Detachment and flow behaviour of anode slimes in high nickel copper electrorefining

Most of the world’s copper is produced via copper electrorefining, where nickel is the most abundant impurity in the process. Previously it has been suggested that nickel affects the adhesion of anode slimes on the anode as well as the porosity of the slime layer that forms. This paper investigates the effects of nickel, oxygen, sulphuric acid and temperature on the detachment of anode slimes from the anode surface. The detachment of particles as a function of both anode and electrolyte composition was studied on laboratory scale using a camera connected to a Raspberry Pi, and particle detection and movement analysed using TrackPy. The results revealed four different slime detachment mechanisms: cloud formation, individual particle detachment, cluster detachment and avalanche. These were found to be dependent on the electrolyte (0, 10, 20, 30 g/dm³ Ni²⁺ & 100, 200 g/dm³ H2SO4), with increasing nickel concentration promoting cluster detachment and increasing sulphuric acid concentration favouring detachment of individual particles. Anode composition (0.05-0.44 wt% O and 0.07-0.64 wt% Ni) was shown to affect the flow direction of anode slimes, with increasing nickel leading to more upward-flowing slimes. Typical particle movement velocities were from -0.5 to 1.0 mm/s regardless of the electrolyte and anode composition, and regardless of the operating temperature (25 °C & 60 °C) for small particles (<0.5 mm). The results also support previous findings that increasing the nickel concentration of the electrolyte leads to a more porous anode slime layer on the anode.