Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-08-10
2002-09-17
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S275100, C204S269000
Reexamination Certificate
active
06451183
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for electrowinning metals from a solution containing metals. This invention is particularly concerned with the production of particulate metal, eg in the form of powder, as distinct from plated metal.
This invention relates particularly but not exclusively to a method and apparatus for electrowinning copper in a powder form from a copper bearing solution, eg a low grade copper solution such as is often found at mines and mineral processing sites, and it will be convenient to hereinafter describe the invention with reference to this example application. However, it is to be clearly understood that the invention also applies to other metals, eg silver, nickel, cobalt and tin.
2. Description of the Related Art
The applicant has previously designed an electrowinning cell for electrowinning metals such as copper and tin from aqueous solutions. The cell is disclosed in the applicant's international patent application number (WO 96/38602) entitled mineral recovery apparatus. The entire contents of this specification are explicitly incorporated into this document by cross-reference.
The above application discloses a cell having a tangential inlet at the bottom of the housing and a tangential outlet at the top of the housing. The orientation of the inlet which directs solution into the cell with a particular orientation in conjunction with the cylindrical housing induces a helical spiral flow through the cell. A rod-like anode extends axially the length of the housing coaxial with the cell and a split sleeve cylindrical cathode bears against the wall of the housing and circumferentially surrounds the anode spaced outwardly therefrom. In use, a potential difference is applied across the flow passage between the cathode and the anode to drive the electrowinning metal production process. The helical flow through the cell from the inlet to the outlet presents copper ions to the cathode continuously to plate out the copper economically even in low grade solutions.
This process progessively plates out a copper tube on the inside of the split sleeve. When the copper plate is about 6 to 8 cm thick (2.4 to 3.14 inches) it is harvested. This is accomplished by removing a top end cap from the cell and lifting the split sleeve out through the top of the cell. This is a labor intensive process and interferes with the otherwise continuous nature of the process.
As a commercial plant using the process contains banks of literally hundreds of cells, the harvesting of the cells in the manner described above is a labor-intensive process. A further disadvantage of the production of copper tubes in the manner described above is that the tubes require specific handling and transport procedures. It would therefore be advantageous if an easier method for harvesting the copper from the electrowinning cells could be devised.
In addition, the electrowinning cell described above may have less than optimum efficiency because of the large gap or distance between the cathode and anode. As a result, a relatively high voltage has to be applied across the cathode and anode and the applicable current density is relatively lower. As the amount of metal produced is directly proportional to the current density across the cathode and anode, it is desirable to have as high a current density per unit amount of electrical power input as possible.
SUMMARY OF INVENTION
According to a first aspect of this invention there is provided a cell for electrowinning a metal in powder form from solution, the cell including:
a housing having an inlet towards one end thereof and an outlet towards an opposed end;
an anode extending substantially axially through the housing;
a cathode surrounding the anode spaced outwardly away from the anode to define a flow passage between the cathode and anode, having a gap of 5 to 25 millimeters (0.20-0.98 inch); and
means for applying a potential difference between the anode and the cathode.
The cell therefore has a substantially narrower gap between the cathode and anode than either electrowinning plate cells or cylindrical cells for producing copper tubes. This assists in increasing the current density between the cathode and the anode, particularly for low conductivity solutions.
More preferably the gap is 5 to 20 millimeters (0.20 to 0.80 inches), even more preferably 10 to 15 millimeters (0.40 to 0.60 inches), most preferably 12 to 13 millimeters (0.47 to 0.51 inches).
Typically, both the anode and the cathode are substantially cylindrical. The cathode may be formed by the wall of the housing or by a sleeve positioned adjacent the wall of the housing. Preferably the cathode is formed by the wall of the housing which is metallic.
Typically one end of the cell has a relatively upper orientation and an opposed end of the cell has a relatively lower orientation in use, and the inlet is positioned at or adjacent the lower end and the outlet is positioned at or adjacent the upper end.
Thus, in use, process solution containing metal ions to be electrowon travels upwardly through the cell from the inlet to the outlet and metal is deposited on the cathode as a powder. Periodically, a flush solution is pumped in a reverse direction through the cell to remove deposited powder metal from the cell for harvesting. It is preferred that the process solution travels up through the cells so that gas generated by the electrowinning process can be vented through a vent associated with an upper region of the cell. It is particularly preferred that flush solution travels downwardly through the cell so that gravity assists with the flushing process. Typically, flushing would be assisted by other factors such as increased pressure of flush solution and passing air bubbles or other means over the cathode to assist in loosening the metal powder.
Preferably, the inlet directs solution into the cell in substantially an axial direction.
Preferably, the outlet is oriented such that flushing fluid which is passed through the cell in a reverse direction is directed axially into the cell through the outlet.
In a preferred form said inlet is defined in said one end of the cell and said outlet is defined in said opposed end of the cell.
The orientation of the inlet and gap of the flow passage facilitates process solution flowing through the flow passage with a turbulent flow. This is quite different from the tangential inlet in the prior art cell which induces a helically spiralling plug flow through the cell from inlet to outlet. Plug flow is fundamentally different from turbulent flow. Turbulent flow assists with the formation of powder metal as distinct from plate metal.
It is similarly advantageous that the flush solution which flows in a reverse direction through the outlet of the cell is directed axially into the cell to promote turbulent flow. This turbulent flow of flush solution assists in dislodging the metal powder from the cathode.
Preferably, the cell further includes means for guiding powder which is washed off the cathode during a flush cycle towards the inlet through which it is drained from the cell, eg a sloping internal surface of the housing.
This reduces the likelihood of metal powder collecting in dead spaces in the bottom of the cell and assists in fully draining metal powder from the cell.
Preferably, the cell further includes cleaning means for clearing metal plate obstructions from the flow passage between the anode and cathode of particulate metal and the cleaning means comprises a mechanical cleaner which is physically moved along the flow passage.
Naturally the process flow parameters are set so as to reduce the likelihood of solid metal, eg dendrites of metal, from depositing on the cathode. Applicant therefore believes that it is highly unlikely that metal plate obstructions such as dendrites will form in the flow passage. However, it is still necessary to provide a means for checking for and removing blockages of metal should they occur to provide a reliable piece of process equipment for use in
Tarrant David Bruce
Treasure Patrick Anthony
Bell Bruce F.
Electrometals Technologies Limited
Hayes & Soloway P.C.
Parsons Thomas H.
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