Note: Descriptions are shown in the official language in which they were submitted.
105~7~3
1 BACKGROUND OF THE INVENTION
The present invention relates to an improved method
for processing pig iron containing vanadium to produce a
valuable slag having a high ratio of vanadium to iron which
is useful in the production of vanadium alloys.
Vanadium in the form of its low-melting ferrovanadium
alloys, is widely used as an alloying agent to impart toughness
and other desirable properties to iron and steel. Among the
most useful vanadium alloying agents are the alloys produced
according to the process of Rathmann and Rasmussen U.S.
Patent 3,420,659 issued January 7, 1969. This process is
carried out in two steps. In the first step a vanadium-
; containing material is smelted with silica, a flux, and a
carbonaceous reducing agent to produce a primary vanadium
silicide having a silicon content of 25 to 60 percent.
Inasmuch as such a sLllcon content is too high for an alloying
agent for iron or steel, the primary silicide is refined in
the second step of the process by melting it with lime and
a vanadium-containing refining agent to increase the vanadium
content of the alloying agent and reduce its silicon content
to less than 20 percent. While the richest source of vanadium
; for the refining step is vanadium pentoxide, this material is
:
very expensive due to the chemical processing required in its
manufacture~ For that reason it is preferred to look else-
where~for the necessary vanadium. A number of relatively
inexpensive sources of vanadium exist such as spent catalysts,
petroleum residues and vanadium-bearing slags from the refining
28 of pig iron.
' '~ -
~' -1- '
,
~ ~ . . . .. .
109'~ 33
To be useful in the refining step of the Rathmann et al
process, a refining agent should contain at least about 8 percent
of vanadium. Materials containing up to about 34 percent
vanadium may be used with advantage. Materials having a higher
content can be economically processed by aluminum reduction
and so are not used in this process normally. Raw materials
containing less than ~ percent or more than 34 percent vanadium
may be blended to produce a refining agent having a suitable
concentration. It should be noted here that while throughout
this specification and appended claims vanadium content of the
various materials J such as ore, slag J pig iron or other material J
is expressed in terms of metallic vanadiumJ those skilled in
the art will appreciate that the vanadium values may be
present in various forms other than metallic vanadium, such
as V203, V204, V205 or some other vanadium compound.
The preerred refining agents for use in the Rathmann
et al. process are vanadium-containing slags derived from the
refining of vanadium-containing pig iron. Such slags are
available in hugh quantities and generally contain more than
~: .
the required 8 percent of vanadium. However, it is also
necessary to the process that ~he slag have a vanadium to iron
weight ratio of at least about 0.5J and preferably from about
0.75 to 1.0 J to be useful directly as a refining agent without
~: :
prlor deironing. Available slags are generally deficient in
- this respect~ For example, the South African Highveld slags
contain 12 to 16 percent vanadium, but their vanadium to iron
27 ratio is less th~n 0.5, typically only about 0.4.
: '
-2-
I . . . . . . .
~ .-, . .
.. . . . . . . .
1097(~3
In the Highveld process titaniferous magnetite ore
from the Bushveld igneous complex of South Africa, containing
about 1 percent vanadium, is fed into large prereduction kilns
together with appropriate amounts of coal, dolomite and silica
and heated to about 1830F. In this way the oxygen content
of the iron ore is reduced to about 70 percent of theoretical,
the coal is charred, and the dolomite is calcined. The hot
partially reduced burden of the kilns is conveyed in
refractory lined hoppers to bins feeding the smelting furnaces.
This material is then smelted in submerged arc electric
furnaces operated at a power input level of 20 to 25 megawatts
to procude hot metal which has the following typical analysis:
3.5 percent carbon, 1.28 percent vanadium, 0.25 percent
silicon, 0.16 percent titanium, 0.065 percent sulfur and
0.075 percent phosphorous. The slag from the smelting
operation generally analyzes: 20 percent TiO2, 18 percent CaO,
17 percent MgO, 19 percent SiO2 and 13 percent A12O3.
The resulting hot metal is blown with oxygen in a
shaking ladle at a temperature maintained below 2550F. with
~ 20 the addition of scrap and ore as necessary. The resulting
; blown metal contains only traces of metalloids and bout
3.1 percent carbon. The slag from the shaking ladle oxygen
blowing operation contains the bulk of the vanadium, typically
;~ about 14 percent vanadium by weight but, as noted above, the
vanadium to iron ratio of such Highveld slag is less than the
level of 0.5 needed in the refining operation of the Rathmann
27 et al. process, being typically about 0.4. For this reason,
--3--
105~'7~33
it is necessary to beneficiate or deiron such slags by
melting them with lime and treating the melt with sufficient
primary silicide from the process to reduce a substantial
part of the iron oxide to metallic iron which is separated
to increase the vanadium to iron ratio of the slag. This
beneficiation process also oxidizes the vanadium, silicon,
- titanium, manganese and chromium values of the primary
silicide and incorporates them in the deironed slag. In
view of the foregoing it is apparent that there has been a
long standing need in the art to provide an inexpensive -
vanadium-containing refining agent for use in the second
step of the Rathmann et al. process containing from about
8 to 34 percent vanadium and having a vandium to iron ratio
of at least about 0.5, and that it would be especially
desirable to provide for this purpose a slag from the
- refining of pig iron which would meet the necessary criteria
without the need for further beneficiation.
It is, therefore, a primary object of the present
invention to pro~ide an improved process for the direct
production, from vanadium-containing pig iron, of a slag
which contains a~ least 8 percent vanadium and which has
a vanadium to iron ra~io of at least about 0.5.
SUMNARY OF THE INVENTIO~
The foregoing and other objects of the invention which
will become apparent hereinafter are achieved by an improved
process for ~he refining of pig iron containing at least
about 0.5 percent vanadium to obtain a slag containing at
28 least about 8 percent vanadium and having a vanadium to iron
.
_4_
109';'083
ratio of at least about 0.5; the improvement consisting of
simultaneously introducing a highly oxidizing gas and a
protective fluid below the upper surface of a bath of the
molten metal maintained at a temperature of 2600F. to 2900F.
Preferably, the process is continued until the carbon content
of the metal is within the range of from about 2 to about 0.02
percent. It has been unexpectedly discovered that this results
in an increased recovery of vanadium and a marked increase
in the vanadium to iron ratio of the slag, thus producing
directly a slag suitable for use in the refining step of the
Rathmann et al. process without the need for beneficiation
or deironing.
It is believed that the unexpected increase in the
vanadium to iron ratio of such slags is due in part to the
; increase in vanadium recovery and to the fact that with
introduction of the highly oxidizing gas below the surface of
the molten pig iron at the stated temperature range, vanadium
is oxidized preferentially as compared to iron, whereby less
iron is oxidized and carried into the slag. Inasmuch as more
of the iron remains in the molten pig iron, the vanadium to
iron ratio o the slag i9 markedly increased to the desired
level of at least about 0.5 and, indeed, generally to much
higher levels, e.g. 0.75 to 1, which are highly desirable in
the Rathmann et al. process.
The pig iron may be obtained from any source so long
as it contains from at least about O.S percent up to about
3 percent vanadium. The preferred pig irons contain about
~8 1 to 2 percent vanadium. Such pig iron is commercially
_5_
. , . -
l~g7~83
available from several sources, for example, Highveld pig
iron from South Africa normally contains somewhat more than
one percent vanadium. Suitable vanadium-containing pig
iron may also be produced by adding vanadium-containing
materials to iron ore having an insufficient concen~ra~ion
of vanadium. For example, the titaniferous magnetite ore
of the Tahawus deposit contains about 0.5 percent vanadium,
but also contains so much titania (about 6 percent) that it
cannot be converted to pig iron by conventional blast furnace
processing. In fact, ores containing as little as 2 percent
titania are unsuitable for blast furnace use. However, ores
of such type may be blended with other vanadium-containing
raw materials, such as petroleum residues or fly ash, and
smelted in an electric furnace to produce pig iron containing
from about 1 to 2 percent vanadium, for example, which would
be useful in the process of the present invention.
The ar~ of simultaneously introducing a highly
. .
oxidizing gas, e.g. oxygen and a protective fluid below the
surfaee of molten pig iron is not new per se. An example of
thé basic process and a converter for the bottom blowing of
ferrous metal to produce steel ~Q-BOP~ is described in
Schempp U.S. Patent 3,839,017 issued October 1, 1974.
Deterioration of the tuyeres and avoidance of this problem
by providing uniform flow of the protecting hydrocarbon around
the tuyeres is described in Knuppel et al. U.S. Patent
.
` 3,852,062 issued December 3j 1974. The novelty of the present
invention resides in the discovery that the use of such
28 techniques with molten pig iron maintained at a temperature of
-6--
.
1097{)83
2600F. to 2900F., the pig iron containing at least 0.5
percent of vanadium, results in the valuable slags of the
present invention which cowld not be produced by the method
previously used in refining such pig iron.
In summary, it has been found that by oxidative
bottom blowing a pig iron containing at least 0.5 percent of
vanadium, while the pig iron is maintained at a temperature
of 2600 to 2900F., a slag can be produced containing at
least 8 percent vanadium and having a vanadium to iron ratio
of at least about 0.5 and, indeed, normally about 0.75 to 1Ø
Such slag is useful directly without further beneficiation
in the refining step of the Rathmann et al. process to
produce a 40~/O or higher grade of ferrovanadium useful as an
alloying agent for iron or steel.
By the term "bottom blowing" is meant to include
those several well known processes in which a highly oxidizing
gas, such as oxygen, is introduced simultaneously with a
cooling fluid? such as methane, beneath the surface of a bath
of molten metal, namely pig iron. Those processes have
been variously designated Q-BOP, LWS, SIP and AOD (see
"Bottom-blown steel processes now number three; Q-BOP, LWS,
and SIP" which appeared in the September 1972 issue of
,~ 33 Magazine, pp. 34-38).
~, DETAILED DESCRIPTION OF THE INVENTION
As noted above, the vanadium-containing pig iron used
in the process of the invention may be obtained from existing
sources and processes such as the Highveld process of South
Africa which provides pig iron typically containing about
29 1.28 percent vanadium. Other available pig iron useful in
-.
_z_
- - , - , . . ~ . . .
, . . ....
.
7()~
the invention may contain from about 0.5 up to about
3 percent vanadium. In an especially preferred embodiment
of the invention the required pig iron is derived from
otherwise uneconomic sources of vanadium. For example,
the Tahawus deposit of titaniferous magnetite ore has not
previously been exploited for its vanadium values despite
the fact that the ore contains about 0.5 percent vanadium.
The reason for this is that the ore also contains about
6 percent titanium dioxide which renders it unsuitable for
conventional blast furnace processing to pig iron. Recovery
of the vanadium values of this ore by conventional roast-leach
methods is possible but uneconomic for the vanadium values
alone, and the by-product magnetite, which is high in
titania, is unattractive to steel producers. -
Residues such as fly ash from the burning of Venezuelan
fuel oil contain vanadium in varying amounts, up to 25 percent
or more vanadium. Those containing 10 percent or more or even
, :
; as low as 5 percent vanadium may be processed economically
by conventional methods to recover vanadium values. However,
it has not been economical to so process residues containing
less than 5 percent vanadium because such residues contain
appreciable amounts o~ carbon and nickel.
In view of the foregoing, large quantities of both
; by-products magnetite and petroleum fly ash containing
significant amounts of vanadium exist and have previously
had no economic-utility. Despite the fact that neither of
these materials alone represent an economically viable source
28 of vanadium, it has been discovered that they may be blended -
.
- - . , . . , . - . -
.. . , ....... . . : ~
. . .
109'^~'0~33
to produce a synthetic vanadium-bearing magnetite ore
containing about 0.75 to about 1.50 percent vanadium and
about 2 to 6 percent titania (TiO2) which can be smelted in
a submerged arc electric furnace. In this way, pig iron
containing about 1 to 2 percent vanadium, suitable for use in
the present invention, is obtained from previously useless
materials. Petroleum fly ashes suitable for use in this
invention may contain from about 2 to about 10 percent,
preferably 5 to 10 percent, vanadium.
A typical commercially available fly ash petroleum
residue useful in the invention contains about 2.4 percent
vanadium, about 7.8 percent sulfur trioxide, about 0.62 percent
nickel oxide, about 47.8 percent carbon and about 40 percent
water. This material is in the form of a very fine powder.
Tahawus magnetite contains about 62-64 percent iron, about
0.4 to 0.6 percent vanadium, about 4 to 6 percent titania
and various other constituents, and has a specific gravity
; of 4.9. Another ore, Chibougamau, is available which contains
about 0.8 percent vanadium, as compared to the 0.9 percent
content of the South African magnetites. These ores are
suitably ground to minus 65 mesh and blended with the
! foregoing fly ash in a weight ratio of ore to fly ash of
about 1.5:1 to 3.5:1~ The blend made in this way may be
pelletized according to conventional procedures or fed
directly to the electric furnace as blended. Other raw
materials such as spent catalyst, petroleum residues other
than fly ash and the like which contain significant vanadium
values may also be blended with Tahawus magnetite or any other
29 iron ore with or without its own content of vanadium to produce
'
,
~09~0~3
a synthetic mixture adapted to be smelted in the electric
furnace to produce a vanadium-containing pig iron useful in
the invention. The pig iron produced from the synthetic
mixture comprising Tahawus magnetite and the fly ash will
have a vanadium content of about 1 to about 2 percent,
typically about 1.5 percent depending largely on the vanadium
content of the fly ash and the proportion thereof in the
blended synthetic ore; a carbon content of about 3.5 to about
4.5 percent, typically about 4 percent; and on the order of
about 0.25 percent each of titanium, manganese and silicone.
SMELTING_THE ORE
The smelting operation may be carried out in a
submerged arc type electric furnace. The general procedures
of submerged arc smelting are described in "Effective Energy
Utilization From Direct Electric Ironmaking" by Thomas E. Ban,
pp. 178-188 of En`ergy Use and Cohservation In The Metals
Indus~2, edited by Chang et al. from the proceedings of a
symposium presented at the annual meeting of American
~~ Institute of Metallurgical Engineers in New York, New York,
-~ 20 February 16-20, 1975.
Submerged arc electric furnaces for ironmaking are
geneally larger than the well-known steel melting furnaces.
~ Sized and proportioned charge, i.e. ore and coke, is allowed
;~ to continuously descend into the furnace crucible through coke
.
loaded feed columns maintained by overhead hoppers. Electro-
thermal smelting is brought about by submerged arcs from the
electrode to the high temperature carbonaceous charge on and
within the molten bath. Dissipation of the electricity
through resistance and myriads of minature arcs in the carbon-
3G bed burden beneath the electrodes supply the electrothermal
-10-
;
11~97()83
energy for direct reduction by the carbon-iron oxide reactions.
This also supplied the high temperature for production of slag
and liquification and carbonization of the metal.
THE SUB~IERGED BLOWING OPERATION
The vanadium-bearing pig iron is first melted by
induction heating according to conventional procedures, if
necessary~ or if the hot metal is available from the smelting
operation, it may be charged directly to a conventional
converter employed in the submerged blowing operation.
The Q-BOP converter which is typical consists of a vessel
arranged to be tilted between a vertical blowing position,
a horizontal receiving position and a downwardly inclined
pouring position. The converter i9 lined with a basic
refractory such as magnetite or periclase (MgO) brick. The
converter is further provided with a plurality of tuyeres
in the bottom. Such tuyeres suitably consist of an inner ~ube
for the delivery of a highly oxidizing gas, e.g. oxygen, and
concentric outer tube. A protective or cooling fluid such
as a hydrocarbon gas, petroleum oil, or inert gas such as
argon or helium, `i8 fed into the converter through the annular
space between the inner and outer tubes of the tuyeres.
Suitable piping and valving between the sources of oxidizing
and protective fluids are provided to permit control of the
timing and pressure of the flow of these fluids into the
converter.
The general procedure is to charge the hot metal at
a temperature of from about 2600 to about 2900F., preferably
about 2700 to 2800~. into the converter disposed in its
29 horizontal receiving position in which the tuyeres are
~ O~ 3
disposed above the horizontal axis. On completion of the
charging the converter is tilted upwardly to the vertical
blow position and the valves are manipulated to initiate
feeding of an oxidizing gas through the inner tube and a
protective fluid through the outer tube of each tuyere. The
pressure of the oxidizing gas is maintained at about
40 to about 90 psig., generally 50 psig. The pressure of
the protective fluid generally will be about half that of the
oxidizing gas, e.g. 20 to 45 psig. The range of operable
pressures and optimum pressures will vary according to the
size and design of the apparatus, fluids employed, and operating
temperatures as known in the art of bottom blown steel
production.
The blowing operation is normally quiet with little
fume discharge from the open mouth of the converter, although
the fluid streams and the reactions taking place do cause
vigorous agitation of the melt. The blowing operation is
continued until at least the theoretical amount of oxidizing
fluid has been introduced based upon oxidation of substantially
`~ 20 the entire vanadium content of the me-lt. The duration of
the blowing period will of course depend upon the size of the
converter, size of the charge and the rate of introduction
of the oxidizing gas, but in general will vary from about
15 to about 30 minutes, about 20 minutes being typical.
The blowing period may, if desired, be carried out in
two stages; the converter being tilted down to horizontal
position and a sample of the partially blown metal is taken
between stages. The converter is then returned to upright
29 blowing position and the oxidizing and protective fluids are
-12-
~097~)83
again fed for a seCond blowing period. At the end of the
second blowing period the converter is tilted to pour
position to discharge the refined melt in a suitable refractory
lined vessel from which it is poured into molds and permitted
to cool and harden into pig iron containing no more than about
0.4 percent vanadium, typically about 0.15 percent.
The slag which is separated from the hot metal, will
contain at least about 8 percent vanadium and will have a
vanadium to iron ratio of at least about 0.5, and typically
about 0.75 to 1, or possibly higher.
A protective covering of pulverized lime is advantageously
added to the hot metal to insulate it during transfer from
the smelter or induction melting furnace to the converter. If
desired, sufficient lime may be charged to the converter to
convert vanadium values to calcium vanadate. While any highly
oxidizing gas may be employed, the preferred gas is oxygen gas.
Similarly, while a wide variety of protective fluids may be
- used to offset the heat of the exothermic blowing reactions
and inhibit deterioration of the refractory lining and
tuyeres, including liquid petroleum oils and fractions,
ethane, propane and other hydrocarbon gases, inert gases such
as argon and nitrogen, also hydrogen and steam, the preferred
protective fluid is methane.
During the submerged blowing operation, important
reactions occur whereby various impurities in the pig iron
are converted to compounds to e~fect their removal from the
pig iron. Thus, sulfur and phosphorous, like vanadium, are
converted to oxideæ and enter into the slag. In addition,
the carbon content of the iron is substantially reduced
through oxidation. The degree of o~idation of carbon is
31 important. The preerential oxidation of vanadium, as compared
1,3 _
-
~7(~
to iron, takes place initially during the blow, whereby the
ratio of vanadium to iron in the slag increases to a value
g:reater than about 0.5 when the carbon content of the metal
falls below about 2 percent. This ratio increases substan-
tially, generally to the range of 0.7 to 1.0, and even higher,
as the carbon content of the metal is further reduced through
oxidation. However, when the carbon content of the metal
falls below about 0.02 percent, the ratio of vanadium to iron
in the slag begins to decrease. Accordingly, the blow
preferably is carried out so as to reduce the carbon content
of the metal to a value in the range of about 2 to 0.02 percent.
The invention will now be described in greater detail -
in conjunction with the following specific examples illustrating
14 preferred embodiments thereof.
--14-
109~0~3
Example I
To illustrate a preferred embodiment of the invention
in which the pig iron is derived from otherwise uneconomic
sources of vanadium, a "synthetic ore" can be made by blending
titaniferous magnetite ore from the Tahawus deposit and a fly
ash derived from South American Petroleum. Such materials have
the following typical analyses.
Fly'Ash From South American Petroleum
`Constituent Percent
.
V25 4.3 (2.4V)
NiO .62
C 47.80
SO3 7.80
' H 0 40.00
.~ .
, T'ah'awus'Magne'ti'te
Consti'tuent P'ercent
;
~,; Fe ' 62 - 64
'!
P2O5 0.02-0.04
~:~ SiO2 1.0-2.0 ' '
'~ 20 M~O 0.06-0.10
, A12O3 3.0-4.0
CaO 0.1-0.2
MgO 0.8-1.0
S 0.1-0.2
,~
: Cr203 0.2-0.3
. V2O5 0.7-1.0 (.3~-.56V~
1~
TiO2 4.0-6.0
28:.: Specific Gravity 4.9
-15-
',~
.1`
10970~3
The magnetite after being reground to minus 65 mesh
(Tyler screen) is blended with the finely powdered fly ash in
a suitable blender until a uniform mixture is achieved. This
mixture may be smelted as such, but it is preferred to
agglomerate it to facilitate handling and smelting. This may
be achieved by the addition of about 5 percent of water binder
to form a paste which can be extruded, dried and broken up to
form pellets about 0.5 inch in diameter for example, or any
other suitable size. The proportions of magnetite to ash may
be varied as desired to provide a synthetic ore containing
vanadium values equivalent to about 0.75 to about 1.5 percent
vanadium. Such a synthetic ore can be smelted as described
herein to provide a pig iron containing about 1 to about 2 per-
cent vanadium which can in turn be refined according to the
invention.
Exam~
In order to test the process of the present invention
on a laboratory scale, a synthetic pig iron was made by melting
together in an induction furnace a commercially available pig
iron (Lot 867 Republic Steel) and a ferrovanadium alloy produced
in the laboratory containing 40.3 percent vanadium and 5.85 per-
cent silicon, the remainder being iron. The pig iron analyzed
as follows:
Pig Iron
Element Percent
C 4 27
Si 0 72
Mn 0.095
S 0.035
P 0.027
Al 0.01
Ti 0.047
Cu 0.01
V 0.016
Cr 0.01
Ni 0.01
Fe 94.75
38 lO0.~0
-16-
~097083
These materials were melted together in a conventional
electrical induction furnace in such proportions as to provide
a synthetic hot metal containing about 1.78 percent vanadium.
This molten metal was covered with a layer of dry pulverized
lime in the transfer ladle as insulation during the five
minute period required to transfer it from the induction furnace
(simulating a smelter in commercial production) to the
converter. The hot metal at a temperature of 2785F. was
introduced to the converter in its horizontal loading posîtion
in which the tuyeres are disposed above the axis of the
converter and the level of molten metal. The laboratory
scale converter used in this test had a volume of about 1.9
cubic feet within the magnesium oxide refractory liner, the
` interior diameter o the vessel being 12" and the effective
height 29". The charge consisted of about 300 lbs. of hot metal.
Dry air was fed through both tubes of the tuyeres from compressed
air cylinders at a pressure of ~5 psig during the charging
operation.
On completion of the charging operation the valves
were operated to switch from dry air, to feed methane at
~ 50 psig through the outer tube and oxygen at 100 psig through
,~
~I the inner tube of each tuyere. The converter was righted to
vertical flow position as the switch in gases was made. The
blowing operation was very quiet with almost complete absence
of fume discharge from~the open mouth of the converter.
Visible vibration did, however, indicate vigorous agitation of
27 the molten metal by the gases and reaction products. The initial
,. : .
-17-
109~0~3
blowing operation continued for 3 mins. and 20 sec. before
the converter was turned down and the system switched back
to air. This period was calculated to provide the theoretical
requirement of oxygen to oxidize the vanadium content of the
charge. After a sample of the bottom blown metal was taken,
the converter was turned up again and further blown with
oxygen and methane until a total of twice the theoretical
oxygen requirement for the vanadium had been introduced to the
melt. The blown metal was then poured into a refractory lined
cast iron pot mold from which samples of slag and metal were
taken.
The final slag analyzed to contain 15.1 percent vanadium
and 29.23 percent iron for a vanadium to iron ratio of 0.52.
Such a slag would be superior to the lower vanadium to iron
ratio slags of the prior art for use in the refining step of
; the Rathmann et al. process for producing ferrovanadium alloys.
The me~al contained 1.22 percent vanadium at the end of the
first blow and 1.26 percent in the final product.
Example III
Synthetic hot metal was prepared as previously. The
methane-oxygen blow was continuous over a 10 minute period
including a 30 second converter turn down for sampling midway
of the test. The test consumed 225 cubic feet of oxygen and
45.4 cubic feet of methane (20 percent volume/volme based
~; on the oxygen). The pressure of both gas systems was 50 psig.
The slag produced in this test had a VtFe ratio of 0.59
which upgraded to 0.72 on a resample from which fine metallic
iron was more completely removed. Total vanadium and carbon
oxidation based on metal analysis was 37 percent and 55 percent
respectively. Of particular interest is the fact that virtually
-18~
70~3
no change occurred in the iron content of the slag (25 percent
to 25.34 percent) from the mid-point of the blow until the blow
was concluded whereas vanadium increased from 4.30 percent to
14.85 percent and most importantly carbon in the metal decreased
from 3.34 percent to 1.85 percent (45 percent decrease).
Normally a carbon change of this magnitude would have been
reflected by increased iron oxidation.
Example IV
Using the same general procedure as the pre~ious
example, a scheduled 15 minute blow was successfully carried to
completion resulting in a slag with a V/~e ratio of 1.25.
Methane-oxygen flow was continuous for the full period including
two 30 second turn-downs for sampling. The test consumed
400 cubic feet of oxygen and 188 cubic feet of methane. The
47 v/v percent methane delivered was far in excess of the
20 v/v percent tuyere protection level established in Example III.
The higher ratio of methane was found to be due to the depletion
of the oxygen supply during the long blow. The cooling effect
of the higher methane ratio was clearly evident as donut-shaped
maQses of metal frozen around each tuyere and substantial
skulling of metal occurred on the upper walls of the converter.
Obviously, the upper pratical cooling limit had been exceeded.
Analytical results of 1.42 percent V and 2.58 percent
Fe in the 7 minute slag sample (no slag was obtained with the
11 minute sample) suggests that the higher methane level
somewhat suppressed both iron and vanadium oxidation, but that
~verall oxidation continued to be selective for vanadium as
reflected by the 0.55 V/Fe ratio. This selectivity of oxidation
29 was confirmed by the 1.25 V/Fe obtained in the final (15 minute~
:, -19 - .
.
~097(~3
slag sample. Analytical results of the 7, 11, and 15 minute
metal samples showed a normal rate of carbon removal as
compared with previous tests. It is surprising that with
90 percent removal of carbon (3.98 percent to 0.41 percent),
residual vanadium was still 1.44 percent (44 percent oxidation).
Even more surprising, however, was the 18.38 percent V
(32.81 percent V205) and 14.72 percent Fe (18.94 FeO) in the
final slag. Assuming 90 percent vanadium recovery and 100%
iron recovery, calculations show that slag of this composition
would produce a ferrovanadium alloy by the Rathmann et al.
process with nominally 42 percent V and 37 percent Fe. The
analyses are tabulated below.
, Percent
; Ratio
'' V '' C ' Fe ' V/Fe
Metal before
,, 2 blow 2.55 3.98
Metal - 7 minute
sample 2.85 2.51 --- ---
,
',~ Slag - 7 minute
',' 20 sample 0.80 --- 2.58 .55
Metal - 11 minute
sample 2.20 1.33 --- ---
~ Final Metal
''~ (15 min.) 1.44 0.41 --- -_-
!:
'~, Final Slag
(lS min.) 18.38 --- 14.72 1.25
, Exa'mp'l'e V
Synthetic hot metal (about 2700F.) was prepared as
`~ Z9 previously by combining 281.25 pounds of the pig iron and
.,
,
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1~97~ 3
18.75 pounds of the ferrovanadium alloy described in Example II.
The methane-oxygen blow was continued until 59 pounds of oxygen
and 4 pounds of methane had been consumed. The pressure of
the oxygen was 44 psig, whereas that of the methane was 18 psig.
Samples of the metal and slag were taken at periodic
intervals during the blow and again at the end of the blow.
Analysis of the various samples of metal and slag are set forth
in the following table.
; Percent
Metal
Sample ~/O C% V~/O Fe% V/Fe
Base 2.05 4.94 -- _- __
10 Minutes 1.32 1.96 10.86 18.14 0.60
12 Minutes 0.84 1.10 14.82 21.13 0.70
14 Minutes 0.50 0.36 17.75 24.41 0.72
16 Minutes 0.02 0.022 19.31 19.09 1.01
Final 0.01 0.016 14.66 28.11 0.52
The foregoing example demonstrates that by means of the
process of this invention over 90% of the vanadium in the pig
iron is oxidi2ed ta produce a slag containing a V/Fe ratio
! greater than 0.5.
It is apparent from the foregoing actual tests that the
submerged~blowing of malten- vanadium-containing pig iron
produces slags containing at least 8 percent vanadium and an
iron to vanadium ratio of at least about 0.5 and generally
considerably higher. Such vanadium to iron ratios are not
27 obtained in slags produced by the Highveld process.
.
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.
~097~3
Consequently~ the present invention makes possible the direct
production of vanadium-bearing slags useful in the refining
step of the Rathmann et al. process to produce valuable
4 ferrovanadium alloys for the alloying of iron and steel.
'
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.
