Preparation and characterization of silica gel from rice hull ash
2008
Bergonio, K.B. | Duldulao, J.B.A., Philippine Rice Research Inst., Maligaya, Science City of Munoz, Nueva Ecija (Philippines). Central Experiment Station | Torres, L.D., Central Luzon State Univ., Science City of Munoz, Nueva Ecija (Philippines). Dept. of Chemistry
Agricultural by-product utilization has been the focus of a great number of scientific studies. Rice hull is one by-product of the rice industry, whose ash in rich in silica. Herein different rice hull ash (RHA) samples: RHA from Oliver Farm (OF), RHA derived from natural burning (NB), laboratory-prepared RHA-1 (LP1-rice hull ashed to 700 deg C, 2 hours), and laboratory prepared RHA-II (LP-II, acid treated rice hull ashed to 700 deg C, 2 hours) were used to produced silica gels by alkaline extraction and acid precipitation. Residual carbon content was determined in the different RHS samples and also silica gels produced. High xerogel recoveries were obtained for NB, LP-1 and LP-II at 62.34, 50.33 and 72.05%, respectively while OF gave a low yield of 13.76%. Surface morphology and crystallinity of the silica gels were observed by scanning electron microscopy (SEM) and x-ray diffraction (XRD). SEM microstructure revealed white-colored compact particles of silica gels, while the XRD spectra confirmed the amorphous nature of the silica gels produced. Silica and mineral contents of silica gels were determined by energy dispersive X-ray (EDX). EDX elemental spectra showed that silica was the most abundant element, present at 34.86, 40.95, 39.74 and 41.47% levels, respectively. Mineral impurities included Na, Cl, and K. Sodium and chloride content in silica gels OF and LP-I was 5.56 and 4.61%, and 6.01 and 7.09%, respectively. Low levels of Na and Cl were noted in xerogels NB (1.58 and 1.45%),and LP-II (2.42 and 1.73%). Potassium impurity was present only in xerogel LP-I at 0.47%
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