WO2010102327A1

WO2010102327A1 - A method of reconditioning a cathode plate

Info

Publication number: WO2010102327A1
Application number: PCT/AU2010/000259
Authority: WO
Inventors: Jason Robert Cerezo
Original assignee: Steelmore Holdings Pty Ltd
Priority date: 2009-03-12
Filing date: 2010-03-09
Publication date: 2010-09-16

Abstract

The invention relates to a method of reconditioning a cathode plate including the first step of applying a first chemical etching solution to a surface of the cathode plate to provide a cleaned surface. The second step involves spraying a second chemical etching solution on to the cleaned surface of the cathode plate at a shallow angle to a plane defined by a face of the cathode plate, wherein the chemical etching solution is sprayed at a sufficient pressure to provide a smoothed glazed surface. A third chemical etching solution is then applied to the smoothed glazed surface of the cathode plate to provide an etched surface.

Description

A METHOD OF RECONDITIONING A CATHODE PLATE

FIELD OF THE INVENTION The invention relates to a method of reconditioning a metallic object. In particular, although not exclusively, the invention relates to a method of reconditioning a cathode plate to a required smoothness.

BACKGROUND TO THE INVENTION The electrolysis of metal ions contained in a solution to give a solid metal product is a well known technique for isolating relatively pure metals. A solid cathode is placed into a metal ion solution and an electric current is applied to the cathode. Electro deposition of the metal onto the cathode then occurs. Periodically, the cathode and the deposited metal product are removed from the solution. The deposited metal product is then separated from the cathode and the cathode is reused.

During use, and particularly during the removal of the deposited metal product, damage to the cathode can occur in the form of scratches, pits and cracks. Once the cathode is damaged, further use will result in deposition of solid metal not only onto the surface of the cathode, but also within the pits and scratches. Some pits and scratches undercut the surface of the cathode and continued use of the cathode can result in further undercutting of the surface. Metal which is deposited into such a pit or scratch is extremely difficult to remove as the deposited metal effectively 'hooks' within the cathode surface. This makes removal of the deposited metal more difficult, and stronger physical efforts are required to remove it such as the use of chisels, crowbars and hammers. However, this results in further damage to the surface of the cathode. Previous solutions to badly damaged cathodes included simply purchasing new ones which increases operation costs significantly. Attempts to recondition a damaged cathode have been carried out using hand grinding and polishing techniques. However, hand polishing requires a human operator and frequently results in an inconsistent finish. Inattention to detail and an inconsistent analysis of the polishing result means that the surface may be insufficiently polished in one area and too polished in another. In order to remove scratches that have undercut the cathode surface a significant depth of the cathode must be polished away. This increases the time and thus cost required to recondition the cathode. A certain degree of roughness is required for the surface of a cathode in order that the deposited metal adheres during the deposition cycle. However, if the surface is too rough, it becomes difficult to remove the deposited metal resulting in damage to the cathode as discussed above.

OBJECT OF THE INVENTION

It is an object of the invention to overcome or at least alleviate one or more of the above problems and/or provide the consumer with a useful or commercial choice. DISCLOSURE OF THE INVENTION

In one form, although it need not be the only or indeed the broadest form, the invention resides in a method of reconditioning a cathode plate including the steps of: applying a first chemical etching solution to a surface of the cathode plate to provide a cleaned surface; spraying a second chemical etching solution on to the cleaned surface of the cathode plate at a shallow angle to a plane defined by a face of the cathode plate, wherein the chemical etching solution is sprayed at a sufficient pressure to provide a smoothed glazed surface; and applying a third chemical etching solution to the smoothed surface of the cathode plate to provide an etched surface.

In a preferred embodiment, the first chemical etching solution, the second chemical etching solution and the third chemical etching solution are the same. It is particularly preferred that the second chemical etching solution is ferric chloride.

Suitably, the first chemical etching solution is applied by spraying.

Preferably the first chemical etching solution is sprayed at a lower pressure that the pressure at which the second chemical etching solution is sprayed. In a preferred embodiment, the first chemical etching solution is sprayed at a pressure which is between 20% and 50% lower than the pressure at which the second chemical etching solution is sprayed. In a particularly preferred embodiment, the first chemical etching solution is sprayed at a pressure between

0.4 - 1.0 bar. Preferably the second chemical etching solution is sprayed at a pressure of 2 bar.

It is preferred that the third chemical etching solution is applied by spraying. In a particularly preferred embodiment the third chemical etching solution is sprayed at a lower pressure that the pressure at which the second chemical etching solution is sprayed.

Suitably, the third chemical etching solution is sprayed at a pressure which is between 20% and 50% lower than the pressure at which the second chemical etching solution is sprayed. In a preferred embodiment, the third chemical etching solution is sprayed at a pressure between 0.4 - 1.0 bar. Suitably, the first chemical etching solution and the second chemical etching solution and the third chemical etching solution are applied by spraying by a chemical etching apparatus.

In a preferred method, the second chemical etching solution is sprayed at an angle of less than 55° to a plane defined by the cleaned surface of the cathode plate. In a particularly preferred method, the second chemical etching solution is sprayed at an angle of less than 45° to a plane defined by the cleaned surface of the cathode plate.

Preferably the method additionally includes the step of applying a neutralizing solution to the etched surface of the cathode plate. In another form, the invention resides in a cathode plate which has been reconditioned by chemical etching.

Further features of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, wherein:

FIG. 1 shows a side view of a schematic of a standard chemical etching apparatus used in an embodiment of a method to recondition a cathode plate;

FIG. 2 shows a perspective view of the standard chemical etching apparatus of FIG. 1 ; FIG. 3 shows a top view of the standard chemical etching apparatus of

FIG. 1 ;

FIG. 4 shows a schematic of the microstructure of a damaged surface of a cathode plate prior to a cleaning step of an embodiment of the reconditioning method; FIG. 5 shows a schematic of the microstructure of a cleaned surface of a cathode plate following a cleaning step of an embodiment of the reconditioning method;

FIG. 6 shows a schematic of the microstructure of a smoothed glazed surface of a cathode plate following a smoothing step of an embodiment of the reconditioning method;

FIG. 7 shows a schematic of the microstructure of an etched surface of a cathode plate following an etching step of an embodiment of the reconditioning method;

FIG. 8 shows a micrograph of a surface of a new cathode plate; FIG. 9 shows a micrograph of a surface of a cathode plate following a period of use; and

FIG. 10 shows a micrograph of a surface of a cathode plate which has been reconditioned by an embodiment of the reconditioning method.

DETAILED DESCRIPTION OF THE INVENTION

Reconditioning of a cathode plate 100 is undertaken using chemical etching to return a damaged surface 110 of the cathode plate 100 to a reusable state. The four steps of the reconditioning method, being cleaning, smoothing, etching and neutralizing of a cathode plate, are discussed further below. FIG 1 shows a side view of a schematic of a standard chemical etching apparatus 200 used to recondition a cathode plate 100. FIG 2 shows a perspective view and FIG 3 shows a top view of the chemical etching apparatus 200. The chemical etching apparatus 200 contains a spray apparatus 300, as well as one or more solution reservoirs 400, pumps (not shown) and heating equipment (not shown). The solution reservoir 400 is in fluid communication with the spray apparatus 300.

The chemical etching apparatus 200 may also include rinsing facilities (not shown) to rinse the cathode plates 100 following the reconditioning process. The chemical etching apparatus 200 may be programmed to undertake each step of the reconditioning method for one cathode plate 100 at a time, or a conveyor system may pass a series of cathode plates 100 through automatically. The chemical etching apparatus 200 may also be configured and programmed to recondition both sides of a cathode plate 100 simultaneously.

The spray apparatus 300 includes one or more spray nozzles 310 directed towards the cathode plate 100. In a preferred embodiment, 130-150 spray nozzles 310 per metre of cathode plate 100 are directed towards the cathode plate 100.

The spray nozzles 310 are oriented at a shallow angle to a plane defined by a face of the cathode plate 100. In a preferred embodiment, the angle of the spray nozzles 310 to the plane of a face of the cathode plate 100 is less than 55°. An angle less than 45° is particularly preferred. The spray nozzles 310 are moveable in a direction which is parallel to the plane of the surface of the cathode plate 100 and perpendicular to the axis of the spray direction.

In a preferred embodiment, a multiplicity of spray nozzles 310 are located on a bar 320 which is moveable in a direction which is parallel to the plane of the surface of the cathode plate 100 and perpendicular to the axis of the spray direction. A multiplicity of bars, or a grid of spray nozzles, may be utilized and oscillated during use in order to spray the majority of the surface of the cathode plate 100 simultaneously and evenly. FIG 4 shows a schematic of the microstructure of a damaged surface 110 of the cathode plate 100 prior to a cleaning step of the reconditioning method.

In one embodiment of the reconditioning method, the cathode plate 100 is placed within the chemical etching apparatus 200. A first chemical etching solution 120 is pumped from the solution reservoir 400 and sprayed through the spray apparatus 300 onto a damaged surface 110 of the cathode plate 100.

Preferably the first chemical etching solution 120 is at a temperature of 60-80⁰C.

The spray nozzles 310 of the spray apparatus 300 are preferably directed to spray at a shallow angle to the cathode plate 100. Suitably, the spray nozzles

310 are also oscillated in a direction which is perpendicular to the spray of the first chemical etching solution 120 and parallel to the plane of the surface of the cathode plate 100. In an alternative embodiment, the cathode plate 100 is oscillated relative to the spray nozzles 310.

Whilst spraying of the first chemical etching solution 120 is preferred, the first chemical etching solution 120 may alternatively be applied by dipping the cathode plate 100 into a bath, pouring the first chemical etching solution 120 onto the damaged surface 110 of the cathode plate 100, or the like.

When the first chemical etching solution 120 is applied by spraying in the standard chemical etching apparatus 200, a low spray pressure is utilized.

Preferably the first chemical etching solution 120 is sprayed at a pressure of approximately 20% to 50% of the full pressure of that which the chemical etching apparatus 200 is capable. Suitably an operating pressure of 0.4-1.0 bar, to produce a spray rate of 0.5-1.3 L/min may be used.

If the first chemical etching solution 120 is sprayed at a high pressure, the damaged surface 110 immediately surrounding each area of electrolytically deposited metal 111 or impurity is significantly etched away. This is due the electrolytically deposited metal 111 causing localized turbulence in the first chemical etching solution 120. A low pressure spray results in the electrolytically deposited metal 111 being etched away without significant etching of the damaged surface 110 which immediately surrounds each area of electrolytically deposited metal 111 or impurity.

The first chemical etching solution 120 is selected to correspond to the cathode plate 100 material and/or to the type of any electrolytically deposited metal which may be present on the cathode plate 100. Ferric chloride is preferably used for the reconditioning of stainless steel, and is also preferred for the removal of electrolytically deposited copper. Application of the first chemical etching solution 120 to the cathode plate

100 removes any electrolytically deposited metal 111 , and/or other dirt or impurities present on the cathode plate 100 and within pits and scratches in the damaged surface 110, including in undercut areas 112, and provides a cleaned surface 130.

FIG 5 shows a schematic of the microstructure of the cleaned surface 130 of a cathode plate 100 following the cleaning step of the reconditioning method.

After the damaged surface 110 of the cathode plate 100 has been cleaned, the cleaned surface 130 is sprayed with a second chemical etching solution 140. Preferably, the second chemical etching solution 140 is sprayed at a pressure of approximately 100% of the full pressure of that which the chemical etching apparatus 200 is capable. An operating pressure of about 2 bar, which produces a spray rate of 2.55 L/min may be used.

The second chemical etching solution 120 is selected to correspond to the cathode plate 100 material. Preferably the second chemical etching solution 140 is ferric chloride for stainless steel cathode plates. Preferably, the second chemical etching solution 140 is the same as the first chemical etching solution

120. The second chemical etching solution 140 is sprayed at a high pressure and at a shallow angle to the plane of the cleaned surface 130 to provide a smoothed glazed surface 150. The degree of smoothing is such that the surface has a shiny or glassy appearance.

As well as smoothing out the cleaned surface 130 of the cathode plate

100, areas of the cleaned surface 130 which overhang undercut areas 112 are removed by the second chemical etching solution. By removing undercut areas 112 at a microstructural level, electrolytically deposited metal 111 , deposited during use of the cathode plate 100, will not "hook" into the smoothed glazed surface 150.

FIG 6 shows a schematic of the microstructure of the smoothed surface 150 of a cathode plate 100 following the smoothing step of the reconditioning method.

After the cleaned surface 140 of the cathode plate 100 has been smoothed, a third chemical etching solution 160 is applied to the smoothed glazed surface 150 to provide an etched surface 170.

In a preferred embodiment, the third chemical etching solution 160 is applied by spraying at a low pressure by a standard chemical etching apparatus 200. Suitably, the third chemical etching solution 160 is sprayed at a pressure of approximately 20% to 50% of the full pressure of that which the chemical etching apparatus 200 is capable. Suitably an operating pressure of 0.4-1.0 bar, to produce a spray rate of between 0.5-1.3 L/min may be used. Whilst spraying of the third chemical etching solution 160 is the preferred method of application, the third chemical etching solution 160 may be applied by dipping the cathode plate 100 into a bath, pouring the third chemical etching solution 160 onto the smoothed glazed surface 150 of the cathode plate 100, or the like. The third chemical etching solution 160 is selected to correspond to the material of the cathode plate 100 and the degree of roughening required. Preferably the third chemical etching solution 160 is the same as either the first chemical etching solution 120 and/or the second chemical etching solution 140. Ferric chloride is preferred as the third chemical etching solution 160 when reconditioning stainless steel cathode plates. When the reconditioned cathode plate 100 is in use, the etched surface 170 allows electrolytically deposited metal 111 to adhere until removal of the electrolytically deposited metal 111 is initiated.

FIG 7 shows a schematic of the microstructure of an etched surface 170 of a cathode plate 100 following the smoothing step of the reconditioning method.

After a period of spraying the third chemical etching solution 160, the cathode plate 100 is removed from the chemical etching apparatus 200 and rinsed with neutralizing solution 180. Alternatively, the neutralizing solution 180 may be applied to the etched surface 170 by the chemical etching apparatus 200. The neutralizing solution 180 is selected for its ability to neutralize the first, second or third chemical etching solutions, and is preferably water.

Application of the neutralizing solution 180 may be by dipping, spraying, pouring or spraying by the standard chemical etching apparatus 200. By applying the neutralizing solution 180, any remaining first, second or third chemical etching solution 120, 140, 160 is removed or neutralized, such that no further etching occurs.

The reconditioned cathode plate 100 is then ready for reuse, such as in an electrowinning or metal refining plant. The cathode plates 100 which can be reconditioned by the method may be designed for use in any standard electrowinning or refining process and may be any shape or size. The cathode plates 100 may include raised portions and masked areas, such as those used in cobalt/nickel refining. Any masking material on such plates may be present during the chemical etching process, or it may be added afterwards. It is standard practice for cathode plates 100 to be fitted with edge strips, however, it is not necessary to remove the edge strips from the cathode plate 100 prior to undergoing the reconditioning method. Indeed, the method of reconditioning the cathode plate 100 also removes any electrolytically deposited metal 111 or impurities which are located at the junction of the edge strips and the damaged surface 110 of the cathode plate 100.

The cathode plate 100 is made from metal, preferably stainless steel. Alternatively, cathode plates 100 made from any metal suitable for chemical etching may be used. The length of time for which the cathode plate 100 is sprayed during each step of the reconditioning method is dependent upon the degree of damage to the cathode plate 100 prior to undergoing the reconditioning method and the surface smoothness required to suit the future use of the cathode plate 100. The preferred surface smoothness is an R_a (arithmetic average of the roughness profile) value between 0.2 to 0.8. Additionally, the reconditioned surface of the cathode plate 100 does not contain significant amounts of undercut surface 112, when the microstructure of the surface is examined.

A cathode plate 100 with a damaged surface 110 in need of reconditioning typically has an Ra of 3-4. By applying an etching solution to the damaged surface 110 in three steps, as described above, and by changing the angle of the spray nozzles to the cathode plate 100 from the standard perpendicular arrangement to a shallow angle, the cathode plate 100 is etched to give a uniform reconditioned surface over the entire face of the cathode plate with an Ra of 0.2-0.8. Additionally, the microstructure of the surface of the cathode plate 100 is reconditioned to remove any areas which have been undercut 112. By directing the second etching solution 140 at a shallow angle to the cathode plate 100 creates turbulence within pits and scratches which have undercut 112 the damaged surface 110 of the cathode plate 100. The turbulent motion of the second etching solution 140 removes overhanging surface areas. This provides a reconditioned surface from which an electrolytically deposited metal can be easily removed without the need for harsh treatment of the cathode plate.

FIG 8 shows a micrograph of a new surface 105 of a new cathode plate 100, prior to use. The new surface 105 is highly polished, with deep intergranular etches 106. This structure provides extensive smooth surface areas 107 allowing for ease of removal of electrolytically deposited metal, while providing a means for mechanical adherence of the electrolytically deposited metal during the deposition process.

FIG 9 shows a micrograph of the damaged surface 110 of a cathode plate 100 following a period of use. The bulk of the smoothed surface grains have been knocked off or otherwise removed with the electrolytically deposited metal, leaving only the rough intergranular subsurface 113 exposed. This results in difficulty in removing the electrolytically deposited metal 111 as it tends to 'hook' into areas which have undercut the damaged surface 110 of the cathode plate 100.

FIG 10 shows a micrograph of the etched surface 170 of a cathode plate 100 which has been reconditioned by the method of FIG. 1. The rough exposed granular surface 171 has been etched to a more rounded shape, resulting in a smoother surface with some undulation to accommodate mechanical adherence of the electrolytically deposited metal 111. The chemical etching method of reconditioning cathode plates provides a more consistent surface finish than that obtained by hand polishing a damaged cathode plate. When the reconditioning method is undertaken in a standard chemical etching apparatus, the method is faster than hand polishing and does not require an operator to determine if the cathode plate has been sufficiently reconditioned.

By applying a chemical etching solution in three stages, the surface is cleaned and smoothed at a microstructural level, followed by controlled roughening. This provides a surface of the cathode plate which allows the adhesion of electrolytically deposited metal during a deposition phase. When removal of the electrolytically deposited metal from the cathode plate is required, however, the electrolytically deposited metal can be easily removed.

Thus the cathode plates are returned to a state where they may be reused in electrowinning type applications with similar results as new cathode plates.

Throughout the specification, the aim has been to describe the invention without limiting the invention to any one embodiment or specific collection of features. Persons skilled in the relevant art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention. For example, the arrangement of the chemical etching apparatus may include the cathode plate being in either a vertical or horizontal orientation.

It will be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit and scope of the invention.

Claims

1. A method of reconditioning a cathode plate including the steps of: applying a first chemical etching solution to a surface of the cathode plate to provide a cleaned surface; spraying a second chemical etching solution on to the cleaned surface of the cathode plate at a shallow angle to a plane defined by a face of the cathode plate, wherein the chemical etching solution is sprayed at a sufficient pressure to provide a smoothed glazed surface; and applying a third chemical etching solution to the smoothed surface of the cathode plate to provide an etched surface.

2. The method of claim 1 , wherein the first chemical etching solution, the second chemical etching solution and the third chemical etching solution are the same solution.

3. The method of claim 1 , wherein the second chemical etching solution is a ferric chloride solution.

4. The method of claim 1 , wherein the first chemical etching solution is applied by spraying.

5. The method of claim 4, wherein the first chemical etching solution is sprayed at a lower pressure than the pressure at which the second chemical etching solution is sprayed.

6. The method of claim 5, wherein the first chemical etching solution is sprayed at a pressure which is between 20% and 50% lower than the pressure at which the second chemical etching solution is sprayed.

7. The method of claim 5, wherein the first chemical etching solution is sprayed at a pressure between 0.4 - 1.0 bar.

8. The method of claim 1 , wherein the second chemical etching solution is sprayed at a pressure of 2 bar.

9. The method of claim 1 , wherein the third chemical etching solution is applied by spraying.

10. The method of claim 9, wherein the third chemical etching solution is sprayed at a lower pressure than the pressure at which the second chemical etching solution is sprayed.

11. The method of claim 10, wherein the third chemical etching solution is sprayed at a pressure which is between 20% and 50% lower than the pressure at which the second chemical etching solution is sprayed.

12. The method of claim 10, wherein the third chemical etching solution is sprayed at a rate of between 0.4 - 1.0 bar.

13. The method of claim 1, wherein the first chemical etching solution and the second chemical etching solution and the third chemical etching solution are applied by spraying by a chemical etching apparatus.

14. The method of claim 1 , wherein the second chemical etching solution is sprayed at an angle of less than 55° to a plane defined by the cleaned surface of the cathode plate.

15. The method of claim 1 , wherein the second chemical etching solution is sprayed at an angle of less than 45° to a plane defined by the cleaned surface of the cathode plate.

16. The method of claim 1 , additionally including the step of applying a neutralizing solution to the etched surface of the cathode plate.

17. A cathode plate which has been reconditioned by the method of claim 1.