Electrolysis: processes – compositions used therein – and methods – Electroforming or composition therefor
Reexamination Certificate
2002-07-08
2004-11-09
Nicolas, Wesley A. (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electroforming or composition therefor
C205S076000, C205S081000, C205S102000, C204S230200, C204S230400
Reexamination Certificate
active
06814847
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for electro deposition of metal.
BACKGROUND ART
There are various processes and apparatus for electro-refining or electro-winning metal.
One particularly successful process for electro-depositing of copper for example is the so-called ISA PROCESS in which copper is deposited on a stainless steel cathode mother plate. The electrolytically deposited copper is then stripped from the cathode by first flexing the cathode to cause at least a part of the copper deposit to separate from the cathode and then wedge stripping or gas blasting the remainder of the copper from the cathode.
In the ISA PROCESS the bottom edge of the cathode mother plate is generally covered with a release compound such as wax or a plastic edge strip to prevent deposition of copper thereon. This allows for removal of the electro-deposited copper as substantially equivalent separate sheets from both sides of the cathode plate. Such waxing of the cathode sheet, however, is time consuming and there is added cost both for applying the wax and for recovering the wax from the stripping process and associated housekeeping.
To avoid these difficulties, some electro-refining/electro-winning operations use a so-called enveloped cathode process. In such a process the lower edge of the cathode sheet is not waxed and the electro-deposited metal is allowed to grow on both sides of the sheet and around the bottom edge of the cathode mother plate.
Removal of the electrolytically deposited envelope of metal is then accomplished by flexing the cathode and pulling back the metal from both sides of the sheet so that it forms a V. The cathode mother plate is then removed from between the electrolytically deposited envelope of metal, the envelope is then closed and rotated from its vertical position to a horizontal position and transported to a stacking/bundling station.
Not only does such a removal process require complex apparatus for opening the metal envelope, removing the cathode mother plate prior to closing of the envelope and rotating the envelope from the vertical to the horizontal position for stacking, such an arrangement is time consuming and generally not as quick as the ISA PROCESS stripping step.
In conjunction with others, the applicant has recently developed a new process in which an envelope of metal is formed on a stainless steel cathode mother plate and then stripped into two separate sheets. This process is subject of co-pending International Patent Application No. PCT/FI99/00979. By way of summary, this process will now be described with reference to
FIGS. 1A-2D
.
The initial step in stripping an electrolytically deposited metal envelope from its cathode mother sheet is to at least partially separate either side of the deposited envelope from the cathode sheet. In this regard, reference is made to
FIGS. 1A-1D
. The enveloped cathode comprises cathode sheets
20
and
30
deposited on the cathode mother sheet
10
and joined along the lower edge thereof by a frangible portion
40
. The cathode mother sheet is firstly flexed to provide separation of at least the upper end portion
50
of the sheets
20
,
30
.
The partially separated envelope as shown in
FIG. 1D
is then subjected to a stripping operation as shown in
FIGS. 2A-2D
. The partially separate sheets
20
and
30
are positioned in a stripping apparatus on rollers or conveyor belt
50
. The apparatus includes a wedge stripper or air blaster
130
. These wedge strippers
130
enter the gap between sheets
20
,
30
and cathode mother sheet
10
. The wedge strippers
130
essentially separate the entire sheet portions
20
and
30
of the electrodeposited envelope from the cathode mother sheet
10
. The sheets
20
and
30
, however, are still held together by the frangible portion
40
extending along the bottom edge of the cathode sheet
10
as shown in FIG.
2
B. To effect full separation of the electrodeposited metal envelope from the cathode mother sheet
10
into separate substantially equivalent sheets
20
and
30
is held by grippers
25
,
35
and rotated about the frangible portion
40
from the substantial vertical position shown in
FIG. 2B
to the substantially horizontal position shown in FIG.
2
C. This rotation separates the deposited metal from the cathode into two substantially equivalent sheets. In many cases, a single rotation of the sheets
20
,
30
from the vertical to the horizontal is all that is required to separate the sheets. This separation of the sheets
20
and
20
from each other as well as the cathode mother plate may be confirmed by the grippers
25
,
35
as follows. The grippers which still hold the sheet
20
,
30
in horizontal position shown in
FIG. 2C
, are adapted to pull the respective sheets slightly outward as shown in FIG.
2
D. If the sheets,
20
,
30
move outwardly in unison with the grippers, separation of the sheets
20
,
30
is confirmed. If, however, the force to move the grippers outward is too great or simply the grippers do not move this indicates that the frangible portion
40
has not in fact separated the sheets
20
,
30
and accordingly further rotation (as shown in
FIG. 2C
) of the sheets may be required.
If further manipulation/rotation of sheets
20
,
30
is required, the apparatus using grippers
25
and
35
rotates sheets
20
and
30
upwardly and downwardly until the aforementioned confirmation of separation of the sheets is effected.
In a preferred embodiment, cathode sheet
10
may be lifted upwardly in the stripping apparatus to provide more clearance between it and the sheets
20
,
30
and frangible portion
40
since manipulation of the sheets
20
and
30
may cause contact between at least the frangible portion
40
and the cathode sheet
10
.
Once the cathode sheets
20
and
30
are separated into substantially equivalent separate sheets, it is a simple matter to transport the sheets out of the apparatus for stacking and subsequent treatment.
The growth of this deposited metal envelope, however, is complex and the applicant has found that under certain process conditions it may be difficult to separate the electro-deposited envelope into two separate sheets. This is particularly true if, for any reason, power supplied to the electrolytic bath is interrupted for any substantial length of time. If this occurs, the metal sheets require rotating or flapping several times to effect separation.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative thereto.
DISCLOSURE OF THE INVENTION
In a first aspect, the present invention provides a method for electro depositing metal on a cathode in an electrolytic cell, said method comprising applying an electric potential to the cell to deposit an envelope of metal on said cathode, said envelope including two substantially equivalent sheets on either side of said cathode joined along at least one edge portion by a frangible region, the metal being removable from the cathode by rotation of the respective sheets about the frangible region,
wherein the direction and quantity of current in the electrolytic cell is monitored such that as current flow approaches or reaches a predetermined value and/or the direction of current flow changes, an auxiliary power supply applies an auxiliary potential to the cell at a level sufficient to maintain a predetermined direction and quantity of current flow in the cell.
Not wishing to be bound by any particular theory, the present applicant has found that power interruption for any considerable period of time (ie. one hour or more) in the cell can result in “lamination” of the metal in the area of the frangible region. To explain, if power is supplied to the electrolytic cell resulting in a “forward” current, deposition of metal from the anode to the cathode is maintained and the metal is deposited in a controlled orderly fashion.
On the other hand, if power is interrupted and later recommenced, the orientation of metal deposition ap
Bailey David
Cutmore John
Copper Refineries Pty Ltd
Nicolas Wesley A.
Stevens Davis Miller & Mosher LLP
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