Note: Descriptions are shown in the official language in which they were submitted.
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RECOVERY OF METALS FROM CALCIUM-RICH MATERIALS
FIELD OF THE INVENTION
The present invention relates to recovery of valuable metals from cal-
cium rich iron containing materials by pyrometallurgical treatment and more
par-
ticularly to process comprising removal of calcium from the calcium rich iron
con-
taining starting material prior to the pyrometallurgical treatment.
BACKGROUND OF THE INVENTION
Some steel plants use iron ore that contains vanadium and other resi-
due metals. These metals and other nonferrous oxides typically end up in the
slag
during the steelmaking process. This slag is typically landfilled and not used
as a
product due to the fact that it contains the said metal oxide residues that
have
been proved to be harmful for the environment. The conventional way to recover
these valuable metals is to subject the said slag to smelting.
During the smelting process most of the iron- and vanadium oxides
(along with other trace alloying metals) are reduced to the metal phase in the
presence of a reductant (typically carbon bearing anthracite, coke or metallic
re-
ductants, typically Al, FeSi or any other reducing substance). Typically the
smelt-
ing vessel is an electric arc furnace (alternating current or direct current
type).
During the smelting process other unreduced oxides form the furnace slag,
Calci-
urn oxide in this slag makes the liquidus temperature of the slag high and as
much
as 24% w/w silica flux of total solid feed to the furnace may be required for
melt-
ing the slag. This amount reflects a situation where the fluxing mix consists
solely
of quartz and calcium content of the feed material is 45% w/w calculated as
CaO.
One of the disadvantages associated with the use of flux material is
that impurities resulting from the flux material end up in the obtained
products.
In this case metal product silicon content will be higher when silica flux is
used.
This is due to the higher silicon oxide input into the furnace compared to the
amount of formed metal, which stays roughly at the same level regardless of
the
used flux amount. Typically some percentage of the silicon fed to the system
re-
ports to the metal phase. Therefore when tonnage of input silicon is higher
while
rest of metal forming components stay the same, the metal silicon content will
be
higher also.
2
The metal phase from the smelting goes to a converting step, where
vanadium and other valuable metals are selectively oxidized to the slag. The
slag
is further treated with salt roasting. In the salt roasting calcium further
forms in-
soluble salts, in particular with vanadium, which causes losses in the
following
hydrometallurgical treatment stages if calcium is not removed to the
sufficient
level in the previous processing steps.
BRIEF DESCRIPTION OF THE INVENTION
An object of the present invention is thus to provide a process for re-
covery of valuable metal(s) from calcium rich iron containing materials so as
to
overcome the above problems.
The invention is based on the surprizing realization that removal of
calcium from calcium rich iron containing starting material prior to pyrometal-
lurgical treatment by leaching allows more efficient pyrometallurgical
treatment.
Removal of calcium from the material lowers the liquidus temperature of the ma-
terial in smelting and thus lowers the required amount of flux material or
even
makes use of flux material redundant. As a result the smelting phase feed
amount,
residual slag amount and energy consumption are significantly lower. Removal
of
calcium may also improve the quality of the products obtained from the pyromet-
allurgical treatment.
This invention can also be utilized to a processing option of feeding the
starting material after removal of calcium straight to roasting without the
previ-
ously explained smelting and converting steps. It is possible to reach such a
low
levels of calcium after the removal of calcium to avoid excessive formation of
in-
soluble calcium salts in the roasting.
Another benefit of the present process is that calcium removal step
removes hydroxides and carbonates bound in calcium such as Ca(OH)2 and CaCO3.
This lowers furnace energy and reductant consumption and makes gas handling
and pressure control of the furnace easier and therefore safer. In the
conventional
smelting process if the slag is stored outside pre-drying under 200 C only re-
moves free water and some of crystal waters and all hydroxides and carbonates
are left to the furnace feed.
Date Recue/Date Received 2022-12-21
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BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described in greater detail by
means of preferred embodiments with reference to the attached drawings, in
which
Figure 1 shows a first example of the present process;
Figure 2 shows a second example of the present process;
Figure 3 shows a third example of the present process; and
Figure 4 shows a fourth example of the present process.
DETAILED DESCRIPTION OF THE INVENTION
Provided herein is a process for recovery of metal(s) from a calcium
rich iron containing material, comprising
(a) leaching calcium one or more times from said calcium rich iron
containing material to obtain a calcium depleted iron containing material; and
(b) subjecting the calcium depleted iron containing material to pyro-
metallurgical treatment to recover metal(s) from said calcium depleted iron
con-
taining material.
The term "calcium rich iron containing material" refers to materials
comprising calcium, iron and optionally other valuable metal(s). Said other
valu-
able metals are typically at least vanadium. Typically the calcium rich iron
con-
taming material comprises at least 20% w/w, in particular at least 25% w/w,
more particularly at least 30% w/w, even more particularly at least 40% w/w,
calcium. Calcium is typically present as CaO, Ca(OH)2, CaCO3, calcium
silicates
and/or other calcium containing compounds. Typically the calcium rich iron con-
taining material comprises at least 5% w/w, in particular at least 10% w/w,
more
particularly at least 15% w/w, iron. In particular the calcium rich iron
containing
material comprises from 5 to 60% w/w iron. Iron is typically present as Fe304,
Fe2O3, FeO, metallic Fe and/or iron silicates.
In particular the calcium rich iron containing material further com-
prises vanadium, typically at least 0.2% w/w, in particular at least 0.5% w/w,
more particular at least 1% w/w, even more particularly at least 1.5% w/w. Va-
nadium is typically present as vanadium oxide(s), in particular V205.
A typical example of a calcium rich iron containing material suitable to
be treated by the present process is slag, such as steel converter slag or
steel mak-
ing slag. A particular example of said calcium rich iron containing material
is LD
slag, also known as basic oxygen furnace slag (BOS) or LD-converter slag, a by-
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product of the Linz-Donawitz process where pig iron is processed into crude
steel.
A particular example of the present process is a process for recovering
iron and vanadium from LD slag, comprising
(o) providing LD slag;
(i) leaching calcium one or more times from said LD slag to obtain cal-
cium depleted LD slag; and
(ii) subjecting the calcium depleted LD slag to pyrometallurgical
treatment to recover iron and vanadium from the calcium depleted LD slag.
The term "comprise" as used herein and hereafter describes the re-
ferred items in a non-limiting manner, e.g. the present processes comprising
de-
fined process stages consist, at least, of the said stages, but may
additionally,
when desired, comprise other process stages. However, the processes comprising
defined process stages may consist of only the said process stages.
In accordance with the present process the present calcium rich iron
containing material is subjected to (a) leaching to remove calcium from the
mate-
rial prior to (b) pyrometallurgical treatment(s).
Figure 1 shows a first example of the present process wherein calcium
rich iron containing material 8 is fed to a calcium removal stage 1, wherein
the
calcium removal is accomplished by leaching in a (calcium poor) leaching
solution
10 to obtain a calcium depleted material 13 and calcium rich leaching solution
9.
The thus obtained calcium depleted iron containing material 13 is then fed to
a
pyrometallurgical treatment stage, which in this example is a smelting stage 3
performed under an elevated temperature and reducing conditions and in the
presence of a flux material 14 to obtain hot metal 17 which comprises the
desired
valuable metals, slag 15 and evaporated material 16. The calcium rich leaching
solution 9 obtained from the calcium removal stage 1 is subjected to calcium
pre-
cipitation 2 by feeding a carbon dioxide containing gas 11 into the calcium
rich
leaching solution to precipitate calcium carbonate (CaCO3) 12 and to obtain a
cal-
cium poor leaching solution 10 which is then recirculated back to the calcium
re-
moval stage 1.
Figure 2 shows a second example of the present process. In the pro-
cess illustrated in Figure 2 a calcium rich iron containing material 8 is
subjected
to a calcium removal stage 1 accomplished by leaching in a (calcium poor)
leach-
ing solution 10 to obtain a calcium depleted iron containing material 13 and
cal-
cium rich leaching solution 9. The thus obtained calcium depleted iron
containing
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material 13 is then fed to a pyrometallurgical treatment stage, which in this
ex-
ample is a roasting stage 5 performed under an elevated temperature, typically
in
the presence of salt(s), to obtain a roasted slag 20 which comprises the
desired
valuable metals. Calcium rich leaching solution 9 obtained from the calcium re-
5 moval stage 1
is subjected to calcium precipitation 2 by feeding a carbon dioxide
containing gas 11 into the calcium rich leaching solution to obtain calcium
car-
bonate (CaCO3) 12 and a calcium poor leaching solution 10 which is
recirculated
to the calcium removal stage 1.
Suitable leaching solutions for removing calcium from the calcium rich
iron containing material in stage (a), and similarly in stage (i), are e.g.
those se-
lected from the group consisting of acetic acid, nitric acid, propionic acid,
aqueous
solutions of ammonium salts, such as aqueous solution of ammonium acetate
(CH3COONH4), ammonium chloride (NH4C1) or ammonium nitrate (NH4NO3),
Preferably the present leaching solution is an aqueous salt solution, in
particular
an aqueous solution of an ammonium salt, more particularly an aqueous solution
of ammonium acetate (CH3COONH4), ammonium chloride (NH4C1) or ammonium
nitrate (NH4NO3), most preferably ammonium chloride (NH4C1). The salt concen-
tration of the aqueous salt solution is typically from 0.2 to 8 M, preferably
0.5 to 5 M,
more preferably 0.5 to 2 M.
Leaching in the calcium removal stage (a), and similarly in stage (i), is
typically performed at a temperature of from 0 to 100 C, preferably from 10 to
70 C, more preferably from 20 to 70 C. Most preferably, the leaching is
performed
at temperature of 20 to 60 C, using an aqueous salt solution. The desired
crystal
form of the precipitated calcium carbonate has an effect on the leaching
tempera-
ture since different crystal forms precipitate in different temperatures and
the
solution is circulated. There is no need to cool down or heat the solution
before
leaching stage.
Leaching in the calcium removal stage (a), and similarly in stage (i),
may be performed one or more times.
As calcium removal is stage (a), and similarly in stage (i), is performed
to lower the calcium concentration in the feed to the pyrometallurgical
treatment
stage (b), and similarly to stage (ii), and in smelting some calcium is needed
to
lower the liquidus temperature of the slag, it is a matter of optimization
whether
the calcium is removed only partly in the calcium removal stage (a), and
similarly
in stage (i), and/or whether some calcium rich iron containing material is fed
di-
rectly to the smelting without calcium removal, or whether calcium is removed
as
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much as possible in the calcium removal stage (a), and similarly in stage (i).
Pref-
erably at least 60% w/w of the calcium present in the calcium rich iron
containing
material is removed.
When calcium is desired to be removed only partly, it is preferred to
perform a single stage leaching in stage (a), and similarly in stage (i), and
prefera-
bly to remove from 60 to 90% w/w, more preferably from 65 to 85% w/w of the
calcium from the calcium rich iron containing material. In this case the
amount of
calcium in the calcium depleted iron containing material is preferably below
25%
w/w, more preferably below 20% w/w, even more preferably below 17% w/w.
When as much calcium as possible is desired to be removed, then
leaching is preferably repeated until at least 70% w/w, more preferably from
75% to 100% w/w, even more preferably from 80% to 99% of the calcium pre-
sent in the calcium rich iron containing material is removed. In this case the
amount of calcium in the calcium depleted iron containing material is
preferably
below 20% w/w, more preferably below 15% w/w, even more preferably below
10% w/w, most preferably below 1% w/w. Typically when calcium is needed to
be removed as much as possible, the calcium leaching stage (a) or (i) is
performed
twice. The number of leaching stages indicated herein refers to number of
times
of taking a fresh (calcium poor) leaching solution to the leaching stage (a),
and
similarly to stage (i). Accordingly the several leaching stages may also be
per-
formed as separate leaching stages wherein leaching is performed in
consecutive-
ly arranged leaching vessels or in a single leaching vessel which is
successively
refilled with fresh (calcium poor) leaching solution.
As discussed above in context of the first and second examples, in step
(a), and similarly in step (i), in addition to the calcium depleted iron
containing
material, a used leaching solution containing calcium dissolved from the
calcium
rich iron containing material is obtained. Herein and hereafter said used
leaching
solution is also referred to as a calcium rich leaching solution. If recovery
and re-
use of said used leaching solution is desired, calcium should be removed from
the
used leaching solution to obtain a calcium poor leaching solution. Preferably
this
is accomplished by precipitation.
A typical example of precipitation of the calcium from the calcium rich
leaching solution is carbonation. This may be accomplished by (c) optionally
first
filtering the used calcium rich leaching solution to remove any residual
calcium
rich iron containing material from said calcium rich leaching solution; and
(d)
bubbling carbon dioxide containing gas, in particular carbon dioxide, into the
cal-
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cium rich leaching solution to precipitate calcium carbonate and thus to
remove
calcium from said calcium rich leaching solution to obtain a regenerated
calcium
poor leaching solution. Said regenerated calcium poor leaching solution may
then
be (e) recycled to stage (a) or (i), respectively. The carbon dioxide required
in
stage (d) may be obtained e.g. from flue gas or other sources. The temperature
of
the carbonation depends on the desired crystal form of the precipitated
calcium
carbonate. Different crystal forms precipitate in different temperatures, for
ex-
ample aragonite can be precipitated at 60 C.
After removal of calcium from the material, the calcium depleted iron
containing material is subjected to a pyrometallurgical treatment stage (b) or
(ii).
Before feeding the calcium depleted iron containing material to the
pyrometallur-
gical treatment stage (b) or (ii) said calcium depleted iron containing
material is
preferably dried.
The present pyrometallurgical treatment stage (b) or (ii) may be any
one or more pyrometallurgical treatment(s) known to a skilled person and found
suitable for recovering desired valuable metals from the treated calcium
depleted
iron containing material. Typically the pyrometallurgical treatment is at
least
smelting or roasting. Preferably the calcium depleted material is subjected to
at
least smelting.
Due to the previous calcium removal stage (a) or (i) the mass flow of
the calcium depleted iron containing material to the pyrometallurgical stage
(b)
or (ii), respectively, is smaller as compared to untreated calcium rich iron
con-
taining material as calcium is one of the major elements in the calcium rich
iron
containing material. This allows reduction of furnace size and decreases the
amount of needed electricity during the pyrometallurgical treatment and/or al-
lows increase of the capacity.
Further, the liquidus temperature of a mixture of said calcium deplet-
ed iron containing material and optional desired amount of untreated calcium
rich iron containing material is lower as compared to the respective untreated
calcium rich iron containing material. Therefore the use of flux materials is
mini-
mized. This is relevant in particular when the material is subjected to
smelting in
stage (b), and similarly in stage (ii).
In cases where reaching of desired slag region requires addition of cal-
cium containing material it may be possible to also add some untreated calcium
rich iron containing material to the pyrometallurgical process stage.
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In accordance with the present process flux material may be used to
reach the correct slag region in the smelting stage. Preferably the amount of
add-
ed flux material (being other than the original calcium rich iron containing
feed
material without calcium removal treatment) is less than 45% w/w, more prefer-
ably less than 15% w/w and in some cases no fluxes are needed. Possible flux
ma-
terials include conventional flux materials such as those selected from the
group
consisting of lime, wollastonite, bauxite, quartz and olivine, as well as
other mate-
rial comprising SiO2, CaO, MgO, and/or A1203.
Furthermore, iron and/or iron pellets or any other material compris-
ing FeO, Fe304, Fe2O3 and/or V205 or other materials containing significant
por-
tion of iron and/or vanadium may be added when desired. Preferably in smelting
the slag region is selected to minimize the fluxing in the smelting. The
following
slag regions are possible: as merwinite, mellilite, rankinite, akermanite,
fosterite,
spinel, monticellite, pseudowollastonite, pyroxene, dicalciumsilicate,
periclase,
anorthite, cordierite, mullite and other similar regions.
When the calcium deplete iron containing material is subjected to
smelting in stage (b), and similarly in stage (ii), the smelting stage may be
per-
formed under conditions known to a skilled person, i.e. under elevated tempera-
ture and reducing conditions and in the presence of optional flux material(s)
as
discussed above. Coke is typically used as a carbon reductant in the smelting
stage; however the carbon reductant can be any other carbon bearing reductant,
such as anthracite. Reductant may also be metallic reductant, use of which
affects
energy consumption and feed rates. The smelting may be followed by converting
when so desired. The smelting and the optional converting may also be followed
by roasting when so desired.
In cases where iron containing material is fed directly to a roasting
process without a smelting phase, it may form insoluble vanadium bearing calci-
um salts if it comprises excessive amounts of calcium. To minimize the
formation
of such salts the calcium needs to be removed from the untreated calcium rich
iron containing as much as possible in the calcium removal stage (a) or (i).
When
the calcium deplete iron containing material is subjected to roasting in stage
(b)
and similarly in stage (ii), the roasting stage may be performed under
conditions
known to a skilled person, i.e. under elevated temperature, typically in the
pres-
ence of salt(s), to obtain a roasted slag. Salts used in the roasting stage
are con-
.. ventionally NaCl, Na2CO3 and Na2SO4.
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The calcium depleted iron containing material is preferably fed into
the pyrometallurgical stage (b) or (ii) as fine material. It may also be
pelletized,
sintered and/or pre-treated by any other suitable means known to a skilled per-
son.
Figure 3 shows a third example of the present process wherein calci-
um rich iron containing material further comprising vanadium 8 is subjected to
a
calcium removal stage 1 accomplished by leaching in a (calcium poor) leaching
solution 10. The obtained calcium depleted iron and vanadium containing materi-
al 13 is then subjected to a smelting stage 3 under elevated temperature and
re-
ducing conditions in the presence of flux material(s) 14 to obtain hot metal
17
which comprises iron and vanadium, slag 15 and evaporated material 16. The
calcium rich leaching solution 9 obtained from the calcium removal stage 1 is
sub-
jected to calcium precipitation 2 by feeding a carbon dioxide containing gas
11
into the calcium rich leaching solution to precipitate calcium carbonate
(CaCO3)
12 and to obtain a calcium poor leaching solution 10 which is recirculated to
the
calcium removal stage 1. Hot metal 17 comprising iron and vanadium obtained
from smelting 3 is then subjected to converting 4 to obtain pig iron 18 and
slag
comprising vanadium and iron 19. The slag 19 is then subjected to roasting 5
per-
formed under an elevated temperature, typically in the presence of salt(s), to
ob-
tam n roasted slag 20 which comprises vanadium and iron and which is then fur-
ther subjected to hydrometallurgical treatment 6 to obtain a stream comprising
iron and vanadium 22 and rejected material 21. The stream comprising iron and
vanadium 22 is then subjected to an aluminothermic reduction treatment 7 to
obtain ferrovanadium 23.
Figure 4 shows a fourth example of the present process wherein calci-
um rich iron containing material further comprising vanadium 8 is subjected to
a
calcium removal stage 1 accomplished by leaching in a (calcium poor) leaching
solution 10. The obtained calcium depleted iron and vanadium containing materi-
al 13 is then subjected to roasting 5 under elevated temperature, typically in
the
presence of salt(s), to obtain a roasted slag 20 which comprises iron and
vanadi-
um. Calcium rich leaching solution 9 obtained from the calcium removal stage 1
is
subjected to calcium precipitation 2 by feeding a carbon dioxide containing
gas 11
into the calcium rich leaching solution to precipitate calcium carbonate
(CaCO3)
12 and to obtain a calcium poor leaching solution 10 which is recirculated to
the
calcium removal stage 1. The roasted slag 20 which comprises iron and vanadium
is further subjected to hydrometallurgical treatment 6 to obtain a stream corn-
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prising vanadium 22 and rejected material 21. The stream comprising the
desired
valuable metals 22 is then subjected to aluminothermic reduction treatment 7
to
obtain ferrovanadium 23.
EXAMPLES
5 The examples
for conventional and Ca-removed material are calculat-
ed with the same assumptions. V production (V content in hot metal) is fixed
to
5000 tpa. V-yield is fixed to 90%. In examples, preheating/prereduction of the
feed material and the availability of the furnace are not taken into account.
Tem-
peratures of tapped hot metal, tapped slag and furnace gas are fixed.
Metallurgical
10 coke is used
as a carbon reductant in the calculation. The electric and heat losses
in electric furnace are not taken into account, because they depend on the
select-
ed furnace type, furnace size and operating parameters. Also in the examples
it is
assumed that the material is fed as a fine material into the furnace
(pelletizing
and sintering/hardening/induration changes the energies and mass balances).
The used slag regions in examples are suitable for the process and are
selected to minimize the fluxing in the smelting.
In examples 4 to 7 the main feed material to the smelting is treated
with calcium removal process. In that process 90% of the calcium containing
compounds is removed from the feed material. The feed material is not altered
in
any other way.
Reference example 1
In the conventional process Ca-rich material is fed directly into the
furnace with quartz and carbon reductant. The slag region is mainly
wollastonite
(can be also similar areas). The total feed rate into furnace is 49.8 t/h and
the to-
tal need for fluxes is 12 t/h. The electric power is 48 MW (excl. losses). The
ener-
gy consumption is 6724 kWh/t of hot metal. Slag/metal ratio is 4.4. The produc-
tion of hot metal is 7.1 t/h and for slag is 31 t/h. The content of V and Si
in hot
metal is 8.1 and 10.9%, respectively.
Reference example 2
In the conventional process Ca-rich material is fed directly into the
furnace with quartz, olivine and carbon reductant. The slag region is mainly
mer-
winite (can be also similar areas). The total feed rate into furnace is 54.8
t/h and
the total need for fluxes is 16.9 t/h. The electric power is 52 MW (excl.
losses).
The energy consumption is 6809 kWh/t of hot metal. Slag/metal ratio is 4.6.
The
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production of hot metal is 7.7 t/h and for slag is 35 t/h. The content of V
and Si in
hot metal is 7.5 and 9.6%, respectively.
Reference example 3
In the conventional process Ca-rich material is fed directly into the
.. furnace with quartz, olivine, bauxite and carbon reductant. The slag region
is
mainly spinel (can be also similar areas). The total feed rate into furnace is
72.0 t/h
and the total need for fluxes is 33.0 t/h. The electric power is 67 MW (excl.
loss-
es). The energy consumption is 8367 kWh/t of hot metal (excl. losses).
Slag/metal
ratio is 5.8. The production of hot metal is 8.1 t/h and for slag is 47 t/h.
The con-
tent of V and Si in hot metal is 7.1 and 9.0%, respectively.
Example 4
In accordance with the present process, Ca removed material is fed di-
rectly into the furnace with Ca-rich material and carbon reductant. The slag
re-
gion is mainly melilite (can be also similar areas). The total feed rate into
furnace
is 23.7 t/h and the total need for fluxes is 7.0 t/h, where 7.0 t/h (all of
the fluxes)
is the original feed material bypassing the Ca removal process. The electric
power
is 24 MW (excl. losses). The energy consumption is 3753 kWh/t of hot metal
(excl.
losses). Slag/metal ratio is 1.6. The production of hot metal is 6.5 t/h and
for slag
is 10 t/h. The content of V and Si in hot metal is 8.8 and 3.3%, respectively.
Example 5
In accordance with the present process, Ca removed material is fed di-
rectly into the furnace with Ca-rich material, quartz, olivine and carbon
reductant.
The slag region is mainly merwinite (can be also similar areas). The total
feed rate
into furnace is 31.8 t/h and the total need for fluxes is 17 t/h, where 12.9
t/h is
the original feed material bypassing the Ca removal process. The electric
power is
MW (excl. losses). The energy consumption is 4489 kWh/t of hot metal (excl.
losses). Slag/metal ratio is 2.3. The production of hot metal is 6.8 t/h and
for slag
is 16 t/h. The content of V and Si in hot metal is 8.4 and 4.7%, respectively.
Example 6
30 In accordance with the present process, Ca removed material is fed di-
rectly into the furnace with dolomite, bauxite and carbon reductant. The slag
re-
gion is mainly spinet (can be also similar areas). The total feed rate into
furnace is
35.2 t/h and the total need for fluxes is 13.3 t/h, where 0 t/h is the
original feed
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material bypassing the Ca removal process. The electric power is 35 MW (excl.
losses). The energy consumption is 5314 kWh/t of hot metal (excl. losses).
Slag/metal ratio is 2.3. The production of hot metal is 6.5 t/h and for slag
is 15 t/h.
The content of V and Si in hot metal is 8.8 and 3.4 %, respectively.
Example 7
In accordance with the present process, Ca removed material is fed di-
rectly into the furnace with Ca-rich material, dolomite, iron
pellets/concentrate
and carbon reductant. In the example the Si in hot metal is diluted to 1.0%
(the
feed rate of the iron bearing material is 26 t/h). The slag region is mainly
merwin-
ite (can be also similar areas). The total feed rate into furnace is 59.8 VII
and the
total need for fluxes is 11.0 t/h, where 4 t/h is the original feed material
bypass-
ing the Ca removal process. The electric power is 71 MW (excl. losses). The
ener-
gy consumption is 2965 kWh/t of hot metal (excl. losses). Slag/metal ratio is
0.6.
The production of hot metal is 23.9 t/h and for slag is 14 t/h. The content of
V and
Si in hot metal is 2.4 and 1.0%, respectively.
Reference example 8
Conventional roasting of such material is done with salt roasting. The
purpose of the roasting is to produce water-soluble vanadium compound. The
conventional feed material comes from the smelting and converting process and
contains very small amounts of calcium. Typically process requires less than
1%
of free lime in the feed material. The amount of salt fed to the roasting is
propor-
tional to the vanadium content of the feed material to roasting. Salts used in
the
roasting are conventionally NaCl, Na2CO3 and Na2SO4.
The calcium containing feed material is not suitable to the convention-
al salt roasting process since a high calcium concentration causes formation
of
vanadium bearing calcium compounds that are insoluble to the subsequent leach-
ing process. Vanadium that is not leached cannot be recovered in the leaching
process. Accordingly in the presence of calcium the vanadium losses in the
subse-
quent leaching stage are too high to reach economical process.
Example 9
In accordance with the present process, when calcium depleted mate-
rial is fed to the roasting the calcium content is significantly lower and the
losses
of vanadium are significantly lower. It has been studied that with slag
calcium-
vanadium ratio is no higher than 0.42 calculated as CaO and V205 respectively
the
CA 03018028 2018-09-17
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13
vanadium recovery of 93% can be achieved in the subsequent leaching process.
This ratio would be achieved with calcium rich feed material used in the
previous
examples when 97% wfw of calcium is removed in the calcium removal stage.
Conclusions
The results of the Examples 1 to 7 are shown in Table 1. As can be
seen, the use of calcium removed slag provides lower smelting power require-
ment and lower Si level in hot metal. Also slag vs. metal ratio is lower when
using
calcium removed slag.
Table 1
# Smelting power requirement Slag/metal V in hot metal Si
in hot metal
MW ratio
1 48 4.4 8.1 10.9
2 52 4.6 7.5 9.6
3 67 5.8 7.1 9.0
4 24 1.6 8.8 3.3
5 30 2.3 8.4 4.7
6 35 2.3 8.8 3.4
7 71 0.6 2.4 1.0
It will be obvious to a person skilled in the art that, as the technology
advances, the inventive concept can be implemented in various ways. The inven-
tion and its embodiments are not limited to the examples described above but
may vary within the scope of the claims.
