Sankar et al.88 Sankar S, Sharma SK, Kaur N, Lee B, Kim DY, Lee S, et al. Biogenerated silica nanoparticles synthesized from sticky, red, and brown rice husk ashes by a chemical method. Ceramics International. 2016;42(4)4875-4885.
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To produce nanosilicon powder from three kinds of rice husk. |
• Combustion of rice husk in the open. • Acid leaching • Incineration at 700ºC under atmospheric conditions |
Spherical, completely amorphous silica particles with large specific surface area and composed only by Si and O from all kinds of rice husk. |
Bakar99 Abu Bakar R, Yahya R, Gan SN. Production of High Purity Amorphous Silica From Rice Husk. Procedia Chemistry. 2016;19:189-195.
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To investigate the ideal conditions to obtain high purity silica. |
• Washing of rice husk with water • Acid leaching • Incineration at 500, 600, 700, 800, and 900 °C for 2 h under atmospheric conditions |
All silicas had amorphous particles, and rice husk leached with HCl produced the highest content of silica (99.582%) at 600 ºC. |
Ma et al.33 Ma X, Zhou B, Gao W, Qu Y, Wang L, Wang Z, et al. A recyclable method for production of pure silica from rice hull ash. Powder Technology. 2012;217:497-501.
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To develop a new, recycling-based technique to produce silica from RHA. |
• Acid leaching of RHA • Extraction in reactor with NH4F • Acid precipitation of silica |
Spherical, completely amorphous silica particles measuring 50 to 60 nm in diameter and containing only Si and O, with yield of 94.6%. |
Liou1010 Liou TH, Yang CC. Synthesis and surface characteristics of nanosilica produced from alkali-extracted rice husk ash. Materials Science and Engineering B. 2011;176(7):521-529.
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To investigate the effect of experimental conditions on the characteristics of the nanosilica obtained. |
• Leaching of rice husk with water and then HCl • Incineration • Extraction with NaOH, forming silicate • Precipitation |
Best results with pH 3, silicate 0.15 M, aging time of 12 h at 50ºC, with 99.48% purity silica. |
Fernandes1111 Fernandes AA. Síntese de Zeólitas e Wolastonita a Partir da Cinza da Casca do Arroz. [Thesis]. São Paulo: Universidade de São Paulo; 2006.
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To evaluate the leaching of RHA with NaOH to easily obtain highly reactive colloidal silica. |
• Extraction of silica with NaOH 1M • Precipitation using H2SO4 drop by drop |
The best Si:Na mass ratio was 4:1, and the highly reactive colloidal silica was obtained at low energy investment. |
Yalçin and Sevinç1212 Yalçin N, Sevinç V. Studies on silica obtained from rice husk. Ceramics International. 2001;27(2):219-224.
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To obtain high purity silica with large specific surface area and to evaluate the competitiveness of silica from rice husk. |
• Washing of rice husk with water • Chemical treatments (acid leaching, alkaline leaching) • Incineration at 600ºC under different conditions (static oven, argon flow, oxygen flow, air flow) |
Amorphous silica particles with maximum specific surface area of 321 m2/g 99.66% purity, depending on the treatment. The highest purity silica was obtained with prior acid treatment and incineration in oxygen atmosphere. |
Kalapathy77 Kalapathy U, Proctor A, Shultz J. A simple method for production of pure silica from rice hull ash. Bioresource Technology. 2000;73(3):257-262.
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Investigate the efficacy of acid leaching of RHA before alkaline extraction and washing of sílica obtained with water. |
• Acid leaching • Extraction of silica with NaOH • Precipitation with HCl • Washing with water |
Initial acid leaching did not improve purity, the washing with water reduced Na and K levels, and silica yield was excellent when extraction was carried out with NaOH 1 N. |
Conradt1313 Conradt R, Pimkhaokham P, Leela-Adisorn U. Nano-structured silica from rice husk. Journal of Non-Crystalline Solids. 1992;145:75-79.
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To obtain high purity silica with large specific surface area and to evaluate the competitiveness of silica from rice husk. |
• Washing rice husk with water • Different chemical treatments (acid leaching, alkaline leaching, and enzymatic digestion) • Incineration at 600ºC (static oven, air flow, steam) |
Except for leaching with NaOH, all other treatments produced amorphous silica with large specific surface area, and high purity silica was obtained with acid leaching with HCl. |
Riveros44 Riveros H, Garza C. Rice husks as a source of high purity silica. Journal of Crystal Growth. 1986;75(1):126-131.
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To optimize the production of silica from rice husk. |
• Washing rice husk with water • Acid leaching • Incineration • Leaching of RHA |
Silica with approximate purity of 99.98% with three washing cycles, 6-h acid leaching, 6 leaching cycles with HCl 3% at 90ºC, and the main contaminant was Ca (100 ppm). |