Investigating the nodulation mechanism of copper cathode based on microscopic approach: As a punch failure factor

Abstract

The presence of nodules on the surface of cathode copper plates was the most important reason for the failure of the punch of mechanical clinching of copper cathode sheets. This study demonstrated a comprehensive investigation into the nodulation growth of copper cathodes in the electrorefining plant based on metallographic analysis. More than 15 random samples were selected from the top, middle, and bottom of the cathodes produced in the Khatoon Abad copper refinery, Iran. Studies were carried out based on the determination of growth modes including field oriented isolated crystal (FT), basis-oriented reproduction (BR), field-oriented texture (FT), and unoriented dispersion (UD). A scanning electron microscope equipped with the EDS spectrometer was used to determine the elemental analysis of the origin of each nodule and investigate the effect of entrapped slimes impurities on the nodules' microstructure. The results confirmed that the physical and chemical adsorption of inhibitors including Fe, Ni and Mn as hydrated phases on the preferred active sites restricted the FT growth mode at the first stages of crystallization. Then, it enhanced the local current density and cathodic polarization promoting the UD growth mode. The same mechanisms occurred when as-received-casted anodes replaced the cathode and caused the formation of cavity at the preferred active site and intense nodulation at the border of the sample. Analysis of this site of nodules’ root revealed that the aggregation of inhibitors at the lower preferred active sites, i.e., lower than 5 mm, provided the possibility of large local current density, polarization and encourage the formation of brittle deposition as MeOH. In this case, the formation of the spongy nodule was dominant.