Reuse of waste catalysts from petrochemical industries for cement substitution

Zeolite catalysts have been widely used in oil refinery and petrochemical i ndustries. Two types of waste catalysts, equilibrium catalyst (Ecat), and e lectrostatic precipitator catalyst (EPcat), can be obtained after fluid cat alytic cracking. This study analyzes the properties of these waste catalyst s and examines the feasibility of reusing them to substitute part of the ce ment required in mortar preparation. These waste catalysts are found to com prise mainly SiO2 and Al2O3. Their catalytic structure is coarse and porous , while their crystal pattern is similar to that of Faujasite zeolite. Thei r specific surface area varies with different types of catalysts. Their spe cific 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 sac rificing the quality of concrete. In fact, the substituted concrete shows a greater compressive strength, 15% higher than that without substitution. T he setting time of the fresh mortar becomes shorter with increasing amount of cement substituted; while the spread flow value decreases with increasin g percentage of cement substitution. Bleeding is reduced and the hydration heat of mortars with 10% and 15% substitution are close to that without sub stitution because these waste catalysts are exothermic. The water absorptiv ity in hardened mortar increases with longer curing age, greater substituti on percentage, and smaller water to cement ratio (W/C). X-ray diffraction a nalysis reveals that when W/C = 0.485 and curing age = 28 days, the crystal patterns of mortars prepared with different amount of cement substituted b y Ecat are similar. According to the results of TCLP analysis, these spent catalysts should be classified as general non-hazardous industrial waste an d they meet the effluent standard. Therefore, reuse of these industrial was te catalysts is feasible and will not result in pollution due to the leachi ng of heavy metals. (C) 2000 Elsevier Science Ltd. All rights reserved.