Claims:1. A method for preparing manganese oxide comprising
subjecting Natural Manganese Dioxide (NMD) ore to reduction roasting in a rotary tube furnace
to obtain the manganese oxide.
2. The method as claimed in claim 1, wherein the NMD comprises manganese dioxide, silicon dioxide, aluminium oxide, calcium oxide, magnesium 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%, preferably about 85% 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 the NMD has particle size of about 0.5mm to about 3 mm.
6. The method as claimed in claim 1, wherein the NMD is fed to the rotary tube furnace at a dispensing rate ranging from about 10% to about 15%.
7. The method as claimed in claim 1, wherein the reduction roasting is performed at a temperature ranging from about 400°C to about 1050°C.
8. The method as claimed in claim 1, wherein the reduction roasting is performed under a reducing atmosphere.
9. The method as claimed in claim 8, wherein the reduction roasting is performed under a reducing atmosphere by purging the furnace with reducing gas selected from a group comprising carbon monoxide (CO) and hydrogen (H2), or a combination thereof.
10. The method as claimed in claim 9, wherein the reduction roasting is performed under a reducing atmosphere by purging the furnace with 100% carbon monoxide (CO) or 100% hydrogen (H2).
11. The method as claimed in claim 9, wherein the reducing gas is purged at a flow rate ranging from about 70 l/hr to about 90 l/hr.
12. The method as claimed in claim 1, wherein the reduction roasting is performed for a time period ranging from about 1 hour to about 2 hours.
13. The method as claimed in claim 1, wherein the rotary tube furnace is maintained at an angle of inclination ranging from about 1 degree to about 5 degrees.
14. The method as claimed in claim 1, wherein the rotary tube furnace is maintained at a tube rotation speed ranging from about 1 rpm to about 5 rpm.
15. The method as claimed in claim 1, wherein the obtained manganese oxide is selected from a group comprising MnO, Mn3O4 and Mn2O3 or any combination thereof.
16. The method as claimed in claim 1, wherein the obtained manganese oxide is a mixture of any of Mn3O4, Mn2O3 and MnO when the temperature of reduction roasting is maintained at about 400°C to about 800°C.
17. The method as claimed in claim 1, wherein the obtained manganese oxide is MnO when the temperature of reduction roasting is maintained at about 800°C to about 1050°C.
18. The method as claimed in claim 1, wherein the obtained manganese oxide is subjected to cooling.
19. The method as claimed in claim 18, wherein the obtained manganese oxide is subjected to cooling in the RTF, in a cooling zone.
20. The method as claimed in claim 18, wherein the cooled manganese oxide is further subjected to secondary cooling.
21. The method as claimed in claim 20, wherein the secondary cooling is performed in a natural atmosphere or forced atmosphere.
22. The method as claimed in claim 21, wherein the secondary cooling is performed in nitrogen or in water or a combination thereof.
23. The method as claimed in claim 1, wherein conversion efficiency of the NMD to manganese oxide ranges from about 90% to about 95%.
24. The method as claimed in claim 1, wherein purity of the manganese oxide formed ranges from about 95% to about 97%.
, Description:FIELD OF INVENTION
[0001] The present disclosure relates to the fields of material science and metallurgy. Particularly, the present disclosure relates to a method for producing manganese oxide. More particularly, the present disclosure allows utilization of natural manganese dioxide (NMD) to produce a high value material.
BACKGROUND
[0002] Manganese is an abundant resource that is embedded in the Earth crust and has wide variety of applications. The most known application is in the steel and metal alloy making industries, in which manganese is used to improve the strength and properties of steel. More than 85% of all manganese consumed goes into steel as an alloying element and after steel, the second most important market for manganese is primary and rechargeable batteries.
[0003] Despite its ubiquity, manganese is rarely found in high enough concentrations to form an ore deposit. Of the hundreds of minerals containing manganese, only around 10 are of mining significance.
[0004] Manganese ore can be classified into low-grade ore (Mn<35%), medium grade ore (Mn 35-45%), and high-grade ore (Mn>45%). Based on the purity of the MnO2 in the ore it can also be classified into naturally occurring manganese dioxide (NMD) where the MnO2 varies between 72-85% and synthetic grade manganese dioxide (SMD) where the MnO2 is >85%. These SMD’s can be further classified into chemical-grade manganese dioxide (CMD) MnO2 85-90% and electrolytic grade manganese dioxide (EMD) where the MnO2 is >90%. Usually, the mineral ores (MnO2) of manganese oxides are insoluble in acids. Therefore, for producing EMD and manganese sulphate etc., it needs to be converted to acid soluble MnO first. This step is critical as it affects the entire process flow route of manganese products. There are generally 2 methods of treating the pyrolusitic ores, where one is a hydrometallurgical route for treating Mn ores for producing SMD and various Mn derivatives, as depicted in Figure 1. The SMDs obtained from leach liquor is further used for producing lower oxides of Mn like Mn2O3, Mn3O4 and MnO. This method has the advantages of strong adaptability and mature technology, but it also has disadvantages such as high energy consumption, high labour intensity, and the flue gas generated during the roasting process pollutes the environment. Further, extreme pressure and temperature are needed to convert high grade Mn salts to low grade Manganese Oxides for battery application, therefore making scalability difficult. The second route is through smelting which is much more predominantly used for industrial scale applications. But said method requires the use of coal powder as reducing agent, therefore posing the risk of environmental pollution.
[0005] The need of the hour is to devise an economical and environmentally friendly method to produce lower manganese oxides. It is also desirable to reduce the reliance on SMDs to produce lower manganese oxides, preferably through an alternate pyrometallurgical route
SUMMARY OF INVENTION
[0006] Addressing the need in the art for an alternate, economical, and environmentally friendly method to produce lower manganese oxides, the present disclosure provides method for preparing manganese oxide comprising subjecting Natural Manganese Dioxide (NMD) ore to reduction roasting in a rotary tube furnace to obtain the manganese oxide.
[0007] In some embodiments, the NMD comprises manganese dioxide at a concentration ranging from about 70% to about 90%, preferably about 85% to about 90%.
[0008] In some embodiments, the reduction roasting is performed at a temperature ranging from about 400°C to about 1050°C.
[0009] In some embodiments, the reduction roasting is performed under a reducing atmosphere. In some embodiments, the reduction roasting is performed under a reducing atmosphere by purging the furnace with reducing gas selected from a group comprising carbon monoxide (CO) and hydrogen (H2), or a combination thereof.
[0010] In some embodiments, the obtained manganese oxide is selected from a group comprising MnO, Mn3O4 and Mn2O3 or any combination thereof.
[0011] In some embodiments, conversion efficiency of the NMD to manganese oxide ranges from about 90% to about 95%.
[0012] In some embodiments, purity of the manganese oxide formed ranges from about 95% to about 97%.
[0013] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0014] 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:
[0015] Figure 1 depicts the conventional hydrometallurgical route for treating Mn ores for producing SMD and various Mn derivatives;
[0016] Figure 2 depicts X-Ray diffractogram of NMD ore employed in the method of the present disclosure;
[0017] Figure 3 depicts SEM- Elemental mapping of NMD ore showing distribution of Mn, Fe oxides and minor trace elements (all the images are drawn to a scale of 200 micron);
[0018] Figure 4 depicts photographic images of reduced NMD ore at 850°C using H2 as reducing gas;
[0019] Figure 5 depicts XRD images of reduced NMD ore at 850°C using H2 as reducing gas;
[0020] Figure 6 depicts SEM- Elemental mapping of reduced NMD ore at 850°C using H2 as reducing gas;
[0021] Figure 7 depicts different points on the reduced NMD ore at 850°C that were selected for elemental analysis;
[0022] Figure 8 depicts photographic images of reduced NMD ore at 950°C;
[0023] Figure 9 depicts comparison of the XRD images of reduced NMD ore at 850°C and 950°C using H2 as reducing gas;
[0024] Figure 10 depicts photographic images of reduced NMD ore at 1050°C using H2 as reducing gas;
[0025] Figure 11 depicts comparison of the XRD images of reduced NMD ore at 950°C and 1050°C using H2 as reducing gas;
[0026] Figure 12 depicts XRD Rietveld analysis of reduced NMD ore at 1050°C using CO as reducing gas;
[0027] Figure 13 depicts reduction in impurities in the reduced ore with increase in reduction temperature;
[0028] Figure 14 depicts XRD images of reduced NMD ore at 600°C using H2 as reducing gas;
[0029] Figure 15 depicts XRD images of reduced NMD ore at 800°C using H2 as reducing gas;
[0030] Figure 16 depicts XRD images of reduced NMD ore at 900°C using H2 as reducing gas;
[0031] Figure 17 depicts XRD images of reduced NMD ore at 1050°C using H2 and CO as reducing gas, respectively; and
[0032] Figure 18 depicts the Rotary Tube Furnace (RTF) employed in the method of the present disclosure.
[0033] The drawings referred to in this description are not to be understood as being drawn to scale except if specifically noted, and such drawings are only exemplary in nature.
DETAILED DESCRIPTION
[0034] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0035] General definitions
[0036] As used herein, the term ‘NMD’ or ‘NMD ore’ is a blackish or brown solid that occurs naturally as the mineral pyrolusite, which is the main ore of manganese. The ore, in some embodiments, further comprises minor amounts of cryptomelane (K(Mn4+, Mn2+)8O16). ‘NMD’ as employed in the present disclosure is high purity manganese dioxide (MnO2) existing naturally with very small amounts of impurities.
[0037] The term ‘reduction roasting’ in the context of the present disclosure refers to the heating of the NMD ore in a Rotary Tube Furnace (RTF) at temperatures ranging between about 400°C to about 1050°C while maintaining a reducing atmosphere in the RTF.
[0038] Reference to the ‘temperature’ of reduction roasting or ‘reduction temperature’ throughout the present disclosure, unless otherwise defined, refers to the temperature maintained in the ‘reduction zone’ of the RTF.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] Disclosure
[0047] The present disclosure provides an energy efficient and environmentally friendly method for preparing manganese oxide that allow utilization of Natural Manganese Dioxide (NMD) as an alternative to conventionally used Synthetic grade Manganese Dioxide (SMD).
[0048] Particularly, the present disclosure provides a method for preparing manganese oxide comprising subjecting Natural Manganese Dioxide (NMD) ore to reduction roasting in a rotary tube furnace to obtain the manganese oxide.
[0049] In some embodiments, the NMD comprises manganese dioxide, silicon dioxide, aluminium oxide, calcium oxide, magnesium oxide, sulphur, potassium oxide, sodium oxide, chromium oxide, Fe(T) and phosphorus or any combination thereof.
[0050] 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%.
[0051] In some embodiments, the manganese dioxide employed is of high purity and is particularly characterized by low content of silicon dioxide and aluminium oxide.
[0052] In some embodiments, the NMD comprises manganese dioxide at a concentration ranging from about 70% to about 90%. In a preferred embodiment, the NMD comprises manganese dioxide at a concentration ranging from about 85% to about 90%.
[0053] In some embodiments, the NMD comprises manganese dioxide at a concentration of about 85%, about 86%, about 87%, about 88%, about 89% or about 90%.
[0054] In some embodiments, 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%.
[0055] In some embodiments, the particle size of the NMD employed ranges about 0.5mm to about 3 mm. In a non-limiting embodiment, said particle size is achieved by any known method routinely practiced in the art such as but not limited to crushing, grinding, and pulverizing of the NMD ore.
[0056] In some embodiments, the particle size of the NMD employed is about 0.5mm, about 1mm, about 1.5mm, about 2mm, about 2.5mm or about 3 mm.
[0057] In some embodiments, the NMD is fed to the rotary tube furnace for reduction roasting at a dispensing rate ranging from about 10% to about 15%. Dispensing rate as defined herein refers to the frequency at which equal amounts of feed i.e., the NMD is fed into the rotary tube furnace. For example, a dispensing rate of about 15% implies that, during operation, at every 15 seconds the feeder of the rotary tube furnace vibrates and feeds an equal amount of NMD into a screw feeder system which ensures equal amount of NMD is introduced into the furnace at equal time intervals.
[0058] In some embodiments, the NMD is fed to the rotary tube furnace for reduction roasting at a dispensing rate of about 10%, about 11%, about 12%, about 13%, about 14% or about 15%.
[0059] In some embodiments, the reduction roasting in the rotary tube furnace is performed at a temperature ranging from about 400°C to about 1050°C. While a further increase in temperature up to 1100°C also leads to reduction of the NMD, the amount of MnO formed remains similar, without any significant increase. Thus, increasing the temperature beyond 1050°C could decrease the energy efficiency of the process.
[0060] In some embodiments, the reduction roasting in the rotary tube furnace is performed at a temperature of about 400°C, about 450°C, about 500°C, about 550°C, about 600°C, about 650°C, about 700°C, about 750°C, about 800°C, about 850°C, about 900°C, about 950°C, about 1000°C or about 1050°C.
[0061] In some embodiments, the present disclosure provides a method for preparing manganese oxide comprising subjecting Natural Manganese Dioxide (NMD) ore to reduction roasting in a rotary tube furnace at a temperature ranging from about 400°C to about 1050°C to obtain the manganese oxide.
[0062] In some embodiments, the reduction roasting is performed under a reducing atmosphere. In a non-limiting embodiment, said reducing atmosphere is achieved by purging the rotary tube furnace with reducing gas selected from a group comprising carbon monoxide (CO) and hydrogen (H2), or a combination thereof.
[0063] In some embodiments, the present disclosure provides a method for preparing manganese oxide comprising subjecting Natural Manganese Dioxide (NMD) ore to reduction roasting in a rotary tube furnace at a temperature ranging from about 400°C to about 1050°C; to obtain the manganese oxide; wherein the rotary tube furnace is purged with reducing gas selected from a group comprising carbon monoxide (CO) and hydrogen (H2), or a combination thereof.
[0064] In some embodiments, the rotary tube furnace is purged with 100% carbon monoxide (CO) or 100% hydrogen (H2).
[0065] In a non-limiting embodiment, the reducing gas is purged into the RTF at a flow rate ranging from about 70 l/hr to about 90 l/hr.
[0066] In a non-limiting embodiment, the reducing gas is purged into the RTF at a flow rate of about 70 l/hr, 75 l/hr, 80 l/hr, 85 l/hr or about 90 l/hr.
[0067] In some embodiments, the reduction roasting of the Natural Manganese Dioxide (NMD) ore is performed for a time period ranging from about 1 hour to about 2 hours.
[0068] In some embodiments, the rotary tube furnace is maintained at an angle of inclination ranging from about 1 degree to about 5 degrees during the reduction roasting.
[0069] In some embodiments, the rotary tube furnace is maintained at an angle of inclination of about 1 degree, about 2 degrees, about 3 degrees, about 4 degrees or about 5 degrees during the reduction roasting.
[0070] In some embodiments, tube rotation speed of the rotary tube furnace is maintained in the range of about 1 rpm to about 5 rpm during the reduction roasting.
[0071] In some embodiments, tube rotation speed of the rotary tube furnace is maintained at about 1 rpm, 2 rpm, 3 rpm, 4 rpm or about 5 rpm during the reduction roasting.
[0072] In some embodiments, the manganese oxide obtained from the above method is selected from a group comprising MnO, Mn3O4 and Mn2O3 or any combination thereof.
[0073] In some embodiments, the specific manganese oxide formed is dependent on the temperature of reduction roasting.
[0074] In some embodiments, when the temperature of reduction roasting is maintained at about 400°C to about 800°C, the obtained manganese oxide is mixture of manganese oxides selected from Mn3O4, Mn2O3 and MnO or any combination thereof.
[0075] In some embodiments, when the temperature of reduction roasting is maintained at about 400°C to about 600°C, the obtained manganese oxide is a mixture of manganese oxides selected from Mn3O4, Mn2O3 and MnO. In a non-limiting embodiment, when the temperature of reduction roasting is maintained at about 400°C to about 600°C, major component of the obtained manganese oxide is Mn3O4 along with minor amounts of Mn2O3 and/or MnO.
[0076] In a non-limiting embodiment, when the temperature of reduction roasting is maintained at about 600°C to about 800°C, the obtained manganese oxide is a mixture of manganese oxides selected from Mn3O4 and MnO.
[0077] In a non-limiting embodiment, when the temperature of reduction roasting is maintained at about 800°C to about 1050°C, the obtained manganese oxide is MnO.
[0078] In some embodiments, with increase in reduction roasting temperature, especially at reduction temperatures ranging between about 800°C to about 1000°C, the association of impurities such as but not limited to potassium and goethite is increasingly interrupted, therefore leading to higher purity of the obtained manganese oxide. In case of NMD ore impurities like goethite, it gets reduced to metallic iron which can also be beneficiated easily, thereby facilitating the capability to improve the manganese oxide purity for direct battery application.
[0079] In some embodiments, the obtained manganese oxide is further subjected to cooling. In a non-limiting embodiment, the rotary tube furnace is designed to comprise a ‘cooling zone’ for cooling the reduced ore and therefore, the aforesaid cooling of the obtained manganese oxide takes place inside the furnace.
[0080] In some embodiments, the cooled manganese oxide is further subjected to secondary cooling.
[0081] In a non-limiting embodiment, the said secondary cooling of the cooled manganese oxide is performed in the collection chamber of the furnace such as but not limited to a glass collection chamber. In some embodiments, the secondary cooling is performed in a natural atmosphere or a forced atmosphere.
[0082] In some embodiments, the said secondary cooling is performed in nitrogen or in water or a combination thereof. In a non-limiting embodiment, the secondary cooling cools the reduced ore to room temperature.
[0083] In some embodiments, the aforesaid method of the present disclosure provides a conversion efficiency of NMD to manganese oxide ranging from about 90% to about 95%.
[0084] In some embodiments, the aforesaid method of the present disclosure provides a conversion efficiency of NMD to manganese oxide of about 90%, about 91%, about 92%, about 93%, about 94% or about 95%.
[0085] In some embodiments, purity of the manganese oxide yielded by the aforesaid method of the present disclosure ranges from about 95% to about 97%.
[0086] In some embodiments, purity of the manganese oxide yielded by the aforesaid method of the present disclosure is about 95%, about 95.5%, about 96%, about 96.5% or about 97%.
[0087] As evident from the above embodiments, the employment of a rotary tube furnace is an important feature of the method of the present disclosure directed towards reduction roasting of NMD to obtain manganese oxide, in a cost-effective and environmentally friendly manner.
[0088] The most commonly used equipment for reduction roasting of manganese mineral ore to manganese monoxide conventionally includes reverberatory furnaces, shaft furnace, fluidized furnace roasting etc. The temperature is quite unstable and difficult to control in these furnaces, thus, producing non-uniform and undesirable quality of roasted products.
[0089] Reverberatory furnaces are now obsolete for electrolytic manganese production due to disadvantages like low output, low conversion rate, huge amount of dust produced, serious environmental pollution etc. Moreover, the temperature is quite unstable and difficult to control on this furnace, thus producing non-uniform and undesirable quality of roasted products. Fluidized bed furnace also has several drawbacks. The reduction of ore and coal happens in the same furnace, but the gas evolved in the furnace are difficult to control and require huge amount of pressure, thereby producing large amount of smoke and dust. The amount of residual carbon in the roasted sample is also high. Thus, making these furnaces totally undesirable for industrial application. Similar to that of the fluidized bed furnace, in shaft furnace also, the reduction of ore and coal happens in the same furnace. The major drawbacks of this furnace include the lack of ore bed ventilation which results in poor gas permeability, poor reducibility of the ore, higher heat consumption. Environmental pollution is also quite large.
[0090] When compared to all other furnaces mentioned above the reduction efficiency of the RTF furnace is quite high as it is able to reduce the ore to its lower oxide much more efficiently when compared to other furnaces. The higher efficiency is due to the furnace tube rotation about its axis ensuring the uniform heating of the feed. In most other furnaces the heating happens either from top or side which led to generation of thermal gradient inside the pellet/feed, thus leading to inefficient reduction. Said drawback is overcome in the method of the present disclosure which is particularly characterized by the employment of a rotary tube furnace (RTF).
[0091] Accordingly, the present disclosure further provides a rotary tube furnace (RTF) for facilitating the reduction roasting of NMD to yield manganese oxide.
[0092] In some embodiments, the RTF comprises a rotating drum driven by a drive unit. The rotating drum is supported on at least one supporting member wherein one end of the rotating tube opens to a hopper/feeder and the other end opens to a collection chamber.
[0093] In some embodiments, rotation of the RTF is facilitated by the drive unit. Said rotation ensures uniform heating to the feed and improves reduction efficiency.
[0094] In a non-limiting embodiment, dispensing rate of the feed into the RTF is maintained at about 10% to about 15% i.e. at every about 10 seconds to about 15 seconds, the feeder vibrates and feeds an equal amount of the NMD into a screw feeder section of RTF.
[0095] In some embodiments, the feeder feeds the NMD into the screw feeder section, which in turn feeds the NMD into the RTF.
[0096] In some embodiments, the furnace tube has 3 zones, a pre-reduction zone, a reduction zone, and a cooling zone.
[0097] In some embodiments, the pre-reduction zone and cooling zone are maintained at temperatures that are about 100°C to about 200°C less than the reduction zone depending on the distance from reduction zone. In some embodiments, the reduction zone is maintained at a temperature ranging from about 400°C to about 1050°C.
[0098] In a non-limiting embodiment, temperature in the RTF is maintained by heating coils, which are usually concentrically wound around the tube in reduction zone. In some embodiments, uniformly distributed heating coils are available at the top and bottom part of the furnace tube at the reduction zone. In a non-limiting embodiment, heat from the reduction zone is transferred to preheat and cooling zone via conduction and convection.
[0099] In some embodiments, in order to facilitate the reduction roasting, the RTF is purged with reducing gas. In some embodiments, the reducing gas is selected from carbon monoxide and hydrogen or a combination thereof.
[00100] The residence time or reduction time of the feed inside the furnace tube can be controlled by varying the tube inclination. In some embodiments, the rotary tube furnace is maintained at an angle of inclination ranging from about 1 degree to about 5 degrees during the reduction roasting.
[00101] In some embodiments, the gases arising as a result of the reduction roasting process inside the RTF are allowed to leave the RTF through an exhaust unit.
[00102] In a non-limiting embodiment, the exhaust unit is positioned at or close to the end of the RTF that opens to a hopper/feeder.
[00103] In some embodiments, the collection chamber is a glass container which facilitates secondary cooling of the manganese oxide arising from the RTF. In some embodiments, the glass unit is supplied with nitrogen and/or water to facilitate the secondary cooling.
[00104] The pictorial representation of the rotary tube furnace (RTF) (200) is provided in Figure 18. Initially the manganese ore is fed into the RTF feeder/hopper (101) whose dispensing rate is maintained at 15% such that the feeder vibrates and feeds the NMD into the screw feeder section below the hopper, which in turn feeds equal amount of material into the furnace tube. The furnace tube basically has 3 zones, a pre-reduction zone (102), a reduction zone (103) and a cooling zone (104). The residence time or reduction time of the feed inside the furnace tube can be controlled by varying the tube inclination. The tube inclination, in some embodiments, is maintained at about 1 degree to about 5 degrees. The RTF rotates on its own axis, thereby ensuring uniform heating to the feed and thus improving the reduction efficiency. The output from the furnace tube falls into a glass chamber or container (105) where it is cooled down to room temperature either in the presence of nitrogen or water. The gases arising from the reduction roasting of the NMD are allowed to leave the RTF through an exhaust unit (106).
[00105] 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.
[00106] 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.
[00107] EXAMPLES:
[00108] EXAMPLE 1: Characterization of starting material
[00109] The NMD ore in the as received conditions was in the form of lumps, which was ground to ensure a 5 mm 100% pass. The ore samples were thoroughly mixed and representative samples were made out of it for each required experiment. The chemical analysis of the NMD ore used for the present study is shown in Table 1.
[00110] Table. 1 Chemical composition of NMD ore
Component Weight percent
MnO2 (equivalent) 86.79
Fe total 4.35
LOI 10.95
SiO2 0.025
Al2O3 0.8
CaO 0.39
MgO 0.047
P 0
S 0.001
K2O 2.3
Cr2O3 0
Na2O 0.021
[00111] The results indicate that the ore is very rich in manganese dioxide wherein said high content of manganese dioxide is almost synonymous to EMD grade manganese ore. Apart from iron and manganese minerals, silica, and alumina are also present in minor quantities. Figure 2 shows the XRD results of NMD ore and it indicates that the ore is mainly a pyrolusite ore (MnO2) with minor amounts of cryptomelane (K(Mn4+, Mn2+)8O16). The iron exists in the form of goethite phase, with silicon dioxide as the other trace element.
[00112] The NMD ore was further characterized using SEM elemental mapping as depicted in Figure 3. Similar to that of XRD and chemical analysis results, the SEM elemental mapping also showed Mn and Fe as the major phases in the ore, said elements existing predominantly in their oxide forms. Both the oxides of Mn and Fe were found to prevail as distinct phases with no interconnections among them. Elemental mapping results also showed the presence of minor amounts of Si, Al, and K oxides, mainly as compounds with Mn, consistent with the XRD results.
[00113] Representative samples of the NMD ore characterized above were subjected to reduction roasting in a rotary tube furnace at different temperatures ranging between about 400°C to about 1050°C either in the presence of H2 and/or CO gas, in the absence of carbon fines, to prepare manganese oxide.
[00114] EXAMPLE 2: Reduction roasting of the ore at 850°C
[00115] About 250 g of the representative NMD ore sample was fed to the RTF feeder whose dispensing rate was kept at about 15% (i.e., every 15 seconds the feeder vibrated and fed equal amount of material into the furnace). H2 was used for maintaining the reduction atmosphere with a constant flow rate of about 80 l/ hr, while the reduction temperature was maintained at about 850°C. The angle of inclination of the RTF was kept at one degree for maximizing the reduction time. The tube rotation speed of the RTF was kept constant at about 4 rpm. The reduction was performed for a period of about 2 hours.
[00116] Figure 4 shows the schematic representation of the input feed sample and the reduced sample. The green color on the reduced sample typically symbolizes the presence of MnO. The reduced samples were further characterized using XRD and SEM as shown in Figures 5 and 6. XRD results showed the presence of MnO as the major component. SEM imaging clearly revealed the presence of MnO as the major component, consistent with the XRD results. Dark regions in the results of SEM imaging represent the presence of Calcium, Silicon and Potassium that too in minor amounts, while the lighter regions are mainly MnO.
[00117] The reduced sample was further subjected to point EDS analysis. The results are provided in Table 2 (Figure 7). Here also presence of MnO as the major phase was quite evident, consistent with the results observed in XRD and SEM elemental mapping. Very minor to negligible amounts of Aluminium, and Silicon etc. were found.
[00118] Table 2. Chemical composition corresponding to different point on the reduced NMD ore at 850°C using H2 as reducing gas
Point O2 Na Mg Al Si K Ca Mn
1 17.57 0.49 0 0.47 0 0.93 0.39 80.15
2 18.53 0.48 0 0.58 0.12 1.04 1.79 77.46
3 19.29 0.64 0 0.60 0.23 0.84 0.46 77.94
4 15.96 0.38 1.22 0.90 2.54 2.69 13.95 62.35
5 17.40 0 0 0.63 0.20 0.89 0.39 80.48

[00119] EXAMPLE 3: Reduction roasting of the ore at 950°C
[00120] About 250 g of the representative NMD ore sample was fed to the RTF feeder whose dispensing rate was kept at about 15% (i.e., every 15 seconds the feeder will vibrate and feed equal amount of material into the furnace). H2 was used for maintaining the reduction atmosphere with a constant flow rate of about 80 l/ hr, while the reduction temperature was maintained at about 950°C. The angle of inclination of the RTF was kept at about one degree for maximizing the reduction time. The tube rotation speed of the RTF was kept constant at about 4 rpm. The reduction was performed for a period of about 2 hours.
[00121] Figure 8 shows the pictorial representation of the input sample and the reduced sample. The intensity of the green color of the reduced sample was found to have slightly increased, which could be because of the increase in the amount of MnO formed. This was further confirmed with the help of XRD characterization technique as shown in Figure 9. The XRD characterization results also showed a clear increase in intensity of the major MnO peak, which was consistent with the results reported in Figure 8.
[00122] EXAMPLE 4: Reduction roasting of the ore at 1050°C
[00123] About 250 g of the representative NMD ore sample was fed to the RTF feeder whose dispensing rate was kept at about 15% (i.e., every 15 seconds the feeder will vibrate and feed equal amount of material into the furnace). H2 was used for maintaining the reduction atmosphere with a constant flow rate of about 80 l/ hr, while the reduction temperature was maintained at about 1050°C. The angle of inclination of the RTF was kept at about one degree for maximizing the reduction time. The tube rotation speed of the RTF was kept constant at about 4 rpm. The reduction was performed for a period of about 2 hours.
[00124] Figure 10 shows the pictorial representation of the input sample and the reduced sample at about 1050°C employing H2 as reducing gas. The intensity of the green color of the reduced sample was found to have increased predominantly as compared to the previous examples, which again signified the increase in the amount of MnO formed. This was further confirmed with the help of XRD characterization as shown in Figure 11. The XRD results also showed a clear increase in intensity of the major MnO peak, which also indicated the increase in the amount of MnO formed.
[00125] Further increase in roasting temperature up to about 1100°C was also attempted but the amount of MnO formed was found to remain similar, thereby indicating the complete conversion of the NMD ore had already taken place at 1050°C. It was therefore concluded that increasing the temperature further could decrease the energy efficiency of the process.
[00126] The above experiment, further, was repeated employing CO as reducing gas for reduction roasting of the NMD ore. The XRD Rietveld analysis of the reduced sample at 1050°C using CO as reducing gas is depicted in Figure 12 shows that the method was able to efficiently reduce the manganese ore to more than 95% as obtained from XRD Rietveld analysis of the reduced sample at 1050°C using CO as reducing gas.
[00127] Between Examples 2-4, it was found that with increase in reduction temperature, the association of minor amounts of potassium with manganese ore was broken. Similarly, other NMD ore impurities were reduced to useful by-products – for example, goethite was reduced to metallic iron. By-products like metallic iron can be beneficiated easily, thereby facilitating the capability to improve the manganese oxide purity for direct battery application (Figure 13).
[00128] EXAMPLE 5: Reduction roasting of the ore at temperatures below 800°C
[00129] About 250 g of the representative NMD ore samples was fed to the RTF feeder whose dispensing rate was kept at about 15% (i.e., every 15 seconds the feeder will vibrate and feed equal amount of material into the furnace). H2 was used for maintaining the reduction atmosphere with a constant flow rate of about 80 l/ hr, while the reduction temperature was maintained at about 600°C. The angle of inclination of the RTF was kept at about one degree for maximizing the reduction time. The tube rotation speed of RTF was kept constant at about 4 rpm. The reduction was performed for a period of about 2 hours.
[00130] Results of the XRD analysis of the reduced ore is provided in Figure 14. Said figure shows that reduction roasting at 600°C leads to formation of Mn3O4, in minor amounts, in addition to MnO.
[00131] When the same experiment was repeated at temperatures between about 400°C to 600°C, it was found that Mn2O3 to Mn3O4 transformation was rapid at temperatures above 400°C. Thus, at reduction roasting temperatures below 600°C, a minor amount of Mn2O3 was formed along with MnO and Mn3O4.
[00132] EXAMPLE 6: Effect of reduction temperature on impurity levels
[00133] About 250 g of the representative NMD ore samples was fed to the RTF feeder whose dispensing rate was kept at about 15% (i.e., every 15 seconds the feeder will vibrate and feed equal amount of material into the furnace). H2 was used for maintaining the reduction atmosphere with a constant flow rate of about 80 l/ hr. The experiment was performed in 2 batches wherein the reduction temperature was maintained at about 800°C and 900°C, respectively. The angle of inclination of the RTF was kept at about one degree for maximizing the reduction time. The tube rotation speed of RTF was kept constant at about 4 rpm. The reduction was performed for a period of about 2 hours.
[00134] Figures 15 and 16 depict the XRD analysis of the formed manganese oxide after reduction roasting at 800°C and 900°C, respectively. A comparison of the two results shows that with an increase in temperature, MnO peak intensity increases along with suppression of the Fe peak. Therefore, with an increase in the reduction roasting temperature, the total amount of MnO formed increases, therefore suppressing the content of other impurities.
[00135] EXAMPLE 7: Effect of choice of reduction atmosphere
[00136] About 250 g of the representative ore samples were fed to the RTF feeder whose dispensing rate was kept at about 15% (i.e., every 15 seconds the feeder will vibrate and feed equal amount of material into the furnace). CO was used for maintaining the reduction atmosphere with a constant flow rate of about 80 l/hr, while the reduction temperature was maintained at about 1050°C. The angle of inclination of the RTF was kept at about one degree for maximizing the reduction time. The tube rotation speed of RTF was kept constant at about 4 rpm. The reduction was performed for a period of about 2 hours.
[00137] Figure 17 shows the XRD comparison of the reduced NMD samples at 1050°C using H2 and CO as reducing gas, respectively. The peak intensity of the major manganese oxide peak was higher when H2 gas was used as reducing gas.
[00138] 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.
[00139] 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.