Recovery of cobalt and molybdenum from spent catalyst using citric acid

Valuable metals play essential roles in various industrial sectors, such as petroleum, petrochemical, and steel industries. Potential secondary resources of these metals can be obtained from spent catalysts, which are a solid waste of the chemical and oil industries. Spent catalysts contain valuable metal compounds such as nickel (Ni), vanadium (V), cobalt (Co), molybdenum (Mo), rhodium (Rh), platinum (Pt), alumina (Al), etc. In this research, the recovery of cobalt and molybdenum from the spent catalyst of Pertamina Refinery Unit IV, Cilacap, Indonesia, was leaching using citric acid. Samples of spent catalyst were analyzed using EDXRF prior to the leaching process. Citric acid at various concentrations of 1.0, 1.5 and 2 M was used as a leaching agent. The leaching experiment was carried out for 300 minutes and sampling was undertaken at 1, 3, 5, 15, 30, 90 and 300 minutes. Each sample was separated between solid and liquid phases using a centrifuge at 400 rpm for 10 minutes. For analysis, 2 ml of the liquid phase was taken and the cobalt and molybdenum concentrations were analyzed using ICP-OES. It was found that at higher the citric acid concentration and temperature, the recovery of cobalt and molybdenum was also higher. The best leaching condition is obtained at a citric acid concentration of 2 M and 60 C, where recovery of cobalt and molybdenum were 17.35 and 2.27, respectively.