Reuse of waste catalysts from petrochemical industries for cement substitution

Zeolite catalysts have been widely used in oil refinery and petrochemical industries. Two types of waste catalysts, equilibrium catalyst (Ecat), and electrostatic precipitator catalyst (EPcat), can be obtained after fluid catalytic cracking. This study analyzes the properties of these waste catalysts and examines the feasibility of reusing them to substitute part of the cement required in mortar preparation. These waste catalysts are found to comprise mainly SiO(2) and Al(2)O(3). Their catalytic structure is coarse and porous, while their crystal pattern is similar to that of Faujasite zeolite. Their specific surface area varies with different types of catalysts. Their specific gravity is 2.48 and their apparent bulk density is about 0.88 g/cm(3). They can substitute up to 15% of the cement content in mortar without sacrificing the quality of concrete. In fact, the substituted concrete shows a greater compressive strength, 15% higher than that without substitution. The setting time of the fresh mortar becomes shorter with increasing amount of cement substituted; while the spread flow value decreases with increasing percentage of cement substitution. Bleeding is reduced and the hydration heat of mortars with 10% and 15% substitution are close to that without substitution because these waste catalysts are exothermic. The water absorptivity in hardened mortar increases with longer curing age, greater substitution percentage, and smaller water to cement ratio (W/C). X-ray diffraction analysis reveals that when W/C = 0.485 and curing age = 28 days, the crystal patterns of mortars prepared with different amount of cement substituted by Ecat are similar. According to the results of TCLP analysis, these spent catalysts should be classified as general non-hazardous industrial waste and they meet the effluent standard. Therefore, reuse of these industrial waste catalysts is feasible and will not result in pollution due to the leaching of heavy metals. (C) 2000 Elsevier Science Ltd. All rights reserved.