Recovery of phosphorus compounds and iron compounds from iron phosphate-containing materials

Abstract

The invention relates to a method for obtaining phosphorus compounds and iron compounds from an iron phosphate-containing material, characterized in that i) the iron phosphate-containing material is reacted with chlorine gas in the presence of a carbon source at a temperature of 300 DEG C to 900 DEG C, and ii) withdrawing the formed chloro-phosphorus compounds, more particularly phosphorus oxychloride and optionally phosphorus trichloride, and ferric chloride in an exhaust gas stream, and iii) separating the ferric chloride from the exhaust gas stream, and iv) separating the chloro-phosphorus compounds.

Description

Technical Field

[0001] The present invention relates to a method for recovering phosphorus compounds and iron compounds from iron phosphate-containing materials. Background Art

[0002] Lithium iron phosphate (LFP) and lithium iron manganese phosphate (LFMP) and variants thereof which may have been doped with further elements, especially metals, are known as cathode materials for batteries, also called cathode active materials (CAMs), and are preferably used in electric vehicles and stationary batteries.

[0003] Due to the significant growth in the lithium-ion battery market, and the fact that each car battery contains between 100kg and 200kg of CAM, the mass of valuable components (such as lithium, phosphorus, and iron, among others) is also significant. This means that recycling these used batteries to recover these raw materials is extremely important. Of particular importance here is lithium, an element whose demand has been increasing in recent years. Equally important is the presence of phosphorus, which is considered a critical raw material in many parts of the world.

[0004] Recycling operations typically involve mechanically breaking up the battery cells (if possible) and pulverizing the remainder, which includes cathode and anode materials, any binders, and additional components, into a substance that is black due to the dark LFP and carbon-containing (especially graphite-containing) anode materials and is therefore called "black powder." Due to technically incomplete separation, black powder may also contain remnants of other battery components, such as metals.

[0005] The literature proposes various methods for recycling black powder containing LFP or pure spent LFP. For example, in Qifang Sun et al., Journal of Alloys and Compounds [Journal of Alloys and Compounds] 818 (2020) 153292, spent LFP-containing material is subjected to heat treatment to obtain a low-Li material, which is converted back to LFP by appropriate addition of lithium carbonate and a carbon source. However, the resulting low-Li end product is very uncertain, which leads to a correspondingly uncertain LFP. The same applies to the method according to Lingyu Guan et al. in Renewable Energy [Renewable Energy] 175 (2021) 559-567, where the LFP released during recycling, together with specific Li, Fe and P reactants and a carbon source, leads to a mixture of old LFP and new LFP, which is also difficult to specify.

[0006] Other methods oxidize the iron (II) present in LFP to iron (III) in different ways (e.g., using hypochlorite or peroxodisulfate or H2O2 in the presence of acid) and extract the lithium released from the crystalline form. The latter is described, for example, by Yang, Yongxia; Meng, Xiangqi; Cao, Hongbin; Lin, Xiao; Liu, Chenming; Sun, Yong; Zhang, Yi; Sun, Zhi, Green Chemistry, 20 / 13 (2018), 3121-3133. However, the iron phosphate (FP) obtained in this way, which is often contaminated, can only be used to a limited extent for LFP production due to the presence of impurities.

[0007] The recovery of lithium alone in the above-described process means that only a small proportion of the mass of LFP used is sent for reuse, which means that the problem of LFP and LFMP recycling can be considered unanswered.

[0008] A common factor in processes for separating lithium from LFP and / or LFMP or black powder containing these is that a large proportion of residues containing iron phosphate material of greater or lesser purity remains, which has to be processed further. Summary of the Invention

[0009] It was therefore an object of the present invention to find a process for obtaining phosphorus and iron compounds from ferric phosphate-containing material which does not generate any large waste streams and thus enables the reuse of the ferric phosphate-containing material, whatever its origin.

[0010] Therefore, the present invention relates to a method for obtaining phosphorus compounds and iron compounds from an iron phosphate-containing material, the method being characterized in that

[0011] i) reacting an iron phosphate-containing material with chlorine (Cl2) at a temperature of 300°C to 900°C in the presence of a carbon source, and

[0012] ii) removing the formed chlorine-phosphorus compounds, in particular phosphorus oxychloride and any phosphorus trichloride, and ferric chloride in the waste gas stream, and

[0013] iii) ferric chloride (preferably by resublimation), and

[0014] iv) Chloro-phosphorus compounds, in particular phosphorus oxychloride and any phosphorus trichloride, are separated from the waste gas stream, preferably by condensation.

[0015] The process according to the invention is preferably suitable for obtaining chloro-phosphorus compounds, in particular phosphorus oxychloride and any phosphorus trichloride, and chloro-iron compounds, in particular iron(III) chloride. DETAILED DESCRIPTION

[0016] Iron phosphate and iron phosphate-containing materials

[0017] In the context of the present invention, iron phosphate should in particular be understood to mean a compound consisting of, to an extent of at least 97% by weight, more preferably at least 99.5% by weight, of elemental iron, phosphorus, manganese, aluminum, nickel, titanium and oxygen (especially elemental iron, phosphorus, manganese and oxygen), and more preferably elemental iron, phosphorus and oxygen. In the crystal structure of iron phosphate, in the context of the present invention, some of the iron lattice sites may also be occupied by one or more of the above-mentioned metal ions. Iron phosphate can also be in the form of a hydrate. Iron phosphate can preferably be iron(III) phosphate FePO4 (especially FePO4·2H2O), iron(II) phosphate (especially Fe3(PO4)2·8H2O) and iron(III) pyrophosphate (especially Fe4(P2O7)3), and compounds having the general formula Fe x Me y PO4, where Me means manganese, aluminum, nickel and titanium (especially manganese), where x is between 0 < x ≤ 3 and y is between 0 ≤ y < 2.5.

[0018] More preferably, iron phosphate can be iron(III) phosphate FePO4 (especially FePO4·2H2O), iron(II) phosphate (especially Fe3(PO4)2·8H2O) and iron(III) pyrophosphate (especially Fe4(P2O7)3).

[0019] The iron phosphate-containing materials for use in the process according to the present invention are in particular materials containing iron phosphate in a proportion of 5% to 100% by weight, preferably 40% to 99% by weight, especially 50% to 99% by weight, more preferably 70% to 99% by weight.

[0020] It is preferred to use materials containing at least one iron phosphate selected from the group consisting of iron(III) phosphate FePO4, iron(II) phosphate (especially Fe3(PO4)2·8H2O, FePO4·2H2O) and iron(III) pyrophosphate (especially Fe4(P2O7)3) or Fe x Me y PO4, where Me means manganese, aluminum, nickel and titanium (especially manganese), and x is between 0 < x ≤ 3 and y is between 0 ≤ y < 2.5, in a proportion of 5% to 100% by weight, preferably 40% to 99% by weight, especially 50% to 99% by weight, more preferably 70% to 99% by weight.

[0021] The proportion of LFP and LFMP in the iron phosphate-containing materials is preferably less than 1% by weight.

[0022] The composition of the material used can also preferably be described by determining the proportions by weight of specific elements in the iron-phosphate-containing material based in each case on the amount of iron-phosphate-containing material, wherein the material used preferably contains:

[0023] 1 to 38% by weight of Fe,

[0024] 1 to 30% by weight of P,

[0025] 0 to 35% by weight of Mn,

[0026] 0% to 35% by weight of Al,

[0027] 0 to 35% by weight of Ni,

[0028] 0 to 35% by weight of Ti,

[0029] 0 to 55% by weight, preferably 0 to 40% by weight, especially 1 to 30% by weight of carbon.

[0030] These amounts may originate primarily from the iron phosphate itself, but also from residual components of the materials used, for example from residues of metallic components or from parts of the anode that may still be present in the black powder even after the Li has been leached. Additional doping elements may also be present. The elemental contents are preferably determined by conventional elemental analysis methods.

[0031] The iron phosphate-containing material used preferably has a water content of less than 1% by weight.

[0032] The iron phosphate-containing material used is preferably as black powder from LFP and / or LFMP or containing them in acid (preferably C1-C 10 The reaction is preferably carried out at a temperature of 20° C. to 90° C. by reacting the LFP-containing material and / or the LFMP-containing material with H O , wherein the LFP-containing material and / or the LFMP-containing material is already largely free of lithium and preferably has a Li content of less than 2% by weight, in particular less than 1% by weight, based on the material.

[0033] The residue is preferably recovered by continuous extraction of the ferric phosphate-containing material over a period of hours to days.

[0034] Metals may also be present in the materials used, preferably in amounts of 0 to 15% by weight, preferably 0 to 5% by weight, in particular Al, Cu, Co and Ni.

[0035] Preferably, the iron phosphate-containing material used contains preferably less than 10% by weight, in particular less than 1% by weight, more preferably less than 0.1% by weight of polymer particles, in particular plastics.

[0036] It is also preferred that the iron phosphate-containing material used contains less than 5% by weight of PVDF (polyvinylidene fluoride) and / or other binders, such as carboxymethylcellulose and / or alginate. The content of all binders is preferably less than 5% by weight.

[0037] The VOC content of the iron phosphate-containing material used is preferably less than 1% by weight, in particular less than 0.1% by weight, more preferably less than 0.01% by weight. VOC (volatile organic compounds) is preferably understood to mean organic compounds having a boiling point in the range of 50° C. to 260° C. at a standard pressure of 101.3 kPa.

[0038] The iron phosphate-containing material used preferably has an average particle size of 0.1 μm to 10 mm. Depending on the size, the particle size can be easily determined by sieving or, for smaller particles, by laser diffraction or laser scattering methods; the best method to be used in a specific case is known to those skilled in the art.

[0039] If the iron phosphate-containing material used has a binder content of more than 1% by weight, based on the material, leaching is preferably carried out by treatment with an organic solvent, in particular acetone, ethyl acetate, methyl ethyl ketone, tetrahydrofuran (THF), ethyl acetoacetate, acetylacetone, dioxane and / or acetic anhydride and mixtures thereof, in order to reduce the content to less than 0.1% by weight.

[0040] If the iron phosphate-containing material has a polymer content of more than 1% by weight, in particular a plastic, it is advantageous to first subject the material to a heat treatment at a temperature of 300° C. to 600° C., preferably under inert gas, in order to reduce the polymer content to less than 0.1% by weight. Alternatively or additionally to leaching with an organic solvent, a possible binder content of more than 1% by weight can also be reduced to less than 0.1% by weight by heat treatment at a temperature of 300° C. to 700° C., preferably under inert gas.

[0041] carbon source

[0042] The carbon source can in principle include any carbon variant (such as graphite, soot, charcoal, coke, activated carbon), as well as carbon-containing gases (such as carbon monoxide, methane or phosgene), liquid materials (such as polyethylene glycol or various oils) or solid materials (such as biowaste or sewage sludge). Sewage sludge is particularly preferred. It preferably contains carbon in a proportion of at least 5% by weight, preferably 20% to 50% by weight, based on the dry mass.

[0043] In the context of the present invention, the term "sewage sludge" refers to any suspension of finely divided particles of a solid matrix in a liquid. Sewage sludge preferably has a carbon content, expressed as a weight percentage of elemental carbon, of at least 5% carbon by weight. In a preferred embodiment, the liquid in which the particles are suspended is wastewater as defined herein. The term "wastewater" is understood to mean all aqueous and / or organic liquids or mixtures thereof that do not have drinking water quality within the range of drinking water standards.

[0044] In specific embodiments, the sewage sludge is in the form of primary sludge, raw sludge, excess sludge, or treated and / or stabilized sewage sludge (aerobic / anaerobic).

[0045] The term "biowaste" is understood to mean all organic waste of animal or vegetable origin that is obtained in households or factories and can be degraded by microorganisms, soil organisms or enzymes. Examples of these may include straw, sawdust, wax, fat and guano.

[0046] The carbon source may be solid, liquid or gaseous. Preferably a solid carbon source is used.

[0047] If the carbon content of the carbon source is less than 70% by weight, it is preferably subjected to pyrolysis before the reaction with chlorine. This is preferably carried out under an inert gas (e.g. nitrogen) at a temperature of 250° C. to 800° C., preferably 350° C. to 550° C., until the gas formation of volatile components is less than 1 l per 1 kg of carbon source used per hour.

[0048] The carbon source used is more preferably sewage sludge.

[0049] The chloride content of the carbon source, especially based on its dry weight, is preferably less than 1% by weight.

[0050] If the iron phosphate-containing material used (for example because it originates from the Li-depleted residue from LFP and / or LFMP or in particular from black powder containing these) already contains at least a portion of a carbon source, it contains in particular preferably 1 to 55% by weight, preferably 1 to 40% by weight, in particular 1 to 30% by weight of carbon, in particular graphite and / or soot.

[0051] Preferably, the sum of iron phosphate and carbon is greater than 70% by weight, preferably greater than 80% by weight, more preferably greater than 90% by weight, based on the iron phosphate-containing material.

[0052] Preferably, the iron phosphate-containing material has a carbon to phosphorus molar ratio of not less than 1.5, preferably from 1.5 to 20, more preferably from 1.5 to 10, especially from 1.5 to 5, most preferably from 1.5 to 4.

[0053] If the material used contains less than 1.5 mol of carbon per 1 mol of phosphorus, based on the iron phosphate present in the material, sufficient carbon is preferably added to the material before the reaction so that the desired ratio is achieved.

[0054] reactor

[0055] The materials to be used in the method according to the invention are preferably introduced into a reactor, which is preferably provided with a layer having resistance under the reaction conditions to be established. Preferred reactor materials are nickel or graphite coated reactors or reactors made of quartz. The reactor used may be a tubular reactor (such as a rotary tubular reactor) or other reactor. Particularly preferred are reactors that allow the material to move during the reaction so as to allow very effective contact between the material and the chlorine. Preferred are fluidized bed equipment and rotary tubular reactors, or reactions in extruder equipment with screw propulsion.

[0056] In the case of a tubular reactor, the reactor length is preferably 0.2 to 40 m. The residence time in the reactor during the reaction is generally determined by the temperature and the likelihood of the material coming into contact with chlorine gas. The residence time in the reactor can be extended, for example, from one minute to 10 hours. The process according to the invention can be carried out batchwise or continuously.

[0057] method:

[0058] Step i)

[0059] The reaction is preferably carried out under the exclusion of air. Any air present in the reactor is preferably replaced with an inert gas (such as nitrogen) at the start of the reaction.

[0060] The reaction with chlorine is carried out at a temperature of 300° C. to 900° C., in particular 350° C. to 800° C. If the process is carried out at a temperature of 300° C. to 320° C., it is advantageous not to completely remove the iron chloride that has escaped from the reactor by subsequently increasing the temperature to 350° C. to 400° C. The temperature is preferably increased after the content of phosphorus compounds in the offgas (measured with the aid of a gas phase IR spectrometer calibrated accordingly in weight percent) is less than 0.1% by weight, in particular less than 0.01% by weight.

[0061] The chlorine gas can be contacted with the material in various ways. Preferably, the chlorine is passed over or through the material, while preferably keeping the material in motion during the reaction for efficient reaction. This can be done in a rotary tube furnace or paddle dryer, where the material is kept in motion. The chlorine gas can also be passed through the material, which can be achieved, for example, in a fluidized bed or fixed bed. Alternatively, the material can be preformed, such as by compaction or granulation, for this purpose.

[0062] The reactor preferably has an outlet for an offgas stream. The offgas stream contains gaseous reaction products, volatile components of the materials and excess chlorine, which can be withdrawn from the reaction space together.

[0063] The reaction is preferably terminated when the proportion of phosphorus compounds (preferably measured with the aid of a gas-phase IR spectrometer calibrated accordingly in weight percent) is less than 0.1% by weight, in particular less than 0.01% by weight.

[0064] Step ii)

[0065] The waste gas stream also contains chlorine-phosphorus compounds (especially phosphorus oxychloride and any phosphorus trichloride), also gaseous iron(III) chloride and also any AlCl 3 (if aluminum is present in the materials used).

[0066] Step iii)

[0067] At reaction temperatures of 300° C. to 320° C., the proportion of ferric chloride in the waste gas stream is generally still relatively small and only increases after the temperature is increased to 350° C. to 600° C. If aluminum is present in the materials used, iron(III) chloride and also AlCl 3 can be separated from the waste gas stream and from one another, preferably by resublimation on surfaces cooled to different temperatures. If ferric chloride and AlCl 3 are present in the waste gas stream together, due to the significant difference in boiling points, the respective chlorides can be resublimed (even in fractionated form) on different surfaces at different temperatures and thus separated very cleanly.

[0068] The preferred precipitation temperature of FeCl3 is not more than 307°C, especially 150°C to 300°C, and the preferred precipitation temperature of AlCl3 is not more than 150°C, especially 110°C to 149°C.

[0069] The iron (III) recovered after the process according to the invention in the form of iron (III) chloride can optionally be separated from the adhering chloro-phosphorus compounds. This can be accomplished by treatment with an acid (e.g., sulfuric acid, preferably concentrated sulfuric acid), by a thermal drying step, or in another manner known to those skilled in the art. Preferably, the iron (III) chloride separated in step iii) is reacted with sulfuric acid, releasing and then optionally condensing any chloro-phosphorus compounds present.

[0070] It is then possible to convert the iron into the desired raw material form, for example for the production of LFP and / or LFMP. Examples here include iron sulfate, iron nitrate, iron phosphate, or various forms of iron oxide.

[0071] Alternatively, even the iron chloride that has not been separated off by resublimation can be introduced directly as a gaseous stream into an aqueous medium containing sulfuric acid or nitric acid, thereby forming the corresponding iron(III) sulfate or iron(III) nitrate. If necessary, a suitable reducing agent is also used in the reaction to obtain iron(II) sulfate, iron(II) nitrate or iron(II) phosphate.

[0072] However, it is preferred to separate the ferric chloride from the waste gas stream by resublimation.

[0073] Step iv)

[0074] In the process according to the invention, chlorine-phosphorus compounds, preferably phosphorus oxychloride and any phosphorus trichloride likewise formed, can be removed from the offgas stream, preferably by means of a condenser, and any excess chlorine can be recycled.

[0075] Phosphorus oxychloride, which is gaseous at the reaction temperature, and any phosphorus trichloride also formed are separated from the waste gas stream by a condenser. Typically, a mixture of phosphorus oxychloride and phosphorus trichloride is formed, the components of which can be further separated by distillation. This allows the phosphorus component to be obtained in very pure form.

[0076] The process according to the invention is preferably characterized in that the offgas stream drawn off from step ii) contains phosphorus trichloride and this (in the form of the phosphorus trichloride-containing chloro-phosphorus compound from step iv) or after separation therefrom) is reacted with chlorine at a temperature of 20° C. to 160° C. to give phosphorus pentachloride.

[0077] A chlorine / phosphorus trichloride molar ratio of 1:20 is preferred.

[0078] Preference is given to the process according to the invention for recovering phosphorus compounds in the form of chloro-phosphorus compounds, in particular in the form of a mixture of phosphorus oxychloride and phosphorus trichloride.

[0079] Phosphorus oxychloride can be converted into polyphosphoric acid or phosphoric acid by a hydrolysis step, from which its salts can be produced (if desired) by neutralization, and these can then optionally be used again for the production of LFP and / or LFMP.

[0080] The weight ratio of phosphorus oxychloride to phosphorus trichloride obtained in the waste gas stream is typically from 10:1 to 1:10.

[0081] The chlorine-phosphorus compounds from the process according to the invention can favor the formation of phosphorus trichloride and, therefore, the preferred reactant for the formation of phosphorus pentachloride, since the process is preferably carried out at temperatures above 500° C. It is also preferred to carry out the process at a carbon / phosphorus ratio of greater than 3 mol / mol. In this way, a phosphorus trichloride / phosphorus oxychloride ratio of greater than 1 can be achieved.

[0082] If the process according to the invention is carried out without a stoichiometric excess of chlorine and if chlorine is therefore practically absent in the offgas stream, the offgas stream containing chlorine-phosphorus compounds (especially phosphorus oxychloride and any phosphorus trichloride) (once it has been freed of ferric chloride) can also preferably be introduced into aqueous solution to obtain the corresponding phosphorus acids (such as phosphates and phosphonic acids), from which any other phosphorus derivatives can then be produced.

[0083] After completion of the process according to the invention, all components of the materials used which are non-volatile under the reaction conditions or their non-volatile reaction products (especially in the form of chlorides) are present in the residue, as well as unconverted iron-phosphate-containing material and unconverted carbon. To further process the residue and recover valuable materials, the residue can be partially dissolved in water, preferably at temperatures of 10° C. to 40° C., and separated from the insoluble components.

[0084] A specific insoluble residue from the method according to the invention is graphite or other carbon (if present in the material used) that has been added or present, and any titanium dioxide. The water-soluble components can then be optionally separated and isolated from each other in the form of their sulfides, chlorides, phosphates, fluorides or other precipitated compounds after their possible presence is determined in a conventional HS separation sequence. For example, manganese and aluminum (if present in the residue) and nickel can be precipitated as sulfides at different pH values, dried and then baked under air to obtain the corresponding sulfates. Titanium can be separated from the insoluble residue in the form of dioxide.

[0085] Within the scope of the present invention, the sulfate obtained can be reused for the production of iron phosphate.

[0086] Examples

[0087] Analysis: The analysis of phosphorus compounds (especially POCl3 and PCl3) is preferably performed by online IR in the exhaust gas stream. For this purpose, the gas stream from the reactor is passed through a glass cuvette that allows the passage of IR radiation in the maximum spectral range, for example by using a window made of a thallium compound. By prior calibration (complete evaporation of a known mass of PCl3 or POCl3 into a nitrogen stream with a known volume flow rate and quantification of the characteristic bands in the IR spectrum), the mass proportion of phosphorus compounds in the exhaust gas stream can be determined.

[0088] The specified weight percentages of different elements are determined by ICP-OES measurement. For this purpose, a weighed amount of solid material is first dissolved in a known amount of acid, and the concentration of the specified element is determined from the calibration measurement in the ICP, and the content of the element in the solid material is determined from this by back calculation.

[0089] Examples

[0090] 120 g of lithium iron phosphate were stirred with 1 liter of 1 molar acetic acid and 250 g of 30% H2O2 at room temperature for 30 minutes. The precipitate was then filtered off with suction, washed three times with water and dried.

[0091] 55 g of the iron phosphate-containing material produced above (having the following analytical data: 36% by weight of Fe, 21% by weight of P, <1% by weight of Li) were thoroughly dry-mixed with 6.6 g of finely ground carbon (activated carbon). The water content was <1% by weight.

[0092] The powder mixture was heated to 600°C in a quartz dish in a heated tubular reactor (made of quartz glass, 120 mm in diameter) under a nitrogen flow. This flow was then switched to a 100 ml / min chlorine flow. This temperature was maintained for 6 hours. After a reaction time of approximately 10 minutes, a chromophore appeared at 593 cm in the IR spectrum of the gas phase. -1 and 1322cm -1 There are two absorption bands at , both of which can be attributed to POCl3.

[0093] The ferric chloride obtained is separated off in a zone cooled to 100° C. together with part of the POCl 3 formed from the offgas stream and then collected together and reacted with sulfuric acid to give ferric sulfate and phosphorus oxychloride. The mixture is distilled.

[0094] The iron sulfate obtained can be used to produce new iron phosphate or LFP / LFMP.

[0095] The distillate obtained, consisting of POCl3, can be used in chemical processes, for example for the production of phosphoric acid esters. It is also possible to use POCl3 to produce polyphosphoric acid or phosphoric acid. According to this method, these are possible raw materials for the production of LFP or LFMP.

[0096] Remaining in the dish were residues of unconverted ferric phosphate and excess carbon (22 g total).

Claims

1. A method for obtaining a phosphorus compound and an iron compound from an iron phosphate-containing material, the method comprising: i) reacting an iron phosphate-containing material with chlorine gas in the presence of a carbon source at a temperature of 300° C. to 900° C., and ii) removing the formed chlorine-phosphorus compounds, in particular phosphorus oxychloride and any phosphorus trichloride, and ferric chloride in the waste gas stream, and iii) the ferric chloride, and iv) separating the chlorine-phosphorus compounds from the waste gas stream.

2. The method according to claim 1, characterized in that The ferric chloride is separated from the offgas stream in step iii) by resublimation.

3. The method according to claim 1 or 2, characterized in that The ferric chloride separated in step iii) is reacted with sulphuric acid, releasing and then optionally condensing any chloro-phosphorus compounds present.

4. The method according to claim 1, wherein The chlorine-phosphorus compounds, in particular phosphorus oxychloride and any phosphorus trichloride, are separated from the waste gas stream in step iv) by condensation.

5. The method according to at least one of claims 1 to 4, characterized in that The iron phosphate consists to an extent of at least 97% by weight, more preferably to an extent of at least 99.5% by weight, of the elements iron, phosphorus, manganese, aluminum, nickel, titanium and oxygen, in particular of the elements iron, phosphorus, manganese and oxygen, and more preferably of the elements iron, phosphorus and oxygen.

6. The method according to at least one of claims 1 to 5, characterized in that The iron phosphate is at least one selected from the group consisting of: iron(III) phosphate FePO4, iron(II) phosphate especially FePO4·2H2O, especially Fe3(PO4)2·8H2O, and iron(III) pyrophosphate especially Fe4(P2O7)3, and a compound having the general formula Fe x Me y PO4, where Me means manganese, aluminum, nickel and titanium, especially manganese, and x is between 0 < x ≤ 3 and y is between 0 ≤ y < 2.

5.

7. The method according to at least one of claims 1 to 6, characterized in that The iron phosphate-containing material used is a material containing iron phosphate in a proportion of 5 to 100% by weight, preferably 40 to 99% by weight, particularly 50 to 99% by weight, more preferably 70 to 99% by weight.

8. The method according to at least one of claims 1 to 7, characterized in that The iron phosphate-containing material used is a material containing at least one iron phosphate from the group consisting of iron (III) phosphate FePO4, iron (II) phosphate, especially FePO4·2H2O, especially Fe3(PO4)2·8H2O, and iron (III) pyrophosphate, especially Fe4(P2O7)3, in a proportion of 5% to 100% by weight, preferably 40% to 99% by weight, especially 50% to 99% by weight, and more preferably 70% to 99% by weight.

9. The method according to at least one of claims 1 to 8, characterized in that The iron phosphate-containing material used is a material containing the following: 0 to 35% by weight of Mn calculated as elemental manganese, 0% to 35% by weight of Al calculated as elemental aluminium, 0% to 35% by weight of Ni calculated as elemental nickel, 0 to 35% by weight of Ti, calculated as elemental titanium, 0 to 55% by weight, preferably 0 to 40% by weight, especially 1 to 30% by weight of carbon.

10. The method according to at least one of claims 1 to 9, characterized in that The iron phosphate-containing material used is a material containing less than 1% by weight of Li calculated as elemental lithium.

11. The method according to at least one of claims 1 to 10, characterized in that The carbon source is selected from the group consisting of graphite, soot, charcoal, coke, activated carbon, carbon monoxide, oil, methane, polyethylene glycol, biowaste, and especially sewage sludge.

12. Method according to at least one of claims 1 to 11, characterized in that The iron phosphate-containing material contains 1 to 55% by weight, preferably 1 to 40% by weight, of carbon, in particular graphite and / or activated carbon and / or soot.

13. The method according to at least one of claims 1 to 12, characterized in that The iron phosphate-containing material has a carbon to phosphorus molar ratio of not less than 1.5, preferably from 1.5 to 20, more preferably from 1.5 to 10, especially from 1.5 to 5, most preferably from 1.5 to 4.

14. The method according to at least one of claims 1 to 13, characterized in that The waste gas stream drawn off in step ii) contains phosphorus oxychloride and phosphorus trichloride, preferably in a weight ratio of 10:1 to 1:

10.

15. Method according to at least one of claims 1 to 14, characterized in that The ferric chloride is separated off in step iii) at a temperature not exceeding 300°C.