Canadian Patents Database / Patent 1056161 Summary

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(12) Patent: (11) CA 1056161
(21) Application Number: 230710
(54) English Title: PRODUCTION OF COBALT FROM COBALT SULFIDE
(54) French Title: OBTENTION DU COBALT A PARTIR DU SULFURE DE COBALT
(52) Canadian Patent Classification (CPC):
  • 53/302
(51) International Patent Classification (IPC):
  • C22B 23/06 (2006.01)
  • C22B 23/02 (2006.01)
(72) Inventors :
  • SOLAR, MAURICE Y. (Not Available)
  • WARNER, JOHN S. (Not Available)
  • SRIDHAR, RAMAMRITHAM (Not Available)
(73) Owners :
  • INCO LIMITED (Canada)
(71) Applicants :
(74) Agent:
(74) Associate agent:
(45) Issued: 1979-06-12
(22) Filed Date:
(30) Availability of licence: N/A
(30) Language of filing: English

English Abstract




ABSTRACT OF DISCLOSURE


A pyrometallurgical process for producing cobalt metal
from a sulfidic cobalt melt containing up to, 35% sulfur while inhibiting
the formation of substantial amounts of cobalt oxide is provided. The
method comprises contacting such a molten bath maintained in a state
of vigorous agitation and at a temperature at least 100°C above the
melting point thereof with an oxygen-containing gas to remove sulfur
therefrom as SO2, while controlling the partial pressure of oxygen
in said gas and the temperature of said bath as the percent sulfur in
said bath decreases to inhibit the oxidation of cobalt to cobalt oxide.


Note: Claims are shown in the official language in which they were submitted.


The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A pyrometallurgical process for desulfurizing a

sulfidic cobalt melt while inhibiting the formation of cobalt oxide

which comprises, establishing a sulfidic cobalt melt containing above

about 1% to about 35% sulfur by weight, vigorously agitating said melt,

contacting said vigorously agitated melt with an oxygen-containing

gas to oxidize and remove the sulfur therein as SO2 while converting

said melt to cobalt metal, the temperature of conversion and the

oxygen content of the inlet gas being correlated with the sulfur

content of the melt, the temperature of conversion being substantially

above the temperature at which cobalt oxide forms as determined by

the bath sulfur-oxygen-temperature curves of the accompanying

drawing, and continuing said conversion treatment wherein the

conversion temperature is increased as the sulfur content of said

melt decreases as determined by said bath sulfur-oxygen-temperature

curves of the accompanying drawing and interpolations thereof until

the melt has been substantially converted to cobalt metal.

2. The process of Claim 1, wherein following reduction
of the sulfur content in the molten bath to about 1%, the molten bath
is further purified by vacuum treatment at a pressure less than about
0.3 atmosphere, during which treatment the oxygen content in the bath
is maintained at about 1.5 to 4 times the sulfur content.
3. A process as described in Claim 2 wherein the vacuum
treatment is at a pressure of less than about 1mm of mercury.

4. A process as described in Claim 2 wherein the vacuum
treatment is carried out for removal of impurities other than sulfur.

13


5. The process of Claim 1, wherein following the
reduction of the sulfur content in the molten bath to below 1%, the
molten bath is further purified by removing said sulfur using a
desulfurizing slag.
6. The method of Claim 5, wherein said desulfurizing
slag is substantially a lime slag.
7. The method of Claim 6, wherein said lime slag
includes a small but effective amount of a desulfurizing metal
selected from the group consisting of aluminum and magnesium,
the amount of said desulfurizing metal being at least stoichiometrically
sufficient to combine with said sulfur.
8. A pyrometallurgical process for desulfurizing a
sulfur-containing cobalt melt while inhibiting the formation of
cobalt oxide which comprises, establishing a molten bath of sulfidic
cobalt containing about 1% to about 35% sulfur by weight, vigorously
agitating said bath, contacting said vigorously agitated bath with
an oxygen-containing gas to oxidize and remove the sulfur therein
as SO2 while converting said bath to cobalt metal, the temperature
of conversion and the oxygen content of the inlet gas being correlated
with the sulfur content of the bath, the temperature of conversion
being substantially above the temperature at which cobalt oxide
forms as determined by the bath sulfur-oxygen-temperature curves
of the accompanying drawing, controlling the oxygen-temperature
relationship of said process by causing the temperature of said
bath to increase as said sulfur content decreases, the percent
oxygen in said inlet gas being substantially proportionately decreased
with the increase in said temperature as determined by the inhibition
of cobalt oxide formation in accordance with the accompanying drawing.

14

and continuing said conversion whereby the temperature is caused to
increase to over about 1600°C and not substantially exceeding 1700°C
as the sulfur content of said bath decreases to below 3% and the oxygen
in the inlet gas is decreased to below about 4% until the sulfur in
said bath is finally reduced to below about 1%.
9. The process of Claim 8, wherein following reduction
of the sulfur content in the molten bath to below 1%, the molten bath
is further purified by vacuum treatment at a pressure less than about
0.3 atmosphere, during which treatment of the oxygen content in the
bath is maintained at about 1.5 to 4 times the sulfur content.
10. The process of Claim 9, wherein the oxygen content
of said bath is controlled by addition of an oxygen bearing solid
selected from the group cobalt oxide or compounds decomposable to
cobalt oxide.
11. The process of Claim 8, wherein following the
reduction of the sulfur content in the molten bath to below 1%, the
molten bath is further purified by removing said sulfur using a
desulfurizing slag.
12. The method of Claim 11, wherein said desulfurizing
slag is substantially a lime slag.
13. The method of Claim 12, wherein said lime slag
includes a small but effective amount of a desulfurizing metal
selected from the group consisting of aluminum and magnesium, the
amount of said desulfurizing metal being at least stoichiometrically
sufficient to combine with said lime.



Note: Descriptions are shown in the official language in which they were submitted.

'[`hi9 inventi()n relates to a novel proce.Ys for the
pyrometallurgical conversion of a sul~idic cobalt melt to yield
metallic cobalt.
State of the Art
It is known to produce metallic nickel from nickel-
containing matte by the pyrometallurgical conversion of the matte
using an oxygen-containing gas as the oxidant.
A process which has been successfully developed for
the treatment of nickel mattes is that disclosed in U.S. Patent
No. 3, 069, 254 (assigned to the same assignee). This patent is
directed to the recovery of nickel from nickel-containing sulfide
.
materials, such as nickel sulfide matte and crude nickel sulfide

precipitates, such as those obtained in processing sulfidic and
.
oxidic nickel ores. These mattes in the molten condition are con-
verted autogenously in a rotary furnace using commercial oxygen
or oxygen-enriched air blown onto the surface of the molten matte
while maintaining it in a turbulent state. The matte is oxidi~ed to
substantially sulfur-free nickel by controlling the oxygen supply and
bath temperature while subjecting the bath to strong mechanically- ~
induced agitation. The foregoing permits rapid nickel sulfide-nickel ~.
oxide reaction and high efficiency of oxygen utilization. ~;
Ac~cording to the patent, any cobalt and iron contained in
the matte is removed by oxidation. For example, cobalt elimination
may be accomplished during routine conversion of the nickel matte for
iron removal by selectively oxidizing the cobalt in the presence of a
flux, such as silica, the cobalt being then skimmed off as a slag.




,

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: ' ' .::


Thus, it is quite apparent that cobalt and iron oxidi;~.e preferentially
to nickel in the matte.
` It has been reported in the literature that iron sulfide
cannot be converted directly to iron metal at practicaL temperatures.
Despite the generally similar chemical behavior of iron and cobalt,
; we have now discovered that it is possible to convert sulfidic cobalt
melts containin~ up to 35% sulfur to cobalt metal containing less than
1% sulfur provided particular care is taken to control the oxygçn
partial pressure and the bath temperature during desulfuri~ation.
The process is applicable for the recovery of cobalt
from cobaltiferous iron sulfides, from cobalt sulfides produced by
the sulfide precipitation of cobalt from leach solutions and from
cobaltiferous oxide ores or scrap.
Object of the Invention
It is thus the object of the invention to provide a pyro~
metallurgical process for converting sulfidic cobalt melts to cobalt
` metal.
Other objects will more clearly appear from the following
description taken in conjunction with the accompanying drawing, wherein
the attached figure illustrates the relationship between temperature, the
sulfur content of the matte and the oxygen in the gas that permit one to
avoid forming substantial amounts of cobalt oxide while carrying out
the invention. ,~ -
Summary of the Invention ; `
The invention is directed to a pyrometallurgical process
for converting a sulfidic cobalt melt containing at least about 1% sulfur or


z


-' "'

5t~
' :
more usually at least abollt 5'~, ~nd llp to ahout 35~ slllfur to rnetallic
cobalt while avoiclin~ sllbstantial rormation Or cohalt oxide. The
;~ process co~mprises estahlishing a molten bath of said sulfidic
material at a temperature of at least 100C above the melting point ,
thereof, vigorously agitating saicl bath, and contacting said bath of
vigorously agitated sulfidic material with an oxygen-containing gas
to remove sulfur as gaseous sulfur dioxide. Unfortunately, the
aforementioned tendency of cobalt to oxidize leads to a competition
between cobalt and sulfur to react with the oxygen in the inlet gas.
The formation of cobalt oxide not only lowers the yield of cobalt but,
in the case where the oxygen-containing gas is being blown onto the
melt surface, an oxide scum can actually slow up or stop the reaction.
Such a scum also severely attacks the refractories of the reaction `
vessel,
: :~: .
Whlle cobalt oxide may form as an intermediate step in the `
conversion reactions, generally no difficulty is encountered so long
as the following reaction proceeds to the right with reasonable velocity~
S (melt) + 2CoO (solid) ~ 2Co (liquid) +52 (gas).
For any given concentration of sulfur dissolved in the melt,
the reaction can be driven further to the right by increasing the melt
temperature and/or by lowering the partial pressure of the gaseous
~ SO2 product. One way to accomplish this latter effect is to dilute the
,.' ~ .
oxygen-containing gas used to contact the melt with a gas such as
.: .:
nitrogen or argon, At high levels of sulfur in the matte (^~15% S),
bath temperature is the more effective means of control. Gases
relatively rich in oxygen are employed to generate heat by the ~ -

- 3 -

. .
' ': ' '
: ~. :., .... .
.: . ::

~LOS~
oxid~tit)n o~ 1r~"- th~rci~y r.li~in~ the hath lemp~rc~ re ~ul~stantia]]y
~vl~ilt~ pro~ llly Ino~ la~ c,r ~ c)~ o(l~(t. ~low~v(:l~
a~ the s~llfur content of ~h(? I~ath (l~r~?ase~ still ~reat~r temper~tllr~;
and/or diiutions of the ~a~ are r~quired to prevent the a~ lmulation of
cobalt oxide. The limitations of pre~ently available refractories rul~:
;; out the continuing increase of temperature as a practicable means for
promoting the reaction so dilution becomes the more effective m~ans
of control. However such dilution tends to lower the bath temp~rature
by reducing the amount of oxygen introduc~d per unit time (i. e. reducing
the rate of heat generation) and by virtue of the sensible heat removed
from the system by the diluting gase~ t lower s~llfur content~ ~ ;
(~lo~/lJ s) heat mttst therefore be supplied from some source other ehan
the oxidation of sulfur. This Lan he done ~31ectrically when the proce9s
i9 conducted in a ves~;e1 provided with induction heating. It can also
be provided chami(:ally by addin~ a strong deoxidi7.ing agent such aff ~ .
silicon to the hath. Or the heat can be provided by the combustion of
hydrocarbon fuel~ with a controlled ~xce0~ of air or oxygen. In this
last case, the gaseous producta of ~:ombustion advantageously act as
diluent~ .
~0 Another very effattiva m~anff for promotin~ tho tonversio
without accunlu1atin~ cxee~Hive amount~ of t obalt oxide i~ lo lowor lhe
partial pre~ur~ of the product SO~ by e onduetin~ the pro~e~s under
vacuum. Thi~ procedure would work at any sulfur eont~nt bue it is
not practicable to pump lar~e volume0 of SC);~ through pros~lltly avail- ~
ab1e vacuum YyDtemD. This procadure is therefor~ used only at low ~ ~-
~ulfur tevel~ (~ay c5% S adva.ntaKeou~ly ~IV/u S). Thi~ approach



-4-

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onveniently lends itself to heatin~ and stirring the molten hath
by electromagnetic means.
It is clear that the successful practice of this invention
requires careful control of bath temperature and the oxygen content
of the inlet gases. The required sulfur-oxygen-temperature
correlation will be apparent from the accompanying drawing which
depicts a cobalt-sulfur binary phase diagram with curves of constant
oxygen partial pressure superimposed thereon correlated to both the
sulfur content of the cobalt melt and the temperature of conversion.

Thus, referring to the Curve B, it will be noted that ~ ;
, when the inlet gas contains 5~0 oxygen, a conversion temperature at
,:, .. . ~ :
least above 1350C, for example, 14nooc and higher is required to ~ ~
.:
desulfurize a melt containing 20% sulfur. When the melt sulfur is
lowered to 14% sulfur with this gas, the bath tempeFature should be ;~
above 1500C to avoid substantial oxide formation.
Similarly, when employing a gas with iO% oxygen `~
(Curve C) to desulfurize a 14% sulfur melt, the bath temperature `
should be above 1540C. Likewise, with a gas containing 21% oxygen
~Curve D) the bath temperature should be above 1560C to desulfurize

~ a bath containing 16% sulfur. Temperatures for desulfurizing cobalt
melts of different sulfur levels with inlet gases of other oxygen contents
can be interpolated from the drawing. ~ .
As will be appreciated, both the oxygen content of the
gaseous stream and the temperature can be varied during the con-
version treatment according to the sulfur remaining in the melt. ;
In carrying out the process, the sulfidic cobalt material,
however derived, is melted to provide a molten bath. The melting



- 5-
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: ,-, . , - , , . . . : , ,

~L~S~

can be carrie(l o~t in any convcnti()nal f~lrnace, sl1cll ,-9 an inc1~1ction
~lrnace, reverberatory f~lrnace, top blown r otary c onverter, or an
e1ectric furnace. The melting temperature will clepend on the initial
sulfur content of the sulficlic cobalt rnaterial. A cobalt sulfide with
a s~llfur content of about 26% has the lowest melting point of about
880C, Sulfidic materials with either higher or lower sulfur contents
have higher melting points. On the lower sulfide side, the melting
point increases to 1495C, the melting point of pure cobalt. It should
be noted that the presence of other impurities can lower the melting
point slightly. Preferably, the temperature of the molten matte
before treatment should be at least about 1200C and, for example, ~`-
at least about 1300C.
The conversion of molten sulfidic cobalt material to
metal should be carried out in a vessel in which good stirring of
,~ the sulfide is provided. It can be a top blown rotary converter, an
. induction unit with adequate stirring or a bottom blown vessel like
the bessemer converter. The vigorous stirring may be produced
by any of the well known methods; for example,~ hy mechanical
stirring, by electromaKnetic mcans or by using porous plugs or
; 20 tuyeres through which inert or oxidizing gases are blown into the
melt below the surface thereof.
The oxidation is carried out advantageously by employing
, ~ .
free oxygen-containing gases. For example, when the sulfur content
of the matte exceeds 15% by weight, the oxygen content of the gaseous
stream is preferably about 10% or more by volume. Oxidants employed
include air, oxygen-enriched air, oxygen and combustion gases

-6- ;;
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.. . . . . .

.
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producecl by coml~ustion of fuel with more than stoichiometric amounts
of air or oxygen or combinations of air an~l oxygen. The oxidant as
mentioned before can be injected through tuyeres or porous plugs or
can be lancod on top of the bath with single or multlple lances or by
a single lance capable of delivering multiple jets of oxidant over the
entire bath surface. When tuyeres or porous plugs are used these may

: .
be shielded with hydrocarbons. :~

; Details of the Invention

Tests were conducted to determine the relationship

between the sulfur content of the sulficlic cobalt material, the oxygen

content of the gaseous stream and the melt temperature necessary to

- ~ avoid the excessive formation of cobalt oxide on the s~urface of the bath.

- ~ Melts containing the specified amount of sulfur were held
, , ~ .
,~ ~ in an g kg induction furnace and, by using a three lance arrangement
` were surface blown with gaseous streams containing a controlled amount
of oxygen. ~ For each oxygen content in the stream, the temperature of ! -
the melt was adjusted until only a light spot of cobalt oxide persisted
on the surace of the melt just below the lance. Thus, for oxygen
contents of 10%, the bath temperature had to be increased as the sulfur
~ . .
~ ~ 20 decreased as illustrated by Curve C to avoid excessive accumulation of ~ ~
:
~ oxide, For gases richer in oxygen than 10%, the temperature required
: : ~
to achieve low sulfur contents exceeded the capabilities of the crucible, :
so further dilution was necessary.
Typical oxygen partial pressures and temperatures

, required to convert sulfidic cobalt melts of varying sulfur contents

to produce negligible oxide formation are given in the following table:

.

- 7 -

. ~, .. . . . . . . . .
: ' ' :' ~. ' .
: . . : . . .
:, ~: : .
. " ~ , ~ . : : .
.. . .

105~

Melt '1/,, Oxy~en irl Melt
W t ~,~" Oxi di z i ng 'r emp
S _ Cl~s C
21 1470
18 21 1520
16 21 15 h O
14 10. ~ 1540
12 10.5 1580
10. 5 1610
_
8 5. 25 1590
6 5. 25 1620
4 _ 5.25 1660 -
0. 6 2. ~ 1700 ~ -
' :, " '
.... . .
If either the oxygen partial pressure is increased or the
temperature is decreased from the values given in the table at the
given sulfur levels, excessive oxide formation occurs. This is
confirmed by referring to the accompanying drawing. Curves A to F
~ were obtained by mathematically modelling the experimental data and
- extrapola.,ing them to lower/higher sulfur contents and to lower/higher
oxygen contents in the oxidizing gas. The resulting cobalt product
which may contain about 1% or less of sulfur after the oxidation
treatment can be further purified by varlous methods. One such
method is vacuum refining of the molten bath. The molten bath from
the oxidation treatment is subjected to a vacuum treatment for
removal of impurities; e. g. antimony, bismuth, lead, zinc,
~-~ cadmium, selenium, tellurium and for final sulfur elimination.
It is desirable for thermodynamic and kinetic reasons to subject the ;
molten bath to a pressure less than 0. 3 atmosphere and advantageously
to a pressure less than about 1 mm of mercury. The oxygen in the bath
required for this treatment is about twice the amount of sulfur present.
Since the solubility of oxygen in liquid cobalt is rather limited
(0.52 wt % Oat 1700C), it is generally not possible to dissolve



,

~OS~

sufficient o~;ygen in the bath to react with all the dissolved s~llfllr,
It is possible to saturate the system with the stoichiometric amount
of required~ oxygen but this solid oxide phase proves troublesome in
operation. It frequently sticks to the crucible walls and tends to
react with them. It is far more desirable to add oxygen to the
system as the process proceeds exercising reasonable care not to
form excessive amounts of solids. This can be done with oxygen-
bearing materials such as cobalt oxide or compounds heat decomposable
- ~ thereto. Alternatively, gaseous oxygen, e. g. in the form of air, can
~ 10 be introduced into or on to the molten bath to overcome any oxygen
. ~ :
- ~ deficiency. During vacuum refining, more favorable kinetics can ~
- be obtained by~vigorous agitation, either by electromagnetic means ~;
`; or by purging with inert gases, and by controlling the oxygen content ~ ~ .
of the melt between 1. 5 and 4. 0 times the sulfur content. -
It has been found that the kinetics of sulfur removal is
; ~ dependent on the ratio of volume/area of the melt and decreases with ~ ~
, . ' .: ,
increasing values of this ratio. Therefore the choice of the vessel
size should be such as to optimize refining kinetics and vessel costs.
Another alternative is to desulfurize the final melt using v
such desulfurizing slag additions as: CaO (l~me slag); CaO +AI;
CaFz + CaO +Alz03; CaO + Mg; CaC2, Mg, Ca etc. The metals Al
- ~ ~ and Mg act as efficient reductants which aid the desulfurizing reaction.
`' In addit~on Mg acts as a desulfurizer and can thus be used alone for
this purpose. The amount of desulfurizing metal added shauld be
at least stoichiometrically sufficient to combine with the sulfur,
taking into account the loss of some metal by oxidation.




' ' ' ' ~

As ill~l~strative of the varic)lls errlhodiments of the
invention, tllc fol]owin~ exa~llplcs .are given: ~ '
E XA M l~L I~ I '
A 3. 6 kg charge of cohalt sulfide containing 22. 4% S ~ ,'
was melted and vigorously stirred by induction heating. The surface
of the meLt was blown with a gaseous stream containing 21% oxygen
by volume at a starting temperature of about 1300C. The oxidation
was carried out for 1. 6 hours, during which period the temperature
of the melt was gradually raised to about 1500C. During this period.
the sulfur was lowered to 15. 5% and the formation of cobalt oxide was '~
substantialIy avoided. The oxygen content of the gaseous stream was
decreased to 10. 5% and the melt was oxidi;~ed for another 0. 75 hours ,`
during which period the sulfur content of the melt was reduced to 9. 5'~
and the melt temperature was increased to 1620C. The oxygent content
of the oxldizlng stream was further decreased to 5. 25% and the melt ,
was blown for another 0. 9 hours, during which period the sulfur content
of the melt was~ reduced to 4. 2% and the melt temperature was increased
to about 1650C. A cobalt melt containing 4. 2% S was blown with a ,
gaseous stream containing 2. h% oxygen for 1. 5 hours while the melt
temperature was increased to about 1700C. This produced a cobalt " ;,
metal containing 0. 61% S and the formation of the cobalt oxide was

substantially inhibited during the entire blow.
'.' :'
EXAMPLE lA -'
, In a comparison test similar to that described in Example I. ,~
an iron sulfide matte containing 14% S was blown with a gaseous stream '
containing oxygen at levels as low as 2% while maintaining the melt at a
: ~ ' ' `' '


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te~lperature of about Ih()0C' ~o l64n~C, C,ontinuous oxide formation
took plac e whic}l causecl corrosion of the crucible resultin~ in a rnel~ ;
break-out within 30 minutes from the start oL the oxidation.
.
EXAMPLE 2
The purpose of this example is to show that following the ,
removal of sulfur from sulfidic cobalt melts to a level below 1% S,
' the resulting product can be further purified by vacuum refining as
follows.
In this instance, an 18 kg melt of cobalt containing 0. 09%
- 10 S was refined at 1650C by introducing 0. Z3% oxygen into the melt
and subjected tc a vacuum treatment at a nominal chamber pressure
of about 0. 6 mm of mercury. After 90 minutes of treatment, the
sulfur content o~ the melt was lowered to less than 0. 0001% S and
the oxygen decreased to 0. 06%.
EXAMPLE 3
.:.~ : ,
This example illustrates the use of slagging techniques
for lowering the final sulfur content of cobalt. In this case, a 5 kg -melt containing 0. 12% S was desulfurized by adding 2% by weight of
:: :
CaO and 0. 6% by weight of aluminum at a melt temperature of 1600C
,~ 20 to yield a cobalt metal product containing 0.01~/o S.

Another 5 kg of cobalt melt containing 0. 12% S was
desulfurized at 1600C by adding 4% by weight of a slag containing
61. 8% CaO, 22. 5% SiO2, 7. 5% A1203, 3. 5% Fe304, 2. 5% MgO and 2%
.. . .
K2O, the desulfurizing being further aided by the addition of 0. IZ% by
weight Al. The resulting cobalt metal product analyzed 0. 02% S.




'- ~'~ ~ ,' ' " :

:: '

As wiL1 be apparent from the foregoing cxanlples, the
sulfur can he substantially completely removed from a sulfidic
cobalt melt~to form cobalt metal while inhibiting substantially the
formal:ion of cobalt oxide.
Although the present invention has been described in
conjunction with preferred embodiments, it is to be understood
that modifications and variations may be resorted to without depart-

ing from the spirit and scope of the invention as those skilled in the ~ ~
; art will readily understand. Such modifications and variations are ~ ~ -
10 considered to be within the purview and scope of the invention and :
~ the appended claims. `
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Sorry, the representative drawing for patent document number 1056161 was not found.

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Title Date
Forecasted Issue Date 1979-06-12
(45) Issued 1979-06-12
Expired 1996-06-12

Abandonment History

There is no abandonment history.

Current owners on record shown in alphabetical order.
Current Owners on Record
INCO LIMITED
Past owners on record shown in alphabetical order.
Past Owners on Record
None
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.

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Drawings 1994-04-22 1 28
Claims 1994-04-22 3 135
Abstract 1994-04-22 1 23
Cover Page 1994-04-22 1 26
Description 1994-04-22 12 512