A Merging-Zone Flow Injection Platform for Sustainable Silica Quantification in Agricultural Waste

The transition to a circular economy necessitates sustainable analytical methods for valorizing agricultural waste, yet the quantification of silica in biomass remains hampered by matrix interferences and the environmental burden of conventional techniques. Herein, we introduce a novel merging-zone flow injection analysis (M-FIA) system for the green and rapid quantification of silica in rice husk. The method innovatively integrates molybdenum blue chemistry with synchronized standard addition, enabling real-time correction of phosphate interference without toxic masking agents. Systematically optimized via design of experiments, the method achieves a low detection limit of 2 μg mL–1, excellent precision (RSD < 1.2%), and a high sample throughput of 20 samples per hour. A pivotal contribution of this work is the pioneering application of the AGREE (Analytical GREEnness) metric, which yielded an exceptional score of 0.86, quantitatively validating the method’s superior environmental profile. This is demonstrated by a drastic reduction in reagent consumption (3 mL per determination), energy demand (<0.1 kW h per sample), and carbon footprint (0.18 kg CO2-eq per sample) compared to existing methods. Comprehensive validation confirmed high accuracy (spike recoveries of 98.5–102.3%) and robust application to silica-rich Iraqi rice husk, quantifying content at 23.3–23.6% w/w. This M-FIA protocol establishes a new paradigm for sustainable analytical chemistry, providing a standardized tool that directly supports the advancement of circular economy initiatives and UN Sustainable Development Goals.