Process for the treatment of phosphate-containing solids by wet chemical digestion to obtain aluminium, calcium, phosphorus and nitrogen compounds

Abstract

A process for obtaining precipitates selected from the group consisting of calcium nitrate, calcium phosphate, calcium sulfate and aluminum hydroxophosphate from phosphate-containing solids and for the optional production of phosphoric acid, the process comprising at least the obtaining of calcium sulfate, characterized in that a) the phosphate-containing solids are reacted with nitric acid or phosphoric acid or a mineral acid mixture of the two acids, b) the acid-insoluble part of the solids is separated, c) by adding sulfuric acid to the filtrate or supernatant a pH value <1 is adjusted, and calcium sulfate precipitate is obtained and separated, and d) at least 10% of the filtrate or supernatant, based on the total amount of filtrate obtained, is recycled for use in step a), and that the phosphate-containing solids are phosphate-containing ash obtained by burning sewage sludge, biodegradable waste, biowaste and / or animal waste in a waste incineration plant.

Description

[0001] The invention relates to a process for the treatment of phosphate-containing solids, in particular phosphate-containing ashes from waste incineration plants and phosphate-containing minerals, by wet-chemical digestion to obtain aluminum, calcium, phosphorus and nitrogen compounds.

[0002] Rock phosphates are required for the production of fertilizers. In order to replace the finite rock phosphates, it is well known that the recovery of phosphorus or phosphates from waste and wastewater is being sought in European industrialized countries (see patent DE 10 2012 015 065 B3). This is also appropriate because rock phosphates are increasingly contaminated with heavy metals such as cadmium and uranium, and these contaminants are found in fertilizers and groundwater.

[0003] A significant phosphate resource in Europe is wastewater from municipal and industrial sewage treatment plants. In Germany alone, approximately 50,000 Mt of phosphorus enter wastewater annually. The vast majority of this is precipitated as metal salts using precipitants such as iron or aluminum salts and separated with the sewage sludge. Today, phosphate-containing sewage sludge is usually incinerated, and the resulting ash is landfilled or otherwise "misappropriated" (e.g., road construction, backfilling), because the phosphorus it contains is not recovered—with a few exceptions in pilot plants.

[0004] Similar to other industrial recycling processes, such as the recovery of iron from scrap, the recovery of paper from waste paper, and the recovery of copper and other metals from electrical appliances, the industrial recovery of phosphorus from waste is also possible. A key prerequisite for this is that the phosphorus-containing residues have a sufficiently high phosphorus concentration and low contamination levels, essentially corresponding to the currently used rock phosphates, ideally without the harmful uranium and cadmium contamination.

[0005] Phosphates are extracted from rock phosphate (rock, with a phosphorus content of approximately 30% P2O5) by acid digestion, preferably with sulfuric acid, producing phosphoric acid and / or calcium phosphate fertilizer (so-called "superphosphate"). The ashes of incinerated sewage sludge or animal waste such as meat and bone meal contain up to 35 wt.% P2O5, but, depending on the precipitant, also up to 25 wt.% iron, aluminum, or calcium oxide. This high metal oxide content, which can be up to ten times higher than in rock phosphate, significantly limits the use of sewage sludge ash as an alternative rock phosphate in industrial processes.A solution to this problem is presented in patent DE 10 2012 015 065 B3. During wastewater treatment, phosphates are bound by aluminum salts and then converted to calcium phosphate. This ensures that the remaining ash, when the sewage sludge is subsequently incinerated, contains primarily calcium phosphate and as few aluminum and iron compounds as possible. The calcium phosphate-rich ash is suitable for use as rock phosphate in the production of fertilizers, but always in combination with accompanying impurities from the ash.

[0006] Ashes resulting from the incineration of sewage sludge, organic waste, biodegradable waste, animal waste, etc., such as animal meal, contain various valuable substances. The following table shows the main components (calculated as oxides) and the valuable substance content of some ashes resulting from sewage sludge incineration: Ash A Ash B Ash C % Fe2O3 21,9 3,1 11,9 % Al2O3 9,3 21,5 12,4 % CaO 15,2 14,5 11,4 % P2O5 21,0 23,0 20,5 % SiO2 18,2 27,0 23,0

[0007] The special value of ashes is based on their content of P2O5, CaO and Al2O3.

[0008] US 4 029 743 A describes a process for extracting phosphoric acid from phosphate rock using an acid mixture with sulfuric acid.

[0009] US 4 402 923 A describes a process for extracting phosphoric acid from phosphate rock using recycled mineral acid water.

[0010] US 4 154 799 A describes a process for extracting phosphate from phosphate rock using dilute sulfuric acid and precipitation of dicalcium phosphate.

[0011] GB 665 257 A describes a process for treating calcium nitrate with nitric acid.

[0012] US 2 114 600 A describes a process for the production of dicalcium phosphate and alkali salts.

[0013] Currently, it is not possible to efficiently and cost-effectively recover the various valuable substances in such ashes as marketable products. The invention described here describes an optionally multi-stage process by which not only calcium phosphate-containing fertilizers but also higher-value phosphates such as pure calcium phosphate and / or calcium nitrate phosphate, phosphoric acid and / or nitrous phosphoric acid, as well as calcium sulfate (gypsum), and aluminum hydroxophosphate can be extracted from ashes.

[0014] The process according to the invention is based on converting the valuable substances from the ash into different products by fractional dissolution in mineral acids and by adding suitable reactants, in particular into products from the group calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4).

[0015] The process according to the invention is also suitable for the digestion and extraction (production) of precipitates selected from the group consisting of calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4) from other phosphate-containing solids such as phosphate-containing minerals and ores.

[0016] The process according to the invention thus enables the sequential (or separate) recovery (production) of precipitates selected from the group consisting of calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4); from phosphate-containing solids, in particular from phosphate-containing ashes and phosphate-containing minerals, or a mixture thereof.

[0017] The method according to the invention is Fig. shown schematically.

[0018] When dissolving the valuable materials from phosphate-containing ashes in stage 1, no hydrochloric acid or other hydrohalic acid is used, as is partly the state of the art today

[0019] For example, when ashes are treated with hydrochloric acid, iron, aluminum, and calcium salts, especially their phosphates, dissolve. Although different fractions of aluminum compounds and / or calcium phosphate can be obtained from the combined digestion solution, the disadvantage is the chloride component, which, because all relevant chlorides are readily soluble, ultimately leaves the process as wastewater or can only be recovered with great effort, e.g., by evaporation.

[0020] This serious disadvantage is impressively solved by the invention in an (optional) multi-stage process in which, in the first stage, diluted nitric acid and / or diluted phosphoric acid are used to treat the solids, e.g., ash or minerals, (the dissolving process in acid), rather than diluted hydrochloric acid. The salts of these acids, such as calcium phosphate or calcium nitrate, are significantly more valuable than, for example, sodium or calcium chloride, so that the salts, especially calcium phosphate and calcium nitrate, can be recovered through precipitation and evaporation processes. Their marketing—primarily as NP fertilizers (NP = nitrogen-phosphorus fertilizers)—makes the entire recycling process economically viable.

[0021] The first stage can essentially be described with the following equations: Ca3(PO4)2 + 6HNO3 = 3Ca(NO3)2 + 2H3PO4 AlPO4 + 3HNO3 = Al(NO3)3 + H3PO4

[0022] From the solids, such as ash, primarily Ca and Al ions dissolve, while Fe ions dissolve only in small quantities and remain in the residue along with the equally sparingly soluble silicates (SiO2). The insoluble components are separated from the acidic digestion solution by filtration using state-of-the-art technology, e.g., a decanter, a vacuum belt filter, or a filter press. To reduce losses, the residue is preferably washed with water in the filter units, and the wash water is recycled to the first process stage as dilution water for the digestion acid.

[0023] Following step 1, calcium sulfate (CaSO4; gypsum) can now be precipitated by adding sulfuric acid (H2SO4) to the resulting filtrate or supernatant after step 1. This occurs in the acidic, filtered digestion solution in the second step according to the chemical equation

[0024] To reduce the need for nitric acid and make the process more economical, a key step in the multi-stage process is the recovery of nitric or phosphoric acid. Thus, almost complete recovery of nitric or phosphoric acid is possible if diluted sulfuric acid is added in a stoichiometric ratio to the calcium content. Surprisingly, precipitation to calcium sulfate (gypsum) is possible even at a pH below 1. The sum of the two steps results in the following chemical equation:

[0025] The calcium sulfate precipitate (gypsum) is filtered, dewatered, and washed with water in a known manner. This acidic wash water is preferably also recycled to the first process stage as dilution water. The dewatered gypsum can be further processed in subsequent process steps outside the process chain described here, e.g., by calcination to anhydrite or by chemical conversion according to patent DE 196 11 454 A1.

[0026] Through repeated recycling, the phosphoric acid concentration is continually increased by the continued dissolution of phosphate from the solid, e.g., ash. It could be raised to a concentration of over 30% H3PO4, if the dissolved aluminum ions weren't a problem. Depending on the Al2O3 content of the solid, e.g., ash, the Al concentration in the digestion acid can rise to over 5%, making it impossible to market. According to the invention, this problem is solved in a third step by precipitating aluminum ions as aluminum hydroxophosphate by adding, preferably, calcium oxide.

[0027] Due to the high salt concentration in the digestion acid, aluminum hydroxophosphate precipitation is surprisingly possible by adding small amounts of hydroxyl ions with only a slight increase in the inherently strongly acidic pH 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 (lime sandstone), sodium hydroxide, or sodium silicate. The aluminum hydroxophosphate precipitate is separated or recovered by filtration according to the state of the art, e.g., using a decanter, a vacuum belt filter, or a filter press.

[0028] The process of the third stage can be described by the following equation: While Ca phosphate and Ca nitrate remain in solution, the Al salts precipitate as a precipitate at pH values ​​of approximately 2.

[0029] After the separation (depletion) of Ca and Al ions in process stages two and three, a slightly contaminated phosphoric acid or nitrous phosphoric acid is produced. This can be concentrated by evaporation and used as phosphoric acid or nitrous phosphoric acid for the production of fertilizers. This acid can be used to digest mineral rock phosphates, which is state-of-the-art.

[0030] Furthermore, the purified phosphoric acid or nitrous phosphoric acid can be recycled and used according to the invention in the first stage to dissolve ingredients from the solids.

[0031] In a preferred variant of the process, in which nitrous phosphoric acid is produced, in the fourth stage the nitrous phosphoric acid is neutralized with limestone (calcium carbonate) or quicklime (calcium oxide) and the precipitate is evaporated to form a mixture of calcium phosphate and calcium nitrate. 2H3PO4 + 2HNO3 + 2CaO = Ca(NO3)2 + Ca(H2PO4)2 + 2H2O

[0032] This mixed product is a preferred NP fertilizer.

[0033] The Fig. shows the process steps in an overview.

[0034] If all four stages 1-4 are carried out consecutively, the valuable substances calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4)) can be obtained from phosphate-containing solids, e.g. ashes, in a single process.

[0035] It is clear that not all four stages of the process necessarily have to be carried out. It is also possible, for example, to obtain only calcium phosphate and calcium sulfate (gypsum) (stages 1, 2, and 4). Alternatively, only stages 1, 3, and 4 can be carried out.

[0036] Interestingly, stages 2 and 3 can also be skipped, so that stage 4 can be performed directly after stage 1.

[0037] Furthermore, the time sequence can be varied, for example by carrying out stage 1, stage 3, then stages 2 and then 4.

[0038] As described in detail above, the resulting phosphoric acid (H3PO4) or the resulting nitrous phosphoric acid (HNO3 / H3PO4) can be recycled after stage 2 and after stage 3 for use in the treatment of the solids in stage 1. This recycling of the Al- and Ca-depleted acid enables a huge cost reduction because less fresh acid is required to dissolve the solids.

[0039] In a first aspect A1, the present invention thus relates to a process for the recovery (production) of precipitates selected from the group consisting of calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4)) from phosphate-containing solids, the process at least comprising the recovery (production) of calcium phosphate (Ca3(PO4)2) and calcium nitrate (CaNO3), characterized in that a) the solids are reacted with nitric acid or phosphoric acid or a mineral acid mixture of the two acids, b) the acid-insoluble part of the solids is separated, c) optionally the filtrate or the supernatant is at least partially recycled for use in step a), d) optionally the filtrate or supernatant is concentrated, preferably by evaporation, to obtain phosphoric acid or nitrous phosphoric acid (HNO3 / H3PO4), e) optionally by adding calcium oxide or calcium carbonate to the filtrate or supernatant, calcium phosphate precipitate and calcium nitrate precipitate (CaNO3) is obtained and separated, preferably carrying out steps a), b) and e).

[0040] In a further alternative embodiment of aspect A1, steps a), b) and d) are preferably carried out.

[0041] In a further alternative embodiment of aspect A1, steps a), b), c) and d) are preferably carried out.

[0042] In a further alternative embodiment of aspect A1, steps a), b), c) and e) are preferably carried out.

[0043] If, in an embodiment of aspect A1, step c) is carried out, preferably at least 10% of the filtrate / supernatant is recycled for use in step a), more preferably at least 20%, even more preferably 20% to 80%, and most preferably 40% to 60%, based on the total amount of filtrate obtained.

[0044] In a second aspect A2, the present invention relates to a process for the recovery (production) of precipitates selected from the group consisting of calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4) from phosphate-containing solids, the process at least comprising the recovery (production) of calcium sulfate (CaSO4), characterized in that a) the solids are reacted with nitric acid or phosphoric acid or a mineral acid mixture of the two acids, b) the acid-insoluble part of the solids is separated, c) a pH value of <1 is adjusted by adding sulphuric acid to the filtrate or supernatant, and calcium sulphate precipitate is obtained and separated.

[0045] Optionally, in a preferred embodiment of aspect A2, the extraction / deposition of the calcium sulfate according to step c) of aspect A2 can be followed by the optional steps c)-e) of aspect A1 as described herein, wherein step d) is preferably carried out.

[0046] Optionally, in a preferred embodiment of aspect A2, the extraction / deposition of the calcium sulfate according to step c) of aspect A2 can be followed by the optional steps c)-e) of aspect A1, as described herein, wherein step e) is preferably carried out.

[0047] Optionally, in an alternative embodiment of aspect A2, the extraction / deposition of the calcium sulfate according to step c) of aspect A2 may be followed by the optional steps c)-e) of aspect A1 as described herein, wherein preferably steps c) and d) are carried out.

[0048] Optionally, in an alternative embodiment of aspect A2, the extraction / deposition of the calcium sulfate according to step c) of aspect A2 may be followed by the optional steps c)-e) of aspect A1 as described herein, wherein preferably steps c) and e) are carried out.

[0049] If, in an embodiment of aspect A2, step c) of aspect A1 is carried out, preferably at least 10% of the filtrate / supernatant is recycled for use in step a), particularly preferably at least 20%, even more preferably 20% to 80%, and most preferably 40% to 60%, based on the total amount of filtrate obtained.

[0050] In a third aspect A3, the present invention relates to a process for the recovery (production) of precipitates selected from the group consisting of calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4) from phosphate-containing solids, the process at least comprising the recovery (production) of aluminum hydroxophosphate (Al(OH)3 × AlPO4), characterized in that a) the solids are reacted with nitric acid or phosphoric acid or a mineral acid mixture of the two acids, b) the acid-insoluble part of the solids is separated, c) by raising the pH value in the filtrate or supernatant, the dissolved aluminium is recovered and separated as aluminium hydroxophosphate precipitate.

[0051] Optionally, in a preferred embodiment of aspect A3, the recovery / deposition of the aluminum hydroxophosphate precipitate according to step c) of aspect A3 can be followed by the optional steps c)-e) of aspect A1 as described herein, wherein step e) is preferably carried out.

[0052] Optionally, in a preferred embodiment of aspect A3, the recovery / deposition of the aluminum hydroxophosphate precipitate according to step c) of aspect A3 can be followed by the optional steps c)-e) of aspect A1 as described herein, wherein step d) is preferably carried out.

[0053] Optionally, in an alternative embodiment of aspect A3, the recovery / deposition of the aluminum hydroxophosphate precipitate according to step c) of aspect A3 may be followed by the optional steps c)-e) of aspect A1 as described herein, wherein preferably steps c) and d) are carried out.

[0054] Optionally, in an alternative embodiment of aspect A3, the recovery / deposition of the aluminum hydroxophosphate precipitate according to step c) of aspect A3 may be followed by the optional steps c)-e) of aspect A1 as described herein, wherein preferably steps c) and e) are carried out.

[0055] If, in an embodiment of aspect A3, step c) of aspect A1 is carried out, preferably at least 10% of the filtrate / supernatant is recycled for use in step a), more preferably at least 20%, even more preferably 20% to 80%, and most preferably 40% to 60%, based on the total amount of filtrate obtained.

[0056] In a fourth aspect A4, the present invention relates to a process for obtaining (producing) precipitates selected from the group consisting of calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4) from phosphate-containing solids, characterized in that a) the solids are reacted with nitric acid or phosphoric acid or a mineral acid mixture of the two acids, b) the acid-insoluble part of the solids is separated, c) calcium sulfate precipitate is obtained and separated by adding sulfuric acid to the filtrate or supernatant, d) by raising the pH value in the filtrate or supernatant, the dissolved aluminium is recovered and separated as aluminium hydroxophosphate precipitate, e) optionally the filtrate or the supernatant is at least partially recycled for use in step a) f) optionally, the filtrate or supernatant is concentrated by water evaporation to obtain phosphoric acid or nitrous phosphoric acid (HNO3 / H3PO4), or g) optionally, calcium phosphate precipitate and / or calcium nitrate precipitate is obtained and separated by adding calcium oxide or calcium carbonate to the filtrate or to the supernatant, or, alternatively, is concentrated by evaporation or spray drying, wherein of the optional steps e)-g, step g) is preferably carried out.

[0057] Optionally, in a preferred embodiment of aspect A4, of the optional steps e)-g), preferably steps e) and g) are carried out.

[0058] Optionally, in a preferred embodiment of aspect A4, of the optional steps e)-g), preferably steps e), f) and g) are carried out.

[0059] Optionally, in a further preferred embodiment of aspect A4, of the optional steps e)-g), preferably steps e) and f) are carried out.

[0060] If, in an embodiment of aspect A4, step e) is carried out, preferably at least 10% of the filtrate / supernatant is recycled for use in step a), more preferably at least 20%, even more preferably 20% to 80%, and most preferably 40% to 60%, based on the total amount of filtrate obtained.

[0061] As already described herein, in the process according to the present invention, the sequence of steps 2 and 3 (precipitation of calcium sulfate, precipitation of aluminum hydroxophosphate) in this order is not mandatory, so that step 1 can also be followed by step 3 (and then step 2).

[0062] In a fifth aspect A5, the present invention thus relates to a process for obtaining (producing) precipitates selected from the group consisting of calcium nitrate (CaNO3), calcium phosphate (Ca3(PO4)2), calcium sulfate (CaSO4), and aluminum hydroxophosphate (Al(OH)3 × AlPO4) from phosphate-containing solids, characterized in that a) the solids are reacted with nitric acid or phosphoric acid or a mineral acid mixture of the two acids, b) the acid-insoluble part of the solids is separated, c) by raising the pH value in the filtrate or supernatant, the dissolved aluminium is recovered and separated as aluminium hydroxophosphate precipitate, d) calcium sulfate precipitate is obtained and separated by adding sulfuric acid to the filtrate or supernatant, e) optionally the filtrate or the supernatant is at least partially recycled for use in step a), f) optionally, the filtrate or supernatant is concentrated by water evaporation to obtain phosphoric acid or nitrous phosphoric acid (HNO3 / H3PO4), or g) optionally, calcium phosphate precipitate and / or calcium nitrate precipitate is obtained and separated by adding calcium oxide or calcium carbonate to the filtrate or to the supernatant, or, alternatively, is concentrated by evaporation or spray drying, wherein of the optional steps e)-g, preferably at least step g) is carried out.

[0063] Optionally, in a preferred embodiment of aspect A5, of the optional steps e)-g), preferably steps e) and g) are carried out.

[0064] Optionally, in a preferred embodiment of aspect A5, of the optional steps e)-g), preferably steps e), f) and g) are carried out.

[0065] Optionally, in a further preferred embodiment of aspect A5, of the optional steps e)-g), preferably steps e) and f) are carried out.

[0066] If, in an embodiment of aspect A5, step e) is carried out, preferably at least 10% of the filtrate / supernatant is recycled for use in step a), particularly preferably at least 20%.

[0067] If, in an embodiment of aspect A5, step e) is carried out, preferably at least 10% of the filtrate / supernatant is recycled for use in step a), more preferably at least 20%, even more preferably 20% to 80%, and most preferably 40% to 60%, based on the total amount of filtrate obtained.

[0068] As described in detail herein, phosphoric acid (H3PO4) is also produced in processes according to the above aspects, so that these processes can of course also be understood as processes for the optional production of phosphoric acid (H3PO4), and corresponding embodiments are part of the present invention.

[0069] In a preferred embodiment of aspects A1 to A5, as well as the corresponding embodiments above, the phosphate-containing solids are selected from phosphate-containing ashes and phosphate-containing minerals, or a mixture thereof.

[0070] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the phosphate-containing ash is obtained by incineration of sewage sludge, biodegradable waste, biowaste and / or animal waste.

[0071] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the phosphate-containing ash is obtained by incinerating sewage sludge, biodegradable waste, biowaste and / or animal waste in a waste incineration plant.

[0072] The term "precipitate" in the context of the invention refers to the separation of a dissolved substance as a solid from a solution, usually triggered by the addition of suitable substances (precipitants). In particular, the term encompasses any completely or partially insoluble precipitate in the form of flakes, droplets, or crystalline material, in any microcrystalline, crystalline, or amorphous form. The term "precipitate" expressly includes any further processing, modification, refining, etc., of the precipitates obtained in the process according to the invention into powders, dusts, bulk materials, granular materials, grit, etc.

[0073] The term “calcium phosphate” in the sense of the invention includes Ca3(PO4)2), CaHPO4 and Ca(H2PO4)2.

[0074] The term "phosphate-containing minerals" refers to all elements or chemical compounds in crystalline form that have been formed by geological processes and contain at least one phosphate, as defined herein. Examples of phosphate-containing minerals within the meaning of the invention are apatite Ca5(PO4)3(F, Cl, OH), e.g., fluorapatite and calcium carbonate-infused phosphorite, wavellite Al3(PO4)(F,OH) 5 H2O, vivianite Fe3(PO4)2 8 H2O, and turquoise CuAl6[(PO4)(OH2)]4 4 H2O. Also included are fluorapatite (apatite-(CaF)), Ca5[F|(PO4)3] ; Chlorapatite (apatite-(CaCl), Ca5[Cl(PO4)3] ; hydroxyapatite (apatite-(CaOH, Ca5[OH|(PO4)3]; fluorostrophite (apatite-(SrOH) and strontium apatite (Sr,Ca)5[(F,OH)|(PO4)3]); carbonate fluorapatite (carbonate fluorapatite), Ca5[F|(PO4,CO3OH)3]; carbonate hydroxyapatite (carbonate hydroxyapatite), Ca5[OH|(PO4,CO3OH)3] ; hydroxyapatite-M apatite-(CaOH)-M and clinohydroxyapatite (Ca,Na)5[(OH,Cl)|(PO4,SO4)3].In particular, the term “phosphate-containing minerals” also includes mineral mixtures and ores containing at least one phosphate-containing mineral as defined herein.

[0075] The term "ash" in the context of the invention refers to any solid residue from the combustion of organic material, for example sewage sludge, biodegradable waste, organic waste and / or animal waste, slaughterhouse waste, e.g., animal meal. Ash consists primarily of oxides and (bi-)carbonates of various metals, e.g., Al2O3, CaO, Fe2O3, MgO, MnO, P2O5, P4O 10 , K2O, SiO2, Na2CO3, NaHCO3, etc.

[0076] The term “phosphate-containing ash” in the sense of the invention refers to ashes, as defined herein, which contain at least one phosphate, as defined herein.

[0077] The term “phosphates” in the sense of the invention refers to P2O5 and P4O 10Furthermore, the term "phosphates" refers to the salts and esters of orthophosphoric acid (H3PO4), and expressly includes the condensates (polymers) of orthophosphoric acid and its esters. In particular, the term "phosphates" refers to metallic salts of phosphoric acid with the general formula X(Y)m(PO4)n, where X and optionally Y are metals 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.

[0078] The term “waste incineration plants” within the meaning of the invention refers to all plants, facilities and the like that are suitable for incinerating the atmospherically combustible components of any type of waste.

[0079] The term “sewage sludge” in the sense of the invention refers to any suspension of finely distributed particles of a solid substance in a liquid.

[0080] In a preferred embodiment, the liquid in which the particles are suspended is a wastewater as defined herein.

[0081] The term "wastewater" as used herein refers to all liquids of an aqueous and / or organic nature, or mixtures thereof, that are not of drinking water quality within the meaning of the Drinking Water Ordinance (TrinkwV) and / or national and / or international drinking water standards (e.g., "DIN 2000 02 / 2017. Central Drinking Water Supply" in Germany). The term wastewater also includes all wastewater pursuant to Section 54 (1) of the German Water Resources Act (WHG).

[0082] In a preferred embodiment, wastewater within the meaning of the invention is water that has been contaminated or altered in its properties or composition through use. Furthermore, the term "wastewater" within the meaning of the invention encompasses water whose properties have been altered by domestic, commercial, agricultural, or other use, as well as the water that flows off with it during dry weather (sewage), as well as the water that runs off collected from precipitation from built-up or paved areas (rainwater). Liquids discharged and collected from waste treatment, storage, and disposal facilities are also considered sewage.Wastewater includes domestic wastewater from toilets (fecal or black water), sanitary facilities, kitchens, and washing machines (washing or gray water), as well as wastewater from businesses that discharge into the public sewer system (commercial or industrial wastewater). Heated water from cooling systems also counts as wastewater. Wastewater generated during the various cleaning and treatment processes of water treatment plants is considered wastewater within the meaning of the invention.

[0083] In a particularly preferred embodiment, the sewage sludge is present as primary sludge, raw sludge, excess sludge, treated and / or stabilized sewage sludge (aerobic / anaerobic).

[0084] The term "biowaste" as used herein refers to all organic waste of animal or plant origin that is generated in a household or business and can be broken down by microorganisms, soil organisms, or enzymes. This includes, for example, food scraps and grass clippings. Biowaste is generally collected separately in the so-called organic waste bin and treated separately through composting and fermentation. The resulting compost and fermentation products are often returned to the environment, for example in horticulture and agriculture. The term biowaste includes waste as defined in the EU Waste Framework Directive, garden and park waste, as well as food and kitchen waste (from households, restaurants, the catering industry, retail, and food processing).

[0085] The term "biodegradable waste" within the meaning of the invention includes, in addition to biowaste 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. In particular, this term includes all organic waste of animal or plant origin from agriculture and forestry that also contains at least one of the following biodegradable materials selected from the list consisting of wood, paper, and cardboard.

[0086] The term “animal waste” within the meaning of the invention includes carcasses of dead, dead or stillborn large or domestic animals - or parts thereof - as well as slaughterhouse waste, spoiled food of animal origin, and animal by-products such as milk, eggs, confiscated goods but also intestinal contents and manure, as well as all other products and manufactures.

[0087] In particular, the term "animal waste" within the meaning of the invention includes meat and animal by-products from pets, wild animals, or farm animals that were killed or died due to disease, particularly animal carcasses contaminated with TSEs, as well as animals and laboratory animals contaminated with chemicals or prohibited substances. Furthermore, meat and by-products with a risk of other non-communicable diseases are included.

[0088] The term "animal waste" within the meaning of the invention also includes killed, i.e., non-slaughtered animals, animal by-products (e.g., milk), and any animal products containing drug residues. Also expressly included are all waste and by-products from slaughterhouses, kitchen and food waste, food of animal origin no longer suitable for human consumption, raw milk, fresh fish, or fresh fish by-products. In particular, this includes: • Kitchen and food waste of any kind, • Fish or other marine animals, as well as fish waste of any kind, • Former animal foods which are no longer intended for human consumption due to other, non-harmful consequences, e.g. packaging defects, • Carcass parts, • Raw milk, • Shells, hatchery by-products and cracked egg by-products, • Hair, fur, horns, etc., • Animal waste from the food industry, • Skins, hooves and horns, pig bristles and feathers of animals, • overcooked meat, • inferior meat, • Meat from animals under considerable stress, • Blood from animals (not ruminants) slaughtered after examination in a slaughterhouse, • Animal carcass parts and by-products obtained during the manufacture of products intended for human consumption, defatted bones and greaves, and meat and bone meal.

[0089] In preferred embodiments of aspects A1 to A5, as well as the associated embodiments above, the incineration of sewage sludge, biodegradable waste, biowaste and / or animal waste takes place in a waste incineration plant at 600° to 1,200°C, preferably at 800° to 900°C.

[0090] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the reaction of the solids takes place with nitric acid.

[0091] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the reaction of the solids takes place with phosphoric acid.

[0092] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the reaction of the solids takes place with a mineral acid mixture of phosphoric acid and nitric acid and does not contain any hydrohalic acids. In particular, the mineral acid mixture does not contain hydrochloric acid.

[0093] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the mineral acid mixture is present in a concentration of 5 wt.% to 50 wt.%, preferably 10 wt.% to 30 wt.% in aqueous dilution.

[0094] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the phosphate-containing ash is mixed with the mineral acid mixture in a reactor, wherein the proportion of ash is 5 wt.% to 50 wt.%, preferably 20 wt.% to 30 wt.%, based on the diluted mineral acid.

[0095] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the mineral acid mixture contains at least phosphoric and nitric acid.

[0096] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the mineral acid mixture contains sulfuric acid in addition to phosphoric and nitric acid.

[0097] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the reaction time between acid and ash is 2 to 300 minutes, preferably 10 to 60 minutes.

[0098] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the reaction temperature is 20°C to 90°C, preferably 60 to 80°C.

[0099] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the acid-insoluble part of the solids is separated by mechanical filtration and / or dewatering processes.

[0100] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the separation of the acid-insoluble part of the solids takes place using dewatering units (e.g. vacuum belt filter, chamber filter press, membrane filter press, sieve belt press, centrifuge).

[0101] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the separation of the acid-insoluble part of the solids is carried out using a vacuum belt filter.

[0102] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, after separation of the acid-insoluble part of the solids, the residue in the filter units is washed with water and the washing water is returned to the first process stage.

[0103] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the addition of sulfuric acid takes place in a dilution of 10 to 98 wt.%, preferably 40 to 80 wt.%

[0104] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the sulfuric acid is added in a molar ratio corresponding to the dissolved calcium concentration of 0.5 Ca to 1.5 SO4 (sulfate), preferably 1.0 Ca to 1.0 SO4 (sulfate).

[0105] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the addition of sulfuric acid takes place in a stirred reactor.

[0106] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the residence time in the stirred reactor after addition of the sulfuric acid is 5 to 60 minutes, preferably 10 to 30 minutes.

[0107] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the reaction temperature (precipitation of calcium sulfate after addition of sulfuric acid) in the stirred reactor is 20° to 90°C, preferably 60° to 90°C.

[0108] In preferred embodiments of aspects A2, A4 and A5, as well as the associated embodiments above, the calcium sulfate precipitate is separated by mechanical filtration and / or dewatering processes.

[0109] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the calcium sulfate precipitate is separated using dewatering units (e.g. vacuum belt filter, chamber filter press, membrane filter press, sieve belt press, centrifuge).

[0110] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the calcium sulfate precipitate is separated using a vacuum belt filter.

[0111] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, after separation of the calcium sulfate precipitate, the residue in the filter units is washed with water and the washing water is returned to the first process stage.

[0112] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, after separation of the calcium sulfate precipitate, the obtained filtrate (diluted mineral acid mixture) is at least partially reused for digestion of the solids.

[0113] In preferred embodiments of aspects A2, A4 and A5, as well as the corresponding embodiments above, the proportion of recirculation of the filtrate is at least 10%, preferably at least 20%, even more preferably 20% to 80%, and most preferably 40% to 60%, based on the total amount of filtrate obtained.

[0114] In preferred embodiments of aspects A3, A4 and A5, as well as the corresponding embodiments above, after separation of the acid-insoluble part of the ash or after separation of the calcium sulfate precipitate, the pH of the filtrate or the supernatant is increased with alkali or alkaline earth hydroxides or oxides, preferably with sodium hydroxide solution, potassium hydroxide solution, sodium silicate solution, calcium hydroxide or calcium carbonate.

[0115] In preferred embodiments of aspects A3, A4 and A5, as well as the corresponding embodiments above, the pH in a stirred reactor is adjusted to 2.0 to 3.0, preferably to 2.0 to 2.5.

[0116] In preferred embodiments of aspects A3, A4 and A5, as well as the corresponding embodiments above, the residence time in the stirred reactor is 5 to 60 minutes, preferably 10 to 30 minutes.

[0117] In preferred embodiments of aspects A3, A4 and A5, as well as the associated embodiments above, the aluminum hydroxophosphate is separated or recovered by mechanical filtration and / or dewatering processes.

[0118] In preferred embodiments of aspects A3, A4 and A5, as well as the corresponding embodiments above, the separation / recovery of the aluminum hydroxophosphate precipitate is carried out using dewatering units (e.g. vacuum belt filter, chamber filter press, membrane filter press, sieve belt press, centrifuge).

[0119] In preferred embodiments of aspects A3, A4 and A5, as well as the corresponding embodiments above, the separation / recovery of the aluminum hydroxophosphate precipitate is carried out using a filter press.

[0120] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the filtrate or supernatant containing nitric acid (HNO3) and / or phosphoric acid (H3PO4), optionally obtained after deposition of Fe silicate and / or calcium sulfate, and / or aluminum hydroxophosphate, is concentrated by evaporation to an acid content of 30 wt% to 70 wt%, preferably 40 wt% to 60 wt%.

[0121] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the pH value in the filtrate or supernatant containing nitric acid (HNO3) and / or phosphoric acid (H3PO4), optionally obtained after deposition of Fe silicate and / or calcium sulfate, and / or aluminum hydroxophosphate, is adjusted to 4 to 12, preferably 6 to 9, by the addition of calcium oxide or calcium carbonate to form calcium precipitates.

[0122] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, calcium oxide or calcium carbonate is added to the filtrate or supernatant containing nitric acid (HNO3) and / or phosphoric acid (H3PO4), optionally obtained after deposition of Fe silicate and / or calcium sulfate, and / or aluminum hydroxophosphate, in a stirred reactor to form calcium precipitates.

[0123] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, after the formation of calcium precipitates, the solid suspension is evaporated or spray-dried by adding heat to such an extent that a solid with a residual moisture content of 0 wt.% to 25 wt.%, preferably of 2 wt.% to 10 wt.%, is formed.

[0124] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the precipitate(s) is / are present as a completely or partially insoluble precipitate in the form of flakes, droplets or crystalline material, in any microcrystalline, crystalline or amorphous form.

[0125] In preferred embodiments of aspects A1 to A5, as well as the corresponding embodiments above, the precipitate(s) is / are further processed, modified, refined, etc. into powders, dusts, bulk materials, granular materials, semolina, etc. Examples

[0126] The entire process is described by the following test procedure: The starting material is ash from a sewage sludge incineration plant. The main components were analyzed as follows: wt.% P2O5 25,0 wt.% CaO 17,5 wt.% Fe2O3 26,9 wt.% Al2O3 6,7 wt.% SiO2 19,5

[0127] 100g of ash is treated in a beaker with 300g of diluted acid. The diluted acid consists of: 70 wt.% water; 15 wt.% HNO3; and 15 wt.% H3PO4. The suspension is stirred for 30 minutes at 40°C and then filtered through a vacuum filter (with filter). The filter cake is then weighed and dried at 100°C. Wet filter cake = 122 g Dried filter cake = 72 g

[0128] This results in 72 g of ash being insoluble in acid out of 100 g, while 28 g (= 28%) are acid-soluble. A total of 275 g of filtrate was reweighed and subsequently analyzed. The analysis results in the following table were compared with theoretical values ​​that would have resulted if the essential ash contents had dissolved 100% (in the filtrate and the wet portion of the filter cake): (100%) (is) acid-soluble wt.% P2O5 17,78* 13,68 88,7% wt.% CaO 5,37 4,80 89,4% wt.% Fe2O3 8,25 0,47 5,7% wt.% Al2O3 2,06 1,56 75,7% wt.% SiO2 5,98 0,02 0,3% *7.69% P2O5 results from the ash, 10.09% P2O5 from the added phosphoric acid.

[0129] The results demonstrate that high redissolution rates of phosphate, calcium, and aluminum are achieved, while iron is only slightly dissolved and silicon, as expected, is almost insoluble in the form of SiO2. The concentration of H3PO4 has increased from 15 wt.% to 13.68 × 1.37 = 18.7 wt.% (1.37 = the conversion factor from P2O5 to H3PO4). Evaporation by a factor of 2 yields an acid containing 37.4% H3PO4 and 30% HNO3. This acid can be used to produce "Nitrophoska" fertilizer or can be neutralized with CaO and then evaporated, forming a double salt of Ca(NO3)2 * Ca(H2PO4)2.

[0130] This process has the disadvantage that, on the one hand, it requires significant quantities of nitric and phosphoric acid, and, on the other hand, impurities from iron and aluminum salts degrade product quality. The process would be economically unviable and severely limit the added value of the end products.

[0131] These problems, which are particularly serious with higher Al concentrations in the sewage sludge ash (which can be up to more than 20% Al2O3), are solved by the multi-stage process according to the invention in stages 2 and 3 as follows: The filter cake (122 g wet weight) from the described first stage (the ash dissolution process) is washed with 100 g of hot water (70-90°C). The resulting wash filtrate is mixed with 200 g of filtrate from the first stage (dilute acid) containing 25 g of sulfuric acid (48 wt.%) in a beaker (total weight = 100 + 200 + 25 = 325 g). After a few minutes, white calcium sulfate precipitates according to the reaction described above. After 30 minutes, the precipitate is filtered through a vacuum suction filter (with filter). 280 g of filtrate and 43 g of gypsum wet filter cake were obtained. The filtrate was analyzed.

[0132] The analysis results in the following table are compared with values ​​obtained from a parallel experiment in which filtrate from the first stage plus wash water were analyzed in the above-mentioned ratios: Filtrate+WW after Ca precipitation PH value 1,9 0,9 wt.% P2O5 9,58 9,43 wt.% CaO 3,70 1,45 wt.% Fe2O3 0,32 0,33 wt.% Al2O3 0,98 1,01

[0133] The data demonstrate that the Ca content is reduced, as is the pH value, because additional H ions have been able to form. The acidic filtrate from the second stage can now be used to dissolve the ash, eliminating the need for H3PO4 dosing because new phosphoric acid is constantly being formed from the phosphate-containing ash. This stage is particularly important in the multi-stage process because the use of sulfuric acid reduces overall acid costs (sulfuric acid is the most cost-effective acid due to its efficiency) and because additional gypsum is obtained.

[0134] With the recycled filtrate (low-calcium dilute acid), the recipe for the first stage is now as follows: 100 g of ash is treated with 300 g of dilute acid in a beaker. The dilute acid consists of 270 g of recyclate and 20 g of HNO3. The suspension is stirred for 30 minutes at 40°C and then filtered through a vacuum filter (with filter). The filter cake is then weighed and dried at 100°C. Wet filter cake = 130 g Dried filter cake = 75 g

[0135] This means that out of 100 g of ash, 75 g did not dissolve in acid, meaning 25 g (= 25%) were acid-soluble. A total of 258 g of filtrate (dilute acid) was reweighed and subsequently analyzed. The analysis results essentially correspond to the results of the first initial stage; only the CaO content was slightly higher at 5.8% CaO (because additional calcium was introduced via the recyclate), while the Al2O3 content increased further from 1.5 to 2.6%. In a third stage, the aluminum concentration in the dilute acid is reduced by adding small amounts of calcium oxide. For this purpose, 150 g of dilute acid is mixed with 1 g of CaO at room temperature. A precipitate formed, which was filtered through a vacuum Nutsche filter (with filter) after 15 minutes. 123 g of filtrate and 25 g of wet filter cake were obtained. The filtrate was analyzed.

[0136] The analysis results in the following table are compared with values ​​obtained from a parallel experiment in which the dilute acid was analyzed before the addition of CaO. Thin acid after Al precipitation PH value 0,9 2,2 wt.% P2O5 9,35 8,95 wt.% CaO 5,84 6,42 wt.% Fe2O3 0,54 0,48 wt.% Al2O3 2,61 0,84

[0137] A slight increase in pH resulted in the formation of an Al-PO4 precipitate, which is evident in the decreased values ​​for P2O5 and Al2O3. The precipitation intentionally reduces the values ​​only slightly, as it is intended to prevent excessive accumulation of Al ions. The precipitate, washed with water and dried, was analyzed as follows: wt.% P2O5 31,3 wt.% CaO 1,1 wt.% Fe2O3 3,5 wt.% Al2O3 56,1

[0138] The precipitate was further treated in a further experiment according to patent DE 10 2012 015 065 B3 2013.07.18 and converted into sodium aluminate solution and a calcium phosphate precipitate.

[0139] The process steps described here can be applied variably depending on the concentration of Ca and Al ions in the digestion acid (or the corresponding oxide concentrations in the ash). The essence of the invention is that the combination of process steps enables economical process management and, above all, low-aluminum end products.

[0140] The purified HNO3-H3PO4 acid is preferably neutralized with CaO to a pH of 6 and concentrated by water evaporation, e.g., by spray drying. A double salt of calcium nitrate and calcium phosphate is formed. According to the invention, a salt with the following composition could be produced: 19.5 wt.% P2O5; 28.5 wt.% CaO; 24.3 wt.% NO3; 0.8 wt.% Al2O3; 0.6 wt.% Fe2O3.

[0141] Fig. shows the different process flows in the diagram.

Claims

[1] Process for the recovery of precipitates selected from the group consisting of calcium nitrate, calcium phosphate, calcium sulfate and aluminum hydroxophosphate from phosphate-containing solids and for the optional production of phosphoric acid, the process comprising at least the recovery of calcium sulfate, characterized by , that a) the phosphate-containing solids are reacted with nitric acid or phosphoric acid or a mineral acid mixture of the two acids, b) the acid-insoluble part of the solids is separated, c) a pH value of <1 is adjusted by adding sulphuric acid to the filtrate or supernatant, and calcium sulphate precipitate is obtained and separated, and d) at least 10% of the filtrate or supernatant, based on the total amount of filtrate obtained, is recycled for use in step a), and that the phosphate-containing solids are phosphate-containing ashes obtained by incineration of sewage sludge, biodegradable waste, biowaste and / or animal waste in a waste incineration plant. [2] Method according to claim 1, characterized by , that e) the filtrate or supernatant is concentrated, preferably by evaporation, to obtain phosphoric acid or nitrous phosphoric acid, and / or f) calcium phosphate precipitate and calcium nitrate precipitate are obtained and separated by adding calcium oxide or calcium carbonate to the filtrate or supernatant. [3] Method according to claims 1 and 2, characterized bythat in step d) at least 20% of the filtrate or supernatant is recycled for use in step a), preferably 20% to 80% of the filtrate or supernatant is recycled for use in step a), and more preferably 40% to 60% of the filtrate or supernatant is recycled for use in step a), based on the total amount of filtrate obtained.

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