Journal of Metals, Materials and Minerals


T Okutani

Publication Date



Highly pure silicon and silicon compounds are required in high technology products such as semiconductors and solar cells. Rice hulls consist of 71 to 87wt% organic components such as cellulose and 13 to 29wt% inorganic components. In rice hulls, 87 to 97wt% of the inorganic components are silica (SiO2). Rice plants absorb water-soluble siliceous ions via the roots. These ions are transported to stems, leaves and rice hulls by sap flow. In rice hulls, siliceous ions accumulate at the cuticle outside of the epidermis. The production of pure silicon compound (SiCl4) and of silicon metal as the starting material for purification from rice hull ash is proposed to utilize rice hull SiO2 in high technology industries. In one process, SiO2 in rice hull ash reacts with Cl2 on the presence of C and is converted to SiCl4. SiO2 + 2Cl2 + 2C → SiCl4 + 2CO The SiCl4 is purified by distillation. The production of SiCl4 from rice hull ash is much more efficient than that from mineral SiO2. In another process, SiO2 in rice hull ash reacts with aluminum (Al) to synthesize Si and Al2O3. 3SiO2 + 4Al → 3Si + 2Al2O3 The reactivity of rice hull SiO2 is higher than that of mineral SiO2. Although rice hulls are now utilized for agricultural materials and fuel, rice hull SiO2 also has high potential for use as industrial raw materials.

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