FIELD OF INVENTION
This invention relates to a method of smelt reduction of high grade refractory chromite ores in
submerged arc furnace (SAF) to enable their use to produce Ferrochrome by maintaining Cr2O3
losses to slag at less than or equal to 10% by weight. The invention further relates to a method for
smelt reduction of chromite ores containing Cr2O3 percentage by weight greater than 50%, Cr:Fe
ratio greater than 2.6 and refractoriness index greater than 2.5. The invention further relates to a
method of designing the input starting material composition feed to submerged arc furnace based
on input chromium (Cr) method such that atleast 25% or more of input Cr by weight in feed burden
is comprised from high grade refractory chromite ores in starting material in the form of sintered
pellets, or lumps or briquettes or any other form of agglomerate prepared from high grade
refractory chrome ore. The invention further relates to making use of tailored fluxes to design a
new slag composition in submerged arc furnace having low melting point slag to enable smelting of
high grade refractory chrome ores. The invention still further relates to a method of producing high
chromium Ferrochrome product having chromium content greater than 63% by weight with carbon
content in the range of 0.1 to 10% by weight.
BACKGROUND OF INVENTION
Chromite ore is prime raw material for production of ferrochrome using the submerged arc furnace
(SAF) process. Globally, most of the ferrochrome is produced by submerged arc furnace route
except a small fraction, by the DC arc furnaces route. The smelt reduction of chromite ores is
carried out in submerged arc furnaces using generally coke as the reductant and quartzite and/or
bauxite as the flux. Chromite ores in the form of lump are smelted in SAF directly whereas chromite
ore fines are agglomerated to pellets or briquettes. Pellets are subjected to sintering process in
vertical shaft furnace or horizontal steel belt sintering furnace prior to smelting in submerged arc
furnace whereas briquettes are usually charged directly to smelting furnace.
Chromite ores in the form of sintered pellets or briquettes or lumps having Cr2O3 content less than
50% by weight are conventionally smelt reduced in submerged arc furnaces to produce
Ferrochrome having less than 63% chromium content by weight. In conventional process, chromite
ore batch is prepared comprising of chromite ores having Cr2O3 content less than 50% by weight in
the form of sintered pellets, briquettes, lumps and their combinations. The required quantity of

reductants consisting of coke or coal for reduction of iron and chromium oxides (FeO, Cr2O3,
Cr2O3) are mixed with ore batch. Quartzite flux to obtain about 25-35% by weight of silica (SiO2) in
slag is then mixed with the batch to prepare composite batch comprising of ores in the form of
sintered pellets, briquettes, lumps, reductants and fluxes. Ferrochrome product having chromium
content less than 63% by weight is then produced by smelt reduction of composite batch (chromite
ores, reductant and fluxes) in submerged arc furnace. Chromite ores in the form of sintered pellets
or briquettes or lumps used in conventional process has Cr2O3 content less than 50% by weight.
The increase in CreO3 content and Cr to Fe ratio in chromite ore makes the ore high grade and
refractory in nature. Therefore smelting reduction of high grade refractory ores is difficult in
submerged arc furnace process. Blending of the high grade refractory chromite ores with the low
grade or conventional ores causes difficulties in the submerged arc furnace operation and also
results in increased Cr2O3 losses to slag. Therefore, in the present invention a process is disclosed
for smelting reduction of high grade refractory chromite ores in submerged arc furnace with >50%
Cr2O3 and Cr to Fe ratio greater than 2.6 with refractoriness index greater than 2.5 to produce
Ferrochrome product having Cr content greater than 63% in submerged arc furnace. The process
in present invention also provides a method for designing the input starting material composition
fed to submerged arc furnace based on input chromium (Cr) method such that atleast 25% or more
of input Chromium by weight in feed burden is comprised from high grade refractory chromite ores
in starting material. The present invention also discloses the use of tailored fluxes to design a new
slag composition in submerged arc furnace having low melting point to enable smelting of high
grade refractory chrome ores.
PRIOR ART
There are five primary processes that are currently in use for the production of ferrochrome. These
include conventional process with open or semiclosed submerged arc furnaces, the conventional
process with closed submerged arc furnace, the Outokumpu process, the DC Arc route and the
Premus process. Each of these processes are discussed briefly below
Conventional Process with Open or Semiclosed Submerged Arc Furnaces: In the
conventional process, a mixture of chrome ore, reductants and flux is fed cold with minimum pre-
processing directly into open/semiclosed type submerged arc furnaces. The furnace off-gases are

cleaned in a bag plant before being vented into the atmosphere. The metal and slag are then
tapped from the furnace for further processing. The primary advantage of this process is that it
requires lowest capital investment and is very flexible in terms of raw materials that can be used in
the process. The main disadvantage of this process is that it is increasingly being perceived as
being less environmentally friendly than other available processes and it has the lowest
efficiencies.
Conventional process with closed submerged arc furnace: In conventional process with closed
submerged arc furnaces, a mixture of sintered pellets, lumpy chromite ores, coke as reductant and
flux are fed to closed submerged arc furnaces. The furnace off-gas is cleaned using wet scrubbers
in the gas cleaning plant. The metal and slag are then tapped for further processing. The primary
advantage of closed submerged arc furnace is that it is energy efficient process as compared to
open or semiclosed furnaces. The main concern of the process includes higher energy
consumption and requires costly metallurgical coke for the smelt reduction process.
Outokumpu process: Fine chrome ore is wet milled and then pelletized using a binder such as
bentonite. The pellets are then sintered and then air cooled and stockpiled. The charge mix
(pellets, lumpy ore, coke and fluxes) may be heated in a pre-heater located above the furnace bins.
Reductants consisting of coke and char, are added to the (preheated) raw materials and fed into
closed submerged arc furnaces. The furnace off-gas is cleaned in wet scrubbers and used as an
energy source in the sintering and preheating processes. The main advantage of this process is
that the sintered pellets and preheating of the charge to the submerged arc furnaces results in
reduced specific energy consumptions and improved chromium recoveries.
DC arc furnace: The furnace uses a single solid carbon electrode and produces a DC arc to an
anode in the bottom of the furnace. The arc is normally an open or semi-submerged one. Raw
materials can be charged either directly into the furnace, or by using a hollow electrode. The
primary advantage of this process is that the process utilizes any of the available raw materials
including 100% chromite fines with minimum or no pre-processing, thus eliminating the need for an
expensive agglomeration plant. Inferior grades of reductants like coal and anthracite can be used
in this process, which is also considered an additional advantage of the process.

Premus Technology: Fine chrome ore, bentonite and a reductant such as anthracite fines are dry
milled, pelletized and preheated before being fed into rotary kilns where partial pre-reduction of the
chromium oxidie and iron oxides take place. The metallized pellets are then hot charged into
closed submerged arc furnaces. The furnace off-gas is cleaned in ventury scrubber and used
throughout the plant as an energy source. Initial capital costs for this process are high and the level
of operational control required to ensure smooth operation of the process is also very high.
A method of refining high chromium alloy by melting and reduction is disclosed in patent
application number JP59113158 wherein chrome ore containing iron oxide as starting material is
reduced in rotary kiln to obtain >90% iron metallization in reduced product. The pre-reduced
material is charged to reduction and melting furnace of top and bottom blown converter type. The
process do not require electrical energy and the pre-reduction of chrome ore enhances the
reduction process in converter. In patent application number US2003150295, a method for
producing Ferrochrome alloy with greater than 80% Cr recovery in submerged arc furnace is
disclosed using coke, coal, char or anthracite reductants and fluxing agent is added to ensure that
the slag liquidus temperature during smelting is 80-150 °C above the Ferrochrome alloy.
CA2010356 discloses a method for manufacturing molten metal containing Cr and Ni comprising of
smelting and reduction of Nickel ore by charging Nickel ore into molten iron bath having top-blow-
oxygen for decarburizing and post combustion. Stirring gas is injected through tuyers and
carbonaceous material with flux is charged to converter to form slag. Further chromium ore is
added and smelt reduction carried out to produce stainless steel an alloy of Iron, Chromium and
Nickel. Dephosphorization and desulphurization steps are performed using lime, fluorite and silica.
In patent application number JP53001620, a process to produce low carbon and high chromium
stainless steel is disclosed wherein desulfurization and dephosphorization is carried out using
calcium fluoride flux after the molten metal of high chromium pig iron is obtained by reducing
chromium ore and iron ore in the blast furnace. The process is used for smelting of oxide material
of iron and chromium such as chrome ore by reducing with coke and removing the phosphorus,
sulphur and carbon to produce high chromium steel. JP58091149 discloses a melting method of
high chromium alloy in a reactor containing iron and chromium oxide materials heated to melt with
carbonaceous materials to produce high CrO alloy with greater than 18% chromium. In succession,
metal of low chromium content is added to reactor where the Cr in slag is decreased. Slag is
removed and ferrochrome is added subsequently to control chromium in metal. In patent

application US4561885, a method of producing refractory material from slag by product of high
carbon ferrochromium is disclosed wherein slag is fused with mixtures of compounds comprising
magnesia, alumina and silica. The method is economical and produces a refractory material which
can be used in steelmaking or other smelting operations. GB911992 discloses an improved
reduction and smelting method for chromite bearing materials wherein chromite bearing ores are
smelted using fluxes such as silica, alumina and basic oxides such as MgO or CaO such that the
slag obtained in the process contains MgO - 0.5 to 1.5 parts by weight, AI2O3 - 0.25 to 1.25 parts
and - - 1 part by weight. In patent application number JP63153207, a method for smelt
reduction of chromium ore is disclosed wherein chromite ore and carbonaceous material and slag
making agent are charged to a converter type furnace and oxygen is blown from top blowing lance.
A stirring gas is blown from bottom and the chromium ore is smelt reduced. After refining and
decarburizing by blowing oxygen, chromium containing steel is produced. ZA9904780 discloses a
method of recovering valuable metals from ferrochromium slag phase wherein the slag phase from
submerged arc furnace is passed through a stripping zone in which valuable metal oxides in slag
phase are reduced to metal. In patent application number CN101608261, a method for producing
high carbon ferrochrome by using chromite powder is disclosed wherein chromite ore powder is
mixed with bonding agent and slag forming agent, performing the pelletizing and the finished
pellets are directly added with solvent and reducing agent to submerged arc furnace to obtain high
carbon ferrochrome. Chromite ore powder is used for slagging and solvent comprises silica stone
and dolomite while reducing agent comprises coke carbon. SU968092 discloses a method for
melting carbonaceous ferrochrome from magnesial chromium ores wherein the viscosity of slag is
lowered and the fluidity interval is expanded by maintaining MgO/Al203 equal to 2.4 to 2.55 and
silica content 30-32% which can be increase upto 35 to 36% while MgO/Al2O3 is preserved. The
method is found to be suitable for magnesia containing ores by maintaining fixed MgO/Al2O3. In
patent application number US4565574, a two stage converter based process is disclosed without
use of electricity wherein chrome ore is continuously supplied to first stage converter along with
bottom blown oxygen, carbonaceous material and inert gas to carry out smelt reduction. In second
stage supply of raw materials is discontinued and supply of bottom blowing materials is controlled
to produce high chromium containing steel. JP9157765 provides a method for smelting reduction
of chromium ore capable of lowering the damage to lining refractory wherein molten slag having
CaO/SiO2 in the range of 0.7 to 1.2 is maintained by adding greater than 30% magnesia containing

material to improve the smelt reduction reactions. In patent application number JP62211344, a
starting material composition for reducing chrome ore is disclosed wherein the blend of coke or
coal, chrome ore and flux in the ratio of 0.1: 1: 0.1 to 0.5 with specific size range of each raw
material is disclosed to manufacture molten ferrochrome and stainless steel.
It can be observed from above, that most of the prior art technologies currently in use for producing
ferrochrome are based on preheating or pre-reduction techniques of chromite ores and subsequent
smelting reduction of the charge materials (preheated or pre-reduced) in submerged arc furnace.
Methods based on the converter type furnaces were also disclosed to produce high chromium
containing steel mainly stainless steel. The prior art technologies were designed mostly for
processing of low refractory nature FeO-rich South African chromite ores to produce charge
chrome with relatively lower chromium content, varying between 50 to 55 percent. On the other
hand, the MgO-rich Indian chromite ores are highly refractory in nature and therefore needs a
different approach. Conventionally, Indian chrome ores with Cr2O3 content less than 50% Cr2O3 by
weight are used to produce ferrochrome containing chromium less than 63% Cr by weight.
However, smelt reduction of Indian chromite ores having Cr2Oa content greater than 50% and Cr to
Fe ratio greater than 2.6 are difficult to process in submerged arc furnace with conventional
approach due to higher smelting temperature requirement in submerged arc furnace to process
high grade refractory chrome ores. Therefore, in the present invention a method for enabling smelt
reduction of high grade refractory chrome ores is disclosed without increasing the overall energy
consumption and minimizing Cr2O3 losses to ferrochrome slag. The current invention also
produces ferrochrome product having greater than 63% chromium content. This invention further
provides a method of designing the input starting material feed burden composition or method of
designing a composite batch prepared to feed periodically to submerged arc furnace such as to
minimize the oxide smelt reduction disturbances in the furnace, based on input chromium (Cr)
method such that atleast 25% or more of input Chromium (Cr) by weight in feed burden is
comprised of high grade refractory chromite ores in the starting material in the form of sintered
pellets or lumps or briquettes or their combinations with conventional chrome ores prepared from
high grade refractory chrome ore and tailored fluxes to provide new slag composition having lower
melting point slag which enables the smelting of high grade refractory chrome ores and minimizes
Cr2O3 losses to slag.

OBJECTS OF THE INVENTION
- It is therefore object of the present invention to provide a method for smelt reduction of high
grade refractory chrome ores in submerged arc furnace to enable their use in ferrochrome
production by minimizing O2O3 losses to slag to less than 10% by weight
- Another object of the present invention is to provide a submerged arc furnace (SAF) based
smelt reduction process for chromite bearing raw materials having Cr2O3 content by weight
greater than 50% and having Cr to Fe ratio greater than 2.6 and refractoriness index greater
than 2.5
- A still further object of the present invention is to provide a method of designing the input
starting material feed or composite batch prepared to feed periodically to submerged arc
furnace based on input chromium (Cr) method such that atleast 25 % or more of input
Chromium (Cr) by weight in the feed or burden is comprised of high grade refractory chrome
ores in the form of sintered pellets or briquettes or lumps or their combinations
- Yet further object of the present invention is to provide a novel slag composition for smelt
reduction of high grade refractory chromite ores by using tailored fluxes to form a slag in
submerged arc furnace operation having low melting point and achieve chromium (Cr)
recovery greater than 85% to metal by minimizing Cr2O3 losses to slag to less than 10% by
weight
- Yet further object of the present invention is to disclose a smelt reduction method in
submerged arc furnace to produce ferrochrome metal product having greater than 63%
chromium and carbon content in the range of 0.1 to 10% by weight
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Variation in %Cr2O3, %MgO and % AI2O3 with Cr to Fe ratio in high grade refractory
chromite chromite ores. The ores have Cr to Fe ratio > 2.6, Cr2O3 > 50%, MgO > 5% and AI2O3 >
2.0%, Refractoriness index (R) >2.5

Figure 2: Variation of refractoriness index (R ) with Cr to Fe ratio in high grade refractory grade
chromite ores. The refractory chrome ores have Cr to Fe ratio > 2.6 and refractoriness index (R) >
2.5
DETAILED DESCRIPTION OF THE INVENTION
High grade refractory chromite ores have O2O3 content greater than 50% by weight, Cr to Fe ratio
greater than 2.6 and refractoriness index greater than 2.5. The variations in chemical composition
(weight %) of oxides such as Cr2O3, MgO and AI2O3 with Cr to Fe ratio in high grade refractory
chromite ores are shown in Figure 1 (shaded area). The chemical composition of typical high grade
refractory chrome ores is also given in Table 1. The refractoriness index (R) for chromite ore is a
measure of total energy requirement to reduce chrome ore and can be used to compare the
relative reducibility of the ore. The higher the refractoriness index the more difficult the ore to
reduce. The refractoriness index is calculated according to equation 1.

All percentages in equation (1) are by weight. The variation in refractoriness index estimated based
on the chemical composition of high grade refractory chromite ores are shown in Figure 2 (shaded
area). It can be seen from Figure 1 and 2 that the high grade refractory chrome ores have Cr2O3
content greater than 50% by weight, Cr to Fe ratio greater than 2.6 and refractoriness index greater
than 2.5. The MgO content by weight is typically greater than 5.0% and AI2O3 content is greater
than 2.0%. The high grade refractory chromite ores as per the method of current invention can be
used in the form of sintered pellets or briquettes or lumps or any other form of agglomerates or
their combinations prepared by using the high grade refractory chrome ores.
For given input chromium weight in feed to SAF or in a composite batch prepared to feed
periodically to submerged arc furnace from high grade or combinations of high grade and low
grade or conventional chrome ores (Cr2O3 < 50% by weight), atleast 25% or more of input
chromium by weight in feed to submerged arc furnace is comprised of high grade refractory
chrome ores. The rest of the chromium (Cr) input in the form of Cr2O3 by weight in feed or in

composite batch prepared to feed to submerged arc furnace can comprise of low grade or
conventional chromite ores (Cr2O3 < 50% by weight) in any of agglomerate form (sintered pellets,
lumps, briquettes, etc). For simplicity, the chromite ores having Cr2O3 content by weight less than
50% are stated as conventional chromite ores in subsequent description. The high grade refractory
chrome ores and or conventional chromite ores can be used in the form of sintered pellets or
briquettes or lumps (hard or friable in nature) or their combinations. The carbonaceous reductant
such as coke or anthracite coal is mixed in the batch to reduce total oxides of iron and chromium in
feed to submerged arc furnace. As per the method of current invention the total input Chromium
(Cr) weight and chromium split ratio among different chromite bearing raw materials in feed or in
composite batch prepared to feed periodically to submerged arc furnace is decided prior to
estimation of quantities of respective chromite bearing raw materials. Conventionally, the weight
ratio of chromite bearing raw materials in submerged arc furnace feed are decided first and then
the reductant requirements are estimated based on required quantity to reduce chromium oxide
and iron oxides. The weight ratio of chromite bearing raw materials is defined as weight of
individual chromite bearing raw material to total weight of chromite bearing raw materials in feed to
SAF or in composite batch prepared to feed periodically to SAF. As per the current invention, it is
however preferred that the total input chromium (Cr) weight and chromium split ratio for different
chromite bearing raw materials in feed to SAF are predetermined prior to estimation of required
quantity of individual chromite bearing raw material in feed. Once the total input chromium weight
and chromium split ratio for chromite bearing raw materials is decided, the weight ratio of various
chromite bearing raw materials and or their individual weights and proportions are estimated
according to selected chromium split ratio. The chromium split ratio is defined as the ratio of
chromium contribution from individual chromite bearing raw material to total input chromium from
all chromite bearing raw materials in feed or in composite batch prepared to feed periodically to
SAF. The total input chromium in feed to submerged arc furnace can be kept constant or varied
suitably based on power rating of furnace and or other process conditions in ferrochrome
production. The comparison of conventional weight ratio approach and chromium split ratio
approach disclosed in current invention is illustrated below with an example.

A chrome ore batch comprising of 100 kg of chrome ore A with Cr2O3=30%, 400 kg of ore B with
Cr2O3=40% and 1000 kg of chrome ore C with Cr2O3=50% is smelt reduced in submerged arc
furnace (SAF)
% weight of A in input = (100)/(100+400+1000) x 100 = 6.67
% weight of B in input = (400)/(100+400+1000) x 100 = 26.67
% weight of C in input = (1000)/(100+400+1000) x 100 = 66.67
Therefore weight ratio of chrome bearing raw materials is as follows
Weight Ratio = 6.67 % A: 26.67% B: 66.67% C
Input Cr2O3 from A = 100 x (30/100) = 30 kg
Input O2O3 from B = 400 x (40/100) = 160 kg
Input Cr2O3 from C = 1000 x (50/100) = 500 kg
Total input Cr2O3 in ore batch = 30+160+500 = 690 kg
Conversion factor from Cr2O3 to Cr = 0.6842
Total input Cr in ore batch = 30 x 0.6842 +160 x 0.6842 + 500 x 0.6842 = 20.51 +109.50 + 342.10
Total input Cr in ore batch = 472.1 kg
% chromium from A = (20.51/472.1) x 100 = 4.34 %
% chromium from B = (109.50/472.1) x 100 = 23.20 %
% chromium from C = (342.10/472.1) x 100 = 72.46 %
Chromium Split Ratio = 4.34% A: 23.20% B: 72.46% C
In conventional approach, the weight ratio is fixed first for chromite bearing raw materials and then
the carbon or carbonaceous material requirement is estimated for reduction of various oxides in the
burden. As per the burden design approach in current invention, the input chromium weight = 472.1
in batch and the chromium split ratio (4.34% A: 23.20% B: 72.46% C) is predetermined or decided
first for given smelting operation. It should be noted that the total input chromium weight in feed or
in composite batch prepared to feed periodically to submerged arc furnace can be suitably varied

or kept constant as per power rating of furnace and or other process conditions (hard or friable
ores, quality and composition of raw materials for smelting, etc).
The following description now illustrates the burden design approach for the above mentioned
example wherein the total input chromium weight is assumed (which is predetermined for given
case as per method of current invention) as 472.1 kg and assumed chromium split ratio as 4.34%
A:23.20%B:72.46%C (which is predetermined for given case as per the method of current
invention)
Thus as per the burden design approach of current invention
Predetermined input chromium weight = 472.1 kg (constant or can be varied for given condition)
Predetermined chromium split ratio for chromite bearing raw materials A, B, C is
4.34% A: 23.20% B: 72.46% C (constant or can be varied for given condition)
As per the predetermined total chromium input weight and chromium split ratio among chromite
bearing raw materials, the weight ratio is estimated as follows
Input chromium requirement from A = (total input chromium requirement) x (% Cr contribution from
A as per chromium split ratio)
Input chromium requirement from A = 472.1 x (4.34/100) = 20.50 kg
Weight of A required = (100 x input chromium requirement from A) / (0.6842 x % Cr2O3 in A)
Weight of A required = (100 x 20.50) / (0.6842 x 30) = 100 kg
Input chromium requirement from B = (total input chromium requirement) x (% Cr contribution from
B as per chromium split ratio)
Input chromium requirement from B = 472.1 x (23.20/100) = 109.51 kg
Weight of B required = (100 x input chromium requirement from B) / (0.6842 x % Cr2O3 in B)
Weight of B required = (100 x 109.51) / (0.6842 x 40) = 400 kg
Input chromium requirement from C = (total input chromium requirement) x (% Cr contribution from
C as per chromium split ratio)

Input chromium requirement from C = 472.1 x (72.46/100) = 342.08 kg
Weight of C required = (100 x input chromium requirement from C) / (0.6842 x % Cr2O3 in C)
Weight of C required = (100 x 342.08) / (0.6842 x 50) = 1000 kg
In the above example, chromite bearing raw materials A, B, C are shown as examples and it is
understood that the burden design approach can be extended to any number and type of chromite
bearing raw materials and or their combinations as long as the total input chromium and chromium
split ratio for different chromite bearing raw materials is defined. Thus, based on the predetermined
total input chromium weight in SAF feed (which is fixed for given batch or feed and can be varied
as per requirement) and predetermined chromium split ratio (which is fixed for given batch or feed
and can be varied as per requirement) the weight ratio of available chromite bearing raw materials
is estimated by keeping the input chromium constant in feed to submerged arc furnace or in
composite batch prepared to feed periodically to submerged arc furnace. In conventional approach
of design since the weight ratio of chromite bearing raw materials is fixed or predetermined in feed,
there are variations in total chromium oxide input fed to submerged arc furnace or smelted in
furnace due to variation in chemical composition of chromite bearing raw materials. The new
design approach overcomes this limitation such that the total chromium oxide fed in submerged arc
furnace or total chromium oxide in composite batch fed periodically to submerged arc furnace is
fixed by total input chromium weight and chromium split ratio as per the method described above.
Thus the new burden design method results in variation in weight ratio of chromite bearing raw
materials, while the total input chromium weight in feed or in composite batch remains constant
which can be predetermined by operator using the fixed chromium input and chromium split ratio
as per suitability to given submerged arc furnace process based on power rating and or other
process conditions for example hard or friable nature of chromite bearing raw materials, type of
agglomerate feed, quality of raw materials, etc. The new method thus eliminates the fluctuations or
disturbances in the furnace operation which may arise due to smelting of variable amount of
chromium oxide in the smelt reduction zone of submerged arc furnace. As per the new design
approach, once the weight ratio of chromite bearing raw materials is estimated using total input
chromium weight and chromium split ratio for different chromite bearing raw materials, the carbon
or carbonaceous material requirements are estimated based on the requirement to reduce oxides
in the burden as per conventional method. As per the preferred method of current invention out of

the total input chromium fed to submerged arc furnace or in composite batch prepared to feed
periodically to submerged arc furnace, atleast 25% or more of chromium is comprised of high
grade refractory chromite ores. Thus in chromium split ratio for smelt reduction of high grade
refractory chromite ores, 25% or more is the component or percentage in chromium split ratio for
smelt reduction of high grade refractory chromite ores. The high grade refractory chrome ores
typically has higher Cr2O3 and MgO by weight and lower alumina (AI2O3 %) and Fe by weight.
Therefore, the smelt reduction of high grade refractory chromite ores needs a different fluxing
approach compared to conventional chromite ores. As per the method of current invention, alumina
containing flux such as bauxite, CaO containing flux such as limestone and Silica (SiO2) containing
flux such as quartz or quartzite are used as tailored fluxes to design a new slag composition having
lower slag melting point. Alumina (AI2O3) in the form of bauxite is added to the composite batch
comprising of high grade refractory chrome ores such that feed burden has MgO/Al2O3 ratio in the
range of 0.8 to 1.2. The limestone is added to the composite batch comprising of high grade
refractory ores such that the resultant slag contains 3% to 10% by weight CaO. The addition of
alumina (AI2O3) in smelt reduction of conventional ores having high alumina typically increases the
melting point of slag, however in smelt reduction process of high grade refractory chrome ores
which have low alumina content, addition of alumina in the form of bauxite do not result in increase
in melting point slag. CaO in limestone or lime is a slag former which helps in formation of low
temperature low melting point slag. The amount of silica flux addition in composite batch is carried
out such that the silica (SiO2 %) in resultant slag from submerged arc furnace has silica in the
range of 25 to 35 % by weight. The limestone and quartzite (silica) or tailored fluxes are also
adjusted to obtain the basicity [(Weight of CaO in kg + Weight of MgO in kg) / (Weight of SiO2 in
kg)] in feed burden or in composite batch prepared to feed periodically to submerged arc furnace in
the range of 0.7 to 1.2 and preferably 0.9 to 1.0. The chemical compositions of reductants and
tailored fluxes used in the current invention are provided in Table 1. Thus the composite batch or
burden wherein atleast 25% or more of total input chromium is comprised of high grade refractory
chromite ores along with reductant coke or anthracite coal, quartzite, bauxite and limestone is fed
to submerged arc furnace for smelt reduction to achieve greater than 85% chromium recovery to
metal and obtain ferrochrome product having chromium content greater than 63%. The typical
chemical composition of ferrochrome metal and slag produced in current invention are given in
Table 2.

Example
An example giving the comparative experimental results of six smelt reduction tests carried out in a
50 kVA submerged arc furnace comprising of high grade refractory chrome ores and conventional
chrome ores are described in the section below. The chemical composition of various chromite
bearing raw materials used in the current invention are provided in Table 3. The chemical
composition of reductant coke is provided in Table 4 and composition of fluxes in Table 5.
Test 1 describes the smelt reduction process of conventional chrome ores having Cr2O3 content by
weight less than 50% and or wherein the chromium input comprised from high grade refractory
chrome ores in feed to submerged arc furnace is less than 25%. In test 1, the raw materials smelt
reduced are sintered pellets, hard lumps, friable lumps with quartzite flux and the weight ratio
typically practiced in conventional process is taken as sintered pellets (68.75%), hard lumps
(25.0%) and friable lumps (6.25%). The corresponding chromium split ratio estimated for this batch
having total input chromium of 3.0 kg was sintered pellets (73.75%), hard lumps (18.31%) and
friable lumps (7.95%). The MgO/Al2O3 ratio maintained is 1.02 in the burden at basicity
(CaO+MgO/SiO2) equal to 0.9 according to conventional smelt reduction practice of chromite ores
in submerged arc furnace.
Test 2 describes the use of the smelt reduction method as per current invention with tailored fluxes
and new slag composition for smelt reduction of conventional chrome ores. In Test 2, the raw
materials smelt reduced are sintered pellets, hard lumps, friable lumps, quartzite along with tailored
fluxes limestone and bauxite. The same chromite raw materials (sintered pellets, hard lumps,
friable lumps) in Test 1, are smelt reduced by fixing the chromium split ratio among chromite raw
materials as sintered pellets (65.0% by weight), hard lumps (21.0% by weight) and friable lumps
(14.0% by weight) such that the total input chromium by weight in feed to submerged arc furnace is
3.0 kg. The estimated weight ratio of chromite raw materials in Test 2 is sintered pellets (60.0% by
weight), hard lumps (29.0% by weight) and friable lumps (11.0% by weight). Quartzite flux is used
along with new tailored fluxes limestone and bauxite such that MgO/Al2O3 ratio maintained is 1.02
and basicity (CaO+MgO/SiO2) equal to 0.9 in the burden. It should be noted that in Test 1 and Test
2, friable lumps has Cr2O3 content by weight greater than 50.0% and refractoriness index of 5.9,
however the percentage of total chromium input to submerged arc furnace comprised from friable

lumps is less than 25 % (In test 1, 7.95% for friable lumps and in Test 2,14.0% for friable lumps)
which is typical in conventional submerged arc furnace practice in ferrochrome production.
Test 3 to 6 describes the method of current invention for smelt reduction of high grade refractory
chrome ores wherein 50% or more input chromium to submerged arc furnace is comprised from
high grade refractory chrome ores. The high grade refractory chromite ore lumps smelt reduced in
Test 3 has Cr2O3 content by weight 53.67%, Cr to Fe ratio 2.64 and refractoriness index 3.8. Hard
lumps are used along with high grade refractory chromite lumps such that the chromium split ratio
is 21.0% by weight for hard lumps and 79.0% by weight for high grade refractory chromite lumps
having Cr2O3 content 53.67%, Cr to Fe ratio 2.64 and refractoriness index 3.8. Total input
chromium by weight in feed to submerged arc furnace was maintained at 3.0kg as was the case in
Test 1 and Test 2. Thus about 79.0% by weight of total chromium input to submerged arc furnace
is comprised from high grade refractory chromite lumps having Cr2O3 content 53.67%, Cr to Fe
ratio 2.64 and refractoriness index 3.8. Quartzite flux is used along with tailored fluxes limestone
and bauxite such that MgO/Al2O3 ratio maintained is 1.02 and basicity (CaO+MgO/SiO2) equal to
0.9 in the burden or composite batch.
The high grade refractory chromite lumps smelt reduced in Test 4 has Cr2O3 content by weight
55.17%, Cr to Fe ratio 3.2 and refractoriness index 4.5. Hard lumps are used along with high grade
refractory chromite lumps such that the chromium split ratio is 21.0% by weight for hard lumps and
79.0% by weight for high grade refractory chromite lumps having Cr2O3 content 55.17%, Cr to Fe
ratio 3.2 and refractoriness index 4.5. Total chromium input by weight in feed to submerged arc
furnace was 3.0kg. Thus about 79.0% by weight of total chromium input to submerged arc furnace
is contributed from high grade refractory chromite lumps having Cr2O3 content 55.17%, Cr to Fe
ratio 3.2 and refractoriness index 4.5. Quartzite flux is used along with tailored fluxes limestone
and bauxite such that MgO/Al2O3 ratio maintained is 1.02 and basicity (CaO+MgO/SiO2) equal to
0.9 in the burden or in composite batch.
The high grade refractory chromite ore lumps smelt reduced in Test 5 has Cr2O3 content by weight
58.19%, Cr to Fe ratio 3.6 and refractoriness index 5.1. Hard lumps are used along with high grade

refractory chromite lumps such that the chromium split ratio is 21.0% by weight for hard lumps and
79.0% by weight for high grade refractory chromite lumps having Cr2O3 content 58.19%, Cr to Fe
ratio 3.6 and refractoriness index 5.1. Total chromium input by weight in feed to submerged arc
furnace is 3.0kg. Thus about 79.0% by weight of total chromium input to submerged arc furnace is
contributed from high grade refractory chromite lumps having Cr2O3 content 58.19%, Cr to Fe ratio
3.6 and refractoriness index 5.1. Quartzite flux is used along with tailored fluxes limestone and
bauxite such that MgO/Al2O3 ratio maintained is 1.02 and basicity (CaO+MgO/SiO2) equal to 0.9 in
the burden.
The high grade refractory chromite ore lumps smelt reduced in Test 6 has Cr2O3 content by weight
59.17%, Cr to Fe ratio 3.9 and refractoriness index 5.7. Hard lumps are used along with high grade
refractory chromite ore in such a preparation such that the chromium split ratio is 21.0% by weight
for hard lumps and 79.0% by weight for high grade refractory chromite having Cr2O3 content
59.17%, Cr to Fe ratio 3.9 and refractoriness index 5.7. Total chromium input by weight in feed to
submerged arc furnace is maintained at 3.0kg. Thus about 79.0% by weight of total chromium input
to submerged arc furnace is contributed from high grade refractory chromite having Cr2O3 content
59.17%, Cr to Fe ratio 3.9 and refractoriness index 5.7. Quartzite flux is used along with tailored
fluxes limestone and bauxite such that MgO/Al2O3 ratio maintained is 1.02 and basicity
(CaO+MgO/SiO2) equal to 0.9 in the burden or in composite batch.
Test 1 to 6 are carried out at constant power input of 55 kWh and for constant input chromium (Cr)
of 3.0 kg in feed to 50 kVA submerged arc furnace. The weights of the various raw materials in kg
(having chemical composition as given in Table 3-5) in composite batches prepared to feed
submerged arc furnace in Test 1 to 6 are given in Table 6. It can be observed from Table 6 that,
Test 1 provides an example case for conventional method and raw materials without use of
limestone and bauxite fluxes. Test 2 provides an example case for improving chromium grade and
recovery of chromium to ferrochrome metal by practicing the method of current invention using
limestone, bauxite fluxes and smelting parameters applied to conventional raw materials and
burden. Test 3 to 6 provides the example case wherein high grade refractory chromite ores are
smelted as per the method of current invention to obtain high chromium (>63.0% by weight)
containing ferrochrome product and minimizing Cr2O3 losses to slag to less than 10% by weight.

The coke used in example cases 2 to 6 was 15% by weight in excess over the amount of carbon
required stoichiometrically for reduction of oxides of chromium and iron in the burden. While 15%
excess carbon is used in the example cases 2 to 6, for practising the method of current invention,
stoichiometric amount of carbon or coke is also sufficient. The chemical composition of
Ferrochrome product and slag obtained in Tests 1 to 6 are given in Table 7. The chromium and
iron recovery to metal, slag to metal ratio by weight and estimated total chromium recovered in kg's
per ton of ferrochrome metal in Tests 1 to 6 is provided in Table 8. The chromium recovery is
estimated as weight ratio of total chromium recovered in Ferrochrome metal (product of weight of
ferrochrome metal and chromium percentage by weight in ferrochrome) to total input chromium in
the burden. Similarly, the iron recovery is estimated as weight ratio of total iron recovered in
ferrochrome metal to total input iron in the burden. It should be noted that the estimated chromium
recovered to ferrochrome metal values in kg/ton provided in Table 8, are estimated based on 1000
kg of ferrochrome metal or alloy.
It can be observed from Table 7 and 8, that in conventional method as in Test 1 (wherein less than
50% of total input chromium is contributed by chromite bearing raw materials having Cr2O3
percentage less than 50% by weight and without addition of tailored fluxes such as limestone and
bauxite in the burden), chromium recovery to metal obtained is 97.7% by weight and chromium
grade in ferrochrome product is 61.0%. The iron recovery is 98.1% by weight and estimated
chromium recovered to metal is 619.1 kg/ton. The tailored fluxes such as limestone and bauxite
are used in burden for smelt reduction of conventional raw materials in Test 2. It was observed that
in Test 2, the chromium recovery to metal obtained is 98.9% by weight and chromium grade in
ferrochrome product is improved to 64.0% by weight. The estimated chromium recovered to metal
has increased from 619.1 kg/ton in Test 1 to 647.0 kg/ton in Test 2. Thus for same input chromium
in burden with addition of tailored fluxes using limestone and bauxite with MgO/Al2O3 ratio of 1.02
and basicity (CaO+MgO/SiO2) of 0.9, additional chromium of about 28 kg is recovered per ton of
ferrochrome metal in Test 2 compared to Test 1. Therefore one of the preferred embodiment of
current invention is also to use limestone and bauxite fluxes to smelt reduce conventional chrome
ores in submerged arc furnace by adjusting MgO/Al2O3 in the range of 0.8 to 1.2 preferably 1.0 and
basicity in the range of 0.7 to 1.2 preferably in the range of 0.9 to 1.0 to obtain a novel slag

composition having low melting point to improve the recovery of chromium and thereby achieve
higher chromium grades of product. The normalized (to 100%) composition of major slag forming
components (CaO, MgO, SiO2, Al2O3), melting point and viscosities of slag (estimated for major
slag forming components CaO, MgO. SiO2, AI2O3) in Test 1 to 6 are given in Table 9. It can be
seen that slag having lower melting point is obtained in Test 2. In Test 3 to 6, high grade refractory
chromite ores are smelt reduced keeping total input chromium constant wherein about 79.0% of
total input chromium is contributed from high grade refractory chromite ores having varying
percentage of Cr2O3 by weight and refractoriness index. Tailored fluxes such as bauxite (AI2O3)
and limestone (CaO) are used to adjust the MgO/Al2O3 ratio in burden to about 1.02 and basicity
0.9. It can be observed from table 7, that the chromium grade (%Cr in metal) in Ferrochrome has
increased from 61% (Test 1) to 69.6% (Test 6) by smelt reduction of high grade refractory chromite
ores by practicing the method of current invention. It can also be observed that the melting point of
slag formed in Test 3 to 6 (Table 9) is lower compared to conventional smelting operation slag
(Test 1). The theoretically estimated melting point of slag in conventional operation (Test 1) slag
was 1821 °C whereas the estimated melting point of slag obtained in smelt reduction of high grade
refractory chromite ores in Test 3 to 6 was 1728 °C, 1757 °C, 1744 °C, 1762 °C respectively. It can
also be observed from Table 8, that the total chromium (Cr) recovered to Ferrochrome metal has
increased from 619.1 kg/ton in conventional operation (Test 1) to 704 kg/ton (Test 6) by smelt
reduction of high grade refractory chromite ore using the burden design method of current
invention and tailored fluxes such as bauxite and limestone and using MgO/Al2O3 ratio (by weight)
in the range of 0.8 to 1.2 preferably 1.0 and basicity in the range of 0.9 to 1.0.
The innovative method of designing the input feed, as described above with examples, ensures to
form a low melting point slag and produce high chromium containing Ferrochrome metal having
greater than 63% chromium content by weight and slag having less than 10% Cr2O3 content by
weight.

WE CLAIM
1. A method for smelt reduction of high grade refractory chromite ores having Cr2O3 content
> 50 weight %, MgO content> 5 weight %, AI2O3 > 2 weight %, chromium to Iron ratio > 2.6
and refractoriness index > 2.5, in submerged arc furnace comprising:
determining the input quantity of chromite bearing ores in the input feed based
upon predetermined total input chromium weight and chromium split ratio of each
chromite bearing ore such that at least 25 % or more of the total input Chromium
(Cr) by weight in the input feed is comprised of high grade refractory chromite
ores; and
adding tailored fluxes comprising Alumina (AI2O3), Calcium Oxide (CaO), and
Silica (SiO2) wherein MgO/Al2O3 ratio in the input feed is in the range of 0.8 to 1.2
and Silica (SiO2 %) in resultant smelt reduction slag from submerged arc furnace
is in the range of 25 to 35 % by weight.
2. The method as claimed in claim 1, wherein amount of the predetermined total chromium
input in the input feed can be varied based upon the type and power rating of the
submerged arc furnace.
3. The method as claimed in claim 1, wherein Cao is added in the form of limestone, Silica is
added in the form of quartz or quartzite and Alumina is added in the form of bauxite.
4. The method as claimed in claim 1, wherein MgO/Al2O3 ratio by weight is preferably 1.0.
5. The method as claimed in claim 1, wherein the basicity {[(CaO, kg)+(MgO, kg)]/[SiO2, kg]}
in the input feed is maintained in the range of 0.7 to 1.2, preferably in the range 0.9 to 1.0.
6. The method as claimed in claim 1, wherein the chromite bearing ores are in the form of
sintered pellets, briquettes, lumps and their combinations thereof.

7. The method as claimed in claim 1, wherein the chromium split ratio is defined as the ratio
of chromium contribution by individual chromite ore to total input chromium in input feed to
submerged arc furnace.