FIELD OF INVENTION:
This invention relates to a process for the production of ferrochrome enriched
with nickel.
BACKGROUND OF THE INVENTION:
Chromite nickeliferrous overburden dump material is generated in huge amounts
along with the production of chromite. 50 Million tonnes of such chromite
overburden is generated in India each year in addition to the 140 Million tonnes
that has already been accumulated over several years of mining. Dumping of the
overburden material is a major problem at mines due to unavailability of space
and environmental concerns. Therefore this huge low grade material should be
utilized in cost-effective way.
Overburden is known to contain valuable nickel in lateritic form. The
various approaches tried out for extracting nickel from chromite overburden
includes leaching (chemical & biological), bioacids, electrochemical, reduction
roasting followed by leaching, microwave heating, etc. The leaching especially
chemical leaching approach suffers from high consumption of leachant and its
disposal after treatment. Nickel concentration by beneficiation is not amenable
option since nickel is present only as minor constituent.
Therefore, high carbon ferrochrome enriched with nickel is produced from
chromite nickeliferrous ore dump material which is a low chromium containing
ore material. A novel process route is designed by preoxidation followed by
reduction of this material using coal as reductant for production of metallized
ferrochrome which is enriched with nickel. The metal product is produced by low
temperature reduction of pre-oxidized nickeliferrous chromite ore material in lab.

OBJECTS OF THE INVENTION:
An object of this invention is to propose a process for the production of
ferrochrome enriched with nickel;
Another object of this invention is to propose a process for production of
ferrochrome enriched with nickel by low temperature reduction of pre-oxidized
chromite nickeliferrous ore;
Still another object of this invention is to propose a process for the production of
ferrochrome enriched with nickel wherein a clear separation of slag and metal
phase takes place at a lower temperature;
Further, object of this invention is to propose a process, which is cost effective;
Still further object of this invention is to propose a process which is 20% energy
saving.
DESCRIPTION OF THE INVENTION:
According to this invention there is provided a process for the production of
ferrochrome enriched with nickel comprising: subjecting the chromite
nickeliferrous ore to oxidation at 800 0C. The microstructure of the oxidized
nickeliferrous ore is shown in Fig. 1. The nickeliferrous chromite ore has different
mineral phases present which consist of Iron oxides, Aluminium iron silicates,
chromite, hercynite, corundum and quartz. This ore having very low Cr: Fe ratio
ranging from 0.28 to 0.32 were oxidized at low temperatures (900°C). The
oxidized sample shows oxidation of FeO phase to Fe2O3 in the chromite
particles.

After oxidation, the chromite nickeliferrous ore is subjected to the step of
reduction using coal as reductant and flux at a low temperature of 1400-1500°C;
And separating the metal and slag phase after quenching into water.
Reduction of the oxidized chromite nickeliferrous ore was carried out using coal
as reductant. Flux used consists of silica source (quartz) and lime. The reduction
experiments carried out using the controlled atmosphere high temperature
furnace. The raw materials used alongwith there composition is given in the
following table.
Table 1: Raw materials and their composition

The experimental studies for reduction were carried out at low temperatures of
1400-1500°C. The coal reductant is used in 10-50% excess of the stichiometric
carbon requirement for reduction of Iron oxides (Fe2O3) and chrome oxides
(Cr2O3) in the ore. Based on the special slag designed, the flux addition was
carried out as quartz addition in the range of 0-10% excess of required for
aluminium oxides and magnesium oxide dissolution to slag. The lime addition
was done in the range of 3-5% of the ore. Reduction was carried out in the
temperature range of 1400-1500°C for 1.5-3.0 hours. It can be seen that the
metal shows total five phases which consists of four phases containing chromium

and iron as major constituent. The fifth phase (features 12, 1) in metal is rich in
Ni. Hence the product ferrochrome enriched wrth nickel. The metal nuggets
produced were having diameter in the range of 0.5-2.0 cms. The metal and slag
phase separation is clear which after quenching in water can be separated by
physical separation methods. The slag and metal obtained after separation are
shown in Fig. 2.
The chemical composition of the metal and slag produced is given in Table 2.
Table 2: Chemical analysis of the ferrochrome enriched with nickel and slag

The microstructure of the ferrochrome enriched with nickel metal is shown in Fig.
3. The point analysis of the respective spots is given in Table 3. It can be seen
from Fig.3 and Table 3, that the nickel is present in the iron rich phases.


Reaction mechanisms:
The oxidation of FeO the chromite ore opens the spinel structure which increases
the reactivity of chromite spinel due to formation of vacancies. The oxidation of
the chromite ores also helps in reducing the reduction time. The reduction
mechanism of chromite ores in absence of lime as flux, generally proceeds as
per the following steps. Chromium oxide reacts at 1200 to 1600°C with carbon to
form one of the carbides Cr3C2, Cr7C3.
3Cr2O3 +13C→2Cr3C2 + 9CO (1150-1200°C)
27Cr3C2 + 5Cr2O3 →13Cr7C3 + 15CO (1200-1600°C)
At still higher temperatures Cr7C3 reacts with Cr2O3 to yield Cr23C6 and finally
above 1820°C the Cr metal is favored product. However due to use of lime as
fluxing component the slag formation reactions plays an important role in carrying
out the reduction of chrome oxides at lower temperatures. In presence of lime as
fluxing component the slag formation reactions take place at lower temperatures
which promotes the chromium reduction by dissolution in slag.

WE CLAIM:
1. A process for the production of ferrochrome enriched with nickel
comprising:
subjecting the chromite nickeliferrous ore to oxidation followed by the step
of reduction using coal as reductant and flux at a low temperature of
1400-1500°C;
separating the metal and slag phase after quenching into water.
2. The process as claimed in claim 1, wherein the said step of reduction
carried out for 1.5 to 3.0 hrs.
3. The process as claimed in claim 1, wherein said flux comprises silica
source (quartz) and lime.
4. The process as claimed in claim 1, wherein the coal reductant is used in
30-50% excess of the stichiometric carbon requirement for reduction of
Iron oxides, chrome oxides in the Ore.
5. The process as claimed in claim 1, wherein the flux addition was carried
out as quartz addition in the range of 0-10% excess of required for
aluminium oxides and magnesium oxide dissolution to slag, the lime
addition done in a range of 3 to 5% of the ore.

A process for the production of ferrochrome enriched with nickel comprising:
subjecting the chromite nickeliferrous ore to oxidation followed by the step of
reduction using coal as reductant and flux at a low temperature of 1400-1500°C;
separating the metal and slag phase after quenching into water.