FIELD OF INVENTION
The present invention relates :o a process for lowering alumina content of
lumpy, fragile manganese ore used for ferromanganese making and in other
industries.
BACKGROUND OF THE INVENTION
Alumina is the major gangue mineral in the most of Indian manganese ores. It
increases the power cost as well as flux consumption in the process of
ferromanganese making. The manganese ores from Orissa, India are
ferruginous and inherently friable due to deposit formation conditions. Mined
high grade alumina rich manganese ores usually contain as high as 7% alumina.
The major mode of occurrences of alumina contributors are free discrete lumps
and fines; locked with other minerals in coarser size ranges and fillers and matrix
material in smaller size ranges.
Ferromanganese plants require manganese ore with high Mn/Fe ratio higher
than 5.5, high manganese content higher than 46%, low alumina (as low as
possible) and in lumpy form (75 to 10mm). The mined high grade manganese
ore feed lumps of ferromanganese plant from Orissa variably contains alumina
higher than 3.5% which demands more operating cost. Any effort to reduce
alumina from the high grade lumpy ores without size reduction is a cost effective
way and is of commercial importance.

The varieties of manganese ores found enriched by pryolusite mineral and this
mineral is brittle as well as softer in nature. Conventional methods of alumina
reduction cannot be applied because of its fragile nature.
SUMMARY OF THE INVENTION
The main object of the present invention therefore, is to provide a suitable
method for lowering the alumina content of lumpy, fragile manganese ore.
This object is achieved by providing a suitable washing method for dislodging the
surface adhering alumina contributing particles from the manganese ore lumps
with minimum loss of manganese.
The method of the present Invention towers the alumina content to less than
3.5% in ferromanganese plant lumpy feed ore sample without size reduction by
dry classification, washing and ore sorting, either manual or optical method.
The present invention thus provides a process for lowering alumina content of
lumpy, fragile manganese ore, comprissig the steps of: crusting run-of-maie
(ROM) ore with high alumina content to -75 mm; dry-classifying said ROM ore at
10 mm and removing -10 mm ore; washing 10-75 mm ore and removing sNme
produced; and manually sorting the lumpy ore on the basis of optical and
physical properties for separating concentrated lumps with low alumina content
from higher alumina content lumps; thereby lowering the alumina content of the
ore.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The process of the present invention can be described with the help of the
accompanying drawing where
Figure 1 shows the process flow sheet for lower rig alumina
Content of lumpy fragile manganese ore.
DETAILED DESCRIPTION
As shown in the process flow sheet of Figure 1, run-of-mine ore (ROM)
containing high alumina, of about 5.06 to 6.71 % by weight, is crushed to -75
mm size. The crushed ore is dn-classified at 10 mm. After dry-classification 6 -
8 % of the total weight of ore containing about 8.17 to 10.80 % alumina in - 10
mm size is separated and removed to the stockyard for further processing.
The remaining 92 - 94 % of -75 to 10 mm size ore containing about 4.9 - 6.4 %
alumina is washed.
In the method of the present invention the ore bed is kept stationary and water
is impinged on it with an optimum pressure and time to remove impurities and to
avoid any fragmentation. The whole processes is optimized with respect to time,
weight loss, and pressure. The optimized process conditions are water impinging
at about 20 psi pressure for 3 tc 5 minute process time.

After washing about 12 - 14 % of the washed ore containing about 9.71 to
12.16 % alumina will be produced in the form of slime which can be removed.
From the balance 86 - 88 % of washed ore lumps containing about 4.58 to 6.03
% alumina 20 - 30 % of the lumps having 6 - 8 % alumina are removed after
manual / optical classification and can be sent to the stockyard for further
processing. 70 - 80 % of the concentrated lump with less than 3.5 % alumina
are separated and manganese ore with a lowered alumina content of less than
3.5% alumina can be taken for plant use.
Thus in the first stage of AI2O3 reduction of fragile lumpy manganese ores of the
initial ore sample the alumina level of between 5.06 to 6.71% is brought down to
4.9 to 6.4 by dry classification at 10mm.
In the second stage of alumina reduction, the product of screening is washed at
20 psi pressure for 5 minutes by water impinging on a stationery ore bed.
Recovery of the process vary between 86-88% and level of alumina comes down
to 4.58 to 6.03% in the samples;.
In the third stage of alumina reduction manual sorting is performed on the
sample lumps on the basis of optical as well as physical properties. It is easy to
segregate the different mineral enriched lumps by following ore sorting
methodology. In this method recovery vary between 70-78% with alumina level
below 3.5%.
The method of the present invention is suitable for alumina reduction in the
lumpy manganese ores used as a process input in ferromanganese making and
in other industries. The sub-processes added help in removing the fines from
the ores to address the dust problem.

WE CLAIM
1. A process of upgrading lumpy, fragile manganese ore on lowering
alumina content in it comprising the steps of crushing run of mine
(ROM) ore containing high alumina content of 5.06-6.71 % by weight to
<75 mm size; dry classifying the said crushed ROM ore at 10 mm and,
separating and removing t to 8% of <10 mm size ore containing 8.17 to
10.80 % by weight alumina; the remaining 92-94 % of < 75 to 10 mm
size crushed ore containing 4.9-6.4% alumina is washed through water
impinging on the bed of said remaining crushed ore to obtain two
fractions of washed ore containing different alumina contents; removing
the first fraction in the form of slime of 12-14 % by weight containing
9.71 to 12.16 % alumina; :he remaining fraction of 86-88% by weight of
washed ore lumps contain 4.58 to 6.03 % wt alumina from which 20-30
% wt of the lumps containing 6-8 % wt alumina is removed through
optical/manual classification and the rest 70-80 % of the remaining
concentrated lump containing less than 3.5 % alumina is separated
through manual sorting thus resulting upgraded lumpy manganese ore
having <3.5 alumina.
2. The process of upgrading lumy, fragile manganese ore as claimed in
claim 1 wherein rejected crushed ore < 10 mm size during dry
classification at 10 mm size during dry classification at 10 mm, rejected
lump on ore sorting after washing are sent to stock yard and recycled
for further processing.

3. The process as claimed in claim 1 wherein the concentrated manganese
ore lump with alumina level brought below 3.5 % for plant use is
resulted of the amount of 70-78 % by wt.
4. The process as claimed in the preceding claims wherein the washing
step is carried out with impinging water at 20 psi pressure for 3 to 5
minutes on a stationery ore bed.
Dated this 23rd day of March 2006.

The present invention relates to a process for lowering alumina content of
lumpy, fragile manganese ore. The process comprises the steps of crushing run-
of-mine (ROM) ore with high alumina content to - 75 mm, dry-classifying said
ROM ore at 10 mm and removing -10 mm ore, washing 10-75 mm ore and
removing slime produced and sorting the lumpy ore on the basis of optical and
physical properties for separating concentrated lumps with low alumina content
from higher alumina content lumps, thereby lowering the alumina content of the
ore.