Electrowinning cell

Details Electrowinning cell Electrowinning cell

1998-12-28

2001-04-10

Valentine, Donald R. (Department: 1741)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S227000, C204S237000, C204S272000, C204S273000, C204S275100, C204S284000

Reexamination Certificate

active

06214179

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method of electrowinning metals such as gold, silver and the like from a metal-rich electrolyte and to an electrowinning cell for use in carrying out the method.
BACKGROUND TO THE INVENTION
Electrowinning cells for the recovery of gold are well known and consist fundamentally of a tank in which a static sandwich arrangement of alternate electrically connected anode and cathode assemblies are located in a flow path between the electrolyte inlet to the tank and an outlet weir from the tank.
In use, in one form of electrowinning, a gold rich eluate is fed into the tank through its inlet to pass between the electrified anodes and cathodes in the tank and from the tank through its outlet. In doing so a gold rich sludge is electrolytically built up on the low adhesion material of the cathodes and in time gravity separates from the cathodes to settle in a sump or gold trap in the base of the tank from where it is periodically removed.
The cathodes in the cells generally consist of steel wool which is trapped between perforated sheets which are made from a suitable plastics material and the anodes each consist of a composite unit which is made up of stainless steel strips.
For security reasons, the cell tank is closed by a lockable lid.
Although electrowinning cells of the above type are reasonably efficient their gold recovery rate is slow and a large percentage of gold remains trapped in the cathode wool which necessitates regular removal of the cathodes from the tank for maximum gold recovery by means of a calcine or acid treatment process. The removal of the gold laden cathodes from the tank is labour intensive and poses severe gold theft security problems.
SUMMARY OF THE INVENTION
A method of electrowinning metal such as gold, silver and the like from an eluate containing the metal in solution according to the invention includes the steps of feeding the eluate into a closed tank which includes a suitably spaced and electrified anode and cathode, electrolytically depositing the metal from the eluate onto the cathode and at least periodically causing the deposited metal to be dislodged from the cathode for removal from the tank.
The deposited metal may be dislodged from the cathode by movement of the cathode in the tank.
The cathode may be moved in the tank in any suitable manner, for example, by vibration, rapping, oscillation, rotation and the like or by any combination of these movements.
The method may further include the step of depositing metal which is dislodged from the cathode in a metal trap which is located on or is in communication with the base of the tank and from which the metal is periodically removed through a security protected outlet.
The method may include the step of feeding eluate which has been exposed to the cathode from the tank through a settling tank, gravity separating particulate metal from the eluate in the settling tank and periodically removing the separated metal from the settling tank.
After a predetermined operating period the barren eluate is drained from the cell system and the cathode is spray cleaned by means of liquid spray nozzles in the tank to remove gold particles which are trapped on or in the cathode.
An electrowinning cell for electrowinning metal such as gold, silver and the like from a metal rich eluate according to the invention includes a tank having an eluate inlet and outlet, a suitably insulated anode and a suitable electrowinning cathode in the tank in the eluate flow path through the tank between its inlet and outlet and means for dislodging metal which has been electrolytically deposited on the cathode from the cathode during use of the cell. The metal dislodging means may be a device or arrangement for moving the cathode in the tank. In addition to the cathode movement generating device or arrangement, the metal dislodging means could include a liquid spray jet arrangement.
The electrowinning cell could be any conventional cell which includes the cathode moving and the liquid spray arrangement of the invention for dislodging the metal from the cathode. In a preferred form of the invention, however, the electrowinning cell tank is for practical purposes permanently closed and the cell includes an axially rotatable shaft which is located in and projects from the tank with the cathode attached to the shaft for rotation with the shaft in the tank, means for rotating the shaft, an anode in the tank on the outside of a path circumscribed by the cathode during its rotation in the tank and suitable electrical connections for connecting the cathode and the anode to a suitable electrical supply.
The shaft rotating means may be adapted periodically to reverse the direction of rotation of the shaft and so the cathode in the tank. Preferably, the tank is a cylindrical vessel, and in one form of the invention the anode is a tubular sleeve which is circular in cross-section and which is concentrically located in the tank, the shaft is coaxially located in the tank with one end portion passing through an end wall of the tank and the cathode is a cathode panel which is attached to the shaft for rotation in the tank at least partially within the anode.
The cathode may, and preferably does, consist of a plurality of cathode panels which project radially from the shaft.
In another form of the invention the anode consists of two sheet metal cylinders which are concentrically spaced from and attached to each other and the cathode is cylindrical in shape and rotatably located between and spaced from the anode cylinders.
The cathode panels and the cylindrical cathode conveniently include a mat of stainless steel wire wool or knitted mesh which is sandwiched between suitably rigid open mesh material. The anode cylinders, in both forms of the cell, may be made from a suitable stainless steel.
Further according to the invention the cell includes suitably positioned liquid spray nozzles in the tank which are directed to spray jets of liquid onto the or each cathode panel as it is rotated in the tank and liquid supply lines to the nozzles.
The shaft rotating means is conveniently a motor which is attached to the tank end from which the steel shaft projects. The motor may be connected to the shaft through a suitable gearbox.
Further according to the invention the eluate inlet to the tank is above the anode and cathode in the tank and the tank outlet is located in its base with the cell including a metal trap which is in communication with the tank outlet below the tank base. The cell conveniently includes a valve for shutting the tank outlet from the metal trap and a security protected metal outlet valve from the trap from which the metal sludge is periodically withdrawn.
The cell of the invention may include a settling tank, on the outside of the cell tank, into which eluate which has passed through the cell tank may be fed from bottom to top to a line for recirculating the eluate through the cell tank feed system while particulate metal in the eluate settles to the bottom of the settling tank in use. The settling tank preferably includes a gold trap as described above.


REFERENCES:
patent: 3477926 (1969-11-01), Snow et al.
patent: 3560366 (1971-02-01), Fisher
patent: 3806434 (1974-04-01), Goold et al.
patent: 3985634 (1976-10-01), Larson et al.
patent: 4028199 (1977-06-01), Holland
patent: 5324396 (1994-06-01), Ferron et al.
patent: 5902465 (1999-05-01), Pang
patent: 6017428 (2000-01-01), Hill

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