Permanent cathode and a method for treating the surface of a permanent cathode

Abstract

The invention relates to a permanent cathode ( 1 ) to be used as an electrode in the electrowinning of metals, including a permanent cathode plate ( 4 ) at least partially made of steel and providing the possibility of electrochemically depositing metal from an electrolytic solution onto its surface ( 6 ), in which case the dimensions of the grain boundaries ( 7 ) on the surface ( 6 ) of the permanent cathode plate ( 4 ) are arranged to be suitable for the adhesion of deposited metal on the surface and the stripping of metal from the surface at least in a part of the surface that is in contact with the electrolyte. The invention also relates to a method for treating the surface of a permanent cathode.

1 . A permanent cathode ( 1 ) to be used as an electrode in the electrowinning of metals, including a permanent cathode plate ( 1 ) at least partially made of steel and providing the possibility of electrochemically depositing metal from an electrolytic solution onto its surface, characterized in that the dimensions of the grain boundaries, such as grain size, width and depth, on the surface of the permanent cathode plate are arranged to be suitable for the adhesion of deposited metal on the surface and the stripping of metal from the surface at least in a part of the surface that is in contact with the electrolyte. 
     
     
         2 . A permanent cathode according to  claim 1 , characterized in that the grain size of the grains in the permanent cathode plate measured by the linear intercept method is 1 to 40 micrometres. 
     
     
         3 . A permanent cathode according to  claim 1 , characterized in that the average grain boundary width W of the permanent cathode plate is 1 to 3 micrometres. 
     
     
         4 . A permanent cathode according to  claim 1 , characterized in that the average grain boundary depth d of the permanent cathode plate is less than 1 micrometre. 
     
     
         5 . A permanent cathode according to  claim 1 , characterized in that the permanent cathode plate comprises a surface area with strong adhesion properties and a surface area with weak adhesion properties, said adhesion properties being dependent on the dimensions of the grain boundaries in said surface area. 
     
     
         6 . A permanent cathode according to  claim 5 , characterized in that the surface area with weak adhesion properties forms a part of the surface that is in contact with the electrolyte and that said surface area is located at a point where the stripping of metal deposit is meant to start. 
     
     
         7 . A permanent cathode according to  claim 1 , characterized in that the permanent cathode plate is at least partially ferritic steel. 
     
     
         8 . A permanent cathode according to  claim 1 , characterized in that the permanent cathode plate is at least partially austenitic steel. 
     
     
         9 . A permanent cathode according to  claim 1 , characterized in that the permanent cathode plate is at least partially duplex steel. 
     
     
         10 . An arrangement to be used for the electrowinning of metals, including an electrolytic bath containing an electrolytic solution in which anodes and permanent cathodes are alternately arranged, said permanent cathodes being supported in the bath by a support element, characterized in that the arrangement includes a permanent cathode according to  claim 1 . 
     
     
         11 . A method for treating the surface of a permanent cathode plate, in which the permanent cathode plate is formed at least partially of steel plate, characterized in that the grain boundaries of the permanent cathode plate surface on at least a part of the surface that is in contact with the electrolyte are treated chemically or electrochemically to achieve the desired surface properties for the adhesion of deposited metal on the surface and the stripping of metal from the surface. 
     
     
         12 . A method according to  claim 11 , characterized in that the surface of the permanent cathode plate is treated until the separating force desired for the surface is achieved. 
     
     
         13 . A method according to  claim 11 , characterized in that the surface of the permanent cathode plate is treated by etching. 
     
     
         14 . A method according to  claim 11 , characterized in that different areas of the permanent cathode plate surface that are in contact with the electrolyte are treated differently to produce an area with strong adhesion and an area with weak adhesion. 
     
     
         15 . A method according to  claim 14 , characterized in that the area with weak adhesion is produced on a part of the cathode plate surface where the stripping of metal deposit is meant to start.