Characterization and extraction of silica particles from green solvent pretreated paddy straw

This paper reports process development for the extraction of silica from paddy straw pretreated with green solvent and its characterization. Paddy straw pretreated with ethyl lactate resulted in a maximum reduction of total solids (11.78%), volatile solids (1.66%), cellulose (4.38%), hemicellulose (28.00%) and lignin (9.64%), while the increase in ash and silica content by 7.18 and 37.30%, respectively. Silica was extracted from 1% pretreated paddy straw using base dissolution and acid precipitation methods and was optimized by response surface methodology (RSM) using three parameters, viz. slurry concentration, and NaOH and HCl normalities to improve the silica yield. Maximum silica yield of 1.57 g per 2.5 g paddy straw ash (PSA) with 62.8% recovery was achieved under the optimized conditions of 2.50% slurry concentration_, 0.55 N NaOH and 1.50 N HCl. Physico-chemical characterization by Fourier-transform infrared spectroscopy confirmed the purity of extracted silica particles by IR peak patterns. Field emission scanning electron microscopy showed an agglomerate form of 50–200 nm amorphous silica. Inductively coupled plasma atomic emission spectroscopy of residual ash inferred its potential as fertilizer in the fields. Hence, green solvent pretreated silica extraction from paddy straw improved the commercial value of underutilized paddy straw and reduced environmental pollution.