Silica Derived from Burned Rice Hulls

• Published in: Materials research (São Carlos, São Paulo, Brazil) São Paulo, Brazil), 2002-10, Vol.5 (4), p.467-474
• Main Authors: Souza, M.F. de, Magalhães, W.L.E., Persegil, M.C.
• Format: Article
• Language: English
• Subjects: amorphous silica; energy; ENGINEERING, CHEMICAL; MATERIALS SCIENCE, MULTIDISCIPLINARY; METALLURGY & METALLURGICAL ENGINEERING; nanosilica; rice hull; thermoelectric plants
• ISSN: 1516-1439; 1980-5373; 1516-1439
• DOI: 10.1590/S1516-14392002000400012

Processes to obtain silica having high specific surface area from burned pre-treated rice hulls allow for the simultaneous recovery of biomass energy and the production of high quality silica at thermoelectric plants without the risk of using corrosive substances in the burning process. The first method involves treatment of the hull with hot organic acid solutions before burning, the second with boiling water, both using an autoclave at temperatures close to 150 C, and the third method renders the hull fragile by treating it at 250 C and reducing it to a fine powder before burning. The first two methods result in white amorphous silica with 500 m2/g of specific surface area. The third method, which does not remove the alkaline elements from the hull, produces an amorphous grey carbon-free powder whose specific surface area can be as high as 250 m2/g. An investigation of the specific surface area of the prepared silica indicates the alkaline elements are not mixed with silica in the hulls nor combined as insoluble compounds. A comparison is made of these processes and the dissolution of silica by sodium hydroxide solutions is discussed. 18 refs.