Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND ARRANGEMENT TO PREPARE CHROMITE
CONCENTRATE FOR PELLETIZING AND SINTERING AND
PELLETIZING FEED
Field of the invention
The invention relates to a method to prepare chromite concentrate for
pelletizing and
sintering as defined in the preamble of independent claim 1.
The invention also relates to an arrangement to prepare chromite concentrate
for
pelletizing and sintering as defined in the preamble of independent claim 6.
The invention also relates to a pelletizing feed as defined in the preamble of
independent
claim 13.
Publication WO 2013/071955 presents a process for the manufacture of
ferrochrome
alloy comprising the steps of providing a pelletizing feed, wherein the
pelletizing feed comprises
chromite concentrate and silicon carbide as the only carbonaceous material and
the only reducing
agent; pelletizing the pelletizing feed to obtain pellets; sintering the
pellets to obtain sintered
pellets; mixing the sintered pellets with external reducing agent to obtain
smelting feed; and
smelting the smelting feed.
Publication WO 2013/071955 presents a pelletizing feed containing chromite
ore, at least
one nickel salt, and silicon carbide as the only carbonaceous material and the
only reducing
agent. The invention also relates to process for manufacturing the pelletizing
feed comprising the
steps providing chromite, at least one nickel salt and silicon carbide, and
mixing chromite, at
least one nickel salt and silicon carbide. The invention also relates to use
of the pelletizing feed
as a starting material for the manufacture of sintering feed. The invention
also relates to a
sintering feed in the form of pellets containing the pelletizing feed. The
invention also relates to
sintered pellets containing the sintering feed. The invention also relates to
process for
manufacturing the sintered pellets. The invention also relates to use of the
sintered pellets as a
component of smelting feed. The invention also relates to smelting feed
comprising sintered
pellets. The invention also relates to process for manufacturing ferrochrome
alloy. The invention
also relates to ferrochrome alloy obtainable by the method.
Both publication WO 2013/071955 and publication WO 2013/071955 suggests that
the
pelletizing feed, from which the sintered pellets are made, may comprise
fluxing agents, such as
limestone, dolomite, quarts, calcite or wollastonite and any mixture thereof.
A reason for adding
fluxing agent to the pelletizing feed is to achieve sufficient compressive
strength of the sintered
pellets which are produced in the subsequent sintering process by using the
pelletizing feed. A
sufficient compressive strength Fl2mm is typically between 180 and 220 kg. A
disadvantage by
using the fluxing agents mentioned in publication WO 2013/071955 and in
publication WO
2013/071955, limestone, dolomite, quarts, calcite or wollastonite and any
mixture thereof, is that
these are relatively expensive.
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Publication US 3,825,638 presents a method for producing cold bound
agglomerates
from particulate iron oxide containing mineral concentrates using a steam
hardenable binder. The
binder is ground down together with iron. oxide material at a high enemy input
to produce a fine
grain additive material. The additive material is then mixed with the mineral
concentrates and
agglomerates are formed from the mixture and steam hardened.
Publication WO 2015/003669 relates to fluxing agents for the agglomeration
process
based on slag from the secondary metallurgy, the use of these fluxing agents
in the process of
agglomeration in the manufacture of the agglomerate designed for the use as a
metallic Charge in
blast furnaces and a process of production of fluxing agents based on slag
from the secondary
metallurgy or based on a mixture of slag from the secondary metallurgy with
other materials.
Objective of the invention
An object of the invention is to provide a method and an arrangement to
prepare chromite
ore for pelletizing and sintering and correspondingly to provide a pelletizing
feed by means of
which a pelletizing feed, containing fluxing agent for obtaining sufficient
strength of the sintered
pellets which are produced in the subsequent sintering process by using the
pelletizing feed, can
be obtained by using less expensive raw material.
Short description of the invention
The method to prepare chromite concentrate for pelletizing and sintering of
the invention
is characterized by the definitions of independent claim 1.
Preferred embodiments of the method are defined in the dependent claims 2 to
5.
The invention relates also to the use of the method according to any of the
claims 1 to 5
in a process for producing ferrochrome alloy from chromite concentrate.
The arrangement to prepare chromite concentrate for pelletizing and sintering
of the
invention is correspondingly characterized by the definitions of independent
claim 6.
Preferred embodiments of the arrangement are defined in the dependent claims 7
to 10.
The invention relates also to the use of the arrangement according to any of
the claims 6
to 10 in an arrangement for producing ferrochrome alloy from chromite
concentrate.
The pelletizing feed is correspondingly characterized by the definitions of
independent
claim 13.
Preferred embodiments of the pelletizing feed are defined in the dependent
claims 14 to
17.
The invention relates also to sintered pellets as defined in claim 18
containing the
pelletizing feed according to any of the claims 13 to 17.
The invention relates also to the in claim 19 defined use of the sintered
pellets according
to claim 18 as a component of smelting feed.
The invention relates also to a smelting feed as defined in claim 20
containing the
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sintered pellets according to claim 18.
The invention relates also to a process as defined in claim 21 for
manufacturing
ferrochrome alloy comprising the step of smelting the smelting feed according
to claim 20.
The invention relates also to ferrochrome alloy as defined in claim 22 and
obtainable by
the process according to claim 21.
The invention is based on that the fluxing agent that is used is at least
partly slag
originating from processing of ferrous metal.
By method, the arrangement and the pelletizing feed, sintered pellets having a
compressive strength Fl2mm of more than 200 kg can be produced.
The compressive strength of the sintered pellets Fl2mm can be calculated
according to the
following formula:
Fl2mm = (12 / D) * FD, where
D: measured diameter of the pellet (mm)
12: reference diameter of the desired pellet (mm)
FD: the measured compressive strength of the pellet (kg/pellet)
List of figures
In the following the invention will described in more detail by referring to
the figures,
which
Figure 1 is a schematic flow chart of a first embodiment of equipment
containing an
arrangement according to an embodiment of the invention,
Figure 2 is a schematic flow chart of a second embodiment of equipment
containing an
arrangement according to an embodiment of the invention,
Figure 3 is a schematic flow chart of a third embodiment of equipment
containing an
arrangement according to an embodiment of the invention, and
Figure 4 is a schematic flow chart of a fourth embodiment of equipment
containing an
arrangement according to an embodiment of the invention.
Detailed description of the invention
First the method to prepare chromite concentrate 5 for pelletizing and
sintering and some
preferred embodiments and variants of the method will be described in greater
detail.
Chromite is the ore which is excavated from the chromite deposit. The chromite
concentrate is the product of the beneficiation plant. The gangue components
are mainly
separated to the wastes for improving the grade of chromite for the
pelletizing and sintering.
The method comprises a providing step for providing a chromite concentrate
feed 1 and
an adding step for adding at least fluxing agent 2 to the chromite concentrate
feed 1 to obtain a
pelletizing feed 12.
A purpose of the fluxing agent 2 is to lower the melting point of the slag
forming
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components in the pelletizing feed 12 and to provide more slag forming
components to the
pelletizing feed 12. Another purpose of the fluxing agent is to during a
sintering process, where
pellets previously formed of the pelletizing feed 12 is sintered into sintered
pellets, to provide
more connections and connections of better quality in the sintered pellets by
melting and
subsequently solidifying the binding silicates in the fluxing agent 2.
The method may include a fine-dividing step for fine-dividing the chromite
concentrate
feed 1 to a particle size distribution of 70 to 90 % below 74 pm, preferably
80 2% below 74 pm,
and more preferably about 80% below 74 p.m for example in a mill 3.
In the adding step of the method, fluxing agent 2 in the form of slag 4
originating from
processing of ferrous metal (including ferroalloys) is added to the chromite
concentrate feed 1.
The particle size distribution of the fluxing agent 2 may be 80 to 100%,
preferably 100 %
below 74 p.m (200 mesh).
The method may include a fine-dividing step for fine-dividing the slag 4 prior
the adding
step for example by milling in a mill 3.
In the adding step of the method, additionally at least one of the following
may be added
to the chromite concentrate feed 1: (i) carbonaceous material 6 such as coke,
(ii) dust 7, and (iii)
binding agent 8 such as bentonite for example sodium-activated calcium
betonite, water-based
binding agent, and/or organic binding agent. The purpose of the possible
binding agent 8 is give
the pellets, which are produced from the pelletizing feed 12, enough dry- and
wet strength so that
the pellets can firstly withstand transportation from a means for forming
pellets such as from a
pelletizing drum or disc 16 to a sintering means such as to a steel belt
sintering furnace 19, where
the pellets are strengthened by performing sintering to produced sintered
pellets and secondly
withstand drying, heating, sintering in the sintering means until a desired
strengthening by
sintering is achieved. The strengthening effect of the binding agent in the
resulting sintered
pellets is quite marginal in comparison to the strengthening effect resulting
from fluxing agent
and gangue minerals in the chromite concentrate in sintering.
Binding agent 8 in the form of bentonite can for example contain the following
in
percentages of weight:
Si02: between 30 and 80 %,
A1203: between 0 and 40 %,
CaO: between 0 and 20 %,
MgO: between 0 and 20 %
Na20: between 0 and 20 %
K20: between 0 and 20 %
Fe203: between 0 and 20 %
Ti02: between 0 and 20 %
Volatiles: between 0 and 50 %
In the adding step of the method, an amount of carbonaceous material 6 may be
added to
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the chromite concentrate feed 1 so that the amount of added carbonaceous
material 6 in the
resulting pelletizing feed 12 in terms of percentages of weight of the
pelletizing feed 12 is
between 0.5 % and 3 %. The particle distribution of the of the carbonaceous
material 6 is
preferably between 70 and 80 % below 74 pm, more preferably 75 2% below 74 pm,
such as
5
75% below 74 p.m. and between 40 and 60 % below 37 pm, more preferably 55 %
below 37 p.m
In the adding step of the method, an amount of dust 7 may be added so that the
amount of
added dust 7 in the resulting pelletizing feed in terms of percentages of
weight of the pelletizing
feed 12 is between 3 and 12 %. The particle distribution of the dust 7 is
preferably between 75
and 100 % below 74 p.m.
In the adding step of the method, an amount of binding agent 8 may be added so
that the
amount of added binding agent 8 in the resulting pelletizing fees in terms of
percentages of
weight of the pelletizing feed 12 is between 0.5 and 3 %, preferably between
0.75 and 2.5 %,
even more preferably between 1.0 and 2.5 %, such as 1.5 %. The particle
distribution of the
binding agent is preferable 100% below 74 p.m.
In the method, slag 4 originating from processing of ferrous metal may be
added to
fluxing agent 2 prior the adding step so that fluxing agent 2 in the form or
at least one of
limestone, dolomite, quarts, or wollastonite and any mixture thereof and
fluxing agent 2 in the
form of slag 4 are at least partly mixed together prior the adding step. Such
embodiments are
illustrated in figures 1 and 3.
In the method, fluxing agent 2 in the form or at least one of limestone,
dolomite, quarts,
or wollastonite and any mixture thereof and fluxing agent 2 in the form of
slag 4 may be
separately added to the chromite concentrate feed 1 in the adding step. Such
embodiments are
illustrated in figures 2 and 4.
In the adding step of the method, fluxing agent 2 containing in percentages of
weight
between 10 and 100 %, preferably between 50 and 100 %, more preferably between
75 and 100
% slag 4 originating from processing of ferrous metal, may be added to the
chromite ore feed 1.
It is also possible to in adding step of the method to add fluxing agent 2
consisting solely of slag
4 originating from processing of ferrous metal to the chromite concentrate
feed 1.
In the adding step of the method, an amount of fluxing agent 2 may be added to
the
chromite concentrate feed 1 so that the resulting pelletizing feed 12 contains
in percentages of
weight between 1 and 10 %, preferably between 2 and 7 %, more preferable
between 3 and 6 %,
such as between 4 and 5 % fluxing agent 2.
The slag 4 originating from processing of ferrous metal and that is used as
fluxing agent
2 in the adding step of the method may contain in percentages of weight:
CaO: between 20 and 50 %, preferably between 35 and 45 %
5i02: between 20 and 50 %, preferably between 30 and 40 %
MgO: between 1 and 20 %, preferably between 5 and 15 %
A1203: between 1 and 20 %, preferably between 5 and 15 %
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Ti02: between 0 and 50 %, preferably between 0 and 15 %,
K20: less than 5 %, preferably less than 1 %
Na20: less than 5 %, preferably less than 1 %
The method may be used process for manufacturing ferrochrome alloy from
chromite
concentrate 5 such as in a process of the type as presented in publication WO
2012/172174.
Next the arrangement to prepare chromite concentrate 5 for pelletizing and
sintering and
some embodiments and variants of the method will be describe in greater
detail.
The arrangement comprises a first feeding arrangement 9 for providing a
chromite
concentrate feed 1, and a second feeding arrangement 10 comprising at least a
first feeding
means (not marked with a reference numeral) for adding fluxing agent 2 to the
chromite ore feed
1 to obtain a pelletizing feed 12.
The arrangement may comprise a mill 2 for fine-dividing the chromite
concentrate feed 1.
The arrangement may comprise a drying means 11 for reducing the moisture
content the
chromite concentrate feed 1.
The first feeding means of the second feeding arrangement 10 is configured to
add to the
chromite concentrate feed 1 fluxing agent 2 containing slag 4 originating from
processing of
ferrous metal.
The second feeding arrangement 10 may comprise additionally at least one of
the
following: a second feeding means (not marked with a reference numeral) for
adding
carbonaceous material 6 such as coke to the chromite ore feed 1, a third
feeding means (not
marked with a reference numeral) for adding dust 7 to the chromite ore feed 1,
and a fourth
feeding means (not marked with a reference numeral) for adding binding agent 8
such as
bentonite to the chromite ore feed 1.
The first feeding means of the second feeding arrangement 10 may be configured
to add
to the chromite concentrate feed 1 fluxing agent 2 containing in percentages
of weight between
10 and 100 %, preferably between 50 and 100 %, more preferably between 75 and
100 % slag 4
originating from processing of ferrous metal.
The first feeding means of the second feeding arrangement 10 may be configured
to add
fluxing agent 2 to the chromite concentrate feed 1 so that the pelletizing
feed 12 obtained
containing in percentages of weight between 1 and 10 %, preferably between 2
and 7 %, more
preferable between 3 and 6 %, such as between 4 and 5 % fluxing agent 2.
The first feeding means of the second feeding arrangement 10 may be configured
to add
fluxing agent 2 in the form of slag 4 originating from processing of ferrous
metal containing in
percentages of weight:
CaO: between 20 and 50 %, preferably between 35 and 45 %
Si02: between 20 and 50 %, preferably between 30 and 40 %
MgO: between 1 and 20 %, preferably between 5 and 15 %
A1203: between 1 and 20 %, preferably between 5 and 15 %
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K20: less than 5 %, preferably less than 1 %
Na20: less than 5 %, preferably less than 1 %
The arrangement may be used in an equipment for manufacturing ferrochrome
alloy from
chromite concentrate 5 such as in an equipment of the type as presented in
publication WO
2012/172174.
The equipment presented in figures 1 and 3 comprises a slurry mixer 13, which
is
configured to mix the chromite concentrate feed 1 discharged from the mill 3.
The equipment presented in figures 1 and 3 comprises a filter 14, which is
configured to
dewater the chromite concentrate feed 1.
The equipment presented in the figures comprises a mixer 15, which is
configured to mix
the pelletizing feed 14 formed of chromite concentrate feed 1 and the fluxing
agent 2 containing
slag 4 and the optional carbonaceous material 6, dust 7, and binding agent 8.
The equipment presented in the figures comprises a pelletizing drum or disc
16, which is
configured to pelletize the pelletizing feed 14 to form pellets 17.
The equipment presented in the figures comprises a roller screen 18, which is
configured
to ensure that uniformly sized pellets only are fed as an even pellet bed to
an endless conveyor
belt of a steel belt sintering furnace 19 so as to form sintered pellets 20 of
the pellets 17.
The equipment presented in the figures comprises a third feeding arrangement
21 for
feeding sintered pellets 21 together with additives such as lumpy ore, coke
and quartz into a
preheating kiln 22, which is configured to preheat the sintered pellets 21
prior charging the
sintered pellets 21 into an smelting furnace 23. From the smelting furnace
ferrochrome alloy 24
is discharged.
The equipment presented in the figures comprises also a high pressure water
scrubber 25
for cleaning gas originating from the smelting furnace.
The equipment presented in figures 3 and 4 comprises also a burning means 25
that is
arranged to receive carbon monoxide (CO) from the high pressure water scrubber
25 and to burn
carbon monoxide (CO) to produce thermal energy for the drying means 11.
Next the pelletizing feed 12 containing chromite concentrate 5 and fluxing
agent 2 and
some embodiments and variants of the pelletizing feed 12 will be described in
greater detail.
The fluxing agent 2 contains slag 4 originating from processing of ferrous
metal.
The pelletizing feed 12 may contain additionally at least one of the
following: (i)
carbonaceous material 6 such as coke, (ii) dust 7, and (iii) binding agent 8
such as bentonite.
The fluxing agent 2 may contain in percentages of weight between 10 and 100 %,
preferably between 50 and 100 %, more preferably between 75 and 100 % slag 4
originating
from processing of ferrous metal.
The pelletizing feed 12 may contain in percentages of weight between 1 and 10
%,
preferably between 2 and 7 %, more preferable between 3 and 6 %, such as
between 4 and 5 %
fluxing agent 2.
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The slag 4 originating from processing of ferrous metal may contain in
percentages of
weight:
CaO: between 20 and 50 %, preferably between 35 and 45 %
Si02: between 20 and 50 %, preferably between 30 and 40 %
MgO: between 1 and 20 %, preferably between 5 and 15 %
A1203: between 1 and 20 %, preferably between 5 and 15 %
K20: less than 5 %, preferably less than 1 %
Na20: less than 5 %, preferably less than 1 %
Examples
Twelve (12) lab tests was performed with test materials Cl and C2 using
bentonite as
binding agent and as fluxing agents wollastonite, calcite, dolomite and slag
originating from a
blast furnace.
The test materials Cl and C3 had the composition in percentages of weight
mentioned in
table 1.
Table 1. Chemical analysis of chromites.
Component Chromite Cl Chromite C2
(Cr tot) (30.5) (39.7)
Cr203 44.6 58.0
(Fe tot) (15.8) (10.6)
Fe203 22.1 14.5
FeO 0.4 0.6
Si02 4.9 0.9
A1203 12.0 10.0
MgO 8.6 11.5
CaO <0.028 <0.028
Volatiles, crystal water 4.5 1.6
The slag had the following composition in percentages of weight:
- MgO: 8.3 %
-A1203: 10.1%
- Si02: 35.9 %
- Ca0: 40.9 %
The pelletizing was carried out on a laboratory disc with a diameter of 400 mm
and a
depth of 150 mm. The moisture content, wet and dry strength of pellets was
measured.
Bentonite was used as a binder in the pelletizing.
The pelletizing mixture consisted of ground chromite concentrate and
wollastonite,
limestone and blast furnace slag as fluxes. The pelletizing batch was mixed
very carefully in a
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twin-shell mixer for 120 minutes.
The mixed batch was fed onto the disc manually. The batch was moistened with a
water
sprayer bottle according to the formation of the pellets. The desired diameter
of pellets is 12 mm.
The amount of fluxes was added according to the characteristics of the
pellets.
After the pelletizing, the diameter and compressive strength of the wet and
dried pellets
was measured. The moisture content of the pellets was also measured.
The aim of the sintering was to perform the tests for achieving a satisfactory
strength of
the sintered pellets, about 200 kg/ pellet (a diameter 12 mm).
The sintering was carried out in high aluminium crucible (0.25 litres) in an
induction
furnace. The sintering temperature was estimated to be in the range of 1300 -
1450 C. Air was
blown to the crucible to achieve oxidising sintering conditions. According to
normal practice the
temperature of the charge is measured during the tests. The batch was cooled
by air and the
samples are taken for analysing.
Table 2: test results:
AddrtNes Pe1tii-ZsdamtrZ3N.
WN.3.glts
Lab Test
. eÃ3 ntorete IWaas.Wne:e Catt.ite 1...1c4mttel .............. Morst
1.)ry .9nV,.,red Moist, Sesterea 113,,nsp.
Tevtiwa
% tyi dry t:est ntaVNtal trart F12
(1<g):
(270% 12
12.1 12,3 110 L 19,1 11i5 15!k
2 C.I
I" .......................................................... 12,0 13,2
t115
1111
a C7'% 1.2
12,1 12,2 12,0 0..0 1<7 224 19.15:1
4 (J70% L2 4 2
2,0 12,2 41,9 1,9 12,1 224 1590
Cl 4 12,0 12,2 1.2,o
IS31
6 CI 72,;:; 1,2 12:0 r>,3 12,0
LO 1.23 1960
7 C2 n% 1,0 12.0 1.12 12,0 1.4
1.0,7 2::t2 14CK}
C2 70% LO 2 .12,0 12,2 110
IA 111J 144 14W
5 .27% =
2 1.2,0 12.2 1.2,?, 1,4 5:5 209 1400
C27%O
12,0 l'>,2 12,1 L4 10,7 207 loi.)
(O% to 2 12.0 112 22.0
1(7 ifiS 1490
12 2 70% LO 2 2. 1.2,0 '112
1.2.1 IA 9,6 W.:3 I4M
As can be seen from table 2, by preparing a pelletizing feed containing 1 % in
terms of
percentages of weight) of bentonite as binding agent and between 4 and 5 % (in
terms of
percentages of weight) of fluxing agent consisting of 100 % slag or 50 % slag
and 50 %
Wollastonite, by pelletizing the pelletizing feed to obtain pellets, and by
sintering the pellets to
obtain sintered pellets, the result was sintered pellets having a compressive
strength Fl2mm of
more than 200 kg.
It is apparent to a person skilled in the art that as technology advances, the
basic idea of
the invention can be implemented in various ways. The invention and its
embodiments are
therefore not restricted to the above examples, but they may vary within the
scope of the claims.
