Abstract
The invention relates to an electrode which can be employed in the cells of plants for the electrolytic extraction of copper and other non-ferrous metals from ionic solutions. The electrode consists of an apparatus comprising at least one anodic panel for the evolution of oxygen or chlorine connected through a plurality of resistors in parallel to at least one distribution structure for electrical current. The panel may optionally exhibit areas of electrical discontinuity. The invention also relates to an electrolyser using the electrode described above.
Claims
1. Anodic apparatus for electrorefinement or electrolytic extraction of non-ferrous metals comprising at least one anodic panel, which is used as an anode and presents at least one surface capable of evolving oxygen or chlorine, and at least one electrical current distribution structure, characterized by the fact that said at least one anodic panel is equipped with at least one zone of partial or total electrical discontinuity, wherein the zone of partial electrical discontinuity is an electrically insulating region measuring at least 1 cm along at least one dimension located within the anodic panel and optionally includes edges, and wherein the zone of total electrical discontinuity is an electrically insulating region measuring at least 1 cm along at least one dimension extending along a whole dimension of the panel, thus subdividing the panel into several subpanels, and said at least one electrical current distribution structure is electrically connected to said at least one anodic panel by a plurality of resistors set in parallel with one another, each resistor of said plurality of resistors having a resistance, measured at 40° C., equal to or greater than 5.Math.10.sup.−5Ω, wherein said at least one anodic panel is equipped with at least a number N1 of electrical connection regions connected with said plurality of resistors and at least a number N2 of zones of electrical discontinuity, said N1 connection regions being arranged along a first vertical strip, said N2 zones of electrical discontinuity being arranged along a second vertical strip; N1 being a number of between 5 and 100 and N2 being greater than 0.5.Math.N1.
2. The apparatus of claim 1, wherein said at least one anodic panel is made up of a substrate made of valve metal or its alloys and at least one catalytic coating.
3. The apparatus of claim 1, wherein said at least one anodic panel is chosen from mesh, perforated plates or louver structures.
4. The apparatus according to claim 1, wherein each anodic panel is electrically connected to at least one electrical current distribution structure by a number of between 15 and 600 resistors set in parallel.
5. The apparatus of claim 1, wherein said plurality of resistors is connected to said at least one anodic panel through a plurality of electrical connection regions situated on the panel and said at least one zone of electrical discontinuity is situated between two neighbouring electrical connection regions.
6. The apparatus of claim 1, wherein said plurality of resistors is connected to said at least one anodic panel through a plurality of electrical connection regions, said anodic panel having a plurality of zones of electrical discontinuity, and for every two neighbouring zones of electrical discontinuity set at a height h1 and h2 with respect to the base of said at least one anodic panel, with h1<h2, there is at least one connection region situated at a height h3, with h1≤h3≤h2.
7. The apparatus of claim 1, wherein said at least one anodic panel is equipped with at least a number N3 of further electrical connection regions connected with said plurality of resistors, said N3 connection regions being arranged along a third vertical strip, and N3 being a number between 5 and 100.
8. The apparatus of claim 7, wherein at least one anodic panel is equipped with at least a number N4 of further zones of electrical discontinuity, with N4 being greater than 0.5.Math.N3, said N4 zones of electrical discontinuity being arranged along a fourth vertical strip.
9. The apparatus according to claim 1, wherein at least one zone of electrical discontinuity is a cut, hole or an insert of electrical insulating material.
10. The apparatus according to claim 1, wherein said at least one zone of electrical discontinuity measures at least 5 cm in length along at least one dimension.
11. The apparatus according to claim 8, wherein said anodic panel comprises at least two titanium anodic subpanels separated from one another, said at least two subpanels being chosen from louver, sheets and expanded mesh structures, and at least two electrical current distribution structures, each electrical current distribution structure being connected to a subpanel by a plurality of resistors set in parallel with one another, each subpanel comprising 5-100 connection regions arranged along a first vertical strip, each connection region being alternated with a horizontal cut having a length of at least 5 cm and each cut having at least one point set at a distance of 0-10 cm from said first vertical strip.
12. The apparatus according to claim 1, wherein said anodic panel is equipped with at least 20 zones of electrical discontinuity and at least 20 connection regions capable of connecting said at least one anodic panel with at least 20 resistors set in parallel with one another, each zone of electrical discontinuity being set at a distance of less than 15 cm from at least one of said connection regions.
13. The apparatus according to claim 1, wherein each resistor of said at least one plurality of resistors has an electrical resistance of between 5.Math.10.sup.−4 and 1Ω.
14. The apparatus according to claim 13, wherein each said resistor has an electrical resistance of between 5 and 100 mΩ.
15. The apparatus according to claim 1, wherein said plurality of resistors set in parallel has an equivalent electrical resistance of between 10.sup.−5 and 10.sup.−3Ω.
16. The apparatus according to claim 1, wherein each resistor of said plurality of resistors is chosen from the group consisting of plates, strips, meshes, cables, fabrics and pads.
17. The apparatus according to claim 1, wherein said plurality of resistors is a sheet, an expanded mesh or a perforated plate of valve metal with zones of electrical discontinuity.
18. The apparatus according to claim 1, wherein said at least one anodic panel and said plurality of resistors are a single piece of a bent sheet, expanded mesh or perforated plate of valve metal.
19. The apparatus according to claim 1, wherein the electrical current distribution structure comprises a sheet or panel made of lead or lead alloys.
20. An electrolyser for electrolytic extraction of non-ferrous metals comprising at least one anodic apparatus as described in claim 1.
Description
BRIEF DESCRIPTION OF THE FIGURES
(1) A number of embodiments of the invention are described by way of example below with reference to the appended drawings, the purpose of which is solely to illustrate the mutual arrangement of the various elements relating to said embodiments of the invention; in particular, the drawings are not to be understood to be scale drawings.
(2) FIGS. 1-13 schematically illustrate a number of embodiments of the anodic apparatus according to the invention.
DETAILED DESCRIPTION OF THE FIGURES
(3) FIG. 1 shows a rear (I), lateral (II) and frontal (III) schematic projection of the anodic apparatus according to the invention. The figure shows an anodic hanger bar (100) connected to a structure (300) for the distribution of electrical current. The latter is connected to an anodic panel (200) through a plurality of resistors (400), connected to the panel through electrical connection regions (500). The front surface of the anodic panel (view III) is the one where the reaction for the release of oxygen or chlorine occurs. The vertical direction is indicated by the arrow (y); which typically coincides with the vertical direction of a conventional electrowinning cell. The base of the anodic panel (200) is positioned at the height indicated by the x axis, which identifies the horizontal reference.
(4) FIG. 2 provides a view from the rear (I), side (II) and bottom (III) of one embodiment of the anodic apparatus according to the invention. In this embodiment the resistors (400) are expanded meshes of titanium welded to the anodic panel (200) in correspondence of the electrical connection regions (500). On the panel there is a zone of electrical discontinuity (600) between each neighbouring pair of connection regions. These zones of discontinuity give rise to a partial fragmentation of the anodic panel along the vertical direction. It has been observed that if there is contact between a dendritic formation and an area of the panel lying between two areas of discontinuity the current may preferably flow through the resistor (or resistors) in proximity of the nearest connection region (or regions). The electrical resistance opposing the current in the event of direct contact between the electrodes will therefore be close to the resistance R.sub.i of the individual resistor. This will in turn be suitably dimensioned by a person skilled in the art in such a way as to ensure that under the operating conditions of the plant the maximum current passing through a contact spot on the panel is kept below a predetermined threshold value in order to preserve the apparatus. On the other hand, under the nominal operating conditions of the plant the electrical resistance offered by the anodic apparatus essentially corresponds to the equivalent electrical resistance R.sub.eq of the parallel circuit formed by the plurality of resistors, where R.sub.eq<<R.sub.i. When the resistors are identical to each other and are present in a number N.sub.R, R.sub.eq will correspond to R.sub.i/N.sub.R. By choosing a suitable number of resistors and an appropriate resistance R.sub.i it is therefore possible to obtain both a small drop in efficiency in the elemental cell while at the same time ensuring that the anodic panel is protected in the event of electric contact between the electrodes.
(5) In the embodiment illustrated in FIG. 2, an insulating element (700) is located between the anodic panel and the current distribution structure (300). This element contributes to prevent the anodic panel and the distribution structure from coming into direct contact by accident. It also constitutes a mechanical supporting element for the panel. The anodic panel, the insulating element and the current distribution structure can be secured together by fastening means (not shown in figure).
(6) FIG. 3 shows a view from the rear (I), front (II) and bottom (III) of an embodiment of the anodic apparatus according to the invention. The anodic panel and the resistors are manufactured from a single flat element which is partly folded back on itself along a vertical direction (050). The folded edge of this flat element is provided with a plurality of horizontal cuts (900) and is in contact with the current distribution structure (300). The horizontal cuts (900) subdivide the folded part of the element into a plurality of resistors (400) in parallel. The cuts extend over the frontal plane of the anodic panel (200), providing the zones of discontinuity (600). The electrical connection regions (500) represent the imaginary separation between the frontal plane where the anodic reaction takes place (i.e. the anodic panel) and the parallel strips which constitute the resistors. The insulating element (700) may be constructed as illustrated in figure or may advantageously extend within the space between the anodic panel (200) and the plurality of resistors (400) in order to prevent any accidental electrical contact between the different elements.
(7) FIG. 4 provides a front (I), side (II) and bottom (III) view of an embodiment of the anodic apparatus according to the invention. This embodiment comprises two anodic panels (200) and (250) connected to the current distribution structure through a plurality of resistors (400) in parallel. Each panel is connected to the plurality of resistors through electrical connection regions (500) located along two different vertical strips. As illustrated in the figure, the connection regions may be different from each other. A plurality of zones of electrical discontinuity (600) are located between the different pairs of connection regions. Insulating element (700) and insulating element (750) are inserted between the anodic panels (200) and (250) and the current distribution structure (300) respectively. Further insulating elements (not shown in the figure) may be advantageously inserted between the resistors connected to the anodic panel (200) and the resistors connected to the anodic panel (250).
(8) FIG. 5 illustrates a rear view of an embodiment of the invention characterised by two current distribution structures (300) and (350), an anodic panel (200) and an anodic hanger bar (100).
(9) The anodic panel (200) comprises a plurality of subpanels (801, 802, 803, 804, 851, 852, 853, 854) which are physically separated from each other. Each subpanel is connected to a current distribution structure through at least one resistor (400). FIG. 6 shows a rear projection of an embodiment of the apparatus according to the invention characterised by two current distribution structures (300, 350) connected to one anodic panel (200), comprising two subpanels (801, 802), through a plurality of resistors. The two current distribution structures are also connected to an anodic hanger bar (100). The latter is electrically connected to an anodic bus-bar (900) illustrated here in cross-section. The anodic panel is provided with a plurality of partial zones of electrical discontinuity, for example horizontal cuts (600) and through holes (650), and a zone of total electrical discontinuity (675).
(10) FIG. 7 provides a front (I), side (II) and bottom (III) view of an embodiment of the anodic apparatus according to the invention. In this embodiment the resistors (400) are expanded meshes of titanium welded on two anodic panels (200, 250) in correspondence of the connection regions (500). On each panel there is a zone of electrical discontinuity (600) between each pair of neighbouring contact regions. These zones of electrical discontinuity give rise to a partial fragmentation of the anodic panel along the vertical direction. An insulating element (700) is located between the anodic panels and the current distribution structure (300). Two further insulating elements (710, 720) ensure that the panels (200, 250) are kept mutually parallel and flat (sometimes the planarity of the panel is compromised by the cuts on its outer edges and or the flexibility of its structure, especially in case valve metal meshes are used), providing further mechanical support to the anodic apparatus. The elements (710, 720) are omitted from the side view (II) to allow the arrangement of the other parts of the apparatus to be seen in the figure. The insulating elements, the current distribution structure and the anodic panels are attached together by fastening means, not shown in figure, such as for example clamps of insulating material and/or bolts.
(11) FIG. 8 provides a front (I), side (II) and bottom (III) view of an embodiment of the anodic apparatus according to the invention. In this embodiment the resistors (400) are strips of titanium folded in an accordion-like fashion and welded to the anodic panel (200) in correspondence of the electrical connection regions (500). A through hole (600) is placed between each neighbouring pair of connection regions (500).
(12) FIG. 9 (I) provides a front view of an embodiment of the anodic apparatus according to the invention. The anodic panel (200) is connected to a current distribution structure (300) through a plurality of resistors (not shown in figure) connected to the panel through connection regions (500). The panel is also provided with a plurality of holes (650) and an insulating element (700).
(13) FIG. 9 (II) provides a front view of the anodic apparatus of FIG. 9 (I), where a first vertical strip (001) and a second vertical strip (002) are emphasized. The electrical connection regions (500) are arranged along said first vertical strip, and the holes (650) are arranged along said second vertical strip. The holes alternate with the neighbouring electrical connection regions in the vertical direction, while maintaining a minimum distance >0 from said regions.
(14) FIG. 10 illustrates a frontal (I), lateral (II), and inclined (III) projection and a projection from below (IV) of one embodiment of the anodic apparatus according to the invention. The anodic panel (200) and the resistors (400) are manufactured from a single flat element. A plurality of horizontal cuts on the anodic panel produces a plurality of strips. One every two strips is pushed back in a direction at right angles to the anodic panel, creating a resistor (400). The resistors are electrically connected in parallel with the current distribution structure (300). The horizontal cuts also identify a plurality of zones of electrical discontinuity (600) corresponding to void left by the resistor strips (400). An insulating element (700) is inserted between the resistors (400) and the anodic panel (200). This ensures that the surface of the resistors is not involved in the gas evolution reaction of the anodic apparatus when the latter is operational within an electrolyser for electrowinning or electrorefining. For clarity, the insulating element (700) is omitted from views III and IV. The electrical connection regions (500) illustrate the area of imaginary separation between the electrochemically active surface of the anodic panel and the parallel strips constituting the resistors.
(15) FIG. 11 provides a front view (I) and a view from below (II) of two elements of the anodic apparatus according to the invention: the anodic panel (200) and the plurality of resistors (400). In this embodiment the anodic panel and the resistors are both made of expanded meshes of titanium. As illustrated in the boxed enlargement of panel (I), the anodic panel (200) has a slightly curved profile in correspondence of the cuts (600) (and cuts (650), profile not shown). Preferably, during the assembly of the anodic apparatus, the anodic panel is mounted in such a way that the curved edges of the zones of electrical discontinuity (600, 650) are re-entrant in the direction of the resistors (and the electrical current distribution structure). The inventors have observed that said curvature may favour the detachment of dendritic formations, when these impinge on, and become attached to, the perimeters of the cuts or holes present on the surface of the anodic panel. The anodic panel exhibits folded edges (210), which may improve its mechanical robustness, preventing the panel from twisting and bending, in particular when the latter is made of expanded meshes or flexible sheets of valve metal. In the present embodiment the plurality of resistors (400) is constructed within a resistive panel (1000) of a single expanded titanium mesh provided with holes. On the basis of their number and size, the holes identify a plurality of parallel strips exhibiting a predetermined electrical resistance. The resistive panel may be shaped and bent as illustrated in the cross section of view II. The resistive panel is connected to the anodic panel by welding the two together along a plurality of regions located in correspondence the of the areas of contact of the two panels when the resistive panel (1000) is located within the anodic panel (200) (i.e. enclosed within its folded edges (210)). The electrical connection regions (500) (only one of which is singled out for clarity) are in this case located in correspondence of the welding points of the resistors, or of the continuous edge of the resistive panel, on the anodic panel. An insulating element may be placed between the resistive panel (1000) and the anodic panel (200) to prevent accidental contacts between the two. Said insulating element may also prevent dendritic formations from growing through the holes (600) and (650) and impinge directly onto the resistive panel (1000). The latter may be connected to a current distribution structure along the central vertical rib. The vertical lateral edges of the anodic panel and of the resistive panel may be continuous. In alternative, the cuts (600) on the anodic panel or the cuts making up the strips of the resistive panel may reach and break up the edges of the respective panels.
(16) An anodic apparatus having two or more current distribution structures may advantageously mount the system described in FIG. 11 on each distribution structure.
(17) FIG. 12 shows a view from the front (I) and bottom (II) of an embodiment of the anodic panel (200) according to the invention. The figure also shows a view from the front (III) and bottom (II) of a corresponding plurality of resistors (400) incorporated in a resistive panel (1000). The anodic panel (200) is provided with a plurality of zones of electrical discontinuity and is provided with two folds (210) along the vertical edge, which improve its mechanical stability. The resistors (400) incorporated in the resistive panel (1000) are made and dimensioned as a number of holes of suitable size made therein. Resistive panel (1000) is connected to anodic panel (200) through a plurality of welds, located for example in correspondence of region (550). In this case region (550) is located on a portion of the folded edge of the anodic panel (200) and not directly on the anodic surface (where the gas evolution reaction takes place). The electrical connection region (500) corresponding to welding region (550) is located on the edge of the panel at the same height as the resistor, and represents (as hereinbefore defined) the portion of the conductive element located on the anodic panel corresponding to the shortest electrical path between the individual resistor and the panel. Some electrical connection regions (500) are illustrated in figure as examples.
(18) FIG. 13 illustrates a frontal (I) and lateral (II) projection of one embodiment of the invention. The anodic panel (200), the current distribution structure (300) and the resistors (400) are incorporated into a single continuous structure which can in turn be integral with (or connected to) the anode hanger bar (100). The current distribution structure (300) coincides with the plurality of resistors (400): this comprises a plurality of bars, preferably 8 or more, capable of conducting current from the anode support bar (100) to the anodic panel (200), offering an electrical resistance of 5.Math.10.sup.−5Ω or more. The anodic panel is equipped with zones of electrical discontinuity (600).
(19) The following examples are included to demonstrate particular embodiments of the invention, whose implementation has been abundantly verified within the range of values claimed. Those skilled in the art should appreciate that the compositions and techniques described in the following examples represent compositions and techniques which the inventors have found to operate well in the implementation of the invention; however, in the light of this description those skilled in the art should be aware that many changes may be made to the specific embodiments disclosed while still achieving a similar or analogous result without going beyond the scope of the invention.
Example 1
(20) A set of laboratory tests was carried out in a single electrodeposition cell having an overall transverse cross-section of 170 mm×170 mm and a height of 1500 mm, containing two cathodes and an anodic apparatus located between them. A sheet of AISI 316 stainless steel of thickness 3 mm, width 150 mm and height 1100 mm (of which 1000 were immersed in the electrolytic solution) was used for the cathodes. The anodic apparatus comprised two panels of titanium arranged in a configuration similar to that simplified in the sketch of FIG. 7. Each panel vertically faced one of the two cathodes at a distance of 40 mm between outer surfaces. The two anodic panels were positioned on opposite sides of the same current distribution structure. Each anodic panel was a louver structure 1 mm thick, 150 mm wide and 1000 mm tall, activated with a mixed coating of iridium and tantalum oxides.
(21) Each panel was connected to the electrical current distribution structure through a connection of 30 resistors placed in parallel, each resistor consisting of an expanded titanium mesh of 2 cm×10 cm in size and characterised by an electrical resistance of 30 mΩ each.
(22) The 30 resistors were connected to each panel through 30 electrical connection regions (i.e. welds) located along a vertical strip. The resistors were also connected to the current distribution structure, which was in turn supported by a conductive hanger bar. Horizontal cuts approximately 10 cm long were created on one vertical side of each panel. Each cut lay between two neighbouring electrical connection regions.
(23) An insulating element was inserted between each panel and the current distribution structure. Two further insulating elements clamped the outer vertical edges of the two panels, maintaining them planar and parallel to each other.
(24) The cell operated using an electrolyte containing 50 g/l of copper as CuSO.sub.4 and 200 g/l of H.sub.2SO.sub.4 and was fed with current of 136.5 A at a constant voltage of 1800 V corresponding to an expected current density of approximately 455 A/m.sup.2. Oxygen was released at the anodic panel and copper was deposited on the cathode.
(25) A dendrite was artificially produced by inserting a screw, as a nucleation centre, in the stainless-steel sheet of one of the two cathodes and perpendicularly to the anodic panel. The tip of the screw was positioned 5 mm from the anodic panel. After 36 hours of operation, growth of copper was observed on the dendrite and this resulted in contact between the dendrite and panel.
(26) The cell was kept in operation for the next 40 hours following contact. When operations ended the cathodes were removed from the cell. The cathode affected by the dendritic formation was removed from the cell without difficulty. The anodic panel opposite to it had a slight surface deterioration, corresponding to the area of contact with the dendrite, of approximately 1 cm×0.5 cm. No holes, deformations or any other significant damages which could affect the functioning of the panel were observed.
(27) When the cell was subsequently put in operation it was observed that copper deposition on the cathodes opposite the anodic panel with the slight surface deterioration was uniform.
Comparison Example 1
(28) The test in example 1 was repeated under the same conditions, except that the anodic apparatus was replaced by an apparatus comprising two panels of titanium 1 mm thick, 150 mm wide and 1000 mm tall, activated with a mixed coating of iridium and tantalum oxide. Each panel was a louver structure directly electrically connected to the same titanium-coated copper bar and supported by a conductive hanger bar. A dendrite was artificially produced by inserting a screw as a centre for nucleation in the stainless-steel sheet of one of the two cathodes, perpendicularly to the anodic panel. The tip of the screw was positioned 5 mm from the anodic panel. After 8 hours' operation growth of copper which led to contact between the dendrite and panel was found on the dendrite.
(29) The cell was kept in operation for the next 20 hours following contact. When operations ended the cathodes were removed from the cell. The cathode affected by the dendritic formation was removed from the opposite anodic panel with difficulty. The latter had a circular hole of diameter approximately 2.5 cm corresponding to the area of contact with the dendrite.
(30) When the cell was subsequently in operation it was observed that copper deposition on the cathode opposite the hole in the anodic panel was non-uniform.
(31) The above description is not intended to limit the invention, which may be used in accordance with various embodiments without thereby going beyond its scope, which is defined by the appended claims.
(32) In the description and the claims in this application the words “comprise” and its variations such as “comprising” and “comprises” do not rule out the presence of other additional elements, components or stages.
(33) The discussion of documents, deeds, materials, apparatus, articles and the like is included in the text solely for the purpose of providing context for this invention; it should not however be understood that this material or part thereof constitutes general knowledge in the field relating to the invention prior to the priority date of each of the claims appended to this application.
