Iron phosphate-comprising materials

Abstract

A method is provided of forming an iron phosphate-comprising material comprising the steps of: (a) reacting an aqueous solution of ferrous iron with an oxidizing agent in the presence of a base while maintaining an acidic pH, resulting in the formation of -FeOOH; (b) reacting the y-FeOOH resulting from step (a) with a phosphorus source, resulting in the formation of an iron phosphate-comprising material; wherein the γ-FeOOH resulting from step (a) is not isolated between steps (a) and (b).

Description

[0001] IRON PHOSPHATE- COMPRISING MATERIALS

[0002] BACKGROUND OF THE INVENTION

[0003] The demand for iron-phosphate material is expected to increase in the future as the world population grows and pressure for sustainable agriculture, steel production, and energy storage increases. As a result, governments are incentivizing local manufacture of key commodity materials critical to infrastructure and economies, in order to reduce dependency on foreign sources.

[0004] Iron-phosphate containing materials play critical roles as food additives, biopesticides, steel surface coatings, adsorption materials, and more. The recent expansion of electric vehicle (EV) manufacturing is projected to cause a future shortage of cobalt and nickel due to the common use of these elements in battery cathode materials. Therefore, alternative earth abundant cathode chemistries such as lithium iron phosphate (also known as LFP, lithium ferrophosphate or LiFePCh) are now being selected as suitable replacements. LFP has an olivine-type crystal structure.

[0005] This shift into energy storage not only requires a greater quantity of material to be manufactured, but it also requires higher purity and homogeneity. To achieve these objectives, higher quality and more refined raw materials must be sourced. In the example of lithium iron phosphate cathode material, the iron source is by far the largest contributor of impurities since it typically comes from waste streams and / or recycled sources.

[0006] The purity of the raw material is critical as it can affect the process, performance, and cycle life of a battery. For example, it is common to use iron sulfate as a raw material in the production of lithium iron phosphate. However, sulfate presents an environmental issue when the material is calcined under high temperature. Other impurities, such as sodium or potassium, compete with lithium, while other metals create nonuniformity in potential over the electrode surface which can lead to dendrite formation and premature failure of the battery.

[0007] One way to remove impurities is to include an intermediate process in which the starting material is transformed (recrystallized) into a compound that can be separated or filtered and washed. Either iron(II) or iron(III) salts can be used in the general formula: mFen++ nA- FemAn

[0008] Where n = 2 or 3 and m = 1 or 2 and A is SO4, NO3, or Cl. The iron salt is then typically reacted with an alkali base in a two-step reaction to form iron oxide.

[0009] Step Step 2: Where n = 2 or 3; m = l or 2; x = 0 - oo; a = 0 or l if b = 0; b = 0 - 2 if a = 0

[0010] North America suppliers of lithium iron phosphate have moved toward starting with a form of iron oxide as the iron source since it is one of the least expensive intermediates to produce, and one of the easiest to convert.

[0011] U.S. Pat. No. 2939767 mentions a chloride process for preparing a-FeOOH.

[0012] Gustavo Navarro et al 2008 J. Phys.: Conf. Ser. 134 012023 discusses the synthesis of y-FeOOH from ferrous chloride (FeCh).

[0013] U.S. Pat. No. 8673497 mentions the use of various iron sources for making lithium iron phosphate, including iron oxides, iron hydroxide, and the iron oxi de- hydroxi des a-FeOOH (geothite), P-FeOOH (akageneite), and y-FeOOH (lepidocrocite). a-FeOOH is the most preferred iron source. The reaction times are long: at least 16 hours when using a-FeOOH and 60 hours when using y-FeOOH.

[0014] Lin et al., CrystEngComm, 2016, 18, 3174 discusses synthesis of iron phosphates via phosphation of P-FeOOH nanorods. Lin emphasizes the importance of P-FeOOH nanorods for the controlled synthesis of FePCU 2H2O with different phases and morphologies.

[0015] There is no prior indication that y-FeOOH would show significantly superior reaction kinetics during the conversion to iron phosphate compared to other forms of iron sources, such as a- FeOOH and P-FeOOH.

[0016] The present application addresses the need for iron-phosphate materials with improved reaction kinetics, faster production times, and fewer steps.

[0017] Citation or identification of any document in this application is not an admission that such represents prior art to the present invention.

[0018] SUMMARY OF THE INVENTION

[0019] The present application discloses a high-speed method for preparing an iron phosphate- comprising material by using lepidocrocite (y-FeOOH), which shows a significant improvement in reaction kinetics (rate of reaction) compared to other iron oxide forms during the conversion to iron phosphate-comprising materials. Moreover, the present invention is ideally suited for efficient production of iron phosphate-comprising materials at industrial scale by providing a process where widely available iron precursors are converted into iron phosphate-comprising materials without intermediate isolation steps. In particular, the invention provides a method of forming an iron phosphate-comprising material comprising the steps of:

[0020] (a) reacting an aqueous solution of ferrous iron with an oxidizing agent in the presence of a base while maintaining an acidic pH, resulting in the formation of y-FeOOH;

[0021] (b) reacting the y-FeOOH resulting from step (a) with a phosphorus source, resulting in the formation of an iron phosphate-comprising material; wherein the y-FeOOH resulting from step (a) is not isolated between steps (a) and (b).

[0022] As previously mentioned, the use of various iron sources, for example a-FeOOH and 0-FeOOH, for preparing iron- phosphate comprising materials is known. Surprisingly, y-FeOOH reacts much faster, making it advantageous over other forms of iron oxides or iron oxide-hydroxides. Though not wishing to be bound by theory, applicants believe that the reason for the higher reactivity of y-FeOOH may be due to its propensity to adopt a smaller particle size with more reactive sites. Moreover, advantageously the y-FeOOH is formed and converted to an ironphosphate comprising material without isolation, thus providing a one-pot process or a process which may be operated continuously.

[0023] DRAWINGS

[0024] Figure 1 is an X-Ray Diffraction (XRD) pattern of the y-FeOOH prepared in Example 1.

[0025] Figure 2A is an XRD pattern of the FePO4 2H2O prepared in Example 3.

[0026] Figure 2B is an XRD pattern of the FePO4 prepared after calcination in Example 3.

[0027] Figure 3 A is a Scanning Electron Microscopy (SEM) image of the 110°C dried sample prepared in Example 16. The image shows primary particles of intergrown platelets mostly between 1 and 3 pm.

[0028] Figure 3B is an SEM image of the 650°C calcined sample prepared in Example 16. The image shows primary particles of intergrown platelets mostly between 1 and 3 pm.

[0029] Figure 4A is an SEM image of the sample prepared in Reference Example 25.

[0030] Figure 4B is an SEM image of the sample prepared in Reference Example 26 that was calcined at 650°C.

[0031] Figure 5A is an XRD pattern of the sample prepared in Reference Example 25.

[0032] Figure 5B is an XRD pattern of the sample prepared in Reference Example 26 that was calcined at 650°C.

[0033] DETAILED DESCRIPTION

[0034] In step (a) of the invention, an aqueous solution of ferrous iron is reacted with an oxidizing agent in the presence of a base while maintaining an acidic pH, resulting in the formation of y-FeOOH. Step (a) uses an aqueous solution of ferrous iron as a starting material. Ferrous iron will be understood as iron in its 2+ oxidation state. Preferred ferrous iron solutions are solutions of ferrous salts, such as ferrous chloride, ferrous sulfate, ferrous gluconate, ferrous fumarate, ferrous succinate, ferrous lactate, ferrous glutamate, ferrous ascorbate, ferrous bisglycinate, ferrous nitrate, ferrous acetate and mixtures thereof; preferably ferrous chloride, ferrous sulfate, and mixtures thereof; most preferably ferrous chloride. However, the process is not limited to just those materials.

[0035] The aqueous solution of ferrous iron can be ferrous salt which is dissolved into water or an existing solution such as pickle liquor or clear liquor. Pickle liquor (or pickling liquor) is an acidic solution, e.g. a hydrochloric acid or sulfuric acid solution, typically a hydrochloric acid solution, used to remove surface impurities from steel such as rust. As the pickle liquor is used, the effectiveness is diminished as the concentration of ferrous chloride or ferrous sulfate increases. The pickle liquor is then considered waste and sold into various industries, most notably it is used for wastewater treatment as a flocculate. Clear liquor is a form of pickle liquor that has been purified where contaminates such as metals other than iron have been selectively removed. Advantageously, the process of the invention can make use of these low-cost sources of iron.

[0036] The oxidizing agent acts to oxidize the ferrous iron (Fe2+) in the starting material to Fe3+in the resulting y-FeOOH. Preferably, the oxidizing agent is an oxygen-containing gas such as air. Thus, step (a) may comprise aerating the aqueous solution of ferrous iron with an oxygencontaining gas, for example by bubbling the gas into the solution, but the invention is not limited to this implementation. Feasible oxidizing agents may be selected from oxygen (O2), hydrogen peroxide, potassium dichromate, sodium hypochlorite, calcium hypochlorite, ozone, potassium perchlorate, potassium chlorate, potassium permanganate, ammonium persulfate, sodium persulfate, and mixtures thereof; preferably oxygen (O2), hydrogen peroxide, sodium hypochlorite, ozone, potassium perchlorate, potassium chlorate, ammonium persulfate, sodium persulfate, and mixtures thereof.

[0037] A base is included during the reaction to form y-FeOOH. In general, the base may be selected from Lewis bases such as ammonia, Arrhenius bases such as sodium hydroxide, and mixtures thereof. The base may be selected from alkali metal hydroxides, ammonia, ammonium hydroxide, barium hydroxide, strontium hydroxide, calcium hydroxide, n-butyl lithium, lithium diisopropylamide, lithium diethylamide, sodium amide, sodium hydride, lithium bis(trimethylsilyl)amide, and mixtures thereof; preferably alkali metal hydroxides, ammonia, ammonium hydroxide, and mixtures thereof. The most preferred base is sodium hydroxide.

[0038] Optionally, neither the base nor the oxidizing agent contains a metal other than an alkali metal. In this way, the level of impurities in the iron phosphate-comprising material product may be reduced. Alternatively, if it is desired to introduce a dopant into the iron phosphate-comprising material product, a base or oxidizing agent could be selected which includes that dopant. The reaction to form y-FeOOH takes place while maintaining an acidic pH, i.e. pH < 7. Preferably, the reaction takes place while maintaining pH < 5. It has been found that maintaining pH < 5 favors the formation of y-FeOOH while minimizing the formation of other materials which could introduce impurities into the ultimate iron phosphate-comprising material product. The reaction to form y-FeOOH typically takes place below 100 °C, such as below 95 °C. The reaction may be performed at room temperature (about 25 °C). Thus, the reaction may be performed at 5-100 °C, 10-95 °C, or 15-90 °C.

[0039] The y-FeOOH formed in step (a) is not isolated before it is reacted with the phosphorus source in step (b). In this way, the invention provides an efficient one-pot or continuous process where a ferrous iron starting material is converted to an iron-phosphate comprising material. Isolation typically involves steps such as filtering, washing, and / or drying to separate a synthesized material from the reaction by-products and reaction medium in which it was prepared. Step (b) may take place in the same reaction vessel as step (a) by adding the phosphorus source to that vessel. Alternatively, step (b) may take place in a different reaction vessel than step (a), for example in a continuous process where a slurry comprising y-FeOOH formed by step (a) is moved to different reaction vessel where step (b) is performed. It is not excluded that step (b) takes place after a time delay following step (a), e.g. after a delay of 12-14 hours.

[0040] In step (b), the y-FeOOH resulting from step (a) is reacted with a phosphorus source, resulting in the formation of an iron phosphate-comprising material. The phosphorus source may be selected from phosphoric acid (H3PO4), phosphorous acid (H3PO3), (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4, U3PO4, Li2HPO4, and LiH2PO4, and mixtures thereof; or from H3PO4, H3PO3, (NH4)H2PO4,(NH4)2HPO4, (NH4)3PO4, and mixtures thereof. The preferred phosphorus source is H3PO4. For example, the phosphorus source can be 75 wt% or 85 wt% H3PO4 in water.

[0041] Step (b) is typically carried out under acidic conditions in an aqueous solution with pH < 5. The preferred reaction pH of step (b) is 0.5-4.0, more preferably 0.5-3.5, most preferably 1.0-2.5. The preferred reaction temperature of step (b) is at least 50°C or 50°C-100°C, more preferably 60°C-90°C, most preferably 70°C-90°C. The preferred reaction time of step (b) is < 7 hours, more preferably 1-6 hours, most preferably 1-5 hours.

[0042] Since iron is present in its 3+ oxidation state in the y-FeOOH made by step (a) and in the desired iron phosphate-comprising material product, it is an advantage of the invention that the iron phosphate-comprising material can be readily formed without the need for control of the atmosphere during the reaction, e.g. without the need to perform the reaction under inert or reducing atmosphere. Accordingly, the reaction of step (b) is typically carried out under noninert atmosphere. A non-inert atmosphere may be defined as one under which the oxidation state of iron in the iron source is maintained in the iron phosphate-comprising material product. For example, a non-inert atmosphere may comprise at least 1 vol% oxygen gas, preferably at least 5 vol% oxygen gas. Air is a preferred non-inert atmosphere. The reaction of step (b) may be performed in the absence of a reducing agent.

[0043] It has been found that the molar ratio of P:Fe influences the speed of the conversion of the y-FeOOH to the iron phosphate-comprising material. The reaction of step (b) may be carried out at a molar ratio of P:Fe of > 3 : 1 , or > 4: 1 , preferably > 6: 1 , or most preferably > 7: 1. The upper limit of the P:Fe ratio may be suitably chosen such that excessive amounts of the phosphorus source are not wasted and / or do not require recovering and recycling. Optionally, the reaction of step (b) is carried out at a molar ratio of P:Fe of < 100: 1, or < 50: 1, or < 20: 1, or < 12: 1. Thus, the reaction of step (b) may be carried out at a molar ratio of P:Fe of 3:1-100: 1, or 4: 1-50: 1, preferably 6: 1-20: 1, most preferably 7: 1-12: 1.

[0044] The reaction of step (b) may be carried out at a molar ratio of P:Fe of < 4:1, < 3: 1, or < 1.5:1. At these lower ratios, other reaction parameters can be controlled to result in conversion of the y-FeOOH to the iron phosphate-comprising material over a commercially useful timescale. If the reaction of step (b) is carried out at a molar ratio of P:Fe of < 1.5:1, < 3:1, or < 4:1, the reaction is preferably carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C. For example, if the reaction of step (b) is carried out at a molar ratio of P:Fe of < 1.5: 1 the reaction may be carried out at a temperature of at least 85 °C. If the reaction of step (b) is carried out at a molar ratio of P:Fe of < 3:1 the reaction may be carried out at a temperature of at least 82 °C. If the reaction of step (b) is carried out at a molar ratio of P:Fe of < 4: 1 the reaction may be carried out at a temperature of at least 80 °C. At these lower ratios, the reaction time may be increased to allow for conversion, in particular if the temperature of the reaction is less than 80°C. For example, if the reaction of step (b) is carried out at a molar ratio of P:Fe of < 1.5:1, < 3: 1, or < 4: 1 and at a temperature of less than 80°C, the reaction may be carried out for a for a time of at least 6 hours, or at least 8 hours, or at least 10 hours.

[0045] The reaction of step (b) is preferably carried out at a molar ratio of P:Fe of least 1: 1, this being the stoichiometric ratio in FePCh, or more preferably at least 1.05: 1.

[0046] It has been found that the use of y-FeOOH allows for a rapid conversion to the iron phosphate- comprising material over a wide range of water contents, as defined by the mass of y-FeOOH relative to the volume of water in the reaction vessel. The reaction of step (b) is preferably carried out at a mass of y-FeOOH relative to the volume of water of < 45 g dm'3, or < 35 g dm'3, or most preferably < 25 g dm'3. Optionally, the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of > 0.1 g dm'3, > 0.5 g dm'3, or > 1 g dm'3.

[0047] The reaction of step (b) may be carried out at a mass of y-FeOOH relative to the volume of water of > 45 g dm'3. At these higher ratios of y-FeOOH to water, other reaction parameters can be controlled to result in conversion of the y-FeOOH to the iron phosphate-comprising material over a commercially useful timescale. If the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of > 45 g dm'3, the reaction is preferably carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C.

[0048] There are other methods for producing iron oxide, most commonly using iron sulfate, a byproduct from the refinement of titanium ore to titanium dioxide. The iron sulfate is then reacted with oxygen and an alkali, such as sodium hydroxide, in a hydrothermal process to a pH of about 4 in which the iron oxide precipitates. Generally, this method yields Fe20s, FesC , and a-FeOOH, but not y-FeOOH. Iron oxide prepared using this process has been known to retain sulfur as an impurity which is not desirable for producing battery materials since it evolves as SOx (sulfur oxides) during calcination. Emission of SOx or other volatile sulfur compounds are either pollutants or have a very low odor threshold. Sulfur also produces detrimental side reactions during battery operations, ultimately shortening its life. Iron oxides produced from the chloride process contain a much lower residual sulfur level and are able to produce cleaner iron oxides. Additionally, iron oxides from the chloride process can form smaller particle iron phosphate-comprising materials which can help improve further reactivity and, potentially, battery material processability and performance. Thus, an advantage of the present invention is that it can minimize the amount of impurities such as sulfur in the iron phosphate-comprising material. In one preferred embodiment the method of the present application would result in an iron phosphate-comprising material with < 1000 ppm sulfur, more preferably < 500 ppm sulfur. The concentration of elements in the iron phosphate-comprising material, including sulfur, can be measured by elemental analysis, for example by ICP-OES.

[0049] Iron-phosphate-comprising materials pertain to any compound in which at least one iron and at least one phosphate are present, and may be in the presence of other compounds, ions, dopants, surfactants, and / or chelating agents, and may be formed in solution with other such compounds, ions, dopants, surfactants, and / or chelating agents present, and may exist as an intermediate created in-situ during the reaction process. If metals other than iron are present in the ironphosphate comprising material, they may be present at less than 10 at.%, preferably less than 5 at.%, most preferably less than 1 at.% relative to the amount of iron in the iron- phosphate comprising material.

[0050] The iron phosphate-comprising material is most preferably not lithium iron phosphate or a material having an olivine-type crystal structure. Materials having an olivine-type crystal structure typically have the general formula M1M2PO4, where M1and M2refer to cations in an octahedral coordination (e.g. M1= vacancy, Na, and / or Li; M2= Mn, Fe, Fe, Mn, and / or Mg) and P corresponds to the tetrahedrally coordinated P5+cation. The crystal structure of a material may be determined by X-ray diffraction as is widely known. The iron phosphate-comprising material formed by the method may be selected from FePC , FePO42FLO, Fe5(PO4)4(OH)22ILO, Fe4(P2O7)3, and Fe3(PO4)28H2O; preferably FePO4and FePO4-2H2O. The material formed by the method may depend on the initial iron species, reaction conditions, such as using an oxidizing or reducing environment, and post processing heat treatment to synthesize the anhydrous varieties. A simplified reaction scheme showing the formation of FePO42H2O is:

[0051] The resulting iron phosphate-comprising material may be isolated by routine methods, such as filtration and centrifugation. Following isolation, the iron phosphate-comprising material may be reacted with a lithium source to form lithium iron phosphate.

[0052] Anhydrous iron phosphate-comprising materials are a common precursor for making lithium iron phosphate. Thus, the method may further comprise a step of calcining the iron phosphate- comprising material to form an anhydrous iron phosphate-comprising material. A preferred anhydrous iron phosphate-comprising material is FePO4.

[0053] Alternatively, the iron phosphate-comprising material, e.g. FePO4-2H2O, may be partially dehydrated, e.g. forming FePO4xH2O where 0<x<2.

[0054] Other iron phosphate-comprising materials can be formed by the method. For example, (NH4)Fe2(PO4)2(OH) 2H2O can be formed in step (b) if ammonium hydroxide is used as the base in step (a). (NH4)Fe2(PO4)2(OH) 2H2O can be converted to FePO4 by calcining.

[0055] Preferably, the FePO4formed by the process adopts a trigonal phase, most preferably adopting the a-quartz structure.

[0056] The iron phosphate-comprising material formed by the method is most preferably not lithium iron phosphate. Thus, typically a lithium source is not present when reacting the y-FeOOH with the phosphorus source. However, in a further step, the iron phosphate-comprising material formed by the method (e.g. after isolation and / or calcination) may be reacted with a lithium source to form lithium iron phosphate. Lithium sources may be selected from lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium oxide (Li2O), lithium sulfate (Li2SO4), lithium chloride (LiCl), hydrates thereof, and mixtures thereof; preferably lithium carbonate (Li2CO3), lithium hydroxide (LiOH), hydrates thereof, and mixtures thereof; most preferably Li2CO3.

[0057] There are several methods of reacting the lithium source and iron phosphate-comprising material to form lithium iron phosphate. Some method variations use a “one-pot” approach where the lithium source, iron phosphate-comprising material, and a reducing agent such as carbon are added together to a mixing vessel. The resulting slurry is then wet milled, spray dried, and calcined in an inert atmosphere ranging from 300 to 1000 °C, typically about 650 °C. During calcination, the inert atmosphere means that there is no oxygen to react with the carbon source. Instead, the carbon source reacts with oxygen present in the raw materials producing CO2 and reducing the iron. Fe3+ions bound to the phosphate are reduced to Fe2+allowing for the positively charged lithium ion to bind with the now negatively charged phosphate, creating lithium iron phosphate.

[0058] The lithium iron phosphate may then be incorporated into an article such as an electrode or a battery cell.

[0059] Since iron phosphate is highly insoluble, the reaction of step (b) is possible in the presence of other compounds, ions, dopants, surfactants, and / or chelating agents, and may be formed in solutions with other such compounds, ions, dopants, surfactants, and / or chelating agents present, and may exist as an intermediate created in-situ during coprecipitation processes.

[0060] Preferably, the iron phosphate-comprising material has a particle size distribution characterized by a D50 of < 20 pm, or < 15 pm, or < 12 pm, or < 8 pm, or < 6 pm, or < 4 pm, or < 3 pm.

[0061] Preferably, the y-FeOOH has a particle size distribution characterized by a D50 of < 50 pm, or < 30 pm, more preferably < 20 pm, or < 15 pm.

[0062] Unless otherwise indicated, the term “Dn” refers to the diameter below which n% by volume of the particle population is found, e.g. the term “D50” refers to the volume-based median particle diameter below which 50% by volume of the particle population is found. Dn values are preferably determined by laser diffraction. For example, Dn values can be determined in accordance with ISO 13320:2009 using Mie theory.

[0063] Uniformity of particle size is an advantageous feature of the iron phosphate after reaction. Thus, preferably the iron phosphate-comprising material has a particle size distribution characterized by a D10, D50, D90 span of < 6, or < 5, or < 4, or < 3, or < 2, or < 1.5, or < 1.

[0064] Particle size distribution span is calculated using the following equation:

[0065] D90 - D10

[0066] D50

[0067] The particle size distribution of the y-FeOOH may also be measured by sedimentation, for example using a disc centrifuge particle size analyzer. The y-FeOOH may have a particle size distribution measured by sedimentation characterized by a Dw50 of < 5 pm, or < 1 pm, or < 500 nm, where Dw50 refers to the diameter below which 50% of the weight of the particle population is found.

[0068] Step (b) may be defined as reacting the y-FeOOH resulting from step (a) with a phosphorus source, resulting in the formation of an iron phosphate-comprising material, wherein: if the reaction of step (b) is carried at a molar ratio of P:Fe of < 3: 1 or < 4: 1, the reaction is carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C; if the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of > 45 g dm'3, the reaction is carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C.

[0069] In one variant: if the reaction of step (b) is carried out at a molar ratio of P:Fe of < 1.5: 1 the reaction is carried out at a temperature of at least 85 °C; if the reaction of step (b) is carried out at a molar ratio of P:Fe of 1.5 : 1 -3 : 1 the reaction is carried out at a temperature of at least 82 °C; if the reaction of step (b) is carried out at a molar ratio of P:Fe of 3: 1-4: 1 the reaction is carried out at a temperature of at least 80 °C; if the reaction of step (b) is carried out at a molar ratio of P:Fe of > 4: 1 the reaction is carried out at a temperature of at least 50 °C; if the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of

[0070] > 45 g dm'3, the reaction is carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C.

[0071] In one variant: if the reaction of step (b) is carried at a molar ratio of P:Fe of < 3: 1 or < 4: 1, the reaction is carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C; if the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of

[0072] > 45 g dm'3, the reaction is carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C; the reaction of step (b) is carried out at pH 0.5-4.0, more preferably 0.5-3.5, most preferably 1.0- 2.5; and iron phosphate-comprising material formed by the method is selected from FePCF and FePC 2H2O.

[0073] In one variant: the y-FeOOH has a particle size distribution characterized by a D50 of < 50 pm, more preferably < 30 pm, or < 20 pm as measured by laser diffraction; the reaction of step (b) is carried out at a temperature of 50°C-100°C; more preferably 60°C- 90°C; most preferably 70°C-90°C; the reaction of step (b) is carried out for a time of < 7 hr, more preferably 1-6 hr., more preferably 1-5 hr., more preferably 2-4 hr., most preferably 2.5-3 hr; if the reaction of step (b) is carried at a molar ratio of P:Fe of < 4:1, the reaction is carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C; if the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of > 45 g dm'3, the reaction is carried out at a temperature of at least 80 °C, more preferably at least 82 °C, or at least 85 °C, such as at about 90°C; the reaction of step (b) is carried out at pH 0.5-4.0, more preferably 0.5-3.5, most preferably 1.0- 2.5; and iron phosphate-comprising material formed by the method is selected from FePCF and FePC 2H2O.

[0074] EMBODIMENTS

[0075] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as “The method of any one of embodiments 1 to 5” or “The method of any preceding embodiment”, every embodiment in this range or every preceding embodiment is meant to be explicitly disclosed for the skilled person, e.g. the wording of this term is to be understood by the skilled person as being synonymous to “The method of any one of embodiments 1, 2, 3, 4 and 5”. Further, it is explicitly noted that the following set of embodiments is not the set of claims determining the extent of protection, but represents a suitably structured part of the description directed to general and specific aspects of the present invention.

[0076] 1. A method of forming an iron phosphate-comprising material, comprising the steps of:

[0077] (a) reacting an aqueous solution of ferrous iron with an oxidizing agent in the presence of a base while maintaining an acidic pH, resulting in the formation of y-FeOOH;

[0078] (b) reacting the y-FeOOH resulting from step (a) with a phosphorus source, resulting in the formation of an iron phosphate-comprising material; wherein the y-FeOOH resulting from step (a) is not isolated between steps (a) and (b).

[0079] 2. The method of any preceding embodiment, wherein the aqueous solution of ferrous iron is selected from ferrous chloride, ferrous sulfate, ferrous gluconate, ferrous fumarate, ferrous succinate, ferrous lactate, ferrous glutamate, ferrous ascorbate, ferrous bisglycinate, ferrous nitrate, ferrous acetate and mixtures thereof.

[0080] 3. The method of any preceding embodiment, wherein the aqueous solution of ferrous iron is pickle liquor. 4. The method of any preceding embodiment, wherein the aqueous solution of ferrous iron is clear liquor.

[0081] 5. The method of any preceding embodiment, wherein the oxidizing agent is selected from oxygen (O2), hydrogen peroxide, potassium dichromate, sodium hypochlorite, calcium hypochlorite, ozone, potassium perchlorate, potassium chlorate, potassium permanganate, ammonium persulfate, sodium persulfate, and mixtures thereof; preferably from oxygen (O2), hydrogen peroxide, sodium hypochlorite, ozone, potassium perchlorate, potassium chlorate, ammonium persulfate, sodium persulfate, and mixtures thereof.

[0082] 6. The method of any preceding embodiment, wherein the oxidizing agent is an oxygencontaining gas such as air.

[0083] 7. The method of any preceding embodiment, wherein step (a) comprises aerating the aqueous solution of ferrous iron with an oxygen-containing gas such as air.

[0084] 8. The method of any preceding embodiment, wherein the base is selected from alkali metal hydroxides, ammonia, ammonium hydroxide, barium hydroxide, strontium hydroxide, calcium hydroxide, n-butyl lithium, lithium diisopropylamide, lithium diethylamide, sodium amide, sodium hydride, lithium bis(trimethylsilyl)amide, and mixtures thereof; preferably from alkali metal hydroxides, ammonia, ammonium hydroxide, and mixtures thereof; most preferably wherein the base is sodium hydroxide.

[0085] 9. The method of any preceding embodiment, wherein neither the base nor the oxidizing agent contains a metal other than an alkali metal.

[0086] 10. The method of any preceding embodiment, wherein the phosphorous source is selected from phosphoric acid (H3PO4), phosphorous acid (H3PO3), (NH^HzPC , (NF ^HPC , (NH4)3PO4, L13PO4, Li2HPO4, and L1H2PO4, and mixtures thereof; or is selected from H3PO4, H3PO3, (NH4)H2PO4,(NH4)2HPO4, (NH4)3PO4, and mixtures thereof; or is H3PO4.

[0087] 11. The method of any preceding embodiment, wherein the iron phosphate-comprising material comprises a sulfur content of <1000 ppm or <500 ppm.

[0088] 12. The method of any preceding embodiment, wherein the iron phosphate-comprising material has a particle size distribution characterized by a D50 of < 20 pm, or < 15 pm, or < 12 pm, or < 10 pm.

[0089] 13. The method of any preceding embodiment, wherein the iron phosphate-comprising material has a particle size distribution span ((D90-D10) / D50) of < 6, or < 5, or < 4, or < 3, or < 2.

[0090] 14. The method of any preceding embodiment, wherein the y-FeOOH has a particle size distribution characterized by a D50 of < 50 pm, or < 30 pm, or < 20 pm, or < 15 pm.

[0091] 15. The method of any preceding embodiment, wherein the reaction of step (b) is carried out in the presence of additional reactants and / or additives selected from the group consisting of ion sources, dopants, surfactants and chelating agents; optionally wherein the reaction is carried out in the presence of additional ion sources and / or dopants.

[0092] 16. The method of any preceding embodiment, wherein the iron phosphate-comprising material is selected from FePC , FePCF 2H2O, Fes / PCF OHh 2H2O, Fe4(P2O?)3, and Fe3(PO4)2 8H2O; optionally wherein the iron phosphate-compnsing material is selected from FePC and FePCF 2H2O.

[0093] 17. The method of any preceding embodiment, wherein the iron phosphate-comprising material is FePC adopting a trigonal phase, most preferably FePC adopting the a-quartz structure.

[0094] 18. The method of any preceding embodiment, wherein the iron phosphate-comprising material is not lithium iron phosphate or a material having an olivine-type crystal structure.

[0095] 19. The method of any preceding embodiment, wherein the reaction of step (b) is carried out at an acidic pH; or at pH < 5, or at pH 0.5-4.0; or at pH 0.5-3.5, or at pH 1.0-2.5.

[0096] 20. The method of any preceding embodiment, wherein if the reaction of step (b) is carried out at a molar ratio of P:Fe of < 1.5:1, < 3:1, or < 4:1, the reaction is carried out at a temperature of at least 80 °C, or at least 82 °C, or at least 85 °C, such as at about 90°C.

[0097] 21. The method of any preceding embodiment, wherein the reaction of step (b) is carried out at a molar ratio of P:Fe of > 3:1, or > 4:1, or > 6:1, or > 7:1.

[0098] 22. The method of any preceding embodiment, wherein the reaction of step (b) is carried out at a molar ratio of P:Fe of < 100: 1, or < 50: 1, or < 20:1, or < 12: 1.

[0099] 23. The method of any preceding embodiment, wherein the reaction of step (b) is carried out at a temperature of 50°C-100°C; or 60°C-90°C; or 70°C-90°C.

[0100] 24. The method of any preceding embodiment, wherein the reaction of step (b) is carried out at for a period of < 7 hr.; or 1-6 hr.; or 1-5 hr.; or 2-4 hr.; or 2.5-3 hr.

[0101] 25. The method of any preceding embodiment, wherein if the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of > 45 g dm'3, the reaction is carried out at a temperature of at least 80 °C, or at least 82 °C, or at least 85 °C, such as at about 90°C

[0102] 26. The method of any preceding embodiment, wherein the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of < 45 g dm'3, or < 35 g dm'3, or < 25 g dm'3and optionally > 0.1 g dm'3, > 0.5 g dm'3, or > 1 g dm'3.

[0103] 27. The method of any preceding embodiment, wherein the reaction of step (b) is carried out under a non-inert atmosphere such as an air atmosphere.

[0104] 28. A method of forming an iron phosphate-comprising material according to any preceding embodiment, wherein if metals other than iron are present in the iron-phosphate comprising material, they are present at less than 10 at.%, or less than 5 at.%, or less than 1 at.% relative to the amount of iron in the iron-phosphate comprising material.

[0105] 29. A method of forming an iron phosphate-comprising material according to any preceding embodiment, which is a one-pot process.

[0106] 30. A method of forming an iron phosphate-comprising material according to any preceding embodiment, which is a continuous process.

[0107] 31. A method of forming an iron phosphate-comprising material according to any preceding embodiment, comprising isolating the resultant iron phosphate-comprising material.

[0108] 32. A method of forming an iron phosphate-comprising material according to embodiment 31, comprising calcining the isolated iron phosphate-comprising material to form an anhydrous iron phosphate-comprising material; optionally wherein the anhydrous iron phosphate- comprising material is FePCk

[0109] 33. A method of forming lithium iron phosphate, comprising following the method of any preceding embodiment, and reacting the iron phosphate-comprising material with a lithium source to form lithium iron phosphate.

[0110] 34. A method of forming an article, comprising following the method of any of embodiments 1-

[0111] 32 to form an iron phosphate-comprising material, or following the method of embodiment

[0112] 33 to form lithium iron phosphate, and forming an article comprising the iron phosphate- comprising material or the lithium iron phosphate.

[0113] 35. The method of embodiment 34, wherein the article is an electrode or a battery cell.

[0114] 36. An iron phosphate-comprising material formed by the method of any of embodiments 1-32.

[0115] 37. Lithium iron phosphate formed by the method of embodiment 33.

[0116] 38. An article comprising the iron phosphate-comprising material formed by the method of any of embodiments 1-32 or the lithium iron phosphate formed by the method of embodiment 33.

[0117] 39. The article of embodiment 38 being an electrode or a battery cell.

[0118] The present invention has been described in detail, including various embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and / or improvements on this invention that fall within the scope and spirit of the invention.

[0119] EXAMPLES

[0120] The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended, nor should they be interpreted to, limit the scope of the invention. The examples show that the inventive process of the present application can be performed with various embodiments and alterations to generate y-FeOOH (lepidocrocite) in- situ without isolation (e.g. a one-pot process) to make iron phosphate.

[0121] Example 1: Synthesis of Lepidocrocite

[0122] In a 3L Morton flask, 44.75g FeCh AH2O crystals were dissolved in 800 mL H2O by stirring at 300 rpm. Air was then bubbled into the solution using a porosity B (70-100 um) diffuser at a rate of 200 mL / min. After 30 mins of aeration, the pH was near 2.9, and then a 35% NaOH solution was added at 0.5 mL / min with the continuation of the air bubbling. The addition of the NaOH is controlled to prevent the pH from exceeding 5.0. Over the course of an hour, an orange-colored precipitate forms in the flask and the addition rate of the NaOH is slowed to 0.1 mL / min to prevent the pH from spiking over 5.0. At this point, the reaction was stirred for an additional 45 minutes while the pH stayed near 5.0 and the reaction was considered to be complete. About a third of the slurry was filtered, washed, and dried at 120°C for 2 hours. The resulting brown colored solid had a D50 particle size of 14.05pm and was shown to be lepidocrocite by powder XRD (see Figure 1). The purpose of Example 1 was to generate a y-FeOOH slurry that will be used to prepare iron phosphate in either a continuous process or with minimal delay (less than approx. 1 hr.) to generate iron phosphate, which is the preferred process for the present invention.

[0123] Example 2: Synthesis of Lepidocrocite

[0124] The remaining material from Example 1 was allowed to stir overnight. Then about half of the remaining slurry was filtered, washed, and dried at 120°C for 2 hours. The resulting brown colored solid had a D50 particle size of 16.26pm and was shown to be lepidocrocite by powder XRD. The purpose of Example 2 was to generate a y-FeOOH slurry and demonstrate that the process of generating iron phosphate can proceed after a time delay (e.g. 12-14 hours). Thus, a continuous process, though preferred, is not an absolute requirement for the process of the present application.

[0125] Note: in Examples 1 and 2, isolation (filtering, washing, drying) was performed in order to analyze the material and demonstrate that it is y-FeOOH. In all subsequent examples (3-31) the y-FeOOH is converted to iron phosphate without isolation.

[0126] Example 3: Synthesis of Iron Phosphate

[0127] Iron phosphate was synthesized subsequently from the lepidocrocite generated using the procedure in Example 1 without isolation by first removing the pH probe and the air diffuser. Next, IL H2O and 162g 75% H3PO4 were added to the flask. The mixing speed was changed to 500 RPM and the flask was heated to 70°C. Stirring continued for 4 hours after reaching 70°C, and after about an hour, the slurry converted from the initial orange color to a pinkish white color. Once cooled, the resultant slurry was vacuum filtered and washed 4 x 250 mL H2O and the filter cake was dried at 110°C for 2 hours to produce Iron Phosphate dihydrate with a pinkish white color. XRD of the dried powder shows dihydrate phase metastrengite II (phosphosiderite) (Figure 2A). Subsequent calcination for 4 hours at 650°C produced the anhydrous Iron Phosphate (FePO4) with an off-white color. XRD of the calcined powder shows the anhydrous oc-quartz phase (Figure 2B). The D50 particle size was 2.38pm. The purpose of Example 3 was to produce Iron Phosphate immediately after the in-situ generation of y-lepidocrocite to demonstrate the continuous process embodiment.

[0128] Example 4: Synthesis of Iron Phosphate

[0129] Iron phosphate was synthesized subsequently from the lepidocrocite generated using the procedure in Example 2 without isolation by following the procedure in Example 3. The slurry converted from the initial orange color to a pinkish white color after about an hour. The dried Iron Phosphate dihydrate had a pinkish white color and the XRD showed the dihydrate phase metastrengite II. The calcined anhydrous Iron Phosphate had an off-white color and the XRD showed the anhydrous oc-quartz phase. The D50 particle size was 2.04pm. The purpose of Example 4 was to show the production of iron phosphate after aging overnight of the in-situ generated of y-FeOOH.

[0130] Example 5: Synthesis of Iron Phosphate

[0131] The procedure of Example 3 was used to synthesize Iron Phosphate except that the air bubbler rate was changed to 250 mL / min and the mixing speed for the first step was changed to 350 RPM. The slurry converted from the initial orange color to a pinkish white color after about an hour. The final calcined sample was an off-white color with a D50 = 2.78 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 5 was to show processing variation in the way of increased mixing and aeration.

[0132] Example 6: Synthesis of Iron Phosphate

[0133] The procedure of Example 5 was used to synthesize Iron Phosphate except that the total water added (800 mL from first step + 1000 mL from second step = 1800 mL) was added in the first step with no additional water added in the second step. The slurry converted from the initial orange color to a pinkish white color after about an hour. The final calcined sample was an off- white color with a D50 = 2.92 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 6 was to simplify the procedure by having all the water added at the beginning of the process.

[0134] Example 7: Synthesis of Iron Phosphate

[0135] The procedure of Example 5 was used to synthesize Iron Phosphate except that the total water added was reduced to 1200 mL and was added in the first step with no additional water added in the second step. The slurry converted from the initial orange color to a pinkish white color after about an hour. The final calcined sample was an off-white color with a D50 = 3.14 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 7 was to test a reduced water level in the procedure.

[0136] Example 8: Synthesis of Iron Phosphate

[0137] The procedure of Example 5 was used to synthesize Iron Phosphate except that the total water added was reduced to 800 mL and was added in the first step with no additional water added in the second step. The slurry converted from the initial orange color to a pinkish white color after about an hour. The final calcined sample was an off-white color with a D50 = 3.82 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 8 was to further reduce the water level in the procedure.

[0138] Example 9: Synthesis of Iron Phosphate

[0139] The procedure of Example 7 was used to synthesize Iron Phosphate except that the mixing speed in the first step was changed to 400 RPM. The slurry converted from the initial orange color to a pinkish white color after about an hour. The final calcined sample was an off-white color with a D50 = 3.27 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 9 was to test increased mixing speed at the lower water level.

[0140] Example 10: Synthesis of Iron Phosphate

[0141] The procedure of Example 9 was used to synthesize Iron Phosphate except that the amount of H3PO4 added was reduced to 100 g. The slurry converted from the initial orange color to a pinkish white color after about 1 hour 45 minutes. The final calcined sample was an off-white color with a D50 = 1.64 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 10 was to test a lower Hs POvFe ratio.

[0142] Example 11 : Synthesis of Iron Phosphate

[0143] The procedure of Example 9 was used to synthesize Iron Phosphate except that the amount of H3PO4 added was reduced to 80 g. The slurry converted from the initial orange color to a pinkish white color after about 1 hour 45 minutes. The final calcined sample was an off-white color with a D50 = 1.80 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 11 was to test further lowering the H3PO4:Fe ratio.

[0144] Example 12: Synthesis of Iron Phosphate

[0145] The procedure of Example 9 was used to synthesize Iron Phosphate except that the amount of H3PO4 added was reduced to 60 g. The slurry converted from the initial orange color to a pinkish white color after about 1 hour 45 minutes. The final calcined sample was an off-white color with a D50 = 2.79 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 12 was to test further lowering the H3PO4:Fe ratio.

[0146] Example 13: Synthesis of Iron Phosphate

[0147] The procedure of Example 9 was used to synthesize Iron Phosphate except that the amount of H3PO4 added was reduced to 45 g. The slurry converted from the initial orange color to a pinkish white color after about 2 hours 30 minutes. The final calcined sample was an off-white color with a D50 = 1.98 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 13 was to test further lowering the lEPC Ee ratio.

[0148] Example 14: Synthesis of Iron Phosphate

[0149] The procedure of Example 9 was used to synthesize Iron Phosphate except that the amount of H3PO4 added was reduced to 32 g. The slurry converted from the initial orange color to a pinkish white color after about 4 hours, so the mixing was continued for an additional 1.5 hours. The final calcined sample was an off-white color with a D50 = 1.43 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 14 was to test further lowering the H3PO4:Fe ratio. Example 15: Synthesis of Iron Phosphate

[0150] The procedure of Example 10 was used to synthesize Iron Phosphate except that the amount of water used in the washing step was changed to 4 x 500 mL. The slurry converted from the initial orange color to a pinkish white color after about an hour. The final calcined sample was an off- white color with a D50 = 1.96 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 15 was to test using extra wash water volume.

[0151] Example 16: Synthesis of Iron Phosphate

[0152] In a IL Morton flask, 22.38 g FeCh 4H2O crystals were dissolved in 600 mL H2O by stirring at 400 rpm. Air was then bubbled into the solution using a porosity B (70-100 um) diffuser at a rate of 200 mL / min. After 30 mins of aeration, the pH was near 2.9, and then a 35% NaOH solution was added at 0.25 mL / min with the continuation of the air bubbling. The addition of the NaOH is controlled to prevent the pH from exceeding 5.0. Over the course of an hour, an orange-colored precipitate forms in the flask and the addition rate of the NaOH is slowed to 0.1 mL / min to prevent the pH from spiking over 5.0. Next, 22.0 g 75% H3PO4 were added to the flask. The mixing speed was changed to 500 RPM and the flask was heated to 80°C. Stirring continued for

[0153] 3 hours after reaching 80°C, and the slurry converted from the initial orange color to a pinkish white color after about an hour. Once cooled, the resultant slurry was vacuum filtered and washed

[0154] 4 x 250 mL H2O and the filter cake was dried at 110°C for 2 hours to produce Iron Phosphate dihydrate with a pinkish white color. Subsequent calcination for 4 hours at 650°C produced the anhydrous Iron Phosphate with an off-white color and a D50 = 1.58 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 16 was to maximize the volume in the flask with parameters adapted accordingly and to also to test using an increased reaction temperature to speed up conversion to Iron Phosphate.

[0155] Example 17: Synthesis of Iron Phosphate

[0156] The procedure of Example 16 was run except using 33.57 g FeCh AH2O, air bubbling at 250 mL / min, max NaOH rate of 0.3 mL / min, 33.1 g 75% H3PO4, and washing with 4 x 500 mL of water. The slurry converted from the initial orange color to a pinkish white color after about 50 minutes. The final calcined sample was an off-white color with a D50 = 1.34 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 17 was to increase the output of the procedure by using 50% more iron chloride and also adapting some parameters accordingly, including faster airflow, faster NaOH pump rate, and increased wash water volume.

[0157] Example 18: Synthesis of Iron Phosphate

[0158] The procedure of Example 17 was run except using 83.2g clear liquor in 550 mL water. The slurry converted from the initial orange color to a pinkish white color after about 50 minutes. The final calcined sample was an off-white color with a D50 = 1.66 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 18 was to show that clear liquor can be the source of iron chloride.

[0159] Example 19: Synthesis of Iron Phosphate

[0160] The procedure of Example 17 was run except using 81.2g pickle liquor in 550 mL water. The slurry converted from the initial orange color to a pinkish white color after about 50 minutes. The final calcined sample was an off-white color with a D50 = 1.37 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example

[0161] 19 was to show that pickle liquor can be the source of iron chloride.

[0162] Example 20: Synthesis of Iron Phosphate

[0163] The procedure of Example 19 was run except using 108.2g pickle liquor in 525 mL water. The slurry converted from the initial orange color to a pinkish white color after about 45 minutes. The final calcined sample was an off-white color with a D50 = 1.43 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example

[0164] 20 was to demonstrate that an even higher iron chloride concentration can be used to further increase the output of the procedure.

[0165] Example 21: Synthesis of Iron Phosphate

[0166] The procedure of example 17 was run except 46.93 g FeSO4 7H2O was used as iron source. The slurry converted from the initial orange color to a pinkish white color after about 1 hour 45 minutes. The final calcined sample was an off-white color with a D50 = 1.45 pm. The purpose of Example 21 was to demonstrate that the procedure can work with ferrous sulfate instead of ferrous chloride.

[0167] Example 22: Synthesis of Iron Phosphate

[0168] In the first phase of lepidocrocite precipitation, 44g FeCh 4H2O crystals were dissolved in 535 mL FEO in a IL Morton flask by stirring at 250 rpm and bubbling N2 gas. Next, 29g of 35% NaOH was added 3g / min and then stirred for 10 minutes. The mixing speed was then changed to 400 RPM and the bubbled gas was switched to air, which was continued until the pH reached 3.5. In the second phase of lepidocrocite precipitation, 12g FeCh 4H2O crystals were added to the flask, which was then heated to 32°C. With air bubbling, 35% NaOH was added at 0.2g / min until the pH was between 4.5 and 5.5. Next, with the air and pH meter removed, 48.6g of 85% H3PO4 was added and then heated to 90°C. During the 3 hour stir, the initially orange colored slurry converted to a pinkish white color after about 45 minutes. Once cooled, the resultant slurry was vacuum filtered and washed 4 x 500 mL H2O and the filter cake was dried at 100°C for 2 hours to produce Iron Phosphate dihydrate with a pinkish white color. Subsequent calcination for 4 hours at 650°C produced the anhydrous Iron Phosphate with an off-white color with a D50 = 2.52 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 22 was to test a 2-phase lepidocrocite precipitation process. Example 23: Synthesis of Iron Phosphate

[0169] The procedure of Example 22 was run except using 107g clear liquor in 473 mL water in the first phase of lepidocrocite precipitation and then adding 29g more clear liquor in the second phase. The slurry converted from the initial orange color to a pinkish white color after about 45 minutes. The final calcined sample was an off-white color with a D50 = 3.73 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 23 was to show that clear liquor can be the source of iron chloride in the 2-phase lepidocrocite precipitation process.

[0170] Example 24: Synthesis of Iron Phosphate

[0171] The procedure of Example 22 was run except using 115g pickle liquor in 465 mL water in the first phase of lepidocrocite precipitation and then adding 31g more pickle liquor in the second phase. The slurry converted from the initial orange color to a pinkish white color after about 45 minutes. The final calcined sample was an off-white color with a D50 = 2.52 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 24 was to show that pickle liquor can be the source of iron chloride in the two phase lepidocrocite precipitation process.

[0172] Example 25: Synthesis of Iron Phosphate

[0173] The procedure of example 22 was run except 62g FeSO4 7H2O crystals was used as iron source in 527 mL water in the first phase of lepidocrocite precipitation and then adding 16.5g more FeSO4-7H2O crystals in the second phase. The slurry converted from the initial orange color to a pinkish white color after about 45 minutes. The final calcined sample was an off-white color with a D50 = 3.59 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 25 was to demonstrate that the procedure can work with ferrous sulfate instead of ferrous chloride.

[0174] Example 26: Synthesis of Iron Phosphate

[0175] In a IL Morton flask, 7.5 g of clear liquor was added to 525 g of DI water and stirred at 200 RPM. A 70-100 mm diffuser tube was inserted with air flow set at 250 mL / min. After raising the mixing speed to 500 RPM, 35% NaOH was pumped in until the pH was in the range of 5.0- 5.5, at which point the remaining 92.5 g of clear liquor was pumped in at 0.8 mL / min while using 35% NaOH to keep the pH in the range of 5.0-5.5. After a stir time of 10 minutes, the air flow was stopped and 29.18g of 75% H3PO4 was added (1.1. H3PO4: Fe ratio), then heated to 80°C. The color of the slurry turned from orange to white at about 55 minutes into the 3 hour stir at 80°C. After allowing for the slurry to cool, it was vacuum filtered, washed 4x500 mL H2O and dried for 2 hours at 110°C, resulting in a pinkish white product. Subsequent calcination at 650°C for 2 hours produced an off-white powder with D50 = 1.30 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 26 was to demonstrate a pumped addition of the clear liquor.

[0176] Example 27: Synthesis of Iron Phosphate

[0177] Example 27 was run like Example 26 except pH range was 4.8-5.2. The color of the slurry turned from orange to white at about 50 minutes into the 3 hour stir at 80°C. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.57 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 27 was to test a lower pH range.

[0178] Example 28: Synthesis of Iron Phosphate

[0179] Example 28 was run like Example 27 except that the initial amount of clear liquor in the flask was 10 g, and 115 g of clear liquor were pumped in and used 36.48g of 75% H3PO4. The color of the slurry turned from orange to white at about 45 minutes into the 3 hour stir at 80°C. The dried sample was pinkish white and the calcined sample was off-white with D50 =1.42 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 28 was to demonstrate that a higher ferrous chloride concentration can be used.

[0180] Example 29: Synthesis of Iron Phosphate

[0181] Example 29 was run like Example 28 except pH range was 4.6-5.0. The color of the slurry turned from orange to white at about 45 minutes into the 3 hour stir at 80°C. The dried sample was pinkish white and the calcined sample was off-white with d50 = 1.83 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 29 was to demonstrate that an ever lower pH range can be used.

[0182] Example 30: Synthesis of Iron Phosphate

[0183] Example 30 was run like Example 28 except that 125g pickle liquor were used, of which the first 6g were charged into the flask initially. Additionally, the pH range was narrowed to 4.85-5.15, and the HsPO^Fe molar ratio was raised from 1.1 to 1.2, thus 40.76 g 75% H3PO4 was used. The color of the slurry turned from orange to white at about 45 minutes into the 3 hour stir at 80°C. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.33 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 30 was to demonstrate that a tighter pH range can be achieved.

[0184] Example 31 : Synthesis of Iron Phosphate

[0185] Example 31 was run like Example 30 except that 125g clear liquor was used instead, and 39.79g of 75% H3PO4 was used to provide a H3PO4:Fe ratio of 1.2. The first 10g of clear liquor were charged into the flask initially. The color of the slurry turned from orange to white at about 45 minutes into the 3 hour stir at 80°C. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.96 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 31 was to demonstrate that the procedure in Example 30 also works with clear liquor.

[0186] Example 32 Synthesis of Iron Phosphate

[0187] Example 32 was run like Example 31 except that the pumped portion of the Clear Liquor was added faster, at 1.0 mL / min. The color of the slurry turned from orange to white at about 40 minutes into the 3 hour stir at 80°C. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.26 pm. The purpose of Example 32 was to demonstrate that a slightly faster clear liquor addition is possible.

[0188] Example 33 Synthesis of Iron Phosphate

[0189] Example 33 was run like Example 31 except that the H3PO4 was added at 0.8 mL / min after the reactor had approached 80°C. The color of the slurry turned from orange to white at about 40 minutes from the end of the H3PO4 addition. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.42 pm. The purpose of Example 33 was to demonstrate that slow addition of H3PO4 is possible.

[0190] Example 34 Synthesis of Iron Phosphate

[0191] Example 34 was run like Example 31 except that the pH target for FeOOH generation was changed to 5.2. The color of the slurry turned from orange to white at about 45 minutes into the 3 hour stir at 80°C. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.25 pm. The purpose of Example 34 was to demonstrate the use of different pH values.

[0192] Example 35 Synthesis of Iron Phosphate

[0193] Example 35 was run like Example 31 except that the pH target for FeOOH generation was changed to 5.4. The color of the slurry turned from orange to nearly white at about 45 minutes into the 3 hour stir at 80°C, and pinkish white at about 90 minutes. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.46 pm. The purpose of Example 35 was to demonstrate the use of different pH values.

[0194] Example 36 Synthesis of Iron Phosphate

[0195] Example 36 was run like Example 34 except that the mixing speed during H3PO4 addition and subsequent stir time was lowered to 400 RPM. The color of the slurry turned from orange to nearly white at about 65 minutes into the 3 hour stir at 80°C, and pinkish white at about 110 minutes. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.22 pm. The purpose of Example 36 was to demonstrate the use of slower stir in the conversion to iron phosphate.

[0196] Example 37 Synthesis of Iron Phosphate Example 37 was run like Example 34 except that the mixing speed during H3PO4 addition and subsequent stir time was lowered to 300 RPM. The color of the slurry turned from orange to nearly white at about 60 minutes into the 3 hour stir at 80°C, and pinkish white at about 110 minutes. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.28 pm. The purpose of Example 37 was to demonstrate the use of slower stir in the conversion to iron phosphate.

[0197] Example 38 Synthesis of Iron Phosphate

[0198] Example 38 was run like Example 34 except that the reaction was heated to 80°C before the 0.6 mL / min H3PO4 addition. The color of the slurry turned from orange to nearly white at about 60 minutes from the end of the H3PO4 addition. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.36 pm. The purpose of Example 38 was to prepare a standard with slow-added H3PO4 for comparison with Examples 39 and 40.

[0199] Example 39 Synthesis of Iron Phosphate

[0200] Example 39 was run like Example 38 except that the mixing speed during H3PO4 addition and subsequent stir time was lowered to 400 RPM. The color of the slurry turned from orange to white gradually over the course of the 3hr stir. The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.40 pm. The purpose of Example 39 was to demonstrate the use of slower stir when coupled with slow H3PO4 addition.

[0201] Example 40 Synthesis of Iron Phosphate

[0202] Example 40 was run like Example 38 except that the mixing speed during H3PO4 addition and subsequent stir time was lowered to 300 RPM. The color of the slurry turned from orange to white gradually, being pinkish white by 3 hr from the end of the H3PO4 addition (3 hr. 40 mins total hot). The dried sample was pinkish white and the calcined sample was off-white with D50 = 1.43 pm. The purpose of Example 40 was to demonstrate the use of slower stir when coupled with slow H3PO4 addition.

[0203] Example 41 Synthesis of Iron Phosphate

[0204] The procedure of Example 23 was run except using 30% NEU OH as the base instead of 35% NaOH. The slurry converted from the initial orange color to a pinkish white color. The final calcined sample was an off-white color with a D50 = 2.66 pm. Powder XRD shows that the product was a phase pure iron phosphate in the oc-quartz phase. The purpose of Example 41 was to show that lepidocrocite can be generated using 30% NH4OH as the base and subsequently converted to iron phosphate.

[0205] Example 42 Synthesis of Iron Phosphate

[0206] The procedure of Example 41 was run except using all 136 g of clear liquor in 473 mL water in one phase. The slurry converted from the initial orange color to a pinkish white color. The final calcined sample was an off-white color with a D50 = 10.6 pm. The purpose of Example 42 was to show that conditions of Example 41 will work with a one phase addition. Example 43 Synthesis of Iron Phosphate

[0207] In a IL Morton flask, 128 g of clear liquor was added to 482 g of DI water and stirred at 200 RPM and heated to 32°C. Then the mixing speed was increased to 500 RPM and a porosity B (70-100 pm) diffuser tube was inserted with air flow set at 500 mL / min. Next, a 30% NH4OH solution was pumped in at 0.6 mL / min until the pH stabilized at 5.2. During the addition, pH initially rises to near 5.2 but falls back to 4.5-4.6 for most of reaction. When a pH of 5.2 is again approached toward the end of the addition, the rate is slowed to avoid over shooting. The resulting lepidocrocite slurry was then heated to 80°C and 39g of 85% H3PO4 (PO4:Pe ratio of 1.2) was added at 0.5 g / min. The color of the slurry remained orange during the subsequent 3 hour stir at 80°C. After allowing the slurry to cool, it was vacuum filtered, washed 4x500 mL H2O and dried for 2 hours at 110°C, and calcined at 650°C for 4 hours. The final product was a pale orange color. Powder XRD shows that the product was a phase pure iron phosphate in the a-quartz phase. The purpose of Example 43 was to test using NH4OH instead of NaOH for the Lepidocrocite generation.

[0208] Example 44 Synthesis of Iron Phosphate

[0209] Example 44 was run like Example 43 except that the amount of H3PO4 was increased to 48.6 g for a PO4:Fe ratio of 1.5. The final slurry of this example was also orange colored, but the calcined product was an off-white color. Powder XRD shows that the product was a phase pure iron phosphate in the a-quartz phase. The purpose of Example 44 was to see if using a higher PO4:Fe ratio would convert when NH4OH is used instead of NaOH for the Lepidocrocite generation.

[0210] Example 45 Synthesis of Iron Phosphate

[0211] Example 45 was run like Example 44 except that the temperature for the phosphate step was 90°C instead of 80°C. The color of the slurry turned from orange to white gradually, being pinkish white by 3hr from the end of the H3PO4 addition (4 hr. 40 mins total hot). The dried sample was pinkish white and the calcined sample was off-white with D50 = 3.22 pm. Both the dried and calcined material were loose, free-flowing powders. The purpose of Example 45 was to demonstrate that a PO4:Fe ratio of 1.5 and a temperature of 90°C can convert lepidocrocite that was generated using NH4OH.

[0212] Example 46 Synthesis of Iron Phosphate using anhydrous ammonia as the base to synthesize lepidocrocite.

[0213] In a 76 L (20-gal) reactor, 45.95 L (12.14 gal) of RO water was added followed by 13.70 L (3.62 gal) of clear liquor. The solution was agitated at about 150-200 rpms and the vessel was heated to about 80°C. After heating, about 0.97 kg (2.14 lbs.) of anhydrous ammonia gas along with a steady stream of dry air were bubbled through the solution subsurface at a steady rate over a period of 3-4 hours until the pH reached about 4.5 - 5.5. As the pH increased an orange-yellow precipitate formed. The color change indicated the formation of lepidocrocite.

[0214] REFERENCE EXAMPLES

[0215] The following reference examples demonstrate the formation of iron phosphate-comprising material from y-FeOOH, a-FeOOH, and 0-FeOOH, including demonstrating the surprisingly quicker rate of formation when using y-FeOOH. The quicker rate of formation of iron phosphate- comprising material is also expected to be seen the invention when the y-FeOOH is formed by reacting an aqueous solution of ferrous iron with an oxidizing agent in the presence of a base while maintaining an acidic pH, and then without isolating the resulting y-FeOOH, the resulting y-FeOOH is reacted with a phosphorus source, resulting in the formation of the iron phosphate- comprising material.

[0216] The y-FeOOH, a-FeOOH (Y5102, ZMAG-5102 equivalent), and Fe^CF, in the following reference examples were provided by Sun Cosmetics, LLC, owned by Sun Chemical, Valparaiso, IN USA. 0-FeOOH was synthesized as described in Reference Example 17A. The particle size distribution was determined by laser diffraction using a Malvern 3000 particle size analyzer. The y-FeOOH had D10 = 0.5 pm, D50 = 9.6 pm, and D90 = 38.4 pm. The a-FeOOH had D10 = 0.33 pm, D50 = 0.61 pm, and D90 = 2.66 pm. The P-FeOOH had D10 = 0.3 pm, D50 = 2.6 pm, and D90 = 33.4 pm.

[0217] The particle size distribution for these materials was also determined by a disc centrifuge particle size analyzer. The particle size was measured in a DI water / Sucrose gradient on the disc centrifuge at 24000 RPM’s. Particle size Distribution by weight results are taken from 0.2-10 microns. The lepidocrocite used had a particle size distribution of Dw10 = 86nm, Dw50 = 163nm, Dw90 = 249 and an iron content of 61-62%.

[0218] The conversion to iron phosphate was marked by the color change to white powder.

[0219] Note: in all of the following reference examples, FeOOH was sieved through 10 mesh (2000 pm screen) prior to the reactions to remove any abnormally large pieces of material.

[0220] For Reference Examples 1-19, 25, and 28-33 particle size distribution was determined by laser diffraction using a Malvern 3000 particle size analyzer.

[0221] Table 1 below, captures the properties of each reference example after the reactions.

[0222] Reference Example 1 A (a-FeOOH / comparative) vs. Example IB (y-FeOOH). Conversion of FeOOH to Iron Phosphate

[0223] A comparison in reaction rate between a-FeOOH and y-FeOOH was conducted using the following procedure: 1 gram of either a-FeOOH (Comparative Example 1A) or y-FeOOH (Example IB) was added to 200mL of 5% H3PO4 (8.9: 1 P:Fe ratio) to a IL Morton flask and stirred with a magnetic stir bar at 300rpm at a temperature of 80°C for 3 hours. The precipitant was vacuum filtered and washed with 4 X lOmL of deionized water and dried at 100°C for 2 hours. After 3 hours there was no color change in the conversion of Ex. 1A, indicating minimal to no reaction took place. In contrast, the conversion of Ex. IB was marked by a more rapid color change from yellow- orange to very pale off-white color indicating the conversion to iron phosphate. Thus, the use of y-FeOOH led to a faster rate of reaction than a-FeOOH, despite the higher particle size of the y-FeOOH than the a-FeOOH used in these examples.

[0224] The material produced by Ex. IB had a particle size distribution of DIO = 2.46pm, D50 = 11.51pm, D90 = 21.23pm with a span of 1.63.

[0225] Reference Example 2 - Conversion of y-FeOOH to Iron Phosphate

[0226] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of DIO = 2.167pm, D50 = 8.47pm, D90 = 13.82pm with a span of 1.38. The purpose of Reference Example 2 is to show that the conversion can be performed at a lower temperature (70°C).

[0227] Reference Example 3 - Conversion of y-FeOOH to Iron Phosphate

[0228] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 90°C. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of DIO = 5.99pm, D50 = 12.43pm, D90 = 19.62pm with a span of 1.10. The purpose of Reference Example 2 is to show that the conversion can be performed at a higher temperature (90°C).

[0229] Reference Example 4 - Conversion of y-FeOOH to Iron Phosphate

[0230] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 60°C. The result was color change to a darker off-white color as compared to reference examples 1 , 2, 3 , etc. indicating a partial conversion to iron phosphate. The material had a particle size distribution of D10 = 1.42pm, D50 = 8.33pm, D90 = 15.74pm with a span of 1.72. The purpose of Reference Example 4 is to show that a further lowering the reaction temperature to 60°C slows the reaction such that only a partial conversion reaction1occurs after 3 hr.

[0231] ' Note: though less preferred, partial conversions are still useful since they are also ironphosphate containing materials which can be used in combination with other processes to reduce the relative time it takes to make an iron-phosphate containing material. Moreover, the increasing the reaction time is expected to result in full conversion.

[0232] Reference Example 5 - Conversion of y-FeOOH to Iron Phosphate Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C and a stir time of 2 hours. The result was color change to a darker off-white color as compared to reference examples 1, 2, 3, etc. indicating a partial conversion to iron phosphate. The material had a particle size distribution of DIO = 4.12pm, D50 = 9.68pm, D90 = 16.43pm with a span of 1.27. The purpose of Reference Example 5 is to show that reducing the time to 2 hr. hours results in a partial conversion reaction1.

[0233] ' Note: though less preferred, partial conversions are still useful since they are also ironphosphate containing materials which can be used in combination with other processes to reduce the relative time it takes to make an iron-phosphate containing material. Moreover, the increasing the reaction time is expected to result in full conversion.

[0234] Reference Example 6 - Conversion of y-FeOOH to Iron Phosphate

[0235] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C and a stir time of 4 hours. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of DIO = 1.73 pm, D50 = 8.53pm, D90 = 15.18pm with a span of 1.58. The purpose of Reference Example 6 is to show that increasing the reaction time to 4 hours has little impact on the reaction, meaning that the reaction was likely complete at 3 hours. The increased mixing time did advantageously reduce the particle size however.

[0236] Reference Example 7 - Conversion of y-FeOOH to Iron Phosphate

[0237] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C, a stir time of 3 hours, and a P:Fe ratio of 12: 1. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of DIO = 2.43 pm, D50 = 12.61pm, D90 = 22.92pm with a span of 1.63. The purpose of Reference Example 7 is to show that increasing the P:Fe ratio from to 12:1 did not impact the reaction, meaning that the reaction is still fully effective at this ratio.

[0238] Reference Example 8 - Conversion of y-FeOOH to Iron Phosphate

[0239] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C, a stir time of 3 hours, and a P:Fe ratio of 6:1. The result was color change to a darker off-white color as compared to reference examples 1, 2, 3, etc. indicating a partial conversion to iron phosphate. The material had a particle size distribution of DIO = 1.28pm, D50 = 7.65pm, D90 = 14.79pm with a span of 1.76. The purpose of Reference Example 8 is to show that decreasing the P:Fe ratio to 6:1 results in a partial conversion reaction1.

[0240] ' Note: though less preferred, partial conversions are still useful since they are also ironphosphate containing materials which can be used in combination with other processes to reduce the relative time it takes to make an iron-phosphate containing material. Moreover, the increasing the reaction time is expected to result in full conversion.

[0241] Reference Example 9 - Conversion of y-FeOOH to Iron Phosphate

[0242] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 80°C, a stir time of 3 hours, and a P:Fe ratio of 6:1. The result was color change to a darker off-white color as compared to reference examples 1, 2, 3, etc. but lighter than example 8 indicating a partial conversion to iron phosphate. The material had a particle size distribution of DIO = 2.95pm, D50 = 11.66pm, D90 = 21.02pm with a span of 1.55. The purpose of Reference Example 9 is to show that increasing the temperature from Reference Example 8 to 80°C results in a partial conversion reaction1, though a slightly darker color indicates a faster reaction than Example 8.

[0243] ' Note: though less preferred, partial conversions are still useful since they are also ironphosphate containing materials which can be used in combination with other processes to reduce the relative time it takes to make an iron-phosphate containing material. Moreover, the increasing the reaction time is expected to result in full conversion.

[0244] Reference Example 10 - Conversion of y-FeOOH to Iron Phosphate

[0245] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours, and a P:Fe ratio of 6:1. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of D10 = 0.89pm, D50 = 4.59pm, D90 = 13.29pm with a span of 2.71. The purpose of Reference Example 10 is to show that increasing the reaction time of Reference Example 8 to 4 hours is sufficient to complete the reaction.

[0246] Reference Example 11 - Conversion of y-FeOOH to Iron Phosphate

[0247] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours, and a P:Fe ratio of 3: 1. The result was a yellow-orange color indicating a minimal conversion to iron phosphate. The material had a particle size distribution of D10 = 0.90pm, D50 = 4.86pm, D90 = 10.61pm with a span of 2.00. The purpose of Reference Example 11 is to show that decreasing the P:Fe ratio in Reference Example 10 to 3: 1 results in minimal or no reaction. However, the Reference Example 11 reaction would likely eventually result in a conversion if allowed to continue for a longer reaction time.

[0248] Reference Example 12 - Conversion of y-FeOOH to Iron Phosphate

[0249] Using the procedure in Reference Examples 1 A / 1B, the conversion of y-FeOOH was conducted at 70°C, a stir time of 5 hours, and a P:Fe ratio of 3: 1. The result was a yellow-orange color indicating a minimal conversion to iron phosphate. The material had a particle size distribution of D10 = 0.98pm, D50 = 5.45pm, D90 = 12.07pm with a span of 2.04. The purpose of Reference Example 12 is to show that increasing the reaction time Reference Example 11 to 5 hours still results in minimal or no reaction. However, the Reference Example 12 reaction would likely eventually result in a conversion if allowed to continue for a longer reaction time.

[0250] Reference Example 13 - Conversion of y-FeOOH to Iron Phosphate

[0251] Using the procedure in Reference Examples 1A / 1B at 2X scale (i.e. double the amount of reactants (y-FeOOH & H3PO4), the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours, and a P:Fe ratio of 6: 1. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of DIO = 1.88pm, D50 = 7.95pm, D90 = 14.78pm with a span of 1.62. The result of doubling the scale of Reference Example 10 is a small increase in the particle size and a decrease in span. The purpose of Reference Example 13 is to show that the reaction will proceed to completion at scaled up (2X scale) manufacturing conditions.

[0252] In Reference Examples 14-19, 20, 21, 25, and 27-33 an overhead mixer was used (Heidolph RZR 2021 with a 6cm flat blade paddle agitator). The purpose of these examples is to show that using an overhead mixer at scaled up manufacturing conditions will result in full conversions

[0253] Reference Example 14 - Conversion of y-FeOOH to Iron Phosphate

[0254] Using the procedure in Reference Examples 1 A / 1B at 2X scale, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours with an overhead mixer at 300rpms, and a P:Fe ratio of 6:1. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of D10 = 1.02pm, D50 = 4.48pm, D90 = 8.47pm with a span of 1.67. The purpose of Reference Example 14 is to shows that using an overhead mixer instead of the magnetic stirrer in Reference Example 13 produces a big drop in particle size. Thus, the reaction is not dependent on any particular mixer or mixing method.

[0255] Reference Example 15 - Conversion of y-FeOOH to Iron Phosphate

[0256] Using the procedure in Reference Examples 1 A / 1B at 2X scale, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours with an overhead mixer at 500rpms, and a P:Fe ratio of 6:1. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of D10 = 0.89pm, D50 = 2.43pm, D90 = 4.57pm with a span of 1.52. The result of increasing the mixing speed from 300rpm of Reference Example 14 to 500rpm is an advantageous drop in particle size and span. The purpose Reference of Example 15 is to show that utilizing a higher mixing speed can be advantageous.

[0257] Reference Example 16 - Conversion of y-FeOOH to Iron Phosphate

[0258] Using the procedure in Reference Examples 1A / 1B at 2X scale with 25% less water, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours with an overhead mixer at 500rpms, and a P:Fe ratio of 6: 1. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of D10 = 0.91pm, D50 = 2.62pm, D90 = 5.00pm with a span of 1.56. The result of reducing the water volume by 25% compared to Reference Example 15 is a slightly larger particle size. The purpose of Reference Example 16 is to show that the reaction can be carried out with 25% reduced water.

[0259] Reference Example 17 - Conversion of y-FeOOH to Iron Phosphate

[0260] Using the procedure in Reference Examples 1A / 1B at 3X scale with 50% less water, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours, a P:Fe ratio of 6: 1 and an overhead mixer at 500rpms. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of D 10 = 1.17pm, D50 = 3.67pm, D90 = 6.78pm with a span of 1.53. The purpose of Reference Example 17 is to show that the reaction can be carried out with 50% reduced water at 3X scale up.

[0261] Reference Example 17A - Conversion of P-FeOOH to Iron Phosphate (comparative)

[0262] P-FeOOH was synthesized by dissolving 130g FeCh 6H2O crystals in 4000mL DI H2O in a 5L Morton flask. The solution was then heated to 80°C and stirred for 2 hours. The particle size of the P-FeOOH measured by laser diffraction on the Malvern 3000 was D10 = 0.3 pm, D50 = 2.6 pm, and D90 = 33.4 pm. This was too small for conventional filtering methods so it was isolated via centrifugation. Two 500 ml portions were centrifuged for 30 min at 3500 RPM. The supernatant was discarded and then refilled with deionized water. This cycle was repeated two additional times. After the final centrifugation, the P-FeOOH was collected. This centrifugation process was repeated on the remaining reaction slurry. The collected P-FeOOH was then dried at 60°C for 24 hours.

[0263] The conversion of P-FeOOH to iron phosphate was conducted using an equivalent procedure to Reference Example 17. The P-FeOOH took 6 hr. to convert and resulted in a particle size distribution of D10 = 3.89mm, D50 = 8.65mm, D90 = 14.42mm with a span of 1.22 compared to the y-FeOOH which took 4 hr. and resulted in a particle size distribution of D10 = 1.17pm, D50 = 3.67pm, D90 = 6.78pm with a span of 1.53. Thus, the use of P-FeOOH led to a slower rate of reaction than y-FeOOH, despite the lower particle size of the P-FeOOH than the y-FeOOH used in these examples.

[0264] Reference Example 18 - Conversion of FeOOH to Iron Phosphate

[0265] Using the procedure in Reference Examples 1A / 1B at 5X scale with 75% less water, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours, a P:Fe ratio of 6: 1 and an overhead mixer at 500rpms. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of D 10 = 1.15pm, D50 = 7.05 pm, D90 = 12.17pm with a span of 1.56. The purpose of Reference Example 18 is to show that the reaction can be carried out with 75% reduced water at 5X scale up Reference Example 19 - Conversion of FeOOH to Iron Phosphate

[0266] Using the procedure in Reference Examples 1A / 1B at 15X scale with 90% less water, the conversion of y-FeOOH was conducted at 70°C, a stir time of 4 hours, a P:Fe ratio of 6: 1 and an overhead mixer at 500rpms. The result was a yellow-orange color indicating a minimal conversion to iron phosphate. The material had a particle size distribution of D 10 = 1.14pm, D50 = 4.70pm, D90 = 10.01 m with a span of 1.88. The purpose of Reference Example 19 is to show that reducing the water volume by 90% results in minimal or no reaction. However, the Reference Example 19 reaction would likely eventually result in a conversion if allowed to continue for a longer reaction time.

[0267] Based on the above Reference Examples, the following preferred reaction conditions for step (b) were noted:

[0268] Preferred pH is acidic; more preferably 0.5-4.0; most preferably 0.5-3.5.

[0269] Preferred reaction temperature is at least 50°C, preferably 50°C-100°C; more preferably 60°C-90°C; most preferably 70°C-90°C. preferred reaction time is < 7 hr.; more preferably 1-6 hr.; more preferably 1-5 hr.; more preferably 2-4 hr.; most preferably 2.5-3 hr.

[0270] Table 1 : Properties of reference examples

[0271] Reference Example 20 - Rate of Reaction for y-FeOOH

[0272] Using the procedure in Reference Examples 1A / 1B at 50X scale with 50% less water, the conversion of y-FeOOH was conducted at 70°C, a P:Fe ratio of 6: 1 and an overhead mixer at 500rpms in a 5L flask. Every 30 minutes during the reaction, a 100 mL sample was removed for filtering, washing, and drying. The initial unreacted y-FeOOH and the subsequent samples through 4.5 hours of reaction time were measured for color. To measure color, a preparation was made by adding 6% of Reference Example 20 to a nitrocellulose lacquer and hand mixing until homogenous. A drawdown was made on a Leneta chart using a 3 mil drawdown bar. Measurements were taken over the white portion of the card using a B YK-mac spectrophotometer at 15 degrees off specular. The hue data in Table 2 shows how the colors progress over the course of the reaction and begins to plateau after about 2.5 hr.

[0273] Reference Example 21 - Rate of Reaction for a-FeOOH (comparative)

[0274] This example was run as in Reference Example 20 using a-FeOOH instead of the y-FeOOH. The 30 minute sampling was done up to 5 hours of reaction time and then a final sample after a total of 21.5 hours of reaction time. The hue data is in Table 3 and shows that there is minimal color change over the 5 hours and only a small change after 21.5 hours indicating the slower reaction of a-FeOOH vs. y-FeOOH despite the lower particle size of the a-FeOOH.

[0275] Table 2: Color data from Reference Example 20: Rate of Reaction for y-FeOOH

[0276] Table 3: Color data from Reference Example 21: Rate of Reaction for a-FeOOH Reference Examples 22-24: The following experiments were conducted to qualify and evaluate the feasibility of converting FeaCE (FeO FeaOa, iron(II,III) oxide, black iron oxide) to iron phosphate and the conversion of y-FeOOH (y-Fe2O3H2O, iron oxi de- hydroxi de, iron oxy hydroxide) in the presence of an alkali to iron phosphate. In all of the following reference examples, y-FeOOH was sieved through 10 mesh (2000 pm screen) before the reactions were performed to remove any abnormally large pieces of material.

[0277] The y-FeOOH had a particle size distribution of Dw10 = 86nm, Dw50 = 163nm, Dw90 = 249nm and Fe3O4had a particle size distribution of Dw10 = 32nm, Dw50 = 453nm, Dw90 = 626nm. The samples were measured using a disc centrifuge particle size analyzer. The reaction was determined by the color changing, more precisely, diminishing color over the time of the reaction. A pale-yellow or white color was the most optimal. The reaction was considered complete when the color stopped changing. The target for initial pH was about 2. After 8 hours, the samples were filtered and dried in a convection oven at 60° C.

[0278] Reference Example 22: Conversion of y-FeOOH to iron phosphate.

[0279] The y-FeOOH was ground with a mortar and pestle. Then, 57.840g of 50% H3PO4 was added to a 250- mL Erlenmeyer flask and heated to 80°C. 3.554g of y-FeOOH was slowly added with vigorous stirring. The volume was increased to 75 mL with reversed osmosis (RO) water. The contents of the flask were stirred every 15 - 30 minutes. The color started to change after about 45 minutes to a milky yellow color, indicating conversion. The reaction continued to progress visually up to 5 hours into digest. There was no change in appearance after about 5 hours. Additionally, at the 5-hour mark, 5% excess 50% H3PO4 (0.392 g) was added in an attempt to complete the conversion. The total digest time was about 8 hours. The initial pH was 1.51 and ended at 1.48. The contents were filtered and washed with 20g RO water. The total filtrate was 96.76 g. The total dry weight was 7.29 g. No agglomerations of unreacted y-FeOOH were present in the final mix. There was clear evidence of a conversion of y- FeOOH to iron phosphate and shows a clear improvement on the rate of reaction. This was highly unexpected as reaction times were considerably faster compared to those in U.S. Pat. No. 8673497.

[0280] Reference Example 23: Conversion of FesCh (black iron oxide) to iron phosphate

[0281] In this experiment, y-FeOOH was converted to FesCE by adding ferrous iron solution stoichiometrically to achieve the correct FeO content, and then adding an alkali in reducing conditions to drive the reaction but prevent oxidation. 55.879g of 50% H3PO4 was added to a 250-mL Erlenmeyer flask and heated to 80°C. 2.315g of FesCh was slowly added with vigorous stirring. The volume was increased to 75 mL with reversed osmosis (RO) water. The contents of the flask were stirred every 15 - 30 minutes. The color started to change after about 2 hours to a slightly grey color, indicating conversion. The reaction continued to progress visually up to 5 hours into digest. There was no change in appearance after about 5 hours. At the 5-hour mark, 5% excess 50% H3PO4 (0.293 g) was added in an attempt to complete the conversion. The total digest time was about 8 hours. The initial pH was 1.47 and ended at 1.91. The contents were filtered and washed with 20g RO water. The total filtrate was 97.37 g. The total dry weight was 4.77 g. There was clear evidence of a conversion of Fe3O4 to iron phosphate, although not complete, shows a clear improvement on the rate of reaction. This was highly unexpected as reaction times were considerably faster compared to those in U.S. Pat. No. 8673497.

[0282] Reference Example 24: Conversion of y-FeOOH to iron phosphate with alkali present.

[0283] In this experiment, 57.840g of 50% H3PO4 and 1.599g of NaOH were added to a 250-mL Erlenmeyer flask and heated to 80°C. The pH had to be adjusted from 3.2, to the target of 2. This was done with an addition of 2.4 mL of 50% HC1. HC1 was chosen with the idea that it may catalyze the reaction. 3.554g of y-FeOOH was slowly added with vigorous stirring. The volume was increased to 75 mL with reversed osmosis (RO) water. The contents of the flask were stirred every 15 - 30 minutes. The color started to change after about 2 hours to a milky yellow color, indicating conversion. The reaction continued to progress visually up to 5 hours into digest. The initial pH was 1.94 and ended at 2.57. There was no change in appearance after 3 hours, however, it was continued to about 5 hours to keep experimental uniformity. At the 5-hour mark, 5% excess 50% H3PO4 (0.392 g) was added in an attempt to complete the conversion. The total digest time was about 8 hours. The contents were filtered and washed with 20g RO water. The total filtrate was 67.69 g. The total dry weight was 5.89 g. No agglomerations of unreacted y-FeOOH were present in the final mix. There was clear evidence of a conversion of y-FeOOH to iron phosphate and shows a clear improvement on the rate of reaction. This was highly unexpected as reaction times were considerably faster compared to those in U.S. Pat. No. 8673497. The final color of the dried material was comparable to the control experiment in Reference Example 22.

[0284] Reference Example 25 - Scale-up of Conversion of FeOOH to Iron Phosphate

[0285] Using the procedure in Reference Example 17, the conversion of y-FeOOH was conducted at a 20X scale instead of 3X. The result was color change to very pale off-white indicating the conversion to iron phosphate. The material had a particle size distribution of D10 = 2.43pm, D50 = 5.28pm, D90 = 9.27pm with a span of 1.30. This example shows that the reaction can be carried out at a 20X scale up.

[0286] An SEM image of the iron phosphate material is provided in Figure 4 A. An XRD pattern of the material is provided in Figure 5A. The pattern confirms that the material is FePCE 2H2O.

[0287] Reference Example 26 - Calcination of Iron Phosphate

[0288] Calcination experiments were conducted using the material produced in Reference Example 25. Calcination was conducted at 200, 300, 400, 550, and 650°C where 6 g were placed into the furnace at temperature and held for 4 hours. The color of the resulting calcined sample depended on the calcination temperature. The initial very pale off-white color became a pale light yellow at 200°C, a pale light orange at both 300°C and 400°C, a pale pinkish color at 550°C, and finally an off-white color at 650°C.

[0289] An SEM image of the iron phosphate material calcined at 650 °C is provided in Figure 4B. An XRD pattern of the material is provided in Figure 5B. The pattern confirms that the material is FePCF adopting the a-quartz structure. Reference Example 27 - Conversion of Fe2O3 to Iron Phosphate (comparative)

[0290] Using the procedure in Reference Example 25, where 18 g of Fe2O3 was substituted for the 20 g of y-FeOOH. The result was only a very little color change, even after running for 27 hours, indicating no conversion to iron phosphate. This example shows that the reaction to make iron phosphate is significantly faster using y-FeOOH compared to Fe2O3.

[0291] Reference Example 28: Conversion of y-FeOOH to iron phosphate

[0292] A slurry of 25g of y-FeOOH in 422.5 mL of DI water and 48.6g of 85% H3PO4 (P:Fe ratio of 1.5: 1) was placed in a IL Morton flask, stirred at 500 PRM and was heated to 90°C. After 3 hours of stirring at 90°C, the resulting color was pinkish white, indicating a conversion to iron phosphate. The precipitant was vacuum filtered and washed with 4 X 500mL of deionized water and dried at 100°C for 2 hours. The material had a particle size distribution of DIO = 1.28pm, D50 = 4.4pm, D90 = 8.24pm with a span of 1.58. The purpose of Reference Example 28 was to demonstrate that a lower P:Fe ratio and a lower water volume can be fully converted to iron phosphate when heated to 90°C. Reference Example 29: Conversion of y-FeOOH to iron phosphate.

[0293] Reference Example 29 was run as Reference Example 28 except that 50g of y-FeOOH was slurried in 800mL of DI water and 173g of 85% H3PO4 (P:Fe ratio of 2.67:1) in a 3L Morton flask. The color of resulting material was pinkish white indicating a conversion to iron phosphate and had a particle size distribution of DIO = 0.80pm, D50 = 3.04pm, D90 = 6.59pm with a span of 1.9. The purpose of Reference Example 29 was to demonstrate that a P:Fe ratio of 2.4:1 can be fully converted to iron phosphate with a lower water volume and when heated to 90°C.

[0294] Reference Example 30: Conversion of y-FeOOH to iron phosphate

[0295] Reference Example 30 was run as Reference Example 28 except that 50g of y-FeOOH was slurried in 825mL of DI water and 130.5g of 85% H3PO4 (P:Fe ratio of 2.01 : 1) in a 3L Morton flask. The color of resulting material was pinkish white indicating a conversion to iron phosphate and had a particle size distribution of D10 = 2.41pm, D50 = 4.11pm, D90 = 6.75pm with a span of 1.06. The purpose of Reference Example 30 was to demonstrate that a P:Fe ratio of 2.1 :1 can be fully converted to iron phosphate with a lower water volume and when heated to 90°C.

[0296] Reference Example 31: Conversion of y-FeOOH to iron phosphate

[0297] Reference Example 31 was run as Reference Example 28 except that 25g of y-FeOOH was slurried in 427.5mL of DI water and 40.5g of 85% H3PO4 (P:Fe ratio of 1.25:1) in a IL Morton flask. The color of resulting material was pale off white indicating a conversion to iron phosphate and had a particle size distribution of D10 = 1.31pm, D50 = 4.10pm, D90 = 7.64pm with a span of 1.55. The purpose of Reference Example 31 was to demonstrate that a P:Fe ratio of 1.25 can be fully converted to iron phosphate with a lower water volume and when heated to 90°C.

[0298] Reference Example 32: Conversion of y-FeOOH to iron phosphate

[0299] Reference Example 32 was run as Reference Example 28 except that 25g of y-FeOOH was slurried in 430.3.5mL of DI water and 35.7g of 85% H3PO4 (P:Fe ratio of 1.1: 1) in a IL Morton flask. The color of resulting material was a darker off white indicating a partial conversion to iron phosphate and had a particle size distribution of DIO = 1.06pm, D50 = 3.70pm, D90 = 7.10pm with a span of 1.63. The purpose of Reference Example 32 was to demonstrate that a P:Fe ratio of 1.1: 1 will be partially converted to iron phosphate with a lower water volume and when heated to 90°C. Reference Example 33: Conversion of y-FeOOH to iron phosphate

[0300] Reference Example 33 was run as Reference Example 28 except that the slurry was heated to 80°C and the pH of the slurry was raised to 1.5 with 35% NaOH before the 3 hour stir time. The color of resulting material was pale off white indicating a conversion to iron phosphate and had a particle size distribution of DIO = 0.60pm, D50 = 1.59pm, D90 = 6.71pm with a span of 3.84. The purpose of Reference Example 33 was to demonstrate that a slurry pH of 1.5 results in a full conversion to iron phosphate.

Claims

CLAIMS1. A method of forming an iron phosphate-comprising material, comprising the steps of:(a) reacting an aqueous solution of ferrous iron with an oxidizing agent in the presence of a base while maintaining an acidic pH, resulting in the formation of y-FeOOH;(b) reacting the y-FeOOH resulting from step (a) with a phosphorus source, resulting in the formation of an iron phosphate-comprising material; wherein the y-FeOOH resulting from step (a) is not isolated between steps (a) and (b).

2. The method of any preceding claim, wherein the aqueous solution of ferrous iron is selected from ferrous chloride, ferrous sulfate, ferrous gluconate, ferrous fumarate, ferrous succinate, ferrous lactate, ferrous glutamate, ferrous ascorbate, ferrous bisglycinate, ferrous nitrate, ferrous acetate and mixtures thereof.

3. The method of any preceding claim, wherein the aqueous solution of ferrous iron is pickle liquor.

4. The method of any preceding claim, wherein the aqueous solution of ferrous iron is clear liquor.

5. The method of any preceding claim, wherein the oxidizing agent is selected from oxygen (O2), hydrogen peroxide, potassium dichromate, sodium hypochlorite, calcium hypochlorite, ozone, potassium perchlorate, potassium chlorate, potassium permanganate, ammonium persulfate, sodium persulfate, and mixtures thereof; preferably from oxygen (O2), hydrogen peroxide, sodium hypochlorite, ozone, potassium perchlorate, potassium chlorate, ammonium persulfate, sodium persulfate, and mixtures thereof.

6. The method of any preceding claim, wherein the oxidizing agent is an oxygen-containing gas such as air.

7. The method of any preceding claim, wherein step (a) comprises aerating the aqueous solution of ferrous iron with an oxygen-containing gas such as air.

8. The method of any preceding claim, wherein the base is selected from alkali metal hydroxides, ammonia, ammonium hydroxide, barium hydroxide, strontium hydroxide, calcium hydroxide, n- butyl lithium, lithium diisopropylamide, lithium diethylamide, sodium amide, sodium hydride, lithium bis(trimethylsilyl)amide, and mixtures thereof; preferably from alkali metal hydroxides, ammonia, ammonium hydroxide, and mixtures thereof; most preferably wherein the base is sodium hydroxide.

9. The method of any preceding claim, wherein neither the base nor the oxidizing agent contains a metal other than an alkali metal.

10. The method of any preceding claim, wherein the reaction to form y-FeOOH takes place while maintaining pH < 5.

11. The method of any preceding claim, wherein the reaction to form y-FeOOH takes place below 100 °C, or at 5-100 °C, or at 10-95 °C, or at 15-90 °C.

12. The method of any preceding claim, wherein the phosphorous source is selected from phosphoric acid (H3PO4), phosphorous acid (H3PO3), (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4, LisPC , Li2HPO4, and LiH2PO4, and mixtures thereof; or is selected from H3PO4, H3PO3, (NH4)H2PO4,(NH4)2HPO4, (NH4)3PO4, and mixtures thereof; or is H3PO4.

13. The method of any preceding claim, wherein the iron phosphate-comprising material comprises a sulfur content of <1000 ppm or <500 ppm.

14. The method of any preceding claim, wherein the iron phosphate-comprising material has a particle size distribution characterized by a D50 of < 20 pm, or < 15 pm, or < 12 pm, or < 10 pm.

15. The method of any preceding claim, wherein the iron phosphate-comprising material has a particle size distribution span ((D90-D10) / D50) of < 6, or < 5, or < 4, or < 3, or < 2.

16. The method of any preceding claim, wherein the y-FeOOH has a particle size distribution characterized by a D50 of < 50 pm, or < 30 pm, or < 20 pm, or < 15 pm.

17. The method of any preceding claim, wherein the reaction of step (b) is carried out in the presence of additional reactants and / or additives selected from the group consisting of ion sources, dopants, surfactants and chelating agents; optionally wherein the reaction is carried out in the presence of additional ion sources and / or dopants.

18. The method of any preceding claim, wherein the iron phosphate-comprising material is selected from FePC , FePCF 2H2O, Fes / PCF OH^ 2H2O, Fe4(P2O?)3, and Fea(PO4)2 8H2O; optionally wherein the iron phosphate-comprising material is selected from FePCF and FePO4 2H2O.

19. The method of any preceding claim, wherein the iron phosphate-comprising material is FePCF adopting a trigonal phase, most preferably FePC adopting the a-quartz structure.

20. The method of any preceding claim, wherein the iron phosphate-comprising material is not lithium iron phosphate or a material having an olivine-type crystal structure.

21. The method of any preceding claim, wherein the reaction of step (b) is carried out at an acidic pH; or at pH < 5, or at pH 0.5-4.0; or at pH 0.5-3.5, or at pH 1.0-2.5.

22. The method of any preceding claim, wherein if the reaction of step (b) is carried out at a molar ratio of P:Fe of < 1.5: 1, < 3: 1, or < 4: 1, the reaction is carried out at a temperature of at least 80 °C, or at least 82 °C, or at least 85 °C, such as at about 90°C.

23. The method of any preceding claim, wherein the reaction of step (b) is carried out at a molar ratio ofP:Fe of > 3: 1, or > 4: 1, or > 6: 1, or > 7: 1.

24. The method of any preceding claim, wherein the reaction of step (b) is carried out at a molar ratio ofP:Fe of < 100: 1, or < 50: 1, or < 20: 1, or < 12:1.

25. The method of any preceding claim, wherein the reaction of step (b) is carried out at a temperature of at least 50 °C; or 50°C-100°C; or 60°C-90°C; or 70°C-90°C.

26. The method of any preceding claim, wherein the reaction of step (b) is carried out at for a period of < 7 hr.; or 1-6 hr.; or 1-5 hr.; or 2-4 hr.; or 2.5-3 hr.

27. The method of any preceding claim, wherein if the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of > 45 g dm'3, the reaction is carried out at a temperature of at least 80 °C, or at least 82 °C, or at least 85 °C, such as at about 90°C28. The method of any preceding claim, wherein the reaction of step (b) is carried out at a mass of y-FeOOH relative to the volume of water of < 45 g dm'3, or < 35 g dm'3, or < 25 g dm'3and optionally > 0.1 g dm'3, > 0.5 g dm'3, or > 1 g dm'3.

29. The method of any preceding claim, wherein the reaction of step (b) is carried out under a noninert atmosphere such as an air atmosphere.

30. A method of forming an iron phosphate-comprising material according to any preceding claim, wherein if metals other than iron are present in the iron-phosphate comprising material, they are present at less than 10 at.%, or less than 5 at.%, or less than 1 at.% relative to the amount of iron in the iron-phosphate comprising material.

31. A method of forming an iron phosphate-comprising material according to any preceding claim, which is a one-pot process.

32. A method of forming an iron phosphate-comprising material according to any preceding claim, which is a continuous process.

33. A method of forming an iron phosphate-comprising material according to any preceding claim, comprising isolating the resultant iron phosphate-comprising material.

34. A method of forming an iron phosphate-comprising material according to any preceding claim, comprising calcining the iron phosphate-comprising material to form an anhydrous iron phosphate-comprising material; optionally wherein the anhydrous iron phosphate-comprising material is FePCk35. A method of forming lithium iron phosphate, comprising following the method of any preceding claim, and reacting the iron phosphate-comprising material with a lithium source to form lithium iron phosphate.

36. A method of forming an article, comprising following the method of any of claims 1-34 to form an iron phosphate-comprising material, or following the method of claim 35 to form lithium iron phosphate, and forming an article comprising the iron phosphate-comprising material or the lithium iron phosphate.

37. The method of claim 36, wherein the article is an electrode or a battery cell.

38. An iron phosphate-comprising material formed by the method of any of claims 1-34.

39. Lithium iron phosphate formed by the method of claim 35.

40. An article comprising the iron phosphate-comprising material formed by the method of any of claims 1-34 or the lithium iron phosphate formed by the method of claim 35.

41. The article of claim 40 being an electrode or a battery cell.

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