Extraction yield and properties of biogenic silica from palm oil fuel ash: effect of re-ashing pretreatment and solvent concentration

Abstract

Pretreatments and extraction conditions can affect the yield and characteristics of biogenic silica (biosilica) from palm oil fuel ash (POFA). This study aimed to examine how reashing pretreatment and varying NaOH concentrations influence the yield and properties of biosilica extracted from POFA by a simple sol-gel method. Re-ashing pretreatment was conducted using a furnace at a temperature of 600°C for 2h. All samples were leached using a citric acid solution. Extraction process was carried out using NaOH solutions with concentrations of 6%, 8%, and 10%). The results showed that re-ashing pretreatment and concentrations of NaOH significantly influenced (p<0.05) the extraction yield, color, crystallinity, and specific surface area of POFA-derived biosilica. Re-ashing pretreatment in combination with a 10% NaOH solution produced the highest extraction yield of biosilica (17.25% w/w) with a bright white color (L=91.83; WI=91.32), SiO2 concentration of 94.68%, crystallinity of 50.10%, and specific BET surface area of 390.80m2/g. XRD patterns confirmed the amorphous nature of POFA-derived biosilica. FTIR spectra revealed the presence of silica functional groups in all samples. This study demonstrated the important roles of re-ashing pretreatment and NaOH concentration in producing POFA-derived biosilica with better yield and properties that could broaden its potential applications.