Chemical and electrochemical recycling of the negative electrodes from spent Ni–Cd batteries

Abstract

In this work, cadmium from Ni–Cd batteries was recycled by chemical precipitation and electrodeposition. Cadmium hydroxide, the material synthesized by chemical precipitation, showed up a hexagonal structure. The structure of the material recovered by chemical precipitation is not affected by the change of temperature at the range between 8.0 and 25 °C. The chemical composition for cadmium hydroxide is: [β-Cd(OH) 2(H 2O) X (SO 4) Y (CO 3) Z ] where X, U, and W are the amounts of substance for H 2O, SO 4 2−, and CO 3 2−, respectively. Electrodepositing was accomplished using the galvanostatic technique. The chronopotentiometric plots present a potential peak that indicates a nucleation stage prior to deposit growth. The largest charge efficiency occurred around 95.0% for a current density between 10.0 and 30.0 mA cm −2. Current density influences the morphology of the deposits. For a current density equal to 10.0 mA cm −2, the deposit micro porosity is larger than that for a current density equal to 50.0 mA cm −2. The deposits formed with current density of 25.0 mA cm −2 possess an intermediate morphology. The energy dispersive X-ray analysis (EDX) spectra of the deposits formed by different current densities have shown the presence of iron, sulphur, and oxygen besides cadmium.