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Abstract
This study presents two routes to produce amorphous silica from an Egyptian rice husk under conditions optimized for least environmental impact and low cost. The first route includes thoroughly washing of the husk sample with water, dry milling and leaching with citric acid. The leaching process was applied in two stages, that is, at 323 K for 180 min and then at 353 K for 60 min. After washing and drying, the leached sample was subjected to a heat treatment in a muffles furnace at four sequential steps. The second route includes all the previously mentioned steps, except the citric acid leaching. The final products were characterized using x-ray fluorescence analysis, carbon content analysis, x-ray diffraction, differential thermal analysis, nitrogen adsorption, mercury intrusion, and scanning electron microscopy. The results show that the citric acid leaching has many advantages with respect to silica yield and porosity as well.
Notes
*D10, D50, D90 is the mean diameter for the smallest 10%, 50%, and 90% of the analyzed powder of RHA-acid-873 K and RHA-873 K.
*Other measured inorganic oxides.
Data are given in mass percentage. Each concentration is the average of three individual samples. Standard deviations are given for uncertainty estimation.
a Nitrogen adsorption.
b Nitrogen adsorption, mean pore diameter, adsorption branch, BJH method.
c Mercury intrusion, mean pore diameter low pressure part (0.88–220 psi).
d Mercury intrusion, whole pressure range.