108] In process step d) of the proposed method, at least a portion of the dissolved phosphate is precipitated in the liquid phase separated in process step c), i.e., the dissolved phosphate is at least partially transferred into the solid phase.

[0109] The precipitation of the dissolved phosphate can be carried out using a process known to those skilled in the art. It may be advantageous to condition the separated liquid phase before or during the process, for example, by setting a desired process temperature or by adding substances such as defoamers or dispersants to the liquid phase to alter its physicochemical properties.

[0110] In a preferred embodiment, the dissolved phosphate is precipitated in the liquid phase separated in process step c) by increasing the pH. The separated liquid phase preferably has a pH of less than 2. If the pH is increased, as provided in this preferred embodiment, the dissolved phosphate precipitates at least partially. The pH range of this phosphate precipitation depends, for example, on the type of phosphate (e.g., aluminum phosphate, iron phosphate, calcium phosphate) that can be formed. In this preferred embodiment, a substance is added to the separated liquid phase to raise the pH of this separated liquid phase, preferably above 2. In a particularly preferred embodiment, the pH is set in a range between 2 and 4.In this pH range, sufficient quantitative precipitation, preferably more than 80% of the dissolved phosphate, typically occurs. In a particularly preferred embodiment, the phosphate is precipitated in the pH range from 2 to 3. The advantage of this embodiment is that, after separation of the precipitated phosphate (process step e)), a (low-phosphate) liquid phase results that has a comparatively low pH. For a possible return of this separated liquid phase to process step a) for the production of a raw material dispersion, it is advantageous if the pH is already low, as this means, for example, that less acid needs to be used.

[0111] To raise or adjust the pH, any substance or mixture of substances that influence the pH in the desired manner can be used. In a preferred embodiment, at least one NaOH or sodium hydroxide solution is added to the separated liquid phase, which leads to an increase in the pH. NaOH or sodium hydroxide solution is inexpensive and is available in sufficiently large quantities. In another preferred embodiment, at least one calcium compound, such as CaO or Ca(OH)2, is added to the separated liquid phase, which leads to an increase in the pH. The advantage of this embodiment is that such compounds are usually inexpensive and, if necessary, at least a portion of Ca phosphates are formed during precipitation. Ca phosphate compounds as precipitation products have a very good fertilizing effect.In another preferred embodiment, a potassium compound, such as KOH, is added to the separated liquid phase, which leads to an increase in the pH value. This is advantageous because potassium is an important nutrient for plants, and the added potassium is separated from the solution at least partially with the precipitated phosphate separated in process step e). As a result, the precipitated phosphate contains potassium as an additional nutrient.

[0112] In another preferred embodiment, the precipitation of the dissolved phosphate is carried out by adding an iron- and / or aluminum-containing component such as Fe / Al chloride, Fe / Al sulfate.

[0113] It is preferred that the phosphate precipitation removes at least 80% of the previously dissolved phosphate. At this level, economically viable phosphate recovery can already be achieved in this process line A. Particularly preferred is the precipitation of more than 90% of the previously dissolved phosphate. This significantly improves the economic operation of the process.

[0114] In process step e) of the proposed method, the precipitated phosphate is at least partially separated from at least a portion of the liquid phase. The separated liquid phase is preferably at least partially recycled to process step a) for the production of a raw material dispersion. The separated precipitated phosphate is at least partially fed to process step g) for the production of the fertilizer according to the invention.

[0115] The at least partial separation of the precipitated phosphate within the meaning of the present invention can be carried out continuously and / or discontinuously in one or more steps, for example by filtration or centrifugation. For this purpose, the processes and technologies listed in process step c) for separating the liquid phase can generally be used.

[0116] Preferably, the resulting moisture content in the separated, precipitated phosphate is less than 60%. In a preferred embodiment, the moisture content after separation is less than 50%. The advantage of this embodiment is that a smaller amount of physically bound water (moisture) is fed into process step g), which is subsequently separated from the produced fertilizer granules, preferably thermally at great expense, to achieve a desired low residual moisture content in the fertilizer granules.

[0117] The liquid phase fed to process step d) contains not only the dissolved phosphate but also other dissolved accompanying components. These accompanying components are dissolved with or simultaneously with the reaction between the inorganic secondary phosphate and the reactant and are preferably not separated off, at least in part, before process step d). Preferably, these accompanying components are at least partially separated off with the precipitated phosphate in process e). For this purpose, the dissolved accompanying components can precipitate or be deliberately precipitated with the phosphate or separately. Or they are at least partially separated off with the physically bound water (moisture) adhering to the precipitated phosphate, in which they are dissolved.As a result, these accompanying components are at least partially transferred into the fertilizer in process line B with the precipitated phosphate and do not arise as waste, which is a clear advantage of this embodiment.

[0118] If the preferential, at least partial, recirculation of the separated liquid phase to process step a) occurs over several cycles under constant process control, an equilibrium cycle with an equilibrium concentration of dissolved components is established in this sub-cycle. The residual moisture adhering to the separated filter cake causes dissolved components to be removed according to the resulting equilibrium concentration.

[0119] In process step f) of the proposed process, a portion of the liquid phase is separated from the raw material dispersion produced in process step a) and fed to process line B and then fed to process step h). The remaining residue from the solid and / or undissolved portion of the raw material suspension, along with the remaining portion of the liquid phase that was not separated, is fed to process step g).

[0120] The amount of liquid phase to be separated in this process step is selected according to the requirements of the subsequent granulation or extrusion in process step g) and / or the requirements for an optional, at least partial, heavy metal removal in process step h). For example, the type of desired granulation determines the proportion of liquid phase to be separated.

[0121] In a particularly preferred embodiment, the moisture content resulting from the partial separation of the liquid phase is 10% to less than 40%. In other words, within the meaning of the invention, it is preferred that the moisture content be in a range between 10 and 40%. The advantage of such a moisture content is that a mixture with this moisture content (also referred to as an "earth-moist mixture") can be directly granulated or extruded, and relatively little liquid phase, for example, in particular water, needs to be evaporated to produce the particularly dry fertilizer granulate. This saves considerable energy costs. In a particularly preferred embodiment, the resulting moisture content is set at 10% to less than 30%. The advantage of this embodiment of the invention is that a mixture with this moisture content can typically be directly granulated using a granulating disc.

[0122] The partial separation of the liquid phase within the meaning of the present invention can be carried out continuously and / or discontinuously in one or more steps, for example by filtration or centrifugation. For this purpose, the processes and technologies listed in process step c) for the separation of the liquid phase can generally be used.

[0123] During the partial separation of the liquid phase, it is preferably not absolutely necessary that all solid components are completely separated from the separated liquid phase. In particular, very fine solid particles, which are preferably referred to as suspended particles within the meaning of the invention, can preferably remain in the separated phase. On the one hand, this simplifies the separation process, for example during filtration or centrifugation, since the complete separation of fine particles in a solid-liquid separation with a high solids load is particularly complex. On the other hand, these fine particles or suspended particles can be advantageously used in process step h) during the optional at least partial separation of the heavy metals, for example as nucleating or crystallization formers.However, if an excessive proportion of undissolved solids enters the separated liquid phase and thus into process step h), this can also be detrimental, for example, if these introduced solids are separated with the heavy metals in process step h). High proportions of solids then increase the remaining heavy metal-containing residue. It is therefore preferable to set a solids content of less than 10%, particularly preferably less than 5%, and most preferably less than 2% in the separated liquid phase.

[0124] In process step g), a mixture of at least a portion of the precipitated phosphate produced in process line A and separated in process step e) and at least a portion of the remaining raw material dispersion with reduced liquid phase from process step f) is produced, which is then fed to a granulation and / or extrusion process.

[0125] The mixing device used to produce the mixture can be, for example, a mixing vessel with agitator, a roller mixer (also known as a tumbling, 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 primarily on the flowability and cohesive strength of the material to be mixed.

[0126] According to the invention, it is preferred that further components be added to the mixture of the precipitated phosphate separated in process step e) and the raw material dispersion with reduced liquid phase from process step f) before, during, or after mixing. By specifically adjusting the type and composition of the resulting mixture, as well as the type and intensity of mixing, it is possible to advantageously influence the ongoing reaction and thus the neutral ammonium citrate solubility of the phosphate, as well as other fertilizer properties.

[0127] In a particularly preferred embodiment of the invention, additional phosphate carriers are added as a further component, for example ammonium phosphate, potassium phosphate, crystallization products from phosphorus elimination, such as struvite, brushite or hydroxylapatite-like Ca-P phase, in an amount such that a fertilizer granulate with a total PjOs content of greater than 35%, particularly preferably greater than 40% and a neutral ammonium citrate-soluble phosphate portion thereof of greater than 80%, particularly preferably greater than 90% results.In another preferred embodiment of the invention, crystallization products from phosphorus elimination, such as struvite, brushite or hydroxylapatite-like Ca-P phase, are added in a range of 1 to 70%, based on the finished fertilizer granulate according to the invention, in such a way that a nutrient or fertilizer granulate with a total PjOs content of greater than 15%, a neutral ammonium citrate-soluble phosphate content of greater than 60% thereof and a water solubility of less than 30%, also based on the total PjOs content, is thereby obtained.In a very special embodiment of the invention, crystallization products from the phosphorus elimination are added in the range of 10 to 40%, based on the finished fertilizer granules according to the invention, resulting in nutrient granules with a total P2O5 content of greater than 15%, with a neutral ammonium citrate-soluble phosphate content thereof, based on total P2O5, of greater than 85% and a water-soluble phosphate content, based on total PjOs, of less than 20%, each based on the composition of the nutrient granules.Therefore, embodiments of the phosphate-enriched, heavy metal-depleted fertilizer granules (10) according to the invention and / or of the method according to the invention are characterized in that at least one additional phosphate carrier, selected from the group comprising ammonium phosphate, potassium phosphate and crystallization products from phosphorus elimination, such as struvite, brushite or hydroxylapatite-like Ca-P phase, is added in a range of 1 to 70%, based on the finished fertilizer granules according to the invention, in such a way that a fertilizer granule with a total PjOs content of greater than 15%, a neutral ammonium citrate-soluble phosphate content of greater than 60% thereof and a water solubility of less than 30%, likewise based on the total PjOs content, is thereby obtained.

[0128] One or more structural materials can also be used as additional components, such as peat, humus, pyrolysis substrates from biomass, biochar from hydrothermal carbonization (HTC), but also sewage sludge, digestate, manure, animal excrement, animal and / or fish meal. The term "digestate" in the sense of the invention describes the liquid and / or solid residue remaining from the fermentation of biomass. The term "manure" in the sense of the invention preferably describes a mixture of feces and urine from farm animals in combination with bedding with a varying water content.

[0129] Therefore, embodiments of the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention and / or of the method according to the invention are characterized in that after process step f) and before and / or during granulation, at least one or more structural substance(s) selected from the group comprising peat, humus, pyrolysis substrates from biomass, biochar (e.g. from hydrothermal carbonization (HTC)), sewage sludge, digestate, liquid manure, animal excrement, animal and fish meal, are added as further components (13).

[0130] Depending on the type and concentration of this or these structural substances, the fertilizing effect can be adjusted and / or a soil-improving effect can be achieved when using the fertilizer granules. The fertilizing effect is preferably influenced by the fact that the structural properties of the produced fertilizer granules and thus their properties, such as porosity, pore size, strength, and / or solubility, can be adjusted by adding the structural substance. This has the advantageous effect that, for example, the nutrient release can be specifically adapted to plant growth and the time-dependent nutrient requirements of the plant. A further advantageous effect of this embodiment is targeted soil improvement through the addition of a structural substance to the fertilizer granules.For example, the structural substance can lead to humus formation, improve soil structure, and / or improve the air and / or water balance of the soil when fertilizers are applied in agriculture. This can, for example, promote root growth, activate soil life, and / or stimulate plant vitality against stress situations.

[0131] In some preferred embodiments of the process according to the invention or of the fertilizer granules according to the invention, the phosphate contained in the final product (fertilizer granules) originates solely from the recycling of the phosphates contained in the starting material (at least one inorganic secondary phosphate). According to the invention, it is preferred that no rock phosphates that were mined conventionally (e.g., from natural deposits) are incorporated into the fertilizer production process according to the invention or are contained in the fertilizer granules according to the invention. In other words, in some embodiments, the fertilizer granules according to the invention do not comprise any conventionally mined rock phosphates / phosphate components. In some embodiments, no conventionally mined rock phosphates / phosphate components are added to the process according to the invention.In embodiments, the phosphate obtained in the fertilizer granulate according to the invention originates exclusively or substantially from the phosphates contained in the at least one inorganic secondary phosphate (starting material) and / or is converted and / or obtained therefrom. In embodiments, the fertilizer granulate according to the invention thus represents a (pure) phosphate recyclate. In embodiments, the process according to the invention thus serves to produce a (pure) phosphate recyclate.

[0132] Thus, the process according to the invention preferably offers the possibility of producing pure phosphate-recycled fertilizers with a higher phosphate content than that of the at least one combustion residue used, without the addition of conventional (conventionally extracted / mined) phosphate-containing solvents or phosphate-containing nutrient components.

[0133] In a preferred embodiment of the invention, humic acid and / or fulvic acid and / or their salts (humates, fulvates) are added as a further component. This further component (13) is preferably added after process step f) and / or before and / or during granulation (see, for example, Figure 1). These (nutrient) substances advantageously have growth-promoting properties. This significantly increases the nutrient uptake capacity of the roots and thus stimulates growth. Their addition promotes plant growth and cell formation. They stimulate cell membranes and metabolic activities, thereby increasing germination rates. Important plant enzymes are also particularly well stimulated. The strong root development supports the nutrient uptake capacity. The plants strengthened in this way are significantly less susceptible to disease.The addition of these substances can increase plant P uptake, as it blocks soil P adsorption and, by complexing with Ca, Al, and Fe, prevents the precipitation of P into poorly soluble compounds. Surprisingly, it was found that the addition of these substances in a range of 0.1 - 25% (based on the finished fertilizer granules according to the invention) results in a significant increase in plant-available phosphate in the soil and thus in increased plant P uptake. The addition of these substances in a proportion between 0.1 and 10% (based on the finished fertilizer granules according to the invention) is particularly preferred, since even in this amount range, a significant increase in the fertilizing effect is achieved and, consequently, the required fertilizer quantity can be reduced by up to 40%.The addition of these substances in a quantity range of 0.1 - 5% (based on the finished fertilizer granulate according to the invention) is particularly advantageous, since in this range a particularly favorable economic ratio results between the costs of these substances and the resulting improved properties.

[0134] In a further preferred embodiment of the invention, organic acids are added as a further component in solid and / or liquid 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. Organic acids play a key role in the phosphate uptake of plants from the soil. In particular, the presence of organic acids in the root system enables plants to absorb sufficient phosphate, with microorganisms typically producing these organic acids in the ecosystem. Surprisingly, it has now been found that plant phosphate uptake is increased if one or more organic acids are already proportionally integrated into the added fertilizer granules, preferably in a total amount of 0.1 to 30% (based on the finished fertilizer granules according to the invention).It is assumed that, with the added organic acids, these preferably directly assume a comparable function in the root area of ​​the plant, without these organic acids first having to be produced by microorganisms. Citric acid, oxalic acid, and / 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, and tartaric acid individually or in combination in a quantity range of 0.1% to 10% (based on the finished fertilizer granulate according to the invention) is particularly preferred, as the absorption-enhancing effect of these acids is particularly favorable in relation to the raw material costs.The listed proportions of organic acids in the fertilizer granules can either be added as an additional component and / or, when organic acids are used as reactants, can be present after the reaction (at least proportionally in this quantity range) and thus transferred into the fertilizer granules.

[0135] pH-adjusting agents, such as alkalis, hydroxides, basic salts, ammonia, or burnt lime, can also be added as additional components. This can, for example, neutralize any remaining acid residues, for example, from the use or formation of acids, and / or specifically adjust the pH of the resulting fertilizer.

[0136] The materials used, such as inorganic secondary phosphate and other components, can be ground individually, in combination, or as a mixture in process step g). This is advantageous, for example, when the particle or aggregate size of individual or multiple feedstocks is not fine enough to achieve sufficient homogeneity, or if this could lead to process-related difficulties, such as blockages. This can be advantageously improved by reducing the particle or aggregate size. The solubility of substances or the compounds they contain can also be improved, for example, the solubility of phosphate-containing ashes or slags. Depending on the type of material to be ground and the desired grain size and grain size distribution, different dry or wet grinding technologies, with or without grinding aids, can be used.The aggregates used for dry or wet grinding can be, for example, ball mills, pin mills, jet mills, bead mills, stirred ball mills, high-performance dispersers and / or high-pressure homogenizers.

[0137] The granulation or extrusion can preferably take place during the production of the mixture and / or subsequently, for example in the same mixing device or in a separate granulation or extrusion unit, which is formed, for example, by pelletizing or granulating plates, granulating drum, or extruder.

[0138] According to the invention, it is preferred that the proportion of the liquid phase not separated in process step b) and thus remaining with the solid in this process step has a significant influence on the reactions taking place, the type of granulation, the product quality and / or the economic viability of the process. The total proportion of the liquid phase before granulation and / or extrusion can be adjusted, for example, via the process control in process step f) and the type and amount of the liquid, moist or dry components added in process step g). If necessary, partial drying can also be carried out before granulation, for example to adjust the total proportion of the liquid phase before granulation and / or extrusion.

[0139] In a preferred embodiment of the invention, the raw material dispersion in process step c) or the moist solid is or will be adjusted so that it contains a moisture content of less than 30%, preferably less than 25%, and particularly preferably less than 20%. The preferably earth-moist mixture can preferably be granulated and / or extruded directly. In addition, relatively cost-effective granulation and / or extrusion processes or technologies, such as roller mixers, shear mixers, plowshare mixers, planetary mixer-kneader mixers, intensive mixers, and / or extrusion processes, can be used. The adhesive tendency required for granulation can preferably also be adjusted by various substances, such as binders. These can, for example, be added additionally.The advantage of this preferred embodiment of the invention is that a good roundness of the granules is achieved in the preferred granule size range and the granulation technology and process costs are favorable to use.

[0140] According to the invention, it is preferred that fertilizer granules have a low moisture content, i.e. physically bound water. In particular, it is preferred that the moisture content is in a range of less than 5%, preferably less than 2%. According to the invention, it may be preferred that the granules produced are dried or at least additionally dried after granulation and / or extrusion. Different drying technologies are available for this purpose, for example contact dryers, in which the thermal energy required for drying is preferably supplied through contact with heating surfaces, convective dryers, in which the thermal energy required for drying is preferably supplied through contact with hot gas, or radiation dryers, in which the thermal energy required for drying is preferably supplied through radiation at a defined frequency.Drying separates the existing liquid phase, such as water, to the required extent. Drying also preferably increases the strength of the granules, for example, by forming binding phases or by a binder exerting its binding effect.

[0141] If crystallization products from phosphorus elimination, such as struvite, brushite, and / or hydroxylapatite-like Ca-P phase, are added to the raw material mixture and are consequently contained in the produced granules or green granules, it is preferred according to the invention that the drying takes place above 100°C, based on the material temperature during drying. These crystallization products preferably contain a large proportion of chemically bound water, which is preferably not "moisture" in the sense of the invention, but rather water that is bound in the crystal structure. In the range above 100°C, this chemically bound water is preferably split off. Separating the water from the granules advantageously increases the percentage of the remaining components.For example, the concentration of nutrients in the granules can be increased, which was previously diluted by the chemically bound water. In a particularly preferred embodiment of the invention, if crystallization products from phosphorus elimination are present, drying takes place in a range of 100-140°C, based on the material temperature during drying. Therefore, within the meaning of the invention, it is particularly preferred that drying takes place in a temperature range between 100 and 140°C. Above 140°C, there is a risk of increasing nitrogen release.

[0142] According to the invention, it is preferred that the fertilizer granules can be produced with as much precision as possible. A granule size that is as uniform as possible advantageously ensures defined, uniform disintegration properties, which is necessary for targeted nutrient supply. Since the presence of oversize and undersize particles can also impair the mechanical application of the fertilizer, according to the invention it is preferred that oversize and undersize particles can be separated from the good particles and, if necessary, returned to the production process, in particular the mixing and / or granulation process, if necessary with prior processing and / or grinding. The term "good particles" according to the invention preferably describes granules in a desired size range for the granules. The terms "oversize particles" and "undersize particles" according to the invention preferably describe granules that are - preferably significantly - larger orsmaller diameters than the grain size. The fertilizer granules produced according to the invention can be coated with one or more coatings for functionalization (e.g., reducing the tendency to clump, increasing strength), for protection (e.g., against moisture), and / or for controlled nutrient release (influencing solubility through the coating). Numerous coating processes and technologies are known to those skilled in the art, with all processes and technologies that produce a desired coating with the desired functionality being suitable.

[0143] The fertilizer granules produced according to the invention can be used for nutrient supply in agriculture, forestry, and / or horticulture, wherein the fertilizer granules comprise at least one inorganic secondary phosphate and a greater than 60% neutral ammonium citrate-soluble P2O3 content. The fertilizer granules produced according to the invention can preferably be used for nutrient supply in agriculture, forestry, and / or horticulture, wherein the fertilizer granules have a higher phosphate concentration compared to the added inorganic secondary phosphate(s) (1) or mixture thereof, and a greater than 60% neutral ammonium citrate-soluble P2O3 content (than the inorganic secondary phosphate(s) (starting material)). It is particularly preferred in this sense that the proposed fertilizer granules can be used in agriculture, forestry, and / or horticulture.

[0144] In process step h) of the proposed process, the liquid phase at least partially separated in process step f) is recycled to process step a) for the production of a raw material dispersion or g) for granulation, optionally with at least partial heavy metal removal. Whether and to what extent heavy metals need to be removed depends, for example, on the heavy metal contamination of the raw materials used, legal requirements, and the desired sustainability requirements of the produced products.

[0145] Before the possible heavy metal separation, either the raw material dispersion in process step a) or f) and / or the separated liquid phase can be conditioned. Such conditioning can include, in particular, measures that enable, improve, and / or promote the heavy metal separation in process step h), for example, a targeted adjustment of the pH value, the precipitation or separation of interfering accompanying and / or nutrient elements, or the setting of a defined concentration, viscosity, and / or temperature.

[0146] Various processes are available for the possible separation of heavy metal ions from the partially separated liquid phase, for example, using an ion exchanger, liquid-liquid separation, activated carbon, bacteria, fungi, algae, a biomass of bacteria, fungi, or algae, a precipitant, nanofilters, and / or electrolysis. Depending on the composition and conditioning of the liquid phase, the processes for heavy metal separation vary in suitability and are preferably selected accordingly. The process used is also selected based on which type of heavy metal is to be separated and in what concentration. This can be measured, for example, by determining which undesirable heavy metals are present in the inorganic secondary phosphate and how much of them is to be separated.The selected heavy metals do not have to be completely separated; if necessary, partial separation is sufficient to achieve the desired heavy metal concentration in the produced fertilizer granules, for example, below the limits of the applicable fertilizer regulations. In another preferred embodiment of the invention, the selective heavy metal separation is carried out by hydroxide precipitation by raising the pH. In another preferred embodiment of the invention, the selective heavy metal separation is carried out by sulfide precipitation by adding, for example, H2S, CH4N2S, Na2S. In principle, the liquid phase, partially or partially purified of heavy metals, can be disposed of in whole or in part or used for another purpose.According to the invention, it is preferred that the liquid phase separated in process step f) is at least partially fed to process step a) and / or process step g). In process step a), the liquid phase serves in particular to adjust the solid-liquid ratio and preferably replaces the above-mentioned water content in the raw material dispersion formulation in an equivalent amount. In process step g), the liquid phase can be used for granulation / extrusion or to adjust the moisture content of the mixture for granulation or extrusion.

[0147] The liquid phase separated in process step f) contains dissolved components, for example, from the reaction between inorganic secondary phosphate and the reactant. If this liquid phase with the dissolved components is at least partially recycled to process step a) during continuous process operation, an equilibrium cycle with an equilibrium concentration of dissolved components is established in this sub-cycle.

[0148] In a preferred embodiment of the invention, the liquid phase separated in process step f) and partially purified or not purified of heavy metals is at least partially recycled to process step a). At the same time, the required reactant(s) are at least partially added to the liquid phase before or during the recycling to process step a), and the liquid phase is thus transferred to process step a) together with at least the partial reactant. If the reactant(s) are acids, for example, the pH can advantageously be lowered by adding the reactant, thus reducing precipitation or crystallization of dissolved constituents from the liquid phase until recycling to process step a).

[0149] In a further aspect, the invention also relates to a device for producing the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention. In preferred embodiments, the device according to the invention comprises a first unit: either at least one first mixing container for supplying and / or mixing at least the inorganic secondary phosphate (1) and the reactant (2), whereby a raw material dispersion is obtained, wherein either the first mixing container is used for the incubation period and / or further containers are present into which the raw material dispersion is transferred and mixed for the incubation period, and subsequently a device for dividing the produced raw material dispersion between process lines A and B or a unit for dividing the at least one inorganic secondary phosphate (1) between process lines A and B,wherein at least one mixing container is connected thereto for supplying and / or mixing at least the respectively divided inorganic secondary phosphate (1) and the reactant (2) to produce a raw material dispersion, wherein either the mixing container is used for the incubation period and / or further containers are present in which the raw material dispersion is transferred and mixed for the incubation period, and further comprising in process line A at least one mixing container at least for supplying the divided raw material dispersion in process line A and the at least one heavy metal precipitant (4), at least one separation unit for separating at least part of the phosphate-containing, low-heavy-metal liquid phase (5) of the raw material dispersion and for discharging the remaining heavy-metal-containing filter cake (6) from the process, wherein the separation unit is integrated into the above mixing container or is separate therefrom,at least one reaction vessel in which the precipitation of phosphate (7) from the phosphate-containing liquid (5) phase takes place at least partially, at least one separation unit for separating at least a portion of the precipitated phosphate (7), in which are integrated and / or separately connected o at least one return unit for the separated liquid phase (8) to the mixing vessel for producing a raw material dispersion analogous to process step a) and / or to the granulation and / or extrusion unit analogous to process step g), and o at least one transfer unit for the separated precipitated phosphate (7) to the granulation and / or extrusion unit analogous to process step g), and in process line B at least one separation unit for separating at least a portion of the liquid phase (3),at least one granulation and / or extrusion unit for granulating and / or extruding at least a portion of the precipitated phosphate (7) produced in process line A and at least a portion of the remaining raw material dispersion with reduced liquid phase (9) from process step f), wherein further components (13) can be fed into this granulation and / or extrusion unit and / or the mixture can be mixed, wherein at least one feed unit from the separation unit is provided for transferring the raw material dispersion into the granulation and / or extrusion unit, at least one return unit for the separated liquid phase (11, 11') without heavy metal separation, or after the partial separation of the heavy metals (12), to the mixing container for the production of a raw material dispersion analogous to process step a), and / or to the granulation and / or extrusion unit.

[0150] In one embodiment, the device for producing the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention comprises a first unit

[0151] ■ either from at least one first mixing container for supplying and / or mixing at least the inorganic secondary phosphate (1) and the reactant (2), whereby a raw material dispersion (3) is obtained, wherein for the incubation period either the first mixing container is used and / or further containers are present into which the raw material dispersion is transferred and mixed for the incubation period, and subsequently a device for dividing the produced raw material dispersion (3) between process lines A and B,wherein in process line A there is followed at least one further mixing container with at least one feed and at least one mixing unit for the feed and mixing of at least the divided raw material dispersion (3) and at least one heavy metal precipitant (4). ■ or a unit comprising a device for dividing the at least one or more inorganic secondary phosphates (1) or the mixture of several inorganic secondary phosphates (1) between process lines A and B, o wherein in process lines A and B there is followed at least one mixing container for the feed and / or mixing of at least the respectively divided inorganic secondary phosphate (1) and the reactant (2), whereby a raw material dispersion (3, 3') is obtained, wherein for the incubation period either the mixing container is used and / or further containers are present in which the raw material dispersion (3,3') for the incubation period and mixed, o wherein in process line A, at least one of these mixing containers has at least one feed of the at least one heavy metal precipitant (4) for feeding and mixing the at least one heavy metal precipitant (4) with the raw material dispersion (3') and / or at least one further mixing container with at least one feed of the raw material dispersion (3') and at least one heavy metal precipitant (4) is connected thereto, and further comprising in process line A,

[0152] ■ at least one separation unit for separating at least part of the phosphate-containing, low-heavy-metal liquid phase (5) of the raw material dispersion (3, 3') and for discharging the remaining heavy-metal-containing filter cake (6) from the process, wherein the separation unit is integrated into the above mixing container or is separate therefrom,

[0153] ■ at least one reaction vessel in which the precipitation of phosphate (7) from the phosphate-containing liquid (5) phase takes place at least partially,

[0154] ■ at least one separation unit for separating at least a portion of the precipitated phosphate (7), wherein o at least one return unit for the separated liquid phase (8) to the mixing container for producing a raw material dispersion (3, 3') analogous to process step a) and / or to the granulating and / or extruding unit analogous to process step g), and o at least one transfer unit for the separated precipitated phosphate (7) to the granulating and / or extruding unit analogous to process step g) are integrated and / or separately connected thereto, and in process line B

[0155] ■ at least one separation unit for separating at least part of the liquid phase (3),

[0156] ■ at least one granulation and / or extrusion unit for granulating and / or extruding at least a portion of the precipitated phosphate (7) produced in process line A and at least a portion of the remaining raw material dispersion with reduced liquid phase (9) from process step f), wherein in this granulation and / or extrusion unit further components (13) can be fed in and / or the mixture can be mixed, wherein at least one feed unit from the separation unit for transferring the raw material dispersion (9) into the granulation and / or extrusion unit is present,

[0157] ■ at least one return unit for the separated liquid phase (11, 11') without heavy metal separation or after the partial separation of the heavy metals (12) to the mixing container for producing a raw material dispersion (3, 3') analogous to process step a) and / or to the granulation and / or extrusion unit.

[0158] A preferred embodiment of the device for producing the phosphate-enriched, heavy metal-depleted fertilizer granulate (10) according to the invention comprises a first unit

[0159] ■ either from at least one first mixing container for supplying and / or mixing at least the inorganic secondary phosphate (1) and the reactant (2), whereby a raw material dispersion (3) is obtained, wherein either the first mixing container is used for the incubation period and / or further containers are present into which the raw material dispersion is transferred and mixed for the incubation period, and subsequently a device for dividing the raw material dispersion (3) produced between process lines A and B, wherein in process line A there is followed by at least one further mixing container with at least one feed and at least one mixing unit for supplying and mixing at least the divided raw material dispersion (3) and at least one heavy metal precipitant (4).

[0160] ■ or a unit comprising a device for dividing the at least one or more inorganic secondary phosphates (1) or the mixture of several inorganic secondary phosphates (1) between process lines A and B, o wherein in each process line A and B there is at least one mixing container for supplying and / or mixing at least the respectively divided inorganic secondary phosphate (1) and the reactant (2), whereby a raw material dispersion (3, 3') is obtained, wherein for the incubation period either the mixing container is used and / or further containers are present in which the raw material dispersion (3, 3') is transferred and mixed for the incubation period,o wherein in process line A, at least one of these mixing vessels has at least one feed of the at least one heavy metal precipitant (4) for feeding and mixing the at least one heavy metal precipitant (4) with the raw material dispersion (3') and / or at least one further mixing vessel with at least one feed of the raw material dispersion (3') and at least one heavy metal precipitant (4) is connected thereto, and further comprising in process line A,

[0161] ■ at least one separation unit for separating at least part of the phosphate-containing, heavy metal-poor liquid phase (5) of the raw material dispersion (3, 3') and for discharging the remaining heavy metal-containing filter cake (6) from the process, wherein the separation unit is integrated into the above mixing vessel or separate therefrom, at least one reaction vessel in which the precipitation of phosphate (7) from the phosphate-containing liquid (5) phase takes place at least partially,

[0162] ■ at least one separation unit for separating at least a portion of the precipitated phosphate (7), wherein o at least one return unit for the separated liquid phase (8) to the mixing container for producing a raw material dispersion (3, 3') analogous to process step a) and / or to the granulating and / or extruding unit analogous to process step g), and o at least one transfer unit for the separated precipitated phosphate (7) to the granulating and / or extruding unit analogous to process step g) are integrated and / or separately connected thereto, and in process line B

[0163] ■ at least one separation unit for separating at least part of the liquid phase (3),

[0164] ■ at least one granulation and / or extrusion unit for granulating and / or extruding at least a portion of the precipitated phosphate (7) produced in process line A and at least a portion of the remaining raw material dispersion with reduced liquid phase (9) from process step f), wherein in this granulation and / or extrusion unit further components (13) can be fed in and / or the mixture can be mixed, wherein at least one feed unit from the separation unit for transferring the raw material dispersion (9) into the granulation and / or extrusion unit is present,

[0165] ■ at least one return unit for the separated liquid phase (11, 11') without heavy metal separation or after the partial separation of the heavy metals (12) to the mixing container for producing a raw material dispersion (3, 3') analogous to process step a) and / or to the granulation and / or extrusion unit.

[0166] In a further aspect, the invention also relates to the use of the phosphate-enriched, heavy metal-depleted fertilizer granules (10) according to the invention for nutrient supply in agriculture, forestry, and / or horticulture. In preferred embodiments, this use according to the invention is characterized in that the phosphate-enriched, heavy metal-depleted fertilizer granules (10) comprise at least one inorganic secondary phosphate (1) and a P2O5 content that is greater than 60% neutral ammonium citrate-soluble. In a further preferred embodiment, the use according to the invention is characterized in that the phosphate-enriched, heavy metal-depleted fertilizer granules (10) have a higher phosphate concentration than the added inorganic secondary phosphate(s) (1) or mixture thereof and a P2O5 content that is greater than 60% neutral ammonium citrate-soluble.

[0167] In one embodiment of the use according to the invention of the phosphate-enriched, heavy metal-depleted fertilizer granules (11), this comprises the use for nutrient supply in agriculture, forestry and / or horticulture, characterized in that the phosphate-enriched, heavy metal-depleted fertilizer granules (10) have a higher phosphate concentration than in comparison to the or the mixture of the added inorganic secondary phosphate(s) (1), and a greater than 60% neutral ammonium citrate-soluble P2O5 content.

[0168] Examples

[0169] The invention is described in more detail with reference to the following exemplary embodiments. Further advantages, features, and details of the invention can be gathered from the further subclaims and the description. The features mentioned therein may be essential to the invention individually or in any combination. Thus, reference can always be made to the disclosure relating to the individual aspects of the invention.

[0170] Example 1:

[0171] In a mixing tank, 200 kg of water and 50 kg of sulfuric acid (95%) are placed and mixed as reactants. 100 kg of sewage sludge ash (P2O5 content 19.0%, of which 38% is neutral ammonium citrate soluble and <1% is water soluble) is added as inorganic secondary phosphate, and the resulting raw material dispersion is mixed. The inorganic secondary phosphate contains 75 mg / kg Pb, 65 mg / kg Ni, 14 mg / kg As, and 2 mg / kg Cd. An incubation time of 30 minutes is observed to allow the inorganic secondary phosphate to react sufficiently with the reactant. After the incubation period, 280 kg of the resulting raw material dispersion is fed to process step b) in process line A, and 70 kg of the resulting raw material dispersion is fed to process step f) in process line B.

[0172] The raw material dispersion fed to process step b) contains 3% of the Pb added with the inorganic secondary phosphate in process line B, 8% of the Ni, 91% of the As, 75% of the Cd, and 98% of the P in dissolved form. In process step b), 1 kg of sodium sulfide is added to the feed raw material dispersion, followed by an incubation period, which represents the reaction time between the heavy metal precipitant sodium sulfide and the raw material dispersion. After the incubation period, 2% of the Pb added with the inorganic secondary phosphate, 8% of the Ni, 5% of the As, 7% of the Cd, and 95% of the P are still dissolved.

[0173] This conditioned raw material dispersion is then fed into a solid-liquid separation process using a membrane filter press. A large portion of the liquid phase is separated from the solids using a membrane filter press, resulting in 105 kg of heavy-metal-containing filter cake as a solid mixture with a moisture content of 40%. This heavy-metal-containing filter cake is removed from the process. The solid-liquid separation also produces a phosphate-containing, heavy-metal-poor liquid phase, which is fed into process step d).

[0174] By adding CaO, the pH of the separated phosphate-containing, heavy metal-poor liquid phase is adjusted to 3. Due to the increase in pH, a large portion of the phosphate precipitates, leaving only 5% of the P added with the inorganic secondary phosphate to process line B in dissolved form. Subsequently, a solid-liquid separation takes place using a membrane filter press, separating the precipitated phosphate and feeding it to process step g) in process line B. The precipitated phosphate contains 35% P2O5 as phosphate and 25% separated accompanying substances from the sewage sludge ash (such as Al, Mg, Fe, K oxide (hydrates / hydroxides). These accompanying substances are processed with the precipitated phosphate in process line B to form fertilizer granules. The separated (low-phosphate) liquid phase is completely fed into the next batch for the production of a raw material dispersion (process step a)).

[0175] In process step f), the 70 kg of feedstock dispersion undergoes solid-liquid separation using a membrane filter press, forming a soil-moist filter cake with 28% residual moisture. The separated liquid phase is fed to process step a) without heavy metal depletion for the production of the next batch of raw material dispersion.

[0176] In process step g), the separated earth-moist filter cake is homogeneously mixed with the precipitated phosphate formed in process line A and then granulated. The resulting green granules are then dried at 110 °C and fractionated into granules with diameters ranging between 2 and 5 mm. The fraction of granules with a diameter of less than 2 mm and the fraction of granules with a diameter greater than 5 mm are returned to the granulation after prior grinding.

[0177] The 61 kg of granules produced in this way, with a residual moisture content of 5%, advantageously exhibit a round and compact granule shape in the 2-5 mm range after the equilibrium cycles described above have been established, with a total P2O5 content of 25%, of which 93% is ammonium citrate-soluble and 15% is water-soluble. The resulting fertilizer granules contain 32 mg / kg Pb, 16 mg / kg Ni, 3 mg / kg As, and 0.4 mg / kg Cd. Thus, the process in process line A removes not only more than 75% of As and Cd, examples of heavy metals well dissolved by the reactant, but also more than 75% of Pb and Ni, examples of heavy metals very poorly dissolved by the reactant.

[0178] Example 2:

[0179] A raw material dispersion is produced analogously to Example 1. By specifically controlling the partial material flows of the raw material dispersion supplied to process lines A and B, respectively, the resulting phosphate enrichment and heavy metal depletion in the fertilizer granules can be adjusted. In Example 2, after the incubation period, 140 kg of the raw material dispersion thus produced are fed to process step b) in process line A, and 210 kg of the raw material dispersion thus produced are fed to process step f) in process line B.

[0180] Process steps b) to h) are carried out analogously to embodiment 1, only with the changed proportions analogous to the changed distribution of the raw material dispersion.

[0181] Process step g) results in 105 kg of fertilizer granules with a residual moisture content of 5% and a total P2O5 content of 17%, of which 94% is ammonium citrate-soluble and 17% is water-soluble. The resulting fertilizer granules contain 82 mg / kg Pb, 42 mg / kg Ni, 8 mg / kg As, and 1.1 mg / kg Cd. Thus, the process removes not only more than 35% of As and Cd, examples of heavy metals well dissolved by the reactant, but also more than 35% of Pb and Ni, examples of heavy metals very poorly dissolved by the reactant.

[0182] The heavy metal depletion in this embodiment is thus lower than in embodiment 1. However, significantly less heavy metal-containing filter cake is produced in this embodiment, amounting to only 52.5 kg (essentially waste). A significantly larger proportion of the non-phosphate components from the inorganic secondary phosphate is transferred into the fertilizer, resulting in a larger amount of fertilizer with a lower phosphate concentration.

[0183] The invention is described in more detail with reference to the following figures. Figures 1 to 3 each show a schematic representation of preferred embodiments of the proposed process in embodiments. Figure 1 describes a preferred embodiment of the proposed two-strand process.

[0184] (comprising strand A and strand B). The preferred embodiment shown uses

[0185] Essentially completely exploit the process engineering advantages of the proposed two-strand

[0186] Process which partially converts an inorganic secondary phosphate containing heavy metals into a phosphate-enriched, heavy metal-depleted fertilizer granulate, whereby the phosphate from the secondary phosphate, which is very poorly available to plants, is converted into a phosphate with very good plant availability.

[0187] In process step a), a raw material dispersion (3, 3') is produced and provided for the two process lines A (left; steps b) to g)) and B (right; steps f) to g) / h)). For this purpose,

[0188] ■ either a common raw material dispersion (3) is first produced in a suitable vessel and this raw material dispersion (3) is then divided and fed to process line A and process line B (Figure 2 describes this variant)

[0189] ■ or the inorganic secondary phosphate (1) is first divided and two separate raw material dispersions (3, 3') are thus produced, with one raw material dispersion (3') then being fed to process line A and the other raw material dispersion (3) to process line B (see Figure 3 describes this embodiment variant).

[0190] The raw material dispersion (3, 3') is produced from at least one inorganic secondary phosphate (1) and at least one reactant (2). An incubation period is allowed to elapse to ensure sufficient reaction between the at least one reactant (2) and the at least one inorganic secondary phosphate (1), during which time the raw material dispersion (3, 3') can be further mixed. The reactant (2) is designed to react with at least portions of the phosphate introduced by the inorganic secondary phosphate (1), thereby increasing the solubility and plant availability of this phosphate.

[0191] The preferred embodiment presented essentially fully utilizes the process-related advantages of producing the raw material dispersion according to the invention with a high proportion of liquid phase. Unlike prior art processes, a raw material dispersion with a high liquid phase proportion is first produced, with the high liquid phase proportion advantageously acting as a buffer for the ongoing reaction. As a result, the reactions that often occur spontaneously and are sometimes highly exothermic when the phosphate-containing secondary raw material is mixed with the mineral acid can be monitored and controlled, and the mixture does not exhibit any disturbing stickiness. Further processing to the granulate only takes place after the reaction between inorganic secondary phosphate (1) and the reactant (2) has largely taken place. The phosphate conversion reaction is thus advantageously separated from the granulation process.

[0192] The raw material dispersion (3, 3') fed to process step b) (process line A) should be conditioned such that the phosphate from the at least one inorganic secondary phosphate (1) is largely in dissolved form, preferably with a proportion greater than 80%. In process step b), a heavy metal precipitant is added to this thus conditioned raw material dispersion (3, 3'). The heavy metal precipitant is intended to at least partially precipitate the heavy metals contained in dissolved form in the raw material dispersion (3, 3'). Dissolved heavy metals result in the raw material dispersion, for example, because the reaction between the at least one reactant (2) and the at least one inorganic secondary phosphate (1) also at least partially dissolves the heavy metals contained in the inorganic secondary phosphate.In process step c), a portion of the liquid phase is separated from the raw material dispersion (3, 3') conditioned in process step b) as a phosphate-containing, heavy metal-poor liquid phase (5) and fed to process step d). The process is preferably controlled such that the separated phosphate-containing, heavy metal-poor liquid phase (5) contains at least 70% of the phosphate added to the raw material dispersion (3, 3') with the inorganic secondary phosphate (1). The remaining heavy metal-containing filter cake (6) from the solid or undissolved portion of the raw material suspension (3, 3') with the remaining portion of the liquid phase (residual moisture) is discharged from the process. Due to the heavy metal precipitation in process step b), these precipitated heavy metals are present in the separated heavy metal-containing filter cake (6).

[0193] In process step d), a precipitation additive (14) is added to the phosphate-containing, heavy metal-poor liquid phase (5). This precipitation additive converts at least a portion of the dissolved phosphate into a solid form. This precipitated phosphate is largely separated from the liquid phase in process step e), meaning that the precipitated phosphate (7) thus separated still contains a portion of residual moisture after the separation step. Preferably, the process is controlled such that the separated precipitated phosphate (7) contains at least 70% of the phosphate added to the raw material dispersion (3, 3') with the inorganic secondary phosphate (1).

[0194] The separated liquid phase (8) is preferably returned to process step a) for producing the raw material dispersion. Alternatively, this separated liquid phase (8) can also be at least partially discharged from the process and / or fed to the granulation in process step i).

[0195] In process step f) (process line B), a portion of the liquid phase is separated as a separated liquid phase (11) from the raw material dispersion (3) produced in process step a) and fed to process step h). The remaining raw material dispersion with reduced liquid phase (9) is fed to process step g). The proposed reaction sequence between inorganic secondary phosphate (1) and reactant (2) in a raw material dispersion with a high liquid phase content has, in particular, the process-related advantages described. If the raw material dispersion is to be granulated directly, a very high water content must be separated off, for example by drying, which is, however, cost-intensive. Accordingly, in the proposed process, a portion of the liquid phase is circulated and mechanically separated prior to granulation and fed back into the production of the raw material dispersion.

[0196] In process step g), the remaining raw material dispersion with reduced liquid phase (9) from process step f) is combined with at least a portion of the precipitated phosphate (7) separated in process step e), and this mixture is granulated and / or extruded. Depending on the set liquid-solid ratio, various granulation or extrusion processes can be used. Before and / or during granulation, additional components (13), such as nutrient-containing components, dispersants and defoamers, structural agents, pH-adjusting agents, urease inhibitors, ammonium stabilizers, and / or water, can be added, in particular to establish a desired nutrient and / or active ingredient composition. At least a portion of the separated liquid phase (11, 11') can also be used, for example, to adjust the solid-liquid ratio.

[0197] This process step g) results in a soil- and plant-specific, heavy metal-depleted fertilizer granulate (10) with an adjusted and constant nutrient composition, wherein inorganic secondary phosphate (1), such as sewage sludge ash, can be used at least as a nutrient source, wherein the phosphate contained therein is made readily available to plants by the action of the reactant (2) and the heavy metals contained in the inorganic secondary phosphate (2) are at least partially separated.

[0198] In process step h), at least partial separation of heavy metals (12) from the liquid phase (11) separated in process step f) can take place, as well as discharge of these heavy metals (12) from the process. Different processes can be used to separate the heavy metals, depending on the type and concentration of the heavy metals to be separated or the conditioning of the separated liquid phase from process step f). Depending on the type of separation process, additives for heavy metal separation, such as precipitants and flocculants, pH adjusters, sacrificial metals, and / or extraction agents, are used. The thus separated liquid phase 11') with reduced heavy metal content, or the separated liquid phase (11) without heavy metal separation, is recycled in process step h) to produce a raw material dispersion analogous to process step a) and / or fed for granulation in process step g).Alternatively, at least part of the separated liquid phase (11) can be discharged.

[0199] The process steps a) to h) can be repeated as often as desired.

[0200] Figure 2 shows a preferred embodiment of the proposed two-strand process (comprising strand A and strand B). In process step a), a common raw material dispersion (3) is produced in a suitable vessel, and this raw material dispersion (3) thus produced is then fed in a divided manner to process strand A (left; steps b) to g)) and process strand B (right; steps f) to g) / h)). The advantage of this embodiment is, for example, that the production of only one raw material dispersion is easier to handle, less complex to control the process, and only one suitable reaction vessel is required to produce the raw material dispersion (3).

[0201] The process steps b) to h) are essentially comparable to the embodiment of the invention shown in Figure 1.

[0202] Figure 3 shows another preferred embodiment of the proposed two-strand process (comprising strand A and strand B). In process step a), the inorganic secondary phosphate (1) is first divided, thereby producing two separate raw material dispersions (3, 3'), with one raw material dispersion (3') being fed to process strand A (left; steps a') to g)) and the other raw material dispersion (3) being fed to process strand B (right; steps a) to g) / h)). The advantage of this is that the raw material dispersions 3 and 3' thus produced can be differently conditioned, adapted to the respective process strand. For example, different reactants (2, 2'), different proportions of liquid phase can be used, or different reaction parameters such as pH or incubation time can be selected in order to specifically adjust the dissolution and conversion reaction between inorganic secondary phosphate (1) and reactant (2).

[0203] Process steps b) to h) are essentially comparable to the embodiment of the invention shown in Figure 1. List of reference symbols

Claims

Patent claims 1. Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) produced from at least one inorganic secondary phosphate (1) by a two-strand process, wherein a raw material dispersion (3, 3') is supplied to process strand A and process strand B, in which this raw material dispersion ■ either in process step a) is produced from at least one inorganic secondary phosphate (1) and at least one reactant (2) and this produced raw material dispersion (3) is fed to process strand A and B in a split manner ■ or in process step a), a') the inorganic secondary phosphate (1) is first divided, two raw material dispersions (3, 3') each comprising a subset of at least one inorganic secondary phosphate (1) and at least one reactant (2, 2') are produced separately from each other, and these separately produced raw material dispersions (3, 3') are fed to process strand A and B, wherein the proportion of a liquid phase in the raw material dispersion (3, 3') is greater than 30% and the incubation time between inorganic secondary phosphate (1) and reactant (2, 2') is between 1 and 100 minutes, wherein process strand A comprises the following process steps: b) addition of at least one heavy metal precipitating agent (4) during and / or after the incubation time; c) separation of a portion of the phosphate-containing, low-heavy-metal liquid phase (5) of the raw material dispersion and removal of the remaining heavy-metal-containing filter cake (6) from the Process,d) Precipitation of phosphate (7) from the phosphate-containing liquid (5) phase, e) Separation of the precipitated phosphate (7) and at least partial recycling of the separated liquid phase (8) into process step a) for the production of a raw material dispersion, wherein process line B comprises the following process steps, f) Separation of a portion of the liquid phase of the raw material dispersion (3), g) Production of a mixture of at least a portion of the precipitated phosphate (7) produced in process line A and at least a portion of the remaining raw material dispersion with reduced liquid phase (9) from process step f), as well as granulation and / or extrusion of this mixture, wherein drying or coating of the granules and / or extrudates may take place, and removal of the phosphate-enriched, heavy-metal-depleted fertilizer granules (10) produced from the process.h) At least partial recycling of the liquid phase 11, 11') separated in process step f) to produce a raw material dispersion analogous to process step a) and / or feeding into process step g), whereby at least partial separation of heavy metals (12) from the liquid phase separated in process step f) and removal of these heavy metals (12) from the process may take place beforehand, and repetition of process steps a) to h)., Process for producing a phosphate-enriched, heavy-metal-depleted fertilizer granulate (11) from at least one inorganic secondary phosphate (1) by a two-strand process, wherein a raw material dispersion (3, 3') is supplied to process strand A and process strand B, in which this raw material dispersion ■ either is produced in process step a) from at least one inorganic secondary phosphate (1) and at least one reactant (2) and this produced raw material dispersion (3) is fed to process strand A and B in a split manner ■ or in process step a), a') the inorganic secondary phosphate (1) is first divided, two raw material dispersions (3, 3') each comprising a subset of at least one inorganic secondary phosphate (1) and at least one reactant (2, 2') are produced separately from each other, and these separately produced raw material dispersions (3, 3') are fed to process strand A and B, wherein the proportion of a liquid phase in the raw material dispersion (3, 3') is greater than 30% and the incubation time between inorganic secondary phosphate (1) and reactant (2, 2') is between 1 and 100 minutes, wherein process strand A comprises the following process steps: b) addition of at least one heavy metal precipitating agent (4) during and / or after the incubation time; c) separation of a portion of the phosphate-containing, low-heavy-metal liquid phase (5) of the raw material dispersion and removal of the remaining heavy-metal-containing filter cake (6) from the Process,d) Precipitation of phosphate (7) from the phosphate-containing liquid (5) phase, e) Separation of the precipitated phosphate (7) and at least partial recycling of the separated liquid phase (8) into process step a) for the production of a raw material dispersion, wherein process line B comprises the following process steps: f) Separation of a portion of the liquid phase of the raw material dispersion (3), g) Production of a mixture of at least a portion of the precipitated phosphate (7) produced in process line A and at least a portion of the remaining raw material dispersion with reduced liquid phase (9) from process step f), as well as granulation and / or extrusion of this mixture, wherein drying or coating of the granules and / or extrudates may take place, and removal of the phosphate-enriched, heavy-metal-depleted fertilizer granules (10) produced from the process.h) At least partial recycling of the liquid phase 11, 11') separated in process step f) to produce a raw material dispersion analogous to process step a) and / or feeding into process step g), whereby at least partial separation of heavy metals (12) from the liquid phase separated in process step f) and removal of these heavy metals (12) from the process may take place beforehand, and repetition of process steps a) to h)., Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to claim 1 or a process according to claim 2, characterized in that the addition of the at least one heavy-metal precipitating agent and the heavy-metal precipitation are carried out at a pH value less than 2, and the separation of a portion of the phosphate-containing, heavy-metal-poor liquid phase (5) of the raw material dispersion and the removal of the remaining heavy-metal-containing filter cake (6) from the process are also carried out at a pH value less than 2. Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to claim 1 or 3 or a process according to claim 2 or 3, characterized in that at least one added heavy-metal precipitating agent is a sulfide.Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to claim 1, 3 or 4 or a process according to claim 2, 3 or 4, characterized in that at least one heavy metal precipitating agent is added during the incubation period. Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to claim 1, 3, 4 or 5 or a process according to claim 2, 3, 4 or 5, characterized in that more than 80% of the total dissolved heavy metals are precipitated from the raw material dispersion by the added at least one heavy metal precipitating agent (4), wherein, after heavy metal precipitation, at least 80% of the previously dissolved P₂O₅ remains dissolved in the raw material dispersion.Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to claim 1, 3, 4, 5 or 6 or method according to claim 2, 3, 4, 5 or 6, characterized in that the phosphate-enriched, heavy-metal-depleted fertilizer granules (10) have a phosphate concentration at least 30% higher than the added inorganic secondary phosphate(s). Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to claim 1, 3, 4, 5, 6 or 7 or method according to claim 2, 3, 4, 5, 6 or 7, characterized in that the phosphate-enriched, heavy-metal-depleted fertilizer granules (10) have a total heavy metal concentration at least 20% lower than the added inorganic secondary phosphate(s).Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to one of claims 1, 3-8 or a method according to one of claims 2-8, characterized in that at least one additional phosphate carrier, selected from the group comprising ammonium phosphate, potassium phosphate and crystallization products from phosphorus elimination, selected from the group comprising struvite, brushite and hydroxylapatite-like Ca-P phase, is added in a range of 1 to 70%, based on the finished fertilizer granules according to the invention, such that a fertilizer granule with a total P2O5 content of greater than 15%, a neutral ammonium citrate-soluble phosphate content of greater than 60% thereof and a water solubility of less than 30%, based on the total P2O5 content, is obtained.Phosphate-enriched, heavy metal-depleted fertilizer granules (11) according to one of claims 1, 3-9 or process according to one of claims 2-9, characterized in that after process step f) and before and / or during granulation at least one or more structural material(s), selected from the group comprising peat, humus, pyrolysis substrates from biomass, biochar, sewage sludge, digestate, manure, animal excrement, animal and fish meal, are added as further components (13). Phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to any one of claims 1, 3-10 or a process according to any one of claims 2-10, characterized in that humic acid and / or fulvic acid and / or their salts (humates, fulvates) are added as a further component (13) after process step f) and before and / or during granulation. Apparatus for producing the phosphate-enriched, heavy-metal-depleted fertilizer granules (11) according to any one of the preceding claims 1 or 3 to 11, comprising a first unit ■ either from at least one first mixing vessel for adding and / or mixing at least the inorganic secondary phosphate (1) and the reactant (2), thereby obtaining a raw material dispersion, wherein for the incubation period either the first mixing vessel is used and / or further vessels are available into which the raw material dispersion is transferred and mixed for the incubation period, and subsequently a device for dividing the generated raw material dispersion onto process strand A and B, ■ or a unit comprising a device for dividing the at least one inorganic secondary phosphate (1) into process strand A and B, wherein at least one mixing vessel for adding and / or mixing at least the respective divided inorganic secondary phosphate (1) and the reactant (2), thereby obtaining a raw material dispersion, wherein for the incubation period either the mixing vessel is used and / or further vessels are available in which the raw material dispersion is transferred and mixed for the incubation period, and further comprising in process strand A ■ at least one mixing vessel for at least the supply of the divided raw material dispersion in process line A and at least one heavy metal precipitating agent (4), ■ at least one separation unit for separating at least a part of the phosphate-containing, low-heavy-metal liquid phase (5) of the raw material dispersion and for removing the remaining heavy-metal-containing filter cake (6) from the process, wherein the separation unit is integrated into or separate from the aforementioned mixing vessel, ■ at least one reaction vessel in which the precipitation of phosphate (7) from the phosphate-containing liquid (5) phase takes place at least partially, ■ at least one separation unit for separating at least a portion of the precipitated phosphate (7), wherein o at least one return unit for the separated liquid phase (8) to the mixing vessel for the production of a raw material dispersion analogous to process step a) and / or to the granulating and / or extrusion unit analogous to process step g), and o at least one transfer unit for the separated precipitated Phosphate (7) to the granulation and / or extrusion unit analogous to process step g) are integrated and / or connect separately, and in process chain B ■ at least one separation unit for separating at least part of the liquid phase (3), ■ at least one granulation and / or extrusion unit for granulating and / or extruding at least a portion of the precipitated phosphate (7) produced in process strand A and at least a portion of the remaining raw material dispersion with reduced liquid phase (9) from process step f), wherein further components (13) can be added to this granulation and / or extrusion unit and / or the mixture is miscible, wherein at least one feed unit from the separation unit is provided for transferring the raw material dispersion into the granulation and / or extrusion unit, ■ at least one return unit for the separated liquid phase (11, 11') without heavy metal separation or after partial separation of the heavy metals (12) to the mixing vessel for the production of a raw material dispersion analogous to process step a) and / or to the granulating and / or extrusion unit. Use of the phosphate-enriched, heavy metal-depleted fertilizer granules (11) according to one or more of claims 1 to 11 for nutrient supply in agriculture, forestry and / or horticulture, characterized in that the phosphate-enriched, heavy metal-depleted fertilizer granules (11) comprise at least one inorganic secondary phosphate (1) and a PjOs content greater than 60% soluble in neutral ammonium citrate.

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