Depolymerization and leachability of spent videotape for cobalt recovery

•Combined alkaline depolymerization and hydro-metallurgical way of Co recovery was offered.•Interconnection between pressure, temperature, and time of depolymerization was explained.•Kinetic of metal residue leaching from videotape with H2SO4 and H3PO4 was studied.•98% of cobalt was leached and recovered as CoC2O4·2H2O with purity of 99.9% Cobalt is a widely used technology-enabling metal that is dominantly recovered as a by-product of copper and nickel. However, mainly because of its economic importance and high supply risks, it is classified as a critical raw material in Europe, increasing the importance of the utilization of secondary cobalt resources. This work presents a study of the recovery of a pure form of cobalt oxalate from spent low-grade VHS videotapes (0.35 wt% of cobalt). Firstly, depolymerization of the videotape was conducted by alkaline hydrolysis resulting in 94.5% polyethylene (PET) depolymerization yield (T = 150 °C, p = 6.9 bar, [NaOH] = 1 mol L-1). Secondly, metal-rich residue (2.3 wt% of cobalt, 54.5 wt% of iron) of alkaline hydrolysis was subjected to hydrometallurgical leaching in two acids (H2SO4 and H3PO4) at 1 M (S/L = 10 g L−1, t = 5 min, T = 80 °C). In the subsequent oxalate precipitation study, 99.9% purity and 98.0% yield of cobalt precipitate could be achieved. This study provides insight into the technical feasibility of the combined alkaline hydrolysis and hydrometallurgical recovery of cobalt from secondary videotape resources.