Process for the preparation of the ethylenediaminote-trachetic acid complex salt of iron(III) and potassium

Description

/ 27 PROCESS FOR PREPARING THE ETHYLENEDIAMINETETRAACETIC ACID COMPLEX SALT OF IRON(III) AND POTASSIUM

[001] The present invention relates to a process for preparing the ethylenediaminetetraacetic acid complex salt of iron(III) and potassium (abbreviated as KFe(III)EDTA) by partially neutralizing the acidic form of EDTA with a basic potassium salt, reacting the partially neutralized EDTA with a source of Fe3O4 from an ethylenediaminetetraacetic acid complex salt of iron and potassium containing iron (II) and (III), oxidizing the iron (II) contained therein with an oxygen-based oxidizing agent and adjusting the pH from 5 to 7 with a basic potassium salt. FUNDAMENTALS OF THE TECHNIQUE

[002] Iron is involved in chlorophyll synthesis and other enzymatic and metabolic processes in plants. Iron deficiency in plants is generally not caused by a lack of iron in the soil, but rather by its low availability in a form that can be absorbed by the plant. Iron availability increases with decreasing soil pH, but altering soil pH is neither easy in practice nor desirable in most cases. In agricultural practice, iron is generally made available to plants by applying iron chelates as a source of iron.

[003] Among the various iron complexes, EDTA potassium salt iron chelates are used as special fertilizers. Although the analogous sodium salt is also useful for providing iron to plants in a readily available form, the potassium salt has the advantage of having a higher dissolution rate and, in addition, of providing potassium, which, unlike sodium, is a primary (macro) plant nutrient (used, for example, in NPK fertilizers), while sodium only contributes to undesirable salinization and is known to be phytotoxic. EDTA chelated iron potassium salt can also be used in hydroponic crops, in greenhouses, and in areas where (further) salinization must be avoided. Petition 870250094424, dated 10 / 15 / 2025, p. 12 / 43 / 27

[004] Several synthetic methods for the preparation of EDTA iron chelate salts are described in the art.

[005] DE 2107079 refers to a process for preparing aqueous solutions of ammonium salts of Fe(III) aminopolycarboxylic complexes. For this purpose, an iron oxide containing iron(III) is reacted with an aminopolycarboxylic acid, such as EDTA, partially neutralized with ammonia or a water-soluble amine, in aqueous medium under heating at 82 to 104°C, and then neutralized with ammonia or an amine. An oxidation step is not mentioned. Transferring the reaction conditions applied to the preparation of the corresponding potassium salt, however, does not produce KFe(III)EDTA in satisfactory yields and with the desired specifications and properties.

[006] Document EP 0471583 A1 refers to a process for the preparation of complex salts of iron amino or hydroxycarboxylic acid by reacting an amino or hydroxycarboxylic acid or a salt or partial salt thereof with an iron oxide and a base in the presence of a ferrous salt (Fe(II)) or metallic iron or the salt of the ferrous complex to be produced as a catalyst, by neutralizing the reaction product and, if desired, oxidizing any ferrous iron to ferric iron. EDTA is considered a suitable aminocarboxylic acid. The preferred catalyst is ferrous sulfate hydrate. Preferably, ammonium ferric EDTA is prepared using ammonium as a base, but sodium ferric EDTA and potassium ferric EDTA are considered to be obtained analogously by using NaOH or KOH, respectively. As suitable iron oxides, magnetite and hydrated α- and γ-iron oxides [Fe(OH)O] are mentioned.The process for preparing ferric-ammonium EDTA is preferably carried out by first mixing water, iron oxide, and a base, followed by the addition of the carboxylic acid. The order of addition is emphasized as important. After reaching the desired reaction temperature, the catalyst is added. The product of... Petition 870250094424, dated 10 / 15 / 2025, page 13 / 43 / 27 reaction is neutralized with ammonia and oxidized in air at about 30°C to give Fe(III)NH4EDTA, which is subsequently converted to (EDTA(NH4)2FeOH) by the addition of more ammonia. The use of catalysts is, however, disadvantageous for obtaining products without foreign ions, since these need to be removed, requiring additional, somewhat tedious, purification steps.

[007] There is a constant need for efficient synthetic methods for the preparation of iron chelates of potassium EDTA salt, especially those with a high iron(III) content, since iron in this oxidation phase is better available to plants. Thus, the objective of the present invention was to provide an efficient process for the preparation of an iron chelate of potassium EDTA salt with a high iron(III) content. The total iron content in the obtained iron and potassium chelate product must be at least 13% by weight relative to the total weight of the product (in the case of pure KFe(III)EDTA, the Fe content is 14.57% by weight relative to the total weight of KFe(III)EDTA), and the Fe2+ content must be less than 1% by weight relative to the total weight of the product.Furthermore, no foreign ions, and especially no sulfate, chloride, or nitrate anions, should be involved, so that the product obtained is free of these anions, without any additional steps in which such anions would have to be removed.

[008] The problem is solved by the invention process described below. SUMMARY OF THE INVENTION

[009] The present invention relates to a process for preparing a complex salt of iron(III) and potassium ethylenediaminetetraacetic acid (abbreviated as KFe(III)EDTA), comprising (i) reacting in an aqueous medium the acidic form of ethylenediaminetetraacetic acid with a basic potassium salt to form a partially neutralized ethylenediaminetetraacetic acid; Petition 870250094424, of 10 / 15 / 2025, page 14 / 43 / 27 (ii) react the reaction mixture obtained in step (i) with a source of Fe3O4 of an iron and potassium ethylenediaminetetraacetic acid complex salt containing iron(II) and iron(III); (iii) oxidize the iron and potassium ethylenediaminetetraacetic acid complex salt obtained in step (ii) [and containing iron(II) and iron(III)] into an iron(III) and potassium ethylenediaminetetraacetic acid complex salt with an oxygen-based oxidizing agent; and (iv) adjust the reaction mixture obtained in step (iii) to a pH of 5 to 7 with a basic potassium salt. DETAILED DESCRIPTION OF THE INVENTION Definitions

[0010] The complex salt of ethylenediaminetetraacetic acid of iron(III) and potassium (abbreviated as KFe(III)EDTA), also called potassium salt of the ethylenediaminetetraacetic acid complex of iron(III), is a complex with iron(III) as the central metal and EDTA as the chelate ligand. The carboxylic groups of EDTA are neutralized, i.e., they are present as carboxylate groups, the counter-cations being Fe(III) and K+.

[0011] KFe(III)EDTA can be schematically represented as follows:

[0012] This is a simplified and idealized view of the KFe(III)EDTA product obtained using the method of the invention, since it could, for example, be present as a hydrate, the central metal therefore being, Petition 870250094424, dated 10 / 15 / 2025, p. 15 / 43 5 / 27 linked to the complex by a water molecule. Furthermore, if the neutralization in step (iv) is not carried out completely, a (small) part of the carboxylate groups may be present in the acidic form. Also, if the oxidation in step (iii) is not complete, a very small part (usually <1%) of the central metal may be Fe(II) (the complex salt in this case can be represented in an idealized form similar to that of KFe(III)EDTA shown above, the difference being Fe2+ as the central metal and the presence of two K+ counter-cations).

[0013] The acidic form of ethylenediaminetetraacetic acid means EDTA in its unneutralized form, that is, as a tetraacid: u II -·OHk .k . II YU' UH THE Invention Models (Ex)

[0014] The general and preferred Ex modalities are summarized in the following non-exhaustive list. Other preferred modalities become evident in the paragraphs following this list.

[0015] A process for preparing iron(III) potassium ethylenediaminetetraacetic acid salt, KFe(III)EDTA, comprising (i) reacting in an aqueous medium the acidic form of ethylenediaminetetraacetic acid with a basic potassium salt to form a partially neutralized ethylenediaminetetraacetic acid; (ii) react the reaction mixture obtained in step (i) with a FesO4 source of an iron and potassium ethylenediaminetetraacetic acid salt containing iron (II) and (III); (iii) oxidize the iron(II) and (III) ethylenediaminetetraacetic acid salt of iron(III) potassium to an iron(III) ethylenediaminetetraacetic acid salt with an oxygen-based oxidizing agent; and Petition 870250094424, dated 10 / 15 / 2025, page 16 / 43 / 27 (iv) adjust the reaction mixture obtained in step (iii) to a pH of 5 to 7 with a basic potassium salt.

[0016] E.2. The process according to embodiment E.1, wherein, in step (i), the basic potassium salt is used in an amount of 0.7 to 1 mol per mol of the acid form of ethylenediaminetetraacetic acid, wherein the amount of the basic potassium salt refers to the amount of potassium in said salt.

[0017] E.3. The process according to embodiment E. 2, wherein, in step (i), the basic potassium salt is used in an amount of 0.7 to 0.9 mol per mol of the acid form of ethylenediaminetetraacetic acid, wherein the amount of the basic potassium salt refers to the amount of potassium in said salt.

[0018] E.4. The process according to embodiment E. 3, wherein, in step (i), the basic potassium salt is used in an amount of 0.75 to 0.85 mol per mol of the acid form of ethylenediaminetetraacetic acid, wherein the amount of the basic potassium salt refers to the amount of potassium in said salt.

[0019] E. 5. The process according to embodiment E. 4, wherein, in step (i), the basic potassium salt is used in an amount of 0.80 to 0.82 mol per mol of the acid form of ethylenediaminetetraacetic acid, wherein the amount of the basic potassium salt refers to the amount of potassium in said salt.

[0020] E.6. The process according to any of the above embodiments, wherein the partially neutralized ethylenediaminetetraacetic acid obtained in step (i) is the monopotassium salt of ethylenediaminetetraacetic acid or a mixture of the monopotassium salt of ethylenediaminetetraacetic acid and the acidic form of ethylenediaminetetraacetic acid.

[0021] E.7. The process according to any of the above embodiments, wherein, in step (i), a basic potassium salt is added to a Petition 870250094424, dated 10 / 15 / 2025, p. 17 / 43 / 27 suspension of the acidic form of ethylenediaminetetraacetic acid in water.

[0022] E.8. The process according to embodiment E.7, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains 0.1 to 10 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0023] E.9. The process according to embodiment E. 8, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains 0.5 to 5 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0024] E. 10. The process according to embodiment E. 9, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains 1 to 5 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0025] E. 11. The process according to embodiment E. 10, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains 2 to 4 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0026] E. 12. The process according to embodiment E. 7, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains from 2 to 10 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0027] E. 13. The process according to embodiment E. 12, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains 2 to 5 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0028] E. 14. The process according to embodiment E. 13, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains 3 to 5 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0029] E. 15. The process according to embodiment E. 14, in which the suspension of the acid form of ethylenediaminetetraacetic acid in water contains 3 to 4 mol of the acid form of ethylenediaminetetraacetic acid per kg of water.

[0030] E.16. The process according to any of the embodiments E. 7 to E. 15, in which the basic potassium salt is added as Petition 870250094424, dated 10 / 15 / 2025, p. 18 / 43 / 27 an aqueous solution.

[0031] E.17. The process according to any of the preceding embodiments, wherein the basic potassium salt used in steps (i) and (iv) is selected from potassium hydroxide (KOH), potassium carbonate (K2CO3), potassium oxide and mixtures thereof.

[0032] E.18. The process according to embodiment E. 17, in which the basic potassium salt used in steps (i) and (iv) is KOH.

[0033] E.19. The process according to any of the above modalities, wherein the source of Fe3O4 is natural or synthetic magnetite.

[0034] E.20. The process according to embodiment E. 19, in which the source of Fe3O4 is natural magnetite.

[0035] E.21. The process according to any of the preceding embodiments, wherein the Fe3O4 source is used in an amount of 0.2 to 0.5 mol per mol of the acid form of ethylenediaminetetraacetic acid (i.e., per mol of the amount of EDTA used in step (i)), wherein the amount of the Fe3O4 source refers to the amount of Fe3O4 contained in said source.

[0036] E.22. The process according to embodiment E. 21, wherein the Fe3O4 source is used in an amount of 0.2 to 0.4 mol per mol of the acid form of ethylenediaminetetraacetic acid, wherein the amount of the Fe3O4 source refers to the amount of Fe3O4 contained in said source.

[0037] E.23. The process according to embodiment E.22, wherein the Fe3O4 source is used in an amount of 0.30 to 0.35 mol per mol of the acid form of ethylenediaminetetraacetic acid, wherein the amount of Fe3O4 source refers to the amount of Fe3O4 contained in said source.

[0038] E.24. The process according to embodiment E.23, wherein the Fe3O4 source is used in an amount of approximately 0.33 mol per mol of the acidic form of ethylenediaminetetraacetic acid, wherein the amount Petition 870250094424, dated 10 / 15 / 2025, p. 19 / 43 / 27, from the Fe3Ü4 source, refers to the quantity of FesOq contained in said source.

[0039] E.25. The process according to any of the above embodiments, wherein step (ii) is carried out at a temperature of 80 to 100°C.

[0040] E.26. The process according to embodiment E. 25, in which step (ii) is carried out at a temperature of 90 to 100°C.

[0041] E.27. The process according to any of the previous embodiments, wherein step (ii) is carried out at a pH of 3 to 5.

[0042] E.28. The process according to embodiment E. 27, wherein step (ii) is carried out at a pH of 3 to 4.5.

[0043] E.29. The process according to any of the previous embodiments, wherein step (iii) is carried out at a pressure from atmospheric pressure at 15 bar (1.5 MPa).

[0044] E.30. The process according to embodiment E.29, in which step (iii) is carried out at a pressure from atmospheric pressure at 10 bar (1 MPa).

[0045] E.31. The process according to embodiment E.30, in which step (iii) is carried out at a pressure from atmospheric pressure at 6 bar (0.6 MPa).

[0046] E.32. The process according to embodiment E.31, in which step (iii) is carried out at a pressure from atmospheric pressure up to 5 bar (0.5 MPa).

[0047] E.33. The process according to embodiment E.32, in which step (iii) is carried out at atmospheric pressure.

[0048] E.34. The process according to embodiment E.30, in which step (iii) is carried out at a pressure from 3 to 10 bar (0.3 to 1 MPa).

[0049] E.35. The process according to embodiment E.34, in which step (iii) is carried out at a pressure from 3 to 6 bar (0.3 to 0.6 MPa).

[0050] E.36. The process according to modality E.35, in which the Petition 870250094424, dated 10 / 15 / 2025, page 20 / 43 / 27 step (iii) is performed at a pressure from 3 to 5 bar (0.3 to 0.5 MPa).

[0051] E.37. The process according to any of the preceding embodiments, wherein the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air, oxygen / nitrogen mixtures other than air and hydrogen peroxide.

[0052] E.38. The process according to embodiment E.37, in which the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air and hydrogen peroxide.

[0053] E.39. The process according to embodiment E.38, in which the oxygen-based oxidizing agent used in step (iii) is selected from oxygen and air.

[0054] E.40. The process according to embodiment E.39, in which the oxygen-based oxidizing agent used in step (iii) is air.

[0055] E.41. The process according to any of the previous embodiments, in which step (iii) is carried out at a temperature of 10 to 100°C.

[0056] E.42. The process according to embodiment E.41, in which step (iii) is carried out at a temperature of 10 to 40°C (especially if the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air and oxygen / nitrogen mixtures other than air).

[0057] E.43. The process according to embodiment E.42, in which step (iii) is carried out at a temperature of 15 to 30°C (especially if the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air and oxygen / nitrogen mixtures other than air).

[0058] E.44. The process according to embodiment E.43, in which step (iii) is carried out at a temperature of 15 to 25°C (especially if the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air and oxygen / nitrogen mixtures other than air).

[0059] E.45. The process according to modality E.44, in which the Petition 870250094424, dated 10 / 15 / 2025, page 21 / 43 / 27 step (iii) is carried out at a temperature of 20 to 25°C (especially if the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air and oxygen / nitrogen mixtures other than air).

[0060] E.46. The process according to embodiment E.41, in which step (iii) is carried out at a temperature of 40 to 100°C (especially if the oxygen-based oxidizing agent used in step (iii) is hydrogen peroxide).

[0061] E.47. The process according to embodiment E.46, in which step (iii) is carried out at a temperature of 50 to 100°C (especially if the oxygen-based oxidizing agent used in step (iii) is hydrogen peroxide).

[0062] E.48. The process according to embodiment E.47, in which step (iii) is carried out at a temperature of 50 to 90°C (especially if the oxygen-based oxidizing agent used in step (iii) is hydrogen peroxide).

[0063] E.49. The process according to any of the previous embodiments, wherein, in step (iv), the reaction mixture obtained in step (iii) is adjusted to a pH of 5 to 6.

[0064] E.50. The process according to any of the previous embodiments, in which, in step (iv), the same basic potassium salt as in step (i) is used.

[0065] E.51. The process according to any of the preceding embodiments, for preparing the iron(III) potassium ethylenediaminetetraacetic acid salt in granule form, further comprising (v) subjecting the reaction product of step (iv) to a granulation step.

[0066] E.52. The process according to embodiment E.51, in which granulation is carried out under fluidized bed conditions.

[0067] Preferably, in step (i), the basic potassium salt is used Petition 870250094424, dated 15 / 10 / 2025, p. 22 / 43 / 27 in an amount of 0.7 to 1 mol, more preferably 0.7 to 0.9 mol, even more preferably 0.75 to 0.85 mol, in particular 0.80 to 0.82 mol, per mole of the acidic form of ethylenediaminetetraacetic acid. The amount of the basic potassium salt therefore refers to the amount of potassium in said salt. Thus, if, for example, a potassium salt of a doubly negatively charged anion is used as a base (therefore containing 2 mol of K per mol of salt), such as potassium carbonate, this salt is preferably used in an amount of 0.35 to 0.5 mol, more preferably 0.35 to 0.45 mol, even more preferably 0.375 to 0.425 mol, in particular 0.40 to 0.41 mol, per mol of the acidic form of ethylenediaminetetraacetic acid.

[0068] When the above amounts of the basic potassium salt are used, the partially neutralized ethylenediaminetetraacetic acid obtained in step (i) is therefore the monopotassium salt of ethylenediaminetetraacetic acid or a mixture of the monopotassium salt of ethylenediaminetetraacetic acid and the acid form of ethylenediaminetetraacetic acid.

[0069] Suitable basic potassium salts are preferably inorganic. Among these, preference is given to bases that do not introduce foreign anions into the reaction mixture. Examples of such bases are potassium hydroxide (KOH), potassium carbonate (K2CO3; the carbonate can be converted to carbonic acid, which decomposes into water and CO2, and the latter can be removed physically, for example, by heating) and potassium oxide. Due to their better solubility, potassium hydroxide and potassium carbonate are preferred. The most efficient, as it is very well soluble in aqueous medium, very basic and does not require any additional steps for its removal, is therefore the most preferred.

[0070] Step (i) is preferably carried out by preparing a suspension of the acidic form of ethylenediaminetetraacetic acid in water and adding the basic potassium salt to said suspension.

[0071] Suspension of the acidic form of ethylenediaminetetraacetic acid Petition 870250094424, dated 15 / 10 / 2025, p. 23 / 43 / 27 in water preferably contains EDTA in an amount of 0.1 to 10 mol per kg of water, more preferably 0.5 to 5 mol per kg of water, even more preferably 1 to 5 mol per kg of water, in particular 2 to 4 mol per kg of water. Since the potassium ethylenediaminetetraacetic acid salt formed by partial neutralization with the basic potassium salt in step (i), as well as the iron and potassium ethylenediaminetetraacetic acid complex salts formed in steps (ii), (iii) and (iv) are relatively well soluble (better, for example, than the respective ammonium or sodium salts), the concentration of ethylenediaminetetraacetic acid in step (i) can be relatively high, thus allowing a reduction in the total amount of wastewater and reducing the energy consumption required to remove the water to obtain the desired KFeEDTA in solid form.Thus, in a particular embodiment, the suspension of the acidic form of ethylenediaminetetraacetic acid in water contains EDTA in an amount of 2 to 10 mol per kg of water, more preferably 2 to 5 mol per kg of water, even more preferably 3 to 5 mol per kg of water or 3 to 4 mol per kg of water.

[0072] The basic potassium salt can be added in substance or as an aqueous solution, but it is preferably added as an aqueous solution. This facilitates the control of exothermic reactions and ensures adequate and rapid distribution in the reaction mixture, which is of particular importance when the reaction is carried out on an industrial scale. The concentration of the potassium salt in said aqueous solution is not critical, but if the concentration of ethylenediaminetetraacetic acid is maintained in more concentrated ranges, it is preferable to use relatively highly concentrated solutions of the potassium salt, such as aqueous solutions containing 30 to 70% by weight or 40 to 60% by weight of the potassium salt, relative to the total weight of the solution.

[0073] The basic potassium salt is preferably added continuously or in portions, the rate of addition generally being such that exothermic reactions can be controlled. Petition 870250094424, dated 10 / 15 / 2025, page 24 / 43 / 27

[0074] The partial neutralization of the acidic form of ethylenediaminetetraacetic acid in step (i) is generally exothermic. The reaction mixture can be cooled during the addition of the basic potassium salt, but this is not necessary if the form and rate of addition of the basic potassium salt are such that the exothermicity can be controlled. It may even be advantageous not to cool the reaction mixture in step (i) (provided that the exothermicity can be controlled, of course), but to use the heat of reaction in the next step, which is preferably carried out at an elevated temperature, as will be explained below.

[0075] The (partial) neutralization reaction occurs instantaneously and therefore, after all the basic potassium salt has been added, the reaction mixture may be subjected to the next step (ii), if desired after cooling (if the neutralization reaction has not been cooled) and / or if desired after isolating the partially neutralized ethylenediaminetetraacetic acid.

[0076] The reaction mixture obtained in step (i) containing the partially neutralized ethylenediaminetetraacetic acid is reacted in step (ii) with a source of Fe3O4. Although it is mostly possible to isolate the partially neutralized ethylenediaminetetraacetic acid from the reaction mixture obtained in step (i) and then subject it to a further reaction with a source of Fe3O4, this is neither necessary nor economical. Therefore, the reaction mixture is preferably used in step (ii) as obtained rather than in step (i) without any intermediate purification / isolation step.

[0077] Fe3O4 is a mixed oxide of Fe(II) and Fe(III) and can be defined more illustratively as Fe2+(Fe3+)2O4.

[0078] Suitable sources of Fe3O4 are, for example, natural magnetite and synthetic magnetite. Synthetic magnetites are essentially pure Fe3O4, while natural magnetites may contain small amounts of impurities (common impurities are Mg, Zn, Mn, Ni, Cr, Ti, V, Al and / or silica). However, as natural magnetites generally Petition 870250094424, dated 10 / 15 / 2025, page 25 / 43 / 27, meet the demands of the current process and, due to their lower costs compared to synthetic magnetites, they are preferentially used as a source of Fe3O4.

[0079] The Fe3O4 source is preferably used in an amount of 0.2 to 0.5 mol, more preferably 0.2 to 0.4 mol, even more preferably 0.30 to 0.35 mol, particularly preferably about 0.33 mol, per mol of the acid form of ethylenediaminetetraacetic acid (i.e., per mol of the amount of EDTA introduced in step (i)), wherein the amount of Fe3O4 source refers to the amount of Fe3O4 contained in said source. “Ca.” means to include some deviation from the exact value, due, for example, to weighing errors. The deviation generally does not exceed ±10%, preferably ±5%.

[0080] Step (ii) is preferably carried out at a temperature of 80 to 100°C, more preferably 90 to 100°C.

[0081] Step (ii) is preferably carried out at a pH of 3 to 5, more preferably 3 to 4.5. Generally, this pH is obtained intrinsically by the partial neutralization of EDTA in step (i) and therefore no further measures to adjust the pH are necessary. If an adjustment of the pH is exceptionally necessary, to avoid the introduction of foreign ions, the desired pH range is preferably defined by the addition of additional EDTA (acidic form thereof), if the pH is too basic, or of the basic potassium salt used in step (i), if the pH is too acidic. The pH adjustment may occur before or during the reaction with the Fe3O4 source; for example, before, during or shortly after the Fe3O4 source is added.

[0082] Step (ii) is preferably carried out by adding the Fe3O4 source to the reaction mixture obtained in step (i). As the reaction is not exothermic, the Fe3O4 source can be added all at once, but also continuously or in portions. The Fe3O4 source can be added as a substance or as an aqueous suspension, but is preferably added in Petition 870250094424, dated 10 / 15 / 2025, page 26 / 43 / 27 substance. During or after the addition of the Fed'H source, the reaction mixture is brought to the desired temperature.

[0083] If partially neutralized ethylenediaminetetraacetic acid has been isolated before being subjected to the reaction in step (ii), it will preferably be first dissolved in water before being mixed with the Fe3U4 source, or the partially neutralized ethylenediaminetetraacetic acid and the Fe3U4 source will first be mixed and then dissolved / suspended in water.

[0084] The reaction in step (ii) leads to a reaction mixture containing, in addition to the desired potassium salt of the Fe(III) EDTA complex, also the potassium salt of the Fe(II) EDTA complex.

[0085] In step (iii), the Fe(II) in said complex compounds is oxidized to Fe(III).

[0086] For this purpose, the product of the reaction in step (ii) is reacted with an oxygen-based oxidizing agent.

[0087] Although it is mostly possible to isolate the potassium salt from the Fe(III) / (Fe(II))-EDTA mixed complex from the reaction mixture obtained in step (ii) and / or remove the unreacted Fe3O4 source, if present (its removal can be carried out, for example, by filtration or sedimentation) and then subject the isolate or the purified reaction mixture to the oxidation step (iii), this is neither necessary nor economical. Therefore, the reaction mixture is preferably used in step (iii) as obtained in step (ii) without any intermediate purification / isolation step.

[0088] The oxygen-based oxidizing agent is preferably selected from oxygen, air, oxygen / nitrogen mixtures other than air (such mixtures generally contain a higher concentration of oxygen than air) and hydrogen peroxide. More preference is given to oxygen, air and hydrogen peroxide. Even more preference is given to air and oxygen. Petition 870250094424, dated 10 / 15 / 2025, page 27 / 43 / 27

[0089] Although oxygen is a very effective oxidizing agent, on an industrial scale, precautionary measures may be necessary for oxygen-rich exhaust gases, which may need to be diluted or have their oxygen depleted before being released into the atmosphere. Furthermore, since common lubricating oils and greases can self-ignite in oxygen-rich atmospheres, specific lubricants or specific non-lubricated equipment are required (the same applies if oxygen / nitrogen-rich mixtures are used as oxidizing agents).

[0090] Hydrogen peroxide, usually used as an aqueous solution containing, for example, about 10, 20, 30, 40 or 50% H2O2, is also an efficient oxidizing agent, but precautionary measures are also necessary, for example, to control exothermic reactions during the oxidation process.

[0091] Surprisingly, air also proved effective. As it does not present any of the problems that can arise with the use of the other oxidizing agents mentioned above, and due to its significantly lower costs, air is given preference as an oxidizing agent in step (iii).

[0092] If a gaseous oxidizing agent is used, such as oxygen, air or oxygen / nitrogen mixtures other than air, step (iii) may be carried out by usual means, such as spraying the reaction mixture obtained in step (b) with said gas. The gas is generally used in compressed form.

[0093] If hydrogen peroxide is used as the oxidizing agent, step (iii) may be carried out by usual means, such as adding an aqueous solution of hydrogen peroxide to the reaction mixture obtained in step (ii). The addition may be carried out continuously or in portions. The rate of addition is generally such that exothermicity can be controlled.

[0094] Step (iii) is preferably carried out at a pressure from atmospheric pressure to 15 bar (1.5 MPa), more preferably at a pressure Petition 870250094424, dated 10 / 15 / 2025, page 28 / 43 / 27 atmospheric pressure at 10 bar (1 MPa). Atmospheric pressure means the local ambient pressure and is therefore approximately 1013.25 hPa ± 200 hPa (1013.25 mbar ± 200 mbar).

[0095] In a more preferred embodiment, step (iii) is performed at atmospheric pressure.

[0096] In another, more preferred embodiment, step (iii) is carried out at a pressure of 2 to 15 bar (0.2 to 1.5 MPa), more preferably 3 to 15 bar (0.3 to 1.5 MPa), even more preferably 3 to 10 bar (0.3 to 1 MPa), for example, 4 to 10 bar (0.4 to 1 MPa), or 3 to 6 bar (0.3 to 0.6 MPa), or 3 to 5 bar (0.3 to 0.5 MPa), or 4 to 6 bar (0.4 to 0.6 MPa).

[0097] If hydrogen peroxide is used as an oxidizing agent, the pressure will generally be atmospheric pressure.

[0098] If oxygen or oxygen / nitrogen mixtures rich in oxygen, the latter containing, for example, 50% or more by weight of oxygen, are used as the oxidizing agent, the reaction pressure will not be critical and may vary between atmospheric pressure and 15 bar (1.5 MPa) (and, of course, higher pressures, but this is neither necessary nor economical).

[0099] If air is used as an oxidizing agent, the reaction pressure may also vary between atmospheric pressure and 15 bar (1.5 MPa) (and, of course, higher pressures, but this is neither necessary nor economical), but oxidation will occur more efficiently at higher pressures, for example, from 2 to 15 bar (0.2 to 1.5 MPa), or from 3 to 15 bar (0.3 to 1.5 MPa), or from 4 to 15 bar (0.4 to 1.5 MPa), or from 3 to 10 bar (0.3 to 1 MPa), or from 4 to 10 bar (0.4 to 1 MPa), or from 4 to 6 bar (0.4 to 0.6 MPa), or from 3 to 5 bar (0.3 to 0.5 MPa). Thus, in the case of using air as an oxidizing agent, step (iii) is preferably carried out at a pressure above ambient pressure, preferably from 2 to 15 bar (0.2 to 1.5 MPa), more preferably from 3 to 15 bar (0.3 to 1.5 MPa), even more preferably from 3 to 10 bar (0.3 to 1 MPa), in particular from 3 to 6 bar (0.3 to 0.6 MPa), for example, from 4 to 6 bar (0.4 to Petition 870250094424, dated 10 / 15 / 2025, p. 29 / 43 / 27 0.6 MPa) or 3 to 5 bar (0.3 to 0.5 MPa).

[00100] Although the reaction temperature in step (iii) can be primarily as high as the temperature in step (ii), the suitable reaction temperature ranging, for example, from 10 to 100°C, it has been found that oxidation rates are higher at lower reaction temperatures if a gaseous oxidizing agent, such as oxygen, air, or oxygen / nitrogen mixtures other than air, are used, and the decomposition of the resulting products is also reduced. Thus, step (iii) is most preferably carried out from 10 to 40°C, even more preferably from 15 to 30°C, in particular from 20 to 30°C or from 20 to 25°C, especially if gaseous oxidizing agents are used. However, it is also possible to carry out step (iii) at higher temperatures, such as 40 to 100°C or 50 to 100°C or 50 to 90°C, for example, to shorten the process time.In the case of hydrogen peroxide, the reaction temperature is preferably in the range of 10 to 100°C, more preferably from 50 to 100°C, and even more preferably from 50 to 90°C, for example, from 70 to 90°C.

[00101] If during step (iii) the amount of water is depleted, which may occur, for example, if a gaseous oxidizing agent, such as air or oxygen, is sprayed through the reaction mixture and water has entered, it will be advisable to replace the depleted water to avoid the formation of precipitates due to an excessive concentration of reactants and products. The replacement of water may be carried out during step (iii) or, more conveniently, after the completion of step (iii), for example, before, during or after the pH adjustment in step (iv).

[00102] The pH of the reaction mixture obtained in step (iii) is generally slightly acidic and, therefore, in step (iv), the reaction mixture obtained in step (iii) is generally adjusted to a pH of 5 to 7, preferably to a pH of 5 to 6, by mixing the reaction mixture obtained in step (iii) with a base, preferably by adding a base to the reaction mixture obtained Petition 870250094424, dated 10 / 15 / 2025, page 30 / 43 / 27 in step (iii). Appropriately, to avoid the introduction of foreign cations or other foreign materials, the base is a basic potassium salt, preferably the same basic potassium salt used in step (i). Here too, the basic potassium salt is preferably added as an aqueous solution.

[00103] The potassium basic salt base is preferably added in an amount to obtain a fully neutralized KFe(III)EDTA, i.e., in an amount such that the molar ratio of the total amount of potassium basic salt used in steps (i) and (iv) and ethylenediaminetetraacetic acid used in step (i) is approximately 1:1. If, in step (i), the potassium basic salt has been added in an amount of 1 mol (or more) per mol of ethylenediaminetetraacetic acid, the pH may already be in the desired range and pH adjustment will not be necessary. In this case, step (iv) may be skipped. “Ca.” in this case also means allowing a deviation of ±10%, preferably ±5%, from the exact ratio.

[00104] Suitable reaction vessels for carrying out steps (i) to (iv) are known to those skilled in the art. If no intermediate isolation or purification step is carried out between the different reaction steps (i) to (iv), the reaction in steps (i) to (iv) may be carried out in the same reaction vessel; wherein, in the case of using oxygen or oxygen-nitrogen mixtures rich in oxygen as oxidizing agents, the conditions mentioned above (specific apparatus without lubricant or special lubricant) shall be applied. Suitable reactors contain at least a means for introducing liquid and solid reagents and, if applicable, a means for introducing gaseous oxidizing agents, as well as a gas outlet (in the case of oxygen or oxygen-nitrogen mixtures rich in oxygen as oxidizing agents, the gas outlet must be connected to suitable equipment for stripping the exhaust gas of oxygen and / or returning it to the reaction).In addition, the reactor conveniently contains one. Petition 870250094424, dated 10 / 15 / 2025, page 31 / 43 / 27 agitator and means for cooling and / or heating; the presence of a pH control sensor is also desirable.

[00105] Steps (i) to (iv) can be carried out alternatively in different reaction vessels, each adapted to the specific needs of the respective step.

[00106] If desired, the product obtained in step (iv) may be subjected to further purification, such as filtration, if necessary after dilution, to remove solid residues from, for example, the Fe3O4 source, especially if it is natural magnetite or unwanted by-products.

[00107] To obtain a solid KFe(III)EDTA product, standard procedures can be applied, such as crystallization, if necessary, after concentration of the aqueous product, for example, by partial evaporation of the water, or total removal of the water, for example, by total evaporation, if desired, under reduced pressure, or by spray drying.

[00108] Preferably, however, KFe(III)EDTA is converted into granules.

[00109] Thus, in a preferred embodiment, the process of the invention is for preparing iron(III) and potassium ethylenediaminetetraacetic acid salt in the form of granules, further comprising (v) subjecting the reaction product of step (iv) to a granulation step.

[00110] Granulation can be carried out by known methods, such as granulation in a high-shear granulator, in a twin-screw granulator or in a fluidized bed granulator. Preferably, granulation is carried out under fluidized bed conditions.

[00111] The invention process leads to the desired KFe(III)EDTA in good yields, with high total iron content, low Fe(II) content, requires no catalyst and avoids the presence of unwanted extraneous anions, such as Petition 870250094424, dated 10 / 15 / 2025, page 32 / 43 / 27 as sulfate, chloride or nitrate. Furthermore, the process can be carried out with low-cost materials, such as natural magnetite as the iron source and air as the oxidizing agent, thus being economical and efficient.

[00112] The following examples serve as further illustration of the invention. EXAMPLES Analysis

[00113] To monitor the progress of the reaction and the conversion of EDTA to the potassium salt of the iron complex, the amount of free EDTA (i.e., acidic form) was determined by titration with a 0.05 mol solution of Fe2(SO4)3.

[00114] The amount of Fe2+ and Fe3+ in the KFe(III)EDTA product was also determined titrimetrically: Determination of Fe2+: In a titration vessel heated to 80°C, 60 ml of 1 N HCl solution were added. A weighted sample of the reaction solution was added and titrated with a 0.1 mol K2Cr2O7 solution. Determination of Fe3+: In a titration vessel heated to 80°C, 60 ml of 1 N HCl solution were added. A weighted sample of the resulting reaction solution was added and titrated with a 0.1 mol TiCl3 solution. Example 1: Synthesis of KFe(III)EDTA - oxidation with air at atmospheric pressure

[00115] a) 1369.7 g (76.032 mol) of water were placed in a 4 L three-necked flask equipped with a stirrer and chiller. 1 kg (3.422 mol) of EDTA (acid form; Trilon® BS, from BASF SE) was added using a powder funnel. A suspension was formed without any exothermic reaction. Under stirring, 311.0 g (2.772 mol, 0.8 mol eq.) of a 50% aqueous KOH solution were added dropwise over 30 minutes. As the reaction of Petition 870250094424, dated 10 / 15 / 2025, p. 33 / 43 / 27 KOH with EDTA is strongly exothermic, the reaction suspension was cooled with ice during the addition. However, analogous experiments without cooling showed that this is not mandatory, and the quality of the partial potassium EDTA salt formed is not affected by higher temperatures.

[00116] b) Under stirring, 261.5 g (1.129 mol) of a natural magnetite (Magnachem® WT-1 from LKAB, Sweden) were added using a powder funnel. The stirred reaction mixture was heated to 95°C and held at this temperature for 5 hours. During heating, a dark reddish-brown solution with a pH around 3 to 4 was formed, with small amounts of unreacted magnetite solid particles. The product suspension was allowed to cool to room temperature.

[00117] c) A strong stream of air was then passed through a frit into the solution for 4 hours.

[00118] d) During the oxidation step, some of the water was removed by the airflow and this loss was replaced. The suspension was then adjusted to a pH of 5.5 by adding 51 ml of 50% (0.45 mol, 0.2 mol eq.) KOH.

[00119] Finally, the reaction solution was filtered through a suction filter to give a clear solution of KFe(III)EDTA.

[00120] Yield: 3335 g of solution containing 1297.8 g of the desired KFe(III)EDTA (C^HuFe^OsK; M = 383.15 g / mol), 99% yield relative to the starting material EDTA. Total Fe content in KFeEDTA: 14% with Fe2+ ~ 0.2 - <1.0%.

[00121] The solution was analyzed by electrospray mass spectrometry (ESI).

[00122] MS: Mr 344 [M]-(C^H^Os^Fe)

[00123] The KFe(III)EDTA solution obtained can be used directly for granulation. Example 2: Synthesis of KFe(III)EDTA - oxidation with oxygen at atmospheric pressure Petition 870250094424, dated 10 / 15 / 2025, page 34 / 43 / 27

[00124] a) 1759 g (97.6 mol) of water were placed in a 4 L three-necked flask equipped with a stirrer and cooler. 1900 g (6.5 mol) of EDTA (acid form; Trilon® BS, from BASF SE) were added using a powder funnel. A suspension was formed without any exothermic reaction. Under stirring and cooling, 590.9 g (5.26 mol, 0.8 mol eq.) of a 50% aqueous KOH solution were added dropwise over 30 minutes, maintaining the temperature below.

[00125] b) Under stirring, 602 g (2.6 mol) of natural magnetite (Magnachem® WT-1 from LKAB) were added using a powder funnel. The stirred reaction mixture was heated to 95°C and held at that temperature for 5 hours. The product suspension was allowed to cool to 20°C.

[00126] c) A 1 L aliquot of this reaction mixture was placed in a 3-necked round-bottom flask equipped with a reflux condenser, thermometer, and an oxygen inlet (immersed glass tube). The equipment must be free of lubricating oil and grease. Oxygen was then passed through the solution for three hours at a flow rate of 30 L / h and an internal temperature of 20 to 25°C.

[00127] d) The suspension was then adjusted to a pH of 5.5 by the addition of KOH.

[00128] Filtration of this reaction suspension through a suction filter produced a clear reddish-brown solution containing KFe(III)EDTA.

[00129] Yield: 99% relative to EDTA starting material.

[00130] Total Fe content in KFeEDTA: 14.5% with Fe2+<0.2%.

[00131] The KFe(III)EDTA solution obtained can be used directly for granulation. Example 3: Synthesis procedure for KFe(III)EDTA - oxidation with pressurized air

[00132] 200 ml of a reaction mixture obtained in analogy to Petition 870250094424, dated 10 / 15 / 2025, page 35 / 43 / 27 example 2b) were placed in an autoclave. Pressurized air ap = 4 bar (0.4 MPa) was passed through the autoclave for 4 hours at 20°C. The composition of the air after the reaction was monitored. When it was no longer possible to measure oxygen uptake, the oxidation was stopped. Oxidation with pressurized air was also carried out at 50°C and 80°C, but the reaction rates were prolonged compared to the reaction at 20°C.

[00133] The suspension was then adjusted to a pH of 5.5 by the addition of KOH. Filtration of this reaction suspension through a suction filter produced a clear reddish-brown solution which was used directly for granulation.

[00134] Yield: 99% relative to EDTA starting material.

[00135] Total Fe content of KFe(III)EDTA (100% active): 14% with Fe2+ ~0.2 - 0.3%.

[00136] The KFe(III)EDTA solution obtained can be used directly for granulation. Example 4: Synthesis procedure for KFe(III) EDTA - oxidation with hydrogen peroxide

[00137] 1.0 l of a reaction mixture obtained by analogy to the example 2b) was placed in a 3-necked round-bottom flask fitted with a reflux condenser, thermometer, and addition funnel and heated to 80°C under stirring. 33.6 mL of a 30% by weight aqueous hydrogen peroxide solution (0.55 mol per mol of FeII) were added over 1 hour. The reaction mixture was then allowed to cool to room temperature, and the suspension was adjusted to a pH of 5.5 by the addition of KOH. Filtration of this reaction suspension through a suction filter yielded a clear reddish-brown solution.

[00138] The KFe(III)EDTA solution obtained can be used directly for granulation. Petition 870250094424, dated 10 / 15 / 2025, page 36 / 43 / 27 Example 5: Synthesis of KFe(III)EDTA - reaction with synthetic magnetite and oxidation with air at atmospheric pressure.

[00139] a) 1369.7 g (76.032 mol) of water were placed in a 4 L three-necked flask equipped with a stirrer and chiller. 1 kg (3.422 mol) of EDTA (acid form; Trilon® BS, from BASF SE) was added using a powder funnel. A suspension was formed without any exothermicity. Under stirring, 311.0 g (2.772 mol, 0.8 mol eq.) of a 50% aqueous KOH solution were added dropwise over 30 minutes. Because the reaction of KOH with EDTA is strongly exothermic, the reaction suspension was cooled to <20°C with ice during the addition.

[00140] b) Under stirring, 261.5 g (1.129 mol) of a synthetic magnetite (Lanxess Bayferrox® 318 M) were added using a powder funnel. The stirred reaction mixture was heated to 95°C and held at that temperature for 3 hours. The product suspension was allowed to cool to room temperature.

[00141] c) A strong stream of air was then passed through a frit into the solution for 8 hours.

[00142] d) During the oxidation step, some of the water was removed by the airflow and this loss was replaced. Finally, the reaction solution was filtered through a suction filter, and the suspension was then adjusted to a pH of 5 by adding 50% KOH, to give a clear solution of KFe(III)EDTA.

[00143] Yield: 83.5% relative to EDTA starting material.

[00144] Total Fe content in KFeEDTA: 13% with Fe2+0.1%. Example 6: Granulation of KFe(III)EDTA

[00145] Granulation was performed using a DMR granulation apparatus. KFe(III)EDTA was used as a model, which was previously completely dried in a drying oven for 24 hours at 95°C and then ground in a laboratory mill (Polymix PX-MFC 90 D). For granulation, 150 mL of Petition 870250094424, dated 10 / 15 / 2025, page 37 / 43 / 27 A saturated solution of KFe(III)EDTA was placed in an open container with stirring and continuously agitated with an anchor stirrer. With a pumping flow rate of 17-19 g / min, the solution was conveyed to the nozzle (1 mm diameter) in the granulation apparatus. The nozzle pressure throughout the granulation was p = 1.5 bar (0.15 MPa) (atomization pressure), the purge gas pressure p = 2.0 bar (0.2 MPa). The differential pressure was detected as p = 27 mbar (0.0027 MPa), the differential pressure at the filter was p = 10 mbar (0.001 MPa), but increased to 16 mbar (0.0016 MPa) during the course of the experiment. The product temperature was set to T = 100°C with a feed air temperature of T = 170°C. The gas pressure during granulation was p = 2.1 bar (0.21 MPa), and the gas flow rate was 25 m³ / h. Nitrogen was used as the gas atmosphere. The material was sieved after granulation was complete.26 g of stable granules were obtained. Petition 870250094424, dated 10 / 15 / 2025, pp. 38 / 43

Claims

1 / 4 CLAIMS 1. Process for preparing the iron(III) and potassium ethylenediaminetetraacetic acid complex salt, KFe(III)EDTA, characterized in that it comprises (i) reacting in an aqueous medium the acidic form of ethylenediaminetetraacetic acid with a basic potassium salt to form a partially neutralized ethylenediaminetetraacetic acid; (ii) reacting the reaction mixture obtained in step (i) with a source of Fe3O4 of an iron and potassium ethylenediaminetetraacetic acid complex salt containing iron (II) and (III); (iii) oxidizing the iron and potassium ethylenediaminetetraacetic acid complex salt containing iron (II) and (III) to an iron(III) and potassium ethylenediaminetetraacetic acid complex salt with an oxygen-based oxidizing agent; and (iv) adjusting the reaction mixture obtained in step (iii) to a pH of 5 to 7 with a basic potassium salt.

2. Process according to claim 1, characterized in that, in step (i), the basic potassium salt is used in an amount of 0.7 to 1 mol, preferably 0.7 to 0.9 mol, more preferably 0.75 to 0.85 mol, in particular 0.80 to 0.82 mol, per mol of the acid form of ethylenediaminetetraacetic acid, wherein the amount of basic potassium salt refers to the amount of potassium in said salt; wherein the partially neutralized ethylenediaminetetraacetic acid obtained in step (i) is the monopotassium salt of ethylenediaminetetraacetic acid or a mixture of the monopotassium salt of ethylenediaminetetraacetic acid and the acid form of ethylenediaminetetraacetic acid.

3. Process according to any of the preceding claims, characterized in that the basic potassium salt used in steps (i) and (iv) is KOH; wherein the KOH is preferably added as an aqueous solution.

4. A process according to any of the preceding claims, characterized in that the source of Fe3O4 is natural or synthetic magnetite.

5. Process according to claim 4, characterized in that the source of Fe3O4 is natural magnetite.

6. Process according to any of the preceding claims, characterized in that the Fe3O4 source is used in an amount of 0.2 to 0.5 mol, preferably 0.2 to 0.4 mol, more preferably 0.30 to 0.35 mol, even more preferably about 0.33 mol, per mole of the acidic form of ethylenediaminetetraacetic acid, wherein the amount of Fe3O4 source refers to the amount of Fe3O4 contained in said source.

7. Process according to any of the preceding claims, characterized in that step (ii) is carried out at a temperature of 80 to 100°C, preferably 90 to 100°C.

8. Process according to any of the preceding claims, characterized in that step (ii) is carried out at a pH of 3 to 5, preferably 3 to 4.

5.

9. Process according to any of the preceding claims, characterized in that step (iii) is carried out at a pressure from atmospheric pressure up to 15 bar (1.5 MPa), preferably from atmospheric pressure up to 10 bar (MPa).

10. Process according to claim 9, characterized in that step (iii) is carried out at atmospheric pressure; or is carried out at a pressure of 3 to 10 bar (0.3 to 1 MPa).

11. Process according to any of the preceding claims, characterized in that the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air, oxygen / nitrogen mixtures other than air and hydrogen peroxide.

12. Process according to claim 11, characterized in that the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air and hydrogen peroxide.

13. Process according to claim 12, characterized in that the oxygen-based oxidizing agent used in step (iii) is air.

14. Process according to any of the preceding claims, characterized in that step (iii) is carried out at a temperature of 10 to 100°C, preferably 10 to 40°C, more preferably 15 to 30°C.

15. Process according to any of the preceding claims, characterized in that the oxygen-based oxidizing agent used in step (iii) is selected from oxygen, air and oxygen / nitrogen mixtures other than air, and step (iii) is carried out at a pressure from atmospheric pressure to 15 bar (1.5 MPa), preferably from atmospheric pressure to 10 bar (1 MPa), and at a temperature of 10 to 40°C, preferably from 15 to 30°C, more preferably from 20 to 25°C; or the oxygen-based oxidizing agent used in step (iii) is hydrogen peroxide, and step (iii) is carried out at atmospheric pressure and at a temperature of 40 to 100°C, preferably from 50 to 100°C, more preferably from 50 to 90°C, in particular from 70 to 90°C.

16. Process according to any of the preceding claims, characterized in that, in step (iv), the reaction mixture obtained in step (iii) is adjusted to a pH of 5 to 6.

17. Process according to any of the preceding claims, characterized in that it is for preparing the complex salt of iron(III) and potassium ethylenediaminetetraacetic acid in the form of granules, further comprising Petition 870250094424, dated 10 / 15 / 2025, page 41 / 43 4 / 4 (v) subjecting the reaction product of step (iv) to a granulation step.

18. Process according to claim 17, characterized in that the granulation is carried out under fluidized bed conditions. Petition 870250094424, dated 10 / 15 / 2025, pp. 42 / 43

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