Acid Isolation Techniques for Silica isolation from Rice Husk and Determination of Its Physicochemical Properties
Siti Mutrofin, Leo Krisna, Diah Mardiana, Rachmat Triandi T
J. Pure App. Chem. Res. Vol 11, No 1 (2022), pp. 72 - 82
Submitted: November 01, 2021     Accepted: April 27, 2022     Published: April 27, 2022


Previous research showed that rice husk has a high silica content so it becomes an alternative for processing rice waste. The acid leaching method is a technique to isolate silica by adding an acid solution. The research aim is to obtain the optimum silica yield and determine the chemical ash content of rice husks (rice IR-64,). Rice husks were first calcined at two various temperatures and times. The average yields obtained were 19.54% (500oC / 1 hr), 18.42% (500oC / 2 hrs), 25.03% (700oC /1 hr), and 22.4% (700oC/2 hrs). The physical appearance of ash was grains and white (700 oC/1hr), that were rinsed with 1 M HCl solution to remove impurities. Added 1 M NaOH was to form sodium silicate. The last step was to isolate silica using different concentrations of HCl and HNO3 (3 M, 2 M, and 1 M). The highest result was 99.87% of silica under HNO3 1 M solution. An infrared study supports that the isolated product was silica, with the presence of prominent peaks at 1102 cm-1 (stretching Si-O) and 471 cm-1 (bending Si-O). A unique peak at 958 cm-1 for Si-O-Ca present at the isolated silica using HCl 3 M, gives information on inosilicate type structure. X-ray diffraction analysis with QualX application showed that silica had cristobalite and wollastonite peaks, and the value of crystallinity index was about 63.91%.

Keywords : rice IR-64, rice husk, silica
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