Sol-gel synthesis, characterization, and catalytic properties of Ni, Cd, Co, and Fe oxides recycled from spent Ni-Cd batteries using citric acid as a leaching agent

This research developed a sustainable, green, hydrometallurgical route for recycling the positive electrodes of Ni-Cd batteries using citric acid as a leaching agent. The mixed oxide was synthesized using a gel precursor that was calcinated at 400 °C for 2 h. The mixed composition of the metal oxide included nickel oxide (NiO), cadmium oxide (CdO), cobalt oxide (Co3O4), and iron oxide (Fe2O3). A scanning electron microscopy (SEM) micrograph showed that the mixed oxide presented no well-defined morphological structure but did present macropores that were about 20 μm in size and micropores that were 1.0 μm in size. Transmission electron microscopy (TEM) images showed that the agglomerate was composed of hexagonal structures that were nanometric in size. The material was applied in a photocatalytic reaction to discolor a textile-reactive black V-2B dye (C26H21O19N5S6Na4). The efficiency of the discoloration reached 86.10% in 480 min, and the catalyzed reaction showed second-order kinetics. Nanoparticles of NiO/CdO/Co3O4/Fe2O3 synthesized using the cathodes of Ni-Cd batteries as raw materials. [Display omitted] •Sol-gel method to synthesize the mixed oxide containing Ni, Cd, Co, and Fe.•Hydrometallurgical recycling of the positive electrodes of Ni-Cd batteries.•Citric acid as a leaching agent of the positive electrodes of Ni-Cd batteries.•Photocatalytic properties study of the recycled material.