Electrorefining Behavior of Copper Shot-Shaped Anode Containing High Levels of Platinum

Abstract

Increased amounts of secondary copper resources with higher levels of impurities are being fed to copper smelters. To avoid passivation problems, low-grade copper that is derived from secondary resources is dissolved in sulfuric-acid solution, and the dissolved copper is recovered by electrowinning. Electrowinning is disadvantageous because of its higher power consumption compared with electrorefining. Based on an electroplating technique that uses basket electrolysis with a ball-shaped anode and another experimental approach of copper-scrap electrorefining in a basket, we investigated an electrorefining method that uses small low-grade copper shots (diameter of several millimeters) as an anode. It is expected that the copper-dissolution ratio will be higher, even with a small elution depth, because of the small primary-anode size and the effect of the three-dimensional shape. In addition, the current density for a shot-shaped anode can be lower than that for a plate-shaped anode at the same current and for the same occupied area, and would result in the inhibition of passivation. Rotating-disk-electrode equipment was used in the electrolysis experiments. Single-layered copper shots that contained 0.9 « 0.2 mass% Pt (18 shots) in a platinum basket were used as an anode, and a copper rotating-disk electrode (7-mm diameter) was used as a cathode. The temporal changes in anode potential were measured at a constant current to investigate the electrolytic properties of a small shot-shaped anode during the electrorefining experiments. The current efficiency and final anode-dissolution ratio exceeded 90% up to an initial anode current density of ³673 A/m 2. Stable electrolysis could be carried out with a copper shot-shaped anode that contained high levels of platinum.

Fundamental Application of Basket Electrolysis Method for Black-Copper Anode

“…Iizuka et al reported that basket electrolysis with CuPt alloy anodes with a Pt content of 1 mass%, which are easily passivated during electrolysis, gave a dissolution ratio that was significantly higher for small shot anodes than for plate anodes. 23) In the basket electrolysis process, the characteristics of the anode film formed on the surface during electrolysis are especially important. In electrolysis with plate anodes, the effect of the anode film on passivation is mainly related to elution of Cu ions into the electrolyte.…”