WO2017056021A1

WO2017056021A1 - Hydrated manganese oxide and a method for the production thereof

Info

Publication number: WO2017056021A1
Application number: PCT/IB2016/055806
Authority: WO
Inventors: Jean-Bruno R.B. SOUPART; Oliver Schilling; Marie-France PITON
Original assignee: Prince Erachem Sprl
Priority date: 2015-09-29
Filing date: 2016-09-28
Publication date: 2017-04-06

Abstract

A hydrated manganese oxide having polycrystalline secondary particles formed of primary particles, wherein the normalized particle size range, nPSR, of the secondary particles is 1.0 or less when calculated according to the formula nPSR=(D90 - D10)/D50, where D90 is the smallest size of the largest 10 volume%, D10 is the largest size of the smallest 10 volume%, and D50 is the median particle size. A method of making the hydrated manganese oxide including a seeding stage where a manganese salt solution and a hydroxide solution are mixed to form a first suspension and the first suspension is agitated while introducing an oxidizing gas, without any addition of manganese salt solution or hydroxide solution, to form a second suspension, and a synthesis stage where manganese salt solution and hydroxide solution are added to the second suspension while continuing agitation and introduction of gas to form a third suspension containing hydrated manganese oxide.

Description

HYDRATED MANGANESE OXIDE AND A METHOD FOR THE PRODUCTION

THEREOF

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to United States Provisional Application No. 62/234,219 filed on September 29, 2015, the disclosure of which is hereby incorporated in its entirety by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] This invention relates to hydrated manganese oxide having a narrow particle size distribution and a method of making such a hydrated manganese oxide.

Description of Related Art

[0001] Hydrated manganese oxides have been described in the literature dating back to the 1940s (see, e.g., W. Feitknecht et al., Hetv. Chim. Acta, vol. 28, pg. 129, 1945) and were at the time identified as a promoter in the desulfurization of fuel gases (as per GB 597,254). High surface area hydrated manganese oxides with an oxidation state above 3 were later proposed for the removal of sulfur oxide compounds from gases (see, e.g., US 3,798,310).

[0002] Generally, the term "hydrohausmannite" has been used to describe collectively mixtures of manganese oxides, manganese hydroxides, and manganese oxi-hydroxides that, after drying at 100-120°C to remove free water and surface water, still lose water when heated to higher temperatures (as in Gmelins Handbuch der anorganischen Chemie. Mangan. Teil CI . 8* ed. Verlag Chemie, Weinheim, 1973).

[0003] These materials are typically produced by combining a manganese (II) salt solution with an alkaline solution to precipitate manganese hydroxide mat is subsequently or simultaneously oxidized by injecting air into the mixture. The resulting solids are filtered from the solution and dried.

[0004] However, because the particle size of a product resulting from such a process is typically difficult to control, the product lacks the flowabilhy and density that are typically needed in the end use applications for these materials, particularly in industrial applications. [0005] Recently developed processes control the growth of die manganese oxide particles more closely to obtain MnaCU with a well-defined particle size and a narrow particle size distribution, resulting in better flowability. For example, KR 100668051 Bl describes preparing MruCU within a particle size range of 5-15 um and a tap density of 2.5-2.6 g/cm³. Similarly, CN 101898796 A focuses on a high-purity manganous-manganic oxide with a similar particle size and tap density and a specific surface area of 1.5-3.0 mVg.

[0006] US 9,150,427 recognizes the need to provide a manganese precursor mat exhibits good reactivity with lithium compounds and proposes preparing a manganese oxide with a certain pore structure by avoiding the formation of substantial amounts of manganese hydroxide during the precipitation reaction. By ensuring that the oxidation potential does not become negative during synthesis, little or no hydroxide is formed during the synthesis of the manganese oxide and little or no water of hydration, also known as combined water, is present in the final product

[0007] Electrolytic manganese dioxide, which is also extensively used in the synthesis of lithium manganese oxide, desirably has combined water, typically at 2.5 to 3.5% by weight It is believed that the combined water, when released, facilitates the reactivity of electrolytic manganese dioxide during the solid-state reaction in which the lithium manganese oxide is formed. Unfortunately, electrolytic manganese dioxide needs to be milled to reach particle sizes suitable for such reactions, which makes it difficult to obtain the desired narrow particle size distribution.

[0008] For such applications, there is, therefore, a need for a manganese oxide that is both hydrated and has a narrow particle size distribution.

SUMMARY OF THE INVENTION

[0009] The present invention is directed to a hydrated manganese oxide comprising polycrystalline secondary particles that are formed of primary particles, wherein the normalized particle size range, nPSR, of the secondary particles is 1.0 or less when calculated according to the following formula nPSR = (D90 - D10)/D50, where D90 is the smallest size of the largest 10 volume% of all secondary particles, D10 is the largest size of the smallest 10 volume% of all secondary particles, and D50 is the median particle size on a volume basis of all secondary particles. The median secondary particle size (D50) may be 5-15 um. The primary particles may be elongated such that a maximum dimension of each primary particle is larger than any dimension of the primary particle in a direction perpendicular to the maximum dimension and at least 75% of the primary particles may have a maximum dimension that is 3 times or more any dimension of the primary particle in a direction perpendicular to the maximum dimansifin

[0010] At least some of the hydrated manganese oxide may have the general formula Mn(H20)wQx, where 1.32 <x< 1.35 and 0.07 < w < 0.2 and the hydrated manganese oxide may have an angle of repose of 40° or less.

[0011] The present invention is also directed to a method of making hydrated manganese oxide comprising a seeding stage and a synthesis stage.

[0012] The seeding stage may comprise mixing a manganese salt solution and a hydroxide solution to form a first suspension and agitating the first suspension while introducing an oxidizing gas into the first suspension, without any addition of manganese salt solution or hydroxide solution, to form a second suspension. The mixing step may include providing an initial volume of water or an aqueous solution comprising anions of the manganese salt and cations of the hydroxide into which the manganese salt solution and the hydroxide solution are mixed.

[0013] The synthesis stage may comprise adding additional manganese salt solution and hydroxide solution to the second suspension while continuing agitation and introduction of oxidizing gas to form a third suspension containing particles of hydrated manganese oxide. The synthesis stage may further comprise stopping the flow of manganese salt solution and hydroxide solution while continuing agitation and the introduction of the oxidizing gas until a concentration of dissolved manganese ions in the final mixture has decreased to 0.2 g/1 or less. After stopping the flow of manganese salt solution and hydroxide solution, hydroxide solution may be added at a rate that maintains the pH of the third suspension above 6.5.

[0014] The method may further comprise separating the hydrated manganese oxide particles from the third suspension and drying the particles.

[0015] The manganese salt may comprise manganese nitrate (Μη(Νθ3)2), manganese sulfate (MnSCU), and/or manganese chloride (MnCk), and the hydroxide may comprise ammonium hydroxide (NHtOH), sodium hydroxide (NaOH), and/or potassium hydroxide (KOH).

[0016] In the seeding stage, the manganese concentration of the first suspension may be 1.25 to 4.0 grams per liter. The manganese salt solution and the hydroxide solution may be mixed such that the molar ratio of hydroxide to manganese is 2.05 to 2.50, or the manganese salt solution and the hydroxide solution may be added simultaneously to a reactor such that the ratio of the molar flow rate of hydroxide to molar flow rate of manganese is 2.05 to 2.50. The oxidizing gas may be introduced for 90 to 600 seconds after adding the manganese salt solution and the hydroxide solution, and the temperature may be maintained at 15°C to 80°C. [0017] In the synthesis stage, the manganese salt solution and the hydroxide solution may be added simultaneously such that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese is 2.0S to 2.S0. The temperature may be maintained at 15°C to 80°C and the oxidation potential may be negative. The third suspension may comprise an ammonium nitrate solution.

[0018] Both the seeding stage and the synthesis stage may be carried out in a reactor having a reactor volume and the volumetric flow rate of the oxidizing gas may 0.5 to 2 reactor volumes per minute.

BRIEF DESCRIPTION OF THE DRAWINGS)

[0019] Figure 1 is a scanning electron microscope photograph at 10,000X of a representative secondary particle of the hydrated manganese oxide according to the present invention;

[0020] Figure 2 is a graph showing oxidation potential as a function of time for the synthesis stage of Inventive Example 1;

[0021] Figure 3 is a scanning electron microscope photograph at 10,000X of a representative secondary particle of the hydrated manganese oxide of Inventive Example 1;

[0022] Figure 4 is a scanning electron microscope photograph at 10,000X of a representative secondary particle of the hydrated manganese oxide of Comparative Example 1; and

[0023] Figure 5 is a scanning electron microscope photograph at 10,000X of a representative secondary particle of the hydrated manganese oxide of Comparative Example 5.

DESCRIPTION OF THE INVENTION

[0024] As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word "about", even if the term does not expressly appear. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include any and all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, all subranges beginning with a minimum value equal to or greater than 1 and ending with a maximum value equal to or less than 10, and all subranges in between, e.g., 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1. Plural encompasses singular and vice versa. When ranges are given, any endpoints of those ranges and/or numbers within those ranges can be combined with the scope of the present invention. "Including", "such as", "for example" and like terms means "including/such as/for example but not limited to". [0025] The present invention is directed to a hydrated manganese oxide and a method of making such a hydrated manganese oxide. The hydrated manganese oxide releases water when heated to a temperature of 180°C or higher, for example, a temperature between 180°C and 950°C, has the general formula of

is characterized by a single-phase x-ray diffraction pattern that can be fit with a tetragonal structure having lattice constants a and c, where

[0026] The hydrated manganese oxide comprises secondary particles mat are aggregates of primary particles. Secondary particles are those aggregates of primary particles that cannot be subdivided further unless a significant amount of energy is added, for example, in a milling or grinding operation. Operations such as blending, mixing, or dispersing in a liquid will not break these aggregates.

[0027] The median particle size (DS0) of the secondary particles is at least 5 um and at most IS um, such as 5-15 um, and the secondary particles have a particle size distribution characterized by a normalized particle size range (nPSR) of 1.0 or less, for example, 0.7 or less, where the normalized particle size range (nPSR) is defined as:

nPSR = (D90 - D10)/D50

where D90 is the smallest size of the largest 10 volume% of all secondary particles,

D10 is the largest size of the smallest 10 volume% of all secondary particles, and

DS0 is the median particle size on a volume basis of all secondary particles.

[0028] This narrow particle size distribution results in good flowability of the hydrated manganese oxide. Good flowability is desirable for transporting material, for example, during packaging, when removing material from a bag to a storage bin, or when moving material from a storage bin to a mixer when using the material. The angle of repose of the hydrated manganese oxide is a good indicator of the flowability of the hydrated manganese oxide. A low angle of repose is associated with better flowability than a large angle of repose. Typically, an angle of repose above 45° indicates poor flowability, while an angle of repose of 35° or below indicates good or even very good flowability. The present hydrated manganese oxide has an angle of repose of 40° or less, for example, 35° or less.

[0029] As shown in Figure 1 and Figure 3, at least some of the primary particles of the hydrated manganese oxide are elongated such that the maximum dimension of each primary particle, herein referred to as the length of the particle, is larger than a dimension of the primary particle in a direction perpendicular to the maximum dimension, herein referred to as the width of the particle. At least 75% of the primary particles visible on a single secondary particle, when viewed in a scanning electron microscope (SEM) photograph at a magnification of, for example, ΙΟ,ΟΟΟΧ, have a length that is at least 3 times the width, i.e., an aspect ratio, length divided by width, of at least 3, for example, at least 80% of the primary particles have a length that is at least 3 times the width.

[0030] An example of hydrated manganese oxide according to the invention is shown in the SEM photograph of Figure 1. This example has a chemical composition of

is characterized by a single-phase x-ray diffraction pattern that can be fit with a tetragonal structure having lattice constants has a median secondary particle

size (D50) of 12.1 um, has a small normalized particle size range of 0.55, has an angle of repose of 38°, and has a surface morphology where 95% of the primary particles have an aspect ratio of 3 or more.

[0031] A method for making such a hydrated manganese oxide comprises a seeding stage and a synthesis stage. According to the process described below, the hydrated manganese oxide of the present invention may be produced in a reactor. As defined herein, a reactor is a subspace of the three-dimensional physical space, said subspace having a finite volume, called the reactor volume. The reactor may be constrained by the interior dimensions of a tank, vessel, beaker, or similar container, collectively referred to herein as a reacting vessel. The reactor volume corresponds to the working volume of the reacting vessel. The reacting vessel may be equipped with a stirrer for agitation, a pH probe for monitoring the pH of the solution in the reactor, an oxidation reduction potential (ORP) probe for monitoring the oxidation potential of the solution in the reactor, an inlet for addition of a manganese salt solution, an inlet for addition of a hydroxide solution, and an inlet through which an oxidizing gas may be introduced into the reactor. The inlet for the oxidizing gas may be located below the impeller of the stirrer. The reacting vessel of the reactor may be temperature-controlled, for example, by a jacket, an internal coil, or a hot plate. It can be appreciated that other systems and reacting vessel designs may be used to produce the hydrated manganese oxide of the present invention.

[0032] In the seeding stage, a manganese salt solution and a hydroxide solution are added to the reactor to form a first suspension believed to comprise manganese hydroxide particles. The suspension is agitated while introducing an oxidizing gas into the suspension without any further addition of manganese salt solution or hydroxide solution to form a second suspension of seed particles. In the synthesis stage, which begins immediately after the completion of the seeding stage when the reactor contains the second suspension of seed particles, additional manganese salt solution and hydroxide solution are added to the reactor while continuing agitation and introduction of oxidizing gas to form a third suspension containing particles of hydrated manganese oxide.

[0033] In the seeding stage, a manganese salt solution and a hydroxide solution are added to the reactor to form a first suspension having at least 1.2S grams per liter and up to 4.0 grams per liter of manganese, such as 1.25-4.0 grams per liter of manganese and 1.3-2.1 grams per liter of manganese, and a molar ratio of hydroxide to manganese of at least 2.0S and up to 2.50, such as 2.05-2.50 or 2.10-2.50. The manganese salt solution and hydroxide solution may be simultaneously added at flow rates such that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese is at least 2.05 and up to 2.50, such as 2.05-2.50 or 2.10-2.50.

[0034] Suitable manganese salts include, but are not limited to, manganese nitrate (Μη(Νθ3)2), manganese sulfate (MnSCU), and/or manganese chloride (MnCk), and the manganese salt solution may have a manganese concentration of at least 50 g/1 and up to 180 g/1, such as 50-180 g/1. Manganese nitrate, manganese sulfate, and manganese chloride are commercially available from Erachem Comilog. Suitable hydroxides include, but are not limited to, ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), and/or potassium hydroxide (KOH), and, the hydroxide solution may be sufficiently concentrated to avoid excessive dilution of the suspension. Ammonium hydroxide, sodium hydroxide, and potassium hydroxide are commercially available commodities. As will be appreciated by those skilled in the art, the maximum concentration of hydroxide depends on the type of hydroxide. As an example, the hydroxide solution may be an ammonium hydroxide solution having a concentration of at least 20 wt% and up to 35 wt% ammonia. Both the manganese salt solution and the hydroxide solution may be aqueous solutions.

[0035] After the manganese salt solution and the hydroxide solution have been mixed, an oxidizing gas, such as air or oxygen, is introduced into the first suspension while the first suspension is agitated. When air is used, the flow rate of the oxidizing gas may be at least 0.5 reactor volume per minute and up to 2 reactor volumes per minute, such as 0.5-2.0 reactor volumes per minute, in order to obtain rapid oxidation of the manganese. The introduction of the oxidizing gas without any further addition of manganese salt solution and hydroxide solution is continued for at least 90 seconds and up to 600 seconds, such as 90-600 seconds. After the introduction of the oxidizing gas for this time period, a second suspension comprising seed particles is formed. Without being bound by theory, it is believed that the seed particles of mis second suspension are hydrated manganese oxide.

[0036] During the seeding stage, the suspension temperature is maintained at at least 15°C and up to 80°C, such as 15°C to 80°C, and 35°C to 55°C. [0037] Optionally, a heel of solution may be initially added to the reactor before the addition of the manganese salt solution and the hydroxide solution. The heel of solution may have an initial volume that is less than 100% of the reactor volume, such as a volume of up to 40% of the reactor volume or up to 35% of the reactor volume. If the reactor is provided with a reacting vessel having a stirrer, then the initial volume may be chosen so as to cover the impeller of the stirrer. The heel of solution may be water or an aqueous solution containing anions of the manganese salt and cations of the hydroxide. For example, ammonium nitrate at a concentration of up to 2 moles per liter may be included in the heel, if the manganese salt is manganese nitrate and the hydroxide is ammonium hydroxide. The temperature of the heel of solution may be controlled at at least 15°C and up to 80°C, such as 15°C to 80°C, and 35°C to 55°C.

[0038] After the completion of the seeding stage, the synthesis stage is commenced by restarting the additions of the manganese salt solution and the hydroxide solution to the reactor. The flow rate of the manganese salt solution may be the same as was used in seeding stage, and the manganese salt solution and hydroxide solution flow rates may be set such mat the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese is at least 2.0S and up to 2.S0, such as 2.05-2.50 or 2.10-2.50. The suspension temperature may be controlled at at least 15°C and up to 80°C, such as 15°C to 80°C, and may be the same temperature that was used in the seeding stage. The addition of the oxidizing gas may be at a flow rate of at least 0.5 reactor volumes per minute and up to 2 reactor volumes per minute, such as 0.5-2 reactor volumes per minute, and may continue at the same rate as in the seeding stage. A negative oxidation potential as measured, for example, by a platinum electrode against a Ag/AgCl reference, is maintained during the synthesis stage. Without being bound by theory, it is believed mat, at a negative oxidation potential, manganese hydroxide intermediaries are formed and the hydroxide associated with these give rise to the combined water in the final product [0039] When the desired total amount of manganese has been added based on the concentration of the manganese salt solution, the reactor volume, and the target synthesis time, the flows of the manganese salt solution and of the hydroxide solution are stopped. The introduction of the oxidizing gas and the stirring are continued until the concentration of dissolved manganese ions in the solution has decreased to 0.2 g/1 or less, typically for another 30-60 minutes. This decrease is facilitated by maintaining the suspension pH above 6.5, for example, by adding hydroxide solution to the reactor as necessary. When the concentration of dissolved manganese has decreased to the desired level, a third suspension comprising hydrated manganese oxide is formed. This completes the synthesis stage. [0040] An overall mean flow rate, MFR, can be calculated by dividing the reactor volume (i.e., the volume of the third suspension) by the total time from the beginning of the seeding stage to the end of the manganese salt solution addition in the synthesis stage. The rate of the addition of the oxidizing gas during the seeding stage and the synthesis stage can then be expressed in terms of the mean flow rate. The flow rate of the oxidizing gas at normal conditions (i.e., 101,325 Pa and 273.15 K) may be in the range of 60 to 600 times the mean flow rate.

[0041] After the synthesis stage, the third suspension is removed from the reactor and the hydrated manganese oxide is separated from the solution, for example, by filtration. The filtrate is a solution containing anions of the manganese salt and cations of the hydroxide. If a manganese nitrate solution and an ammonium hydroxide solution are used in the process, the filtrate is an ammonium nitrate solution that can be utilized as a fertilizer in agriculture.

[0042] The hydrated manganese oxide is dried such as in air at a temperature of at least 70°C and up to 160°C, such as 70°C to 160°C, which results in the inventive hydrated manganese oxide.

EXAMPLES

[0043] In the following examples, the chemical composition surface

morphology, crystal structure, particle size distribution, normalized particle size range, and flowability of the hydrated manganese oxide were determined using the following procedures. Average Oxidation State of Manganese

[0044] In order to determine the average oxidation state of the manganese, which is 2x, where x is defined by the Mn content of the material was determined by

potentiometric titration using potassium permanganate after dissolving the hydrated manganese oxide in hydrochloric acid (as described in Glover et al. (ed.), Handbook of Manganese Dioxide Battery Grade, The International Battery Material Association (IB A, Inc.), 1989). The Mn content, %Mn, was expressed as a percentage of the weight of the material characterized. The MnCh content was determined by potentiometric titration using potassium permanganate after dissolving the hydrated manganese oxide in an acidic ferrous sulfate solution where the ferrous ions reduce the higher oxides of manganese. The MnCh content, %MnCh, was expressed as a percentage of the weight of the material characterized. Half of the average oxidation state, x, was then calculated from the Mn and MnCh contents using the following formula:

Combined Water [0045] The water of hydration, also referred to as the combined water, in the product is calculated by determining the weight of the total water content in the product and subtracting the weight of the surface water. The weight of the surface water is determined by heating the product to a temperature above 100°C, such as 120°C. In present examples, the surface water content of the product was the weight loss of the sample after 2 hours at 120°C in a forced-air oven. The weight lost was divided by the initial weight of the sample to give %Surface Water, i.e., the weight percent of surface water in the material.

[0046] The total water content of the product was determined using a LECO TruSpec CHN (carbon/hydrogen/nitrogen) analyzer. The analyzer was first calibrated using certified standard SX43-02 (supplied by Dillinger Hutte Laboratory). The hydrated manganese oxide sample was placed into the analyzer and gradually heated up to 950°C. A detector measured the amount of water vapor coming off the sample, which was reported as the total water. The total water was then normalized with respect to the sample weight to arrive at %TotalWater, i.e., the weight percent of total water in the material.

[0047] The weight percent of combined water was obtained by subtracting the weight percent of surface water from the weight percent of total water, i.e., %CombinedWater = %TotalWater - %SurfaceWater. The molar ratio of combined water to manganese, w in was then calculated using the following formula:

Powder X-rav Diffraction

[0048] Powder X-ray diffraction data were taken on a Siemens D5000 using CuKα radiation at scattering angles between 15° and 75°. The x-ray tube was operated at 40 kV and 40 mA. The goniometer was advanced continuously at 0.04° in 38 seconds. Data was recorded every 0.04°. The divergence and anti-scatter slits were fixed at 0.992°, and the receiving slit was 0.6 mm. The resulting pattern was subjected to a Rietveld refinement using LHPM 7 (as disclosed inD. B. Wiles etal.,J. Appl.. Cryst., vol. 14, page 149, 1981; C. J. Howard etal., AAEC Report No. Ml 12, 1986). The refinement was conducted with the assumption that the pattern was consistent with one obtained from a single-phase material with the tetragonal space group I4i/amd. As part of the refinement, a number of parameters were allowed to vary, including the lattice constants. If the resulting best fit had a Bragg R-factor of less than 5, then the initial assumption for the fit was deemed correct, that is the material was deemed to be single phase with a tetragonal structure. Furthermore, the lattice constants obtained from the fit can be used to accurately describe the material.

Surface Morphology [0049] The aspect ratio of the primary particles was determined from photographs taken of the aggregates of primary particles at a magnification of 10.000X with a scanning electron microscope (SEM). The aspect ratio was determined for several primary particles by measuring the longest dimension (length) of each primary particle and the dimension (width) of each primary particle in a direction perpendicular to the longest dimension with a ruler. For each primary particle, the aspect ratio of the primary particle was detennined by dividing the length by the width. When evaluating the inventive material, regions on the photograph with primary particles having an aspect ratio of less than 3 were marked with an ellipse and the area of the ellipse was determined. The sum of the areas having primary particles with low-aspect- ratios, i.e., aspect ratios less than 3, was divided by the total area of the hydrated manganese oxide that was visible in the photograph and multiplied by 100%. This percentage was subtracted from 100% to determine the percentage of primary particles with an aspect ratio of 3 or more. For materials where a majority of the primary particles had aspect ratios of less than 3, regions on the photographs with primary particles having an aspect ratio of 3 or more were marked with an ellipse and the area of die ellipse was determined. The sum of the areas having primary particles with high aspect ratios, i.e., aspect ratios 3 or more, was divided by the total area of the hydrated manganese oxide that was visible in the photograph and multiplied by 100% to determine the percentage of primary particles with an aspect ratio of 3 or more. Particle Size Distribution

[0050] The size distribution of the secondary particles was determined using a Beckman Coulter LS13320 particle size analyzer. As described by the instrument manufacturer, a small amount of sample is introduced into the instrument so that the obscuration is in the right range. The instrument provides, among other data, the median particle size on a volume basis (DS0), the largest size of the smallest 10 volume-percent of all particles (D10), and the smallest size of the largest 10 volume-percent of all particles (D90). For purposes of this invention, the normalized particle size range (nPSR) is defined as (D90 - D10)/D50. The particle size distribution is deemed to be narrow when the nPSR is 1.0 or less, such as 0.7 or less.

Angle of Repose

[0051] The angle of repose of the hydrated manganese oxide was determined as a measure of flowability using a Powder Characteristics Tester from Hosokawa Micron.

[0052] The experimental parameters for the following examples are summarized in Table 1.

INVENTIVE EXAMPLE 1

[0053] A heel of water was added to a tank with an 8 m³ reactor volume so that the impeller of the agitator was well covered. Agitation was started and the water was heated to 40°C. An aqueous manganese nitrate solution of about 120 g/1 manganese and an aqueous ammonium hydroxide solution (25% wt% of ammonia) were added to the heel over 120 seconds. The flow rates of the aqueous manganese nitrate solution and aqueous ammonium hydroxide solutions were set such that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.40. The amount of manganese added resulted in a concentration of 1.3 g of manganese per liter of suspension. A first suspension of particles formed. Air injection at 800 Nm³/h was commenced and seeds were allowed to form without any further introduction of solution. After 480 seconds of air injection, the synthesis stage was started when the addition of the manganese nitrate and ammonium hydroxide solutions were resumed such that ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.23. When the reactor volume was filled after about 4.5 hours, the addition of the aqueous manganese nitrate solution was stopped and the residual dissolved manganese was allowed to precipitate over the next 45 minutes. During this period, ammonium hydroxide was added as necessary to maintain the pH above 6.5. In this example, the mean flow rate was 1.78 m³/h resulting in a normal air injection rate of 450 times the mean flow rate. A temperature near 40°C was maintained during the entire process. The oxidation potential during the synthesis stage was near -100 mV, as shown in Figure 2.

[0054] The solids were then separated from the liquid by filtration and the filter cake was dried in air at 150°C. The dried material was analyzed, and the results are summarized in Table 2.

[0055] Figure 3 shows an SEM photograph of a representative secondary particle of the hydrated manganese oxide of Inventive Example 1. The particle is polycrystalline in nature and substantially all (94%) of the primary particles on the surface of the secondary particle have an aspect ratio of 3 or greater.

INVENTIVE EXAMPLE 2

[0056] Material was prepared in a manner similar to the method described in Inventive Example 1, except that the manganese concentration of the first suspension was 1.6 g/1 and the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.42 during the seeding stage. The oxidation potential during the synthesis stage was near -60 mV.

[0057] The dried material was analyzed, and the results are summarized in Table 2.

INVENTIVE EXAMPLE 3

[0058] 1.5 liters of water was added to a beaker with a 5-liter reactor volume so that the Rushton impeller of an agitator was well covered. The water was preheated to 40°C and then agitation was started at about 900 rpm. An aqueous manganese nitrate solution (122 g/1 Mn) and an aqueous ammonium hydroxide solution (30% wt% of ammonia) were added over 120 seconds. The flow rates of the aqueous manganese nitrate solution and aqueous ammonium hydroxide solution were set such that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.29. The amount of manganese added resulted in a manganese concentration in the first suspension of 2.0 g/1. Air injection at 4 Nl/min (0.8 reactor volumes per minute) was commenced without any further introduction of solution. After 360 seconds, the synthesis stage was started when the addition of manganese nitrate and ammonium hydroxide solutions were resumed such that the ratio of the molar flow of hydroxide to the molar flow rate of manganese was 2.20. When the reactor volume was filled after 4 hours, the addition of the aqueous manganese nitrate solution was stopped and the residual dissolved manganese was allowed to precipitate over the next 45 minutes. During this period, ammonium hydroxide was added as necessary to maintain the pH above 6.5. In this example, the mean flow rate was 0.021 1/min resulting in a normal air injection rate of 192 times the mean flow rate. A temperature near 40°C was maintained during the entire process. The oxidation potential during the synthesis stage was near -80 mV.

[0059] The solids were then separated from the liquid by filtration and the filter cake was dried in air at 120°C. The dried material was analyzed, and the results are summarized Table 2.

INVENTIVE EXAMPLE 4

[0060] Material was prepared in a manner similar to the method described in Inventive Example 3, except that manganese concentration of the first suspension was 1.8 g/1 and the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.2S during the seeding stage. The oxidation potential during the synthesis stage was near -70 mV.

[0061] The dried material was analyzed, and the results are summarized in Table 2.

INVENTIVE EXAMPLE 5

[0062] Material was prepared in a manner similar to the method described in Inventive Example 4, except that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese during the seeding and synthesis stages were set at 2.43 and 2.39, respectively. The oxidation potential during the synthesis stage was near -40 mV.

[0063] The dried material was analyzed, and the results are summarized in Table 2.

INVENTIVE EXAMPLE 6

[0064] Material was prepared in a manner similar to the method described in Inventive Example 4 except that the manganese concentration of the first suspension was 1.9 g/L the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.19 in the seeding stage, and the temperature was set at 50°C. The oxidation potential during the synthesis stage was near -90 mV.

[0065] The dried material was analyzed, and the results are summarized in Table 2.

INVENTIVE EXAMPLE 7

[0066] Material was prepared in a manner similar to the method described in Inventive Example 3, except that the manganese concentration of the first suspension was 3.8 g/1 and the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.14 in the seeding stage. The oxidation potential during the synthesis stage was near -SO mV.

[0067] The dried material was analyzed, and the results are summarized in Table 2.

INVENTIVE EXAMPLE 8

[0068] Material was prepared in a manner similar to the method described in Inventive Example 3, except that the manganese concentration of the first suspension was 1.9 g/1 and the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese during both the seeding and the synthesis stages was set at 2.0S. The oxidation potential during the synthesis stage was near -5 mV.

[0069] The dried material was analyzed, and the results are summarized in Table 2.

COMPARATIVE EXAMPLE 1

[0070] Material was prepared in a manner similar to the method described in Inventive Example 2, except the seeding stage was absent. After adding and heating the heel of water, agitation, air injection, and the addition of aqueous manganese nitrate solution and aqueous ammonium hydroxide solution were commenced simultaneously. The manganese salt solution and hydroxide solution additions were continued without interruption for 4 hours. The ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.1S. The oxidation potential during the synthesis stage was near +10 mV.

[0071] The dried material was analyzed, and the results are summarized in Table 2.

[0072] Figure 4 shows an SEM photograph of a representative aggregate of primary particles of the material of Comparative Example 1 , which has a very different surface morphology from the hydrated manganese oxide of the invention (Figure 3). The primary particles do not exhibit a distinct long side. Instead, the primary particles have dimensions in all directions mat are approximately equal, i.e., most of the primary particles have aspect ratios of less than 3, such as close to 1. Only 3% of the primary particles have an aspect ratio of 3 or more. [0073] The w value for Comparative Example 1 is only 0.06 indicating that the manganese oxide contains less combined water man the hydrated manganese oxide of the present invention.

COMPARATIVE EXAMPLE 2

[0074] A heel of 1 liter of water was added to a beaker with a 5 -liter reactor volume and heated to 40°C. 2.5 liters of aqueous manganese nitrate solution of 120 g/1 of manganese was added to the reactor while stirring. After the temperature stabilized at 40°C, air was bubbled into the reactor below the impeller. Then, aqueous ammonium hydroxide solution of 23.7 wt% of ammonia was added until the pH reached 8.1. Oxidation with air continued for another 45 minutes. The solids were then separated from the liquid by filtration and dried in air at 120 °C.

[0075] The dried material was analyzed, and the results are summarized in Table 2. The resulting material had a low w value of 0.0SS and a large normalized particle size range (nPSR) of 50.

COMPARATIVE EXAMPLE 3

[0076] Material was prepared in a manner similar to the method described in Inventive Example 3, except that the manganese concentration of the first suspension was 1.2 g/1 and the reaction was stopped after 3 hours.

[0077] The dried material was analyzed, and the results are summarized in Table 2. The resulting material had a large normalized particle size range (nPSR) of 1.32.

COMPARATIVE EXAMPLE 4

[0078] Material was prepared in a manner similar to the method described in Inventive Example 3, except that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese during both addition steps was set at 2.78.

[0079] The dried material was analyzed, and the results are summarized in Table 2. The resulting material had a large normalized particle size range (nPSR) of 1.88.

COMPARATIVE EXAMPLE 5

[0080] 1.5 liters of water was added to a beaker with a 3.5-liter reactor volume so mat the Rushton impeller of an agitator was well covered. The water was preheated to 40°C and then agitation was started at about 900 rpm. An aqueous manganese nitrate solution of about 120 g/1 manganese and an aqueous ammonium hydroxide solution were added over 120 seconds. The flow rates of the aqueous manganese nitrate solution and aqueous ammonium hydroxide solution of 24.8 wt% of ammonia were set such that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese was 2.20. Over the course of the 120 seconds, the reactor volume was filled, resulting in a manganese concentration of the first suspension of 67 g/1. Air injection at 4 Nl/min (1.14 reactor volumes per minute) was commenced without any further introduction of solution and continued for 65 minutes. In this example, the mean flow rate was 1.751/min resulting in a normal air injection rate of 2.3 times the mean flow rate. The solids were then separated from the liquid by filtration and the filter cake was dried in air at 120°C.

[0081] The dried material was analyzed, and the results are summarized in Table 2. The resulting material is a hydrohausmannite according to the prior art. This prior art hydrohausmannite has a large normalized particle size range (nPSR) of 1.88, an angle of repose of 43° suggesting that the material lacks the desired flowability. Figure 5 shows a SEM photograph of the material.

COMPARATIVE EXAMPLE 6

[0082] Commercially available MtuCU (trimanganese tetraoxide) powder available from Erachem Comilog sprl under the tradename MruCU LH was provided. The material has a large normalized particle size range (nPSR) of 3.2 and an angle of repose of 46°.

CLAUSES

[0083] Clause 1: A hydrated manganese oxide comprising polycrystalline secondary particles that are formed of primary particles, wherein the normalized particle size range, nPSR, of the secondary particles is 1.0 or less when calculated according to the following formula: nPSR = (D90 - DIOyDSO, where D90 is the smallest size of the largest 10 volume% of all secondary particles, D10 is the largest size of the smallest 10 volume% of all secondary particles, and DS0 is the median particle size on a volume basis of all secondary particles.

[0084] Clause 2: The hydrated manganese oxide of clause 1, wherein at least some of the hydrated manganese oxide has the general formula

<w < 0.2.

[0085] Clause 3 : The hydrated manganese oxide of clause 1 or 2, wherein the median secondary particle size (D50) is 5-15 um.

[0086] Clause 4: The hydrated manganese oxide of any of clauses 1 to 3, wherein the primary particles are elongated such that a maximum dimension of each primary particle is larger than any dimension of the primary particle in a direction perpendicular to the maximum dimension.

[0087] Clause 5: The hydrated manganese oxide of any of clauses 1 to 4, wherein at least 75% of the primary particles have a maximum dimension that is 3 times or more any dimension of the primary particle in a direction perpendicular to the maximum dimension.

[0088] Clause 6: The hydrated manganese oxide of any of clauses 1 to 5, wherein the angle of repose is 40° or less.

[0089] Clause 7: A method of making hydrated manganese oxide comprising: (a) a seeding stage comprising mixing a manganese salt solution and a hydroxide solution to form a first suspension; and agitating the first suspension while introducing an oxidizing gas into the first suspension, without any addition of manganese salt solution or hydroxide solution, to form a second suspension; and (b) a synthesis stage comprising adding additional manganese salt solution and hydroxide solution to the second suspension while continuing agitation and introduction of oxidizing gas to form a third suspension containing particles of hydrated manganese oxide.

[0090] Clause 8: The method of clause 7, wherein, in the seeding stage, the manganese concentration of the first suspension is 1.25 to 4.0 grams per liter. [0091] Clause 9: The method of clause 7 or 8, wherein, in the seeding stage, the manganese salt solution and the hydroxide solution are mixed such that the molar ratio of hydroxide to manganese is 2.05 to 2.50.

[0092] Clause 10: The method of any one of clauses 7 to 9, wherein, in the seeding stage, the manganese salt solution and the hydroxide solution are added simultaneously to a reactor such that the ratio of the molar flow rate of hydroxide to molar flow rate of manganese is 2.05 to 2.50.

[0093] Clause 11 : The method of any one of clauses 7 to 10, wherein, in the seeding stage, the oxidizing gas is introduced for 90 to 600 seconds after adding the manganese salt solution and the hydroxide solution.

[0094] Clause 12: The method of any one of clauses 7 to 11, wherein, in the seeding stage, the temperature is maintained at 15°C to 80°C.

[0095] Clause 13: The method of any one of clauses 7 to 12, wherein, in the synthesis stage, the manganese salt solution and the hydroxide solution are added simultaneously such that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese is 2.05 to 2.50.

[0096] Clause 14: The method of any one of clauses 7 to 13, wherein, in the synthesis stage, the temperature is maintained at 15°C to 80°C.

[0097] Clause 15 : The method of any one of clauses 7 to 14, wherein, during the synthesis stage, an oxidation potential is negative.

[0098] Clause 16: The method of any one of clauses 7 to 15, wherein, in both the seeding stage and the synthesis stage are carried out in a reactor having a reactor volume and, the volumetric flow rate of the oxidizing gas is 0.5 to 2 reactor volumes per minute.

[0099] Clause 17: The method of any one of clauses 7 to 16, wherein the synthesis stage further comprises stopping the flow of manganese salt solution and hydroxide solution while continuing agitation and the introduction of the oxidizing gas until a concentration of dissolved manganese ions in the final mixture has decreased to 0.2 g/1 or less.

[00100] Clause 18: The method of clause 17, wherein, during the finishing step, hydroxide solution is added at a rate that maintains the pH of the third suspension above 6.5.

[00101] Clause 19: The method of any one of clauses 7 to 18, further comprising separating the hydrated manganese oxide particles from the final solution and drying the particles.

[00102] Clause 20: The method of any one of clauses 7 to 19, wherein the final solution comprises an ammonium nitrate solution. [00103] Clause 21: The method of any one of clauses 7 to 20, wherein the manganese salt comprises manganese nitrate manganese sulfate (MnSO₄), and/or manganese

chloride (MnCb).

[00104] Clause 22: The method of any one of clauses 7 to 21, wherein the hydroxide comprises ammonium hydroxide , sodium hydroxide (NaOH), and/or potassium hydroxide (KOH).

[00105] Clause 23 : The method of any one of clauses 7 to 22, wherein, in the seeding stage, the mixing step includes providing an initial volume of water or an aqueous solution comprising anions of the manganese salt and cations of the hydroxide into which the manganese salt solution and the hydroxide solution are mixed.

[00106] Clause 24: A method for the production of a hydrated manganese oxide that generates an ammonium nitrate solution as a byproduct.

[00107] Clause 25: The method of clause 24, wherein the hydrated manganese oxide comprises the hydrated manganese oxide of any of clauses 1-6 and/or is produced by the methods of any of clauses 7-23.

[00108] Clause 26: The method of clause 24 or clause 25, wherein the byproduct is beneficially used as a fertilizer in agriculture.

[00109] Whereas particular aspects of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims

THE INVENTION CLAIMED IS

1. A hydrated manganese oxide comprising polycrystalline secondary particles that are formed of primary particles,

wherein the normalized particle size range, nPSR, of the secondary particles is 1.0 or less when calculated according to the following formula:

where D90 is the smallest size of the largest 10 volume% of all secondary particles, D 10 is the largest size of the smallest 10 volume% of all secondary particles, and DS0 is the median particle size on a volume basis of all secondary particles.

2. The hydrated manganese oxide of claim 1, wherein at least some of the hydrated manganese oxide has the general formula

3. The hydrated manganese oxide of claim 1 , wherein the median secondary particle

4. The hydrated manganese oxide of claim 1, wherein the primary particles are elongated such that a maximum dimension of each primary particle is larger than any dimension of the primary particle in a direction perpendicular to the maximum dimension.

5. The hydrated manganese oxide of claim 4, wherein at least 75% of the primary particles have a maximum dimension that is 3 times or more any dimension of the primary particle in a direction perpendicular to the maximum dimension.

6. The hydrated manganese oxide of claim 1, wherein the angle of repose is 40° or less.

7. A method of making hydrated manganese oxide comprising:

(a) a seeding stage comprising:

mixing a manganese salt solution and a hydroxide solution to form a first suspension; and

agitating the first suspension while introducing an oxidizing gas into the first suspension, without any addition of manganese salt solution or hydroxide solution, to form a second suspension; and

(b) a synthesis stage comprising:

adding additional manganese salt solution and hydroxide solution to the second suspension while continuing agitation and introduction of oxidizing gas to form a third suspension containing particles of hydrated manganese oxide.

8. The method of claim 7, wherein, in the seeding stage, the manganese concentration of the first suspension is 1.25 to 4.0 grams per liter.

9. The method of claim 7, wherein, in the seeding stage, the manganese salt solution and the hydroxide solution are mixed such that the molar ratio of hydroxide to manganese is 2.05 to 2.50.

10. The method of claim 7, wherein, in the seeding stage, the manganese salt solution and the hydroxide solution are added simultaneously to a reactor such that the ratio of the molar flow rate of hydroxide to molar flow rate of manganese is 2.05 to 2.50.

11. The method of claim 7, wherein, in the seeding stage, the oxidizing gas is introduced for 90 to 600 seconds after adding the manganese salt solution and the hydroxide solution.

12. The method of claim 7, wherein, in the seeding stage, the temperature is maintained at 15°C to 80°C.

13. The method of claim 7, wherein, in the synthesis stage, the manganese salt solution and the hydroxide solution are added simultaneously such that the ratio of the molar flow rate of hydroxide to the molar flow rate of manganese is 2.05 to 2.S0.

14. The method of claim 7, wherein, in the synthesis stage, the temperature is maintained at 15°C to 80°C.

15. The method of claim 7, wherein, during the synthesis stage, an oxidation potential is negative.

16. The method of claim 7, wherein, in both the seeding stage and the synthesis stage are carried out in a reactor having a reactor volume and, the volumetric flow rate of the oxidizing gas is 0.5 to 2 reactor volumes per minute.

17. The method of claim 7, wherein the synthesis stage further comprises stopping the flow of manganese salt solution and hydroxide solution while continuing agitation and the introduction of the oxidizing gas until a concentration of dissolved manganese ions in the third suspension has decreased to 0.2 g/1 or less.

18. The method of claim 17, wherein, after stopping the flow of manganese salt solution and hydroxide solution, hydroxide solution is added at a rate that maintains the pH of the third suspension above 6.5.

19. The method of claim 7, further comprising separating the hydrated manganese oxide particles from the third suspension and drying the particles.

20. The method of claim 19, wherein the third suspension comprises an ammonium nitrate solution.

21. The method of claim 7, wherein the manganese salt comprises manganese nitrate (Mn(NOs)2), manganese sulfate (MnS0₄), and/or manganese chloride (MnCb).

22. The method of claim 7, wherein the hydroxide comprises ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), and/or potassium hydroxide (KOH).

23. The method of claim 7, wherein, in the seeding stage, the mixing step includes providing an initial volume of water or an aqueous solution comprising anions of the manganese salt and cations of the hydroxide into which the manganese salt solution and the hydroxide solution are mixed.