Geopolymer synthesized from spent fluid catalytic cracking catalyst and its heavy metal immobilization behavior

Porous geopolymers (GP) are energy saving, environment-friendly and simple in preparation, which has attracted increasing attention from both academia and industry. In this paper, geopolymer with excellent immobilization capability of heavy metals was prepared by chemical forming method. The spent fluid catalytic cracking (sFCC) catalyst, a hazardous solid waste in China, was exploited as aluminosilicate precursor. The influences of particle size of sFCC catalyst, type of activator agent solutions, mass ratios of SiO₂/Na₂O and (SiO₂ + Na₂O)/sFCC catalyst on the compressive strength of GP and the leaching toxicity of Ni were investigated in detail. Under the optimum conditions, the leaching toxicity of Ni is reduced to below 0.01 ppm, much lower than the national standard 5 ppm. The as-obtained GP was also examined by SEM, XRD and FTIR with the aim to understand the synthesis and immobilization mechanism using the sFCC catalyst as the raw material. The results show a new aluminosilicate zoisite phase with three-dimensional network structure forms. Ni element enters the grid of GP, involved in the formation of three-dimensional network structure. Besides, partial Ni element replaces the position of alkaline metal and chemical bonds AlO₄.