Silica Derived from Burned Rice Hulls

Abstract

Three new processes to obtain silica having high specific surface area from burned pre-treated rice hulls are presented and discussed. These procedures 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 to150 °C, while 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 that can show 500 m 2 /g of specific surface area. The third method, which does not remove the alkaline elements from the hull, produces an amorphous gray carbon-free powder whose specific surface area can be as high as 250 m 2 /g. An investigation of the specific surface area of the prepared silica indicates the alkaline elements are not mixed with silica in the hulls or combined as insoluble compounds. A comparison is made of these processes and the dissolution of silica by sodium hydroxide solutions is discussed.

Qualitative feed restriction for heavy swines: effect on digestibility and weight of organs of digestive tract, and environmental impact of feces

“…In addition to the presence of lignin, another factor that contributes to the low digestibility of rice hulls fiber is silica, an inert material resistant to digestion, and which is inversely proportional to the capacity of microorganisms to act on cellulose (Pond, 1988). Ash content of the rice hulls was approximately 16%, of which almost 96% may consist of silica (Souza et al, 2002).…”

“…Taking into account the dietary increment of Mn, particularly, this mineral is characterized for reducing Ca and P availability. In addition, its own availability is decreased due to its interaction with dietary fiber and phytates, as occurs with the reduction in Zn availability by the presence of fiber (Underwood and Suttle, 1999). The effect of fiber on endogenous nitrogen excretion must also be considered.…”

Obtaining high purity silica from rice hulls

“…% consists of silica. 3 Thermal treatments of the rice hulls up to 400 o C under inert atmosphere are typically unable to completely eliminate the lignin, yielding a black char/silica composite. 4,5 Thus, many options for leaching and extracting silica have been developed.…”

Caracterização de cinza obtida por combustão de casca de arroz em reator de leito fluidizado

“…1 Os principais componentes da casca são celulose e hemicelulose (50%), além de lignina (26%) e componentes orgânicos (4%), como óleos e proteínas. A quantidade restante inclui os materiais inorgânicos (SiO 2 , Al 2 O 3 , K 2 O, Na 2 O, MgO, CaO, Fe 2 O 3 , MnO, P 2 O 5 ).…”

“…A quantidade restante inclui os materiais inorgânicos (SiO 2 , Al 2 O 3 , K 2 O, Na 2 O, MgO, CaO, Fe 2 O 3 , MnO, P 2 O 5 ). 1 A cinza de casca de arroz (CCA) é o produto da transformação termoquímica da CA. As condições dos diferentes processos de conversão (pirólise, gaseificação e/ou combustão) determinam as características físico-químicas do produto final.…”