Claims:WE CLAIM:
1. A method for producing stoichiometric manganese ferrite, comprising:
a. preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
b. roasting the pellets; and
c. cooling the roasted pellets
to obtain the stoichiometric manganese ferrite.
2. The method as claimed in claim 1, wherein the NMD comprises manganese dioxide, silicon dioxide, aluminium oxide, calcium oxide, sulphur, potassium oxide, sodium oxide, chromium oxide, Fe(T) and phosphorus or any combination thereof.
3. The method as claimed in claim 1, wherein the NMD comprises manganese dioxide at a concentration ranging from about 70% to about 90%.
4. The method as claimed in claim 1, wherein the NMD comprises silicon dioxide at a maximum concentration of about 0.025%; and wherein the NMD comprises aluminium oxide at a maximum concentration of about 2.08%.
5. The method as claimed in claim 1, wherein preparing the pellets in step (a) comprises:
mixing the NMD and the mill scale;
compressing the mixture to form pellets; and
subjecting the pellets to drying.
6. The method as claimed in claim 5, wherein the NMD and the mill scale are mixed at a ratio ranging from about 1:1.5 to about 1:3.
7. The method as claimed in claim 5, wherein the NMD and the mill scale are further mixed with a binder.
8. The method as claimed in claim 7, wherein the binder is selected from a group comprising bentonite Corn starch, sodium carboxymethylcellulose, citric acid, borax pentahydrateor any combination thereof.
9. The method as claimed in claim 7, wherein the binder is mixed with the NMD and the mill scale at a weight of about 1% to about 5% of the total weight of the NMD and Mill scale mixture.
10. The method as claimed in any of claims 5-9, wherein the NMD and the mill scale are further mixed with activated carbon.
11. The method as claimed in claim 10, wherein the activated carbon is mixed with the NMD and the mill scale at a weight of about 7% to about 15% of the total weight of the NMD and Mill scale mixture
12. The method as claimed in claim 5, wherein the pellets are dried at a temperature ranging from about 100°C to about 150°C.
13. The method as claimed in claim 1, wherein the roasting is performed at a temperature ranging from about 1200°C to about 1400°C.
14. The method as claimed in claim 1, wherein the roasting is performed for a period of about 2 hours to about 4 hours.
15. The method as claimed in claim 1, wherein the roasting is performed in presence of air.
16. The method as claimed in claim 1, wherein the cooling is performed at a high cooling rate ranging from about 100°C/second to about 150°C/second.
17. The method as claimed in claim 1, wherein the cooling is performed by water cooling.
18. The method as claimed in claim 1, wherein the manganese ferrite exhibits uniform stoichiometry. , Description:FIELD OF INVENTION
[001] The present disclosure relates to the fields of material science and metallurgy. Particularly, the present disclosure relates to a method for producing manganese ferrite. More particularly, the present disclosure provides the method for producing manganese ferrite using natural manganese dioxide (NMD) and mill scale.
BACKGROUND
[002] Manganese ferrite (MnFe2O4) which is non-toxic, non-corrosive, environmentally friendly and has high thermal resistance finds wide use in microwave devices, magnetic recording media, inductance components apart from its use in fine chemical engineering, ceramic engineering and environmental protection. Co-precipitation, thermal decomposition, and microwave hydrothermal process are some of the methods employed for the production of MnFe2O4 nanoparticles. Solid state reaction of Fe2O3 and Mn2O3 at elevated temperature is the most widely used method for the preparation of MnFe2O4. Some examples for preparation of manganese ferrite are disclosed below:
[003] US 3271191 describes a quick method to prepare manganese ferrite and manganese-magnesium ferrite films involving mixing of nitrates of Manganese, Iron and magnesium in alcohol and immersing the substrate into that mixture followed by heating the substrate in the temperature range 400-700°C before cooling it to room temperature. Alumina and fused quartz are described as suitable substrates.
[004] US 3751385 provides a method of manganese ferrite preparation which is meant for use as a catalyst in the oxidative dehydrogenation of organic compounds. The method described therein uses Fe2O3 and MnCO3 as precursors to produce manganese ferrite. Precursors mixed with 0.1-20 wt.% carbon black and small fraction of manganese chloride and chromium oxide are made into a cake form which is calcined at 600°C and 700°C in nitrogen atmosphere. The resulting manganese ferrite is an oxidative dehydrogenation catalyst.
[005] While the above processes to prepare manganese-ferrite have been reported in the art, said processes use costly precursors and usually involve multiple complex unit operation steps. Scalability of manganese ferrite is therefore a major concern. Therefor there is a need in the art an improved, alternative method addressing issues pertaining to scalability and process economy.

SUMMARY OF THE DISCLOSURE
[006] Addressing the aforesaid issues, the present disclosure provides a method for producing stoichiometric manganese ferrite, comprising:
a. preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
b. roasting the pellets; and
c. cooling the roasted pellets
to obtain the stoichiometric manganese ferrite.
[007] In some embodiments, the NMD comprises manganese dioxide, silicon dioxide, aluminium oxide, calcium oxide, sulphur, potassium oxide, sodium oxide, chromium oxide, Fe(T) and phosphorus or any combination thereof.
[008] In some embodiments, the NMD comprises manganese dioxide at a concentration ranging from about 70% to about 90%.
[009] In some embodiments, the NMD comprises silicon dioxide at a maximum concentration of about 0.025%; and aluminium oxide at a maximum concentration of about 2.08%.
[0010] In some embodiments, preparing the pellets in step (a) comprises:
mixing the NMD and the mill scale;
compressing the mixture to form pellets; and
subjecting the pellets to drying.
[0011] In some embodiments, while preparing the pellets, the NMD and the mill scale are mixed at a ratio ranging from about 1:1.5 to about 1:3.
[0012] In some embodiments, while preparing the pellets, the NMD and the mill scale are further mixed with a binder.
[0013] In some embodiments, the binder is selected from a group comprising bentonite Corn starch, sodium carboxymethylcellulose, citric acid, borax pentahydrateor any combination thereof.
[0014] In some embodiments, the binder is mixed with the NMD and mill scale at a weight of about 1% to about 5% of the total weight of the NMD and Mill scale mixture.
[0015] In some embodiments, the roasting of the pellets is performed at a temperature ranging from about 1200°C to about 1400°C. In some embodiments, the roasting is performed for a period of about 2 hours to about 4 hours.
[0016] In some embodiments, the roasting is performed in presence of air.
[0017] In some embodiments, the cooling is performed at a high cooling rate ranging from about 100°C/second to about 150°C/second. Said cooling, in some embodiments, is performed by water cooling.
[0018] In some embodiments, the manganese ferrite obtained by the above defined method exhibits uniform stoichiometry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where:
[0020] Figure 1 depicts XRD of the reaction product for pellets comprising mill scale, NMD and activated carbon roasted at A-600°C, B-700°C, C-800°C, D-900°C, E-1000°C, F-1100°C, and G-1200° C;
[0021] Figure 2 depicts XRD of the reaction products for pellets comprising mill scale, NMD and activated carbon roasted at A-1100° C with air cooling, B-1100° C with water cooling, C- 1200° C with air cooling, D-1200° C with water cooling;
[0022] Figure 3 depicts XRD of the reaction product of pellets comprising mill scale and NMD roasted at A-1200° C followed by air cooling, B-1200° C followed by water cooling, C-1300° C followed by air cooling, and D- 1300° C followed by water cooling;
[0023] Figure 4 depicts effect of holding time on the structure of the reaction product for pellets comprising mill scale and NMD processed at (A) 1300° C for 2 hours (B)1300° C for 4 hours (C)1300° C for 6 hours (D) 1350° C for 2 hours (D)1350° C for 4 hours;
[0024] Figure 5 depicts SEM-EDS at center region 1 of the pellet comprising mill scale and NMD processed at 1300°C for 6 hours;
[0025] Figure 6 depicts SEM-EDS at center region 2 of the pellet comprising mill scale and NMD processed at 1300°C for 6 hours;
[0026] Figure 7 depicts SEM-EDS at edge region of the pellet comprising mill scale and NMD processed at 1350°C for 4 hours;
[0027] Figure 8 depicts SEM-EDS at mantle region of the pellet comprising mill scale and NMD processed at 1350°C for 4 hours; and
[0028] Figure 9 depicts SEM-EDS at center region of the pellet comprising mill scale and NMD processed at 1350°C for 4 hours.
DETAILED DESCRIPTION
General definitions
[0029] As used herein, the term ‘mill scale’ refers to a scale or coating of iron oxide that forms on heated iron or steel on contact with air. Mill scale is typically known to comprise a mixture of iron oxides.
[0030] As used herein, the term ‘NMD’ is a blackish or brown solid that occurs naturally as the mineral pyrolusite, which is the main ore of manganese. ‘NMD’ as employed in the present disclosure is high purity manganese dioxide (MnO2) existing naturally with very small amounts of impurities.
[0031] The term ‘roasting’ in the context of the present disclosure refers to the solid-state processing of pellets prepared from mill scale and NMD, by subjecting the pellets to high temperatures sufficient enough to facilitate reduction of NMD.
[0032] As used herein, the term ‘water cooling’ refers to reducing the temperature of heated pellets by contacting the pellets with water, typically characterized by high cooling rate of at least about 100°C/second.
[0033] As used herein, the phrase ‘stoichiometric manganese ferrite’ or ‘stoichiometric Mn ferrite’ refers to Mn ferrite (MnFe2O4) having about 17 wt.% to about 23 wt.% Manganese (Mn), about 45 wt.% to about 57 wt.% Iron (Fe) and about 24 wt.% to about 28 wt.% Oxygen (O), wherein said ranges envisage all values derivable therefrom such as but not limited to 17.10 wt%, 17.11 wt%, 17.12 wt% and so on, upto 23 wt% of Mn; 45.10 wt%, 45.12 wt%, 45.13 wt% and so on, upto 57 wt% of Fe; and 24.10 wt%, 24.11 wt%, 24.12 wt% and so on, upto 28 wt% of O.
[0034] As used herein, the term ‘comprising’ when placed before the recitation of steps in a method means that the method encompasses one or more steps that are additional to those expressly recited, and that the additional one or more steps may be performed before, between, and/or after the recited steps. For example, a method comprising steps a, b, and c encompasses a method of steps a, b, x, and c, a method of steps a, b, c, and x, as well as a method of steps x, a, b, and c. Furthermore, the term ‘comprising’ when placed before the recitation of steps in a method does not (although it may) require sequential performance of the listed steps, unless the content clearly dictates otherwise. For example, a method comprising steps a, b, and c encompasses, for example, a method of performing steps in the order of steps a, c, and b, the order of steps c, b, and a, and the order of steps c, a, and b, etc.
[0035] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The suffix ‘(s)’ at the end of any term in the present disclosure envisages in scope both the singular and plural forms of said term.
[0036] As used in this specification and the appended claims, the singular forms ‘a’, ‘an’ and ‘the’ includes both singular and plural references unless the content clearly dictates otherwise. The use of the expression ‘at least’ or ‘at least one’ suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. As such, the terms ‘a’ (or ‘an’), ‘one or more’, and ‘at least one’ can be used interchangeably herein.
[0037] Numerical ranges stated in the form ‘from x to y’ include the values mentioned and those values that lie within the range of the respective measurement accuracy as known to the skilled person. If several preferred numerical ranges are stated in this form, of course, all the ranges formed by a combination of the different end points are also included.
[0038] The terms ‘about’ or ‘approximately’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, are meant to encompass variations of and from the specified value, such as variations of +/-10% or less, +/-5% or less, +/-1% or less, and +/-0.1% or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier ‘about’ or ‘approximately’ refers is itself also specifically, and preferably, disclosed.
[0039] As used herein, the terms ‘include’, ‘have’, ‘comprise’, ‘contain’ etc. or any form said terms such as ‘having’, ‘including’, ‘containing’, ‘comprising’ or ‘comprises’ are inclusive and will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
[0040] As regards the embodiments characterized in this specification, it is intended that each embodiment be read independently as well as in combination with another embodiment. For example, in case of an embodiment 1 reciting 3 alternatives A, B and C, an embodiment 2 reciting 3 alternatives D, E and F and an embodiment 3 reciting 3 alternatives G, H and I, it is to be understood that the specification unambiguously discloses embodiments corresponding to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I; B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H; C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I, unless specifically mentioned otherwise.
Disclosure
[0041] The present disclosure provides a method for producing manganese ferrite (MnFe2O4). Particularly, the present disclosure provides a method for producing stoichiometric manganese ferrite.
[0042] Provided in the present disclosure is a method for producing stoichiometric manganese ferrite, comprising:
preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
high temperature processing of the pellets; and
cooling of the processed pellets
to obtain the stoichiometric manganese ferrite.
[0043] More particularly, provided herein is a method for producing stoichiometric manganese ferrite, comprising:
preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
roasting the pellets; and
cooling the roasted pellets
to obtain the stoichiometric manganese ferrite.
[0044] In some embodiments, the NMD employed in the method is natural manganese dioxide of high purity.
[0045] In some embodiments, the NMD comprises manganese dioxide, potassium oxide, silicon dioxide, aluminium oxide, calcium oxide, sulphur, potassium oxide, sodium oxide, chromium oxide, Fe(T) and phosphorus or any combination thereof. In some embodiments, the Fe(T) is majorly composed of goethite, FeOOH.
[0046] In some embodiments, the NMD comprises manganese dioxide at a concentration ranging from about 70% to about 90%. In some embodiments, the NMD comprises manganese dioxide at a concentration of about 70%, about 75%, about 80%, about 85% or about 90%.
[0047] In some embodiments, the NMD comprises silicon dioxide at a concentration ranging from about 0.001% to about 0.025%; aluminum oxide at a concentration ranging from about 0.8% to about 2.08%; calcium oxide at a concentration ranging from about 0.027% to about 0.39%; sulphur at a concentration ranging from about 0% to about 0.001%; potassium oxide at a concentration ranging from about 1.29% to about 2.3%; sodium oxide at a concentration ranging from about 0% to about 0.021%; chromium oxide at a concentration ranging from about 0% to about 0.021%; Fe(T) at a concentration ranging from about 1.26% to about 4.35% ; and phosphorus at a concentration ranging from about 0% to about 0. 085%.
[0048] In some embodiments, the manganese dioxide employed is of high purity and is particularly characterized by low content of silicon dioxide and aluminium oxide.
[0049] In some embodiments, the manganese dioxide comprises silicon dioxide at a maximum concentration of about 0.025%.
[0050] In some embodiments, the manganese dioxide comprises aluminium oxide at a maximum concentration of about 2.08%.
[0051] In some embodiments, the manganese dioxide comprises silicon dioxide at a maximum concentration of about 0.025%; and aluminium oxide at a maximum concentration of about 2.08%.
[0052] Mill scale is a solid waste generated in steel plants and it normally gets utilized in the steel value chain itself. In some embodiments, the mill scale comprises mixed iron oxides.
[0053] In some embodiments, the mill scale comprises iron oxide selected from a group comprising mixed iron oxides iron (II) oxide (FeO), iron (III) oxide (Fe2O3), and iron (II, III) oxide (Fe3O4, magnetite) or any combination thereof.
[0054] In some embodiments, the mill scale further comprises impurities such as but not limited to manganese dioxide, aluminium oxide, silicon oxide, sulphur, potassium dioxide and chromium oxide in very small quantities.
[0055] Owing to their high Manganese (Mn) and Iron (Fe) content and less impurity content, both mill scale and high purity NMD are suitable precursors to produce manganese ferrite. The method of the present disclosure allows utilization of natural manganese dioxide (NMD) and mill scale which are otherwise used for low grade applications, to produce a high value material.
[0056] In some embodiments, preparing the pellets in step (a) of the above method comprises:
mixing the NMD and the mill scale;
compressing the mixture to form pellets; and
subjecting the pellets to drying.
[0057] In some embodiments, the NMD and the mill scale are mixed at a ratio ranging from about 1:1.5 to about 1:3.
[0058] In some embodiments, the NMD and the mill scale are mixed at a ratio of about 1:1.5, about 1:2, about 1:2.5 or about 1:3.
[0059] In an exemplary embodiment, the NMD and the mill scale are mixed at a ratio of about 1:1.6.
[0060] In some embodiments, the mixing is performed by any method routinely practiced in the art. In some embodiments, the mixing is performed by any method selected from a group comprising manual or mechanized versions of agitation, pulverization, crushing and grinding or any combination thereof.
[0061] In some embodiments, the mixing is performed manually, through hand mixing.
[0062] In some embodiments, the NMD and the mill scale are further mixed with a binder before the pelletizing.
[0063] In some embodiments, the binder is selected from a group comprising bentonite, corn starch, sodium carboxymethylcellulose, citric acid and borax pentahydrate or any combination thereof.
[0064] In some embodiments, the binder, when mixed with the NMD and the mill scale, is added at a weight of about 1% to about 5% of the total weight of the NMD and Mill scale mixture.
[0065] In some embodiments, the binder, when mixed with the NMD and the mill scale, is added at a weight of about 1%, about 2%, about 3%, about 4% or about 5% of the total weight of the NMD and Mill scale mixture.
[0066] While the pelletizing or the compression into pellets of desired size may be performed by any manual or mechanical method routinely practiced in the art, in a non-limiting embodiment, the pellets are prepared by hand.
[0067] Accordingly, in some embodiments, preparing the pellets in step (a) of the above method comprises:
mixing the NMD and the mill scale with a binder;
compressing the mixture to form pellets; and
subjecting the pellets to drying.
[0068] In some embodiments, the pellets optionally comprise activated carbon. The activated carbon helps further improve the kinetics of Mn ferrite formation.
[0069] In some embodiments, the activated carbon, when mixed with the NMD and the mill scale, is added at a weight of about 7% to about 15% of the total weight of the NMD and Mill scale mixture.
[0070] In some embodiments, the activated carbon, when mixed with the NMD and the mill scale, is added at a weight of about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14 or about 15% of the total weight of the NMD and Mill scale mixture.
[0071] Accordingly, in some embodiments, preparing the pellets in step (a) of the above method comprises:
mixing the NMD and the mill scale with a binder and activated carbon;
compressing the mixture to form pellets; and
subjecting the pellets to drying.
[0072] In some embodiments, the pellets are dried at a temperature ranging from about 100°C to about 150°C.
[0073] In some embodiments, the pellets are dried at a temperature of about 100°C, about 110°C, about 120°C, about 130°C, about 140°C or about 150°C.
[0074] In some embodiments, the pellets are of size ranging from about 2 cm to about 4 cm.
[0075] In some embodiments, the pellets are prepared to have a size of about 2 cm, about 2.5cm, about 3cm, about 3.5cm or about 4 cm.
[0076] In some embodiments, the roasting of the pellet is performed at a temperature ranging from about 1200°C to about 1400°C.
[0077] In some embodiments, the roasting of the pellet is performed at a temperature of about 1200°C, about 1300°C, about 1350°C or about 1400°C.
[0078] Accordingly, in some embodiments, provided herein is a method for producing stoichiometric manganese ferrite, comprising:
preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
roasting the pellets at a temperature ranging from about 1200°C to about 1400°C; and
cooling the roasted pellets
to obtain the stoichiometric manganese ferrite.
[0079] In some embodiments, the roasting is performed for a period of about 2 hours to about 4 hours.
[0080] In a non-limiting embodiment, the roasting is performed for a period of about 2 hours, about 2.5 hours, about 3 hours, about 3.5 hours or about 4 hours.
[0081] In some embodiments, said roasting of the pellet is performed in a furnace such as but not limited to a box furnace, tube furnace and muffle furnace.
[0082] In exemplary embodiments, the roasting is performed in presence of air.
[0083] In some embodiments, the cooling of the roasted pellets is performed at a high cooling rate.
[0084] In some embodiments, the cooling of the roasted pellets is performed at a cooling rate ranging from about 100°C/second to about 150°C/second. In some embodiments, the cooling is performed for a duration of about 4 minutes to about 5 minutes.
[0085] In some embodiments, the cooling of the roasted pellets is performed at a cooling rate of about 100°C/second, about 105°C/second, about 110°C/second, about 115°C/second, about 120°C/second, about 125°C/second, about 130°C/second, about 135°C/second, about 140°C/second, about 145°C/second or about 150°C/second. In some embodiments, said cooling is performed for a duration of about 4 minutes, 4.5 minutes or about 5 minutes.
[0086] In an exemplary embodiment, the cooling of roasted pellets is performed at a cooling rate of about 150°C/second for a duration of about 4 minutes to about 5 minutes.
[0087] In some embodiments, the cooling of the roasted pellets at the aforementioned cooling rates is performed by water cooling.
[0088] Accordingly, in some embodiments, provided herein is a method for producing stoichiometric manganese ferrite, comprising:
preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
roasting the pellets; and
cooling the roasted pellets at a cooling rate ranging from about 100°C/second to about 150°C/second
to obtain the stoichiometric manganese ferrite.
[0089] In some embodiments, provided herein is a method for producing stoichiometric manganese ferrite, comprising:
preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
roasting the pellets; and
subjecting the roasted pellets to water cooling at a cooling rate ranging from about 100°C/second to about 150°C/second
to obtain the stoichiometric manganese ferrite.
[0090] In some embodiments, provided herein is a method for producing stoichiometric manganese ferrite, comprising:
preparing pellets comprising natural manganese dioxide (NMD) and mill scale;
roasting the pellets at a temperature ranging from about 1200°C to about 1400°C; and
subjecting the roasted pellets to water cooling at a cooling rate ranging from about 100°C/second to about 150°C/second to obtain the stoichiometric manganese ferrite.
[0091] In some embodiments, the stoichiometric manganese ferrite is uniformly formed across the pellet. Accordingly, the manganese ferrite produced by the method of the present disclosure exhibits uniform stoichiometry.
[0092] It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.
[0093] Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.
EXAMPLES

EXAMPLE 1: Solid state synthesis of manganese ferrite
[0094] NMD in the as received condition from mines was in the form of a lump. It was crushed using a jaw crusher followed by a roll crusher and then pulverized in a ball mill. Mill scale was received in the form of fines. Chemical analysis of the NMD and the mill scale powder is shown in Table 1.

Table 1: Chemical analysis of NMD and mill scale (values in wt.%)
Component MnO2 Fe(T) Al2O3 CaO SiO2 S P K2O Na2O LOI Cr2O3
NMD 83.81 1.94 2.08 0.027 0.056 0.001 0.085 1.29 0.021 10.52 -
Mill scale 0.34 73.84 0.054 - 0.079 0.008 - 0.008 0.021 - 0.021
Table 1 indicates that the NMD and the mill scale employed were of high purity with low impurity content.
[0095] About 90 grams of NMD and about 152 grams of mill scale were mixed along with about 5 grams of bentonite and about 5-10 ml water to prepare a mixture. The mixture was pelletized by hand to prepare pellets having size in the range of about 2cm-4cm. The resultant green pellets were dried in the hot air oven at a temperature of 150 °C for about 1 hour to remove the moisture from them. Solid state processing of the dried pellets into manganese ferrite was carried out by roasting the pellets in a box furnace at a temperature of about 1250 °C for about 4 hours. Further, the roasted pellets were subjected to cooling at a cooling rate of about 150°C/sec through water cooling to obtain pellets comprising stoichiometric phase of manganese ferrite.
[0096] Further studies were conducted to analyze the effect of roasting temperature, holding conditions, cooling rate and presence of activated carbon in the pellets on the formation of stoichiometric manganese ferrite.
EXAMPLE 2: Analysis of effect of roasting temperature on formation of stoichiometric manganese ferrite
[0097] The procedure of Example 1 was repeated for different batches, with the incorporation of activated carbon in the pellets. The pellet mixture was prepared by mixing NMD:mill scale:bentonite:activated carbon at a ratio of about 1:1.6:0.056:0.2.
[0098] The roasting temperature was varied between the different batches. The roasting was performed at temperatures of about 600°C, about 700°C, about 800°C, about 900°C, about 1100°C and about 1200°C for a holding time of about 4 hours. The samples were heated to the desired temperature and during the holding time, Argon (Ar) gas was purged to maintain inert atmosphere. After the roasting, the processed samples were cooled in air, at a cooling rate of about 15°C/sec.
[0099] Figure 1 shows the XRD pattern of manganese ferrite produced at different temperatures.
[00100] Figure 1A indicates that there was no formation of either stoichiometric or non-stoichiometric manganese ferrite after roasting at about 600°C. However, the MnO2 present in the mixture was reduced to Mn2O3.
[00101] Figure 1C indicates the oxides of Fe and Mn present in the pellets were partially converted to non-stoichiometric manganese ferrite phase after roasting at about 800°C. Peaks corresponding to Fe2O3 were present in the XRD pattern of the reaction product.
[00102] Figure 1E indicates that the oxides of Fe and Mn present in the pellets were partially converted to manganese ferrite phase after roasting at about 1000°C. Peaks corresponding to Fe2O3 were present in the XRD pattern of the reaction product. Thus, the reaction product obtained at 1000°C was a mixture of manganese ferrite and oxides of Mn and Fe.
[00103] Figure 1G indicates that the oxides of Fe and Mn present in the pellets were completely converted to manganese ferrite phase post roasting at about 1200°C. No peaks corresponding to Fe2O3 and MnO2 were present in the XRD pattern of the reaction product. However, the manganese ferrite phase formed in the pellets had a non-stoichiometric composition.
[00104] Further experiments were carried out to study the effect of parameters such as holding time, holding atmosphere, cooling rate and presence of different amount of activated carbon on the formation of stoichiometric manganese ferrite.
EXAMPLE 3: Analysis of the effect of cooling rate and incorporation of activated carbon on formation of stoichiometric manganese ferrite
[00105] Two sets of experiments, with and without incorporation of activated carbon in the pellets, were performed to understand the effect of cooling rate on the formation of stoichiometric manganese ferrite.
With carbon
[00106] 4 batches of pellets were prepared comprising NMD, mill scale, bentonite and activated carbon at a ratio of about 1:1.6:0.052:0.2 The pellets were subjected to roasting at temperatures of about 1100°C and about 1200°C for a holding time of about 4 hours. During the holding time, inert atmosphere was maintained by purging Ar gas. Separate batches of pellets roasted at about 1100°C and about 1200°C were subjected to air cooling and pressurized water cooling, to analyze the effect of cooling rate on the formation of stoichiometric manganese ferrite. The rate of cooling in case of air cooling was maintained at about 15°C/sec and in case of water cooling at about 150°C/sec.
Without carbon
[00107] 4 batches of pellets were prepared comprising NMD, mill scale and bentonite at a ratio of about 1:1.6:0.052. The pellets were subjected to roasting at temperatures of about 1200°C and about 1300°C for a holding time of about 4 hours. During the holding time, inert atmosphere was maintained by purging Ar gas. Separate batches of pellets roasted at about 1200°C and about 1300°C were subjected to air cooling and pressurized water cooling, to analyze the effect of cooling rate on the formation of stoichiometric manganese ferrite. The rate of cooling in case of air cooling was maintained at about 15°C/sec and in case of water cooling at about 150°C/sec.
[00108] Figures 2 (for samples with carbon) and 3 (for samples without carbon) show the effect of cooling rate on the stoichiometry of ferrite formed in the final product for samples with and without carbon at different processing temperatures.
[00109] Figure 2 depicts the XRD of the reaction product produced employing the following conditions: A- Roasting at 1100° C followed by air cooling, B- Roasting at 1100°C followed by water cooling, C- Roasting at 1200° C followed by air cooling, D- Roasting at 1200° C followed by water cooling. Figures 2A and 2B show that roasting at 1100°C resulted in partial conversion into manganese ferrite. Between Figures 2C and 2D, the final product cooled in water showed formation of stoichiometric manganese ferrite while the air-cooled sample showed formation of non-stoichiometric manganese ferrite.
[00110] Figure 3 depicts the XRD of the reaction product produced employing the following conditions: A-Roasting at 1200° C followed by air cooling, B- Roasting at 1200° C followed by water cooling, C-Roasting at 1300° C followed by air cooling, and D- Roasting at 1300° C followed by water cooling. Between Figures 3A and 3B, the final product cooled in water showed formation of stoichiometric manganese ferrite while the air-cooled sample showed partial conversion into non-stoichiometric manganese ferrite. Figure 3C indicates that the oxides of Fe and Mn present in the pellets were almost completely converted to manganese ferrite phase. However, the manganese ferrite formed was non-stoichiometric. Figure 3D indicates that unlike in the sample in Figure 3C, the manganese ferrite formed was stoichiometric manganese ferrite.
[00111] To conclude, it was observed that in case of both samples, with and without carbon, the final product cooled in water showed formation of stoichiometric manganese ferrite while the air-cooled sample showed formation of non-stoichiometric manganese ferrite. Between samples comprising and lacking activated carbon, it was observed that samples without activated carbon showed more uniform formation of stoichiometric manganese ferrite (Figures 2 and 3).
EXAMPLE 4: Analysis of the effect of holding time on formation of stoichiometric manganese ferrite
[00112] To study the effect of holding time on the uniform manganese ferrite formation, roasting was carried out for different durations at different temperature using pellets prepared without any activated carbon, and without maintaining any inert atmosphere during the roasting.
[00113] Pellets comprising NMD, mill scale and bentonite at a ratio of about 1:1.6:0.052 were prepared. The pellets were subjected to roasting at temperatures of about 1300°C and about 1350°C for a holding time of about 2 hours, about 4 hours or about 6 hours, without maintaining inert atmosphere. The cooling was performed by water cooling. The rate of cooling was maintained at about 150°C/sec.
[00114] Figure 4 depicts the effect of holding time on the structure of the reaction product for the following processing conditions: (A) Roasting 1300° C for a holding time of 2 hours (B) Roasting 1300° C for a holding time of 4 hours (C) Roasting 1300° C for a holding time of 6 hours (D) Roasting 1350° C for a holding time of 2 hours (D) Roasting 1350° C for a holding time of 4 hours. The figure clearly shows that irrespective of the holding time, the reaction product obtained after roasting at both, 1300°C and 1350°C, were stoichiometric manganese ferrite i.e., MnFe2O4. No peaks corresponding to Fe2O3 and MnO2 were present in the XRD patterns of the reaction products, therefore confirming complete conversion of the Mn and Fe oxides into manganese ferrite.
[00115] The pellets were further subjected to SEM-EDS analysis to check the impact of holding time on uniformity of the stoichiometric phase formed.
[00116] Figures 5 and 6 depict the results of the SEM-EDS analysis at two different positions at the center of a pellet processed at about 1300°C for about 6 hours. The results of the analysis are further provided in Tables 2 and 3 below –
Table 2: SEM-EDS results at center region-1 of pellet processed at 1300°C for 6 hours
Element Region 1 Region 2 Region 3
Fe 54.25 54.85 54.4
Mn 20.47 19.8 20.27
O 24.89 24.99 24.9
Al 0.39 0.36 0.43

Table 3: SEM-EDS results at center region-2 of pellet processed at 1300°C for 6 hours
Element Region 1 Region 2 Region 3
Fe 41.87 41.76 41.73
Mn 26.62 32.58 32.88
O 30.64 25.21 24.95
Al 0.59 0.45 0.44

[00117] While SEM-EMD analysis at the position shown in figure 5 indicates formation of stoichiometric manganese ferrite, analysis at a different position in the center of pellet shown in figure 6 indicates non-stoichiometric manganese ferrite formation. The above results therefore show that composition was different at the two positions in the pellet processed at 1300°C for 6 hours.
[00118] Figures 7, 8 and 9 depict the results of the SEM-EDS analysis at three different positions in a pellet processed at about 1350°C for about 4 hours. While figure 7 shows the EDS analysis at the edge region of the processed pellet, figures 8 and 9 show the EDS analysis at the mantle and center region, respectively. The results of the analysis are further provided in Tables 4, 5 and 6, below –
Table 4: SEM-EDS at edge region of pellet processed at 1350°C for 4 hours
Element Region 1 Region 2 Region 3
Fe 56.47 56.41 55.98
Mn 17.77 17.79 18.14
O 25.41 25.43 25.52
Al 0.35 0.37 0.36

Table 5: SEM-EDS at mantle region of pellet processed at 1350°C for 4 hours
Element Region 1 Region 2 Region 3
Fe 54.86 55.62 55.61
Mn 19.94 19.65 19.72
O 24.87 24.35 24.34
Al 0.33 0.38 0.34

Table 6: SEM-EDS at center region of pellet processed at 1350°C for 4 hours
Element Region 1 Region 2 Region 3 Region 4
Fe 55.96 55.69 55.1 55.55
Mn 19.27 19.21 19.18 19.37
O 24.43 24.73 25.35 24.78
Al 0.33 0.37 0.38 0.3

[00119] The above results indicate that the formation of stoichiometric manganese ferrite i.e. MnFe2O4 was uniform all over in the pellets processed at about 1350°C for about 4 hours.
[00120] Therefore, through the SEM-EDS analysis, it was found that between the pellets processed at about 1300°C for about 6 hours and about 1350°C for about 4 hours, the former had MnFe2O4 formed non uniformly across the pellet while the latter had MnFe2O4 formed uniformly throughout the pellet.
[00121] The foregoing description fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the general concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments in this disclosure have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein, without departing from the principles of the disclosure.
[00122] Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.