Valorisation of Sugarcane Bagasse Ash from Malawian Sugar Mills for Zeolite Precursor Synthesis: A Compositional and Thermal Analysis

This study investigates the chemical suitability of sugarcane bagasse ash (SBA) sourced from three Malawian sugar production facilities of Nchalo, Dwangwa, and Salima, for use as a precursor in zeolite synthesis. SBA samples were thermally treated at 500 °C, 600 °C, and 800 °C, followed by elemental characterisation using X-ray fluorescence spectroscopy. Emphasis was placed on the quantification of silicon dioxide (SiO₂) and aluminium oxide (Al₂O₃), both of which serve as essential precursors in hydrothermal zeolite formation. Across all samples and temperatures, silica concentrations remained consistently high, with Dwangwa ash at 600 °C recording the highest level at 76.22%. Alumina content exhibited greater variability, with Nchalo ash at 800 °C yielding the most enriched profile at 15.97%. Although silica levels met the criteria for zeolite production, measured alumina concentrations were insufficient to achieve the required Si/Al molar ratio for direct synthesis. As a corrective measure, the study incorporated secondary aluminium sources, such as recycled metallic waste, to meet stoichiometric thresholds and enable effective framework formation. Variations in oxide content were traced to both calcination-induced phase transitions and regional differences in soil composition, which influence mineral uptake during cultivation. Statistical analysis confirmed that source location materially affects ash composition, with clay-dominant soils in the Nchalo region contributing to higher Al₂O₃ content. The results establish SBA as a viable source of silica and a partial source of alumina for engineered zeolite synthesis, contingent on precise process control and composition adjustment. This approach promotes the reuse of agro-industrial residues and supports the production of cost-effective water treatment materials using regionally available resources.