Note: Descriptions are shown in the official language in which they were submitted.
1071833
This invention relates to the recovery of metal
values, particularly from ores or concentrates thereof.
In the production of metals from ores, a smelting
procedure using coke and a flux generally is practised, with
liquid metal being tapped at intervals, followed by solidifi-
cation, cleaning and sizing of the metal or alloy. In addition,
the process is difficult to control, the slag generally is
high in metal values and requires recycling and impure products
- often are produced.
In accordance with the present invention, there is
provided a method of recovery of metal values in substantially
pure carbide form, the metal being selected from the group
consisting of titanium, zirconium, hafnium, vanadium, niobium,
tantalum, chromium, molybdenum, tungsten, manganese, iron,
cobalt and nickel, which comprises subjecting the metal
values in oxide and/or hydroxide form in ores or concentrates
thereof also containing gangue constituents to a single step
solld state reduction and carburization reaction with carbon
to convert the metal values to the corresponding carbide and,
after completion of the solid state reaction, beneficiating
the resultant mass to separate the metal carbide in substan-
tially pure form from the gangue constituents.
Metal carbides exhibit distinctly different physical ~ -
properties from the various gangue constituents of ores and
hence standard beneficiation methods may be used to recover
the metal carbides, generally in substantially pure form,
when the recovery is made from ores and concentrates thereof.
Such beneficiation techniques include gravity, flotation,
magnetic and electrostatic treatments.
The elemental metal may be formed from the separated
carbide by another solid state reaction with the metal oxide
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~071833
in accordance with the equation:
Me3C + MeO > 4Me + C
The conditions utilized to obtain the carbide and
the elemental metal may vary widely and depend on the particu-
lar metal involved. In general, a shaft or rotary kiln may
be employed and the invention may be used on both low and
high grade ores.
In instances where the metal, the ore and the
conditions are such that large amounts of the metal silicate
and aluminate may be formed in preference to the carbide,
thereby leading to only low recoveries of the metal values
in the form of the carbide, it is preferred to incorporate
time into the reaction mixture in order to provide a competing
reaction for the silica~and alumina to form calcium silicate -
and calcium aluminate rather than the metal silicates and
aluminates, thereby resulting in an improved yield of the
metal carbide.
The invention is applicable to the formation of a
large number of carbides from their ores. The metals are
titanium, zirconium, hafnium, vanadium, niobium, tantalum,
chromium, molybdenum, tungsten, manganese, iron, cobalt and
nickel. Where two or more such metals are present in the
ore, selective carburization may be employed to recover -
individual metal carbides, such as by varying the quantities
of carbon used, temperature, gas composition, catalysts and
time.
The present invention has particular application in
the production of ferro-alloys which are used as addition
agents to steel. Particular ferro-alloys which are commonly
employed are high-carbon ferrochromium and high-carbon ferro~
manganese.
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1071833
By the i~rocedure of the present invention, an iron-
chromium or iron-manganese ore may be carburized to provide
a mixture of iron and chromium carbides or iron and manganese
carbides. Following beneficiation, the carbides may be
converted to the metal. Depending on the degree of complete-
ness
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of the conversion of carbide to the metal, the resulting metal
alloy, either ferro-chrome or ferro-manganese, may have a
low-carbon content. In many applications in the steel
industry low-carbon alloys are preferred to the currently
employed high-carbon alloys.
The invention will be described hereinafter with
particular reference to production of manganese and alloys
thereof, but it will be understood that the principles
described hereinafter with reference thereto also apply to
10 the other elements mentioned above, with suitable modification
for the particular element chosen.
- Commonly employed high-carbon ferromanganese has the
approximate composition 78 to 82% Mn, 7~C, 1~ Si and the
balance Fe, and is produced by submerged arc smelting of
manganese ores. Low carbonf i.e. 0.07 to 1.5~ C, materials
have been produced in open electric-arc furnaces by reacting -
manganese-silicon alloys with the ore. High carbon iron-
manganese alloys for the steel-ïndustry also are produced in
blast furnace operations.
The production of manganese carbide from the oxide -~
in the ore in accordance with the present invention requires
reaction with carbon and removal o~ the carbon monoxide as it
is produced. This removal of carbon monoxide may be achieved
by flushing the reaction vessel with an inert gas having a
- partial pressure of CO below about 0.1 atmospheres, or by
maintaining the reaction vessel under a vacuum. The reaction
proceeds according to the equation:
7 MnO + 10C ) Mn7C3 + 7CO
The reduction step may be carried out over a wide
30 range of temperatures, preferably about 1100 to 1200C.,
although higher temperatures up to about 1350Cr ~ or higher
may be used. Loss of manganese in the form of stable o~ounds
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- 107~833
such as manganese silicates and aluminates may be prevented by
adding a sufficient quantity of lime to the ore as discussed
above.
After separation of the carbide from the resulting
gangue constitutents by standard beneficiation techniques,
there is obtained a manganese carbide product. Since iron
oxide generally is present in manganese ores, usually the
carbide product consists of a mixture of manganese carbide and
iron carbide. It may be possible by selective reduction to
obtain pure manganese carbide with the iron oxide being
reduced to the metal. Pure manganese carbide then may be
recovered.
The recovered carbide may be converted to the metal,
or an- alloy of metals where the recovered carbide is a mixture
of metal carbides, by reaction with the metal oxide or mixture
of oxides in accordance with the equation:
Mn7C3 + 3MnO --~10Mn + 3CO
This reaction is carried out in such a manner as to
remove the carbon monoxide as it is formed, typically by
flushing with an inert gas, such as argon. Generally,a higher
reaction temperature such as about 1100 to 1625C.,-is required
than that utilized for the carburization step. -
Where the metal involved is chromium, different -~ -
temperature conditions may be employed, for example, the
carburization step may be carried out at a temperature of
about 1025 to 1425C. or higher and the reaction between the
carbide and oxide at a temperature of about 1300 C. to 1750C.
or higher.
EXAMPLES
The invention is illustrated by the following Examples:
-` 1071~33
Exa~le I
An ore concentrate containing 26.9% Cr and 22.4%
Fe was mixed with the stoichiometric ~uantity of finely-
divided (-400 mesh) graphite containing 95% fixed carbon to
form Cr3C2 from the chromium and Fe3C from the iron.
Two separate samples of the concentrate were provided,
sized as follows:
Sample 1 Sample 2
wt.g. wt.g.
+200 0.85 ~-
-200 ~ 4003.90 0.25
-400 + 5001.37 1.20
-500 4.43 4.6
TOTAL 10.55 6.05
The charges for each test were slurried, stirred for -
10 minutes, partially dried and pelletized to pellets of
approximately 3/4 inch diameter.
The pellets were held for about 7 hours and 20 minutes
at a temperature of about 1300 to 1400 C. under a stream of
argon flowing at 0.05 CF/min.
The products, after cooling overnight, were observed
to be dark gray in colour and strongly magnetic. The product
pellets from test 1 weighed 84.6g from a charge of 126g and
the pellets from test 2 weighed 56.5g from a charge of 90g.
Part of the products from test 2 was shatter boxed
and a sample was found to contain 28.0% Cr, 26.0% Fe, 4.58%
C-and the balance gangue. A recovery of 79.0% of Cr was
obtained.
The shatter boxed product from test 2 was subjected to
low intensity dry magnetic separation. 73.0% of the chromium
values in the original charge were recovered in the magnetic
fraction which graded 39.9% Cr, 35.2% Fe and 5.16%C. An
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107~833
X-ray diffraction analysis indicated the fraction contained
70% Cr7C3, 20% metallic Fe and the balance minor unidentified
substances.
Ex {
An ore containing 49.3% Mn, 2.8% Fe, 5.9% SiO2 and
3.52%Al2O3 was ground to 97% -200 mesh and was mixed with
finely ground (100%-150 mesh) graphite containing 70% fixed
carbon in a quantity of about 100% excess of the quantity
necessary to form Mn7C3 and Fe3C from the manganese and iron
values of the ore.
The ore, carbon and a small amount of binder were
thoroughly mixed and pressed to form compacts sized about
1" diameter and about 1" long. Samples of compacts were fired
at different temperatures under a reduced pressure for different
time periods. The conditions are reproduced in the following
Table I:
TAB~E I
- Test No. Reduced Pressure Heating Time Temperature
mm. Hg. (hrs.) (average)
1 0.8 1 2228F
(1220C) -
2 0.8 2 23790F
(1304C)
Following the firing, the products were subjected to
elutrlation to obtain samples rich in manganese carbide and at
high manganese recoveries.
Example III
A charge of 100 gms of the same ore as used in Example
II (100%-200mesh), 26.6 gms of CaO (100%-200 mesh) and 28.7
gms of graphite (100%-400 mesh, 95% fixed carbon) was mixed
with water and the resultant slurry was thoroughly stirred and
partially dried to give a thick paste which was formed into
pellets approximately 1~" in diameter The pellets were
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1071833
allowed to dry overnight.
Samples of the pellets were heated to a reaction
temperature while being subjected to a vacuum and held at the
reaction temperature for a certain period of time. The
conditions are outlined in the following Talble II:
TABLE II
Test No. Heating up Heating Time MaxO Temp. Lowest
Time (min.) (min.) C. Pressure
attained
1 854 1343 3xlO 3mm Hg.
10 2 76120 1371 46 cm Hg.
After cooling, the~product was subjected to a
heavy liquid separation using Clerici solution and the fractions
.~ .
analyzed for Mn, Fe and C contents. The results are reproduced
in the following Table III:
TABLE III
Fe C Mh
Test No. Wt.% Wt.gm. Wt.% Wt.gm. Wt.~ Wt.gm. Wt.% Wt.gm. Distri-
_ _ bution %
l Product 100 19
Sink 49.47 9.4 2.12 0.20 6.68 0.62 77.8 7.31 77.7 - -
Float 50.53 9.6 1.85 0.17 11.70 1.12 21.9 2.10 22.3
2 Produ~ct 100 10 --
Sink 72.0 7.2 4.50 0.324 6.54 0.47 85.80 6.17 82.6
Float 28.0 2.8 3.14 0.087 18.00 0.50 46.6 1.3 17.4 -
The present invention therefore provides a process
for the recovery of metal values from ores by direct
carburization of the metal oxide values of the ore. Mbdifications
are possible within the scope of the invention.
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