Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Treating electrode – diaphram – or membrane during synthesis
Reexamination Certificate
1999-01-15
2001-06-12
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Treating electrode, diaphram, or membrane during synthesis
C204S227000, C204S230300, C204S269000, C204S274000, C204S280000, C204S281000, C204S286100
Reexamination Certificate
active
06245209
ABSTRACT:
BACKGROUND OF THE INVENTION:
This invention relates to refining of ores and more particularly to electro-refining systems and methods.
In electro-refining, semi pure copper anodes are suspended in acid next to a cathode. The anode is given a positive charge of direct current while the cathode is given a negative charge. This charge causes the copper ions to transfer from the anode to the cathode and the impurities fill to the bottom of the tank.
In solvent Extraction-Electro-winning (SXEW) the copper is leached out of the ore, the leachate is concentrated and pumped into tanks similar to electro-refining. The difference is in Electro-winning the copper enters the tank in liquid solution, The anode is not impure copper, it is permanent and usually lead. The direct current voltage between the anode and cathode is greater in Electro-winning than in electro-refining because the dissolving of the impure copper in acid generates some voltage.
In either case the cathode can be permanent, usually stainless steel or titanium, or a starter sheet. The starter sheet consists of a one day deposit of copper suspended from a metal bar, usually copper and immersed in the tank. Copper is deposited on all surfaces of the starter sheet and this copper along with the starter sheet is harvested every 7 to 14 days at a weight of 240 to 400 pounds.
The direct current flowing thru each cathode is quite high, from 350 to 700 amps. Each tank or cell can have from 35 to 60 Cathodes.
As the temperature of the surface of the cathode is increased the rate and quality of copper deposition is increased. Currently all of the electrolyte flowing tbru the cell is heated to keep the surface of the cathode warml When the electrolyte gets too hot the permanent lead anode is degraded and more acid vapors at evolved and enter the atmosphere of the cell house.
In the case of a permanent cathode of stainless steel of titanium, care must be taken to prevent the copper from depositing around the edge and locking itself on the metal. Usually a non conducting edge strip is attached to the cathode to keep the copper off the edges. Wax is sometimes deposited on the bottom edge for the same reason. The wax process is messy and must be cleaned off and redeposited after each harvest of copper.
It is clear that there is a need for an improved electro-refining system. Another Type of metal refining cell is the “bi-polar” cell. In this type of cell the current flows sequentially throu the cell from one end to the other. One side of each metal plate is the anode and the other is the cathode. In the case of SXEW, lead or carbon is bonded to a sheet of stainless steel. A series of these plates are placed parallel to each other ina tank with groves in the sides and bottom to receive them. A direct durrent is induced at one end of the tank and flows from panel to panel to the other end. The new and novel cathode in this invention can be readily adapted the perform in the bi-polar cell by bonding lead, carbon, graphite or some other nobel material on the anode of the panel.
SUMMARY OF THE INVENTION
The invention creates an electro-refining system in which the deposited metal is harvested without the need to remove the cathode from the electrolite. Since the invention allows the harvesting to be conducted without the removal of the cathode, the electro-refining process is much faster and more easily accomplished. Further, since the cathodes are not being constantly removed and inserted into the slurry bath, there is minimal chance of damaging the cathodes.
The cathode has an interiorcavity permitting steam to be introduced to heat the cathode. In the preferred embodiment, baffles are used to direct the steam flow through the cavity so that the cathode is uniformly heated.
The introduction of the steam into the cavity within the cathode is accomplished in several different ways. The preferred technique is to utilize the support brackets which contain an opening which nests onto a steam outlet. The opening in the support bracket channels the steam into the cavity.
During the deposition process, heating of the cathode encourages the deposition process. In one embodiment of the invention, the cathode is treated to two levels of heating. The first lower level is to encourage the deposition process; the second, much higher level is to assist in the removal of the deposited metals.
When the deposited material is to be harvested, the steam raises the temperature of the cathode above the boiling point of water. At this stage, moisture trapped between the deposited metal and the cathode vaporize, expand, and break the bond between the deposited metal and the cathode.
Using a lifting bracket which was installed before the deposition process and into which the deposited metal has been formed, the now-released sheet of deposited metal is easily removed. The bracket/deposited metal is removed from the electrolyte without the need to remove the cathode. A new bracket is then placed over the cathode and the deposition process is begun anew.
This invention deals with:
A. A different way to prevent the copper from depositing around the edge of a cathode;
B. An improved method to separate the copper from the cathode at harvest; and
C. An improved method to increase the surface temperature of the cathode.
An improved cathode for electro-refining or electro-winning is created in which two thin stainless steel or titanium sheets, 0.024 to 0.0157 inches thick, are resistance welded to each other on 1½ to 4 inch centers. This sandwich is then resistance, seam welded all around the outside edge to form an air tight assembly. This assembly is then inflated between two fixture plates that allow the thin surface sheets to expand to the width between the fixtures. This stretching of the metal flattens the assembly and forms a hollow chamber. The thin sheets can also be formed before welding to eliminate the inflation step.
The welded and inflated assembly is attached to two solid copper hanger bars/bracket and a non-conducting material is inserted between the two thin sheets into the grove that extends all around the outside edge. The non-conducting material can be a hot melt adhesive, a castable ceramic, a filled reactive resin like vinyl ester, or solid plastic strips that are staked in place. Two non conducting panels of fiberglass reinforced plastic or formed thermoplastic, with vertical grooves separated by interval between the cathodes can be attached on each side of a group of cathodes to prevent the metal from depositing around the edge. These panels can also be reinforced with plastic pipe that is drilled in such a way to allow for the introduction of fresh electrolyte between each anode/cathode pair. Not only do these panels prevent the deposition of metal around the edge that impedes harvest but they also hold the anodes and cathodes at more preciseintervals then ever before.
While the cathode is immersed in the cell and copper is being deposited, very hot water from 120* F to 200* F is circulated inside the electro-deposition plate. This hot water heats the surface where the copper is being deposited and improves the process.
In one embodiment, when the cathode is ready for harvest it is removed from the cell and transported to a stripping device. Here the hot water is replaced 20 to 60 psig steam that rapidly heats the cathode and flashes the moisture in a coating on the surface of the cathode between the newly deposited copper and the stainless or titanium. The flashed steam exerts a 20 to 60 psig force to strip the copper of the cathode.
The cathode, when in the electro-deposition process, is subjected to a high current flow. The direct current flowing through each cathode is quite high, from 250 to 600 amps. Each tank or cell has 45 to 60 cathodes or more. This means that the combined current through each cell can be as high as 36,000 amps.
If a short forms between a cathode and an anode, the entire current flow will try to flow through one cathode causing massive damage to the cathode and potentially to the entire system.
In the preferred e
Ogram Mark E.
Valentine Donald R.
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