Claims:WE CLAIM:
1. A process for producing La2FeMnO6 from iron ore slime, comprising:
- leaching the iron ore slime to obtain an iron source;
- reacting the iron source, a lanthanum source and a manganese source to obtain a precipitate; and
- calcining the precipitate to obtain La2FeMnO6.

2. The process as claimed in claim 1, wherein the iron ore slime has a composition comprising:
- Fe2O3 in an amount of about 75% to 81%,
- FeO in an amount of about 3% to 4%,
- Al2O3 in an amount of about 5% to 7%,
- SiO2 in an amount of about 6% to 7%, and
- P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%.

3. The process as claimed in claim 1, wherein the leaching of iron ore slime comprises:
i) leaching the iron ore slime to obtain a solution;
ii) filtering the solution; and
iii) recrystallizing the filtered solution to obtain the iron source.

4. The process as claimed in claim 3, wherein the leaching of step i) comprises treating the iron ore slime with a leaching agent, followed by boiling and cooling to obtain the solution.

5. The process as claimed in claim 4, wherein the leaching agent is an acid selected from the group comprising hydrochloric acid (HCl), nitic acid (HNO3), sulphuric acid (H2SO4) and combinations thereof.

6. The process as claimed in claim 3, wherein the filtering of step ii) removes impurities selected from the group comprising Al2O3, SiO2, CaO, MgO, P2O5, TiO2, other non-traceable elements and combinations thereof.

7. The process as claimed in claim 1, wherein the iron source is an iron salt; and wherein the iron source is selected from ferric chloride (FeCl3), ferrous chloride (FeCl2) and a combination thereof.

8. The process as claimed in claim 1, wherein the lanthanum source is lanthanum nitrate hexahydrate (La2(NO3)3.6H2O).

9. The process as claimed in claim 1, wherein the manganese source is manganese sulfate monohydrate (MnSO4.H2O).

10. The process as claimed in claim 1, wherein the reaction of the iron source, the lanthanum source and the manganese source to obtain the precipitate comprises:
a) preparing a solution comprising the iron source and a surfactant, a solution comprising the lanthanum source and a surfactant, a solution comprising the manganese source and a surfactant;
b) mixing the solutions of step a);
c) adding a precipitating agent to the solution obtained in step b) and adjusting pH to about 10 to 11, preferably about 10.5, to obtain a precipitate;
d) heating the precipitate obtained in step c) at a temperature ranging from about 110℃ to 120℃, preferably 120℃ for a period of about 20 hours to 24 hours, preferably about 24 hours to obtain the precipitate.

11. The process as claimed in claim 10, wherein the surfactant is cetyltrimethyl ammonium bromide (CTAB).

12. The process as claimed in claim 10, wherein the precipitating agent is selected from the group comprising ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), potassium hydroxide (KOH) and combinations thereof.

13. The process as claimed in claim 1, wherein the precipitate is washed with methanol (CH3OH) and chloroform (CHCl3), and dried.

14. The process as claimed in claim 1, wherein calcination is carried out in air at a temperature ranging from about 900℃ to 1050 ℃, preferably about 1000℃ for a period of about 6 hours to 8 hours, preferably about 6 hours to obtain the La2FeMnO6.

15. The process as claimed in any of the claims 1-14, wherein the process comprises:
a) leaching the iron ore slime having a composition comprising:
- Fe2O3 in an amount of about 75% to 81%,
- FeO in an amount of about 3% to 4%,
- Al2O3 in an amount of about 5% to 7%,
- SiO2 in an amount of about 6% to 7%, and
- P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%, in presence of a leaching agent to obtain a solution,
b) filtering the solution to remove impurities selected from the group comprising Al2O3, SiO2, CaO, MgO, P2O5, TiO2, other non-traceable elements and combinations thereof,
c) recrystallizing the filtered solution to obtain iron chloride selected from ferric chloride (FeCl3) or ferrous chloride (FeCl2) or a combination thereof;
d) preparing: i) a solution by adding CTAB to the iron chloride and stirring, ii) a solution by dissolving lanthanum nitrate hexahydrate in water and adding CTAB and stirring, and iii) a solution by adding CTAB to manganese sulfate monohydrate and stirring;
e) mixing the solutions i), ii) and iii) of step d);
f) adding NH4OH and adjusting pH to about 10.5, to obtain a precipitate;
g) heating the precipitate obtained in step f) at a temperature of about 120℃ for a period of about 24 hours to obtain a precipitate; and
h) calcining the precipitate obtained in step g) in presence of air at a temperature of about 1000℃ for a period of about 6 hours to obtain the La2FeMnO6.

16. The process as claimed in any of the claims 1-15, wherein the obtained La2FeMnO6 is a La2FeMnO6 nanostructure having a particle size ranging from about 80 to 100 nm.

17. La2FeMnO6 nanoparticles obtained by the process as claimed in any of the claims 1-16, wherein said La2FeMnO6 has a particle size ranging from about 80 to 100 nm.

18. The process as claimed in any of the claims 1-16 or the La2FeMnO6 nanoparticles as claimed in claim 17, wherein the La2FeMnO6 nanoparticles are employed as electrocatalyst for generation of oxygen.

19. Use of iron ore slime having a composition comprising:
- Fe2O3 in an amount of about 75% to 81%,
- FeO in an amount of about 3% to 4%,
- Al2O3 in an amount of about 5% to 7%,
- SiO2 in an amount of about 6% to 7%, and
- P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%, to prepare La2FeMnO6.
, Description:TECHNICAL FIELD
The present disclosure relates to solid-state synthesis of double perovskites. The disclosure particularly provides synthesis of La2FeMnO6 nanostructures.

BACKGROUND OF THE DISCLOSURE
Steel is one of the key materials for economic growth of various industries such as automotive, construction, transportation etc. As reported by World Steel Association (WSA), in 2018 total 1808 million tonnes (MT) of crude steel was produced worldwide where India stood the second place with total production of 93.31 MT crude steel. During steel-making process in the blast furnace, highly pure and stable iron oxide ore (hematite) is widely utilized as a raw material. However, during beneficiation processes of iron ore, an inseparable part termed as “slime” is obtained and this is discarded as a waste. In India, during iron ore mining and processing, around 15% to 25% of the mined ore is normally unutilized and discarded as slime. In general, a particle size ~ 25 μm are being discarded during the processing of iron ore. The primary drawback during the processing of iron ore in the mines is the production of said size reduced fines/slimes with high clay content. Despite the fact that said iron ore slime contains high amount of iron minerals, slimes cannot be used directly because lower grade iron ore or slime feeding in blast furnaces can choke the feeder of the furnaces along with possessing other disadvantages. Thus, impurities create various difficulties during the iron ore recycling process and iron ore slime is therefore discarded as a waste.

Synthesis of useful materials from waste or discards is one of the major thrust areas in today’s world. In this regard, perovskite transition metal oxides are studied widely for their uniqueness in structural, magnetic, optical and electronic properties. The double perovskites with general formula A2BB'O6 have gained interest, where A is an alkaline earth or rare earth element and B and B′ is a 3d transition metal. The double perovskites are industrially important due to their application potential in magnetic recording media, high-dielectric constant, ferroelectric, photo-catalysis, high temperature superconductivity and magneto-resistive devices operating at room temperature etc. The synthesis process and the ionic radii of cations in perovskite structure have its impact on the structural aspect with variation between rhombohedral, tetragonal, orthorhombic or even monoclinic symmetries. Among the double perovskites, lanthanum (La) based compounds have received much attention due to their different structural, magnetic and electrical properties. In the La2FeMnO6 [LFMO] double perovskite, La3+ with the ionic radius (1.06 Å) occupies position A of the complex orthorhombic perovskite structure, whereas Fe3+ (ionic radius 0.64 Å) and Mn3+ (ionic radius 0.58 Å) cations occupy the B and B′ positions, respectively. The presence of Jahn-Teller ion (Mn3+) leads to a distorted structure with the tilting of BO6 and B'O6 octahedra. The presence of La3+, Fe3+ and Mn3+ ions make the compound structurally stable and magnetically interesting with its complex magnetic ordering. Previously, LFMO has been synthesized by Pechini method, Sol-gel process, ICR technique, citrate-nitrate gel combustion, solid state process etc. However, in all such synthetic routes, pure and expensive iron sources such as Fe2O3, Fe(NO3)3.9H2O, Fe(NO3)3.6H2O etc have been employed which make the LFMO synthesis costlier.

Thus, there is a need in the art to develop an alternate, simple and cost-effective process for synthesizing La2FeMnO6 (LFMO). The present disclosure attempts to address said need.

STATEMENT OF THE DISCLOSURE
The present disclosure relates to a process for producing La2FeMnO6 (LFMO) from iron ore slime, comprising:
leaching the iron ore slime to obtain an iron source;
reacting the iron source, a lanthanum source and a manganese source to obtain a precipitate; and
calcining the precipitate to obtain La2FeMnO6.

The present disclosure further provides La2FeMnO6 nanoparticles obtained by the process as described above, wherein said La2FeMnO6 has a particle size ranging from about 80 to 100 nm.

The present disclosure also relates to use of iron ore slime having a composition comprising: Fe2O3 in an amount of about 75% to 81%, FeO in an amount of about 3% to 4%, Al2O3 in an amount of about 5% to 7%, SiO2 in an amount of about 6% to 7%, and P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%, to synthesize La2FeMnO6.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 depicts Powder X-ray diffraction (PXRD) patterns of iron ore slime.

Figure 2 depicts SEM morphology and EDXS analysis of iron ore slime.

Figure 3 depicts PXRD and EDXS analysis of the recrystallized sample obtained by leaching of iron ore slime.

Figure 4 illustrates the process flow diagram of La2FeMnO6 synthesis.

Figure 5 depicts PXRD patterns of the synthesized La2FeMnO6 nanostructures.

Figure 6 depicts Transmission Electron Microscopy (TEM) and EDXS analysis of the synthesized La2FeMnO6 nanostructures.

Figure 7 depicts electrocatalytic performance of La2FeMnO6 nanostructures and comparison with bare graphite sheet (GS) [Figure 7a and 7b]. Figures 7c and 7d show comparative Nyquist spectra of nanostructured La2FeMnO6 and GS and the curve data fitted with CPE model.

DETAILED DESCRIPTION OF THE DISCLOSURE
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 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. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having”, or “including but not limited to” wherever used, 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.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The term “about” as used herein encompasses variations of +/- 10% and more preferably +/- 5%, as such variations are appropriate for practicing the present invention.

As used herein, the term ‘iron ore slime’ or ‘slime’ refers to the slime material that is generated during beneficiation or processing of iron ore. In some embodiments, the ‘iron ore slime’ is a slime material having a particle size of less than 20 microns generated during beneficiation or processing of iron ore. In some embodiments, the iron ore is selected from the group comprising magnetite, maghemite, hematite, goethite, limonite and siderite. In some embodiments, the slime material has a composition comprising: Fe2O3 in an amount of about 75% to 81%, FeO in an amount of about 3% to 4%, Al2O3 in an amount of about 5% to 7%, SiO2 in an amount of about 6% to 7%, and P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%.

A primary object of the present disclosure is to advantageously utilize ‘slime’, a discard/waste which is generated during beneficiation/processing of iron ore. More particularly, the present disclosure aims at conversion of iron ore slime into an industrially important compound - La2FeMnO6 (LFMO) double perovskite. Said LFMO has utility in various fields including but not limiting to electrochemical oxygen generation during water splitting i.e. utility as an electrocatalyst for generation of oxygen.

Accordingly, to meet the above objective, the present disclosure provides a synthetic route/process for producing La2FeMnO6 (LFMO) from iron ore slime comprising:
leaching the iron ore slime to obtain an iron source,
reacting the iron source, a lanthanum source and a manganese source to obtain a precipitate, and
calcining the precipitate to obtain La2FeMnO6.

Iron ore slime contains iron and other gangue materials/impurities such as Al2O3, SiO2, CaO and MgO. Among these gangue materials, Al2O3 and SiO2 are the major contaminants present in the iron ore slime. In some embodiments of the above described process, the iron ore slime has a composition comprising:
Fe2O3 in an amount of about 75% to 81%,
FeO in an amount of about 3% to 4%,
Al2O3 in an amount of about 5% to 7%,
SiO2 in an amount of about 6% to 7%, and
P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%, including all values and ranges therefrom.

In some embodiments, the composition of iron ore slime comprises Fe2O3, FeO, Al2O3, SiO2, P2O5, TiO2, CaO, MgO and other non-traceable elements such that the total wt% sums up to 100 %. In some embodiments, in addition to the above defined iron ore slime composition, the slime comprises additional impurities/elements/compounds which are inherent and result from the beneficiation/processing of iron ores. Such additional impurities/elements/compounds are not defined herein but is well understood to a person skilled in the art.

In some embodiments of the above described process, the leaching of iron ore slime to obtain iron source comprises:
leaching the iron ore slime to obtain a solution,
filtering the solution, and
recrystallizing the filtered solution to obtain the iron source.

In some embodiments of the above described process, the leaching of the iron ore slime [step i)] comprises treating the iron ore slime with a leaching agent, followed by boiling and cooling to obtain the solution.

In some embodiments of the above described process, the leaching agent employed for leaching the iron ore slime is an acid selected from the group comprising hydrochloric acid (HCl), nitic acid (HNO3), sulphuric acid (H2SO4) and combinations thereof. In some embodiments, the leaching agent is hydrochloric acid (HCl). In some embodiments, the leaching agent is nitic acid (HNO3). In some embodiments, the leaching agent is sulphuric acid (H2SO4). In some embodiments, the leaching agent is a combination of hydrochloric acid (HCl), nitic acid (HNO3) and sulphuric acid (H2SO4). In some embodiments, the leaching agent is any two leaching agents selected from hydrochloric acid (HCl), nitic acid (HNO3) and sulphuric acid (H2SO4).

In some embodiments of the above described process, the filtering step during the leaching of the iron ore slime [step ii)] removes impurities selected from the group comprising Al2O3, SiO2, CaO, MgO, P2O5, TiO2 and combinations thereof.

In some embodiments of the above described process, the iron source obtained after leaching the iron ore slime is an iron salt.

In some embodiments of the above described process, the iron source obtained after leaching the iron ore slime is selected from ferric chloride (FeCl3), ferrous chloride (FeCl2) and a combination thereof. In some embodiments, the iron source is ferric chloride (FeCl3). In some embodiments, the iron source is ferrous chloride (FeCl2). In some embodiments, the iron source is a combination of ferric chloride (FeCl3) and ferrous chloride (FeCl2).

In some embodiments of the above described process, the lanthanum source is lanthanum nitrate hexahydrate (La2(NO3)3.6H2O).

In some embodiments of the above described process, the manganese source is manganese sulfate monohydrate (MnSO4.H2O).

In some embodiments of the above described process, the reaction of the iron source, the lanthanum source and the manganese source to obtain the precipitate comprises:
preparing a solution comprising the iron source and a surfactant, a solution comprising the lanthanum source and a surfactant, a solution comprising the manganese source and a surfactant;
mixing the solutions of step a);
adding a precipitating agent to the solution obtained in step b) and adjusting pH to about 10 to 11, to obtain a precipitate;
heating the precipitate obtained in step c) at a temperature ranging from about 110℃ to 120℃ for a period of about 20 hours to 24 hours to obtain the precipitate.

In some embodiments of the above described process, the reaction of the iron source, the lanthanum source and the manganese source to obtain the precipitate comprises:
preparing a solution comprising the iron source and a surfactant, a solution comprising the lanthanum source and a surfactant, a solution comprising the manganese source and a surfactant;
mixing the solutions of step a);
adding a precipitating agent to the solution obtained in step b) and adjusting pH to about 10.5, to obtain a precipitate;
heating the precipitate obtained in step c) at a temperature of about 120℃ for a period of about 24 hours to obtain the precipitate.

In some embodiments of the above described process, the surfactant employed is cetyltrimethyl ammonium bromide (CTAB).

In some embodiments of the above described process, the precipitating agent is selected from the group comprising ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), potassium hydroxide (KOH) and combinations thereof. In some embodiments, the precipitating agent is ammonium hydroxide (NH4OH). In some embodiments, the precipitating agent is sodium hydroxide (NaOH). In some embodiments, the precipitating agent is potassium hydroxide (KOH). In some embodiments, the precipitating agent is a combination of NH4OH, NaOH and KOH. In some embodiments, the precipitating agent is any two compounds selected from NH4OH, NaOH and KOH.

In some embodiments of the above described process, the precipitate is washed with methanol (CH3OH) and chloroform (CHCl3), and dried.

In some embodiments of the above described process, calcination of the precipitate is carried out in air at a temperature ranging from about 900℃ to 1050 ℃ for a period of about 6 hours to 8 hours to obtain the La2FeMnO6. In some embodiments, the calcination is carried out at a temperature of 900℃, 920℃, 950℃, 970℃, 990℃, 1000℃, 1020℃, 1050℃ or any values or ranges therefrom. In some embodiments, the calcination is carried out for a period of 6 hours, 7 hours, 8 hours, or any values or ranges therefrom.

In some embodiments of the above described process, calcination of the precipitate is carried out in air at a temperature of about 1000 ℃ for a period of about 6 hours to obtain the La2FeMnO6.

The present disclosure provides a process for producing La2FeMnO6 from iron ore slime, comprising:
leaching the iron ore slime in presence of an acid leaching agent to obtain a solution;
filtering the solution to remove impurities;
recrystallizing the filtered solution to obtain an iron source selected from ferric chloride (FeCl3) or ferrous chloride (FeCl2) or a combination thereof;
reacting the iron source, a lanthanum source and a manganese source to obtain a precipitate, comprising:
preparing a solution comprising the iron source and a surfactant, a solution comprising the lanthanum source and a surfactant, a solution comprising the manganese source and a surfactant,
mixing the solutions,
adding a precipitating agent and adjusting pH to about 10 to 11 to obtain a precipitate.
heating the precipitate at a temperature ranging from about 110℃ to 120℃ for a period of about 20 hours to 24 hours to obtain the precipitate;
and
calcining the precipitate in presence of air at a temperature of about 900℃ to 1050 ℃ for a period of about 6 hours to 8 hours to obtain the La2FeMnO6.

In some embodiments, the process for producing La2FeMnO6 from iron ore slime comprises:
leaching the iron ore slime having a composition comprising:
Fe2O3 in an amount of about 75% to 81%,
FeO in an amount of about 3% to 4%,
Al2O3 in an amount of about 5% to 7%,
SiO2 in an amount of about 6% to 7%, and
P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%, in presence of a leaching agent to obtain a solution;
filtering the solution to remove impurities selected from the group comprising Al2O3, SiO2, CaO, MgO, P2O5, TiO2, other non-traceable elements and combinations thereof;
recrystallizing the filtered solution to obtain iron chloride selected from ferric chloride (FeCl3) or ferrous chloride (FeCl2) or a combination thereof;
preparing: i) a solution by adding CTAB to the iron chloride and stirring, ii) a solution by dissolving lanthanum nitrate hexahydrate in water and adding CTAB and stirring, and iii) a solution by adding CTAB to manganese sulfate monohydrate and stirring;
mixing the solutions i), ii) and iii) of step d);
adding NH4OH and adjusting pH to about 10.5, to obtain a precipitate;
heating the precipitate obtained in step f) at a temperature of about 120℃ for a period of about 24 hours to obtain a precipitate; and
calcining the precipitate obtained in step g) in presence of air at a temperature of about 1000℃ for a period of about 6 hours to obtain the La2FeMnO6.

In some embodiments, the La2FeMnO6 obtained by the above described process of the present disclosure is La2FeMnO6 nanoparticles.

In some embodiments, the La2FeMnO6 obtained by the above described process of the present disclosure is a La2FeMnO6 nanostructure having a particle size ranging from about 80 to 100 nm, including all values and ranges therefrom.

The present disclosure further provides La2FeMnO6 nanoparticles obtained by the process as described herein, wherein said La2FeMnO6 has a particle size ranging from about 80 to 100 nm, including all values and ranges therefrom.

In some embodiments, the La2FeMnO6 obtained herein is employed as an electrocatalyst for generation of oxygen.

The present disclosure also relates to the use of iron ore slime having a composition comprising:
Fe2O3 in an amount of about 75% to 81%,
FeO in an amount of about 3% to 4%,
Al2O3 in an amount of about 5% to 7%,
SiO2 in an amount of about 6% to 7%, and
P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%, to prepare La2FeMnO6.

The present invention thus relates to a simple and alternate approach towards the synthesis of nanostructured La2FeMnO6 from iron based waste (slime) and corresponding application of the synthesized La2FeMnO6 for oxygen generation. Particularly, in the presently described process, the iron ore slime which is an industrial waste is utilized for synthesis of La2FeMnO6 nanoparticles. The present invention therefore provides a technology that has the capability to convert the industrial waste into an industrially important product (La2FeMnO6) which can be further utilized as an electrocatalyst for oxygen generation.

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.

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.

INCORPORATION BY REFERENCE
All references, articles, publications, patents, patent publications, and patent applications (if any) cited herein are incorporated by reference in their entireties for all purposes. However, mention of any reference, article, publication, patent, patent publication, and patent application cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.

EXAMPLES

Example 1: Characterization of Iron Ore Slime
Iron ore slime, a waste generated during beneficiation of iron ore was utilized for synthesis of La2FeMnO6. Said iron ore slime contains iron and other gangue materials/impurities such as Al2O3, SiO2, CaO, MgO etc. The slime material has a composition comprising: Fe2O3 in an amount of about 75% to 81%, FeO in an amount of about 3% to 4%, Al2O3 in an amount of about 5% to 7%, SiO2 in an amount of about 6% to 7%, and P2O5, TiO2, CaO, MgO and other non-traceable elements in an amount of about less than 1%. Powder X-ray diffraction (PXRD) patterns of iron ore slime confirmed that the slime composed of hematite [Fe2O3, Rhombo H axes with space group R-3c (167)] and maghemite-C [Fe2O3, Cubic phase with space group P4132 (213)] phase (Figure 1). SEM morphology confirmed that the iron ore slime composed of ~20-40 µm particles (Figure 2a). The EDXS analysis (Figure 2b) of iron ore slime further shows the presence of iron, silicon and aluminum in the matrix.

Example 2: Synthesis of La2FeMnO6 (LFMO) from Iron Ore Slime
For synthesis of La2FeMnO6, a lanthanum source - lanthanum nitrate hexahydrate (La2(NO3)3.6H2O), a manganese source - manganese sulfate monohydrate (MnSO4.H2O), a surfactant - cetyltrimethyl ammonium bromide (CTAB) were used as initial precursors without further purification. Iron chloride derived from leaching of iron ore slime was used as the iron source. Said leaching of iron ore slime comprised steps of: i) leaching the iron ore slime to obtain a solution; ii) filtering the solution; and iii) recrystallizing the filtered solution to obtain said iron source (iron chloride). NH4OH used as a precipitating agent during the process for the preparation of the target complex through hydrothermal route.

Synthesis of La2FeMnO6 starting from iron ore slime was carried out in two steps. In the first step, the slime was preliminarily treated with concentrated HCl as a leachant and boiled for about 30 minutes and cooled. After that, the solution was filtrated to remove impurities. The final solution was re-crystallized. PXRD study of the re-crystallized sample was carried out and it confirmed the presence of hexagonal iron chloride (FeCl3) with minor amount of Fe2O3 which may be due to surface oxidation during the re-crystallization (Figure 3a). The EDXS analysis (Figure 3b) showed the presence of only Fe, Cl and O in the matrix.

In the second step, La2FeMnO6 nanoparticles were synthesized using the iron chloride obtained above. For this purpose, hydrothermal route was adopted followed by calcination. At first, about 50 ml of 0.05 mM of La2(NO3)3.6H2O was dissolved in distilled water and 50 mM of CTAB was added and stirred well to make a homogeneous solution. Similarly, separate solutions of FeCl3 and MnSO4.H2O were prepared. About 25 ml of 0.05 mM FeCl3 or 0.05 mM MnSO4.H2O was stirred at about 800 rpm for about 1 hour with the addition of 25 mM of CTAB, respectively. After that all the 3 prepared solutions were placed in a beaker and again stirred at about 800 rpm for about 1 hour. After that, about 10 ml of NH4OH solution was added as precipitating agent to the solution with constant stirring for about 30 minutes. The pH of the solution was adjusted at 10.5. The obtained precipitates were separated through centrifugation and dried in oven at about 70 C, dispersed in methanol solvent and put in teflon lined hydrothermal reactor followed by heating at about 120 C for about 24 hours. Further, the teflon was cooled and the precipitates were washed with a mixture of 50% CH3OH and 50% of CHCl3 for 5 times. These precipitates were dried completely and calcined in air at about 1000 C for about 6 hours to obtain the desired compound La2FeMnO6. The process flow diagram of La2FeMnO6 synthesis is illustrated in Figure 4.

PXRD patterns of the obtained La2FeMnO6 sample are depicted in Figure 5. The diffraction peaks confirm the formation of cubic phase of La2FeMnO6. Transmission Electron Microscopy (TEM) studies of the sample further shows the formation of nanoparticles of size between 80-100 nm (Figure 6a). The EDXS (Figure 6b) analysis showed presence of only La, Mn, Fe and O in the matrix.

Example 3: Properties/Performance of synthesized La2FeMnO6 (LFMO)
For electrochemical measurement, 10 mg of the as-synthesized La2FeMnO6 was dispersed in 300 µl ethanol by ultrasonication. Further, 20µL Nafion was added in said dispersion and sonicated for about 15 minutes. The prepared dispersion (about 60 µL) was drop casted on graphite sheet and allowed to dry in room temperature. All electrochemical studies were carried out in a standard three-electrode system on Autolab PGSTAT30 electrochemical workstation at room temperature in 1M KOH. Before the electrochemical measurement, N2 was purged in the prepared electrolyte for about 30 minutes. For the electrochemical measurement, 3.5M Ag/AgCl and Pt were used as reference and counter electrode respectively. The La2FeMnO6 was drop casted on graphite sheet, which is used as a working electrode. Linear sweep voltammetry (LSV) was conducted in the potential range 1.2 to 2 V vs. RHE for oxygen evolution reaction (OER) measurement at 10 mV/s scan rate. Electrochemical impedance was measured in a frequency range from 0.01 Hz up to 100 kHz at 10 mV amplitude. The impedance spectrum was analysed with FRA software (Nova 1.1). All the potentials were measured with respect to Ag/AgCl. In the present manuscript, the entire potential window has been shown against the reversible hydrogen electrode (RHE). The electrocatalytic performance of La2FeMnO6 nanostructures was compared with bare graphite sheet (GS) as shown in Figure 7a. In the present study, it was observed that La2FeMnO6 showed efficient electrocatalytic activity towards the OER in the operating potential window. The onset potential (potential at which current density will be 1 mA/cm2) of the La2FeMnO6 is 1.68 V, whereas GS has highest onset potential (1.83V vs RHE). The observed results showed that La2FeMnO6 required lower overpotential (η= 640 mV ) to achieve 10 mA/cm2 current density. The value of Tafel slope for La2FeMnO6 and GS are 84 mV/dec and 137 mV/dec respectively. All the electrochemical data has been summarized in Table 1 below. The Ag/AgCl (EAg/AgCl) potentials were converted to reversible hydrogen electrode (RHE) using the Nernst equation as follows:
E_RHE=E_(Ag/AgCl)+0.059×pH+E_(Ag/AgCl)^0
where E_(Ag/AgCl)^0 is the standard electrode potential at 25°C.

Table 1: Summary of electrocatalytic performance of La2FeMnO6 in 1M KOH solution
Materials Onset potential
(V vs. RHE) Over potential
mV Tafel slope
(mV/dec) Rct
(ohm)
Graphite 1.83 - 137 ~ 1600
LFMO 1.68 640 84 ~ 580

Electrochemical Impedance spectroscopy (EIS) was also done for La2FeMnO6 nanostructures in order to justify the performance of different shape and size of La2FeMnO6 nanostructures towards electrocatalytic activity for OER activity as it gives clear idea about the ease of electron transfer from the surface of electrode to electrolyte interface. This technique revealed information about charge transfer process and electronic conductivity of La2FeMnO6 and GS towards OER studies. Figure 7c shows the comparative Nyquist spectra of nano structured La2FeMnO6. Measurements were carried out at potential 1.7 V vs. RHE for each of the material mentioned above. The curve data were fitted with CPE model (Figure 7d) and it comprises of three components, first RS which is solution resistance which is 13.4 Ω for La2FeMnO6 and 17.6 Ω for GS. Second is Rct which is called charge transfer resistance. Smaller the Rct higher will be the electronic conductivity and higher will be the electrocatalytic activity. Rct value for La2FeMnO6 was 580 Ω and for GS it was more than 1600 Ω. As the charge transfer resistance decreases, it is a suggestion of rapid charge transfer ability towards OER and as a result catalytic activity increases for La2FeMnO6. These are in good agreement with electrocatalytic property from LSV and Tafel plots.

Thus, the present invention is focused on designing a synthetic route/process for producing La2FeMnO6 nanostructures via solid state method using spent industrial waste (iron ore slime) and study their oxygen evolution properties. The invention successfully achieves this purpose wherein the process comprises recovery of high purity iron compound from iron ore slime and its subsequent transformation to La2FeMnO6 nanostructures. Transmission electron microscope studies of as obtained La2FeMnO6 shows the formation nano particles of size 80 to 100 nm. EDXS confirms the presence of La, Fe, Mn and O elements in the prepared compound. Electrocatalytic study additionally reveals that the synthesized La2FeMnO6 nanostructures offer better oxygen generation activity in terms of low onset potential (1.68 V), over potential (640 mV) and Tafel slope (84 mV/dec) in 1M KOH solution. This nanostructured La2FeMnO6 derived from the industrial iron ore slime can be used as a smart electrocatalyst for generation of oxygen.