ANODE STRUCTURE FOR METAL ELECTROWINNING CELLS

Abstract

An anodic structure for electrowinning cells having an anode hanger bar, a support structure of insulating material, at least one anode mesh having a valve metal substrate provided with a catalytic coating, said at least one anode being subdivided into at least two reciprocally insulated sub-meshes, said sub-meshes being individually supplied with electrical current through conductive means connected with said anode hanger bar, the anodic structure being further provided with at least one electronic system having at least one current probe and at least one actuator for individually measuring and controlling current supply to each of said sub-meshes.

Claims

1. An anodic structure for electrowinning cells comprising an anode hanger bar, a support structure of insulating material, at least one anode mesh having a valve metal substrate provided with a catalytic coating, said at least one anode mesh being subdivided into at least two reciprocally insulated sub-meshes, said sub-meshes being individually supplied with electrical current through conductive means connected with said anode hanger bar, the anodic structure being further provided with at least one electronic system comprising at least one current probe and at least one actuator for individually measuring and controlling current supply to each of said sub-meshes.

2. The anodic structure according to claim 1 wherein said at least one anode mesh is subdivided into sub-meshes of area ranging from 25 cm.sup.2 to 225 cm.sup.2.

3. The anodic structure according to claim 1, wherein said conductive means are metal plates, bars or cables.

4. The anodic structure according to claim 3, wherein said metal bars, plates or cables are made of electrically conductive material with electric resistivity at 20 C. of 1.510.sup.8 to 3.010.sup.8 m.

5. The anodic structure according to claim 4, wherein said electrically conductive material is chosen among copper, aluminium or alloys thereof.

6. The anodic structure according to claim 1, wherein said reciprocally insulated sub-meshes are secured to said support structure of insulating material by fastening means.

7. The anodic structure according to claim 1, wherein said conductive means and said at least one electronic system are embedded and sealed inside said insulating support structure by means of resins or plastics.

8. The anodic structure according to claim 1, wherein each sub-mesh is equipped with said at least one electronic system.

9. The anodic structure according to claim 1, wherein said electronic system comprises active or passive electronic components.

10. The anodic structure according to claim 9, wherein said passive electronic components are thermistors or resettable fuses.

11. System for deposition of metal in a metal electrowinning plant comprising at least one anodic structure according to claim 1.

12. System for metal deposition in a metal electrowinning plant comprising at least one anodic structure according to claim 10, wherein each sub-mesh is equipped with at least one resettable fuse, and wherein each said resettable fuse comprises: a positive temperature coefficient; a hold current value equal to a predefined current value, wherein said predefined current value corresponds to the maximum nominal current that is supplied to each individual sub-mesh; and a trip current value lower than the maximum safety current for each sub-mesh.

13. Method for deposition of metal in a metal electrowinning plant comprising at least one anodic structure according to claim 1, comprising: detecting the current in each sub-mesh of each anode mesh at predefined time intervals by means of the electronic system; determining the sub-meshes of each anode mesh corresponding to a relative maximum of current; and discontinuing current supply to said sub-meshes corresponding to a relative maximum of current until the subsequent detection.

14. Method for deposition of metal in a metal electrowinning plant comprising at least one anodic structure according to claim 1, comprising: detecting the current in each sub-mesh of each anode mesh at predefined time intervals by means of the electronic system; determining the sub-meshes of each anode mesh corresponding to a relative maximum of current; and discontinuing current supply to said sub-meshes corresponding to a relative maximum of current if the detected current exceeds a predefined threshold until the subsequent detection.

15. Method for deposition of metal in a metal electrowinning plant comprising at least one anodic structure according to claim 1, comprising: detecting the current in each sub-mesh of each anode mesh at predefined time intervals by means of the electronic system; and discontinuing current supply to the sub-meshes in which the current exceeds a predefined threshold until the subsequent detection.

16. Method for deposition of metal in a metal electrowinning plant comprising at least one anodic structure according to claim 1, comprising: detecting the current in each sub-mesh of each anode mesh at predefined time intervals by means of the electronic system; calculating for each anode mesh the average current value in the sub-meshes; and discontinuing the current supply to the sub-meshes in which the difference between the detected current and the average current, expressed in percentage of the average current of each anode mesh, exceeds a predefined threshold until the subsequent detection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG. 1 shows a three dimensional view of the anodic structure according to the invention having both anode meshes subdivided into one hundred sub-meshes.

[0049] FIG. 2 shows a scheme of sub-mesh to anode hanger bar connection and a possible system of active current adjustment/disconnection associated therewith.

[0050] FIG. 3 shows a scheme of the connections of the sub-meshes to the anode hanger bar and a possible system of passive current adjustment/disconnection associated therewith.

[0051] FIG. 4 shows a schematic representation of the anodic structure according to the invention implementing a passive control system with polyfuses, panels (I) and (II) show frontal and side views of the anodic structure; panels (III) and (IV) respectively show the designated cross section of the anodic structure and a blow up of the designated portion of the cross-section.

[0052] FIG. 5 shows a schematic representation of the anodic structure according to the invention implementing an active control system comprising a MCU and power transistors, panels (I) and (II) show frontal and side views of the anodic structure; panels (III) and (IV) respectively show the designated cross section of the anodic structure and a blow up of the designated portion of the cross-section.

DETAILED DESCRIPTION OF THE DRAWINGS

[0053] In FIG. 1 there is shown an anode hanger bar 100, supporting two anode meshes mechanically connected to a support structure of five vertical bars 110. The frontal anode mesh 101, which partially hides the posterior anode mesh (not referenced), is subdivided into 100 sub-meshes, such as sub-mesh 102. Also shown are electrical connection cables 103, the insulation gap 104 between sub-meshes, and cathode 106. The electronic system of current adjustment can be placed in correspondence of location 1051. In addition, or in alternative, the electronic system of current adjustment can be placed directly in correspondence of the sub-mesh to be controlled, such as position 1052 for sub-mesh 102.

[0054] In FIG. 2 there is shown a schematic diagram of an active electric microcircuit indicating the area corresponding to the electronic system circuit 105, connected to sub-mesh 102 via the relevant connection cable 103, on one side, and to the anode hanger bar 100 on the other side. The active electronic system circuit 105 comprises a resistor 109 and a combination of control 107 and active component 108. The latter component may be, for example, a transistor, a MOSFET, a switch transistor or a load switch. Elements 107 and 108 can compare the drop of voltage at the resistor with a predefined reference voltage; when the resistor drop of voltage is bigger than the voltage reference for a preset period of time, element 107 triggers the gate lock of element 108.

[0055] In FIG. 3 there is shown a diagram of a passive electric system indicating the area corresponding to the passive electronic device 101, which can be a positive temperature coefficient thermistor or resettable fuse, connected to sub-mesh 102 via the relevant connection cable 103, on one side, and the anode hanger bar 100 on the other.

[0056] In FIG. 4, panels I and II show, respectively, a front and side view of an anodic structure implementing passive current probe and control components comprising electrically conductive hanger bar 100 with terminal contacts 101, and two anode meshes each divided into 36 sub-meshes, such as sub-mesh 102. Sub-mesh 102 is connected to the supporting means 110 through conductive and chemically resistant rivets 300, which can be made, for example, of titanium or alloys thereof. Panel III shows the cross section of the anodic structure of Panel I taken along the dash-dotted line. The region enclosed in the dashed area comprising supporting means 110 and sub-mesh 102 is enlarged in panel IV, which shows a blow-up of the connection between sub-mesh 102 and the supporting means 110. The supporting means 110, which are electrically connected to the anode hanger bar (not shown), comprise conductive bar 500, which is fixed to printed circuit board 450 via rivets 350. Conductive bar 500 is connected to one pin of Polyfuse 410 via printed circuit board track 550. The second pin of Polyfuse 410 is in electrical contact with sub-mesh 102 through rivet 300. Polyfuse 410 is enclosed in thermally insulating region 250 (which can be filled, for example, with thermally insulating foam or air). An overlay of electrically insulating and chemical resistant material 200 seals, insulates and protects from the electrolyte the above mentioned components and circuits with the exception of rivet 300, which partially emerges from the supporting means and secures sub-mesh 102 to structure 110.

[0057] In FIG. 5, panels I and II show, respectively, a front and side view of an anodic structure implementing active current control components comprising electrically conductive hanger bar 100 with terminal contacts 101, and two anode meshes consisting of 66 sub-meshes, such as sub-mesh 102. The anodic structure further comprises at least one MCU 130. Cable connection 120 connects the MCU to the cathodic intercell bar or on the cathodic balance bar, if any, on one side, and to the hanger bar 100, on the other side (connections not shown). Sub-mesh 102 is connected to the supporting means 110 through conductive and chemically resistant rivets 300, which can be made, for example, of titanium or alloys thereof. Panel III shows the cross section of the anodic structure of Panel I taken along the dash-dotted line. The region enclosed in the dashed area comprising supporting means 110 and sub-mesh 102 is enlarged in panel IV. Panel IV shows a blow-up of the connection between sub-mesh 102 and the supporting means 110. The supporting means 110, which are electrically connected to the anode hanger bar (not shown), comprise conductive bar 500, which is fixed to printed circuit board 450 via rivets 350. Conductive bar 500 is connected to one terminal of transistor 420 via printed circuit board track 550. Transistor 420 is further connected with shunt resistance 430, which is in electrical contact with sub-mesh 102 via rivet 300. The connection between the shunt resistance 430 and the MCU 130, and the connection between the latter and the gate of transistor 420 are not shown in figure. These connections respectively carry the input and output signals to/from the MCU, which can be equipped with an analog to digital converter (not shown). Transistor 420 and shunt resistance 430 can be connected according to the diagram of FIG. 2 to an additional control transistor (not shown). An overlay of electrically insulating and chemical resistant material 200, such as resin or plastic, seals, insulates and protects from the electrolyte the above mentioned components and circuits with the exception of rivet 300, which partially emerges from the supporting means and secures sub-mesh 102 to structure 110.

[0058] Some of the most significant results obtained by the inventor are presented in the following examples, which are not intended to limit the scope of the invention.

Example 1

[0059] A laboratory test campaign was carried out inside an electrowinning cell, containing a cathode and an anode equipped with an active current control electronic system. A 3 mm thick, 50 mm wide and 1000 mm high AISI 316 stainless steel sheet was used as the cathode; the anode consisted of a 2 mm thick, 150 mm wide and 1000 mm high titanium expanded mesh, activated with a coating of mixed oxides of iridium and tantalum, subdivided into sub-meshes of 1 dm.sup.2 each. The cathode and the anode were vertically facing each other with a gap of 40 mm between the outer surfaces. A dendrite was produced artificially by inserting a screw, as a nucleation centre, into the stainless steel plate perpendicularly to the anode, the tip of the screw being spaced 4 mm apart from the anode. Each sub-mesh was electrically connected to the anode hanger bar and to the electronic system according to the diagram of FIG. 2. For each sub-mesh, the electronic system comprised two different MOSFET transistors, one working as the power switch 108, and the other as controller 107. The power switch was characterised by a drain-source breakdown voltage of 30V, and an on resistance of 8 m at a gate threshold voltage of 10V. The controller transistor was characterised by a drain-source breakdown voltage of 30V, and an on resistance of 85 m at a gate threshold voltage of 4.5 V. In place of resistor 109 of FIG. 2, a shunt resistance of 2 m was used. A 32-bit, 67 MHz MCU recorded the current values of each sub-mesh at time intervals of 1 milliseconds, calculating the relative deviation from the average current of each sub-mesh. The MCU was programmed to interrupt the current in the sub-meshes where the relative deviation exceeded 5%. In addition, a wireless ZigBee radio communication system was installed on the anode and sent the information collected by the MCU to a main control computer, for managing and alert purposes. After 4 days of operation a lateral growth of copper was evidenced on the dendrite, not reaching the anode surface. The production of copper in the areas facing the remaining sub-meshes showed no irregularities.

Counterexample 1

[0060] The anodic structure of Example 1 was tested in the same conditions without activating the electronic control system. The dendrite reached the anode surface after 4 hours of operation, irreparably damaging the anode.

Example 2

[0061] A laboratory test campaign was carried out in a laboratory cell simulating an electrowinning cell, containing a cathode and an anodic structure equipped with a passive current control electronic system. A 3 mm thick, 150 mm wide and 1000 mm high AISI 316 stainless steel sheet was used as cathode; the anode consisted of a 180 mm long copper hanger bar, 20 mm wide and 40 mm high, and of a 1 mm thick, 155 mm wide and 1030 mm high titanium expanded mesh, activated with a coating of mixed oxides of iridium, subdivided into 18 sub-meshes, each 75 mm wide and 110 mm high, with a gap of 8 mm between each couple of sub-meshes. The anodic structure was also equipped with a LED, a ZigBee radio communication device and a booster with an output voltage of 3.3 V. The booster was used to power the LED and ZigBee device, which were installed for alert and operation managing purposes. Each sub-mesh was electrically connected to the anode hanger bar and to the electronic system according to the diagram of FIG. 3. More specifically, the electronic system comprised a positive temperature coefficient polyfuse characterised by a hold and trip current specifications at 23 C. of 14.0 A and 23.8 A respectively (a temperature dependent characterization of these parameters was carried out by the inventor in order to assess and verify the polyfuse performance at the operating temperatures of the cell. The hold current at 40 C. was 12.2 A and the trip current was 25.4 A). Each sub-mesh was further connected to a diode. The total of 18 diodes were connected to form a diode-OR circuit that supplied power to the booster and only activated the LED in case of electrical contact between one or more sub-meshes and the cathode.

[0062] The cathode and the anode were vertically facing each other with a gap of 35 mm between the outer surfaces. A dendrite was produced artificially by inserting a screw, as a nucleation centre, into the cathodic stainless steel plate perpendicularly to the anode mesh; the tip of the screw being spaced 4 mm apart from the anode. After 1 day of operation in potentiostatic conditions, with a cell voltage of 1.8V, the copper deposited on the tip of the screw would contact the facing anode submesh, resulting in a copper deposition on the specific submesh, the lighting up of the LED and a warning signal from the ZigBee communication device to a main central computer. The test was continued for 60 hours and during such transient the copper would grow along the edges of the submesh panel. At the end of the test, no mechanical damage due to shorting was present on the anode mesh; the current would be in the range of 55-65 A. Eventually, the production of copper in the areas facing the remaining sub-meshes showed no irregularities.

Counterexample 2

[0063] An anodic structure similar to that of Example 2 was tested in the same conditions without providing it with the electronic control system. The dendrite reached the anode surface after 1 day of operation, irreparably damaging the anode mesh.

[0064] The previous description shall not be intended as limiting the invention, which may be used according to different embodiments without departing from the scopes thereof, and whose extent is solely defined by the appended claims.

[0065] Throughout the description and claims of the present application, the term comprise and variations thereof such as comprising and comprises are not intended to exclude the presence of other elements, components or additional process steps.