Stabilization/Solidification of Toxic Elements in Cement Pastes Containing a Spent FCC Catalyst

Huge amounts of spent fluid catalytic cracking (FCC) catalysts, also called Ecat, are produced worldwide, every year. Alternatives to the traditional landfill disposal are imperative to reduce the environmental contamination and the production of hazardous solid wastes. The leaching of iron, nickel, antimony, and vanadium from Ecat was investigated using the toxicity characteristic leaching procedure (TCLP) to assess the risk of contamination of the aquatic environment. The concentrations of these elements in the leachate of a cement paste containing 15% Ecat were much reduced as compared to those leached from the Ecat sample and were below the limits established in the water quality criteria of the United States Environmental Protection Agency (USEPA 2004). The solidification/stabilization (S/S) of Fe, Ni, V, and Sb in the cement paste containing Ecat was influenced by the chemical properties and stability of the products formed with cement-hydrated phases and by the erosion of the cement paste exposed to the leaching environments. The S/S mechanisms were less effective in seawater and this was related to reactions of cement-hydrated phases with the salts usually present in seawater. The results indicated that the solidification/stabilization (S/S) process was efficient enough to prevent the excessive leaching of these toxic elements.