Recycling. Recovery of Nickel and Cobalt from Spent Catalyst by Means of Solvent Extraction with Synergistic Mixtures of Picolylamine in Combination with DNNSA.

Abstract

The total dissolution of spent hydrodesulfurization catalyst (HDS) in sulfuric acid yields an acidic solution containing a certain amount of rare metals like molybdenum, vanadium, cobalt, nickel, and a small amount of iron as well as large excess of aluminum. In order to recover Co and Ni from the raffinate after the selective extraction of Mo and V with phosphinic acid extractants such as CYANEX 272 and PIA-8, a systematic investigation was conducted on the synergistic extraction with the mixed solvents consisting of dinonylnaphthalenesulfonic acid (DNNSA) and a series of N-alkyl-bis-picolylamine such as tri-decyl-picolylamine (TDPA), oleylpicolylamine (OLPA), and octa-decyl-picolylamine (ODPA). It was elucidated that all of these mixtures could exhibit a good synergistic effect for the extraction of Co, and Ni, while, the extraction of Al was considerably suppressed. In particular, the mixture of TDPA, or OLPA in combination with DNNSA appeared to be the most feasible and economic because it has rapid extraction rate, good phase separation, and high selectivity for Co and Ni over Al. Stripping of the loaded Ni and Co can be achieved by 0.5 and 1 M sulfuric acid and hydrochloric acid, respectively. However, smooth phase disengagement was not observed, which should be improved in future, for example by employing picolylamines with highly branched alkyl chains at tail position.