Procedure for the treatment of phosphate-containing ash from waste incineration plants by wet chemical decomposition to obtain aluminum, calcium, phosphorus and nitrogen compounds

Abstract

A process for obtaining precipitates, selected from the group of calcium nitrate, calcium phosphate, calcium sulfate and aluminum hydroxophosphate, from phosphate-containing ash from waste incineration plants and for the optional production of phosphoric acid, the process comprising at least the obtaining of calcium sulfate, characterized in that a) the solid substances / ashes are reacted with nitric acid or phosphoric acid or a mixture of mineral acids of the two acids, b) the acid-insoluble part of the solid substances is separated, c) By adding sulfuric acid to the filtrate or supernatant, a pH value of < 1 is adjusted, and calcium sulfate precipitate is obtained and separated, and d) the filtrate or supernatant is returned at least partially for use in step a), e) Optionally, the filtrate or supernatant is concentrated, preferably by evaporation, to obtain phosphoric acid or nitrous phosphoric acid, f) Optionally, calcium phosphate precipitate and calcium nitrate precipitate are obtained and separated by adding calcium oxide or calcium carbonate to the filtrate or supernatant.

Description

Procedure for the treatment of phosphate-containing ash from waste incineration plants by wet chemical decomposition to obtain aluminum, calcium, phosphorus and nitrogen compounds The invention relates to a process for treating phosphate-containing waste, in particular phosphate-containing ash from waste incineration plants, by wet chemical decomposition to obtain aluminum, calcium, phosphorus and nitrogen compounds, comprising at least the obtaining (generation) of calcium sulfate (Ca(SO4)) and in particular for the optional production of phosphoric acid (H3PO4). Natural phosphates are required for fertilizer production. To replace limited natural phosphates, it is generally known that industrialized European countries are pursuing the recovery of phosphorus or phosphates from waste and wastewater (see patent document DE 102012015065 B3). This is also indicated by the fact that natural phosphates are increasingly contaminated with heavy metals such as cadmium and uranium, and this contamination is found in fertilizers and groundwater. A key phosphate resource in Europe is wastewater from municipal and industrial wastewater treatment plants. Approximately 50,000 Mg (t) of phosphorus enters wastewater annually in Germany alone and is mostly precipitated with the help of precipitating agents such as iron or aluminum salts and separated with the sludge. Currently, phosphate-containing sludge is generally incinerated, and the resulting ash is either disposed of or otherwise misappropriated (e.g., road construction, landscaping), as the phosphorus it contains is not recovered, except in a few cases at test facilities. EP 2 602 013 discloses a procedure for the recovery of phosphorus compounds from wastewater sludge ash. Similar to other industrial recycling processes, such as iron recovery from scrap metal, paper recovery from waste paper, and copper and other metal recovery from electrical equipment, industrial phosphorus recovery from waste is also possible. An essential requirement for this is that the phosphorus-containing waste has a sufficiently high phosphorus concentration and low contamination, and that it essentially corresponds to the natural phosphates currently in use, ideally without harmful uranium and cadmium contamination. Phosphates are obtained from natural phosphate rock (with a phosphorus content of approximately 30% P₂O₅) through acid digestion, preferably with sulfuric acid, resulting in phosphoric acid and / or calcium phosphate fertilizer (the so-called "superphosphate"). The ash from incinerated sewage sludge or animal waste, such as animal meal, contains up to 35% P₂O₅ by weight; however, depending on the precipitating agent, it can also contain up to 25% iron, aluminum, or calcium oxide by weight. This high metal oxide content, which can be up to ten times higher than in natural phosphate, considerably limits the use of sewage sludge ash as an alternative natural phosphate source in industrial processes.A solution to this problem is described in patent document DE 102012015065 B3, which involves binding phosphates during wastewater treatment with aluminum salts and then transforming them into calcium phosphate. This ensures that, during subsequent incineration of the residual sludge, the resulting ash contains primarily calcium phosphate and, as far as possible, minimal aluminum and iron compounds. The calcium phosphate-rich ash is suitable for use as a natural phosphate source for fertilizer production, although this is always necessary in conjunction with any accompanying contaminants in the ash. Ash, which results from the incineration of sewage sludge, organic waste, biodegradable waste, animal waste, etc., such as animal meal, contains various materials. The following table shows the main components (calculated as oxides) and material content of some ash samples produced during the incineration of sewage sludge: Ash A Ash B Ash C % of Fe2O3 21.9 3.1 11.9 % of AhO3 9.3 21.5 12.4 % CaO 15.2 14.5 11.4 % of P2O5 21.0 23.0 20.5 % of SiO2 18.2 27.0 23.0 The particular value of ash is based on its content of P2O5, CaO and Ah O3. Currently, it is not possible to efficiently and economically recover the various materials in this type of ash as marketable products. The invention described herein outlines an optional multi-step process for recovering high-value phosphates, such as phosphoric acid, as well as calcium sulfate (gypsum) and, in some cases, aluminum hydrophosphate, from ash. The process according to the invention is based on transforming the ash materials by fractional separation into mineral acids and by adding suitable reagents, into different products, in particular into products of the calcium phosphate group (Ca3(PO4)2), calcium sulfate (CaSO4) and aluminum hydroxophosphate (Al(OH)3xAPO4), the process comprising at least obtaining calcium sulfate (CaSO4) and being suitable in particular for the optional production of phosphoric acid (H3PO4). An explanation of the procedure is reproduced schematically in drawing 1. When separating the phosphate-containing ash materials in step 1, no hydrochloric acid or other hydrohalogenated acid is expressly used, as is currently the state of the art. When ash is treated with hydrochloric acid, iron, aluminum, and calcium salts, preferably their phosphates, are separated. While it is true that different fractions of aluminum compounds and calcium phosphate can be obtained from the combined decomposition solution, the disadvantage lies in the chloride component. Since all the chlorides involved are readily soluble, they ultimately leave the process as wastewater or can only be recovered in a very laborious way, for example, by evaporation. This serious disadvantage is impressively overcome by the invention of a (optionally) multi-step process in which, in the first step, dilute phosphoric acid is used instead of dilute hydrochloric acid for ash treatment (the acid separation process). The salts of these acids, such as calcium phosphate, have a significantly higher value compared to, for example, sodium or calcium chloride. Therefore, through precipitation and evaporation processes, these salts, particularly calcium phosphate, can be obtained, and their sale, especially as fertilizer, makes the entire recycling process economical. The first step can be described in a general embodiment essentially also with the following equations: Ca3 (PO4 ) 2 + 6HNO3 = 3Ca (NO3) 2 + 2H3PO4 AlPO4 + 3HNO3 = Al(NO3)3 + H3 PO4 Of the solid substances, such as ash, mainly Ca and Al ions dissolve, while Fe ions dissolve only in small quantities and remain in the residue along with the also barely soluble silicates (SiO2). The insoluble components are separated according to the state of the art by filtration of the acid decomposition solution, for example, using a decanter, a vacuum belt filter, or a filter press. Preferably, to reduce losses, the residue in the filter assemblies is washed with water, and the wash water is returned as dilution water for the decomposition acid in the first process step. Following step 1, calcium sulfate (CaSO4; gypsum) can be precipitated by adding sulfuric acid (H2SO4) to the resulting filtrate or supernatant after step 1.This occurs in the filtered acid decomposition solution, in the second step according in particular to the second chemical equation which can be seen below. 3Ca(N0 3)2 + 3H2SO4 = 3CaS0 4 + 6HNO3 CaHPCU + H2SO4 = CaS0 4 +i H3P0 4 To reduce the need for nitric acid and make the process more economical, an important step in the multi-step procedure is the recovery of nitric or, in particular, phosphoric acid. Near-complete recovery of nitric or phosphoric acid is possible when dilute sulfuric acid is added in stoichiometric proportions to the calcium content, resulting in the precipitation of calcium sulfate (gypsum) surprisingly effectively even at a pH below 1. The sum of these two steps results in the following chemical equation: Ca3 (P0 4) 2 + 6H 3Ca (NO3) 2 + 3 ------ The calcium sulfate precipitate (gypsum) is filtered, dehydrated, and washed with water in a known manner. Preferably, this acidic wash water is also returned as dilution water to the first process step. The dehydrated gypsum can be further processed in additional steps outside the process chain described here, for example, by calcination to produce anhydrite or by chemical reaction according to patent document DE 19611454 A1. Through repeated recirculation, and thus through continued dilution of phosphate from the ash, the phosphoric acid concentration can be further increased and could reach a concentration of over 30% H3PO4, provided the dissolved aluminum ions are not a significant concern. Depending on the AhO3 content of the ash, the Al content in the decomposition acid can reach over 5%, rendering it unsuitable for commercial use. This problem is resolved in a third step, where aluminum ions are precipitated by the addition of, preferably, calcium oxide as aluminum hydroxophosphate. Due to the high salt concentration in the decomposition acid, the precipitation of aluminum hydroxophosphate is surprisingly possible even with the addition of small amounts of hydroxyl ions, resulting in only a very slight increase in the already strongly acidic pH value, from approximately 1 to 1.5 to approximately 2.0 to 2.5. This is preferably achieved by adding calcium oxide (CaO), but also by adding calcium hydroxide, calcium carbonate, calcium silicate (limestone), sodium hydroxide, or sodium silicate. The aluminum hydroxophosphate precipitate is then separated or obtained by filtration according to the state of the art, for example, using a decanter, a vacuum belt filter, or a filter press. The process of the third step can be described by the following equation: 2AI (N03) 3 + 2 H3P04 + 4Ca0 = AI (OH) 3 x AIPCU + CaHP04 + 3Ca (N03) 2 + H20 While the calcium phosphate and calcium nitrate remain in solution, the aluminum salts precipitate as a precipitate at pH values ​​of approximately 2. Following the separation (depletion) of Ca and Al ions in process steps 2 and 3, phosphoric acid or nitrous phosphoric acid with only minimal contamination is obtained. This can be concentrated by evaporation and used as phosphoric acid or nitrous phosphoric acid for fertilizer production. Natural mineral phosphates can be decomposed with this acid, which is a prior art. The washed phosphoric acid (or in principle also nitrous phosphoric acid) can, in addition, be returned and used according to the invention in the first step for dissolving substances from the ash. In a general variant of the procedure, in which case nitrous phosphoric acid results, the nitrous phosphoric acid is neutralized in the fourth step with limestone (calcium carbonate) or quicklime (calcium oxide) and the precipitate is evaporated, so that a mixture of calcium phosphate or calcium nitrate results. 2H3PO4 + 2HNO3 + 2CaO = Ca (NO3 ) 2 + Ca (H2 PO4) 2 + 2H2O This blended product is a preferred NP fertilizer. Image 2 shows the process steps in an overview view. If the four steps 1-4 are carried out successively, then the materials calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4) and aluminum hydroxophosphate ((Al(OH)3xAlPO4) can be obtained in a single process from solid substances containing phosphate, for example ash, at the same time. It can be seen that in no case do all four steps of the procedure have to be carried out. It is also possible, for example, to obtain only calcium phosphate and calcium sulfate (gypsum) (steps 1, 2, 4). Alternatively, only steps 1, 3, and 4 can be carried out. Interestingly, steps 2 and 3 can also be skipped, so that step 4 can be carried out directly after step 1. Furthermore, the temporal order can be varied, in that it is carried out, for example, after step 1, step 3, and then steps 2 and then 4. As described in detail above, the phosphoric acid (H3PO4) resulting from step 2 and step 3 will be returned for use in the ash treatment in step 1. This feedback of the Al and Ca depleted acid allows for a huge reduction in costs, since less fresh acid is required for ash dilution. The present invention relates to a process for obtaining (generating) selected precipitates of the calcium nitrate group (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3xAPO4) from phosphate-containing ash from waste incineration plants and for the optional production of phosphoric acid (H3PO4), the process comprising at least the obtaining (generation) of calcium sulfate (CaSO4), characterized in that a) the solid substances (ash) are reacted with nitric acid or phosphoric acid or a mixture of inert acids of the two acids, b) the acid-insoluble part of the solid substances is separated, c) By adding sulfuric acid to the filtrate or supernatant, a pH value of < 1 is adjusted, and calcium sulfate precipitate is obtained and separated, and d) the filtrate or supernatant is returned at least partially for use in step a), e) Optionally, the filtrate or supernatant is concentrated, preferably by evaporation, to obtain phosphoric acid or nitrous phosphoric acid (HNO3 / H3PO4), f) It is optionally obtained and separated by adding calcium oxide or calcium carbonate to the filtrate or supernatant, calcium phosphate precipitate and calcium nitrate precipitate. In a preferred embodiment of the invention, at least 10% of the filtrate / supernatant is returned for use in step a), particularly preferably at least 20%, more preferably from 20% to 80%, and most preferably from 40% to 60%, referring to the total amount of filtrate obtained. As described in detail in this regard, the process according to the invention also results in phosphoric acid (H3PO4), so that the process according to the invention is a process for the (optional) production of phosphoric acid (H3PO4), and corresponding embodiments are part of the present invention. In preferred embodiments of the invention, phosphate-containing ash is obtained through incineration of residual sludge, biodegradable waste, organic waste and / or animal waste. In preferred embodiments of the invention, phosphate-containing ash is obtained through incineration of residual sludge, biodegradable waste, organic waste and / or animal waste in a waste incineration facility. The term "precipitate" as used in the invention refers to the separation of a dissolved substance as a solid from a solution, usually by adding suitable substances (precipitating agent). The term particularly includes any precipitate that is completely or partially insoluble in the form of flocs, droplets, or crystalline material, in any microcrystalline, crystalline, or amorphous form. The term "precipitate" explicitly includes any further processing, modification, refining, etc., of the precipitates obtained in the process according to the invention, resulting in powders, dust, fine powder, bulk product, granular materials, granules, etc. The term "calcium phosphate" in the sense of the invention comprises Ca3(PO4)2, CaHPO4, and Ca(H2PO4)2. The term "ash" in the sense of the invention refers to any solid residue from the incineration of organic material, for example, sewage sludge, biodegradable waste, organic waste, and / or animal waste, slaughterhouse waste, for example, animal meal. The ash consists mainly of oxides and (bi)carbonates of various metals, for example, AhO3, CaO, Fe2O3, MgO, MnO, P2O5, P4O10, K2O, SO2, Na2CO3, NaHCo3, etc. The concept "phosphate-containing ash" within the meaning of the invention refers to ash, as defined herein, which contains at least one phosphate, as defined herein. The term "phosphates" within the meaning of the invention refers, in part, to P2O5 and P4O10. The term "phosphates" also refers to salts and esters of orthophosphoric acid (H3PO4) and explicitly includes condensates (polymers) of orthophosphoric acid and its esters. The term "phosphates" refers in particular to metallic salts of phosphoric acid with the general formula X(Y)m(PO4)n, where X, and optionally Y, is a metal selected from the group consisting of aluminum, beryllium, bismuth, lead, cadmium, chromium, iron, gallium, indium, potassium, cobalt, copper, magnesium, manganese, molybdenum, sodium, nickel, osmium, palladium, rhodium, ruthenium, strontium, titanium, vanadium, tungsten, zinc, and tin. The concept of "waste incineration facilities" within the meaning of the invention refers to all facilities, plants and the like, which are suitable for the atmospherically incinerable incineration of any type of waste. The concept of "residual sludge" in the sense of the invention refers to any suspension of finely distributed particles of a solid substance in a liquid. In a preferred embodiment, the liquid in which the particles are suspended is wastewater as defined herein. The term "wastewater" as used in this invention refers to all liquids of an aqueous and / or organic nature, or mixtures thereof, that do not meet the quality standards for drinking water as defined by applicable drinking water regulations (TrinkwV, from the German Trinkwasserverordnung) and / or applicable national and / or international drinking water standards (e.g., DIN 2000 in Germany). The term "wastewater" also includes all wastewater as defined in paragraph 54, section 1 of the German Water Resources Act (Wasserhaushaltsgesetz (WHG)). In a preferred embodiment, wastewater, as defined in the invention, refers to water contaminated by use or altered in its properties or composition. The term "wastewater," as defined in the invention, also includes water altered in its properties due to domestic, industrial, agricultural, or other uses, and water that flows along with it in dry weather (contaminated water), as well as water that flows from built-up areas or accumulates on solid surfaces during rainfall (rainwater). Liquids discharged from and collected at waste treatment, storage, and disposal facilities are also considered contaminated water.Contaminated waters are domestic wastewater from toilets (sewage or black water), sanitary facilities, kitchens, and washing machines (wash water or grey water), as well as wastewater from businesses that is diverted to the public sewer system (commercial or industrial wastewater). Heated water from cooling systems is also considered wastewater. Wastewater resulting from various cleaning and treatment techniques in water preparation facilities is considered wastewater within the meaning of this invention. In a particularly preferred embodiment, the residual sludge is presented as primary sludge, raw sludge, supernatant sludge, as treated and / or stabilized (aerobically / anaerobically) residual sludge. The concept of "organic waste" as it pertains to the invention refers to all organic waste of animal or plant origin generated in a household or farm and which can be broken down by microorganisms, living organisms inhabiting the soil, or enzymes. Examples of such waste include food scraps and grass clippings. Organic waste is generally collected separately in a designated organic waste container and treated separately through composting and fermentation. The resulting compost and fermentation products are often returned to the environment, including in horticulture and agriculture.In this respect, the concept of organic waste includes both waste as defined in the concept of garden and park waste, as well as food and kitchen waste as defined in the EU Waste Framework Directive (from households, restaurants, catering establishments, retail trade and processing on food products farms). The concept of "biodegradable waste" within the meaning of the invention comprises, in addition to organic waste as defined herein, all organic waste of animal or plant origin from agriculture and forestry that can be degraded by microorganisms, soil organisms, or enzymes. This concept specifically includes all organic waste of animal or plant origin from agriculture and forestry that also contains at least one of the following biodegradable substances, selected from the list consisting of wood, paper, and cardboard. The concept of "animal waste" within the meaning of the invention comprises animal bodies of large or domestic animals that have died of natural causes, been killed or stillborn, or parts thereof, as well as slaughterhouse waste, rotten food of animal origin and animal by-products such as milk, eggs, waste materials, but also intestinal contents and manure, as well as all other products and preparations. The term "animal waste" includes, in particular, for the purposes of this invention, meat and animal by-products from domestic, wild, or farm animals that have been slaughtered due to disease or have died of natural causes, including carcasses of animals contaminated with TSE, as well as animals and experimental animals contaminated with prohibited chemicals or substances. Meat and by-products that pose a risk of other non-communicable diseases are also included. The concept of "animal waste" within the meaning of the invention also includes slaughtered animals (i.e., animals not slaughtered), animal by-products (e.g., milk), and any animal products containing drug residues. It also explicitly includes all waste and by-products from slaughterhouses, kitchen and food waste, food no longer fit for human consumption of animal origin, raw milk, and fresh fish or fresh fish by-products. Specifically included are: kitchen and food waste of any kind, Fish or other marine animals, as well as fish waste of any kind, Animal-based foodstuffs which, due to other non-harmful health consequences, for example, due to packaging defects, are no longer intended for human consumption, Parts of slaughtered animals, Raw milk, Eggshells, incubation by-products and by-products of cracked eggs, Hair, fur, horns, etc. Animal waste from the food industry, Animal hides, hooves and horns, bristles and feathers, Layered meats, Low quality meat, Meat from animals subjected to significant stress, Blood from animals (not ruminants), which were killed following an inspection at a slaughterhouse, Parts of slaughtered animal bodies and by-products resulting during the production of certain products for human consumption, defatted bones and cracklings, as well as animal meal. In preferred embodiments of the invention, the incineration of residual sludge, biodegradable waste, organic waste and / or animal waste, takes place in a waste incineration plant at 600° to 1,200°C, preferably at 800° to 900°C. In preferred embodiments of the invention, the reaction of the solid substances (ash) occurs with nitric acid. In preferred embodiments of the invention, the reaction of the solid substances (ash) occurs with phosphoric acid. In preferred embodiments of the invention, the reaction of the solid substances (ash) is carried out with a mixture of mineral acids consisting of phosphoric acid and nitric acid and does not contain hydrohalogenated acids. In particular, the mixture of mineral acids does not contain hydrochloric acid. In preferred embodiments of the invention, the mixture of mineral acids is presented in a concentration of 5% by weight to 50% by weight, preferably from 10% by weight to 30% by weight in aqueous dilution. In preferred embodiments of the invention, the phosphate-containing ash is mixed in a reactor with the mineral acid mixture, the ash proportion being 5% by weight to 50% by weight, preferably 20% by weight to 30% by weight, referring to the diluted mineral acid. In preferred embodiments of the invention, the mineral acid mixture contains at least phosphoric and nitric acid. In preferred embodiments of the invention, the mixture of mineral acids contains, in addition to phosphoric and nitric acid, sulfuric acid. In preferred embodiments of the invention, the reaction time between acid and ash is from 2 to 300 minutes, preferably from 10 to 60 minutes. In preferred embodiments of the invention, the reaction temperature is from 20 °C to 90 °C, preferably from 60 to 80 °C. In preferred embodiments of the invention, the acid-insoluble part of the solid substances is separated by mechanical filtration and / or dehydration procedures. In preferred embodiments of the invention, the separation of the acid-insoluble part of the solid substances is carried out with dehydration groups (e.g., vacuum belt filters, chamber filter press, membrane filter press, sieve belt press, centrifuge). In preferred embodiments of the invention, the separation of the acid-insoluble part of the solid substances is carried out with a vacuum belt filter. In preferred embodiments of the invention, after the separation of the acid-insoluble part from the solid substances, the residue is washed in the filter groups with water and the wash water is returned to the first process step. In preferred embodiments of the invention, the addition of sulfuric acid occurs with a dilution of 10 to 98% by weight, preferably 40 to 80% by weight. In preferred embodiments of the invention, sulfuric acid is added in a molar ratio such that the concentration of dissolved calcium corresponds to 0.5 Ca to 1.5 SO4 (sulfate), preferably 1.0 Ca to 1.0 SO4 (sulfate). In preferred embodiments of the invention, the addition of sulfuric acid takes place in a stirred reactor. In preferred embodiments of the invention, the residence time in the stirring reactor after the addition of sulfuric acid is from 5 to 60 minutes, preferably from 10 to 30 minutes. In preferred embodiments of the invention, the reaction temperature (precipitation of calcium sulfate after addition of sulfuric acid) in the stirred reactor is from 20° to 90°C, preferably from 60° to 90°C. In preferred embodiments of the invention, the calcium sulfate precipitate is separated by mechanical filtration and / or dehydration procedures. In preferred embodiments of the invention, the separation of the calcium sulfate precipitate occurs with dehydration groups (e.g., vacuum belt filters, chamber filter press, membrane filter press, sieve belt press, centrifuge). In preferred embodiments of the invention, the separation of the calcium sulfate precipitate is carried out with a vacuum belt filter. In preferred embodiments of the invention, after separation of the calcium sulfate precipitate, the residue is washed in the filter groups with water and the wash water is returned to the first process step. In preferred embodiments of the invention, after separation of the calcium sulfate precipitate, the filtrate obtained (diluted mineral acid mixture) is used at least partially again for the decomposition of the solid substances. In preferred embodiments of the invention, the proportion of the filtrate feedback is at least 10%, preferably at least 20%, more preferably from 20% to 80%, and most preferably from 40% to 60%, referring to the total amount of filtrate obtained. In preferred embodiments of the invention, the filtrate or supernatant containing phosphoric acid (H3PO4), optionally obtained after separation of Fe silicate and / or calcium sulfate, and / or aluminum hydroxophosphate, is concentrated by evaporation to an acid content of 30% by weight to 70% by weight, preferably 40% by weight to 60% by weight. In preferred embodiments of the invention, the pH value is adjusted in the filtrate or supernatant, containing phosphoric acid (H3PO4), optionally obtained after separation of Fe silicate and / or calcium sulfate, and / or aluminum hydroxophosphate, by adding calcium oxide or calcium carbonate, forming calcium precipitates, from 4 to 12, preferably from 6 to 9. In preferred embodiments of the invention, the addition of calcium oxide or calcium carbonate to the filtrate or supernatant, containing phosphoric acid (H3PO4), optionally obtained after separation of Fe silicate and / or calcium sulfate, and / or aluminum hydroxophosphate, occurs in a stirred reactor, forming calcium precipitates. In preferred embodiments of the invention, after the formation of calcium precipitates, the solid substance suspension is evaporated or spray-dried by supplying heat to such an extent that a solid substance with a residual moisture content of 0% by weight to 25% by weight, preferably 2% by weight to 10% by weight, is obtained. In preferred embodiments of the invention, the precipitate or precipitates are presented as a completely or partly insoluble precipitate, in the form of flocs, droplets or crystalline material, in any microcrystalline, crystalline or amorphous form. In preferred embodiments of the invention, the precipitate or precipitates are further processed, modified, refined, etc., resulting in powders, dust, fine powder, bulk product, granular materials, granules, etc. Examples The complete process is described by way of example through the following trial development, which explains the procedure according to the invention, without reproducing it exactly: The starting material is ash from a waste sludge incineration plant. The essential components were analyzed as follows; % by weight of P2O5 250 % by weight of CaO 175 % by weight of Fe2O3 269 % by weight of Al2O3 67 % by weight of SiO2 195 100 g of ash are treated in a laboratory beaker with 300 g of dilute acid. The dilute acid consists of: 70% by weight water; 15% by weight HNO3 and 15% by weight H3PO4. The suspension is stirred for 30 minutes at 40 °C and then filtered through a vacuum suction filter. The filter cake is then weighed and subsequently dried at 100 °C. Wet filter cake = 122 g Dried filter cake = 72 g From this, it can be calculated that out of 100 g of ash, 72 g did not dissolve in acid. 28 g (= 28%) are acid-soluble. A total of 275 g of filtrate were recovered and subsequently analyzed. The results were compared with the theoretical values ​​shown in the following table, which would have resulted if the essential ash components had been 100% dissolved (in the filtrate and wet proportion of the filter cake). (100%) _____ (Actual) _________ Acid soluble % by weight of P2O5 17.78* 13.68 88.7% % by weight of CaO 5.37 4.80 89.4% % by weight of Fe2O3 8.25 0.47 5.7% % by weight of Al2O3 2.06 1.56 75.7% % by weight of SiO2 5.98 0.02 0.3% *7.69% of P2O5 result from the ash, 10.09% of P2O5 from the added phosphoric acid. The results show that high redissolution rates are achieved for phosphate, calcium, and aluminum, while iron dissolves only in a reduced form, and silicon, as expected, is almost insoluble as SiO2. The concentration of H3PO4 has increased from 15% by weight to 13.68 x 1.37 = 18.7% by weight (1.37 being the conversion factor for P2O5 to H3PO4). Evaporation at a rate of 2 yields an acid containing 37.4% H3PO4 and 30% HNO3. This acid can be used for fertilizer production or neutralized with CaO and then evaporated, resulting in a double salt of Ca(NO3)2 * Ca(H2PO4)2. This procedure has the disadvantage that, on the one hand, it requires significant quantities of nitric and phosphoric acid, and on the other hand, contamination from iron and aluminum salts worsens the quality of the product. The process would be economically unviable, and the added value of the final products would be very limited. These problems, which are particularly significant with high concentrations of Al in the ash from wastewater sludge (which can exceed 20% AhO3), are addressed through a multi-step process in steps 2 and 3 as follows: the filter cake (122 g wet weight) from step 1 (the ash solution process) is washed with 100 g of hot water (70–90 °C). The resulting washed filtrate is mixed with 200 g of filtrate from step 1 (diluted acid) and 25 g of sulfuric acid (48% by weight) in a beaker (total weight = 100 + 200 + 25 = 325 g). After a few minutes, white calcium sulfate precipitates, corresponding to the reaction described above. After 30 minutes, the precipitate is filtered through a vacuum suction device (with a filter). 280 g of filtrate and 43 g of wet gypsum filter cake were obtained. The filtrate was analyzed. The following table compares the analysis results, which are from a parallel test, in which the filtrate from step 1 plus wash water were analyzed in the proportions mentioned above: ____________________ Filtrate + wash water After Ca precipitation pH value 1.9 0.9 % by weight of P2O5 9.58 9.43 % by weight of CaO 3, 70 1, 45 % by weight of Fe2O3 0.32 0.33 % by weight of Al2O3 0.98 1.01 The data clarifies that the Ca content is reduced, as is the pH value, since additional H+ ions were able to form. The acid filtrate from the second step can now be used after dissolving the ash, making it possible to completely forgo the dosage of H3PO4, as new phosphoric acid is constantly being formed from the phosphorus-containing ash. This step is particularly noteworthy in the multi-step process, as the use of sulfuric acid generally reduces acid costs (sulfuric acid is, in terms of efficiency, the most economical acid), and because gypsum is also obtained. With the recycled filtrate (calcium-poor dilute acid), the formulation for step 1 is now as follows: 100 g of ash are treated in a laboratory beaker with 300 g of dilute acid. The dilute acid consists of 270 g of recycled filtrate and 20 g of HNO3. The suspension is stirred for 30 minutes at 40 °C and then filtered through a vacuum suction filter. The filter cake is then weighed and subsequently dried at 100 °C. Wet filter cake = 130 g Dried filter cake = 75 g From this, it can be calculated that out of 100 g of ash, 75 g did not dissolve in the acid, meaning that 25 g (= 25%) are acid-soluble. A total of 258 g of filtrate (dilute acid) were recovered and subsequently analyzed. The analysis results essentially correspond to the results of the initial step 1, except that the CaO content was slightly higher at 5.8 wt% (since additional calcium was introduced through recycling), while the AhO3 content continued to increase from 1.5 to 2.6%. In a third step, the aluminum concentration in the dilute acid was reduced by adding small amounts of calcium oxide. To do this, 150 g of dilute acid, at room temperature, were mixed with 1 g of CaO. A precipitate formed, which was filtered after 15 minutes through a vacuum suction device (with a filter). 123 g of filtrate and 25 g of wet filter cake were obtained. The filtrate was analyzed. The analysis results in the following table compare values, which result from a parallel test, in which case the diluted acid was analyzed before the addition of CaO. ____________________ Dilute acid After precipitation of Al pH value 0.9 2.2 % by weight of P2O5 9.35 8.95 % by weight of CaO 5, 84 6, 42 % by weight of Fe2O3 0.54 0.48 % by weight of Al2O3 2.61 0.84 A minimal increase in pH resulted in the formation of an Al-PO4 precipitate, which is reflected in the reduced values ​​of P2O5 and Al2O3. The values ​​were deliberately reduced only minimally through precipitation, as excessive enrichment of Al ions was to be avoided. The precipitate, washed with water and dried, was analyzed as follows: % by weight of P2O5 31.3 % by weight of CaO 1, 1 % by weight of Fe2O3 3.5 % by weight of Al2O3 56.1 The precipitate has been further processed in a further trial in accordance with patent document DE 10 2012015065 B32013.07.18 and has been transformed into a sodium aluminate solution and a calcium phosphate precipitate. The process steps described herein must be used variably depending on the concentration of Ca and Al ions in the decomposition acid (or the corresponding oxide concentrations in the ash). The nature of the invention lies in the fact that by combining the process steps, an economical process can be implemented, and above all, low-aluminum end products are obtained. The HNO3-H3PO4 acid is preferably neutralized with CaO to a pH of 6 and concentrated by water evaporation, for example, by spray drying. This results in a double salt of calcium nitrate and calcium phosphate. According to the invention, a salt with the following composition can be generated: 19.5 wt% P2O5; 28.5 wt% CaO; 24.3 wt% NO3; 0.8 wt% Al2O3; 0.6 wt% Fe2O3. Figure 3 shows the different process developments schematically.

Claims

1. A process for obtaining precipitates, selected from the group of calcium nitrate, calcium phosphate, calcium sulfate, and aluminum hydroxophosphate, from phosphate-containing ash from waste incineration plants and for the optional production of phosphoric acid, the process comprising at least the production of calcium sulfate, characterized in that: a) the solid substances / ash are reacted with nitric acid or phosphoric acid or a mixture of mineral acids of the two acids; b) the acid-insoluble portion of the solid substances is separated; c) by adding sulfuric acid to the filtrate or supernatant, a pH value of < 1 is adjusted, and a precipitate of calcium sulfate is obtained and separated; and d) the filtrate or supernatant is at least partially returned for use in step a); e) optionally, the filtrate or supernatant is concentrated, preferably by evaporation.For the production of phosphoric acid or nitrous phosphoric acid, f) optionally, by adding calcium oxide or calcium carbonate to the filtrate or supernatant, calcium phosphate precipitate and calcium nitrate precipitate are obtained and separated.

2. A process according to claim 1, characterized in that steps a), b), c), d), and e) are carried out.

3. A process according to claim 1, characterized in that steps a), b), c), d), and f) are carried out.

4. A process according to claims 1, 2, and 3, characterized in that in step d), at least 10% of the filtrate / supernatant is returned for use in step a), preferably at least 20%, more preferably from 20% to 80%, and most preferably from 40% to 60%, with respect to the total amount of filtrate obtained.

5. Method according to claims 1 to 4,characterized in that it is a process for the production of phosphoric acid.

6. Process according to claims 1 to 5, characterized in that the phosphate-containing ash is obtained by incineration of phosphate-containing sewage sludge, biodegradable waste, organic waste and / or animal waste in a waste incineration plant.

7. Process according to claims 1 to 6, characterized in that the reaction of the phosphate-containing ash occurs in step (a) with phosphoric acid.

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