Abstract
A two-stage continuous process was developed for improved silica extraction from rice husk. The two-stage continuous process consists of attrition ball milling and alkaline leaching methods. To find the optimum conditions for the continuous process, the effects of alkaline leaching parameters, such as the alkaline solution type and reaction conditions, on the silica extraction yield were investigated in a batch process. The use of NaOH showed a slightly higher silica yield than KOH. The optimum reaction conditions were found to be 0.2 M, 80 °C, 3 h, and 6% (w/v) for the reaction concentration, temperature, duration time, and solid content, respectively. Attrition ball milling was used to make micron-sized rice husk particles and to improve the fluidity of the rice husk slurry. The two-stage continuous process was performed using optimum conditions as determined based on the results of the batch experiment. The two-stage continuous extraction was stably operated for 80 h with an 89% silica yield. During the operation, the solid content remained consistent at 6% (w/v). The obtained silica was characterized using inductively coupled plasma–optical emission spectrometry (ICP–OES), X-ray diffraction (XRD), and the Brunauer–Emmett–Teller (BET) method.
Highlights
Rice is a major agricultural product across the world, and its annual production was approximately 996 million tons in 2018 [1]
Rice husk is composed of approximately 70–80% organic substances such as cellulose, hemicellulose, and lignin, and the remaining 20–30% comprises inorganic compounds [5,6]
This study developed a two-stage continuous silica extraction process from rice husk using attrition ball milling and alkaline leaching methods
Summary
Rice is a major agricultural product across the world, and its annual production was approximately 996 million tons in 2018 [1]. Has various applications in different industries, e.g., (a) as an industrial fuel for paddy processing and in the generation of process steam in power plants; (b) as a fertilizer and substrate or pet food fiber; (c) as an ingredient for the preparation of activated carbon or substrate for silica and silicon compound production, and (d) as raw material for brick production [3,4]. Rice husk is composed of approximately 70–80% organic substances such as cellulose, hemicellulose, and lignin, and the remaining 20–30% comprises inorganic compounds [5,6]. A major inorganic component is silica, which accounts for approximately. The use of “biosilica” (rice husk-derived silica) as an alternative for silica in various industrial applications would mitigate high energy consumption, natural resource depletion, and greenhouse gas emissions [3]
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