Valorization of sugarcane bagasse ash into multi-nutrient potassium silicate fertilizer: Process optimization and life cycle assessment

Effective waste management strategies increasingly emphasize resource recovery and the conversion of waste into value-added products. We propose a sustainable pathway for producing multi-nutrient potassium silicate (K 2 SiO 3 ) fertilizer by valorizing sugarcane bagasse fly ash (FBA), an abundant agro-industrial waste. Potassium silicate was synthesized via KOH fusion following acid pretreatment (HCl or HNO 3 ) of 0.25- and 2-mm FBA fractions to extract fulvic acid and nutrients before fusion. The effects of fusion temperature on K and Si recovery were investigated over the range 200–900 °C, and fulvic and humic acids in the final fertilizer products were quantified. Acid pretreatment produced a nutrient-rich leachate containing fulvic acid and multiple plant nutrients (N, P, K, Ca, Mg, Fe, Mn, Si, and Zn), which can be recovered as a valuable by-product. The acid-washing step increased the Si concentration to 0.86% in the final K 2 SiO 3 fertilizer, while retaining measurable amounts of nutrients and fulvic and humic acids. A fusion temperature of 300 °C was identified as optimal, achieving Si contents comparable to those obtained at 900 °C, while substantially reducing energy requirements. Life cycle assessment revealed considerable reductions in environmental impacts compared to conventional K 2 SiO 3 production from silica at 1100 °C, with reductions of 9.27–9.65-fold in aquatic ecotoxicity and eutrophication. Climate change impacts were mitigated by up to a factor of 25 when nutrient reclamation was accounted for. This study highlights the potential of FBA as a secondary resource for producing multifunctional fertilizers, contributing to waste reduction, resource efficiency, and environmentally sustainable agriculture.