Abstract
Nickel behavior has a significant role in the electrorefining of copper, and although it has been extensively studied from the anode and electrolyte point of view over the past decades, studies on nickel contamination at the cathode are limited. In the current paper, three possible contamination mechanisms—particle entrapment, electrolyte inclusions and co-electrodeposition—were investigated. Copper electrorefining (Cu-ER) was conducted at the laboratory scale, and the cathodes were analyzed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and flame atomic absorption spectroscopy (AAS). Particle entrapment was studied by adding NiO and Fe2O3 to the system to simulate nickel anode slime, and the experiments were replicated with industrial anode slime material. The possibility of electrolyte entrapment due to nodulation was explored through the addition of graphite to produce nodules on the cathode. Co-electrodeposition was analyzed by experiments that utilized a Hull cell. The results indicate that particle entrapment can occur at the cathode and is a major source of the nickel contamination in Cu-ER, whereas nickel compounds were not shown to promote nodulation. Inclusions of bulk electrolytes within the surface matrix were observed, proving that electrolyte entrapment is possible. As co-electrodeposition of Ni in Cu-ER is thermodynamically unlikely, these experimental results also verify that it does not occur to any significant extent.
Highlights
Copper electrorefining is the most common method for the production of high-purity copper cathodes
One of the typical impurities found in copper electrorefining is nickel, which mainly dissolves into the electrolyte, it may be found within the different compounds that form anode slimes
It can be concluded that particle entrapment is the most significant source of cathode contamination by nickel in normal electrorefining operations
Summary
Copper electrorefining is the most common method for the production of high-purity copper cathodes. Copper metal is dissolved from a copper anode to the electrolyte and deposited on the cathode using electricity. Impurities within the copper anode either dissolve into the electrolyte or form anode slime, which settles predominantly to the bottom of the electrorefining cell. One of the typical impurities found in copper electrorefining is nickel, which mainly dissolves into the electrolyte, it may be found within the different compounds that form anode slimes. Due to the increased emphasis on circular economy and recycling, the concentration of nickel in anodes is expected to increase as nickel is a common alloying element used to improve the strength and corrosion resistance of copper products. Nickel concentrations can differ significantly between different refineries from approximately 80 to 27,600 μg/g on the anode and from 0.3 to 23 g/L in the electrolyte. Ni concentrations in the anode can vary from 50–9000 μg/g and 15–19 g/L in the electrolyte [1]
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