Closing the Waste Loop: A Sustainable Process of Extracting Lanthanum, Mullite, Silica, and Alumina from Spent Fluidized Cracking Catalysts

A sustainable process for the utilization of spent fluid catalytic cracking (FCC) to the rare earth element (REE) lanthanum, silica (SiO2), alumina (Al2O3), and mullite has been developed. The solid catalyst waste obtained from refineries is generally dumped into landfills, which subsequently creates not only land claiming but also environmental concerns related to air and water pollution. Here, the developed process involves acid/base leaching followed by selective precipitation. Also, it involves the recovery of silica using CO2 precipitation under atmospheric conditions and finally the recovery of solid alumina using recycled acid and base solutions, which generates CO2 for the next cycle. The obtained solution mainly contains a metal salt; the base metal hydroxide can be regenerated using calcium hydroxide treatment. This indicates no solid landfill material, a CO2-neutral process, zero waste, and no wastewater.