A method for manufacturing a prussian white compound

Abstract

The present disclosure generally relates to a Prussian White compound comprising: a) reacting a first precursor selected from NaCN and KCN with a salt selected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCI2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCI2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCI2, and combinations thereof to form a second precursor defined by the formula A4X1(CN)6 and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K, and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn; b) reacting the second and third precursors with an acid selected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCI, and HCIO2 under conditions that allow for a Prussian White compound to be formed and for HCN to be formed as a by-product, wherein the Prussian White compound is defined by the formula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2; c) recycling said HCN by reacting NaOH or KOH with said HCN to form said first precursor; and d) introducing said first precursor into said step a). The present disclosure also relates to a system for manufacturing a Prussian White compound.

Description

[0001]A METHOD FOR MANUFACTURING A PRUSSIAN WHITE COMPOUND TECHNICAL FIELD The present invention relates to a method for manufacturing a Prussian whitecompound and to a system for manufacturing the Prussian white compound.BACKGROUND To date, lithium-ion based batteries (LIB) dominate the market for rechargeable batteries. However, the technology is associated with drawbacks, particularly since the availability of lithium resources is limited. Furthermore, the disposal of spent LIBs is challenging both from a recycling and waste management perspective. Specific precautions are typically required to handle spent LIBs in a safe manner, and improper disposal may have a negative environmental impact. Sodium ion batteries (SIBs) have emerged as attractive alternatives to LIBs. SIBs offer environmental advantages due to the abundance of sodium resources and the reduced environmental impact associated with sodium extraction and processing. The performance of a sodium ion battery is largely dependent on the properties of the cathode material. Prussian White (PW) is an environmentally friendly cathode material, which has gained considerable attention due to its high theoretical capacity and rate performance. Prussian White has a crystal structure with an open three-dimensional framework and large interstitial voids, which makes it capable of storing sodium ions in an efficient manner. Prussian White may be synthesized via co-precipitation, in which an aqueous solution of precursor salts, e.g. sodium ferrocyanide (Na4Fe(CN)6) and iron sulfate (FeSO4) are mixed and reacted under conditions that lead to the formation of an insoluble product, Prussian White, to precipitate out of the solution. Alternatively, Prussian White may be synthesized via acid decomposition, as described in e.g. WO2018 / 056890A1. Acid decomposition involves treating a transition metal cyanide-containingprecursor, e.g. sodium ferrocyanide (Na4Fe(CN)6) with an acid under conditions leading todecomposition of the precursor. The acidic environment and specific reaction conditionscause some of the cyanide groups (CN) to dissociate from the transition metal cyanide-containing precursor and combine with hydrogen ions (H+) to form HCN gas. The remaining free metal ions then react with residual transition metal cyanide-containing precursor to form Prussian white. While the acid decomposition synthesis route can achieve Prussian White having a high sodium / potassium content (compared to co-precipitation), the production of HCN gas during synthesis is associated with several challenges. HCN is toxic and requires stringent safety measures for handling and disposal. Furthermore, improper management of HCN can lead to severe environmental risks. Furthermore, in the synthesis of Prussian White, large amounts of virgin starting materials are typically consumed, which is associated with high costs and high energy demands. In view of this, there is a need to provide an improved method to synthesize Prussian White via the acid decomposition route, which is cost-efficient, safe, and associated with a significantly reduced environmental or climate impact. SUMMARY It is an object of the present invention to at least partially overcome the problems of the prior art, and to provide a more sustainable method for manufacturing Prussian white compounds. This and other objects, which will become apparent in thefollowing, are accomplished by a method of manufacturing a Prussian white compound and asystem for manufacturing a Prussian White compound, as defined in the independent claims. According to a first aspect of the invention, there is provided a method for manufacturing a Prussian White compound comprising: a) reacting a first precursor selected from NaCN and KCN with a salt selectedfrom the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2,CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2,Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2,MnC2O4, MnCl2, and combinations thereof to form a second precursor defined by the formulaA4X1(CN)6and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K,and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn;b) reacting said second and third precursors with an acid selected from thegroup consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 underconditions that allow for a Prussian White compound to be formed and for HCN to be formedas a by-product, wherein said Prussian White compound is defined by the formulaAaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, and 0 ≤ y ≤ 0.2; c) recycling said HCN by reacting NaOH or KOH with said HCN to form saidfirst precursor; andd) introducing said first precursor into said step a). According to a second aspect of the invention, there is provided a system for manufacturing a Prussian White compound comprising: a) a reactor unit configured to conduct a first reaction of a first precursorselected from NaCN and KCN with a salt selected from the group consisting of CoSO4,Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2,Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2,MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereofto form a second precursor defined by the formula A4X1(CN)6and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K, and wherein X1and X2are individuallyselected from Co, Cr, Fe, and Mn; andto conduct a second reaction of said second and third precursors with an acidselected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl,and HClO2 under conditions that allow for a Prussian White compound to be formed and forHCN to be formed as a by-product, wherein said Prussian White compound is defined by theformula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2; and b) a scrubbing device arranged in fluid communication with said reactor unit ,wherein said scrubbing device is configured to conduct a third reaction of NaOH or KOHwith said HCN to form said first precursor, and wherein said scrubbing device is configured to feed said first precursor intosaid reactor unit. The inventive method and system have proven to be highly promising formanufacturing a Prussian white compound suitable as an electrode active material, and inparticular a cathode active material. The present invention is based on the finding that HCN produced as a by-product during the acid decomposition of the second and third precursors may be reacted with NaOH or KOH to form the first precursor. Said formed first precursormay be used in the manufacture of additional second and third precursors, and subsequentlyPrussian white compound. Thus, the efficiency is increased and less virgin first precursor is consumed. Expressed differently, in the present invention, the HCN is recycled to form new first precursor which may be used for manufacturing additional Prussian white compound. This advantageously decreases the need for virgin first precursor material. Thus, the manufacturing method is environmentally friendly and cost-effective. Another advantage associated with the method of the present disclosure is that time-consuming and labor-intensive recovery, destructions steps, and / or waste packaging and transporting steps of the HCN may be avoided. The HCN produced during the process is scrubbed using NaOH (or KOH) to form NaCN (or KCN), which, as mentioned hereinbefore is re-introduced into the manufacturing process. In this regard, the method of the present disclosure may decrease strenuous handling and disposal of toxic HCN. Accordingly, a safer, less hazardous, and more sustainable method to synthesize Prussian White compounds is provided. It is understood that some of the advantages discussed in relation to the first aspect also apply to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS The various aspects of the present disclosure, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which: Figure 1 shows a flowchart explaining the steps of a method in accordance with exemplary embodiments of the present disclosure; Figure 2 schematically illustrates a system in accordance with exemplaryembodiments of the present disclosure; Figures 3a-e illustrate the XRD patterns obtained for the Prussian white particles produced in Example 1; Figure 4 illustrates the XRD pattern obtained for the Prussian white particles produced in Example 2. The figures are not necessarily to scale, and generally only show parts that are necessary in order to elucidate the inventive concept, wherein other parts may be omitted or merely suggested. DETAILED DESCRIPTION The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present disclosure to the skilled person.Figure 1 is a schematic flow-chart describing the steps of the method accordingto a first aspect of the invention. In the first aspect of the invention, there is provided a method 100 for manufacturing a Prussian White compound comprising: a) reacting (101) a first precursor selected from NaCN and KCN with a saltselected from the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2,CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4,Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2,Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereof to form a second precursor definedby the formula A4X1(CN)6and a third precursor defined by the formula A4X2(CN)6, whereinA is Na or K, and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn;b) reacting (102) said second and third precursors with an acid selected from thegroup consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 underconditions that allow for a Prussian White compound to be formed and for HCN to be formedas a by-product, wherein said Prussian White compound is defined by the formulaAaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, and 0 ≤ y ≤ 0.2;c) recycling (103) said HCN by reacting NaOH or KOH with said HCN to formsaid first precursor; andd) introducing (104) said first precursor into said step a).Herein, the term “precursor” refers to a compound or substance that precedes and partakes in the formation of another compound during a chemical reaction. The inventive method and system have proven to be highly promising formanufacturing a Prussian white compound suitable as an electrode active material, and inparticular a cathode active material. The present invention is based on the finding that HCN produced as a by-product during the acid decomposition of the second and third precursors may be reacted with NaOH or KOH to form the first precursor. Said formed first precursormay be used in the manufacture of more second and third precursors, and subsequentlyPrussian white compound. Thus, the efficiency is increased and less virgin first precursor is consumed. Expressed differently, in the present invention, the HCN is recycled to form new first precursor which may be used for manufacturing additional Prussian white compound. This advantageously decreases the need for virgin first precursor material. Thus, themanufacturing method is environmentally friendly, efficient, and cost-effective.Another advantage associated with the method of the present disclosure is that time-consuming and labor-intensive recovery, destructions steps, and / or waste packaging and transporting steps of the HCN may be avoided. In addition, conventional Prussian White synthesis methods typically require lengthy drying and recovering steps, separate sodium enrichment steps, and the use of complex mechanochemical post-synthesis modifications, all of which may be regarded as inconvenient for large scale production. In the method of the present disclosure, the Prussian White compound obtained in step b) may be recovered and subsequently dried. Only one drying step is required. As demonstrated in the Example section, the Prussian White compound obtained is associated with high sodium content and low Fe(CN)6 vacancy content and is a promising cathode active material. Typically, the method of the present disclosure is an in-line method.Accordingly, all steps a)-d) of the method are performed continuously without interruption.This eliminates the need for intermediate recovery, drying, or sodium enrichment steps. This is beneficial to reduce processing time and energy consumption, minimize handling and contamination risks, enhancing efficiency and product quality, and avoiding the use of toxic and costly organic solvents. The inventors have further found that the reaction of step a) is exothermal. This advantageously allows for a more cost-effective and environmentally friendly method as less or in some examples no additional heat needs to be supplied from an external heat source to obtain optimal or at least more optimal reaction conditions in step b). An external heat source may for example be a hot plate, an oil bath, an oven, or an electrical heat tracing system. The second precursor, defined by the formula A4X1(CN)6 may be the same as the third precursor defined by the formula A4X2(CN)6. This will be the case if the cation of the salts used in step a) are the same, or if only one salt, such as FeSO4is used in step a). Accordingly, in the Prussian White compound formed in step b), defined by AaX1[X2(CN)6]1-y, X1 and X2 will be the same, e.g. Fe.For example, step b) may comprise the reaction: 2Na4Fe(CN)6 + 3 H2SO4 ^ Na2Fe[Fe(CN)6] + 6 HCN + 3 Na2SO4.Alternatively, the second precursor, defined by the formula A4X1(CN)6 may be different from the third precursor defined by the formula A4X2(CN)6. This will be the case if the cations of the salts used in the reactions are different, e.g. if two different salts are utilized, such as FeSO4 and CoSO4 in step a). Accordingly, in the Prussian White compoundformed in step b), defined by AaX1[X2(CN)6]1-y, X1 and X2 will be different, e.g. Fe, and Co,respectively. For example, step b) may comprise the reaction:Na4Fe(CN)6 + Na4Mn(CN)6 + 3 H2SO4 ^ Na2Mn[Fe(CN)6] + 6 HCN + 3Na2SO4.As illustrated in figure 1, the method may comprise a step of drying the Prussian White compound obtained in step b) (denoted 105 in figure 1). The method may comprise the steps of: -separating the Prussian White compound obtained in step b);- drying the Prussian White compound.The separation step may for example be performed using a filter press or a centrifuge. The step of drying may be performed by means known to the skilled person. The step of drying may for example be performed using a rotary dryer, a fluidized bed dryer, a spray dryer, a vacuum dryer, or a conveyor dryer. It is understood that the first precursor, the salt, the second and third precursors, and / or the acid may be at least partially dissolved / dissociated in a solvent, such as substantially completely dissolved in a solvent, during step a) and b). In other words, e.g., step a) may comprise reacting a dissolved first precursor with a dissolved salt. Additionally,e.g., step b) may comprise reacting dissolved second and third precursors with a dissociatedacid. Herein, “dissolved / dissociated” refers to a molecule separated into one or more cationsand one or more anions. Herein, the term "virgin first precursor material" refers to a first precursormaterial which has not been recycled through the process of the present disclosure. VirginNaCN (or KCN) may for example be produced by reacting HCN with NaOH (or KOH).Herein, the term “salt” refers to a compound comprising positively charged ions (cations) and negatively charged ions (anions) that are ionically bonded. In a dissolved state the cation(s) and the anion(s) of the salt are dissociated into individual ions. Salt anddissolved salt are known to the person skilled in the art.Reacting the second and third precursors with an acid “under conditions thatallow for a Prussian White compound to be formed” means performing step b) at atemperature of from 75 to 98°C, preferably from 80 to 95°C, preferably from 85 to 95°C andat a pH of from 1.8 to 4.5, preferably from 2 to 3.5. Step b) may be performed during 1 to 24hours, such as 2 to 20 hours, preferably 3 to 12 hours, more preferably 4 to 8 hours. It is contemplated that such conditions trigger acid decomposition of the second and thirdprecursors, whereby the Prussian White compound is formed. Reacting the second and thirdprecursors with an acid may thus be an acid decomposition reaction. Expressed differently,the conditions of step b) allow for acid decomposition of the second and third precursors. Herein, the term “recycling” refers to the process of recovering and treating by- products to produce compounds which may be entered into a production cycle. Herein, the term “by-product” refers to a secondary product or substance that is produced during a chemical reaction or manufacturing process but is not the primary intended product. In other words, by-products are generated alongside the primary intended product. Herein, the term “cathode active material” refers to a material that can reversibly insert ions, such as sodium ions, during cell charge and discharge cycles. CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2, CrSO4,Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2, Fe(CH3CO2)2,Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, andMnCl2 are also known as cobolt(II) sulfate, cobolt(II) phosphate, cobolt(II) acetate, cobolt(II)oxalate, cobolt(II) formate, cobolt chloride, chromium(II) sulfate, chromium(II) phosphate,chromium(II) acetate, chromium(II) oxalate, chromium(II) formate, chromium chloride,ferrous sulfate, ferrous phosphate, ferrous acetate, ferrous formate, ferrous oxalate, ferrouschloride, manganese(II) sulfate, manganese(II) phosphate, manganese(II) acetate,manganese(II) oxalate, manganese(II) formate, and manganese chloride, respectively.H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 are also known as sulfuric acid, acetic acid, oxalic acid, formic acid, phosphoric acid, phosphorous acid, hydrochloric acid, and chlorous acid respectively. NaCN and KCN are also known as sodium cyanide and potassium cyanide, respectively. The term “Prussian White compound” means a compound defined by the formula AaX1[X2(CN)6]1-y, wherein A is Na or K, 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2, X1and X2areindividually selected from Co, Cr, Fe, and Mn. Preferably, X1 and X2 are selected from Feand Mn. The Prussian White compound comprises iron (Fe), manganese (Mn), cobolt (Co),or chromium (Cr) ions which are linked through cyanide (CN) bridges, forming a three-dimensional framework. The framework forms a cubic-like arrangement, in which each iron, manganese, cobolt or chromium ion is surrounded by six cyanide groups. Sodium orpotassium ions reside within the cavities or interstitial sites of the cubic arrangement formedby e.g. Fe[Fe(CN)6] or Mn[Mn(CN)6] units. Herein, Prussian white compound encompassesboth hydrated and dehydrated Prussian white compounds. Hydrated Prussian white compounds may be understood as Prussian whitecompounds having water molecules arranged in voids and / or interstitial spaces of the crystalstructure. The water molecules may be bonded through a hydrogen bond with the nitrogen of the (CN)6, a metal-ligand bond with one of the transition metal cations, or an ion-dipole bond with sodium. Dehydrated Prussian white compounds may be understood as Prussian white compounds substantially free of water molecules arranged in voids and / or interstitial spaces of the crystal structure. The amount of water molecules arranged in voids and / or interstitial spaces of the crystal structure may be determined using Thermogravimetric Analysis (TGA). In some embodiments, X1 and X2 are Fe or Mn. Preferably, X1 and X2 are Fe,and A is Na. The method of the present disclosure may yield Prussian white compounds defined by the formula AaX1[X2(CN)6]1-y, wherein A is Na, 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2, X1and X2are Fe. The method of the present disclosure may yield such Prussian White compound having a high sodium-content and a high degree of crystallinity. The chemical composition of the Prussian white compound may be measured by methods known in the art. For example, an inductively coupled plasma (ICP) spectrometer(e.g., PerkinElmer Avio 200), CHNOS elemental analysis and / or Mössbauer spectrometry(e.g., an MS 96 spectrometer) may be used to measure a content of element(s) in a sample ofthe Prussian white compound. The Prussian white compound is a solid and may be in theform of particles, i.e. discrete portions of solid matter. Typically, the particles have a DV50 value of from 1 to 50μm, preferably from 10 to 45μm, more preferably in the range of from 12 to 30μm, as determined according to ISO 13320:2009. Herein, the term “DV50 value” refers to a particle diameter below which 50% of the sample volume exists. The DV50 value may also be understood as the median particle size by volume or the volumetric particle size distribution. DV50 as such is known to the person skilled in the art. A DV50 value of a sample volume (a plurality of particles) may be measured using, e.g., a PSA 1090 L / D (Anton Paar) instrument. The DV50 may bedetermined according to ISO 13320:2009 or ASTM B822-20.In some embodiments, the step a) is conducted at a pH of from 9 to 14, preferably from 10 to 13. This pH range is beneficial to improve the quality and yield of the second and third precursors, which is important for producing Prussian White with a high sodium (or potassium) content. At pH levels below 9, the second and third precursors can still form, however, undesirable co-precipitation of “poor-quality” Prussian White as well as the formation of unwanted iron solids (e.g. iron hydroxide and iron oxyhydroxide) may also occur, which may lead to reduced material performance and a decreased yield. By performing step a) of the method at a pH level of from 9 to 14, preferably from 10 to 13, the potentially formed Prussian White is unstable, and the second and third precursors become the dominant species, ensuring a high yield and superior product quality. The alkaline pH may be controlled by performing step a) in the presence of analkaline additive. Hence, in step a), the first precursor may be reacted with the salt in thepresence of an alkaline additive, preferably wherein the alkaline additive is selected from thegroup consisting of NH4OH, NaOH, Na3PO4, Na2CO3, KOH, and K2CO3.NH4OH, NaOH, Na3PO4, Na2CO3, KOH, and K2CO3are also known as ammonium hydroxide, sodium hydroxide, trisodium phosphate, sodium carbonate, potassium hydroxide, and potassium carbonate, respectively. In some embodiments, said salt is defined by a first cation and a first anion; saidacid being defined by a second cation and a second anion, wherein said second anion of saidacid in said step b) corresponds to said first anion of said salt in said step a). Providing said second anion of said acid in said step b) corresponding to said first anion of said salt in said step a) advantageously allows for a cost-effective process as only one type of anion (and any accompanying by-products thereof) stemming from the first and second anion must be handled during down-stream processing steps such as effluent treatment. Having different anions of the acid and the salt may lead to two types of residual anions and / or the formation of (at least) one more by-product which may need to be separated and / or processed using different more complex methods. In other words, a consistent chemical environment is provided, which secures that the formation of Prussian White compound proceeds efficiently, and that unwanted by- products or side reactions (with e.g. foreign anions) are not formed. In some embodiments, step b) is performed at a temperature of from 65 to 95°C, preferably from 75 to 95°C. The inventors have found that a temperature range of from 65 to 95°C, preferably from 75 to 95°C, ensures that the Prussian White compound can be obtained in a high yield and with a high sodium (or potassium) content as well as a low vacancy content. In this regard, labor-intensive separate sodium (or potassium) enrichment steps, typically associated with conventional Prussian White synthesis routes, may be avoided. Additionally, the temperatures of from 65 to 95°C, preferably from 75 to 95°C decreases the solubility of HCN in, i.e., an aqueous solution. This advantageously allows for an increased amount of HCN being off-gased, i.e, exiting the aqueous solution and entering a headspace of a reactor vessel. Thus, an increased amount of gaseous HCN may be directed to reacting with the NaOH or KOH. Furthermore, a temperature in the above-mentioned range triggers acid decomposition of the second and third precursors. In some embodiments, step b) is performed at a pH of from 1.8 to 4.5, preferably from 2 to 3.5. The inventors have found that these pH intervals are particularlysuitable for the decomposition of the second and third precursors and result in a significantlyhigher yield of Prussian white compound. In some embodiments of the preceding claims, the step a) is conducted at a temperature of from 15 to 95°C, such as 20-95°C, such as 60 to 95°C. The specifiedtemperatures of step a) provide a high yield of the second and third precursors and enable arelatively fast reaction rate. In some embodiments, said salt is FeSO4, and said step a) comprises reacting: NaCN with FeSO4 to form Na4Fe(CN)6, orKCN with FeSO4 to form K4Fe(CN)6.In some embodiments, said salt is FeSO4, and said step a) comprises the reaction: 6NaCN + FeSO4 ^ Na4Fe(CN)6 + Na2SO4, or6 KCN + FeSO4 ^ K4Fe(CN)6 + K2SO4.In some embodiments, said salt is Fe3(PO4)2, and said step a) comprises reacting: NaCN with Fe3(PO4)2 to form Na4Fe(CN)6, orKCN with Fe3(PO4)2 to form K4Fe(CN)6.In some embodiments, said salt is Fe3(PO4)2, and said step a) comprises the reaction: In embodiments wherein the salt in step a) is Fe(CH3CO2)2, step a) comprises reacting: NaCN with Fe(CH3CO2)2 to form Na4Fe(CN)6, orKCN with Fe(CH3CO2)2 to form K4Fe(CN)6.Step a) may comprise the reaction:6 NaCN + Fe(CH3CO2)2 ^ Na4Fe(CN)6 + 2 NaH3C2O2, or6 KCN + Fe(CH3CO2)2 ^ K4Fe(CN)6 + 2 KH3C2O2.In some embodiments, said salt is Fe(HCO2)2, and said step a) comprisesreacting: NaCN with Fe(HCO2)2 to form Na4Fe(CN)6, orKCN with Fe(HCO2)2 to form K4Fe(CN)6.In some embodiments, said salt is Fe(HCO2)2, and said step a) comprises the reaction: 6NaCN + Fe(HCO2)2 ^ Na4Fe(CN)6 + 2 NaHCO2, or6 KCN + Fe(HCO2)2 ^ K4Fe(CN)6 + 2 KHCO2.In some embodiments, said salt is FeC2O2, and said step a) comprises reacting: NaCN with FeC2O2 to form Na4Fe(CN)6, orKCN with FeC2O2 to form K4Fe(CN)6.In some embodiments, said salt is FeC2O2, and said step a) comprises the reaction: 6NaCN + FeC2O2 ^ Na4Fe(CN)6 + Na2C2O2, or6 KCN + FeC2O2 ^ K4Fe(CN)6 + K2C2O2.In some embodiments, said salt is FeCl2, and said step a) comprises reacting: NaCN with FeCl2 to form Na4Fe(CN)6, orKCN with FeCl2 to form K4Fe(CN)6.In some embodiments, said salt is FeCl2, and said step a) comprises the reaction: 6NaCN + FeCl2 ^ Na4Fe(CN)6 + 2 NaCl, or6 KCN + FeCl2 ^ K4Fe(CN)6 + 2 KCl.In some embodiments, said salt is MnSO4, and said step a) comprises reacting: NaCN with MnSO4 to form Na4Mn(CN)6, orKCN with MnSO4 to form K4Mn(CN)6.In some embodiments, said salt is MnSO4, and said step a) comprises the reaction: 6NaCN + MnSO4 ^ Na4Mn(CN)6 + Na2SO4, or In some embodiments, said salt is Mn3(PO4)2, and said step a) comprises reacting: NaCN with Mn3(PO4)2 to form Na4Mn(CN)6, orKCN with Mn3(PO4)2 to form K4Mn(CN)6.In some embodiments, said salt is Mn3(PO4)2, and said step a) comprises the reaction: 18 NaCN + Mn3(PO4)2 ^3 Na4Mn(CN)6 + 2 Na3PO4, or In embodiments wherein the salt in step a) is Mn(CH3CO2)2, step a) may comprise reacting: NaCN with Mn(CH3CO2)2 to form Na4Mn(CN)6, orKCN with Mn(CH3CO2)2 to form K4Mn(CN)6.Step a) may comprise the reaction: 6NaCN + Mn(CH3CO2)2 ^ Na4Mn(CN)6 + 2 NaH3C2O2, or6 KCN + Mn(CH3CO2)2 ^ K4Mn(CN)6 + 2 KH3C2O2.In some embodiments, said salt is Mn(HCO2)2, and said step a) comprises reacting: NaCN with Mn(HCO2)2 to form Na4Mn(CN)6, orKCN with Mn(HCO2)2 to form K4Mn(CN)6.In some embodiments, said salt is Mn(HCO2)2, and said step a) comprises the reaction: 6NaCN + Mn(HCO2)2 ^ Na4Mn(CN)6 + 2 NaHCO2, or6 KCN + Mn(HCO2)2 ^ K4Mn(CN)6 + 2 KHCO2.In some embodiments, said salt is MnC2O2, and said step a) comprises reacting: NaCN with MnC2O2 to form Na4Mn(CN)6, orKCN with MnC2O2 to form K4Mn(CN)6.In some embodiments, said salt is MnC2O2, and said step a) comprises the reaction: 6NaCN + MnC2O2 ^ Na4Mn(CN)6 + Na2C2O2, or6 KCN + MnC2O2 ^ K4Mn(CN)6 + K2C2O2.In some embodiments, said salt is MnCl2, and said step a) comprises reacting: NaCN with MnCl2 to form Na4Mn(CN)6, orKCN with MnCl2 to form K4Mn(CN)6.In some embodiments, said salt is MnCl2, and said step a) comprises the reaction: 6NaCN + MnCl2 ^ Na4Mn(CN)6 + 2 NaCl, or6 KCN + MnCl2 ^ K4Mn(CN)6 + 2 KCl.In some embodiments, step a) and / or step b) is / are conducted in the presence ofwater, such as in an aqueous solution. In other words, the second and third precursors can beformed in an aqueous solution during step a) and reacted in the aqueous solution during step b). Accordingly, steps of time-consuming purification and crystallization of the second andthird precursors can be avoided. In addition, this advantageously allows for anenvironmentally friendly process as the use of costly and toxic organic solvents may be avoided. Furthermore, water has a relatively good heat / thermal storage capacity. Thus, the heat generated from the reaction in step a) heats the aqueous solution and may be substantially maintained and consequently benefit the reaction of step b). In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reacting: Na4Fe(CN)6 with H2SO4 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H2SO4 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: 2K4Fe(CN)6 + 3 H2SO4 ^ K2Fe[Fe(CN)6] + 6 HCN + 3 K2SO4.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reacting: Na4Fe(CN)6 with H4C2O2 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H4C2O2 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: 2Na4Fe(CN)6 + 6 H4C2O2 ^ Na2Fe[Fe(CN)6] + 6 HCN + 6 NaH3C2O2, or In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reacting: Na4Fe(CN)6 with H2C2O4 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H2C2O4 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: 2Na4Fe(CN)6 + 3 H2C2O4 ^ Na2Fe[Fe(CN)6] + 6 HCN + 3 Na2C2O4, or In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reacting Na4Fe(CN)6 with H2CO2 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H2CO2 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: 2Na4Fe(CN)6 + 6 H2CO2 ^ Na2Fe[Fe(CN)6] + 6 HCN + 6 NaHCO2, or In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reacting: Na4Fe(CN)6 with H3PO4 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with 2 H3PO4 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: 2K4Fe(CN)6 + 6 H3PO4 ^ K2Fe[Fe(CN)6] + 6 HCN + 6 KH2PO4.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reacting: Na4Fe(CN)6 with H3PO3 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with H3PO3 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reacting Na4Fe(CN)6 with HCl to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with HCl to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: 2Na4Fe(CN)6 + 6 HCl ^ Na2Fe[Fe(CN)6] + 6 HCN + 6 NaCl, or In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises reactingNa4Fe(CN)6 with HClO2 to form NaaFe[Fe(CN)6] and HCN, orK4Fe(CN)6 with HClO2 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.In some embodiments, both said second and third precursors are Na4Fe(CN)6,or K4Fe(CN)6, said step b) comprises the reaction: 2Na4Fe(CN)6 + 6 HClO2 ^ Na2Fe[Fe(CN)6] + 6 HCN + 6 NaClO2, or2 K4Fe(CN)6 + 6 HClO2 ^ K2Fe[Fe(CN)6] + 6 HCN + 6 KClO2.In some embodiments, said step c) comprises the reaction: The products NaCN or KCN obtained in step c) are introducible into the step a) of the method according to the present disclosure. The product water (H2O) is environmentally friendly and may, in some embodiments, be introduced in the method of the present disclosure. In some embodiments, said step a) is performed in a first reactor vessel, and said step b) is performed in a second reactor vessel arranged downstream of and in fluid communication with said first reactor vessel, and wherein said step c) is performed in a scrubbing device arranged in fluid communication with said first and / or said second reactor vessel. This is beneficial since the reaction conditions of step a) may differ from thereaction conditions of step b), particularly with respect to pH. Hence, the reaction conditionsfor steps a), and b), respectively may be optimized in the first, and second reactor vessel, respectively. Furthermore, undesired co-precipitation of poor-quality Prussian White is avoided. This may occur if the pH level is shifted between an alkaline pH (in step a) and an acidic pH (in step b) in the same reactor vessel. A fluid communication advantageously allows for an efficient transport of fluids to and from said reactor vessel, second reactor vessel (when present), and scrubbing device. The fluid communication increases the safety as it allows for avoiding steps of extracting fluids to separate transport vessels and, e.g., manually moving such transport vessels within a factory or to an external facility. It has been found that the method of the present disclosure advantageously maybe conducted batch-wise or semi-continuous / continuous.It is understood that each of the first reactor vessel, the second reactor vessel, and the scrubbing device may be provided with at least one inlet and at least one outlet respectively. Said at least one inlet and at least one outlet are configured to facilitate transport of fluids. Herein, the term “reactor vessel” refers to a structure designed to contain and control chemical reactions under specific conditions of pressure, temperature, and chemical environment. The reactor vessel(s) is / are typically constructed from materials resistant to the chemicals involved and capable of withstanding the operational conditions, including, e.g., pressures and temperatures. Suitable materials for withstanding at least two cycles are known to the person skilled in the art. Herein, the term “fluid” includes liquid and gas. Herein, the term “fluid communication” refers to an arrangement and connection of pathways, channels, conduits, or passages that allow the transfer or flow of fluids (liquids and / or gases) between different components, such as reactor vessel and scrubbing devices, within a system. Fluid communication may be facilitated using valves, pumps, seals, and other mechanisms to regulate flow rates, pressure, and direction, thereby facilitating efficient and effective transport of fluids. Herein, the term “scrubbing device” refers to an apparatus adapted to remove, e.g., contaminants or specific compounds for a gas or liquid stream. In particular, a scrubbing device refers to a device configured to house / facilitate a reaction between HCN and NaOH / KOH to form NaCN / KCN. In some embodiments, said scrubbing device is a venturi scrubber, a packed- bed scrubber, or a spray tower scrubber. In some embodiments, the scrubbing device comprises two or more scrubber units independently selected from a venturi scrubber, a packed bed scrubber, or a spray tower. This advantageously allows for combining characteristic features of different types of scrubber units. In the example of the two or more scrubber units, said scrubber units may be arranged in series and / or in parallel. Preferably, at least two scrubber units are arranged in series and at least one of the scrubber units is a venturi scrubber configured to receive HCN from the first and / or second reactor vessel. Venturi scrubbers, packed bed scrubbers, and spray tower scrubbers are known to the person skilled in the art. In some embodiments, said HCN formed in said step b) is directed to said scrubbing device by a carrier agent or by providing a pressure differential between said scrubbing device and said first and / or second reactor vessel. Directing the HCN formed in said step b) to said scrubbing device by a carrier agent or by providing a pressure differential between said scrubbing device and said first and / or second reactor vessel advantageously allows for relatively rapidly moving the HCN from the first and / or second reactor vessel to the scrubbing device. Thereby the risk of unwanted HCN polymerization, on e.g., reactor vessel walls or pipes, is reduced. Additionally, this decreases the amount of HCN (in gas phase) in a headspace in the first and / or second reactor vessel. In other words, the partial pressure of the HCN in the headspaceis decreased allowing for more HCN to be released from, e.g., a reactor liquid and betransported to the scrubbing device. In some embodiments, said carrier agent is an inert gas, such as nitrogen gas or argon gas, preferably nitrogen gas. Utilizing an inert gas has been found advantageous as substantially no unwanted side reactions between the HCN and the carrier agent molecules occur, and oxidation of the Prussian white compound is prevented. In some embodiments, the pressure differential is provided by applying a vacuum or by providing a lower pressure in said scrubbing device relative to said first and / or second reactor vessel. In some embodiments, said step d) of introducing said first precursor into said step a) comprises: i) collecting said first precursor in an aqueous solution in said scrubbing device; and ii) introducing said aqueous solution comprising said first precursor into said first reaction vessel. This advantageously allows for avoiding separate steps of time-consuming and cost-intensive steps of crystallizing the first precursor prior to introducing said first precursor into the first reaction vessel. Furthermore, by conducting step i) and ii) it is relatively easy to maintain a closed system, thereby avoiding unwanted reactions with ambient air. Figure 2 describes a system according to a second aspect of the invention. According to the second aspect of the invention, there is provided a system 200 for manufacturing a Prussian White compound comprising: a) a reactor unit 201 configured to conduct a first reaction of a first precursorselected from NaCN and KCN with a salt selected from the group consisting of CoSO4,Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2,Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2,MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereof to form a second precursor defined by the formula A4X1(CN)6and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K, and wherein X1and X2are individuallyselected from Co, Cr, Fe, and Mn; andto conduct a second reaction of said second and third precursors with an acidselected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl,and HClO2 under conditions that allow for a Prussian White compound to be formed and forHCN to be formed as a by-product, wherein said Prussian White compound is defined by theformula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2; and b) a scrubbing device 202 arranged in fluid communication with said reactor unit 201, wherein said scrubbing device 202 is configured to conduct a third reaction of NaOH or KOH with said HCN to form said first precursor, and wherein said scrubbing device 202 is configured to feed said first precursor intosaid reactor unit 201.Herein, a device, such as a reactor unit, configured to conduct a reaction, refers to a device able to facilitate and control chemical and / or physical reactions under specified conditions. The device is equipped with the necessary structural, mechanical, and controlcomponents known in the art. The reactor unit may comprise one or more than one reactorvessels. Hence, the reactor unit may also be referred to as a reactor assembly. In some embodiments, said first reaction is conducted in a first reaction vessel of said reactor unit, and wherein said second reaction is conducted in a second reactor vessel of said reactor unit. The effects and features of the second aspect are largely analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect. It is further noted that the inventive concepts relate to all possible combinations of features unless explicitly stated otherwise. EXAMPLES Example 1: Synthesis of Prussian white compound and recycling of HCN Cycle 1 A first aqueous solution comprising 202.66 g of a first precursor being virgin NaCN (aq) was prepared and arranged in a reactor. The volume of the first aqueous solution was 720 ml, and the pH was about 12. A total amount of about 191.66 g of FeSO4⋅7H2O (s) was added to the first aqueous solution over a period of one (1) hour (also referred to as addition period). The NaCN was reacted with the (now dissolved) FeSO4(aq) to form a second aqueous solution comprising (dissolved) Na4Fe(CN)6(aq). The first aqueous solution was agitated using an over-head stirrer throughout the addition period and a subsequent 10- minute-long aging period. The temperature of the first aqueous solution before the addition of FeSO4⋅7H2O was 20 °C and the resulting second aqueous solution had an increased temperature. After the aging period, the second aqueous solution was filtered to produce a filtrate substantially free from solids, i.e., by-products, such as iron hydroxides. The filtrate was arranged in a reactor. An acid decomposition reaction of the Na4Fe(CN)6present in the filtrate was instigated by heating said filtrate to a temperature of about 85 °C and introducingsulfuric acid to reach a pH of about 2.9 to form a slurry. The slurry was maintained at saidtemperature and said pH for about six (6) hours. The slurry was agitated and a flow of N2 gaswas used as carrier agent for the HCN and was directed through the headspace in the reactor in order to minimize oxidation of the formed Prussian white compounds. After the six (6)hours of reaction, a solid-liquid separation (filtering step) was carried out on the slurry toobtain a filter cake. Said filter cake was washed with deionized water and subsequently dried, thereby obtaining Prussian white compounds in the form of particles. During the above-mentioned acid decomposition reaction HCN was formed as a by-product. The HCN in gas phase was transported to a scrubber system where it was contacted with an aqueous solution comprising NaOH. This led to the formation of a scrubber solution comprising NaCN (l) (also referred to as recycled NaCN). Cycle 2-5 Cycle 2 was carried out in a similar manner to Cycle 1. In Cycle 2, virgin NaCNwas introduced into the scrubber solution obtained from Cycle 1 to reach a targetconcentration of (dissolved) NaCN of about 341.27 g / L. The remaining steps of Cycle 1 wererepeated to obtain a new set of Prussian white particles and scrubber solution comprising recycled NaCN (l). Cycle 3 was conducted in a similar fashion to Cycle 2 with the main differencebeing using the scrubber solution from Cycle 2 instead of Cycle 1. Cycle 4 and 5 wereconducted following the same pattern. The amounts of reactants used in each of the cycles as well as the amount of Prussian white produced are presented in table 1.Cycle # FeSO4⋅7H2O [g] Virgin NaCNRecycled NaCN Obtained [g] [g] Prussian white [g] 1191.6 202.66 N / A 106.32 191.6 160.3 42.0 73.13 191.6 161.6 41.0 85.04 191.6 187.37 15.5 102.05 191.6 122.35 79.6 102.1Table 1: Summary of amount of virgin reactants used, recycled NaCN used, and Prussian white obtained. Example 2: Synthesis and characterization of Prussian white compound A first aqueous solution comprising NaCN and NaOH was prepared and arranged in a reactor. The volume of the first aqueous solution was 1.05 L, and the pH was above 12. In the first aqueous solution, the concentration of (dissolved) NaCN was 45.8 g / L and (dissolved) NaOH was 36.0 g / L. A total amount of about 77 g of FeSO4*7H2O (s) was added to the first aqueous solution over a period of one (1) hour (also referred to as addition period). The NaCN was reacted with the (now dissolved) FeSO4 to form a second aqueous solution comprising (dissolved) Na4Fe(CN)6. The first aqueous solution was agitated using a magnetic stirrer throughout the addition period. The temperature of the first aqueous solution before the addition of FeSO4⋅7H2O was 20 °C and the resulting second aqueous solution had an increased temperature. After the addition period, the second aqueous solution was filtered to produce a filtrate substantially free from solids, i.e., by-products, such as iron hydroxides. The filtrate was arranged in a reactor. An acid decomposition reaction of the Na4Fe(CN)6present in the filtrate was instigated by heating said filtrate to a temperature of about 85 °C and introducing sulfuric acid to reach a pH of about 2.9 to form a slurry. The slurry was maintained at said temperature for about 12 hours. The slurry was agitated and a flow of N2gas was used through the head space in the reactor in order to minimize oxidation of the formed Prussian white compounds. After the 12 hours of reaction, a solid-liquid separation (filtering step) was carried out on the filtrate to obtain a filter cake. Said filter cake was washed with deionized water and subsequently dried, thereby obtaining Prussian white compounds in the form of particles. X-ray diffraction XRD and Rietveld refinement was conducted to determine the crystal structure of the Prussian white particles obtained from each of the cycles 1-5 of Example 1 and the Prussian white particles of Example 2. The XRD was conducted using a Bruker D8 Advance diffractometer equipped with a Cu Kα (λ1 = 1.540596 Å, λ2 = 1.544390 Å) source and a LYNXEYE XE-T detector over the range of 10-120 (2^) with a scanning step of 0.021°. The resulting X-ray diffractograms of the Prussian white particles from Cycles 1-5 are shown in Figure 3a-d, respectively, and the Prussian white particles of Example 2 are shown in Figure 4. The Prussian white particles of Cycle 1-5 and Example 2 were concluded to be crystalline. The Prussian white particle of Cycle 1-5 had a hydrated rhombohedral crystalstructure with an R3^ space group symmetry. The Prussian white particles had a combinationof hydrated rhombohedral crystal structure with an R3^ space group symmetry and hydratedmonoclinic phase with a P21 / n space group symmetry. It is understood that as a plurality of particles are measured at the same time. It is contemplated that some particles may consist of said hydrated rhombohedral crystal, some of said hydrated monoclinic phase, and some a combination thereof. Such Prussian white particles have been found to be a promising cathode active material due to a high sodium content and low Fe(CN)6 vacancy content. The high sodium content allows for producing battery cells having a high specific capacity (milliampere hours / gram). The rhombohedral crystal structure and the particular monoclinic structure identified through XRD indicate a high sodium content. Particle Size Analysis Particle size distribution (PSD), Dv50 (volumetric particle size distribution), of the Prussian white particles from Cycle 1-5 was measured using a PSA 1090 L / D (Anton Paar). The results of the Particle Analysis are presented in table 2.Cycle # DV50 [µm]1 13.22 16.93 14.24 10.65 11.2Table 2: Summary of the volumetric particle size distribution of the Prussian white particles obtained in Cycles 1-5. Clearly, in view of Example 1 and 2, the method of the present disclosure advantageously allows for an environmentally friendly and cost-effective way of manufacturing Prussian white particles by recycling the by-product HCN to form a precursor which can be used in a subsequent synthesis cycle. Additionally, the Prussian white particlesobtained in each of Examples 1 and 2 have a high sodium content making them particularlysuitable for use as cathode active material in battery cells. Terms, definitions and embodiments of all aspects of the present disclosure apply mutatis mutandis to the other aspects of the present disclosure. Even though the present disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the present disclosure, from a study of the drawings, the disclosure, and the appended claims. Furthermore, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

1. CLAIMS 1. A method for manufacturing a Prussian White compound comprising: a) reacting a first precursor selected from NaCN and KCN with a salt selectedfrom the group consisting of CoSO4, Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2,CrSO4, Cr3(PO4)2, Cr(CH3CO2)2, Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2,Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2, MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2,MnC2O4, MnCl2, and combinations thereof to form a second precursor defined by the formulaA4X1(CN)6and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K,and wherein X1 and X2 are individually selected from Co, Cr, Fe, and Mn;b) reacting said second and third precursors with an acid selected from thegroup consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3, HCl, and HClO2 underconditions that allow for a Prussian White compound to be formed and for HCN to be formedas a by-product, wherein said Prussian White compound is defined by the formulaAaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, and 0 ≤ y ≤ 0.2;c) recycling said HCN by reacting NaOH or KOH with said HCN to form saidfirst precursor; andd) introducing said first precursor into said step a).

2. The method according to claim 1, wherein said step a) is performed at a pH of from 9 to 14, preferably from 10 to 13.

3. The method according to claim 1 or claim 2, wherein said salt is defined by a first cationand a first anion; said acid being defined by a second cation and a second anion, wherein said second anion of said acid in said step b) corresponds to said first anion of said salt in said step a).

4. The method according to any one of the preceding claims, wherein said step b) is performed at a temperature of from 65 to 95^C, preferably from 75 to 95^C.

5. The method according to any one of the preceding claims, wherein said step b) is performed at a pH of from 1.8 to 4.5, preferably from 2 to 3.

5.

6. The method according to any one of the preceding claims, wherein said salt is FeSO4, and wherein said step a) comprises the reaction:6 NaCN + FeSO4 ^ Na4Fe(CN)6 + Na2SO4, or6 KCN + FeSO4 ^ K4Fe(CN)6 + K2SO4.

7. The method according to any one of the preceding claims, wherein both said second andthird precursors are Na4Fe(CN)6, or K4Fe(CN)6, and wherein said step b) comprises reactingNa4Fe(CN)6 with H2SO4 to form NaaFe[Fe(CN)6] and HCN, or K4Fe(CN)6 with 3 H2SO4 to form KaFe[Fe(CN)6] and HCN, wherein 1.8 < a ≤ 2.

8. The method according to any one of the preceding claims, wherein said step c) comprises the reaction:

9. The method according to any one of the preceding claims, wherein said step a) is performed in a first reactor vessel, and wherein said step b) is performed in a second reactor vessel arranged downstream of and in fluid communication with said first reactor vessel, and wherein said step c) is performed in a scrubbing device arranged in fluid communication with said first and / or said second reactor vessel.

10. The method according to claim 9, wherein said scrubbing device is a venturi scrubber, a packed-bed scrubber, or a spray tower scrubber.

11. The method according to claim 9 or claim 10, wherein said HCN formed in said step b) is directed to said scrubbing device by a carrier agent or by providing a pressure differential between said scrubbing device and said first and / or second reactor vessel.

12. The method according to claim 11, wherein said carrier agent is an inert gas, preferably nitrogen gas.

13. The method according to any one of claims 9-12, wherein said step d) of introducing said first precursor into said step a) comprises: i) collecting said first precursor in an aqueous solution in said scrubbing device; andii) introducing said aqueous solution comprising said first precursor into said first reaction vessel.

14. A system (200) for manufacturing a Prussian White compound comprising: a) a reactor unit (201) configured to conduct a first reaction of a first precursorselected from NaCN and KCN with a salt selected from the group consisting of CoSO4,Co3(PO4)2, Co(CH3CO2)2, Co(HCO2)2, CoC2O4, CoCl2, CrSO4, Cr3(PO4)2, Cr(CH3CO2)2,Cr(HCO2)2, CrC2O4, CrCl2, FeSO4, Fe3(PO4)2, Fe(CH3CO2)2, Fe(HCO2)2, FeC2O4, FeCl2,MnSO4, Mn3(PO4)2, Mn(CH3CO2)2, Mn(HCO2)2, MnC2O4, MnCl2, and combinations thereofto form a second precursor defined by the formula A4X1(CN)6 and a third precursor defined by the formula A4X2(CN)6, wherein A is Na or K, and wherein X1and X2are individuallyselected from Co, Cr, Fe, and Mn;and to conduct a second reaction of said second and third precursors with anacid selected from the group consisting of H2SO4, H4C2O2, H2C2O4, H2CO2, H3PO4, H3PO3,HCl, and HClO2 under conditions that allow for a Prussian White compound to be formedand for HCN to be formed as a by-product, wherein said Prussian White compound is definedby the formula AaX1[X2(CN)6]1-y, wherein 1.8 < a ≤ 2, 0 ≤ y ≤ 0.2; and b) a scrubbing device (202) arranged in fluid communication with said reactorunit (201), wherein said scrubbing device (202) is configured to conduct a third reaction ofNaOH or KOH with said HCN to form said first precursor, and wherein said scrubbing device (202) is configured to feed said first precursorinto said reactor unit (201).

15. The system (200) according to claim 14, wherein said first reaction is conducted in a firstreaction vessel of said reactor unit (201), and wherein said second reaction is conducted insaid first reactor vessel or in a second reactor vessel of said reactor unit (201).

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