Towards efficient extraction of La(III) from spent FCC catalysts by alkaline pre-treatment

In Vietnam, Dzung Quat Refinery disposes about 7300 tonnes of spent fluid catalytic cracking (SFCC) catalysts per year. The recovery of rare earth metals (La(III), Ce(III),…) contained in SFCC catalysts using acid leaching process has attracted much attention of scientific community. In this study, the effect of alkaline pre-treatment of spent catalysts prior to the acid leaching process on the leaching yield of La(III) was investigated. The results showed that alkaline pre-treatment caused zeolite destruction, which had a positive effect on the leaching of La(III). High leaching yields of La(III), 80% and 86%, were achieved when the SFCC catalysts were pre-treated with NaOH and NH3, respectively, before leaching with 2 M HNO3 solution at 50 °C. These results were comparable with the one obtained from the sample that was leached by 7 M HNO3 at 50 °C without the initial alkaline pre-treatment. NH3 pre-treatment significantly enhanced the zeolite destruction in the SFCC catalysts and increased La(III) leaching yield compared to the NaOH pre-treatment. It is likely due to NH3 interactions with contaminant metals (e.g. Ni, V, and Fe), which were deposited on catalysts during cracking process.