A Green Electroslag Technology for Cadmium Recovery from Spent Ni-Cd Batteries Under Protective Flux with Electromagnetic Stirring by Electrovortex Flows

The recycling of nickel–cadmium batteries poses a significant environmental challenge due to cadmium’s high biotoxicity. This study proposes a green method for recovering cadmium from cadmium oxide (CdO) using carbon (coal) in the presence of a molten binary flux (KCl:NaCl = 0.507:0.493, melting point 667 °C). The flux’s relatively low density and conductivity enable cadmium reduction beneath and through the flux layer. Brown coal (5–25 mm) served as the reductant. The reduction of cadmium from cadmium oxide with carbon (brown coal) took place in the temperature range from 667 °C to 700 °C. To enhance the process, electrovortex flows (EVF) were employed—generated by the interaction between non-uniform AC electric currents and their self-induced magnetic fields resembling conditions in a fluidised bed reactor. The graphite crucible acted as both one of the electrodes, with a graphite rod as the second electrode. As Cd and CdO are denser than both the flux and coal, the reduction proceeded below the flux layer. The flux facilitated CdO transport to the reductant, speeding up the reaction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the formation of metallic cadmium beneath and within the flux layer. This method demonstrates the feasibility of flux-assisted cadmium recovery without prior mixing and offers a foundation for further optimisation of sustainable battery recycling.