Claims:We claim:
1. A method for manufacturing manganese ferroalloys from low grade manganese ores, said method comprising:
reduction roasting of the low-grade manganese ores to obtain pre-reduced roasted ores;

crushing of the roasted ores followed by magnetic separation to obtain Mn enriched roasted manganese ore fines;

briquetting the roasted manganese ore fines with binder and sludge to obtain reactive composite briquettes; and

smelting of the composite briquettes in a furnace to obtain the manganese ferroalloys.

2. The method as claimed in claim 1, wherein the reduction roasting of the low-grade manganese ores is carried out in a kiln at a high temperature of about 1000 °C.

3. The method as claimed in claim 1, wherein the roasted manganese ore fines comprise Mn at about 41 wt.% to about 5.1wt. %, SiO2 at about 5 to about 7 wt. %, Al2O3 at about 3 to about 6 wt.%, C at about 4 wt.% to 8 wt.% along with Mn:Fe ratio of about 2.8 to about 4.

5. The method as claimed in claim 1, wherein the roasted manganese ore fines have an average particle size less than 5 mm with a material density of about 3.5 gm/cm3 to about 4.5 gm/cm3 and bulk Vickers hardness of about 800 VHN to about 1200 VHN.

6. The method as claimed in claim 1, wherein the briquetting is an extrusion briquetting.

7. The method as claimed in claim 1, wherein the furnace is a submerged arc furnace.

8. The method as claimed in claim 1, wherein the composite briquettes use up to 15 % of the ore burden in the submerged furnace.

9. The method as claimed in claim 1, wherein the composite briquettes reduce carbon rate by 5 % to 10 % during smelting in the submerged arc furnace.

10. The method as claimed in claim 1, wherein the sludge improves chemical and physical properties of the briquettes.

11. A composite briquette comprising roasted manganese ore fines and binder along with sludge.

12. The composite briquette as claimed in claim 11, wherein the composite briquette comprises binder at about 5 wt. % to about 7 wt.%, moisture at about 14 wt.% to about 18 wt.%, the sludge at about 20 wt. % to about 45 wt.% and balance being roasted manganese ore fines.

13. The composite briquette as claimed in claim 11, wherein the roasted manganese ore fines are obtained by reduction roasting of low-grade manganese ores and comprise Mn at about 41 to about 51wt%, SiO2 at about 5 to about 7 wt. %, Al2O3 at about 3 to about 6 wt.% and C at about 4 to 8 wt.% along with Mn:Fe ratio of about 2.8 to about 4.

14. The composite briquette as claimed in claim 11, wherein the sludge is a Gas Cleaning Plant (GCP) sludge and comprises Mn at about 40 wt.% to about 46 wt.%, Fe at about 4 wt.% to about 7 wt.%, SiO2 at about 10 wt.%, Al2O3 at about 5 wt.% and C at about 3 wt.% along with Mn: Fe ratio of about 5 to 10.16.

15. The composite briquette as claimed in claim 11, wherein the composite briquette comprises the roasted manganese ore fines to sludge in a ratio of about 1:1 to 4:1.

16. The composite briquette as claimed in claim 11, wherein the binder is selected from a group comprising cement, bentonite, molasses, lime and combination thereof.

17. The composite briquette as claimed in claim 11, wherein the composite briquette without the sludge has a Cold Compressive Strength of about 90 kgf/briquette to about 170 kgf/briquette and the composite briquette with the sludge has a Cold Compressive Strength of about 164 kgf/briquette to about 190 kgf/briquette.

18. The composite briquette as claimed in claim 11, wherein the composite briquette without the sludge has a Briquette Length of about 41 mm to about 54 mm and the composite briquette with the sludge has a Briquette Length of about 43 mm to about 66 mm.

19. The composite briquette as claimed in claim 11, wherein the composite briquette without the sludge has a decrepitation index (DI) ranging from about 10 % to about 11.8 % and the composite briquette with the sludge has a decrepitation index (DI) ranging from about 10 % to about 13%.

20. The composite briquette as claimed in claim 11, wherein the composite briquette without the sludge has a Drop Index ranging from about 71 % to about 85 % and the composite briquette without sludge has a Drop Index ranging from about 92 % to about 96 %.

21. The composite briquette as claimed in claim 11, wherein the composite briquette without the sludge has an Abrasion Index ranging from about 1.38 to about 2.53and the composite briquettes without sludge has an Abrasion Index ranging from about 3 % to about 5 %.
, Description:
TECHNICAL FIELD

The present disclosure relates in general to the field of material science and metallurgy. Particularly, but not exclusively, the present disclosure relates to a method of manufacturing manganese ferro alloys employing roasted manganese ore fines. Further embodiments of the disclosure relate to composite briquette(s) comprising roasted manganese ore fines.

BACKGROUND OF THE DISCLOSURE

Manganese alloys are used mainly in steel making. Manganese alloys, such as Ferromanganese (Mn: 65 wt.% to 80 wt.%, C: 6 wt.% to 8 wt.%), Silicomanganese (Si: 14 wt.% to 28% wt.%, Mn: 50 wt.% to 74 wt.% %), Spiegeleisen (Mn: 6wt.% to 30 wt.%, C: 4.5wt.% to 6.5 wt.%) are used for these purposes. Selection of alloy for steel making depends on purpose (deoxidising agent, alloying agent, cleansing) and targeted grade of steel (low carbon, medium carbon, high and ultra-high carbon steel). These alloys may be produced by using a suitable ore blend of desired Mn content (36 wt.% to 51 wt.%) and Mn/Fe ratio (2.5 to 7) depending upon the requirement of targeted alloys and are mostly prepared by carbothermic reduction of manganese ores in a submerged arc furnace using suitable amount of fluxes.

It is known that the higher Mn/Fe ratio (>3.5) ores are widely preferred in the ferroalloy making, however the desired Mn/Fe ratio may be maintained only by blending of low and high Mn/Fe ratio ores currently. The selective mining of high grade ores for this purpose caused dearth of high-grade resource and hence, the mining industry is searching for a suitable beneficiation technique to upgrade the low Mn/Fe ratio ores.

In the prior art [US5270022; US3399054; CN103667833A], roasting of high-grade manganese carbonate and oxide ores is commonly employed in manganese compound making. The high-grade manganese ores are roasted to convert high Mn oxides (MnO2) into lower manganese oxides (MnO) which may be easy to leach out for producing manganese compounds. On the other hand, low grade ferruginous manganese ores are roasted to convert paramagnetic iron oxides (Fe2O3, FeO(OH)) into ferromagnetic iron oxides for easy magnetic separation of iron phases from manganese bearing phases. However, reduction roasting of low-grade ferruginous manganese ores and process of utilization of roasted manganese ores fines in a submerged arc furnace for ferromanganese making is not yet fully scaled up mainly due to technoeconomic issues. Currently, the available submerged arc furnace-based ferroalloy making technologies mainly use lumpy ore feed and can take only limited quantity of fines in the feed burden mainly due to adverse impact of fines on gas permeability inside the furnace. Further, the conventional powder agglomeration processes such as palletisation, briquetting and sintering have been used for the utilization of natural manganese ore fines; However, the conventional sintering process cannot use the fines without proper blending of coarser fractions. Roasted fines as well as fine particle surfaces are heat treated and become inactive and show poor agglomeration, granulation and melting characteristics during sintering. Also, most of the developed agglomeration techniques are made for oxide fines and a blend of fines of diverse properties is difficult to convert into an agglomerate or briquette.

Hence, there is a need for an economical and technically viable approach for utilizing low grade manganese ores and ore fines in manufacturing of manganese ferroalloys.

The present disclosure is directed to overcome one or more limitations stated above or any other limitation associated with the prior arts.

SUMMARY OF THE DISCLOSURE

One or more shortcomings of the prior art are overcome by method and a product as disclosed and additional advantages are provided through the method as described in the present disclosure.

Additional features and advantages are realized through the method and composite of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

In a non-limiting embodiment of the present disclosure, a method for manufacturing manganese ferroalloys from low grade manganese ores is provided.

In an embodiment of the present disclosure, the method involves reduction roasting of the low-grade manganese ores to obtain pre-reduced roasted ores. Roasted ores are then crushed, followed by magnetic separation to obtain Mn enriched roasted manganese ore fines. Further, the method involves briquetting the roasted manganese ore fines with binder and sludge to obtain reactive composite briquettes; The composite briquettes are smelted in a furnace to obtain the manganese ferroalloys.

In an embodiment of the present disclosure, the reduction roasting of the low-grade manganese ores is carried out in a kiln at a high temperature of about 1000 °C.

In an embodiment of the present disclosure, the roasted manganese ore fines comprise Mn at about 40 wt.% to about 51 wt%, SiO2 at about 5 wt. % to about 7 wt. %, Al2O3 at about 3 to about 6 wt.%, C at about 4 wt.% to about 8 wt.% along with Mn:Fe ratio of about 2.8 to about 4.

In an embodiment of the present disclosure, the roasted manganese ore fines have an average particle size less than 5 mm with a material density of about 3.5 gm/cm3 to about 4.5 gm/cm3 and bulk Vickers hardness of about 800 VHN to about 1200 VHN.

In an embodiment of the present disclosure, the briquetting is an extrusion briquetting.

In an embodiment of the present disclosure, the furnace is a submerged arc furnace.

In an embodiment of the present disclosure, the composite briquettes use up to 15 % of the ore burden in the submerged furnace.

In an embodiment of the present disclosure, the composite briquettes reduce carbon rate by 5 % to 10 % during smelting in the submerged arc furnace.

In an embodiment of the present disclosure, the sludge improves chemical and physical properties of the briquettes.

In yet another non-limiting embodiment of the present disclosure, a composite briquette comprising roasted manganese ore fines and binder is disclosed.

In yet another non-limiting embodiment of the present disclosure, a composite briquette comprising roasted manganese ore fines and binder along with sludge is disclosed.

In an embodiment of the present disclosure, the composite briquette comprises binder at about 5 wt. % to about 7 wt.%, moisture at about 14 wt.% to about 18 wt.%, sludge at about 20 wt. % to about 45 wt.% and balance being roasted manganese ore fines.

In an embodiment of the present disclosure, the roasted manganese ore fines are obtained by reduction roasting of low-grade manganese ores and comprise Mn at about 41 wt.% to about 51 wt%, SiO2 at about 5 to about 7 wt. %, Al2O3 at about 3 to about 6 wt.% and C at about 4 wt.% to 8 wt.% along with Mn:Fe ratio of about 2.8 to about 4.

In an embodiment, the sludge is a Gas Cleaning Plant (GCP) sludge and comprises Mn at about 40 wt.% to about 46%, Fe at about 4 wt.% to about 7 wt.%, SiO2 at about 10 wt.%, Al2O3 at about 5 wt.% and C at about 3 wt.% along with Mn: Fe ratio of about 5 to 10.16.

In an embodiment of the present disclosure, the composite briquette comprises the roasted manganese ore fines to sludge in a ratio of about 1:1 to 4:1.

In an embodiment of the present disclosure, the binder is selected from a group comprising cement, bentonite, molasses, lime and combination thereof.

In an embodiment of the present disclosure, the composite briquette without the sludge has a Cold Compressive Strength of about 90 kgf/briquette to about 170 kgf/briquette.

In an embodiment of the present disclosure, the composite briquette without the sludge has a Briquette Length of about 41 mm to about 54 mm.

In an embodiment of the present disclosure, the composite briquette without the sludge has a decrepitation index (DI) ranging from about 10 % to about 11.8 %.

In an embodiment of the present disclosure, the composite briquette without the sludge has a Drop Index ranging from about 71 % to about 85 %.

In an embodiment of the present disclosure, the composite briquette without the sludge has an Abrasion Index ranging from about 3 % to about 5 %.
In an embodiment of the present disclosure, the composite briquette with the sludge has a Cold Compressive Strength of about 164 kgf/briquette to about 190 kgf/briquette.

In an embodiment of the present disclosure, the composite briquette with the sludge has a Briquette Length of about 43 mm to about 66 mm.

In an embodiment of the present disclosure, the composite briquette with the sludge has a decrepitation index (DI) ranging from about 10 % to about 13%.

In an embodiment of the present disclosure, the composite briquette with the sludge has a Drop Index ranging from about 92 % to about 96 %

In an embodiment of the present disclosure, the composite briquette with the sludge has an Abrasion Index ranging from about 1.38 to about 2.53

It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.

The foregoing summary is illustrative only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the figure and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE

Figure.1 is a flowchart illustrating a method for manufacturing the manganese ferro alloys from low grade manganese ores, according to an exemplary embodiment of the present disclosure.

The figure depicts embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the method illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent methods do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figure. It is to be expressly understood, however, that the figure is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

In the present disclosure, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figure and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method/product that comprises a list of acts/features or components does not include only those but may include other acts/features or components not expressly listed or inherent to such method/product. In other words, one or more acts/features or components in a method/product proceeded by “comprises”, “comprising” does not, without more constraints, preclude the existence of other acts or additional acts/additional features or components which are not expressly listed or inherent.

Embodiments of the present disclosure discloses a method for manufacturing manganese ferroalloys from low grade manganese ores and a composite briquette comprising roasted manganese ore fines and binder along with or without sludge.

Accordingly, the method involves reduction roasting of the low-grade manganese ores to obtain pre-reduced roasted ores. Roasted ores are then crushed, followed by magnetic separation to obtain manganese enriched roasted ore fines. Further, the method involves briquetting the roasted manganese ore fines with binder in the presence or absence of sludge to obtain reactive composite briquettes. The composite briquettes are smelted in a furnace to obtain the manganese ferroalloys.

The composite briquette without the sludge has a Cold Compressive Strength of about 90 kgf/briquette to about 170 kgf/briquette, Briquette Length of about 41 mm to about 54 mm, a Decrepitation Index (DI) ranging from about 10 % to about 11.8 %, a Drop Index ranging from about 71 % to about 85 % and an Abrasion Index ranging from about 3 % to about 5 %. Addition of sludge greatly improves the briquette’s physical properties and there by improve the process of ferro manganese alloy making. The composite briquette with the sludge has a Briquette Length of about 43 mm to about 66 mm, a Cold Compressive Strength of about 164 kgf/briquette to about 190 kgf/briquette, a Decrepitation Index (DI) ranging from about 10 % to about 13%, a Drop Index ranging from about 92 % to about 96 % and an Abrasion Index ranging from about 1.38 to about 2.53. The composite briquettes use up to 15 % of the ore burden in the submerged furnace. Further, the composite briquettes reduce carbon rate by 5 % to 10 % during smelting in the submerged arc furnace.

The method is now described with reference to the flowchart blocks as depicted in Figure 1 and is as below. The order in which the method is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the scope of the subject. The method is particularly applicable to the manganese ferro alloys from low grade manganese ores and it may also be extended to other type of manganese ferro alloys prepared from different grade of manganese ores as well.

The method of manufacturing the manganese ferro alloys from low grade manganese ores comprises steps of: reduction, crushing followed by magnetic separation, briquetting and smelting. The various processing steps are described in their respective order below:

At block 101, the low grade manganese ores are subjected to reduction roasting process in order to remove the excess iron content by converting paramagnetic iron phases (Fe2O3, FeO(OH) into ferromagnetic phases [Fe2O3, FeO, Fe (m)]. The reduction roasting of the low-grade manganese ores is carried out in a kiln at a high temperature of about 1000 °C. Reduction roasting and cooling of the natural minerals, oxides may impart various changes in physicochemical properties of these ores, such as change in size, chemical composition, phase composition, brittleness, surface energy, zeta potential, moisture content, porosity, etc.

Now, reference is made to block 102 which involves crushing and magnetic separation process. In an embodiment, crushing involves powdering of the reduction roasted ores into ore fines. Ore fines are fed into magnetic separator equipment for the separation of ferromagnetic phases. After magnetic separation process, Mn enriched roasted manganese ore fines depleted with Fe content are obtained. The roasted manganese ore fines comprise MnO, Mn2O3, Mn3O4, Fe(m), FeO, Fe3O4, Fe-MnO, SiO2, Al2O3 and unburnt coal. Mn at about 41 wt.%, to about 51%, SiO2 at about 5 to about 7 wt. %, Al2O3 at about 3 to about 6 wt.%, C at about 4 wt.% to 8 wt.% along with Mn:Fe ratio of about 2.8 to about 4. These roasted manganese ore fines have an average particle size less than 5 mm with a material density of about 3.5 gm/cm3 to about 4.5 gm/cm3 and bulk Vickers hardness of about 800 VHN to about 1200 VHN. These properties may be different from the conventional manganese ores which are mostly composed of MnO2 and Fe2O3 phases, with relatively lower VHN number and without any unburnt coal.

At block 103, the roasted manganese ore fines are combined with binder and sludge to obtain reactive composite briquettes. The briquettes are obtained by extrusion briquetting.

At block 104, the composite briquettes are smelted in a furnace to obtain manganese ferroalloys.

Further embodiments of the present disclosure will now be described with examples on the methodology for effective utilization of roasted manganese ore fines in the manufacture of ferroalloys and a composite briquette comprising these roasted manganese ore fines.

Example 1: Characterization of roasted manganese ores
The roasted manganese ores fines (Mn :41-51%, Mn/Fe :2.8-4%; SiO2: 5-7%, Al2O3 :3-6%, C :4-8%) of <5mm were collected from manganese ore roasting plant for the trials. Chemical and mineralogical analysis of the samples were carried out and found that these fines mainly contain MnO, Mn2O3, Mn3O4, Fe(m), FeO, Fe3O4, Fe-MnO, SiO2, Al2O3 and unburnt coal. Particle size D80 was 3mm and ~ 50 % material was below 1mm. Density of the material was measured and found that it varies between 3.5 to 4.5 gm/cc where the variation is contributed by unburnt coal and metallic phases. The bulk vickers hardness of the samples were measured and reported between 800-1200 VHN. These properties are different from the conventional manganese ores which are mostly composed of MnO2 and Fe2O3 phases, with relatively lower VHN number and without any unburnt coal.

Example 2: Selection of suitable feeding process and comparative analysis
The methodology of the present disclosure was developed based on the trials and test work of three different phases, i.e. (a) Direct use of fines, (b) sintering of fines, (c) composite briquetting of fines. It was observed that the conventional briquetting methodology is not as effective for these fines and extrusion briquetting process was developed along with the suitable binder, quantity, particle size etc. All the three techniques were compared during ferroalloy making and found that the developed extrusion briquetting based methodology is most effective to utilize the fines. These fines were first fed directly to the submerged arc furnace as a feed blend up to 5- 10 % of the total ore in the burden. Even though the ores were roasted and do not show any decomposition phenomena, it was observed that when percentage of fines in the furnace feed increased more than 8 %, it started impacting the gas permeability and slight crust formation indicators were observed. So, agglomeration process was tried instead of using these materials as fines.

The fines were charged to a pot sintering plant along with the natural ore fines. The roasted fines were added 5 to 15 % of the ore fines feed to the pot sinter, but the heat treated/roasted fines behave differently in the pot and 30 to 40 % of these fines reported into recycling fines mainly due to fine size and higher melting point which impacted liquid phase formation during sintering. So, the results indicated that the roasted fines do not sinter efficiently in a conventional pot sinter used at ferroalloy plants and need a more suitable technology for effective utilization.

Extrusion briquetting is known method for agglomeration of natural ore fines, however it's success depends largely on the material fineness, plasticity, moisture content and binder dosage. During the process, the roasted fines showed different characteristics than the conventional ore fines. Further, ferromanganese plant gas cleaning plant sludge was added during the process which not only increases the fineness of roasted ore but improves plasticity as well. Different ore to sludge ratios (1:1 to 1:4) have been tried along with different binders [cement (4-8%), bentonite (1-2%), molasses (5-10%), lime (1-2%), etc]. Lab scale extrusion briquetting studies have been carried out and cold compressive strength of the briquettes was measured as shown in table 1. From the table, it can be seen that good quality extrusion briquettes can be made using ~5 % cement, 1 % bentonite, 15-18% water and addition of 20-30% of sludge in the roasted fines. So, the plant trials were conducted with the proposed combination. A comparative analysis of all these methods are given in Table 2.

Table 1: Cold compressive strength of composite briquettes produced in different conditions.

Test-1 Test-2 Test-3 Test-4 Test-5 Test-6
Sample % % % % % %
Roasted Mn Ore 95 94 93 94 64 49
GCP Sludge 0 0 0 0 30 45
Cement 4 5 6 5 5 5
Bentonite 1 1 1 1 1 1
Moisture 14 15 16 15 17 18
CCS (Avg., Kgf) 90 164 170 164 184 190
Green strength (kgf) 11.3 12 15.8 12.2 16 16
Briquette length (mm) 41 43 54 43 62 66

Table 2: Comparative analysis of different methods for utilization of roasted Mn ore fines

Material form Properties Process Performance Observations
Fines Size: <3mm
Free flowing
Low moisture and no decomposition 5-10 % of feed charged

Crust formation after 10 % replacement of ore in the burden It is a known method. However, better properties of the roasted fines give marginal improvement.
Sinter Size: <3mm
Tumbler Index: 60-70 % 5-10 % natural ore fines replaced by roasted fines in sinter bed.

Poor sinterability of fines mainly due to heat treated surface.

Higher recycling fines Sintering is a known process to use natural ore fines, but sintering of roasted fines need improvement and require additional steps such as granulation, etc.
Conventional Briquettes Cold Compressive Strength: 50-70 kgf/briquette
Drop Index: 85
Used the conventional binder – Molasses and lime.

Replaced 10-15 % ore using the briquettes.

Generate more handling fines: 25%

High Decrepitation Index :14-16.2 %
The process is known for natural fines; however, it does not perform well mainly due to different characteristics of roasted fines such as heat-treated surface, mixed carbon, etc.
Extrusion Briquettes
(Roasted fines only) Binders: Cement
(5%)+ Bentonite (1%)
PSD: <3mm, (D80:1.5mm)
Briquette Strength :90-170kgf/briquette

Green strength: 11-14 kgf/briq.

Briquette length: 41-54mm

Low Decrepitation Index :10-11.8 %

Extrusion briquetting of roasted pre-reduced Mn ore fines is difficult mainly due to poor plasticity, however the briquettes produced show moderate strength for use.

These are composite briquettes which contain reductant and fluxing agent
Extrusion Briquettes
(Roasted fines+ GCP sludge) GCP sludge :30 %
Binder: Cement
(5%)+ Bentonite (1%)
PSD: <3mm, (D80:0.7mm)
Briquette Strength :164-190kgf/briquette

Green strength: 12-16 kgf/briq.

Briquette length: 43-66mm

Low Decrepitation Index :10-12.2 %

Drop Index :>92 % at commercial scale

Addition of GCP sludge in roasted fines increases the flow and plasticity of material and briquettes of good strength and length can be produced by this process.

Briquettes contain reductant and fluxing agent which help in quicker reduction.

Example 3: Extrusion briquetting of fine blends
Extrusion briquetting trials were carried out using blend of 165 tons of roasted manganese ore fines and 50 tons of GCP sludge fines using a 20 tph plant capacity machine. The sludge (D80: 0.15mm) and roasted fines (D80: 3mm) have been blended into 1:4 and moisture content was kept between 15-18 % to achieve the desired size and quality composite briquettes. Cement and bentonite mixture were used as binder and three different levels were kept (5, 6, 7 %). Quality of green briquettes were measured in terms of flow of composite briquettes from extruder, length of briquette coming out from extruder and average length of briquette at yard. These were further tested in the furnace for ferroalloy making.
(a) Chemical analysis of extrusion blend: The chemical analysis of different materials used in the blend is given in table 3. It shows that the average Mn in blend was ~40% with Mn/Fe :3.8 which is suitable to use as a feed blend in ferromanganese making.

Table 3: Composition of roasted ore fines blend for extrusion briquetting

Materials Mn, % Fe, % SiO2 , % Al2O3, % CaO, % C, % Mn/Fe
Roasted fines 40.47 12.87 10.25 7.16 7 3.14
GCP sludge 46.12 4.54 9.63 5.14 3 10.16
41.78 10.93 10.11 6.69 5 3.82
Binder - 3.00 20.00 5.51 66 0
W. Avg. Composition 39.79 10.56 10.58 6.63 3.14 4.8 3.77

(b) Extrusion and green strength: Briquettability of roasted fines and sludge mixture (4:1) is good to produce suitable quality green briquettes for handling purposes at the yard. The tested blend required relatively more moisture for briquetting than the conventional sludges. The composite briquettes of 10 to 150mm length were made using different binders and the average composite briquette length was 50mm which is like the manganese ore lumps used during the ferroalloy making. The average drop strength of green briquette was >5 before it fully crumbles into <10mm particles. Roasted fines can be successfully briquetted along with 25 % sludge using ~6% binder and 16% moisture. Sludge addition optimized the chemistry and plasticity to produce better quality composite briquettes.

(c) Characterisation of Composite Briquettes: The drop index of the composite briquettes was tested and found it to vary between 92 to 97 % and generates only < 2 % material of <0.5mm which is considered a good index value to use in the submerged arc furnace as shown in Table 4. Cold compressive strength of the briquettes was tested and found that it improves with binder dosage and varies between 265 kgf to 367 kgf. It was seen that the use of 7 % binder dosage is able to produce composite briquettes of highest strength, however there was enough strength in the composite briquettes produced using 5 and 6 % binder dosage without a significant difference as shown in Table 5.

Table 4 : Drop Index of compiste briquettes of roasted Mn ore fines

Binder Drop Index (+6mm) Abrasion Index (-0.05mm)
Blend (5 %) 92.77 2.53
Blend (6 %) 93.71 2.11
Blend (7 %) 96.62 1.38

Table 5 : Cold Compressive Stregth (CCS) of compiste briquettes

Binder CCS (Min) CCS(Max) CCS(Avg.)
Blend (5 %) 55 254 150
Blend (6 %) 157 379 250
Blend (7 %) 252 397 325

The most critical property is Decrepitation Index of composite briquettes which control the formation of fines during heating/smelting of composite briquettes in the submerged arc furnace. The samples of known weight (250gm) were heated in a muffle furnace from room temperature to 800°C and were kept for 2 hours 800°C in normal atmosphere. The heating causes the water evaporation, manganese oxide decomposition and reduction of manganese and iron oxides. It was seen that roasted composite briquettes showed lowest decomposition whereas composite briquettes with natural fines showed maximum decomposition mainly due to decomposition and reduction of higher manganese and iron oxides which were not present in the roasted fines. Similar performance was observed in the furnace also and the results are shown in Table 6.

Table 6 : Decripitation Index of compiste briquettes

Ore Types %, DI Index
Mn Ore lumps 13.20
Brqieuttes (Natural Ore fines) 16.2
Briquettes (roasted fines) 11.8
Brqieuttes (Sludge+roasted fines) 12.2

Example 4: Smelting reduction of composite Briquettes in Submerged Arc Furnace
In the conventional process, the ores of different composition are blended and charged in the furnace along with coke and fluxes. So, composite briquettes were charged in the ore and in different proportion to replace the natural ores. These composite briquettes were having carbon and CaO also as an additional ingredient than the natural ores. Therefore, these elements were accounted during preparation of burden composition sheet. The briquette replaced the 5, 7.5, 10, 12.5 and 15 % of the ore in the burden during different tests of two commercial furnaces of 9 &15 MVA and data were measured for 3 shifts for each case. Various process parameters were measured and controlled to minimize the deviation in process and product grades due to use of briquettes in the burden. Process conditions were monitored and controlled to achieve the best results (Telphur fines and S, P, etc. were also measured to avoid any unwanted impact).
Example 5: Regulating the furnace operation
It was observed that addition of briquettes did not increase the fines generation in the handling system as well as gas cleaning system throughout the trials. The briquettes were made of roasted ore fines, GCP sludge and coal which make them a special feed for the furnace which have different properties such as porosity, lower oxides, metallic iron, coal, CaO, etc than the ore lumps. These properties improved permeability and conductivity of burden to improve the smelting-reduction characteristics. Addition of briquettes in the burden resulted in better smelting reduction and smooth furnace operation. It could able to reduce the carbon rate by 5 to 10 %. It was accepted that process conditions (Power: ~2650 kWh/ton & Coke rate :125 kg/batch, production: 59 & 76 t/tap) and product grade (Mn :68-71 % & MnO: 27-35%) remained as per normal operation. The process details are given in table 7.
Table 7: Process performance during usage of roasted Mn ore fines in a submerged arc furnace

Briquetting Trials – Furnace 1 (9 MVA)
Metal Slag Power kWh/ton Coke Rate (kg/ batch, Avg)
Day Mn% P% Si% MnO% SiO2% Fe2O3% Al2O3% CaO% MgO%
Normal Operation Min 68.18 0.27 0.26 27.00 23.12 1.28 21.42 10.89 5.35 2630 120
Max 70.75 0.30 1.00 34.99 25.76 1.80 23.47 11.48 6.63 2670 130
Avg 69.49 0.28 0.46 31.42 24.10 1.51 22.33 11.18 5.77 2650 125
1 0.0% 69.29 0.27 0.87 28.40 25.02 1.74 23.06 11.47 6.19 2644 126.5
2 5% 70.39 0.27 0.54 30.48 24.86 1.76 22.78 11.51 6.10 2644.0 118
3 7.5% 69.60 0.26 0.66 31.35 23.84 1.4 22.3 11.14 5.6 2667.0 117
4 10.0% 68.82 0.26 0.64 29.33 24.66 1.56 22.9 11.35 6.05 2638.0 119
5 12.5% 69.98 0.26 0.46 28.79 24.84 1.6 23 11.38 6.1 2654.0 119.5
6 15.0% 71.10 0.26 0.90 29.00 25.1 1.68 23.1 11.47 6.35 2657.0 118

Equivalents:

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.


While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. Various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Referral Numerals

Referral Numerals Description
101-104 Flowchart blocks
101 Reduction roasting
102 Crushing and magnetic separation
103 Briquetting
104 Smelting