WO2001007684A2 - Method and apparatus for electrowinning powder metal from solution - Google Patents

Abstract

A cell (1) for electrowinning a metal in powder form from solution is disclosed. The cell (1) includes a housing (2) having an inlet (3) towards one end thereof and an outlet (4) towards an opposed end. The cell has a cylindrical anode (6) extending substantially axially through the housing (2) and a cathode (7) surrounding the anode (6) spaced outwardly away therefrom. The anode (6) and cathode (7) define a flow passage (8) therebetween having a gap of 5 to 25 millimetres. In use the cell has a substantially vertical orientation with the inlet (3) at the bottom and the outlet (4) at the top. During the flow of process solution through the cell (1) metal powder is deposited on the cathode (7). Periodically the flow process solution is interrupted and flush solution is passed in a reverse direction through the cell to remove powder metal from the cathode (7). A bank of cells in which the individual cells are connected in parallel to respectively an inlet main and an outlet main is also disclosed.

Claims

10 operatively connected together such that process solution containing metal to be electrowon can be passed through each of the banks in series.

Typically flush solution is passed in a reverse direction through the banks of cells.

Typically the flush solution is only passed through a single bank of cells at any one time. It is not passed through all the banks in series in a reverse direction.

The plant may comprise at least three banks of cells in series. The exact number of banks for any particular application will depend on the initial grade of process solution and the target grade of the product solution as well as the current density in the cells.

Typically only one bank of cells has the flow of process solution therethrough interrupted for flushing at any one time. That way the flow of process solution through the plant can be continuous, only one bank of cells being taken out of production for flushing at any one time.

Detailed Description

An apparatus and a method in accordance with this invention may manifest itself in a variety of forms. It will be convenient to hereinafter describe in detail several preferred embodiments of the invention with reference the accompanying drawings. The purpose of providing these drawings is to instruct persons having an interest in the subject matter of the invention how to carry the invention into practical effect. It is to be clearly understood however that the specific nature of this description does not supersede the generality of the preceding broad description, in the drawings:

Fig. 1 is a sectional front view of a cell in accordance with the invention in a normal process flow condition; 1 1

Fig. 2 is a sectional front view of the cell of Fig. 1 in a flush flow condition;

Fig. 3 is a front view of a bank of the cells of Fig. 1 operatively coupled to each other; and

Fig. 4 is a process flow sheet of a plurality of banks of cells of Fig. 3.

In Figs. 1 and 2 reference numeral I refers generally to a cell in accordance with the invention.

The cell 1 comprises broadly a housing 2 having an inlet 3 at the lower end thereof and an outlet 4 at the upper end thereof. The cell 1 further includes an axially extending anode 6 and a cathode 7 spaced radially away from the anode 6. The anode 6 and cathode 7 define a flow passage 8 therebetween through which process solution is passed from the inlet 3 to the outlet 4. The cell also includes electrical power and an electrical circuit for applying a potential difference across the cell between the anode 6 and the cathode 7. In use the cell alternates between a process flow condition illustrated in Fig. 1 and a flush flow condition illustrated in Fig. 2.

The housing 2 comprises broadly an elongate circular cylindrical body 10, eg made of stainless steel, and end caps 1 1 and 12, eg made of engineering plastics material, mounted on each end of the cylindrical body 10. Typically the end caps 1 1 and 12 are permanently mounted to the body 10 although this is not necessary. In the illustrated embodiment the ends of the body are flanged and the end caps are mounted to the body by bolts passing through the flanges and the end caps.

In preferred forms the body 10 has a diameter of 6 inches (152.4 millimetres) or 8 inches (203.2 millimetres). The inlet 3 which is axially extending is defined in the bottom end cap 12 of the housing 2 which directs 12

process solution axially into the housing 2. In the illustrated embodiment the inlet 3 is positioned off centre although the precise position of the inlet is not essehiial. The inlet is positioned off centre to accommodate a centrally positioned support member which is described in more detail below.

The inlet 3 and outlet 4 will typically have a diameter of 35 to 40 millimetres. This is to facilitate a flow rate of about 1000 to 3500 litres per hour through the cells during the normal process flow conditions and 6000 to 10,000 litres per hour during the flush flow condition.

The outlet 4 extends axially away from the upper end cap 1 1 of the housing in a similar fashion to the inlet 3. The outlet 4 is however centrally positioned as illustrated. When powder metal is flushed from the cell the outlet

4 acts as an inlet for the flush solution and the inlet 3 acts as an outlet for the flush solution as will be described in more detail below.

The cathode 7 is formed by the wall of the body 10 which is made of electrically conductive material as described above.

The anode 6 is similarly cylindrical being sized to leave a relatively small gap and flow passage 8 between the anode 6 and the cathode 7. Typically the width of the flow passage is of the order of 10 to 15 millimetres. Consequently the difference in diameter between cathode and anode is typically about 1 inch (25.4 millimetres). In the illustrated embodiment the anode 6 has a diameter of 7 inches and the cathode 7 has a diameter of 8 inches.

The anode 6 is supported by a support 15 projecting through the lower end cap 12 of the housing 2. The member 15 is substantially centrally positioned which is why the inlet 3 is off centre. The member 15 is positively attached to both the end cap 12 and the anode 6 to support the anode in the appropriate vertical position aligned with the cathode. 13

Naturally the upper and lower ends 18 and 19 of the anode 6 are closed so as to direct solution around the anode 7 into the flow passage 8. The upper end of the anode 6 comprises a conical flow formation 20 for directing flush solution entering the housing 2 around the anode 6 and through the flow passage 8.

The end caps 1 1 and 12 space the inlet 3 and outlet 4 axially away from the ends of the cathode 7 and anode 6. This defines chambers 21 and 22 adjacent the inlet 3 and outlet 4. In the illustrated embodiment the chamber 22 has a flow surface 23 which slopes inwardly from the sides of the end cap 12 towards the inlet 3. This assists in guiding or directing powder metal towards the inlet 3 when it is flushed off the cathode 7.

In the process flow condition, process solution containing metal ions for electrowinning, eg Cu ions, is passed upwardly through the cell from the inlet 3 to the outlet 4 as shown in Fig. 1. While the process solution is being passed through the flow passage 8 a voltage is applied across the flow passage from the cathode 7 to the anode 6. This causes deposited metal, eg in the form of metal particles or metal powder, to deposit on the cathode 7. After some time when the solid copper has at least partially occluded the flow passage 8, the flow of process solution through the cell 1 is interrupted.

The cell induces powder metal to deposit on the cathode. The formation of powder as distinct from plate metal is promoted by: turbulent flow in the flow passage, reducing the flow rate of process solution and thereby the velocity of the solution over the cathode when compared with applicant's prior art cell, reducing the current density and treating a relatively low grade solution. Certain process parameters will yield the formation of powder metal depending on the grade of process solution.

The lower the grade of metal in solution the more likely the metal is to produce powder. Further the lower the velocity of fluid through the cell and the current density the more likely the solution is to produce powder metal as 14

distinct from plate metal. Further turbulent flow through the cell as distinct from plug flow also promotes the formation of powder.

Thereafter a flow of flush solution is commissioned in a reverse or downward direction from the outlet 4 to the inlet 3. The flush solution, assisted by gravity, dislodges the powder metal deposited on the cathode 7 and displaces it down the cathode 7 towards the inlet 3. The inlet 3 acts as an outlet in the flush flow condition.

The tapered walls of the chamber defined by the end cap 12 assists in guiding the powder metal towards and through the outlet 3. The pressure of the flush solution is typically higher than the process solution to assist the flushing process.

From the inlet 3 the powder metal is typically conveyed, eg by means of the flush solution in a gravity drain, to a downstream collection or further processing point.

The flush flow condition is usually carried out for 20 to 25 seconds although this specific time is not critical. After the metal has been flushed from the cell the flow of flush solution is interrupted and the flow of process solution is restored.

In Fig. 3 reference numeral 30 refers generally to a bank of cells. Each of the cells is as described above with reference to Figs.1 and 2. Accordingly the same reference numerals will be used to refer to the components of the cells as in Figs. 1 and 2.

Each bank of cells 30 comprises a plurality of cells 1 , typically 5 to 20, connected in parallel. An inlet main 32 is operatively coupled to the inlets 3 of each of the cells 1 and an outlet main 34 is operatively coupled to the outlets 4 of each of the cells 1.