English abstract
In the process of preparation of Portland clinker, imported bauxite was substituted with two types of materials: natural rock kaolin and waste by-product, spent alumina catalyst (SAC) and reduced fluid cracking catalyst (RFCC), from petroleum refinery in the Sultanate of Oman. Different clinkers were prepared using four different raw meal (RM) samples, i.e. one with bauxite as a reference sample (RM-Bxtret), one with kaolin (RM KL), one with spent alumina Catalyst (RM-SAC) and another with reduced fluid catalytic cracking catalyst (RM-RFCC). The clinker samples obtained were ground with 5% gypsum (CaSO4-2H20) for preparation of cement. Powder X-ray diffraction, thermal analysis, X-ray fluorescence, optical microscopy and scanning electron microscopey were used to characterize samples (raw materials, raw mix, clinker, and cement). Rietveld refinement shows that, in all clinkers prepared, alite was formed with hexagonal (R) lattice whereas belite was monoclinic with a higher volume compared to the known B Ca2SiO4. The main mineralogical phase contents were calculated in accordance with the Bogue equations and found to be of acceptable composition, similar to those of industrially manufactured clinkers. The study of sintering behavior of the raw mix shows that clinker prepared using kaolin has the lowest free lime content compared to the other prepared clinker samples. The physical and mechanical properties (specific area, setting time, heat of hydration, soundness and compressive strength) of prepared cement samples were studied and tested according to the international standard EN 197-1:2000, Class 42.5N (LA). The cement prepared using kaolin, Cmt-KL, has shown higher compressive strength by 6.4 % compared to the reference sample. Also, the setting time of Cmt-KL and Cmt-RFCC shows lower values compared to Cmt-SAC and the reference sample Cmt-BxtRef. In general, the results show that substitution of bauxite in the preparation of cement by kaolin, RFCC and SAC gave results that fall within the required standard specification for ordinary Portland cement (CEMI, EN 197-1:2000) in terms of chemical composition, physical and mechanical properties. These results demonstrate that the spent catalysts (SAC and RFCC) and natural kaolin could be utilized to replace bauxite in the manufacturing of Portland clinker. This could potentially solve the environmental problem of disposal of spent catalysts from refinery companies as well as reduce the cost of cement production.
