FIELD OF THE INVENTION
The present invention relates to an improved process for production of high-
carbon ferromanganese alloy. The present invention further relates to a new and
effective blend of raw materials used in the process.
BACKGROUND OF THE INVENTION
High carbon ferromanganese alloy contains Mn: 70-75%, C: 6-8%, Si: 0.3% and
P: 0.2-0.35%. The ferromanganese alloy is used as an alloying element during
production of steel. It is also used for deoxidation and desulphurization of steel.
The alloy is commercially produced by carbothermic smelting reduction of
manganese ores in submerged arc furnaces. In the smelting process, the lumpy
manganese ores, reductant (coke) and flux (dolomite/limestone) are charged in
the submerged arc furnace. After smelting by coke, oxides of Mn, Fe, P and Si
get reduced and form molten ferromanganese. Oxides of gangue minerals (AI203,
Si02, Mg0, etc) combine with fluxes to form slag. Part of the Manganese oxide
also combines with the slag. The basicity of the slag plays a critical role in the
overall slag and metal behavior inside the furnace. The operational performance
of the SAF depends on the gas-slag-metal reactions and equilibrium in the
various zones of the furnace. The process yield, power consumption, and coke
rate of the process depend on the complex reactions taking place inside different
zones in the submerged arc furnace.

The manganese ores in India vary widely in their content of manganese, iron,
silica, alumina, lime, magnesia, and phosphorus. The manganese to iron ratio is
a very important parameter which decides the quality of the ore and the
proportion of feed blend to produce a particular grade of the alloy. Another
crucial constituent of the ore is its silica content. Silica present in the ore plays a
very important role in maintaining proper slag chemistry, temperature and
overall separation of slag and metal from the furnace. The right composition of
silica in the feed blend is critical for operational efficiency and productivity. The
manganese ores of having low silica content (0.5-3%) is not suitable to obtain
desired composition of 6-7% of silica in the feed blend. Accordingly, to prior art,
siliceous ore is used as a source of silica input for the ferromanganese furnaces
which increases production cost of high-carbon ferromanganese alloys. In brief,
the disadvantages of prior art processes for production of ferromanganese alloys
are:
The ore blend for the production of high-carbon ferromanganese requires 6-7%
silica. Silica is a very important component which affects the gas-slag-metal
equilibrium in the furnace. The basicity, viscosity and the overall separation of
slag and metal is affected by the silica composition in the slag. The silica also
affects metal recovery, coke consumption and power consumption in the
furnace. The ferromanganese producers in the Odisha region meet this silica
requirement by purchasing high-silica manganese ores from external sources.

This ore comprises a major chunk of their total ore requirement. The high cost of
this ore, combined with the increasing costs of coke and power increases the
overall cost of production.
Problems with the Prior Art production technique of ferromanganese alloy.
1. Depletion of high grade and high-silica manganese ores in India.
2. Low silica content of commonly found manganese ores in India.
3. Limited availability of high-silica ores in India.
4. High cost of siliceous ores including transportation cost.
5. High cost of production due to high coke and power costs.
6. High phosphorous content in the alloy.
7. Re-processing, handling and storage of slag and associated reject
leading to environment degradation.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved process for
production of high-carbon ferromanganese alloy in which a perfect blend of
quartz, high-Mn0 slag along with low-silica ore is used for ferromanganese
production process.
Another object of the invention is to propose an improved process for
production of high-carbon ferromanganese alloy which reduces the cost of
production of the alloy.

A still another object of the invention is to propose an improved process for
production of high-carbon ferromanganese alloy which reduces power
consumption and carbon consumption in the production process of the alloy.
A further object of the invention is to propose an improved process for
production of high-carbon ferromanganese alloy which allows internal
recycling of ferromanganese slag for its effective disposal and value creation.
A still further object of the invention is to propose an improved process for
production of high-carbon ferromanganese alloy which reduces environmental
pollution by lessening carbon emissions from the alloy production process.
SUMMARY OF THE INVENTION
The invention primarily focuses on the re-engineering of the prior art process
of production of high-carbon ferromanganese alloys to include high-Mn0 slag
and quartz into the raw material blend so as to replace the high-silica
manganese ores. Process chemistry modifications have correspondingly been
made to ensure that the composition of Mn0-Si02-AI203 phases is such that
the slag is at its lowest liquidus temperature.
High-silica slag (Mn: Fe=25, Si02: 25-30%) and quartz (silica: 95-98%). A
substantial reduction in consumption of high-silica ore has been achieved by
use of quartz and slag. The MnO content in the molten slag has gone down
from the earlier 35-37% to 32-34% because of higher silica input. The
electrode

Penetration has been increased from 1000 mm earlier to 940 mm so as to
ensure higher silica recovery from quartz and slag. The temperature of the
molten slag and metal are also higher by an average of 20°C. To reduce
manganese vapour losses from the slag, the tapping cycle has been
restructured from 12 MWH to 10.5-11MWH. This has also been done as the
molten slag reaches the liquidus stage at a faster rate. The temperatures of
the top zone of the furnace, waste gas and furnace auxiliaries have also
remained largely unaffected by this. The throughput of the furnaces has
increased because of a higher smelting rate. The feeding of quartz (Si02:98%)
has reduced the consumption of high silica medium grade ore (Mn: 30-40%,
silica: 5-15%) and increase the consumption of high manganese-bearing
materials thereby increasing furnace throughput.
According to the invention, for production of high-carbon ferromanganese
alloy having manganese: 70% carbon: 6-7%, silicon: 0.35% phosphorous:
0.25%. a blend of quartz and high-MnO slag are used in a blend
composition:-

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a process flow diagram of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In the production of ferromanganese alloys, silica plays a very critical role in the
following parameters- slag chemistry and basicity, molten metal and slag
behaviour and their flow out from the submerged arc furnace. According to the
prior art, to ensure a silica content of 6-7% in the ore blend, high cost siliceous
ore having Mn: 25-45% and Si02: 20-35% and costs 3-4 times more than
commonly available ore is used in production of ferromanganese alloy.


The composition of slag plays a very important role in the overall smelting
process. The ideal composition of slag is given in Table 2.



However a number of operational difficulties were encountered during the initial
experiments:

Insufficient recovery of silica from quartz was leading to silica deficiency in the
furnace. This led to problems of slag-metal separation, slag boil, high
temperatures of shell and water cooled auxiliaries. Crust formation inside the
furnace leading to higher fines generation, problems, with the gas cleaning
system and higher coke and energy consumption.
Thereafter, numerous thermodynamic computations and laboratory studies were
carried out to study the smelting reduction reactions of feed blends with different
sources of silica and composition. Characterization studies of different ores were
carried out to study the phase compositions and the phase association. The
decomposition of the ores indifferent temperatures depends hugely on it.
Decrepitation test of ores from different mines was done to ensure that the ores
which were being fed to the furnace showed less than 10% decrepitation . Ores
from the mines which consistently showed more than 10% decrepitation were
rejected.
High temperature studies of quartz and slag were carried out to understand the
silica recovery at different temperatures.
Reducibility tests and thermo-gravimetric analyses of slag were also done.
After sufficient data were collected and opportunities were collected and
opportunities mapped, the plant trials were undertaken. Firstly, high-Mn0 slag
was tried with siliceous ore.

Feed Blend: Captive Mn ores. Purchased high-silica ore, high-Mn0 slag

Trials with various sizes (10-80, 10-60, 10-50 mm) carried out. The right
percentage of slag in the burden was then established. The tapping consumption
was accordingly fine-tuned. However, higher amount of alumina in the slag
resulted in the precipitation of MnA1204 spinel phase which in turn increased
slag viscosity and liquidus temperature.

This required a higher silica input to dissolve the spinels. Thus, there wasn't a
substantial difference in the ore consumption of costly siliceous ore, and thus
quartz, as a source of silica was planned to be tried out along with high-silica
ore.
The feed blend was prepared accordingly.


Quartz of different sizes (10-60, 6-25, 10-50 mm) were tried out. As the
dissociation of quartz lumps in the slag, requires a higher temperature and
constitutes sluggish process, electrode penetration was changed for proper slag
chemistry and temperature. The recovery of silica from quartz was a matter of
concern and the basicity and fluidity of slag were closely monitored. A few
problems surfaced again. There was crust formation inside the furnace along
with breakdowns in the gas cleaning system, problems with slag-metal
separation etc. Thus, though a substantial amount of silica was coming in, quartz
by itself brought in a number of concerns.
The charging of high-Mn0 slag provided the advantages like high Mn:Fe ratio,
high silica and manganese recovery, lower liquidus temperature of slag, lower
specific power consumption. The disadvantages were its high alumina content
and limited scope of replacement of high-silica ore. The use of quartz had the
advantages of it being rich in silica (>97%) and thus, a small fraction of the
batch size would be occupied by it, providing more opportunities to feed higher
manganese input into the furnace. It would not act as the primary source of
silica but would supplement the silica from other sources like slag and ore.
Thus both quartz and high-Mn0 slag were blended with high-silica ore and
charged into the furnace.


Trials were carried out with various electrode-penetration levels, tapping-
consumption durations and Mn0 levels in slag. The trials continued till the
process had been stabilized. According to the invention, the furnaces are now
operable with a blend of 5% purchased high-silica ore, 8% slag and 3% quartz
per batch of feed as compared to prior art level of 19% high-silica ore.

Thus on a comparative basis, the data before the use of quartz and siag and
after its use has been provided below:


ADVANTAGES OF THE INVENTION
1. Reduction in consumption of high-silica ore by 50% on a year-on-year
basis.
2. A reduction in medium grade ore consumption by 19%.
3. A reduction in carbon consumption by 6%.
4. A reduction in smelting power consumption by 7% per ton of alloy.
5. A decrease in phosphorous content of the alloy due to almost negligible
phosphorous in the slag being fed into the furnace.
6. An increase in manganese recovery by 0.8% in the alloy due to the use of
slag as a manganese-bearing material.
7. A decrease in carbon emissions in ferromanganese production process by
0.164 T of CO2e per ton of alloy.

WE CLAIM:
1. An improved process for production of high-carbon ferromanganese alloy,
comprising the steps of:-
- preparing a raw material blend consisting of by weight low-silica
containing manganese ore 65%, coke 16%, quartz 3%, dolomite 9% and
high-Mn0 slag 7%;
- injecting the raw material blend in a submerged arc furnace,
- inputting into the furnace an electrode paste simultaneously supplying
electrical power for smelting process; and
- tapping slag and alloy from the furnace after a predetermined power
consumption by the furnace,
wherein the low-silica manganese ore consists of manganese (46-48%),
Fe(8-9%), Si02 (2.5%); the high Mn0 slag contains Mn0 (33%); Si02 (28%);
Al203 (17%), Ca0 (10%); Mg0 (6.0%); the quartz contains 90%, Si02; the
dolomite contains Ca0 (28%), Mg0 (9%), silica (4%); and the coke contains
fixed carbon (82%). And ash (15-18%) wherein the smelting power inputted
is around 2600 KWH/T of alloy and wherein the electrode paste containing
84% FC is injected in 16KG/T of the alloy.

2. The process as claimed in claim 1, wherein the size fractions (in mm) of
the manganese ore, quartz, high-Mn0 slag, dolomite, and coke are 10-70,
10-50, 10-60, 10-70 and 8-25 respectively.
3. The process as claimed in claim 1, wherein the process parameters
include metal temperature 1290°C, slag temperature 1390°C and electrode
penetration 950 mm.
4. The process as claimed in any of the preceding claims, wherein the
produced alloy contains manganese 70%, phosphorous 0.25%, silicon
0.35% and carbon 6.5%.
5. The process as claimed in any of the preceding claims wherein the slag
composition includes Mn0 (34%), Si02 (28%); Fe203 (1.10%), AI203
(16.5%), Ca0 (9.8%), Mg0 (6.7%) with basicity of 0.59.

ABSTRACT

The invention relates to an improved process for production of high-carbon
ferromanganese alloy, comprising the steps of preparing a raw material blend
consisting of by weight low-silica containing manganese ore 65%, coke 16%,
quartz 3%, dolomite 9% and high-Mn0 slag 7%; injecting the raw material blend
in a submerged arc furnace, inputting into the furnace an electrode paste
simultaneously supplying electrical power for smelting process; and tapping slag
and alloy from the furnace after a predetermined power consumption by the
furnace, wherein the low-silica manganese ore consists of manganese (46-48%),
Fe(8-9%), Si02 (2.5%); the high Mn0 slag contains Mn0 (33%); Si02 (28%);
Al203 (17%), CaO (10%); Mg0 (6.0%); the quartz contains Si02 (90%); the
dolomite contains Ca0 (28%), Mg0 (9%), silica (4%); and the coke contains
fixed carbon (82%) and ash (15-18%) wherein the smelting power inputted is
around 2600 KWH/T of alloy and wherein the electrode paste containing 84% FC
is injected in 16KG/T of the alloy.