Method for processing ash or ash fractions

Abstract

The present invention relates to a process for processing bottom ash or post ash fractions containing iron and / or aluminum as well as copper, comprising the following steps: a) extraction of the bottom ash or post ash fraction with an aqueous mineral acid to obtain a mineral-acidic aqueous extract (E) and a solid (F), wherein the extract (E) contains mineral-acidic iron and aluminum salts as well as copper salts in dissolved form; b) separation of the acidic aqueous extract (E) from the solid (F); c) separation of the copper from the extract (E) obtained in step b) by electrolysis of the extract (E) to obtain a copper-depleted extract (E');d) Optionally, precipitation of a salt mixture comprising aluminium and iron in the form of their mineral salts from the extract (E') obtained in step c) by measures to reduce the solubility of the aluminium salts and the iron salts in the extract (E') followed by solid-liquid separation to obtain one of the salt mixtures as a solid (F'). The present invention further relates to the use of the work-up products obtained by the process as phosphate precipitants.

Description

[0001] The present invention relates to a process for processing bottom ash or bottom ash fractions containing iron and / or aluminium as well as copper.

[0002] Household waste is predominantly thermally treated today, meaning it is incinerated to generate thermal energy. The residue remaining from this process is called bottom ash. Bottom ash consists primarily of silicate components, iron, and non-ferrous metals such as calcium, iron, aluminum, magnesium, and copper, which can be present in the form of oxides, salts, silicates, or even in elemental form.

[0003] Typically, bottom ash is a heterogeneous mixture of different fractions, such as unburned material, shards, stones, ceramics, sand, slag, and metal parts. A large proportion of bottom ash is already processed, with elemental ferrous and non-ferrous metals usually being separated beforehand and reintroduced into the material cycle as scrap. The remainder is separated into various fractions using screening and other physical methods. Some of these fractions are used in road and landscape construction, others in underground construction, and still others must be disposed of in landfills. The possibilities for utilizing bottom ash in this way are naturally limited. Given the increasing amount of household waste and thus bottom ash, problems with its disposal are to be expected.

[0004] There has long been an effort to recover the copper contained in bottom ash, which is particularly concentrated in the 0-10 mm fraction. This fraction often has a copper content comparable to that of low-copper copper ores, frequently around 0.2-0.4 wt%, based on this fraction, and is considered elemental copper. Copper recovery from bottom ash has thus far failed because even from the comparatively copper-rich 0-10 mm fraction, such recovery has not been economically viable. Furthermore, due to the high accompanying concentrations of iron, aluminum, magnesium, calcium, halides, and other, sometimes toxic, transition metals, this bottom ash fraction could not be utilized and had to be disposed of in landfills.

[0005] Therefore, there is a need for further possibilities of utilizing bottom ash, especially copper-containing bottom ash fractions such as the 0-10mm bottom ash fraction.

[0006] Phosphate recovery in wastewater treatment plants, process water, and other phosphate-containing water streams is often achieved through the use of inorganic flocculants. These typically contain iron(II), iron(III), and / or aluminum salts, and optionally calcium, magnesium, or other transition metal salts in the form of acidic aqueous solutions.

[0007] These solutions are comparatively expensive and sometimes not available in the required quantities. Given the increasing importance of phosphate recovery from such water streams, supply shortages of inorganic flocculants are to be expected.

[0008] Surprisingly, it was found that the multi-stage aqueous digestion process of bottom ash or bottom ash fractions containing iron, aluminium and copper, described in more detail below, using mineral acids such as hydrochloric acid or sulfuric acid, yields products suitable as phosphate precipitants and particularly suitable for the recovery of phosphate from wastewater streams generated in sewage treatment plants.

[0009] Accordingly, the present invention relates to a process for the processing of bottom ash or bottom ash fractions containing iron and / or aluminium as well as copper, comprising the following steps: a) Extraction of the bottom ash or the bottom ash fraction with an aqueous mineral acid to obtain a mineral-acidic aqueous extract (E) and a solid (F), wherein the extract (E) contains mineral iron and / or aluminum salts as well as copper salts in dissolved form; b) Separation of the acidic aqueous extract (E) from the solid (F); c) Separation of the copper from the extract (E) obtained in step b) by electrolysis of the extract (E) to obtain a copper-depleted extract (E'); d) Optionally, precipitation of a salt mixture comprising aluminum and iron in the form of their mineral salts from the extract (E') obtained in step c) by measures to reduce the solubility of the aluminum salts and the iron salts in the extract (E') followed by solid-liquid separation to obtain one of the salt mixtures as a solid (F').

[0010] If necessary, steps c) or d) may be followed by a preparation step e) in which the extract (E') obtained in step c) or the salt mixture or solid (F') obtained in step d) is prepared as an aqueous phosphate precipitant.

[0011] The invention also relates to the use of the extract (E') obtained in step c) of the process according to the invention as a phosphate precipitating agent.

[0012] The invention further relates to the use of the salt mixture obtainable in step d) of the process according to the invention as a phosphate precipitating agent.

[0013] The process according to the invention has a number of advantages. In particular, it opens up a further economically viable use for bottom ash. Firstly, a valuable material, namely a phosphate precipitant, can be surprisingly obtained inexpensively from the large quantity of bottom ash, a "waste material." This phosphate precipitant's performance is at least comparable to that of commercially available phosphate precipitants, the production of which requires expensive pure substances, and thus represents a cost-effective alternative. Supply bottlenecks with inorganic flocculants can be avoided in this way. Simultaneously, the recovery of the copper contained in the bottom ash becomes economically attractive due to the coupling of the phosphate precipitant production with the supply of the phosphate precipitants.At the same time, the bottom ash is at least partially put to economically viable use, thus reducing the costs of its disposal. Since the digestion solution typically contains iron in addition to copper, the copper electrolysis is coupled with the oxidation of Fe(II) to Fe(III). This results in a low voltage, which facilitates copper deposition and reduces or even completely prevents the side reaction of oxygen formation at the anode. Furthermore, the formation of Fe(III) leads to a higher capacity for phosphate precipitation relative to the iron content.

[0014] In principle, any grate ash and grate ash fractions containing iron and / or aluminium and copper can be used in the process according to the invention.

[0015] It has proven advantageous not to use the entire bottom ash, but rather to first fractionate the bottom ash and remove the unburned material, i.e., organic, unburned components from the combustion residue of household waste such as wood, paper, or plastic, and then to use the bottom ash thus depleted in the process according to the invention. This can be done in a manner known per se, for example, by sieving or classifying, e.g., air classification or eddy current classification, of the combustion residue, or by combinations of these measures in a manner known per se. Accordingly, a preferred embodiment of the invention relates to a process in which, in step a), a fractionated bottom ash is used from which the unburned material has been previously removed. In particular, a bottom ash that has undergone at least one coarse sieving stage will be used.This step is usually carried out directly at the processing plants and is performed with mesh sizes of, for example, 32 mm, 40 mm, 45 mm, 50 mm, or 120 mm. For external bottom ash processors, this first screening step is typically at 50 mm or 45 mm. Depending on the mesh size of the screening and the composition of the municipal waste, the proportion of recyclable bottom ash can vary.

[0016] If necessary, metallic components will be removed before step a). This can be done, for example, by screening, e.g., air screening, eddy current screening, or ballistic separation, and / or by magnetic separation. Accordingly, a preferred embodiment of the invention relates to a process in which, in step a), fractionated bottom ash is used from which the metallic components have previously been removed. In particular, bottom ash that has undergone at least one coarse screening stage will be used. This step is generally carried out directly at the plant and is performed with mesh sizes of, for example, 32 mm, 40 mm, 45 mm, 50 mm, or 120 mm. At external bottom ash processors, this first screening stage is, for example, 50 mm or 45 mm. Depending on the mesh size of the screening and the composition of the municipal solid waste, the proportion of recyclable bottom ash can vary.In particular, in step a) a fractionated bottom ash will be used, from which both the unburned material and metallic components have previously been removed.

[0017] According to the invention, the grate ash or grate ash fraction used in step a) contains aluminum and / or iron as well as copper. These elements are typically not present, or at least not exclusively, in elemental form, but can be present, for example, in the form of oxides, sulfides, or other salts, e.g., carbonates, silicates, sulfates, or halides. In particular, grate ash fractions are used which contain aluminum and / or iron as well as copper in the following proportions: Aluminum: 0 to 80,000 mg / kg, e.g. 10,000 to 80,000 mg / kg, in particular 10,000 to 50,000 mg / kg, based on the total weight of the bottom ash and calculated as elemental aluminium; Iron: 0 to 300,000 mg / kg, e.g. 5,000 to 300,000 mg / kg, often 5,000 to 150,000 mg / kg or 5,000 to 100,000 mg / kg, but also higher in magnetically separated fractions, for example up to 300,000 mg / kg, based on the total weight of the bottom ash and calculated as elemental iron; Copper: 1000 mg / kg to 7,000 mg / kg, based on the total weight of the bottom ash and calculated as elemental copper, wherein the total aluminum and iron content is at least 5000 mg / kg, preferably 10,000 mg / kg, and specifically at least 15,000 mg / kg, and is particularly in the range of 10,000 to 300,000 mg / kg, preferably in the range of 10,000 to 230,000 mg / kg, and specifically in the range of 15,000 to 150,000 mg / kg. The metal contents specified here and below refer to the dry matter content of the bottom ash, i.e., bottom ash that has been dried to constant weight.

[0018] The bottom ash fraction used in step a) often contains calcium in addition to the aforementioned elements, e.g., in the form of carbonates, oxides, or sulfates. The calcium content can vary considerably depending on the bottom ash fraction and its origin, and is frequently in the range of 50,000 to 300,000 mg / kg, based on the total weight of the bottom ash and calculated as elemental calcium.

[0019] The bottom ash typically contains significant amounts of silicon in silicate form. The silicon content varies depending on the ash fraction and its origin, often ranging from 50,000 to 400,000 mg / kg, based on the total weight of the ash and calculated as elemental silicon.

[0020] Furthermore, the bottom ash fraction used in step a) may contain one or more elements from the following groups, which are different from the aforementioned elements iron, aluminium, copper and calcium: Alkali metals and alkaline earth metals such as sodium, potassium, magnesium, strontium or barium; heavy metals such as lead, cadmium, cobalt, chromium, manganese, nickel, mercury, titanium, tungsten, zirconium, zinc or tin; non-metals and metalloids such as silicon, for example in the form of silicates, halogens such as fluorine or chlorine, especially in the form of halides, sulfur, for example in the form of sulfate or phosphorus, for example in the form of phosphate.

[0021] The composition of the bottom ash can be determined by elemental analysis in a manner known per se. Suitable methods for this include inductively coupled plasma optical emission spectroscopy (ICP-OES), atomic absorption spectroscopy, and X-ray fluorescence spectroscopy. The analysis of the metal and metalloid content is generally carried out according to the specifications of DIN EN ISO 11885 (2009-09).

[0022] For the process according to the invention, it proves advantageous to use a so-called 0-10 mm grate ash fraction, as this has a high content of copper, iron, and aluminum. This refers to a grate ash fraction with a maximum particle size of 10 mm. The maximum particle size specified here refers to the sieve fraction determined by sieving. This grate ash fraction is typically obtained by classifying grate ash from which the unburned material and scrap have first been removed.

[0023] In step a), the bottom ash or bottom ash fraction, in particular the 0-10 mm bottom ash fraction, is extracted with an aqueous mineral acid, yielding a mineral-acidic aqueous extract (E) containing dissolved iron and aluminum salts as well as copper salts from the bottom ash or bottom ash fraction used. Mineral-acidic salts are defined as the salts of the metals extracted in step a) from the bottom ash or bottom ash fraction, which have the acid anion of the mineral acid used as their anion; in the case of hydrochloric acid, the chlorides, and in the case of sulfuric acid, the sulfates or hydrogen sulfates.

[0024] The extraction in step a) is carried out by treating the bottom ash or bottom ash fraction with the aqueous mineral acid, analogous to known extraction processes for inorganic materials using mineral acid. Generally, the bottom ash is mixed directly with the mineral acid. Preferably, the mineral acid is used in such a quantity that a suspension of the bottom ash or bottom ash fraction is obtained in the aqueous mineral acid. Alternatively, the aqueous mineral acid can be passed through a bed of bottom ash or bottom ash fraction. In this case, a specific quantity of the aqueous mineral acid is preferably passed through the bed of bottom ash or bottom ash fraction in a closed loop until the desired degree of extraction is achieved.

[0025] Preferably, the mineral acid is used in an amount of at least 1 kg per kg of bottom ash or bottom ash fraction, for example in an amount of 1 kg to 100 kg, in particular in an amount of 2 kg to 50 kg and especially in an amount of 5 kg to 20 kg, per kg of bottom ash or bottom ash fraction.

[0026] In the extraction process, a mineral acid is preferably used whose pKa value is equal to or lower than that of hydrochloric acid. Such mineral acids and their pKa values ​​are known to those skilled in the art and can be found in relevant reference tables. Sulfuric acid and hydrochloric acid are preferred mineral acids.

[0027] For the extraction performance in step a), it has proven advantageous to carry out the extraction at a pH of no more than 1, in particular no more than 0.7 or 0.5. Lower pH values, such as 0 or below, are also possible, but not necessary. The pH can be adjusted in a known manner by adding mineral acid. Naturally, the pH can be monitored during the extraction, for example using a pH electrode, and maintained within these limits if necessary by adding more acid.

[0028] The pH values ​​given here and below refer to values ​​determined at 25°C and 1 bar using a pH electrode.

[0029] For the extraction performance in step a), it has proven advantageous if the aqueous mineral acid used has a concentration of at least 5 molar equivalents H+, e.g. 5 to 20 molar equivalents H+ per liter.

[0030] The extraction in step a) is usually carried out at a temperature in the range of 10 to 100 °C, preferably 15 to 80 °C, particularly 20 to 50 °C.

[0031] The extraction in step a) is usually carried out at a pressure in the range of atmospheric pressure (101 ± 20 kPa), but can also be carried out at higher pressures, for example up to 150 kPa, e.g. at pressures in the range of 80 to 150 kPa.

[0032] The duration of the treatment of the bottom ash or bottom ash fraction with the mineral acid in step a) is generally at least 24 h, in particular at least 48 h, and is frequently in the range of 24 to 480 h, especially in the range of 48 to 240 h. The treatment is generally carried out until at least 50 mol% of the iron, aluminium and copper contained in the bottom ash or bottom ash fraction has been extracted.

[0033] For improved extraction performance, it has proven advantageous to pass an oxygen-containing gas, such as air or oxygen, through the mixture of mineral acid and bottom ash during extraction. Preferably, one passes 1 to 200 times the volume of air per hour, equal to the volume of the aqueous mineral acid and bottom ash or bottom ash fraction mixture, through the mixture. Generally, care is taken to ensure a fine distribution of the air within the mixture.

[0034] Step a) can be carried out successfully both discontinuously and continuously. The method according to the invention can also be carried out on an industrial scale. Suitable devices are known to those skilled in the art.

[0035] In step b), the acidic aqueous extract (E) is separated from the solid (F). The separation is carried out in a manner known per se, using conventional solid-liquid separation methods, e.g., by sedimentation, decantation, centrifugation, or filtration, or by a combination of these methods.

[0036] If the mineral acid is passed through a bed of bottom ash or bottom ash fraction, the solid-liquid separation occurs during the extraction in step a), so that further separation is not necessary. Any particles of bottom ash or bottom ash fraction that may be entrained during the passing process can be removed from the extract (E), for example, by filtration or centrifugation.

[0037] The resulting solid material (F) is usually recycled or used using known methods, for example as backfill material in road construction.

[0038] The extract (E) obtained in step b) is subjected to electrolysis in step c) to recover the copper it contains. The electrolysis in step c) is carried out in a manner known per se, analogous to the electrolytic deposition of copper from aqueous acidic solutions. In this way, copper is recovered as a valuable material, and an aqueous solution depleted of copper, hereinafter also referred to as extract (E'), is obtained. This extract contains the other metals extracted from the bottom ash or bottom ash fraction in step a), in particular iron and aluminum, and optionally calcium, magnesium, and various heavy metals.

[0039] This removal of copper from the extract (E) typically takes place as a recovery electrolysis, i.e. in the form of electrolysis in which the copper is reduced by electrolysis at the cathode and deposited on it as metal.

[0040] The electrolysis of aqueous copper-containing solutions for copper extraction has long been known and can be carried out analogously for copper removal and thus also for copper recovery. Preferably, the electrolysis is performed at pH values ​​of no more than pH 2, particularly at pH values ​​in the range of pH 0 to pH 2. The electrolysis can be carried out, for example, at temperatures in the range of 10 to 50 °C. The electrolysis can be performed in undivided or divided electrolysis cells. Preferably, the electrolysis is potentiostatic. Preferably, voltages in the range of 0.5 to 4 V are used. The current density is preferably in the range of 1 to 150 mA / cm². Preferably, at least 90%, and in particular at least 95%, of the copper contained in the extract (E) will be removed in this way.

[0041] The removal of copper from the extract (E) by electrolysis can be carried out in a manner known per se, as described, for example, in Modern Electroplating, Schlesinger, Mordechay, Paunovic, Milan (Editors), Electrochemical Society Series, 5th Edition 2010, New York, Wiley & Sons Ltd. Copper is generally used as the cathode material, so that the deposited copper, in the form of the entire electrode, can be used for further processing or purification. Carbon-containing materials, such as glassy carbon or graphite, are generally used as the anode material. Copper deposition can be carried out in a divided or undivided electrolysis cell.

[0042] The electrolytic deposition of copper in the presence of iron leads to a reduced current efficiency, as the Fe(II) / Fe(III) redox couple reacts at the electrodes. At the cathode, for example, Fe(III) can be reduced to Fe(II), and at the anode, Fe(II) can be oxidized to Fe(III). In these cases, it can be advantageous to carry out the copper deposition in a divided cell. There are otherwise no special requirements regarding the cell geometry or the separators. Simple materials such as glass frits or ceramic membranes can be used as separators. The procedure involves removing the copper from the catholyte and feeding the copper-depleted catholyte into the anode compartment, where Fe(II) is oxidized to Fe(III). This yields an extract (E') with an increased proportion of Fe(III) relative to the iron content. Furthermore, the side reaction, i.e.,The formation of oxygen is largely avoided, so that lower clamping voltages can be used.

[0043] The copper-depleted extract (E') obtained in step c) typically has a pH in the range of pH 0 to pH 2. The extract typically contains iron, aluminum, and optionally calcium and magnesium. The concentrations of these metals in the extract (E') are typically in the following ranges. i) 5 to 91 g / kg aluminium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental aluminium; and / or ii) 5 to 885 g / kg iron in the form of a mineral salt, in particular in the form of its chloride or sulfate; optionally iii) 0 to 148 g / kg, e.g. 1 to 148 g / kg calcium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental calcium; iv) 0 to 280 g / kg, e.g. 1 to 280 g / kg magnesium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental magnesium.

[0044] The elemental composition of the previously described extracts (E) and (E'), as well as the elemental composition of the solids (F) and (F'), can be determined by elemental analysis in a manner known per se. Suitable methods for this purpose include, in particular, inductively coupled plasma optical emission spectroscopy (ICP-OES), atomic absorption spectroscopy, and X-ray fluorescence spectroscopy. The analysis of the metal and metalloid content is generally carried out according to the specifications of DIN EN ISO 11885 (2009-09).

[0045] In addition to iron, aluminum, and possibly calcium and magnesium, the copper-depleted extract (E') obtained in step c) often contains one or more heavy metals such as lead, cadmium, cobalt, chromium, manganese, nickel, mercury, titanium, tungsten, zirconium, zinc, or tin, as well as potentially residual amounts of copper. Even though their concentrations in the extract (E') are generally low, these heavy metals can be problematic for the direct use of the extract as a phosphate precipitant. Therefore, it may be desirable to largely or completely separate them from the iron and aluminum mineral salts contained in the extract (E').

[0046] Surprisingly, the heavy metal salts contained in the extract (E') are largely or completely separated from the aluminum and iron salts and any calcium and / or magnesium salts present in the extract (E') by causing the precipitation of a salt mixture comprising aluminum and iron in the form of their mineral salts in the extract (E') through measures to reduce the solubility of the aluminum and iron salts in the extract (E') and subsequently carrying out a solid-liquid separation. This yields a solid (F') that essentially contains mineral salts of aluminum and iron, and optionally mineral salts of calcium and possibly magnesium, but essentially none of the aforementioned heavy metals or their salts. The mineral salts are, in particular, the chlorides, sulfates, and hydrogen sulfates.

[0047] In particular, the reduction in the solubility of the aluminium salts and the iron salts in the extract (E') is effected by shifting the solubility product, especially by adding anions of the aluminium salts and the iron salts, especially by adding sulfate or chloride.

[0048] Preferably, the anions are added in such a way that the concentration of the anion in the extract (E') is in the range of 3 to 18.3 mol / L.

[0049] In particular, a concentrated mineral acid, such as sulfuric acid, hydrochloric acid, or HCl gas, especially sulfuric acid, is added to the extract (E') in step d) to reduce the solubility of the aluminum and iron salts. The pH of the extract (E') may drop to pH < 1 upon addition of a mineral acid without this being detrimental.

[0050] The precipitation in step d) preferably takes place at temperatures in the range of 0 to 50 °C, preferably in the range of 1 to 40 °C, and particularly in the range of 5 to 30 °C.

[0051] The precipitation in step d) is usually carried out at a pressure in the range of atmospheric pressure (101 ± 20 kPa), but can also be carried out at higher pressures, for example up to 150 kPa, e.g. at pressures in the range of 80 to 150 kPa. When using HCl gas, pressures up to 4260 kPa can also be used.

[0052] Following precipitation in step d), a solid-liquid separation is carried out to separate the salt mixture, also referred to here as the solid (F'), from the remaining aqueous liquid phase. The separation is performed in a manner known per se, using conventional solid-liquid separation methods, e.g., by sedimentation, decantation, centrifugation, or filtration, or by a combination of these methods.

[0053] The resulting solid (F') is suitable, like the extract (E'), as a phosphate precipitating agent. In contrast to the extract (E), the solid (F') contains significantly fewer heavy metals relative to the total iron and aluminum content. While the heavy metal content (lead, cadmium, chromium, nickel, mercury, and nickel) in the extract (E') is frequently in the range of 0.1 to 5 wt.%, often 0.2 to 2 wt.%, relative to the total iron and aluminum content in the extract (E), the heavy metal content (lead, cadmium, chromium, mercury, and nickel) in the solid (F') is frequently in the range of 0 to <1 wt.%, relative to the total iron and aluminum content in the solid (F'). The copper and zinc content in the extract (E') is frequently in the range of 0.5 to <16 wt.%, particularly in the range of 0.5 to 10 wt.%. The copper and zinc content in the solid (F') is often in the range of 0 to <10 wt. %, in particular 0 to 0.2 wt. %,.

[0054] In particular, the solid (F') contains i) 0 to 220 g / kg, e.g. 5 to 200 g / kg aluminium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental aluminium; ii) 0 to 440 g / kg, e.g. 10 to 400 g / kg iron in the form of a mineral salt, in particular in the form of its chloride or sulfate; wherein the total amount of iron and aluminium is at least 20 g / kg and in particular in the range of 50 to 400 g / kg; and optionally iii) 0 to 180 g / kg, e.g. 0.1 to 180 g / kg calcium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental calcium; iv) 0 to 15 g / kg, e.g. 0.1 to 15 g / kg magnesium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental magnesium; and preferably has a total content of the heavy metals lead, cadmium, chromium, nickel, mercury, and nickel of less than 1.3 g / kg based on the total content of iron and aluminum. The content of copper and zinc in the solid (F') is less than 2.0 g / kg based on the total content of iron and aluminum.

[0055] The salt mixture obtained in step d), i.e. the solid (F'), can then be prepared as an aqueous phosphate precipitant (step e)).

[0056] Step e) can be carried out simply by dissolving the solid (F') in water, in a mineral acid (optionally diluted with water), in the mineral acid extract (E) (optionally diluted with water), or in the mineral acid extract (E'), or in mixtures thereof. Suitable mineral acids are, in particular, hydrochloric acid and / or sulfuric acid. In one embodiment, the mineral acid extract (E) or the mineral acid extract (E'), optionally diluted with water, is used for dissolving. Optionally, further hydrochloric acid and / or sulfuric acid is added for dissolving. Preferably, the mineral acid extracts (E) or (E') and the mineral acid are used in a total amount in such a ratio to the solid (F') that a pH value between 0.5 and 6 is achieved. If the solid (F') is incompletely dissolved, it is preferably necessary to separate any undissolved components.

[0057] All descriptions of steps a), b), c), d) and e) of this invention relate to both laboratory and industrial scales. The steps can be performed continuously or discontinuously.

[0058] The ready-made phosphate precipitant typically contains the following metals, based on the total weight of the phosphate precipitant: i) 0 to 200 g / kg aluminium, e.g. 5 to 200 g / kg, in particular 10 to 150 g / kg aluminium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental aluminium; ii) 0 to 500 g / kg iron, e.g. 5 to 500 g / kg, in particular 8 to 450 g / kg in the form of a mineral salt, in particular in the form of its chloride or sulfate; wherein the total amount of iron and aluminium is at least 10 g / kg and in particular is in the range of 10 to 450 g / kg, calculated as the total amount of elemental iron and aluminium; optionally iii) 0 to 35 g / kg, e.g. 0.1 to 35 g / kg calcium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental calcium; iv) 0 to 10 g / kg, e.g. 0.5 to 10 g / kg magnesium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental magnesium; and preferably has a total content of the heavy metals lead, cadmium, chromium, nickel, mercury and zinc of less than 0.2 g / kg, in particular less than 0.1 g / kg.

[0059] The pH value of the prepared phosphate precipitant is typically a maximum of pH 2.0 at 25°C and 1 bar.

[0060] In an advantageous embodiment of the process according to the invention, a portion of the bottom ash or bottom ash fraction is extracted in step a) first with hydrochloric acid and then in step a') with sulfuric acid. The extracts (E1) and (E2) obtained are then subjected separately to electrolysis to remove copper. Subsequently, the copper-depleted extracts (E1') and (E2') are combined, and the solid (F') is obtained according to the procedure described in step d). In particular, the following procedure will be used: a1) Extraction of an initial quantity of the bottom ash or the bottom ash fraction with aqueous hydrochloric acid to obtain an aqueous hydrochloric acid extract (E1) and a solid (F1); b1) Separation of the aqueous hydrochloric acid extract (E1) from the solid (F1); c1) Optionally, removal of the copper from the extract (E1) obtained in step b1) by electrolysis of the extract (E1) to obtain a copper-depleted extract (E1'); a2) Extraction of the bottom ash or the bottom ash fraction, previously treated with hydrochloric acid and depleted of Ca and Mg, with aqueous concentrated sulfuric acid to obtain an aqueous sulfuric acid extract (E2) and a solid (F2); b2) Separation of the aqueous sulfuric acid extract (E2) from the solid (F2); c2) Depleting the copper from the extract (E2) obtained in step b2) by electrolysis of the extract (E2) to obtain a copper-depleted extract (E2');d') Precipitation of a salt mixture comprising aluminium and iron in the form of their mineral salts from the extract (E2') obtained in step c2) by adding sulfuric acid, followed by solid-liquid separation to obtain the salt mixture as a solid (F2'). e') Optionally dissolving the solid (F2') in the hydrochloric acid extract (E1) or, in particular, (E1') and optionally separating the solution (L) obtained from the undissolved material.

[0061] Here, steps a1) and a2), b1) and b2), c1) and c2), d') and e') are carried out analogously to steps a), b), c), d) and e).

[0062] Step e') can be carried out simply by dissolving the solid (F2') in the hydrochloric acid extract (E1) or the hydrochloric acid extract (E1') or mixtures of (E1) with (E1'). If necessary, further hydrochloric acid and / or sulfuric acid is added for dissolution. Preferably, the hydrochloric acid extracts (E1) or (E1') and the acid are used in a ratio to the solid (F2') such that a pH value between 0.5 and 6 is achieved.

[0063] In step e'), the sulfate anion is easily exchanged for the iron and aluminum sulfates contained in the solid (F2'), which are thereby converted into chlorides. This is due to the lower solubility product of the sulfate salts compared to the solubility product of the chlorides. A complex ion exchange process using a membrane is not required. The resulting aqueous hydrochloric acid solutions of aluminum and / or iron are particularly advantageous because, when used for phosphate precipitation in wastewater treatment plants, they not only cause phosphate precipitation but also inhibit the growth of filamentous bacteria due to their content of acidic halogen salts of iron and aluminum.

[0064] Any undissolved material that may be obtained in step e') is usually high-purity gypsum, which can be used in the usual way.

[0065] The phosphate precipitants obtainable according to the invention, i.e. the liquid-prepared solids (F') or the extracts (E') can be used in a manner known per se for the precipitation of phosphate from wastewater and exhibit an effect comparable to conventional inorganic phosphate precipitants.

[0066] The following examples serve to illustrate the invention. Examples I. Analytical Methods Inductively coupled plasma optical emission spectroscopy (ICP-OES):

[0067] The samples were measured using the Shimadzu Germany ICPE-9820 with an echelle semiconductor detector (CCD). The procedures were generally carried out in accordance with the specifications of DIN EN ISO 11885 (2009-09). X-ray fluorescence spectroscopy:

[0068] The analyses were performed using semi-quantitative X-ray fluorescence analysis. The Omnian program was used as the evaluation software. This technique detects all elements with atomic number 9 and above (fluorine). With the exception of halogens and precious metals, all elements are calculated as oxides and normalized to 100% by including the estimated proportion of lighter elements. Atomic absorption spectrometry (AAS):

[0069] The procedure was carried out in accordance with the specifications of DIN EN ISO 12846 (2012-06) II. Production of phosphate precipitating agents Example 1: Production of a phosphate precipitant from bottom ash by digestion with HCl (steps a) to c)) Steps a) and b)

[0070] Ten kilograms of bottom ash (fraction with grain sizes of approximately 0 to 10 mm) were slowly added to 7 liters of 37% aqueous hydrochloric acid. The pH was then adjusted to 0.5 by adding another 0.6 liters of the 37% aqueous hydrochloric acid. The mixture was then aerated and stirred for 7 days.

[0071] Undissolved solids were then separated from the digestion solution by sedimentation followed by filtration. This yielded 6.8275 kg of solids and 5.5 L of filtrate.

[0072] The solid obtained by sedimentation was separated into two fractions by sieving: a coarse fraction with grain sizes of 3 to 10 mm and a medium-coarse fraction with grain sizes of >0.1 to <3 mm. Filtration also yielded a fraction of fine material with grain sizes smaller than 0.1 mm, as well as the filtrate.

[0073] The coarse and medium-coarse fractions were further subdivided by using a magnet to separate the magnetic from the non-magnetic components. Additionally, glass and ceramic fragments were manually removed from the non-magnetic components of the coarse fraction to gain a clearer picture of the mineral content. Thus, the medium-coarse fraction was divided into two sub-fractions and the coarse fraction into three, as summarized in Table 1 below. Table 1: Solid fractions obtained fraction sub-faction Grain sizes (estimated) Fine - <0.1 mm Medium-coarse Magnetic component >0.1 - <3 mm Non-magnetic component Rough Magnetic component 3 - 10 mm Non-magnetic component - mineral Non-magnetic component - glass and ceramics

[0074] The recovered solid fractions, with the exception of the non-magnetic glass / ceramic component of the coarse fraction, were analyzed for their composition. The results are summarized in Tables 2 to 6. Table 2: Semi-quantitative analysis of the fine fraction by X-ray fluorescence spectroscopy ingredient Portion [%] SiOz 34,60 Cl 21,47 CaO 14,43 Al2O3 8,04 SO 3 6,32 Fe2O3 5,99 TiOz 1,89 P2O5 1,30 K2O 1,27 NazO 1,22 MqO 1,14 CuO 0,58 ZnO 0,50 BaO 0,35 F 0,31 MnO 0,22 Cr 2 O 3 0,12 PbO, ZrO2, NiO, SrO, Co3O4, SnOz < 0,1 Table 3: Semi-quantitative analysis of the non-magnetic fraction of the medium-coarse fraction by X-ray fluorescence spectroscopy ingredient Portion [%] SiOz 71,41 Al2O3 9,31 CaO 5,48 NazO 3,09 K2O 2,54 Fe2O3 1,85 Cl 1,73 MqO 1,62 TiOz 1,18 P2O5 0,54 SO 3 0,42 BaO 0,18 ZnO 0,17 CuO 0,14 MnO, PbO, ZrO2, Cr2O3, SrO, WO3, Co3O4, NiO < 0,1 Table 4: Semi-quantitative analysis of the magnetic fraction of the medium-coarse fraction by X-ray fluorescence spectroscopy ingredient Portion [%] SiOz 49,16 Fe2O3 19,41 Al2O3 9,63 CaO 7,96 NazO 2,66 MqO 2,30 TiOz 1,98 K2O 1,92 Cl 1,77 P2O5 0,98 SO 3 0,55 Cr 2 O 3 0,31 BaO 0,30 MnO 0,27 CuO 0,26 ZnO 0,22 NiO, ZrO2, PbO, SrO, Co3O4, SnOz, Sb2O3 < 0,1 Table 5: Semi-quantitative analysis of the non-magnetic fraction of the coarse fraction by X-ray fluorescence spectroscopy ingredient Portion [%] SiOz 63,36 CaO 10,36 Al2O3 9,87 NazO 3,95 Fe2O3 3,61 K2O 2,15 MqO 1,80 Cl 1,46 TiOz 1,11 P2O5 0,76 SO 3 0,50 BaO 0,27 CuO 0,18 MnO 0,16 ZnO 0,16 PbO, Cr 2 O 3 , ZrOz, SrO, WO 3 , NiO, Co 3 O 4 < 0,1 Table 6: Semi-quantitative analysis of the magnetic fraction of the coarse fraction by X-ray fluorescence spectroscopy ingredient Portion [%] SiOz 48,24 Fe2O3 16,46 CaO 13,15 Al2O3 8,68 NazO 3,78 MqO 2,22 K2O 1,48 TiOz 1,46 Cl 1,25 P2O5 1,08 SO 3 0,59 CuO 0,32 MnO 0,31 BaO 0,29 ZnO 0,26 Cr 2 O 3 0,12 SrO, Co 3 O 4 , PbO, ZrOz, NiO, WO 3 , SnOz < 0,1 Step c)

[0075] The obtained filtrate was subjected to two electrolysis steps to remove copper. The electrolyses were each carried out at room temperature and a pH <1. Copper deposition was achieved potentiostatically (1.4 V) within 3 days. The resulting copper-depleted solution can be used as a phosphate precipitant.

[0076] The copper-depleted digestion solution was analyzed for its composition. The results for the digestion solution are summarized in Table 7. Table 7: Analysis of the copper-depleted digestion solution ingredient Concentration [mg / L] Analysis methods aluminum 17500 DIN EN ISO 11885 (2009-09) 1)< iron 26100 DIN EN ISO 11885 (2009-09) 1)< Calcium 63200 DIN EN ISO 11885 (2009-09) 1)< magnesium 6910 DIN EN ISO 11885 (2009-09) 1)< Lead 425 DIN EN ISO 11885 (2009-09) 1)< cadmium 4,9 DIN EN ISO 11885 (2009-09) 1)< chrome 95,2 DIN EN ISO 11885 (2009-09) 1)< nickel 73,9 DIN EN ISO 11885 (2009-09) 1)< mercury < 0,01 DIN EN ISO 12846 (2012-08) 2)< copper 1600 DIN EN ISO 11885 (2009-09) 1)< zinc 2850 DIN EN ISO 11885 (2009-09) 1)< chloride 245000 DIN 38405 D1-2 (1985-12) 1) by inductively coupled plasma optical emission spectroscopy (ICP-OES) 2) by atomic absorption spectrometry Example 2: Production of a phosphate precipitant from bottom ash by digestion with H₂SO₄ Steps a) and b)

[0077] Ten kilograms of bottom ash (fraction with particle sizes of approximately 0 to 10 mm) were slowly added to 3 liters of a 37% aqueous H₂SO₄ solution. An additional 2.5 liters of water were added to improve stirrability. The pH was then adjusted to 0.5 by adding 1.4 liters of 98% H₂SO₄. The mixture was then aerated and stirred for 7 days.

[0078] Undissolved solids were then separated by sedimentation and subsequent filtration. Step c)

[0079] Cu deposition can be carried out analogously to Example 1, step c) at room temperature and a pH <1, and is usually performed potentiostatically (1.4 V). The digestion solution obtained as filtrate can be used directly as a phosphate precipitant.

[0080] Prior to electrolysis, the digestion solution was analyzed for its composition by inductively coupled plasma optical emission spectroscopy (ICP-OES). The results are summarized in Table 8. Table 8: Analysis of the digestion solution obtained by H₂SO₄ digestion ingredient Concentration [mg / L] aluminum 29480 iron 41600 Calcium 304 magnesium 8680 Lead 1,49 nickel 303 chrome 261 copper 4200 cadmium 15,3 zinc 6920 Step d)

[0081] 98% sulfuric acid was added to the extract in an equal volume ratio and cooled for several days. The precipitated solid and the resulting solution were separated. The composition of both was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The results are summarized in Tables 9 and 10. Table 9: Analysis of the solid after precipitation ingredient Mass fraction wt % aluminum 1,28 iron 2,27 Calcium 0,02 magnesium 0,23 Lead 0 nickel 0 chrome 0 copper 0,07 cadmium 0 zinc 0,29 Table 10: Analysis of the solution after precipitation ingredient Concentration [mg / L] aluminum 7180 iron 9770 Calcium 2970 magnesium 2060 Lead 0,75 nickel 3170 chrome 2640 copper 938 cadmium 0 zinc 1170 III. Use of phosphate precipitants obtained from bottom ash Example 3: Treatment of wastewater inlet samples with phosphate precipitant

[0082] The following three wastewater influent samples were treated with the phosphate precipitant obtained as a digestion solution in Example 1. The digestion of the wastewater samples was carried out according to DIN EN ISO 6878:2004-09 (D11) Section 7 LAWA AQS Guidelines P13. For this purpose, 300 ml of a wastewater sample digested with K₂S₂O₈ (a mixture of 900 mL wastewater sample, 9 mL 4.5 M sulfuric acid, and 90 ml of aqueous K₂S₂O₈ (50 g / L)) was digested for 90 min in a sealed container at 110°C. After cooling, the mixture was titrated to pH 6–7 with 1 M NaOH and 0.02 mL of the liquid phosphate precipitant was added. Sample 1: Wastewater inflow during rainy weather (January 27, 2024) Sample 2: Wastewater inflow during dry weather with rainwater runoff (January 30, 2024) Sample 3: Wastewater inflow during dry weather with rainwater runoff (January 31, 2024)

[0083] Phosphate analysis of the initial samples and the treated sample was carried out according to: "Photometric determination of phosphorus compounds (total phosphate) using ammonium molybdate according to DIN EN ISO 6878:2004-09 (D11) Section 7 LAWA AQS leaflets P13. (see Table 11). Table 11: Comparison of the phosphorus contents of samples 1 to 3 before and after treatment with the phosphate precipitant obtained in Example 2 sample Phosphorus content before treatment [mg / L] Phosphorus content after treatment [mg / L] 1 1,68 0,91 2 3,18 1,16 3 3,45 0,70

Claims

1. Process for obtaining and processing bottom ash or bottom ash fractions containing iron and / or aluminium and copper, comprising the following steps: a) extraction of the bottom ash or bottom ash fraction with an aqueous mineral acid to obtain a mineral-acidic aqueous extract (E) and a solid (F), wherein the extract (E) contains mineral-acidic iron salts and / or aluminium salts and copper salts in dissolved form; b) separation of the acidic aqueous extract (E) from the solid (F); c) depletion of the copper from the extract (E) obtained in step b) by electrolysis of the extract (E) to obtain a copper-depleted extract (E');d) optionally precipitation of a salt mixture comprising aluminium and iron in the form of their mineral salts from the extract (E') obtained in step c) by measures to reduce the solubility of the aluminium salts and the iron salts in the extract (E') followed by solid-liquid separation to obtain one of the salt mixture as a solid (F').; 2. The method according to claim 1, wherein the extraction is carried out at a pH of at most pH 1.

3. Method according to one of the preceding claims, wherein in step a) a grate ash fraction is used which was obtained by removing unburned material from the grate ash.

4. Method according to one of the preceding claims, wherein in step a) a bottom ash fraction with a particle size of at most 10 mm is used.

5. Method according to any of the preceding claims, wherein the bottom ash or bottom ash fraction contains calcium.

6. A method according to any one of the preceding claims, wherein the aqueous mineral acid used in step a) has a concentration of at least 5 molar equivalents of H + per liter.

7. Method according to any of the preceding claims, wherein the aqueous mineral acid used in step a) is selected from aqueous sulfuric acid and aqueous hydrochloric acid.

8. Method according to one of the preceding claims, wherein in step a) at least 1 kg aqueous mineral acid is used per kg bottom ash or bottom ash fraction.

9. Method according to one of the preceding claims, wherein during the extraction in step a) an oxygen-containing gas is passed through the mixture formed from aqueous mineral acid and bottom ash.

10. Method according to one of the preceding claims, wherein in step d) to reduce the solubility of the aluminium salts and the iron salts in the extract E', the extract (E') is treated with an aqueous mineral acid, in particular with sulfuric acid.

11. Method according to any of the preceding claims, wherein the salt mixture obtained in step d) is prepared as an aqueous phosphate precipitating agent.

12. A method according to any one of the preceding claims, comprising the following steps: a1) extraction of a first quantity of the bottom ash or the bottom ash fraction with aqueous hydrochloric acid to obtain an aqueous hydrochloric acid extract (E1) and a solid (F1); b1) separation of the aqueous hydrochloric acid extract (E1) from the solid (F1); c1) optionally depleting the copper from the extract (E1) obtained in step b1) by electrolysis of the extract (E1) to obtain a copper-depleted extract (E1'); a2) extraction of the bottom ash or the bottom ash fraction previously treated with hydrochloric acid and depleted of Ca and Mg with aqueous concentrated sulfuric acid to obtain an aqueous sulfuric acid extract (E2) and a solid (F2); b2) separation of the aqueous sulfuric acid extract (E2) from the solid (F2);c2) Depleting the copper from the extract (E2) obtained in step b2) by electrolysis of the extract (E2) to obtain a copper-depleted extract (E2'); d) Precipitation of a salt mixture comprising aluminium and iron in the form of their mineral salts from the extract (E2') obtained in step c2) by the addition of sulfuric acid, followed by solid-liquid separation to obtain the salt mixture as a solid (F2'); e) Optionally dissolving the solid (F2') in the hydrochloric acid extract (E1) or (E1') and optionally separating the resulting solution (L) from the undissolved material.

13. Use of a salt mixture obtainable in step d) of the method according to any of the preceding claims as a phosphate precipitating agent.

14. Use of a copper-depleted extract (E'), (E1') or (E2') obtainable in step c), c1) or c2) of the process according to any one of claims 1 to 12 or of a salt mixture obtained by dissolving the salt mixture obtained in step d) of the process according to any one of claims 1 to 12 in an aqueous mineral acid and / or in one of the extracts (E'), (E1) or (E1') as a phosphate precipitating agent.

15. Use according to any one of claims 13 to 14, wherein the phosphate precipitant is in the form of an acidic aqueous solution which, based on the total weight of the phosphate precipitant, contains the following components: i) 0 to 200 g / kg aluminum in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental aluminum; ii) 0 to 500 g / kg iron in the form of a mineral salt, calculated as elemental iron; wherein the total amount of iron and aluminum is at least 10 g / kg and in particular is in the range of 10 to 450 g / kg, calculated as the total amount of elemental iron and aluminum; and optionally iii) 0 to 35 g / kg calcium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental calcium; iv) 0 to 10 g / kg magnesium in the form of a mineral salt, in particular in the form of its chloride or sulfate, calculated as elemental magnesium.

Images