FIELD OF THE INVENTION:
This invention relates to a process for the preparation of green and fired
chromite pellets with improved properties.
BACKGROUD OF THE INVENTION;
Chromite green pellets are made from the mixer of chromite filter cake
along with coke fines and bentonite as binder. Green pellets are prepared
in pelletizing disc. Green pellets after screening are fired in a shaft
furnace at around 1300°C.
However, it is necessary to improve the green and dry strength of the
chromite pellets as well as the mean strength of the fired chromite pellets
for efficient performance and reduced electric consumption of the
submerged arc furnaces during the manufacture of ferrochrome.
OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a process for the
preparation of green and fired chromite pellets with improved properties.
It is a further object of this invention to propose a process for the
preparation of green and fired chromite pellets which have improved
green and dry strength.
It is another object of this invention to propose a process for the
preparation of green and fired chromite pellets which have uniform and
controlled size.
Yet another object of this invention to propose a process for the
preparation of green and fired chromite pellets, in the pellets having
increased mean strength.
These and other object of the invention will be apparent from the ensuing
description.
DETAILED DESCRIPTION OF THE INVENTION:
Thus according to this invention is provided a process for the preparation
of green and fired chromite pellets.
In accordance with this invention an alkaline compound is used to
improve the pelletization characteristics of chromite filter cake.
A diluted solution of the sodium based alkaline compound is mixed to
the pelletizing mix in the range of 0.01-0.05 weight percentage of the
binder. With the addition of this compound in the range of 0.01-0.05%,
green and dry strength of pellets is improved.
Chromite fines are mixed with coke fines, the coke fines being added in 1
to 10% by weight of the chromite fines, preferably in 1 to 3% by weight.
The mixture is ball milled with water to provide a slurry. The slurry is
then subjected to filtration to a moisture content of 6 to 20%, to obtain
the chromite filter cake.
The chromite filter cake with coke is mixed with bentonite as binder. This
mixture contains 49% Cr2O3, 13% Fe (t) and 6% silica. This mixer is
divided in to 2 parts as Mix-A and Mix-B. Green pellets are directly
prepared from Mix-A. An alkaline compound is mixed to Mix-B in the
range of 0.01-0.05 weight percent of binder. The green pellets are
prepared from Mix-B. Green pellets from Mix-A and Mix-B are fired to
1200°C to 1300°C.
The invention will now be explained in greater detail with the help of the
following non-limiting example. However, the invention is not limited to
the ranges provided in the description and examples, and variations
thereof would still be within the scope of the invention.
EXAMPLE:
One tonne of chromite fines is mixed with 10 kgs of coke fines and
mixture is ball milled with water, to obtain a slurry. The slurry is filtered
to a moisture content of 10%, to obtain the chromite filter cake.
One tonne of chromite filter cake with coke is mixed with 10 kgs of
bentonite as binder. This mixture contains 49% Cr203, 13% Iron (t) and
6% silica. About l-5gms of a sodium based alkaline compound is mixed
with the mixture and green pellets are prepared. The green pellets are
fired to 1200°C to obtain the fired green pellets.
Properties of green and fired pellets of Mix-A and Mix-B are given in the
following table.

By the method according to this invention, size of the green pellets is
controlled during balling to the required size; the green and dry strength
of the chromite pellet is increased by 65% and 40% respectively; mean
strength of the fired chromite pellet is increased remarkably by 53% and
there is considerably less dust generation as observed during firing of the
green pellets.
WE CLAIM:
1. A process for the preparation of green pellets from chromite
filter cake, comprising adding a binder to chromite filter cake,
followed by a alkaline compound, mixing thoroughly to obtain a
mixture, preparing pellets from the mixture, followed by firing
the same to obtain fired green pellets.
2. The process as claimed in claim 1, wherein the chromite filter
cake is prepared by mixing coke fines and chromite fines or
chromite concentrate, and ball milling the mixture, followed by
adding water to obtain a slurry, followed by filtration of the
slurry to obtain the chromite filter cake.
3. The process as claimed in claim 2, wherein coke is mixed in 1 to
10%, preferably 1 to 3% by weight of the chromite fines.
4. The process as claimed in claim 2, wherein the slurry is filtered
to reduce the moisture content to 6 to 20%.
5. The process as claimed in claim 1, wherein the binder is added
in a proportion of 1 to 3% by weight, preferably 1 to 3% by
weight of the filter cake.
6. The process as claimed in claim 1, wherein the binder is
bentonite.
7. The process as claimed in claim 1, wherein the alkaline
compound is selected from sodium hydroxide, sodium
carbonate, potassium carbonate and the like.
8. The process as claimed in claim 1, wherein the alkaline
compound is added in a range of 0.01 to 0.05 percent by weight
of the binder.

This invention relates to a process for the preparation of green pellets
from chromite filter cake, comprising adding a binder to chromite
filter cake, followed by a alkaline compound, mixing thoroughly to
obtain a mixture, preparing pellets from the mixture, followed by
firing the same to obtain fired green pellets.