Synthesis of geopolymers based on spent catalyst from petrol refineries

Abstract

Geopolymers are class of alkali activated materials obtained by alkali activation of aluminosilicate precursors. The main product of alkali activation reaction is amorphous aluminosilicate, “geopolymer” gel. Due to highly interconnected, threedimensional structure of aluminosilicate gel, geopolymers can show high compressive strength and good durability, and can be regarded as alternative to Portland cement in some applications. Spent catalyst from fluid catalytic cracking process (spent FCCC) is an inorganic by-product from petrol refineries. It consists mostly of zeolite (usually faujasite) and amorphous aluminosilicate matrix, and SiO2 and Al2O3 make about 90 % of its chemical composition. In this work, spent FCCC was used as a precursor for geopolymer synthesis. Prior to chemical activation, spent FCCC was ground in a planetary ball mill. Alkali activation was carried out using sodium silicate solutions with different SiO2/Na2O ratios. The reaction was performed at 65 °C for 24 h. Synthesized geopolymer paste samples were analyzed using scanning electron microscopy and X-ray powder diffraction. The results showed that alkali activation of the spent FCCC sample converted zeolitic phase to aluminosilicate geopolymer gel. Determination of the mechanical properties of the synthesized geopolymer mortar samples indicated that using the optimal modulus of the activating solution can produce geopolymers with compressive strength higher than 70 MPa. The obtained results confirmed potential to use spent FCCC as starting material for geopolymer production.